HGF and Signaling Pathways in Hepatic Tissue Assembly

项目总结/摘要 这是一个修改后的赠款续期申请，现在已经是第五年了，旨在了解HGF的作用， 肝组织组装中的信号通路。我们最近的研究表明，HGF及其 受体Met，以及EGF受体和EGFR相关配体）构成仅有的两种受体 能够将促有丝分裂信号传递至肝细胞的酪氨酸激酶（在无血清培养基中， 施用于整个动物、大鼠或小鼠）。我们还发现HGF/Met和EGFR是唯一的 两种能够促进肝细胞向胆管上皮细胞转分化的信号系统， 文化HGF/Met和EGFR的这些独特作用非常显著。许多其他受体酪氨酸 激酶在肝细胞中表达，它们的配体能够激活同源受体， 促有丝分裂信号仅限于HGF/Met和EGFR。我们最近应用了短期击倒（KD）， HGF/Met或EGFR通过shRNA表达，并证明两者对肝再生具有抑制作用， 一个信号不能完全补偿另一个信号，影响范围不同， 复杂性EGFR KD之后是ErbB家族其他成员的代偿性增加， MET的上调。在每种情况下，都存在显著但非致死性的促凋亡途径激活。 我们在大鼠中进一步扩展了这些研究，并进行了HGF/Met和EGFR的双重KD，随后进行了免疫组化。 部分肝切除术（PHx）。结果是完全的肝功能衰竭，伴随着大量的细胞凋亡和大部分细胞坏死。 肝细胞和肝实质塌陷。当使用双KD时，未观察到这种效果。 没有PHx。这项拟议的研究旨在确定导致肝功能衰竭的信号， 假设参与肝再生的许多细胞因子（例如TNF和TGF β 1）也可以作为 当EGFR和MET的促有丝分裂信号均不能 功能除了实验研究，我们还将分析表达和激活状态， 上述受体以及能够在人肝脏中诱导肝细胞死亡和肝衰竭的细胞因子 从暴发性肝坏死病例中获得的材料。最后，我们将评估 EGFR KD后出现的代偿机制，并确定这些机制的消除是否 机制本身也能导致肝功能衰竭。这些研究的结合可能使我们能够 了解导致大面积肝坏死的机制，这是早期肝硬化的异常不协调。 参与肝再生的信号，并允许设计治疗干预措施，以预防大规模肝再生。 基于合理的机制方案。

PROJECT SUMMARY/ABSTRACT This is a revised renewal application for a grant, now in its 5th year, aiming to understand the role of HGF and signaling pathways in hepatic tissue assembly. Our recent studies have demonstrated that HGF and its receptor Met, as well as EGF receptor and the EGFR associated ligands) constitute the only two receptor tyrosine kinases capable of delivering a mitogenic signal to hepatocytes (in serum-free media and when administered to the whole animal, rat or mouse). We have also showed that HGF/Met and EGFR are the only two signaling systems capable of promoting transdifferentiation of hepatocytes to biliary epithelial cells in culture. These unique effects of HGF/Met and EGFR are highly significant. Many other receptor tyrosine kinases are expressed in hepatocytes and their ligands are capable of activating the cognate receptor, yet mitogenic signals are limited to HGF/Met and EGFR. We have recently applied short term knock down (KD) of either HGF/Met or EGFR by ShRNA and demonstrated that both have inhibitory effects on liver regeneration, that the one signal cannot compensate totally for the other, and that the effects are different in scope and complexity. KD of EGFR was followed by compensatory increases in other members of the ErbB family and upregulation of MET. In each instance, there was significant but not lethal activation of pro-apoptotic pathways. We further extend these studies in rats and performed a double KD of both HGF/Met and EGFR followed by partial hepatectomy (PHx). The result was complete liver failure, with massive apoptosis and necrosis of most hepatocytes and collapse of the hepatic parenchyma. This effect was not seen when double KD was performed without PHx. The proposed study will aim to determine the signals that lead to liver failure under the hypothesis that many cytokines involved in liver regeneration (e.g. TNF and TGFb1) can also function as agents that bring hepatocyte death and liver failure when the mitogenic signals of both EGFR and MET fail to function. In addition to the experimental studies, we will also analyze expression and status of activation of the above receptors as well cytokines capable of inducing hepatocyte death and liver failure in human liver material obtained from cases of fulminant hepatic necrosis.. Finally we will assess the importance of the compensatory mechanisms emerging after KD of EGFR and determine whether abrogation of these mechanisms is capable to also lead to liver failure by itself. The combination of these studies may allow us to understand the mechanisms that lead to massive hepatic necrosis as an aberrant dis-coordination of the early signals involved in liver regeneration and allow design of therapeutic interventions for prevention of massive hepatic necrosis based on rational mechanistic schemes.