The FXYD1 protein plays a protective role against pulmonary hypertension and arterial remodeling via redox and inflammatory mechanisms

Pulmonary hypertension (PH) consists of a heterogenous group of diseases that culminate in increased pulmonary arterial pressure and right ventricular (RV) dysfunction. We sought to investigate the role of FXYD1, a small membrane protein that modulates Na+-K+-ATPase function, in the pathophysiology of PH. We mined online transcriptome databases to assess FXYD1 expression in PH. We characterized the effects of FXYD1 knockout (KO) in mice on right and left ventricular (RV and LV) function using echocardiography and measured invasive hemodynamic measurements under normal conditions and after treatment with bleomycin sulfate or chronic hypoxia to induce PH. Using immunohistochemistry, immunoblotting, and functional assays, we examined the effects of FXYD1 KO on pulmonary microvasculature and RV and LV structure and assessed signaling via endothelial nitric oxide synthase (eNOS) and inflammatory pathways. FXYD1 lung expression tended to be lower in samples from patients with idiopathic pulmonary arterial hypertension (IPAH) compared with controls, supporting a potential pathophysiological role. FXYD1 KO mice displayed characteristics of PH including significant increases in pulmonary arterial pressure, increased muscularization of small pulmonary arterioles, and impaired RV systolic function, in addition to LV systolic dysfunction. However, when PH was stimulated with standard models of lung injury-induced PH, there was no exacerbation of disease in FXYD1 KO mice. Both the lungs and left ventricles exhibited elevated nitrosative stress and inflammatory milieu. The absence of FXYD1 in mice results in LV inflammation and cardiopulmonary redox signaling changes that predispose to pathophysiological features of PH, suggesting FXYD1 may be protective.NEW & NOTEWORTHY This is the first study to show that deficiency of the FXYD1 protein is associated with pulmonary hypertension. FXYD1 expression is lower in the lungs of people with idiopathic pulmonary artery hypertension. FXYD1 deficiency results in both left and right ventricular functional impairment. Finally, FXYD1 may endogenously protect the heart from oxidative and inflammatory injury.

High-Resolution Transthoracic Echocardiography Accurately Detects Pulmonary Arterial Pressure and Decreased Right Ventricular Contractility in a Mouse Model of Pulmonary Fibrosis and Secondary Pulmonary Hypertension

Background To date, assessment of right ventricular (RV) function in mice has relied extensively on invasive measurements. Echocardiographic advances have allowed adaptation of measures used in humans for serial, noninvasive RV functional assessment in mice. We evaluated the diagnostic performance of tricuspid annular plane systolic excursion (TAPSE), RV peak systolic myocardial velocity (s'), RV myocardial performance index (MPI), and RV fractional area change (FAC) in a mouse model of pulmonary hypertension. Methods and Results Echocardiography was performed on mice at baseline and 3 weeks after induction of pulmonary hypertension using inhaled bleomycin or saline, including adapted measures of TAPSE, s', MPI, and FAC. RV systolic pressure was measured by invasive catheterization, and RV contractility was measured as the peak slope of the RV systolic pressure recording (maximum change pressure/change time). Postmortem morphological assessment of RV hypertrophy was performed. RV systolic pressure was elevated and maximum change pressure/change time was reduced in bleomycin versus control (n=8; P=0.002). Compared with controls, bleomycin mice had reduced TAPSE (0.79±0.05 versus 1.06±0.04 mm; P=0.003), s' (21.3±1.2 versus 29.2±1.3 mm/s; P<0.001), and FAC (20.3±0.7% versus 31.0±1.3%; P<0.001), whereas MPI was increased (0.51±0.03 versus 0.37±0.01; P=0.006). All measures correlated with RV systolic pressure and maximum change pressure/change time. Intraobserver and interobserver variability were minimal. Receiver operating characteristic curves demonstrated that TAPSE (<0.84 mm), s'(<23.3 mm/s), MPI (0.42), and FAC (<23.3%) identified maximum change pressure/change time ≤2100 mm Hg/s with high accuracy. Conclusions TAPSE, s', MPI, and FAC are measurable consistently using high-resolution echocardiography in mice, and are sensitive and specific measures of pulmonary pressure and RV function. This validation opens the opportunity for serial noninvasive measures in mouse models of pulmonary hypertension, enhancing the statistical power of preclinical studies of novel therapeutics.

Targeting triglycerides to lower residual cardiovascular risk

INTRODUCTION

Dyslipidemia therapeutics have primarily focused on lowering levels of low-density lipoprotein cholesterol. However, many patients continue to experience cardiovascular events, despite effective lowering of LDL-C. This has prompted efforts to target additional risk factors to achieve more effective prevention of cardiovascular disease. Emerging evidence suggests that triglyceride rich lipoproteins play a causal role in atherosclerosis, highlighting the potential for specific therapeutic lowering.

AREAS COVERED

(1) Evidence to support the causal role of triglyceride rich lipoproteins in atherosclerotic cardiovascular disease. (2) Use of existing lipid modifying therapies to target triglyceride rich lipoproteins. (3) Development of novel therapeutic agents that target triglyceride rich lipoproteins and their potential impact on cardiovascular risk.

EXPERT OPINION/COMMENTARY

Evidence from preclinical, observational and genetic studies highlight the role of triglyceride rich lipoproteins in the causal pathway of atherosclerotic cardiovascular disease. A number of existing agents have the potential to reduce residual cardiovascular risk associated with hypertriglyceridemia. However, emerging agents have the potential to substantially and preferentially lower triglyceride levels beyond contemporary therapeutics. How they will modulate cardiovascular risk will ultimately be determined by large clinical outcomes trials. They do provide the opportunity to substantially influence the way we target dyslipidemia in the prevention of cardiovascular disease.

