In hypertension, the kidney is not always the heart of the matter

Magnesium and Hypertension: Decoding Novel Anti-hypertensives

Hypertension (HTN) is a complex multifactorial disease that is one of the most prevalent disorders in our modern world. It can lead to fatal complications like coronary artery disease (CAD) and congestive heart failure (CHF) in high-risk individuals. The silent nature of HTN also contributes to its immense caseload and, today, with a number of combinations and various antihypertensive agents, patient compliance is becoming increasingly difficult. This article has reviewed the role and mechanisms of magnesium (Mg) in reducing HTN in the human body so as to provide more information that may help include it as a mainstream antihypertensive regimen. This review has also shed light on the cardioprotective nature of Mg against pathologies like CHF with special mention to patient groups who are at high risk for low Mg levels. Many studies included in this article solidify the former link, but some also provide contradicting data.

Fetal Undernutrition Programming, Sympathetic Nerve Activity, and Arterial Hypertension Development

A wealth of evidence showed that low birth weight is associated with environmental disruption during gestation, triggering embryotic or fetal adaptations and increasing the susceptibility of progeny to non-communicable diseases, including metabolic and cardiovascular diseases, obesity, and arterial hypertension. In addition, dietary disturbance during pregnancy in animal models has highlighted mechanisms that involve the genesis of arterial hypertension, particularly severe maternal low-protein intake (LP). Functional studies demonstrated that maternal low-protein intake leads to the renal decrease of sodium excretion and the dysfunction of the renin-angiotensin-aldosterone system signaling of LP offspring. The antinatriuretic effect is accentuated by a reduced number of nephron units and glomerulosclerosis, which are critical in establishing arterial hypertension phenotype. Also, in this way, studies have shown that the overactivity of the central and peripheral sympathetic nervous system occurs due to reduced sensory (afferent) renal nerve activity. As a result of this reciprocal and abnormal renorenal reflex, there is an enhanced tubule sodium proximal sodium reabsorption, which, at least in part, contributes directly to arterial hypertension development in some of the programmed models. A recent study has observed that significant changes in adrenal medulla secretion could be involved in the pathophysiological process of increasing blood pressure. Thus, this review aims to compile studies that link the central and peripheral sympathetic system activity mechanisms on water and salt handle and blood pressure control in the maternal protein-restricted offspring. Besides, these pathophysiological mechanisms mainly may involve the modulation of neurokinins and catecholamines pathways.

A paradoxical increase of force development in saphenous and tail arteries from heterozygous ANO1 knockout mice

A Ca²⁺‐activated Cl⁻ channel protein, ANO1, is expressed in vascular smooth muscle cells where Cl⁻ current is thought to potentiate contraction by contributing to membrane depolarization. However, there is an inconsistency between previous knockout and knockdown studies on ANO1’s role in small arteries. In this study, we assessed cardiovascular function of heterozygous mice with global deletion of exon 7 in the ANO1 gene. We found decreased expression of ANO1 in aorta, saphenous and tail arteries from heterozygous ANO1 knockout mice in comparison with wild type. Accordingly, ANO1 knockdown reduced the Ca²⁺‐activated Cl⁻ current in smooth muscle cells. Consistent with conventional hypothesis, the contractility of aorta from ANO1 heterozygous mice was reduced. Surprisingly, we found an enhanced contractility of tail and saphenous arteries from ANO1 heterozygous mice when stimulated with noradrenaline, vasopressin, and K⁺‐induced depolarization. This difference was endothelium‐independent. The increased contractility of ANO1 downregulated small arteries was due to increased Ca²⁺ influx. The expression of L‐type Ca²⁺ channels was not affected but expression of the plasma membrane Ca²⁺ ATPase 1 and the Piezo1 channel was increased. Expressional analysis of tail arteries further suggested changes of ANO1 knockdown smooth muscle cells toward a pro‐contractile phenotype. We did not find any difference between genotypes in blood pressure, heart rate, pressor response, and vasorelaxation in vivo. Our findings in tail and saphenous arteries contrast with the conventional hypothesis and suggest additional roles for ANO1 as a multifunctional protein in the vascular wall that regulates Ca²⁺ homeostasis and smooth muscle cell phenotype.

Effects of nebivolol versus other antihypertensive drugs on the endothelial dysfunction in patients with essential hypertension

We aim to determine whether nebivolol has a better effect on endothelial dysfunction compared with other β-blockers or other classes of antihypertensive drugs. Searches of the PubMed, Embase etc. were performed to analyze all the randomized controlled trials using nebivolol to treat essential hypertension. The primary end points included a measurement of peripheral endothelial function by brachial flow mediated vasodilatation (FMD) or forearm blood flow (FBF). A random-effect model was used to perform the meta-analysis when the studies showed significant heterogeneity, otherwise a descriptive analysis was conducted. Ten studies (689 patients) were included in qualitative analysis, four of which were included in quantitative synthesis. Meta-analysis showed that the changed FMD value before and after treatment with nebivolol was not statistically different from those treated with other β-blockers [mean difference = 1.12, 95% confidence interval (CI): −0.56, 2.81, P=0.19]. Descriptive analysis indicated that nebivolol did not have a better endothelium-protective effect than other classes of antihypertensive drugs including olmesartan and perindopril. Nebivolol is not a unique endothelial function-protective agent distinguished from other β-blockers or other classes of antihypertensive drugs. Reversal of endothelial dysfunction is a key point in the prevention and therapy of essential hypertension.

