Patent Application
20230151075
Low back pain (LBP) is a common health problem, which most people (80%) experience at some point, especially in older adults. Rubin, 2007; Hartvigsen et al., 2006; Hartvigsen et al., 2004; and Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015. In the United States alone, the direct and indirect costs associated with LBP surpass $90 billion per year, with similar adjusted rates in other countries. Samartzis and Grins, 2017. Ninety percent of LBP is nonspecific LBP, which has no apparent pathoanatomical cause. Krismer and van Tulder, 2007; Koes et al., 2006. Several lumbar structures, such as intervertebral disc, facet joints, are plausible sources of nonspecific LBP, but the pain cannot be reliably attributed to those structures by clinical tests. Hancock et al., 2007; Maher et al., 2017; and Hartvigsen et al., 2018. Importantly, intervertebral disc (IVD) degeneration is frequently observed in asymptomatic patients, indicating that disc degeneration, per se, is not painful in some patients. Hurri and Karppinen, 2004; Borenstein et al., 2001. Hence, identifying the source of LBP and related mechanisms is essential to develop effective treatments for LBP.
Further, osteoarthritis (OA) is a leading cause of disability as the most common degenerative joint disorder and chronic pain is the most prominent symptom of osteoarthritis (OA), affecting nearly 40 million people in the US. Pain itself also is a major risk factor for the development of future functional limitation and disability in OA patients. Unfortunately, OA pain treatment remains challenging and represents a large unmet medical need. It is not clear what causes OA pain, and currently there is no effective way to relieve it. Available therapies (NSAIDs, steroids, visco-supplementation, such as intra-articular injection of hyaluronic acid) only alleviate mild joint OA pain. Relief from chronic OA pain remains an unmet medical need and still major reason for seeking surgical intervention. Despite these efforts, the origins of pain and its molecular mechanisms remain poorly understood.
In some aspects, the presently disclosed subject matter provides a method for treating low back pain (LBP) and/or osteoarthritic pain in a subject in need of treatment thereof, the method comprising administering to the subject a composition comprising a recombinant parathyroid hormone (PTH) and a pharmaceutically acceptable carrier.
In certain aspects, the low back pain comprises a nonspecific low back pain.
In certain aspects, the administering of the recombinant parathyroid hormone (PTH) inhibits osteoclast activity-induced sensory innervation in a vertebral endplate of the subject.
In other aspects, the administering of the recombinant parathyroid hormone (PTH) increases the intervertebral disc (IVD) space by decreasing the volume and porosity of sclerotic endplates.
In yet other aspects, the administering of the recombinant parathyroid hormone (PTH) prevents endplate remodeling and sclerosis.
In even yet other aspects, the administering of the recombinant parathyroid hormone (PTH) reduces sensory nerve fibers.
In other aspects, the administering of the recombinant parathyroid hormone (PTH) reduces the porosity of sclerotic endplates.
In particular aspects, the administering of the recombinant parathyroid hormone (PTH) treats the osteoarthritic pain by one or more of inhibition of nerve innervation, inhibition of subchondral bone deterioration, inhibition of articular cartilage degeneration, attenuation of joint degeneration, decelerating subchondral bone deterioration, and sustaining of subchondral bone microarchitecture by remodeling.
In some aspects, the method further comprises administering at least one other agent in combination with the administering of the recombinant parathyroid hormone (PTH).
In certain aspects, the at least one other agent is selected from the group consisting of paracetamol, an opioid, a non-steroidal anti-inflammatory drug, a skeletal muscle relaxant, a triptan, an α2-agonist, a local anesthetic, a tricyclic antidepressant, a benzodiazepine, a steroid, a visco supplement, and combinations thereof.
In particular aspects, the low back pain is associated with one or more of spine degeneration, lumbar disc herniation (LDH), scoliosis, cancer, and an infection.
In some aspects, the recombinant PTH comprises a full-length PTH protein or a fragment of PTH. In particular aspects, the recombinant parathyroid hormone comprises teriparatide (PTH(1-34′)). In other aspects, the recombinant parathyroid hormone comprises an intact parathyroid hormone (iPTH).
In certain aspects, the composition is administered to the subject at least once a day.
In other aspects, the presently disclosed subject matter provides the use of a recombinant parathyroid hormone to treat low back pain (LBP) or osteoarthritic pain in a subject in need thereof.
Certain aspects of the presently disclosed subject matter having been stated hereinabove, which are addressed in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying Examples and Drawings as best described herein below.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee.
Having thus described the presently disclosed subject matter in general terms, reference will now be made to the accompanying Figures, which are not necessarily drawn to scale, and wherein:
The presently disclosed subject matter now will be described more fully hereinafter with reference to the accompanying Figures, in which some, but not all embodiments of the inventions are shown. Like numbers refer to like elements throughout. The presently disclosed subject matter may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein: rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Indeed. many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated Figures. Therefore, it is to be understood that the presently disclosed subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.
In some embodiments, the presently disclosed subject matter provides a method for treating low back pain (LBP) and/or osteoarthritic pain in a subject in need of treatment thereof, the method comprising administering to the subject a composition comprising a recombinant parathyroid hormone (PTH) and a pharmaceutically acceptable carrier.
In certain embodiments, the low back pain comprises a nonspecific low back pain.
In certain embodiments, the administering of the recombinant parathyroid hormone (PTH) inhibits osteoclast activity-induced sensory innervation in a vertebral endplate of the subject.
As used herein, the term “inhibit,” and grammatical derivations thereof, refers to the ability of a presently disclosed compound, e.g., a recombinant parathyroid hormone (PTH), to block, partially block, interfere, decrease. or reduce, for example, osteoclast activity-induced sensory innervation in a vertebral endplate. Thus, one of ordinary skill in the art would appreciate that the term “inhibit” encompasses a complete and/or partial decrease in an activity, e.g., a decrease by at least 10%. in some embodiments, a decrease by at least 20%, 30%, 50%, 75%, 95%, 98%, and up to and including 100%.
In particular embodiments, the administering of the recombinant parathyroid hormone (PTH) treats the osteoarthritic pain by one or more of inhibition of nerve innervation, inhibition of subchondral bone deterioration, inhibition of articular cartilage degeneration. attenuation of joint degeneration, decelerating subchondral bone deterioration, and sustaining of subchondral bone microarchitecture by remodeling.
In other embodiments, the administering of the recombinant parathyroid hormone (PTH) increases the intervertebral disc (IV D) space by decreasing the volume and porosity of sclerotic endplates.
In yet other embodiments, the administering of the recombinant parathyroid hormone (PTH) prevents endplate remodeling and sclerosis.
In even yet other embodiments, the administering of the recombinant parathyroid hormone (PTH) reduces sensory nerve fibers.
In other embodiments, the administering of the recombinant parathyroid hormone (PTH) reduces the porosity of sclerotic endplates.
In some embodiments, the method further comprises administering at least one other agent in combination with the administering of the recombinant parathyroid hormone (PTH).
In certain embodiments, the at least one other agent is selected from the group consisting of paracetamol, an opioid, a non-steroidal anti-inflammatory drug, a skeletal muscle relaxant, a triptan, an α2-agonist, a local anesthetic, a tricyclic antidepressant, a benzodiazepine, a steroid, a visco supplement, and combinations thereof.
In particular embodiments, the low back pain is associated with one or more of spine degeneration, lumbar disc herniation (LDH), scoliosis, cancer, and an infection.
In some embodiments, the recombinant PTH comprises a full-length PTH protein or a fragment of PTH. In particular embodiments, the recombinant parathyroid hormone comprises teriparatide (PTH(I-34′)). In other embodiments, the recombinant parathyroid hormone comprises an intact parathyroid hormone (iPTH).
In certain embodiments, the composition is administered to the subject at least once a day.
In other embodiments, the presently disclosed subject matter provides the use of a recombinant parathyroid hormone to treat low back pain (LBP) or osteoarthritic pain in a subject in need thereof.
As used herein, the term “treating” can include reversing, alleviating, inhibiting the progression of, preventing or reducing the likelihood of the disease, disorder, or condition to which such term applies, or one or more symptoms or manifestations of such disease, disorder or condition. Preventing refers to causing a disease, disorder, condition, or symptom or manifestation of such, or worsening of the severity of such, not to occur. Accordingly, the presently disclosed compounds can be administered prophylactically to prevent or reduce the incidence or recurrence of the disease, disorder, or condition.
The “subject” treated by the presently disclosed methods in their many embodiments is desirably a human subject, although it is to be understood that the methods described herein are effective with respect to all vertebrate species, which are intended to be included in the term “subject.” Accordingly, a “subject” can include a human subject for medical purposes. such as for the treatment of an existing condition or disease or the prophylactic treatment for preventing the onset of a condition or disease, or an animal subject for medical, veterinary purposes, or developmental purposes. Suitable animal subjects include mammals including, but not limited to, primates, e.g., humans, monkeys, apes, and the like; bovines, e.g., cattle, oxen, and the like; ovines, e.g., sheep and the like; caprines, e.g., goats and the like; porcines, e.g., pigs, hogs, and the like: equines, e.g., horses. donkeys, zebras, and the like; felines, including wild and domestic cats; canines, including dogs; lagomorphs, including rabbits, hares, and the like; and rodents, including mice, rats, and the like. An animal may be a transgenic animal. In some embodiments, the subject is a human including, but not limited to, fetal, neonatal, infant, juvenile, and adult subjects. Further, a “subject” can include a patient afflicted with or suspected of being afflicted with a condition or disease. Thus, the terms “subject” and “patient” are used interchangeably herein. The term “subject” also refers to an organism, tissue, cell, or collection of cells from a subject.
In general, the “effective amount” of an active agent or drug delivery device refers to the amount necessary to elicit the desired biological response. As will be appreciated by those of ordinary skill in this art, the effective amount of an agent or device may vary depending on such factors as the desired biological endpoint, the agent to be delivered, the makeup of the pharmaceutical composition, the target tissue, and the like.
The term “combination” is used in its broadest sense and means that a subject is administered at least two agents, more particularly a recombinant parathyroid hormone (PTH) and at least one other agent. In some embodiments, the at least one other agent is selected from the group consisting of paracetamol, opioids, non-steroidal anti-inflammatory drugs (NSAIDs, including COX-2 inhibitors), and skeletal muscle relaxants. In other embodiments, the at least one other agent is selected from the group consisting of triptans, α2-agonists, and local anesthetics. In chronic cases, the at least one other agents is a tricyclic antidepressant and/or a benzodiazepine.
More particularly, the term “in combination” refers to the concomitant administration of two (or more) active agents for the treatment of a, e.g., single disease state. As used herein, the active agents may be combined and administered in a single dosage form, may be administered as separate dosage forms at the same time, or may be administered as separate dosage forms that are administered alternately or sequentially on the same or separate days. In one embodiment of the presently disclosed subject matter. the active agents are combined and administered in a single dosage form. In another embodiment, the active agents are administered in separate dosage forms (e.g., wherein it is desirable to vary the amount of one but not the other). The single dosage form may include additional active agents for the treatment of the disease state.
Further, the recombinant parathyroid hormone (PTH) described herein can be administered alone or in combination with adjuvants that enhance stability of the recombinant parathyroid hormone (PTH), alone or in combination with one or more antibacterial agents, facilitate administration of pharmaceutical compositions containing them in certain embodiments, provide increased dissolution or dispersion, increase inhibitory activity, provide adjunct therapy, and the like, including other active ingredients. Advantageously, such combination therapies utilize lower dosages of the conventional therapeutics, thus avoiding possible toxicity and adverse side effects incurred when those agents are used as monotherapies.
The timing of administration of a recombinant parathyroid hormone (PTH) and at least one additional therapeutic agent can be varied so long as the beneficial effects of the combination of these agents are achieved. Accordingly, the phrase “in combination with” refers to the administration of a recombinant parathyroid hormone (PTH) and at least one additional therapeutic agent either simultaneously, sequentially, or a combination thereof. Therefore, a subject administered a combination of a recombinant parathyroid hormone (PTH) and at least one additional therapeutic agent can receive a recombinant parathyroid hormone (PTH) and at least one additional therapeutic agent at the same time (i.e., simultaneously) or at different times (i.e., sequentially, in either order, on the same day or on different days), so long as the effect of the combination of both agents is achieved in the subject.
When administered sequentially, the agents can be administered within 1, 5, 10, 30, 60, 120, 180, 240 minutes or longer of one another. In other embodiments, agents administered sequentially, can be administered within 1, 5, 10, 15, 20 or more days of one another. Where the recombinant parathyroid hormone (PTH) and at least one additional therapeutic agent are administered simultaneously, they can be administered to the subject as separate pharmaceutical compositions, each comprising either a recombinant parathyroid hormone (PTH) or at least one additional therapeutic agent, or they can be administered to a subject as a single pharmaceutical composition comprising both agents.
