Acute alcohol intoxication increases atrogin-1 and MuRF1 mRNA without increasing proteolysis in skeletal muscle

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2008-06, Vol.294 (6), p.R1777-R1789
• Main Authors: Vary, Thomas C, Frost, Robert A, Lang, Charles H
• Format: Article
• Language: English
• Subjects: Alcohol; Alcohol Drinking - metabolism; Alcoholic Intoxication - metabolism; Animals; Appetite, Obesity, Digestion, and Metabolism; Cell culture; Central Nervous System Depressants - pharmacology; Ethanol - pharmacology; Glucocorticoids - metabolism; Insulin-Like Growth Factor I - metabolism; Male; Muscle Fibers, Fast-Twitch - drug effects; Muscle Fibers, Fast-Twitch - metabolism; Muscle Proteins - metabolism; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Musculoskeletal system; Polyubiquitin - metabolism; Protein Denaturation - drug effects; Proteins; Proteomics; Rats; Rats, Sprague-Dawley; Ribonucleic acid; RNA; RNA, Messenger - metabolism; SKP Cullin F-Box Protein Ligases - metabolism; Toxicity; Tripartite Motif Proteins; Ubiquitin-Protein Ligases - metabolism
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00056.2008

Department of Cellular and Molecular Physiology, Penn State University, College of Medicine, Hershey, Pennsylvania Submitted 26 January 2008 ; accepted in final form 6 April 2008 Acute alcohol intoxication decreases muscle protein synthesis, but there is a paucity of data on the ability of alcohol to regulate muscle protein degradation. Furthermore, various types of atrophic stimuli appear to regulate ubiquitin-proteasome-dependent proteolysis by increasing the muscle-specific E3 ligases atrogin-1 and MuRF1 (i.e., "atrogenes"). Therefore, the present study was designed to test the hypothesis that acute alcohol intoxication increases atrogene expression leading to an elevated rate of muscle protein breakdown. In male rats, the intraperitoneal injection of alcohol dose- and time-dependently increased atrogin-1 and MuRF1 mRNA in gastrocnemius, the latter of which was most pronounced. A comparable change was absent in the soleus and heart. The ability of in vivo-administered ethanol to increase atrogene expression was independent of the route of alcohol administration (intraperitoneal vs. oral), as well as of nutritional status (fed vs. fasted) and gender (male vs. female). The increase in atrogin-1 and MuRF1 was independent of alcohol metabolism, and the overproduction of endogenous glucocorticoids and could not be prevented by maintaining the circulating concentration of insulin-like growth factor-I. Despite marked changes in atrogene expression, acute alcohol in vivo did not alter the release of either 3-methylhistidine (MH) or tyrosine from the isolated perfused hindlimb, suggesting that the rate of muscle proteolysis remains unchanged. Moreover, alcohol did not increase the directly determined rate of protein degradation in isolated epitrochlearis muscles or cultured myocytes. Finally, no increase in atrogene expression or 3-MH release was detected in muscle from rats fed an alcohol-containing diet. Our results indicate that although acute alcohol intoxication increases atrogin-1 and MuRF1 mRNA preferentially in fast-twitch skeletal muscle, this change was not associated with increased rates of muscle proteolysis. Therefore, the loss of muscle mass/protein in response to chronic alcohol abuse appears to result primarily from a decrement in muscle protein synthesis, not an increase in degradation. protein degradation; protein breakdown; ubiquitin-proteasome; 3-methylhistidine; glucocorticoid; IGF-I Address for reprint requests and other correspondence: C.