Growth Hormone Regulation of Sex Differences in Liver Metabolism

7.项目总结/摘要 肝脏转录组中的性别差异在小鼠和人类中都很普遍，并且在很大程度上受到以下因素的调节： 生长激素（GH）。这个项目的长期目标是阐明这些性别差异，以更好地了解 GH影响的许多临床相关性别差异的机制基础;这些包括性别- 肝脏药物和类固醇代谢以及脂质代谢特征的差异，以及发生率和严重程度的差异 肝脏病理学，如非酒精性脂肪肝（NAFLD）和肝纤维化相关 肝细胞癌的发展。我们最近在小鼠模型中的研究表明，GH通过 它的垂体分泌的性别特异性时间模式-在男性中是脉动的，在女性中是持续的-并且通过GH- 刺激肝脏STAT 5的激活，以建立性别差异表观基因组环境，使性别- GH在肝脏中的具体作用。我们确定了几千个基因组区域标记为假定的增强子 具有STAT 5和其他必需的GH调节的肝脏转录因子的性别偏好结合位点;并且我们 显示需要组蛋白-H3赖氨酸27三甲基标记（H3 K27 me 3）的Ezh 1/Ezh 2的性别特异性沉积 特别是在男性肝脏中抑制许多偏向女性的基因。此外，200多个性别特异性，GH- 发现了受调节的和核富集的长非编码RNA（lncRNA），并且发现了 调节H3 K27 me 3和其他染色质标记在性别特异性基因上的性别差异沉积， 它们的增强子通过分析大量的多样性远交小鼠肝脏来鉴定。该项目建立 在这些进展，以阐明基本机制，转录和表观遗传调控的基础上， 生长激素的性别偏见的基因表达对正常的肝功能至关重要。拟议的工作有两个主要目标： 1)发现与性别偏见肝脏疾病相关的性别偏见基因转录的关键特征 通过识别功能活跃的性别偏向增强子，这些增强子包含了大多数脂肪代谢的遗传风险因素， 肝脏疾病，并阐明它们在染色质环结构域和亚结构域内的组织，以及它们的 与性别偏向基因启动子的相互作用; 2）发现性别特异性的GH调节的lncRNA在 在性别偏向的增强子和基因处建立和维持性别分化的染色质状态，以支持 肝脏基因转录的性别差异，然后阐明其对GH- 活化的STAT 5对抗诱导非酒精性脂肪肝疾病和其他肝脏病理的肝脏应激。 总之，这项工作将确定关键的机械特征，使生长激素，其性别依赖的血浆模式， 调节数百个控制肝脏代谢过程的基因的性别偏见表达， 对人类健康和肝脏疾病的影响，并可能将分子特征与病理生理结果联系起来。的 通过改变GH作用的机制焦点，所获得的结果将对该领域的研究产生重大影响 从相关性和推断功能到因果关系。这些研究也将作为一个范例的脉动 通过复杂的表观遗传机制起作用的其他内分泌因子的激素作用。

7. Project Summary/Abstract Sex differences in the liver transcriptome are widespread in both mice and humans and are largely regulated by growth hormone (GH). The long-term goal of this project is to elucidate these sex differences to better understand the mechanistic underpinnings of the many clinically relevant sex differences impacted by GH; these include sex- differences in hepatic drug and steroid metabolism and lipid metabolic profiles, and in the incidence and severity of liver pathologies, such as non-alcoholic fatty liver disease (NAFLD) and liver fibrosis associated with development of hepatocellular carcinoma. Our recent studies in the mouse model revealed that GH acts through its sex-specific temporal patterns of pituitary secretion – pulsatile in males and persistent in females — and via GH- stimulated activation of liver STAT5, to establish a sex-differential epigenomic environment that enables the sex- specific actions of GH in the liver. We identified several thousand genomic regions marked as putative enhancers that have sex-biased binding sites for STAT5 and other essential GH-regulated liver transcription factors; and we showed that sex-specific deposition by Ezh1/Ezh2 of histone-H3 lysine 27 trimethyl marks (H3K27me3) is required specifically for the repression of many female-biased genes in male liver. Further, more than 200 sex-specific, GH- regulated and nuclear-enriched long, non-coding RNAs (lncRNAs) were discovered, and strong candidates for regulation of the sex-differential deposition of H3K27me3 and other chromatin marks at sex-specific genes and their enhancers were identified by analysis of a large panel of Diversity Outbred mouse livers. This project builds on these advances to elucidate fundamental mechanisms that underlie the transcriptional and epigenetic regulation by GH of sex-biased gene expression essential for normal liver function. The work proposed has two major aims: 1) to discover critical features that underpin sex-biased gene transcription associated with sex-biased liver disease by identifying functionally active sex-biased enhancers, which harbor the majority of genetic risk factors for fatty liver disease, and to elucidate their organization within chromatin loop domains and subdomains, and their interactions with sex-biased gene promoters; and 2) to discover the role of sex-specific, GH-regulated lncRNAs in establishing and maintaining the sex-differentiated chromatin states at sex-biased enhancers and genes to support sex differences in liver gene transcription, and then elucidate their contributions to the protective effects of GH- activated STAT5 against hepatic stresses that induce non-alcoholic fatty liver disease and other liver pathologies. Together, this work will identify key mechanistic features that enable GH, and its sex-dependent plasma patterns, to regulate the sex-biased expression of hundreds of genes that control liver metabolic processes with a major impact on human health and liver disease, and may link molecular features to pathophysiological outcomes. The results obtained will have a high impact on research in this field by shifting the mechanistic focus of GH action from correlation and inferred function to causality. These studies will also serve as a paradigm for the pulsatile hormone action of other endocrine factors that act through complex epigenetic mechanisms.