Mitochondria play essential roles in normal neuronal physiology, from energy production to Ca2+ buffering to synaptic differentiation and plasticity. The intracellular distribution of mitochondria needs to be precisely matched to the demand for these organelles, a task particularly difficult for neurons due to their highly polarized morpholog and their dynamic patterns of neuronal activity and synaptic plasticity in vivo. Because abnormal mitochondrial distribution and function has been consistently observed at early stages of neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD) as well as neuropsychiatric disorders, understanding the genetic control of mitochondrial distribution in neurons has assumed a high priority in neuroscience research. Unfortunately, progress in this area has been impeded by the lack of identified regulatory molecules governing this process. In the proposed project, we aim to define the role of PAR-1 (partitioning defective 1), an evolutionarily conserved Ser/Thr kinase, in the regulation of neuronal mitochondrial distribution. PAR-1 was initially identified as a gene required for the asymmetric cell division in early C. elegans embryos. Work from our lab and that of others has established a critical role for PAR-1 in regulating synaptic structure and function in Drosophila and mammals. Our most recent work shows that PAR-1 plays an important role in directing neuronal mitochondrial distribution. Additional studies indicate that PAR-1 genetically and physically interacts with mitochondrial rho GTPase (Miro), a conserved key component of the mitochondrial transport machinery, and that PAR-1 regulates the GTPase activity of Miro as well as the interaction between Miro and the mitochondrial fusion regulator mitofusin (Mfn). These findings led logically to the central hypothesis of the current application: that the PAR-1/Miro axis functions as a novel regulatory node through which diverse signals can impact mitochondrial distribution, and that deregulated PAR-1/Miro signaling contributes to the mitochondrial maldistribution and the ensuing synaptic dysfunction and eventual neurodegeneration as occurring in diseases. This hypothesis will be tested by determining the mechanism of how PAR-1/Miro signaling regulates mitochondrial distribution in Drosophila (Aim 1); by testing the effect of restoring PAR-1/Miro-directed mitochondrial distribution on the disease phenotypes of Drosophila models of AD (the Abeta-42 model) and PD (the LRRK2-G2019S model) (Aim 2); and by testing the effect of restoring PAR-1/Miro-directed mitochondrial distribution on the disease phenotypes of patient-specific, Abeta-42 and LRRK2-G2019S-related human neuronal models of AD and PD (Aim 3). Successful completion of these aims will be facilitated by innovative methods and strategies for visualizing and manipulating mitochondrial distribution in vivo in Drosophila and in human neuronal models of AD and PD. We expect that the information to be generated from this project will be fundamental to basic neuroscience research and of high clinical relevance.