Sigma-1 receptor overexpression promotes proliferation and ameliorates cell apoptosis in β-cells

Abstract

Sigma-1 receptor (Sig-1r) is a class of orphan receptors, the potential role of which in pancreatic islet cells remains poorly understood. The present study aimed to investigate the role of Sig-1r in islet β-cell proliferation and examine the effects of Sig-1r on islet β-cell injury under lipotoxic conditions. Sig-1r-overexpressing Min6 cells were generated by lentiviral vector transfection. The effect of Sig-1r overexpression on cell proliferation detected by edu staining, cell cycle progression by propidium iodide (Pi), apoptosis by annexin V-aPc/Pi, mitochondrial membrane potential by Mitolite red and cytoplasmic ca2+ levelsby Fura-2/aM in islet β-cells were measured by flow cytometry. Western blot analysis was used to measure protein expression levels of endoplasmic reticulum (er) stress markers glucose-regulated protein 78 and c/eBP homologous protein, mitochondrial apoptotic proteins Bcl-2-associated X and Bcl-2 and cyto- chrome c. in addition, aTP levels and insulin secretion were separately measured using aTP assay and mouse insulin eliSa. Mitochondria-associated er membrane (MaM) structures in Min6 cells were then detected using transmission electron microscopy. Protein disulfide isomerase expression and possible colocalization between inositol 1,4,5-trisphos- phate receptor and voltage-dependent anion channel 1 were examined using immunofluorescence. Sig-1R overexpression was found to promote β-cell proliferation by accelerating cell cycle progression. Furthermore, Sig-1r overexpression Sigma-1 receptor (Sig-1R) is a class of orphan receptors, the potential role of which in pancreatic islet cells remains poorly understood. The present study aimed to investigate the role of Sig-1R in islet β-cell proliferation and examine the effects of Sig-1R on islet β-cell injury under lipotoxic conditions. Sig-1R-overexpressing MIN 6 cells were generated by lentiviral vector transfection. The effect of Sig-1R overexpression on cell proliferation detected by EdU staining, cell cycle progression by propidium iodide (PI), apoptosis by Annexin V-APC/PI, mitochondrial membrane potential by Mitolite Red and cytoplasmic Ca2+ levelsby Fura-2/AM in islet β-cells were measured by flow cytometry. Western blot analysis was used to measure protein expression levels of endoplasmic reticulum (ER ) stress markers glucose-regulated protein 78 and C/EBP homologous protein, mitochondrial apoptotic proteins Bcl-2-associated X and Bcl-2 and cytochrome c. In addition, ATP levels and insulin secretion were separately measured using ATP Assay and mouse insulin ELI SA. Mitochondria-associated ER membrane (MAM) structures in MIN 6 cells were then detected using transmission electron microscopy. Protein disulfide isomerase expression and possible colocalization between inositol 1,4,5-trisphosphate receptor and voltage-dependent anion channel 1 were examined using immunofluorescence. Sig-1R overexpression was found to promote β-cell proliferation by accelerating cell cycle progression. Furthermore, Sig-1R overexpressionameliorated the apoptosis rate whilst impairing insulin secretion induced by palmitic acid by relieving ER stress and mitochondrial dysfunction in MIN 6 cells. Sig-1R overexpression also promoted Ca2+ transport between mitochondria and ER by increasing the quantity of ER adjacent to mitochondria in the 50-nm range. It was concluded that Sig-1R overexpression conferred protective effects on β-cells against lipotoxicity as a result of the promotion of cell proliferation and inhibition of ER stress and oxidative stress, by regulating the structure of MAM.