Control of Insulin Release by Transient Receptor Potential Melastatin 3 (TRPM3) Ion Channels.
BACKGROUND/AIMS
The release of insulin in response to increased levels of glucose in the blood strongly depends on Ca2+ influx into pancreatic beta cells by the opening of voltage-gated Ca2+ channels. Transient Receptor Potential Melastatin 3 proteins build Ca2+ 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 Ca2+ 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.


METHODS
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 Ca2+ 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.


RESULTS
TRPM3 channels triggered the activity of voltage-gated Ca2+ channels and both channels together contributed to insulin release after TRPM3 activation. Trpm3-deficient INS-1 cells lacked pregnenolone sulfate-induced Ca2+ signals just like the pregnenolone sulfate-induced insulin release. Both, glucose-induced Ca2+ 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.


CONCLUSION
The present study suggests an important role for TRPM3 channels in the control of glucose-dependent insulin release.
['Becker|Alexander|A|', 'Mannebach|Stefanie|S|', 'Mathar|Ilka|I|', 'Weissgerber|Petra|P|', 'Freichel|Marc|M|', 'Loodin|Asia Perveen|AP|', 'Fecher-Trost|Claudia|C|', 'Belkacemi|Anouar|A|', 'Beck|Andreas|A|', 'Philipp|Stephan Ernst|SE|']
D000818:Animals D020013:Calcium Signaling D002460:Cell Line D000078790:Insulin Secretion D050417:Insulin-Secreting Cells D051379:Mice D008817:Mice, Mutant Strains D051381:Rats D050053:TRPM Cation Channels
INS-1 Transient receptor potential M3 channels (TRPM3) Calcium Glucose-stimulated insulin secretion CRISPR/Cas Trpm3 knockout