When administered in combination, the effective concentration of each of the agents to elicit a particular biological response may be less than the effective concentration of each agent when administered alone, thereby allowing a reduction in the dose of one or more of the agents relative to the dose that would be needed if the agent was administered as a single agent. The effects of multiple agents may, but need not be, additive or synergistic. The agents may be administered multiple times.
In some embodiments, when administered in combination, the two or more agents can have a synergistic effect. As used herein, the terms “synergy,” “synergistic,” “synergistically” and derivations thereof, such as in a “synergistic effect” or a “synergistic combination” or a “synergistic composition” refer to circumstances under which the biological activity of a combination of a recombinant parathyroid hormone (PTH) and at least one additional therapeutic agent is greater than the sum of the biological activities of the respective agents when administered individually.
Synergy can be expressed in terms of a “Synergy Index (SI),” which generally can be determined by the method described by F. C. Kull et al., Applied Microbiology 9, 538 (1961), from the ratio determined by:
Q
a
/Q
A
+Q
b
/Q
B=Synergy Index (SI)
wherein:
QA is the concentration of a component A. acting alone, which produced an end point in relation to component A;
Generally. when the sum of Qa/QA and Qb/QB is greater than one, antagonism is indicated. When the sum is equal to one, additivity is indicated. When the sum is less than one. synergism is demonstrated. The lower the SI, the greater the synergy shown by that particular mixture. Thus, a “synergistic combination” has an activity higher that what can be expected based on the observed activities of the individual components when used alone. Further, a “synergistically effective amount” of a component refers to the amount of the component necessary to elicit a synergistic effect in, for example, another therapeutic agent present in the composition.
In another aspect, the present disclosure provides a pharmaceutical composition including a recombinant parathyroid hormone (PTH) alone or in combination with one or more additional therapeutic agents in admixture with a pharmaceutically acceptable excipient. One of skill in the art will recognize that the pharmaceutical compositions include the pharmaceutically acceptable salts of the compounds described above.
In therapeutic and/or diagnostic applications, the compounds of the disclosure can be formulated for a variety of modes of administration, including systemic and topical or localized administration. Techniques and formulations generally may be found in Remington: The Science and Practice of Pharmacy (20th ed.) Lippincott, Williams & Wilkins (2000).
Depending on the specific conditions being treated, such agents may be formulated into liquid or solid dosage forms and administered systemically or locally. The agents may be delivered, for example, in a timed- or sustained-slow release form as is known to those skilled in the art. Techniques for formulation and administration may be found in Remington: The Science and Practice of Pharmacy (20th ed.) Lippincott, Williams & Wilkins (2000). Suitable routes may include oral, buccal, by inhalation spray, sublingual, rectal, transdermal, vaginal, transmucosal, nasal or intestinal administration; parenteral delivery, including intramuscular, subcutaneous, intramedullary injections, as well as intrathecal, direct intraventricular, intravenous, intra-articular, intra-sternal, intra-synovial, intra-hepatic, intralesional, intracranial, intraperitoneal, intranasal, or intraocular injections or other modes of delivery.
For injection, the agents of the disclosure may be formulated and diluted in aqueous solutions. such as in physiologically compatible buffers such as Hank's solution, Ringer's solution, or physiological saline buffer. For such transmucosal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art.
Use of pharmaceutically acceptable inert carriers to formulate the compounds herein disclosed for the practice of the disclosure into dosages suitable for systemic administration is within the scope of the disclosure. With proper choice of carrier and suitable manufacturing practice, the compositions of the present disclosure, in particular. those formulated as solutions. may be administered parenterally, such as by intravenous injection. The compounds can be formulated readily using pharmaceutically acceptable carriers well known in the art into dosages suitable for oral administration. Such carriers enable the compounds of the disclosure to be formulated as tablets, pills, capsules, liquids, gels, syrups, slurries, suspensions and the like, for oral ingestion by a subject (e.g., patient) to be treated.
For nasal or inhalation delivery, the agents of the disclosure also may be formulated by methods known to those of skill in the art, and may include, for example, but not limited to, examples of solubilizing. diluting, or dispersing substances. such as saline; preservatives, such as benzyl alcohol: absorption promoters; and fluorocarbons.
Pharmaceutical compositions suitable for use in the present disclosure include compositions wherein the active ingredients are contained in an effective amount to achieve its intended purpose. Determination of the effective amounts is well within the capability of those skilled in the art, especially in light of the detailed disclosure provided herein. Generally, the compounds according to the disclosure are effective over a wide dosage range. For example, in the treatment of adult humans, dosages from 0.01 to 1000 mg, from 0.5 to 100 mg. from 1 to 50 mg per day. and from 5 to 40 mg per day are examples of dosages that may be used. A non-limiting dosage is 10 to 30 mg per day. The exact dosage w % ill depend upon the route of administration, the form in which the compound is administered, the subject to be treated, the body weight of the subject to be treated, the bioavailability of the compound(s), the adsorption, distribution, metabolism, and excretion (ADME) toxicity of the compound(s), and the preference and experience of the attending physician.
In addition to the active ingredients, these pharmaceutical compositions may contain suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the active compounds into preparations which can be used pharmaceutically. The preparations formulated for oral administration may be in the form of tablets, dragees, capsules, or solutions.
Pharmaceutical preparations for oral use can be obtained by combining the active compounds with solid excipients, optionally grinding a resulting mixture, and processing the mixture of granules. after adding suitable auxiliaries, if desired, to obtain tablets or dragee cores. Suitable excipients are, in particular, fillers such as sugars, including lactose, sucrose, mannitol, or sorbitol; cellulose preparations, for example, maize starch, wheat starch, rice starch, potato starch, gelatin, gum tragacanth, methyl cellulose, hydroxypropylmethyl-cellulose, sodium carboxymethyl-cellulose (CMC), and/or polyvinylpyrrolidone (PVP: povidone). If desired. disintegrating agents may be added, such as the cross-linked polyvinylpyrrolidone, agar, or alginic acid or a salt thereof such as sodium alginate.
Dragee cores are provided with suitable coatings. For this purpose, concentrated sugar solutions may be used. which may optionally contain gum arabic, talc, polyvinylpyrrolidone, carbopol gel, polyethylene glycol (PEG), and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. Dye-stuffs or pigments may be added to the tablets or dragee coatings for identification or to characterize different combinations of active compound doses.
Pharmaceutical preparations that can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin, and a plasticizer, such as glycerol or sorbitol. The push-fit capsules can contain the active ingredients in admixture with filler such as lactose, binders such as starches, and/or lubricants such as talc or magnesium stearate and, optionally, stabilizers. In soft capsules, the active compounds may be dissolved or suspended in suitable liquids, such as fatty oils, liquid paraffin, or liquid polyethylene glycols (PEGs). In addition, stabilizers may be added.
Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this presently described subject matter belongs.
Following long-standing patent law convention, the terms “a,” “an,” and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to “a subject” includes a plurality of subjects, unless the context clearly is to the contrary (e.g., a plurality of subjects), and so forth.
Throughout this specification and the claims, the terms “comprise,” “comprises,” and “comprising” are used in a non-exclusive sense, except where the context requires otherwise. Likewise, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.
For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing amounts, sizes, dimensions, proportions, shapes, formulations, parameters, percentages, quantities, characteristics, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about” even though the term “about” may not expressly appear with the value, amount or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are not and need not be exact, but may be approximate and/or larger or smaller as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art depending on the desired properties sought to be obtained by the presently disclosed subject matter. For example, the term “about,” when referring to a value can be meant to encompass variations of, in some embodiments, +100% in some embodiments±50%, in some embodiments±20%, in some embodiments±10%, in some embodiments f 5%, in some embodiments ±1%, in some embodiments±0.5%, and in some embodiments t 0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.
Further, the term “about” when used in connection with one or more numbers or numerical ranges, should be understood to refer to all such numbers, including all numbers in a range and modifies that range by extending the boundaries above and below the numerical values set forth. The recitation of numerical ranges by endpoints includes all numbers, e.g., whole integers, including fractions thereof, subsumed within that range (for example, the recitation of 1 to 5 includes 1, 2, 3, 4, and 5, as well as fractions thereof, e.g., 1.5, 2.25, 3.75, 4.1, and the like) and any range within that range.
The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter. The synthetic descriptions and specific examples that follow are only intended for the purposes of illustration, and are not to be construed as limiting in any manner to make compounds of the disclosure by other methods.
Spinal pain is a major clinical problem. Its origins and underlying mechanisms, however, remain unclear. In some embodiments, the presently disclosed subject matter provides that in mice, osteoclasts induce sensory innervation in the porous endplates, which contributes spinal hypersensitivity in mice. Sensory innervation of the porous areas of sclerotic endplates in mice was confirmed. Lumbar spine instability (LSI), or aging, induces spinal hypersensitivity in mice. In these conditions, elevated levels of PGE2, which activate sensory nerves leading to sodium influx through Nav1.8 channels, were observed. Further, knockout of PGE2 receptor 4 in sensory nerves significantly reduced spinal hypersensitivity. Inhibition of osteoclast formation by knockout Rankl in the osteocytes significantly inhibited LSI-induced porosity of endplates, sensory innervation, and spinal hypersensitivity. Knockout of Netrin-1 in osteoclasts abrogates sensory innervation into porous endplates and spinal hypersensitivity. These findings suggest that osteoclast-initiated porosity of endplates and sensory innervation are potential therapeutic targets for spinal pain.
Low back pain (LBP) is a common health problem, which most people (80%) experience at some point, especially in older adults. Rubin, 2007: Hartvigsen et al., 2006; Hartvigsen et al., 2004: and Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015.
In the United States alone, the direct and indirect costs associated with LBP surpass $90 billion per year, with similar adjusted rates in other countries. Samartzis and Grivas, 2017. 90% of LBP is nonspecific LBP, which has no apparent pathoanatomical cause. Krismer and van Tulder, 2007: Koes et al., 2006. Several lumbar structures, such as intervertebral disc, facet joints, are plausible sources of nonspecific LBP, but the pain cannot be reliably attributed to those structures by clinical tests. Hancock et al., 2007; Maher et al., 2017; and Hartvigsen et al., 2018. Importantly, intervertebral disc (IVD) degeneration is frequently observed in asymptomatic patients, indicating that disc degeneration, per se, is not painful in some patients. Hurn and Karppinen, 2004: Borenstein et al., 2001. Hence, identifying the source of LBP and related mechanisms is essential to develop effective treatments for LBP.
The positive association between vertebral endplate signal changes (i.e., Modic changes) and LBP has been shown by magnetic resonance imaging (MRI) examination. Rahme and Moussa, 2008; Luoma et al., 2016. Modic changes are common MRI findings in patients with nonspecific LBP. It is believed to be a factor independently associated with the increased risk of LBP. Jensen et al., 2008: Maatta et al., 2015: and Jensen et al., 2014. The size of Modic change lesions positively correlates with LBP. Jarvinen et al., 2015. Histological analysis further showed that the presence of endplate lesions was associated with LBP. Wang et al., 2012. During aging, endplates undergo ossification with elevated osteoclasts and become porous. Bian et al., 2016: Bian et al., 2017; Rodriguez et al., 2012; and Papadakis et al., 2011. Histological and micro CT analysis further revealed that sclerotic endplates are highly porous. Rodriguez et al., 2012. Progressively more porous endplates with narrowed IVD space are characteristics of spinal degeneration. Rodriguez et al., 2012; Taher et al., 2012. Since pain is produced by nociceptors, LBP may be caused by sensory innervation into endplates. Moreover, nerve density was higher in porous endplates than in normal endplates or degenerative nucleus pulposus. Fields et al., 2014. Zoledronic acid and denosumab, drugs that inhibit osteoclast activities, have shown analgesic effects in patients with Modic changes associated LBP, Cai et al., 2018; Koivisto et al., 2014, with the implication of a potential role of osteoclast activity in sensory nerve innervation.
Prostaglandin E2 (PGE2) is an inflammatory mediator released at the focal inflamed tissue and a neuromodulator that alters neuronal excitability. Four types of G-protein-coupled EP receptors (EP1-EP4) mediate the functions of PGE2. EP4 receptor is considered the primary mediator of PGE2-evoked inflammatory pain hypersensitivity and sensitization of sensory neurons. Lin et al., 2006: Southall and Vasko, 2001. It was recently reported that PGE2, produced from arachidonic acid by the enzymatic activity of cyclooxygenase 2 (COX2), during bone remodeling activates PGE2 receptor 4 (EP4) in CGRP+ sensory nerves to tune down sympathetic tones further inducing osteoblastic differentiation of MSCs. Chen et al, 2019. Specific EP4 receptor antagonists could reduce acute and chronic pain, including osteoarthritis pain. Lin et al., 2006; Clark et al., 2008: Kirkby Shaw et al., 2016; Nakao et al., 2007. The tetrodotoxin-resistant (TX-R) sodium channel Nav1.8 is a potential drug target for pain. Nav1.8 is expressed primarily in small and medium-sized dorsal root ganglion (DRG) neurons and their fibers. Janis et al., 2007: Coggeshall et al., 2004: and Schuelert and McDougall, 2012. PGE2 could modulate the TTX-R sodium current in DRG neurons and promote Nav1.8 trafficking to the cell surface. Liu et al., 2010; England et al., 1996.
