Background: MODY includes a very heterogenous group of monogenic diabetes mellitus characterized by beta-islet cell dysfuction. We previously reported 3 new gene mutations of PTPRD, SYT9 and WFS1 in Korean MODY children (Horm Res Paediatr,2015). We investigated whether the PTPRD, SYT9 and WFS1 mutation overexpression vectors affect insulin synthesis and secretion in human pancreatic beta cells.
Materials & Methods: We used 1.4E7β cell lines for human pancreatic β-cells. PTPRD, SYT9 and WFS1 genes wild type (WT) vectors, mutation type (MUT) vectors, and siRNAs were transfected into the cells, and insulin secretion and cellular functions of insulin synthesis were examined.
Results: 1.4E7β cells were transfected with PTPRD, SYT9 and WFS1-WT vectors, -MT vectors, siRNA and a scramble siRNA as a negative control. PTPRD-WT, SYT9-WT and WFS1-WT were highly expressed in 1.4E7β cells. PTPRD-MUT, SYT9-MUT and WFS1-MUT were like normal control (1.4E7β cells without transfection). These 3 gene knockdowns by siRNAs confirmed a decrease in protein synthesis. Firstly, we evaluated changes in ATP/ADP ratio in PTPRD, SYT9 and WFS1-WT or MUT transfected 1.4E7β cells. When compared with normal control (1.4E7β cells without transfection), the increase in intracellular ATP after high glucose stimulation was nearly 290% in PTPRD-WT, SYT9-WT and WFS1-WT. However, PTPRD-MUT and WFS1-MUT inhibits glucose stimulated intracellular ATP. SYT9-MUT has no effect on ATP/ADP ratio increased by glucose. Secondarily, we examined changes in the surface expression levels of Kir6.2 which is closely related to insulin secretion using surface biotinylation/streptavidin purification and subsequent. The increase in Kir6.2 surface (s-Kir6.2) was increased by stimulation of glucose in PTPRD-WT, SYT9-WT and WFS1-WT. However, PTPRD-MUT, SYT9-MUT and WFS1-MUT inhibits glucose stimulated s-Kir6.2 expression. Among them, PTPRD-MUT highly reduced s-Kir6.2 expression by glucose in 1.4E7β cells. Thirdly, Metabolic disturbances like a hyperglycemia in a certain type of diabetes mellitus etc induce endoplasmic reticulum (ER) stress which represents decline in synthesis of insulin in pancreatic β-cells. The effect of mutations of PTPRD, SYT9 and WFS1 on glucose induced ER stress was performed. Glucose treatment highly increased ER stress markers (BiP, CHOP and pPERK) in PTPRD-WT, SYT(-WT and WFS1-WT. PTPRD-MUT highly inhibits glucose induced all 3 stress markers in 1.4E7β cells. Interestingly, SYT9-MUT highly inhibits only glucose induced BiP expression. WFS1-MUT moderately inhibits glucose induced BiP and CHOP expression in 1.4E7β cells.
Conclusion: Our results confirmed that single-point mutations of PTPRD, SYT9 and WFS1 showed impaired glucose-induced insulin release and synthesis in human pancreatic β-cells.
19 Sep 2019 - 21 Sep 2019