Reconstitution of an endothelial nitric-oxide synthase (eNOS), hsp90, and caveolin-1 complex in vitro. Evidence that hsp90 facilitates calmodulin stimulated displacement of eNOS from caveolin-1

Genetic Manipulation of Caveolin-1 in a Transgenic Mouse Model of Aortic Root Aneurysm: Sex-Dependent Effects on Endothelial and Smooth Muscle Function

Marfan syndrome (MFS) is a systemic connective tissue disorder stemming from mutations in the gene encoding Fibrillin-1 (Fbn1), a key extracellular matrix glycoprotein. This condition manifests with various clinical features, the most critical of which is the formation of aortic root aneurysms. Reduced nitric oxide (NO) production due to diminished endothelial nitric oxide synthase (eNOS) activity has been linked to MFS aortic aneurysm pathology. Caveolin-1 (Cav1), a structural protein of plasma membrane caveolae, is known to inhibit eNOS activity, suggesting its involvement in MFS aneurysm progression by modulating NO levels. In this study, we examined the role of Cav1 in aortic smooth muscle and endothelial function, aortic wall elasticity, and wall strength in male and female MFS mice (FBN1+/Cys1041Gly) by generating developing Cav1-deficient MFS mice (MFS/Cav1KO). Our findings reveal that Cav1 ablation leads to a pronounced reduction in aortic smooth muscle contraction in response to phenylephrine, attributable to an increase in NO production in the aortic wall. Furthermore, we observed enhanced aortic relaxation responses to acetylcholine in MFS/Cav1KO mice, further underscoring Cav1's inhibitory impact on NO synthesis within the aorta. Notably, van Gieson staining and chamber myography analyses showed improved elastin fiber structure and wall strength in male MFS/Cav1KO mice, whereas these effects were absent in female counterparts. Cav1's regulatory influence on aortic root aneurysm development in MFS through NO-mediated modulation of smooth muscle and endothelial function, with notable sex-dependent variations.

The Adhesion GPCR ADGRL2/LPHN2 Can Protect Against Cellular and Organismal Dysfunction

The most common trigger of sepsis and septic shock is bacterial lipopolysaccharide (LPS). Endothelial cells are among the first to encounter LPS directly. Generally, their function is closely linked to active endothelial NO Synthase (eNOS), which is significantly reduced under septic conditions. LPS treatment of endothelial cells leads to their activation and apoptosis, resulting in loss of integrity and vascular leakage, a hallmark of septic shock. Hence, therapies that prevent endothelial leakage or restore the endothelial barrier would be invaluable for patients. Adhesion GPCRs (aGPCRs) have been largely overlooked in this context, although particularly one of them, ADGRL2/LPHN2, has been implicated in endothelial barrier function. Our study shows that overexpression of ADGRL2 protects endothelial cells from LPS-induced activation, apoptosis, and impaired migration. Mechanistically, ADGRL2 preserves eNOS activity by shifting its binding from Caveolin-1 to Heat Shock Protein 90. Furthermore, ADGRL2 enhances antioxidative responses by increasing NRF2 activity. Notably, we found that this function may be evolutionarily conserved. In the absence of lat-2, a homolog of ADGRL2 in Caenorhabditis elegans, worms show higher ROS levels and altered stress response gene expression. Additionally, lat-2 mutants have a significantly reduced lifespan, altogether indicating a protective role of ADGRL2 against oxidative stress across species.

Combined Pharmacological Modulation of Translational and Transcriptional Activity Signaling Pathways as a Promising Therapeutic Approach in Children with Myocardial Changes

Myocardial hypertrophy is the most common condition that accompanies heart development in children. Transcriptional gene expression regulating pathways play a critical role both in cardiac embryogenesis and in the pathogenesis of congenital hypertrophic cardiomyopathy, neonatal posthypoxic myocardial hypertrophy, and congenital heart diseases. This paper describes the state of cardiac gene expression and potential pharmacological modulators at different transcriptional levels. An experimental model of perinatal cardiac hypoxia showed the downregulated expression of genes responsible for cardiac muscle integrity and overexpressed genes associated with energy metabolism and apoptosis, which may provide a basis for a therapeutic approach. Current evidence suggests that RNA drugs, theaflavin, neuraminidase, proton pumps, and histone deacetylase inhibitors are promising pharmacological agents in progressive cardiac hypertrophy. The different points of application of the above drugs make combined use possible, potentiating the effects of inhibition in specific signaling pathways. The special role of N-acetyl cysteine in both the inhibition of several signaling pathways and the reduction of oxidative stress was emphasized.

Role of the portal system in liver regeneration: From molecular mechanisms to clinical management

The liver has a strong regenerative capacity that ensures patient recovery after hepatectomy and liver transplantation. The portal system plays a crucial role in the dual blood supply to the liver, making it a significant factor in hepatic function. Several surgical strategies, such as portal vein ligation, associating liver partition and portal vein ligation for staged hepatectomy, and dual vein embolization, have highlighted the portal system's importance in liver regeneration. Following hepatectomy or liver transplantation, the hemodynamic properties of the portal system change dramatically, triggering regeneration via shear stress and the induction of hypoxia. However, excessive portal hyperperfusion can harm the liver and negatively affect patient outcomes. Furthermore, as the importance of the gut-liver axis has gradually been revealed, the effect of metabolites and cytokines from gut microbes carried by portal blood on liver regeneration has been acknowledged. From these perspectives, this review outlines the molecular mechanisms of the portal system's role in liver regeneration and summarizes therapeutic strategies based on the portal system intervention to promote liver regeneration.

Advances in the molecular mechanisms of statins in regulating endothelial nitric oxide bioavailability: Interlocking biology between eNOS activity and L-arginine metabolism

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A, are widely used to treat hypercholesterolemia. In addition, statins have been suggested to reduce the risk of cardiovascular events owing to their pleiotropic effects on the vascular system, including vasodilation, anti-inflammation, anti-coagulation, anti-oxidation, and inhibition of vascular smooth muscle cell proliferation. The major beneficial effect of statins in maintaining vascular homeostasis is the induction of nitric oxide (NO) bioavailability by activating endothelial NO synthase (eNOS) in endothelial cells. The mechanisms underlying the increased NO bioavailability and eNOS activation by statins have been well-established in various fields, including transcriptional and post-transcriptional regulation, kinase-dependent phosphorylation and protein-protein interactions. However, the mechanism by which statins affect the metabolism of L-arginine, a precursor of NO biosynthesis, has rarely been discussed. Autophagy, which is crucial for energy homeostasis, regulates endothelial functions, including NO production and angiogenesis, and is a potential therapeutic target for cardiovascular diseases. In this review, in addition to summarizing the molecular mechanisms underlying increased NO bioavailability and eNOS activation by statins, we also discuss the effects of statins on the metabolism of L-arginine.

