UC San Diego

Neurodegenerative Disease is a current and growing health crisis. Recent research into the neurodegenerative disease field has identified mitochondria and microtubules as two systems that are particularly crucial for sustained neuronal health and function. Due to their extremely polarized cellular structure, their extreme energy demands, and their post-mitotic nature, neurons are exquisitely sensitive to breakdowns in either their energy production or molecular transport. However, exactly how deficits in these systems cause or worsen neurodegenerative disease is still an open area of research. This work aims to glean important information regarding the role of mitochondria and microtubules in neurodegenerative disease through researching the classic mouse model of cerebellar and retinal degeneration, the purkinje cell degeneration mouse.

Chapter II investigates if the pcd phenotypes can be rescued through disruption of mitochondrial dynamics. Mitochondrial dynamics is the opposing forces of fission and fusion that regulate mitochondrial structure and function. We elucidated a genetic interaction between Nna1 and Drp1 in flies, as knockdown of Drp1 lead to suppression of the larval lethality and mitochondrial fragmentation of nnaDPL90 flies. However, a similar dosage reduction of Drp1 in mice failed to rescue pcd pathology. Additionally, disruption of either Pink1 or Parkin, regulators of mitophagy also failed to suppress any pcd phenotypes.

In Chapter III, we endeavored to generate mammalian cell culture models of pcd in order to further investigate the role of Nna1. We generated Nna1 knockout RPE1 cells using CRISPR/Cas9 and also developed a cerebellar granule neuron based model. Collectively these models reproduced mitochondrial dysfunction, and altered mitochondrial trafficking in primary neurons. Additionally, these cells as well as degenerating Purkinje cells in pcd mice, showed altered tubulin post translational landscapes.

Chapter IV investigates if Nna1, like many other proteins, is degraded when cells are exposed to mitochondrial toxins. We find that Nna1 is degraded specifically in the response of mitochondrial stress and this degradation is dependent on the proteasome. We identify the E3 Ubiquitin ligase Parkin as the likely regulator of Nna1 degradation.