alpha-Synuclein (alpha-syn), a protein involved in the pathogenesis of Parkinson's disease (PD), is known to accumulate in mitochondria, disrupt mitochondrial function. However, the molecular mechanisms that link these pathological responses have not been investigated. In rats overexpressing alpha-syn in the substantia nigra (SN) through adeno-associated virus (AAV) transduction, about 50% of tyrosine hydroxylase positive neurons were lost after 24 weeks. Overexpression of alpha-syn was also associated with morphological deformation of mitochondria and depolarization of the mitochondrial membrane potential (Delta Psi m). Both co-immunoprecipitation and confocal microscopy demonstrated that mitochondrial alpha-syn associated with adenylate translocator (ANT), a component of the mitochondrial permeability transition pore (mPTP). The depolarization of Delta Psi m was partially reversed in vitro by bongkrekic acid (BKA), an inhibitor of ANT, suggesting that the molecular association between alpha-syn and ANT facilitated Delta Psi m depolarization. Concomitant with alpha-syn accumulation in mitochondria, abnormal mitochondrial morphology, Delta Psi m depolarization, and loss of TH-positive neurons, there was a decrease in apoptosis-inducing factor (AIF) within the mitochondrial matrix, suggesting possible translocation to the cytosol. Our findings suggest that overexpression of alpha-syn may cause mitochondrial defects in dopaminergic neurons of the substantia nigra through an association with adenylate translocator and activation of mitochondria-dependent cell death pathways. Disruption of normal mitochondrial function may contribute to the loss of dopaminergic neurons in Parkinson's disease. (C) 2011 Elsevier Ltd. All rights reserved.