Elucidating cellular mechanisms underlying neurodegeneration

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Giant axonal neuropathy (GAN) is an early-onset, autosomal recessive neurodegenerative disease that impacts the central and peripheral nervous systems. Pathologically, GAN is characterized by the disorganization and aggregation of intermediate filaments (IF). Formed from self-assembling subunits, the IF network spans the cell from the nucleus to the periphery. In GAN, many cell types show abnormalities in the organization of IF, but neurons clearly bear the brunt of the pathology. Axons swell with the accumulation of neuronal IF, and degenerate to cause the neurological symptoms of GAN. The gene mutated in GAN encodes gigaxonin, a protein that belongs to the BTB/Kelch family of E3 ligase-like adaptor proteins. These proteins typically play a role in ubiquitin-proteasome mediated protein degradation. Based on our own data that GAN degrades neuronal IFs, we hypothesize that neurofilament aggregation creates steric roadblocks in neurites that interfere with intracellular transport of organelles such as mitochondria and lysosomes, resulting in downstream pathology. Furthermore, our preliminary data suggest gigaxonin plays a direct role in autophagy via degradation of other substrates. We hypothesize that the disruption of this critical process exacerbates GAN neuropathology by dysregulation of protein and organellar quality control. This proposal comprehensively tests these models; thus the overall goal of our research is to understand the cellular pathogenesis of GAN with a view to inspiring novel treatment strategies.