Rapamycin Abrogates Aggregation of Human α-Synuclein Expressed in Fission Yeast via an Autophagy-Independent Mechanism

Aggregation of alpha-synuclein (α-Syn) is implicated in the pathogenesis of several neurodegenerative disorders, such as Parkinson's disease and Dementia with Lewy bodies, collectively termed synucleinopathies. Thus, tremendous efforts are being made to develop strategies to prevent or inhibit α-Syn aggregation. Here, we genetically engineered fission yeast to express human α-Syn C-terminally fused to green fluorescent protein (GFP) at low and high levels. α-Syn was localized at the cell tips and septa at low-level expression. At high-level expression, α-Syn was observed to form cytoplasmic aggregates. Notably, rapamycin, a natural product that allosterically inhibits the mammalian target of rapamycin (mTOR) by forming a complex with FKBP12, and Torin1, a synthetic mTOR inhibitor that blocks ATP binding to mTOR, markedly reduced the number of cells harboring α-Syn aggregates. These mTOR inhibitors abrogate α-Syn aggregation without affecting α-Syn expression levels. Rapamycin, but not Torin1, failed to reduce α-Syn aggregation in the deletion cells of fkh1⁺, encoding FKBP12, indicating the requirement of FKBP12 for rapamycin-mediated inhibition of α-Syn aggregation. Importantly, the effect of rapamycin was also observed in the cells lacking atg1⁺, a key regulator of autophagy. Collectively, rapamycin abrogates human α-Syn aggregation expressed in fission yeast via an autophagy-independent mechanism mediated by FKBP12.