Patent Application
20230272389
The present invention relates to miRNA interference technology. More specifically the invention relates to engineered circular miRNA sponges that carry a plurality of binding sites directed to at least two types of miRNA and separated by non-identical spacers, allowing for the inhibition of functional classes of miRNAs; to construction vectors; and uses of said miRNA sponges for the treatment of diseases.
As fine-tuners of gene expression, miRNAs play essential roles in normal development and homeostasis, dysregulation of which has been implicated in the pathogenesis of various diseases. Hence, targeting candidate miRNAs presents an exploitable therapeutic avenue. The first anti-miRNA therapeutic drug, Miravirsen, has shown efficacy in phase II clinical trials against Hepatitis C Virus infection with minimal side effects [Janssen, H. L. A., et al. N. Engl. J. Med. 368: 1685-1694 (2013)]. While the continuous development and optimisation of existing miRNA interference technology has conferred therapeutic benefits in clinical trials, many challenges remain. These include short half-lives, off-target effects and potential accumulation of non-metabolisable molecules such as LNA nucleotides.
Circular RNAs (circRNAs) belong to an emerging class of noncoding RNA that exist in circular instead of canonical linear form. The cellular splicing mechanism plays a central role in the biogenesis of circRNAs from pre-mRNAs. circRNA are generated through a back-splicing reaction where the 5′ splice donor site of a downstream exon is fused to the 3′ splice acceptor site of an upstream exon. Recently, there has been emerging evidence of endogenous circRNAs functioning as miRNA sponges. The first two circRNAs to be elucidated as miRNA sponges were ciRS-7 and circSRY [Hansen, T. B., et al., Nature 495: 384-388 (2013)]. More than 70 seed sites for miR-7 were identified in ciRS-7, and 16 miR-138 sites were identified in circSRY. Of note, following miR-7 binding, ciRS-7 levels remained unaffected, whereas co-tested linear miR-7 sponge constructs saw an approximate 2-fold decrease in abundance, presumably the result of exonucleolytic degradation. Thus, the circularity of the circRNA may confer resistance to degradation upon miRNA binding [Hansen, T. B., et al., Nature 495: 384-388 (2013)]. circRNAs are also protected against RNase-mediated exonucleolytic decay due to non-requirement of a 5′ cap and a 3′ polyA tail [Ebbesen, K. K., et al., Biochim. Biophys. Acta 1859: 163-168 (2016)]. This is consistent with the typical observation of deadenylation and decapping when miRNA bind to their canonical linear mRNA targets [Ebbesen, K. K., et al., Biochim. Biophys. Acta 1859: 163-168 (2016)].
An example of an application for circRNAs is in the prophylaxis or treatment of heart failure, which is the final common pathology for a myriad of cardiovascular diseases such as hypertension, metabolic syndrome, valve disease and others [Creemers, E. E., et al., Nat. Rev. Genet. 12: 357-362 (2011)]. It is a major cause of mortality and morbidity worldwide and poses a significant healthcare burden, with the pressing need for novel therapeutic approaches.
Pathological hypertrophy associates with cardiac dysfunction and fibrotic remodelling, leading to wall stiffness, which compromises systolic and diastolic function, and ultimately progresses to heart failure. Cardiac hypertrophy is one of the strongest prognostic factors in patients with heart disease, and reduction in pathological hypertrophy or adverse myocardial remodelling represents a therapeutic goal for cardiovascular pharmacotherapy. It was recently shown that miR-212/132 family expression is upregulated in cardiomyocytes following hypertrophic stimuli, and miR-212/132 necessarily drive pathological hypertrophy [Ucar, A., et al., Nat. Commun. 3: 1078 (2012)]. Pharmacological targeting of miR-132 by antagomiRs reduces cardiac hypertrophy progression, and abrogates heart failure in rodent models [Ucar, A., et al., Nat. Commun. 3: 1078 (2012)], and is currently entering Phase I clinical trials [Foinquinos, A., et al., Nat. Commun. 11: 1-10 (2020)].
There is a need to provide improved miRNA interference technology that could be used in pharmaceutical drugs and therapy.
In this application, the inventors constructed a circular miRNA sponge, termed “circmiR”, which was engineered as a custom sponge to sequester target miRNAs of interest. As proof of concept, the mouse pressure-overload induced cardiac hypertrophy disease model was chosen to test the circmiR of the invention. Hence, the circmiR was designed to target the miR-212/132 family to test its effectiveness as a miRNA inhibitor compared with the current gold standard antagomir technology as a new development for pharmacotherapy.
