Hepatocyte Growth Factor and The Pancreatic Beta Cell

描述（由申请人提供）：我们之前已经证明肝细胞生长因子（HGF）在β细胞增殖、功能和胰岛移植中具有有益作用。最近，我们已经破译了HGF在β细胞存活中的双重作用。一方面，HGF在缺氧、营养剥夺、链脲佐菌素介导的细胞毒性和细胞因子诱导的细胞死亡情况下保护β细胞。另一方面，在体外实验中，HGF增强了糖脂毒性诱导的β细胞死亡。在代谢方面，HGF减少脂肪酸氧化，提高β细胞中的神经酰胺含量。在信号传导方面，hgf介导的β细胞促生存信号Akt的激活在糖脂毒性损伤下被消除。肥胖患者的循环HGF水平明显高。综上所述，这些结果表明HGF可能参与体内肥胖/ 2型糖尿病患者的β细胞衰竭。为了解决这个问题，在特异性目标1中，我们将描述在肥胖/ 2型糖尿病患者体内胰腺β细胞中破坏HGF/c-met信号的功能后果。功能p53水平的改变经常导致许多细胞类型的凋亡增加。然而，p53是否在直接控制肥胖/ 2型糖尿病患者胰腺β细胞死亡中具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：(1)糖脂毒性上调β细胞中p53的表达和激活；（ii）特异性p53抑制剂聚氟乙烯酯-1抑制p53转激活可阻断糖脂毒性介导的β细胞凋亡；（iii） p53缺失小鼠β细胞比野生型β细胞更能抵抗糖脂毒性诱导的细胞凋亡；（iv）在β细胞中过度表达p53的转基因小鼠表现出葡萄糖耐受不良。重要的是，最近一项肥胖/ 2型糖尿病与相关数量性状的综合关联研究发现，肥胖/ 2型糖尿病患者TP53基因中存在一个单核苷酸多态性变异（Arg72Pro）。Arg72-p53变异体具有更高的凋亡潜能，可能是由于其在线粒体中的定位增加。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，在特异性目标2中，我们将破译在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Specific Aim 3中，我们将分析p53介导人β细胞凋亡的相关性，以及在体外糖脂毒性环境下p53诱导β细胞凋亡的机制。在啮齿动物和人类β细胞的体外和小鼠体内的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. PUBLIC HEALTH RELEVANCE: Studies in the current proposal will decipher the role of HGF and p53 in obesity/Type 2 diabetes conditions. These studies can provide new cues on how to protect and enhance beta cell mass in diabetes and they can lead to future therapeutic strategies for the treatment of diabetic patients.