Hao Wang1, Yun Ji1, Guoyao Wu2, Kaiji Sun1, Yuli Sun1, Wei Li1, Bin Wang1, Beibei He1, Qing Zhang1, Zhaolai Dai1, Zhenlong Wu3. 1. State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and. 2. State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and Department of Animal Science, Texas A&M University, College Station, TX. 3. State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and bio2046@hotmail.com.
Abstract
BACKGROUND: Besides serving as a substrate for protein synthesis, L-tryptophan (L-Trp) is used via serotonin-, kynurenine-, and niacin-synthetic pathways to produce bioactive compounds crucial for whole-body homeostasis. It is unknown whether L-Trp itself can regulate metabolic pathways in animal cells. OBJECTIVE: This study tested the hypothesis that L-Trp may activate mammalian target of rapamycin (mTOR) complex 1 and enhance expression of tight junction (TJ) proteins in intestinal porcine epithelial cells. METHODS: Jejunal enterocytes, intestinal porcine epithelial cell line 1 (IPEC-1) isolated from newborn pigs, were cultured in customized Dulbecco's modified Eagle medium (DMEM) supplemented with or without L-Trp for the indicated time periods. Cell proliferation, L-Trp metabolism, protein turnover, mRNA abundance for L-Trp transporters [solute carrier family 3 member 1 (SLC3A1), solute carrier family 6 member 14 (SLC6A14), solute carrier family 6 member 19 (SLC6A19), and Na(+)/K(+) ATPase subunit-α1 (ATP1A1)], abundance of proteins involved in mTOR signaling, and TJ proteins were determined. RESULTS: L-Trp was not degraded in IPEC-1 cells. Compared with basal medium containing 0.04 mmol/L L-Trp, 0.4 and 0.8 mmol/L L-Trp enhanced (P < 0.05) protein synthesis by 45-52% and cell growth by 17% and 25% on day 1 and 72% and 51% on day 2, respectively, while reducing (P < 0.05) protein degradation by 12% and 22%, respectively. These effects of L-Trp were associated with mTOR activation and increased (P < 0.05) mRNA abundance for L-Trp transporters (SLC6A19, SLC6A14, and SLC3A1) by 1.5-2.7 fold and ATP1A1 by 3 fold. L-Trp also upregulated (P < 0.05) the abundance of occludin, claudin-4, zonula occludens (ZO) 1 and 2 by 0.5-2 fold but did not affect expression of claudin-1 or ZO-3 in IPEC-1 cells. CONCLUSION: L-Trp is not catabolized by pig small intestinal epithelial cells but can regulate intracellular protein turnover and expression of TJ proteins in these cells.
BACKGROUND: Besides serving as a substrate for protein synthesis, L-tryptophan (L-Trp) is used via serotonin-, kynurenine-, and niacin-synthetic pathways to produce bioactive compounds crucial for whole-body homeostasis. It is unknown whether L-Trp itself can regulate metabolic pathways in animal cells. OBJECTIVE: This study tested the hypothesis that L-Trp may activate mammalian target of rapamycin (mTOR) complex 1 and enhance expression of tight junction (TJ) proteins in intestinal porcine epithelial cells. METHODS: Jejunal enterocytes, intestinal porcine epithelial cell line 1 (IPEC-1) isolated from newborn pigs, were cultured in customized Dulbecco's modified Eagle medium (DMEM) supplemented with or without L-Trp for the indicated time periods. Cell proliferation, L-Trp metabolism, protein turnover, mRNA abundance for L-Trp transporters [solute carrier family 3 member 1 (SLC3A1), solute carrier family 6 member 14 (SLC6A14), solute carrier family 6 member 19 (SLC6A19), and Na(+)/K(+) ATPase subunit-α1 (ATP1A1)], abundance of proteins involved in mTOR signaling, and TJ proteins were determined. RESULTS:L-Trp was not degraded in IPEC-1 cells. Compared with basal medium containing 0.04 mmol/L L-Trp, 0.4 and 0.8 mmol/L L-Trp enhanced (P < 0.05) protein synthesis by 45-52% and cell growth by 17% and 25% on day 1 and 72% and 51% on day 2, respectively, while reducing (P < 0.05) protein degradation by 12% and 22%, respectively. These effects of L-Trp were associated with mTOR activation and increased (P < 0.05) mRNA abundance for L-Trp transporters (SLC6A19, SLC6A14, and SLC3A1) by 1.5-2.7 fold and ATP1A1 by 3 fold. L-Trp also upregulated (P < 0.05) the abundance of occludin, claudin-4, zonula occludens (ZO) 1 and 2 by 0.5-2 fold but did not affect expression of claudin-1 or ZO-3 in IPEC-1 cells. CONCLUSION:L-Trp is not catabolized by pig small intestinal epithelial cells but can regulate intracellular protein turnover and expression of TJ proteins in these cells.
Authors: Richard D Semba; Indi Trehan; Marta Gonzalez-Freire; Klaus Kraemer; Ruin Moaddel; M Isabel Ordiz; Luigi Ferrucci; Mark J Manary Journal: Adv Nutr Date: 2016-09-15 Impact factor: 8.701