Impact of reduced uterine perfusion pressure model of preeclampsia on metabolism of placenta, maternal and fetal hearts

Preeclampsia is a cardiovascular pregnancy complication characterised by new onset hypertension and organ damage or intrauterine growth restriction. It is one of the leading causes of maternal and fetal mortality in pregnancy globally. Short of pre-term delivery of the fetus and placenta, treatment options are limited. Consequently, preeclampsia leads to increased cardiovascular disease risk in both mothers and offspring later in life. Here we aim to examine the impact of the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia on the maternal cardiovascular system, placental and fetal heart metabolism. The surgical RUPP model was induced in pregnant rats by applying silver clips around the aorta and uterine arteries on gestational day 14, resulting in ~ 40% uterine blood flow reduction. The experiment was terminated on gestational day 19 and metabolomic profile of placentae, maternal and fetal hearts analysed using high-resolution ¹H NMR spectroscopy. Impairment of uterine perfusion in RUPP rats caused placental and cardiac hypoxia and a series of metabolic adaptations: altered energetics, carbohydrate, lipid and amino acid metabolism of placentae and maternal hearts. Comparatively, the fetal metabolic phenotype was mildly affected. Nevertheless, long-term effects of these changes in both mothers and the offspring should be investigated further in the future.

Protocol for the Stimulating β3-Adrenergic Receptors for Peripheral Artery Disease (STAR-PAD) trial: a double-blinded, randomised, placebo-controlled study evaluating the effects of mirabegron on functional performance in patients with peripheral arterial disease

INTRODUCTION

There is currently only one approved medication effective at improving walking distance in people with intermittent claudication. Preclinical data suggest that the β₃-adrenergic receptor agonist (mirabegron) could be repurposed to treat intermittent claudication associated with peripheral artery disease. The aim of the Stimulating β₃-Adrenergic Receptors for Peripheral Artery Disease (STAR-PAD) trial is to test whether mirabegron improves walking distance in people with intermittent claudication.

METHODS AND ANALYSIS

The STAR-PAD trial is a Phase II, multicentre, double-blind, randomised, placebo-controlled trial of mirabegron versus placebo on walking distance in patients with PAD. A total of 120 patients aged ≥40 years with stable PAD and intermittent claudication will be randomly assigned (1:1 ratio) to receive either mirabegron (50 mg orally once a day) or matched placebo, for 12 weeks. The primary endpoint is change in peak walking distance as assessed by a graded treadmill test. Secondary endpoints will include: (i) initial claudication distance; (ii) average daily step count and total step count and (iii) functional status and quality of life assessment. Mechanistic substudies will examine potential effects of mirabegron on vascular function, including brachial artery flow-mediate dilatation; MRI assessment of lower limb blood flow, tissue perfusion and arterial stiffness and numbers and angiogenesis potential of endothelial progenitor cells. Given that mirabegron is safe and clinically available for alternative purposes, a positive study is positioned to immediately impact patient care.

ETHICS AND DISSEMINATION

The STAR-PAD trial is approved by the Northern Sydney Local Health District Human Research Ethics Committee (HREC/18/HAWKE/50). The study results will be published in peer-reviewed medical or scientific journals and presented at scientific meetings, regardless of the study outcomes.

TRIAL REGISTRATION NUMBER

ACTRN12619000423112; Results.

The Riskier Lipid: What Is on the HORIZON for Lipoprotein (a) and Should There Be Lp(a) Screening for All?

PURPOSE OF REVIEW

Despite widespread targeting of cardiovascular risk factors, many patients continue to experience clinical events. This residual risk has stimulated efforts to develop novel therapeutic approaches to target additional factors underscoring cardiovascular disease. This review aimed to summarize existing evidence supporting targeting of Lp(a) as a novel cardioprotective strategy.

RECENT FINDINGS

Increasing evidence has implicated lipoprotein (a) [Lp(a)] in the pathogenesis of both atherosclerotic and calcific aortic valve disease. Therapeutic advances have produced novel agents that selectively lower Lp(a) levels, which have now progressed to evaluate their impact on cardiovascular events in large clinical outcome trials. Evidence continues to accumulate suggesting that targeting Lp(a) may be effective in reducing cardiovascular risk. With advances in Lp(a) targeted therapeutics, clinical trials now have the opportunity to determine whether this strategy will be effective for high-risk patients.

FXYD1 Is Protective Against Vascular Dysfunction

[Figure: see text].

β 3 Adrenergic Receptor Stimulation Promotes Reperfusion in Ischemic Limbs in a Murine Diabetic Model

Aims/Hypothesis: Peripheral arterial disease (PAD) is a major burden, resulting in limb claudication, repeated surgical interventions and amputation. There is an unmet need for improved medical management of PAD that improves quality of life, maintains activities of daily life and reduces complications. Nitric oxide (NO)/redox balance is a key regulator of angiogenesis. We have previously shown beneficial effects of a β₃ adrenergic receptor (β₃AR) agonist on NO/redox balance. We hypothesized that β₃AR stimulation would have therapeutic potential in PAD by promoting limb angiogenesis.

Methods: The effect of the β₃AR agonist CL 316,243 (1–1,000 nmol/L in vitro, 1 mg/kg/day s. c) was tested in established angiogenesis assays with human endothelial cells and patient-derived endothelial colony forming cells. Post-ischemia reperfusion was determined in streptozotocin and/or high fat diet-induced diabetic and non-diabetic mice in vivo using the hind limb ischemia model.

Results: CL 316,243 caused accelerated recovery from hind limb ischemia in non-diabetic and type 1 and 2 diabetic mice. Increased eNOS activity and decreased superoxide generation were detected in hind limb ischemia calf muscle from CL 316, 243 treated mice vs. controls. The protective effect of CL 316,243 in diabetic mice was associated with >50% decreases in eNOS glutathionylation and nitrotyrosine levels. The β₃AR agonist directly promoted angiogenesis in endothelial cells in vitro. These pro-angiogenic effects were β₃AR and NOS-dependent.