Class II phosphatidylinositol 3-kinase α and β isoforms are required for vascular smooth muscle Rho activation, contraction and blood pressure regulation in mice

Class II phosphatidylinositol 3-kinases (PI3K), PI3K-C2α and PI3K-C2β, are involved in cellular processes including endocytosis, cilia formation and autophagy. However, the role of PI3K-C2α and PI3K-C2β at the organismal level is not well understood. We found that double knockout (KO) mice with both smooth muscle-specific KO of PI3K-C2α and global PI3K-C2β KO, but not single KO mice of either PI3K-C2α or PI3K-C2β, exhibited reductions in arterial blood pressure and substantial attenuation of contractile responses of isolated aortic rings. In wild-type vascular smooth muscle cells, double knockdown of PI3K-C2α and PI3K-C2β but not single knockdown of either PI3K markedly inhibited contraction with reduced phosphorylation of 20-kDa myosin light chain and MYPT1 and Rho activation, but without inhibition of the intracellular Ca²⁺ mobilization. These data indicate that PI3K-C2α and PI3K-C2β play the redundant but essential role for vascular smooth muscle contraction and blood pressure regulation mainly through their involvement in Rho activation.

Sex differences in vascular reactivity in mesenteric arteries from a mouse model of acute intermittent porphyria

BACKGROUND AND AIMS

Acute intermittent porphyria (AIP) results from a partial deficiency of porphobilinogen deaminase (PBGD). Symptomatic AIP patients, most of whom are women, experience acute attacks characterized by severe abdominal pain and abrupt increases in blood pressure. Here, we characterized the reactivity of mesenteric arteries from male and female AIP mice with ~30% of normal PBGD activity and wild type C57BL/6 mice.

METHODS

An acute porphyric attack was induced in AIP mice by treatment with phenobarbital. Vascular responses to K⁺, phenylephrine (PE), acetylcholine (ACh), and hemin were determined (Wire Multi Myograph).

RESULTS

Maximal contraction to PE was increased in arteries from male and female AIP mice (p < .05) during an induced attack of acute porphyria. Female AIP arteries had increased sensitivity to PE (p < .05) even after nitric oxide (NO) blockade with N_ω-nitro-L-arginine methyl ester (L-NAME) (p < .05). Maximal relaxation to ACh was similar in males and females with lower sensitivity in female AIP arteries (p < .05). Hemin induced greater relaxation in AIP arteries in both males and females (p < .05).

SUMMARY/CONCLUSIONS

Sex differences in this AIP mouse model include a pro-contractile response in females. These alterations may contribute to the increased blood pressure during an acute attack and provide a novel mechanism of action whereby heme ameliorates the attacks.

RSK2 contributes to myogenic vasoconstriction of resistance arteries by activating smooth muscle myosin and the Na+/H+ exchanger

Smooth muscle contraction is triggered when Ca²⁺/calmodulin-dependent myosin light chain kinase (MLCK) phosphorylates the regulatory light chain of myosin (RLC₂₀). However, blood vessels from Mlck-deficient mouse embryos retain the ability to contract, suggesting the existence of additional regulatory mechanisms. We showed that the p90 ribosomal S6 kinase 2 (RSK2) also phosphorylated RLC₂₀ to promote smooth muscle contractility. Active, phosphorylated RSK2 was present in mouse resistance arteries under normal basal tone, and phosphorylation of RSK2 increased with myogenic vasoconstriction or agonist stimulation. Resistance arteries from Rsk2-deficient mice were dilated and showed reduced myogenic tone and RLC₂₀ phosphorylation. RSK2 phosphorylated Ser¹⁹ in RLC in vitro. In addition, RSK2 phosphorylated an activating site in the Na⁺/H⁺ exchanger (NHE-1), resulting in cytosolic alkalinization and an increase in intracellular Ca²⁺ that promotes vasoconstriction. NHE-1 activity increased upon myogenic constriction, and the increase in intracellular pH was suppressed in Rsk2-deficient mice. In pressured arteries, RSK2-dependent activation of NHE-1 was associated with increased intracellular Ca²⁺ transients, which would be expected to increase MLCK activity, thereby contributing to basal tone and myogenic responses. Accordingly, Rsk2-deficient mice had lower blood pressure than normal littermates. Thus, RSK2 mediates a procontractile signaling pathway that contributes to the regulation of basal vascular tone, myogenic vasoconstriction, and blood pressure and may be a potential therapeutic target in smooth muscle contractility disorders.

