Wild-type GBA1 increases the α-synuclein tetramer-monomer ratio, reduces lipid-rich aggregates, and attenuates motor and cognitive deficits in mice

Loss-of-function mutations in acid beta-glucosidase 1 (GBA1) are among the strongest genetic risk factors for Lewy body disorders such as Parkinson's disease (PD) and Lewy body dementia (DLB). Altered lipid metabolism in PD patient-derived neurons, carrying either GBA1 or PD alpha S mutations, can shift the physiological alpha-synuclein (alpha S) tetramer-monomer (T:M) equilibrium toward aggregation-prone monomers. A resultant increase in pSer129+ alpha S monomers provides a likely building block for alpha S aggregates. 3K alpha S mice, representing a neuropathological amplification of the E46K PD-causing mutation, have decreased alpha S T:M ratios and vesicle-rich alpha S+ aggregates in neurons, accompanied by a striking PD-like motor syndrome. We asked whether enhancing glucocerebrosidase (GCase) expression could benefit alpha S dyshomeostasis by delivering an adeno-associated virus (AAV)-human wild-type (wt) GBA1 vector into the brains of 3K neonates. Intracerebroventricular AAV-wtGBA1 at postnatal day 1 resulted in prominent forebrain neuronal GCase expression, sustained through 6 mo. GBA1 attenuated behavioral deficits both in working memory and fine motor performance tasks. Furthermore, wtGBA1 increased alpha S solubility and the T:M ratio in both 3K-GBA mice and control littermates and reduced pS129+ and lipid-rich aggregates in 3K-GBA. We observed GCase distribution in more finely dispersed lysosomes, in which there was increased GCase activity, lysosomal cathepsin D and B maturation, decreased perilipinstabilized lipid droplets, and a normalized TFEB translocation to the nucleus, all indicative of improved lysosomal function and lipid turnover. Therefore, a prolonged increase of the alpha S T:M ratio by elevating GCase activity reduced the lipid-and vesicle-rich aggregates and ameliorated PD-like phenotypes in mice, further supporting lipid modulating therapies in PD.

Automated summary

Loss-of-function mutations in GBA1 are strong genetic risk factors for Lewy body disorders, enhancing GCase activity can improve αS dyshomeostasis and reduce lipid-rich aggregates, ameliorating PD-like phenotypes.