Phosphorylation of eukaryotic initiation factor eIF2Bε in skeletal muscle during sepsis

We reported that the inhibition of protein synthesis in skeletal muscle during sepsis correlated with reduced eukaryotic initiation factor eIF2B activity. The present studies define changes in eIF2Bε phosphorylation in gastrocnemius of septic animals. eIF2B kinase activity was significantly elevated 175% by sepsis compared with sterile inflammation, whereas eIF2B phosphatase activity was unaffected. Phosphorylation of eIF2Bε-Ser⁵³⁵ was significantly augmented over 2-fold and 2.5-fold after 3 and 5 days and returned to control values after 10 days of sepsis. Phosphorylation of glycogen synthase kinase-3 (GSK-3), a potential upstream kinase responsible for the elevated phosphorylation of eIF2Bε, was significantly reduced over 36 and 41% after 3 and 5 days and returned to control values after 10 days of sepsis. The phosphorylation of PKB, a kinase thought to directly phosphorylate and inactivate GSK-3, was significantly reduced ∼50% on day 3, but not on days 5 or 10, postinfection compared with controls. Treatment of septic rats with TNF-binding protein prevented the sepsis-induced changes in eIF2Bε and GSK-3 phosphorylation, implicating TNF in mediating the effects of sepsis. Thus increased phosphorylation of eIF2Bε via activation of GSK-3 is an important mechanism to account for the inhibition of skeletal muscle protein synthesis during sepsis. Furthermore, the study presents the first demonstration of changes in eIF2Bε phosphorylation in vivo.