Enhanced electron flux and reduced calmodulin dissociation may explain "calcium-independent" eNOS activation by phosphorylation

The Ever-Expanding Influence of the Endothelial Nitric Oxide Synthase

Nitric oxide (NO) generated by the endothelial NO synthase (eNOS) plays an essential role in the maintenance of vascular homeostasis and the prevention of vascular inflammation. There are a myriad of mechanisms that regulate the activity of the enzyme that may prove to represent interesting therapeutic opportunities. In this regard, the kinases that phosphorylate the enzyme and regulate its activity in situations linked to vascular disease seem to be particularly promising. Although the actions of NO were initially linked mainly to the activation of the guanylyl cyclase and the generation of cyclic GMP in vascular smooth muscle cells and platelets, it is now clear that NO elicits the majority of its actions via its ability to modify redox-activated cysteine residues in a process referred to as S-nitrosylation. The more wide spread use of mass spectrometry to detect S-nitrosylated proteins has helped to identify just how large the NO sphere of influence is and just how many cellular processes are affected. It may be an old target, but the sheer impact of eNOS on vascular health really justifies a revaluation of therapeutic options to maintain and protect its activity in situations associated with a high risk of developing cardiovascular disease.

Promotion of nitric oxide production: mechanisms, strategies, and possibilities

The discovery of nitric oxide (NO) and the role of endothelial cells (ECs) in its production has revolutionized medicine. NO can be produced by isoforms of NO synthases (NOS), including the neuronal (nNOS), inducible (iNOS), and endothelial isoforms (eNOS), and via the non-classical nitrate-nitrite-NO pathway. In particular, endothelium-derived NO, produced by eNOS, is essential for cardiovascular health. Endothelium-derived NO activates soluble guanylate cyclase (sGC) in vascular smooth muscle cells (VSMCs), elevating cyclic GMP (cGMP), causing vasodilation. Over the past four decades, the importance of this pathway in cardiovascular health has fueled the search for strategies to enhance NO bioavailability and/or preserve the outcomes of NO's actions. Currently approved approaches operate in three directions: 1) providing exogenous NO, 2) promoting sGC activity, and 3) preventing degradation of cGMP by inhibiting phosphodiesterase 5 activity. Despite clear benefits, these approaches face challenges such as the development of nitrate tolerance and endothelial dysfunction. This highlights the need for sustainable options that promote endogenous NO production. This review will focus on strategies to promote endogenous NO production. A detailed review of the mechanisms regulating eNOS activity will be first provided, followed by a review of strategies to promote endogenous NO production based on the levels of available preclinical and clinical evidence, and perspectives on future possibilities.

Alcohol-induced gut microbial reorganization and associated overproduction of phenylacetylglutamine promotes cardiovascular disease

The mechanism(s) underlying gut microbial metabolite (GMM) contribution towards alcohol-mediated cardiovascular disease (CVD) is unknown. Herein we observe elevation in circulating phenylacetylglutamine (PAGln), a known CVD-associated GMM, in individuals living with alcohol use disorder. In a male murine binge-on-chronic alcohol model, we confirm gut microbial reorganization, elevation in PAGln levels, and the presence of cardiovascular pathophysiology. Fecal microbiota transplantation from pair-/alcohol-fed mice into naïve male mice demonstrates the transmissibility of PAGln production and the CVD phenotype. Independent of alcohol exposure, pharmacological-mediated increases in PAGln elicits direct cardiac and vascular dysfunction. PAGln induced hypercontractility and altered calcium cycling in isolated cardiomyocytes providing evidence of improper relaxation which corresponds to elevated filling pressures observed in vivo. Furthermore, PAGln directly induces vascular endothelial cell activation through induction of oxidative stress leading to endothelial cell dysfunction. We thus reveal that the alcohol-induced microbial reorganization and resultant GMM elevation, specifically PAGln, directly contributes to CVD.

Early pathological mechanisms in a mouse model of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) constitutes more than half of all HF cases, yet evidence-based therapies remain lacking due to limited understanding of its underlying pathological mechanisms. Our study aimed to uncover early pathological mechanisms in HFpEF by exposing mice to dietary conditions resembling a Western diet-rich in fats, salt, and low in fiber-alongside excess mineralocorticoids to replicate significant aspects of human HFpEF. Echocardiography was performed at both 3-wk and 6-wk intervals postchallenge, revealing cardiac alterations as early as 3 wk. While ejection fraction remained preserved, mice exhibited signs of diastolic dysfunction, reduced stroke volume, and left atrial enlargement. In addition, changes in pulmonary flow velocities were noted by the 3-wk mark, suggesting elevated pulmonary pressure. Extracardiac comorbidities included organ congestion, increased adiposity, impaired glucose tolerance, and hypercholesterolemia. Molecular analyses unveiled evidence of low-grade inflammation, oxidative stress, and impaired NO-cGMP-PKG signaling, contributing to the observed decrease in titin phosphorylation, thereby impacting myocardial stiffness. In addition, impaired nitric oxide (NO) signaling might have influenced the alterations observed in coronary flow reserve. Moreover, dysregulation of calcium signaling in cardiomyocytes and reduced sarcoplasmic reticulum (SR) load were observed. Interestingly, elevated phosphorylation of cMyBP-C was linked to preserved ejection fraction despite reduced SR load. We also observed intestinal atrophy, possibly due to a high-fat diet, low dietary fiber intake, and diminished gut perfusion, potentially contributing to systemic low-grade inflammation. These findings reveal how excess mineralocorticoid salt-induced hypertension and dietary factors, like high-fat and low-fiber intake, contribute to cardiac dysfunction and metabolic disturbances, offering insights into early HFpEF pathology in this model.NEW & NOTEWORTHY Our study demonstrates that feeding mice a Western diet rich in fat and salt and low in fiber alongside excess mineralocorticoids replicates aspects of human HFpEF. Cardiac alterations including diastolic dysfunction and decreased stroke volume with preserved ejection fraction were observed. Extracardiac effects included organ congestion, adiposity, glucose intolerance, and intestinal atrophy. Molecular analysis revealed inflammation, oxidative stress, impaired NO-cGMP-PKG signaling pathways, and altered calcium signaling in cardiomyocytes, shedding light on early pathological changes in HFpEF.

Aortic Cellular Heterogeneity in Health and Disease: Novel Insights Into Aortic Diseases From Single-Cell RNA Transcriptomic Data Sets

Aortic diseases such as atherosclerosis, aortic aneurysms, and aortic stiffening are significant complications that can have significant impact on end-stage cardiovascular disease. With limited pharmacological therapeutic strategies that target the structural changes in the aorta, surgical intervention remains the only option for some patients with these diseases. Although there have been significant contributions to our understanding of the cellular architecture of the diseased aorta, particularly in the context of atherosclerosis, furthering our insight into the cellular drivers of disease is required. The major cell types of the aorta are well defined; however, the advent of single-cell RNA sequencing provides unrivaled insights into the cellular heterogeneity of each aortic cell type and the inferred biological processes associated with each cell in health and disease. This review discusses previous concepts that have now been enhanced with recent advances made by single-cell RNA sequencing with a focus on aortic cellular heterogeneity.

Differential superoxide production in phosphorylated neuronal nitric oxide synthase mu and alpha variants

Neuronal nitric oxide synthase (nNOS) is regulated by phosphorylation in vivo, yet the underlying biochemical mechanisms remain unclear, primarily due to difficulty in obtaining milligram quantities of phosphorylated nNOS protein; detailed spectroscopic and rapid kinetics investigations require purified protein samples at a concentration in the range of hundreds microM. Moreover, the functional diversity of the nNOS isoform is linked to its splice variants. Also of note is that determination of protein phosphorylation stoichiometry remains as a challenge. To address these issues, this study first expanded a recent genetic code expansion approach to produce phosphorylated rat nNOSμ and nNOSα holoproteins through site-specific incorporation of phosphoserine (pSer) at residues 1446 and 1412, respectively; this site is at the C-terminal tail region, a NOS-unique regulatory element. A quantitative mass spectrometric approach was then developed in-house to analyze unphosphorylated peptides in phosphatase-treated and -untreated phospho-nNOS proteins. The observed pSer-incorporation efficiency consistently exceeded 80%, showing high pSer-incorporation efficiency. Notably, EPR spin trapping results demonstrate that under l-arginine-depleted conditions, pSer1412 nNOSα presented a significant reduction in superoxide generation, whereas pSer1446 nNOSμ exhibited the opposite effect, compared to their unphosphorylated counterparts. This suggests that phosphorylation at the C-terminal tail has a regulatory effect on nNOS uncoupling that may differ between variant forms. Furthermore, the methodologies for incorporating pSer into large, complex protein and quantifying the percentage of phosphorylation in recombinant purified protein should be applicable to other protein systems.

