Our long-term goal is to characterize the changes in intracellular calcium ([Ca2+]i) homeostasis as a mediator of cytokine-induced b-cell dysfunction in diabetes. We have sufficient and compelling evidence providing the rationale for our testable hypothesis that 'TNF-a-induced dysregulation of intracellular calcium, [Ca2+]i, activates NF-kB transcription that in turn leads to b-cell apoptosis.' The focus of this proposal is on [Ca2+]i dysregulation as a mediator of cytokine-induced NF-kB activation that leads to b-cell death. Three specific aims are: Aim 1: Determine the activation of NF-kB caused by cytokine-induced [Ca2+]i dysregulation. In RIN cells, human b-cells, and human islets, we will study TNF-a-induced (a) dysregulation of [Ca2+]i by measuring [Ca2+]i and [Ca2+]i buffering capacity using ratiometric fluorescence imaging with Fura2, (b) degradation of the IkBa subunit by using a FunctionELISA, (c) translocation of NF-kB from cytoplasm to nucleus by immunofluorescence, and (d) NF-kB-dependent transcription by measuring the DNA binding activity of NF-kB using ELISA. Aim 2: Characterization of candidate gene screen of TNF-a regulated genes in b-cells. The levels of mRNA, isolated from control and TNF-a-treated human b-cells and RIN cells, encoding a panel of six TNF-a-induced differentially expressed genes thought to participate in b-cell apoptosis will be measured by semiquantitative multiplex PCR. We will show how these six TNF-a-induced differentially expressed genes contribute to b-cell function in human b-cells. We will measure the levels of phosphorylated JNK and phosphorylated-p38 in control and TNF-a-treated RIN cells and human b-cells in presence of added insulin growth factor-1 (IGF-1) to test our hypothesis that 'TNF-a-induced activation of p38 and c-JUN N- terminal MAP kinases in b-cells that leads to b-cells death could be attenuated by IGF1'. Aim 3: Determine the execution of b-cell death by mitochondria-induced caspase activation. We hypothesize that 'TNF-a- induced co-localization of Bax with Bcl-2 in mitochondria in b-cells will result in release of mitochondrial cytochrome c, which, when liberated to the cytosol, will activate caspase-3 and execute b-cell death'. In RIN cells and human b-cells, we will study the TNF-a-induced: (a) changes in subcellular localizations of Bcl-2 and Bax and the spatial interaction between these two proteins by using fluorescent-labeled antibodies in conjunction with fluorescence resonance energy transfer (FRET) protocols; (b) release of cytochrome c by using immunofluorescence microscopy; (c) activation of caspase 3 by using immunofluorescence microscopy, and (d) changes in cell replication, apoptotic rates, and insulin secretion. The results of the proposed studies under the three AIMS should provide novel mechanistic insights into the cellular signals and interplay of downstream effectors in b-cell death or survival due to [Ca2+]i dysregulation in type 1 and type 2 diabetes. Our experimental design will identify critical target molecules and cellular steps for designing efficacious therapeutic strategies and interventions for juvenile and late onset diabetes. PUBLIC HEALTH RELEVANCE: Diabetes, a complex and incurable disease is managed by insulin supplementation. Our innovative studies will provide insights into molecular and physiological mechanisms that cause the death of insulin secreting pancreatic cells, and novel strategies to prevent beta cell death that culminates in diabetes type 1 and 2 in millions of Americans to avert their dependence on daily injections of insulin.
