Protective role of olesoxime in alpha-synuclein-induced mitochondrial dysfunction

Authors

• A Rovini
• M Queralt-Martin
• P Gurnev
• T Rostovtseva
• S Bezrukov

Abstract

Parkinson’s disease (PD) is a neurodegenerative disease associated with loss of dopaminergic neurons and presence of Lewy bodies, whose main protein component is alpha-synuclein (a-syn). The molecular determinants underlying a-syn secretion, aggregation, and intracellular toxicity are still unclear. Yet, in vitro and in vivo studies of the effects of overexpression of either wild type or mutant forms of a-syn have reported mitochondrial abnormalities and ability of a-syn to bind to the outer and inner mitochondrial membranes. Recently, using a channel reconstitution assay, our lab showed that a-syn interacts with the outer mitochondrial membrane voltage-dependent anion channel (VDAC). Moreover, under certain conditions a-syn can either partially block this channel or translocate through it. Olesoxime is a drug candidate which has been shown to provide significant pro-survival benefits in a human neuronal model of a-syn-mediated toxicity. The dual goal of this work is to address a tentative mechanism of olesoxime protection against a-syn-induced mitochondrial dysfunctions and to clarify the role of VDAC in a-syn toxicity and olesoxime protection. Since VDAC permeability and mitochondrial membrane potential are closely related, we first assayed the effect of olesoxime treatment (10 micromolar, 24 h) on mitochondrial membrane potential in human neuroblastoma cells overexpressing a-syn. First, compared to control cells (empty vector), a-syn expression resulted in a significant reduction of membrane potential probed by the mitotracker dye. Second, olesoxime treatment significantly attenuated this loss of membrane potential while it did not affect this parameter by itself, that is, without a-syn expression. We then assessed the a-syn and olesoxime putatively common target, VDAC, using multi-channel VDAC voltage-gating protocol. We observed that olesoxime promotes VDAC closure. In single-channel experiments we found that olesoxime prevented a-syn translocation through VDAC. To interact with VDAC, a-syn first binds to membrane lipids, thus we wanted to see whether olesoxime effect could result from a lower a-syn membrane binding. Fluorescence correlation spectroscopy revealed that olesoxime did not affect a-syn binding to liposomes with the membrane lipid composition matching channel experiments. Current efforts are dedicated to confirm our in vitro results in a-syn overexpressing cells to gain insights into VDAC’s role in a-syn- and olesoxime-mediated effects.

Scientific Focus Area: Molecular Biology and Biochemistry

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