Conclusion/Interpretation:β₃AR stimulation increased angiogenesis in diabetic ischemic limbs, with demonstrable improvements in NO/redox balance and angiogenesis elicited by a selective agonist. The orally available β₃AR agonist, Mirabegron, used for overactive bladder syndrome, makes translation to a clinical trial by repurposing of a β₃AR agonist to target PAD immediately feasible.

The novel P2X7 receptor antagonist PKT100 improves cardiac function and survival in pulmonary hypertension by direct targeting of the right ventricle

In pulmonary hypertension (PH) a proinflammatory milieu drives pulmonary vascular remodeling, maladaptive right ventricular (RV) remodeling, and right-sided heart failure. There is an unmet need for RV-targeted pharmaco-therapies to improve mortality. Targeting of the P2X7 receptor (P2X7R) reduces pulmonary pressures; however, its effects on the RV are presently unknown. We investigated the effect of P2X7 receptor (P2X7R) inhibition on the pulmonary vasculature and RV remodeling using the novel P2X7R antagonist PKT100. C57BL/6 mice were administered intratracheal bleomycin or saline and treated with PKT100 (0.2 mg·kg^-1·day^-1) or DMSO vehicle. RV was assessed by right heart catheterization and echocardiography, 21 days posttreatment. Cytokines in serum and bronchoalveolar lavage fluid (BALF) were analyzed by ELISA and flow cytometry. Lungs and hearts were analyzed histologically for pulmonary vascular and RV remodeling. Focused-PCR using genes involved in RV remodeling was performed. Right ventricular systolic pressure (RVSP) was elevated in bleomycin-treated mice (30.2 ± 1.1; n = 7) compared with control mice (23.5 ± 1.0; n = 10; P = 0.008). PKT100 treatment did not alter RVSP (32.4 ± 1.8; n = 9), but it substantially improved survival (93% vs. 57% DMSO). There were no differences between DMSO and PKT100 bleomycin mice in pulmonary inflammation or remodeling. However, RV hypertrophy was reduced in PKT100 mice. Bleomycin decreased echocardiographic surrogates of RV systolic performance, which were significantly improved with PKT100. Four genes involved in RV remodeling (RPSA, Rplp0, Add2, and Scn7a) were differentially expressed between DMSO and PKT100-treated groups. The novel P2X7R inhibitor, PKT100, attenuates RV hypertrophy and improves RV contractile function and survival in a mouse model of PH independently of effects on the pulmonary vasculature. PKT100 may improve ventricular response to increased afterload and merits further investigation into the potential role of P2X7R antagonists as direct RV-focused therapies in PH.NEW & NOTEWORTHY This study demonstrates the therapeutic potential for right-sided heart failure of a novel inhibitor of the P2X7 receptor (P2X7R). Inflammatory signaling and right ventricular function were improved in a mouse model of pulmonary fibrosis with secondary pulmonary hypertension when treated with this inhibitor. Importantly, survival was also improved, suggesting that this inhibitor, and other P2X7R antagonists, could be uniquely effective in right ventricle (RV)-targeted therapy in pulmonary hypertension. This addresses a major limitation of current treatment options, where the significant improvements in pulmonary pressures ultimately do not prevent mortality due to RV failure.

Endothelial C-Type Natriuretic Peptide Is a Critical Regulator of Angiogenesis and Vascular Remodeling

BACKGROUND

Angiogenesis and vascular remodeling are complementary, innate responses to ischemic cardiovascular events, including peripheral artery disease and myocardial infarction, which restore tissue blood supply and oxygenation; the endothelium plays a critical function in these intrinsic protective processes. C-type natriuretic peptide (CNP) is a fundamental endothelial signaling species that coordinates vascular homeostasis. Herein, we sought to delineate a central role for CNP in angiogenesis and vascular remodeling in response to ischemia.

METHODS

The in vitro angiogenic capacity of CNP was examined in pulmonary microvascular endothelial cells and aortic rings isolated from wild-type, endothelium-specific CNP^-/-, global natriuretic peptide receptor (NPR)-B^-/- and NPR-C^-/- animals, and human umbilical vein endothelial cells. These studies were complemented by in vivo investigation of neovascularization and vascular remodeling after ischemia or vessel injury, and CNP/NPR-C expression and localization in tissue from patients with peripheral artery disease.

RESULTS

Clinical vascular ischemia is associated with reduced levels of CNP and its cognate NPR-C. Moreover, genetic or pharmacological inhibition of CNP and NPR-C, but not NPR-B, reduces the angiogenic potential of pulmonary microvascular endothelial cells, human umbilical vein endothelial cells, and isolated vessels ex vivo. Angiogenesis and remodeling are impaired in vivo in endothelium-specific CNP^-/- and NPR-C^-/-, but not NPR-B^-/-, mice; the detrimental phenotype caused by genetic deletion of endothelial CNP, but not NPR-C, can be rescued by pharmacological administration of CNP. The proangiogenic effect of CNP/NPR-C is dependent on activation of G_i, ERK1/2, and phosphoinositide 3-kinase γ/Akt at a molecular level.

CONCLUSIONS

These data define a central (patho)physiological role for CNP in angiogenesis and vascular remodeling in response to ischemia and provide the rationale for pharmacological activation of NPR-C as an innovative approach to treating peripheral artery disease and ischemic cardiovascular disorders.