One aspect of the presently disclosed study is to demonstrate that osteoclasts initiate porosity of endplates with sensory innervation into porous areas. The presently disclosed data show that Calcitonin Gene-Related Peptide positive (CGRP+) nociceptive nerve fibers and blood vessels were increased in the cavities of sclerotic endplates. The elevated PGE2 in porous endplates induces sodium influx into the cells to stimulate sensory nerves that leads to spinal pain. Inhibition of osteoclast activity attenuated sensory innervation in porous endplates and pain behavior.
Lumbar spine instability (LSI) was established in mice as a spine degeneration model for spine pain behavior testing. Bian et al., 2016; Ariga et al., 2001; and Miyamoto et al., 2001. The vocalization threshold was first measured in response to force applied on the L4/L5 disc region. Pressure tolerance decreased significantly at 4, 8, and 12 weeks after LSI surgery relative to mice that underwent sham surgery (
In parallel, symptomatic LBP during aging in these behavior tests was evaluated. Similarly, the threshold of pressure tolerance (
An increase in osteoclasts at the onset of endplate sclerosis was previously shown. Bian et al., 2016. Therefore, the potential role of osteoclasts in the sensory innervation of endplates was evaluated in this study. Tartrate-resistant acid phosphatase (TRAP) staining demonstrated that the number of TRAP+ osteoclasts in endplates increased significantly at 2 weeks after LSI and remained at a high level until 8 weeks after LSI surgery (
To determine whether spine degeneration during aging could induce sclerosis and sensory innervation in vertebral endplates, the caudal endplates of L4/5 from aged mice and young mice were analyzed. The porosity of endplates in aged mice increased significantly relative to young mice, as determined by 3-dimensional microcomputed tomography (μCT) analysis (
To examine the potential involvement of sclerosis and sensory innervation of the endplates with pain behavior, the pathological changes in the endplates of the lower lumbar spines from patients with or without LBP history was evaluated. Severe endplate lesions were observed in patients with a history of frequent LBP, whereas the cartilaginous structure was preserved in patients without a history of frequent LBP, despite disc herniation (
TRAP staining showed that abundant TRAP+ osteoclasts localized at the bone surface in the sclerotic endplates (
To demonstrate CGRP+ sensory innervation in endplates during spine degeneration, a retrograde tracing experiment in both LSI and aged mice was conducted. The red fluorescent tracer, Dil, was injected in the left part of the caudal endplates of L4/5 in mice at 8 weeks after LSI surgery (
The anterograde tracing experiment was performed by labeling the L1 and L2 DRG neurons in both sides with injection of Dil at 8 weeks after LSI or sham surgery. Abundant Dil-labeled sensory nerves were seen in the porous areas of endplates of L4/5 in LSI mice, but not in sham surgery mice (
To elucidate the signaling mechanism of endplate sclerosis-mediated pain behavior, the expression of several inflammatory cytokines in the endplates of LSI and sham surgery mice was examined by using quantitative real-time polymerase chain reaction (qRT-PCR). It was found that messenger ribonucleic acid levels of prostaglandin E synthase (PGES), cox2, interleukin (IL)-1β, IL-17, IL-2, and tumor necrosis factor (TNF)-α increased significantly in the lumbar endplates at 4 weeks after LSI relative to sham surgery, especially PGES (
To examine the potential role of PGE2/EP4 in pain transduction, a sensory neuron specific EP4 knockout mice (AvilCre; EP4flox/flox, named EP4 mice) was generated. TRAP staining demonstrated that there was no significant difference in the number of TRAP+ osteoclasts in endplates between EP4f/f and EP4−/− mice of sham surgery group or LSI surgery group (
To evaluate whether the PGE2/EP4 pathway in sensory fibers is associated with spinal pain behavior, pain behavior tests, including pressure tolerance, spontaneous activity, and von Frey analysis, were performed. The threshold of pressure tolerance in response to pressure stimulation was lower in EP4−/− mice relative to EP4f/f mice after LSI surgery (
To evaluate whether CGRP+ sensory innervation in the endplates is induced by osteoclasts, Dmp1-Cre mice were bred with osteocyte-derived receptor activator of nuclear factor kappa-B ligand (Rankl) floxed mice to generate Dmp1Cre: Ranklflox/flox mice (named Rankl−/− mice) to knock out Rankl specifically in DMP1+ osteocytes. Deficiency of Rankl in osteocytes leads to a decrease in osteoclast number and a severe osteopetrotic phenotype. Nakashima et al., 2011: Xiong et al., 2011. The trabecular BV/TV, Th.N, and Tb.Th increased and Tb.Sp decreased significantly in RANKL−/− mice relative to RANKLf/f mice in μCT analysis (
To examine whether osteoclast activity-induced sensory innervation in endplates is associated with spinal pain behavior, pain behavior tests, including pressure tolerance, spontaneous activity, and von Frey analysis, were performed. The threshold of pressure tolerance was significantly lower in Rankl−/− mice relative to Ranklf/f mice after LSI surgery (
Netrin-1 is an important axon guidance factor to attract nerve protrusion. Moore et al., 2012; Serafini et al., 1996: and Hand and Kolodkin, 2017. It was previously reported that osteoclasts can secret Netrin-1 to attract sensory nerve growth. Zhu et al., 2019. Immunostaining demonstrated that TRAP+ osteoclasts were the source of Netrin-1 in sclerotic endplates after LSI surgery (
To determine whether osteoclast-derived Netrin-1 is responsible for sensory innervation, Trap-Cre mice were cross-bred with Netrin-1 floxed mice to knockout Netrin-1 in TRAP+ lineage cells (TrapCre; Netrin-1flox/flox, named Netrin-1−/− mice). Safranin O and fast green staining demonstrated that the instability-induced sclerosis of endplates was not different in Netrin-1−/− mice compared with their age-matched littermates (herein, Netrin-1f/f mice) (
Pain behavior tests demonstrated that pressure hyperalgesia (
LBP is difficult to diagnose and treat because of limited knowledge about its source. Current treatments, including activity modification, physical therapy, and pharmaceutical agents aim to alleviate the pain, but not to modify the disease. Maher et al, 2017: Foster et al., 2018. Surgical treatment, such as disc replacement and lumbar fusion, are the most common final treatments. Efforts to understand the causes of LBP have focused largely on sensory innervation in the degenerative IVD. Garcia-Cosamalon et al., 2010. However, IVD degeneration is frequently asymptomatic. Importantly, endplates undergo sclerosis during aging and become porous, which is clinically associated with LBP. Lotz et al., 2013; Dudli et al., 2016; and Brown et al., 1997. It has previously been shown that aberrant mechanical loading induces sclerosis of the endplates with elevated osteoclast activity and activates excessive TGF-01 to recruit mesenchymal stromal cells. Bian, 2016. Here, elevated level of PGE2 and sensory innervation in the porous sclerotic endplates was observed. PGE2 could activate its receptor EP4 in the newly innervated sensory nerves to cause spinal pain. It was recently reported that sensory nerves can monitor bone density changes through the concentration of PGE2. Osteoblast-secreted PGE2 activates its receptor EP4 in the sensory nerves to tune down sympathetic tone for osteoblastic bone formation. Chen et al., 2019. The porosity of the sclerotic endplates resembles low bone mineral density to promote PGE2 concentration and sensory innervation causing pain. These results indicate that PGE2 is a key mediator of pain hypersensitivity and endplate sclerosis. These findings suggest that inhibition of endplate sclerosis to reduce sensory innervation or blocking the PGE2/EP4 pathway could ameliorate spinal pain behavior.
Sensory nerves and CD31+EMCN+ vessels appeared largely in the porous areas of the sclerotic endplates. Osteoclast resorption likely causes the porosity of sclerotic endplates. Osteoclastic lineage cells secrete Netrin-1 to induce CGRP+ sensory nerve fiber extrusion and innervation in the space generated by osteoclast resorption. In addition, Netrin-1 is suggested to be a potential pro-angiogenic factor that promotes endothelial cell migration and capillary-like tube formation. Park et al., 2004; Tu et al., 2015. It has been shown that pre-osteoclasts secrete platelet-derived growth factor-BB to induce angiogenesis coupled with osteogenesis during bone formation. Xie et al., 2014. Thus, osteoclast activity in the sclerotic endplates is the primary cause of sensory innervation and angiogenesis for LBP. Indeed, decreased osteoclasts in Rankl−/− mice led to significantly decreased sensory innervation and angiogenesis in the endplates. Moreover, the density of sensory innervation and angiogenesis was reduced significantly by conditional knockout of Netrin-1 in TRAP+ osteoclastic cells. Therefore, osteoclast lineage cells instigate porosity of sclerotic endplates and spinal pain behavior.
The IVD and the endplate act in as a functional unit in the spine. A previous study revealed that aberrant mechanical loading induced hypertrophy of chondrocytes and calcification of the endplates, leading to an osteoclast-initiated remodeling sclerotic process. As a result, the expansion of mineralized endplates narrowed the intervertebral space and generated pathological static compression on the intervertebral disc, leading to its degeneration. Bian, 2016. The AF has been suggested as the main source of discogenic pain. In the physiological condition, only the outer third of the AF is innervated by sensory nerves, whereas in degenerative discs, the nerve can grow into the middle third, or even the inner third of the AF. Ohtori et al, 2015. In the current study, innervation of CGRP+ sensory fibers into the AF in WT mice after LSI surgery was observed, but the LSI-induced newly innervated sensory nerves in the AF were not decreased in Rankl−/− and Netrin-1−/− mice. On the other hand, during sclerosis of the endplates, osteoclast resorption generates porous areas and abundant sensory innervation along with angiogenesis. Importantly, the density of CGRP+ sensory nerve fibers in endplates and spinal pain behavior were significantly ameliorated in Rankl−/− and Netrin-1−/− mice after LSI surgery. These results indicate that osteoclast-induced sensory innervation in the sclerotic endplates is the primary source of nociceptors for spinal pain.
The sign of the hind paw mechanical allodynia is considered as the secondary indicator of spinal pain-associated behaviors. Several studies reported that the hind paw mechanical allodynia develops in low back pain animal models as the secondary hypersensitivity. Shuang et al., 2015; Kim et al., 2011; Millecamps et al., 2015: and Kim et al., 2015. Among these works of literature, one study about the lumbar facet joint osteoarthritis-induced spinal pain excluded the local inflammation or nerve injury (with negative straight leg raising test). Kim et al., 2015. These data also show the development of hind paw mechanical allodynia in the LSI model. One study demonstrated that the mouse sciatic nerve predominantly origins from the L3 and L4 DRG by injecting retrograde labeling in the hind paw. Rigaud et al., 2008. The presently disclosed retrograde tracing data demonstrated that L3 DRG is also the partial origin of sensory nerves in the endplates of L4/5 in LSI mice. In addition, the dorsal horn of spinal cord receives inputs from several segmental DRGs. Traub and Mendell, 1988; Kato et al., 2004. The major monosynaptic input for the dorsal horn neurons in L4 segment is from the L4-L6 DRGs, the dorsal horn neurons in L3 segment is from the L2-L5 DRGs. Pinto et al., 2008. These anatomical features might be the basis of the hind paw mechanical hypersensitivity in the LSI model.
Human endplate samples were obtained from patients undergoing spinal fusion surgery in the Department of Spine Surgery at Xiangya Hospital (Changsha, China). Ethics committee approvals and patient consent were obtained before harvesting human tissue samples. Detailed information about the patients and groups is provided in Table 1.
C57BL/6J (WT) male mice were purchased from Charles River Laboratories (Wilmington, Mass.). The mice were anesthetized at 2 months of age with ketamine (Vetalar, Ketaset, Ketalar; 100 mg/kg, intraperitoneally) and xylazine (Rompun, Sedazine, AnaSed; 10 mg/kg, intraperitoneally). Then, the LSI model was created by resecting the L3-L5 spinous processes and the supraspinous and interspinous ligaments to induce instability of the lumbar spine. Bian, 2016: Ariga et al., 2001; Miyamoto et al., 1991. Sham operations were performed by only detachment of the posterior paravertebral muscles from L3-L5 on a separate group of mice. For the time-course experiments, mice were euthanized with an overdose of isoflurane (Forane, Baxter) inhalation at 2, 4, 8, or 12 weeks after LSI or sham surgery (10-12 per group). For the aging-induced endplate degeneration model, 3- and 20-month-old C57BL/6J (WT) male mice were purchased from Jackson Laboratory (10-12 per group).
