Therapeutic Peptide SS-31 Modulates Membrane Binding and Aggregation of Alpha-Synuclein and Restores Impaired Mitochondrial Function

Membrane binding and aggregation properties of alpha-synuclein are closely associated with Parkinson's disease and a class of related syndromes named as synucleinopathy. This study explored the potential of SS-31 (Elamipretide), a therapeutic tetrapeptide with alternating cationic and aromatic residues and known properties of mitochondrial inner membrane binding and oxidative stress reduction, in modulating alpha-synuclein interaction with the lipid membranes and mitigating impairment of mitochondrial function induced by alpha-synuclein oligomers. It was demonstrated by both fluorescence correlation spectroscopy and fluorescence anisotropy that SS-31 displaces both wild-type and N-terminus acetylated alpha-synuclein from negatively charged small unilamellar vesicles in a dose-dependent manner. Thioflavin-T assay and transmission electron microscopy (TEM) showed that SS-31 inhibits membrane-induced alpha-synuclein aggregation and alters the morphology of alpha-synuclein fibrils. Moreover, Seahorse Mito Stress Test indicated that SS-31 restores impaired mitochondrial function in alpha-synuclein oligomer-treated neuroblastoma cells. Finally, confocal imaging revealed that SS-31 hinders cellular uptake of alpha-synuclein oligomers, possibly by modifying cell membrane electrostatics. These findings underscore the multifaceted protective role of SS-31 against mitochondrial dysfunction caused by alpha-synuclein aggregation. Consequently, SS-31 emerges as a promising therapeutic candidate to attenuate neurodegeneration pertinent to alpha-synuclein misfolding and aggregation. There is a good potential for further refinement of such peptide against many diseases linked to mitochondrial dysfunction and oxidative stress.