Breeding selection of rainbow trout for high or low muscle adiposity differentially affects lipogenic capacity and lipid mobilization strategies to cope with food deprivation

The present study evaluates the transcriptional regulation of lipid metabolism, adiponectin system and oxidative stress genes in two rainbow trout lines selected over seven generations for low (lean line, LL) or high (fat line, FL) muscle adiposity, and subjected to different fasting regimes. Under feeding conditions, FL fish had higher muscle lipid content, plasma triglycerides (TG) and non-esterified fatty acids (NEFAs) than the LL fish. Besides, FL fish had higher fatty acid synthase (fasn) mRNA levels in adipose tissue (AT) and white muscle (WM), and higher lipoprotein lipase (lpl) mRNA levels in WM, suggesting an increased lipogenic capacity and fatty acid uptake in the fatty genotype. In response to fasting, the two fish lines displayed a different trend in muscle lipid mobilization, plasma TG levels changes and lipid metabolism-related genes expression patterns. There were different fasn expression profiles between the fish lines in both, AT and WM, in agreement with the changes observed in plasma TG levels. The FL fish had higher adiponectin receptor 2 mRNA levels in WM and adiponectin mRNA levels in AT than LL fish after 1 and 4 weeks of fasting respectively, indicating a difference between genotypes in the adiponectin system. Furthermore, oxidative stress genes mRNA levels in both fish lines showed a different pattern between AT and WM upon fasting, probably indicating a higher protective effect in WM. Overall, the present study reveals a distinct metabolic regulation for each genotype, highlighting their different strategies in response to food deprivation.