Characterisation of eicosanoid-regulating genes in Atlantic salmon: insights into the control of pro-inflammatory and anti-inflammatory lipid mediators

Towards addressing infectious disease associated economic losses in the aquaculture sector, nutritional interventions have potential to control inflammation and improve resistance to pathogens. Plant-based oils are increasingly used in salmon feeds as alternatives but are high in omega-6 polyunsaturated acids (PUFAs) with limited marine-derived omega-3 PUFA (DHA and EPA) content. Fatty acids play a central role in the ability of animals to initiate, control, and resolve inflammatory responses via the eicosanoids, potent oxygenated lipid derivatives of PUFAs. Omega-6 FAs are precursors for pro-inflammatory (20-carbon) eicosanoids, whilst omega-3 FAs are anti-inflammatory in promoting the production of eicosanoids important for the resolution of inflammation. The repertoire of genes encoding key enzymes involved in synthesis of salmonid inflammatory lipid mediators is not well characterised in salmonids. Key genes including cyclooxygenase cox, lipoxygenase lox, prostaglandin receptors ptger1, ptger4, and leukotriene receptor ltb4r2 retain duplicated paralogous genes following the salmonid genome duplication (ssWGD). We examined expression of these gene families in head kidney tissue of freshwater stage Atlantic salmon (Salmo salar) parr following immune stimulation with heat-inactivated Vibrio anguillarum to provoke a pro-inflammatory response or Poly I:C which drives an antiviral / interferon response. We identified a significant upregulation in one paralogue of cyclooxygenase, cox2a2, and the receptor paralogue ptger1a1 in Vibrio-stimulated fish. We identified downregulated expression of alox5, ptger4, and ltb4r2 paralogues in response to both Vibrio and Poly I: C. Overall, this research helps towards defining paralogue-specific responses of genes involved with eicosanoid and resolving lipid mediator production and function. These insights can inform future studies aimed at identifying molecular biomarkers and understanding mechanisms of immune regulation in Atlantic salmon.