Differential roles of eNOS in late effects of VEGF-A on hyperpermeability in different types of endothelial cells

Vascular endothelial growth factor (VEGF)-A induces endothelial hyperpermeability, but the molecular pathways remain incompletely understood. Endothelial nitric oxide synthase (eNOS) regulates acute effects of VEGF-A on permeability of endothelial cells (ECs), but it remains unknown whether and how eNOS regulates late effects of VEGF-A-induced hyperpermeability. Here we show that VEGF-A induces hyperpermeability via eNOS-dependent and eNOS-independent mechanisms at 2 days after VEGF-A stimulation. Silencing of expression of the eNOS gene (NOS3) reduced VEGF-A-induced permeability for dextran (70 kDa) and 766 Da-tracer in human dermal microvascular ECs (HDMVECs), but not in human retinal microvascular ECs (HRECs) and human umbilical vein ECs (HUVECs). However, silencing of NOS3 expression in HRECs increased permeability to dextran, BSA and 766 Da-tracer in the absence of VEGF-A stimulation, suggesting a barrier-protective function of eNOS. We also investigated how silencing of NOS3 expression regulates the expression of permeability-related transcripts, and found that NOS3 silencing downregulates the expression of PLVAP, a molecule associated with trans-endothelial transport via caveolae, in HDMVECs and HUVECs, but not in HRECs. Our findings underscore the complexity of VEGF-A-induced permeability pathways in ECs and the role of eNOS therein, and demonstrate that different pathways are activated depending on the EC phenotype.

The Chemical Inhibitors of Endocytosis: From Mechanisms to Potential Clinical Applications

Endocytosis is one of the major ways cells communicate with their environment. This process is frequently hijacked by pathogens. Endocytosis also participates in the oncogenic transformation. Here, we review the approaches to inhibit endocytosis, discuss chemical inhibitors of this process, and discuss potential clinical applications of the endocytosis inhibitors.

Metabolic reprogramming, oxidative stress, and pulmonary hypertension

Mitochondria are highly dynamic organelles essential for cell metabolism, growth, and function. It is becoming increasingly clear that endothelial cell dysfunction significantly contributes to the pathogenesis and vascular remodeling of various lung diseases, including pulmonary arterial hypertension (PAH), and that mitochondria are at the center of this dysfunction. The more we uncover the role mitochondria play in pulmonary vascular disease, the more apparent it becomes that multiple pathways are involved. To achieve effective treatments, we must understand how these pathways are dysregulated to be able to intervene therapeutically. We know that nitric oxide signaling, glucose metabolism, fatty acid oxidation, and the TCA cycle are abnormal in PAH, along with alterations in the mitochondrial membrane potential, proliferation, and apoptosis. However, these pathways are incompletely characterized in PAH, especially in endothelial cells, highlighting the urgent need for further research. This review summarizes what is currently known about how mitochondrial metabolism facilitates a metabolic shift in endothelial cells that induces vascular remodeling during PAH.

Role of Nitric Oxide in Megakaryocyte Function

Megakaryocytes are the main members of the hematopoietic system responsible for regulating vascular homeostasis through their progeny platelets, which are generally known for maintaining hemostasis. Megakaryocytes are characterized as large polyploid cells that reside in the bone marrow but may also circulate in the vasculature. They are generated directly or through a multi-lineage commitment step from the most primitive progenitor or Hematopoietic Stem Cells (HSCs) in a process called "megakaryopoiesis". Immature megakaryocytes enter a complicated development process defined as "thrombopoiesis" that ultimately results in the release of extended protrusions called proplatelets into bone marrow sinusoidal or lung microvessels. One of the main mediators that play an important modulatory role in hematopoiesis and hemostasis is nitric oxide (NO), a free radical gas produced by three isoforms of nitric oxide synthase within the mammalian cells. In this review, we summarize the effect of NO and its signaling on megakaryopoiesis and thrombopoiesis under both physiological and pathophysiological conditions.

Dynamic cycling with a unique Hsp90/Hsp70-dependent chaperone machinery and GAPDH is needed for heme insertion and activation of neuronal NO synthase

Heat shock protein 90 (Hsp90) is known to mediate heme insertion and activation of heme-deficient neuronal nitric oxide (NO) synthase (apo-nNOS) in cells by a highly dynamic interaction that has been extremely difficult to study mechanistically with the use of subcellular systems. In that the heme content of many critical hemeproteins is regulated by Hsp90 and the heme chaperone GAPDH, the development of an in vitro system for the study of this chaperone-mediated heme regulation would be extremely useful. Here, we show that use of an antibody-immobilized apo-nNOS led not only to successful assembly of chaperone complexes but the ability to show a clear dependence on Hsp90 and GAPDH for heme-mediated activation of apo-nNOS. The kinetics of binding for Hsp70 and Hsp90, the ATP and K⁺ dependence, and the absolute requirement for Hsp70 in assembly of Hsp90•apo-nNOS heterocomplexes all point to a similar chaperone machinery to the well-established canonical machine regulating steroid hormone receptors. However, unlike steroid receptors, the use of a purified protein system containing Hsp90, Hsp70, Hsp40, Hop, and p23 is unable to activate apo-nNOS. Thus, heme insertion requires a unique Hsp90-chaperone complex. With this newly developed in vitro system, which recapitulates the cellular process requiring GAPDH as well as Hsp90, further mechanistic studies are now possible to better understand the components of the Hsp90-based chaperone system as well as how this heterocomplex works with GAPDH to regulate nNOS and possibly other hemeproteins.

Vascular endothelium deploys caveolin-1 to regulate oligodendrogenesis after chronic cerebral ischemia in mice

Oligovascular coupling contributes to white matter vascular homeostasis. However, little is known about the effects of oligovascular interaction on oligodendrocyte precursor cell (OPC) changes in chronic cerebral ischemia. Here, using a mouse of bilateral carotid artery stenosis, we show a gradual accumulation of OPCs on vasculature with impaired oligodendrogenesis. Mechanistically, chronic ischemia induces a substantial loss of endothelial caveolin-1 (Cav-1), leading to vascular secretion of heat shock protein 90α (HSP90α). Endothelial-specific over-expression of Cav-1 or genetic knockdown of vascular HSP90α restores normal vascular-OPC interaction, promotes oligodendrogenesis and attenuates ischemic myelin damage. miR-3074(-1)-3p is identified as a direct inducer of Cav-1 reduction in mice and humans. Endothelial uptake of nanoparticle-antagomir improves myelin damage and cognitive deficits dependent on Cav-1. In summary, our findings demonstrate that vascular abnormality may compromise oligodendrogenesis and myelin regeneration through endothelial Cav-1, which may provide an intercellular mechanism in ischemic demyelination.

Cell-To-Cell Communication in the Resistance Vasculature

The arterial vasculature can be divided into large conduit arteries, intermediate contractile arteries, resistance arteries, arterioles, and capillaries. Resistance arteries and arterioles primarily function to control systemic blood pressure. The resistance arteries are composed of a layer of endothelial cells oriented parallel to the direction of blood flow, which are separated by a matrix layer termed the internal elastic lamina from several layers of smooth muscle cells oriented perpendicular to the direction of blood flow. Cells within the vessel walls communicate in a homocellular and heterocellular fashion to govern luminal diameter, arterial resistance, and blood pressure. At rest, potassium currents govern the basal state of endothelial and smooth muscle cells. Multiple stimuli can elicit rises in intracellular calcium levels in either endothelial cells or smooth muscle cells, sourced from intracellular stores such as the endoplasmic reticulum or the extracellular space. In general, activation of endothelial cells results in the production of a vasodilatory signal, usually in the form of nitric oxide or endothelial-derived hyperpolarization. Conversely, activation of smooth muscle cells results in a vasoconstriction response through smooth muscle cell contraction. © 2022 American Physiological Society. Compr Physiol 12: 1-35, 2022.

