TET3-mediated epigenetic regulation of hepatic glucose production

精确控制肝葡萄糖生成（HGP）是维持全身葡萄糖稳态的关键。进化上保守的转录因子HNF 4 α在肝脏分化和功能中的作用已被广泛研究。HNF 4 α包含两个启动子P2和P1，它们通过选择性剪接以发育和组织特异性方式驱动多种HNF 4 α亚型。目前的教条是P2衍生的同种型在胎儿发育期间占主导地位;然而，出生后，P1衍生的同种型接管，指导广泛的肝功能，包括肝细胞生成。发现HNF 4 α的胎儿亚型是成人肝脏中HGP所必需的。这种亚型在禁食期间急性诱导，并在2型糖尿病（T2 D）中慢性增加。P2亚型诱导发生在对TET 3上调的反应中，TET 3是一种新的DNA去甲基化酶，以前没有显示出参与HGP。此外，肝脏特异性敲除TET 3或P2亚型单独改善了T2 D饮食和遗传小鼠模型中的葡萄糖稳态。假设TET 3是HGP的一种新的调节剂，通过表观遗传学诱导HNF 4 α胎儿亚型。为了验证这一假设，TET 3特异性地重新激活P2启动子的分子途径将被解剖。这些方法将涉及分子、生物化学和全基因组方法以及小鼠和人原代肝细胞和小鼠模型。这些研究完成后，将确定TET 3特异性诱导HNF 4 α胎儿亚型增强HGP的机制。如果成功，这些研究有望发现T2 D的新治疗靶点。

Precise control of hepatic glucose production (HGP) is pivotal to maintain whole-body glucose homeostasis. The evolutionarily conserved transcription factor HNF4α has been extensively studied for its role in hepatic differentiation and function. Hnf4α contains two promoters, P2 and P1, which drive multiple HNF4α isoforms via alternative splicing in a development- and tissue-specific manner. The current dogma is that the P2-derived isoform predominates during fetal development; however, after birth the P1-derived isoform takes over, directing a wide range of liver functions including gluconeogenesis. It is found that the fetal isoform of HNF4α is required for HGP in adult liver. This isoform is acutely induced during fasting and chronically increased in type-2 diabetes (T2D). P2 isoform induction occurs in response to upregulation of TET3, a member of a new class of DNA demethylases not previously shown to be involved in HGP. Furthermore, liver-specific knockdown of either TET3 or the P2 isoform alone improves glucose homeostasis in dietary and genetic mouse models of T2D. It is hypothesized that TET3 is a novel regulator of HGP by epigenetically inducing the HNF4α fetal isoform. To test the hypothesis, the molecular pathways by which TET3 specifically reactivates the P2 promoter will be dissected. The approaches will involve molecular, biochemical, and genome-wide approaches as well as mouse and human primary hepatocytes and mouse models. Upon completion of these studies the mechanisms by which TET3 specifically induces the HNF4α fetal isoform to enhance HGP will be defined. If successful, these studies hold the promise of discovering new therapeutic targets for T2D.