Modulation of the nitric oxide/cGMP pathway in cardiac contraction and relaxation: Potential role in heart failure treatment

Evidence exists that heart failure (HF) has an overall impact of 1-2 % in the global population being often associated with comorbidities that contribute to increased disease prevalence, hospitalization, and mortality. Recent advances in pharmacological approaches have significantly improved clinical outcomes for patients with vascular injury and HF. Nevertheless, there remains an unmet need to clarify the crucial role of nitric oxide/cyclic guanosine 3',5'-monophosphate (NO/cGMP) signalling in cardiac contraction and relaxation, to better identify the key mechanisms involved in the pathophysiology of myocardial dysfunction both with reduced (HFrEF) as well as preserved ejection fraction (HFpEF). Indeed, NO signalling plays a crucial role in cardiovascular homeostasis and its dysregulation induces a significant increase in oxidative and nitrosative stress, producing anatomical and physiological cardiac alterations that can lead to heart failure. The present review aims to examine the molecular mechanisms involved in the bioavailability of NO and its modulation of downstream pathways. In particular, we focus on the main therapeutic targets and emphasize the recent evidence of preclinical and clinical studies, describing the different emerging therapeutic strategies developed to counteract NO impaired signalling and cardiovascular disease (CVD) development.

Growth State-Dependent Activation of eNOS in Response to DHA: Involvement of p38 MAPK

Our laboratory previously reported that docosahexaenoic acid (DHA) differentially activates p38 mitogen-activated protein kinase (MAPK) in growing and quiescent human endothelial cells, which represent the dysfunctional and healthy states in vivo, respectively. Since endothelial nitric oxide synthase (eNOS) activity differs between healthy and dysfunctional endothelial cells, and p38 MAPK reportedly regulates both the activity and expression of eNOS, we hypothesized that the beneficial actions of DHA on endothelial cells are due to eNOS activation by p38 MAPK. The contribution of mitogen- and stress-activated protein kinase (MSK), a p38 MAPK substrate, was also investigated. Growing and quiescent EA.hy926 cells, prepared on Matrigel^®-coated plates, were incubated with inhibitors of p38MAPK or MSK before adding DHA. eNOS phosphorylation and levels were quantified by Western blotting. Treatment with 20 µM DHA activated eNOS in both growth states whereas 125 µM DHA suppressed eNOS activation in growing cells. Quiescent cells had higher basal levels of eNOS than growing cells, while 125 µM DHA decreased eNOS levels in both growth states. p38 MAPK inhibition enhanced eNOS activation in quiescent cells but suppressed it in growing cells. Interestingly, 125 µM DHA counteracted these effects of p38 MAPK inhibition in both growth states. MSK was required for eNOS activation in both growth states, but it only mediated eNOS activation by DHA in quiescent cells. MSK thus affects eNOS via a pathway independent of p38MAPK. Quiescent cells were also more resistant to the apoptosis-inducing effect of 125 µM DHA compared to growing cells. The growth state-dependent regulation of p38MAPK and eNOS by DHA provides novel insight into the molecular mechanisms by which DHA influences endothelial cell function.

Arbitrary Ca2+ regulation for endothelial nitric oxide, NFAT and NF-κB activities by an optogenetic approach

Modern western dietary habits and low physical activity cause metabolic abnormalities and abnormally elevated levels of metabolites such as low-density lipoprotein, which can lead to immune cell activation, and inflammatory reactions, and atherosclerosis. Appropriate stimulation of vascular endothelial cells can confer protective responses against inflammatory reactions and atherosclerotic conditions. This study aims to determine whether a designed optogenetic approach is capable of affecting functional changes in vascular endothelial cells and to evaluate its potential for therapeutic regulation of vascular inflammatory responses in vitro. We employed a genetically engineered, blue light-activated Ca²⁺ channel switch molecule that utilizes an endogenous store-operated calcium entry system and induces intracellular Ca²⁺ influx through blue light irradiation and observed an increase in intracellular Ca²⁺ in vascular endothelial cells. Ca²⁺-dependent activation of the nuclear factor of activated T cells and nitric oxide production were also detected. Microarray analysis of Ca²⁺-induced changes in vascular endothelial cells explored several genes involved in cellular contractility and inflammatory responses. Indeed, there was an increase in the gene expression of molecules related to anti-inflammatory and vasorelaxant effects. Thus, a combination of human blue light-activated Ca²⁺ channel switch 2 (hBACCS2) and blue light possibly attenuates TNFα-induced inflammatory NF-κB activity. We propose that extrinsic cellular Ca²⁺ regulation could be a novel approach against vascular inflammation.

The role of arginine and endothelial nitric oxide synthase in the pathogenesis of Covid-19 complicated by metabolic syndrome

This literature review presents the role of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO), as well as arginine, the enzyme substrate, in the disease of metabolic syndrome and COVID-19 (SARS-CoV-2 virus). Metabolic syndrome is a combination of obesity, insulin resistance, hyperglycemia, dyslipidemia and hypertension. It has been shown that in elderly people, patients with obesity, metabolic syndrome, type 2 diabetes mellitus (DM2), and patients with COVID-19, endothelial dysfunction (ED) and vascular endothelial activation are detected. ED is the main cause of a number of pathological conditions during the development of COVID-19 and earlier in patients with metabolic syndrome, while a sharp drop in the level of nitric oxide (NO) is detected due to a decrease in the expression and activity of eNO synthase and enzyme depletion, which leads to a violation of the integrity of bloodvessels, that is, to vasoconstrictive, inflammatory and thrombotic conditions, followed by ischemia of organs and edema of tissues. It should be noted that metabolic syndrome, DM2, hypertension and obesity, in particular, are age-related diseases, and it is known that blood glucose levels increase with age, which reduces the bioavailability of NO in endothelial cells. Defects in the metabolism of NO cause dysfunction in the pulmonary blood vessels, the level of NO decreases, which leads to impaired lung function and coagulopathy. The review presents possible mechanisms of these disorders associated with ED, the release of eNO synthase, changes in phosphorylation and regulation of enzyme activity, as well as insulin resistance. A modern view of the role of the polymorphism of the eNO synthase gene in the development of these pathologies is presented. To increase the level of endothelial NO, drugs are offered that regulate the bioavailability of NO. These include arginine, agonist NO – minoxidil, steroid hormones, statins, metformin. However, further research and clinical trials are needed to develop treatment strategies that increase NO levels in the endothelium.

Layer-specific Nos3 expression and genotypic distribution in bicuspid aortic valve aortopathy

OBJECTIVES

We hypothesized that expression and activity of nitric oxide synthase-3 enzyme (Nos3) in bicuspid aortic valve (BAV) aortopathy are related to tissue layer and Nos3 genotype.

METHODS

Gene expression of Nos3 and platelet and endothelial cell adhesion molecule-1 (Pecam1) and NOS activity were measured in intima-containing media and adventitial specimens of ascending aortic tissue. The presence of 2 Nos3 single-nucleotide polymorphisms (SNPs; -786T/C and 894G/T) was determined for non-aneurysmal (NA) and aneurysmal patients with BAV (n = 40, 89, respectively); patients with tricuspid aortic valve (TAV) and aneurysm (n = 151); and NA patients with TAV (n = 100).

RESULTS

Elevated Nos3 relative to Pecam1 and reduced Pecam1 relative to a housekeeping gene were observed within intima-containing aortic specimens from BAV patients when compared with TAV patients. Lower Nos3 in the adventitia of aneurysmal specimens was noted when compared with specimens of NA aorta, independent of valve morphology. NOS activity was similar among cohorts in media/intima and decreased in the diseased adventitia, relative to control patients. Aneurysmal BAV patients exhibited an under-representation of the wild-type genotype for -786 SNP. No differences in genotype distribution were noted for 894 SNP. Primary intimal endothelial cells from patients with at least 1 C allele at -786 SNP exhibited lower Nos3 when compared with wild-type cells.

