Arginine‐Mediated Stimulation of Intestinal Epithelial Cell Protein Synthesis Is mTOR‐Dependent But NO‐Independent

Abstract

Arginine (ARG) is an indispensable amino acid in neonates and required for growth. Evidence indicates that intestinal epithelial cells (IEC) are capable of ARG transport, catabolism and synthesis, and express nitric oxide synthase (NOS) to produce NO from ARG. Our aim was to determine whether ARG directly stimulates IEC proliferation, survival and protein synthesis and whether this effect is NO‐dependent and mediated via mammalian target of rapamycin (mTOR). Neonatal porcine IEC (IPEC‐J2) were cultured in a serum‐free Dulbecco's Modified Eagles Medium (DMEM) without ARG. After 4‐d incubation, we found an increase in cell number (+175%), cell protein (+75%) and DNA content (+50%) with a maximal response at a physiological dose of ARG (0.1 mM). The expression of inducible NOS in IPEC‐J2 cells was confirmed by western blot. The ARG‐induced protein synthesis response was not inhibited by NO inhibitors (L‐NAME or aminoguanidine). Protein synthesis was not increased by addition of a NO donor (SNAP) or the ARG precursor, proline in absence of ARG. However, ARG‐induced protein synthesis was markedly decrease (‐40%) by rapamycin, an inhibitor of mTOR. We also found ARG (0.5 mM) increased phospho and total mTOR and p70S6 kinase level in IPEC‐J2 cells. We conclude that ARG‐mediated stimulation of IEC protein synthesis is m‐TOR‐dependent but NO‐independent. (Funded by Ajinomoto Amino Acid Research Program).