A role and regulation of glucose responsive lipolysis in pancreatic beta cells

T2 D是美国退伍军人的一个主要健康问题，对身体、经济和情感造成了重大影响。 因此，迫切需要一种有效且广泛适用的治疗方法。 β细胞中脂质的过度积累被认为有助于T2 D的发展。 实验数据支持脂质过载激活多种应激途径，包括炎症、ER 应激、氧化应激和线粒体功能障碍最终导致功能性β细胞的丧失 马萨诸塞州我们已经发现证据表明，来自T2 D供体的人胰岛中甘油三酯（TG）的积累是 与脂解失调相关，这是一种以前未被认识到的T2 D胰岛缺陷，可加速TG 在T2 D胰岛中积累。葡萄糖激活非糖尿病人胰岛中的脂解，但不激活T2 D胰岛中的脂解。 此外，我们的初步数据表明，脂肪分解的失调损害胰岛素分泌， 降低突触融合蛋白1a（Stx 1a）的稳定性，Stx 1a是一种对胞吐作用很重要的SNARE复合蛋白。 当我们使用人假胰岛测试脂解调节异常的影响时， 主要TG脂肪酶（ATGL）下调，ATGL缺陷的人假胰岛表现出脂质过多 小滴（LD）积累和受损的胰岛素分泌沿着Stx 1a的蛋白酶体降解。 重要的是，Stx 1a的减少是人类T2 D胰岛中报告的缺陷。因此，我们假设 对葡萄糖应答的脂解失调降低了Stx 1a的稳定性并损害了胰岛素分泌， T2 D胰岛。为了理解T2 D胰岛缺陷背后的分子机制，必须 确定葡萄糖如何上调β细胞中的脂解，为什么葡萄糖不能上调T2 D中的脂解 胰岛，以及脂肪分解中的损伤如何减少Stx 1a。我们将用人类的方式来处理我们的问题。 假胰岛和INS 1细胞作为模型，因为它们在LD形成中表现出与人胰岛的相似性， 脂肪分解的调节和ATGL缺乏的表型。我们希望能获得关于 脂质动员的失调如何通过以下目的引起T2 D中的β细胞功能障碍。 具体目标1：确定ATGL增加脂肪分解以响应葡萄糖的机制， 非糖尿病β细胞 我们将系统地测试葡萄糖增加INS 1细胞和非糖尿病细胞中脂解的潜在靶点。 人类β细胞目标1a将测试哪些葡萄糖产生的信号调节β细胞中的脂解。目标1b-d 将测试葡萄糖是否通过修饰ATGL、共脂肪酶或围脂蛋白来增加脂解。 具体目标2：确定2型糖尿病β细胞中脂解失调的机制 目的1剖析葡萄糖调节β细胞脂解的机制。利用信息 从目标1，我们将确定为什么T2 D胰岛不能响应于葡萄糖增加脂解，以及如何 我们可以恢复二型糖尿病胰岛的脂解作用。 具体目的3：检验缺陷性脂解使T2 D胰岛中的stx 1a不稳定的假设 提出Stx 1a有助于T2 D中胰岛素分泌的损害，因为Stx 1a在胰岛中减少。 T2 D模型和受T2 D影响的人类胰岛。然而，尚不清楚为什么Stx 1a在T2 D中减少 小岛我们的初步数据表明，脂肪分解功能受损可能导致2型糖尿病患者Stx 1a减少 小岛因此，我们将检验以下假设：减少的脂解有助于减少T2 D胰岛中的Stx 1a 通过减少棕榈酰化加速Stx 1a的降解。 我们的研究结合了药理学和分子方法，以增加我们对 T2 D中β细胞功能障碍的发病机制。获得的信息可能会引导我们找到一个新的目标 通过恢复β细胞中的LD动员来改善T2 D中的β细胞功能。

T2D is a major health problem for US veterans that imposes significant physical, financial, and emotional tolls. Thus, there is a strong and urgent need for an effective and widely applicable therapy. Excessive accumulation of lipids in beta cells is considered to contribute to the development of T2D. Experimental data supports that lipid overload activates multiple stress pathways including inflammation, ER stress, oxidative stress, and mitochondrial dysfunction ultimately leading to the loss of functional beta cell mass. We have found evidence that the accumulation of triglycerides (TG) in human islets from T2D donors is associated with dysregulation of lipolysis, a previously unrecognized defect in T2D islets that accelerates TG accumulation in T2D islets. Glucose activates lipolysis in non-diabetic human islets but not in T2D islets. Furthermore, our preliminary data indicates that the dysregulation of lipolysis impairs insulin secretion by reducing the stability of syntaxin1a (Stx1a), one of the SNARE complex proteins important for exocytosis. When we tested the impact of dysregulation of lipolysis using human pseudoislets in which the expression of the principal TG lipase (ATGL) is down-regulated, ATGL deficient human pseudoislets showed excessive lipid droplet (LD) accumulation and impaired insulin secretion along with proteasomal degradation of Stx1a. Importantly, the reduction of Stx1a is a defect reported in human T2D islets. Thus, we hypothesize that the dysregulation of lipolysis in response to glucose reduces the stability of Stx1a and impairs insulin secretion in T2D islets. To understand molecular mechanism behind the defects in T2D islets, it will be imperative to determine how glucose upregulates lipolysis in beta cells, why glucose fails to upregulate lipolysis in T2D islets, and how the impairment in lipolysis reduces Stx1a. We will approach our questions using human pseudoislets and INS1 cells as models since they exhibit similarity with human islets in LD formation, the regulation of lipolysis, and phenotypes of ATGL deficiency. We expect to obtain novel information regarding how dysregulation of lipid mobilization causes beta cell dysfunction in T2D through the following aims. Specific aim 1: Determine a mechanism by which ATGL increases lipolysis in response to glucose in non-diabetic beta cells We will systematically test potential targets by which glucose increases lipolysis in INS1 cells and non-diabetic human beta cells. Aim 1a will test which glucose generated signals regulates lipolysis in beta cells. Aim 1b-d will test whether glucose increases lipolysis by modifying ATGL, co-lipases, or perilipins. Specific aim 2: Determine a mechanism by which lipolysis is dysregulated in type 2 diabetic beta cells Aim 1 dissects a mechanism by which glucose regulates lipolysis in beta cells. Leveraging on the information from Aim 1, we will determine why T2D islets are unable to increase lipolysis in response to glucose and how we can restore lipolysis in T2D islets. Specific Aim 3: Test the hypothesis that defective lipolysis destabilizes stx1a in T2D islets Stx1a is proposed to contribute to the impairment of insulin secretion in T2D as Stx1a is reduced in islets of T2D models and human islets affected by T2D. However, it has been unknown why Stx1a is reduced in T2D islets. Our preliminary data implicates that the impairment of lipolysis may cause the reduction of Stx1a in T2D islets. Thus, we will test the hypothesis that reduced lipolysis contributes to the reduction of Stx1a in T2D islets through accelerating degradation of Stx1a due to reduced palmitoylation. Our study combines pharmacological and molecular approaches to increase our understanding of the pathogenesis of beta cell dysfunction in T2D. The information obtained will potentially lead us to a novel target that improves beta cell function in T2D by restoring LD mobilization in beta cells.