Role of IAPP in Islet Dysfunction in Diabetes

描述(申请人提供)：人类2型糖尿病(T2 DM)的胰岛是由胰岛淀粉样多肽(IAPP)衍生的胰岛淀粉样蛋白，IAPP是一种与胰岛素共表达和分泌的蛋白质。人IAPP(HIAPP)在溶液中有形成低聚物的倾向。这些低聚物似乎形成在膜上，导致非选择性的膜渗漏，例如钙离子进入胞浆。在这笔赠款支持的研究中，我们证实了T2 DM患者的细胞质量减少，细胞凋亡率增加。我们在高表达人IAPP的啮齿动物中复制了T2 DM的胰岛和代谢表型，并证明了IAPP的毒性形式在分泌途径中形成细胞内，导致内质网(ER)应激诱导细胞凋亡和细胞器(线粒体)损伤。我们已经证实，T2 DM患者的细胞内还存在有毒的hIAPP寡聚体，钙离子泄漏到胞浆中，导致对钙离子敏感的蛋白酶Calain过度激活。总而言之，这些特征再现了由淀粉样蛋白(如阿尔茨海默氏症)的蛋白毒性介导的神经退行性疾病中的特征。在神经退行性疾病中，人们越来越认识到，淀粉样蛋白的蛋白毒性部分是通过破坏细胞机制来传递的，这些机制包括去除错误折叠和聚集的蛋白质、泛素/蛋白酶体系统和自噬。在拟议的研究中，我们建议进行研究，以实现以下目标。1)建立IAPP寡聚体诱导细胞凋亡和功能障碍的具体机制。2)确定hIAPP毒性寡聚体是否损害了保护蛋白毒性的泛素蛋白小体系统，如果是，则通过何种机制(S)。3)确定自噬--清除有毒寡聚体和受损细胞器的细胞系统--是否被hIAPP有毒寡聚体扰乱，如果是，通过什么机制。这项研究计划将使我们能够阐明人类细胞丢失的根本原因，并建立防止这种情况的基本方法。

DESCRIPTION (provided by applicant): The islet in humans with type 2 diabetes (T2DM) is characterized by islet amyloid derived from islet amyloid polypeptide (IAPP), a protein that is co-expressed and secreted with insulin. Human IAPP (hIAPP) has the propensity to form oligomers in solution. These oligomers appear to form in membranes inducing non selective membrane leakage, for example of Ca2+ into cytosol. In studies supported by this grant we established that ¿-cell mass is decreased in humans with T2DM, with increased ¿-cell apoptosis. We reproduced the islet and metabolic phenotype of T2DM in rodents over expressing human IAPP, and documented that the toxic form of IAPP oligomers form intracellularly within the secretory pathway leading to endoplasmic reticulum (ER) stress induced apoptosis as well as organelle (mitochondrial) damage. We have established that ¿-cells in humans with T2DM are also characterized by intracellular formation of toxic hIAPP oligomers, leakage of Ca2+ into cytosol leading to hyperactivation of the Ca2+ sensitive protease calpain. Collectively these characteristics reproduce those in neurodegenerative diseases mediated by proteotoxicity of amyloidogenic proteins (e.g. Alzheimers). In the neurodegenerative diseases there is an increasing appreciation that proteotoxicity by amyloidogenic proteins is mediated in part through disruption of the cellular mechanisms that remove misfolded and aggregated proteins, the ubiquitin/proteosome system and autophagy. In the proposed studies we propose studies to address the following aims. 1) To establish the specific mechanisms by which IAPP oligomers induce ¿-cell apoptosis and dysfunction. 2) To establish if the ubiquitin proteosome system to protect against proteotoxicty is impaired by hIAPP toxic oligomers, and if so through which mechanism(s). 3) To establish if autophagy, the cellular system for removal of toxic oligomers and damaged organelles, is disrupted by hIAPP toxic oligomers, and if so, through which mechanisms. This program of studies would allow us to shed light into the underlying cause of loss of ¿-cells in humans, and to establish a rationale approach to preventing this.