Inhibition of translation initiation by endotoxin and interferon gamma in skeletal muscle cells is nitric oxide synthase (NOS) dependent

Abstract

Excess production of inflammatory mediators during the innate immune response can induce tissue damage, sepsis and shock. Among these mediators nitric oxide (NO) is bactericidal for microorganisms and yet suicidal for the host when in excess. Inflammation inhibits protein synthesis in skeletal muscle but the affect of excess NO on protein synthesis is unknown. The purpose of the present study was to test the hypothesis that endogenous NO negatively affects translation initiation and elongation in C2C12 myotubes. LPS and IFN individually had no affect on protein synthesis but in combination they inhibited protein synthesis by 80%. The combination of LPS and IFN dramatically down regulated the auto-phosphorylation of mTOR and its substrates S6K1 and 4EBP-1. The phosphorylation of ribosomal protein S6 was decreased whereas phosphorylation of elongation factor-2 (eEF-2) was enhanced consistent with defects in both initiation and elongation. Loss of S6 phosphorylation occurred 8–12 h after the addition of LPS and IFN and coincided with a prolonged expression of NOS2 mRNA and protein. Pre-treatment of myotubes with L-NAME prevented the LPS/IFN-induced decrease in protein synthesis and restored signaling downstream of mTOR. The results suggest that LPS and IFN induce NOS-2 which generates excess NO that consequently has a negative affect on translation initiation and elongation in skeletal muscle. (GM38032)