Cardiolipin Promotes Pore-Forming Activity of Alpha-Synuclein Oligomers in Mitochondrial Membranes

Aggregation of the amyloid-forming alpha-synuclein (alpha S) protein is closely associated with the etiology of Parkinson's disease (PD), the most common motor neurodegenerative disorder. Many studies have shown that soluble aggregation intermediates of alpha S, termed oligomers, permeabilize a variety of phospholipid membranes; thus, membrane disruption may represent a key pathogenic mechanism of alpha S toxicity. Given the centrality of mitochondrial dysfunction in PD, we therefore probed the formation of ion-permeable pores by alpha S oligomers in planar lipid bilayers reflecting the complex phospholipid composition of mitochondrial membranes. Using single-channel electrophysiology, we recorded distinct multilevel conductances (100-400 pS) with stepwise current transitions, typical of protein-bound nanopores, in mitochondrial-like membranes. Crucially, we observed that the presence of cardiolipin (CL), the signature phospholipid of mitochondria' membranes, enhanced alpha S-lipid interaction and the membrane pore-forming activity of alpha S oligomers. Further, preincubation of isolated mitochondria with a CL-specific dye protected against alpha S oligomer-induced mitochondrial swelling and release of cytochrome c. Hence, we favor a scenario in which alpha S oligomers directly porate a local lipid environment rich in CL, for instance outer mitochondrial contact sites or the inner mitochondrial membrane, to induce mitochondrial dysfunction. Pharmacological modulation of alpha S pore complex formation might thus preserve mitochondrial membrane integrity and alleviate mitochondrial dysfunction in PD.