Shear stress stimulates nitric oxide signaling in pulmonary arterial endothelial cells via a reduction in catalase activity: role of protein kinase C delta

Mitochondrial fission produces a Warburg effect via the oxidative inhibition of prolyl hydroxylase domain-2

Excessive mitochondrial fission and a shift to a Warburg phenotype are hallmarks of pulmonary hypertension (PH), although the mechanistic link between these processes remains unclear. We show that in pulmonary arterial endothelial cells (PAEC), Drp1 overexpression induces mitochondrial fission and increases glycolytic ATP production and glycolysis. This is due to mitochondrial reactive oxygen species (mito-ROS)-mediated activation of hypoxia-inducible factor-1α (HIF-1α) signaling, and this is linked to hydrogen peroxide (H2O2)-mediated inhibition of prolyl hydroxylase domain-2 (PHD2) due to its cysteine 326 oxidation and dimerization. Furthermore, these findings are validated in PAEC isolated from a lamb model of PH, which are glycolytic (Shunt PAEC), exhibit increases in both H2O2 and PHD2 dimer levels. The overexpression of catalase reversed the PHD2 dimerization, decreased HIF-1α levels, and attenuated glycolysis in Shunt PAEC. Our data suggest that reducing PHD2 dimerization could be a potential therapeutic target for PH.

PKCδ regulates the vascular biology in diabetic atherosclerosis

Diabetes mellitus, known for its complications, especially vascular complications, is becoming a globally serious social problem. Atherosclerosis has been recognized as a common vascular complication mechanism in diabetes. The diacylglycerol (DAG)-protein kinase C (PKC) pathway plays an important role in atherosclerosis. PKCs can be divided into three subgroups: conventional PKCs (cPKCs), novel PKCs (nPKCs), and atypical PKCs (aPKCs). The aim of this review is to provide a comprehensive overview of the role of the PKCδ pathway, an isoform of nPKC, in regulating the function of endothelial cells, vascular smooth muscle cells, and macrophages in diabetic atherosclerosis. In addition, potential therapeutic targets regarding the PKCδ pathway are summarized. Video Abstract.

Endothelin-1 acutely increases nitric oxide production via the calcineurin mediated dephosphorylation of Caveolin-1

Endothelin (ET)-1 is an endothelial-derived peptide that exerts biphasic effects on nitric oxide (NO) levels in endothelial cells such that acute exposure stimulates-while sustained exposure attenuates-NO production. Although the mechanism involved in the decrease in NO generation has been identified but the signaling involved in the acute increase in NO is still unresolved. This was the focus of this study. Our data indicate that exposing pulmonary arterial endothelial cells (PAEC) to ET-1 led to an increase in NO for up to 30min after which levels declined. These effects were attenuated by ET receptor antagonists. The increase in NO correlated with significant increases in pp60Src activity and increases in eNOS phosphorylation at Tyr83 and Ser1177. The ET-1 mediated increase in phosphorylation and NO generation were attenuated by the over-expression of a pp60Src dominant negative mutant. The increase in pp60Src activity correlated with a reduction in the interaction of Caveolin-1 with pp60Src and the calcineurin-mediated dephosphorylation of caveolin-1 at three previously unidentified sites: Thr91, Thr93, and Thr95. The calcineurin inhibitor, Tacrolimus, attenuated the acute increase in pp60Src activity induced by ET-1 and a calcineurin siRNA attenuated the ET-1 mediated increase in eNOS phosphorylation at Tyr83 and Ser1177 as well as the increase in NO. By using a Caveolin-1 celluSpot peptide array, we identified a peptide targeting a sequence located between aa 41-56 as the pp60Src binding region. This peptide fused to the TAT sequence was found to decrease caveolin-pp60Src interaction, increased pp60Src activity, increased eNOS pSer1177 and NO levels in PAEC and induce vasodilation in isolated aortic rings in wildtype but not eNOS knockout mice. Together, our data identify a novel mechanism by which ET-1 acutely increases NO via a calcineurin-mediated dephosphorylation of caveolin-1 and the subsequent stimulation of pp60Src activity, leading to increases in phosphorylation of eNOS at Tyr83 and Ser1177.

