11-cis-retinal and Heart-Failure

Cardiac myocyte oxidative stress and apoptosis are considered important mechanisms for the development of heart failure (HF). Chronic HF is characterized by increased circulating catecholamines to augment cardiac output. Long-term stimulation of myocardial β-adrenergic receptors (β-ARs) is deleterious in cardiac myocytes, however, the potential mechanisms underlying increased cell death are unclear. We hypothesize that GRK2, a critical regulator of myocardial β-AR signaling, plays an important role in mediating cellular oxidative stress and apoptotic cell death in response to β-agonist stimulation. Stimulation of H9c2 cells with a non-selective β-agonist, isoproterenol (Iso) caused increased oxidative stress and apoptosis. There was also increased Nox4 expression, but no change in Nox2, the primary NADPH isoforms and major sources of ROS generation in cardiac myocytes. Adenoviral-mediated overexpression of GRK2 led to similar increases in ROS production and apoptosis as seen with Iso stimulation. These increases in oxidative stress were abolished by pre-treatment with the non-specific Nox inhibitor, apocynin, or siRNA knockdown of Nox4. Adenoviral-mediated expression of a GRK2 inhibitor prevented ROS production and apoptosis in response to Iso stimulation. β-Arrestins are signaling proteins that function downstream of GRK2 in β-AR uncoupling. Adenoviral-mediated overexpression of β-arrestins increased ROS production and Nox4 expression. Chronic β-agonist stimulation in mice increased Nox4 expression and apoptosis compared to PBS or AngII treatment. These data demonstrate that GRK2 may play an important role in regulating oxidative stress and apoptosis in cardiac myocytes and provides an additional novel mechanism for the beneficial effects of cardiac-targeted GRK2 inhibition to prevent the development of HF.

Topics: Acetophenones; Adrenergic beta-Agonists; Angiotensin II; Animals; Apoptosis; Arrestins; beta-Arrestins; Cell Line; Cyclic AMP; G-Protein-Coupled Receptor Kinase 2; Heart Failure; Isoproterenol; Membrane Glycoproteins; Microscopy, Confocal; Mitochondria; Myocytes, Cardiac; NADPH Oxidase 2; NADPH Oxidase 4; NADPH Oxidases; Oxidative Stress; Phosphorylation; Rats; Reactive Oxygen Species; Receptors, Adrenergic, beta; Rhodopsin; RNA Interference; RNA, Small Interfering; Signal Transduction

Treatment of rats with monocrotaline (MCT) leads to pulmonary hypertension, right ventricular (RV) hypertrophy, and finally to RV heart failure. This is associated with characteristic changes in right ventricular beta-adrenoceptors (beta-AR), neuronal noradrenaline transporter (NAT) density and activity (uptake1), and G protein-coupled receptor kinase (GRK) activity. This study aimed to find out factors that determine beta-AR, uptake1, and GRK changes. Thus, 6-week-old rats were treated with 50 mg/kg MCT subcutaneous or 0.9% saline. Within 13 to 19 days after MCT application (group A), RV weight (222+/-6 versus 147+/-5 mg) and RV/left ventricular (LV) weight ratio (0.42+/-0.01 versus 0.29+/-0.01) were significantly increased, whereas plasma noradrenaline, RV beta-AR density, RV NAT density and activity, and RV GRK activity were not significantly altered. Twenty-one to twenty-eight days after MCT (group B), however, not only RV weight (316+/-4 versus 148+/-2 mg) and RV/LV weight ratio (0.61+/-0.01 versus 0.3+/-0.01) were markedly increased but also plasma noradrenaline (645+/-63 versus 278+/-18 pg/mL); now, RV beta-AR density (13.4+/-1.3 versus 26.5+/-1.1 fmol/mg protein), RV NAT density (50.9+/-11.3 versus 79.6+/-2.9 fmol/mg protein), and RV NAT activity (65.4+/-7.4 versus 111.8+/-15.9 pmol [3H]-NA/mg tissue slices/15 min) were significantly decreased and RV-membrane GRK activity (100+/-15 versus 67+/-6 [32P]-rhodopsin in cpm) significantly increased. LV parameters of MCT-treated rats were only marginally different from control LV. We conclude that in MCT-treated rats ventricular hypertrophy per se is not sufficient to cause characteristic alterations in the myocardial beta-AR system often seen in heart failure; only if ventricular hypertrophy is associated with neurohumoral activation beta-ARs are downregulated and GRK activity is increased.

Topics: Animals; Binding, Competitive; Cell Membrane; Disease Models, Animal; Eye Proteins; Fluoxetine; G-Protein-Coupled Receptor Kinase 1; Heart Failure; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; Male; Monocrotaline; Myocardium; Norepinephrine; Norepinephrine Plasma Membrane Transport Proteins; Organ Size; Protein Kinases; Rats; Rats, Wistar; Receptors, Adrenergic, beta; Receptors, Neurotransmitter; Rhodopsin; Symporters