mRNA expression of fatty acid transporters in rainbow trout: in vivo and in vitro regulation by insulin, fasting and inflammation and infection mediators.

In the present study, we analyzed endocrine and nutritional regulation of fatty acid (FA) transporters mRNA expression fatty acid transport protein (FATP1) and fatty acid translocase (CD36) in rainbow trout in vivo and in adipocytes and myocytes in vitro. The expression of FATP1 increased with adipocyte and that of CD36 with myocyte in vitro differentiation suggesting a different role for each transporter during the two cell differentiation programs. Food deprivation (15, 25 and 35 days) increased FATP1 and CD36 mRNA expression in white muscle, red muscle and adipose tissue while insulin administration decreased the FATP1 expression in adipose tissue in vivo (21.6 pmol/g body mass) and in vitro (1 μM) in adipocytes. In trout myotubes insulin (1 μM) decreased FATP1 and increased CD36 mRNA expression. Thus, regulation of FA transporters expression by insulin is complex and directed to specific tissue needs. Although FATP1 and CD36 mRNA levels are controlled by insulin, it appears that FATP1 respond more clearly to situations of hyper and hypo-insulinemia in trout muscle and adipose tissue than CD36. FATP1 and CD36 transcription was also modulated by growth hormone in cultured myotubes and isolated adipocytes. Lipopolysaccharide administration (E. coli, serotype O26:B6, 6 μg/g body mass) decreased FATP1 mRNA expression in red muscle, adipose tissue and liver after 24h according to changes in lipid metabolism during infection. Tumor necrosis factor (TNFα) (100 ng/ml) reduced FATP1 expression in isolated adipocytes. Further, insulin (1μM) and IGF-I (100 nM) increased the FA uptake in rainbow trout myotubes through the PI3K/Akt signaling pathway. Overall, we demonstrated not only that feeding condition regulates FATP1 and CD36 mRNA expression in a tissue-specific manner, but also that insulin is an important regulator of these genes in vivo and in vitro and also it stimulates FA uptake in trout muscle cells.