mTOR SIGNALING IS A COMPONENT OF INTESTINAL REPAIR IN PIGLET ROTAVIRUS ENTERITIS:

Recent identification of the mTOR pathway as a key regulator of amino acid sensing, mRNA translation, and protein synthesis led us to investigate its role in viral diarrhea. We hypothesized that during rotavirus enteritis, malnutrition would reduce jejunal protein synthetic rate and mTOR signaling via its immediate downstream target, ribosomal p70 s6 kinase (p70s6k). Methods: Newborn Yorkshire piglets were artificially fed from birth and half were infected with porcine rotavirus on d5 of life. Study groups included controls, infected, infected/50% protein-calorie malnourished, and infected and treated with arginine (ARG, 0.3 g/kg/d) and/or rapamycin (1 mg/m2). Results: At the peak of diarrhea (on days 3 and 5 post-inoculation), western blotting revealed four-fold induction of p70s6k phosphorylation and p70s6k level (p < 0.05) compared with uninfected tissue. In vitro jejunal protein synthetic rate increased 2-fold (p < 0.05) during infection. Malnutrition did not alter the level of p70s6k activation or the increase in gut permeability caused by infection. Immunolocalization revealed that infection produced a major induction of cytoplasmic p70s6k and of nuclear phospho-p70s6k in the crypt and lower villus. In vitro jejunal protein synthesis and p70s6k phosphorylation increased 3-fold in response to L-arginine. In vivo, rapamycin treatment of infected piglets increased gut permeability 2.5-fold, while ARG reversed the rapamycin effect, did not impact the diarrhea, and enhanced staining of phosphorylated p70s6k and ribosomal protein S6 over the entire villus epithelium. Conclusions: Rotavirus infection resulted in increased jejunal protein synthesis and activation of mTOR in the crypt. Intestinal activity of mTOR/p70s6k was not influenced by malnutrition, but was enhanced by ARG.