基于化学遗传学工具Gi-DREADD对胰岛α细胞旁分泌调节机制及其在糖尿病模型中的生理功能研究

胰岛α细胞及其分泌的胰高血糖素在糖尿病发生发展过程中起着不容忽视的作用。直接阻断胰高血糖素受体虽然可以有效地降低血糖但是会造成脂代谢异常。靶向α细胞直接调控胰高血糖素的分泌将可能成为更加安全的糖尿病长期治疗手段。我们基于化学遗传学工具Gi-DREADD建立了世界上首个可以在不破坏α细胞功能和胰岛结构、不影响胰高血糖素原基因表达水平的情况下，靶向实时调控胰高血糖素体内分泌水平的小鼠模型。初步实验发现胰高血糖素在体内可以通过旁分泌的方式调控胰岛素的分泌，它的缺失反而会导致糖耐受的减弱。下一步，我们将进一步深入研究胰岛内部α细胞和β细胞之间的旁分泌调节机制，并系统地分析α细胞在不同生理病理状态下调节血糖平衡的作用。本项目旨在利用化学遗传学工具Gi-DREADD研究α细胞对于机体代谢平衡以及糖尿病发生发展的影响，探讨靶向α细胞的Gi结合性受体作为更加安全的糖尿病治疗方案的可能性。

Glucagon, a polypeptide hormone secreted from α-cells of the pancreatic islets of Langerhans, plays a key role in the regulation of glucose homeostasis. It counteracts the actions of insulin in the liver and other tissues and contributes to impaired glucose homeostasis in type 1 and 2 diabetes. At present, the role of glucagon secretion from α-cells in the pathophysiology of diabetes is not well understood. Thus, a better understanding of α-cell physiology and pathophysiology is likely to provide novel insights into impaired glucose homeostasis characteristic for type 1 and 2 diabetes and to identify novel targets for the development of antidiabetic drugs. In vitro studies suggest that α-cell glucagon can modulate β-cell function. However, it remains unknown whether this intra-islet cross-talk plays a role in regulating glucose homeostasis in vivo, primarily due to the lack of suitable animal models. To address this issue, we established a novel mouse line that enabled us to acutely suppress glucagon secretion from pancreatic α-cells in a drug-dependent fashion in vivo. This mouse line expressed an inhibitory designer G protein-coupled receptor (GPCR) in α-cells only. This designer GPCR represents a DREADD (designer receptor exclusively activated by a designer drug) that is selectively coupled to inhibitory G proteins of the Gi family. Importantly, this DREADD, referred to as GiD, can be selectively activated by clozapine-N-oxide (CNO), a small molecule that is otherwise pharmacologically inert. CNO-induced activation of GiD almost completely shut off glucagon secretion in vivo and caused significantly impaired insulin secretion, hyperglycemia, and glucose intolerance. In addition, we also found that intra-islet glucagon signaling is required for the efficient release of insulin in vivo and for the proper regulation of blood glucose homeostasis. These new findings indicate that intra-islet glucagon signaling is essential for the proper function of pancreatic β-cells and glucose homeostasis in vivo. Next, we will further study the molecular mechanisms of intra-islet glucagon stimulated insulin release and the physiological role of pancreatic α-cells in the pathophysiology of diabetes. Strategies aimed at enhancing intra-islet glucagon signaling could prove useful and long-term safe to promote insulin secretion for therapeutic purposes.