Dephosphorylation of CatC at Ser-18 improves salt and oxidative tolerance via promoting its tetramerization in rice

Catalase (CAT) is a vital antioxidant enzyme, while phosphorylation pivotally regulates its function. Many phosphosites have been identified in CAT, but their functions remained largely elusive. We functionally studied five phosphoserines (Ser-9, -10, -11, -18, and -205) of CatC in rice (Oryza sativa L.). Phospho-Ser-9 and - 11 and dephospho-Ser-18 promoted the enzymatic activity of CatC and enhanced oxidative and salt tolerance in yeast. Phosphorylation status of Ser-18 did not affect CatC peroxisomal targeting and stability, but dephospho-Ser-18 promoted CatC tetramerization to enhance its activity. Moreover, overexpression of dephospho-mimic form CatC^S18A in rice significantly improved the tolerance to salt and oxidative stresses by inhibiting the H₂O₂ accumulation. Together, these results elucidate the mechanism underlying dephosphorylation at Ser-18 promotes CatC activity and salt tolerance in rice. Ser-18 is a promising candidate phosphosite of CatC for breeding highly salt-tolerant rice.

Biomechanical and Mechanobiological Drivers of the Transition From PostCapillary Pulmonary Hypertension to Combined Pre-/PostCapillary Pulmonary Hypertension

Combined pre-/postcapillary pulmonary hypertension (Cpc-PH), a complication of left heart failure, is associated with higher mortality rates than isolated postcapillary pulmonary hypertension alone. Currently, knowledge gaps persist on the mechanisms responsible for the progression of isolated postcapillary pulmonary hypertension (Ipc-PH) to Cpc-PH. Here, we review the biomechanical and mechanobiological impact of left heart failure on pulmonary circulation, including mechanotransduction of these pathological forces, which lead to altered biological signaling and detrimental remodeling, driving the progression to Cpc-PH. We focus on pathologically increased cyclic stretch and decreased wall shear stress; mechanotransduction by endothelial cells, smooth muscle cells, and pulmonary arterial fibroblasts; and signaling-stimulated remodeling of the pulmonary veins, capillaries, and arteries that propel the transition from Ipc-PH to Cpc-PH. Identifying biomechanical and mechanobiological mechanisms of Cpc-PH progression may highlight potential pharmacologic avenues to prevent right heart failure and subsequent mortality.

Vein of Galen aneurysmal malformation: rationalizing medical management of neonatal heart failure

Neonates who present in high output heart failure secondary to vein of Galen aneurysmal malformation can be difficult to manage medically due to the complex physiology that results from the large shunt through the malformation. Though the cardiac function is often normal, right ventricular dilation, severe pulmonary hypertension, and systemic steal can result in inadequate organ perfusion and shock. This report recommends medical management for stabilization of neonates prior to definitive management with endovascular embolization. IMPACT: Vein of Galen aneurysmal malformation (VGAM) is a rare intracranial arteriovenous malformation, which can present in the neonatal period with high output heart failure. Heart failure secondary to VGAM is often difficult to manage and is associated with high mortality and morbidity. Despite optimal medical management, many patients require urgent endovascular embolization for stabilization of their heart failure. This report offers discrete recommendations that can be used by clinicians as guidelines for the medical management of heart failure in newborns with VGAM.

H2O2 Mediates VEGF- and Flow-Induced Dilations of Coronary Arterioles in Early Type 1 Diabetes: Role of Vascular Arginase and PI3K-Linked eNOS Uncoupling

In diabetes, the enzyme arginase is upregulated, which may compete with endothelial nitric oxide (NO) synthase (eNOS) for their common substrate L-arginine and compromise NO-mediated vasodilation. However, this eNOS uncoupling can lead to superoxide production and possibly vasodilator hydrogen peroxide (H₂O₂) formation to compensate for NO deficiency. This hypothesis was tested in coronary arterioles isolated from pigs with 2-week diabetes after streptozocin injection. The NO-mediated vasodilation induced by flow and VEGF was abolished by NOS inhibitor L-NAME and phosphoinositide 3-kinase (PI3K) inhibitor wortmannin but was not affected by arginase inhibitor N^ω-hydroxy-nor-L-arginine (nor-NOHA) or H₂O₂ scavenger catalase in control pigs. With diabetes, this vasodilation was partially blunted, and the remaining vasodilation was abolished by catalase and wortmannin. Administration of L-arginine or nor-NOHA restored flow-induced vasodilation in an L-NAME sensitive manner. Diabetes did not alter vascular superoxide dismutase 1, catalase, and glutathione peroxidase mRNA levels. This study demonstrates that endothelium-dependent NO-mediated coronary arteriolar dilation is partially compromised in early type 1 diabetes by reducing eNOS substrate L-arginine via arginase activation. It appears that upregulated arginase contributes to endothelial NO deficiency in early diabetes, but production of H₂O₂ during PI3K-linked eNOS uncoupling likely compensates for and masks this disturbance.