Targeting mechanosensitive endothelial TXNDC5 to stabilize eNOS and reduce atherosclerosis in vivo

Although atherosclerosis preferentially develops at arterial curvatures and bifurcations where disturbed flow (DF) activates endothelium, therapies targeting flow-dependent mechanosensing pathways in the vasculature are unavailable. Here, we provided experimental evidence demonstrating a previously unidentified causal role of DF-induced endothelial TXNDC5 (thioredoxin domain containing 5) in atherosclerosis. TXNDC5 was increased in human and mouse atherosclerotic lesions and induced in endothelium subjected to DF. Endothelium-specific Txndc5 deletion markedly reduced atherosclerosis in ApoE-/- mice. Mechanistically, DF-induced TXNDC5 increases proteasome-mediated degradation of heat shock factor 1, leading to reduced heat shock protein 90 and accelerated eNOS (endothelial nitric oxide synthase) protein degradation. Moreover, nanoparticles formulated to deliver Txndc5-targeting CRISPR-Cas9 plasmids driven by an endothelium-specific promoter (CDH5) significantly increase eNOS protein and reduce atherosclerosis in ApoE-/- mice. These results delineate a new molecular paradigm that DF-induced endothelial TXNDC5 promotes atherosclerosis and establish a proof of concept of targeting endothelial mechanosensitive pathways in vivo against atherosclerosis.

Endothelial Contribution to Warfarin-Induced Arterial Media Calcification in Mice

Arterial media calcification (AMC) is predominantly regulated by vascular smooth muscle cells (VSMCs), which transdifferentiate into pro-calcifying cells. In contrast, there is little evidence for endothelial cells playing a role in the disease. The current study investigates cellular functioning and molecular pathways underlying AMC, respectively by, an ex vivo isometric organ bath set-up to explore the interaction between VSMCs and ECs and quantitative proteomics followed by functional pathway interpretation. AMC development, which was induced in mice by dietary warfarin administration, was proved by positive Von Kossa staining and a significantly increased calcium content in the aorta compared to that of control mice. The ex vivo organ bath set-up showed calcified aortic segments to be significantly more sensitive to phenylephrine induced contraction, compared to control segments. This, together with the fact that calcified segments as compared to control segments, showed a significantly smaller contraction in the absence of extracellular calcium, argues for a reduced basal NO production in the calcified segments. Moreover, proteomic data revealed a reduced eNOS activation to be part of the vascular calcification process. In summary, this study identifies a poor endothelial function, next to classic pro-calcifying stimuli, as a possible initiator of arterial calcification.

The role of caveolae in endothelial dysfunction

Caveolae, the specialized cell-surface plasma membrane invaginations which are abundant in endothelial cells, play critical roles in regulating various cellular processes, including cholesterol homeostasis, nitric oxide production, and signal transduction. Endothelial caveolae serve as a membrane platform for compartmentalization, modulation, and integration of signal events associated with endothelial nitric oxide synthase, ATP synthase β, and integrins, which are involved in the regulation of endothelial dysfunction and related cardiovascular diseases, such as atherosclerosis and hypertension. Furthermore, these dynamic microdomains on cell membrane are modulated by various extracellular stimuli, including cholesterol and flow shear stress. In this brief review, we summarize the critical roles of caveolae in the orchestration of endothelial function based on recent findings as well as our work over the past two decades.

Critical Role of Caveolin-1 Loss/Dysfunction in Pulmonary Hypertension

Pulmonary hypertension (PH) is a rare disease with a high morbidity and mortality rate. A number of systemic diseases and genetic mutations are known to lead to PH. The main features of PH are altered vascular relaxation responses and the activation of proliferative and anti-apoptotic pathways, resulting in pulmonary vascular remodeling, elevated pulmonary artery pressure, and right ventricular hypertrophy, ultimately leading to right heart failure and premature death. Important advances have been made in the field of pulmonary pathobiology, and several deregulated signaling pathways have been shown to be associated with PH. Clinical and experimental studies suggest that, irrespective of the underlying disease, endothelial cell disruption and/or dysfunction play a key role in the pathogenesis of PH. Endothelial caveolin-1, a cell membrane protein, interacts with and regulates several transcription factors and maintains homeostasis. Disruption of endothelial cells leads to the loss or dysfunction of endothelial caveolin-1, resulting in reciprocal activation of proliferative and inflammatory pathways, leading to cell proliferation, medial hypertrophy, and PH, which initiates PH and facilitates its progression. The disruption of endothelial cells, accompanied by the loss of endothelial caveolin-1, is accompanied by enhanced expression of caveolin-1 in smooth muscle cells (SMCs) that leads to pro-proliferative and pro-migratory responses, subsequently leading to neointima formation. The neointimal cells have low caveolin-1 and normal eNOS expression that may be responsible for promoting nitrosative and oxidative stress, furthering cell proliferation and metabolic alterations. These changes have been observed in human PH lungs and in experimental models of PH. In hypoxia-induced PH, there is no endothelial disruption, loss of endothelial caveolin-1, or enhanced expression of caveolin-1 in SMCs. Hypoxia induces alterations in membrane composition without caveolin-1 or any other membrane protein loss. However, caveolin-1 is dysfunctional, resulting in cell proliferation, medial hypertrophy, and PH. These alterations are reversible upon removal of hypoxia, provided there is no associated EC disruption. This review examined the role of caveolin-1 disruption and dysfunction in PH.

An Overview of NO Signaling Pathways in Aging

Nitric Oxide (NO) is a potent signaling molecule involved in the regulation of various cellular mechanisms and pathways under normal and pathological conditions. NO production, its effects, and its efficacy, are extremely sensitive to aging-related changes in the cells. Herein, we review the mechanisms of NO signaling in the cardiovascular system, central nervous system (CNS), reproduction system, as well as its effects on skin, kidneys, thyroid, muscles, and on the immune system during aging. The aging-related decline in NO levels and bioavailability is also discussed in this review. The decreased NO production by endothelial nitric oxide synthase (eNOS) was revealed in the aged cardiovascular system. In the CNS, the decline of the neuronal (n)NOS production of NO was related to the impairment of memory, sleep, and cognition. NO played an important role in the aging of oocytes and aged-induced erectile dysfunction. Aging downregulated NO signaling pathways in endothelial cells resulting in skin, kidney, thyroid, and muscle disorders. Putative therapeutic agents (natural/synthetic) affecting NO signaling mechanisms in the aging process are discussed in the present study. In summary, all of the studies reviewed demonstrate that NO plays a crucial role in the cellular aging processes.

