Higher insulin sensitivity in EDL muscle of rats fed a low-protein, high-carbohydrate diet inhibits the caspase-3 and ubiquitin-proteasome proteolytic systems but does not increase protein synthesis

• Published in: The Journal of nutritional biochemistry Vol. 34; pp. 89 - 98
• Main Authors: dos Santos, Maísa Pavani, Batistela, Emanuele, Pereira, Mayara Peron, Paula-Gomes, Silvia, Zanon, Neusa Maria, Kettelhut, Isis do Carmo, Karatzaferi, Christina, Andrade, Claudia Marlise Balbinotti, de França, Suélem Aparecida, Baviera, Amanda Martins, Kawashita, Nair Honda
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-08-2016
• Subjects: Animals; Carrier Proteins - genetics; Carrier Proteins - metabolism; Caspase 3 - metabolism; Diet, Carbohydrate Loading - adverse effects; Diet, Protein-Restricted - adverse effects; Down-Regulation; Extensor digitorum longus; Foot; Growing rats; Insulin Resistance; Insulin sensitivity; Low-protein, high-carbohydrate diet; Male; Muscle Development; Muscle, Skeletal - enzymology; Muscle, Skeletal - metabolism; Phosphoproteins - genetics; Phosphoproteins - metabolism; Phosphorylation; Proteasome Endopeptidase Complex - metabolism; Protein Biosynthesis; Protein Processing, Post-Translational; Protein synthesis; Protein Tyrosine Phosphatases - genetics; Protein Tyrosine Phosphatases - metabolism; Proteolysis; Proteolytic pathways; Random Allocation; Rats, Wistar; Ribosomal Protein S6 Kinases, 70-kDa - genetics; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; Ubiquitination; Extensor digitorum longus; Protein synthesis; Insulin sensitivity; Proteolytic pathways; Low-protein, high-carbohydrate diet; Growing rats
• ISSN: 0955-2863; 1873-4847
• DOI: 10.1016/j.jnutbio.2016.04.008

Compared with the extensor digitorum longus (EDL) muscle of control rats (C), the EDL muscle of rats fed a low-protein, high-carbohydrate diet (LPHC) showed a 36% reduction in mass. Muscle mass is determined by the balance between protein synthesis and proteolysis; thus, the aim of this work was to evaluate the components involved in these processes. Compared with the muscle from C rats, the EDL muscle from LPHC diet-fed rats showed a reduction (34%) in the in vitro basal protein synthesis and a 22% reduction in the in vitro basal proteolysis suggesting that the reduction in the mass can be associated with a change in the rate of the two processes. Soon after euthanasia, in the EDL muscles of the rats fed the LPHC diet for 15days, the activity of caspase-3 and that of components of the ubiquitin-proteasome system (atrogin-1 content and chymotrypsin-like activity) were decreased. The phosphorylation of p70S6K and 4E-BP1, proteins involved in protein synthesis, was also decreased. We observed an increase in the insulin-stimulated protein content of p-Akt. Thus, the higher insulin sensitivity in the EDL muscle of LPHC rats seemed to contribute to the lower proteolysis in LPHC rats. However, even with the higher insulin sensitivity, the reduction in p-E4-BP1 and p70S6K indicates a reduction in protein synthesis, showing that factors other than insulin can have a greater effect on the control of protein synthesis.