Nitric Oxide Mediates IL-1β Stimulation of Heat Shock Protein but Not IL-1β Inhibition of Glutamic Acid Decarboxylase

Abstract

Interleukin-1β (IL-1β) has been implicated to play an important role in the autoimmune β cell lesion of insulin-dependent diabetes mellitus (IDDM) because of its inhibition of insulin secretion, direct islet cytotoxicity and alteration of islet cell antigen expression. We have previously demonstrated that IL-1β inhibits glutamic acid decarboxylase-65 (GAD-65) and increases heat shock protein-70 (HSP-70) expression in islet cells. IL-1β stimulates the inducible form of nitric oxide (NO) synthase and the resultant increased NO mediates many of IL-1β's effects. In this study we investigated the role of the NO pathway in mediating the effects of IL-1β on GAD-65 and HSP-70 expression and on insulin secretion. Islets isolated from Sprague-Dawley rats were cultured with IL-1β and aminoguanidine (AG), an inhibitor of inducible NO synthase, individually and in combination for 24 h. Accumulated nitrite production, insulin release and islet expression of GAD-65 and HSP-70 were measured. We found that (1) IL-1β at 10U/ml increased nitrite production, inhibited insulin release, increased HSP-70 expression and decreased GAD-65 expression. (2) AG alone at 1 mM/ml had no effect on nitrite production, insulin release, GAD-65 and HSP-70 expression. (3) In combination, AG completely blocked IL-1β increased nitrite production, reversed IL-1β inhibited insulin release by approximately 50%, completely reversed IL-1β increased HSP-70 expression, but did not reverse IL-1β inhibited GAD-65 expression. Our findings indicate that the effect of IL-1β on HSP-70 expression is mediated by NO production, whereas a NO-independent pathway is involved in the effect of IL-1β on GAD-65 expression and insulin secretion.