Characterization of a Novel Caveolin Modulator That Reduces Vascular Permeability and Ocular Inflammation

Purpose

Caveolin (Cav) regulates various aspect of endothelial cell signaling and cell-permeable peptides (CPPs) fused to domains of Cav can reduce retinal damage and inflammation in vivo. Thus, the goal of the present study was to identify a novel CPP that improves delivery of a truncated Cav modulator in vitro and in vivo.

Methods

Phage display technology was used to identify a small peptide (RRPPR) that was internalized into endothelial cells. Fusions of Cav with the peptide were compared to existing molecules in three distinct assays, vascular endothelial growth factor-A (VEGF) induced nitric oxide (NO) release, VEGF induced vascular leakage, and in a model of immune mediated uveitis.

Results

RRPPR was internalized efficiently and was potent in blocking NO release. Fusing RRPPR with a minimal Cav inhibitory domain (CVX51401) dose-dependently blocked NO release, VEGF induced permeability, and retinal damage in a model of uveitis.

Conclusions

CVX51401 is a novel Cav modulator that reduces VEGF and immune mediated inflammation.

Translational Relevance

CVX51401 is an optimized Cav modulator that reduces vascular permeability and ocular inflammation that is poised for clinical development.

Heat therapy: mechanistic underpinnings and applications to cardiovascular health

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and novel therapies are drastically needed to prevent or delay the onset of CVD to reduce the societal and healthcare burdens associated with these chronic diseases. One such therapy is "heat therapy," or chronic, repeated use of hot baths or saunas. Although using heat exposure to improve health is not a new concept, it has received renewed attention in recent years as a growing number of studies have demonstrated robust and widespread beneficial effects of heat therapy on cardiovascular health. Here, we review the existing literature, with particular focus on the molecular mechanisms that underscore the cardiovascular benefits of this practice.

Endothelial caveolin and its scaffolding domain in cancer

Since the initial reports implicating caveolin-1 (CAV1) in neoplasia, the scientific community has made tremendous strides towards understanding how CAV1-dependent signaling and caveolae assembly modulate solid tumor growth. Once a solid neoplastic tumor reaches a certain size, it will increasingly rely on its stroma to meet the metabolic demands of the rapidly proliferating cancer cells, a limitation typically but not exclusively addressed via the formation of new blood vessels. Landmark studies using xenograft tumor models have highlighted the importance of stromal CAV1 during neoplastic blood vessel growth from preexisting vasculature, a process called angiogenesis, and helped identify endothelium-specific signaling events regulated by CAV1, such as vascular endothelial growth factor (VEGF) receptors as well as the endothelial nitric oxide (NO) synthase (eNOS) systems. This chapter provides a glimpse into the signaling events modulated by CAV1 and its scaffolding domain (CSD) during endothelial-specific aspects of neoplastic growth, such as vascular permeability, angiogenesis, and mechanotransduction.

Loss of cholinergic innervation differentially affects eNOS-mediated blood flow, drainage of Aβ and cerebral amyloid angiopathy in the cortex and hippocampus of adult mice

Vascular dysregulation and cholinergic basal forebrain degeneration are both early pathological events in the development of Alzheimer’s disease (AD). Acetylcholine contributes to localised arterial dilatation and increased cerebral blood flow (CBF) during neurovascular coupling via activation of endothelial nitric oxide synthase (eNOS). Decreased vascular reactivity is suggested to contribute to impaired clearance of β-amyloid (Aβ) along intramural periarterial drainage (IPAD) pathways of the brain, leading to the development of cerebral amyloid angiopathy (CAA). However, the possible relationship between loss of cholinergic innervation, impaired vasoreactivity and reduced clearance of Aβ from the brain has not been previously investigated. In the present study, intracerebroventricular administration of mu-saporin resulted in significant death of cholinergic neurons and fibres in the medial septum, cortex and hippocampus of C57BL/6 mice. Arterial spin labelling MRI revealed a loss of CBF response to stimulation of eNOS by the Rho-kinase inhibitor fasudil hydrochloride in the cortex of denervated mice. By contrast, the hippocampus remained responsive to drug treatment, in association with altered eNOS expression. Fasudil hydrochloride significantly increased IPAD in the hippocampus of both control and saporin-treated mice, while increased clearance from the cortex was only observed in control animals. Administration of mu-saporin in the TetOAPPSweInd mouse model of AD was associated with a significant and selective increase in Aβ40-positive CAA. These findings support the importance of the interrelationship between cholinergic innervation and vascular function in the aetiology and/or progression of CAA and suggest that combined eNOS/cholinergic therapies may improve the efficiency of Aβ removal from the brain and reduce its deposition as CAA.

Heat shock protein 90 enhances the electron transfer between the FMN and heme cofactors in neuronal nitric oxide synthase

Heat shock protein 90 (Hsp90) is a key regulator of nitric oxide synthase (NOS) in vivo. Despite its functional importance, little is known about the underlying molecular mechanism. Here, purified dimeric human Hsp90α was used to investigate whether (and if so, how) Hsp90 affects the FMN-heme interdomain electron transfer (IET) step in NOS. Hsp90α increases the IET rate for rat neuronal NOS (nNOS) in a dose-saturable manner, and a single charge-neutralization mutation at conserved Hsp90 K585 abolishes the effect. The kinetic results with added Ficoll 70, a crowder, further indicate that Hsp90 enhances the FMN-heme IET through specific association with nNOS. The Hsp90-nNOS docking models provide hints on the putative role of Hsp90 in constraining the available conformational space for the FMN domain motions.

Unbiased proteomics identifies plasminogen activator inhibitor-1 as a negative regulator of endothelial nitric oxide synthase

Nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS) is a critical mediator of vascular function. eNOS is tightly regulated at various levels, including transcription, co- and posttranslational modifications, and by various protein-protein interactions. Using stable isotope labeling with amino acids in cell culture (SILAC) and mass spectrometry (MS), we identified several eNOS interactors, including the protein plasminogen activator inhibitor-1 (PAI-1). In cultured human umbilical vein endothelial cells (HUVECs), PAI-1 and eNOS colocalize and proximity ligation assays demonstrate a protein-protein interaction between PAI-1 and eNOS. Knockdown of PAI-1 or eNOS eliminates the proximity ligation assay (PLA) signal in endothelial cells. Overexpression of eNOS and HA-tagged PAI-1 in COS7 cells confirmed the colocalization observations in HUVECs. Furthermore, the source of intracellular PAI-1 interacting with eNOS was shown to be endocytosis derived. The interaction between PAI-1 and eNOS is a direct interaction as supported in experiments with purified proteins. Moreover, PAI-1 directly inhibits eNOS activity, reducing NO synthesis, and the knockdown or antagonism of PAI-1 increases NO bioavailability. Taken together, these findings place PAI-1 as a negative regulator of eNOS and disruptions in eNOS-PAI-1 binding promote increases in NO production and enhance vasodilation in vivo.

