Structurally distinct α-synuclein fibrils induce robust parkinsonian pathology

Objective: Alpha-synuclein (α-syn) is a major component of Lewy bodies, which are the pathological hallmark in Parkinson's disease, and its genetic mutations cause familial forms of Parkinson's disease. Patients with α-syn G51D mutation exhibit severe clinical symptoms. However, in vitro studies showed low propensity for α-syn with the G51D mutation. We studied the mechanisms associated with severe neurotoxicity of α-syn G51D mutation using a murine model generated by G51D α-syn fibril injection into the brain. Methods: Structural analysis of wild-type and G51D α-syn-fibrils were performed using Fourier transform infrared spectroscopy. The ability of α-syn fibrils forming aggregates was first assessed in in vitro mammalian cells. An in vivo mouse model with an intranigral injection of α-syn fibrils was then used to evaluate the propagation pattern of α-syn and related cellular changes. Results: We found that G51D α-syn fibrils have higher β-sheet contents than wild-type α-syn fibrils. The addition of G51D α-syn fibrils to mammalian cells overexpressing α-syn resulted in the formation of phosphorylated α-syn inclusions at a higher rate. Similarly, an injection of G51D α-syn fibrils into the substantia nigra of a mouse brain induced more widespread phosphorylated α-syn pathology. Notably, the mice injected with G51D α-syn fibrils exhibited progressive nigral neuronal loss accompanied with mitochondrial abnormalities and motor impairment. Conclusion: Our findings indicate that the structural difference of G51D α-syn fibrils plays an important role in the rapidly developed and more severe neurotoxicity of G51D mutation-linked Parkinson's disease.