94-OR: Pathogenic Action of GAD65 Autoantibodies on Islet Function in Type 1 Diabetes

A hallmark of T1D is the appearance of autoantibodies directed against islet cell antigens including insulin and the 65kDa isoform of glutamate decarboxylase (GAD65). Based on unsuccessful attempts to trigger diabetes in mice using autoantibodies isolated from T1D patients, autoantibodies are widely viewed as having no role in the pathogenesis of T1D. However, beta cells in mice lack expression of GAD65. We revisited the issue of pathogenic effects of autoantibodies by testing the effects of GAD65 monoclonal autoantibodies (GAD65mAb) derived from blood of human T1D patients and subjects that were GAD65Ab-positive on rat and human islets. The paradigm-shifting results of our previous studies demonstrated the ability of one of the GAD65mAb idiotypes to penetrate and accumulate in beta cells and affect insulin secretory function. In the current study we have performed more detailed analyses of the effects of this GAD65mAb idiotype (b78) on rat, mouse and human islets. The results are summarized as 1. suppression of ISR by b78 in a time- and concentration-dependent fashion (half maximal effect < 0.05 mg/mL, much less than physiological levels of blood IgG, and the maximal reduction in ISR (about 40%) was reached 3 days after exposure; 2. suppression of ISR by b78 paralleled decreases in ATP production, apparently mediated by a step in the electron transport chain or oxidative phosphorylation; 3. the effect of b78 was not toxic to islets as its effects on ISR and ATP was reversible within 4 hrs of its removal; 4. effects on islets are dependent on the presence of GAD65 as no effect on mouse islets was observed; effects of GAD65mAb on human and rat islets were similar. Finally, 3 days following IP injection of b78 into conscious rats resulted in elevated glucose levels during IP glucose tolerance tests. Thus, contrary to historical perspectives, an islet autoantibody can directly impair secretory function in islets in vitro and in vivo through a mechanism that appeared to involve inhibition of mitochondrial energetics.