CONCLUSIONS

These findings of differential Nos3 in media/intima versus adventitia depending on valve morphology or aneurysm reveal new information regarding aneurysmal pathophysiology and support our ongoing assertion that there are distinct mechanisms giving rise to ascending aortopathy in BAV and TAV patients.

The Intestinal Redox System and Its Significance in Chemotherapy-Induced Intestinal Mucositis

Chemotherapy-induced intestinal mucositis (CIM) is a significant dose-limiting adverse reaction brought on by the cancer treatment. Multiple studies reported that reactive oxygen species (ROS) is rapidly produced during the initial stages of chemotherapy, when the drugs elicit direct damage to intestinal mucosal cells, which, in turn, results in necrosis, mitochondrial dysfunction, and ROS production. However, the mechanism behind the intestinal redox system-based induction of intestinal mucosal injury and necrosis of CIM is still undetermined. In this article, we summarized relevant information regarding the intestinal redox system, including the composition and regulation of redox enzymes, ROS generation, and its regulation in the intestine. We innovatively proposed the intestinal redox "Tai Chi" theory and revealed its significance in the pathogenesis of CIM. We also conducted an extensive review of the English language-based literatures involving oxidative stress (OS) and its involvement in the pathological mechanisms of CIM. From the date of inception till July 31, 2021, 51 related articles were selected. Based on our analysis of these articles, only five chemotherapeutic drugs, namely, MTX, 5-FU, cisplatin, CPT-11, and oxaliplatin were shown to trigger the ROS-based pathological mechanisms of CIM. We also discussed the redox system-mediated modulation of CIM pathogenesis via elaboration of the relationship between chemotherapeutic drugs and the redox system. It is our belief that this overview of the intestinal redox system and its role in CIM pathogenesis will greatly enhance research direction and improve CIM management in the future.

Electronic Cigarette Exposure Causes Vascular Endothelial Dysfunction Due to NADPH Oxidase Activation and eNOS Uncoupling

We recently reported a mouse model of chronic electronic cigarette (e-cig) exposure-induced cardiovascular pathology, where long-term exposure to e-cig vape (ECV) induces cardiac abnormalities, impairment of endothelial function, and systemic hypertension. Here, we delineate the underlying mechanisms of ECV-induced vascular endothelial dysfunction (VED), a central trigger of cardiovascular disease. C57/BL6 male mice were exposed to ECV generated from e-cig liquid containing 0, 6, or 24 mg/ml nicotine for 16 and 60 weeks. Time-dependent elevation in blood pressure and systemic vascular resistance were observed, along with an impairment of acetylcholine-induced aortic relaxation in ECV-exposed mice, compared to air-exposed control. Decreased intravascular nitric oxide (NO) levels and increased superoxide generation with elevated 3-nitrotyrosine levels in the aorta of ECV-exposed mice were observed, indicating that ECV-induced superoxide reacts with NO to generate cytotoxic peroxynitrite. Exposure increased NADPH oxidase expression, supporting its role in ECV-induced superoxide generation. Downregulation of endothelial nitric oxide synthase (eNOS) expression and Akt-dependent eNOS phosphorylation occurred in the aorta of ECV-exposed mice, indicating that exposure inhibited de novo NO synthesis. Following ECV exposure, the critical NOS cofactor tetrahydrobiopterin was decreased, with a concomitant loss of its salvage enzyme, dihydrofolate reductase. NADPH oxidase and NOS inhibitors abrogated ECV-induced superoxide generation in the aorta of ECV exposed mice. Together, our data demonstrate that ECV exposure activates NADPH oxidase and uncouples eNOS, causing a vicious cycle of superoxide generation and vascular oxidant stress that triggers VED and hypertension with predisposition to other cardiovascular disease.

Nitric oxide regulates adhesiveness, invasiveness, and migration of anoikis-resistant endothelial cells

Anoikis is a type of apoptosis that occurs in response to the loss of adhesion to the extracellular matrix (ECM). Anoikis resistance is a critical mechanism in cancer and contributes to tumor metastasis. Nitric oxide (NO) is frequently upregulated in the tumor area and is considered an important player in cancer metastasis. The aim of this study was to evaluate the effect of NO on adhesiveness, invasiveness, and migration of anoikis-resistant endothelial cells. Here, we report that anoikis-resistant endothelial cells overexpress endothelial nitric oxide synthase. The inhibition of NO release in anoikis-resistant endothelial cells was able to decrease adhesiveness to fibronectin, laminin, and collagen IV. This was accompanied by an increase in cell invasiveness and migration. Furthermore, anoikis-resistant cell lines displayed a decrease in fibronectin and collagen IV protein expression after L-NAME treatment. These alterations in adhesiveness and invasiveness were the consequence of MMP-2 up-regulation observed after NO release inhibition. The decrease in NO levels was able to down-regulate the activating transcription factor 3 (ATF3) protein expression. ATF3 represses MMP-2 gene expression by antagonizing p53-dependent trans-activation of the MMP-2 promoter. We speculate that the increased release of NO by anoikis-resistant endothelial cells acted as a response to restrict the MMP-2 action, interfering in MMP-2 gene expression via ATF3 regulation. The up-regulation of nitric oxide by anoikis-resistant endothelial cells is an important response to restrict tumorigenic behavior. Without this mechanism, invasiveness and migration potential would be even higher, as shown after L-NAME treatment.

Neurovascular protection by adropin in experimental ischemic stroke through an endothelial nitric oxide synthase-dependent mechanism

Adropin is a highly-conserved peptide that has been shown to preserve endothelial barrier function. Blood-brain barrier (BBB) disruption is a key pathological event in cerebral ischemia. However, the effects of adropin on ischemic stroke outcomes remain unexplored. Hypothesizing that adropin exerts neuroprotective effects by maintaining BBB integrity, we investigated the role of adropin in stroke pathology utilizing loss- and gain-of-function genetic approaches combined with pharmacological treatment with synthetic adropin peptide. Long-term anatomical and functional outcomes were evaluated using histology, MRI, and a battery of sensorimotor and cognitive tests in mice subjected to ischemic stroke. Brain ischemia decreased endogenous adropin levels in the brain and plasma. Adropin treatment or transgenic adropin overexpression robustly reduced brain injury and improved long-term sensorimotor and cognitive function in young and aged mice subjected to ischemic stroke. In contrast, genetic deletion of adropin exacerbated ischemic brain injury, irrespective of sex. Mechanistically, adropin treatment reduced BBB damage, degradation of tight junction proteins, matrix metalloproteinase-9 activity, oxidative stress, and infiltration of neutrophils into the ischemic brain. Adropin significantly increased phosphorylation of endothelial nitric oxide synthase (eNOS), Akt, and ERK1/2. While adropin therapy was remarkably protective in wild-type mice, it failed to reduce brain injury in eNOS-deficient animals, suggesting that eNOS is required for the protective effects of adropin in stroke. These data provide the first causal evidence that adropin exerts neurovascular protection in stroke through an eNOS-dependent mechanism. We identify adropin as a novel neuroprotective peptide with the potential to improve stroke outcomes.

Protein kinase N2 mediates flow-induced endothelial NOS activation and vascular tone regulation

Formation of NO by endothelial NOS (eNOS) is a central process in the homeostatic regulation of vascular functions including blood pressure regulation, and fluid shear stress exerted by the flowing blood is a main stimulus of eNOS activity. Previous work has identified several mechanosensing and -transducing processes in endothelial cells, which mediate this process and induce the stimulation of eNOS activity through phosphorylation of the enzyme via various kinases including AKT. How the initial mechanosensing and signaling processes are linked to eNOS phosphorylation is unclear. In human endothelial cells, we demonstrated that protein kinase N2 (PKN2), which is activated by flow through the mechanosensitive cation channel Piezo1 and Gq/G11-mediated signaling, as well as by Ca2+ and phosphoinositide-dependent protein kinase 1 (PDK1), plays a pivotal role in this process. Active PKN2 promoted the phosphorylation of human eNOS at serine 1177 and at a newly identified site, serine 1179. These phosphorylation events additively led to increased eNOS activity. PKN2-mediated eNOS phosphorylation at serine 1177 involved the phosphorylation of AKT synergistically with mTORC2-mediated AKT phosphorylation, whereas active PKN2 directly phosphorylated human eNOS at serine 1179. Mice with induced endothelium-specific deficiency of PKN2 showed strongly reduced flow-induced vasodilation and developed arterial hypertension accompanied by reduced eNOS activation. These results uncover a central mechanism that couples upstream mechanosignaling processes in endothelial cells to the regulation of eNOS-mediated NO formation, vascular tone, and blood pressure.

