Growth Hormone Regulation of Sex Differences in Liver Metabolism

7.项目摘要/摘要 肝脏转录组中的性别差异在小鼠和人类中普遍存在，并在很大程度上受到 生长激素(GH)。这个项目的长期目标是阐明这些性别差异，以便更好地理解 生长激素影响的许多临床相关性别差异的机制基础；其中包括性别- 肝脏药物和类固醇代谢和脂代谢特征以及发病率和严重程度的差异 肝脏病理，如非酒精性脂肪性肝病(NAFLD)和与 肝细胞癌的发展。我们最近在小鼠模型中的研究表明，生长激素通过 其特定性别的脑垂体分泌的时间模式--男性为搏动性，女性为持续性--并通过生长激素-- 刺激肝脏STAT5的激活，以建立性别差异的表观基因组环境，使性别- 生长激素在肝脏中的特定作用。我们鉴定了数千个被标记为可能的增强子的基因组区域。 对STAT5和其他必需的生长激素调节的肝脏转录因子具有性别偏见的结合位点；我们 显示Ezh1/Ezh2需要组蛋白-H3赖氨酸27三甲基标记(H3K27me3)的性别特异性沉积 特别是对男性肝脏中许多偏向女性的基因的抑制。此外，超过200名性别特定的GH- 受调控的和核富含的长非编码RNA(LncRNAs)被发现，并成为 H3K27me3和其他染色质标记的性别差异沉积在性别特异基因和 它们的增强剂是通过对一大批多样化的近交系小鼠肝脏进行分析而确定的。此项目构建 关于这些进展以阐明转录和表观遗传调控的基本机制 由生长激素引起的性别偏见基因表达是正常肝功能所必需的。拟议的工作有两个主要目标： 1)发现与性别偏见肝病相关的性别偏见基因转录的关键特征 通过识别具有功能活性的性别偏向增强子，这些增强子包含了大多数肥胖的遗传风险因素 肝病，并阐明它们在染色质环区和亚区内的组织，以及它们的 与性别偏见基因启动子的相互作用；以及2)发现性别特异的生长激素调节的lncRNAs在 在性别偏见的增强子和基因上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，并阐明它们在GH-1保护作用中的作用。 激活STAT5，对抗导致非酒精性脂肪性肝病和其他肝脏病理的肝脏应激。 总之，这项工作将确定使生长激素及其性别相关的血浆模式得以实现的关键机制特征， 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。这个 通过改变生长激素作用的机制焦点，所获得的结果将对这一领域的研究产生重大影响 从关联和推断函数到因果关系。这些研究也将作为脉搏的范例 通过复杂的表观遗传机制发挥作用的其他内分泌因素的激素作用。

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.