Sustained hypertension despite endothelial-specific eNOS rescue in eNOS-deficient mice

eNOS plays essential roles in the developing heart and aorta linked to disruption of Notch signalling

eNOS (NOS3) is the enzyme that generates nitric oxide, a signalling molecule and regulator of vascular tone. Loss of eNOS function is associated with increased susceptibility to atherosclerosis, hypertension, thrombosis and stroke. Aortopathy and cardiac hypertrophy have also been found in eNOS null mice, but their aetiology is unclear. We evaluated eNOS nulls before and around birth for cardiac defects, revealing severe abnormalities in the ventricular myocardium and pharyngeal arch arteries. Moreover, in the aortic arch, there were fewer baroreceptors, which sense changes in blood pressure. Adult eNOS null survivors showed evidence of cardiac hypertrophy, aortopathy and cartilaginous metaplasia in the periductal region of the aortic arch. Notch1 and neuregulin were dysregulated in the forming pharyngeal arch arteries and ventricles, suggesting that these pathways may be relevant to the defects observed. Dysregulation of eNOS leads to embryonic and perinatal death, suggesting mutations in eNOS are candidates for causing congenital heart defects in humans. Surviving eNOS mutants have a deficiency of baroreceptors that likely contributes to high blood pressure and may have relevance to human patients who suffer from hypertension associated with aortic arch abnormalities.

Activation of the aryl hydrocarbon receptor by clozapine induces preadipocyte differentiation and contributes to endothelial dysfunction

BACKGROUND

The superior therapeutic benefit of clozapine is often associated with metabolic disruptions as obesity, insulin resistance, tachycardia, higher blood pressure, and even hypertension.

AIMS

These adverse vascular/ metabolic events under clozapine are similar to those caused by polycyclic aromatic hydrocarbons (PAHs), and clozapine shows structural similarity to well-known ligands of the aryl hydrocarbon receptor (AhR). Therefore, we speculated that the side effects caused by clozapine might rely on AhR signaling.

METHODS

We examined clozapine-induced AhR activation by luciferase reporter assays in hepatoma HepG2 cells and we proved upregulation of the prototypical AhR target gene Cyp1A1 by realtime-PCR (RT-PCR) analysis and enzyme activity. Next we studied the physiological role of AhR in clozapine's effects on human preadipocyte differentiation and on vasodilatation by myography in wild-type and AhR-/- mice.

RESULTS

In contrast to other antipsychotic drugs (APDs), clozapine triggered AhR activation and Cyp1A1 expression in HepG2 cells and adipocytes. Clozapine induced adipogenesis via AhR signaling. After PGF2α-induced constriction of mouse aortic rings, clozapine strongly reduced the maximal vasorelaxation under acetylcholine in rings from wild-type mice, but only slightly in rings from AhR-/- mice. The reduction was also prevented by pretreatment with the AhR antagonist CH-223191.

CONCLUSION

Identification of clozapine as a ligand for the AhR opens new perspectives to explain common clozapine therapy-associated adverse effects at the molecular level.

Disturbed nitric oxide signalling gives rise to congenital bicuspid aortic valve and aortopathy

Patients with a congenital bicuspid aortic valve (BAV), a valve with two instead of three aortic leaflets, have an increased risk of developing thoracic aneurysms and aortic dissection. The mechanisms underlying BAV-associated aortopathy are poorly understood. This study examined BAV-associated aortopathy in Nos3^−/− mice, a model with congenital BAV formation. A combination of histological examination and in vivo ultrasound imaging was used to investigate aortic dilation and dissections in Nos3^−/− mice. Moreover, cell lineage analysis and single-cell RNA sequencing were used to observe the molecular anomalies within vascular smooth muscle cells (VSMCs) of Nos3^−/− mice. Spontaneous aortic dissections were found in ascending aortas located at the sinotubular junction in ∼13% of Nos3^−/− mice. Moreover, Nos3^−/− mice were prone to developing aortic dilations in the proximal and distal ascending aorta during early adulthood. Lower volumes of elastic fibres were found within vessel walls of the ascending aortas of Nos3^−/− mice, as well as incomplete coverage of the aortic inner media by neural crest cell (NCC)-derived VSMCs. VSMCs of Nos3^−/− mice showed downregulation of 15 genes, of which seven were associated with aortic aneurysms and dissections in the human population. Elastin mRNA was most markedly downregulated, followed by fibulin-5 expression, both primary components of elastic fibres. This study demonstrates that, in addition to congenital BAV formation, disrupted endothelial-mediated nitric oxide (NO) signalling in Nos3^−/− mice also causes aortic dilation and dissection, as a consequence of inhibited elastic fibre formation in VSMCs within the ascending aorta.

Summary: Nitric oxide defects link bicuspid aortic valve formation and aortopathy through inhibition of elastic fibre formation in vascular smooth muscle cells within the ascending aorta of Nos3^−/− mice.