The biological impact of blood pressure-associated genetic variants in the natriuretic peptide receptor C gene on human vascular smooth muscle

Elevated blood pressure (BP) is a major global risk factor for cardiovascular disease. Genome-wide association studies have identified several genetic variants at the NPR3 locus associated with BP, but the functional impact of these variants remains to be determined. Here we confirmed, by a genome-wide association study within UK Biobank, the existence of two independent BP-related signals within NPR3 locus. Using human primary vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) from different individuals, we found that the BP-elevating alleles within one linkage disequilibrium block identified by the sentinel variant rs1173771 was associated with lower endogenous NPR3 mRNA and protein levels in VSMCs, together with reduced levels in open chromatin and nuclear protein binding. The BP-elevating alleles also increased VSMC proliferation, angiotensin II-induced calcium flux and cell contraction. However, an analogous genotype-dependent association was not observed in vascular ECs. Our study identifies novel, putative mechanisms for BP-associated variants at the NPR3 locus to elevate BP, further strengthening the case for targeting NPR-C as a therapeutic approach for hypertension and cardiovascular disease prevention.

NMR insight into myosin-binding subunit coiled-coil structure reveals binding interface with protein kinase G-Iα leucine zipper in vascular function

Nitrovasodilators relax vascular smooth-muscle cells in part by modulating the interaction of the C-terminal coiled-coil domain (CC) and/or the leucine zipper (LZ) domain of the myosin light-chain phosphatase component, myosin-binding subunit (MBS), with the N-terminal LZ domain of protein kinase G (PKG)-Iα. Despite the importance of vasodilation in cardiovascular homeostasis and therapy, our structural understanding of the MBS CC interaction with LZ PKG-1α has remained limited. Here, we report the 3D NMR solution structure of homodimeric CC MBS in which amino acids 932-967 form a coiled-coil of two monomeric α-helices in parallel orientation. We found that the structure is stabilized by non-covalent interactions, with dominant contributions from hydrophobic residues at a and d heptad positions. Using NMR chemical-shift perturbation (CSP) analysis, we identified a subset of hydrophobic and charged residues of CC MBS (localized within and adjacent to the C-terminal region) contributing to the dimer-dimer interaction interface between homodimeric CC MBS and homodimeric LZ PKG-Iα. ¹⁵N backbone relaxation NMR revealed the dynamic features of the CC MBS interface residues identified by NMR CSP. Paramagnetic relaxation enhancement- and CSP-NMR-guided HADDOCK modeling of the dimer-dimer interface of the heterotetrameric complex exhibits the involvement of non-covalent intermolecular interactions that are localized within and adjacent to the C-terminal regions of each homodimer. These results deepen our understanding of the binding restraints of this CC MBS·LZ PKG-Iα low-affinity heterotetrameric complex and allow reevaluation of the role(s) of myosin light-chain phosphatase partner polypeptides in regulation of vascular smooth-muscle cell contractility.

The roles of sensitization and neuroplasticity in the long-term regulation of blood pressure and hypertension

After decades of investigation, the causes of essential hypertension remain obscure. The contribution of the nervous system has been excluded by some on the basis that baroreceptor mechanisms maintain blood pressure only over the short term. However, this point of view ignores one of the most powerful contributions of the brain in maintaining biological fitness-specifically, the ability to promote adaptation of behavioral and physiological responses to cope with new challenges and maintain this new capacity through processes involving neuroplasticity. We present a body of recent findings demonstrating that prior, short-term challenges can induce persistent changes in the central nervous system to result in an enhanced blood pressure response to hypertension-eliciting stimuli. This sensitized hypertensinogenic state is maintained in the absence of the inducing stimuli, and it is accompanied by sustained upregulation of components of the brain renin-angiotensin-aldosterone system and other molecular changes recognized to be associated with central nervous system neuroplasticity. Although the heritability of hypertension is high, it is becoming increasingly clear that factors beyond just genes contribute to the etiology of this disease. Life experiences and attendant changes in cellular and molecular components in the neural network controlling sympathetic tone can enhance the hypertensive response to recurrent, sustained, or new stressors. Although the epigenetic mechanisms that allow the brain to be reprogrammed in the face of challenges to cardiovascular homeostasis can be adaptive, this capacity can also be maladaptive under conditions present in different evolutionary eras or ontogenetic periods.

Vascular Type 1A Angiotensin II Receptors Control BP by Regulating Renal Blood Flow and Urinary Sodium Excretion

Inappropriate activation of the type 1A angiotensin (AT1A) receptor contributes to the pathogenesis of hypertension and its associated complications. To define the role for actions of vascular AT1A receptors in BP regulation and hypertension pathogenesis, we generated mice with cell-specific deletion of AT1A receptors in smooth muscle cells (SMKO mice) using Loxp technology and Cre transgenes with robust expression in both conductance and resistance arteries. We found that elimination of AT1A receptors from vascular smooth muscle cells (VSMCs) caused a modest (approximately 7 mmHg) yet significant reduction in baseline BP and exaggerated sodium sensitivity in mice. Additionally, the severity of angiotensin II (Ang II)-dependent hypertension was dramatically attenuated in SMKO mice, and this protection against hypertension was associated with enhanced urinary excretion of sodium. Despite the lower BP, acute vasoconstrictor responses to Ang II in the systemic vasculature were largely preserved (approximately 80% of control levels) in SMKO mice because of exaggerated activity of the sympathetic nervous system rather than residual actions of AT1B receptors. In contrast, Ang II-dependent responses in the renal circulation were almost completely eliminated in SMKO mice (approximately 5%-10% of control levels). These findings suggest that direct actions of AT1A receptors in VSMCs are essential for regulation of renal blood flow by Ang II and highlight the capacity of Ang II-dependent vascular responses in the kidney to effect natriuresis and BP control.

