Sec61 and ER Stress in Beta-cell Function and Type 2 Diabetes

描述（由申请人提供）：在表型驱动的基因筛选中，我们发现了一个糖尿病小鼠家族中Sec61a1的突变，以确定影响细胞功能的新基因。Sec61a1编码内质网（ER）易位通道的蛋白质传导亚基，负责蛋白质进入内质网。Sec61a1突变小鼠的糖尿病与细胞凋亡和内质网大量扩张相关。扩张的内质网与内质网应激一致，内质网内未折叠蛋白质的积累。细胞对内质网应激产生反应，即未折叠蛋白反应，包括上调蛋白折叠伴侣（如Bip），以及在内质网应激无法缓解的情况下上调促凋亡转录因子Chop。在糖尿病Sec61a1突变动物中，Bip和Chop均上调。因此，我们的假设是Sec61a1突变导致内质网应激、细胞凋亡和糖尿病。本提案中的实验旨在验证这一假设，了解Sec61a1突变导致内质网应激的机制，并询问内质网应激是否在2型糖尿病的一部分-细胞功能障碍中起作用。公共卫生相关性：2型糖尿病（T2D）的发展是一个双重打击过程，涉及外周组织的胰岛素抵抗和胰腺细胞通过增加胰岛素分泌来补偿胰岛素抵抗的失败。对人类的前瞻性研究已经确定了胰岛素抵抗和细胞功能障碍在T2D中的致病作用。伴随T2D的细胞衰竭的本质是什么？尸检研究表明，由于细胞凋亡，T2D与细胞质量的相对减少有关，这一发现在小鼠模型中得到了支持。文献中有证据支持细胞损失的几种机制，包括氧化应激、糖毒性、脂肪毒性和细胞因子诱导的细胞死亡。在这些研究中，我们将研究内质网应激和内质网应激诱导的细胞凋亡在细胞功能障碍中的作用。内质网应激在细胞死亡中的作用的证据来自以新生儿糖尿病为标志的人类遗传综合征，以及各种小鼠模型，包括我们自己实验室的一种新型糖尿病小鼠模型。通过小鼠的正向遗传方法，我们发现了一个内质网易位通道蛋白Sec61a1突变的糖尿病小鼠家族。初步数据表明，老鼠患上糖尿病是因为它们在大约四周大的时候就开始失去细胞。这种损失与内质网应激的增加有关。内质网应激的机制可能与Sec6a1突变导致的蛋白质加工或降解缺陷有关。本文描述的研究试图利用这种和其他糖尿病小鼠模型来回答有关t2dm中细胞功能障碍本质的一些基本问题。Sec61a1的突变是如何导致内质网应激、细胞凋亡和糖尿病的？内质网应激是否在T2D中常见的细胞功能障碍中起作用？希望对细胞功能障碍的进一步了解将导致更有效的治疗T2D的药物。

DESCRIPTION (provided by applicant): In a phenotype-driven, genetic screen to identify novel genes that affect ¿-cell function, we found a mutation in Sec61a1 in a family of mice with diabetes. Sec61a1 encodes the protein conducting subunit of the endoplasmic reticulum (ER) translocation channel, which is responsible for protein import into the ER. Diabetes in Sec61a1 mutant mice is correlated with ¿-cell apoptosis and massively distended ER. The distended ER is consistent with ER stress, an accumulation of unfolded proteins within the ER. The cell mounts a response to ER stress, the unfolded protein response, which includes up regulation of protein folding chaperones (e.g. Bip), and, in the case that ER stress cannot be relieved, up regulation of the proapoptotic transcription factor Chop. Bip and Chop are both up regulated in diabetic Sec61a1 mutant animals. Thus, our hypothesis is that Sec61a1 mutation leads to ER stress, ¿-cell apoptosis, and diabetes. The experiments in this proposal are designed to test this hypothesis, to understand the mechanism by which Sec61a1 mutation leads to ER stress, and to ask if ER stress plays a role in the ¿-cell dysfunction that is part of type 2 diabetes. PUBLIC HEALTH RELEVANCE: The development of type 2 diabetes (T2D) is a two-hit process involving insulin resistance in peripheral tissues and a failure of pancreatic ¿-cells to compensate for insulin resistance by increased insulin secretion. Prospective studies in humans have established the causative role of both insulin resistance and ¿-cell dysfunction in T2D. What is the nature of the ¿-cell failure that accompanies T2D? Autopsy studies have shown that T2D is associated with a relative decrease in ¿-cell mass due to apoptosis, a finding that has been supported in mouse models. There is evidence in the literature to support any of several mechanisms of ¿-cell loss, including oxidative stress, glucotoxicity, lipotoxicity, and cytokine-induced cell death. In these studies we will examine the role of endoplasmic reticulum (ER) stress and ER stress-induced apoptosis in ¿- cell dysfunction. Evidence for a role of ER stress in ¿-cell death comes from human genetic syndromes marked by neonatal diabetes, and various mouse models including a novel mouse model of diabetes from our own lab. Via a forward genetic approach in the mouse, we have identified a family of diabetic mice with a mutation in the ER translocation channel protein Sec61a1. Preliminary data indicate that the mice become diabetic because they lose ¿-cells beginning at about four weeks of age. This loss correlates with an increase in ER stress. The mechanism of ER stress likely relates to a defect in protein processing or degradation due to the Sec6a1 mutation. The studies described herein seek to exploit this and other mouse models of diabetes to answer some fundamental questions about the nature of ¿-cell dysfunction in T2D. How does this mutation in Sec61a1 lead to ER stress, ¿-cell apoptosis, and diabetes and does ER stress play a role in the ¿- cell dysfunction normally seen in T2D? It is hoped that an increased understanding of ¿-cell dysfunction will lead to more effective drugs against T2D.