Development and Manipulation of a Drosophila Model for Toxic Effects of Mutated M1 Spastin in Hereditary Spastic Paraplegia Treatment

Hereditary Spastic Paraplegia (HSP) is an adult-onset disease most commonly caused by mutation of SPAST, which encodes the microtubule-severing protein, Spastin. Haploinsufficiency of spastin is a widely accepted pathological hypothesis for HSP, however, this definition of HSP has yet to find a well-functioning treatment. Based on our preliminary and published data, we predict that there is an additional gain-of-function aspect to the disease. Human SPAST has two isoforms, M1 and M87, which are produced via two start-codons. Evidence suggests that mutation of the longer M1 isoform is associated with a more toxic phenotype than mutation of the shorter M87 isoform in vivo. We believe that the M1 mutant effects can provide a mechanistic basis for the disease. Using the UAS-Gal4 system we introduced human M1 or M87 bearing one of the common mutations found in human patients, C448Y, into the nervous system of Drosophila melanogaster. We began with confirming that flies containing the mutations show a significant decrease in motor function (measured by contractions, climbing and flight motor ability). The flies expressing M1-C448Y have a significant decrease in motor ability, confirming that our flies exhibit the M1-specific toxicity seen in HSP patients. Microtubule dynamics are altered in patients with Spastin mutation; therefore, we decided to focus on stabilizing microtubules by using the drug Vinblastine. We were able to recover certain aspects motor function in M1 mutant animals after vinblastine treatment, suggesting that the microtubules must be destabilized in the M1 mutation. In order to understand the morphology of this disease at the muscular level, we used the neural-muscular junction (NMJ) of larva, a well-established model. We saw that there was an increase in synaptic bouton number in M1-C448Y-expressing flies. These data suggest that targeting microtubule stabilization is an improved method of treatment from the treatment options currently available to patients with HSP.M.S., Neuroscience -- Drexel University, 201