Direct contribution of vascular mineralocorticoid receptors to blood pressure regulation

Hypertension is an extremely prevalent cardiovascular risk factor and current antihypertensive therapies do not adequately treat hypertension in many affected individuals. Thus, a better understanding of mechanisms of hypertension could lead to novel therapies. Mineralocorticoid receptors (MR) are known to regulate blood pressure by responding to aldosterone in the kidney to regulate sodium retention. Recent evidence supports a direct contribution of the vasculature to control of BP and suggests the possibility that MR antagonists may also lower blood pressure by acting on extrarenal MR. This review summarizes existing research considering the role of the vascular MR in regulating vasoreactivity and blood pressure. Multiple studies indicate a role for vascular MR in modulating vasoconstriction and vasorelaxation. Activation of MR in vascular endothelial and smooth muscle cells leads to increased reactive oxygen species production and decreased availability of nitric oxide, important regulators of vascular reactivity. Transgenic mouse models, including an endothelial MR overexpressing mouse and a smooth muscle cell-specific MR-knockout mouse, support a direct role for vascular MR in control of blood pressure. This new evidence demonstrating that vascular MR directly contribute to control of vasoreactivity and blood pressure supports vascular MR and the pathways they control as novel therapeutic targets to treat hypertension.

Regulation of intraocular pressure by soluble and membrane guanylate cyclases and their role in glaucoma

Glaucoma is a progressive optic neuropathy characterized by visual field defects that ultimately lead to irreversible blindness (Alward, 2000; Anderson et al., 2006). By the year 2020, an estimated 80 million people will have glaucoma, 11 million of which will be bilaterally blind. Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Elevated intraocular pressure (IOP) is currently the only risk factor amenable to treatment. How IOP is regulated and can be modulated remains a topic of active investigation. Available therapies, mostly geared toward lowering IOP, offer incomplete protection, and POAG often goes undetected until irreparable damage has been done, highlighting the need for novel therapeutic approaches, drug targets, and biomarkers (Heijl et al., 2002; Quigley, 2011). In this review, the role of soluble (nitric oxide (NO)-activated) and membrane-bound, natriuretic peptide (NP)-activated guanylate cyclases that generate the secondary signaling molecule cyclic guanosine monophosphate (cGMP) in the regulation of IOP and in the pathophysiology of POAG will be discussed.

Increased constrictor tone induced by ouabain treatment in rats

Ouabain (Oua)-induced hypertension in rodents provides a model to study cardiovascular changes associated with human hypertension. We examined vascular function in rats after a long-term treatment with Oua. Systolic blood pressure was measured by tail-cuff plethysmography in male Sprague-Dawley rats treated with Oua (≈ 25 µg/d) or placebo for 8 weeks. Blood pressure increased in Oua-treated animals, reaching 30% above baseline systolic blood pressure after 7 weeks. At the end of treatment, vascular responses were studied in mesenteric resistance arteries (MRAs) by wire myography. Contraction to potassium chloride in intact and denuded arteries showed greater sensitivity in Oua-treated animals. Contraction to phenylephrine and relaxation to acetylcholine were similar between groups with a lower response to sodium nitroprusside in Oua-treated arteries. Sensitivity to endothelin-1 was higher in Oua-treated arteries. Na⁺-K⁺ ATPase activity was decreased in MRAs from Oua-treated animals, whereas protein expression of the Na⁺-K⁺ ATPase α₂ isoform was increased in heart and unchanged in mesenteric artery. Preincubation with indomethacin (10⁻⁵ M) or Nω-nitro-L-arginine methyl ester (10⁻⁴ M) abolished the differences in potassium chloride response and Na⁺-K⁺ ATPase activity. Changes in MRAs are consistent with enhanced vascular smooth muscle cell reactivity, a contributor to the increased vascular tone observed in this model of hypertension.

Disruption of vascular Ca2+-activated chloride currents lowers blood pressure

High blood pressure is the leading risk factor for death worldwide. One of the hallmarks is a rise of peripheral vascular resistance, which largely depends on arteriole tone. Ca2+-activated chloride currents (CaCCs) in vascular smooth muscle cells (VSMCs) are candidates for increasing vascular contractility. We analyzed the vascular tree and identified substantial CaCCs in VSMCs of the aorta and carotid arteries. CaCCs were small or absent in VSMCs of medium-sized vessels such as mesenteric arteries and larger retinal arterioles. In small vessels of the retina, brain, and skeletal muscle, where contractile intermediate cells or pericytes gradually replace VSMCs, CaCCs were particularly large. Targeted disruption of the calcium-activated chloride channel TMEM16A, also known as ANO1, in VSMCs, intermediate cells, and pericytes eliminated CaCCs in all vessels studied. Mice lacking vascular TMEM16A had lower systemic blood pressure and a decreased hypertensive response following vasoconstrictor treatment. There was no difference in contractility of medium-sized mesenteric arteries; however, responsiveness of the aorta and small retinal arterioles to the vasoconstriction-inducing drug U46619 was reduced. TMEM16A also was required for peripheral blood vessel contractility, as the response to U46619 was attenuated in isolated perfused hind limbs from mutant mice. Out data suggest that TMEM16A plays a general role in arteriolar and capillary blood flow and is a promising target for the treatment of hypertension.

