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Phosphorylation of eukaryotic initiation factor eIF2Bepsilon in skeletal muscle during sepsis
Thomas C Vary1, Gina Deiter, Scot R Kimball
1Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA. tvary@psu.edu
Abstract:
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 eIF2Bepsilon 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 eIF2Bepsilon-Ser(535) 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 eIF2Bepsilon, 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 approximately 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 eIF2Bepsilon and GSK-3 phosphorylation, implicating TNF in mediating the effects of sepsis. Thus increased phosphorylation of eIF2Bepsilon 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 eIF2Bepsilon phosphorylation in vivo.
Insights
Sepsis inhibits skeletal muscle protein synthesis by increasing eukaryotic initiation factor 2B (eIF2B) phosphorylation. This study demonstrates that glycogen synthase kinase-3 (GSK-3) activation mediates this sepsis-induced eIF2B modification in vivo.
Area of Science:
- Biochemistry
- Molecular Biology
- Physiology
Background:
- Sepsis leads to decreased protein synthesis in skeletal muscle.
- Reduced eukaryotic initiation factor 2B (eIF2B) activity is linked to this inhibition.
- The specific mechanisms of eIF2B regulation during sepsis require further elucidation.
Purpose of the Study:
- To investigate the changes in eIF2Bepsilon phosphorylation in skeletal muscle during sepsis.
- To identify the upstream kinases involved in sepsis-induced eIF2Bepsilon phosphorylation.
- To determine the role of tumor necrosis factor (TNF) in mediating these effects.
Main Methods:
- Measurement of eIF2B kinase and phosphatase activity in gastrocnemius muscle of septic rats.
- Analysis of eIF2Bepsilon and glycogen synthase kinase-3 (GSK-3) phosphorylation levels via Western blotting.
- Assessment of protein kinase B (PKB) phosphorylation.
- Evaluation of the effects of TNF-binding protein treatment on phosphorylation patterns.
Main Results:
- Sepsis significantly increased eIF2B kinase activity and eIF2Bepsilon phosphorylation.
- GSK-3 phosphorylation was reduced, while its activity was increased, suggesting it mediates eIF2Bepsilon phosphorylation.
- PKB phosphorylation was reduced on day 3 post-infection.
- TNF-binding protein treatment attenuated the sepsis-induced changes in eIF2Bepsilon and GSK-3 phosphorylation.
Conclusions:
- Increased phosphorylation of eIF2Bepsilon, mediated by GSK-3 activation, is a key mechanism for inhibiting skeletal muscle protein synthesis during sepsis.
- This study provides the first in vivo evidence of altered eIF2Bepsilon phosphorylation during sepsis.
- TNF plays a significant role in mediating sepsis-induced changes in eIF2Bepsilon and GSK-3 phosphorylation.