Disruption of genes encoding eIF4E binding proteins-1 and -2 does not alter basal or sepsis-induced changes in skeletal muscle protein synthesis in male or female mice.

Lyle L Moldawer,Maithili Navaratnarajah,Anne M Pruznak,Scot R Kimball,Gina Deiter,Charles H Lang,Lydia Kutzler,Jennifer L Steiner

doi:10.1371/journal.pone.0099582

Lyle L Moldawer, Maithili Navaratnarajah + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0099582

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Journal: PloS one	Publication Date: Jun 19, 2014
Citations: 14	License type: CC BY 4.0

Affiliation: Penn State Milton S. Hershey Medical Center

Abstract

Sepsis decreases skeletal muscle protein synthesis in part by impairing mTOR activity and the subsequent phosphorylation of 4E-BP1 and S6K1 thereby controlling translation initiation; however, the relative importance of changes in these two downstream substrates is unknown. The role of 4E-BP1 (and -BP2) in regulating muscle protein synthesis was assessed in wild-type (WT) and 4E-BP1/BP2 double knockout (DKO) male mice under basal conditions and in response to sepsis. At 12 months of age, body weight, lean body mass and energy expenditure did not differ between WT and DKO mice. Moreover, in vivo rates of protein synthesis in gastrocnemius, heart and liver did not differ between DKO and WT mice. Sepsis decreased skeletal muscle protein synthesis and S6K1 phosphorylation in WT and DKO male mice to a similar extent. Sepsis only decreased 4E-BP1 phosphorylation in WT mice as no 4E-BP1/BP2 protein was detected in muscle from DKO mice. Sepsis decreased the binding of eIF4G to eIF4E in WT mice; however, eIF4E•eIF4G binding was not altered in DKO mice under either basal or septic conditions. A comparable sepsis-induced increase in eIF4B phosphorylation was seen in both WT and DKO mice. eEF2 phosphorylation was similarly increased in muscle from WT septic mice and both control and septic DKO mice, compared to WT control values. The sepsis-induced increase in muscle MuRF1 and atrogin-1 (markers of proteolysis) as well as TNFα and IL-6 (inflammatory cytokines) mRNA was greater in DKO than WT mice. The sepsis-induced decrease in myocardial and hepatic protein synthesis did not differ between WT and DKO mice. These data suggest overall basal protein balance and synthesis is maintained in muscle of mice lacking both 4E-BP1/BP2 and that sepsis-induced changes in mTOR signaling may be mediated by a down-stream mechanism independent of 4E-BP1 phosphorylation and eIF4E•eIF4G binding.

Highlights

The loss of skeletal muscle and lean body mass (LBM) is a central feature of septic and critically ill patients [1,2]
The absolute whole body mass as well as the LBM and fat mass all increased from 1 month to 12 months of age (P,0.05, ANOVA repeated measures) for both male and female WT and double knockout (DKO) mice
Body weight and LBM did not differ between WT and DKO at any time point examined for either male (Figure 1A and 1C, respectively) or female (Figure 1B and 1D, respectively) mice; fat mass was increased in DKO at 12 months of age in both male and female mice (Figure 1E and 1F)

Summary

Introduction

The loss of skeletal muscle and lean body mass (LBM) is a central feature of septic and critically ill patients [1,2]. This cachexic state is noteworthy as it is associated with increased complications and delayed recovery from sepsis [3,4] as well as increased mortality [5,6]. Infection in general and bacterial products and inflammatory mediators in particular produce an anabolic resistance to hormonal- and nutrient-stimulated increases in protein synthesis [9,10,11]. The ability of sepsis and LPS from the cell wall of gramnegative bacteria to stimulate the local and systemic production of inflammatory mediators [tumor necrosis factor-alpha (TNFa), interleukin (IL)-6, nitric oxide synthase (NOS)-2] and/or reduce anabolic stimuli [e.g., insulin-like growth factor (IGF)-I] appears central to mTOR inhibition [9,15,16,17,18,19]

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