Ser129D mutant alpha-synuclein induces earlier motor dysfunction while S129A results in distinctive pathology in a rat model of Parkinson's disease

Alpha-synuclein phosphorylated at serine 129 (S129) is highly elevated in Parkinson's disease patients where it mainly accumulates in the Lewy bodies. Several groups have studied the role of phosphorylation at the S129 in alpha-synuclein in a rat model for Parkinson's disease using recombinant adeno-associated viral (rAAV) vectors. The results obtained are inconsistent and accordingly the role of S129 phosphorylation in alpha-synuclein toxicity remains unclear. This prompted us to re-examine the neuropathological and behavioral effects of the S129 modified alpha-synuclein species in vivo. For this purpose, we used two mutated forms of human alpha-synuclein in which the S129 was replaced either with an alanine (S129A), to block phosphorylation, or with an aspartate (S129D), to mimic phosphorylation, and compared them with the wild type alpha-synuclein. This approach was similar in design to previous studies, however our investigation of dopaminergic degeneration also included performing a detailed study of the alpha-synuclein induced pathology in the striatum and the analysis of motor deficits. Our results showed that overexpressing S129D or wild type alpha-synuclein resulted in an accelerated dopaminergic fiber loss as compared with S129A alpha-synuclein. Furthermore, the motor deficit seen in the group treated with the mutant S129D alpha-synuclein appeared earlier than the other two forms of alpha-synuclein. Conversely, S129A alpha-synuclein showed significantly larger pathological alpha-synuclein-positive inclusions, and slower dopaminergic fiber loss, when compared to the other two forms of alpha-synuclein, suggesting a neuroprotective effect of the mutation. When examined at long-term, all three alpha-synuclein forms resulted in pathological accumulations of alpha-synuclein in striatal fibers and dopaminergic cell death in the substantia nigra. Our data show that changes in the S129 residue of alpha-synuclein influence the rate of pathology and neurodegeneration, with an overall deleterious effect of exchanging S129 to a residue mimicking its phosphorylated state. (c) 2013 Elsevier Inc. All rights reserved.