The present invention optimises crucial parameters in engineered circmiRs such as the number and type of binding sites to be incorporated, as well as between-site spacer sizes. Cardiomyocyte-specific in vivo delivery of optimised circmiRs, targeting the miR-212/132 family, attenuated left ventricular hypertrophy. Furthermore, circmiRs exhibited improved efficacy, compared to equimolar pharmacological antagomirs in vitro, and enhanced stability compared to linear counterparts. To the best of our knowledge, the present invention introduces the first instance of therapeutic application of a targeted miRNA interference technology, circmiRs, in vivo. The optimum parameters were determined for other miRNA targets to determine a set of optimized parameters applicable when constructing circmiRs to a target.
The present invention provides an isolated circular RNA polynucleotide microRNA sponge, comprising:
In some embodiments, the isolated circular RNA polynucleotide microRNA sponge comprises five to ten of each of two different microRNA bulged binding sites. For example, the microRNA sponge may comprise an even number of binding sites, such as 6, 10, 12, 14, 16, or more binding sites.
In some embodiments, the circular RNA polynucleotide contains a total of 12 microRNA binding sites.
In some embodiments, the isolated circular RNA polynucleotide contains spacers of 6 to 24 nucleotides, preferably 12 nucleotides, in length between microRNA binding sites.
In some embodiments, the different microRNA binding sites are alternated in the circular RNA polynucleotide.
In some embodiments, the bulge in each respective binding site is created by a one base deletion and two base mismatches at positions 9-11 nt from the 3′ end of each binding site.
In some embodiments, the isolated circular RNA polynucleotide comprises:
In some embodiments, the isolated circular RNA polynucleotide comprises twelve bulged binding sites selected from the group comprising, six miR-132 bulged binding sites alternating with six miR-212 bulged binding sites; six miR-17-5p bulged binding sites alternating with six miR-18a-5p bulged binding sites; and six miR-20b-5p bulged binding sites alternating with six miR-106a-5p bulged binding sites; and spacers of twelve nucleotides between each binding site.
In some embodiments, the isolated circular RNA polynucleotide comprises bulged binding sites, wherein:
In some embodiments, the isolated circular RNA polynucleotide comprises bulged binding sites, wherein:
In some embodiments, the isolated circular RNA polynucleotide comprises the nucleic acid sequence selected from the nucleic acid sequences set forth in the group comprising:
In some embodiments, the isolated circular RNA polynucleotide can be used as a medicament. For example, the circular RNA polynucleotide may be used in the treatment of cardiomyopathy, if the circular RNA polynucleotide comprises miR-132 bulged binding sites and miR-212 bulged binding sites.
For example, the circular RNA polynucleotide may be used in the treatment of cancer, if the circular RNA polynucleotide comprises miR-17-5p bulged binding sites and miR-18a-5p bulged binding sites, or comprises miR-20b-5p bulged binding sites and miR-106a-5p bulged binding sites.
In a second aspect, the invention provides a pharmaceutical composition comprising a circular RNA polynucleotide; and at least one of a pharmaceutically acceptable diluent, carrier and adjuvant.
In a third aspect, the invention provides an isolated DNA expression construct comprising a nucleic acid sequence encoding the circular RNA polynucleotide, operably linked to a promoter, inverted complementary introns flanking the RNA polynucleotide microRNA sponge sequence, a splice acceptor site (SA) and a splice donor site (SD).
In some embodiments. the expression construct comprises a nucleic acid sequence encoding the circular RNA polynucleotide of any aspect of the invention. In some embodiments, the expression construct comprises a nucleic acid sequence encoding the circular RNA polynucleotide set forth in SEQ ID NO: 13, SEQ ID NO: 14, or SEQ ID NO: 15.
In a fourth aspect, the invention provides an expression vector comprising the DNA expression construct.
In some embodiments, the expression vector comprises a constitutive promoter such as CMV, CAG or EF-1 alpha or an inducible promoter such as TRE, or a cardiac- or cardiomyocyte-specific promoter.
In some embodiments, the promoter is selected from the group comprising a cardiac troponin T promoter (cTnT), an α-myosin heavy chain (α-MHC) promoter and a myosin light chain (MLC2v) promoter.
In some embodiments, the expression vector is a virus expression vector, preferably selected from the group comprising Lentivirus, Adenovirus and Adeno-associated virus (AAV).
In a fifth aspect, the invention provides an isolated circular RNA polynucleotide, pharmaceutical composition, expression construct or expression vector of any aspect of the invention for the treatment, amelioration or prevention of a disease or medical disorder associated with the presence or over-expression of a plurality of microRNA.
In some embodiments, the plurality of microRNA comprises miR-132 and miR-212, miR-17-5p and miR-18a-5p, or miR-20b-5p and miR-106a-5p.
In some embodiments, the disease or medical disorder is:
In a sixth aspect, the invention provides a use of a circular RNA polynucleotide, pharmaceutical composition, expression construct, or expression vector of any aspect of the invention for the manufacture of a medicament for the treatment, amelioration or prevention of a disease or medical disorder associated with the presence or over-expression of a plurality of microRNA.
