Research Project
9296235
A hallmark of the immune system is its ability to mount a more effective and rapid response against secondary exposure to a pathogen. The mechanisms by which the adaptive immune system accomplishes this task center around DNA rearrangements and selection of the most effectively-responding cells. However, it has recently become evident that innate immune cells also exhibit memory, and that unlike adaptive immune cells, innate immune cells can exhibit memory towards different pathogens as well as the same one encountered during the initial exposure. This process, called trained immunity, can present as enhanced protection from heterologous infection following vaccination. On the other hand, diseases characterized by inflammation may be exacerbated by the induction of trained immunity. Preliminary work from our lab as well as others? has suggested that trained immunity is driven by altered transcriptional responses, with inherited chromatin structures playing an important role in propagating memory across cell divisions. Our studies have defined a subset of genes that display more rapid induction upon a second exposure to a stimulus in a lymphocyte-to- macrophage transdifferentiation model. These ?memory? genes display a reduction in trimethylation of lysine 27 of histone H3 (H3K27me3), and inhibiting H3K27me3 demethylation results in impaired memory formation at these loci. We have undertaken a pilot unbiased screen for additional chromatin factors that could influence memory formation, and have identified 23 genes that scored highly and are currently being validated. In this work, we plan to extend our findings to macrophages and NK cells, two cell types of the innate immune system thought to exhibit memory. We will establish protocols to elicit a memory response in these cells, using stimuli that mimic pathogen exposure or cytokine signaling, and examine which genes exhibit memory in each context. Using chromatin immunoprecipitation approaches, we will identify chromatin modifications that accompany the induction of transcriptional memory, and we will employ small-molecule and shRNA-based screening approaches to identify chromatin regulators responsible for the establishment or maintenance of memory. Finally, we will extend our results to a mouse model of diet-induced obesity, a pathology exacerbated by inflammation of adipose tissues by pro-inflammatory macrophage activity. We will examine whether macrophage transcriptional memory plays a role in a second induction of obesity following a period of weight loss. We expect our studies to elucidate the chromatin-based molecular mechanisms underlying the establishment and maintenance of transcriptional memory, and reveal how these mechanisms play a role in the pathological context of diet-induced obesity.
