Natural resistance of human beta cells toward nitric oxide is mediated by heat shock protein 70

Human beta cells exhibit increased resistance against nitric oxide (NO) rad icals as compared with rodent islet cells. Here we tested whether endogenou s heat shock protein 70 (hsp70) accounts for the resistance of human cells. Stable transfection of the human beta cell line CM with an antisense hsp70 mRNA-expressing plasmid (ashsp70) caused selective suppression (>95%) of s pontaneously expressed hsp70 but not of hsc70 or GRP75 protein. ashsp70 tra nsfection abolished the resistance of CIM cells to the NO donors (Z)-1-(2-( 2-aminoethyl)-N-(2-ammonioethyl)amino)diazen-1-ium-1,2-diolate and sodium n itroprusside and increased the proportions of necrotic cells 3-5-fold (p < 0.05) and of apoptotic cells about S-fold (p < 0.01), Re-induction of hsp70 expression by heat shock re-established resistance to NO toxicity. hsp70 d id not exert its protective effect at the level of membrane lipid integrity because radical induced lipid peroxidation appeared independent of hsp70 e xpression. However, after NO exposure only hsp70-deficient cells showed sig nificantly decreased mitochondrial activity, by 40-80% (p < 0.01). These re sults suggest a key role of hsp70 in the natural resistance of human beta c ells against NO induced injury, by preserving mitochondrial function. These findings provide important implications for the development of beta cell p rotective strategies in type 1 diabetes and islet transplantation.