The Avil-Cre mouse strain was provided by Dr. Xinzhong Dong (The Johns Hopkins School of Medicine, Baltimore, Md.). The EP4flox/flox mouse strain was obtained from Dr. Brian L. Kelsall (National Institutes of Health, Bethesda, Md.). The Trap-Cre mouse strain was obtained from Dr. J. J. Windle (Virginia Commonwealth University, Richmond, Va.). The Netrin-1flox/flox mouse strain was provided by Dr. H. K Eltzschig (University of Texas Health Science Center at Houston, Houston. Tex.). Dnp1-Cre and Ranklflox/flox mouse strains were purchased from the Jackson Laboratory (Bar Harbor, Me.).
Heterozygous male Avil-Cre mice were crossed with EP4flox/flox mice. The offspring were intercrossed to generate the following genotypes: WT, Avil-Cre (mice expressing (re recombinase driven by Advilin promoter). EP4flox/flox (mice homozygous for the EP4 flox allele, referred to as FP4f/f herein) and Avil-Cre, EP4flox/flox (conditional deletion of EP4 in Advillin lineage cells, referred to as EP4−/− herein). Heterozygous Dmp1-Cre mice were crossed with Ranklflox/flox; the offspring were intercrossed to generate the following genotypes: WT, Dnp1-Cre (mice expressing Cre recombinase driven by Dmp1 promoter), Ranklflox/flox (mice homozygous for the Rankl flox allele, referred to as Ranklf/f herein), Dmp1-Cre; Ranklflox/flox (conditional deletion of Rankl in DMP1+ lineage cells, referred to as Rankl−/− herein) mice. Heterozygous Trap-Cre mice were crossed with Netrin-1flox/flox; the offspring were intercrossed to generate the following genotypes: WT, Trap-Cre (mice expressing Cre recombinase driven by Trap promoter). Netrin-1flox/flox (mice homozygous for the Netrin-1 flox allele, referred to as Netrin-1f/f herein). Trap-Cre: Netrin-1flox/flox (conditional deletion of Netrin-1 in TRAP+ lineage cells, referred to as Netrin-1−/− herein) mice. The genotypes of the mice were determined by PCR analyses of genomic DNA, which was extracted from mouse tails within the following primers: Avil-Cre: Forward: 5′-CCCTGTTCACTGTGAGTAGG-3′ (SEQ ID NO: 1). Reverse: 5′-GCGATCCCTGAACATGTCCATC-3′(SEQ ID NO: 2). WT: 5′-AGTATCTGGTAGGTGCTTCCAG-3′(SEQ ID NO: 3): FP4 loxP allele Forward: 5′-TCTGTGAAGCGAGTCCTTAGGCT-3′(SEQ ID NO: 4). Reverse: 5′-CGCACTCTCTCTCTCCCAAGGAA-3′(SEQ ID NO: 5): Dmp1-Cre. Forward: 5′-CCCGCAGAACCTGAAGATG-3′(SEQ ID NO: 6), Reverse: 5′-GACCCGGCAAAACAGGTAG-3′(SEQ ID NO: 7), Rankl loxP allele: Forward: 5′-CTGGGAGCGCAGGTTAAATA-3′(SEQ ID NO: 8), Reverse: 5′-GCCAATAATTAAAATACTGCAGGAAA-3′(SEQ ID NO: 9); Trap-Cre: Forward: 5′-ATATCTCACGTACTGACGGTGGG-3′(SEQ ID NO: 10), Reverse: 5′-CTGTTTCACTATCCAGGTTACGG-3′(SEQ ID NO. 11); Netrin-1 loxP allele: Forward: 5′-AGGTAAAGTCTCCTACGCGG-3′(SEQ ID NO: 12). Reverse: 5′-CTTCCAAACCTGAACCGCCC-3′(SEQ ID NO: 13). LSI or sham surgery was performed in 2-month-old male EP4f/f, EP4−/−, Rankl−/−, Rankl−/−, Netrin-1f/f, and Netrin-1−/− mice. These mice were euthanized with an overdose of isoflurane inhalation at 4 or 8 weeks after LSI or sham surgery (12 per group) All mice were maintained at the animal facility of The Johns Hopkins University School of Medicine. All experimental protocols were approved by the Animal Care and Use Committee of The Johns Hopkins University, Baltimore. Md.
Mice were euthanized with an overdose of isoflurane inhalation and flushed with phosphate-buffered saline (PBS) for 5 min followed by 10% buffered formalin perfusion for 5 min via the left ventricle. Then, the lower thoracic and whole lumbar spine were dissected and fixed in 10% buffered formalin for 48 h, transferred into PBS, and examined by high-resolution sCT (Skyscan1172). The scanner was set at a voltage of 55 kVp, a current of 181 μA, and a resolution of 9.0 μm per pixel to measure the endplates and vertebrae. The ribs on the lower thoracic spine were included for identification of L4-L5 unit localization. Images were reconstructed and analyzed using NRecon v 1.6 and CTAn v 1.9 (Skyscan US, San Jose, Calif.), respectively. Coronal images of the L4-L5 unit were used to perform 3-dimensional histomorphometric analyses of the caudal endplate. Coronal images of the L5 vertebrae were used to perform 3-dimensional histomorphometric analyses of the trabecular bone or cortical bone (anterior shell). Three-dimensional structural parameters analyzed were total porosity and Tb.Sp for the endplates, trabecular BV/TV, Tb.N. Tb.Th, and Th. Sp for L5 vertebrae. Six consecutive coronal-oriented images were used for showing 3-dimensional reconstruction of the endplates and the vertebrae using 3-dimensional model visualization software. CTVol v2.0 (Skyscan US).
1.5.5 Histochemistry, Immunohistochemistry, and Histomorphometry
At the time of euthanasia, the L3-L5 lumbar spine and DRGs were collected and fixed in 10% buffered formalin for 48 h or overnight. Then, the spine samples were decalcified in 10% or 0.5M EDTA (pi 7.4) for 14 or 5 d and embedded in paraffin or optimal cutting temperature (OCT) compound (Sakura Finetek. Torrance. Calif.). Four-μm-thick coronal-oriented sections of the L4-L5 lumbar spine were processed for Safranin O and fast green, TRAP (Sigma-Aldrich), and immunohistochemistry staining using a standard protocol. Thirty-μm-thick coronal-oriented sections were prepared for sensory nerve- and blood vessel-related immunofluorescent staining, and ten-μm-thick coronal-oriented sections were used for other immunofluorescent staining using a standard protocol. The sections were incubated with primary antibodies to mouse endomucin (1:50, sc-65495. Santa Cruz Biotechnology), CD31 (1:50, ab28364, Abcam). CGRP (1:100, ab81887, Abcam), PGP9.5 (1:100, ab10404. Abcam), DCC (1:100, ab201260, Abcam), Netrin-1 (1:100, ab39370, Abcam), TRAP (1:200, ab185716, Abcam). Cox-2 (1:100, ab15191. Abcam), EP4 (1:10, ab92763, Abcam), IB4 (1:100, I21411. Thermo Fisher Scientific, Waltham, Mass.), Nav 1.8 (1:100, ab93616, Abeam) PGE2 (1:100, ab2318, Abeam) overnight at 4° C. Then, the corresponding secondary antibodies were added onto the sections for 1 h while avoiding light. For immunohistochemistry, a horseradish peroxidase-streptavidin detection system (Dako) was subsequently used to detect the immunoactivity, followed by counterstaining with hematoxylin (Sigma-Aldrich). For immunofluorescent staining, the sections were counterstained with 4′,6-diamidino-2-phenylindole (DAPI, Vector, H-1200). The sample images were observed and captured by a fluorescence microscope (Olympus BX51, DP71) or confocal microscope (Zeiss LSM 780). ImageJ (NIH) software was used for quantitative analysis. Endplate scores were calculated as described previously. Boos et al., 2002; Masuda et al., 2005.
2-month-old male C57BL/6J mice (Charles River) were used to perform LSI or sham surgery (6 per group). The mice were anesthetized with ketamine and xylazine at 8 weeks after surgery. For the retrograde nerve tracing experiment, the caudal endplate of L4-L5 was adequately exposed with a ventral approach. Then, 2 μL Dil (Molecular Probes; 2 mg/mL in methanol) was injected into the left part of caudal endplate of L4-L5 using borosilicate glass capillaries after drilling a hole at left part of endplate. The drilling holes were sealed with bone wax immediately after injection to prevent tracer leakage. After Dil injection, the wound was sutured, and a heating pad was used to protect mice during recovery from anesthesia Mice were euthanized with an overdose of isoflurane inhalation, and the DRGs (T12-L6) were isolated for immunofluorescence at 1 week after Dil injection. Ten-μm-thick frozen sections were used, and the Dil signals were inspected under 564-nm excitation using a confocal microscope (LSM 780, Zeiss).
For the anterograde tracing experiment, 2-month-old male C57BL/6J mice (Charles River) were used to perform LSI or sham surgery and 3- and 20-month-old male C57BL/6J mice (Jackson Laboratory) were prepared for the aging-induced endplate degeneration model (6 per group). The aging model mice and the operated mice were anesthetized at 8 weeks after surgery with ketamine and xylazine. The L1 and L2 DRGs were adequately exposed with a dorsal approach. Then, 2 μL Dil (Molecular Probes; 2 mg/mL in methanol) was injected into the DRGs using borosilicate glass capillaries. After Dil injection, the wound was sutured, and a heating pad was used to protect mice during recovery from anesthesia. Mice were euthanized with an overdose of isoflurane inhalation, and the L3-L5 spine was collected for immunofluorescence at 1 week after Dil injection. Thirty-μm-thick coronal-oriented frozen sections were used, and the Dil signals were inspected under 564-nm excitation using a confocal microscope (LSM 780, Zeiss).
1.5.7 qRT-PCR
Total RNA was extracted from lumbar spinal endplate tissue samples using TRIzol reagent (Invitrogen. Carlsbad, Calif.) according to the manufacturer's instructions. The purity of RNA was tested by measuring the ratio of absorbance at 260 nm over 280 nm. For qRT-PCR, 1 μg RNA was reverse transcribed into complementary DNA using the SuperScript First-Strand Synthesis System (Invitrogen), then qRT-PCR was performed with SYBR Green-Master Mix (Qiagen, Hilden, Germany) on a C1000 Thermal Cycler (Bio-Rad Laboratories, Hercules, Calif.). Relative expression was calculated for each gene by the 2−
The concentrations of PGE2 and netrin-1 in the L3-L5 endplates were determined by using the PGE2 Parameter Assay Kit (KGE004B, R&D Systems) and Mouse Netrin-1 ELISA Kit (EKC37454, Biomatik, Wilmington, Del.) according to the manufacturer's instructions (3 per group), respectively.
DRG neuron culture was processed as described previously. Saijilafu and Zhou, 2012. Briefly, the dishes or coverslips for DRG neuron culture were coated with 50 μL working solution containing 100 μg/mL Poly-D-Lysine and 10 g/mL Laminin at 37° C. To prepare the neuron culture medium, alpha minimum essential medium (α-MEM) was supplemented with 1× penicillin-streptomycin solution (500 units of penicillin and 500 μg of streptomycin, Gibco Laboratories, Gaithersburg, Md.), 5% fetal bovine serum (Gibco), 1× GlutaMAX-1 supplement (35050-061, Thermo Fisher Scientific), and the antimitotic reagents containing 20 μM 5-fluoro-2-deoxyuridine (F0503, Sigma-Aldrich) and 20 μM uridine (U3003, Sigma-Aldrich). For the serum-free medium, the fetal bovine serum was replaced with the supplement B27. After euthanizing the 6- to 8-week-old mice, the lumbar DRGs were harvested and stored in microfuge tubes with α-MEM medium placed on ice. DRG neurons were digested and dissociated with 1 mg/mL collagenase A solution (10103578001, Roche, Basel, Switzerland) in a 37° C. incubator for 90 min followed by 1× TrypLE Express solution (15140-122, Thermo Fisher) at 37° C. for 20 min. Then, TrypLE Express solution was removed, and DRGs were washed gently 3 times with 1 mL prepared culture medium (containing 5% fetal bovine serum). Tissue was triturated by gently pipetting up and down 20-30 times in 1 mL prepared culture medium. After trituration, the DRG neuron suspension was filtered (40-μm strainer) following non-dissociated tissue settlement to the bottom of the microfuge and transferred to another tube. After centrifugation (800 r.p.m for 4 min at room temperature), the cell pellet was resuspended and cultured in a precoated dish.