Comparison of cytotoxicity of cigarette smoke extract derived from heat-not-burn and combustion cigarettes in human vascular endothelial cells

The present study compared the properties of mainstream smoke generated from heat-not-burn (HNB) cigarettes and a combustion cigarette (hi-lite™ brand). Three types of cigarette heating devices were used to generate cigarette smoke at different heating temperatures [Ploom S™ (200 °C), glo™ (240 °C), and IQOS™ (300-350 °C)]. Mainstream smoke was generated using the following puffing regimen: volume, 55 mL; duration, 3 s; and interval, 30 s. The rank order of particulate phase (nicotine and tar) amounts trapped on a Cambridge filter was Ploom S < glo < IQOS < hi-lite. Heated cigarette-derived smoke extract (hCSE) from the devices except for Ploom S, and burned CSE (bCSE) decreased mitochondrial metabolic activity (glo < IQOS < hi-lite) in human vascular endothelial cells. Furthermore, the cytotoxicity was reduced by removing the particulate phase from the mainstream smoke. Endothelial nitric oxide synthase activity was reduced by nicotine- and tar-free CSE of IQOS and hi-lite (IQOS < hi-lite), but not Ploom S and glo. These inhibitory effects were diminished by removing the carbonyl compounds from the mainstream smoke. These results indicated that the cytotoxicity of hCSE was lower than that of bCSE in vascular endothelial cells.

Omeprazole suppresses endothelial calcium response and eNOS Ser1177 phosphorylation in porcine aortic endothelial cells

BACKGROUND

Although high doses of proton pump inhibitors can elicit an anticancer effect, this strategy may impair vascular biology. In particular, their effects on endothelial Ca²⁺ signaling and production of endothelium-derived relaxing factor (EDRF) are unknown. To this end, we investigated the effects of high dosages of omeprazole on endothelial Ca²⁺ responses and EDRF production in primary cultured porcine aortic endothelial cells.

METHODS AND RESULTS

Omeprazole (10-1000 μM) suppressed both bradykinin (BK)- and thapsigargin-induced endothelial Ca²⁺ response in a dose-dependent manner. Furthermore, omeprazole slightly attenuated Ca²⁺ mobilization from the endoplasmic reticulum, whereas no inhibitory effects on endoplasmic reticulum Ca²⁺-ATPase were observed. Omeprazole decreased BK-induced phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser1177 and tended to decrease BK-induced nitric oxide production. Production of prostaglandin I₂ metabolites, especially 6-keto-prostaglandin 1α, also tended to be reduced by omeprazole.

CONCLUSION

Our results are the first to indicate that high doses of omeprazole may suppress both store-operated Ca²⁺ channels and partially the G protein-coupled receptor/phospholipase C/inositol 1,4,5-triphosphate pathway, and decreased BK-induced, Ca²⁺-dependent phosphorylation of eNOS(Ser1177). Thus, high dosages of omeprazole impaired EDRF production by attenuating intracellular Ca²⁺ signaling.

The Mechanisms of L-Arginine Metabolism Disorder in Endothelial Cells

L-arginine is a key metabolite for nitric oxide production by endothelial cells, as well as signaling molecule of the mTOR signaling pathway. mTOR supports endothelial cells homeostasis and regulates activity of L-arginine-metabolizing enzymes, endothelial nitric oxide synthase, and arginase II. Disruption of the L-arginine metabolism in endothelial cells leads to the development of endothelial dysfunction. Conflicting results of the use of L-arginine supplement to improve endothelial function reveals a controversial role of the amino acid in the endothelial cell biology. The review is aimed at analysis of the current data on the role of L-arginine metabolism in the development of endothelial dysfunction.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

Endothelial dysfunction and transcriptome aberration in mouse aortas induced by black phosphorus quantum dots and nanosheets

Black phosphorus (BP) nanomaterials have shown great potential in versatile applications including biomedicine and potentially interact with vessel walls following intravenous injection in biomedical usage or environmental exposure. However, it remains unknown whether the exposure to BP nanomaterials induces alterations of the endothelium and further vascular injury. Herein, the endothelial function of human umbilical vein endothelial cells (HUVECs) and the structure and transcriptome of C57BL/6 mouse aortas are evaluated after the exposure to BP quantum dots (BPQDs) and nanosheets (BPNSs). BPNSs with irregular shapes and larger lateral size are more prone to inhibit in vitro angiogenesis at non-cytotoxic concentrations and markedly trigger platelet adhesion to HUVECs compared to BPQDs. Decreased nitric oxide (NO) production resulting from endothelial NO synthase (eNOS) dysregulation is involved in the BP-induced endothelial dysfunction. Both BPQDs and BPNSs at 0.8 and 6.4 μg mL-1 inhibit eNOS enzymatic activity through dephosphorylation of eNOS-Ser1177 and phosphorylation of eNOS-Thr495, but unlike BPQDs, BPNSs also downregulate eNOS expression. Despite no pathological damage in the structure of mouse aortas, BPQDs and BPNSs trigger aberration of aortic transcriptome involved in vasoconstriction abnormality, metabolic disturbance, and immune perturbation. This study demonstrates the adverse effect of BP nanomaterials on vasculature, and suggests that the morphological attribute of BP plays a crucial role in the vascular risks.

Signalling mechanisms in the cardiovascular protective effects of estrogen: With a focus on rapid/membrane signalling

In modern society, cardiovascular disease remains the biggest single threat to life, being responsible for approximately one third of worldwide deaths. Male prevalence is significantly higher than that of women until after menopause, when the prevalence of CVD increases in females until it eventually exceeds that of men. Because of the coincidence of CVD prevalence increasing after menopause, the role of estrogen in the cardiovascular system has been intensively researched during the past two decades in vitro, in vivo and in observational studies. Most of these studies suggested that endogenous estrogen confers cardiovascular protective and anti-inflammatory effects. However, clinical studies of the cardioprotective effects of hormone replacement therapies (HRT) not only failed to produce proof of protective effects, but also revealed the potential harm estrogen could cause. The "critical window of hormone therapy" hypothesis affirms that the moment of its administration is essential for positive treatment outcomes, pre-menopause (3-5 years before menopause) and immediately post menopause being thought to be the most appropriate time for intervention. Since many of the cardioprotective effects of estrogen signaling are mediated by effects on the vasculature, this review aims to discuss the effects of estrogen on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) with a focus on the role of estrogen receptors (ERα, ERβ and GPER) in triggering the more recently discovered rapid, or membrane delimited (non-genomic), signaling cascades that are vital for regulating vascular tone, preventing hypertension and other cardiovascular diseases.

Nitric oxide and the brain. Part 2: Effects following neonatal brain injury-friend or foe?

Nitric oxide (NO) has critical roles in a wide variety of key biologic functions and has intricate transport mechanisms for delivery to key distal tissues under normal conditions. However, NO also plays important roles during disease processes, such as hypoxia-ischemia, asphyxia, neuro-inflammation, and retinopathy of prematurity. The effects of exogenous NO on the developing neonatal brain remain controversial. Inhaled NO (iNO) can be neuroprotective or toxic depending on a variety of factors, including cellular redox state, underlying disease processes, duration of treatment, and dose. This review identifies key gaps in knowledge that should prompt further investigation into the possible role of iNO as a therapeutic agent after injury to the brain. IMPACT: NO is a key signal mediator in the neonatal brain with neuroprotective and neurotoxic properties. iNO, a commonly used medication, has significant effects on the neonatal brain. Dosing, duration, and timing of administration of iNO can affect the developing brain. This review article summarizes the roles of NO in association with various disease processes that impact neonates, such as brain hypoxia-ischemia, asphyxia, retinopathy of prematurity, and neuroinflammation. The impact of this review is that it clearly describes gaps in knowledge, and makes the case for further, targeted studies in each of the identified areas.