In some embodiments, the microRNA comprises miR-132 and miR-212, miR-17-5p and miR-18a-5p, or miR-20b-5p and miR-106a-5p.
In some embodiments, the disease or medical disorder is cardiomyopathy or cancer.
In a seventh aspect, the invention provides a method for the treatment, amelioration or prevention of a disease or medical disorder associated with the presence or over-expression of a plurality of microRNA, comprising the step of administering an efficacious amount of a circular RNA polynucleotide, pharmaceutical composition, expression construct, or expression vector of any aspect of the invention to a human or non-human animal in need of such treatment.
In some embodiments, the microRNA comprises miR-132 and miR-212, miR-17-5p and miR-18a-5p, or miR-20b-5p and miR-106a-5p.
In some embodiments, wherein the disease or medical disorder is cardiomyopathy or cancer.
In an eighth aspect, the invention provides a method of optimizing the structure of a circular RNA polynucleotide microRNA sponge comprising a plurality of bulged binding sites directed to human or non-human animal target miRNA, comprising the steps;
In some embodiments, the sponge comprises alternating binding sites.
In a ninth aspect, the invention provides an isolated circular RNA polynucleotide microRNA sponge produced according to the abovementioned method.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.
Bibliographic references mentioned in the present specification are for convenience listed at the end of the examples. The whole content of such bibliographic references is herein incorporated by reference.
Certain terms employed in the specification, examples and appended claims are collected here for convenience.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.
As used herein, ranges can be expressed as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that when a value is disclosed that “less than or equal to” the value, “greater than or equal to the value” and possible ranges between values are also disclosed, as appropriately understood by the skilled artisan. For example, if the value “10” is disclosed the “less than or equal to 10” as well as “greater than or equal to 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.
As used herein, the term “miRNA” and “microRNA” are interchangeable. miRNA refers to a small single-stranded non-coding RNA molecule that functions in RNA silencing and post-transcriptional regulation of gene expression. In the examples, “miRNA” may be further abbreviated as “miR”.
The phrases “nucleic acid” or “nucleic acid sequence,” as used herein, refer to an oligonucleotide, nucleotide, polynucleotide, or any fragment thereof, to DNA or RNA of genomic or synthetic origin which may be single-stranded or double-stranded and may represent the sense or the antisense strand, to peptide nucleic acid (PNA), or to any DNA-like or RNA-like material. Nucleic acid molecules can be naturally occurring, recombinant, or synthetic. The term “nucleotide” may be further abbreviated as “nt”.
As used herein, the term “oligonucleotide”, refers to a nucleic acid sequence of at least about 6 nucleotides to 60 nucleotides, preferably about 15 to 30 nucleotides, and most preferably about 20 to 25 nucleotides, which can be used in PCR amplification or in a hybridization assay or microarray. As used herein, the term “oligonucleotide” is substantially equivalent to the terms “amplimers,” “primers,” “oligomers,” and “probes,” as these terms are commonly defined in the art.
As will be appreciated by those of skill in the art, in certain embodiments, the nucleic acid further comprises a plasmid sequence. The plasmid sequence can include, for example, one or more sequences of a promoter sequence, a selection marker sequence, or a locus-targeting sequence. Methods of introducing nucleic acid compositions into cells are well known in the art.
It would be understood that oligonucleotides used in the present invention may be structurally and/or chemically modified to, for example, prolong their activity in samples potentially containing nucleases, during performance of methods of the invention, or to improve shelf-life in a kit. Thus, the circular miRNA sponge or any oligonucleotide primers or probes used according to the invention may be chemically modified. In some embodiments, said structural and/or chemical modifications include the addition of tags, such as fluorescent tags, radioactive tags, biotin, a 5′ tail, the addition of phosphorothioate (PS) bonds, 2′-O-Methyl modifications and/or phosphoramidite C3 Spacers during synthesis.
As used herein, the term “comprising” or “including” is to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps or components, or groups thereof. However, in context with the present disclosure, the term “comprising” or “including” also includes “consisting of”. The variations of the word “comprising”, such as “comprise” and “comprises”, and “including”, such as “include” and “includes”, have correspondingly varied meanings.
A person skilled in the art will appreciate that the present invention may be practiced without undue experimentation according to the methods given herein. The methods, techniques and chemicals are as described in the references given or from protocols in standard biotechnology and molecular biology textbooks. Standard molecular biology techniques known in the art and not specifically described were generally followed as described in Sambrook and Russel, Molecular Cloning: A Laboratory Manual, Cold Springs Harbor Laboratory, New York (2001).
