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in
skeletal muscle during sepsis
Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
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 eIF2B
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 eIF2B
-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 eIF2B
, 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 eIF2B
and GSK-3 phosphorylation,
implicating TNF in mediating the effects of sepsis. Thus increased
phosphorylation of eIF2B
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 eIF2B
phosphorylation in vivo.
glycogen synthase kinase-3; protein kinase B; tumor necrosis
factor-binding protein; gastrocnemius; psoas; infection; eukaryotic
initiation factor 2B phosphatase; eIF2B
kinase
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