Binary exposure to hypoxia and perfluorobutane sulfonate disturbs sensory perception and chromatin topography in marine medaka embryos

Perfluorobutane sulfonate (PFBS), an environmental pollutant of emerging concern, is previously shown to dynamically interact with hypoxia on aquatic developmental toxicities. However, the molecular mechanisms underlying the interaction remain unknown. In this follow-up study, marine medaka embryos were exposed to 0 and 3.3 mg/L of PFBS under normoxia (6.9 mg/L) or hypoxia (1.7 mg/L) condition till 15 days post-fertilization. High-throughput transcriptomic sequencing was employed to filter differentially expressed genes and provide mechanistic insight into interactive action between hypoxia and PFBS. The results showed that hypoxia alone and the coexposure paradigm were similarly potent to modify transcriptional profiles, with the majority of genes significantly down-regulated. In contrast, transcriptional toxicity of PFBS was relatively milder. Functional annotation analyses found that hypoxia and coexposure groups mainly impacted phototransduction signaling by decreasing the transcriptions of cyclic nucleotide-gated (CNG) cation channels and retinol transport genes. However, this study demonstrated the first toxicological evidence that toxic effects of PFBS targeted the perception of chemical stimulus through olfactory and gustatory receptors. The addition of PFBS moderately exacerbated the toxic actions of hypoxia, which largely shaped the transcriptional pattern of coexposure group. In addition, gene interactive networks were constructed for hypoxia and coexposure groups, underlining the increased chromatin deacetylation and methylation to epigenetically repress genome-wide transcriptional initiation. Overall, PFBS and hypoxia interact to interrupt the embryonic development of sensory systems, which may compromise the individual fitness and survival, especially during early life stages when precocious perception of food and escape from predators are essential.

Interaction between hypoxia and perfluorobutane sulfonate on developmental toxicity and endocrine disruption in marine medaka embryos

The co-occurrence of hypoxia and xenobiotics is extremely common in natural environments, highlighting the necessity to elicit their interaction on aquatic toxicities. In the present study, marine medaka embryos were exposed to various concentrations (nominal 0, 1, 3.3 and 10 mg/L) of perfluorobutane sulfonate (PFBS), an environmental pollutant of emerging concern, under either normoxia (6.9 mg/L) or hypoxia (1.7 mg/L) condition. After acute exposure till 15 days post-fertilization, single or combined toxicities of PFBS and hypoxia on embryonic development (e.g., mortality, hatching and heartbeat) and endocrine systems were investigated. Sex and thyroid hormones were measured by enzyme-linked immunosorbent assay. Transcriptional changes of endocrine genes were determined by quantitative real-time PCR assays. Co-exposure to 10 mg/L PFBS and hypoxia caused a further reduction in survival rate and heart beat compared to single exposure. PFBS induced a precocious hatching, while no larvae hatched under hypoxia condition. By disturbing the balance of sex hormones, either PFBS or hypoxia single exposure produced an anti-estrogenic activity in medaka larvae. However, PFBS and hypoxia combinations reversed to estrogenic activity in co-exposed larvae. Variation in disrupting pattern may be attributed to the interactive effects on steroidogenic pathway involving diverse cytochrome P450 enzymes. Regarding thyroid system, PFBS exposure caused detriments of multiple processes along thyroidal axis (e.g., feedback regulation, synthesis and transport of thyroid hormones, receptor-mediated signaling and thyroid gland development), while hypoxia potently impaired the development and function of thyroid gland. Combinations of PFBS and hypoxia interacted to dysregulate the function of thyroid endocrine system. In summary, the present study revealed the dynamic interaction of PFBS pollutant and hypoxia on aquatic developmental toxicities and endocrine disruption. Considering the frequent co-occurrence of xenobiotics and hypoxia, current results would be beneficial to improve our understanding about their interactive mechanisms and provide baseline evidences for accurate ecological risk evaluation.