Chaperone mediated degradation of aggregated alpha synuclein

Aggregation and cytotoxicity of misfolded alpha-synuclein is postulated to be crucial in the disease process of neurodegenerative disorders such as Parkinson's disease and dementia with Lewy bodies. Overexpression of C-terminally modified alpha-synuclein and synphilin-1 produce intracellular alpha-synuclein aggregates in human H4 cells (McLean et al., Neuroscience, 2001). We have previously demonstrated that overexpression of heat shock protein 70 (Hsp70) dramatically reduces the number of alpha-synuclein aggregates in a cell culture model (McLean et al., J. Neurochem., 2002), and Hsp70 has also been shown to prevent dopaminergic cell death in a drosophila model of alpha-synuclein (Auluck et al., Science, 2002). In this study we detected misfolded and aggregated alpha-synuclein in a triton X-100 insoluble fraction as well as a high molecular weight product by gel electrophoresis of temporal neocortex from DLB patients but not from controls. We also found similar triton X-100 insoluble forms of alpha-synuclein in an alpha-synuclein transgenic mouse model, and in an in vitro model of alpha-synuclein aggregation. Introducing the molecular chaperone Hsp70 into the in vivo model by breeding alpha-synuclein transgenic mice with Hsp70 overexpressing mice led to a significant reduction in both the high molecular weight and detergent insoluble alpha-synuclein species. Concomitantly, we found that Hsp70 overexpression in vitro similarly reduced detergent insoluble alpha-synuclein species and protected cells from alpha-synuclein induced cellular toxicity in an ATPase domain dependent manner. Since CHIP (C-terminus of Hsp70-interacting protein) is believed to modulate heat shock protein mediated refolding and degradation, we examined the effect of CHIP overexpression in this system, and found that it also dramatically reduces high molecular weight alpha-synuclein. Taken together, these data demonstrate that the molecular chaperone Hsp70 possibly via interacting with CHIP can reduce the amount of misfolded, aggregated alpha-synuclein species in vivo and in vitro, and protect from alpha-synuclein dependent toxicity.