The Role of Pancreatic ÃÂò-cell Store-Operated Calcium Entry in Fatty Acid Metabolism

摘要 2型糖尿病(T2 DM)的患病率正在以惊人的速度增长，突显了 更好地了解本综合征的病理生理机制。由于外周增加而发展为T2 DM 在肥胖的背景下发展起来的胰岛素抵抗，再加上 胰腺β细胞。许多因素被认为是导致T2 DM患者β细胞死亡和功能障碍的原因 包括内质网(ER)应激、β细胞钙稳态失调和脂毒性 非酯化游离脂肪酸(FFA)水平增加。这项研究项目的目标是定义FFA是如何 改变β细胞钙(Ca~(2+))动态平衡，触发T2 DM向高血糖状态的转变。这个 维持旺盛的胰岛素分泌和胰岛素产生水平依赖于完整的钙信号。 β细胞，部分是由于内质网管腔内高水平的钙离子隔离而形成的。存储操作的钙离子 Entry(SOCE)是一种响应内质网钙离子耗竭而重新填充内质网钙库的机制。SOCE 被内质网钙离子传感器STIM1激活，它与质膜Orai或Trp阳离子形成络合物 频道。这些复合体的形成允许SOCE诱导的钙离子从细胞外空间内流到 补充耗尽的内质网钙离子储存。我们实验室以前的工作表明，在T2 DM患者中，β细胞SOCE受损 STIM1表达减少，导致内质网应激和胰岛素分泌减少。初步数据 已表明，慢性棕榈酸酯治疗引起的脂毒性应激导致SOCE功能障碍，减少 STIM1表达、钙蛋白激活和β细胞死亡。最后，在INS-1β细胞中消融STIM1导致了 FFA治疗后细胞内脂滴积聚。基于这一科学前提，这个项目 将检验STIM1诱导的SOCE在胰腺正常脂肪处理中起关键作用的假设 β细胞，而功能失调的SOCE导致对脂毒应激的易感性增加。要解决这个问题 假设，β细胞特异性STIM1(Δβ)和STIM1 INS-1基因敲除小鼠模型 将利用β信元。目标1的目标是探索STIM1缺失导致 脂滴堆积、脂解缺陷、cAMP信号转导和内质网对脂毒应激的易感性 应激导致钙蛋白酶诱导的细胞死亡。在目标2中，将利用STIM1Δβ小鼠来定义生理 高脂饮食下β细胞STIM1缺失对全身葡萄糖稳态的影响。已被占用 总之，这项研究将为SOCE作为潜在的治疗靶点提供一种新的机制洞察。 2型糖尿病的进展性进展。这一奖学金将用于资助两年的研究生研究培训。 以及印第安纳大学医学科学家培训计划(MSTP)的两年临床培训 医学院，在卡梅拉·埃文斯-莫利纳博士的指导下。积极、协作的环境 伊利诺伊大学糖尿病和代谢疾病中心(CDMD)的领导将确保培训计划的成功。

Abstract The prevalence of Type 2 Diabetes Mellitus (T2DM) is increasing at an alarming rate, highlighting the need to better understand the pathophysiology this syndrome. T2DM develops as a result of increased peripheral insulin resistance that develops in the setting of obesity, coupled with inadequate insulin secretion from the pancreatic β cells. A number of factors are thought to contribute to β cell death and dysfunction in T2DM including endoplasmic reticulum (ER) stress, β cell calcium dyshomeostasis and lipotoxicity resulting from increased levels of non-esterified free fatty acids (FFA). The goal of this research project is to define how FFAs alter β cell calcium (Ca2+) homeostasis and triggers the transition to a state of hyperglycemia in T2DM. The maintenance of robust levels of insulin secretion and insulin production depends on intact Ca2+ signaling in the β cell, in part patterned by the sequestration of high levels of Ca2+ within the ER lumen. Store-operated Ca2+ entry (SOCE) is a mechanism that functions to refill ER Ca2+ stores in response to ER Ca2+ depletion. SOCE is activated by the ER Ca2+ sensor STIM1, which forms complexes with plasmalemmal Orai or TRP cation channels. The formation of these complexes allows SOCE-induced Ca2+ influx from the extracellular space to refill depleted ER Ca2+ stores. Previous work in our lab has shown that β cell SOCE is impaired in T2DM due to a reduction in the expression of STIM1, leading to ER stress and reduced insulin secretion. Preliminary data have shown that lipotoxic stress induced by chronic palmitate treatment leads to dysfunctional SOCE, reduced STIM1 expression, calpain activation, and β cell death. Lastly, STIM1 ablation in INS-1 β cells led to an intracellular accumulation of lipid droplets following FFA treatment. Based on this scientific premise, this project will test the hypothesis that STIM1-induced SOCE plays a critical role in normal lipid handling in the pancreatic β cell, while dysfunctional SOCE leads to increased susceptibility to lipotoxic stress. To address this hypothesis, β-cell specific knockout mouse model of STIM1 (STIM1Δβ) and STIM1 knockout (STIM1KO) INS-1 β cells will be utilized. The goal of Aim 1 is to explore the cellular mechanisms by which loss of STIM1 leads to susceptibility to lipotoxic stress through lipid droplet accumulation, defective lipolysis, cAMP signaling and ER stress leading to calpain-induced cell death. In Aim 2, STIM1Δβ mice will be utilized to define the physiological impact of the loss of β cell STIM1 on whole body glucose homeostasis in response to a high-fat diet. Taken together, this study will provide a novel mechanistic insight into SOCE as a potential therapeutic target in the progressive development of T2DM. This fellowship award will support two years of graduate research training and two years of clinical training in the Medical Scientist Training Program (MSTP) of Indiana University (IU) School of Medicine, under the mentorship of Dr. Carmella Evans-Molina. The active, collaborative environment of IU Center for Diabetes and Metabolic Diseases (CDMD) will ensure a successful training program.