Deciphering the TLR-mediated immunotoxic adverse outcome pathway of pentachlorophenol in marine medaka (Oryzias melastigma)

Pentachlorophenol (PCP) is a persistent organic pollutant commonly detected in marine environments, and recent studies have confirmed its adverse effects on the immune systems of aquatic organisms. However, the potential molecular mechanisms of action and subsequent downstream damage caused by PCP remain unclear. This study employed transcriptomics, metabolomics, biochemical and histopathological analyses, and molecular dynamics simulations to explore the immunotoxic effects and associated downstream damage induced by PCP in marine medaka ( Oryzias melastigma ). The results indicated that PCP at environmentally relevant concentrations (1 and 10 μg/L) activates the Toll-like receptor (TLR) signaling pathway, significantly upregulating the expression levels of pro-inflammatory cytokines and triggering inflammatory responses. Using the adverse outcome pathway (AOP) analysis framework, the binding of PCP to TLR5 was identified as the molecular initiating event. This event triggers a series of key events, activation of the TLR signaling pathway, an enhanced inflammatory response, increased oxidative stress levels, disrupted amino acid metabolism, and liver injury, ultimately leading to impaired immune system function (adverse outcome). This study establishes the mechanistic linkage between TLR5 and metabolic dysfunction in PCP immunotoxicity, providing novel toxicological insights and theoretical support for the ecological risk assessment of PCP and related marine pollutants. • PCP at environmentally relevant concentrations causes immunotoxicity in marine medaka. • Binding of PCP to TLR5 activates TLR signaling as the molecular initiating event. • TLR-driven key event triggers subsequent oxidative stress and metabolic disruption. • AOP framework of PCP immunotoxicity clarifies causal chains from MIE to liver damage.