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 of materials 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-κB, and the three major MAPK cascades (JNK, p38 and ERK), were activated by rt-lep in in vitro incubations with blood leucocytes of the rainbow trout Oncorhynchus mykiss. We also showed that rt-lep causes a decrease in superoxide anion production in trout blood leucocytes. Thus our data indicate that as in mammals also in teleosts leptin plays pleiotropic activities. Importantly, its actions in fishes do not always conform to the picture emerging for mammals.
Keywords: CD4; CD8; ERK; ERK1/2; IL-12; IL-6; JNK; Leptin; MAPK; NF-κB; Rainbow trout leucocytes; Signaling; Superoxide anion; TNF-α; c-Jun N-terminal kinase; cluster of differentiation 4; cluster of differentiation 8; extracellular signal-regulated kinase 1/2; extracellular-signal-regulated kinase; interleukin 12; interleukin 6; mitogen-activated protein kinases; nuclear factor kappa-light-chain-enhancer of activated B cells; p38 MAP kinase; protein 38 mitogen activated kinase; tumor necrosis factor alpha.
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