María J. Montero

Vav3 proto-oncogene deficiency leads to sympathetic hyperactivity and cardiovascular dysfunction

Although much is known about environmental factors that predispose individuals to hypertension and cardiovascular disease, little information is available regarding the genetic and signaling events involved. Indeed, few genes associated with the progression of these pathologies have been discovered despite intensive research in animal models and human populations. Here we identify Vav3, a GDP-GTP exchange factor that stimulates Rho and Rac GTPases, as an essential factor regulating the homeostasis of the cardiovascular system. Vav3-deficient mice exhibited tachycardia, systemic arterial hypertension and extensive cardiovascular remodeling. These mice also showed hyperactivity of sympathetic neurons from the time of birth. The high catecholamine levels associated with this condition led to the activation of the renin-angiotensin system, increased levels of kidney-related hormones and the progressive loss of cardiovascular and renal homeostasis. Pharmacological studies with drugs targeting sympathetic and renin-angiotensin responses confirmed the causative role and hierarchy of these events in the development of the Vav3-null mouse phenotype. These observations uncover the crucial role of Vav3 in the regulation of the sympathetic nervous system (SNS) and cardiovascular physiology, and reveal a signaling pathway that could be involved in the pathophysiology of human disease states involving tachycardia and sympathetic hyperactivity with unknown etiologies.

Novel Nox homologues in the vasculature: focusing on Nox4 and Nox5.

The Noxes (NADPH oxidases) are a family of ROS (reactive oxygen species)-generating enzymes. Of the seven family members, four have been identified as important sources of ROS in the vasculature: Nox1, Nox2, Nox4 and Nox5. Although Nox isoforms can be influenced by the same stimulus and co-localize in cellular compartments, their tissue distribution, subcellular regulation, requirement for cofactors and NADPH oxidase subunits and ability to generate specific ROS differ, which may help to understand the multiplicity of biological functions of these oxidases. Nox4 and Nox5 are the newest isoforms identified in the vasculature. Nox4 is the major isoform expressed in renal cells and appear to produce primarily H2O2. The Nox5 isoform produces ROS in response to increased levels of intracellular Ca2+ and does not require the other NADPH oxidase subunits for its activation. The present review focuses on these unique Noxes, Nox4 and Nox5, and provides novel concepts related to the regulation and interaction in the vasculature, and discusses new potential roles for these isoforms in vascular biology.

The Rho/Rac exchange factor Vav2 controls nitric oxide–dependent responses in mouse vascular smooth muscle cells

The regulation of arterial contractility is essential for blood pressure control. The GTPase RhoA promotes vasoconstriction by modulating the cytoskeleton of vascular smooth muscle cells. Whether other Rho/Rac pathways contribute to blood pressure regulation remains unknown. By studying a hypertensive knockout mouse lacking the Rho/Rac activator Vav2, we have discovered a new signaling pathway involving Vav2, the GTPase Rac1, and the serine/threonine kinase Pak that contributes to nitric oxide-triggered blood vessel relaxation and normotensia. This pathway mediated the Pak-dependent inhibition of phosphodiesterase type 5, a process that favored RhoA inactivation and the subsequent depolymerization of the F-actin cytoskeleton in vascular smooth muscle cells. The inhibition of phosphodiesterase type 5 required its physical interaction with autophosphorylated Pak1 but, unexpectedly, occurred without detectable transphosphorylation events between those 2 proteins. The administration of phosphodiesterase type 5 inhibitors prevented the development of hypertension and cardiovascular disease in Vav2-deficient animals, demonstrating the involvement of this new pathway in blood pressure regulation. Taken together, these results unveil one cause of the cardiovascular phenotype of Vav2-knockout mice, identify a new Rac1/Pak1 signaling pathway, and provide a mechanistic framework for better understanding blood pressure control in physiological and pathological states.