An inquest into regulatory mechanism of caveolin by ischemic preconditioning against orchidectomy-challenged rat heart

Lower level of testosterone in men is related to major risks of cardiovascular diseases. This risk may increase due to the opening of mitochondrial permeability transition pore (mPTP). The mPTP is also regulated by ischemic preconditioning (IPC) and a membrane protein known as caveolin. The cardioprotective effect of IPC is the most effective methodologies used in testosterone deficiency. Daidzein (DDZ) a caveolin inhibitor shows cardioprotective action. The experiment has been designed to evaluate the pretreated DDZ effect in IPC-mediated cardioprotective action in orchidectomy (OCZ)-challenged rat heart. The experiment was designed on male Wistar rats with/without OCZ. The level of testosterone is decreased by OCZ which reduces general body growth. Isolated heart from normal and OCZ rat was tied up on Langendorff's perfused apparatus and followed by ischemic reperfusion (IR) and IPC cycle. To investigate the cardioprotective effect of DDZ in heart with testosterone deficiency, a total of nine groups, each consisting of six rats (n = 6) were as follows: Sham, IR, IPC, IPC + OCZ, IPC + DDZ, IPC + OCZ + DDZ, IPC + sodium nitrite, IPC + OCZ + sodium nitrite, IPC + OCZ + DDZ + sodium nitrite. Hemodynamic parameters, cellular injury (infarct size, LDH, CKMB and cardiac troponin-T), oxidative stress, mitochondrial function, integrity and immunoblot analysis were assessed for each group. The experimental data showed that DDZ potentiated IPC-mediated increase in the heart rate, left ventricular diastolic pressure, coronary flow; + dp/dt_max, and - dp/dt_max. The pretreated DDZ decreases the action of LDH and CKMB, myocyte size, cardiac collagen content, infarct size and ventricular fibrillation and attenuation in oxidative stress and mitochondrial dysfunction in OCZ-challenged rat heart in all sets of experiments. Sodium nitrite, a producer of nitric oxide (NO), enhanced potentiating effects of DDZ on IPC-mediated cardioprotection in OCZ-challenged rats. These observations show that the downregulation of caveolin through impaired opening of mPTP during reperfusion and caveolin might be a potential adjuvant to IPC against cardiac injury in OCZ-challenged rats.

Emerging roles of protein O-GlcNAcylation in cardiovascular diseases: Insights and novel therapeutic targets

Cardiovascular diseases (CVDs) are the leading cause of death globally. While the major focus of pharmacological and non-pharmacological interventions has been on targeting disease pathophysiology and limiting predisposing factors, our understanding of the cellular and molecular mechanisms underlying the pathogenesis of CVDs remains incomplete. One mechanism that has recently emerged is protein O-GlcNAcylation. This is a dynamic, site-specific reversible post-translational modification of serine and threonine residues on target proteins and is controlled by two enzymes: O-linked β-N-acetylglucosamine transferase (OGT) and O-linked β-N-acetylglucosaminidase (OGA). Protein O-GlcNAcylation alters the cellular functions of these target proteins which play vital roles in pathways that modulate vascular homeostasis and cardiac function. Through this review, we aim to give insights on the role of protein O-GlcNAcylation in cardiovascular diseases and identify potential therapeutic targets in this pathway for development of more effective medicines to improve patient outcomes.

Hypoglycemia increases endothelial-dependent vasodilation through suppressing phosphorylation at Threonine 495/497 site of endothelial nitric oxide synthase

OBJECTIVE

Phosphorylation plays an essential role in the regulation of endothelial nitric oxide synthase (eNOS) activity. However, the phosphorylation of eNOS under hypoglycemia and whether hypoglycemia changes eNOS activity is unknown. This paper aims to clarify the regulation of eNOS phosphorylation and its activity change under hypoglycemia.

METHODS

Bovine aortic endothelial cells (BAECs) and Sprague-Dawley rats were treated with hypoglycemia, and the phosphorylation of eNOS was subjected to western blot. Blood nitric oxide (NO) concentration was determined by NO kit and endothelial-dependent vasodilation was detected by multi-wire myograph.

RESULTS

In both BAECs and rats' thoracic aorta, hypoglycemia induced eNOS phosphorylation decrease specifically on Threonine (Thr) 497. Inhibition of ubiquitination of protein kinase C α subunit (PKCα) reverses the decrease of eNOS phosphorylation in hypoglycemia. Ubiquitinated PKCα can be reversed by AMPK knockdown. In rats, insulin induced hypoglycemia increased the concentration of NO in arterial blood, and progressively enhanced the endothelium-dependent vasodilation of the thoracic and mesenteric aorta.

CONCLUSIONS

In vitro, the activation of AMPK may lead to the expression of PKCα by regulating ubiquitination, resulting in a decrease in the level of P-eNOS Thr497 phosphorylation under hypoglycemia. In vivo, insulin-induced hypoglycemia produces a beneficial cardiovascular effect on rats.

Translational insight into prothrombotic state and hypercoagulation in nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is an emerging and threatening pathological condition, ranging from fatty liver (FL) to chronic steatohepatitis (NASH), liver cirrhosis, and eventually to hepatocellular carcinoma (HCC). Recent findings suggest that patients with NAFLD have a higher risk of cardiovascular events and thromboembolism and that this risk is independent of metabolic diseases that are frequently associated with NAFLD, such as diabetes, hyperlipidaemia, and obesity. The vascular involvement of NAFLD might be considered its systemic burden, conditioning higher mortality in patients affected by the disease. These clinical findings suggested the existence of a prothrombotic state in NAFLD, which is partially unexplored and whose underlying mechanisms are to date not completely understood. Here, we review the mechanisms involved in the pathogenesis of the prothrombotic state in NAFLD across the progression from the healthy liver through the different stages of the disease. We focused on the possible role of several metabolic features of NAFLD possibly leading to hypercoagulation other than endothelial and platelet activation, such as insulin-resistance, nitric oxide production regulation, and gut microbiota homeostasis. Also, we analysed the involvement of plasminogen activator inhibitor-1 (PAI-1) and thromboinflammation taking place in NAFLD. Finally, we described factors striking a prothrombotic imbalance in NASH cirrhosis, with a particular focus on the pathogenesis of portal vein thrombosis.

The vital role for nitric oxide in intraocular pressure homeostasis

Catalyzed by endothelial nitric oxide (NO) synthase (eNOS) activity, NO is a gaseous signaling molecule maintaining endothelial and cardiovascular homeostasis. Principally, NO regulates the contractility of vascular smooth muscle cells and permeability of endothelial cells in response to either biochemical or biomechanical cues. In the conventional outflow pathway of the eye, the smooth muscle-like trabecular meshwork (TM) cells and Schlemm's canal (SC) endothelium control aqueous humor outflow resistance, and therefore intraocular pressure (IOP). The mechanisms by which outflow resistance is regulated are complicated, but NO appears to be a key player as enhancement or inhibition of NO signaling dramatically affects outflow function; and polymorphisms in NOS3, the gene that encodes eNOS modifies the relation between various environmental exposures and glaucoma. Based upon a comprehensive review of past foundational studies, we present a model whereby NO controls a feedback signaling loop in the conventional outflow pathway that is sensitive to changes in IOP and its oscillations. Thus, upon IOP elevation, the outflow pathway tissues distend, and the SC lumen narrows resulting in increased SC endothelial shear stress and stretch. In response, SC cells upregulate the production of NO, relaxing neighboring TM cells and increasing permeability of SC's inner wall. These IOP-dependent changes in the outflow pathway tissues reduce the resistance to aqueous humor drainage and lower IOP, which, in turn, diminishes the biomechanical signaling on SC. Similar to cardiovascular pathogenesis, dysregulation of the eNOS/NO system leads to dysfunctional outflow regulation and ocular hypertension, eventually resulting in primary open-angle glaucoma.