Heavy Metal–Resistant Plant Growth–Promoting Citrobacter werkmanii Strain WWN1 and Enterobacter cloacae Strain JWM6 Enhance Wheat (Triticum aestivum L.) Growth by Modulating Physiological Attributes and Some Key Antioxidants Under Multi-Metal Stress

Due to wastewater irrigation, heavy metal (HM) exposure of agricultural soils is a major limiting factor for crop productivity. Plant growth–promoting bacteria (PGPB) may lower the risk of HM toxicity and increase crop yield. In this context, we evaluated two HM-resistant PGPB strains, i.e., Citrobacter werkmanii strain WWN1 and Enterobacter cloacae strain JWM6 isolated from wastewater-irrigated agricultural soils, for their efficacy to mitigate HM (Cd, Ni, and Pb) stress in a pot experiment. Increasing concentrations (0, 50, 100, and 200 ppm) of each HM were used to challenge wheat plants. Heavy metal stress negatively affected wheat growth, biomass, and physiology. The plants under elevated HM concentration accumulated significantly higher amounts of heavy metals (HMs) in shoots and roots, resulting in increased oxidative stress, which was evident from increased malondialdehyde (MDA) content in roots and shoots. Moreover, alterations in antioxidants like superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT) were observed in plants under HM stress. The severity of damage was more pronounced with rising HM concentration. However, inoculating wheat with Citrobacter werkmanii strain WWN1 and Enterobacter cloacae strain JWM6 (107 CFU ml–1) improved plant shoot length (11–42%), root length (19–125%), fresh weight (41–143%), dry weight (65–179%), and chlorophyll a (14%-24%) and chlorophyll b content (2–24%) under HM stress. Citrobacter werkmanii strain WWN1 and Enterobacter cloacae strain JWM6 either alone or in co-inoculation enhanced the antioxidant enzyme activity, which may lower oxidative stress in plants. However, seeds treated with the bacterial consortium showed an overall better outcome in altering oxidative stress and decreasing HM accumulation in wheat shoot and root tissues. Fourier transform infrared spectroscopy indicated the changes induced by HMs in functional groups on the biomass surface that display effective removal of HMs from aqueous medium using PGPB. Thus, the studied bacterial strains may have adequate fertilization and remediation potential for wheat cultivated in wastewater-irrigated soils. However, molecular investigation of mechanisms adopted by these bacteria to alleviate HM stress in wheat is required to be conducted.

Targeting the lung endothelial niche to promote angiogenesis and regeneration: A review of applications

Lung endothelial cells comprise the pulmonary vascular bed and account for the majority of cells in the lungs. Beyond their role in gas exchange, lung ECs form a specialized microenvironment, or niche, with important roles in health and disease. In early development, progenitor ECs direct alveolar development through angiogenesis. Following birth, lung ECs are thought to maintain their regenerative capacity despite the aging process. As such, harnessing the power of the EC niche, specifically to promote angiogenesis and alveolar regeneration has potential clinical applications. Here, we focus on translational research with applications related to developmental lung diseases including pulmonary hypoplasia and bronchopulmonary dysplasia. An overview of studies examining the role of ECs in lung regeneration following acute lung injury is also provided. These diseases are all characterized by significant morbidity and mortality with limited existing therapeutics, affecting both young children and adults.

