The A53T alpha-synuclein mutation increases iron-dependent aggregation andtoxicity

Parkinson's disease (PD) is the most common motor disorder affecting the el derly. PD is characterized by the formation of Lewy bodies and death of dop aminergic neurons. The mechanisms underlying PD are unknown, but the discov eries that mutations in alpha-synuclein can cause familial PD and that alph a-synuclein accumulates in Lewy bodies suggest that alpha-synuclein partici pates in the pathophysiology of PD. Using human BE-M17 neuroblastoma cells overexpressing wild-type, A53T, or A30P alpha-synuclein, we now show that i ron and free radical generators, such as dopamine or hydrogen peroxide, sti mulate the production of intracellular aggregates that contain alpha-synucl ein and ubiquitin. The aggregates can be identified by immunocytochemistry, electron microscopy, or the histochemical stain thioflavine S. The amount of aggregation occurring in the cells is dependent on the amount of alpha-s ynuclein expressed and the type of alpha-synuclein expressed, with the amou nt of alpha-synuclein aggregation following a rank order of A53T > A30P > w ild-type > untransfected. In addition to stimulating aggregate formation, a lpha-synuclein also appears to induce toxicity. BE-M17 neuroblastoma cells overexpressing alpha-synuclein show up to a fourfold increase in vulnerabil ity to toxicity induced by iron. The vulnerability follows the same rank or der as for aggregation. These data raise the possibility that alpha-synucle in acts in concert with iron and dopamine to induce formation of Lewy body pathology in PD and cell death in PD.