TAZ and YAP in Non-Alcoholic Steatohepatitis and its Complications

非酒精性脂肪性肝炎（NASH）是全球慢性肝病的主要原因。的 病理生理学是从温和脂肪变性进展为NASH、纤维化和肝细胞性脂肪变性的基础。 癌症（HCC）在很大程度上仍然是未知的，并且目前没有FDA批准的药物来治疗NASH。 这两名PI最近发表了人类和小鼠NASH肝脏中的肝细胞（HC）升高， 转录因子TAZ的水平和沉默HC TAZ抑制脂肪变性至NASH纤维化 进展我们已经证明，密切相关的蛋白质雅普在NASH中也升高，并且HC在NASH中也升高。 令人惊讶的是，雅普抑制脂肪变性、NASH和纤维化。我们还发现HC胆固醇 积累是人类NASH的一个关键特征，通过阻断它们的蛋白酶体而增加HC TAZ/雅普。 降解最后，我们在NASH诱导的HCC中发现了高水平的TAZ/雅普，我们的初步研究表明， HC-TAZ沉默防止NASH向HCC的进展。本提案的目的是探讨 假设胆固醇诱导的HC TAZ和雅普升高调节向NASH的进展， 纤维化和HCC以及TAZ可以代表所有疾病阶段治疗靶点。要求1 探讨了HC雅普如何抑制脂肪变性的机制和后果。我们将测试 假设HC雅普（a）抑制参与从头脂肪生成和甘油三酯合成的基因， 通过HC YAP介导的过氧化物酶体增殖物激活物的减少，和（B）诱导参与脂肪酸氧化的基因。然后我们将 检验阻断HC雅普通过其促脂肪变性作用促进NASH纤维化的假设， 增加HC TAZ。我们还将检测早期脂肪肝中HC-YAP的强制表达是否能 预防脂肪变性和向NASH的进展。目的2探讨HC TAZ上调的机制 NASH中的雅普。我们认为，由E3连接酶TrCP介导的TAZ/雅普的蛋白酶体降解， 在NASH中抑制，其机制涉及HC中的胆固醇积累。我们假设 HC膜胆固醇的升高改变细胞信号传导以阻断TAZ上位点的磷酸化， TrCP识别所需的雅普或直接抑制TrCP本身。目的3探讨胆固醇的作用- TAZ/雅普通路在NASH诱导的HCC中的作用我们假设，胆固醇诱导的TAZ积累-两者 通过胆固醇摄取和HMG-CoA还原酶介导的途径-促进HCC的发展， 晚期NASH我们将首先测试基因靶向是否可以预防NASH向HCC的进展 HC TAZ，如飞行员数据、HC雅普和HC TAZ +雅普所示。然后我们将测试假设（a） 胆固醇诱导的HC-TAZ加速NASH-纤维化-HCC序列;（B）胆固醇诱导的TAZ和 雅普还通过细胞自主机制驱动肿瘤起始HC的恶性转化;和（c） 他汀类抑制TAZ/雅普和NASH诱导HCC。这些目标的成功实现将提供关键的新的 这些信息有助于推进我们对NASH及其并发症的发现的治疗转化。

Non-alcoholic steatohepatitis (NASH) is the leading cause of chronic liver disease worldwide. The pathophysiology that underlies the progression from bland steatosis to NASH, fibrosis, and hepatocellular carcinoma (HCC) remains largely unknown, and there are currently no FDA-approved drugs to treat NASH. The two PIs have recently published that hepatocytes (HCs) in human and mouse NASH liver have elevated levels of the transcription factor TAZ and that silencing HC TAZ suppresses steatosis-to-NASH fibrosis progression. We have since shown that the closely related protein YAP is also elevated in NASH and that HC YAP, surprisingly, suppresses steatosis, NASH, and fibrosis. We have also shown that HC cholesterol accumulation, a key feature of human NASH, increases HC TAZ/YAP by blocking their proteasomal degradation. Finally, we found high levels of TAZ/YAP in NASH-induced HCC, and our pilot studies show that HC-TAZ silencing prevents NASH-to-HCC progression. The objective of this proposal is to explore the hypothesis that cholesterol-induced elevations in HC TAZ and YAP modulate the progression to NASH, fibrosis, and HCC and that TAZ may represent a therapeutic target for all disease stages. Aim 1 explores the mechanisms and consequences of how HC YAP suppresses steatosis. We will test the hypothesis that HC YAP (a) represses genes involved in de novo lipogenesis and triglyceride synthesis, in part via HC YAP-mediated decrease in PPAR and (b) induces genes involved in fatty acid oxidation. We will then test the hypothesis that blocking HC YAP promotes NASH fibrosis via its pro-steatotic actions and possibly by increasing HC TAZ. We will also test whether forced expression of HC-YAP in early fatty liver disease can prevent steatosis and the progression to NASH. Aim 2 investigates the mechanism of up-regulation of HC TAZ and YAP in NASH. We propose that proteasomal degradation of TAZ/YAP mediated by the E3 ligase TrCP is inhibited in NASH and the mechanism involves cholesterol accumulation in HCs. We hypothesize that elevation of HC membrane cholesterol alters cell signaling to block the phosphorylation of sites on TAZ and YAP required for TrCP recognition or directly inhibit TrCP itself. Aim 3 explores the role of the cholesterol- TAZ/YAP pathway in NASH-induced HCC. We hypothesize that cholesterol-induced TAZ accumulation – both via cholesterol uptake and HMG-CoA reductase-mediated pathways - promotes the development of HCC in advanced NASH. We will first test if the progression from NASH to HCC can be prevented by genetic targeting of HC TAZ, as suggested by pilot data, HC YAP, and HC TAZ + YAP. We will then test the hypotheses that (a) cholesterol-induced HC-TAZ accelerates the NASH-fibrosis-HCC sequence; (b) cholesterol-induced TAZ and YAP also drive malignant transformation in tumor-initiating HC via cell-autonomous mechanisms; and (c) statins inhibit TAZ/YAP and NASH-induced HCC. Successful completion of these aims will provide critical new information to help advance therapeutic translation of our discoveries for NASH and its complications.