Quality control of mitochondrial components is critical for long-term function of the nervous system. However most of our understanding of mitochondrial quality control comes from studies in cultured cells. One critical component missing in culture systems is the presence of supportive glial cells. Recently documented observations of ?transmitophagy? and ?exophers? have raised the idea that glial cells may assist neurons in the turnover of neuronal mitochondria, a process termed here as transcellular mitochondrial degradation (TMD). However the extent to which TMD occurs in different contexts and its mechanism remains unknown. This project builds from striking phenotypes observed in the Drosophila nervous system following knockdown of vacuolar sorting protein VPS13D, which has recently been linked to recessive ataxia and spastic paraplegia with mitochondrial defects. Preliminary data indicate that VPS13D mutants accumulate novel intermediates in mitochondrial destruction pathways that reveal strong defects in cell autonomous mitophagy, and in addition, non-cell autonomous phenotypes that suggest the transfer of destruction intermediates to glial cells. The proposal aims are designed to understand the relationship of these defects to previously known pathways of mitophagy, and will build new assays in the Drosophila nervous system to ?catch? potential transfer of mitochondrial destruction intermediates from neurons to glial cells.
Aim 1 will determine the role of the mitophagy regulator Parkin in the VPS13D mutant defects and will carry out ultrastructural characterization of the mitochondrial intermediates.
Aim 2 will take advantage of bipartite gene expression strategies in Drosophila that allow for coincident labeling and genetic manipulation of organelles in both neurons and glial cells to definitely test and track the existence of transfer. These assays will build an experimental framework for studying glial-neuron communication mechanisms and will enable future work to understand the mechanism and prevalence of TMD in diverse contexts.
Defects in the clearance of damaged mitochondrial components is a strong theme across many neurodegenerative diseases. This project develops new approaches to study the adaptive contributions made by glial cells to impairments in neuronal mitochondria, and tests the possibility that neighboring glia directly assist in clearing damaged mitochondrial components from neurons. The project has potential to identify new markers of degeneration pathology in glial cells and will expand our understanding of glial-neural interactions in the nervous system.