Biobanking for discovery of novel cardiovascular biomarkers using imaging-quantified disease burden: protocol for the longitudinal, prospective, BioHEART-CT cohort study

INTRODUCTION

Coronary artery disease (CAD) persists as a major cause of morbidity and mortality worldwide despite intensive identification and treatment of traditional risk factors. Data emerging over the past decade show a quarter of patients have disease in the absence of any known risk factor, and half have only one risk factor. Improvements in quantification and characterisation of coronary atherosclerosis by CT coronary angiography (CTCA) can provide quantitative measures of subclinical atherosclerosis-enhancing the power of unbiased 'omics' studies to unravel the missing biology of personal susceptibility, identify new biomarkers for early diagnosis and to suggest new targeted therapeutics.

METHODS AND ANALYSIS

BioHEART-CT is a longitudinal, prospective cohort study, aiming to recruit 5000 adult patients undergoing clinically indicated CTCA. After informed consent, patient data, blood samples and CTCA imaging data are recorded. Follow-up for all patients is conducted 1 month after recruitment, and then annually for the life of the study. CTCA data provide volumetric quantification of total calcified and non-calcified plaque, which will be assessed using established and novel scoring systems. Comprehensive molecular phenotyping will be performed using state-of-the-art genomics, metabolomics, proteomics and immunophenotyping. Complex network and machine learning approaches will be applied to biological and clinical datasets to identify novel pathophysiological pathways and to prioritise new biomarkers. Discovery analysis will be performed in the first 1000 patients of BioHEART-CT, with validation analysis in the following 4000 patients. Outcome data will be used to build improved risk models for CAD.

ETHICS AND DISSEMINATION

The study protocol has been approved by the human research ethics committee of North Shore Local Health District in Sydney, Australia. All findings will be published in peer-reviewed journals or at scientific conferences.

TRIAL REGISTRATION NUMBER

ACTRN12618001322224.

New opportunities for targeting redox dysregulation in cardiovascular disease

Despite substantial promise, the use of antioxidant therapy to improve cardiovascular outcomes has been disappointing. Whilst the fundamental biology supporting their use continues to build, the challenge now is to differentially target dysregulated redox signalling domains and to identify new ways to deliver antioxidant substances. Looking further afield to other disciplines, there is an emerging ‘tool-kit’ containing sophisticated molecular and drug delivery applications. Applying these to the cardiovascular redox field could prove a successful strategy to combat the increasing disease burden. Excessive reactive oxygen species production and protein modifications in the mitochondria has been the target of successful drug development with several positive outcomes emerging in the cardiovascular space, harnessing both improved delivery mechanisms and enhanced understanding of the biological abnormalities. Using this as a blueprint, similar strategies could be applied and expanded upon in other redox-hot-spots, such as the caveolae sub-cellular region, which houses many of the key cardiovascular redox proteins such as NADPH oxidase, endothelial nitric oxide synthase, angiotensin II receptors, and beta adrenoceptors. The expanded tool kit of drug development, including gene and miRNA therapies, nanoparticle technology and micropeptide targeting, can be applied to target dysregulated redox signalling in subcellular compartments of cardiovascular cells. In this review, we consider the opportunities for improving cardiovascular outcomes by utilizing new technology platforms to target subcellular ‘bonfires’ generated by dysregulated redox pathways, to improve clinical outcomes.

Modified redox signaling in vasculature after chronic infusion of the insulin receptor antagonist, S961

BACKGROUND

Type 2 diabetes and associated vascular complications cause substantial morbidity and mortality. It is important to investigate mechanisms and test therapies in relevant physiological models, yet few animal models adequately recapitulate all aspects of the human condition.

OBJECTIVE

We sought to determine the potential of using an insulin receptor antagonist, S961, in mice for investigating vascular pathophysiology.

METHODS

S961 was infused into mice for 4 weeks. Blood glucose was monitored, and insulin was measured at the end of the protocol. Blood pressure and pressor responses to vasodilators were measured in cannulated mice, and vascular reactive oxygen and nitrogen species were measured in isolated tissue.

RESULTS

S961 infusion-induced hyperglycemia and hyperinsulinemia. There was evidence of increased vascular reactive oxygen and nitrogen species and modification of NO-mediated signaling. Pressor responses to a NO donor were attenuated, but responses to bradykinin were preserved.

CONCLUSIONS

Infusion of S961, an insulin receptor antagonist, results in the production of a mouse model of type 2 diabetes that may be useful for investigating redox signaling in the vasculature of insulin-resistant mice over the short term. It is limited by both the transient nature of the hyperglycemia and incomplete functional analogy to the human condition.

The Regulation of Pulmonary Vascular Tone by Neuropeptides and the Implications for Pulmonary Hypertension

Pulmonary hypertension (PH) is an incurable, chronic disease of small pulmonary vessels. Progressive remodeling of the pulmonary vasculature results in increased pulmonary vascular resistance (PVR). This causes secondary right heart failure. PVR is tightly regulated by a range of pulmonary vasodilators and constrictors. Endothelium-derived substances form the basis of most current PH treatments. This is particularly the case for pulmonary arterial hypertension. The major limitation of current treatments is their inability to reverse morphological changes. Thus, there is an unmet need for novel therapies to reduce the morbidity and mortality in PH. Microvessels in the lungs are highly innervated by sensory C fibers. Substance P and calcitonin gene-related peptide (CGRP) are released from C-fiber nerve endings. These neuropeptides can directly regulate vascular tone. Substance P tends to act as a vasoconstrictor in the pulmonary circulation and it increases in the lungs during experimental PH. The receptor for substance P, neurokinin 1 (NK1R), mediates increased pulmonary pressure. Deactivation of NK1R with antagonists, or depletion of substance P prevents PH development. CGRP is a potent pulmonary vasodilator. CGRP receptor antagonists cause elevated pulmonary pressure. Thus, the balance of these peptides is crucial within the pulmonary circulation (Graphical Abstract). Limited progress has been made in understanding their impact on pulmonary pathophysiology. This is an intriguing area of investigation to pursue. It may lead to promising new candidate therapies to combat this fatal disease. This review provides a summary of the current knowledge in this area. It also explores possible future directions for neuropeptides in PH.

