DIETARY COD PROTEIN IMPROVES THE IGF1-AKT/PKB SIGNALING PATHWAY IN RAT SKELETAL MUSCLE DURING RECOVERY FROM INJURY

The objective of this study was to identify molecular mechanisms underlying the beneficial effects of cod protein feeding on skeletal muscle recovery through detailed analyses of the IGF1-Akt/PKB signaling pathway. Acute mucle injury was induced by injecting bupivacaine in one tibialis anterior of Wistar rats fed isoenergetic diets containing either casein (C), cod protein (CP), or casein supplemented with a mixture of arginine, glycine, taurine and lysine (C+), matching their respective levels as in CP; downstream IGF1-Akt/PKB (protein kinase B) effectors were measured post-injury. Rats fed the CP-diet exhibited a 50% reduction of the muscle ring finger1 (MuRF1) level compared with those fed the C-diet (p=0.01), while the reduction induced by the C+-diet was intermediary to, but did not differ significantly (p=0.07) from the C-diet at day 2 post-injury. These findings indicate a decrease in the ubiquitination of muscle proteins and their degradation in the CP-group partly because of its high levels of arginine, glycine, taurine and lysine. Futhermore, phospho-Akt Ser473, a phosphorylation required for maximum activation of Akt, was increased in the CP-group at day 5 (p<0.0001) and day 28 post-injury (p=0.002) compared with C, and at day 5 compared with C+ (p=0.0005). The phosphorylated form of GSK-3 was also increased with CP feeding at day 28 post-injury compared with C (p=0.05), suggesting enhanced protein synthesis in the CP group. C+ enhanced phospho-Akt Ser473 compared with C (p=0.008) only at day 28 post-injury, with no effect on GSK-3 phosphorylation. Therefore, CP may reduce protein degradation induced by muscle injury through early modulation of the ubiquitination process, while enhancing muscle protein synthesis through Akt phosphorylation at later time points.