Mineralocorticoid receptors in vascular disease: connecting molecular pathways to clinical implications

The mineralocorticoid receptor (MR), a steroid-hormone-activated transcription factor, plays a substantial role in cardiovascular diseases. MR antagonists (MRAs) have long been appreciated as effective treatments for heart failure and hypertension; however, recent research suggests that additional patient populations may also benefit from MRA therapy. Experimental evidence demonstrates that in addition to its classic role in the regulating sodium handling in the kidney, functional MR is expressed in the blood vessels and contributes to hypertension, vascular inflammation and remodeling, and atherogenesis. MR activation drives pathological phenotypes in smooth muscle cells, endothelial cells, and inflammatory cells, whereas MRAs inhibit these effects. Collectively, these studies demonstrate a new role for extrarenal MR in cardiovascular disease. This review summarizes these new lines of evidence and how they contribute to the mechanisms of atherosclerosis, pulmonary and systemic hypertension, and vein graft failure, and describes new patient populations that may benefit from MRA therapy.

Pathophysiology of hypertension in the absence of nitric oxide/cyclic GMP signaling

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling system is a well-characterized modulator of cardiovascular function, in general, and blood pressure, in particular. The availability of mice mutant for key enzymes in the NO-cGMP signaling system facilitated the identification of interactions with other blood pressure modifying pathways (e.g. the renin-angiotensin-aldosterone system) and of gender-specific effects of impaired NO-cGMP signaling. In addition, recent genome-wide association studies identified blood pressure-modifying genetic variants in genes that modulate NO and cGMP levels. Together, these findings have advanced our understanding of how NO-cGMP signaling regulates blood pressure. In this review, we will summarize the results obtained in mice with disrupted NO-cGMP signaling and highlight the relevance of this pathway as a potential therapeutic target for the treatment of hypertension.

Assessing murine resistance artery function using pressure myography

Pressure myograph systems are exquisitely useful in the functional assessment of small arteries, pressurized to a suitable transmural pressure. The near physiological condition achieved in pressure myography permits in-depth characterization of intrinsic responses to pharmacological and physiological stimuli, which can be extrapolated to the in vivo behavior of the vascular bed. Pressure myograph has several advantages over conventional wire myographs. For example, smaller resistance vessels can be studied at tightly controlled and physiologically relevant intraluminal pressures. Here, we study the ability of 3(rd) order mesenteric arteries (3-4 mm long), preconstricted with phenylephrine, to vaso-relax in response to acetylcholine. Mesenteric arteries are mounted on two cannulas connected to a pressurized and sealed system that is maintained at constant pressure of 60 mmHg. The lumen and outer diameter of the vessel are continuously recorded using a video camera, allowing real time quantification of the vasoconstriction and vasorelaxation in response to phenylephrine and acetylcholine, respectively. To demonstrate the applicability of pressure myography to study the etiology of cardiovascular disease, we assessed endothelium-dependent vascular function in a murine model of systemic hypertension. Mice deficient in the α1 subunit of soluble guanylate cyclase (sGCα1(-/-)) are hypertensive when on a 129S6 (S6) background (sGCα1(-/-S6)) but not when on a C57BL/6 (B6) background (sGCα1(-/-B6)). Using pressure myography, we demonstrate that sGCα1-deficiency results in impaired endothelium-dependent vasorelaxation. The vascular dysfunction is more pronounced in sGCα1(-/-S6) than in sGCα1(-/-B6) mice, likely contributing to the higher blood pressure in sGCα1(-/-S6) than in sGCα1(-/-B6) mice. Pressure myography is a relatively simple, but sensitive and mechanistically useful technique that can be used to assess the effect of various stimuli on vascular contraction and relaxation, thereby augmenting our insight into the mechanisms underlying cardiovascular disease.

