Abstract: | Ca2+ may trigger apoptosis in β-cells. Hence, the control of intracellular Ca2+ may represent a potential approach to prevent β-cell apoptosis in diabetes. Our objective was to investigate the effect and mechanism of action of plasma membrane Ca2+-ATPase (PMCA) overexpression on Ca2+-regulated apoptosis in clonal β-cells. Clonal β-cells (BRIN-BD11) were examined for the effect of PMCA overexpression on cytosolic and mitochondrial [Ca2+] using a combination of aequorins with different Ca2+ affinities and on the ER and mitochondrial pathways of apoptosis. β-cell stimulation generated microdomains of high [Ca2+] in the cytosol and subcellular heterogeneities in [Ca2+] among mitochondria. Overexpression of PMCA decreased [Ca2+] in the cytosol, the ER, and the mitochondria and activated the IRE1α-XBP1s but inhibited the PRKR-like ER kinase-eIF2α and the ATF6-BiP pathways of the ER-unfolded protein response. Increased Bax/Bcl-2 expression ratio was observed in PMCA overexpressing β-cells. This was followed by Bax translocation to the mitochondria with subsequent cytochrome c release, opening of the permeability transition pore, and apoptosis. In conclusion, clonal β-cell stimulation generates microdomains of high [Ca2+] in the cytosol and subcellular heterogeneities in [Ca2+] among mitochondria. PMCA overexpression depletes intracellular [Ca2+] stores and, despite a decrease in mitochondrial [Ca2+], induces apoptosis through the mitochondrial pathway. These data open the way to new strategies to control cellular Ca2+ homeostasis that could decrease β-cell apoptosis in diabetes. |