Antihypertensive effects of Trichiurus lepturus myosin hydrolysate in spontaneously hypertensive rats

In this study, the blood pressure-lowering effects of Trichiurus lepturus myosin hydrolysate (TMH) and its possible mechanism were investigated in spontaneously hypertensive rats (SHRs). After gavage administration of TMH for 4 h, systolic blood pressure (SBP) was significantly decreased in SHRs. Furthermore, the SBP of SHRs remained low at 1 month after daily TMH treatment at 400 mg kg-1. Meanwhile, plasma levels of angiotensin II, bradykinin and nitric oxide in SHRs were ameliorated by TMH. Western blotting also suggested that TMH down-regulated the expression of ICAM-1 and VCAM-1, indicating a strong anti-inflammatory effect. Additionally, nitrotyrosine and collagen I were down-regulated, revealing a significant anti-oxidant effect of TMH. No obvious side effects or toxicity were observed in normal Wistar rats given TMH. Various pathogenic factors related to hypertension were improved by TMH, which may explain the underlying mechanism by which TMH synergistically reduces blood pressure.

Nephron-Specific Disruption of Nitric Oxide Synthase 3 Causes Hypertension and Impaired Salt Excretion

BACKGROUND

In vitro studies suggest that nephron nitric oxide synthase 3 (NOS3) modulates tubule Na⁺ transport.

METHODS AND RESULTS

To assess nephron NOS3 relevance in vivo, knockout (KO) mice with doxycycline-inducible nephron-wide deletion of NOS3 were generated. During 1 week of salt loading, KO mice, as compared with controls, had higher arterial pressure and Na⁺ retention, a tendency towards reduced plasma renin concentration, and unchanged glomerular filtration rate. Chronic high salt-treated KO mice had modestly decreased total NCC and total SPAK/OSR1 versus controls, however percent phosphorylation of NCC (at T⁵³) and of SPAK/OSR1 was increased. In contrast, total and phosphorylated NKCC2 (at T^96/101) were suppressed by 50% each in KO versus control mice after chronic salt intake. In response to an acute salt load, KO mice had delayed urinary Na⁺ excretion versus controls; this delay was completely abolished by furosemide, partially reduced by hydrochlorothiazide, but not affected by amiloride. After 4 hours of an acute salt load, phosphorylated and total NCC were elevated in KO versus control mice. Acute salt loading did not alter total NKCC2 or SPAK/OSR1 in KO versus control mice but increased the percent phosphorylation of NKCC2 (at T^96/101 and S¹²⁶) and SPAK/OSR1 in KO versus control mice.

CONCLUSIONS

These findings indicate that nephron NOS3 is involved in blood pressure regulation and urinary Na⁺ excretion during high salt intake. Nephron NOS3 appears to regulate NKCC2 and NCC primarily during acute salt loading. These effects of NOS3 may involve SPAK/OSR1 as well as other pathways.

Selective impairment of blood pressure reduction by endothelial nitric oxide synthase dimer destabilization in mice

OBJECTIVES

Endothelial dysfunction and oxidative stress are associated with hypertension but whether endothelial superoxide may play a role in the early development of essential hypertension remains uncertain. We investigated whether endothelial nitric oxide synthase (eNOS)-derived endothelial oxidative stress is involved in the regulation of SBP.

METHODS

Wild-type eNOS [mice with endothelium-specific overexpression of bovine endothelial NO-synthase (eNOS-Tg)] or a novel dimer-destabilized eNOS-mutant harboring a partially disrupted zinc-finger [mice with endothelium-specific overexpression of destabilized bovine eNOS destabilized by replacement of Cys 101 to Ala (C101A-eNOS-Tg)] was introduced in C57BL/6 in an endothelial-specific manner. Mice were monitored for aortic endothelium-dependent relaxation, SBP, levels of superoxide and several posttranslational modifications indicating activity and/or increased vascular oxidative stress. Some groups of mice underwent voluntary exercise training for 4 weeks or treatment with the superoxide dismutase mimetic Tempol.

RESULTS

C101A-eNOS-Tg showed significantly increased superoxide generation, protein-tyrosine-nitration and eNOS-tyrosine-nitration, eNOS-S-glutathionylation, eNOS phosphorylation and AMP kinase-α phosphorylation at Thr172 in aorta, skeletal muscle, left ventricular myocardium and lung as compared with eNOS-Tg and wild-type controls. Exercise training increased phosphorylation of eNOS at Ser and AMP kinase-α in wild-type. These physiologic adaptations were absent in C101A-eNOS-Tg. Maximal aortic endothelium-dependent relaxation was similar in all strains. C101A-eNOS-Tg displayed normal SBP despite higher levels of eNOS, whereas eNOS-Tg showed significant hypotension. Tempol completely reversed the occurring protein modifications and significantly reduced SBP in C101A-eNOS-Tg but not in wild-type.

CONCLUSION

Oxidative stress generated by endothelial-specific expression of genetically destabilized C101A-eNOS selectively prevents SBP-reducing activity of vascular eNOS, while having no effect on aortic endothelium-dependent relaxation. These data suggest that oxidative stress in microvascular endothelium may play a role for the development of essential hypertension.