Cigarette Smoke Extract and Its Cytotoxic Factor Acrolein Inhibit Nitric Oxide Production in Human Vascular Endothelial Cells

Acrolein (ACR), a highly reactive α,β-unsaturated aldehyde, is a major cytotoxic factor in nicotine- and tar-free cigarette smoke extract (CSE). There are conflicting results regarding endothelial functions despite the fact that both CSE and ACR cause cellular damage. Several lines of evidence indicate that CSE impairs endothelium-derived nitric oxide (NO)-dependent vasodilation by reducing the activity and protein expression of endothelial NO synthase (eNOS), whereas ACR elicits endothelium-dependent vasorelaxation by increasing the production of NO and expression of eNOS. To clarify whether CSE and its cytotoxic factor ACR cause endothelial dysfunction, this study examined the effects of CSE and ACR on human vascular endothelial EA.hy926 cells. CSE and ACR reduced the phosphorylation of eNOS at serine (Ser)1177 and total expression of eNOS. The CSE- and ACR-induced decrease in the phosphorylation and expression of eNOS was counteracted by glutathione (reduced form), an antioxidant. Basal NO production was inhibited by CSE, ACR, NG-nitro-L-arginine methyl ester (a competitive eNOS inhibitor), and nominally Ca2+-free solution supplemented with BAPTA-AM (a membrane permeable Ca2+ chelator). These results indicate that CSE and ACR increase oxidative stress, and reduce NO production by reducing the activity and total protein level of eNOS.

Functional implications of vascular endothelium in regulation of endothelial nitric oxide synthesis to control blood pressure and cardiac functions

The endothelium is the innermost vascular lining performing significant roles all over the human body while maintaining the blood pressure at physiological levels. Malfunction of endothelium is thus recognized as a biomarker linked with many vascular diseases including but not limited to atherosclerosis, hypertension and thrombosis. Alternatively, prevention of endothelial malfunctioning or regulating the functions of its associated physiological partners like endothelial nitric oxide synthase can prevent the associated vascular disorders which account for the highest death toll worldwide. While many anti-hypertensive drugs are available commercially, a comprehensive description of the key physiological roles of the endothelium and its regulation by endothelial nitric oxide synthase or vice versa is the need of the hour to understand its contribution in vascular homeostasis. This, in turn, will help in designing new therapeutics targeting endothelial nitric oxide synthase or its interacting partners present in the cellular pool. This review describes the central role of vascular endothelium in the regulation of endothelial nitric oxide synthase while outlining the emerging drug targets present in the vasculature with potential to treat vascular disorders including hypertension.

Combination therapy with pemafibrate (K-877) and pitavastatin improves vascular endothelial dysfunction in dahl/salt-sensitive rats fed a high-salt and high-fat diet

Background

Statins suppress the progression of atherosclerosis by reducing low-density lipoprotein (LDL) cholesterol levels. Pemafibrate (K-877), a novel selective peroxisome proliferator-activated receptor α modulator, is expected to reduce residual risk factors including high triglycerides (TGs) and low high-density lipoprotein (HDL) cholesterol during statin treatment. However, it is not known if statin therapy with add-on pemafibrate improves the progression of atherosclerosis. The aim of this study was to assess the effect of combination therapy with pitavastatin and pemafibrate on lipid profiles and endothelial dysfunction in hypertension and insulin resistance model rats.

Methods

Seven-week-old male Dahl salt-sensitive (DS) rats were divided into the following five treatment groups (normal diet (ND) plus vehicle, high-salt and high-fat diet (HD) plus vehicle, HD plus pitavastatin (0.3 mg/kg/day), HD plus pemafibrate (K-877) (0.5 mg/kg/day), and HD plus combination of pitavastatin and pemafibrate) and treated for 12 weeks. At 19 weeks, endothelium-dependent relaxation of the thoracic aorta in response to acetylcholine was evaluated.

Results

After feeding for 12 weeks, systolic blood pressure and plasma levels of total cholesterol were significantly higher in the HD-vehicle group compared with the ND-vehicle group. Combination therapy with pitavastatin and pemafibrate significantly reduced systolic blood pressure, TG levels, including total, chylomicron (CM), very LDL (VLDL), HDL-TG, and cholesterol levels, including total, CM, VLDL, and LDL-cholesterol, compared with vehicle treatment. Acetylcholine caused concentration-dependent relaxation of thoracic aorta rings that were pre-contracted with phenylephrine in all rats. Relaxation rates in the HD-vehicle group were significantly lower compared with the ND-vehicle group. Relaxation rates in the HD-combination of pitavastatin and pemafibrate group significantly increased compared with the HD-vehicle group, although neither medication alone ameliorated relaxation rates significantly. Western blotting experiments showed increased phosphorylated endothelial nitric oxide synthase protein expression in aortas from rats in the HD-pemafibrate group and the HD-combination group compared with the HD-vehicle group. However, the expression levels did not respond significantly to pitavastatin alone.

Conclusions

Combination therapy with pitavastatin and pemafibrate improved lipid profiles and endothelial dysfunction in hypertension and insulin resistance model rats. Pemafibrate as an add-on strategy to statins may be useful for preventing atherosclerosis progression.

Endothelial dysfunction due to selective insulin resistance in vascular endothelium: insights from mechanistic modeling

Previously, we have used mathematical modeling to gain mechanistic insights into insulin-stimulated glucose uptake. Phosphatidylinositol 3-kinase (PI3K)-dependent insulin signaling required for metabolic actions of insulin also regulates endothelium-dependent production of the vasodilator nitric oxide (NO). Vasodilation increases blood flow that augments direct metabolic actions of insulin in skeletal muscle. This is counterbalanced by mitogen-activated protein kinase (MAPK)-dependent insulin signaling in endothelium that promotes secretion of the vasoconstrictor endothelin-1 (ET-1). In the present study, we extended our model of metabolic insulin signaling into a dynamic model of insulin signaling in vascular endothelium that explicitly represents opposing PI3K/NO and MAPK/ET-1 pathways. Novel NO and ET-1 subsystems were developed using published and new experimental data to generate model structures/parameters. The signal-response relationships of our model with respect to insulin-stimulated NO production, ET-1 secretion, and resultant vascular tone, agree with published experimental data, independent of those used for model development. Simulations of pathological stimuli directly impairing only insulin-stimulated PI3K/Akt activity predict altered dynamics of NO and ET-1 consistent with endothelial dysfunction in insulin-resistant states. Indeed, modeling pathway-selective impairment of PI3K/Akt pathways consistent with insulin resistance caused by glucotoxicity, lipotoxicity, or inflammation predict diminished NO production and increased ET-1 secretion characteristic of diabetes and endothelial dysfunction. We conclude that our mathematical model of insulin signaling in vascular endothelium supports the hypothesis that pathway-selective insulin resistance accounts, in part, for relationships between insulin resistance and endothelial dysfunction. This may be relevant for developing novel approaches for the treatment of diabetes and its cardiovascular complications.

Specific O-GlcNAc modification at Ser-615 modulates eNOS function

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and devastating disease characterized by vascular smooth muscle and endothelial cell proliferation leading to a narrowing of the vessels in the lung. The increased resistance in the lung and the higher pressures generated result in right heart failure. Nitric Oxide (NO) deficiency is considered a hallmark of IPAH and altered function of endothelial nitric oxide synthase (eNOS), decreases NO production. We recently demonstrated that glucose dysregulation results in augmented protein serine/threonine hydroxyl-linked N-Acetyl-glucosamine (O-GlcNAc) modification in IPAH. In diabetes, dysregulated glucose metabolism has been shown to regulate eNOS function through inhibition of Ser-1177 phosphorylation. However, the link between O-GlcNAc and eNOS function remains unknown. Here we show that increased protein O-GlcNAc occurs on eNOS in PAH and Ser-615 appears to be a novel site of O-GlcNAc modification resulting in reduced eNOS dimerization. Functional characterization of Ser-615 demonstrated the importance of this residue on the regulation of eNOS activity through control of Ser-1177 phosphorylation. Here we demonstrate a previously unidentified regulatory mechanism of eNOS whereby the O-GlcNAc modification of Ser-615 results in reduced eNOS activity and endothelial dysfunction under conditions of glucose dysregulation.

