Elevated TFEB expression with limited activation in peripheral blood mononuclear cells reflects altered lysosomal enzyme dynamics in Parkinson's disease

Background: Lysosomal dysfunction is recognized as a key pathological feature of Parkinson's disease (PD); however, its peripheral signatures remain unclear. Methods: This study evaluated the peripheral profiles of lysosomal hydrolases and their regulation by transcription factor EB (TFEB), focusing on α-galactosidase A (GLA) and β-mannosidase in the peripheral blood mononuclear cells (PBMCs) of 63 PD patients and 44 healthy controls. Lysosomal enzyme activities in PBMC homogenates and serum were quantified using a fluorometric enzymatic assay with kinetic analysis. Protein concentrations were measured by ELISA, and TFEB activation status was evaluated by its phosphorylation level using western blotting. Results: GLA activity and protein concentrations were higher in the PBMCs of patients, but not for β-mannosidase. TFEB protein concentrations were also elevated and showed positive correlations with lysosomal enzyme protein concentrations. TFEB phosphorylation status showed that the ratio of non-phosphorylated to total TFEB did not differ between PD and controls. However, within the PD group, this ratio negatively correlated with TFEB concentrations, suggesting a potential uncoupling between TFEB expression and its functional activation status. Furthermore, both serum-to-PBMC ratios of GLA activity and protein concentration were lower in PD and were associated with PBMC counts, indicating impaired enzyme release from PBMC. Conclusions: Elevated TFEB expression in PBMCs may reflect a compensatory response to PD-related cellular stress. However, this response may be functionally insufficient due to limited TFEB activity, potentially leading to reduced lysosomal enzyme release. Thus, peripheral TFEB-related lysosomal abnormalities may serve as indicators of systemic autophagy-lysosome dysregulation in PD.