Preliminary exploration of transcriptomic responses to cortisol, POPs and their combination in primary Arctic pilot whale fibroblasts

Details

Supervisors

Debier, Cathy ; Van Essche, Maud

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

enPilot whales (Globicephala melas), inhabiting Arctic and sub Arctic waters, are increasingly exposed to climate‑driven environmental change as well as other anthropogenic stressors, including pollution and noise. Such pressures can disrupt hormonal balance and elevate circulating stress hormones, such as glucocorticoids (e.g., cortisol), whose chronic release is associated with adverse health effects. As high-level predators, pilot whales also accumulate exceptionally elevated levels of persistent organic pollutants (POPs), positioning them among the most contaminated marine mammals worldwide. Yet, the combined effects of chemical pollutants and physiological stress remain poorly understood in cetaceans. In this context, cell cultures and in vitro exposure systems offer a relevant framework to investigate the impacts of multiple environmental stressors alone and in combination. Using minimally invasive methods, primary fibroblast cultures were derived from skin biopsies collected from free‑ranging pilot whales in Norwegian waters. These cultures were then used to investigate the global transcriptional responses to cortisol and POPs, alone or in combination, in pilot whale cells. Different concentrations of (i) cortisol (CORT), (ii) a POP mixture, and (iii) a combination of the POP mixture and cortisol (POPs-CORT) were tested to draw a dose response curve and assess sub-lethal concentrations ((i) 2.5x POPs, (ii) 2 µM cortisol, (iii) 2.5x POPs + 2 µM cortisol) for downstream analyses. Subsequently, the global transcriptional responses of cells exposed to these sublethal concentrations were studied using an unbiased transcriptomic approach based on RNA sequencing (RNA-seq). Viability assays revealed that, under the combined conditions, cortisol did not significantly alter the cytotoxic response to POPs. Bioinformatic analyses of RNA-seq data indicated that a total of 723 genes were differentially expressed across the three conditions, including 302 genes uniquely regulated by a single treatment (136 for CORT, 9 for POPs, and 157 for POPs-CORT), 200 shared between two conditions (6 for CORT and POPs, 13 for POPs and POPs-CORT, and 181 for CORT and POPs-CORT), and 10 common to all three. Overall, the POPs condition displays the highest similarity to the control condition, whereas CORT and POPs-CORT conditions induce broader transcriptional shifts, though not necessarily through the same genes. Furthermore, although the POPs-CORT condition showed the highest number of DEG, there was no evidence of a clear interaction between the two stressors. These findings suggest that CORT and POPs co-exposure does not induce strong synergistic effects at the cytotoxic or transcriptomic levels, although the underlying molecular pathways and interaction types require further investigation. The results of the present study highlight cause-and-effect relationships, contributing to a better understanding of the impacts of multiple stressors on marine mammal physiology, an essential aspect for conservation efforts.