Mechanobiology of Pulmonary Diseases: A Review of Engineering Tools to Understand Lung Mechanotransduction

Cells within the lung micro-environment are continuously subjected to dynamic mechanical stimuli which are converted into biochemical signaling events in a process known as mechanotransduction. In pulmonary diseases, the abrogated mechanical conditions modify the homeostatic signaling which influences cellular phenotype and disease progression. The use of in vitro models has significantly expanded our understanding of lung mechanotransduction mechanisms. However, our ability to match complex facets of the lung including three-dimensionality, multicellular interactions, and multiple simultaneous forces is limited and it has proven difficult to replicate and control these factors in vitro. The goal of this review is to (a) outline the anatomy of the pulmonary system and the mechanical stimuli that reside therein, (b) describe how disease impacts the mechanical micro-environment of the lung, and (c) summarize how existing in vitro models have contributed to our current understanding of pulmonary mechanotransduction. We also highlight critical needs in the pulmonary mechanotransduction field with an emphasis on next-generation devices that can simulate the complex mechanical and cellular environment of the lung. This review provides a comprehensive basis for understanding the current state of knowledge in pulmonary mechanotransduction and identifying the areas for future research.

Cellular mechanosignaling in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by sustained elevated pulmonary arterial pressures in which the pulmonary vasculature undergoes significant structural and functional remodeling. To better understand disease mechanisms, in this review article we highlight recent insights into the regulation of pulmonary arterial cells by mechanical cues associated with PAH. Specifically, the mechanobiology of pulmonary arterial endothelial cells (PAECs), smooth muscle cells (PASMCs) and adventitial fibroblasts (PAAFs) has been investigated in vivo, in vitro, and in silico. Increased pulmonary arterial pressure increases vessel wall stress and strain and endothelial fluid shear stress. These mechanical cues promote vasoconstriction and fibrosis that contribute further to hypertension and alter the mechanical milieu and regulation of pulmonary arterial cells.

The Emerging Roles of Antioxidant Enzymes by Dietary Phytochemicals in Vascular Diseases

Vascular diseases are major causes of death worldwide, causing pathologies including diabetes, atherosclerosis, and chronic obstructive pulmonary disease (COPD). Exposure of the vascular system to a variety of stressors and inducers has been implicated in the development of various human diseases, including chronic inflammatory diseases. In the vascular wall, antioxidant enzymes form the first line of defense against oxidative stress. Recently, extensive research into the beneficial effects of phytochemicals has been conducted; phytochemicals are found in commonly used spices, fruits, and herbs, and are used to prevent various pathologic conditions, including vascular diseases. The present review aims to highlight the effects of dietary phytochemicals role on antioxidant enzymes in vascular diseases.

Signaling Toward Reactive Oxygen Species-Scavenging Enzymes in Plants

Reactive oxygen species (ROS) are signaling molecules essential for plant responses to abiotic and biotic stimuli as well as for multiple developmental processes. They are produced as byproducts of aerobic metabolism and are affected by adverse environmental conditions. The ROS content is controlled on the side of their production but also by scavenging machinery. Antioxidant enzymes represent a major ROS-scavenging force and are crucial for stress tolerance in plants. Enzymatic antioxidant defense occurs as a series of redox reactions for ROS elimination. Therefore, the deregulation of the antioxidant machinery may lead to the overaccumulation of ROS in plants, with negative consequences both in terms of plant development and resistance to environmental challenges. The transcriptional activation of antioxidant enzymes accompanies the long-term exposure of plants to unfavorable environmental conditions. Fast ROS production requires the immediate mobilization of the antioxidant defense system, which may occur via retrograde signaling, redox-based modifications, and the phosphorylation of ROS detoxifying enzymes. This review aimed to summarize the current knowledge on signaling processes regulating the enzymatic antioxidant capacity of plants.

Activation of the mechanosensitive Ca2+ channel TRPV4 induces endothelial barrier permeability via the disruption of mitochondrial bioenergetics

