Abstract
β-cell apoptosis is a significant contributor to β-cell dysfunction in diabetes and ER stress is among the factors that contributes to β-cell death. We previously identified that the Ca²⁺-independent phospholipase A&sub2;β (iPLA&sub2;β), which in islets is localized in β-cells, participates in ER stress-induced β-cell apoptosis. Here, direct assessment of iPLA&sub2;β role was made using β-cell-specific iPLA&sub2;β overexpressing (RIP-iPLA&sub2;β-Tg) and globally iPLA&sub2;β-deficient (iPLA&sub2;β-KO) mice. Islets from Tg, but not KO, express higher islet iPLA&sub2;β and neutral sphingomyelinase, decrease in sphingomyelins, and increase in ceramides, relative to WT group. ER stress induces iPLA&sub2;β, ER stress factors, loss of mitochondrial membrane potential (∆Ψ), caspase-3 activation, and β-cell apoptosis in the WT and these are all amplified in the Tg group. Surprisingly, β-cells apoptosis while reduced in the KO is higher than in the WT group. This, however, was not accompanied by greater caspase-3 activation but with larger loss of ∆Ψ, suggesting that iPLA&sub2;β deficiency impacts mitochondrial membrane integrity and causes apoptosis by a caspase-independent manner. Further, autophagy, as reflected by LC3-II accumulation, is increased in Tg and decreased in KO, relative to WT. Our findings suggest that (1) iPLA&sub2;β impacts upstream (UPR) and downstream (ceramide generation and mitochondrial) pathways in β-cells and (2) both over- or under-expression of iPLA&sub2;β is deleterious to the β-cells. Further, we present for the first time evidence for potential regulation of autophagy by iPLA&sub2;β in islet β-cells. These findings support the hypothesis that iPLA&sub2;β induction under stress, as in diabetes, is a key component to amplifying β-cell death processes.