The direct and indirect effects of α-synuclein on microtubule stability in the pathogenesis of Parkinson's disease

Despite decades of research, the mechanism of Parkinson's disease pathogenesis remains unclear. Studies have focused heavily on the protein alpha-synuclein, which is the primary component of Lewy bodies, the pathologic inclusions that are the hallmark of Parkinson's on the cellular level. While the roles of alpha-synuclein in causing mitochondrial dysfunction and disruptions to the proteasomal system have been well documented, recently, its role in effecting microtubule dynamics has been investigated as a potential source of pathogenicity. Here, we evaluate the evidence for and against the role of alpha-synuclein in destabilizing microtubules, causing axonal transport deficits and eventually neurodegeneration. We present evidence for a model where alpha-synuclein has both a direct and indirect effect on microtubule stability. Directly, it may act as a microtubule-associated protein, binding to microtubules and directly effecting their dynamics. Indirectly, it may promote the hyperphosphorylation of the microtubule stabilizing protein, tau, leading to tau aggregation with other microtubule stabilizing proteins, hence indirectly causing microtubule destabilization. This model provides insights into the function of alpha-synuclein and tau in Parkinson's disease pathogenesis and raises the possibility that this role that may also be conserved in Alzheimer's disease.