Role of the Renin-Angiotensin System in Glucose Homeostasis

项目摘要/摘要 在治疗2型糖尿病(T2D)时，同时针对两者缺陷的药物很少 β-细胞功能和质量。血管紧张素(1-7)是肾素-血管紧张素系统的代谢物，可以填补这一空白； 然而，其潜在的作用机制尚不完全清楚。我们的数据显示， 血管紧张素(1-7)的胰岛素调节作用依赖于它对血管紧张素(1-2)二肽的水解。 后者还在β细胞中传递促进生存和增殖的作用。血管紧张素(1-2)激活G蛋白- 偶联受体家族C组6成员A(GPRC6A)，我们发现它在胰岛a细胞表达。此外， 血管紧张素(1-2)增加细胞来源的胰升糖素样肽-1(GLP-1)的释放，提示它通过 GPRC6A在a细胞上以旁分泌方式促进胰岛素分泌。事实上，在GLP-1受体缺陷 在胰岛，我们发现血管紧张素(1-2)不能促进胰岛素的分泌；但它能促进β-细胞的分泌 存活和增殖得以保留。后者提示，血管紧张素(1-2)S的作用部分是通过GLP-1受体实现的。 独立自主。基于这些新的数据，我们假设血管紧张素(1-2)通过内、外途径增强β细胞的功能。 胰岛旁分泌信号转导，并通过一种新的不依赖于β-1的机制促进GLP-1细胞的存活/增殖。 以下具体目标解决了这一假设，目的是改善T2D的治疗选择： 具体目的1.确定血管紧张素(1-2)增加胰岛来源的GLP-1的机制 和胰岛素分泌。白喉毒素诱导的a细胞破坏的小鼠(体内)和胰岛(体外) 细胞特异性GPRC6A基因敲除将被用来确定血管紧张素(1-2)介导的血管紧张素转换酶是否增加 胰岛素的释放分别需要a细胞或a细胞GPRC6A。我们将探讨GLP-1升高的机制 释放并确认在有或没有GLP-1受体或GPRC6A阻断的情况下在人胰岛中的关键发现。 特定目的2.确定介导β-细胞存活和增殖的信号通路/蛋白 血管紧张素转换酶(1-2)对人胰岛的作用血管紧张素(1-2)抑制细胞凋亡的能力 人胰岛在非糖尿病和非糖尿病条件下，β细胞的去分化和促进增殖将被检测。 糖尿病的情况。将确定独立于GLP-1或GPRC6A的机制的贡献。 血管紧张素(1-2)作用的效应物将使用无偏倚磷蛋白组学来识别，然后- 胰岛的功能研究将作为筛选效应器的初步筛选，可以作为治疗的靶向。 具体目的3.确定Ang(1-2)是否改善体内人胰岛功能/存活，以及 血管紧张素转换酶(1-7)是否需要水解才能发挥抗糖尿病作用。我们将利用人类的小岛 移植模型测定血管紧张素(1-2)改善β细胞功能/存活和血糖的能力 糖尿病小鼠。此外，我们将测试血管紧张素(1-7)的促胰岛素作用是否需要它的水解， 就像在体外的情况一样。后者对于T2D的临床处理具有非常重要的意义，因为它将提示 目前正在开发的抗水解血管紧张素(1-7)类药物的用途。

PROJECT SUMMARY/ABSTRACT In treating type 2 diabetes (T2D), there is a paucity of medications simultaneously targeting deficits in both β-cell function and mass. Angiotensin(1-7), a metabolite of the renin-angiotensin system, may fill this gap; however, its underlying mechanisms of action are incompletely understood. Our data reveal that the insulinotropic action of angiotensin(1-7) is dependent on its hydrolysis to the dipeptide, angiotensin(1-2), the latter also conveying pro-survival and proliferative effects in β cells. Angiotensin(1-2) activates G-protein- coupled receptor family C group 6 member A (GPRC6A), which we show is expressed in islet a cells. Further, angiotensin(1-2) increases a cell-derived glucagon-like peptide-1 (GLP-1) release, suggesting it acts via GPRC6A on the a cell to promote insulin secretion in a paracrine fashion. Indeed, in GLP-1 receptor deficient islets, we find that angiotensin(1-2) fails to potentiate insulin secretion; however, its ability to enhance β-cell survival and proliferation is retained. The latter suggests angiotensin(1-2)’s action is, in part, GLP-1 receptor- independent. Based on these novel data, we hypothesize angiotensin(1-2) enhances β-cell function via intra- islet paracrine signaling, and promotes β-cell survival/proliferation via a novel GLP-1-independent mechanism. The following specific aims address this hypothesis, with the goal of improving treatment options in T2D: Specific Aim 1. To determine the mechanism by which angiotensin(1-2) increases islet-derived GLP-1 and insulin secretion. Mice (in vivo) and islets (in vitro) with diphtheria toxin-induced a-cell destruction or a cell-specific GPRC6A knockout will be used to determine whether angiotensin(1-2)-mediated increases in insulin release require a cells or a-cell GPRC6A, respectively. We will probe mechanisms for increased GLP-1 release, and confirm key findings in human islets with and without GLP-1 receptor or GPRC6A blockade. Specific Aim 2. To identify signaling pathways/proteins mediating the β-cell survival and proliferative effects of Ang(1-2) in human islets. The ability of angiotensin(1-2) to inhibit apoptosis, reduce dedifferentiation and enhance proliferation of β cells will be examined in human islets under non-diabetic and diabetic conditions. The contribution of mechanisms independent of GLP-1 or GPRC6A will be determined. Effectors of angiotensin(1-2) action will be identified using non-biased phosphoproteomics, then loss-/gain-of- function studies in islets will serve as a preliminary screen for effectors that could be targeted therapeutically. Specific Aim 3. To determine whether Ang(1-2) improves human islet function/survival in vivo, and whether hydrolysis of Ang(1-7) is required for its anti-diabetic effects. We will utilize a human islet transplant model to determine the ability of angiotensin(1-2) to improve β-cell function/survival and glycemia in diabetic mice. Further, we will test whether the insulinotropic action of angiotensin(1-7) requires its hydrolysis, as is the case in vitro. The latter is highly significant for clinical management of T2D because it will inform on the utility of hydrolysis-resistant angiotensin(1-7)-based medications currently in development.