Effect of Cytokines on Beta Cell Function

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Cytokines such as interleukin-1beta (IL-1), tumor necrosis factor-alpha (TNF), and interferon-gamma (IFN) have profound effects on islet cells: 1) they inhibit insulin synthesis and secretion by the beta cell, 2) they destroy beta-cells, and 3) they are produced by immune and inflammatory cells infiltrating islets in the insulitis of type I diabetes mellitus (IDDM), and in the course of immune rejection of transplanted islets. The rationale for these studies is that the identification of the molecular mechanisms mediating cytokine-induced beta-cell death will facilitate the development of novel preventive and therapeutic strategies. Thus, the long-term goal of this project is to understand the mechanisms of cytokine-induced beta-cell death, involved in the pathogenesis of type I diabetes. In particular, IL-1 has been shown to inhibitor insulin biosynthesis and secretion, oxidative metabolism, and results in beta-cell death. However, a key question is whether IL-1 can induce apoptosis and/or necrosis of beta-cells. Our preliminary data suggest that IL-1 induces apoptosis in insulin-secreting beta-cell lines. In addition, we have shown that IL-1 stimulates the activity of 2 stress-activated kinases: p38 and JNK. We wish to determine whether p38 and JNK is necessary for cytokine- induced beta-cell death, and can expression of dominant-negative mutants prevent IL-1 induced beta-cell death. We have also discovered the presence of a novel secretory cytokine uniquely present in the islets of Langerhans. This novel cytokine defines a new class of cytokine. A major goal is to elucidate its role in the pathogenesis of diabetes. The following 3 aims will address the mechanisms of cytokine-induced beta-cell death. Aim 1: To determine whether cytokines-induced beta-cell death is due to necrosis or apoptosis. A combinations of morphological, biochemical and cell biological techniques will be used to address this issue. Aim 2: To determine whether activation of p38 JNK is required for cytokine-induced beta-cell death. Stable beta-cell lines expressing p38, JNK, and kinase-inactive mutants will be generated and studied of their response to cytokine. Aim 3: To elucidate the role of the novel islet-specific cytokine in respect to beta-cell function.