Implicating endothelial cell senescence to dysfunction in the ageing and diseased brain

Cerebrovascular endothelial cells (CECs) are integral components of both the blood-brain barrier (BBB) and the neurovascular unit (NVU). As the primary cell type of the BBB, CECs are responsible for the tight regulation of molecular transport between the brain parenchyma and the periphery. Additionally, CECs are essential in neurovascular coupling where they help regulate cerebral blood flow in response to regional increases in cellular demand in the NVU. CEC dysfunction occurs during both normative ageing and in cerebrovascular disease, which leads to increased BBB permeability and neurovascular uncoupling. This MiniReview compiles what is known about the molecular changes underlying CEC dysfunction, many of which are reminiscent of cells that have become senescent. In general, cellular senescence is defined as an irreversible growth arrest characterized by the acquisition of a pro-inflammatory secretory phenotype in response to DNA damage or other cellular stresses. We discuss evidence for endothelial cell senescence in ageing and cardiovascular disease, and how CEC senescence may contribute to age-related cerebrovascular dysfunction.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

eNOS-NO-induced small blood vessel relaxation requires EHD2-dependent caveolae stabilization

Endothelial nitric oxide synthase (eNOS)-related vessel relaxation is a highly coordinated process that regulates blood flow and pressure and is dependent on caveolae. Here, we investigated the role of caveolar plasma membrane stabilization by the dynamin-related ATPase EHD2 on eNOS-nitric oxide (NO)-dependent vessel relaxation. Loss of EHD2 in small arteries led to increased numbers of caveolae that were detached from the plasma membrane. Concomitantly, impaired relaxation of mesenteric arteries and reduced running wheel activity were observed in EHD2 knockout mice. EHD2 deletion or knockdown led to decreased production of nitric oxide (NO) although eNOS expression levels were not changed. Super-resolution imaging revealed that eNOS was redistributed from the plasma membrane to internalized detached caveolae in EHD2-lacking tissue or cells. Following an ATP stimulus, reduced cytosolic Ca2+ peaks were recorded in human umbilical vein endothelial cells (HUVECs) lacking EHD2. Our data suggest that EHD2-controlled caveolar dynamics orchestrates the activity and regulation of eNOS/NO and Ca2+ channel localization at the plasma membrane.

Hypoxia-induced pulmonary hypertension and chronic lung disease: caveolin-1 dysfunction an important underlying feature

Caveolin-1 (cav-1) has been shown to play a significant role in the pathogenesis of pulmonary hypertension (PH). In the monocrotaline model of PH, the loss of endothelial cav-1 as well as reciprocal activation of proliferative and anti-apoptotic pathways initiate the disease process and facilitate its progression. In order to examine the role of cav-1 in hypoxia-induced PH, we exposed rats and neonatal calves to hypobaric hypoxia and obtained hemodynamic data and assessed the expression of cav-1 and related proteins eNOS, HSP90, PTEN, gp130, PY-STAT3, β-catenin, and Glut1 in the lung tissue. Chronic hypoxic exposure in rats (48 h-4 weeks) and calves (two weeks) did not alter the expression of cav-1, HSP90, or eNOS. PTEN expression was significantly decreased accompanied by PY-STAT3 activation and increased expression of gp130, Glut1, and β-catenin in hypoxic animals. We also examined cav-1 expression in the lung sections from steers with chronic hypoxic disease (Brisket disease) and from patients with chronic lung disease who underwent lung biopsy for medical reasons. There was no cav-1 loss in Brisket disease. In chronic lung disease cases, endothelial cav-1 expression was present, albeit with less intense staining in some cases. In conclusion, hypoxia did not alter the cav-1 expression in experimental models. The presence of cav-1, however, did not suppress hypoxia-induced activation of PY-STAT3 and β catenin, increased gp130 and Glut1 expression, or prevent the PTEN loss, indicating cav-1 dysfunction in hypoxia-induced PH.

Dysfunction of Cerebrovascular Endothelial Cells: Prelude to Vascular Dementia

Vascular dementia (VaD) is the second most common type of dementia after Alzheimer's disease (AD), characterized by progressive cognitive impairment, memory loss, and thinking or speech problems. VaD is usually caused by cerebrovascular disease, during which, cerebrovascular endothelial cells (CECs) are vulnerable. CEC dysfunction occurs before the onset of VaD and can eventually lead to dysregulation of cerebral blood flow and blood-brain barrier damage, followed by the activation of glia and inflammatory environment in the brain. White matter, neuronal axons, and synapses are compromised in this process, leading to cognitive impairment. The present review summarizes the mechanisms underlying CEC impairment during hypoperfusion and pathological role of CECs in VaD. Through the comprehensive examination and summarization, endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathway, Ras homolog gene family member A (RhoA) signaling pathway, and CEC-derived caveolin-1 (CAV-1) are proposed to serve as targets of new drugs for the treatment of VaD.

Expression dynamics of HSP90 and nitric oxide synthase (NOS) isoforms during heat stress acclimation in Tharparkar cattle

Six male Tharparkar cattle of 2-3 years old were selected for the study. After 15-day acclimation at thermoneutral zone (TNZ) in psychrometric chamber, animals were exposed at 42 °C for 6 h up to 23 days followed by 12 days of recovery period. Blood samples were collected during control period at TNZ (days 1, 5, and 12), after heat stress exposure (day 1, immediate heat stress acclimation (IHSA); days 2 to 10, short-term heat stress acclimation (STHSA); days 15 to 23, long-term heat stress acclimation (LTHSA); days 7 and 12, recovery period), and peripheral blood mononuclear cells (PBMCs) were isolated for RNA and protein extraction. The messenger RNA (mRNA) and protein expression in PBMCs were determined by qPCR and western blot, respectively. Samples at TNZ were taken as control. The mRNA expression of HSP90, iNOS, and eNOS was significantly upregulated (P < 0.05) on day 1 (ISHA) as compared to control, remained consistent during STHSA, again increased during LTHSA, and finally reduced to basal level during recovery period. The protein expression of HSP90, iNOS, and eNOS were akin to their transcript pattern. PBMC culture study was conducted to study transcriptional abundance of HSP90, iNOS, and eNOS at different temperature-time combinations. The present findings indicate that HSP90, iNOS, and eNOS could possibly play an important role in mitigating thermal insults and confer thermotolerance during long-term heat stress exposure in Tharparkar cattle.

