University of Pennsylvania School of Medicine, 700 CRB, 415 Curie Blvd., Philadelphia, PA 19104-6149, USA.
Mol Cell Biol. 2010 May;30(9):2078-89. doi: 10.1128/MCB.01651-09. Epub 2010 Feb 22.
The nuclear receptor peroxisome proliferator activator receptor gamma (PPARgamma) is the target of antidiabetic thiazolidinedione drugs, which improve insulin resistance but have side effects that limit widespread use. PPARgamma is required for adipocyte differentiation, but it is also expressed in other cell types, notably macrophages, where it influences atherosclerosis, insulin resistance, and inflammation. A central question is whether PPARgamma binding in macrophages occurs at genomic locations the same as or different from those in adipocytes. Here, utilizing chromatin immunoprecipitation and high-throughput sequencing (ChIP-seq), we demonstrate that PPARgamma cistromes in mouse adipocytes and macrophages are predominantly cell type specific. In thioglycolate-elicited macrophages, PPARgamma colocalizes with the hematopoietic transcription factor PU.1 in areas of open chromatin and histone acetylation, near a distinct set of immune genes in addition to a number of metabolic genes shared with adipocytes. In adipocytes, the macrophage-unique binding regions are marked with repressive histone modifications, typically associated with local chromatin compaction and gene silencing. PPARgamma, when introduced into preadipocytes, bound only to regions depleted of repressive histone modifications, where it increased DNA accessibility, enhanced histone acetylation, and induced gene expression. Thus, the cell specificity of PPARgamma function is regulated by cell-specific transcription factors, chromatin accessibility, and histone marks. Our data support the existence of an epigenomic hierarchy in which PPARgamma binding to cell-specific sites not marked by repressive marks opens chromatin and leads to local activation marks, including histone acetylation.
过氧化物酶体增殖物激活受体 γ（PPARγ）是抗糖尿病噻唑烷二酮类药物的靶标，这类药物可改善胰岛素抵抗，但有副作用，限制了其广泛应用。PPARγ是脂肪细胞分化所必需的，但它也在其他细胞类型中表达，特别是巨噬细胞，在这些细胞中，它影响动脉粥样硬化、胰岛素抵抗和炎症。一个核心问题是，巨噬细胞中的 PPARγ 结合是否发生在与脂肪细胞相同或不同的基因组位置。在这里，我们利用染色质免疫沉淀和高通量测序（ChIP-seq），证明了小鼠脂肪细胞和巨噬细胞中 PPARγ 的顺式作用元件主要是细胞类型特异性的。在巯基乙醇酸盐诱导的巨噬细胞中，PPARγ与造血转录因子 PU.1 在开放染色质和组蛋白乙酰化的区域共定位，除了与脂肪细胞共享的一些代谢基因外，还靠近一组独特的免疫基因。在脂肪细胞中，巨噬细胞特有的结合区域被具有抑制性组蛋白修饰标记，通常与局部染色质紧缩和基因沉默有关。当 PPARγ 被引入前脂肪细胞时，它只与富含抑制性组蛋白修饰的区域结合，在这些区域，它增加了 DNA 可及性，增强了组蛋白乙酰化，并诱导了基因表达。因此，PPARγ 功能的细胞特异性受细胞特异性转录因子、染色质可及性和组蛋白标记的调节。我们的数据支持存在一个表观基因组层次结构，其中 PPARγ 结合到非抑制性标记标记的细胞特异性位点，打开染色质，并导致局部激活标记，包括组蛋白乙酰化。
