Mechanisms of TLE3 Action in Adipose Subtype-selective Gene Expression

描述（由申请人提供）：脂肪组织以甘油三酯的形式储存膳食能量，并在代谢需要时通过甘油三酯水解释放游离脂肪酸，在能量稳态中发挥重要作用。鉴于脂肪组织在肥胖症、胰岛素抵抗、心血管疾病等代谢性疾病发病机制中的作用，对脂肪细胞分化的研究变得越来越重要。哺乳动物有不同的特殊类型的脂肪组织：白色脂肪组织（WAT）和棕色脂肪组织（BAT）。WAT储存能量，而BAT专门以热的形式消耗储存的化学能，可能具有抗肥胖功能。最近的研究表明，在暴露于寒冷、ß-肾上腺素能激动剂或噻唑烷二酮类药物时，WAT具有固有的可塑性，可以表现出BAT的遗传和生理特征。这种表型开关的中心是过氧化物酶体增殖物激活受体γ (PPARγ)，它是WAT和BAT分化的主要转录调节因子。PPARγ是终端脂肪细胞分化所必需的，因为缺乏这种核受体的小鼠缺乏WAT和BAT。PPARγ指导脂肪亚型特异性基因表达程序的机制尚不清楚。我们最近发现，TLE3是一种双功能的WAT特异性PPARγ共调节因子，可形成活性和抑制性转录复合物，分别驱动WAT和抑制BAT分化。此外，我们未发表的ChIP-Seq和RNA-Seq初步数据显示，1)全基因组范围的TLE3结合与脂肪生成调控位点的PPARγ富集和脂肪亚型特异性基因表达的调控相关，2)TLE3结合在含有几种不同促脂肪转录因子基序的DNA区域富集。在这个提议中，我们的目标是确定PPARγ:TLE3轴在转录因子成核和WAT和bat特异性基因表达的表观遗传修饰中的作用。我们还将研究TLE3消融对整体脂肪细胞基因表达和PPARγ占据基因启动子/增强子的影响。总的来说，本提案中使用的概念和方法将强调转录程序和脂肪特异性表型之间的复杂平衡，这可能有助于对肥胖和代谢紊乱患者的能量消耗进行治疗性操纵。

DESCRIPTION (provided by applicant): Adipose tissue plays an important role in energy homeostasis by storing dietary energy in the form of triglyceride and releasing free fatty acids through hydrolysis of triglycerides in times of metabolic need. The study of adipocyte differentiation is becoming increasingly important given the role of adipose tissue in the pathogenesis of metabolic diseases such as obesity, insulin resistance, and cardiovascular diseases. Mammals have distinct specialized types of adipose tissue: white adipose tissue (WAT) and brown adipose tissue (BAT). WAT stores energy whereas BAT is specialized to dissipate stored chemical energy in the form of heat and may have anti-obesity function. Recent studies have revealed an inherent plasticity of WAT to exhibit genetic and physiological features of BAT upon exposure to cold, ß-adrenergic agonists, or thiazolidinediones. The center of this phenotypic switch is peroxisome proliferator- activated receptor gamma (PPARγ), a master transcriptional regulator of both WAT and BAT differentiation. PPARγ is required for terminal adipocyte differentiation, as mice deficient for this nuclear receptor lack both WAT and BAT. The mechanism by which PPARγ directs adipose subtype-specific gene expression programs is still unclear. We recently discovered TLE3 as a dual-function WAT-specific PPARγ coregulator that forms both active and repressive transcriptional complexes to respectively drive WAT and suppress BAT differentiation. Moreover, our unpublished preliminary ChIP-Seq and RNA-Seq data show that i) genome-wide TLE3 binding correlates with both PPARγ enrichment on adipogenic regulatory sites and the regulation of adipose subtype-specific gene expression and ii) TLE3 binding is enriched in DNA regions containing several different pro-adipogenic transcription factor motifs. In this proposal we aim to determine the role of PPARγ:TLE3 axis in the nucleation of transcription factors and epigenetic modifications for WAT- and BAT-specific gene expression. We will also examine the consequence of TLE3 ablation on global adipocyte gene expression and PPARγ occupancy on gene promoter/enhancers. Overall, the concepts and methodologies used in this proposal will highlight the intricate balance between transcriptional programs and adipose-specific phenotype that may facilitate therapeutic manipulation of energy expenditure in patients with obesity and metabolic disorders.