Parkinsonian Neurotoxin 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and α-Synuclein Mutations Promote Tau Protein Phosphorylation at Ser²⁶² and Destabilize Microtubule Cytoskeleton in Vitro*

In Parkinson disease (PD) brain, a progressive loss of dopaminergic neurons leads to dopamine depletion in the striatum and reduced motor function. Lewy bodies, the characteristic neuropathological lesions found in the brain of PD patients, are composed mainly of α-synuclein protein. Three point mutations in the α-synuclein gene are associated with familial PD. In addition, genome-wide association studies indicate that α-synuclein and Tau protein synergistically increase disease susceptibility in the human population. To determine the mechanism by which α-synuclein and Tau act together, we have used PD-causing neurotoxin MPTP and pathogenic α-synuclein mutants A30P, E46K, and A53T as models. We found that exposure of human neuroblastoma M17 cells to MPTP enhances the intracellular α-synuclein protein level, stimulates Tau protein phosphorylation at Ser²⁶², and induces apoptosis. In mouse brain, ablation of α-synuclein function significantly suppresses Tau phosphorylation at Ser²⁶². In vitro, α-synuclein binds to phosphorylated Ser²¹⁴ of Tau and stimulates PKA-catalyzed Tau phosphorylation at Ser²⁶². PD-associated α-synuclein mutations increase α-synuclein binding to Tau and stimulate Tau phosphorylation at Ser²⁶². In HEK-293 cells, α-synuclein and its all PD-associated mutants destabilize the microtubule cytoskeleton in a similar extent. In contrast, when co-expressed with Tau, these PD-associated mutants destabilize microtubules with significantly higher potency than WT. Our results demonstrate that α-synuclein is an in vivo regulator of Tau protein phosphorylation at Ser²⁶² and suggest that PD-associated risk factors such as environmental toxins and α-synuclein mutations promote Tau phosphorylation at Ser²⁶², causing microtubule instability, which leads to loss of dopaminergic neurons in PD brain.