Genetic Dissection of Age-dependent Neuroprotection Mechanisms in Drosophila

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DESCRIPTION (provided by applicant): Our long-term aim is to elucidate molecular mechanisms of neural signaling in Drosophila. Here we focus on analysis of mutants with defects in maintenance of neuronal viability. We have discovered several mutations among our collection, including wstd and comt, that exhibit shortened lifespan and age-dependent, progressive neurodegeneration providing us with novel starting points to dissect neuroprotective mechanisms. Our goals are to determine the in vivo roles of the affected proteins using genetic, molecular, biochemical, and histological techniques to analyze how defects in these proteins result in the observed phenotypes. wstd encodes the glycolytic enzyme, triose phosphate isomerase (Tpi) responsible for the interconversion of DHAP (dihydroxyacetone phosphate) and GAP (glyceraldehyde 3-phosphate), only the latter of which is able to continue through glycolysis. Mutations of Tpi in humans result in Triosephosphate isomerase deficiency, characterized by early death and neurodegeneration but the underlying mechanism has remained unclear. We hypothesize that the enzymatic block in Tpi-deficient flies and humans leads to excess accumulation of methylglyoxal (MG), which reacts with target proteins to generate advanced glycation end products (AGEs) causing loss of protein activity, cross-linking, aggregation, and ultimately neuronal death. We propose genetic and biochemical experiments to test and refine this hypothesis. comt, which encodes NSF-1 (N-ethyl- maleimide sensitive fusion protein), exhibits a deficit in lysosomes and accumulation of ubiquitinated protein complexes in parallel with neurodegeneration. We hypothesize that comt is deficient in autophagy. Experiments are proposed to test this hypothesis and to dissect the step(s) in the process that are impaired. Additional mechanisms of neuroprotection will be investigated by phenotypic and molecular analysis of other mutants in our collection that exhibit neurodegeneration. Neuroprotective mechanisms are essential for proper neural communication and their disruption leads to some of the most devastating human neurological disorders. Detailed understanding of these mechanisms is thus of fundamental biological as well as medical importance. Drosophila has already proven to be a potent experimental system for elucidating these mechanisms. Moreover, both wstd and comt have direct links with human neurodegenerative disorders. Consequently, our proposed analyses should have broad biological and medical significance by contributing important new information that will advance our understanding of the underlying molecules and mechanisms that maintain neuronal viability and integrity.