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

对于美国退伍军人来说，T2D是一个主要的健康问题，会带来巨大的身体、经济和情感上的损失。 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聚被认为是导致T2D的原因之一。 实验数据支持脂质过载激活包括炎症、内质网在内的多条应激途径 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 质量。我们发现有证据表明，来自T2D捐赠者的人胰岛中甘油三酯(TG)的积累是 与脂解失调有关，这是一种以前未被发现的T2D胰岛缺陷，可加速TG 在T2D胰岛中蓄积。葡萄糖可激活非糖尿病人胰岛的脂解作用，但不能激活T2D胰岛。 此外，我们的初步数据表明，脂肪分解的失调通过以下方式损害胰岛素的分泌 降低合成素1a(Stx1a)的稳定性，这是一种对胞吐起重要作用的SNARE复杂蛋白。 当我们使用人类假性胰岛来测试脂解失调的影响时，其中表达了 主要甘油三酯脂肪酶(ATGL)表达下调，ATGL缺乏的人伪胰岛表现为脂肪过多 随着Stx1a蛋白酶体的降解，液滴(LD)堆积和胰岛素分泌受损。 重要的是，Stx1a的减少是在人类T2D胰岛中报道的缺陷。因此，我们假设 糖引起的脂解失调降低了Stx1a的稳定性，并损害了胰岛素的分泌 T2D胰岛。为了了解T2D胰岛缺陷背后的分子机制，有必要对 确定葡萄糖如何上调β细胞中的脂肪分解，为什么葡萄糖未能上调T2D中的脂肪分解 胰岛，以及脂解损伤如何降低Stx1a。我们将使用人类来解决我们的问题 伪胰岛和INS1细胞作为模型，因为它们在LD形成过程中表现出与人类胰岛相似的特征，所以 脂解调节和ATGL缺乏症的表型。我们希望获得有关以下方面的新信息 脂类动员的失调如何通过以下目的导致T2D中的β细胞功能障碍。 具体目标1：确定ATGL增加脂肪分解对葡萄糖的反应的机制 非糖尿病β细胞 我们将系统地测试葡萄糖增加INS1细胞和非糖尿病患者脂肪分解的潜在靶点 人类的β细胞。目的1a将测试哪些葡萄糖产生的信号调节β细胞中的脂肪分解。目标1b-d 将测试葡萄糖是否通过修饰ATGL、辅脂酶或Perilipins来增加脂肪分解。 特定目标2：确定2型糖尿病β细胞脂解失调的机制 目的1剖析葡萄糖调节β细胞脂解作用的机制。充分利用这些信息 从目标1，我们将确定为什么T2D胰岛不能增加对葡萄糖的脂解反应，以及如何 我们可以恢复T2D胰岛的脂肪分解。 具体目标3：验证有缺陷的脂解作用破坏T2D胰岛stx1a稳定性的假设 Stx1a被认为与T2D的胰岛素分泌障碍有关，因为Stx1a在 T2D模型和受T2D影响的人胰岛。然而，为什么Stx1a在T2D中减少一直是未知的 小岛。我们的初步数据表明，脂解功能的受损可能导致T2D中Stx1a的减少 小岛。因此，我们将检验这一假设，即脂肪分解减少有助于T2D胰岛中Stx1a的减少 通过减少棕榈酰化而加速Stx1a的降解。 我们的研究结合了药理学和分子方法来增加我们对 T2D中β细胞功能障碍的发病机制。所获得的信息可能会把我们引向一个新的目标 这通过恢复β细胞中LD的动员来改善T2D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.