The loss of pancreatic (-cells in type 1A diabetes (TID) occurs principally through cell-mediated autoimmune attack though the precise mechanisms that result in the demise of an individual (-cells is unclear. Soluble cytokines clearly play an important role both in signaling between effector cells and can initiate defensive and or apoptotic responses in the target. Microarray gene expression profiling of human and mouse islets exposed to a series of pro-inflammatory cytokines have revealed a remarkable induction of Indoleamine 2, 3 dioxygenase (IDO) in islets in response to IFN(. IDO catalyzes the initial, rate-limiting step of Tryptophan (Trp) catabolism along the Kynurenine (Kyn) pathway. IDO protein was up-regulated and increased enzymatic activity of IDO was noted in the IFN(-treated islet samples. 1 (-methyl tryptophan (1 MT) and Interleukin 4 (IL 4) were able to inhibit the IDO specific activity in vitro. Immunohistochemically IDO was localized in more than one cell type in the islets. In addition, co exposure of IL1(, IFN( and TNF( to human islets resulted in induction of both IDO and inducible form of Nitrous oxide synthase (iNOS). We hypothesize that short term IDO activation may protect islets from cytotoxic damage through depletion of superoxides and maintenance of redox potential, and that the release of Trp metabolites such as 3-OH-Kyn, 3-hydroxyanthranilate, quinolinate and picolinic acid could provide bystander inhibition of immune cell function. In the longer term the various metabolites may feed back on the islets themselves and could ultimately lead to (-cell attrition. The current proposal focuses on the signal biology and function of IDO and the metabolites generated during the catabolism of Trp in the context of our hypotheses. Specifically we aim to 1) To investigate the JAK STAT signal transduction pathway involved in IDO induction in mouse and human islets. 2) Document the relationship between IDO and iNOS in islets during co-induction by cytokine cocktail (IL1( + IFN( + TNF() and its effect on islet cell survival. 3) Determine the effects of short and long-term activation of IDO by exploring the antioxidant activities of IDO and Trp metabolites on islet cell function and survival. The results will provide insight into the molecular mechanism of IDO signaling, modulation of IDO gene, and protein. More critically, its interaction with iNOS and other agents that can alter the cellular redox potential will better help us understand its immunoregulatory and antioxidant role in the context of an immune attack in TID. These studies should provide new insight into the pathogenesis of TID and develop new strategies for therapeutic treatment and control of the disease.
