Glucocorticoid-regulated transcription networks in macrophage biology

巨噬细胞（MΦ）驱动的炎症是脂肪组织代谢疾病发病机制的核心。

Macrophage (MΦ)-driven inflammation is central to the pathogenesis of metabolic disease in adipose tissue, liver, vascular endothelium and the skin. However, MΦ are extremely diverse in their ontogeny, epigenomes, transcriptomes and function. Indeed, `lean' adipose tissue M2-like MΦ are anti-inflammatory, facilitate fatty acid oxidation and sensitize adipocytes to insulin. In the skin, homeostatic tissue-repairing MΦ are essential responders to damage, and defective wound healing is a striking comorbidity of metabolic disorder. Signals for homeostatic MΦ 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 MΦ bear the transcriptional signature of nuclear factor (NF)κB and overproduce mediators of chronic inflammation (TNF, IL1β, 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 MΦ. Given that Klf4 itself is a GR target, GRIP1 could mediate the multi-level integration of M2 transcription programs in vivo when MΦ 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 MΦ in vitro and in vivo. Our central hypothesis is that GC and IL4 create partially overlapping yet distinct chromatin environments in homeostatic MΦ, 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 MΦ ex vivo; 2) Assess the impact of GRIP1 loss on the phenotypic and metabolic properties of homeostatic MΦ 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 MΦ, 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 MΦ which, unlike inflammatory MΦ activation, remains poorly defined.