PPARgamma as an architectural regulator of gene expression in endocrine signaling

项目总结 核激素受体(NHR)的经典观点是它们是配体激活的转录 作为DNA结合、脂类控制的基因组开关的因子。一组NHR作为异源二聚体 与专有的异二聚体伙伴维甲酸X受体(RXR)结合。RXR的主要合作伙伴之一是 过氧化体增殖物激活受体γ(PPAR)。PPAR被视为一种修饰的脂肪酸 前列腺素调节转录因子对脂肪细胞分化和脂代谢产物的贡献 诱导多种细胞类型的转录调节，包括巨噬细胞。使用传统的配基中心 方法，我们和其他人能够识别PPAR靶基因和配体调节过程，包括 胆固醇摄取和外流、抑制炎症反应、调节胰岛素敏感性和促进 巨噬细胞的组织修复。这些发现使该受体成为新陈代谢的关键内分泌调节因子。 以及这类细胞中的炎症。以前研究的一个主要弱点是它只关注配体- 受体的活性依赖，没有考虑配体非依赖性受体。因此，有一个 我们对受体生物学和作用的理解存在很大差距。最新的全基因组测定 结合部位在脂肪细胞中鉴定出至少两个数量级以上的基因组结合部位 巨噬细胞作为受调控的基因将是必要的。这促使我们探索PPAR：rxr环路 另一种极化的巨噬细胞。我们已经收集了初步证据表明：(1) 巨噬细胞PPARγ：RXR在STAT6诱导的IL-4极化中显著延长；(2) 染色质结合的PPARγ在交替极化的巨噬细胞中主要是配体不敏感的；(3) PPARγ：RXR异源二聚体是基因组的结构元件，(4)异源二聚体赋予 通过保留的基因增强子循环实现转录记忆。这使我们能够将新的假设表述为 如下：PPAR的很大一部分是配体不敏感的；(A)对 IL-4使巨噬细胞极化，并通过循环利用 粘附素复合体和/或CTCF；(B)建立转录细胞记忆和(C)有助于 巨噬细胞组织规范和转录适应。我们建议在三个层面上进行测试。 在染色质和基因组折叠水平上，我们将确定PPAR的表观基因组作用。在手机上 我们将确定PPAR在染色质开放和转录记忆中所起的作用。最后，在 在体内水平，将探讨PPAR对肺巨噬细胞功能的贡献以及对病毒感染的反应。 这一结果可能会为研究巨噬细胞的表观基因组编程开辟新的途径 在慢性炎症和代谢性疾病和组织再生中的翻译潜力。

PROJECT SUMMARY The canonical view of Nuclear Hormone Receptors (NHRs) is that these are ligand-activated transcription factors acting as DNA-bound, lipid-controlled genomic switches. A group of NHRs are acting as heterodimers with the obligate heterodimeric partner Retinoid X Receptor (RXR). One of the key partners of RXR is the Peroxisome Proliferator-Activated Receptor gamma (PPAR). PPAR is viewed as a modified fatty acid and prostanoid regulated transcription factor essential for fat cell differentiation and contributing to lipid metabolite induced transcriptional regulation in many cell types including macrophages. Using traditional ligand centric approaches, we and others were able to identify PPAR target genes and ligand regulated processes including cholesterol uptake and efflux, inhibition of inflammatory responses, regulating insulin sensitivity and promoting tissue repair in macrophages cells. These findings make this receptor a key endocrine regulator of metabolism and inflammation in this cell type. A major weakness of prior research was that it focused solely on ligand- dependent activities of the receptors and did not consider ligand-independent ones. Therefore, there is a substantial gap in our understanding of receptor biology and action. Recent genome-wide determinations of binding sites identified at least two orders of magnitude more genomic binding sites in fat cells and macrophages as regulated genes would necessitate. This prompted us to explore PPAR:RXR cistromes in alternatively polarized macrophages. We have gathered preliminary evidence to suggest that (1) The macrophage PPARγ:RXR cistrome is greatly extended upon IL-4 polarization directed by STAT6; (2) Chromatin-bound PPARγ is predominantly ligand-insensitive in alternatively polarized macrophages; (3) PPARγ:RXR heterodimers are architectural elements of the genome, and (4) the heterodimer confers transcriptional memory via retained gene-enhancer looping. This allows us to formulate new hypotheses as follows: A large fraction of PPAR:RXR heterodimers is ligand-insensitive; (a) Contributing to the epigenome of IL-4 polarized macrophages and provides links between enhancers and promoters via looping utilizing the cohesin complex and/or CTCF; (b) Establishes transcriptional cellular memory and (C) Contributes to macrophage tissue-specification and transcriptional adaptation. We are proposing to test these at three levels. At the chromatin and genome folding level we will determine the epigenomic roles for PPAR. At the cellular level we will determine the role PPAR plays in opening of chromatin and transcriptional memory. Finally at the in vivo level, contribution of PPAR to lung macrophage function and response to viral infection will be explored. The results will likely open up new avenues of research into the epigenomic programming of macrophages with translational potential in chronic inflammatory and metabolic disease and tissue regeneration.