The primary DRG neurons were treated with 20 μM PGE2(14010, Cayman Chemical, Ann Arbor, Mich.) for 30 min; 10 μM PKA inhibitor (H-89, BML-E1196, Enzo Life Sciences, Farmingdale, N.Y.) for 1 h. Western blot analysis was conducted on the protein lysates from the cultured primary DRG neurons. The supernatants of lysates were collected after centrifugation and separated by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and then blotted on the Nitrocellulose Blotting Membranes (Bio-Rad Laboratories). Specific antibodies were applied for incubation, and the proteins were detected by using an enhanced chemiluminescence kit (Amersham Bioscience, RNP2108). The antibodies used for western blot were pCREB (1:1000, 9198, Cell Signaling Technology), CREB (1:000, 9197, Cell Signaling Technology), pPKA (1:1000, 5661, Cell Signaling Technology), PKA (1:1000, 4782S. Cell Signaling Technology), and p-tubulin (1:2000, MA5-16308, Invitrogen). The original blots are provided in the Source Data file.
For sodium indication. ANG-2 AM (Teflabs, Austin, Tex.) was used according to the manufacturer's protocol. Briefly, 1 mM stock solution of ANG-2 AM was diluted to twice the original volume with a solution of 20% Pluronic F-127 (Thermo Fisher Scientific) in DMSO. Then, the ANG-2 AM/Pluronic F-127 solution was dispersed to final concentration at 5 μM ANG-2 AM and 0.1% Pluronic F-127 with serum-free culture medium. After incubation for 1 h at 37° C., the cell loading medium was removed. The cells were washed with serum-free and dye-free medium and prepared for sodium imaging. The sterile imaging buffer contained 5.4 mM KCL, 160 mM NaCL, 20 mM HEPES, 1.3 mM CaCL2, 0.8 mM MgSO4, 0.78 mM NaH2PO4, and 5 mM glucose (pH 7.4) The sodium imaging was monitored and captured using a confocal microscope (Zeiss LSM 780).
In different sets of experiments, the DRG neurons were treated with 20 μM PGE2 (14010, Cayman Chemical, Ann Arbor, Mich.) for 5 min. 10 μM PKA inhibitor (H-89, BML-E1196, Enzo Life Sciences, Farmingdale, N.Y.) for 1 h, dibutyryl-cAMP (28945. Sigma-Aldrich) for 5 min, or siRNA oligo for Nav 1.8 (GE Healthcare Dharmacon, Lafayette, Colo.). The siRNA transfection was by using Lipofectamine RNAiMAX Transfection Reagent (Thermo Fisher Scientific) using a standard protocol.
For immunostaining, the DRG neurons were washed 3 times with PBS, followed by fixation by 4% paraformaldehyde (PFA) for 20 min at room temperature. The immunofluorescent staining used a standard protocol. The coverslips were incubated with primary antibodies to mouse CREB (1.100, 9197. Cell Signaling Technology), p-CREB (1:100, ab32096, Abcam), CGRP (1:100, ab81887, Abeam), PKA (1:100, 4782, Cell Signaling Technology), and p-PKA (1:100, ab227848, Abcam) overnight at 4° C. Then, the corresponding secondary antibodies were added onto the coverslips for 1 h while avoiding light. The coverslips were counterstained with 4′,6-diamidino-2-phenylindole (DAPI, Vector, H-1200). The sample images were observed and captured using a microscope (Olympus BX51, DP71).
Behavioral testing was performed before surgery and weekly after surgery. All behavioral tests were performed by the same investigator, who was blinded to the study groups. Vocalization thresholds in response to the force of an applied force gauge (SMALGO algometer: Bioseb. Pinellas Park, Fla.) were measured as pressure hyperalgesia. Yu et al., 2012.
A 5-mm-diameter sensor tip was directly pressed on the dorsal skin over L4-L5 (0.5 cm above the line connecting posterior iliac crest) while the mice were gently restrained. The pressure force was increased at 50 g/sec until an audible vocalization was made. The curve of pressure force was recorded by using BIO-CIS software (Bioseb) to ensure the force increased gradually. A cutoff force of 500 g was used to prevent tissue trauma. Two tests were performed 15 min apart, and the mean value was calculated as the nociceptive threshold.
Spontaneous wheel-running activity was recorded using activity wheels designed for mice (model BIO-ACTIVW-M, Bioseb). Cobos et al., 2012. The software enabled recording of activity in a cage similar to the mice's home cage, with dimensions of 35×20×13 cm, and the wheel (diameter: 23 cm, lane width: 5 cm) could be spun in both directions. The device was connected to an analyzer that automatically records the spontaneous activity. The mice had ad libitum access to food and water. The distance traveled, mean speed, maximum speed, and total active time during 2 days were evaluated for each mouse.
The hind paw withdrawal frequency in response to a mechanical stimulus was determined using von Frey filaments of 0.7 mN and 3.9 mN (Stoelting, Wood Dale, Ill.). Mice were placed on a wire metal mesh grid covered with a clear plastic cage. Mice were allowed to acclimatize to the environment for 30 min before testing Von Frey filaments were applied to the mid-plantar surface of the hind paw through the mesh floor with enough pressure to buckle the filaments. Probing was performed only when the mouse's paw was in contact with the floor. A trial consisted of application of a von Frey filament to the hind paw 10 times at 1-sec intervals. If withdraw occurred after application, it was recorded, and the next application was performed similarly when the mouse's paw was again in contact with the floor. Mechanical withdrawal frequency was calculated as the percentage of withdrawal times in response to 10 applications.
Straight leg raising test was performed by stretching the hindlimb (knee joint fully extended) and flexing the hip for 2 seconds. The number of vocalizations in 5 leg stretch-and-lifts were recorded. Kim et al., 2015: Kroin et al., 2005. The negative result indicates that the nerve root compression is not involved in the hyperalgesia developed after LSI surgery.
All data analyses were performed using SPSS, version 15.0, software (IBM Corp.). Data are presented as means±standard deviations. For comparisons between two groups, unpaired, two-tailed Student's t-tests were used. For comparisons among multiple groups, one-way ANOVA with Bonferroni's post hoc test was used. For all experiments. P<0.05 was considered to be significant. All inclusion/exclusion criteria were preestablished, and no samples or animals were excluded from the analysis. No statistical method was used to predetermine the sample size. The experiments were randomized, and the investigators were blinded to allocation during experiments and outcome assessment. The same sample was not measured repeatedly.
Low back pain (LBP) is a common clinical and public health problem. LBP profoundly affects quality of life and daily physical activity, especially in the elderly population, increasing risk of frailty and loss of socioeconomic function. It is estimated that disability-adjusted life-years (DALYs) caused by low back pain has risen from 17th in 1990 to 13th in 2017 in China among all diseases. Zhou et al., 2019, and was the first leading cause of years lived with disability (YLD) worldwide in 2016. Global, regional, and national incidence, prevalence, and years lived with disability for 328 diseases and injuries for 195 countries, 1990-2016: a systematic analysis for the Global Burden of Disease Study 2016. With an aging population and developing society, the socioeconomic burden is enormous. An estimated 149 million work days are lost every year in the United States alone because of LBP, Manchikanti, 2000, with total costs estimated to be $100-200 billion annually. Katz, 2006.
Several pathologies, like lumbar disc hemiation (LDH), scoliosis, tumor and infection, can result in low back pain. The gold standard therapy remains orthopedic surgical intervention, including: disc arthroplasty, decompression, artificial disc replacement, and spinal fusion. Wenger and Cifu, 2017; Hartvigsen et al., 2018. However, non-specific LBP (i.e., without known pathoanatomical cause) accounts for about 90% of total LBP cases, Koes et al., 2006, including the asymptomatic early-stage disc degenerative disease (DDD).
Despite the high prevalence of non-specific LBP, no ideal intervention is available. Instead, education and reassurance, pharmacological and non-pharmacological therapies have been adopted in various guidelines, but none of these therapies are targeted. In terms of pharmaceutical efficacy and WHO analgesic ladder, the four major classes of medications indicated for acute LBP are paracetamol, opioids, non-steroidal anti-inflammatory drugs (NSAIDs, including COX-2 inhibitors), and skeletal muscle relaxants, while tricyclic antidepressants and benzodiazepines are recommended for chronic cases. Maher et al., 2017.
Other minor classes, such as triptans, 2-agonists, and local anesthetics, have more specific, but limited effects on certain types of pain (i.e., mostly acute) or related disorders. These medications are accompanied with side effects ranging from addiction, respiratory depression, constipation (opioids), gastrointestinal and cardiovascular damage (NSAIDs), to a myriad of negative central nervous system (CNS) effects (anticonvulsants and antidepressants). Additionally, LBP is prone to recurrence after withdrawal. In all of these circumstances, it is believed that patients need not pain killers, but disease modifying therapies that abrogate or abolish pain. Due to the limited understanding of non-specific LBP pathogenesis during early- and middle-staged DDD, however, there is no disease modifying drugs (DMDs) to prevent and treat it.
Most evidence presented thus far attributes low back pain to DDD in the lumbar region. Luoma et al., 2000. This evidence suggests its etiology is multifactorial and affected by genetics, Battie et al., 2008; gender, Miller et al., 1988; aging, Powell et al., 1986; high mechanical stress, Videman et al., 1995; and disc dystrophy, Benneker et al., 2005. Gullbrand et al., 2015. The anatomically intact intervertebral disc (IVD), especially the nucleus pulposus (NP), is commonly considered an avascular organ except for the outer annulus fibrosus (AF) layer. Nutrients reach the IVD predominantly by diffusion through the vertebral endplate, so the NP has precarious nutrition. Rodriguez et al., 2012. Endplate has been demonstrated to be remodeled during aging, undergoing gradual ossification with elevated osteoclasts number and increased porosity, Rodriguez et al., 2012, Jia et al., 2016; Bian et al, 2016; Bian et al., 2017; and Papdakis et al., 2011, thereby leading to disc degeneration. Gruber et al., 2005; Gruber et al., 2007. In previous studies. Wei et al, 2015; Zhou et al., 2013, an intervertebral disc degeneration model was established in rhesus monkeys by injecting pingyangmycin, an anti-endothelial drug, into the sub-endplate region to block the blood sinus in the endplate. These studies supported the dystrophy disorder hypothesis.
Moreover, the endplate degeneration also showed a high correlation with LBP. Jensen et al., 2008. Patients with osteoporosis are usually affected with discogenic LBP, so this phenomenon was reproduced in an OVX-induced osteoporosis rhesus monkey model. The disc degeneration in the OVX group was more severe than that of the control. Zhong et al., 2016. Endplate remodeling also was confirmed by increased calcification and porosity, as well as decreased vascularization in the endplates adjacent to the degenerated IVDs. These pathological features exacerbated degeneration of the IVDs in the animals with osteoporosis. The data suggested that the endplate becomes sclerotic from elevated remodeling of the cartilage under normal physiological weight bearing during aging. In addition, similar endplate changes were observed under aberrant mechanical loading in the lumbar spine instability (LSI) mice model. Bian, 2016. Endplates become sclerotic after LSI because high levels of TGF-β are activated by osteoclast-mediated resorption of the cartilage matrix. A more recent study revealed that sensory innervation accompanies the osteoclast-mediated initiation of endplate sclerosis, resulting in LBP (unpublished results). Without wishing to be bound to any one particular theory, it is thought that LBP can be attenuated by preventing endplate remodeling and sclerosis, ultimately slowing disc degeneration.
Parathyroid hormone (PTH), a systemic hormone that regulates calcium homeostasis, plays a major role in orchestrating bone remodeling by modulating the bone marrow microenvironment and the signaling of local factors. Bikle et al., 2002; Canalis et al., 1989: Miyakoshi et al., 2001: Pfeilschifter et al., 1995: Wein and Kronenberg, 2018: Fan et al., 2017: Wan et al., 2008; Yu et al., 2012; and Qui et al., 2010.
Teriparatide (PTH(1-34′)) is an analogue of PTH and consists of the first (N-terminus) 34 amino acids. It is an FDA-approved anabolic agent to stimulate bone formation for treatment of osteoporosis. PTH(1-34′) not only improved bone density in patients with osteoporosis, but also attenuated LBP in various cases. For example, PTH ameliorated LBP for at least 18 months after discontinuation. Fahrleitner-Pammer et al., 2011: Jakob et al., 2012, which suggests the pain relief resulted from structural remodeling of the spine components, apart from the improvement of osteoporotic conditions. Although several clinical studies have reported similar phenomena, Fahrleitner-Pammer et al., 2011; Langdahl et al., 2016: and Koski et al., 2013, no biological mechanism has been described.
It also has been recently reported that the cilia of NP cells mediates mechanotransduction to maintain anabolic activity in the IVD. Zheng et al., 2018. It was found that mechanical stress promotes transport of the type 1 parathyroid hormone receptor (PTH1R) to the cilia and enhances PTH signaling in NP cells. Daily injection of PTH effectively attenuated disc degeneration of aged mice by direct signaling through NP cells. Given sensory innervation in the pores of endplate is associated with LBP, daily injection of PTH can increase bone formation and attenuate disc degeneration in animals and provide relief of back pain. In the present example, the role of sensory innervation in vertebral endplates and the remodeling of sclerotic endplates in the attenuation of LBP after daily injection of PTH was investigated.
