The p66^Shc redox adaptor protein is induced by saturated fatty acids and mediates lipotoxicity-induced apoptosis in pancreatic beta cells

Aims/hypothesis: The role of the redox adaptor protein p66^Shc as a potential mediator of saturated fatty acid (FA)-induced beta cell death was investigated. Methods: The effects of the FA palmitate on p66^Shc expression were evaluated in human and murine islets and in rat insulin-secreting INS-1E cells. p66^Shc expression was also measured in islets from mice fed a high-fat diet (HFD) and from human donors with different BMIs. Cell apoptosis was quantified by two independent assays. The role of p66^Shc was investigated using pancreatic islets from p66^Shc−/− mice and in INS-1E cells with knockdown of p66^Shc or overexpression of wild-type and phosphorylation-defective p66^Shc. Production of reactive oxygen species (ROS) was evaluated by the dihydroethidium oxidation method. Results: Palmitate induced a selective increase in p66^Shc protein expression and phosphorylation on Ser³⁶ and augmented apoptosis in human and mouse islets and in INS-1E cells. Inhibiting the tumour suppressor protein p53 prevented both the palmitate-induced increase in p66^Shc expression and beta cell apoptosis. Palmitate-induced apoptosis was abrogated in islets from p66^Shc−/− mice and following p66^Shc knockdown in INS-1E cells; by contrast, overexpression of p66^Shc, but not that of the phosphorylation-defective p66^Shc mutant, enhanced palmitate-induced apoptosis. The pro-apoptotic effects of p66^Shc were dependent upon its c-Jun N-terminal kinase-mediated phosphorylation on Ser³⁶ and associated with generation of ROS. p66^Shc protein expression and function were also elevated in islets from HFD-fed mice and from obese/overweight cadaveric human donors. Conclusions/interpretation: p53-dependent augmentation of p66^Shc expression and function represents a key signalling response contributing to beta cell apoptosis under conditions of lipotoxicity.