Glucocerebrosidase dysfunction in GBA1 carriers: insights from blood and macrophage analyses

Mutations in the GBA1 gene, which encodes the lysosomal enzyme glucocerebrosidase (GCase), are the most common genetic factor associated with Parkinson's disease (PD). These mutations are classified as "severe" or "mild" based on the residual GCase activity. This study aimed to compare the biochemical characteristics of peripheral blood and macrophages derived from peripheral blood mononuclear cells (PBMC-derived macrophages) from PD patients with GBA1 mutations (GBA1-PD) and healthy GBA1 mutation carriers (GBA1-carriers).

31 GBA1-PD patients, 24 GBA1-carriers and 247 controls were enrolled. We assessed GCase activity, levels of the lysosphingolipid hexosylsphingosine (HexSph) and the proteins GCase, alpha-synuclein, and cathepsin D as well as GCase translocation to lysosomes in PBMC-derived macrophages. Biochemical analysis of PBMC-derived macrophages revealed similar impairments in GCase activity, lysosomal translocation, elevated HexSph and alpha-synuclein, and decreased cathepsin D in both GBA1-PD and GBA1-carriers compared to controls. However, when the mutations were divided according to their severity, almost all differences were only observed in the carriers of "severe" mutations. The ratio of GCase activity to HexSph level in blood significantly differed between GBA1-PD and GBA1-carriers. Additionally, we retrospectively analyzed data on GCase activity and HexSph level in blood of GBA1-PD patient during the presymptomatic period prior motor symptom onset, following oral ambroxol treatment (1200 mg per day).

Biochemical alterations in GCase function are linked to GBA1 mutations independent of PD status, with "severe" mutations notably impacting lysosomal function and multiple cellular processes. We propose the GCase activity to HexSph ratio as a novel biomarker for disease progression and monitoring therapeutic response.