HEK293T and H9C2 cells were maintained in DMEM (GE Healthcare Life Science) supplemented with 10% FBS (Capricorn Scientific), 100 U/ml penicillin and 100 μg/ml streptomycin (Nacalai Tesque, Inc) in a humidified atmosphere at 37° C., 5% CO2. Transient transfection of plasmids and/or miRNA mimics (Qiagen) into both cell lines was carried out with Lipofectamine 2000 reagent (Invitrogen) according to manufacturer's protocol.
circmiR Construct Design
The miRNA sponge sequence was constructed using Ultramer DNA oligos (Integrated DNA Technologies (IDT)) designed to contain either 2, 4, or 6 miRNA binding sites. Binding sites were designed as the reverse complement of the mature sequences of mmu-miR-132-3p or mmu-miR-212-3p (miRBase). Bulged sites carried one deletion and two base mismatches outside the seed regions as described [Gentner, B., Schira, G., Giustacchini, A., Amendola, M., Brown, B. D., Ponzoni, M., and Naldini, L. (2009) Nat. Methods 6, 63-66], while perfect sites had complete complementarity to the mature miRNA sequences (Table 1). Spacers of different lengths having random, non-identical, sequences (such as spacers having polynucleotide sequences set forth in SEQ ID NOs: 27, 28, 29, 30, 31 and 32) and a scrambled sequence (circScram) were created using a random oligo generator (mkwakDOTorg/oligorand/). The online RNAhybrid tool [Kruger, J., and Rehmsmeier, M. (2006) Nucleic Acids Res. 34, W451-W454; Rehmsmeier, M., Steffen, P., Hochsmann, M., and Giegerich, R. (2004) RNA 10, 1507-1517] was used to confirm binding of designed miRNA sponge sequences to target miR-212/132 sequences.
1.1 kb of the 5′ intronic sequence upstream and 1.1 kb of the 3′ intronic sequence downstream of exon 2 of the mouse Slc8a1 locus (encoding a known Slc8a1 circRNA) was PCR-amplified using primers shown in Table 1. Both fragments were cloned into an AAV9-cTnT-eGFP plasmid backbone (gift from Dr. Jiang Jianming, Cardiovascular Research Institute, National University of Singapore). The miRNA sponge oligos were cloned between these fragments to generate circmiRs carrying 2 or 6 binding sites. For circmiRs carrying 8, 12 or 16 binding sites, additional miRNA sponge oligos were sequentially cloned according to Blachinsky, E., et al., [BioTechniques 36: 933 (2004), incorporated herein by reference] between the inverted intronic repeats. The linear sponge sequence comprised of 12 bulged miRNA binding sites, constructed by sequential cloning [Blachinsky, E., et al., BioTechniques 36: 933 (2004)] of miRNA sponge oligos carrying 6 binding sites into the AAV9-cTnT-eGFP plasmid, without inverted intronic repeats. circScram was constructed by inserting a scrambled sequence, ordered as a gBlock gene fragment (IDT), between the inverted intronic repeats in the AAV9-cTnT-eGFP plasmid. The entire circmiR/linear/circScram sponge sequences were cloned into pCAG-mCherry plasmid backbones for in vitro applications.
The presence of repeat sequences results in a high frequency of recombination events that interferes with techniques used to construct the sponge such as PCR, cloning and Sanger sequencing. While the bases in the non-seed interaction region of miRNAs could be altered to introduce randomization and prevent repetitiveness, studies have shown that the non-seed interaction region is important. Pairing outside the seed region allows for differential gene targeting. Despite harbouring the same seed sequence, miR-132 and miR-212 exert different roles in endothelial biology depending on their pairing with additional 3′ sequences present within target sites that allow for specific targeting [Kumarswamy, R., et al., European heart journal 35: 3224-3231 (2014)]. Thus, it is important to preserve the sequence of miRNA binding site as much as possible to bind each different miRNA. Instead, altering the binding sites for each different miRNA and randomizing the sequences of the spacers were carried out.
We introduced randomisation of bases in the spacers. A total of eleven 12 nt spacers were used in one trial (Table 2) and of these, five 12 nt spacer sequences were used twice at different positions and one 12 nt spacers sequence was used once.