To examine the potential effect of PTH on spinal degeneration and pain, lumbar spine instability (LSI) and aging mouse models were established. LSI or sham mice were injected with PTH and hyperalgesia tests of pressure tolerance were performed for their low back pain (
Whether PTH-reduced LBP modified spine degeneration also was examined. Previous studies have demonstrated that sclerosis of endplates decreases IVD space and increased porosity and volume of the endplate in both LSI and aging mice. Indeed, endplates in 4-month sham-operation mice showed few cavities detected in μCT images (
As previously reported, innervation of nerve fiber in the porous endplates or the inner 2/3 of annulus fibrosus were the sources of LBP. The change of sensory innervation in the sclerotic endplates and annulus fibrosus after iPTH was then examined. PGP9.5 is a broad marker of nerve fibers. Immunostaining of intervertebral disc sections with PGP9.5 showed that there is no PGP9.5 positive fibers in the sham endplates except for the periphery of annulus fibrosus (
To determine which kinds of nerve fibers grow into the endplate, a retrograde of DIL was performed by injecting it into L4-5 endplate as previously reported. L1-L2 DRG sections were immuno-stained with antibodies against PGP9.5, CGRP, IB4, P2X3, PIEZO2 or NF200 respectively for different sensory nerve fibers. The results showed that there were no DIL positive neuron in sham-operated mice (
2.2.4 PTH-Induced Remodeling of Sclerotic Endplates Reduces their Porosity
To understand the potential mechanism of PTH treatment in increase of IVD space and reducing sensory innervation, whether PTH induces remodeling of sclerotic endplates was examined. Trap staining and osteocalcin immunostaining revealed that osteoclasts and osteoblasts were not observed in the endplates of sham operated mice, but significantly increased in the endplates post LSI surgery and aged mice (
As the sensory nerve fibers were detected in the cavities, axon attractive factor Netrin-1, NGF played an important role in sensory innervation in the endplates. To examine if axon attractive and repulsive factors play a role in the reduction of sensory nerve fibers after iPTH, the mRNA expression of the potential factor by qPCR was measured. The results showed that iPTH stimulated expression of Slit-3 and Sema-3a in the endplates of LSI, but reduced the expression of NGF and inflammatory factors including PGE2 related genes although there was no significant change in netrin-1 in the bone formation. The observation suggested iPTH-induced decrease of porosity and increase of secretion of axon repulsive factors likely results in reduction of sensory innervation in the endplates.
It has been previously shown that PGE2 secreted by osteoblastic cells activates PGE2 receptor 4 (EP4) in sensory nerves to maintain bone homeostasis by modulation of sympathetic activity through the central nervous system (Chen et al., 2019) and PGE2 levels in the bone are positively correlated with bone density. Porous endplates resemble osteoporotic bone elevated PGE2 levels, which stimulate sensory nerves that lead to LBP (in press). Thus, whether porosity structure of endplates enhances mechanical loading-stimulated PGE2 secretion by finite element analysis was examined (
PTH binds to the type 1 parathyroid hormone receptor (PTH1R), which is expressed in high levels in osteoblast and osteocyte cells in bone and regulates bone homeostasis through activation of adenylate cyclase and phospholipase C. Deletion of PTH1R ensures blocking of the PTH signaling cascade. Knockout of PTH1R in osteocalcin-positive osteoblast cells of LSI mice was induced to confirm the nerve repulsion role of PTH at the remolding of porosity endplate. Similarly to wild type mice with PTH treatment, the total porosity and endplate volume were significantly reduced in the PTHR f/f mice after 2 months iPTH treatment post-surgery relative to the vehicle treatment.
As reported in a previous study, daily injection of PTH effectively attenuated disc degeneration of aged mice with expressed aggrecan by direct signaling through NP cells, which cannot only induce DRG growth cone collapse, but also inhibit DRG axonal growth. Zheng, L., et al., 2018. Knockout of PTH1R was induced in notochord cells of LSI mice to confirm if the nerve repulsion factors from nucleus pulposus after PTH treatment.
2.27 iPTH Attenuates Endplate Sclerosis and Disc Degeneration in Aging Monkey
To confirm the effects of iPTH in the disc degeneration, especially the endplate sclerosis, eight aging monkeys, which had similar disc degenerated grade in L1-L5 lumbar, were screened and half of them were treated for 3 months with iPTH, the others were treated with vehicle (
In addition, the signals change of disc after 3 months post-iPTH-treated-3 m also was monitored. Although the high signals of disc at iPTH 3 m had been reduced when stopping the injection of iPTH for 3 m, the signals of disc at vehicle group at 6 m had become lower as compared that at 0 m and 3 m. Further, the results of pfirrmann grade of vehicle 6 m were significantly increased than that at 0 m. Meanwhile, the decreased values of T1ρ and T2 map within 6 m in vehicle group also confirmed disc degeneration with aging, while the T1ρ and T2 map values increased after iPTH treatment, especially the T2 map values continued high expression in PTH group at 6 m, stopping the injection of iPTH for 3 m, indicated the function of disc regeneration after iPTH.
In summary, the endplate as the main structure contributing the nutrient diffusion from vertebrate to disc, which had been evaluated by micro-CT and tissue staining. As found in the above description of mice, large bone marrow cavities occurred in front of the endplate in aging monkey, but the porosity was significantly reduced in the iPTH-treated group. Moreover, the area of cartilage in the endplate also showed that they were significantly increased after iPTH. Thus, these data further demonstrated that iPTH can reduce sensory innervation and spine pain by remodeling of the porous endplate.
Osteoarthritis (OA) is a debilitating and leading prevalent joint degeneration characterized by joint pain and disability. The current treatment of OA fails to attenuate OA progression and decrease joint pain effectively. Here it is shown that PTH attenuates OA pain by inhibition of nerve innervation and subchondral bone deterioration and articular cartilage degeneration in DMM mouse model. It was found that sensory nerve innervation for OA pain is significantly decreased in PTH-treated DMM mice compared with vehicle-treated DMM mice. In parallel, deteriorated subchondral bone microarchitecture defined as higher trabecular pattern factor (Tb.pf), structure model index (SMI), and increased thickness of subchondral bone plate (SBP.Th) in vehicle-treated DMM control is attenuated by PTH treatment. PGE2 in subchondral bone is increased in response to large porosity of subchondral bone in DMM mice. Furthermore, uncoupled subchondral bone remodeling by increased TGFβ signaling is regulated by PTH-induced endocytosis of the PTH1R-TβRII complex. Notably, conditional knockout the PTH type I receptor in nestin+ MSCs eliminates PTH-induced improved deteriorated subchondral bone microarchitecture, subsequent and PGE2 concentration in the subchondral bone and decreased sensory nerve innervation for OA pain. These studies reveal that PTH attenuates OA progression and OA pain by inhibition of subchondral bone microarchitecture deterioration and sensory nerve innervation.
Osteoarthritis (OA) is a leading cause of disability as the most common degenerative joint disorder, MMWR. Morbidity and mortality weekly report. 2009, and chronic pain is the most prominent symptom of osteoarthitis (OA), affecting nearly 40 million people in the US. Peat et al., 2001. Pain itself is also a major risk factor for the development of future functional limitation and disability in OA patients. Lane et al., 2010. Unfortunately, OA pain treatment remains challenging and represents a large unmet medical need. It is not clear what causes OA pain, and currently there is no effective way to relieve it. Available therapies (NSAIDs, steroids, visco-supplementation such as intra-articular injection of hyaluronic acid) only alleviate mild joint OA pain. Geba et al., 2002; Karlsson et al., 2002.
Relief from chronic OA pain remains an unmet medical need and still major reason for seeking surgical intervention. Despite the efforts, the origins of pain and its molecular mechanisms remain poorly understood. Significant efforts have been focused on synovium inflammation mediated sensitization of sensory neurons. Malfait and Schnitzer, 2013. Yet, OA pain can develop at very early stages without inflammation and independently of progressive cartilage degeneration. Many asymptomatic patients have osteoarthritic radiographic changes while other patients have OA pain with no radiographic indications. Bedson and Croft, 2008: Dieppe and Lohmander, 2005: Hannan et al., 2000. Some patients with bilateral radiographic OA yet present with unilateral knee pain. Far less attention has been paid to subchondral bone than to synovium, and the investigations into the mechanism how subchondral bone remodeling generates OA pain are lacking
The sources and mechanisms for OA pain remain unclear. Multiple tissues including synovium, Kc et al., 2016, ligament, Ikeuchi et al., 2012, and meniscus, Mapp and Walsh, 2012, were suggested to be the sites where pain is originated. In particular, significant efforts have focused on synovium inflammation (synovitis) and cartilage degeneration. Malfait and Schnitzer, 2013. Intriguingly, subchondral bone marrow edema-like lesions (BMLs) are highly correlated with OA pain. Yusuf et al., 2011; Kwoh, 2013. Zoledronic acid, which inhibits osteoclasts activity, reduces the BML size and concomitantly alleviates pain. Laslett et al., 2012. Furthermore, OA patients report rapidly pain relief after removal of partial subchondral bone with deteriorated cartilage by total knee replacement. Isaac et al., 2005; Reilly et al., 2005.
Subchondral bone remodeling is increased during OA progression. Zhen and Cao, 2014. It is shown that osteoclasts initiate aberrant bone remodeling and increase the secretion of netrin-1, which triggers abnormal sensory nerve innervation in the subchondral bone and causes OA pain. Subchondral bone marrow edema-like lesions (BMLs) are highly correlated with pain in OA patients. Kwoh, 2013; Laslett et al., 2012.
Analysis of the NIH Osteoarthritis Initiative (OAI) data also suggested that patients taking bisphosphonate experienced significantly reduced knee pain at year 2 and 3. Laslett et al., 2014. Bone homeostasis is maintained by temporal-spatial activation of TGF to couple bone resorption and formation. Zhen and Cao, 2014, in which subchondral bone is maintained in a native microarchitecture with blood vessels and nerves intertwined under normal condition. However, excessive active TGFβ in the subchondral bone induces aberrant bone remodeling at the onset of OA to promote its progression. Specifically, high levels of active TGFβ recruit Nestin+ MSCs and Osterix+ osteoprogenitors in clusters, leading to abnormal bone formation and angiogenesis. Zhen et al., 2013. Increased osteoclast activity is associated with angiogenesis at the onset of OA. Zhen et al., 2013; Xie et al., 2014. Since nerves and blood vessels develop together, the increased osteoclast activity likely induces abnormal sensory nerve innervation in the subchondral bone for the OA pain.
Parathyroid hormone (PTH), an FDA-approved anabolic agent for osteoporosis, regulates bone remodeling and calcium metabolism. Qiu et al., 2010; Pfeilschifter et al., 1995; Tang et al., 200) Woolf, 2011. The parathyroid gland, the main production site of the PTH, evolved in amphibians, Mease et al., 2011, and represents the transition of aquatic to terrestrial life, Suokas et al., 2012, adapting terrestrial locomotion from aquatic vertebrates. PTH is the hormone that PTH is demonstrated to induce cartilage regeneration for injury-induced OA, Sampson et al., 2011, Intermittent PTH stimulates subchondral bone and articular cartilage repair in the treatment of focal osteochondral defects. Orth et al., 2013.
The PTH is also shown to prevent the deterioration of the subchondral bone and cartilage degeneration during OA. Yan et al., 2014. It has been shown that PTH is demonstrated to interact with locally osteopotric factors to orchestrate with an anabolic signaling network of the coupling of bone resorption and formation. Qiu et al., 2010; Pfeilschifter et al., 1995. TGF-β elicits its cellular response through the ligand-induced formation of a heteromeric complex containing TGF-β types I (TβRI) and II (TβRII) kinase receptors. Tang et al., 2009; Wrana et al., 1992.
Several lines of evidence have indicated that PTH and TGF-β work in concert to exert their physiological activities in bone. PTH induces endocytosis of PTH1R with TβRII as a complex and signaling of both PTH and TGFβ is coordinately regulated during endocytosis. Qiu et al., 2010.
This study investigates whether iPTH could attenuate pain by modifying OA as it has positive effect on both OA subchondral bone and articular cartilage. It was found that PTH reduces OA pain and attenuates progression of OA by preventing subchondral bone deterioration and cartilage degeneration in OA mice. PTH reduces sensory nerve innervation in the subchondral bone and OA pain through maintaining subchondral bone micro-architecture of sustaining of coupled bone remodeling.
