Cardiac overstimulation by the sympathetic nervous system (SNS) is a salient characteristic of heart failure, reflected by elevated circulating levels of catecholamines. The success of beta-adrenergic receptor (betaAR) antagonists in heart failure argues for SNS hyperactivity being pathogenic; however, sympatholytic agents targeting alpha2AR-mediated catecholamine inhibition have been unsuccessful. By investigating adrenal adrenergic receptor signaling in heart failure models, we found molecular mechanisms to explain the failure of sympatholytic agents and discovered a new strategy to lower SNS activity. During heart failure, there is substantial alpha2AR dysregulation in the adrenal gland, triggered by increased expression and activity of G protein-coupled receptor kinase 2 (GRK2). Adrenal gland-specific GRK2 inhibition reversed alpha2AR dysregulation in heart failure, resulting in lowered plasma catecholamine levels, improved cardiac betaAR signaling and function, and increased sympatholytic efficacy of a alpha2AR agonist. This is the first demonstration, to our knowledge, of a molecular mechanism for SNS hyperactivity in heart failure, and our study identifies adrenal GRK2 activity as a new sympatholytic target.

Background— Diminished cardiac S100A1 protein levels are characteristic of ischemic and dilated human cardiomyopathy. Because S100A1 has recently been identified as a Ca 2+ -dependent inotropic factor in the heart, this study sought to explore the pathophysiological relevance of S100A1 levels in development and progression of postischemic heart failure (HF). Methods and Results— S100A1-transgenic (STG) and S100A1-knockout (SKO) mice were subjected to myocardial infarction (MI) by surgical left anterior descending coronary artery ligation, and survival, cardiac function, and remodeling were compared with nontransgenic littermate control (NLC) and wild-type (WT) animals up to 4 weeks. Although MI size was similar in all groups, infarcted S100A1-deficient hearts (SKO-MI) responded with acute contractile decompensation and accelerated transition to HF, rapid onset of cardiac remodeling with augmented apoptosis, and excessive mortality. NLC/WT-MI mice, displaying a progressive decrease in cardiac S100A1 expression, showed a later onset of cardiac remodeling and progression to HF. Infarcted S100A1-overexpressing hearts (STG-MI), however, showed preserved global contractile performance, abrogated apoptosis, and prevention from cardiac hypertrophy and HF with superior survival compared with NLC/WT-MI and SKO-MI. Both Gq-protein–dependent signaling and protein kinase C activation resulted in decreased cardiac S100A1 mRNA and protein levels, whereas Gs-protein–related signaling exerted opposite effects on cardiac S100A1 abundance. Mechanistically, sarcoplasmic reticulum Ca 2+ cycling and β-adrenergic signaling were severely impaired in SKO-MI myocardium but preserved in STG-MI. Conclusions— Our novel proof-of-concept study provides evidence that downregulation of S100A1 protein critically contributes to contractile dysfunction of the diseased heart, which is potentially responsible for driving the progressive downhill clinical course of patients with HF.

Abstract-NO is known to have several important vasculoprotective actions. Although NO is synthesized by 3 different NO synthase (NOS) isoforms, the vasculoprotective action of individual NOS isoforms remains to be clarified. Permanent ligation of the left common carotid artery was performed in control, endothelial NOS (eNOS) knockout (eNOS-KO), and inducible NOS (iNOS) knockout (iNOS-KO) mice. Four weeks after the procedure, neointimal formation and reduction of cross-sectional vascular area (constrictive remodeling) were noted in the left carotid artery.In the eNOS-KO mice, the extent of neointimal formation was significantly larger than in the control or iNOS-KO mice, whereas the extent of vascular remodeling was the highest in the iNOS-KO mice compared with other 2 strains. Antiplatelet therapy with aspirin or antihypertensive treatment with bunazosin failed to inhibit the accelerated neointimal formation in the eNOS-KO mice. These results indicate that eNOS and iNOS have different vasculoprotective actions against the vascular lesion formation caused by blood flow disruption in vivo: NO derived from eNOS inhibits neointimal formation, whereas NO derived from iNOS suppresses the development of constrictive remodeling. Indeed, reduction of production and/or action of NO predisposes the blood vessel to arteriosclerosis. 1-3 NO is synthesized by 3 different isoforms of NO synthase (NOS). Endothelial NOS (eNOS) and neuronal NOS are constitutively expressed mainly in endothelial cells and nitrergic nerves, respectively, synthesizing a small amount of NO under basal conditions and on stimulation by various agonists. 1-3 By contrast, inducible NOS (iNOS) is expressed when stimulated by inflammatory stimuli, synthesizing a large amount of NO in a transient manner. [1][2][3] Recent advances in genetic engineering have led to the development of mice that are deficient in specific target genes, including eNOS 4 and iNOS. 5,6 The mice that are deficient in the eNOS gene (eNOS-KO mice) have been reported to have mild hypertension, 4 whereas mice that are deficient in the iNOS gene (iNOS knockout [KO] mice) have been reported to have altered immune response and reduced tolerability against infections. 5 Although the possible vasculoprotective actions of NOS have been examined in a different model for eNOS (cuff placement around the femoral artery) 6 and iNOS (cardiac transplant model), 7 the possible difference in the vasculoprotective roles of those NOS isoforms remains to be clarified in the same model.Thus, the present study was designed to address this point in the carotid artery ligation model in mice. 8 MethodsThe present study was reviewed and approved by the Scientific Committee of Kyushu University. AnimalsiNOS-KO mice were provided by Dr Mudgett (Merck Research Laboratories, Rahway, NJ), 4 and eNOS-KO mice were provided by Dr Fishman (Harvard Medical School, Boston, Mass). 5 For wild genotype control, we used C57BL/6 mice. 4,5 In preliminary studies, we confirmed no endothelial production of NO in eNOS-KO mice an...