High expression levels of the D686N Parkinson's disease mutation in VPS35 induces α-synuclein-dependent toxicity in yeast

Parkinson's disease (PD) is a common neurodegenerative disorder that affects ~2% of the human population aged >65. α-synuclein serves a role in the pathogenesis of PD as it is a primary component of Lewy bodies, a pathological feature of PD. Endosomal-lysosomal dysfunction may be a key factor involved in the pathophysiology of PD, and may cause PD-associated neurodegeneration via α-synuclein-dependent and -independent mechanisms. The D620N mutation in the endosomal-lysosomal gene, vacuolar protein sorting-associated protein 35 (VPS35), has been linked to PD. To clarify the underlying cellular mechanism of the VPS35 D620N mutation in PD, cell growth and endosomal-lysosomal functions were investigated in Saccharomyces cerevisiae (sc) yeast cells that exhibited various expression levels of sc VPS35, in the presence or absence of non-toxic expression levels of α-synuclein. Overexpression of the sc VPS35 D686N mutation (the yeast equivalent of D620N) did not lead to toxicity in yeast. However, the co-expression of high copy numbers of sc VPS35 D686N and low copy numbers of α-synuclein caused toxicity, whereas the co-expression of sc VPS35 wild-type and α-synuclein did not. In addition, the sc VPS35 D686N mutant enhanced α-synuclein aggregation. Fragmentation of vacuoles and subsequent inhibition of lysosome function was evident in yeast cells bearing the sc VPS35 mutant. The results of the present study suggested that α-synuclein and sc VPS35 were interlinked via the endosomal-lysosome pathway, which is important for the pathogenesis of PD.