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

描述(申请人提供)：在一项表型驱动的遗传学筛查中，我们在一个糖尿病小鼠家族中发现了Sec61a1突变。Sec61a1编码内质网(ER)转位通道的蛋白质传导亚单位，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有关。膨胀的内质网与内质网应激是一致的，内质网内未折叠的蛋白质积累。细胞对内质网应激做出反应，即未折叠的蛋白质反应，包括上调蛋白质折叠伴侣(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的表达。BIP和CHOP在糖尿病Sec61a1突变动物中均表达上调。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。这项建议中的实验旨在检验这一假设，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作为2型糖尿病一部分的细胞功能障碍中发挥作用。公共卫生相关性：2型糖尿病(T2D)的发展是一个双重过程，涉及外周组织的胰岛素抵抗和胰腺细胞无法通过增加胰岛素分泌来补偿胰岛素抵抗。在人类中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而来的电池失效的本质是什么？尸检研究表明，T2D与因细胞凋亡而导致的细胞质量相对减少有关，这一发现已在小鼠模型中得到支持。文献中有证据支持细胞丢失的几种机制中的任何一种，包括氧化应激、糖毒性、脂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的小鼠糖尿病模型。通过小鼠的正向遗传方法，我们已经确定了一个糖尿病小鼠家族，该家族在ER易位通道蛋白Sec61a1中存在突变。初步数据表明，小鼠患糖尿病是因为它们在大约四周大的时候就失去了细胞。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。这里描述的研究试图利用这个和其他糖尿病小鼠模型来回答一些关于T2D中细胞功能障碍本质的基本问题。Sec61a1的这种突变是如何导致内质网应激、细胞凋亡和糖尿病的？内质网应激在T2D中常见的细胞功能障碍中发挥作用吗？人们希望，对细胞功能障碍的更多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.