3.3.1 iPIH Attenuates Osteoarthritic Pain and Joint Degeneration
To investigate the effect of PTH on OA pain, PTH was administered subcutaneously in OA mice post DMM for two months. Pain behavior tests were performed including paw withdrawal threshold (PWT), pressure application measurement (PAM) and gait analysis at different timepoints (
3.3.2 iPTH Induces Regression of Sensory Nerve Fibers in Subchondral Bone in OA Mice
To examine the potential mechanism of PTH-reduced OA pain, the effect of iPTH on sensory nerve innervation in subchondral bone was examined. The immunostaining of subchondral bone sections revealed that calcitonin gene-related peptide (CGRP)+ and substance P (SP)+ sensory nerve fibers significantly increased in vehicle-treated DMM mice relative to sham operated mice, and iPTH ameliorated them(
3.3.3 iPTH Sustains Subchondral Bone Micro-Architecture
To examine PTH effect on subchondral bone changes in OA, PTH was administered daily subcutaneously in mice post DMM for 8 weeks and analyzed the effect over time. iPTH sustained the micro-architecture of tibial subchondral bone after DMM relative to sham-operated mice and DMM vehicle mice as determined by μCT analysis (
3.3.4 iPTH Attenuate Elevated Active TGF-§ Signaling by Endocytosis of TGFβIIR
To explore the potential mechanism of PTH restoring coupled subchondral bone remodeling, the effect of PTH on osteoblast-lineage cell was detected. Immunostaining of nestn+ and osterix+ osteoprogenitors were largely located on the bone surface in sham group and DMM PTH group while nestin+ and osterix+ osteoprogenitors in subchondral bone marrow dramatically increased in DMM vehicle group (
TβRII was largely localized at mesenchymal stromal cell (MSC) membrane and the amount of cell-surface TβRII was decreased significantly after stimulated with PTH (
To examine the effect of PTH treatment on progressive OA, a 4-week treatment with vehicle or PTH was initiated 4 weeks post sham surgery or DMM. This delayed regimen was employed to examine the impact of treatment in the clinical situation where the therapy is initiated after a diagnosis of OA. Delayed regime of iPTH significantly inhibited decrease of PWTs and PAMs in DMM mice relative to DMM vehicle group (
To validate PTH attenuate OA progression and OA pain through maintaining subchondral bone microarchitecture after DMM, conditional knockout of PTH1R was induced in nestin+ MSCs of DMM mice. Nestin-CreTMER::PTH1Rfl/fl (PTH1R−/−) mice were injected with tamoxifen to delete PTH1R in the nestin+ MSCs, unresponsive to PTH to eliminate PTH-induced endocytosis of TGFβIIR. There were no significantly difference in osteoarthritic pain reflected by PWT and PAM and gait analysis between DMM PTH and vehicle PTH1R−/− mice while iPTH effectively attenuated OA pain reflected by improved PAM and PWT and gait analysis for DMM PTH1Rfl/fl (PTH1R+/+) mice relative to DMM vehicle PTH1R+/+ group (
Similarly, iPTH failed to prevent joint degeneration in DMM PTH1R−/− mice. The SOFG staining showed that proteoglycan loss in articular cartilage was not prevented in the DMM PTH PTH1R−/− mice (
The current routine treatments of OA including non-steroidal anti-inflammatory drugs and analgesics have limited therapeutic effect. Hochberg et al., 2012. These drugs are palliative treatment with progressive pathological joint changes and unsustained pain relief. Surgical joint replacement is the only alternative for end-stage of OA. Thomas et al., 2009. The only purportedly disease-modifying therapy for OA is to provide cartilage proteoglycan components via dietary or via intra-articular injection. Zhang et al., 2008: Vangsness et al., 2009; Brzusek and Petron, 2008: Brander and Stadler, 2009.
No consensus, however, is reached on the efficacy of oral ingestion of aggrecan sugar moieties, Zhang et al., 2008, and intra-articular injection of hyaluronic acid have pain relief only up to 6 months. Brander and Stadler, 2009. Thus, the development of an effective disease-modifying treatment of the OA joint with pain relief is urgently needed. In the current study, it was found that PTH could be a potential disease-modifying therapy of OA, considering that PTH reduce OA pain and attenuate progression of OA by preventing subchondral bone deterioration and cartilage degeneration. The OA pain relief and prevention of progressive OA were due to PTH-induced maintain of subchondral bone micro-architecture by restoration of coupled bone remodeling and prevention of nerve innervation.
In this study, no significant protection of articular cartilage degeneration was observed when intermittent PTH was applied to Nestin-CreTMER::PTH1Rfl/fl DMM mice compared with PTH-treated DMM PTH1Rfl/fl mice, suggesting that PTH-induced sustain of subchondral bone microarchitecture is critical for protection of articular cartilage during OA. Specifically, the decreased density of CORP+ sensory nerve in subchondral bone in Dmp1-Ranklfl/fl and Trap-Ntnfl/fl is obviously associated with significant pain relief reflected by Catwalk and Von Frey. Zhu et al., 2019, indicating that sensory nerve of subchondral bone might be an important origin of OA pain. OA pain of joint (activation and sensitization of nociceptive neurons) occurs episodically during movement and loading of the joint and this pain may be evoked by specific activity such as pinch-evoked pain hypersensitivity. Felson, 2009.
The primary knee hyperalgesia of OA has recently been measured by withdrawal threshold of direct knee press using a Pressure Application Measurement (PAM) device in DMM mice. Miller et al., 2017. The secondary hyperalgesia of knee developed after OA is also suggested to be measured by mechanical hypersensitivity of hind paw. Zhu et al., 2019. Sing of central sensitization, manifesting as pain hypersensitivity, has been described, such as mechanical allodynia (pain caused by a stimulus that does not normally evoke pain), reduced pain pressure thresholds, and enhanced temporal summation. Woolf, 2011: Mease et al., 2011; Suokas et al., 2012.
Various and complementary method are carried out for global measure of OA pain in this study. The development of pain behavior involves gait alterations due to pain during activities that shouldn't cause pain, such as pain during walking or loading. The movement-provoked pain behaviors reflected by gait analysis is effectively inhibited in PTH-treated DMM mice. The better mechanical hypersensitivity reflected by Von Frey filament stimulation applied to operated hind paw and better performance of operated hind paw in PTH-treated DMM mice are consistent with lower density of sensory nerve in subchondral bone of PTH-treated DMM mice.
Articular cartilage and subchondral bone forms as a mechanical and biological functional unit. Currently. OA is considered as a disease of the whole joint and the capacity of cross talk between articular cartilage and subchondral bone is enhanced with alteration of subchondral bone in OA. Zhu et al., 2019: Felson, 2009. The PTH mainly affected subchondral bone and articular cartilage of the joint, little literature established that PTH have direct effect on synovium, muscle or other soft tissues. It was commonly suggested that OA pain mainly originate from synovium, ligament. Kc et al., 2016; menisci, Ashraf et al., 2011; subchondral bone, Reimann and Christensen, 1977; and muscle and joint capsule. Hirasawa et al., 2000.
The degeneration of articular cartilage, especially hyaline cartilage, unlikely itself gives rise to pain, because cartilage is normally not innervated. Schaible, 2012. But it was reported that osteochondral junction was innervated by sensory nerve originated from osteochondral junction (or subchondral bone). Sun et al., 2007. It was also validated that there was no correlation between joint nociception and articular damage. McDougall et al., 2009. That suggested that PTH-induced chondro-protective and chondro-regenerative effect on articular cartilage has little relationship with pain relief during OA treatment. Additionally, PTH is also expected to promote bone resorption of old or micro-damaged subchondral bone of OA to provide basis for new bone formation than sustain subchondral bone micro-architecture.
TrkA-positive nerve fibers were observed at innervated sites of incipient primary ossification, coincident with NGF expression in cells adjacent to centers of incipient ossification. Tomlinson et al., 2016. That suggest that nerve sustains bone homeostasis by locating adjacent bone surface in normal condition. Intermittent PTH spatially redistributes smaller blood vessels not larger vessels closer to bone-forming site for providing a favorable microenvironment for growth. Roche et al., 2014; Prisby et al., 2011.
Altogether, the PTH induced alteration of vessel suggested that remodeling of bone vascular morphology is necessary for PTH osteoanabolic effect and its hemodynamic function. Recently, a subgroup of capillary, named type H vessel, with high level of CD31 and endomucin in the murine skeletal system was identified and found to mediated growth of bone vasculature, sustain perivascular osteoprogenitors and coupled angiogenesis to osteogenesis. Kusumbe et al., 2014.
Consistently, the type H vessel intensity significantly increased in subchondral bone of PTH treated DMM mice than that of vehicle treated DMM mice. Osteoblast-derived VEGF were required for coupling of angiogenesis and osteogenesis by stimulating recruitment of blood vessels and osteoclast, to make sure blood vessel provide favorable microenvironment for osteogenesis. Hu and Olsen, 2016.
Type H vessel was expected to locate around bone surface in the subchondral bone marrow of PTH treated DMM mice, which also suggested that osteoprogenitor cell was recruited to bone resorption bone surface after PTH treated with type H vessel providing molecular microenvironment for coupled angiogenesis and osteogenesis. Considering blood vessel and nerve fiber course was often alongside one another due to sharing similar mechanism about wiring neural and vascular networks. Carmeliet and Tessier-Lavigne, 2005, it was thought that nerve fiber may undergo similar remodeling to small vessel after PTH treatment, that may one of reasons of PTH induced pain relief in osteoarthritis.
PGE2 secreted osteoblast that sensed lower bone volume control bone homeostasis and promote regeneration by sensory nerve. Chen et al., 2019. The larger cavity of subchondral bone due to less loading stress (biomechanical adaptation of the bone) during OA was sense by local osteoblast, which secrets PGE2 to sustain bone homeostasis. Both peripheral and spinal hyperexcitability related to pathophysiological pain states were inhibited even reversed during development of inflammation and established hyperexcitability by the selective cyclooxygenase-2 (COX-2) inhibitors. Woolf and Salter, 2000; Telleria-Diaz et al., 2010.
The higher concentration of PGE2 of subchondral bone, as an inflammation factors, may be one of main reasons of OA pain. The PTH-sustained subchondral bone micro-architecture with even cavity maybe associated with lower concentration of PGE2, resulted in relatively mild OA pain. Additionally, intermittent PTH promoted bone formation and boosted bone mass by endocytosis of LRP6/PTH1R complex, enhancing BMP signaling. Yu et al., 2012. Subsequently, PTH-induced bone formation then inhibited PGE2 formation due to osteoblast sensing increased bone volume.
Subchondral bone osteoblasts of osteoarthritis are resistant PTH stimulation, which could be attributed to reduced expression or altered recycling process of PTH1R. Hilal et al., 1998. That is consistent with reported lower PTH receptor level in OA compared to normal osteoblast. Hilal et al., 2001. Endogenous PGE2 in subchondral bone could repress PTH-dependent response in OA osteoblasts, further contribute to abnormal bone remodeling and bone sclerosis in OA. The blunted PTH signaling due to elevated PGE2 and IGF1, Hilal et al., 2001, signaling during OA partially explained why there only a slightly increased in BV/TV of subchondral bone in PTH-treated DMM mice relative to vehicle-treated DMM mice. Conversely, decrease expression of PGE2 of OA subchondral bone after PTH treatment compared to vehicle OA mice might partially restore normal PTH signaling, which was in part due to relatively decreased inflammation and PTH-induced anabolic effect and sustained microarchitecture of subchondral bone where PTH retards osteoarthritis progression.
Cell senescence of osteoblasts and osteocytes have been identified with trabecular and cortical bone and cartilage in older animals. Farr et al., 2016: Philipot et al., 2014. Given the vital role of these cells in bone remodeling and joint function, the accumulation of these senescent cells contributes to the promotion of OA. Excessive TGF-β/Smad activation is one of the predominant pathways that accelerate damage-induced and developmentally cellular senescence. Rapisarda et al., 2017; Lyu et al., 2018. TGF-β signaling inhibition by PTH during OA may contribute to reduction of cellular senescence to attenuate OA progression.
PTH was reported to provoke early osteoarthritis by induced alteration of normal subchondral bone micro-architecture. Orth et al., 2014. The PTH-induced altered structural parameters of subchondral bone cause thickening of the calcified layer, leading to osteoarthritic cartilage degeneration. A previous study revealed that normal concentration of active TGF-β, as a coupling factor of bone remodeling, induces migration of bone marrow MSCs to bone resorption site for bone formation. Tang et al., 2009.
High concentrations of active TGF-β1 signaling in the subchondral bone leads to aberrant bone remodeling, which is a key step in the pathogenesis of OA. Zhen et al., 2013. Excessive TGF β signaling of subchondral bone MSC in OA joint was inhibited to approach normal condition by PTH-induced endocytosis where coupled bone remodeling was partially restored, while the PTH-induced osteoarthritis of normal femoral joint may be attributed to disturbance of couple bone remodeling due to normal TGF β signaling inhibited by PTH. Furthermore, abnormally low mineralization (becomes sclerotic although hypomineralized) of subchondral bone during osteoarthritis was reversed in part by PTH anabolic effect to maintain relative normal cartilage stress, Grynpas et al., 1991, while abnormally higher mineralization of normal subchondral bone induced by PTH may accelerate cartilage degeneration.
