Pathogenic Mechanisms of Cytosolic and Membrane-Enriched alpha-Synudein Converge on Fatty Acid Homeostasis

-alpha-Synuclein (alpha S) plays a key role in Parkinson's disease. Although Parkinson's disease is typically "sporadic," inherited alpha S missense mutations provide crucial insights into molecular mechanisms. Here, we examine two clinical mutants, E46K and G51D, which are both in the conserved N-terminus that mediates transient alpha S-membrane interactions. However, E46K increases and G51D decreases alpha S-membrane interactions. Previously, we amplified E46K via the 11-residue repeat motifs, creating "3K" (E35K+E46K+E61K). Here, we engineered these motifs to amplify G51D (V40D+G51D+V66D = "3D") and systematically compared E46K/3K versus G51D/3D. We found that 651D increased cytosolic alpha S in neural cells and 3D aggravates this. G51D, and 3D even more, reduced alpha S multimer-to-monomer (0660:0614) ratio. Both amplified variants caused cellular stress in rat primary neurons and reduced growth in human neuroblastoma cells. Importantly, both 3K- and 3D-induced stress was ameliorated by pharmacologically inhibiting stearoyl-CoA desaturase or by conditioning the cells in palmitic (16:0) or myristic (14:0) acid. SCD inhibition lowered lipid-droplet accumulation in both 3D- and 3K-expressing cells and benefitted G51D by normalizing multimer:monomer ratio, as reported previously for E46K. Our findings suggest that, despite divergent cytosol/membrane partitioning, both G51D and E46K neurotoxicity can be prevented by decreasing fatty-acid unsaturation as a common therapeutic approach.