Mechanical ventilation is a life-saving intervention in critically ill patients with respiratory failure due to acute respiratory distress syndrome (ARDS), a refractory lung disease with an unacceptable high mortality rate. Paradoxically, mechanical ventilation also creates excessive mechanical stress that directly augments lung injury, a syndrome known as ventilator-induced lung injury (VILI). The specific mechanisms involved in VILI-induced pulmonary capillary leakage, a key pathologic feature of VILI are still far from resolved. The mechanoreceptor, transient receptor potential cation channel subfamily V member 4, TRPV4 plays a key role in the development of VILI through unresolved mechanism. Endothelial nitric oxide synthase (eNOS) uncoupling plays an important role in sepsis-mediated ARDS so in this study we investigated whether there is a role for eNOS uncoupling in the barrier disruption associated with TRPV4 activation during VILI. Our data indicate that the TRPV4 agonist, 4α-Phorbol 12,13-didecanoate (4αPDD) induces pulmonary arterial endothelial cell (EC) barrier disruption through the disruption of mitochondrial bioenergetics. Mechanistically, this occurs via the mitochondrial redistribution of uncoupled eNOS secondary to a PKC-dependent phosphorylation of eNOS at Threonine 495 (T495). A specific decoy peptide to prevent T495 phosphorylation reduced eNOS uncoupling and mitochondrial redistribution and preserved PAEC barrier function under 4αPDD challenge. Further, our eNOS decoy peptide was able to preserve lung vascular integrity in a mouse model of VILI. Thus, we have revealed a functional link between TRPV4 activation, PKC-dependent eNOS phosphorylation at T495, and EC barrier permeability. Reducing pT495-eNOS could be a new therapeutic approach for the prevention of VILI.

TGF-β1 attenuates mitochondrial bioenergetics in pulmonary arterial endothelial cells via the disruption of carnitine homeostasis

Transforming growth factor beta-1 (TGF-β1) signaling is increased and mitochondrial function is decreased in multiple models of pulmonary hypertension (PH) including lambs with increased pulmonary blood flow (PBF) and pressure (Shunt). However, the potential link between TGF-β1 and the loss of mitochondrial function has not been investigated and was the focus of our investigations. Our data indicate that exposure of pulmonary arterial endothelial cells (PAEC) to TGF-β1 disrupted mitochondrial function as determined by enhanced mitochondrial ROS generation, decreased mitochondrial membrane potential, and disrupted mitochondrial bioenergetics. These events resulted in a decrease in cellular ATP levels, decreased hsp90/eNOS interactions and attenuated shear-mediated NO release. TGF-β1 induced mitochondrial dysfunction was linked to a nitration-mediated activation of Akt1 and the subsequent mitochondrial translocation of endothelial NO synthase (eNOS) resulting in the nitration of carnitine acetyl transferase (CrAT) and the disruption of carnitine homeostasis. The increase in Akt1 nitration correlated with increased NADPH oxidase activity associated with increased levels of p47^phox, p67^phox, and Rac1. The increase in NADPH oxidase was associated with a decrease in peroxisome proliferator-activated receptor type gamma (PPARγ) and the PPARγ antagonist, GW9662, was able to mimic the disruptive effect of TGF-β1 on mitochondrial bioenergetics. Together, our studies reveal for the first time, that TGF-β1 can disrupt mitochondrial function through the disruption of cellular carnitine homeostasis and suggest that stimulating carinitine homeostasis may be an avenue to treat pulmonary vascular disease.

Fast relaxation and desensitization of angiotensin II contraction in the pulmonary artery via AT1R and Akt-mediated phosphorylation of muscular eNOS

Angiotensin II (AngII) triggers a transient contraction of pulmonary arteries (PAs) followed by protracted desensitization. Based on the unconventional eNOS expression in PA smooth muscle cells (PASMCs), we hypothesized that activation of smooth muscle eNOS by AngII might be responsible for fast relaxation and tachyphylaxis. Using dual-wire myograph, mechanically endothelium-denuded rat PA [E(-)PA] showed AngII concentration-dependent transient contractions (ΔT_AngII, 95% decay within 1 min), which were abolished by losartan (AT1R antagonist). Neither PD123319 (AT2R antagonist) nor A779 (MasR antagonist) affected ΔT_AngII. When the vessels were pretreated with L-NAME (NOS inhibitor), ODQ (guanylate cyclase inhibitor), or KT5823 (PKG inhibitor), ΔT_AngII of E(-)PA became larger and sustained, whereas nNOS or iNOS inhibitors had no such effect. Immunoblotting of human PASMCs (hPASMCs) also showed eNOS expression, and AngII treatment induced activating phosphorylations of Ser¹¹⁷⁷ in eNOS and of Ser⁴⁷³ in Akt (Ser/Thr protein kinase B), an upstream signal of eNOS phosphorylation. In addition, L-NAME co-treatment promoted AngII-induced Ser¹⁹ phosphorylation of myosin light chain. In hPASMCs, AngII abolished plasma membrane expression of AT1R, and recovery by washout took more than 1 h. Consistent with the data from hPASMCs, the second application of AngII to E(-)PA did not induce contraction, and significant recovery of ΔT_AngII required prolonged washout (> 2 h) in the myography study. L-NAME treatment before the second application facilitated recovery of ΔT_AngII. Muscular eNOS plays an auto-inhibitory role in ΔT_AngII of PAs. The molecular changes investigated in hPASMCs revealed eNOS phosphorylation and internalization of AT1R by AngII. We propose that the rat PA smooth muscle eNOS-induced lusitropy and slow recovery of AT1R from tachyphylaxis might counterbalance the excessive contractile response to AngII, contributing to the distinctive low-pressure pulmonary circulation.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