Smooth muscle cell mineralocorticoid receptors: role in vascular function and contribution to cardiovascular disease

The mineralocorticoid receptor (MR), a member of the steroid receptor family, regulates blood pressure by mediating the effects of the hormone aldosterone on renal sodium handling. In recent years, it has become clear that MR is expressed in vascular smooth muscle cells (SMCs), and interest has grown in understanding the direct role of SMC MR in regulating vascular function. This interest stems from multiple clinical studies where MR inhibitor treatment reduced the incidence of cardiovascular events and mortality. This review summarizes the most recent advances in our understanding of SMC MR in regulating normal vascular function and in promoting vascular disease. Many new studies suggest a role for SMC MR activation in stimulating vascular contraction and contributing to vessel inflammation, fibrosis, and remodeling. These detrimental vascular effects of MR activation appear to be independent of changes in blood pressure and are synergistic with the presence of endothelial dysfunction or damage. Thus, in humans with underlying cardiovascular disease or cardiovascular risk factors, SMC MR activation may promote hypertension, atherosclerosis, and vascular aging. Further exploration of the molecular mechanisms for the effects of SMC MR activation has the potential to identify novel therapeutic targets to prevent or treat common cardiovascular disorders.

Genetic modifiers of hypertension in soluble guanylate cyclase α1-deficient mice

Nitric oxide (NO) plays an essential role in regulating hypertension and blood flow by inducing relaxation of vascular smooth muscle. Male mice deficient in a NO receptor component, the α1 subunit of soluble guanylate cyclase (sGCα1), are prone to hypertension in some, but not all, mouse strains, suggesting that additional genetic factors contribute to the onset of hypertension. Using linkage analyses, we discovered a quantitative trait locus (QTL) on chromosome 1 that was linked to mean arterial pressure (MAP) in the context of sGCα1 deficiency. This region is syntenic with previously identified blood pressure-related QTLs in the human and rat genome and contains the genes coding for renin. Hypertension was associated with increased activity of the renin-angiotensin-aldosterone system (RAAS). Further, we found that RAAS inhibition normalized MAP and improved endothelium-dependent vasorelaxation in sGCα1-deficient mice. These data identify the RAAS as a blood pressure-modifying mechanism in a setting of impaired NO/cGMP signaling.

Mineralocorticoid receptors in vascular function and disease

The mineralocorticoid receptor (MR), a member of the steroid receptor family, regulates blood pressure by mediating the effects of the hormone aldosterone (Aldo) on renal sodium handling. Over the past decade, it has become clear that MR is expressed in the cardiovascular system and interest has grown in understanding the direct role of the MR in regulating vascular function and contributing to cardiovascular disease. This interest stems from multiple clinical studies in which drugs that decrease MR activation also reduce the incidence of heart attacks, strokes, and mortality out of proportion to modest changes in systemic blood pressure. The presence of functional mineralocorticoid receptors in vascular smooth muscle and endothelial cells is now well established and, while still controversial, data supports the vasculature as an Aldo-responsive tissue. This review summarizes recent advances in our understanding of the role of vascular MR in regulating normal vascular function and in promoting vascular disease. In vitro data, in vivo animal studies, and human data are reviewed suggesting a role for MR-activation in promoting vascular oxidative stress, inhibiting vascular relaxation, and contributing to vessel inflammation, fibrosis, and remodeling. These detrimental vascular effects of MR activation appear to be independent of changes in blood pressure and are synergistic with the presence of endothelial dysfunction or damage. Thus, in humans with underlying cardiovascular disease or cardiovascular risk factors, vascular MR activation may promote vascular aging and atherosclerosis thereby contributing to the pathophysiology of heart attack, stroke, and possibly even hypertension. Further exploration of the molecular mechanisms for the detrimental vascular effects of MR activation has the potential to identify novel therapeutic targets to prevent or treat common cardiovascular disorders.

Role of myosin light chain kinase in regulation of basal blood pressure and maintenance of salt-induced hypertension

Vascular tone, an important determinant of systemic vascular resistance and thus blood pressure, is affected by vascular smooth muscle (VSM) contraction. Key signaling pathways for VSM contraction converge on phosphorylation of the regulatory light chain (RLC) of smooth muscle myosin. This phosphorylation is mediated by Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) but Ca(2+)-independent kinases may also contribute, particularly in sustained contractions. Signaling through MLCK has been indirectly implicated in maintenance of basal blood pressure, whereas signaling through RhoA has been implicated in salt-induced hypertension. In this report, we analyzed mice with smooth muscle-specific knockout of MLCK. Mesenteric artery segments isolated from smooth muscle-specific MLCK knockout mice (MLCK(SMKO)) had a significantly reduced contractile response to KCl and vasoconstrictors. The kinase knockout also markedly reduced RLC phosphorylation and developed force. We suggest that MLCK and its phosphorylation of RLC are required for tonic VSM contraction. MLCK(SMKO) mice exhibit significantly lower basal blood pressure and weaker responses to vasopressors. The elevated blood pressure in salt-induced hypertension is reduced below normotensive levels after MLCK attenuation. These results suggest that MLCK is necessary for both physiological and pathological blood pressure. MLCK(SMKO) mice may be a useful model of vascular failure and hypotension.