Luciferase Reporter Assays
miRNA-132/212 binding sites were cloned downstream of the Renilla luciferase gene of the psiCHECK-2 vector (Promega). 5×104 HEK293T cells were co-transfected with 50 ng of the psiCHECK-2-miR-212/132 or empty psiCHECK-2 vector, 50 ng of circmiR/circScram vectors and 10 μmol of equal molar mix of miR-212/132 mirVana™ miRNA mimics (Qiagen), using Lipofectamine™ 2000 reagent (Invitrogen) according to manufacturer's instructions. T7 synthesised circmiRs or miRvana™ miRNA inhibitors (Qiagen) were also co-transfected with μmol of equal molar mix of miR-212/132 mirVana™ miRNA mimics (Qiagen). H9C2 cells (a kind gift from Dr Zhou Yue, Cardiovascular Research Institute, National University of Singapore) were co-transfected with 50 ng of psiCHECK-2-miR-212/132 or empty psiCHECK-2 vector, 200 ng of circmiR/circScram vectors and 0.2 μmol of equal molar mix of miR-212/132 mirVana™ miRNA mimics (Qiagen). Luciferase activity was measured 48 h after transfection using the Dual-Glo™ Luciferase Assay System (Promega) according to manufacturer's protocol and read on a GloMax™ multi-plate reader (Promega). Results are expressed as Renilla luciferase normalised against Firefly luciferase.
RNA Isolation, cDNA Synthesis, and Real-Time qPCR
Total RNA was extracted from either isolated adult mouse cardiomyocytes or HEK293T cells using TRIzol™ Reagent (Thermo Fisher Scientific) according to standard procedures. Complementary DNA (cDNA) was synthesised with random primers using the gScript™ cDNA Synthesis Kit (Quantabio). Quantitative PCR (qPCR) was performed with Perfecta™ SYBR™ Green FastMix™ (Quantabio) on a LightCycler™ 480 (Roche) according to manufacturers' instructions using primers listed in Table 3. Primer design to distinguish between circmiR and linear sponge has been detailed in
All animal procedures were approved by the National University of Singapore Institutional Animal Care and Use Committee and were undertaken in strict accordance with Singapore National Advisory Committee for Laboratory Animal Research guidelines. Adult mice were housed in individually ventilated cages, with sex-matched littermates, under standard conditions. Food and water were available ad libitum. TAC or sham surgery was performed on 8-week-old male C57BL/6 mice as previously described [Rockman, H. A., et al., Proc. Natl. Acad. Sci. U.S.A 88: 8277-8281 (1991), incorporated herein by reference]. Left ventricular cardiomyocytes were isolated as previously described [Ackers-Johnson, M., et al., Circ. Res. 119: 909 (2016), incorporated herein by reference] from AAV-treated mice 4 weeks after surgery. Transthoracic echocardiography was performed according to manufacturer's guide for small animal echocardiography (Vevo™ 2100 Imaging System, Visualsonics). Doppler velocity measurements of right and left carotid arteries across the aortic constriction was performed at weeks 1 and 4 post-TAC mice to confirm the consistency of the surgical procedure (Vevo™ 2100 Imaging System, Visual Sonics).
circScram, circmiRs and linear sponge constructs were cloned into AAV9-cTnT-eGFP vectors as described above. The target AAV9 vectors were packaged by a triple transfection method with helper plasmids pAdΔF6 and pAAV2/9 (Penn Vector Core) as previously described [Wakimoto, H., et al., Curr. Protoc. Mol. Biol. 115: 23-16 (2016), incorporated herein by reference]. All constructs were administered at a titer of 5×1010 virus genome (vg)/kg via thoracic cavity injection to 7-week-old mice.
Mice were anesthetised by isoflurane inhalation. The heart was arrested in diastole by injecting 500 μl of a 15% potassium chloride solution into the inferior vena cava. Hearts were excised and flushed with saline solution via retrograde perfusion. Aorta and auricles were trimmed, and hearts were dried by removing excess fluid with forceps. Heart weight was measured, after which hearts were immersed in 4% buffered formalin and embedded in paraffin blocks according to standard procedures.
5 μM sections were co-stained with cardiac troponin I (cTnl; Abcam, ab56357) and biotinylated wheat germ agglutinin (WGA; Vectorlabs, B-1025) with streptavidin-linked Alexa Fluor™ 488 conjugate (Life Technologies). Images were analysed using the NIKON-NIS-Elements Viewer software and ImageJ [Schneider, C. A., Rasband, W. S., and Eliceiri, K. W. Nat. Methods 9: 671-675 (2012), incorporated herein by reference]. For each heart, the diameters of 200 cardiomyocytes were counted and a mean value was obtained, with experimenters blinded to experimental condition until data collection was finalised.
