Long-term oral regimen of glucocerebrosidase activator reduces a-synuclein oligomer accumulation in aged LRRK2 mutant mouse brains - therapeutic implication of Parkinson’s disease

Deposition of misfolded a-synuclein (a-syn) aggregates in brain is a pathological hallmark of Parkinson’s disease (PD). Accumulation of toxic soluble a-syn seeds in patient cerebrospinal fluid represents a prodromal marker of synucleinopathies in PD, contributing to progressive neurodegeneration. Deficiency in beta-glucocerebrosidase (GCase), a lysosomal enzyme for glucocerebroside metabolism, is evident in PD linking functionally with pathogenic LRRK2 (leucine-rich repeat kinase 2) mutation and synucleinopathies. However, whether GCase activation ameliorates synucleinopathies in PD brains is unclear. Here, we explored how GCase activity affected Ser129-a-syn phosphorylation, and whether long-term treatment of a brain-penetrant GCase chaperone (Ambroxol; ABX) attenuated a-syn oligomer accumulation in aged mutant LRRK2 ^R1441G mouse brains. Acute ABX treatment (50µM) significantly increased cellular GCase activity and reduced Ser129-a-syn phosphorylation in human SH-SY5Y neuronal cells and murine fibroblasts. Real-time DQ-BSA degradation assay revealed lysosomal dysfunction in mutant LRRK2 ^R1441G MEFs, which was attenuated by ABX treatment. Single oral gavage of ABX (400mg/kg) in mice achieved peak drug level in serum and brain within 6 hours post-administration. Spontaneous feeding of ABX in food pellet over 18 weeks (average daily dose: 45.9mg/kg/day) elevated brain GCase activity in aged wildtype and mutant striatum without affecting body weight. This chronic regimen significantly reduced a-syn oligomer level in mutant striatum yet without an effect on total a-syn and Ser129-phosphorylation levels. This is the first study demonstrating attenuation of synucleinopathies by chronic GCase activation in aged mouse brains vulnerable to PD, suggesting early intervention to alter progression of synucleinopathies as a key determinant of clinical outcomes of PD.