Pancreatic Islets Dynamics Regulating Glucagon Secretion

胰岛动态调节胰高血糖素分泌

• 批准号: 9068608
• 负责人: David W Piston
• 金额: $ 33.17万
• 依托单位: WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9068608
• 关键词: Alpha Cell; Architecture; Behavior; Beta Cell; Biosensor; Blood Glucose; Cell Communication; Cell physiology; Cell secretion; Cells; Communication; D Cells; Development; Diabetes Mellitus; Electrophysiology (science); Eph Family Receptors; Ephrins; Exocytosis; Gap Junctions; Gene Expression Profile; Genetic; Glucagon; Glucose; Goals; Health; Hormones; Human; Hyperglycemia; Hypoglycemia; Image; In Vitro; Insulin; Islet Cell; Islets of Langerhans; Knowledge; Label; Lead; Life; Measurement; Measures; Mediating; Mediator of activation protein; Metabolic; Methods; Microfluidics; Molecular; Molecular Biology; Mus; Paracrine Communication; Pathogenesis; Pathology; Pathway interactions; Pattern; Phenotype; Physiological; Play; Prevention; RNA Interference; Regulation; Research; Role; Signal Pathway; Signal Transduction; Somatostatin; Somatostatin Receptor; Testing; Therapeutic; Variant; Virus Diseases; blood glucose regulation; cell growth regulation; cell type; diabetic; diabetic patient; in vivo; insulin secretion; islet; new therapeutic target; novel; pancreatic juice; paracrine; prevent; protein expression; quantitative imaging; research study; response; success; therapeutic target; treatment strategy; type I and type II diabetes

DESCRIPTION (provided by applicant): The islet of Langerhans plays an important role in blood glucose homeostasis through regulated hormone secretion. The therapeutic success of insulin has led most islet research to focus on �-cells, although other islet hormones including glucagon (secreted by �-cells) and somatostatin (secreted by �-cells) have important physiological actions. Glucagon plays a critical role in the pathology of diabetes, but the mechanisms that regulate glucagon secretion remain poorly understood. Interactions with other islet cell types are likely involved in glucose-inhibition of glucagon secretion (GIGS), since inhibition is lost in vivo after �-cells are destroyed in Type I or fail in advanced Type 2 diabete. GIGS is also lost in vitro when �-cells are isolated from the islet. The composition, architecture, and protein expression patterns of islet cell types vary between species, but the amplitude and temporal pattern of GIGS is nearly identical regardless of species. Thus, we propose to leverage species similarities towards uncovering molecular mechanisms underlying GIGS. The secretory product of �-cells, somatostatin, is a promising molecular mediator of this interaction because GIGS is lost in islets with a genetic deletion of somatostatin, and the somatostatin receptor subtype 2 dominates its signaling in both human and mouse �-cells. However, somatostatin alone does not inhibit glucagon secretion from isolated �-cells, which suggests that somatostatin must combine with other cell-cell interactions in the islet for proper GIGS. One potential juxtacrine signaling mechanism that can inhibit exocytosis is ephrinA-EphA forward signaling, and transcriptome studies show that EphA4 is the only Eph receptor expressed in both human and mouse �-cells. We have shown that islet glucagon secretion is suppressed in response to glucose even though �-cell Ca2+ levels are elevated. This effect parallels that seen in islets lacking �-cell gap junctions, where insulin secretion can be inhibited by juxtacrine communication mediated by ephrinA-EphA signaling even when Ca2+ levels are elevated. Since the �-cell contains only a single Eph receptor sub-type and it is closely related to the �-cell, we speculate that a similar mechanism may play a role in GIGS from islet �-cells. Thus, we hypothesize that GIGS requires both paracrine signaling by somatostatin from �-cells in the islet and juxtacrine communication from �-cells via EphA4 forward signaling. This hypothesis will be tested via three specific aims: 1) determine the role of juxtacrine EphA4 forward signaling on islet glucagon secretion; 2) determine the role of somatostatin-mediated paracrine signaling combined with EphA juxtacrine signaling on GIGS from �-cells in intact islets; 3) determine the roles of these paracrine and juxtacrine signaling pathways on GIGS from human islets of healthy and Type II diabetic donors. These experimental results will further our understanding of �-cell function in mouse and human islets. This mechanistic information will provide novel therapeutic targets for the regulation of glucagon, which is an emerging opportunity for preventing hypoglycemic episodes and normalizing blood glucose in diabetic patients.

描述（由申请人提供）：朗格汉斯胰岛通过调节激素分泌在血糖稳态中发挥重要作用，尽管其他胰岛激素包括胰高血糖素（由胰高血糖素分泌），但胰岛素的治疗成功已导致大多数胰岛研究集中在β细胞上。 β细胞）和生长抑素（由β细胞分泌）具有重要的生理作用，但其调节机制在糖尿病病理学中发挥着关键作用。胰高血糖素分泌与其他胰岛细胞类型的相互作用可能与胰高血糖素分泌的葡萄糖抑制（GIGS）有关，因为在 I 型糖尿病中β细胞被破坏或在晚期 GIGS 中失败后，体内抑制作用消失。当从胰岛中分离出α-细胞时，其组成、结构、 胰岛细胞类型的蛋白质表达模式因物种而异，但无论物种如何，GIGS 的幅度和时间模式几乎相同。因此，我们建议利用物种相似性来揭示 GIGS 的分子机制。生长抑素是这种相互作用的一种有前途的分子介导物，因为生长抑素基因缺失的胰岛中 GIGS 丢失，并且生长抑素受体亚型 2 在人和小鼠中主导其信号传导然而，单独的生长抑素并不能抑制分离的β细胞的胰高血糖素分泌，这表明生长抑素必须与胰岛中的其他细胞间相互作用结合才能实现适当的GIGS，一种可以抑制胞吐作用的潜在近分泌信号机制是肝配蛋白A-。 EphA 正向信号传导和转录组研究表明，EphA4 是在人类和小鼠 β 细胞中表达的唯一 Eph 受体。即使β细胞Ca2+水平升高，胰​​高血糖素分泌也会受到抑制，这种效应与缺乏β细胞间隙连接的胰岛中观察到的情况相似，即使在Ca2+时，胰岛素分泌也会受到肝配蛋白A-EphA信号介导的近分泌通讯的抑制。由于α-细胞仅含有单一Eph受体亚型且与α-细胞密切相关，因此我们推测类似的机制可能在其中发挥作用。因此，我们探索了 GIGS 需要来自胰岛 β 细胞的生长抑素的旁分泌信号，以及来自 β 细胞通过 EphA4 正向信号传导的近分泌通讯。该假设将通过三个具体目标进行检验：1)确定近分泌EphA4正向信号对胰岛胰高血糖素分泌的作用2)确定生长抑素介导的旁分泌信号联合的作用；完整胰岛的 GIGS 上的 EphA 近分泌信号传导；3) 确定健康和 II 型糖尿病供体的人类胰岛中这些旁分泌和近分泌信号传导途径的作用这些实验结果将进一步了解 β 细胞功能。这一机制信息将为胰高血糖素的调节提供新的治疗靶点，这是预防低血糖发作和使血糖正常化的新兴机会。糖尿病患者。