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。 朗格汉斯胰岛内的α(α)和β(β)细胞分泌。然而，在那里 是我们对生长抑素受体下游的基本信号机制理解上的一个关键差距 (SSTR)激活，以及在某些情况下这些激活如何有利于抑制胰岛素分泌以及 在其他情况下抑制高血糖素的分泌。通过对纯化的α和β细胞群体进行转录转录分析 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 特定的SST响应。这些观察的核心是SSTR轮廓，它提供了 无论哪种细胞类型在α和β细胞之间都是根本不同的，这两种细胞类型都表达SSTR3On 原代纤毛，而α细胞在其细胞表面另外表达SSTR2。生长抑素信号通常是 提示导致胰岛内钙和/或cAMP的抑制，但SST的作用相对重要 在这些平行的信令级联上，人们并不了解。此外，我还发现了一种新的SSTR介导的 主动驱动丝状肌动蛋白(F-肌动蛋白)重塑的效应机制 分泌颗粒胞吐。因此，我的中心假设是SSTR3在β细胞上的选择性激活 而α细胞上的SSTR2或SSTR3会通过对质量的不同影响而减弱胰岛素和胰升糖素的分泌 以及Ca~(2+)和cAMP反应以及下游F-肌动蛋白聚合的动力学。我将继续这一假设。 通过两个独立的目标，以完整的胰岛的高通量功能成像为基础。首先，我会利用 转基因小鼠品系，其中次级信使的荧光报告将被严格地α或 β细胞。然后，这些胰岛将受到单独的SSTR激动剂和拮抗剂的影响，以了解 已确定的细胞特异性SSTR的个体贡献。第二，F-肌动蛋白动力学的荧光记者将 用于活体成像实验，从功能上确定SSTR激活对F-肌动蛋白的贡献 聚合和改造。这些结果将与纯化的下一代测序数据相结合 Sst和Sstr型特异性拮抗剂处理的α和β细胞群体。这一目标的结果将是 描述潜在的F-肌动蛋白对SST的反应，有助于整体激素的衰减。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力量 以高分辨率表征一种新的机制和细胞类型特异性反应。总而言之， 这些目标的结果是重要的，因为它们将导致对这些机制的更全面的理解 通过SST在不同代谢条件下成功地抑制胰岛素和胰升糖素的释放。这 了解这一点对于开发细胞特异性SSTR激动剂具有重要意义，目的是减弱特定的 细胞群，对影响3000多万人的I型和II型糖尿病的靶向治疗 在美利坚合众国的个人。

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.