School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan.
School of Computing, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan.
Diabetes. 2022 Sep 1;71(9):1946-1961. doi: 10.2337/db21-0644.
There is increasing evidence that dopamine (DA) functions as a negative regulator of glucose-stimulated insulin secretion; however, the underlying molecular mechanism remains unknown. Using total internal reflection fluorescence microscopy, we monitored insulin granule exocytosis in primary islet cells to dissect the effect of DA. We found that D1 receptor antagonists rescued the DA-mediated inhibition of glucose-stimulated calcium (Ca2+) flux, thereby suggesting a role of D1 in the DA-mediated inhibition of insulin secretion. Overexpression of D2, but not D1, alone exerted an inhibitory and toxic effect that abolished the glucose-stimulated Ca2+ influx and insulin secretion in β-cells. Proximity ligation and Western blot assays revealed that D1 and D2 form heteromers in β-cells. Treatment with a D1-D2 heteromer agonist, SKF83959, transiently inhibited glucose-induced Ca2+ influx and insulin granule exocytosis. Coexpression of D1 and D2 enabled β-cells to bypass the toxic effect of D2 overexpression. DA transiently inhibited glucose-stimulated Ca2+ flux and insulin exocytosis by activating the D1-D2 heteromer. We conclude that D1 protects β-cells from the harmful effects of DA by modulating D2 signaling. The finding will contribute to our understanding of the DA signaling in regulating insulin secretion and improve methods for preventing and treating diabetes.
越来越多的证据表明，多巴胺 (DA) 作为葡萄糖刺激胰岛素分泌的负调节剂发挥作用；然而，其潜在的分子机制尚不清楚。本研究采用全内反射荧光显微镜，监测原代胰岛细胞中胰岛素颗粒的胞吐作用，以剖析 DA 的作用。结果发现，D1 受体拮抗剂可挽救 DA 介导的葡萄糖刺激的钙 (Ca2+) 流抑制，从而表明 D1 在 DA 介导的胰岛素分泌抑制中起作用。单独过表达 D2，而不是 D1，会产生抑制和毒性作用，从而消除葡萄糖刺激的 Ca2+内流和 β 细胞中的胰岛素分泌。邻近连接和 Western blot 分析显示，D1 和 D2 在 β 细胞中形成异源二聚体。用 D1-D2 异源二聚体激动剂 SKF83959 处理可短暂抑制葡萄糖诱导的 Ca2+内流和胰岛素颗粒胞吐作用。共表达 D1 和 D2 使 β 细胞能够绕过 D2 过表达的毒性作用。DA 通过激活 D1-D2 异源二聚体，短暂抑制葡萄糖刺激的 Ca2+流和胰岛素分泌。总之，D1 通过调节 D2 信号转导，保护 β 细胞免受 DA 的有害影响。这一发现将有助于我们理解 DA 信号在调节胰岛素分泌中的作用，并改善预防和治疗糖尿病的方法。
