Eukaryotic initiation factor 4E (eIF4E) availability regulates skeletal muscle protein synthesis rates (Ks) following exercise

The purpose of this study was to define the roles of nutrition and hormones in regulating muscle Ks at the level of translation initiation. In particular, we examined the interaction of the mRNA cap binding protein, eIF4E, with the translational inhibitor, 4E-BP1, in mediating the acute modulation of muscle Ks during exercise (Ex) recovery. Male rats were divided into 5 groups: sedentary, fasted [CF]; sedentary, meal-fed [CM]; Ex, fasted [EF]; Ex, fed a 100% carbohydrate meal immediately post-Ex [EC]; Ex, fed a mixed meal (54% CHO, 14% PRO, 12% FAT) immediately post-Ex [EM]. Animals ran for 2 h at 26 m/min and were killed 1 h later. Plasma corticosterone and the Group Insulin Corticoster- Muscle Ks eIF4E·4E-BP1 (% (n=4) (μg/L) one (μg/L) (%/day) total muscle eIF4E) CF 0.4 b 566 b 12.1 ab 5.8 b CM 1.6 a 467 b 13.9 a 5.4 b EF 0.3 b 764 a 9.0 c 22.8 a EC 1.3 a 782 a 9.6 c 13.6 ab EM 1.2 a 357 b 11.7 b 5.0 b Means in a column not sharing the same letter(s) are different (P < 0.02). amount of eIF4E present in the inactive eIF4E·4E-BP1 complex were inversely correlated to muscle Ks (P < 0.01). We are the first to report a relationship between eIF4E availability and muscle Ks following Ex. Our data suggest that muscle protein synthesis recovery is promoted by a combination of increased insulin, low corticosterone and dietary amino acids.