Mechanisms of Somatostatin-Mediated Inhibition of Insulin and Glucagon

生长抑素（SST）是一种主要的抑制性激素，能够减弱胰高血糖素和胰岛素 分别来自胰岛内的α（α）和β（β）细胞的分泌。但 是我们理解生长抑素受体下游基本信号传导机制的一个关键空白 （SSTR）激活，以及在某些情况下这些如何有利于抑制胰岛素分泌， 抑制胰高血糖素分泌等。通过纯化α和β细胞群的转录组学分析 我已经确定了两者之间的关键差异和潜在的相似之处，这可能开始解释他们的细胞 特定SST响应。这些观察的核心是SSTR谱，它提供了输入信号， α细胞和β细胞之间的任一细胞类型是根本不同的，两种细胞类型都表达SSTR 3。 初级纤毛，而α细胞另外在其细胞表面上表达SSTR 2。生长抑素信号通常是 提示SST可导致胰岛内钙和/或cAMP的抑制，但SST作用的相对重要性 对这些并行信号级联的影响尚不清楚。此外，我还发现了一种新的SSTR介导的 一种积极驱动丝状肌动蛋白（F-肌动蛋白）重塑的效应机制， 分泌颗粒胞吐作用因此，我的中心假设是β细胞上SSTR 3的选择性激活 而α细胞上的SSTR 2或SSTR 3通过不同的质量效应而减弱胰岛素和胰高血糖素的分泌 以及Ca 2+和cAMP反应和下游F-肌动蛋白聚合的动力学。我将继续这个假设 通过完整胰岛的高通量功能成像锚定的两个独立的目标。首先我会利用 转基因小鼠系，其中第二信使的荧光报告分子将被严格递送到α或 β细胞。然后将这些胰岛经受单独的SSTR激动剂和拮抗剂，以了解SSTR激动剂和拮抗剂的作用。 识别的细胞特异性SSTR的个体贡献。第二，F-肌动蛋白动力学的荧光报告者将 用于活体成像实验，以在功能上确定SSTR激活对F-肌动蛋白的贡献 聚合和重塑。这些结果将结合纯化的下一代测序数据， 用SST和SSTR类型特异性拮抗剂处理的α和β细胞群。这一目标的结果将 表征潜在的F-肌动蛋白对SST的反应，从而促进整体激素衰减。这些 这些方法是创新的，因为它们利用了大量人群的高通量功能成像的能力 以高分辨率表征新机制和细胞类型特异性反应。总的来说， 这些目标的结果是重要的，因为它们将导致对机制的更全面的理解 SST通过该方法成功地减弱了不同代谢条件下胰岛素和胰高血糖素的释放。这 理解在开发细胞特异性SSTR激动剂中具有重要意义，该激动剂旨在减弱特异性 细胞群，影响超过3000万人的I型和II型糖尿病的靶向治疗 在美国的个人。

Somatostatin (SST) is a major inhibitory hormone that is capable of attenuating both glucagon and insulin secretion from alpha (α) and beta (β) cells respectively within the pancreatic islet of Langerhans. However, there is a critical gap in our understanding of the basic signaling mechanisms downstream of Somatostatin Receptor (SSTR) activation, and how these favor the inhibition of insulin secretion under some circumstances and the inhibition of glucagon secretion under others. Through transcriptomic analysis of purified α and β cell populations I have identified key differences and potential similarities between both which may begin to explain their cell specific SST response. Central to these observations, the SSTR profile which provides the input signal between either cell type is fundamentally different between α and β cells, with both cell types expressing SSTR3 on primary cilia, while α cells additionally express SSTR2 on their cell surface. Somatostatin signaling is typically suggested to lead to the inhibition of calcium and/or cAMP in the islet, but the relative importance of SST’s effect on these parallel signaling cascades is not understood. Furthermore, I have identified a novel SSTR mediated effector mechanism that actively drives the remodeling of filamentous actin (F-actin) with implications for secretory granule exocytosis. As such, my central hypothesis is that selective activation of SSTR3 on β cells and SSTR2 or SSTR3 on α cells will attenuate insulin and glucagon secretion via distinct effects on the quality and kinetics of Ca2+ and cAMP responses and downstream F-actin polymerization. I will pursue this hypothesis through two separate aims anchored by high throughput functional imaging of intact islets. First, I will leverage transgenic mouse lines in which fluorescent reporters of secondary messengers will be delivered to strictly α or β cells. These islets will then be subjected to individual SSTR agonists and antagonists to understand the individual contributions of identified cell specific SSTRs. Second, fluorescent reporters of F-actin dynamics will be employed in live imaging experiments to functionally determine the contribution of SSTR activation on F-actin polymerization and remodeling. These results will be coupled next generation sequencing data of purified populations of α and β cells treated with SST and SSTR type specific antagonists. The results of this aim will characterize an underlying F-actin response to SST contributing to overall hormone attenuation. These approaches are innovative as they leverage the power of high throughput functional imaging of large populations of cells to characterize both a novel mechanism and cell type specific response in high resolution. Collectively, the results of these aims are significant as they will result in a more complete understanding of the mechanisms by which SST succeeds in attenuating insulin and glucagon release under different metabolic conditions. This understanding carries significant weight in developing cell specific SSTR agonists aimed at attenuating specific cell populations, with implications in targeted treatment of type I and II diabetes affecting over 30 million individuals in the United States of America.