Alpha-synuclein aggregation in the presence of mitochondrial lipid membranes : implications for Parkinson’s disease

Abstract

Parkinson’s disease (PD) is characterised by the hallmark deposition of Lewy Bodies in the brain, which are made up of pathogenic molecular forms of the α-Synuclein (α-Syn) protein and are strongly implicated in PD pathology. Although cellular membranes are increasingly recognised as important targets of α-Syn toxicity, the interplay between α Syn and biomembranes is still not completely understood. This is especially the case for the familial A30P α-Syn mutant, with different studies presenting contradictory results. In the present work, biomimetic vesicles and isolated mitochondria were used to explore the effects of phospholipids, especially the mitochondrial lipid cardiolipin (CL), on the fibril formation kinetics, membrano-toxic effects and mitochondrial dysfunction caused by monomeric and oligomeric A30P α-Syn, compared to the wild-type (WT) protein. The kinetic aggregation experiments indicate that CL-enriched membranes dramatically speed up and promote the aggregation of A30P α-Syn. Moreover, A30P monomers and oligomers exhibited enhanced perturbation and permeabilisation of CL-containing mito mimetic membranes. Using bilayer electrophysiology, A30P was confirmed to interact with CL membranes and found to alter membrane conductance through different mechanisms, including a non-specific increase in membrane conductance compatible with membrane thinning, or by step-current transitions typical of the membrane incorporation of ion-conducting channels or pores. In a higher order biological model, in this case isolated respiring mitochondria, A30P monomers and oligomers causing mitochondrial swelling and the release of Cyt c from the intermembrane space, key indicators of mitochondrial dysfunction. A30P oligomers, but not monomers, also hyperpolarised mitochondria. Collectively, this study proposes a novel framework linking mutant A30P α-Syn with an enhanced membrane toxicity in the presence of CL, including mitochondria. Such findings can have important implications for PD pathogenesis in cases of autosomal dominant inheritance of the A30P mutation. Particularly, since mitochondrial dysfunction may lead to dopaminergic neuron loss in the substantia nigra, which is pathognomonic of PD.