SUMO化调控β细胞内质网应激介导T1D遗传易感性的机制研究

Type 1 diabetes (T1D) is a polygenic disease characterized by the autoimmune-mediated pancreatic β cell destruction and absolute insulin deficiency. In 2004, our research team first reported that altered sumoylation function contributes to the increased T1D susceptibility, but the underlying molecular mechanisms, however, are yet to be fully addressed. More recently, we noted that other than regulating the function of immune cells to mediate autoimmune responses, sumoylation also modulates the functionality of ERp57, a key protein disulfide isomerase responsible for protein folding and posttranslational modifications in the endoplasmic reticulum (ER), and through which altered sumoylation function mediates ER stress in β cells. This application will rely on those observations and employ β cell specific sumoylation deficiency or transgenic mice combined with T1D model NOD and NOD.scid mice，to conduct following studies: 1). Confirm that altered sumoylation function induces ER stress in β cells both in animals and humans; 2). Demonstrate that ER stress resulted from altered sumoylation function impairs β cell function and induces β cell apoptosis, and by which it initiates or exacerbates T1D autoimmune responses; and 3). Dissect the molecular mechanisms by which altered sumoylation function dysregulates ERp57 activity to induce autoimmune responses and mediate β cell apoptosis. Those studies will not only bring novel insight into the understanding of T1D pathogenesis, but also provide experimental data for developing novel and effective therapeutic strategies against T1D in clinical settings.

易感基因触发自身免疫和诱导β细胞内质网应激导致β细胞凋亡是1型糖尿病（Type 1 Diabetes, T1D）的重要发病机制，但易感基因诱导β细胞内质网应激的相关机制尚未阐明。申报者所在团队率先揭示SUMO化调控T1D遗传易感性，并阐明SUMO化调控T细胞功能诱发自身免疫应答。申报者后续研究进一步揭示SUMO化修饰二硫键异构酶ERp57活性介导β细胞内质网应激。本课题拟以β细胞内质网应激为切入点，应用β细胞SUMO化缺失或增强小鼠模型并结合T1D动物模型NOD和NOD.scid小鼠：确证SUMO化调控T1D进程中小鼠及人β细胞内质网应激；阐明SUMO化调控内质网应激介导β细胞功能损伤/凋亡和诱导T1D自身免疫应答；厘清SUMO化修饰ERp57诱导自身免疫应答和介导β细胞凋亡的分子机制。上述研究不仅厘清易感基因诱发 T1D 的分子机制，而且为开发新而有效的T1D防治策略提供理论和实验依据。

既往研究已经表明，SUMO化修饰对胰岛β细胞的多种生理活动具有重大意义。然而，SUMO化修饰是否参与调节β细胞胰岛素原折叠和内质网应激还有待阐明。我们的研究结果发现,小鼠胰岛β细胞中Ubc9基因缺失导致成熟胰岛素减少，胰岛素原的错误折叠增加和严重的内质网应激；反之，Ubc9基因过表达则可以逆转这些表型。通过胰岛SUMO化修饰蛋白质谱分析，发现SUMO化修饰可能参与多个蛋白质二硫键异构酶家族（PDIs）成员的翻译后修饰，并进一步验证了成员之一——PDIA3的SUMO化修饰发生在K332和K366。有趣的是，SUMO化修饰PDIA3明显加剧胰岛素原错误折叠和毒胡萝卜素诱导的内质网应激；而破坏PDIA3的SUMO化修饰则显著改善胰岛素原错误折叠和内质网应激。而且，在β细胞中特异性敲除Pdia3也得到与破坏PIDIA3的SUMO化修饰相同的效果。综上所述，在本研究中，我们揭示了SUMO化修饰可能通过修饰多个靶蛋白来正向/负向调控胰岛β细胞中内质网的功能，并深入阐释了SUMO化修饰PDIA3加剧β细胞中胰岛素原分子错误折叠和内质网应激的分子机制。同时，我们的研究也将为研发临床糖尿病进展过程中胰岛β细胞功能障碍的治疗药物提供了新的思路和方法。