Abstract 9608: Upregulation of Cardiac Beta3-Adrenergic Receptor-Activated iNOS Uncoupling Promotes Diabetic Cardiomyopathy in Type II Diabetic Mice: Role of Oxidant Stress

Abstract

Background: Recent evidence highlights oxidative stress as an important mechanism to cardiac dysfunction in type 2 diabetes (T2D) and altered β 3 -adrenergic receptor (AR)-activated nitric oxide synthase (NOS) pathway contributing to this process. However, the NOS isoforms involved are controversial. The mechanism of how β 3 -AR stimulation impacts ROS, SERCA2a, and cardiac function in T2D is unclear. We tested the hypothesis that oxidant stress from upregulation of LV β 3 -AR-activated iNOS uncoupling promotes T2D cardiomyopathy. Methods: We compared myocyte β 1 - and β 3 -AR, NOS, peroxynitrite (NT), NADPH and SERCA2a expressions and myocyte functional responses to β- and β 3 -AR stimulation with isoproterenol (ISO,10 -8 M) and BRL-37344 (BRL,10 -8 M), respectively, in the absence and presence of iNOS inhibitor, 1400W (10 -5 M) of female mice over 14 weeks (W): 7 normal and 7 with T2D induced by 14 W high-fat diet (HFD) intake, but after HFD for 4 W receiving streptozotocin (STZ, 40 mg/kg/day, i.p. 5 days). Results: Versus normal myocytes, T2D myocytes had significantly increased protein levels of β 3 -AR (0.25 vs 0.14) and iNOS (0.25 vs 0.15) accompanied with increased oxidative stress indicated by significantly-elevated NT formation, NADPH (P67 -phox , 33% and p22 -phox , 29%) and decreased GTPCH expression (0.43 vs 0.85) and activity. T2D myocytes had significantly decreased β 1 -AR (0.35 vs 0.49) and SERCA2a (0.19 vs 0.29). These changes were associated with reduced cell contraction (dL/dt max , 75.4 vs 133.7 μm/s), relaxation (dR/dt max , 59.6 vs 113.8 μ m/s), and [Ca 2+ ] iT (0.16 vs 0.21) accompanied by diminished β-AR-stimulated positive inotropic response, but enhanced β 3 -AR-induced negative inotropic response. Only in T2D myocytes, pretreatment with 1400W improved basal cell function and augmented ISO-increased dL/dt max (64.5%) and [Ca 2+ ] iT (29.2%), but significantly limited BRL-induced decrease in dL/dt max (12.7%) and [Ca 2+ ] iT (9.8%). Conclusions: T2D is associated with contrasting changes on myocyte β 1 - and β 3 -AR expression with decreased SERCA2a and increased iNOS. Upregulation of β 3 -AR triggers iNOS uncoupling, leading to oxidative stress, thus promoting intrinsic myocyte dysfunction with impaired [Ca 2+ ] i regulation and reduced β-AR reserve.