Hormonal Regulation of Liver Metabolism

摘要/摘要 非酒精性脂肪性肝病(NAFLD)代表肝脏中过量脂肪的堆积 (脂肪变性)没有或有炎症/纤维化(非酒精性脂肪性肝炎-NASH)。非酒精性脂肪肝通常 在肥胖和2型糖尿病中观察到，但也在与以下疾病相关的非肥胖患者中观察到 心血管疾病。到目前为止，还没有经过验证的医学疗法来逆转NAFLD。为了发展 有效的治疗，关键是要了解控制肝脏脂肪堆积和 相关的肝脏损伤。因为临床和实验研究都证明了肝脏生长激素 (GH)-NAFLD的信号转导减少，增加GH可以减少人类和小鼠的NAFLD，我们最近的研究 研究的重点是确定生长激素如何调节这些影响。我们使用了独特的鼠标模型 成人起病的肝细胞生长激素受体(GHR)丢失和GH信号通过以下途径控制脂肪变性 抑制新生脂肪生成(DNL)，这是生长激素以前没有意识到的作用。其他初步数据， 结合已发表的报告，我们提出了这样的假设：GH通过 GHR/Stat5b介导的糖酵解调节，以保护肝脏免受损伤。以下具体目标(SA) 将检验这一假设。SA1-确定GHR信号是否通过Stat5直接抑制肝脏 DNL和预防NAFLD进展。Expt SA1a，将确定增强Stat5b活性是否可以抑制 DNL并通过表达组成活性形式的Stat5b(Stat5bCA)来预防NAFLD 肝细胞生长激素受体。由于Stat5b增强肝脏IGF1的表达并提高循环中的IGF1水平，因此Stat5bCA 将在联合敲除肝细胞GHR和IGF1的小鼠中表达，以确定其有什么作用 Stat5b不依赖于IGF1。Expt SA1B，将确定是否需要GHR介导的Stat5b激活来控制 DNL，通过在缺乏内源性GHR的成年小鼠的肝细胞中表达突变的GHR，其中 突变受体不能激活Stat5b，但可以激活其他JAK2依赖和独立的通路。在一个 小鼠的亚群，肝细胞IGF1的表达将被重组，以防止因IGF1而发生的继发性变化 损失。SA2-确定肝细胞GHR/Stat5b信号的丢失是否独立于标准胰岛素 增强糖酵解驱动的DNL的信号。除SA2a外，将确定肝细胞GHR丢失和 当胰岛素和碳水化合物进入肝脏时，Stat5b活性恢复调节糖酵解通量和DNL 通过评估糖酵解、TCA中间体和新形成的脂肪的[1-13C]葡萄糖丰富程度进行控制 在高胰岛素-高血糖钳夹条件下，缺乏肝细胞生长激素受体的小鼠的酸，没有或 使用Stat5bCA。Expt SA2B，将确定糖酵解介导的转录因子ChREBP是否需要 增强肝细胞GHR丧失后的DNL、脂肪变性和肝损伤，通过产生成体发病的小鼠， ChREBPα和GHR对肝细胞的抑制作用。这些研究的完成将加强我们的基础 了解生长激素直接调控肝细胞碳水化合物/脂代谢和 保护肝脏免受损伤，最终目标是推出治疗非酒精性脂肪肝的新的“可药物”靶点。

Summary/Abstract Non-alcoholic fatty liver disease (NAFLD) represents a spectrum of excess fat accumulation in the liver (steatosis) without or with inflammation/fibrosis (non-alcoholic steatohepatitis - NASH). NAFLD is commonly observed in obesity and type 2 diabetes, but is also observed in non-obese patients associated with cardiovascular disease. To date, there are no proven medical therapies to reverse NAFLD. In order to develop effective treatments, it is critical to understand the basic mechanisms controlling hepatic fat accumulation and associated liver damage. Since both clinical and experimental studies demonstrate hepatic growth hormone (GH)-signaling is reduced in NAFLD and increasing GH can reduce NAFLD both in humans and mice, our recent work has focused on determining how GH mediates these effects. We have used unique mouse models with adult-onset loss of the hepatocyte GH receptor (GHR) and demonstrated GH signaling controls steatosis by suppressing de novo lipogenesis (DNL), an action of GH not previously appreciated. Additional preliminary data, coupled with published reports, led us to formulate the HYPOTHESIS: GH directly controls hepatocyte DNL via GHR/Stat5b-mediated regulation of glycolysis, to protect the liver from injury. The following Specific Aims (SA) will test this hypothesis. SA1 - Determine if the GHR signals through Stat5 to directly suppress hepatic DNL and prevent NAFLD progression. Expt SA1A, will determine if enhancing Stat5b activity can suppress DNL and prevent NAFLD by expressing a constitutively active form of Stat5b (Stat5bCA) in mice lacking the hepatocyte GHR. Since Stat5b enhances hepatic IGF1 expression and raises circulating IGF1 levels, Stat5bCA will be expressed in mice with combined knockdown of hepatocyte GHR and IGF1, to determine what actions of Stat5b are IGF1-independent. Expt SA1B, will establish if GHR-mediated Stat5b activation is required to control DNL, by expressing a mutant GHR in the hepatocyte of adult mice lacking the endogenous GHR, where this mutant receptor cannot activate Stat5b, but can active other JAK2-dependent and independent pathways. In a subset of mice, hepatocyte IGF1 expression will be reconstituted, to prevent secondary changes due to IGF1 loss. SA2 – Determine if loss of hepatocyte GHR/Stat5b signaling acts independent of canonical insulin signaling to augment glycolysis-driven DNL. Expt SA2A, will determine if hepatocyte GHR loss and restoration of Stat5b activity regulates glycolytic flux and DNL when insulin and carbohydrate input to the liver is controlled, by assessing [1-13C] glucose enrichment of glycolytic, TCA intermediates and newly formed fatty acids, under hyperinsulinemic-hyperglycemic clamp conditions, in mice lacking the hepatocyte GHR, without or with Stat5bCA. Expt SA2B, will establish if the glycolysis-mediated transcription factor, Chrebp, is required to enhance DNL, steatosis and liver injury after hepatocyte GHR loss, by generating mice with adult-onset, hepatocyte knockdown of both Chrebpα and GHR. Completion of these studies will enhance our basic understanding of the mechanisms by which GH directly controls hepatocyte carbohydrate/lipid metabolism and protects the liver against injury, with the ultimate goal of unveiling novel “druggable” targets to treat NAFLD.