Dopaminergic (DA) neurons are sensitive to oxidative insults and degenerate in age-related neurodegenerative diseases. A morphologic form of regulated cell death characterized by prominent autophagic vacuoles (AVs) has been identified in neurons. Autophagy is normally a highly regulated process sequestering cytoplasmic components for lysosomal degradation. However, dysregulated or excessive autophagy can be harmful to cells, producing a condition that can be conceptualized as """"""""autophagic stress."""""""" Although AVs are observed in degenerating DA neurons in Parkinson disease and its in vitro and in vivo models, the role of autophagy in DA neuronal injury remains to be elucidated. Our studies indicate that oxidative neurotoxins elicit increased mitochondrial autophagy in DA neurons. Moreover, the regulation of this injury-induced autophagy is different from that of nutrient-deprivation systems. This proposal investigates the hypotheses that: autophagy contributes to neurite retraction and cell death in injured DA neurons, and that reactive oxygen species and MARK signals regulate injury-induced autophagy. We will use the complex I inhibitor MPP+ to produce mitochondria-targeted injury, and the redox cycling 6- hydroxydopamine to model generalized oxidative stress, comparing acute and chronic treatments. A combination of molecular, biochemical, live cell imaging and transgenic approaches will be applied to DA cell lines, primary midbrain cultures and mice to determine the role of autophagy in DA neurite retraction and cell death, and to study MAPK and oxidative phospholipid signals involved in its regulation. Completion of these studies will yield important insights into mechanisms by which autophagic responses regulate DA neurite degeneration and cell death during oxidative neuronal injuries. Relevance: Mitchondrial impairment and autophagic stress are prominent features of Parkinson/Lewy body disease. In contrast to physiologic conditions, inducing autophagy in the presence of dysregulating pathologic forces may promote cell death. A better understanding of mechanisms that contribute to autophagic stress will help focus future research efforts to restore balance to the system. Thus, studying the role and regulation of autophagic responses in oxidatively-injured neurons may enhance development of novel therapies applicable to age-related neurodegenerative diseases and other brain disorders involving oxidative stress.
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