2型糖尿病胰岛β细胞保护作用新靶点PPA1的功能及作用机制研究

The pancreatic beta cell failure played a key role during the development and outcome of type 2 diabetes. It is well known that blood levels of glucose and fatty acid keep increasing with the development of Type 2 Diabetes, and caused the beta cell failure and dysfunction. Therefore, how to protect fatty acid induced pancreatic beta cell apoptosis was important for the prevention and treatment of type 2 diabetes. A series of studies had shown the importance of transcription factor FoxO1 in pancreatic beta cell maintenance, however, the effect of high activated FoxO1 seems still controversial in beta cells. On one hand, high transcriptional activity of FoxO1 was closely related to the beta cell dysfunction; on the other hand, high expression of FoxO1 can also protect beta cell from Oxidative Stress induced failure through up-regulating its target genes. Our previous study shown that high expression of Ppa1, one of the FoxO1 target genes, could effectively protect beta cell from fatty acid induced beta cell apoptosis. Moreover, interference of Ppa1 can also significantly increase the apoptosis rate caused by palmitate treatment. Therefore, we suppose that Ppa1 may responsible for the protective effect of FoxO1 on beta cells. So in the present study, we aim to demonstrate the effect of Ppa1 on beta cell proliferation and function maintenance using a series of in vivo and in vitro studies, including the establishment of Ppa1 knockout mice. And we will further explore the molecular mechanism of Ppa1 that might be involved, trying to provide a potential target for the treatment of Type 2 Diabetes in the future.

胰岛β细胞损伤是影响2型糖尿病发生的主要因素之一，如何对胰岛β细胞进行有效的保护成为糖尿病防治中的研究热点。研究显示，转录因子FoxO1对胰岛β细胞的功能和应激反应起着双重调控作用，一方面FoxO1转录活性的增加与胰岛细胞的功能障碍相关，另一方面，在细胞应激初期FoxO1也可以通过对其靶基因的调控增强细胞的抗应激能力。我们的前期研究表明，FoxO1靶基因Ppa1的过表达能够显著降低脂肪酸诱导的胰岛细胞凋亡，而Ppa1的干扰则使细胞的凋亡明显增加。由此，我们推测，Ppa1可能是FoxO1对细胞发挥保护性调控作用时所启动的一个下游靶基因。该项目旨在细胞和模式动物水平上，借助于各种分子生物学和转基因小鼠的技术手段，在高脂等2型糖尿病环境中，研究Ppa1对胰岛β细胞增殖或功能的影响及其作用机制。本项目的完成将有助于阐明胰岛β细胞中FoxO1作用机制，并为胰岛β细胞的保护提供一个较为直接的作用靶点。

胰岛β细胞损伤是影响2型糖尿病发生的主要因素之一，如何对胰岛β细胞进行有效的保护成为糖尿病防治中的研究热点。无机焦磷酸酶（Inorganic Pyrophosphatase，PPA1）是一种催化一分子无机焦磷酸转化为两分子磷酸盐离子的酶，近年来诸多研究表明PPA1与细胞的高能量代谢状况相关，也与细胞的活化关系密切。我们的研究发现PPA1的的过表达能够显著降低脂肪酸诱导的胰岛细胞凋亡，而PPA1的干扰则使细胞的凋亡明显增加，说明可以将PPA1发展为2型糖尿病发展过程中保护胰岛β细胞功能的潜在靶点。另外，脂肪组织是调节机体能量平衡的一个重要器官，成人脂肪细胞存在每年约10％的更新，且BMI越高对脂肪细胞更新的速率需求越高，脂肪细胞分化异常与机体胰岛素抵抗及2型糖尿病的发生密切相关。我们在细胞层面与动物水平对PPA1基因在脂肪分化过程中的作用进行了研究，发现干扰PPA1可以明显抑制3T3-L1脂肪细胞的成脂能力、分化后期的胰岛素敏感性和细胞因子的表达。机制研究显示， PPA1的干扰造成线粒体数目、形态和功能均出现明显下降。对PPA1基因敲除小鼠的表型分析显示，PPA1敲除鼠正常饮食下表现为明显的胰岛素抵抗；高脂饮食下表现为进一步肥胖，IPGTT与IPITT损伤更为严重，这些说明PPA1在能量代谢中发挥着非常重要的调节作用。PPA1功能的阐明将为肥胖及2型糖尿病的防治提供一个新的靶点。