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Effects of energy deficit, dietary protein, and feeding on intracellular regulators of skeletal muscle proteolysis

John W. Carbone, Lee M. Margolis, James P. McClung, Jay J. Cao, Nancy E. Murphy, Edward R. Sauter, Gerald F. Combs, Andrew J. Jr., Stefan M. Young
Journal of Federation of American Societies for Experimental Biology 2013 v.27 no. pp. 5104-5111
Western blotting, adults, biopsy, dietary protein, energy, energy deficiencies, gene expression, men, messenger RNA, muscle protein, muscles, proteasome endopeptidase complex, protein intake, proteolysis, quantitative polymerase chain reaction, skeletal muscle, ubiquitin, weight control, women
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.