|Ph.D Student||Harel Chava|
|Subject||Glucose Transporters in Cardiomyocytes: Regulation of Their|
Expression and Function in Physiological and
|Department||Department of Medicine||Supervisor||Professor Emeritus Eddy Karnieli|
Free fatty acids (FFA) regulate glucose homeostasis and cellular glucose transport. Hyperlipidemia (HL) and Type 2 Diabetes Mellitus (DM2) are associated with coronary artery disease (CAD). However, whether lipotoxicity modulates glucose transporter (GLUT) gene expression is largely unknown. We studied the effects of HL on GLUT1 and GLUT4 gene expression in cardiac muscle. Our data in human heart muscle biopsies (obtained during elective coronary surgery) show that a) in either DM2 or HL patients, 30% lower levels GLUT4 protein were observed, while GLUT1 levels were slightly elevated, compared to controls; b) GLUT1 mRNA was slightly elevated in either DM2 or HL, while GLUT4 mRNA levels were not affected. GLUT promoter (GLUT-P) regulation was assessed in H9C2 cardiac myotubes transiently transfected with GLUT1 or GLUT4 promoter reporters incubated in presence of FFA (0-300 uM, 24 hr). Endogenous expression of GLUT1 and GLUT4 protein in H9C2 myotubes was confirmed by confocal microscopy. We found that a) stearic, oleic, and linoleic acids suppressed basal GLUT4-P activity by 60-70%; b) arachidonic acid dose-dependently suppressed GLUT1-P and GLUT4-P activity to a maximum of 35% and 75%, respectively, while ETYA (non-metabolized analogue) exerted a smaller suppression effect. 5'-deletion analysis of GLUT4-P revealed that a -675/-66 bp region is sufficient to retain arachidonate suppression effect. We thus suggest that impaired glucose uptake, insulin resistance and DM2 associated with CAD, are secondary to the lipotoxicity (exhibited as hyperlipidemia and high FFA levels) -induced suppression of GLUT1 & GLUT4 gene expression in cardiac muscle.