Analysis of the effects of emerging contaminants on the bottlenose dolphin (Tursiops truncatus) skin transcriptome: development of potential biomarkers

Chemical pollution represents one of the main threats for the marine ecosystem conservation. Persistent chemicals can bioaccumulate and biomagnify through the food web, leading to higher levels of exposure in predator species such as fish, cetaceans and humans.1,2 Among the emerging chemical contaminants are perfluorooctanoic acid (PFOA), used to make fluoropolymers, and bisphenol A (BPA), a monomer used in epoxy resins and polycarbonate plastics, present in many hard plastic bottles and metal-based food storage. BPA and PFOA are worldwide distributed compounds and are considered dangerous factors because of their agonist or antagonist effects on the endocrine receptors.3,4 Here, we applied an ex vivo assay using skin biopsy slices from the common bottlenose dolphin (Tursiops truncatus) combined with global gene expression analysis in response to BPA or PFOA chemical exposure.5,6 The skin was collected from a stranded dolphin on the coast of Tuscany. Right after death, small slices of skin biopsy were excised, cultured and independently treated with different concentrations of BPA or PFOA (0.1, 1, and 10 mg/ml). RNA from the different treatments was extracted and hybridized to species-specific custom-made microarray. Genes involved in the activation of immune response, endocrine pathways, lipid homeostasis and adipogenesis pathways were among the genes found to be differentially expressed. The expression of 7 significantly regulated genes was quantified through quantitative real time-PCR to validate the microarray results. The genes were also tested for their potential role of biomarkers of emerging contaminant exposure. Expression levels of 3 genes (BCAP31, MTSS1 and CDC42α) were also quantified on the skin transcriptome of three live cetaceans (Grampus griseus, Stenella coeruleoalba, Balaenoptera physalus) sampled in the Pelagos Sanctuary off the coast of Ligurian and Thyrrenian (Mediterranean Sea) seas on September 2014. Despite the small set analyzed, we could observe major difference in the expression of these genes between the toothed whale (Odontoceti) and the baleen whales (Mysticeti). Balaenoptera physalus showed level of expression much greater than the toothed whales (G. griseus and S. coeruleoalba) for the 3 genes tested: 34.53 fold for BCAP31, 20.53 fold for CDC42α, and 54.48 fold for MTSS1. This difference could be inferred to the different feeding methods and subsequent contaminant accumulation between Odontoceti and Mysticeti, as previously suggested.7 Deeper analysis on a broader group of animals sampled from different contaminated areas is needed in order to better understand genes and pathways mostly affected by emerging contaminants, which will lead to a selection of species-specific biomarkers of exposure.