Adiponectin effects and gene expression in rainbow trout: an in vivo and in vitro approach

Here we present the presence of adiponectin and adiponectin receptors [type 1 (adipoR1) and type 2 (adipoR2)] in rainbow trout (Oncorhynchus mykiss) tissues and cell cultures together with the response to different scenarios. In response to fasting, adiponectin expression was up-regulated in adipose tissue, while the expression of its receptors increased in white and red muscle. Insulin injection decreased adipoR1 expression in white and red muscles. We deduce that the adipoRs in trout muscle show opposite responses to increasing insulin plasma levels, which may maintain sensitivity to insulin in this tissue. Adiponectin expression was inhibited by the inflammatory effect of lipopolysaccharide (LPS) in adipose tissue and red muscle. Moreover, results indicate that LPS may lead to mobilization of fat reserves, increasing adipoR1 expression in adipose tissue. The effects of LPS could be mediated through tumour necrosis factor α (TNFα), at least in red muscle. Insulin, growth hormone and TNFα all diminished expression of adipoR2 in adipocytes and adipoR1 in myotubes, while insulin increased the expression of adipoR2 in the muscle cells. Adiponectin activates Akt in rainbow trout myotubes, which may lead to an increase in fatty acid uptake and oxidation. Overall, our results show that the adiponectin system responds differently to various physiological challenges and that it is hormonally controlled in vivo and in vitro. To the best of our knowledge, this is the first time this has been demonstrated in teleosts, and it may be a valuable contribution to our understanding of adipokines in fish.