REGULATION OF GLUTAMIC-ACID DECARBOXYLASE DIABETES AUTOANTIGEN EXPRESSION IN HIGHLY PURIFIED ISOLATED ISLETS FROM MACACA-NEMESTRINA

Macaca nemestrina, which may have larger and more numerous pancreatic islets than other species, was used for large scale islet isolation by ductal collagenase perfusion and Ficoll gradient centrifugation. The average yield was 51,000 islet equivalents per pancreas, or 8,750 isle ts equivalents per g. The average purity was 91%, often exceeding 95%. These are the highest reported size, purity, and yield per g of any n onautomated primate islet series. Perifusion with glucose, arginine, a nd isobutylmethylxanthine showed appropriate biphasic insulin secretio n. Unlike that in the rat, human islet glutamic acid decarboxylase (GA D) isoform expression is restricted. However, glycemic regulation of G AD expression has been shown only in rats. We, therefore, tested hypot heses that M. nemestrina islets also have restricted GAD expression, t hat GAD expression in primates is stimulated by glucose, and that this stimulation remains restricted to the 64,000 mol wt (GAD65) isoform. Immunoprecipitation of labeled islet extracts showed that GAD65 expres sion increased 16.7 +/- 0.6-fold during high glucose in vitro culture. After controlling for observed increases in protein synthesis, specif ic glucose stimulation was still 4.2 +/- 0.2-fold. Specific antisera r evealed no GAD67 expression under basal conditions, and isoform restri ction was maintained during stimulation. Increased GAD65 synthesis thu s accounts for glucose stimulation of 64K expression. These time- and concentration-dependent effects of glucose suggest that hyperglycemia increases autoantigenicity and may accelerate beta-cell destruction in primates, supporting a role for beta-cell rest in insulin-dependent d iabetes mellitus prevention.