The Receptor-Like Cytoplasmic Kinase STRK1 Phosphorylates and Activates CatC, Thereby Regulating H2O2 Homeostasis and Improving Salt Tolerance in Rice

Salt stress can significantly affect plant growth and agricultural productivity. Receptor-like kinases (RLKs) are believed to play essential roles in plant growth, development, and responses to abiotic stresses. Here, we identify a receptor-like cytoplasmic kinase, salt tolerance receptor-like cytoplasmic kinase 1 (STRK1), from rice (Oryza sativa) that positively regulates salt and oxidative stress tolerance. Our results show that STRK1 anchors and interacts with CatC at the plasma membrane via palmitoylation. CatC is phosphorylated mainly at Tyr-210 and is activated by STRK1. The phosphorylation mimic form CatC^Y210D exhibits higher catalase activity both in vitro and in planta, and salt stress enhances STRK1-mediated tyrosine phosphorylation on CatC. Compared with wild-type plants, STRK1-overexpressing plants exhibited higher catalase activity and lower accumulation of H₂O₂ as well as higher tolerance to salt and oxidative stress. Our findings demonstrate that STRK1 improves salt and oxidative tolerance by phosphorylating and activating CatC and thereby regulating H₂O₂ homeostasis. Moreover, overexpression of STRK1 in rice not only improved growth at the seedling stage but also markedly limited the grain yield loss under salt stress conditions. Together, these results offer an opportunity to improve rice grain yield under salt stress.

Vascular remodeling: A redox-modulated mechanism of vessel caliber regulation

Vascular remodeling, i.e. whole-vessel structural reshaping, determines lumen caliber in (patho)physiology. Here we review mechanisms underlying vessel remodeling, with emphasis in redox regulation. First, we discuss confusing terminology and focus on strictu sensu remodeling. Second, we propose a mechanobiological remodeling paradigm based on the concept of tensional homeostasis as a setpoint regulator. We first focus on shear-mediated models as prototypes of remodeling closely dominated by highly redox-sensitive endothelial function. More detailed discussions focus on mechanosensors, integrins, extracellular matrix, cytoskeleton and inflammatory pathways as potential of mechanisms potentially coupling tensional homeostasis to redox regulation. Further discussion of remodeling associated with atherosclerosis and injury repair highlights important aspects of redox vascular responses. While neointima formation has not shown consistent responsiveness to antioxidants, vessel remodeling has been more clearly responsive, indicating that despite the multilevel redox signaling pathways, there is a coordinated response of the whole vessel. Among mechanisms that may orchestrate redox pathways, we discuss roles of superoxide dismutase activity and extracellular protein disulfide isomerase. We then discuss redox modulation of aneurysms, a special case of expansive remodeling. We propose that the redox modulation of vascular remodeling may reflect (1) remodeling pathophysiology is dominated by a particularly redox-sensitive cell type, e.g., endothelial cells (2) redox pathways are temporospatially coordinated at an organ level across distinct cellular and acellular structures or (3) the tensional homeostasis setpoint is closely connected to redox signaling. The mechanobiological/redox model discussed here can be a basis for improved understanding of remodeling and helps clarifying mechanisms underlying prevalent hard-to-treat diseases.

Unique aspects of the developing lung circulation: structural development and regulation of vasomotor tone

This review summarizes our current knowledge on lung vasculogenesis and angiogenesis during normal lung development and the regulation of fetal and postnatal pulmonary vascular tone. In comparison to that of the adult, the pulmonary circulation of the fetus and newborn displays many unique characteristics. Moreover, altered development of pulmonary vasculature plays a more prominent role in compromised pulmonary vasoreactivity than in the adult. Clinically, a better understanding of the developmental changes in pulmonary vasculature and vasomotor tone and the mechanisms that are disrupted in disease states can lead to the development of new therapies for lung diseases characterized by impaired alveolar structure and pulmonary hypertension.