Synthetic circmiR Generation
Based on established methods, the 3′ and 5′ group I permutated intron-exon (PIE) sequences [Umekage, S., and Kikuchi, Y. J. Biotechnol. 139: 265-272 (2009)] from the T4 phage were synthesised as gBlocks (IDT). These were inserted downstream of a T7 promoter in the pcDNA3.1 plasmid vector (Addgene). A miRNA sponge sequence carrying 12 bulged binding sites was cloned between these intron-exon sequences. To create a linear RNA control for comparison of exonuclease degradation susceptibility, the exon and 5′ half intron of the PIE sequence downstream the miRNA sponge sequence was removed by restriction enzyme digestion during plasmid linearisation prior to in vitro transcription. Both circular and linear constructs were then synthesised by in vitro transcription from linearised plasmid DNA template using TranscriptAid T7 High Yield Transcription Kit (Thermo Fisher Scientific). RNA was purified from the reactions using TRIzol™ LS reagent (Thermo Fisher Scientific). To confirm circularisation, 1 μg of RNA was digested with 2 U RNase R (Epicentre) at 37° C. for 30 minutes. Digests were separated on 2% agarose gels and bands were visualised using the ChemiDoc™ Imaging System (BioRad). Molar concentrations of synthetic circmiR were calculated using the NEBioCalculator™ tool (nebiocalculatorDOTnebDOTcom/#!/ssrnaamt).
1.2×105 HEK293T cells per well were seeded on 24-well culture plates. 0.25 μg of plasmids driving either circmiR or linear sponge expression were transfected using jetPRIME™ transfection reagent (Polyplus Transfection). Alternatively, 0.5 μg of T7 synthesised circmiRs and linear sponge RNA constructs were transfected using Lipofectamine™ 2000 (Invitrogen). 48 hours post-transfection, cells were treated with 10 μg/mL actinomycin D (Sigma Aldrich) in fresh media. Cells were harvested at 0-, 6-, 12-, 24-, 48-, 72-hour time points post-actinomycin treatment. RNA was isolated and equal RNA quantities were subjected to reverse-transcriptase-PCR and qPCR as described above. Each RNA level was normalised against the 0-h time point to calculate log2 fold change.
All results are presented as mean+standard error of the mean (SEM). Two-tailed, unpaired Student's t-test was performed for comparison between two groups. One-way ANOVA followed by the Benjamini-Hochberg adjustment was used to compare more than two groups. All tests were performed using GraphPad Prism 7 Software. P<0.05 was considered significant.
Design and Circularisation of miRNA Sponge Sequences
miRNA binding sites (MBS) were engineered as illustrated in
The miRNA sponge was designed initially to carry a total of 12 alternating bulged miRNA binding sites, 6 for each of miR-132 and miR-212, with a 6 nucleotide (nt) separation space between miRNA binding sites (
To circularise the miRNA sponge, the sequence was flanked with inverted complementary introns (
Functional Efficacy Testing and Optimisation of circmiR Design In Vitro
First, to validate circmiR function, miR-132 and -212 binding sites were inserted into the 3′-untranslated region (UTR) of a Renilla luciferase construct from the dual-luciferase reporter system. Co-transfecting this construct with miR-132 and miR-212 mimics into HEK293T cells caused a significant reduction in Renilla activity, as expected (
The circmiR structural design was next optimised by testing the effect of different spacer lengths, type of binding sites and total number of binding sites. Previously, linear miRNA sponges showed effective miRNA inhibition with short spacers between miRNA binding sites [Otaegi, G., et al., Front. Neurosci. 5: 146 (2012)]. However, short spacer sequences in a circular structure may conceivably exert tension on neighbouring binding sites, affecting miRNA binding. To examine whether longer spacer lengths are preferable, bulged circmiRs with different spacer lengths were constructed: 6, 12, 24, 36, 72 nt. The 12-nt spacer construct produced the greatest rescue effect (
Bulged circmiR constructs were also generated containing 2, 6, 8, 12 and 16 binding sites, separated by 12-nt spacers, per sponge. The rescue effect of circmiR increased with increasing number of binding sites, but no significant difference was seen between circmiRs containing 12 and 16 binding sites (
Altogether, we concluded an optimal circmiR design, comprising of 12-nt spacers with 12 bulged miRNA binding sites. This design was used for all further experiments.
In Vivo circmiR Administration Attenuates Disease in a Mouse TAC Model
Hypertrophic stimuli reportedly upregulate cardiomyocyte expression of miR-132 and miR-212, which are necessary to drive pathological hypertrophy [Ucar, A., et al., Nat. Commun. 3: 1078 (2012)]. We confirmed the upregulation of both miR-132 and miR-212 in our in vivo transverse aortic constriction (TAC) cardiac pressure overload mouse model, although at a later timepoint than previously reported (
Next, adeno-associated virus (AAV) serotype 9 vectors were employed to deliver and express constructs in vivo, specifically in cardiomyocytes (CMs), using the cardiac troponin T (cTnT) promoter [Jiang, J., et al., Science 342: 111-114 (2013)]. AAV vectors expressing either circScram, circmiR or a linear miR-212/132 sponge (linsp) were injected intra-peritoneally one week before TAC surgery (
Cardiac function was evaluated by weekly echocardiographic measurements. Ejection fraction, a parameter of systolic cardiac function, was significantly compromised in TAC-operated circScram mice, whereas both circmiR and linsp mouse groups showed improved preservation of cardiac function up to 4 weeks post-TAC (
The heart weight to tibia length ratio, another measure of cardiac hypertrophy, increased post-TAC in both circScram and linsp mice, whereas heart weight in circmiR mice remained similar to sham levels (
The expression levels of canonical CM stress markers Nppa, Nppb and Myh7 were significantly increased post-TAC in circScram-treated hearts compared to sham levels (
CircmiRs are More Stable than Linear miRNA Sponges
The stability of circmiRs in comparison to linear miRNA sponge constructs was investigated. HEK293T cells were transfected with plasmids driving either circmiR or linear sponge expression, or with synthetically generated circmiR or linear sponge constructs. Transcription was inhibited with actinomycin D and total RNA was harvested at indicated time points.