Vascularized Cardiac Spheroids as Novel 3D in vitro Models to Study Cardiac Fibrosis

Spheroid cultures are among the most explored cellular biomaterials used in cardiovascular research, due to their improved integration of biochemical and physiological features of the heart in a defined architectural three-dimensional microenvironment when compared to monolayer cultures. To further explore the potential use of spheroid cultures for research, we engineered a novel in vitro model of the heart with vascularized cardiac spheroids (VCSs), by coculturing cardiac myocytes, endothelial cells, and fibroblasts isolated from dissociated rat neonatal hearts (aged 1-3 days) in hanging drop cultures. To evaluate the validity of VCSs in recapitulating pathophysiological processes typical of the in vivo heart, such as cardiac fibrosis, we then treated VCSs with transforming growth factor beta 1 (TGFβ1), a known profibrotic agent. Our mRNA analysis demonstrated that TGFβ1-treated VCSs present elevated levels of expression of connective tissue growth factor, fibronectin, and TGFβ1 when compared to control cultures. We demonstrated a dramatic increase in collagen deposition following TGFβ1 treatment in VCSs in the PicroSirius Red-stained sections. Doxorubicin, a renowned cardiotoxic and profibrotic agent, triggered apoptosis and disrupted vascular networks in VCSs. Taken together, our findings demonstrate that VCSs are a valid model for the study of the mechanisms involved in cardiac fibrosis, with the potential to be used to investigate novel mechanisms and therapeutics for treating and preventing cardiac fibrosis in vitro.

Redox modification of caveolar proteins in the cardiovascular system- role in cellular signalling and disease

Rapid and coordinated release of a variety of reactive oxygen species (ROS) such as superoxide (O₂^.-), hydrogen peroxide (H₂O₂) and peroxynitrite, in specific microdomains, play a crucial role in cell signalling in the cardiovascular system. These reactions are mediated by reversible and functional modifications of a wide variety of key proteins. Dysregulation of this oxidative signalling occurs in almost all forms of cardiovascular disease (CVD), including at the very early phases. Despite the heavily publicized failure of "antioxidants" to improve CVD progression, pharmacotherapies such as those targeting the renin-angiotensin system, or statins, exert at least part of their large clinical benefit via modulating cellular redox signalling. Over 250 proteins, including receptors, ion channels and pumps, and signalling proteins are found in the caveolae. An increasing proportion of these are being recognized as redox regulated-proteins, that reside in the immediate vicinity of the two major cellular sources of ROS, nicotinamide adenine dinucleotide phosphate oxidase (Nox) and uncoupled endothelial nitric oxide synthase (eNOS). This review focuses on what is known about redox signalling within the caveolae, as well as endogenous protective mechanisms utilized by the cell, and new approaches to targeting dysregulated redox signalling in the caveolae as a therapeutic strategy in CVD.

The NRF2 activator DH404 attenuates adverse ventricular remodeling post-myocardial infarction by modifying redox signalling

BACKGROUND

The novel synthetic triterpenoid, bardoxolone methyl, has the ability to upregulate cytoprotective proteins via induction of the nuclear factor erythroid-2-related factor 2 (Nrf2) pathway. This makes it a promising therapeutic agent in disease states characterized by dysregulated oxidative signalling. We have examined the effect of a Nrf2 activator, dihydro-CDDO-trifluoroethyl amide (DH404), a derivative of bardoxolone methyl, on post-infarct cardiac remodeling in rats.

METHODS/RESULTS

DH404, administered from day 2 post myocardial infarction (MI: 30min transient ischemia followed by reperfusion) resulted in almost complete protection against adverse ventricular remodeling as assessed at day 28 (left ventricular end-systolic area: sham 0.14±0.01cm², MI vehicle 0.29±0.04cm² vs. MI DH404 0.18±0.02cm², P<0.05); infarct size (21.3±3.4% MI vehicle vs. 10.9±2.3% MI DH404, P<0.05) with associated benefits on systolic function (fractional shortening: sham 71.9±2.6%, MI vehicle 36.2±1.9% vs. MI DH404 58.6±4.0%, P<0.05). These structural and functional benefits were associated with lower myocardial expression of atrial natriuretic peptide (ANP, P<0.01 vs. MI vehicle), and decreased fibronectin (P<0.01 vs. MI vehicle) in DH404-treated MI rats at 28 days. MI increased glutathionylation of endothelial nitric oxide synthase (eNOS) in vitro - a molecular switch that uncouples the enzyme, increasing superoxide production and decreasing nitric oxide (NO) bioavailability. MI-induced eNOS glutathionylation was substantially ameliorated by DH404. An associated increase in glutaredoxin 1 (Grx1) co-immunoprecipitation with eNOS without a change in expression was mechanistically intriguing. Indeed, in parallel in vitro experiments, silencing of Grx1 abolished the protective effect of DH404 against Angiotensin II-induced eNOS uncoupling.

CONCLUSION

The bardoxolone derivative DH404 significantly attenuated cardiac remodeling post MI, at least in part, by re-coupling of eNOS and increasing the functional interaction of Grx1 with eNOS. This agent may have clinical benefits protecting against post MI cardiomyopathy.

