Redistribution of DAT/α-Synuclein Complexes Visualized by "In Situ" Proximity Ligation Assay in Transgenic Mice Modelling Early Parkinson's Disease

Alpha-synuclein, the major component of Lewy bodies, is thought to play a central role in the onset of synaptic dysfunctions in Parkinson's disease (PD). In particular, a-synuclein may affect dopaminergic neuron function as it interacts with a key protein modulating dopamine (DA) content at the synapse: the DA transporter (DAT). Indeed, recent evidence from our "in vitro" studies showed that alpha-synuclein aggregation decreases the expression and membrane trafficking of the DAT as the DAT is retained into alpha-synuclein-immunopositive inclusions. This notwithstanding, "in vivo" studies on PD animal models investigating whether DAT distribution is altered by the pathological overexpression and aggregation of alpha-synuclein are missing. By using the proximity ligation assay, a technique which allows the "in situ" visualization of protein-protein interactions, we studied the occurrence of alterations in the distribution of DAT/alpha-synuclein complexes in the SYN120 transgenic mouse model, showing insoluble alpha-synuclein aggregates into dopaminergic neurons of the nigrostriatal system, reduced striatal DA levels and an altered distribution of synaptic proteins in the striatum. We found that DAT/alpha-synuclein complexes were markedly redistributed in the striatum and substantia nigra of SYN120 mice. These alterations were accompanied by a significant increase of DAT striatal levels in transgenic animals when compared to wild type littermates. Our data indicate that, in the early pathogenesis of PD, alpha-synuclein acts as a fine modulator of the dopaminergic synapse by regulating the subcellular distribution of key proteins such as the DAT.