Background: Store-operated Ca2+ entry (SOCE) is activated by endoplasmic reticulum (ER) Ca2+ sensor STIM1 which senses depletion of Ca2+ from the ER, and induces extracellular Ca2+ influx through Orai1 to the cytosol to maintain intracellular Ca2+ homeostasis in various cell types, however the role of SOCE in pancreatic β-cells remains largely unknown. GPR40 plays an important role in potentiation of glucose-induced insulin secretion (GIIS) by long-chain fatty acids and its activation enhances Ca2+-release from ER by activating inositol 1,4,5-triphosphate (IP3) receptor. Therefore, we hypothesized that SOCE contributed to GPR40-mediated GIIS potentiation. To test the hypothesis, we examined the role of SOCE modulator, STIM1 in MIN6 cells and β-cell specific STIM1-deficient mice (βSTIM1 cKO).
Methods: Fasiglifam(fas) was used for GPR40 agonist. STIM1 or Orai1 knockdowned (KD) MIN6 cells were analyzed for insulin secretion or intracellular Ca2+-dynamics. MIN6 cells were also transfected with pEX-SP-YFP-STIM1(23-685) and Orai1-CFP to analyze intracellular trafficking of STIM1 in response to fas. Insulin secretion from βSTIM1 cKO islets and OGTT was also analyzed to reveal physiological role of STIM1.
Results: STIM1 or Orai1 KD MIN6 cells and islets from βSTIM1 cKO similarly abolished fas-mediated potentiation of GIIS and fas-induced elevation of intracellular Ca2+ levels, while there was little effect on GIIS itself. STIM1-YFP was rapidly translocated from the ER to the plasma membrane and merged with Orai1-CFP in response to fas which was cancelled by pretreatment of IP3 receptor antagonist, xestospongin C. In OGTT, blood glucose levels were similar in control mice and βSTIM1 cKO without fas administration, however fas-mediated glucose lowering and insulin increasing effect were significantly lower compared with control.
Conclusion: GPR40 signal activates STIM1 and SOCE activated by STIM1 is essential for GPR40-mediated potentiation of GIIS.
R. Usui: None. D. Yabe: Advisory Panel; Self; Abbott. Research Support; Self; Astellas Pharma Inc. Speaker's Bureau; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Daiichi Sankyo Company, Limited, Eli Lilly and Company, Merck Sharp & Dohme Corp., Novo Nordisk Inc., Ono Pharmaceutical Co., Ltd., Sanofi K.K., Taisho Pharmaceutical Co., Ltd., Takeda Pharmaceutical Company Limited. M. Fauzi: None. A. Botagarova: None. H. Goto: None. S. Tokumoto: None. H. Tatsuoka: None. Y. Tahara: None. S. Kobayashi: None. T. Manabe: None. Y. Baba: None. T. Kurosaki: None. M. Ogura: Research Support; Self; Takeda Pharmaceutical Company Limited. Speaker's Bureau; Self; AstraZeneca, Boehringer Ingelheim International GmbH, Daiichi Sankyo Company, Limited, Eli Lilly and Company, Kyowa Hakko Kirin Co., Ltd., Merck & Co., Inc., Mitsubishi Tanabe Pharma Corporation, Novo Nordisk Inc., Ono Pharmaceutical Co., Ltd., Sanofi, Takeda Pharmaceutical Company Limited. K. Nagashima: None. N. Inagaki: Research Support; Self; Astellas Pharma Inc., Boehringer Ingelheim Pharmaceuticals, Inc., Daiichi Sankyo Company, Limited, Japan Tobacco Inc., Kyowa Hakko Kirin Co., Ltd., Merck Sharp & Dohme Corp., Mitsubishi Tanabe Pharma Corporation, Novartis Pharmaceuticals Corporation, Ono Pharmaceutical Co., Ltd., Sanofi, Sumitomo Dainippon Pharma Co., Ltd., Takeda Pharmaceutical Company Limited.
Japan Society for the Promotion of Science; Japan Association for Diabetes Education and Care