Alpha-Galactosidase A: a novel target for reducing alpha-synuclein toxicity

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PROJECT SUMMARY The pathological accumulation of alpha-synuclein (α-syn) is believed to play a major role in Parkinson's disease (PD) pathogenesis. The autophagy-lysosome pathway (ALP) provides for the high-capacity clearance of α-syn and its dysfunction is well-documented in PD. Inhibiting the ALP has been shown to induce α-syn accumulation. Conversely, excess α-syn has been shown to inhibit the ALP. Because the lysosome is critical for α-syn clearance we believe its continued investigation will further delineate mechanisms of PD pathogenesis and foster development of PD therapeutics. Alpha-Galactosidase A (α-Gal A) is a soluble lysosomal enzyme, with mutations causing the rare lysosomal disorder Fabry disease. While it is unknown if α- syn accumulates in Fabry patients, our analysis of postmortem PD brains indicates a decrease in α-Gal A activity specific to specimens with increased α-syn pathology. Our preliminary data also indicate reduced α-Gal A activity in neuroblastoma cells following the conditional over-expression of α-syn. Together with our report of α-syn pathology and altered ALP markers in α-Gal A-deficient mouse brain, these findings suggest a strong link between α-Gal A deficiency and α-syn accumulation. However, whether α-Gal A deficiency exacerbates the neurotoxic potential of α-syn is unknown. Increasing α-Gal A activity via enzyme replacement therapy (ERT) is clinically approved therapy for Fabry disease. Because ERT has limited CNS bioavailability, there is a critical gap in understanding its potential for treating PD. To help bridge this gap we developed novel research tools to increase α-Gal A activity in neuronal systems, including its dose-responsive increase in neuronal cells via ERT, and transgenic mice that exhibit two-fold increases in α-Gal A brain activity. Our preliminary data in neuroblastoma cells shows that α-Gal A ERT enhances the clearance of over-expressed α-syn. However, whether increasing α-Gal A activity attenuates α-syn-associated neurotoxicity has not been tested. Taken together, we hypothesize that α-syn-associated neurotoxicity is exacerbated by α-Gal A deficiency and is attenuated by increasing α-Gal A activity. In Aim 1 we will determine if α-Gal A-deficiency in primary neuron cultures exacerbates neurotoxicity resulting from the exogenous addition of α-syn pre-formed fibrils (PFFs) in a manner concomitant with ALP disruption. We will also determine if α-Gal A–deficient mice exhibit exacerbated loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra following AAV2-mediated over- expression of human wild-type α-syn. In Aim 2 we will determine if α-syn PFF-mediated neurotoxicity in primary neuron cultures is attenuated by α-Gal A ERT or the transgenic over-expression of α-Gal A and if this protection is regulated by the ALP. We will also determine if α-Gal A over-expressing mice exhibit a reduction in TH-positive neuron loss resulting from AAV2-α-syn. If our hypothesis is correct, it would suggest that α-Gal A deficiency regulates α-syn pathogenesis, a mechanism worthy of future investigation, and would accelerate the development of therapeutics for PD that act by increasing CNS α-Gal A activity.