As anticipated [Jeck, W. R., et al., RNA 19: 141-157 (2013); Meganck, R. M., et al., Mol. Ther. Nucleic Acids 13: 89-98 (2018)], measured by qPCR, positive control 18S abundance was highly stable across the 72 h time period, whereas a decrease in abundance of the less stable c-Myc transcript (MYC) was observed, exhibiting a half-life of 6 h. Plasmid-expressed circmiRs were resistant to nuclease degradation and were stable for up to 72 h (
Examples 1 to 3 demonstrated that the optimal design best suited for custom circmiRs targeting miR-212/132 comprised of a total of 12 alternate miRNA binding sites (6 for each miRNA) separated by a 12-nucleotide (nt) spacer. Comparing binding site type, bulged binding sites with an imperfect complementarity to the target miRNAs were effective whereas perfect binding sites failed to show any miRNA inhibitory effect in the luciferase assay.
Here, we extended our circmiR design to target 2 different sets of miRNAs, namely, miR-17-5p and miR-18a-5p (circmiR 1) as well as miR-20b-5p and miR-106a-5p (circmiR 2) (see Tables 5 and 6).
As per the previous example, the binding sites for these miRNAs were alternated to reduce the frequency of recombination events that interferes with techniques used to construct the sponge such as PCR, cloning and Sanger sequencing.
Either miR-17-5p and miR-18a-5p or miR-20b-5p and miR-106a-5p binding sites were inserted into the 3′-UTR of a Renilla luciferase construct from the dual-luciferase reporter system. It is worthwhile noting that these miRNAs have high endogenous expression within HEK293T cells that removes the need for including miRNA mimics in the experiment. Transfecting this construct, Luc 3′ UTR_miR, into HEK293T cells resulted in significant reduction in Renilla activity (
To examine whether the same spacer length requirements as before were optimal for circmiRs 1 and 2, 12 bulged binding sites were separated by different spacer lengths: 6, 12, 24, 36, 72-nt. Both circmiRs 1 and 2 exerted the largest rescue effect with a 12-nt spacing consistently as before (
The type of binding site to be included was also tested by comparing circmiRs with bulged or perfect binding sites. Across different spacer lengths, bulged sites were more effective in rescuing Renilla activity compared to perfect sites (
Bulged circmiR constructs were generated to contain 2, 6, 8, 12 and 16 binding sites, separated by 12-nt spacers, per sponge. The rescue effect of circmiR 1 increased with increasing number of binding sites as expected (
The full nucleotide sequence of a circular RNA sponge comprising 6 bulged miR-17-5p alternating with 6 bulged miR-18a-5p binding sites, and 2 copies of 12 nt spacers SEQ ID NO: 27, 28, 29, 30 and 31 and 1 copy of spacer SEQ ID NO: 32 and slc8a1 exon 2 flanking sequences is set forth in SEQ ID NO: 14. The full nucleotide sequence of a circular RNA sponge comprising 6 bulged miR-20b-5p alternating with 6 bulged miR-106a-5p binding sites, and 2 copies of spacers SEQ ID NO: 27, 28, 29, 30 and 31 and 1 copy of spacer SEQ ID NO: 32 and slc8a1 exon 2 flanking sequences is set forth in SEQ ID NO: 15. The full nucleotide sequence of a circular RNA sponge comprising 6 perfect miR-17-5p and 6 perfect miR-18a-5p binding sites, 12 nt random sequence spacers and slc8a1 exon 2 flanking sequences is set forth in SEQ ID NO: 17. The full nucleotide sequence of a circular RNA sponge comprising 6 perfect miR-20b-5p and 6 perfect miR-106a-5p binding sites, 12 nt random sequence spacers and slc8a1 exon 2 flanking sequences is set forth in SEQ ID NO: 18.
Altogether, three pairs of miRNA binding sites were engineered into circmiR sponges and tested to determine optimum performance features, with the result that an optimal circmiR design would comprise 12 bulged miRNA binding sites with 12-nt spacers having random, non-identical sequences.
