Role of Platelet derived growth factor receptor-a in Liver Patho-biology

描述（由申请人提供）：慢性肝病是美国常见的发病原因，约550万美国人患有肝纤维化和肝硬化。慢性肝损伤可由多种损伤单独或联合造成，包括酒精、病毒性肝炎、代谢缺陷或其他。肝硬化可进一步并发肝功能衰竭、门静脉高压症和肝细胞癌（HCC），使慢性肝病成为美国第12大死亡原因和主要的社会经济负担。美国国立卫生研究院肝脏研究行动计划确定了诸如理解正常肝细胞功能的细胞和分子过程等领域；肝脏再生发育；肝纤维化；对肝脏健康产生全面的影响。目前的资助重点是了解一个鲜为人知的分子在肝细胞生物学中的作用，血小板衍生生长因子受体- α (PDGFRα)基于过去几年的一些有趣的观察。PDGFRα的高表达和磷酸化在小鼠肝脏发育的早期阶段被发现。具体来说，肝母细胞和未成熟肝细胞在肝脏早期发育阶段表现出高表达，这与持续的细胞增殖和细胞存活相一致。在胚胎肝培养中阻断PDGFRα证实了这些作用，因此值得深入研究。同样，我们已经发现，在小鼠肝切除三分之二或部分肝切除（PH）后的肝脏再生过程中，PDGFRα在时间上急剧增加。最后，在肝纤维化患者和小鼠胆管结扎（BDL）后的肝细胞中观察到PDGFRα上调。为了明确地解决PDGFRα在肝脏生长发育中的作用，我们已经建立了几种小鼠模型，使我们能够解决“PDGFRα是肝细胞增殖和存活的关键介质，其调节中的异常导致肝脏稳态的显着破坏，导致肝脏生长紊乱，包括异常发育，再生，纤维化和肝硬化”的总体假设。我们建议通过三个具体目标来研究这一假设，这三个目标是不同的，并采用平衡的体内和体外方法。在目的1中，我们建议通过全面的个体发生分析来研究PDGFRα信号在早期肝脏发育中的作用和调控。这些研究将通过在肝母细胞中缺乏PDGFRα的条件无效小鼠的产生来补充。在目标2中，我们将在部分肝切除模型中研究肝再生过程中的PDGFRα信号传导，然后利用实验室生成的新型动物模型研究肝细胞中PDGFRα过表达和缺失对再生反应的影响。在目标3中，我们将在胆管结扎和四氯化碳给药的小鼠模型中研究PDGFRα信号在肝纤维化和肝硬化中的作用。这些研究将通过在我们实验室的新型转基因小鼠肝细胞中检测PDGFRα缺失或过表达的疾病过程的细胞和分子基础来补充，并利用物种特异性PDGFRα阻断抗体来确定这些模型中疾病进展的影响，以解决治疗效果。因此，这一高度重要的建议将明确和全面地解决PDGFRα在肝脏健康和疾病中的作用和调节。

DESCRIPTION (provided by applicant): Chronic liver disease is a common cause of morbidity in the U.S.A. with around 5.5 million Americans suffering from hepatic fibrosis and cirrhosis. Chronic liver injury can be the result of any number of insults alone or in combination, including alcohol, viral hepatitis, metabolic defect or others. Cirrhosis can be further complicated by liver failure, portal hypertension and development of hepatocellular cancer (HCC), making chronic liver disease as the 12th leading cause of mortality in the U.S.A and a major socio-economic burden. The NIH action plan for liver research, identifies areas such as understanding cellular and molecular processes of normal liver cell functioning; liver regeneration and development; and hepatic fibrosis; to make an overall impact on liver health. The present grant is focused on understanding the role of a lesser known molecule in hepatocyte biology, platelet derived growth factor receptor-alpha (PDGFRα) based on some intriguing observations made over last several years. High expression and phosphorylation of PDGFRα was identified during early stages of liver development in mice. Specifically, hepatoblasts and immature hepatocytes displayed high expression at early hepatic developmental stages that coincide with ongoing cell proliferation and cell survival. Blocking PDGFRα in embryonic liver culture verified these effects thus warranting an in depth investigation. Similarly, we have identified a dramatic increase in PDGFRα temporally during liver regeneration after two-third or partial hepatectomy (PH) in mice. Lastly, PDGFRα upregulation was observed in hepatocytes during hepatic fibrosis in patients, and after bile duct ligation (BDL) in mice. In order to unequivocally address the role of PDGFRα in liver growth & development, we have generated several mouse models that will enable us to address the overarching hypothesis that 'PDGFRα is a critical mediator of hepatocyte proliferation and survival and aberrations in its regulation lead to significant disruption of liver homeostasis leading to disorders of hepatic growth including aberrant development, regeneration, fibrosis & cirrhosis'. We propose to investigate this hypothesis through three specific aims, which are distinct and employ balanced in vivo and in vitro approaches. In aim 1, we propose to investigate PDGFRα signaling in early liver development via comprehensive ontogenic analysis to address its role and regulation. These studies will be complemented by generation of conditional null mice that lack PDGFRα in hepatoblasts. In aim 2, we will study PDGFRα signaling during liver regeneration in partial hepatectomy model and then address the impact of PDGFRα overexpression and deletion in hepatocytes on regenerative response utilizing novel animal models generated in the lab. In aim 3, we will study PDGFRα signaling in hepatic fibrosis and cirrhosis in murine models of bile duct ligation and carbon tetrachloride administration. These studies will be complemented by examining the cellular and molecular basis of the disease process in absence or overexpression of PDGFRα in hepatocytes in novel transgenic mice in our lab and complemented by utilization of species-specific PDGFRα blocking antibodies to determine impact on disease progression in these models to address therapeutic efficacy. Thus, this highly significant proposal will unequivocally and comprehensively address the role and regulation of PDGFRα in liver health and disease.