糖尿病前期胰岛微血管内皮细胞SIRT1表达异常对胰岛α及β细胞功能的影响

Islet endothelial cells (IEC) play important roles in beta cell growth, differentiation and insulin secretion. The number of IEC is found decreased in type 2 diabetes. In our former research, we found that the islet of OLETF rats in pre-diabetic phase is hypoxia, which infers that the number of IEC is already decreased in pre-diabetes, and can not meet the needs of beta cell proliferation in the control of normal plasma glucose. SIRT1 is an important regulator of endothelial cell proliferation and angiogenesis in hypoxia. But in our research, we found the expression of SIRT1 is decreased in pre-diabetic situation. So we hypotheses that, the decreased expression or activity of SIRT1 may play key roles in the low level of IEC proliferation and angiogenesis, which may inturn lead to abnormal function of beta cell and alpha cell. So, in this research, we will carry out both in vivo and in vitro study to analyze the roles of SIRT1 in the promotion of IEC proliferation and angiogenesis in pre-diabetes by siRNA technique, SIRT1 gene transfection and other bio-molecular techniques. Later, we will construct co-culture system to study the direct effects of SIRT1 high expressing IEC on beta cell and alpha cell proliferation and secreting function. Our results will be helpful in the understanding of the mechanism of abnormal angiogenesis of IEC and its association with beta cell and alpha cell functions, and will offer important clues for SIRT1 in the prevention of abnormal angiogenesis in pre-diabetes.

2型糖尿病时胰岛微血管内皮细胞（IEC）数量下降是胰岛β细胞功能进行性衰退的重要原因。前期工作中我们发现OLETF大鼠于糖尿病前期IEC数量已经下降，胰岛处于低氧状态，同时发现SIRT1表达下降，而SIRT1具有促进内皮细胞增殖及血管新生的作用。据此提出"糖尿病前期SIRT1下调导致IEC增殖及血管新生异常，进而促进胰岛α细胞及β细胞功能损伤"的假说。为此，本研究采用SIRT1 siRNA、SIRT1基因转染等分子生物学技术，从细胞水平揭示SIRT1下调在高糖或高脂培养IEC增殖和血管新生功能受损中的关键作用及信号途径；进一步应用共培养系统研究SIRT1高表达的IEC对高糖或高脂培养胰岛α细胞和β细胞功能的改善作用及分子机制；并以SIRT1激动剂干预糖尿病前期OLETF大鼠，体内验证SIRT1的保护作用；以从胰岛微环境角度揭示α细胞及β细胞功能紊乱的机制，并为糖尿病前期的干预提供新的靶点。

2型糖尿病时胰岛微环境异常是胰岛β细胞功能进行性衰退的重要原因，但机制不清。我们首先发现，胰岛微血管内皮细胞（IEC)可通过分泌一氧化氮（NO）和肝细胞生长因子（HGF）及Laminin而促进共培养系统中胰岛β细胞的增殖及胰岛素分泌；同时发现在2型糖尿病前期大鼠，IEC已出现数量下降，其与α及β细胞的比邻关系和相对数量已发生改变，并随着糖尿病的进展而不断恶化。因此证实IEC异常参与了胰岛β细胞的进行性衰退及胰岛α细胞的不适当高分泌，从而构成了2型糖尿病发生发展的重要机制。同时发现糖尿病时SIRT1表达及活性下降，而应用慢病毒载体高表达SIRT1可促进IEC表达一氧化氮合酶而促进其分泌NO，并通过未知机制促进HGF及Laminin分泌，最终改善共培养系统中胰岛β细胞的增殖及胰岛素分泌。体外研究进一步证实应用SIRT1激动剂白藜芦醇干预糖尿病前期OLETF大鼠，可改善胰岛IEC的数量及胰岛微环境，并改善OLETF大鼠的血糖。本研究不仅为微胰岛微环境异常参与了2型糖尿病的发生发展提供了直接有力的证据，而且为SIRT1激动剂在2型糖尿病治疗及预防中的应用提供坚实的理论依据，也为1型糖尿病治疗中应用基因工程技术改造内皮细胞功能而改善移植胰岛β细胞的存活开辟了新的研究方向。