Arginine activates intestinal p70(S6k) and protein synthesis in piglet rotavirus enteritis

We previously showed that phosphorylation of p70 S6 kinase (p70(S6k)) in the intestine is increased during viral enteritis. In this study, we hypothesized that during rotavirus infection, oral Arg, which stimulates p70(S6k) activation, will further stimulate intestinal protein synthesis and mucosal recovery, whereas the p70(S6k) inhibitor rapamycin (Rapa) will inhibit mucosal recovery. Newborn piglets were fed a standard milk replacer diet supplemented with Arg (0.4 g x kg(-1) x d(-1), twice daily by gavage), Rapa (2 mg x m(-2) x d(-1)), Arg + Rapa, or saline (controls). They were infected on d 6 of life with porcine rotavirus. Three days postinoculation, we measured the piglets' body weight, fecal rotavirus excretion, villus-crypt morphology, epithelial electrical resistance in Ussing chambers, and p70(S6k) activation by Western blotting and immunohistochemistry. We previously showed a 2-fold increase in jejunal protein synthesis during rotavirus diarrhea. In this experiment, Arg stimulated jejunal protein synthesis 1.3-fold above standard medium, and the Arg stimulation was partially inhibited by Rapa. Small bowel stimulation of p70(S6k) phosphorylation and p70(S6k) levels were inhibited >80% by Rapa. Immunohistochemistry revealed a major increase of p70(S6k) and ribosomal protein S6 phosphorylation in the crypt and lower villus of the infected piglets. However, in Arg-treated piglets, p70(S6k) activation occurred over the entire villus. Jejunal villi of the Rapa-treated group showed inactivation of p70(S6k) and a decrease in mucosal resistance (reflecting increased permeability), the latter of which was reversed by Arg. We conclude that, early in rotavirus enteritis, Arg has no impact on diarrhea but augments intestinal protein synthesis in part by p70(S6k) stimulation, while improving intestinal permeability via a mammalian target of rapamycin/p70(S6k)-independent mechanism.