Molecular analysis of insulin resistance in isolated ventricular cardiomyocytes of obese Zucker rats.
Isolated ventricular cardiomyocytes obtained from lean and genetically (fa/fa) obese Zucker rats were used to correlate alterations of insulin-induced glucose transport activation and GLUT-4 translocation to possible defects of the insulin signaling cascade. Maximal stimulation with insulin was found to produce an unaltered translocation of GLUT-4 to the plasma membrane (4.2- and 3.7-fold increase for lean and obese rats, respectively). However, a largely reduced sensitivity of 3-O-methylglucose transport could be detected in obese rats at physiological doses of insulin (completely unresponsive at 8 x 10(-11) M compared with 3-fold stimulation of glucose transport in lean controls). Tyrosine phosphorylation of the insulin receptor beta-subunit and the insulin receptor substrate 1 (IRS-1) was stimulated identically in cardiomyocytes from both lean and obese rats. Labeling of cells with [33P]orthophosphate revealed a marked increase in the serine and/or threonine phosphorylation of IRS-1 in the obese group (370% of lean controls), with a concomitant reduction in IRS-1 abundance (30-40%). The reduced sensitivity of glucose transport at 8 x 10(-11) M insulin was then found to correlate to a completely blunted response of IRS-1-associated phosphatidylinositol 3-kinase activity in cardiomyocytes from obese rats. Those data show that cardiac insulin resistance of obesity involves defective insulin signaling at low concentrations of the hormone, whereas GLUT-4 translocation is fully operative in the isolated cell. It is suggested that hyperphosphorylation of IRS-1 may significantly contribute to the pathogenesis of insulin resistance in the heart.
Kolter
T
T
Laboratory of Molecular Cardiology, Diabetes Research Institute, Düsseldorf, Germany.
Uphues
I
I
Eckel
J
J
D019325:3-O-Methylglucose / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D051275:Glucose Transporter Type 4; D006321:Heart / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*; D006352:Heart Ventricles; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D007700:Kinetics; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D009206:Myocardium / Q000378:metabolism*; D009765:Obesity / Q000235:genetics / Q000503:physiopathology*; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D051381:Rats; D011924:Rats, Zucker; D011972:Receptor, Insulin / Q000378:metabolism; D012016:Reference Values
D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; C495694:Slc2a4 protein, rat; D019325:3-O-Methylglucose; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011972:Receptor, Insulin