GBA1 deficiency negatively affects physiological alpha-synuclein tetramers and related multimers

Accumulating evidence suggests that alpha-synuclein (alpha-syn) occurs physiologically as a helically folded tetramer that resists aggregation. However, the mechanisms underlying the regulation of formation of alpha-syn tetramers are still mostly unknown. Cellular membrane lipids are thought to play an important role in the regulation of alpha-syn tetramer formation. Since glucocerebrosidase 1 (GBA1) deficiency contributes to the aggregation of alpha-syn and leads to changes in neuronal glycosphingolipids (GSLs) including gangliosides, we hypothesized that GBA1 deficiency may affect the formation of alpha-syn tetramers. Here, we show that accumulation of GSLs due to GBA1 deficiency decreases alpha-syn tetramers and related multimers and increases alpha-syn monomers in CRISPR-GBA1 knockout (KO) SH-SY5Y cells. Moreover, alpha-syn tetramers and related multimers are decreased in N370S GBA1 Parkinson's disease (PD) induced pluripotent stem cell (iPSC)-derived human dopaminergic (hDA) neurons and murine neurons carrying the heterozygous L444P GBA1 mutation. Treatment with miglustat to reduce GSL accumulation and overexpression of GBA1 to augment GBA1 activity reverse the destabilization of alpha-syn tetramers and protect against alpha-syn preformed fibril-induced toxicity in hDA neurons. Taken together, these studies provide mechanistic insights into how GBA1 regulates the transition from monomeric alpha-syn to alpha-syn tetramers and multimers and suggest unique therapeutic opportunities for PD and dementia with Lewy bodies.