Vasoactive actions of nitroxyl (HNO) are preserved in resistance arteries in diabetes

Endothelial dysfunction is a major risk factor for the vascular complications of diabetes. Increased reactive oxygen species (ROS) generation, a hallmark of diabetes, reduces the bioavailability of endothelial vasodilators, including nitric oxide (NO·). The vascular endothelium also produces the one electron reduced and protonated form of NO·, nitroxyl (HNO). Unlike NO·, HNO is resistant to scavenging by superoxide anions (·O₂^─). The fate of HNO in resistance arteries in diabetes is unknown. We tested the hypothesis that the vasodilator actions of endogenous and exogenous HNO are preserved in resistance arteries in diabetes. We investigated the actions of HNO in small arteries from the mesenteric and femoral beds as they exhibit marked differences in endothelial vasodilator function following 8 weeks of streptozotocin (STZ)-induced diabetes mellitus. Vascular reactivity was assessed using wire myography and ·O₂^─ generation using lucigenin-enhanced chemiluminescence. The HNO donor, Angeli's salt, and the NO· donor, DEA/NO, evoked relaxations in both arteries of control rats, and these responses were unaffected by diabetes. Nox2 oxidase expression and ·O₂^─ generation were upregulated in mesenteric, but unchanged, in femoral arteries of diabetic rats. Acetylcholine-induced endothelium-dependent relaxation was impaired in mesenteric but not femoral arteries in diabetes. The HNO scavenger, L-cysteine, reduced this endothelium-dependent relaxation to a similar extent in femoral and mesenteric arteries from control and diabetic animals. In conclusion, HNO and NO· contribute to the NO synthase (NOS)-sensitive component of endothelium-dependent relaxation in mesenteric and femoral arteries. The role of HNO is sustained in diabetes, serving to maintain endothelium-dependent relaxation.

Functional pharmacological characterization of SER100 in cardiovascular health and disease

BACKGROUND AND PURPOSE

SER100 is a selective nociceptin (NOP) receptor agonist with sodium-potassium-sparing aquaretic and anti-natriuretic activity. This study was designed to characterize the functional cardiovascular pharmacology of SER100 in vitro and in vivo, including experimental models of cardiovascular disease.

EXPERIMENTAL APPROACH

Haemodynamic, ECG parameters and heart rate variability (HRV) were determined using radiotelemetry in healthy, conscious mice. The haemodynamic and vascular effects of SER100 were also evaluated in two models of cardiovascular disease, spontaneously hypertensive rats (SHR) and murine hypoxia-induced pulmonary hypertension (PH). To elucidate mechanisms underlying the pharmacology of SER100, acute blood pressure recordings were performed in anaesthetized mice, and the reactivity of rodent aorta and mesenteric arteries in response to electrical- and agonist-stimulation assessed.

KEY RESULTS

SER100 caused NOP receptor-dependent reductions in mean arterial blood pressure and heart rate that were independent of NO. The hypotensive and vasorelaxant actions of SER100 were potentiated in SHR compared with Wistar Kyoto. Moreover, SER100 reduced several indices of disease severity in experimental PH. Analysis of HRV indicated that SER100 decreased the low/high frequency ratio, an indicator of sympatho-vagal balance, and in electrically stimulated mouse mesenteric arteries SER100 inhibited sympathetic-induced contractions.

CONCLUSIONS AND IMPLICATIONS

SER100 exerts a chronic hypotensive and bradycardic effects in rodents, including models of systemic and pulmonary hypertension. SER100 produces its cardiovascular effects, at least in part, by inhibition of cardiac and vascular sympathetic activity. SER100 may represent a novel therapeutic candidate in systemic and pulmonary hypertension.

Accelerated age-related decline in renal and vascular function in female rats following early-life growth restriction

Many studies report sexual dimorphism in the fetal programming of adult disease. We hypothesized that there would be differences in the age-related decline in renal function between male and female intrauterine growth-restricted rats. Early-life growth restriction was induced in rat offspring by administering a low-protein diet (LPD; 8.7% casein) to dams during pregnancy and lactation. Control dams were fed a normal-protein diet (NPD; 20% casein). Mean arterial pressure (MAP) and renal structure and function were assessed in 32- and 100-wk-old offspring. Mesenteric artery function was examined at 100 wk using myography. At 3 days of age, body weight was ∼24% lower ( P < 0.0001) in LPD offspring; this difference was still apparent at 32 wk but not at 100 wk of age. MAP was not different between the male NPD and LPD groups at either age. However, MAP was greater in LPD females compared with NPD females at 100 wk of age (∼10 mmHg; P < 0.001). Glomerular filtration rate declined with age in the NPD male, LPD male and LPD female offspring (∼45%, all P < 0.05), but not in NPD female offspring. Mesenteric arteries in the aged LPD females had reduced sensitivity to nitric oxide donors compared with their NPD counterparts, suggesting that vascular dysfunction may contribute to the increased risk of disease in aged females. In conclusion, females growth-restricted in early life were no longer protected from an age-related decline in renal and arterial function, and this was associated with increased arterial pressure without evidence of renal structural damage.

Endothelial C-type natriuretic peptide maintains vascular homeostasis

The endothelium plays a fundamental role in maintaining vascular homeostasis by releasing factors that regulate local blood flow, systemic blood pressure, and the reactivity of leukocytes and platelets. Accordingly, endothelial dysfunction underpins many cardiovascular diseases, including hypertension, myocardial infarction, and stroke. Herein, we evaluated mice with endothelial-specific deletion of Nppc, which encodes C-type natriuretic peptide (CNP), and determined that this mediator is essential for multiple aspects of vascular regulation. Specifically, disruption of CNP leads to endothelial dysfunction, hypertension, atherogenesis, and aneurysm. Moreover, we identified natriuretic peptide receptor-C (NPR-C) as the cognate receptor that primarily underlies CNP-dependent vasoprotective functions and developed small-molecule NPR-C agonists to target this pathway. Administration of NPR-C agonists promotes a vasorelaxation of isolated resistance arteries and a reduction in blood pressure in wild-type animals that is diminished in mice lacking NPR-C. This work provides a mechanistic explanation for genome-wide association studies that have linked the NPR-C (Npr3) locus with hypertension by demonstrating the importance of CNP/NPR-C signaling in preserving vascular homoeostasis. Furthermore, these results suggest that the CNP/NPR-C pathway has potential as a disease-modifying therapeutic target for cardiovascular disorders.