Differential effects of heat shock protein 90 and serine 1179 phosphorylation on endothelial nitric oxide synthase activity and on its cofactors

Endothelial nitric oxide synthase (eNOS) is responsible for maintaining systemic blood pressure, vascular remodeling and angiogenesis. Previous studies showed that bovine eNOS serine 1179 (Serine 1177 for human eNOS) phosphorylation enhanced NO synthesis. Meanwhile, heat shock protein 90 (Hsp90) plays a critical role in maintenance of eNOS structure and function. However, the regulatory difference and importance between Serine 1179 phosphorylation and Hsp90 on eNOS activity have not been evaluated. In current studies, S1179D eNOS was employed to mimic phospho-eNOS and exhibited markedly increased enzyme activity than wild type eNOS (WT eNOS). Hsp90 showed a dose-dependent increase for both WT eNOS and S1179D eNOS activity at the presence of all eNOS cofactors, such as Calcium/Calmodulin (Ca2+ /CaM), BH4, and NADPH etc. The enhancement effects were abolished by dominant-negative mutant Hsp 90 protein. ENOS-cofactors dynamic assay showed that Hsp90 enhanced WT eNOS affinity to NADPH, L-arginine, and CaM but not to Ca2+ and BH4. The impact of eNOS Serine 1179 phosphorylation and Hsp90 on eNOS affinity to cofactors has also been compared. Different from the effect of Hsp90 on eNOS affinity to specific cofactors, Serine 1179 phosphorylation significantly increased eNOS affinity to all cofactors. Moreover, VEGF-induced eNOS phosphorylation in bovine aortic endothelial cells (BAECs) and more NO generation from eNOS compared to control. Inhibition of Hsp90 by geldanamycin decreased eNOS activity and decreased endothelial viability. In conclusion, by changing eNOS structure, Hsp90 profoundly affected eNOS functions, including change of affinity of eNOS to cofactors like Ca2+, L-arginine, BH4 and further affecting NO generation capability. These specific cofactors regulated by Hsp 90 could become potential therapeutic targets of the eNOS-related diseases in future.

Nitric oxide and hydrogen sulfide: the gasotransmitter paradigm of the vascular system

There are several reviews on NO and hydrogen sulfide (H₂ S) and their role in vascular diseases in the current relevant literature. The aim of this review is to discuss, within the limits of present knowledge, the interconnection between these two gasotransmitters in vascular function. In particular, the review focuses on the role played by the balance between the NO and H₂ S pathways in either physiological or pathological conditions. The distinction between physiology and pathology has been made in order to dissect the molecular basis of this crosstalk, highlighting how and if this balance varies, depending upon the vascular status. Perspectives and possible novel therapeutic approaches are also discussed.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Contemporary Approaches to Modulating the Nitric Oxide-cGMP Pathway in Cardiovascular Disease

Endothelial cells lining the vessel wall control important aspects of vascular homeostasis. In particular, the production of endothelium-derived nitric oxide and activation of soluble guanylate cyclase promotes endothelial quiescence and governs vasomotor function and proportional remodeling of blood vessels. Here, we discuss novel approaches to improve endothelial nitric oxide generation and preserve its bioavailability. We also discuss therapeutic opportunities aimed at activation of soluble guanylate cyclase for multiple cardiovascular indications.

Improving the Outcome of Vein Grafts: Should Vascular Surgeons Turn Veins into Arteries?

Autogenous vein grafts remain the gold standard conduit for arterial bypass, particularly for the treatment of critical limb ischemia. Vein graft adaptation to the arterial environment, i.e., adequate dilation and wall thickening, contributes to the superior performance of vein grafts. However, abnormal venous wall remodeling with excessive neointimal hyperplasia commonly causes vein graft failure. Since the PREVENT trials failed to improve vein graft outcomes, new strategies focus on the adaptive response of the venous endothelial cells to the post-surgical arterial environment. Eph-B4, the determinant of venous endothelium during embryonic development, remains expressed and functional in adult venous tissue. After surgery, vein grafts lose their venous identity, with loss of Eph-B4 expression; however, arterial identity is not gained, consistent with loss of all vessel identity. In mouse vein grafts, stimulation of venous Eph-B4 signaling promotes retention of venous identity in endothelial cells and is associated with vein graft walls that are not thickened. Eph-B4 regulates downstream signaling pathways of relevance to vascular biology, including caveolin-1, Akt, and endothelial nitric oxide synthase (eNOS). Regulation of the Eph-B4 signaling pathway may be a novel therapeutic target to prevent vein graft failure.

Inflammation-induced caveolin-1 and BMPRII depletion promotes endothelial dysfunction and TGF-β-driven pulmonary vascular remodeling

Endothelial cell (EC) activation and vascular injury are hallmark features of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Caveolin-1 (Cav-1) is highly expressed in pulmonary microvascular ECs and plays a key role in maintaining vascular homeostasis. The aim of this study was to determine if the lung inflammatory response to Escherichia coli lipopolysaccharide (LPS) promotes priming of ECs via Cav-1 depletion and if this contributes to the onset of pulmonary vascular remodeling. To test the hypothesis that depletion of Cav-1 primes ECs to respond to profibrotic signals, C57BL6 wild-type (WT) mice (Tie2.Cre^-;Cav1^fl/fl ) were exposed to nebulized LPS (10 mg; 1 h daily for 4 days) and compared with EC-specific Cav1^-/- (Tie2.Cre⁺;Cav1^fl/fl ). After 96 h of LPS exposure, total lung Cav-1 and bone morphogenetic protein receptor type II (BMPRII) expression were reduced in WT mice. Moreover, plasma albumin leakage, infiltration of immune cells, and levels of IL-6/IL-6R and transforming growth factor-β (TGF-β) were elevated in both LPS-treated WT and EC-Cav1^-/- mice. Finally, EC-Cav1^-/- mice exhibited a modest increase in microvascular thickness basally and even more so on exposure to LPS (96 h). EC-Cav1^-/- mice and LPS-treated WT mice exhibited reduced BMPRII expression and endothelial nitric oxide synthase uncoupling, which along with increased TGF-β promoted TGFβRI-dependent SMAD-2/3 phosphorylation. Finally, human lung sections from patients with ARDS displayed reduced EC Cav-1 expression, elevated TGF-β levels, and severe pulmonary vascular remodeling. Thus EC Cav-1 depletion, oxidative stress-mediated reduction in BMPRII expression, and enhanced TGF-β-driven SMAD-2/3 signaling promote pulmonary vascular remodeling in inflamed lungs.

Inwardly rectifying K+ channels are major contributors to flow-induced vasodilatation in resistance arteries

KEY POINTS

Endothelial inwardly rectifying K⁺ (Kir2.1) channels regulate flow-induced vasodilatation via nitric oxide (NO) in mouse mesenteric resistance arteries. Deficiency of Kir2.1 channels results in elevated blood pressure and increased vascular resistance. Flow-induced vasodilatation in human resistance arteries is also regulated by inwardly rectifying K⁺ channels. This study presents the first direct evidence that Kir channels play a critical role in physiological endothelial responses to flow.

ABSTRACT

Inwardly rectifying K⁺ (Kir) channels are known to be sensitive to flow, but their role in flow-induced endothelial responses is not known. The goal of this study is to establish the role of Kir channels in flow-induced vasodilatation and to provide first insights into the mechanisms responsible for Kir signalling in this process. First, we establish that primary endothelial cells isolated from murine mesenteric arteries express functional Kir2.1 channels sensitive to shear stress. Then, using the Kir2.1^+/- heterozygous mouse model, we establish that downregulation of Kir2.1 results in significant decrease in shear-activated Kir currents and inhibition of endothelium-dependent flow-induced vasodilatation (FIV) assayed in pressurized mesenteric arteries pre-constricted with endothelin-1. Deficiency in Kir2.1 also results in the loss of flow-induced phosphorylation of eNOS and Akt, as well as inhibition of NO generation. All the effects are fully rescued by endothelial cell (EC)-specific overexpression of Kir2.1. A component of FIV that is Kir independent is abrogated by blocking Ca²⁺ -sensitive K⁺ channels. Kir2.1 has no effect on endothelium-independent and K⁺ -induced vasodilatation in denuded arteries. Kir2.1^+/- mice also show increased mean blood pressure measured by carotid artery cannulation and increased microvascular resistance measured using a tail-cuff. Importantly, blocking Kir channels also inhibits flow-induced vasodilatation in human subcutaneous adipose microvessels. Endothelial Kir channels contribute to FIV of mouse mesenteric arteries via an NO-dependent mechanism, whereas Ca²⁺ -sensitive K⁺ channels mediate FIV via an NO-independent pathway. Kir2 channels also regulate vascular resistance and blood pressure. Finally, Kir channels also contribute to FIV in human subcutaneous microvessels.

