Assessing the effect of GBA1 gain-of-function mutations on neuronal organelle homeostasis and on α-synuclein accumulation and spreading

Introduction: One of the pathological features of Parkinson’s disease (PD) is the intraneuronal accumulation of Lewy bodies, which are enriched in misfolded proteins such as α-synuclein (aSyn), lipids, and nucleic acids. Mutations in the GBA1 gene, which encodes the lysosomal enzyme β-glucocerebrosidase (GCase), represent the strongest genetic risk factors for developing PD. Recent findings indicate that GBA1 gain-of-function mutations leading to increased retention of GCase in the endoplasmic reticulum (ER) may initiate pathogenic cascades in neurons. This retention can disrupt organelle homeostasis, induce ER stress, alter Golgi morphology, and promote aSyn aggregation and spread. Aim: Our study investigates how diminished enzymatic activity of GCase and distinct GBA1 mutations affect its retention in the ER and examines the downstream impact on ER stress, Golgi apparatus structure, and aSyn accumulation and propagation. Methods: Biochemical and enzymatic characterization was performed. High-resolution microscopy images of cellular models treated with GCase inhibitor and transfected with two mutants (N370S and L444P) were analyzed. Results and conclusion: Wild-type GCase shows progressive localization to lysosomes over time, with reduced quantity in senescent neurons. In contrast, the mutants show progressive ER retention over time and modify the Golgi morphology. Reduced enzymatic activity of GCase triggers ER stress in a time-dependent manner. Additionally, GCase inhibition is associated with increased aSyn content in a time-dependent manner. All of these changes potentially contribute to the accumulation and prion-like spreading of aSyn in PD and shed light into pathogenic mechanisms in PD and related disorders.