Effects of recombinant trout leptin in superoxide production andNF-B/MAPK phosphorylation in blood leukocytes

Studies in mammals indicate that leptin is a multifunctional cytokine involved in regulation of energy metabolism and the modulation of the immune function. However, evidence for an immunomodulatory effect of leptin in fish is still missing. At least in part, this lack of knowledge is due to the absence ofmaterials and models. In this study, we produced trout recombinant leptin (rt-lep) and tested its capacity to trigger cellular pathways, usually active in mammal immune system cells. STAT3, NF-B, and the threemajor MAPK cascades (JNK, p38 and ERK), were activated by rt-lep in in vitro incubations with bloodleucocytes of the rainbow trout Oncorhynchus mykiss. We also showed that rt-lep causes a decrease insuperoxide anion production in trout blood leucocytes. Thus our data indicate that as in mammals alsoin teleosts leptin plays pleiotropic activities. Importantly, its actions in fishes do not always conform to the picture emerging for mammals.