Transcriptional Factor Aryl Hydrocarbon Receptor (Ahr) Controls Cardiovascular and Respiratory Functions by Regulating the Expression of the Vav3 Proto-oncogene

Aryl hydrocarbon receptor (Ahr) is a transcriptional factor involved in detoxification responses to pollutants and in intrinsic biological processes of multicellular organisms. We recently described that Vav3, an activator of Rho/Rac GTPases, is an Ahr transcriptional target in embryonic fibroblasts. These results prompted us to compare the Ahr−/− and Vav3−/− mouse phenotypes to investigate the implications of this functional interaction in vivo. Here, we show that Ahr is important for Vav3 expression in kidney, lung, heart, liver, and brainstem regions. This process is not affected by the administration of potent Ahr ligands such as benzo[a]pyrene. We also report that Ahr- and Vav3-deficient mice display hypertension, tachypnea, and sympathoexcitation. The Ahr gene deficiency also induces the GABAergic transmission defects present in the Vav3−/− ventrolateral medulla, a main cardiorespiratory brainstem center. However, Ahr−/− mice, unlike Vav3-deficient animals, display additional defects in fertility, perinatal growth, liver size and function, closure, spleen size, and peripheral lymphocytes. These results demonstrate that Vav3 is a bona fide Ahr target that is in charge of a limited subset of the developmental and physiological functions controlled by this transcriptional factor. Our data also reveal the presence of sympathoexcitation and new cardiorespiratory defects in Ahr−/− mice.

Long-term treatment with nebivolol improves arterial reactivity and reduces ventricular hypertrophy in spontaneously hypertensive rats.

&NA; The aim of this study was to assess the effects of long‐term nebivolol therapy on high blood pressure, impaired endothelial function in aorta, and damage observed in heart and conductance arteries in spontaneously hypertensive rats (SHR). For this purpose, SHR were treated for 9 weeks with nebivolol (8 mg/kg per day). Untreated SHR and Wistar Kyoto rats were used as hypertensive and normotensive controls, respectively. The left ventricle/body weight ratio was used as an index of cardiac hypertrophy, and to evaluate vascular function, responses induced by potassium chloride, noradrenaline, acetylcholine, and sodium nitroprusside were tested on aortic rings. Aortic morphometry and fibrosis were determined in parallel by a quantitative technique. Systolic blood pressure, measured by the tail‐cuff method, was lower in treated SHR than in the untreated group (194 ± 3 versus 150 ± 4 mm Hg). The cardiac hypertrophy index was significantly reduced by the treatment. In aortic rings, treatment with nebivolol significantly reduced the maximal response to both KCl and NA in SHR. In vessels precontracted with phenylephrine relaxant, activity due to acetylcholine was higher in normotensive rats than in SHR and the treatment significantly improved this response. The effect of sodium nitroprusside on aortic rings was similar in all groups. Medial thickness and collagen content were significantly reduced in comparison with SHR. In conclusion, the chronic antihypertensive effect of nebivolol in SHR was accompanied by an improvement in vascular structure and function and in the cardiac hypertrophy index.

In vitro antioxidant activity of pravastatin provides vascular protection

The production of reactive oxygen species plays roles during the development of endothelial dysfunction and it represents a significant prognostic factor for evaluating the risk of cardiovascular disease. Although statins target cholesterol biosynthesis, the beneficial effects on cardiovascular disease remain to be fully elucidated. In this work, we explored the in vitro effects of pravastatin on vascular functionality. We studied the effect of the incubation with this statin on acetylcholine relaxation using aorta from spontaneously hypertensive rats (SHR). Consistent with a cholesterol-independent mechanism of action, we show that pravastatin induces a significant improvement of endothelium-dependent relaxation that is not completely reversed by mevalonic acid. Assays with 250microM of lucigenin were carried out to verify whether such action could be mediated by the scavenger properties of pravastatin. Treatment of aortic rings derived from Wistar rats with lucigenin promotes superoxide generation (O(2)(-)) and the subsequent loss of both endothelium-dependent and independent relaxations. The addition of pravastatin reduced the lucigenin-triggered O(2)(-) levels as well as its inhibitory effects on acetylcholine- and sodium nitroprusside-dependent responses. These effects were not counteracted by mevalonic acid, further supporting the idea that the effects of pravastatin do not entail alterations in cholesterol biosynthesis. In conclusion, this study can contribute to elucidate the mechanism responsible for the antioxidant activity of pravastatin, and describes relationship between a scavenger effect of pravastatin and the improvement of vascular reactivity.

