The modulation of mTOR signaling on dietary carbohydrate utilization in largemouth bass (Micropterus salmoides)

Glucose intolerance is prevalent in teleost fish species, making them prone to dietary carbohydrate-induced fatty liver disease. However, the underlying mechanism is not well understood. In the present study, the possible role of mTOR signaling in the regulation of glucose metabolism was examined in largemouth bass (Micropterus salmoides), an economically important carnivorous aquaculture species. An 8-wk feeding trial was conducted with largemouth bass, in which they were fed different isonitrogenous and isolipidic diets supplemented with leucine (Leu), rapamycin (Rap), or an mTOR activator (mTOR-S). The results demonstrated that mTOR stimulation significantly enhanced the growth performance and feed utilization, while mTOR inhibition had the opposite effect in largemouth bass. More importantly, mTOR stimulation significantly reduced plasma glucose levels and concomitantly increased insulin levels. Furthermore, mTOR stimulation increased glycolysis and TCA cycle activities, augmented hepatic ATP levels and suppressed AMPK phosphorylation. Accordingly, mTOR stimulation also reduced SREBP1 activity, decreased hepatic lipid content and increased glycogen content. These results demonstrated that mTOR stimulation could promote postprandial glucose utilization in largemouth bass. This could provide a new strategy for improving dietary carbohydrate tolerance in aquaculture feed formulation.