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

描述(申请人提供)：慢性肝病是美国发病率的常见原因，约有550万美国人患有肝纤维化和肝硬变。慢性肝脏损伤可以是任何数量的侮辱单独或组合的结果，包括酒精、病毒性肝炎、代谢缺陷或其他。肝硬变可能会进一步复杂化 肝功能衰竭、门脉高压和肝细胞癌的发展，使慢性肝病成为美国第12大致死原因，并成为主要的社会经济负担。NIH肝脏研究行动计划确定了一些领域，如了解正常肝细胞功能的细胞和分子过程；肝脏再生和发育；以及肝纤维化；对肝脏健康产生全面影响。根据过去几年的一些有趣的观察，目前的拨款重点是了解在肝细胞生物学中一种鲜为人知的分子--血小板衍生生长因子受体-α(PDGFR？)的作用。在小鼠肝脏发育的早期阶段，发现了PDGFR的高表达和磷酸化。具体地说，肝母细胞和未成熟肝细胞在肝脏发育的早期阶段表现出高表达，这与正在进行的细胞增殖和细胞存活相一致。在胚胎肝培养中阻断PDGFR证实了这些效应，因此有必要进行深入的研究。同样，我们在小鼠肝切除三分之二或部分肝切除(PH)后的肝再生过程中发现PDGFR在暂时性的显著增加。最后，在肝纤维化患者和胆管结扎(BDL)小鼠的肝细胞中观察到PDGFR的上调。为了毫不含糊地阐述 在肝脏生长和发育中，我们已经建立了几个小鼠模型，将使我们能够解决主导假设，即‘PDGFR’是肝细胞增殖和生存的关键调节因子，其调节中的异常会导致肝脏动态平衡的显著破坏，导致肝脏生长紊乱，包括发育异常、再生、纤维化和硬化。我们建议通过三个特定的目标来研究这一假说，这三个目标是截然不同的，并采用了平衡的体内和体外方法。在目标1中，我们建议通过全面的个体发育分析来研究PDGFR在肝脏早期发育中的信号转导，以解决其作用和调控。这些研究将通过在肝母细胞中缺乏PDGFR的条件性缺失小鼠的产生来补充。在目标2中，我们将研究部分肝切除模型中肝再生过程中的PDGFR？信号，然后利用实验室建立的新的动物模型研究PDGFR？在肝细胞中的过度表达和缺失对再生反应的影响。在目的3中，我们将在胆管结扎和四氯化碳注射的小鼠模型上研究PDGFR信号在肝纤维化和肝硬变中的作用。这些研究将通过在我们实验室的新型转基因小鼠的肝细胞中检测PDGFR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PDGFR阻断抗体来确定对这些模型中的疾病进展的影响，以解决治疗效果。因此，这项意义重大的提案将明确而全面地阐述PDGFR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 (PDGFR¿) based on some intriguing observations made over last several years. High expression and phosphorylation of PDGFR¿ 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 PDGFR¿ in embryonic liver culture verified these effects thus warranting an in depth investigation. Similarly, we have identified a dramatic increase in PDGFR¿ temporally during liver regeneration after two-third or partial hepatectomy (PH) in mice. Lastly, PDGFR¿ 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 PDGFR¿ in liver growth & development, we have generated several mouse models that will enable us to address the overarching hypothesis that 'PDGFR¿ 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 PDGFR¿ 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 PDGFR¿ in hepatoblasts. In aim 2, we will study PDGFR¿ signaling during liver regeneration in partial hepatectomy model and then address the impact of PDGFR¿ overexpression and deletion in hepatocytes on regenerative response utilizing novel animal models generated in the lab. In aim 3, we will study PDGFR¿ 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 PDGFR¿ in hepatocytes in novel transgenic mice in our lab and complemented by utilization of species-specific PDGFR¿ 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 PDGFR¿ in liver health and disease.