We used GBA +/L444P mice, a-synuclein knockout (SNCA -/- ) mice at 8 months of age, and adeno-associated virus (AAV)-human GBA overexpression to investigate the rescue effect of DA neuronal loss and susceptibility by MPTP. Mitochondrial morphology and functional assay were used to identify mitochondrial defects in GBA +/L444P mice. Motor behavioral test, immunohistochemistry, and HPLC were performed to measure dopaminergic degeneration by MPTP and investigate the relationship between GBA mutation and a-synuclein. Mitochondrial immunostaining, qPCR, and Western blot were also used to study the effects of a-synuclein knockout or GBA overexpression on MPTP-induced mitochondrial defects and susceptibility.

Results

L444P GBA heterozygous mutation reduced GBA protein levels, enzymatic activity and a concomitant accumulation of a-synuclein in the midbrain of GBA +/L444P mice. Furthermore, the deficiency resulted in defects in mitochondria of cortical neurons cultured from GBA +/L444P mice. Notably, treatment with MPTP resulted in a significant loss of dopaminergic neurons and striatal dopaminergic fibers in GBA +/L444P mice compared to wild type (WT) mice. Levels of striatal DA and its metabolites were more depleted in the striatum of GBA +/L444P mice. Behavioral deficits, neuroinflammation, and mitochondrial defects were more exacerbated in GBA +/L444P mice after MPTP treatment. Importantly, MPTP induced PD-like symptoms were significantly improved by knockout of a-synuclein or augmentation of GBA via AAV5-hGBA injection in both WT and GBA +/L444P mice. Intriguingly, the degree of reduction in MPTP induced PD-like symptoms in GBA +/L444P a-synuclein (SNCA) -/- mice was nearly equal to that in SNCA -/- mice after MPTP treatment.

Conclusion

Our results suggest that GBA deficiency due to L444P GBA heterozygous mutation and the accompanying accumulation of a-synuclein render DA neurons more susceptible to MPTP intoxication. Thus, GBA and a-synuclein play dual physiological roles in the survival of DA neurons in response to the mitochondrial dopaminergic neurotoxin, MPTP.

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