PNNL

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) are diverse and ubiquitous environmental pollutants associated with adverse human health effects. Many studies focus on the carcinogenic effects of a limited number of PAHs. There is an increasing need to understand the mechanisms of developmental toxicity of more varied yet environmentally relevant PAHs. We applied a systems biology approach in zebrafish to evaluate, classify, and define mechanisms of PAH toxicity. A previous study characterized the bioactivity profiles of 123 PAHs in developing zebrafish. Based on responses ranging from complete inactivity to acute mortality, we classified the PAHs into eight bins, selected 16 representative PAHs, and developmentally exposed zebrafish to the concentration of each PAH that induced 80% phenotypic effect. We conducted RNA sequencing at 48 hours post fertilization (hpf) to identify gene expression changes as a result of PAH exposure. The number of differentially expressed genes (DEGs) correlated with bioactivity and logKOW of the 16 PAHs. Using the Context Likelihood of Relatedness program, we inferred a network that links the PAHs based on coordinated gene responses altered as a function of PAH exposure. The PAHs formed two major clusters: cluster B consisted of PAHs that were generally more bioactive, significantly elevated cyp1a transcript levels, and induced AHR2-dependent Cyp1a protein expression in the skin confirmed by morpholino knockdown studies. Cyp1a expression was associated with transcriptomic response, but not with PAH bioactivity. Despite predominantly activating AHR2, the cluster B PAHs enriched unique pathways which likely points to differing molecular signaling between the PAHs downstream of AHR2.