Experimental and Clinical Pharmacology and Toxicology / Center for Molecular Signalling (PZMS), Saarland University, Homburg, Germany.
Pharmakologisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany.
Cell Physiol Biochem. 2020 Nov 10;54(6):1115-1131. doi: 10.33594/000000304.
BACKGROUND/AIMS: The release of insulin in response to increased levels of glucose in the blood strongly depends on Ca influx into pancreatic beta cells by the opening of voltage-gated Ca channels. Transient Receptor Potential Melastatin 3 proteins build Ca permeable, non-selective cation channels serving as pain sensors of noxious heat in the peripheral nervous system. TRPM3 channels are also strongly expressed in pancreatic beta cells that respond to the TRPM3 agonist pregnenolone sulfate with Ca influx and increased insulin release. Therefore, we hypothesized that in beta cells TRPM3 channels may contribute to pregnenolone sulfate- as well as to glucose-induced insulin release.
We used INS-1 cells as a beta cell model in which we analysed the occurrence of TRPM3 isoformes by immunoprecipitation and western blotting and by cloning of RT-PCR amplified cDNA fragments. We applied pharmacological as well as CRISPR/Cas9-based strategies to analyse the interplay of TRPM3 and voltage-gated Ca channels in imaging experiments (FMP, Fura-2) and electrophysiological recordings. In immunoassays, we examined the contribution of TRPM3 channels to pregnenolone sulfate- and glucose-induced insulin release. To confirm our findings, we generated beta cell-specific Trpm3-deficient mice and compared their glucose clearance with the wild type in glucose tolerance tests.
TRPM3 channels triggered the activity of voltage-gated Ca channels and both channels together contributed to insulin release after TRPM3 activation. Trpm3-deficient INS-1 cells lacked pregnenolone sulfate-induced Ca signals just like the pregnenolone sulfate-induced insulin release. Both, glucose-induced Ca signals and the glucose-induced insulin release were strongly reduced. Accordingly, Trpm3-deficient mice displayed an impaired decrease of the blood sugar concentration after intraperitoneal or oral administration of glucose.
The present study suggests an important role for TRPM3 channels in the control of glucose-dependent insulin release.
背景/目的：血糖水平升高会引起胰岛素释放，这强烈依赖于电压门控钙通道打开引起的胰腺β细胞内钙离子流入。瞬时受体电位 melastatin 3 蛋白（TRPM3）组成钙通透性、非选择性阳离子通道，作为外周神经系统有害热的疼痛感受器。TRPM3 通道在胰腺β细胞中也有强烈表达，TRPM3 激动剂孕烯醇酮硫酸盐可引起其钙离子内流和胰岛素释放增加。因此，我们假设在β细胞中，TRPM3 通道可能有助于孕烯醇酮硫酸盐以及葡萄糖诱导的胰岛素释放。
我们使用 INS-1 细胞作为β细胞模型，通过免疫沉淀和 Western blot 以及 RT-PCR 扩增 cDNA 片段的克隆来分析 TRPM3 同工型的发生情况。我们应用药理学和 CRISPR/Cas9 策略，在成像实验（FMP、Fura-2）和电生理记录中分析 TRPM3 和电压门控钙通道之间的相互作用。在免疫测定中，我们研究了 TRPM3 通道对孕烯醇酮硫酸盐和葡萄糖诱导的胰岛素释放的贡献。为了证实我们的发现，我们生成了β细胞特异性 Trpm3 缺陷型小鼠，并在葡萄糖耐量试验中比较了它们与野生型的葡萄糖清除率。
TRPM3 通道触发电压门控钙通道的活性，并且在 TRPM3 激活后，两种通道共同促进胰岛素释放。缺乏 Trpm3 的 INS-1 细胞缺乏孕烯醇酮硫酸盐诱导的钙信号，就像缺乏孕烯醇酮硫酸盐诱导的胰岛素释放一样。葡萄糖诱导的钙信号和葡萄糖诱导的胰岛素释放都显著减少。因此，Trpm3 缺陷型小鼠在腹腔内或口服给予葡萄糖后，血糖浓度的下降受到严重损害。
本研究表明 TRPM3 通道在控制葡萄糖依赖性胰岛素释放中起重要作用。
