Characterization of Dopamine Neuron Axonal Mitochondria Specialization and its Relevance to Parkinson’s Disease - Project Summary Parkinson’s disease (PD) is the most common motor neurodegenerative disease and, as one of the fastest growing neurological disorders in prevalence, disability-adjusted life years, and deaths, an increasingly significant public health issue. Its core motor symptoms are caused by the dysfunction and death of dopamine (DA) neurons in the Substantia Nigra pars compacta (SNpc). These neurons are particularly vulnerable, and understanding the molecular underpinnings of this enhanced vulnerability may be critical for developing disease- modifying treatments. Due to the irreversible nature of neurodegeneration, neuroprotective therapies are likely to be most effective when targeting early, more reversible forms of neuronal dysfunction. In PD, one such early pathological feature is the degeneration of SNpc DA neuron axons, which are lost earlier than the cell bodies and whose degeneration more closely correlates with the decline of efficacy of dopamine replacement therapy (the primary symptomatic treatment for PD). Because axon loss may be targeted prior to cell death, identifying its mechanisms may be essential for developing neuroprotective therapies. Prior work indicates that axonal mitochondria are dynamically regulated and specialized to support axonal function and survival. In this proposal, I seek to identify mechanisms by which axonal mitochondria are specialized to promote the function and survival of SNpc DA neuron axons, and to identify how alterations in these processes may contribute to PD pathophysiology. In Aim 1, I will develop a novel molecular labeling and volumetric imaging platform for characterizing baseline features of mitochondria in the axons of SNpc DA neurons, such as their density across different striatal subregions, and quantify their spatial relationship to presynaptic structures. In Aim 2, I will implement an immunopurification strategy (Mitotag) for separately isolating axonal and somatodendritic mitochondria from SNpc DA neurons, and carry out proteomics and functional assays to identify the molecular and functional specialization of axonal mitochondria. In Aim 3, I will then carry out similar experiments in a viral PD mouse model to identify how alterations to axonal mitochondria may contribute to axonal degeneration. Using these findings as a guide, I will then carry out overexpression or knockdown experiments to evaluate whether rescuing axonal mitochondrial defects could alleviate axonal degeneration in PD. By delving into the fundamental biology of how mitochondria are specialized to sustain axonal survival and probing how their functions are perturbed in disease, this proposal will help shed light into basic principles of neuronal maintenance and function while potentially identifying early mechanisms of disease that can be targeted before irreversible cell death.