Renal actions of RGS2 control blood pressure

G protein-coupled receptors (GPCRs) have key roles in cardiovascular regulation and are important targets for the treatment of hypertension. GTPase-activating proteins, such as RGS2, modulate downstream signaling by GPCRs. RGS2 displays regulatory selectivity for the Gαq subclass of G proteins, and mice lacking RGS2 develop hypertension through incompletely understood mechanisms. Using total body RGS2-deficient mice, we used a kidney crosstransplantation strategy to examine separately the contributions of RGS2 actions in the kidney from those in extrarenal tissues with regard to BP regulation. Loss of renal RGS2 was sufficient to cause hypertension, whereas the absence of RGS2 from all extrarenal tissues including the peripheral vasculature did not significantly alter BP. Accordingly, these results suggest that RGS2 acts within the kidney to modulate BP and prevent hypertension. These data support a critical role for the renal epithelium and/or vasculature as the final determinants of the intra-arterial pressure in hypertension.

Little ROCK is a ROCK1 pseudogene expressed in human smooth muscle cells

Background

Sequencing of the human genome has identified numerous chromosome copy number additions and subtractions that include stable partial gene duplications and pseudogenes that when not properly annotated can interfere with genetic analysis. As an example of this problem, an evolutionary chromosome event in the primate ancestral chromosome 18 produced a partial duplication and inversion of rho-associated protein kinase 1 (ROCK1 -18q11.1, 33 exons) in the subtelomeric region of the p arm of chromosome 18 detectable only in humans. ROCK1 and the partial gene copy, which the gene databases also currently call ROCK1, include non-unique single nucleotide polymorphisms (SNPs).

Results

Here, we characterize this partial gene copy of the human ROCK1, termed Little ROCK, located at 18p11.32. Little ROCK includes five exons, four of which share 99% identity with the terminal four exons of ROCK1 and one of which is unique to Little ROCK. In human while ROCK1 is expressed in many organs, Little ROCK expression is restricted to vascular smooth muscle cell (VSMC) lines and organs rich in smooth muscle. The single nucleotide polymorphism database (dbSNP) lists multiple variants contained in the region shared by ROCK1 and Little ROCK. Using gene and cDNA sequence analysis we clarified the origins of two non-synonymous SNPs annotated in the genome to actually be fixed differences between the ROCK1 and the Little ROCK gene sequences. Two additional coding SNPs were valid polymorphisms selectively within Little ROCK. Little ROCK-Green Fluorescent fusion proteins were highly unstable and degraded by the ubiquitin-proteasome system in vitro.

Conclusion

In this report we have characterized Little ROCK (ROCK1P1), a human expressed pseudogene derived from partial duplication of ROCK1. The large number of pseudogenes in the human genome creates significant genetic diversity. Our findings emphasize the importance of taking into consideration pseudogenes in all candidate gene and genome-wide association studies, as well as the need for complete annotation of human pseudogenome.

Regulation of vascular contractility and blood pressure by the E2F2 transcription factor

BACKGROUND

Recent studies have identified a polymorphism in the endothelin-converting enzyme (ECE)-1b promoter (-338C/A) that is strongly associated with hypertension in women. The polymorphism is located in a consensus binding sequence for the E2F family of transcription factors. E2F proteins are crucially involved in cell-cycle regulation, but their roles in cardiovascular function are poorly understood. Here, we investigated the potential role of E2F2 in blood pressure regulation.

METHODS AND RESULTS

Tail-cuff measurements of systolic and diastolic blood pressures were significantly higher in E2F2-null (E2F2(-/-)) mice than in their wild-type littermates, and in ex vivo ring assays, aortas from the E2F2(-/-) mice exhibited significantly greater contractility in response to big endothelin-1. Big endothelin-1 is activated by ECE-1, and mRNA levels of ECE-1b, the repressive ECE-1 isoform, were significantly lower in E2F2(-/-) mice than in wild-type mice. In endothelial cells, chromatin immunoprecipitation assays confirmed that E2F2 binds the ECE-1b promoter, and promoter-reporter assays indicated that E2F2 activates ECE-1b transcription. Furthermore, loss or downregulation of E2F2 led to a decline in ECE-1b levels, to higher levels of the membranous ECE-1 isoforms (ie, ECE-1a, -1c, and -1d), and to deregulated ECE-1 activity. Finally, Sam68 coimmunoprecipitated with E2F2, occupied the ECE-1b promoter (chromatin immunoprecipitation), and repressed E2F2-mediated ECE-1b promoter activity (promoter-reporter assays).

CONCLUSIONS

Our results identify a cell-cycle-independent mechanism by which E2F2 regulates endothelial function, arterial contractility, and blood pressure.

The four-and-a-half LIM domain protein 2 regulates vascular smooth muscle phenotype and vascular tone

In response to vascular injury, differentiated vascular smooth muscle cells (vSMCs) undergo a unique process known as "phenotype modulation," transitioning from a quiescent, "contractile" phenotype to a proliferative, "synthetic" state. We have demonstrated previously that the signaling pathway of bone morphogenetic proteins, members of the transforming growth factor beta family, play a role in the induction and maintenance of a contractile phenotype in human primary pulmonary artery smooth muscle cells. In this study, we show that a four-and-a-half LIM domain protein 2 (FHL2) inhibits transcriptional activation of vSMC-specific genes mediated by the bone morphogenetic protein signaling pathway through the CArG box-binding proteins, such as serum response factor and members of the myocardin (Myocd) family. Interestingly, FHL2 does not affect recruitment of serum response factor or Myocd, however, it inhibits recruitment of a component of the SWI/SNF chromatin remodeling complex, Brg1, and RNA polymerase II, which are essential for the transcriptional activation. This is a novel mechanism of regulation of SMC-specific contractile genes by FHL2. Finally, aortic rings from homozygous FHL2-null mice display abnormalities in both endothelial-dependent and -independent relaxation, suggesting that FHL2 is essential for the regulation of vasomotor tone.