Collecting duct-specific knockout of nitric oxide synthase 3 impairs water excretion in a sex-dependent manner

Nitric oxide (NO) inhibits collecting duct (CD) Na⁺ and water reabsorption. Mice with CD-specific knockout (KO) of NO synthase 1 (NOS1) have salt-sensitive hypertension. In contrast, the role of NOS3 in CD salt and water reabsorption is unknown. Mice with CD NOS3 KO were generated with loxP-flanked exons 9-12 (encodes the calmodulin binding site) of the NOS3 gene and the aquaporin-2 promoter-Cre transgene. There were no differences between control and CD NOS3 KO mice, irrespective of sex, in food intake, water intake, urine volume, urinary Na⁺ or K⁺ excretion, plasma renin concentration, blood pressure, or pulse during 7 days of normal (0.3%), high (3.17%), or low (0.03%) Na⁺ intake. Blood pressure was similar between genotypes during DOCA-high salt. CD NOS3 KO did not alter urine volume or urine osmolality after water deprivation. In contrast, CD NOS3 KO male, but not female, mice had lower urine volume and higher urine osmolality over the course of 7 days of water loading compared with control mice. Male, but not female, CD NOS3 KO mice had reduced urinary nitrite+nitrate excretion compared with controls after 7 days of water loading. Urine AVP and AVP-stimulated cAMP accumulation in isolated inner medullary CD were similar between genotypes. Western analysis did not reveal a significant effect of CD NOS3 KO on renal aquaporin expression. In summary, these data suggest that CD NOS3 may be involved in the diuretic response to a water load in a sex-specific manner; the mechanism of this effect remains to be determined.

NO-Synthase Activity in Patients with Coronary Heart Disease Associated with Hypertension of Different Age Groups

Background

Coronary heart disease is the leading cause of death and disability worldwide. Hypertension is a major independent risk factor for the development of CHD. Abnormalities in NO generation or activity have been proposed as a major mechanism of CHD. The purpose of this article is to determine the activity of eNOS and iNOS in patients with isolated CHD and CHD associated with HT of different age groups.

Methods

Fifty patients with isolated CHD and 42 patients with CHD associated with HT were enrolled in this study. NOS activity was determined by nitrite anion formed in the reaction.

Results

A statistically significant increase in iNOS activity is observed in elderly donors. In patients with isolated coronary heart disease cNOS activity is statistically significantly reduced with respect to the control group. The reduction of enzymatic activity of cNOS is more expressed in elderly patients than in middle-aged patients with coronary heart disease. Alterations in eNOS activity are more expressed in patients with coronary heart disease associated with hypertension than in patients with isolated coronary heart disease. Against the background of cNOS inhibition in the patients, a sharp increase in iNOS activity is observed.

Conclusions

It has been shown that disturbance of endothelial function in patients with coronary heart disease associated with hypertension is characterized by reduced endothelial NO synthesis by cNOS and increased systemic NO synthesis due to increased iNOS activity. It has been found that the lack of endothelial NO and hyperproduction of »harmful« NO by iNOS are more expressed in elderly patients.

Impact of eNOS-Dependent Oxidative Stress on Endothelial Function and Neointima Formation

AIMS

Vascular oxidative stress generated by endothelial NO synthase (eNOS) was observed in experimental and clinical cardiovascular disease, but its relative importance for vascular pathologies is unclear. We investigated the impact of eNOS-dependent vascular oxidative stress on endothelial function and on neointimal hyperplasia.

RESULTS

A dimer-destabilized mutant of bovine eNOS where cysteine 101 was replaced by alanine was cloned and introduced into an eNOS-deficient mouse strain (eNOS-KO) in an endothelial-specific manner. Destabilization of mutant eNOS in cells and eNOS-KO was confirmed by the reduced dimer/monomer ratio. Purified mutant eNOS and transfected cells generated less citrulline and NO, respectively, while superoxide generation was enhanced. In eNOS-KO, introduction of mutant eNOS caused a 2.3-3.7-fold increase in superoxide and peroxynitrite formation in the aorta and myocardium. This was completely blunted by an NOS inhibitor. Nevertheless, expression of mutant eNOS in eNOS-KO completely restored maximal aortic endothelium-dependent relaxation to acetylcholine. Neointimal hyperplasia induced by carotid binding was much larger in eNOS-KO than in mutant eNOS-KO and C57BL/6, while the latter strains showed comparable hyperplasia. Likewise, vascular remodeling was blunted in eNOS-KO only.

INNOVATION

Our results provide the first in vivo evidence that eNOS-dependent oxidative stress is unlikely to be an initial cause of impaired endothelium-dependent vasodilation and/or a pathologic factor promoting intimal hyperplasia. These findings highlight the importance of other sources of vascular oxidative stress in cardiovascular disease.

CONCLUSION

eNOS-dependent oxidative stress is unlikely to induce functional vascular damage as long as concomitant generation of NO is preserved. This underlines the importance of current and new therapeutic strategies in improving endothelial NO generation.