L-Tryptophan Activates Mammalian Target of Rapamycin and Enhances Expression of Tight Junction Proteins in Intestinal Porcine Epithelial Cells

卷:145

Wang, Hao ; Ji, Yun ; Wu, Guoyao ; Sun, Kaiji ; Sun, Yuli ; Li, Wei ; Wang, Bin ; He, Beibei ; Zhang, Qing ; Dai, Zhaolai ; Wu, Zhenlong

关键词: tryptophan;    cell proliferation;    mammalian target of rapamycin;    tight junction;    intestinal epithelial cells;    pig;   

DOI  :  10.3945/jn.114.209817

学科分类：食品科学和技术

【 摘 要 】

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-alpha 1 (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.