Chronic ethanol feeding impairs AMPK and MEF2 expression and is associated with GLUT4 decrease in rat myocardium

Chronic and heavy alcohol consumption is one of the causes of heart diseases. However, the effects of ethanol on insulin sensitivity in myocardium has been unclear. To investigate the effects of ethanol on the expression of AMP-activated protein kinase (AMPK), myocyte enhancer factor 2 (MEF2) and glucose transporter 4 (GLUT4), all of which are involved in the regulation of insulin sensitivity, in the myocardium, we performed three parts of experiments in vivo and in vitro. I: Rats were injected with 5-amino-4-imidazolecarboxamide ribonucleotide (AICAR, 0.8 mg.kg(-1)) for 2 h. II: Rats received different dose (0.5, 2.5 or 5 g.kg(-1).d(-1)) of ethanol for 22-week. III: Primary neonatal rat cardiomyocytes were isolated and treated with or without 100 mM ethanol or 1 mM AICAR for 4 h. The cardiac protein and mRNA expression of AMPK alpha subunits, MEF2 and GLUT4 were observed by western-blotting and RT-PCR, respectively. Serum TNF alpha levels were assessed by ELISA. The results showed chronic ethanol exposure induced insulin resistance. Ethanol decreased the mRNA levels of AMPK alpha 1 and alpha 2, the protein levels of total- and phospho-AMPK alpha in cardiomyocytes. Similarly, ethanol showed inhibitory effects on both the mRNA and protein levels of MEF2A and 2D, and GLUT4 in a dose-response-like fashion. Correlation analysis implied an association between phospho-AMPK alpha and MEF2A or MEF2D, and between the levels of MEF2 protein and GLUT4 transcription. In addition, ethanol elevated serum TNF alpha level. Taken together, chronic ethanol exposure decreases the expression of AMPK alpha and MEF2, and is associated with GLUT4 decline in rat myocardium.