Inhibition of phosphodiesterase 2 augments cGMP and cAMP signaling to ameliorate pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is a life-threatening disorder characterized by increased pulmonary artery pressure, remodeling of the pulmonary vasculature, and right ventricular failure. Loss of endothelium-derived nitric oxide (NO) and prostacyclin contributes to PH pathogenesis, and current therapies are targeted to restore these pathways. Phosphodiesterases (PDEs) are a family of enzymes that break down cGMP and cAMP, which underpin the bioactivity of NO and prostacyclin. PDE5 inhibitors (eg, sildenafil) are licensed for PH, but a role for PDE2 in lung physiology and disease has yet to be established. Herein, we investigated whether PDE2 inhibition modulates pulmonary cyclic nucleotide signaling and ameliorates experimental PH.

METHODS AND RESULTS

The selective PDE2 inhibitor BAY 60-7550 augmented atrial natriuretic peptide- and treprostinil-evoked pulmonary vascular relaxation in isolated arteries from chronically hypoxic rats. BAY 60-7550 prevented the onset of both hypoxia- and bleomycin-induced PH and produced a significantly greater reduction in disease severity when given in combination with a neutral endopeptidase inhibitor (enhances endogenous natriuretic peptides), trepostinil, inorganic nitrate (NO donor), or a PDE5 inhibitor. Proliferation of pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension was reduced by BAY 60-7550, an effect further enhanced in the presence of atrial natriuretic peptide, NO, and treprostinil.

CONCLUSIONS

PDE2 inhibition elicits pulmonary dilation, prevents pulmonary vascular remodeling, and reduces the right ventricular hypertrophy characteristic of PH. This favorable pharmacodynamic profile is dependent on natriuretic peptide bioactivity and is additive with prostacyclin analogues, PDE5 inhibitor, and NO. PDE2 inhibition represents a viable, orally active therapy for PH.

Activation of neuronal transient receptor potential vanilloid 1 channel underlies 20-hydroxyeicosatetraenoic acid-induced vasoactivity: role for protein kinase A

A rise in intraluminal pressure triggers vasoconstriction in resistance arteries, which is associated with local generation of the vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE). Importantly, dysregulation of 20-HETE synthesis and activity has been implicated in several cardiovascular disease states, including ischemic disease, hypertension, and stroke; however, the exact molecular pathways involved in mediating 20-HETE bioactivity are uncertain. We investigated whether 20-HETE activates the transient receptor potential vanilloid 1 (TRPV1) and thereby regulates vascular function and blood pressure. We demonstrate that 20-HETE causes dose-dependent increases in blood pressure, coronary perfusion pressure (isolated Langendorff), and pressure-induced constriction of resistance arteries (perfusion myography) that is substantially attenuated in TRPV1 knockout mice and by treatment with the neurokinin 1 receptor antagonist RP67580. Furthermore, we show that both channel activation (via patch-clamping of dorsal root ganglion neurons) and vessel constriction are enhanced under inflammatory conditions, and our findings indicate a predominant role for protein kinase A-mediated sensitization of TRPV1 in these phenomena. Finally, we identify a prominence of these pathway in males compared with females, an effect we relate to reduced protein kinase A-induced phosphorylation of TRPV1. 20-HETE-induced activation of TRPV1, in part, mediates pressure-induced myogenic constriction and underlies 20-HETE-induced elevations in blood pressure and coronary resistance. Our findings identify a novel vasoconstrictor 20-HETE/TRPV1 pathway that may offer potential for therapeutic targeting in cardiovascular diseases associated with elevated 20-HETE implicated in dysregulated organ blood flow, such as stroke or hypertension.

Distinct endothelial pathways underlie sexual dimorphism in vascular auto-regulation

BACKGROUND AND PURPOSE

Pre-menopausal females have a lower incidence of cardiovascular disease compared with age-matched males, implying differences in the mechanisms and pathways regulating vasoactivity. In small arteries, myogenic tone (constriction in response to raised intraluminal pressure) is a major determinant of vascular resistance. Endothelium-derived dilators, particularly NO, tonically moderate myogenic tone and, because the endothelium is an important target for female sex hormones, we investigated whether NO-mediated moderation of myogenic tone differed between the sexes.

EXPERIMENTAL APPROACH

Pressure-diameter or relaxation concentration-response curves to the NO donor spermine-NO or soluble guanylate cyclase (sGC) stimulation (BAY41-2272) were constructed before and following drug intervention in murine mesenteric resistance arteries. Hypotensive responses to activators of the NO-sGC pathway were determined. Quantitative PCR and Western blotting were used for expression analysis.

KEY RESULTS

NO synthase inhibition enhanced myogenic tone of arteries of both sexes while block of endothelium-derived hyperpolarizing factor (EDHF) enhanced responses in arteries of females only. Spermine-NO concentration-dependently relaxed mesenteric arteries isolated from either sex. However, while inhibition of sGC activity attenuated responses of arteries from male mice only, endothelial denudation attenuated responses of arteries from females only. BAY41-2272 and spermine-NO-induced vasodilatation and hypotension were greater in males than in females.

CONCLUSIONS AND IMPLICATIONS

NO moderated myogenic tone in arteries of male mice by a sGC-dependent pathway while EDHF was the predominant endothelial regulator in arteries of females. This is a potentially important sexual dimorphism in NO-mediated reactivity and further implicates EDHF as the predominant endothelial vasodilator in female resistance arteries.

Sexual dimorphism in rodent models of hypertension and atherosclerosis

Approximately one third of all deaths are attributed to cardiovascular disease (CVD), making it the biggest killer worldwide. Despite a number of therapeutic options available, the burden of CVD morbidity continues to grow indicating the need for continued research to address this unmet need. In this respect, investigation of the mechanisms underlying the protection that premenopausal females enjoy from cardiovascular-related disease and mortality is of interest. In this review, we discuss the essential role that rodent animal models play in enabling this field of research. In particular, we focus our discussion on models of hypertension and atherosclerosis.