Compared to other anti-miR technology implemented to date, circmiRs, without the requirement for chemical modifications, are likely to be well tolerated in biological systems. The present invention demonstrates the successful construction of three different improved artificial circmiR sponges as miR-132 and miR-212; miR-17-5p and miR-18a-5p; and miR-20b-5p and miR-106a-5p antagonists and in vivo testing of artificial circmiRs targeting miR-132 and miR-212 in a cardiopathy model.
In our study, we used long flanking introns to maximise circularisation efficiency. However, if the circmiR design needs to be more compact due to viral vector space constraints, shorter flanking introns could be incorporated.
Alternating binding sites for any two miRNA pairs and including non-identical spacers reduces consecutive repeat sequences undergo recombination events. Recombination within the sponge sequence would make circmiRs difficult to construct that is not ideal. Importantly, we found that circmiRs constructed with 12 perfect sites showed poor miRNA inhibitory effect compared to bulged circmiRs. This could be due to the susceptibility of circmiRs containing perfect binding sites to degradation upon miRNA binding, by Ago2-mediated cleavage, or by RISC mediated endonucleolytic cleavage. The differences in spatial and structural distribution have varying effects on circmiR functionality. Hence, circmiR design plays utmost importance to its resulting structure that in turn determines its effectiveness as a miRNA inhibitor.
In a recent study describing the synthesis of a circular sponge comprising of 8 miRNA binding sites, both bulged or perfect binding sites were equally effective for miRNA inhibition [Jost, I., et al., RNA Biol. 15: 1032-1039 (2018)]. This discrepancy could be accounted for by the shorter post-transfection (4 hours) luciferase activity measurement during which susceptibility of the bulged or perfect binding sites to degradation may not be detected.
In the in vivo study presented herein, both circmiR and linsp, bearing binding sites for miR-132 and miR-212, attenuated cardiac hypertrophy and heart failure progression to a similar extent. This effect concurs with a previous study in which the pharmacologic inhibition of miR-132 by antagomir injection suppressed pressure-overload induced hypertrophy [Ucar, A., et al. Nat. Commun. 3: 1078 (2012)]. While ideal as proof-of-concept, cardiac AAV vector systems drive high levels of constant expression [Goncalves, M. A. (2005) Virol. J. 2, 43; McCarty, D. M., Young, S. M., and Samulski, R. J. (2004) Annu. Rev. Genet. 38, 819-845], which therefore likely preclude the benefit of the higher stability circmiR compared to its linear counterpart. However, therapeutically, a pharmacological agent that is more precisely and temporally dose-controlled is typically more desirable. It is in this context that we propose that the markedly improved stability of a directly administered synthetic circmiR may have the advantage against linear therapeutics.
Thus far, few publications have described the in vitro synthesis of circular miRNA sponges. A circular sponge that inhibits miR-21 in gastric carcinoma cells, and another that inhibits miR-122 from Hepatitis C Virus, have been reported to function in vitro [Jost, I., et al., (2018) RNA Biol. 15: 1032-1039; Liu, X., et al. (2018) Mol. Ther. Nucleic Acids 13: 312-321]. Notably, both studies employed enzymatic ligation of linear RNA generated from in vitro transcription as the method of RNA circularisation. We and others have recently shown efficacy of expressing endogenous circRNAs in mammalian models of disease [Lim, T. S. B., et al., (2019) Cardiovasc. Res. 115: 1998-2007; Shen, S. Y., et al. (2019) Ann Rheum Dis 78: 826-836]. In the present study, we utilised endogenous splice machinery to generate custom-designed circular miRNA sponges and delivered them into an in vivo mouse model using AAVs.
Modified miRNA inhibitors are currently the gold standard in clinical trials. Biopharmaceutical companies have several miRNA inhibitors in clinical pipelines with chemistries tweaked in various ways. The key advantage of circRNAs that stands out in its development into a miRNA sponge is that without any chemical modifications, these molecules are resistant to nuclease degradation that makes them more stable than linear RNAs. CircmiR half-lives are naturally longer than linear miRNA inhibitors, which would greatly reduce the cost of innovation in terms of having to tweak the aforementioned RNA chemistries. Furthermore, circmiRs are biodegradable, the mechanism for which still remains to be discovered, reducing the risk of plausible long-term toxicity with modified oligonucleotide chemistries.
Our findings demonstrate the promising potential of circmiRs as therapeutic miRNA antagonists. We have applied this treatment and demonstrate benefits in an in vivo model of cardiovascular disease, which represents the primary cause of death globally, and anticipate that future development can expand this scope significantly.
Any listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that such document is part of the state of the art or is common general knowledge.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10202006446X | Jul 2020 | SG | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2021/050385 | 7/2/2021 | WO |