Endothelial cell prostaglandin E2 receptor EP4 is essential for blood pressure homeostasis

Prostaglandin E2 and its cognate EP1-4 receptors play important roles in blood pressure (BP) regulation. Herein, we show that endothelial cell-specific (EC-specific) EP4 gene-knockout mice (EC-EP4-/-) exhibited elevated, while EC-specific EP4-overexpression mice (EC-hEP4OE) displayed reduced, BP levels compared with the control mice under both basal and high-salt diet-fed conditions. The altered BP was completely abolished by treatment with l-NG-nitro-l-arginine methyl ester (l-NAME), a competitive inhibitor of endothelial nitric oxide synthase (eNOS). The mesenteric arteries of the EC-EP4-/- mice showed increased vasoconstrictive response to angiotensin II and reduced vasorelaxant response to acetylcholine, both of which were eliminated by l-NAME. Furthermore, EP4 activation significantly reduced BP levels in hypertensive rats. Mechanistically, EP4 deletion markedly decreased NO contents in blood vessels via reducing eNOS phosphorylation at Ser1177. EP4 enhanced NO production mainly through the AMPK pathway in cultured ECs. Collectively, our findings demonstrate that endothelial EP4 is essential for BP homeostasis.

Mathematical Model Predicts Effective Strategies to Inhibit VEGF-eNOS Signaling

The endothelial nitric oxide synthase (eNOS) signaling pathway in endothelial cells has multiple physiological significances. It produces nitric oxide (NO), an important vasodilator, and enables a long-term proliferative response, contributing to angiogenesis. This signaling pathway is mediated by vascular endothelial growth factor (VEGF), a pro-angiogenic species that is often targeted to inhibit tumor angiogenesis. However, inhibiting VEGF-mediated eNOS signaling can lead to complications such as hypertension. Therefore, it is important to understand the dynamics of eNOS signaling in the context of angiogenesis inhibitors. Thrombospondin-1 (TSP1) is an important angiogenic inhibitor that, through interaction with its receptor CD47, has been shown to redundantly inhibit eNOS signaling. However, the exact mechanisms of TSP1's inhibitory effects on this pathway remain unclear. To address this knowledge gap, we established a molecular-detailed mechanistic model to describe VEGF-mediated eNOS signaling, and we used the model to identify the potential intracellular targets of TSP1. In addition, we applied the predictive model to investigate the effects of several approaches to selectively target eNOS signaling in cells experiencing high VEGF levels present in the tumor microenvironment. This work generates insights for pharmacologic targets and therapeutic strategies to inhibit tumor angiogenesis signaling while avoiding potential side effects in normal vasoregulation.

Cardioprotective effect of sonic hedgehog ligand in pig models of ischemia reperfusion

Sonic hedgehog (SHH) signaling pathway is involved in embryonic tissue patterning and development. Our previous work identified, in small rodent model of ischemia reperfusion, SHH as a specific efficient tool to reduce infarct size and subsequent arrhythmias by preventing ventricular repolarization abnormalities. The goal of the present study was to provide a proof of concept of the cardioprotective effect of SHH ligand in a porcine model of acute ischemia.

Methods: The antiarrhythmic effect of SHH, either by a recombinant peptide (N-SHH) or shed membrane microparticles harboring SHH ligand (MPs^SHH+), was evaluated in a first set of pigs following a short (25 min) coronary artery occlusion (CAO) followed by 24 hours-reperfusion (CAR) (Protocol A). The infarct-limiting effect was evaluated on a second set of pigs with 40 min of coronary artery occlusion followed by 24 hours reperfusion (Protocol B). Electrocardiogram (ECG) was recorded and arrhythmia's scores were evaluated. Area at risk and myocardial infarct size were quantified.

Results: In protocol A, administration of N-SHH 15 min. after the onset of coronary occlusion significantly reduced the occurrence of ventricular fibrillation compared to control group. Evaluation of arrhythmic score showed that N-SHH treatment significantly reduced the overall occurrence of arrhythmias. In protocol B, massive infarction was observed in control animals. Either N-SHH or MPs^SHH+ treatment reduced significantly the infarct size with a concomitant increase of salvaged area. The reduction in infarct size was both accompanied by a significant decrease in systemic biomarkers of myocardial injury, i.e., cardiac troponin I and fatty acid-binding protein and an increase of eNOS activation.

Conclusions: We show for the first time in a large mammalian model that the activation of the SHH pathway by N-SHH or MPs^SHH+ offers a potent protection of the heart to ischemia-reperfusion by preventing the reperfusion arrhythmias, reducing the infarct area and the circulating levels of biomarkers for myocardial injury. These data open up potentially theranostic prospects for patients suffering from myocardial infarction to prevent the occurrence of arrhythmias and reduce myocardial tissue damage.

Shenfu Injection Promotes Vasodilation by Enhancing eNOS Activity Through the PI3K/Akt Signaling Pathway In Vitro

Vasomotor dysfunction is one of the key pathological aspects of shock and heart failure (HF). Shenfu injection (SFI) has been widely used for the treatment of shock and HF in China. Pharmacological studies have suggested that SFI can reduce peripheral circulation resistance and improve microcirculation. However, whether it has a regulatory effect on macrovascular has not been elucidated. In this study, we used thoracic aorta rings isolated from Wistar rats and the human umbilical vein cell line (EA.hy926) to explore the vasodilative activity of SFI and its potential mechanisms. The relaxation due to SFI was measured after pre-treatment with selective soluble guanylate cyclase (sGC) inhibitor or cyclooxygenase (COX) inhibitor and compared with the vasodilation effect of SFI only treated with norepinephrine (NE). The contents of NO, endothelin-1 (ET-1), endothelial nitric oxide synthase (eNOS), COX-1, 6-K-PGF_1α, and caveolin-1 were evaluated respectively. Additionally, the level of eNOS mRNA and total eNOS and its phosphorylation were studied to investigate the potential mechanisms involved. Experimental results showed that SFI markedly attenuated NE-induced vasoconstriction but that this effect was significantly eliminated after pre-incubation with the selective sGC inhibitor 1-H-[1, 2, 4] oxadiazolo [4, 3-α] quinoxaline-1-one (ODQ), instead of the COX inhibitor indomethacin (INDO). SFI significantly increased the eNOS content and up-regulated the eNOS mRNA expression, while it did not affect the content of COX-1 and 6-K-PGF_1α. SFI also markedly increased NO content but significantly reduced the content of ET-1 and caveolin-1 in the cell supernatant. Furthermore, it promoted the expression of total eNOS and the phosphorylation of eNOS at serine (Ser) 1177 but inhibited the phosphorylation at threonine (Thr) 495, which was significantly reversed by PI3K-specific inhibitor LY294002. In conclusion, our study showed the vasodilation effect of SFI in thoracic aorta is mediated entirely by enhancing eNOS activity through the PI3K/Akt signaling pathway, providing novel knowledge on the effect of SFI on shock and HF for future clinical applications.

An emerging perspective on sex differences: Intersecting S-nitrosothiol and aldehyde signaling in the heart

Cardiovascular disease is the leading cause of the death for both men and women. Although baseline heart physiology and the response to disease are known to differ by sex, little is known about sex differences in baseline molecular signaling, especially with regard to redox biology. In this review, we describe current research on sex differences in cardiac redox biology with a focus on the regulation of nitric oxide and aldehyde signaling. Furthermore, we argue for a new perspective on cardiovascular sex differences research, one that focuses on baseline redox biology without the elimination or disruption of sex hormones.

The roles of FGF21 in atherosclerosis pathogenesis

FGF21 is a peptide hormone that regulates homeostasis of lipid and glucose as well as energy metabolism. It is mainly expressed and secreted in liver and adipose tissues, and it is expressed in lower amounts in the aorta. Recent clinical and preclinical studies indicate increased serum FGF21 levels in atherosclerosis patients. Also, FGF21 therapy has been reported to reduce the initiation and progression of atherosclerosis in animal models and in vitro studies. Moreover, growing evidence indicates that administration of exogenous FGF21 induces anti-atherosclerotic effects, because of its ability to reduce lipid profile, alleviation of oxidative stress, inflammation, and apoptosis. Therefore, FGF21 can not only be considered as a biomarker for predicting atherosclerosis, but also induce protective effects against atherosclerosis. Besides, serum levels of FGF21 increase in various diseases including in diabetes mellitus, hypertension, and obesity, which may be related to initiating and exacerbating atherosclerosis. On the other hand, FGF21 therapy significantly improves lipid profiles, and reduces vascular inflammation and oxidative stress in atherosclerosis related diseases. Therefore, further prospective studies are needed to clarify whether FGF21 can be used as a prognostic biomarker to identify individuals at future risk of atherosclerosis in these atherosclerosis-associated diseases. In this review, we will discuss the possible mechanism by which FGF21 protects against atherosclerosis.

