The activity of alpha-ketoglutarate dehydrogenase (KGDHC), a key enzyme of the tricarboxylic acid cycle is reduced in brains of individuals with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Wernicke Korsakoff syndrome. The reduction in KGDHC activity is not just secondary to neurodegeneration, since the decline occurs not only in brain areas selective vulnerable to degeneration but also in areas without overt neuropathology. The surprising frequency of the decline in KGDHC activity suggests that this is an important response to neuronal injury and may be critical step in the cascade of events that leads to eventual death. A reasonable explanation for the decline in activity is that KGDHC is particularly sensitive to a variety of cellular insults and that in select regions the reduction in activity diminishes the cell's ability to respond to further insults resulting in neurodegeneration. For example, KGDHC in pulmonary cells is particularly sensitive to free radicals and the resulting deficit in KGDHC interferes with subsequent cellular responses. Understanding both the mechanism by which KGDHC activity is decreased in neuronal injury and the consequences of impaired KGDHC activity on cellular signal transduction systems may be helpful for the development of therapeutic strategies to reverse neurodegeneration resulting from a number of noxious events including oxidative stress. The experiments will use a neuron-like cell line (PC12 cells) and primary cultures of neurons, microglia and astrocytes to test a hypothesis with two interactive components (1) KGDHC activity is especially sensitive to factors known to lead to cell death (e.g., excess reactive oxygen species or elevated calcium) or to abnormal proteins associated with neurodegeneration (e.g., mutant presenilins or amyloid-beta-peptide). (2) As a corollary, cellular functions are sensitive to even mild reductions in KGDHC activities. The role of KGDHC in cellular processes will be assess as a function of cellular membrane potentials, calcium homeostasis and level of reactive oxygen species. The underlying basis for the enhanced sensitivity of KGDHC will be determined by treating the cells and then examining the molecular changes in KGDHC. Together, these studies will provide a mechanistic test of whether the sensitivity of KGDHC to external factors is a critical step in a cascade of events that leads to neuronal death in several neurodegenerative disorders including Alzheimer's disease.
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