20-Hydroxyeicosatetraenoic acid (20-HETE) is a novel activator of transient receptor potential vanilloid 1 (TRPV1) channel

TRPV1 is a member of the transient receptor potential ion channel family and is gated by capsaicin, the pungent component of chili pepper. It is expressed predominantly in small diameter peripheral nerve fibers and is activated by noxious temperatures >42 °C. 20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P-450 4A/4F-derived metabolite of the membrane phospholipid arachidonic acid. It is a powerful vasoconstrictor and has structural similarities with other TRPV1 agonists, e.g. the hydroperoxyeicosatetraenoic acid 12-HPETE, and we hypothesized that it may be an endogenous ligand for TRPV1 in sensory neurons innervating the vasculature. Here, we demonstrate that 20-HETE both activates and sensitizes mouse and human TRPV1, in a kinase-dependent manner, involving the residue Ser(502) in heterologously expressed hTRPV1, at physiologically relevant concentrations.

Maternal vitamin D deficiency leads to cardiac hypertrophy in rat offspring

The aim of this study was to determine the effect of vitamin D deficiency from conception until 4 weeks of age on the development of the heart in rat offspring. Sprague-Dawley (SD) rats were fed either a vitamin D deplete or vitamin D-replete diet for 6 weeks prior to pregnancy, during pregnancy and throughout lactation. Cardiomyocyte number was determined in fixed hearts of offspring at postnatal day 3 and 4 weeks of age using an optical disector/fractionator stereological technique. In other litters, cardiomyocytes were isolated from freshly excised hearts to determine the proportion of mononucleated and binucleated cardiomyocytes. Maternal vitamin D deficiency had no effect on cardiomyocyte number, cardiomyocyte area, or the proportion of mononucleated/binucleated cardiomyocytes in 3-day-old male and female offspring. Importantly, however, vitamin D deficiency led to an increase in left ventricle (LV) volume that was accompanied by an increase in cardiomyocyte number and size, and in the proportion of mononucleated cardiomyocytes at 4 weeks of age. Our findings suggest that exposure to vitamin D deficiency in utero and early life leads to delayed maturation and subsequent enhanced growth (proliferation and hypertrophy) of cardiomyocytes in the LV. This may lead to altered cardiac function later in life.

Nephrogenesis and the renal renin-angiotensin system in fetal sheep: effects of intrauterine growth restriction during late gestation

Previous studies have shown that intrauterine growth restriction (IUGR) can impair nephrogenesis, but uncertainties remain about the importance of the gestational timing of the insult and the effects on the renal renin-angiotensin system (RAS). We therefore hypothesized that induction of IUGR during late gestation alters the RAS, and this is associated with a decrease in nephron endowment. Our aims were to determine the effects of IUGR induced during the later stages of nephrogenesis on 1) nephron number; 2) mRNA expression of angiotensin AT(1) and AT(2) receptors, angiotensinogen, and renin genes in the kidney; and 3) the size of maculae densae. IUGR was induced in fetal sheep (n = 7) by umbilical-placental embolization from 110 to 130 days of the approximately 147-day gestation; saline-infused fetuses served as controls (n = 7). Samples of cortex from the left kidney were frozen, and the right kidney was perfusion fixed. Total kidney volume, nephron number, renal corpuscle volume, total maculae densae volume, and the volume of macula densa per glomerulus were stereologically estimated. mRNA expression of AT(1) and AT(2) receptors, angiotensinogen, and renin in the renal cortex was determined. In IUGR fetuses at 130 days, body and kidney weights were significantly reduced and nephron number was reduced by 24%. There was no difference in renin, angiotensinogen, or AT(1) and AT(2) receptor mRNA expression levels in the IUGR kidneys compared with controls. We conclude that fetal growth restriction late in nephrogenesis can lead to a marked reduction in nephron endowment but does not affect renal corpuscle or macula densa size, or renal RAS gene expression.

Intrauterine growth restriction delays cardiomyocyte maturation and alters coronary artery function in the fetal sheep

There is now extensive evidence suggesting that intrauterine perturbations are linked with an increased risk of developing cardiovascular disease. Human epidemiological studies, supported by animal models, have demonstrated an association between low birth weight, a marker of intrauterine growth restriction (IUGR), and adult cardiovascular disease. However, little is known of the early influence of IUGR on the fetal heart and vessels. The aim of this study was to determine the effects of late gestational IUGR on coronary artery function and cardiomyocyte maturation in the fetus. IUGR was induced by placental embolization in fetal sheep from 110 to 130 days of pregnancy (D110-130); term approximately D147; control fetuses received saline. At necropsy (D130), wire and pressure myography was used to test endothelial and smooth muscle function, and passive mechanical wall properties, respectively, in small branches of left descending coronary arteries. Myocardium was dissociated for histological analysis of cardiomyocytes. At D130, IUGR fetuses (2.7 +/- 0.1 kg) were 28% lighter than controls (3.7 +/- 0.3 kg; P = 0.02). Coronary arteries from IUGR fetuses had enhanced responsiveness to the vasoconstrictors, angiotensin II and the thromboxane analogue U46619, than controls (P < 0.01). Endothelium-dependent and -independent relaxations were not different between groups. Coronary arteries of IUGR fetuses were more compliant (P = 0.02) than those of controls. The incidence of cardiomyocyte binucleation was lower in the left ventricles of IUGR fetuses (P = 0.02), suggestive of retarded cardiomyocyte maturation. We conclude that late gestational IUGR alters the reactivity and mechanical wall properties of coronary arteries and cardiomyocyte maturation in fetal sheep, which could have lifelong implications for cardiovascular function.