4-Phenylbutyric acid mitigates polystyrene microplastic-induced hepatotoxicity in zebrafish via modulating the Mettl3-mediated ER stress pathway

Microplastics (MPs), as widespread environmental contaminants, have raised significant concerns regarding their ecological risks in aquatic ecosystems. Their toxicological mechanisms in freshwater organisms are not well studied, with a dearth of potential mitigation strategies. Here, we established a zebrafish ( Danio rerio ) exposure model using polystyrene MPs (5 μm diameter, 1000 ng/L) to systematically investigate their hepatotoxicity mechanisms. After 7 days of exposure, MPs exhibited accumulation in gill, liver, and intestinal tissues, with histopathological evidence confirming substantial disruption of hepatic architecture. Molecular analyses revealed that MPs exposure activated key endoplasmic reticulum (ER) stress markers (GRP78, PERK, IRE1α, ATF6), upregulated pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), and triggered apoptosis-related biomarkers (Caspase 3/9 and Bax), suggesting an ER stress-inflammatory-apoptosis cascade as the underlying mechanism of hepatotoxicity. Intervention with 4-phenylbutyric acid (4-PBA), a canonical ER stress inhibitor, demonstrated its therapeutic potential by targeting Mettl3 to modulate ER stress signaling networks, effectively suppressing MPs-induced inflammatory responses, apoptotic protein expression, and ER ultrastructural damage. This work not only elucidates the molecular basis of MPs-induced hepatotoxicity in freshwater fish through ER stress axis activation but also validates the feasibility of 4-PBA as a target intervention agent, which provides critical insights for ecological risk assessment and bioremediation strategies in aquatic environments contaminated by MPs. • Plastic waste in aquatic ecosystems degrades into microplastics (MPs), which bioaccumulate in fish livers, potentially impairing hepatic functions. • MPs exposure triggers oxidative and endoplasmic reticulum (ER) stress in zebrafish livers, culminating in apoptotic cell death, consistent with prior findings. • The ER stress inhibitor 4-phenylbutyrate (4-PBA) mitigates MPs-induced hepatotoxicity. • Methyltransferase-like 3 (Mettl3) is a potential molecular target of 4-PBA in zebrafish, providing novel mechanistic insights into its hepatoprotective effects.