Cytokines downregulate the sarcoendoplasmic reticulum pump Ca²⁺ ATPase 2b and deplete endoplasmic reticulum Ca²⁺, leading to induction of endoplasmic reticulum stress in pancreatic β-cells

Cytokines and free radicals are mediators of β-cell death in type 1 diabetes. Under in vitro conditions, interleukin-1β (IL-1β) + γ-interferon (IFN-γ) induce nitric oxide (NO) production and apoptosis in rodent and human pancreatic β-cells. We have previously shown, by microarray analysis of primary β-cells, that IL-1β + IFN-γ decrease expression of the mRNA encoding for the sarcoendoplasmic reticulum pump Ca²⁺ ATPase 2b (SERCA2b) while inducing expression of the endoplasmic reticulum stress-related and proapoptotic gene CHOP (C/EBP [CCAAT/enhancer binding protein] homologous protein). In the present study we show that cytokine-induced apoptosis and necrosis in primary rat β-cells and INS-1E cells largely depends on NO production. IL-1β + IFN-γ, via NO synthesis, markedly decreased SERCA2b protein expression and depleted ER Ca²⁺ stores. Of note, β-cells showed marked sensitivity to apoptosis induced by SERCA blockers, as compared with fibroblasts. Cytokine-induced ER Ca²⁺ depletion was paralleled by an NO-dependent induction of CHOP protein and activation of diverse components of the ER stress response, including activation of inositol-requiring ER-to-nucleus signal kinase 1α (IRE1α) and PRK (RNA-dependent protein kinase)-like ER kinase (PERK)/activating transcription factor 4 (ATF4), but not ATF6. In contrast, the ER stress-inducing agent thapsigargin triggered these four pathways in parallel. In conclusion, our results suggest that the IL-1β + IFN-γ-induced decrease in SERCA2b expression, with subsequent depletion of ER Ca²⁺ and activation of the ER stress pathway, is a potential contributors mechanism to β-cell death.