Leucine Affects α-Amylase Synthesis through PI3K/Akt-mTOR Signaling Pathways in Pancreatic Acinar Cells of Dairy Calves

Abstract

Dietary nutrient utilization, particularly starch, is potentially limited by digestion in dairy cow small intestine because of shortage of α-amylase. Leucine acts as an effective signal molecular in the mTOR signaling pathway, which regulates a series of biological processes, especially protein synthesis. It has been reported that leucine could affect α-amylase synthesis and secretion in ruminant pancreas, but mechanisms have not been elaborated. In this study, pancreatic acinar (PA) cells were used as a model to determine the cellular signal of leucine influence on α-amylase synthesis. PA cells were isolated from newborn Holstein dairy bull calves and cultured in Dulbecco's modifed Eagle's medium/nutrient mixture F12 liquid media containing four leucine treatments (0, 0.23, 0.45, and 0.90 mM, respectively), following α-amylase activity, zymogen granule, and signal pathway factor expression detection. Rapamycin, a specific inhibitor of mTOR, was also applied to PA cells. Results showed that leucine increased ( p < 0.05) synthesis of α-amylase as well as phosphorylation of PI3K, Akt, mTOR, and S6K1 while reduced ( p < 0.05) GCN2 expression. Inhibition of mTOR signaling downregulated the α-amylase synthesis. In addition, the extracellular leucine dosage significantly influenced intracellular metabolism of isoleucine ( p < 0.05). Overall, leucine regulates α-amylase synthesis through promoting the PI3K/Akt-mTOR pathway and reducing the GCN2 pathway in PA cells of dairy calves. These pathways form the signaling network that controls the protein synthesis and metabolism. It would be of great interest in future studies to explore the function of leucine in ruminant nutrition.

Amino acids stimulate glycyl‐tRNA synthetase nuclear localization for mammalian target of rapamycin expression in bovine mammary epithelial cells

“…Thus, we build the in vitro cell culture model that additional amino acids (Met, Leu, or Lys) adding into the culture medium at the selected concentrations (0.6 mM) can significantly promote milk synthesis and activation of the mTOR signaling. The in vitro cell culture models in some literatures are similar to ours (Chen et al, ; Dong et al, ; Guo et al, ; Li et al, ).…”

Review: Nutritional regulation of intestinal starch and protein assimilation in ruminants

“…The milk-fed calf may have differing mechanisms of regulation compared with the previous studies in mature ruminants. However, leucine has been shown to up-regulate pancreatic α-amylase in pancreatic acinar cells isolated from new-born calves and maintained in culture (Guo et al, 2018a). They demonstrated an upregulation of the m-TOR signalling pathway that may have resulted in increased α-amylase synthesis.…”

Leucine‐induced promotion of post‐absorptive EAA utilization and hepatic gluconeogenesis contributes to protein synthesis in skeletal muscle of dairy calves

“…The increase in protein synthesis of LD muscle was mediated by an increase in translation initiation, as indicated by an increased activation of the translation initiation factors, 4E-BP1 and S6K1 (Wilson et al, 2011). The response appeared mediated by enhanced activation of the mTOR signalling pathway, as indicated by enhanced phosphorylation of 4E-BP1 and S6K1, resulting in increased efficiency of mRNA translation and competitively using EAAs for protein synthesis (Anthony et al, 2004;Averous, Gabillard, Seiliez, & Dardevet, 2012;Averous et al, 2016;Guo et al, 2018). Hong and Layman (1984) found that leucine supplementation increased skeletal muscle weight, and others also found that BCAAs increased the LD muscle weight in piglets (Zheng et al, 2016(Zheng et al, , 2017 and promoted skeletal muscle protein synthesis (Zheng et al, 2017).…”