Abstract 3390: G- Protein Coupled Receptor Kinase-2 (GRK2) Induces Insulin Resistance in Cardiac Myocytes
Recent studies described a role for GRK2 in insulin resistance as we have found that increased GRK2 after a myocardial infarction (MI) in rats is associated with reduced glucose uptake. In fact, this can occur in early stage even before the development of depressed cardiac function. Moreover, we found that cardiac gene therapy with the GRK2 inhibitor βARKct, restores glucose uptake. The aim of the present study was to study the mechanisms by which GRK2 may impart insulin resistance in myocytes. Neonatal rat ventricular myocytes (NRVMs) were stimulated with insulin (ins 10−7 M for 10 min) with or without isoproterenol pre-stimulation (iso, 10−7 M). We observed that both ins and iso alone induced GLUT4 translocation to the membrane (1.8±0.05 and 2.1±0.10 fold over basal, p<0.05) while iso pre-stimulation blunted ins-induced GLUT4 translocation (0.79±0.10 fold over basal, n.s.). Iso, and surprisingly, ins were both able to produce GRK2 translocation to the membrane (2.9±0.4 and 3.6±0.8 fold over basal, p<0.05). To demonstrate the role of GRK2 in β-adrenergic induced insulin resistance we performed overexpression of this kinase by adenovirus (AdGRK2) in NRVMs and used AdGFP as a control. Ins induced GLUT4 translocation in AdGFP treated cells (2.01±0.3 fold over basal, p <0.05), while GRK2 overexpression did not allow for ins-induced translocation (0.77±0.2 fold over basal, n.s.). In vivo, we used micro-PET to measure myocardial glucose uptake in transgenic mice with cardiac overexpression of GRK2 (BK12 mice) and non-transgenic control mice (NLC’s). Post-Mi NLC mice had an increased glucose uptake versus sham mice (0.38±0.02 vs 0.18±0.01, mg/ml/min, p<0.05), while no difference was observed in the BK12 group (0.24±0.06 vs 0.34±0.07, n.s). Echocardiography measurement did not show significant differences in cardiac dimension and function among groups. At 6 weeks post-MI both NLC and BK12 mice presented a reduced glucose uptake versus shams and cardiac function was significant depressed in both MI group but more depressed in BK12 mice. Our in vitro data demonstrate the role of GRK2 in inducing insulin resistance in cardiomyocytes while in vivo data show that GRK2 overexpression causes an acute loss of favorable glucose metabolism in early stage of post-MI HF.