Nitric oxide: what's new to NO?

Nitric oxide (NO) is one of the critical components of the vasculature, regulating key signaling pathways in health. In macrovessels, NO functions to suppress cell inflammation as well as adhesion. In this way, it inhibits thrombosis and promotes blood flow. It also functions to limit vessel constriction and vessel wall remodeling. In microvessels and particularly capillaries, NO, along with growth factors, is important in promoting new vessel formation, a process termed angiogenesis. With age and cardiovascular disease, animal and human studies confirm that NO is dysregulated at multiple levels including decreased production, decreased tissue half-life, and decreased potency. NO has also been implicated in diseases that are related to neurotransmission and cancer although it is likely that these processes involve NO at higher concentrations and from nonvascular cell sources. Conversely, NO and drugs that directly or indirectly increase NO signaling have found clinical applications in both age-related diseases and in younger individuals. This focused review considers recently reported advances being made in the field of NO signaling regulation at several levels including enzymatic production, receptor function, interacting partners, localization of signaling, matrix-cellular and cell-to-cell cross talk, as well as the possible impact these newly described mechanisms have on health and disease.

Modulating Vascular Hemodynamics With an Alpha Globin Mimetic Peptide (HbαX)

The ability of hemoglobin to scavenge the potent vasodilator nitric oxide (NO) in the blood has been well established as a mechanism of vascular tone homeostasis. In endothelial cells, the alpha chain of hemoglobin (hereafter, alpha globin) and endothelial NO synthase form a macromolecular complex, providing a sink for NO directly adjacent to the production source. We have developed an alpha globin mimetic peptide (named HbαX) that displaces endogenous alpha globin and increases bioavailable NO for vasodilation. Here we show that, in vivo, HbαX administration increases capillary oxygenation and blood flow in arterioles acutely and produces a sustained decrease in systolic blood pressure in normal and angiotensin II-induced hypertensive states. HbαX acts with high specificity and affinity to endothelial NO synthase, without toxicity to liver and kidney and no effect on p50 of O2 binding in red blood cells. In human vasculature, HbαX blunts vasoconstrictive response to cumulative doses of phenylephrine, a potent constricting agent. By binding to endothelial NO synthase and displacing endogenous alpha globin, HbαX modulates important metrics of vascular function, increasing vasodilation and flow in the resistance vasculature.

Acute hot water immersion is protective against impaired vascular function following forearm ischemia-reperfusion in young healthy humans

Ischemia-reperfusion (I/R) injury is a primary cause of poor outcomes following ischemic cardiovascular events. We tested whether acute hot water immersion protects against forearm vascular I/R. Ten (5 male, 5 female) young (23 ± 2 yr), healthy subjects participated in two trials in random order 7-21 days apart, involving: 1) 60 min of seated rest (control), or 2) 60 min of immersion in 40.5°C water (peak rectal temperature: 38.9 ± 0.2°C). I/R was achieved 70 min following each intervention by inflating an upper arm cuff to 250 mmHg for 20 min followed by 20 min of reperfusion. Brachial artery flow-mediated dilation (FMD) and forearm postocclusive reactive hyperemia (RH) were measured as markers of macrovascular and microvascular function at three time points: 1) preintervention, 2) 60 min postintervention, and 3) post-I/R. Neither time control nor hot water immersion alone affected FMD (both, P > 0.99). I/R reduced FMD from 7.4 ± 0.7 to 5.4 ± 0.6% (P = 0.03), and this reduction was prevented following hot water immersion (7.0 ± 0.7 to 7.7 ± 1.0%; P > 0.99). I/R also impaired RH (peak vascular conductance: 2.6 ± 0.5 to 2.0 ± 0.4 ml·min^-1·mmHg^-1, P = 0.003), resulting in a reduced shear stimulus (SR_AUC·10^-3: 22.5 ± 2.4 to 16.9 ± 2.4, P = 0.04). The post-I/R reduction in peak RH was prevented by hot water immersion (2.5 ± 0.4 to 2.3 ± 0.4 ml·min^-1·mmHg^-1; P = 0.33). We observed a decline in brachial artery dilator function post-I/R, which may be (partly) related to damage incurred downstream in the microvasculature, as indicated by impaired RH and shear stimulus. Hot water immersion was protective against reductions in FMD and RH post-I/R, suggesting heat stress induces vascular changes consistent with reducing I/R injury following ischemic events.

Posttranscriptional and transcriptional regulation of endothelial nitric-oxide synthase during hypoxia: the role of microRNAs

Understanding the cellular pathways that regulate endothelial nitric oxide (eNOS, NOS3) expression and consequently nitric oxide (NO) bioavailability during hypoxia is a necessary aspect in the development of novel treatments for cardiovascular disorders. eNOS expression and eNOS-dependent NO cellular signaling during hypoxia promote an equilibrium of transcriptional and posttranscriptional molecular mechanisms that belong to both proapoptotic and survival pathways. Furthermore, NO bioavailability results not only from eNOS levels, but also relies on the presence of eNOS substrate and cofactors, the phosphorylation status of eNOS, and the presence of reactive oxygen species (ROS) that can inactivate eNOS. Since both NOS3 levels and these signaling pathways can also be a subject of posttranscriptional modulation by microRNAs (miRNAs), this class of short noncoding RNAs contribute another level of regulation for NO bioavailability. As miRNA antagomirs or specific target protectors could be used in therapeutic approaches to regulate NO levels, either by changing NOS3 mRNA stability or through factors governing eNOS activity, it is critical to understand their role in governing eNOS activity during hypoxa. In contrast to a large number of miRNAs reported to the change eNOS expression during hypoxia, only a few miRNAs modulate eNOS activity. Furthermore, impaired miRNA biogenesis leads to NOS3 mRNA stabilization under hypoxia. Here we discuss the recent studies that define miRNAs’ role in maintaining endothelial NO bioavailability emphasizing those miRNAs that directly modulate NOS3 expression or eNOS activity.

