The enzyme at the center of the story is glucocerebrosidase, or GCase, encoded by the GBA1 gene. Inside lysosomes, the cell’s acidic recycling compartments, GCase cleaves the lipid glucosylceramide into glucose and ceramide. When GBA1 carries a pathogenic mutation, such as the well-characterized L444P variant, the enzyme’s structure and catalytic activity falter. Glucosylceramide then accumulates in the lysosome, degrading the organelle’s overall function. That matters enormously for Parkinson’s disease, because lysosomes are responsible for clearing monomeric alpha-synuclein, the protein that clumps into the toxic oligomers and fibrils found in the brains of patients. Defective GCase impairs alpha-synuclein clearance, and aggregated alpha-synuclein in turn blocks GCase trafficking to the lysosome, creating a self-reinforcing pathological loop.

Mutations in GBA1 are the single most common genetic risk factor for Parkinson’s disease, carried by an estimated 5 to 20 percent of patients worldwide, and they are associated with earlier onset, faster progression, and steeper cognitive decline. To model this vulnerability, the Verona team used double-transgenic mice that express human A53T alpha-synuclein while carrying either a wild-type Gba1 allele or the L444P mutation. These animals reproduce the bidirectional damage loop central to GBA1-associated disease, showing impaired lysosomal function, reduced GCase activity, alpha-synuclein pathology, and subtle motor deficits. Age-matched C57BL/6J mice served as healthy controls. The researchers studied the animals at 16 to 18 months of age, a post-symptomatic stage, with five mice per genotype.

The central question was deceptively simple: does GCase activity oscillate across the 24-hour day? Circadian biology offered good reason to think it might. The molecular clock, driven by transcription factors such as BMAL1, is known to regulate autophagic-lysosomal degradation, and the transcription factor EB, or TFEB, drives rhythmic oscillations in lysosomal activity. Physical activity adds another layer, since exercise entrains peripheral clocks and has been shown to activate lysosomal function through the AMPK-SIRT1-TFEB signaling pathway. The team therefore measured plasma GCase activity at four Zeitgeber times, ZT2, ZT8, ZT14, and ZT20, where ZT0 marks lights-on, under both a standard 12-hour light/dark cycle and a reversed one, before and after two weeks of daily, fixed-time rotarod training.

The rotarod, a rotating rod that accelerates from 4 to 40 rpm over 300 seconds, served double duty as both exercise and motor assessment. Mice trained either during their rest phase, at ZT4 under standard lighting, or during their active phase, at ZT16 after the light/dark cycle was inverted. Blood was drawn gently by submandibular venipuncture, plasma was separated and frozen, and GCase activity was quantified with a fluorometric assay using the synthetic substrate 4-methylumbelliferyl-beta-D-glucopyranoside, with fluorescence of the released 4-methylumbelliferone read at 365 nanometers excitation and 495 nanometers emission.

The behavioral results were striking. At the start of training, both mutant strains fell from the rod significantly sooner than controls, consistent with genotype-linked motor vulnerability. After two weeks of daily practice, however, all groups reached comparable performance. When training was paused and the light cycle inverted, the L444P mice relapsed to significantly shorter fall latencies, but two weeks of training during their active phase rescued their performance to control levels. Both mutant strains also performed better overall when trained during the dark phase, their natural active period, echoing growing evidence that exercise timing shapes training adaptations through circadian regulation of skeletal muscle metabolism.

The enzymatic data told an equally compelling story. In healthy C57BL/6J mice housed under a reversed cycle, GCase activity remained stable during the rest phase and peaked in the early active phase, a genuine time-of-day pattern confirmed by both repeated-measures ANOVA and cosinor analysis. In the hSNCA(A53T)Gba1(+/+) mutants, this pattern was inverted, with higher activity during the rest phase and a decline during the early active phase, suggesting that alpha-synuclein overexpression disrupts the enzyme’s temporal regulation. The L444P mutants fared worst, showing uniformly reduced, essentially flat activity around the clock, underscoring how the pathogenic variant erases rhythmic control altogether.

Daily, fixed-time exercise partially reorganized these broken patterns. After two weeks of rotarod training during the active phase, both mutant strains developed more defined temporal profiles, with the hSNCA(A53T)Gba1(+/+) mice showing higher activity in the late active phase and the L444P mice displaying a significant rise at the onset of the resting phase. Overall enzyme levels remained below those of controls, but the rhythm itself was partially rescued. The effect was more robust when training occurred during the mice’ active phase than during their rest phase, consistent with the idea that exercise acts as a powerful zeitgeber, a time-giving cue that reinforces daily rhythms across tissues and genotypes.

The authors are careful about the limits of their evidence. The sample size was small, the control strain was not fully background-matched, and the study was conducted under light/dark cycles rather than constant conditions, so the data demonstrate Zeitgeber-time-dependent variation rather than formally proven endogenous circadian regulation. Plasma GCase, moreover, is a clinically accessible readout that may not directly mirror lysosomal enzyme activity inside the brain. Still, the repeated-measures design, the consistency of individual animal trajectories, and the convergence of statistical approaches support the conclusion that the daily pattern is a genuine biological phenomenon rather than a statistical artifact.

The therapeutic implications are tantalizing. If GCase activity follows a daily rhythm and responds to scheduled exercise, then chronotherapy, the optimization of drug dosing and administration timing according to the body’s internal clock, could improve the efficacy of GCase-targeted treatments for GBA1-associated Parkinson’s disease. Exercise scheduling itself might serve as an adjunct strategy, aligning physical activity with the endogenous activity rhythm to support lysosomal function. Future work measuring GCase protein and mRNA levels should clarify the molecular cascade triggered by timed exercise, but the message from Verona is already clear: in the battle against Parkinson’s-linked protein buildup, when you move may matter nearly as much as how much.

Subject of Research: Daily regulation of glucocerebrosidase activity and impact of fixed-time rotarod training in a mouse model of Gba1-associated Parkinson's disease

Article Title: Daily regulation of glucocerebrosidase activity and impact of fixed-time rotarod training in a mouse model of Gba1-associated Parkinson's disease

Article References: Bertasini, C., Tavakolian Haghighi, S., Bruno, M. G., Paio, F., Artusi, C. A., Brunelli, M., Schena, F., Venturelli, M., Moretti, U., Romanelli, M. G., & Paolone, G. (2026). Daily regulation of glucocerebrosidase activity and impact of fixed-time rotarod training in a mouse model of Gba1-associated Parkinson's disease. Frontiers in Cellular Neuroscience, 20, Article 1924016. https://doi.org/10.3389/fncel.2026.1924016

Image Credits: AI Generated

DOI: 10.3389/fncel.2026.1924016

Keywords: Daily, regulation, glucocerebrosidase, activity, impact, fixed-time, rotarod, training, mouse, model, Gba1-associated, Parkinson's