【作者】 邓向群；

【导师】 陈璐璐；

【作者基本信息】 华中科技大学 ， 内科学， 2007， 博士

【摘要】 蛋白质的乙酰化/去乙酰化调节是机体快速调节酶蛋白活性的重要方式之一,在体内,导致2型糖尿病胰岛β细胞凋亡的多种蛋白质和细胞因子活性受乙酰化/去乙酰化调节。SIRT1是哺乳动物中氨基酸序列最接近酵母基因沉默信息调节因子2(Sir2)的同系物,具有强大的NAD+依赖的组蛋白脱乙酰基酶活性,其对诸多底物如P53、FOXO、Ku70、NF-κB、PGC-1α、TAFI68、P300、PCAF等均具有强大的去乙酰化作用,可能参与细胞凋亡、细胞周期调控、基因转录、物质代谢和其他一些细胞调节通路。本文主要讨论了SIRT1的去乙酰化调节作用与2型糖尿病胰岛β细胞凋亡、高脂喂养诱导的非酒精性脂肪肝病(NAFLD)的关系。在高脂喂养和2型糖尿病的大鼠模型中,应用小剂量链脲佐菌素(35mg/kg)处理的大鼠随机血糖明显升高而空腹血糖正常。在此慢性高血糖基础上,分别给予普通饲料喂养及高脂喂养模拟糖毒性和脂毒性。结果,在正常的血糖水平下,高脂血症对β细胞分泌功能并未造成明显损害,但长期慢性高血糖则可独立影响胰岛β细胞功能,并且显著促进脂毒性对胰岛β细胞功能的损害。研究结果表明,脂毒性对胰岛β细胞的损害作用需要慢性高血糖环境,脂毒性依赖于糖毒性。在糖脂毒性对胰岛β细胞功能损害中,慢性高血糖显著促进β细胞的凋亡,胰岛β细胞SIRT1的mRNA及蛋白表达显著降低;脂毒性在高血糖背景下进一步增加β细胞的凋亡,SIRT1的mRNA及蛋白表达进一步显著降低,糖脂毒性在胰岛β细胞凋亡中具有协同促进作用。热卡限制明显增加SIRT1在β细胞中mRNA及蛋白表达,降低胰岛β细胞的凋亡率。结果表明,SIRT1表达降低可能是显著促进2型糖尿病胰岛β细胞凋亡的重要机制之一。肝脏的组织病理学分析表明,单纯高脂喂养3个月的大鼠发生明显的NAFLD。同时,肝脏SIRT1表达明显降低,线粒体产生显著的退行性改变。进行1个月严格的热卡限制后,肝脏SIRT1表达增加,NAFLD病理改变显著改善,显示SIRT1表达在高脂喂养诱导的NAFLD中发挥重要作用。热卡限制通过增加SIRT1的表达,改善胰岛素抵抗和线粒体功能失常,进而减轻氧化应激达到治疗NAFLD的效果。我们的研究结果显示,SIRT1表达改变在2型糖尿病胰岛β细胞凋亡及NAFLD的发生和转归中发挥重要作用,SIRT1表达降低可能是多种器官疾病的普遍性机制。在糖尿病和NAFLD的治疗中,SIRT1可能成为一个新的治疗靶点。更多还原

【Abstract】 The acetylation/deacetylation regulation of proteins is one of important modes by which organism quickly regulates activity of zymoprotein. In vivo, many kinds of proteins and cell factors which can induce apoptosis of islet beta-cell in type 2 diabetes are controlled by this regulation. The mammalian Sir2 orthologue, SIRT1, as an NAD+ dependent deacetylase, deacetylates various substrates such as the p53 tumor suppressor, the FOXO transcription factors, the transcriptional coactivator PGC-1α, Ku70, NF-κB, TAFI68, P300, PCAF, and so on. It may be involved in apoptosis, cell cycle regulation, genetic transcription, substance metabolism and many other cellular and organismal regulatory pathways. The thesis mainly discusses the relationship between SIRT1 deacetylation and apoptosis of islet beta-cell in type 2 diabetes, nonalcoholic fatty liver disease (NAFLD) induced by high fat feeding.In the rat models of high fat feeding and type 2 diabetes, the random blood sugar of rats with low dose streptozotocin (35mg/kg) injection increased significantly, but the fasting blood sugar was normal. On the base of chronic hyperglycemia, rats were fed with normal chow and high fat diet respectively to mimic glucotoxicity and lipotoxicity. As a result, hyperlipemia had no obvious impairment to beta-cell when glycemia was normal. The long-term chronic hyperglycemia, however, had independent impacts on function of islet beta-cell. Furthermore, chronic hyperglycemia dramaticly promoted function impairment of beta-cell by lipotoxicity. The finding shows that chronic hyperglycemia is necessary for lipotoxicity impairment to islet beta-cell, and lipotoxicity is dependent on glucotoxicity.The chronic hyperglycemia promoted dramaticly apoptosis of islet beta-cell when glucolipotoxicity impaired function of beta-cell. The mRNA and protein expression of SIRT1 in islet beta-cell reduced significantly. Lipotoxicity further increased apoptosis of beta-cell in the background of chronic hyperglycemia. The mRNA and protein expression of SIRT1 further decreased obviously. The glucotoxicity and lipotoxicity cooperated on apoptosis of islet beta-cell. Calorie restriction apparently raised the mRNA and protein expression of SIRT1 in beta-cell, and then lowered apoptosis ratio of islet beta-cell. These results indicate that depressed SIRT1 expression may be the one of important mechanisms by which prominently facilitates beta-cell apoptosis in type 2 diabetes.The histopathology of liver suggests that rats fed with high fat diet for three months developed typical NAFLD. In these high fat feeding rats, the SIRT1 expression of liver reduced significantly and the mitochondria displayed retrogression changes. After strict calorie restriction for one month, the SIRT1 expression of liver increased and the pathology changes of NAFLD was obviously improved, shows that the SIRT1 expression plays an important role in NAFLD induced by high fat feeding. Calorie restriction improves insulin resistance and mitochondrion malfunction by increased SIRT1 expression, and then ameliorates oxidative stress to treat NAFLD.Our findings make clear that the changes of SIRT1 expression take an important action in islet beta-cell apoptosis of type 2 diabetes and development and turnover of NAFLD. Reduced SIRT1 expression may be a general mechanism of various diseases. As expected, SIRT1 possibly becomes a new target in treatment of diabetes and NAFLD.更多还原