Identification of Differential ER-Alpha Versus ER-Beta Mediated Activation of eNOS in Ovine Uterine Artery Endothelial Cells

Endothelial nitric oxide (NO) production is partly responsible for maintenance of uterine vasodilatation during physiologic states of high circulating estrogen levels, e.g., pregnancy. Although 3%–5% of estrogen receptors (ER-alpha/beta) localize to the endothelial plasmalemma, these receptors are responsible for the nongenomic vasodilator responses. Estradiol induces endothelial NO synthase (eNOS) activation to increase NO production; however, it is unknown if eNOS regulation is dependent on both ERs. We hypothesize that ER-alpha and/or ER-beta are capable of changing eNOS phosphorylation and increasing NO production in uterine artery endothelial cells (UAECs). UAECs were 1) treated with vehicle or increasing concentrations (0.1–100 nM) or timed treatments (0–30 min) of estradiol and 2) pretreated with the inhibitors ICI 182,780 (nonspecific ER), 1,3-Bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-alpha specific), or 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP; ER-beta specific) followed by estradiol to analyze the changes in eNOS stimulatory ^Ser1177eNOS and ^Ser635eNOS versus inhibitory ^Thr495eNOS via Western blot analysis. UAECs were also pretreated with MPP, PHTPP, or MPP + PHTTP followed by estradiol or treated with the agonists estradiol, 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol, 2,3-bis(4-hydroxyphenyl)-propionitrile, or ATP to quantify total NOx levels (NO₂+NO₃). Estrogen and ER-alpha activation induced an increase in ^Ser1177eNOS and ^Ser635eNOS, a decrease in ^Thr495eNOS, and an increase in NOx levels. In contrast, ER-beta activation only reduced ^Thr495eNOS without changes in ^Ser1177eNOS or ^Ser635eNOS. However, ER-beta activation increased NOx levels. Lastly, the antagonism of both receptors induced a reduction in basal and stimulated NOx levels in UAECs. These data demonstrate that 1) eNOS phosphorylation changes occur via ER-alpha- and ER-beta-dependent mechanisms and 2) ER-alpha and ER-beta can both increase NO levels independently from each other.

Phosphorylation inactivation of endothelial nitric oxide synthesis in pulmonary arterial hypertension

The impairment of vasodilator nitric oxide (NO) production is well accepted as a typical marker of endothelial dysfunction in vascular diseases, including in the pathophysiology of pulmonary arterial hypertension (PAH), but the molecular mechanisms accounting for loss of NO production are unknown. We hypothesized that low NO production by pulmonary arterial endothelial cells in PAH is due to inactivation of NO synthase (eNOS) by aberrant phosphorylation of the protein. To test the hypothesis, we evaluated eNOS levels, dimerization, and phosphorylation in the vascular endothelial cells and lungs of patients with PAH compared with controls. In mechanistic studies, eNOS activity in endothelial cells in PAH lungs was found to be inhibited due to phosphorylation at T495. Evidence pointed to greater phosphorylation/activation of protein kinase C (PKC) α and its greater association with eNOS as the source of greater phosphorylation at T495. The presence of greater amounts of pT495-eNOS in plexiform lesions in lungs of patients with PAH confirmed the pathobiological mechanism in vivo. Transfection of the activating mutation of eNOS (T495A/S1177D) restored NO production in PAH cells. Pharmacological blockade of PKC activity by β-blocker also restored NO formation by PAH cells, identifying one mechanism by which β-blockers may benefit PAH and cardiovascular diseases through recovery of endothelial functions.

Caveolae and Caveolin-1 Integrate Reverse Cholesterol Transport and Inflammation in Atherosclerosis

Lipid disorder and inflammation play critical roles in the development of atherosclerosis. Reverse cholesterol transport is a key event in lipid metabolism. Caveolae and caveolin-1 are in the center stage of cholesterol transportation and inflammation in macrophages. Here, we propose that reverse cholesterol transport and inflammation in atherosclerosis can be integrated by caveolae and caveolin-1.

Uncoupling Caveolae From Intracellular Signaling In Vivo

RATIONALE

Caveolin-1 (Cav-1) negatively regulates endothelial nitric oxide (NO) synthase-derived NO production, and this has been mapped to several residues on Cav-1, including F92. Herein, we reasoned that endothelial expression of an F92ACav-1 transgene would let us decipher the mechanisms and relationships between caveolae structure and intracellular signaling.

OBJECTIVE

This study was designed to separate caveolae formation from its downstream signaling effects.

METHODS AND RESULTS

An endothelial-specific doxycycline-regulated mouse model for the expression of Cav-1-F92A was developed. Blood pressure by telemetry and nitric oxide bioavailability by electron paramagnetic resonance and phosphorylation of vasodilator-stimulated phosphoprotein were determined. Caveolae integrity in the presence of Cav-1-F92A was measured by stabilization of caveolin-2, sucrose gradient, and electron microscopy. Histological analysis of heart and lung, echocardiography, and signaling were performed.

CONCLUSIONS

This study shows that mutant Cav-1-F92A forms caveolae structures similar to WT but leads to increases in NO bioavailability in vivo, thereby demonstrating that caveolae formation and downstream signaling events occur through independent mechanisms.

Stromal cell-derived factor 2 is critical for Hsp90-dependent eNOS activation

Endothelial nitric oxide synthase (eNOS) catalyzes the conversion of l-arginine and molecular oxygen into l-citrulline and nitric oxide (NO), a gaseous second messenger that influences cardiovascular physiology and disease. Several mechanisms regulate eNOS activity and function, including phosphorylation at Ser and Thr residues and protein-protein interactions. Combining a tandem affinity purification approach and mass spectrometry, we identified stromal cell-derived factor 2 (SDF2) as a component of the eNOS macromolecular complex in endothelial cells. SDF2 knockdown impaired agonist-stimulated NO synthesis and decreased the phosphorylation of eNOS at Ser(1177), a key event required for maximal activation of eNOS. Conversely, SDF2 overexpression dose-dependently increased NO synthesis through a mechanism involving Akt and calcium (induced with ionomycin), which increased the phosphorylation of Ser(1177) in eNOS. NO synthesis by iNOS (inducible NOS) and nNOS (neuronal NOS) was also enhanced upon SDF2 overexpression. We found that SDF2 was a client protein of the chaperone protein Hsp90, interacting preferentially with the M domain of Hsp90, which is the same domain that binds to eNOS. In endothelial cells exposed to vascular endothelial growth factor (VEGF), SDF2 was required for the binding of Hsp90 and calmodulin to eNOS, resulting in eNOS phosphorylation and activation. Thus, our data describe a function for SDF2 as a component of the Hsp90-eNOS complex that is critical for signal transduction in endothelial cells.

Mechanisms and consequences of endothelial nitric oxide synthase dysfunction in hypertension

Reduced nitric oxide bioavailability contributes to endothelial dysfunction and hypertension. The endothelial isoform of nitric oxide synthase (eNOS) is responsible for the production of nitric oxide within the endothelium. Loss of eNOS cofactor tetrahydrobiopterin to initial increase in oxidative stress leads to uncoupling of eNOS, in which the enzyme produces superoxide anion rather than nitric oxide, further substantiating oxidative stress to induce vascular pathogenesis. The current review focuses on recent advances on the molecular mechanisms and consequences of eNOS dysfunction in hypertension, and potential novel therapeutic strategies restoring eNOS function to treat hypertension.