Gene encoding enzymes in the urea cycle and polyamine synthesis are modulated during an inflammatory response in rainbow trout (Oncorhynchus mykiss)

The urea cycle and the genes encoding the major enzymes is still poorly characterised in teleost fish and to date there is no information as to how these genes are regulated during inflammation. Central to the urea cycle is the metabolism of arginine and its precursor amino acids, ornithine and citrulline. In salmonids, arginine is an essential amino acid as sufficient quantities cannot be synthesised endogenously and must be obtained in the diet. Arginine has roles in both the inflammatory innate immune response and subsequent tissue healing. To further understand the role of the urea cycle and related cycles (polyamine synthesis and nitric oxide production) in teleosts, we characterised gene families encoding the key enzymes in this pathway, their expression during an inflammatory response and changes in the free amino acid levels in the blood plasma following Aeromonas salmonicida challenge. Due to two whole genome duplication events in salmonid evolutionary history, several genes in these pathways have paralogous copies, with divergent expression patterns. The modulation of the genes involved in the urea cycle during inflammation could open up new lines of research for both fish health and nutrition.