Role of IAPP in Islet Dysfunction in Diabetes

描述（由申请人提供）：2型糖尿病（T2DM）患者的胰岛以胰岛淀粉样蛋白为特征，来源于胰岛淀粉样蛋白多肽（IAPP），这是一种与胰岛素共表达和分泌的蛋白质。人IAPP （hIAPP）具有在溶液中形成低聚物的倾向。这些低聚物似乎在膜中形成，诱导非选择性膜渗漏，例如Ca2+进入细胞质。在该基金支持的研究中，我们发现T2DM患者的细胞质量下降，细胞凋亡增加。我们在过表达人类IAPP的啮齿类动物中重现了T2DM的胰岛和代谢表型，并记录了IAPP低聚物的毒性形式在分泌途径内形成细胞内，导致内质网（ER）应激诱导的细胞凋亡以及细胞器（线粒体）损伤。我们已经确定T2DM患者的¿-细胞也具有细胞内形成有毒hIAPP低聚物的特征，Ca2+渗漏到细胞质中导致Ca2+敏感蛋白酶calpain的过度活化。总的来说，这些特征再现了由淀粉样蛋白的蛋白质毒性介导的神经退行性疾病（例如阿尔茨海默氏症）。在神经退行性疾病中，越来越多的人认识到淀粉样蛋白的蛋白质毒性部分是通过破坏细胞机制来介导的，细胞机制可以去除错误折叠和聚集的蛋白质、泛素/蛋白体系统和自噬。在建议的研究中，我们建议研究以解决以下目标。1)建立IAPP低聚物诱导细胞凋亡和功能障碍的具体机制。2)确定hIAPP毒性低聚物是否破坏了泛素蛋白体系统以防止蛋白质毒性，如果是，通过何种机制。3)确定hIAPP毒性低聚物是否破坏了细胞自噬（清除有毒低聚物和受损细胞器的细胞系统），如果是，通过何种机制。这一研究项目将使我们能够揭示人类细胞丧失的潜在原因，并建立一种预防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.