Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/17/2013
Publication Date: 8/5/2013
Publication URL: http://handle.nal.usda.gov/10113/58085
Citation: Carbone, J.W., Margolis, L.M., Mcclung, J.P., Cao, J.J., Murphy, N.E., Sauter, E.R., Combs, G.F., Young, A.J., Pasiakos, S.M. 2013. Effects of energy deficit, dietary protein, and feeding on intracellular regulators of skeletal muscle proteolysis. Journal of Federation of American Societies for Experimental Biology. 27(12):5104-5111. Interpretive Summary: Energy deficit, in general, decreases total body and skeletal muscle mass. We demonstrated previously that consuming dietary protein at levels twice and three times the current RDA preserved lean body mass in response to short-term energy deficit. This study further examined effects of levels of dietary protein during short-term energy deficit on proteolysis and associated gene expression in normal-weight adults. Thirty-two men and 7 women participated in the study. Volunteers consumed diets providing protein at 0.8, 1.6, or 2.4g·kg-1·d-1 for 31 days in a randomized-block design. Ten days of weight maintenance (days 1-10) preceded 21 days of energy deficit (days 11-31), during which total daily energy deficit was 40% achieved by reduced dietary energy intake (~30%) and increased physical activity (~10%). Muscle biopsy samples were collected during weight maintenance (day 10) and energy deficit (day 31) under fasted and fed conditions. Results showed that energy deficit upregulated ubiquitin proteasome system associated gene expression in fasted conditions with mRNA expression of MuRF1 1.2-fold and atrogin-1 1.3-fold higher (P < 0.05) for energy deficit than weight maintenance. Our data also showed that consuming a protein containing meal attenuated ubiquitin-mediated proteolysis, independent of habitual protein intake and energy deficit.
Technical Abstract: This study examined ubiquitin-mediated proteolysis and associated gene expression in normal-23 weight adults consuming varying levels of dietary protein during short-term energy deficit. 24 Using a randomized-bock design, 32 men and 7 women were assigned to diets providing protein 25 at 0.8 (RDA), 1.6 (2X-RDA), and 2.4 (3X-RDA) g·kg-1·d-1 for 31 days. A 10-day weight 26 maintenance period was immediately followed by 21 days of energy deficit (60% of daily 27 requirements). Muscle biopsy samples were collected during weight maintenance (day 10) and 28 energy deficit (day 31) under fasted (FAST) and fed (FED, 480 kcals, 20 grams of protein) 29 conditions. Ubiquitin-mediated proteolysis and associated gene expression were assessed using 30 fluorescence-based assays, western blotting, and real-time qRT-PCR. In fasted conditions, 31 energy deficit upregulated ubiquitin proteasome system (UPS) associated gene expression, as 32 mRNA expression of MuRF1 was 1.2-fold and atrogin-1 was 1.3-fold higher (P < 0.05) for 33 energy deficit than weight maintenance. However, consuming a protein containing meal 34 attenuated UPS-mediated proteolysis independent of energy status or dietary protein; as activity 35 of the 26S proteasome’s ß1, ß2, and ß5 subunits were lower (P < 0.05) for FED than FAST. 36 Muscle protein ubiquitylation was also 45% lower (P < 0.05) for FED than FAST, regardless of 37 dietary protein and energy manipulations. These data demonstrate that, independent of habitual 38 protein intake, and despite increased MuRF1 and atrogin-1 mRNA expression during short-term 39 energy deficit, consuming a protein containing meal attenuates ubiquitin-mediated proteolysis.