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Skeletal muscle protein synthesis and degradation exhibit sexual dimorphism after chronic alcohol consumption but not acute intoxication

Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania

Submitted 12 November 2006 ; accepted in final form 24 January 2007

Epidemiological evidence suggests alcoholic myopathy is more severe in females than males, but comparable animal studies are lacking that make elucidating the biochemical locus for this defect problematic. The present study determined whether skeletal muscle protein synthesis and markers of degradation exhibit a sexual dimorphic response to either chronic alcohol consumption or acute intoxication. Male and female rats were fed an alcohol-containing diet, pair-fed for 26 wk (chronic), or received an intraperitoneal injection of alcohol (acute). In males, chronic alcohol decreased gastrocnemius protein synthesis by 20%. This reduction was associated with a twofold increase in the inactive eukaryotic initiation factor (eIF) 4E·4E-binding protein 1 (4E-BP1) complex and a 60% reduction in the active eIF4E·eIF4G complex. This redistribution of eIF4E was associated with decreased phosphorylation of both 4E-BP1 and eIF4G (50–55%). The phosphorylation of ribosomal protein S6 was also reduced 60% in alcohol-consuming male rats. In contrast, neither rates of protein synthesis nor indexes of translation initiation in muscle were altered in alcohol-fed female rats despite blood alcohol levels comparable to males. Chronic alcohol ingestion did not alter atrogin-1 or muscle RING finger-1 mRNA content (biomarkers of muscle proteolysis) in males but increased their expression in females 50–100%. Acute alcohol intoxication produced a comparable decrease in muscle protein synthesis and translation initiation in both male and female rats. Our data demonstrate a sexual dimorphism for muscle protein synthesis, translation initiation, and proteolysis in response to chronic, but not acute, alcohol intoxication; however, they do not support evidence indicating females are more sensitive toward the development of alcoholic skeletal muscle myopathy.

ribosomal protein S6; 4E-binding protein 1; eukaryotic initiation factor 4G; insulin-like growth factor I; proteolysis

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