Probing the interaction between the coiled coil leucine zipper of cGMP-dependent protein kinase Ialpha and the C terminus of the myosin binding subunit of the myosin light chain phosphatase

Nitric oxide and nitrovasodilators induce vascular smooth muscle cell relaxation in part by cGMP-dependent protein kinase I (PKG-Ialpha)-mediated activation of myosin phosphatase (MLCP). Mechanistically it has been proposed that protein-protein interactions between the N-terminal leucine zipper (LZ) domain of PKG-Ialpha ((PKG-Ialpha(1-59)) and the LZ and/or coiled coil (CC) domain of the myosin binding subunit (MBS) of MLCP are localized in the C terminus of MBS. Although recent studies have supported these interactions, the critical amino acids responsible for these interactions have not been identified. Here we present structural and biophysical data identifying that the LZ domain of PKG-Ialpha(1-59) interacts with a well defined 42-residue CC motif (MBS(CT42)) within the C terminus of MBS. Using glutathione S-transferase pulldown experiments, chemical cross-linking, size exclusion chromatography, circular dichroism, and isothermal titration calorimetry we identified a weak dimer-dimer interaction between PKG-Ialpha(1-59) and this C-terminal CC domain of MBS. The K(d) of this non-covalent complex is 178.0+/-1.5 microm. Furthermore our (1)H-(15)N heteronuclear single quantum correlation NMR data illustrate that this interaction is mediated by several PKG-Ialpha residues that are on the a, d, e, and g hydrophobic and electrostatic interface of the C-terminal heptad layers 2, 4, and 5 of PKG-Ialpha. Taken together these data support a role for the LZ domain of PKG-Ialpha and the CC domain of MBS in this requisite contractile complex.

High blood pressure arising from a defect in vascular function

Hypertension, a major cardiovascular risk factor and cause of mortality worldwide, is thought to arise from primary renal abnormalities. However, the etiology of most cases of hypertension remains unexplained. Vascular tone, an important determinant of blood pressure, is regulated by nitric oxide, which causes vascular relaxation by increasing intracellular cGMP and activating cGMP-dependent protein kinase I (PKGI). Here we show that mice with a selective mutation in the N-terminal protein interaction domain of PKGIalpha display inherited vascular smooth muscle cell abnormalities of contraction, abnormal relaxation of large and resistance blood vessels, and increased systemic blood pressure. Renal function studies and responses to changes in dietary sodium in the PKGIalpha mutant mice are normal. These data reveal that PKGIalpha is required for normal VSMC physiology and support the idea that high blood pressure can arise from a primary abnormality of vascular smooth muscle cell contractile regulation, suggesting a new approach to the diagnosis and therapy of hypertension and cardiovascular diseases.

Cardiovascular effects of a novel potent and highly selective azaindole-based inhibitor of Rho-kinase

BACKGROUND AND PURPOSE

Rho-kinase (ROCK) has been implicated in the pathophysiology of altered vasoregulation leading to hypertension. Here we describe the pharmacological characterization of a potent, highly selective and orally active ROCK inhibitor, the derivative of a class of azaindoles, azaindole 1 (6-chloro-N4-{3,5-difluoro-4-[(3-methyl-1H-pyrrolo[2,3-b]pyridin-4-yl)oxy]-phenyl}pyrimidine-2,4-diamine).

EXPERIMENTAL APPROACH

Pharmacological characterization of azaindole 1 was performed with human recombinant ROCK in vitro. Vasodilator activity was determined using isolated vessels in vitro and different animal models in vivo.

KEY RESULTS

This compound inhibited the ROCK-1 and ROCK-2 isoenzymes with IC50 s of 0.6 and 1.1 nM in an ATP-competitive manner. Although ATP-competitive, azaindole 1 was inactive against 89 kinases (IC50>10 microM) and showed only weak activity against an additional 21 different kinases (IC50=1-10 microM). Only the kinases TRK und FLT3 were inhibited by azaindole 1 in the sub-micromolar range, albeit with IC50 values of 252 and 303 nM, respectively. In vivo, azaindole 1 lowered blood pressure dose-dependently after i.v. administration in anaesthetized normotensive rats. In conscious normotensive and spontaneously hypertensive rats azaindole 1 induced a dose-dependent decrease in blood pressure after oral administration without inducing a significant reflex increase in heart rate. In anaesthetized dogs, azaindole 1 induced vasodilatation with a moderately elevated heart rate.

CONCLUSIONS AND IMPLICATIONS

Azaindole 1 is representative of a new class of selective and potent ROCK inhibitors and is a valuable tool for the elucidation of the role of ROCK in the cardiovascular system.