Patients with diabetes and neuropathy report a significantly decreased quality of life secondary to diabetic neuropathic pain (DNP). Patients with DNP experience lower extremity burning or "shock-like sensations" with increased sensitivity to both painful (hyperalgesia) and nonpainful stimuli (allodynia). Despite the high morbidity of DNP, mechanisms underlying the onset and progression of this complication are poorly understood. Our goal is to identify specific proteins that could serve as therapeutic targets in the treatment of DNP. As a first step, we quantitated DNP in a genetic model of type 2 diabetes, the db/db mouse. By 8 weeks of age, these mice experience thermal and mechanical allodynia. These signs of DNP correspond with nerve growth factor (NGF) up-regulation, tropomysin-related kinase (Trk) A receptor activation, subsequent p38 kinase activation, and increased substance P (SP) expression in dorsal root ganglion (DRG) neurons. This proposal will test the hypothesis that NGF signaling in DRG neurons underlies the development of diabetes- induced pain behavior in type 2 diabetes. We hypothesize that diabetes-enhanced NGF expression activates TrkA receptors on DRG neurons, leading to downstream activation of p38 kinase-SP pathway. Activation of this pathway leads to thermal hyperalgesia and mechanical allodynia in animal models of type 2 diabetes and to DNP in man.
Type 2 diabetes is increasing to epidemic proportions within the United States. A common complication of type 2 diabetes is DNP. Currently, DNP is difficult to manage and is responsible for significant patient morbidity and poor quality of life. In this proposal we seek to identify new therapeutic targets for DNP based upon a more thorough understanding of the pathogenesis of this disorder.
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