Cardiovascular effects of nebivolol in spontaneously hypertensive rats persist after treatment withdrawal

Objectives We observed previously that nebivolol treatment for 2 months reduced cardiovascular lesions in spontaneously hypertensive rats (SHR). Therefore, we investigated whether this beneficial effect is increased with a longer treatment, and its persistence after withdrawal. Methods Male SHR were treated with 8 mg/kg per day of nebivolol (N-SHR) for 6 months. A separate group was also given identical treatment but they were then monitored for a further 3 months after drug withdrawal. SHR and Wistar–Kyoto rats (WKY) receiving vehicle were used as controls. Systolic blood pressure and heart rate were measured using the tail-cuff method. Left ventricular weight/body weight ratio was calculated as the hypertrophy index. Cardiac and vascular fibrosis was evaluated on sections stained with sirious red. Vascular reactivity was evaluated on aortic rings through acetylcholine and sodium nitroprusside responses. The effect of treatment on vascular structure was assessed by lumen diameter, wall thickness and medial cross-sectional area determination. Results Blood pressure was reduced in N-SHR. After withdrawal it increased progressively, without reaching the values of the hypertensive controls. Cardiac hypertrophy and collagen content both in heart and aorta were significantly reduced, and these changes persisted after nebivolol suppression. Acetylcholine-induced relaxant response was improved by nebivolol and maintained after withdrawal. Medial thickness and cross-sectional area were significantly reduced in both conductance and resistance arteries, and these effects persisted after withdrawal. Conclusion The nebivolol antihypertensive effect was accompanied by an important reduction of hypertrophy and collagen deposition in both vascular and left ventricle tissue, which was maintained after a long period of therapy withdrawal.

Differential effects of quinidine on transmembrane action potentials of normal and infarcted canine Purkinje fibers

Summary Fourteen days after proximal ligation of the left anterior descending coronary artery (LAD) of mongrel dogs, the effects of quinidine on action potentials of normal and infarcted Purkinje fibers were evaluated. The concentration-dependent (10-7-3 × 10-5 M) and frequency-dependent (1 and 3 Hz) actions of quinidine were evaluated by the following parameters: maximum upstroke velocity (Vmax), action potential duration at 50 and 95% repolarization (APD50, APD95), effective refractory period (ERP), resting membrane potential (RMP), and action potential amplitude (APA). Quinidine reduced Vmax in normal and abnormal Purkinje fibers in a concentration-and frequency-dependent manner; these effects were more pronounced in infarcted tissue. The APD50 was shortened significantly at 1 Hz in noninfarcted Purkinje fibers, whereas in infarcted Purkinje fibers quinidine had no effect on APD50. The APD95 was not significantly altered by quinidine in normal Purkinje fibers; in infarcted areas APD95 was significantly prolonged at 1 and 3 Hz. The effective refractory period (ERP) was prolonged in normal and infarcted Purkinje fibers, these effects were more marked in ischemically damaged fibers. No effects were observed on resting membrane potential (RMP). APA was reduced significantly after quinidine at 1 and 3 Hz; there was no difference between normal and infarcted tissue. These data indicate a differential effect of quinidine in normal and infarcted Purkinje fibers which may be an important mechanism of action of quinidine in infarcted tissue.

Vav3 Is Involved in GABAergic Axon Guidance Events Important for the Proper Function of Brainstem Neurons Controlling Cardiovascular, Respiratory, and Renal Parameters

Vav3 is a phosphorylation GDP/GTP exchange factor for Rho/Rac GTPases. Recently, it has been described that Vav3 knockout mice develop hypertension and sympathoexcitation. In this work, we report the neurological cause of this phenotype.

Electrophysiologic and antiarrhythmic effects of D-sotalol

There is extensive experimental and clinical experience concerning the antiarrhythmic potency of DL-sotalol, a β-adrenergic antagonist that lengthens the cardiac action potential duration. More recently, its dextrorotatory isomer, D-sotalol, has been evaluated in experimental studies and preliminary clinical trials. Whereas the isomer is almost free of β-blocking activity, both experimental and clinical data demonstrate the potent class III activity of D-sotalol. Further investigations, particularly in patients with life-threatening arrhythmias, are needed to delineate the clinical usefulness of this compound.