Macrophage (M?)-driven inflammation is central to the pathogenesis of metabolic disease in adipose tissue, liver, vascular endothelium and the skin. However, M? are extremely diverse in their ontogeny, epigenomes, transcriptomes and function. Indeed, `lean' adipose tissue M2-like M? are anti-inflammatory, facilitate fatty acid oxidation and sensitize adipocytes to insulin. In the skin, homeostatic tissue-repairing M? are essential responders to damage, and defective wound healing is a striking comorbidity of metabolic disorder. Signals for homeostatic M? programming (e.g., interleukin [IL]4 and glucocorticoids [GC]) initiate via cognate transcription factors (STAT6 and the GC nuclear receptor [GR]) gene expression cascades that ultimately converge upon the `master regulator' kruppel-like factor (KLF)4 that activates many M2-specific genes. Conversely, M1-like inflammatory M? bear the transcriptional signature of nuclear factor (NF)?B and overproduce mediators of chronic inflammation (TNF, IL1?, iNOS, Ccl2). Although an M1/M2 imbalance is strongly linked to metabolic dysfunction and impaired wound healing, the specific epigenomic and transcriptional networks underlying homeostatic polarization of different M2 populations remain obscure. In fact, only limited data exist on the mechanisms of KLF4 function as a transcription factor, and virtually none on its genome-wide distribution or role in programming individual M2 subsets. Unexpectedly, we discovered that a nuclear receptor cofactor ? the GR-interacting protein (GRIP)1 ? serves as a coactivator for KLF4 facilitating M2 polarization of mouse bone marrow-derived M?. Given that Klf4 itself is a GR target, GRIP1 could mediate the multi-level integration of M2 transcription programs in vivo when M? encounter distinct polarizing signals, e.g., GC and IL4, simultaneously. The objective of this application is to understand the epigenomics, transcriptomics and higher order chromatin interactions of homeostatic M? in vitro and in vivo. Our central hypothesis is that GC and IL4 create partially overlapping yet distinct chromatin environments in homeostatic M?, and that by serving as a shared cofactor for GR and KLF4, GRIP1 facilitates the physiologically relevant functional convergence of M2- like transcription programs in vivo.
Our Specific Aims are to: 1) Dissect the global contribution of GRIP1 to GR and KLF4 enhancer formation and to the core M2-like transcription program through genome-wide approaches in GC- and IL4-polarized M? ex vivo; 2) Assess the impact of GRIP1 loss on the phenotypic and metabolic properties of homeostatic M? ex vivo and on their ability to undergo epigenomic and transcriptional programming, and support tissue repair in vivo; 3) Chart the first map of higher-order chromatin and GRIP1- dependent enhancer-promoter interactions in homeostatic M?, and identify the mechanistic determinants of the GRIP1:KLF4 cross-talk. The successful completion of this project will yield a comprehensive analysis of global chromatin interactions, the core transcriptome as well as GRIP1-dependent molecular mechanisms of homeostatic programming of M? which, unlike inflammatory M? activation, remains poorly defined.
Obesity and metabolic disease lead to many complications such as type 2 diabetes, heart disease and chronic non-healing ulcers often resulting in amputations. It is well- known that in metabolic disease, immune cells called macrophages cause chronic inflammation in fat, blood vessels and damaged skin, however, we discovered that a macrophage protein called GRIP1 can suppress these actions and promote the develpment of a special type of anti-inflammatory protective macrophages. Our project investigates how GRIP1 alters macrophage biology, which should help better understand metabolic disease and other inflammatory conditions and potentially find new ways to cure them.
