title: Gene expression in Atlantic salmon skin in response to infection with the parasitic copepod Lepeophtheirus salmonis, cortisol implant, and their combination.
abstract: BACKGROUND
  The salmon louse is an ectoparasitic copepod that causes major economic losses in the aquaculture industry of Atlantic salmon. This host displays a high level of susceptibility to lice which can be accounted for by several factors including stress. In addition, the parasite itself acts as a potent stressor of the host, and outcomes of infection can depend on biotic and abiotic factors that stimulate production of cortisol. Consequently, examination of responses to infection with this parasite, in addition to stress hormone regulation in Atlantic salmon, is vital for better understanding of the host pathogen interaction.
  
  
  RESULTS
  Atlantic salmon post smolts were organised into four experimental groups: lice + cortisol, lice + placebo, no lice + cortisol, no lice + placebo. Infection levels were equal in both treatments upon termination of the experiment. Gene expression changes in skin were assessed with 21 k oligonucleotide microarray and qPCR at the chalimus stage 18 days post infection at 9°C. The transcriptomic effects of hormone treatment were significantly greater than lice-infection induced changes. Cortisol stimulated expression of genes involved in metabolism of steroids and amino acids, chaperones, responses to oxidative stress and eicosanoid metabolism and suppressed genes related to antigen presentation, B and T cells, antiviral and inflammatory responses. Cortisol and lice equally down-regulated a large panel of motor proteins that can be important for wound contraction. Cortisol also suppressed multiple genes involved in wound healing, parts of which were activated by the parasite. Down-regulation of collagens and other structural proteins was in parallel with the induction of proteinases that degrade extracellular matrix (MMP9 and MMP13). Cortisol reduced expression of genes encoding proteins involved in formation of various tissue structures, regulators of cell differentiation and growth factors.
  
  
  CONCLUSIONS
  These results suggest that cortisol-induced stress does not affect the level of infection of Atlantic salmon with the parasite, however, it may retard repair of skin. The cortisol induced changes are in close concordance with the existing concept of wound healing cascade.
authors.affiliation: Nofima, Norwegian Institute of Food, Fisheries and Aquaculture Research, P,O, Box 5010, Ås N-1430 Bergin, Norway. Aleksei.Krasnov@nofima.no
authors.forename: Aleksei
authors.initials: A
authors.lastname: Krasnov
authors.forename: Stanko
authors.initials: S
authors.lastname: Skugor
authors.forename: Marijana
authors.initials: M
authors.lastname: Todorcevic
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Glover
authors.forename: Frank
authors.initials: F
authors.lastname: Nilsen
mesh_terms: D000818:Animals; D033342:Copepoda / Q000378:metabolism*; D005393:Fish Diseases / Q000235:genetics* / Q000276:immunology / Q000469:parasitology; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D006854:Hydrocortisone / Q000494:pharmacology*; D007249:Inflammation / Q000235:genetics / Q000276:immunology; D053858:Metabolic Networks and Pathways / Q000187:drug effects; D020317:Salmo salar / Q000235:genetics* / Q000276:immunology / Q000469:parasitology; D012867:Skin / Q000276:immunology / Q000378:metabolism* / Q000469:parasitology; D059467:Transcriptome; D014945:Wound Healing / Q000235:genetics / Q000276:immunology
chemical_list: D006854:Hydrocortisone