Chronic hyperglycemia in type 2 diabetes (T2D) causes pancreatic β-cell dysfunction, which is well known as glucose toxicity (GT), whereas the treatment of T2D improves that dysfunction. However, its underlying molecular mechanism has not yet been clarified. In this study, we aimed to identify and analyze a novel factor whose gene expression was altered by GT (GT-sensitive) and involved in β-cell function. For this purpose, type 2 diabetic db/db mice were treated with empagliflozin to selectively alleviate GT, as we recently reported (Shimo N, et al., 2015). Using the islet RNA from empagliflozin-treated (E) and untreated (U) mice, we performed DNA microarray analysis, and only 43 factors out of 33,779 probes showed more than two times as high signal levels in E as U. Among them, we focused on Tmem163, which is reported to be associated with T2D risk in GWAS and involved in the regulation of intracellular zinc levels. The Tmem163 mRNA expression levels in islets were significantly lower in U than normal control mice, and higher in E than U, which indicated that Tmem163 was GT-sensitive. The tissue distribution analysis by immunohistochemistry and immunoelectron microscopy revealed that Tmem163 was highly localized in pancreatic β-cells and accumulated in the membrane of insulin granule. Next, we found that Tmem163 knockdown significantly reduced glucose-stimulated and KCl-stimulated insulin secretion in MIN6 cells. In vivo, Tmem163 null mice (N) were comparable in body weight and blood glucose levels, but showed decreased glucose tolerance and insulin secretion in intraperitoneal glucose tolerance test, compared with wild type mice. Furthermore, the zinc content of islets in N tended to be lower than a hetero knockout mouse, suggesting a mechanism for β-cell dysfunction. These in vitro and in vivo findings suggest that the decreased expression of the novel GT-sensitive gene Tmem163 in islets causes the insufficient insulin secretion from pancreatic β-cells induced by chronic hyperglycemia.
N. Shimo: Speaker's Bureau; Self; Daiichi Sankyo Company, Limited. T. Matsuoka: None. D. Kawamori: Research Support; Self; Japan Society for the Promotion of Science, Japan Diabetes Society. Speaker's Bureau; Self; Ajinomoto Co., Inc., Astellas, K.K., Daiichi Sankyo Company, Limited, Dai-nippon Sumitomo Pharmaceutials, MSD K.K., Sanofi K.K., Sanwa Kagaku Kenkyusho Co., Ltd., Takeda Pharmaceuticals, Kowa Pharmaceuticals, Eli Lilly and Company. S. Takebe: None. T. Miyatsuka: Research Support; Self; Eli Lilly and Company, Japan Society for the Promotion of Science, Daiichi Sankyo Company, Limited, Novartis Pharma K.K., Astellas Pharma Inc., MSD K.K., Takeda Pharmaceutical Company Limited. I. Shimomura: Research Support; Self; Appliance Company, Panasonic Corporation. Speaker's Bureau; Self; Astellas Pharma Inc., AstraZeneca, Covidien Japan Inc.. Research Support; Self; Daiichi Sankyo Company, Limited. Speaker's Bureau; Self; Daiichi Sankyo Company, Limited. Research Support; Self; Eli Lilly Japan K.K., Eli Lilly Japan K.K., Kaken Pharmaceutical Co., Ltd.. Speaker's Bureau; Self; Kowa Pharmaceutical Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Mochida Pharmaceutical Co., Ltd., MSD K.K., Nippon Boehringer Ingelheim Co. Ltd., Novartis Pharma K.K.. Research Support; Self; Novo Nordisk Pharma Ltd.. Speaker's Bureau; Self; Novo Nordisk Pharma Ltd., Ono Pharmaceutical Co., Ltd.. Research Support; Self; Roche DC Japan K.K., Rohto Pharmaceutical Co., Ltd. Speaker's Bureau; Self; Rohto Pharmaceutical Co., Ltd, Sanwa Kagaku Kenkyusho Co., Ltd.. Research Support; Self; Sanofi K.K.. Speaker's Bureau; Self; Sanofi K.K.. Research Support; Self; Shionogi & Co., Ltd.. Speaker's Bureau; Self; Sumitomo Dainippon Pharma Co., Ltd.. Research Support; Self; Taisho Toyama Pharmaceutical Co., Ltd.. Speaker's Bureau; Self; Taisho Toyama Pharmaceutical Co., Ltd.. Research Support; Self; Takeda Pharmaceutical Company Limited. Speaker's Bureau; Self; Takeda Pharmaceutical Company Limited. Research Support; Self; Teijin Pharma Limited. Speaker's Bureau; Self; Teijin Pharma Limited.