Hyper-activation of pp60Src limits nitric oxide signaling by increasing asymmetric dimethylarginine levels during acute lung injury

The molecular mechanisms by which the endothelial barrier becomes compromised during lipopolysaccharide (LPS) mediated acute lung injury (ALI) are still unresolved. We have previously reported that the disruption of the endothelial barrier is due, at least in part, to the uncoupling of endothelial nitric oxide synthase (eNOS) and increased peroxynitrite-mediated nitration of RhoA. The purpose of this study was to elucidate the molecular mechanisms by which LPS induces eNOS uncoupling during ALI. Exposure of pulmonary endothelial cells (PAEC) to LPS increased pp60^Src activity and this correlated with an increase in nitric oxide (NO) production, but also an increase in NOS derived superoxide, peroxynitrite formation and 3-nitrotyrosine (3-NT) levels. These effects could be simulated by the over-expression of a constitutively active pp60^Src (Y527FSrc) mutant and attenuated by over-expression of dominant negative pp60^Src mutant or reducing pp60^Src expression. LPS induces both RhoA nitration and endothelial barrier disruption and these events were attenuated when pp60^Src expression was reduced. Endothelial NOS uncoupling correlated with an increase in the levels of asymmetric dimethylarginine (ADMA) in both LPS exposed and Y527FSrc over-expressing PAEC. The effects in PAEC were also recapitulated when we transiently over-expressed Y527FSrc in the mouse lung. Finally, we found that the pp60-^Src-mediated decrease in DDAH activity was mediated by the phosphorylation of DDAH II at Y207 and that a Y207F mutant DDAH II was resistant to pp60^Src-mediated inhibition. We conclude that pp60^Src can directly inhibit DDAH II and this is involved in the increased ADMA levels that enhance eNOS uncoupling during the development of ALI.

Redox regulation of epidermal growth factor receptor signaling during the development of pulmonary hypertension

The development of pulmonary hypertension (PH) involves the uncontrolled proliferation of pulmonary smooth muscle cells via increased growth factor receptor signaling. However, the role of epidermal growth factor receptor (EGFR) signaling is controversial, as humans with advanced PH exhibit no changes in EGFR protein levels and purpose of the present study was to determine whether there are post-translational mechanisms that enhance EGFR signaling in PH. The EGFR inhibitor, gefinitib, significantly attenuated EGFR signaling and prevented the development of PH in monocrotaline (MCT)-exposed rats, confirming the contribution of EGFR activation in MCT induced PH. There was an early MCT-mediated increase in hydrogen peroxide, which correlated with the binding of the active metabolite of MCT, monocrotaline pyrrole, to catalase Cys377, disrupting its multimeric structure. This early oxidative stress was responsible for the oxidation of EGFR and the formation of sodium dodecyl sulfate (SDS) stable EGFR dimers through dityrosine cross-linking. These cross-linked dimers exhibited increased EGFR autophosphorylation and signaling. The activation of EGFR signaling did not correlate with pp60(src) dependent Y845 phosphorylation or EGFR ligand expression. Importantly, the analysis of patients with advanced PH revealed the same enhancement of EGFR autophosphorylation and covalent dimer formation in pulmonary arteries, while total EGFR protein levels were unchanged. As in the MCT exposed rat model, the activation of EGFR in human samples was independent of pp60(src) phosphorylation site and ligand expression. This study provides a novel molecular mechanism of oxidative stress stimulated covalent EGFR dimerization via tyrosine dimerization that contributes into development of PH.