Mechanistic Role of the Calcium-Dependent Protease Calpain in the Endothelial Dysfunction Induced by MPO (Myeloperoxidase)

MPO (myeloperoxidase) is a peroxidase enzyme secreted by activated leukocytes that plays a pathogenic role in cardiovascular disease, mainly by initiating endothelial dysfunction. The molecular mechanisms of the endothelial damaging action of MPO remain though largely elusive. Calpain is a calcium-dependent protease expressed in the vascular wall. Activation of calpains has been implicated in inflammatory disorders of the vasculature. Using endothelial cells and genetically modified mice, this study identifies the µ-calpain isoform as novel downstream signaling target of MPO in endothelial dysfunction. Mouse lung microvascular endothelial cells were stimulated with 10 nmol/L MPO for 180 minutes. MPO denitrosylated µ-calpain C-terminus domain, and time dependently activated µ-calpain, but not the m-calpain isoform. MPO also reduced Thr¹⁷² AMPK (AMP-activated protein kinase) and Ser¹¹⁷⁷ eNOS (endothelial nitric oxide synthase) phosphorylation via upregulation of PP2A (protein phosphatase 2) expression. At the functional level, MPO increased endothelial VCAM-1 (vascular cell adhesion molecule 1) abundance and the adhesion of leukocytes to the mouse aorta. In MPO-treated endothelial cells, pharmacological inhibition of calpain activity attenuated expression of VCAM-1 and PP2A, and restored Thr¹⁷² AMPK and Ser¹¹⁷⁷ eNOS phosphorylation. Compared with wild-type mice, µ-calpain deficient mice experienced reduced leukocyte adhesion to the aortic endothelium in response to MPO. Our data first establish a role for calpain in the endothelial dysfunction and vascular inflammation of MPO. The MPO/calpain/PP2A signaling pathway may provide novel pharmacological targets for the treatment of inflammatory vascular disorders.

Endothelial NOS: perspective and recent developments

Endothelial NOS (eNOS), and its product NO, are vital components of the control of vasomotor function and cardiovascular homeostasis. In the present review, we will take a deep dive into eNOS enzymology, function and mechanisms regulating endothelial NO. The mechanisms regulating eNOS and NO synthesis discussed here include alterations to transcriptional, post-translational modifications and protein-protein regulations. Also, we will discuss the phenotypes associated with various eNOS mutants and the consequences of a disrupted eNOS/NO cascade, highlighting the importance of eNOS function and vascular homeostasis. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Generation and characterization of functional phosphoserine-incorporated neuronal nitric oxide synthase holoenzyme

Phosphorylation is an important pathway for the regulation of nitric oxide synthase (NOS) at the posttranslational level. However, the molecular underpinnings of NOS regulation by phosphorylations remain unclear to date, mainly because of the problems in making a good amount of active phospho-NOS proteins. Herein, we have established a system in which recombinant rat nNOS holoprotein can be produced with site-specific incorporation of phosphoserine (pSer) at residue 1412, using a specialized bacterial host strain for pSer incorporation. The pSer1412 nNOS protein demonstrates UV-Vis, far-UV CD and fluorescence spectral properties that are identical to those of nNOS overexpressed in other bacterial strains. The protein is also functional, possessing normal NO production and NADPH oxidation activities in the presence of abundant substrate L-Arg. Conversely, the rate of FMN-heme interdomain electron transfer (IET) in pSer1412 nNOS is considerably lower than that of wild-type (wt) nNOS, while the phosphomimetic S1142E mutant possesses similar electron transfer kinetics to that of wt. The successful incorporation and high yield of pSer1412 into rat nNOS and the significant change in the IET kinetics upon the phosphorylation demonstrate a highly useful method for incorporating native phosphorylation sites as a substantial improvement to commonly used phosphomimetics.

Differential effect of hydroxyapatite nano-particle versus nano-rod decorated titanium micro-surface on osseointegration

Coating materials applied for intraosseous implants must be optimized to stimulate osseointegration. Osseointegration is a temporal and spatial physiological process that not only requires interactions between osteogenesis and angiogenesis but also necessitates a favorable immune microenvironment. It is now well-documented that hierarchical nano-micro surface structures promote the long-term stability of implants, the interactions between nano-micro structure and the immune response are largely unknown. Here, we report the effects of microporous titanium (Ti) surfaces coated with nano-hydroxyapatite (HA) produced by micro-arc oxidation and steam-hydrothermal treatment (SHT) on multiple cell behavior and osseointegration. By altering the processing time of SHT it was possible to shift HA structures from nano-particles to nano-rods on the microporous Ti surfaces. Ti surfaces coated with HA nano-particles were found to modulate the inflammatory response resulting in an osteoimmune microenvironment more favorable for osteo-/angio-genesis, most likely via the activation of certain key signaling pathways (TGF-β, OPG/RANKL, and VEGF). By contrast, Ti surfaces coated with nano-rod shaped HA particles had a negative impact on osteo-/angio-genesis and osteoimmunomodulation. In vivo results further demonstrated that Ti implant surfaces decorated with HA nano-particles can stimulate new bone formation and osseointegration with enhanced interaction between osteocytes and implant surfaces. This study demonstrated that Ti implants with micro-surfaces coated with nano-particle shaped HA have a positive impact on osseointegration.

STATEMENT OF SIGNIFICANCE

Osteo-/angio-genesis are of importance during osteointegration of the implants. Recent advances unravel that immune response of macrophages and its manipulated osteoimmunomodulation also exerts a pivotal role to determine the fate of the implant. Surface nano-micro modification has evidenced to be efficient to influence osteogenesis, however, little is known links nano-microstructured surface to immune response, as well the osteoimmunomodulation. This study demonstrates that the nano-particles decorated micro-surface, compared with the nano-rods decorated micro-surface enables osteogenesis and angiogenesis concurrently that has not been investigated previously. This study also unravels that the immune response of macrophages can be manipulated by the nano-micro surface, especially the nano-dimension matters, leading to a differential effect on osteointegration. The additional knowledge obtained from this study may provide foundation and reference for future design of the coating materials for implantable materials.

Phosphodiesterase type 5 in men with vasculogenic and post-radical prostatectomy erectile dysfunction: is there a molecular difference?

OBJECTIVES

To clarify the molecular basis of penile erection at the human level and distinguish the mechanisms underlying vasculogenic and post-radical prostatectomy (RP) erectile dysfunction (ED) subtypes.

PATIENTS AND METHODS

Erectile tissue was obtained from men without history of ED who underwent penile surgery for Peyronie's disease (control group, n = 5) and from men with ED who underwent penile prosthesis implantation (n = 17). ED was categorized into vasculogenic (n = 8) and post-RP (n = 9) subtypes. Penile erectile tissue samples were collected for molecular analyses of protein expressions of neuronal and endothelial isoforms of nitric oxide synthase (nNOS and eNOS, respectively), phospho-nNOS (Ser-1412), phospho-eNOS (Ser-1177), phospho-protein kinase B (Ser-473), phosphodiesterase type 5 (PDE5), α-smooth muscle actin, phospho-myosin phosphatase target subunit 1, RhoA/Rho-associated protein kinase (ROCK)-α, ROCK-β, 4-hydroxy-2-nonenal, and nNOS and eNOS uncoupling by Western blot.

RESULTS

Vasculogenic ED was characterized by decreased eNOS protein expression and eNOS and nNOS phosphorylation on their activatory sites (Ser-1177 and Ser-1412, respectively), uncoupled eNOS, upregulated PDE5 protein expression, increased ROCK activity, and increased oxidative stress in erectile tissue. Post-RP ED was characterized by decreased nNOS protein expression, increased nNOS phosphorylation on its activatory site (Ser-1412), uncoupled nNOS, downregulated PDE5 protein expression, and increased oxidative stress in erectile tissue.

CONCLUSION

The mechanisms of vasculogenic and post-RP ED in the human penis involve derangements in constitutive nitric oxide synthase function, PDE5 protein expression and ROCK activity, and increased oxidative stress, which conceivably provide a molecular basis for chronically reduced nitric oxide bioavailability and increased smooth muscle contraction contributing to erectile impairment. Selective differences in PDE5 protein expression suggest distinct molecular mechanisms are in play for these ED subtypes.