Two major challenges facing investigators in diabetes are to elucidate the cellular events responsible for destruction of the pancreatic beta-cell associated with insulin-dependent diabetes mellitus (IDDM) and to identify specific signal transduction mechanisms which mediate abnormal insulin secretory responses associated with non insulin-dependent diabetes mellitus (NIDDM). Interleukin-1 (IL-1) has been proposed to initiate beta-cell destruction. Our studies have demonstrated that the biochemical events which mediate the inhibitory and possibly cytotoxic effects of IL-1 on the B-cell may be separated into an early transcriptional and a later translational phase. We will characterize these early events with emphasis on gene expression and the synthesis of new proteins which may serve either as neoantigens or impair necessary metabolic activities of the beta-cell. New evidence also suggests that IL-1 promotes the generation of nitric oxide radicals and this may reflect the induction of a new enzymatic pathway which integrates these early transcriptional and translational events with the cytotoxic effects of IL-1 on the beta-cell. An abnormal insulin secretory response of beta-cells to the fuel class of insulin secretagogues, in particular, D-glucose, is a metabolic defect associated with NIDDM. Beta-cells purified by fluorescence activated cell sorting (FACS) obtained from both rodent and human islets have provided important new insights and indicate that a cAMP-dependent pathway represents a signal transduction mechanism specifically activated by fuel secretagogues but not by muscarinic agonists. The important role of changes in intracellular Ca2+, the activation and function of cAMP- dependent protein kinase A, protein kinase C, and the Ca2+ and calmodulin- dependent protein kinase will be assessed with regard to their unique roles in mediating insulin secretion by these different classes of stimuli. The role of G-proteins such as Gi in mediating decreases in cAMP and ion fluxes caused by physiologic inhibitors of insulin secretion, e.g. somatostatin and epinephrine, will also be examined. Our studies also indicate that an abnormality in glucose-induced insulin secretion may result from the absence of a cytoskeletal response normally mediated by cAMP which is required for the modulation of microfilament assembly that may regulate terminal steps in exocytosis. Studies with both islets and FACS purified beta-cells indicate that the microfilamentous components of the cytoskeleton (actin polymerization and depolymerization) are dramatically affected by alterations of cAMP levels, intracellular Ca2+, and by agents that modify myosin light chain kinase activity. These results suggest that glucose-induced insulin secretion may be uniquely dependent on modulation of the beta-cell cytoskeleton and that defects in this exocytotic pathway may be specific to fuel secretagogues and possibly related to abnormal insulin secretory responses associated with NIDDM.
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