The development of osteophytes in the joint margins is a key feature of osteoarthritis, especially in DMM model, Wright et al., 2009. Considering bone anabolic effects induced by PTH-PTH1R signaling, there might be a potential increased incidence of osteophyte formation when PTH was applied in the treatment of osteoarthritis. Three-dimensional reconstructions generated from micro-CT data of all groups was collected for the detection of osteophyte formation. Interestingly, PTH-treated mice did not lead to an increased incidence of osteophyte formation during osteoarthritis compared to the vehicle-treated control group.
In the current study, the subcutaneously concentration of PTH (40 μg/kg/day) is effective for the treatment of OA in DMM mice. Based on published literatures showing that the effective does of PTH for the treatment of osteoarthritis ranged from subcutaneous injection (40 μg/kg), Sampson et al., 2011, to intraperitoneally injection (80 μg/kg) for mice. Dutra et al., 2017, which was comparable to the concentration here. Notably, the dose of 40 μg/kg/day for the treatment of DMM mice in this study was significantly higher than accepted and optimal concentration for other species, such as guinea pig(15 μg/kg/day), Yan et al., 2014; rabbit (10 μg/kg/day), Orth et al., 2014; and rat (15 μg/kg/day). Ma et al., 2017. It was anticipated that there was a species-associated shift for effective concentration of PTH supporting the effect of PTH-induced OA pain relief and restoration of coupled bone remodeling then the further attenuation of OA progression.
C57BL6J mice (WT mice. Stock number: 000664) were purchased from Jackson Laboratory, 10-weeks old male mice were anesthetized with xylazine and ketamine and then transected meniscotibial ligament that connects lateral side of medial meniscus with intercondylar eminence of tibia to induce mechanical instability associated osteoarthritis on the left knee, Sham operations of DMM were done on independent mice. For immediate treatment group, beginning 3 days after surgery, PTH (40 μg/kg/day) or the equivalent volume of vehicle (PBS) was injected subcutaneously daily until sacrifice. For the time-course experiment, operated mice were euthanized at 2, 4, 8, and 12 weeks postoperatively (n=8 per treatment group). Regarding to delayed treatment group, PTH (40 μg/kg/day) or the equivalent volume of vehicle (PBS) was injected subcutaneously daily from 4 weeks to 8 weeks after surgery, then these mice were sacrificed (n=8 per treatment group).
Nestin-creERT2 mice (Stock number: 016261) and R26R-EYFP (Stock number:006148) were purchased from Jackson Laboratory. Mice with floxed PTH1R (PTH1Rflox/flox) were obtained from the lab of Dr. Henry Kronenberg. Kobayashi et al., 2002.
The genotype of transgenic mice was determined by PCR analyses of genomic DNA isolated from mouse tails. The floxed PTH1R allele was identified with primers lox1F (5′-TGGACGCAGACGATGTCTTTACCA-3′ (SEQ ID NO: 28)) and lox1R (5′-ACATGGCCATGCCTGGGTCTGAGA-3′ (SEQ ID NO: 29)). The genotyping for the creERT2 transgene was performed by PCR with the primers Cre F (5′-ACCAGAGACGGAAATCCATCGCTC-3′ (SEQ ID NO: 30)) and Cre R (5′-TGCCACGACCAAGTGACAGCAATG-3′ (SEQ ID NO: 31)). Nestin-creERT2:: PTH 1R flox/flox mice were generated by crossing Nestin-creERT2 mice with PTH1R flox/flox mice. Then these mice were backcross with PTH1R flox/flox mice to generate Nestin-creERT2::PTH1R flox/flox and PTH 1R flox/flox mice. DMM or sham operations were performed on 10-week old Nestin-creERT2::PTH1R flox/flox and PTH1R flox/flox male mice. Three days before surgery, the mice were treated with either 100 mg/kg body weight of tamoxifen or vehicle three times per week for 4 and 8 weeks. Additionally, the mice (n=8 per treatment group) were treated with either PTH (40 μg/kg/day) or the equivalent volume of vehicle (PBS) subcutaneously daily for 4 and 8 weeks, 3 days after surgery.
Bone marrow stromal cell was obtained from 8-weeks old WT mice as described by Soleimani and Nadri, 2009. Cells (Passage 3-5) were maintained in Iscove's modified Dulbecco's medium (Invitrogen) supplemented with 10% fetal calf serum (Atlanta Biologicals), 10% horse serum (Thermo Scientific), and 1% penicillin-streptomycin (Mediatech). MSCs were cultured in 6 well plates at a density of 1.8×105 cells per well, then MSC were starved for 6 h before treatment. Human PTH (1-34) and PTH (7-34) was purchased from Bachem, Inc. (Torrance, Calif.), 100 nM of or PTH(7-34), or 2 ng of TGF-β1, was used for cell treatment as indicated.
The concentration of active TGF-β1 in the serum was determined using the TGF-β1 ELISA Development kit (human: R&D Systems. DB100B; mouse: R&D Systems, MB100B) and following the manufacturer's instructions.
After mice were killed by carbon dioxide (CO2) inhalation and perfused by phosphate buffer saline (PBS) and fixed by 10% buffered formalin via the left ventricle, the left knee joints were resected and fixed in 10% buffered formalin for 24 hours, decalcified in 0.5M ethylenediamine tetraacetic acid (pH 7.4) for 21 days, and embedded in paraffin or Optimal Cutting Temperature Compound (O.C.T. compound, VWR, 25608-930). The blocks were sectioned at 4 μm intervals using a Paraffin Microtome (for paraffin blocks) or 30 μm intervals using a using a Microm cryostat (for frozen blocks). Four-μm sagittal oriented sections of the operated knee joint medial compartment for hematoxylin and eosin (H&E) staining and safranin o (Sigma-Aldrich, S2255) and fast green (Sigma-Aldrich, F7252) staining. Tartrate resistant acid phosphatase staining was performed using the manufacturer's protocol (Sigma-Aldrich, 387A-1KT), followed by counterstaining with Methyl Green (Sigma-Aldrich, M884). Immunostaining including immunohistochemistry and immunofluorescence were performed using standard protocol. The tissue sections were incubated with primary antibodies to mouse pSmad2/3 (ThermoFisher Scientific, 444-244G, 1:100), mouse osterix (Abcam, ab22552, 1:200), mouse CD31 (Abcam, ab28364, 1:100), mouse endomucin (Santa Cruz, V.7C7, 1:50), mouse osteocalcin (Abcam, ab93876, 1:200), mouse nestin (Ayes Labs, Inc., 1:300, lot NES0407), mouse CGRP 0, mouse Substance P ( ), and mouse PGP9.5 ( ) overnight at 4° C. in a humidifier chamber. The sections were washed three times with Tris-buffered saline. For immunohistochemical staining, the slides were incubated with secondary antibodies in blocking solution at room temperature for 1 hours, and subsequently Chromogenic Substrates (Dako, K3468) was used to detect the immunoactivity, followed by counterstaining with hematoxylin (Sigma-Aldrich, H9627). For immunofluorescence staining, slides were incubated with secondary antibodies conjugated with fluorescence at room temperature for 1 hour, while avoiding light and mounted on slides with Prolong Gold Mounting Reagent with DAPI (Life Technologies, P36935). Isotype-matched controls, such as polyclonal rabbit IgG (R&D Systems, AB-105-C) and monoclonal rat IgG2A (R&D Systems, 54447), and polyclonal goat IgG (R&D Systems, AB-108-C) were used as negative controls under same condition and concentration. A Zeiss 780 confocal microscope or an Olympus DP72 microscope (Microscope Camera, Olympus, Tokyo, Japan) was used for image capture. Quantitative histomorphometric analysis was conducted in a blinded fashion with Image-Pro Plus Software version 6.0 (Media Cybernetics Inc., Rockville, Md.). The numbers of positive stained cells in five random visual fields of five sequential sections per mouse in each group were counted and normalized to the number per millimeter of adjacent bone surface (for TRAP staining quantification) or per square millimeter of bone marrow. For type H vessel and nerve quantification, the percentage area of positive staining was calculated by measuring the positive area and normalized to that of sham mice per (set to 1) in each group. Quantifications were performed using ImageJ 1.48u4 software.
The left knee joint was dissected from mice free of soft tissue and fixed overnight in 10% formalin, and then analyzed by high resolution μCT (Skyscan 1172). The scanner was set at a voltage of 65 kV and a current of 153 μA and a resolution of 9 μm per pixel. The images were reconstructed, analyzed for HO bone volume, and visualized by NRecon v1.6, CTAn v 1.9, and CTVol v2.0, respectively. Cross-sectional images of the tibiae subchondral bone. The region of interest was defined as the whole medial compartment of subchondral bone and cross-sectional sagittal image of the tibiae subchondral bone were used for three-dimensional histomorphometric analysis. A total of six consecutive image from medial tibial plateau were used for 3D reconstruction. Cross-sectional sigittal images of the tibiae subchondral bone were used to perform three-dimensional histomorphometric analysis. The following three-dimensional structural parameters were analyzed in this study: BV/TV: trabecular bone volume per tissue volume, SMI: structure model index. Tb.pf: trabecular pattern factor. SBP: subchondral bone thickness, and Tb.Th: trabecular thickness.
Detail automated analysis of gait was performed on walking mice using a “CATWALK” system (Noldus) pre-surgery, 2, 4, 6 and 8 weeks post-surgery. All experiments were performed at the same period of the day (12:00 PM-4:00 PM) and analyzed as previously reported method. Hamers et al., 2006; Hamers et al., 2001.
The recording was carried in a completely dark room with exception of the light from the computer screen. Briefly, mice were trained to cross the Catwalk walkway daily for 7 days before DMM or sham operation. During the test, each mouse was placed individually in the Catwalk walkway and allowed to walk freely and traverse form one side to the other side of the walkway glass plate. Light from an encased fluorescent lamp was emitted inside the glass plate and completely internally reflected. When the mouse paws contacted the glass plate, light was reflected down and the illuminated contact area was recorded with a high-speed color video camera positioned underneath the glass plate connected to a computer running Catwalk software v9.1 (Noldus). Comparison was made between the ipsilateral (left) and the contralateral (right) hind paw in each run of each animal at each time point. In the present study, the following parameters were analyzed: contact area; intensity and swing speed.
The 50% paw withdrawal threshold was measured by Von Frey hair algesiometry. Mice was habituated to elevated Plexiglas chambers and wire mesh flooring prior to assessments of allodynia. Then, ipsilateral hind paw mechano-sensitivity was measured by a modification of the Dixon up-down method. Dixon, 1980. Allodynia were evaluated by application of von Frey hair in ascending order of known bending force (force range: 0.07 g, 0.4 g, 0.6 g, 1 g, 1.4 g, 2 g, 4 g, or 6 g). The von Frey hair was applied perpendicular to the plantar surface of the hind paw (avoiding the toe pads) for 2-3 s, once a withdrawal response was occurred the paw was re-tested starting with the next descending von Frey hair until no response occurred. Four more measurements were made after the first difference were observed. The 50% PWT was determined by the following formula: 50% PWT=10Xf+kδ/10000, where Xf is the exact value of the final test of von Frey hair, K is the tabular value for the pattern of the last 6 positive/negative responses, and S is the mean difference (in log units) between stimuli. The threshold force required to elicit withdrawal of the paw (median 50% withdrawal) was determined twice on each hind paw (and averaged) on each testing day, with sequential measurements separated by at least 5 min.
All data were analysis were performed using SPSS 22.0 analysis software (SPSS Inc). The data are presented as the mean±standard deviation (SD). Unpaired two-tailed Student's t-test were used for comparison between two groups and one-way analysis of variance (ANOVA) followed by were used to determined significant difference between multiple groups. The level of significance as set at p<0.05. All inclusion/exclusion criteria were pre-established, and no samples or animals were excluded from the analysis. No statistical method was used to predetermine the sample size. The experiments were randomized. The investigators were not blinded to allocation during experiments and outcome assessment.
All publications, patent applications, patents, and other references mentioned in the specification are indicative of the level of those skilled in the art to which the presently disclosed subject matter pertains. All publications, patent applications, patents, and other references are herein incorporated by reference to the same extent as if each individual publication, patent application, patent, and other reference was specifically and individually indicated to be incorporated by reference. It will be understood that, although a number of patent applications, patents, and other references are referred to herein, such reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art.
Although the foregoing subject matter has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be understood by those skilled in the art that certain changes and modifications can be practiced within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 62/942,945, filed Dec. 3, 2019, the contents of which are incorporated by reference herein. Incorporated by reference in its entirety herein is a computer-readable nucleotide/amino acid sequence listing submitted concurrently herewith and identified as follows: One 5,918 Byte ASCII (Text) file named “38153-601_ST25,” created on Dec. 2, 2020.
This invention was made with Government support under AR071432 awarded by the National Institutes of Health (NIH). The Government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/062879 | 12/2/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62942945 | Dec 2019 | US |
