Hepatocyte Growth Factor and The Pancreatic Beta Cell

描述(申请人提供)：我们先前已经证明，肝细胞生长因子(HGF)对胰岛细胞的增殖、功能和移植有有益的作用。最近，我们破译了HGF在β细胞存活中的双重作用。一方面，HGF在缺氧、营养缺乏、链脲佐菌素介导的细胞毒性和细胞因子诱导的细胞死亡的情况下对β细胞具有保护作用。另一方面，HGF在体外可增强葡萄糖脂氧性诱导的β细胞死亡。在代谢方面，HGF减少了脂肪酸氧化，增加了β细胞中神经酰胺的含量。在信号方面，HGF介导的β细胞促生存信号Akt的激活在存在糖脂毒性损伤时被取消。肥胖者循环中的HGF水平明显较高。综上所述，这些结果表明HGF可能参与了体内肥胖症/2型糖尿病的β细胞衰竭。为了解决这个问题，在特定的目标1中，我们将描述肥胖/2型糖尿病条件下体内胰腺β细胞内HGF/c-MET信号中断的功能后果。功能性P53水平的改变通常会导致许多细胞类型的凋亡率增加。然而，在肥胖症/2型糖尿病中，P53是否在直接控制胰岛β细胞死亡方面有任何调节作用尚不清楚。我们实验室的初步数据清楚地表明：(I)糖脂毒性上调P53在β细胞中的表达和激活；(Ii)特定的P53抑制剂Pifithin-1抑制P53的反式激活，阻止GLO-L毒性介导的BETA细胞凋亡；(Iii)P53基因缺失的小鼠BA型细胞比野生型BETA细胞对GLLO-L毒性诱导的凋亡更具抵抗力；以及(Iv)在BETA细胞中过表达P53的转基因小鼠表现出葡萄糖耐受不良。重要的是，最近一项关于肥胖/2型糖尿病及其相关数量性状的综合关联研究已经在肥胖/2型糖尿病患者中发现了TP53基因的单核苷酸多态变异(Arg72Pro)。Arg72-P53突变体具有更高的凋亡潜能，可能是通过增加线粒体的定位来实现的。综上所述，这些研究清楚地强调了P53表达/激活/定位的改变与胰腺β细胞凋亡、胰岛素分泌受损、糖脂毒性和肥胖/2型糖尿病之间的潜在联系。为了解决这一点，在特定的目标2中，我们将破译基础和肥胖条件下体内β细胞中功能获得、功能丧失和P53的72Arg变体的功能后果。在特定的目标3中，我们将分析P53在介导人β细胞凋亡中的相关性，以及在体外糖脂毒性环境中P53诱导BETA细胞凋亡的机制。在体外和在小鼠体内对啮齿动物和人类β细胞进行的拟议研究将提供有价值的信息，以确定在肥胖介导的2型糖尿病情况下保护β细胞免受功能障碍和死亡的途径。

DESCRIPTION (provided by applicant): We have previously shown that hepatocyte growth factor (HGF) has beneficial effects in beta cell proliferation, function and islet transplantation. More recently, we have deciphered a dual role of HGF in beta cell survival. On one hand, HGF protects beta cells in situations of hypoxia, nutrient deprivation, streptozotocin-mediated cytotoxicity and cytokine-induced cell death. On the other hand, HGF potentiates beta cell death induced by gluco-lipoxicity in vitro. Metabolically, HGF decreases fatty acid oxidation and enhances ceramide content in beta cells. In terms of signaling, HGF-mediated activation of the beta cell pro-survival signal Akt is abolished in the presence of a gluco-lipotoxic insult. Circulating HGF levels are markedly high in obesity. Taken together, these results indicate that HGF might participate in beta cell failure in obesity/Type 2 diabetes in vivo. To address this question, in Specific Aim 1 we will characterize the functional consequences of disrupting HGF/c-met signaling in the pancreatic beta cell in vivo in obese/Type 2 diabetes conditions. Alterations in functional p53 levels often lead to increased apoptosis in many cell types. However, whether p53 has any regulatory role in directly controlling pancreatic beta cell death in obesity/Type 2 diabetes is unknown. Preliminary data from our lab clearly indicate that (i) gluco-lipotoxicity upregulates p53 expression and activation in beta cells; (ii) inhibition of p53 transactivation with the specific p53 inhibitor pifithrin-1 blocks gluco- lipotoxicity-mediated beta cell apoptosis; (iii) p53-null mouse beta cells are more resistant than wild-type beta cells to gluco-lipotoxicity-induced apoptosis; and, (iv) transgenic mice overexpressing p53 in the beta cell display glucose intolerance. Importantly, a recent comprehensive association study of obesity/type 2 diabetes and related quantitative traits has identified a single nucleotide polymorphism variant (Arg72Pro) in the TP53 gene in obese/Type 2 diabetic patients. Arg72-p53 variant has a higher apoptotic potential possibly through increased localization in the mitochondria. Taken together, these studies clearly highlight the potential link between alterations in p53 expression/activation/localization and pancreatic beta cell apoptosis, impaired insulin secretion, gluco-lipotoxicity and obesity/Type 2 diabetes. To address this point, in Specific Aim 2, we will decipher the functional consequences of gain-of-function, loss-of-function and the 72Arg variant of p53 in the beta cell in vivo under basal and obesity conditions. In Specific Aim 3, we will analyze the relevance of p53 in mediating human beta cell apoptosis and the mechanisms involved in p53-induced beta cell apoptosis in a gluco-lipotoxic environment in vitro. The proposed studies in rodent and human beta cells in vitro and in mice in vivo will provide valuable information to identify pathways to protect beta cells against dysfunction and death in situations of obesity- mediated Type 2 diabetes.