Acute rapamycin treatment improved glucose tolerance through inhibition of hepatic gluconeogenesis in rainbow trout (Oncorhynchus mykiss)

Abstract

Our aim was to investigate the potential role of TOR (target of rapamycin) signaling pathway in the regulation of hepatic glucose metabolism in rainbow trout. Fasted fish were first treated with a single intraperitoneal injection of rapamycin or vehicle and then submitted to a second intraperitoneal administration of glucose 4 h later. Our results revealed that intraperitoneal administration of glucose induced hyperglycemia for both vehicle and rapamycin treatments, which peaked at 2 h. Plasma glucose level in vehicle-treated fish was significantly higher than in rapamycin-treated fish at 8 and 17 h, whereas it remained at the basal level in rapamycin-treated fish. Glucose administration significantly enhanced the phosphorylation of Akt and ribosomal protein S6 kinase (S6K1) in vehicle-treated fish, while rapamycin completely abolished the activation of S6K1 in rapamycin-treated fish, without inhibiting the phosphorylation of Akt on Thr-308 or Ser-473. Despite the lack of significant variation in phosphoenolpyruvate carboxykinase mRNA abundance, mRNA abundance for glucokinase (GK), glucose 6-phosphatase (G6Pase) I and II, and fructose 1,6-bisphosphatase (FBPase) was reduced by rapamycin 17 h after glucose administration. The inhibition effect of rapamycin on GK and FBPase was further substantiated at the activity level. The suppression of GK gene expression and activity by rapamycin provided the first in vivo evidence in fish that glucose regulates hepatic GK gene expression and activity through a TORC1-dependent manner. Unlike in mammals, we observed that acute rapamycin treatment improved glucose tolerance through the inhibition of hepatic gluconeogenesis in rainbow trout.

Hepatic fatty acid biosynthesis is more responsive to protein than carbohydrate in rainbow trout during acute stimulations

“…It is worthy to note that rapamycin markedly decreased plasma glucose levels 8 h after controlled feeding and suppressed the expression of G6Pase I and G6Pase II (data not shown), in line with our previous finding showing that acute rapamycin administration reduced the hyperglycemia induced by intraperitoneal glucose injection via inhibiting hepatic gluconeogenesis at both gene expression and enzyme activity levels in rainbow trout (16). Interestingly, rapamycin also enhanced plasma FAA levels 8 h after controlled feeding.…”

“…Rainbow trout, a relevant carnivorous fish model, which possess relatively high-dietary protein/AAs requirements, poor utilization of dietary carbohydrates, and "glucose-intolerant" phenotype (16), was used as a current research model. To prevent the other nutrient intake changes (except dietary carbohydrate or protein intake), we employed a controlled-feeding method for in vivo studies.…”

Amino Acids Attenuate Insulin Action on Gluconeogenesis and Promote Fatty Acid Biosynthesis via mTORC1 Signaling Pathway in trout Hepatocytes

“…The time intervals were chosen based on the phosphorylation peaks of TOR signaling pathway or relevant metabolic gene expression peaks, respectively (data not shown). [36] were added before being stored the culture dish at -80°C overnight. Then cells were scraped, collected, and lysed on ice for 30 min.…”

“…qRT-PCR was performed as previously described [36]. Quantitative RT-PCR analyses were focused on several key enzymes of hepatic metabolism, which were glucokinase (GK; EC 2.7.1.2), 6-phosphofructo-1-kinase (6PF1K; EC 2.7.1.11), pyruvate kinase (PK; EC 2.7.1.40) and transcription factor hypoxia-inducible factor 1-alpha (HIF-1α) for glycolysis; glucose transporter 2 (GLUT2) for glucose transport ; glucose-6-phosphatase (G6Pase; EC 3.1.3.9) for glucose dephosphorylation; fructose-1,6-bisphosphatase (FBPase; EC 3.…”

Dietary arginine requirement for gibel carp (Carassis auratus gibelio var. CAS III) reduces with fish size from 50g to 150g associated with modulation of genes involved in TOR signaling pathway

“…Dietary arginine supplementation increasing TOR signaling activity was reported in neonatal pigs and rats (Hidetoshiban et al, 2004;Yao et al, 2008). In fish, the nutritional regulation of major kinases involved in the TOR pathway has been elucidated (Lansard et al, 2009(Lansard et al, , 2010Belghit et al, 2013;Dai et al, 2014). Chen et al (2012a) first discovered that dietary arginine increased relative expression of TOR and 4E-BP in tissues and organs in Jian carp Cyprinus carpio var.…”