Sphingolipid changes in Parkinson L444P GBA mutation fibroblasts promote α-synuclein aggregation

ABSTRACT

Intraneuronal accumulation of aggregated α-synuclein is a pathological hallmark of Parkinson’s disease. Therefore, mechanisms capable of promoting α-synuclein deposition bear important pathogenetic implications. Mutations of the glucocerebrosidase 1 (GBA) gene represent a prevalent Parkinson’s disease risk factor. They are associated with loss of activity of a key enzyme involved in lipid metabolism, glucocerebrosidase, supporting a mechanistic relationship between abnormal α-synuclein-lipid interactions and the development of Parkinson pathology. In this study, the lipid membrane composition of fibroblasts isolated from control subjects, patients with idiopathic Parkinson’s disease (iPD) and Parkinson patients carrying the L444P GBA mutation (PD-GBA) was assayed using shotgun lipidomics. The lipid profile of PD-GBA fibroblasts differed significantly from that of control and iPD cells. It was characterized by an overall increase in sphingolipid levels. It also featured a significant change in the proportion of ceramide, sphingomyelin and hexosylceramide molecules with shorter and longer hydrocarbon chain length; levels of shorter-chain molecules were increased while the percent of longer-chain sphingolipids was decreased in PD-GBA lipid extracts. The extent of this shift was correlated to the degree of reduction of fibroblast glucocerebrosidase activity. In a second set of experiments, lipid extracts from control and PD-GBA fibroblasts were added to incubations of recombinant α-synuclein. The kinetics of α-synuclein aggregation, as assessed by the binding of thioflavin T to amyloid structures, was significantly accelerated after addition of PD-GBA extracts as compared to control samples. Amyloid fibrils collected at the end of these incubations contained lipids, indicating α-synuclein-lipid co-assembly. Lipids extracted from α-synuclein fibrils were also analysed by shotgun lipidomics. Data revealed that the lipid content of these fibrils was significantly enriched of shorter-chain sphingolipids. Taken together, findings of this study indicate that the L444P GBA mutation and consequent enzymatic loss are associated with a distinctly altered membrane lipid profile that provides a biological fingerprint of this mutation in Parkinson fibroblasts. This altered lipid profile, which includes an increased content of shorter-chain sphingolipids, could also be an indicator of increased risk for α-synuclein aggregate pathology. Shorter-chain molecules may act as preferred reactants during lipid-induced α-synuclein fibrillation.