Inhibition of formation of α-synuclein inclusions by mannosylglycerate in a yeast model of Parkinson's disease

Background: Protein aggregation in the brain is a central hallmark in many neurodegenerative diseases. In Parkinson's disease, α-synuclein (α-Syn) is the major component of the intraneuronal inclusions found in the brains of patients. Current therapeutics is merely symptomatic, and there is a pressing need for developing novel therapies. Previously we showed that mannosylglycerate (MG), a compatible solute typical of marine microorganisms thriving in hot environments, is highly effective in protecting a variety of model proteins against thermal denaturation and aggregation in vitro.

Methods: Saccharomyces cerevisiae cells expressing eGFP-tagged α-Syn, were further engineered to synthesize MG. The number of cells with fluorescent foci was assessed by fluorescence microscopy. Fluorescence spectroscopy and transmission electron microscopy were used to monitor fibril formation in vitro.

Results: We observed a 3.3-fold reduction in the number of cells with α-Syn foci and mild attenuation of α-Syn-induced toxicity. Accordingly, sucrose gradient analysis confirmed a clear reduction in the size-range of α-Syn species in the cells. MG did not affect the expression levels of α-Syn or its degradation rate. Moreover, MG did not induce molecular chaperones (Hsp104, Hsp70 and Hsp40), suggesting the implication of other mechanisms for α-Syn stabilization. MG also inhibited α-Syn fibrillation in vitro.

Conclusions: MG acts as a chemical chaperone and the stabilization mechanism involves direct solute/protein interactions.

General significance: This is the first demonstration of the anti-aggregating ability of MG in the intracellular milieu. The work shows that MG is a good candidate to inspire the development of new drugs for protein-misfolding diseases.