Decreased Vacuolar Ca(2+) Storage and Disrupted Vesicle Trafficking Underlie Alpha-Synuclein-Induced Ca(2+) Dysregulation in S. cerevisiae

The yeast Saccharomyces cerevisiae is a powerful model to study the molecular mechanisms underlying α-synuclein (α-syn) cytotoxicity. This is due to the high degree of conservation of cellular processes with higher eukaryotes and the fact that yeast does not endogenously express α-synuclein. In this work, we focused specifically on the interplay between α-syn and intracellular Ca(2+) homeostasis. Using temperature-sensitive SEC4 mutants and deletion strains for the vacuolar Ca(2+) transporters Pmc1 and Vcx1, together with aequorin-based Ca(2+) recordings, we show that overexpression of α-syn shifts the predominant temporal pattern of organellar Ca(2+) release from a biphasic to a quasi-monophasic response. Fragmentation and vesiculation of vacuolar membranes in α-syn expressing cells can account for the faster release of vacuolar Ca(2+). α-Syn further significantly reduced Ca(2+) storage resulting in increased resting cytosolic Ca(2+) levels. Overexpression of the vacuolar Ca(2+) ATPase Pmc1 in wild-type cells prevented the α-syn-induced increase in resting Ca(2+) and was able to restore growth. We propose that α-syn-induced disruptions in Ca(2+) signaling might be an important step in initiating cell death.