The most common complication of diabetes is neuropathy, which occurs in more than 50% of diabetic patients. Previous research shows that diabetic hyperglycemia is associated with apoptosis in neurons. This proposal aims to understand how glucose kills and IGF-I rescues neurons in both cell culture and animal models of diabetic neuropathy. Our work has resulted in a novel theory. In diabetic neurons, high glucose up-regulates reactive oxygen species (ROS) including nitric oxide (NO) and peroxinitrites. This results in depolarization of the inner mitochondrial (Mt) membrane, release of cytochrome c into the cytosol, and induction of caspase mediated programmed cell death (PCD). In contrast, insulinlike growth factor I (IGF-I), activates the IGF-I receptor and regulates uncoupling proteins 2 and 3 (UCP2 and UCP3) through a phosphatidylinositol 3kinase (PI3K)-mediated pathway. Regulation of UCP2 or UCP3 results in stabilization of the Mt membrane potential, and inhibits activation of initiator caspases, including caspase-9, and effector caspases, such as caspase-3. Interrupting hyperglycernic ROS induced PCD may offer new therapy for diabetic neuropathy. This model will be tested both in vitro and in vivo, using primary sensory neurons, PC12 cells, and a rat model of type II diabetes. We have 3 Aims: 1) Characterize glucose and IGFI control of ROS induced PCD, 2) characterize IGF-I up-regulation of UCPs in preventing ROS induced mitochondrial dysfunction and PCD, and 3) characterize the role of ROS, NO, and UCPs in diabetic neuropathy.
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