Rotenone exposure in zebrafish Parkinson's disease model reveals NURR1-TOP2B dysregulation and gut-brain axis-associated pathology.

Parkinson's disease (PD) is a progressive neurodegenerative disorder in which early gastrointestinal dysfunction and oxidative stress are increasingly implicated through the gut-brain axis. Zebrafish (Danio rerio) offer a tractable model for PD research; However, to our knowledge, there is currently no consensus on the rotenone concentration that effectively mimics both brain and gut pathology, leaving the dose required to induce integrated central-peripheral pathology unresolved. Adult zebrafish were exposed to 2.5 or 5 µg/L rotenone for 28 days, and behavioral, biochemical, histological, and transcriptional changes were assessed in the brain and intestine. Rotenone induced concentration-dependent impairments in locomotion, anxiety-like behavior, and cognition, with pronounced deficits at 5 µg/L. Histopathological damage in both the brain and intestine was observed at 2.5 & 5 µg/L. Oxidative stress was evident, with elevated reactive oxygen species (ROS) levels in the brain at both concentrations and in the intestine only at 5 µg/L, accompanied by increased lipid peroxidation (LPO) at the higher concentration. Antioxidant enzyme activities, including superoxide dismutase (SOD) and glutathione peroxidase (GPx), were significantly disrupted. Transcriptional analysis revealed upregulation of γ1-synuclein and top2b alongside downregulation of nr4a2a (Nurr1) in both tissues. Pro-inflammatory cytokines il6 and tnfa were also markedly elevated. In conclusion, these findings establish 5 µg/L rotenone as an optimized exposure for inducing reproducible, systemically integrated PD-like pathology in zebrafish and underscore NURR1-TOP2B dysregulation as a molecular correlate of gut-brain axis-associated dysfunction.