Mathematical model for shear stress dependent NO and adenine nucleotide production from endothelial cells

We developed a mass transport model for a parallel-plate flow chamber apparatus to predict the concentrations of nitric oxide (NO) and adenine nucleotides (ATP, ADP) produced by cultured endothelial cells (ECs) and investigated how the net rates of production, degradation, and mass transport for these three chemical species vary with changes in wall shear stress (τw). These simulations provide an improved understanding of experimental results obtained with parallel-plate flow chambers and allows quantitative analysis of the relationship between τw, adenine nucleotide concentrations, and NO produced by ECs. Experimental data obtained after altering ATP and ADP concentrations with apyrase were analyzed to quantify changes in the rate of NO production (RNO). The effects of different isoforms of apyrase on ATP and ADP concentrations and nucleotide-dependent changes in RNO could be predicted with the model. A decrease in ATP was predicted with apyrase, but an increase in ADP was simulated due to degradation of ATP. We found that a simple proportional relationship relating a component of RNO to the sum of ATP and ADP provided a close match to the fitted curve for experimentally measured changes in RNO with apyrase. Estimates for the proportionality constant ranged from 0.0067 to 0.0321 μM/s increase in RNO per nM nucleotide concentration, depending on which isoform of apyrase was modeled, with the largest effect of nucleotides on RNO at low τw (<6 dyn/cm(2)).

The role of endothelial mechanosensitive genes in atherosclerosis and omics approaches

Atherosclerosis is the leading cause of morbidity and mortality in the U.S., and is a multifactorial disease that preferentially occurs in regions of the arterial tree exposed to disturbed blood flow. The detailed mechanisms by which d-flow induces atherosclerosis involve changes in the expression of genes, epigenetic patterns, and metabolites of multiple vascular cells, especially endothelial cells. This review presents an overview of endothelial mechanobiology and its relation to the pathogenesis of atherosclerosis with special reference to the anatomy of the artery and the underlying fluid mechanics, followed by a discussion of a variety of experimental models to study the role of fluid mechanics and atherosclerosis. Various in vitro and in vivo models to study the role of flow in endothelial biology and pathobiology are discussed in this review. Furthermore, strategies used for the global profiling of the genome, transcriptome, miR-nome, DNA methylome, and metabolome, as they are important to define the biological and pathophysiological mechanisms of atherosclerosis. These "omics" approaches, especially those which derive data based on a single animal model, provide unprecedented opportunities to not only better understand the pathophysiology of atherosclerosis development in a holistic and integrative manner, but also to identify novel molecular and diagnostic targets.

Inducing Persistent Flow Disturbances Accelerates Atherogenesis and Promotes Thin Cap Fibroatheroma Development in D374Y-PCSK9 Hypercholesterolemic Minipigs

BACKGROUND

Although disturbed flow is thought to play a central role in the development of advanced coronary atherosclerotic plaques, no causal relationship has been established. We evaluated whether inducing disturbed flow would cause the development of advanced coronary plaques, including thin cap fibroatheroma.

METHODS AND RESULTS

D374Y-PCSK9 hypercholesterolemic minipigs (n=5) were instrumented with an intracoronary shear-modifying stent (SMS). Frequency-domain optical coherence tomography was obtained at baseline, immediately poststent, 19 weeks, and 34 weeks, and used to compute shear stress metrics of disturbed flow. At 34 weeks, plaque type was assessed within serially collected histological sections and coregistered to the distribution of each shear metric. The SMS caused a flow-limiting stenosis, and blood flow exiting the SMS caused regions of increased shear stress on the outer curvature and large regions of low and multidirectional shear stress on the inner curvature of the vessel. As a result, plaque burden was ≈3-fold higher downstream of the SMS than both upstream of the SMS and in the control artery (P<0.001). Advanced plaques were also primarily observed downstream of the SMS, in locations initially exposed to both low (P<0.002) and multidirectional (P<0.002) shear stress. Thin cap fibroatheroma regions demonstrated significantly lower shear stress that persisted over the duration of the study in comparison with other plaque types (P<0.005).

CONCLUSIONS

These data support a causal role for lowered and multidirectional shear stress in the initiation of advanced coronary atherosclerotic plaques. Persistently lowered shear stress appears to be the principal flow disturbance needed for the formation of thin cap fibroatheroma.

Pulmonary hypertension caused by pulmonary venous hypertension

The effect of pulmonary venous hypertension (PVH) on the pulmonary circulation is extraordinarily variable, ranging from no impact on pulmonary vascular resistance (PVR) to a marked increase. The reasons for this are unknown. Both acutely reversible pulmonary vasoconstriction and pathological remodeling (especially medial hypertrophy and intimal hyperplasia) account for increased PVR when present. The mechanisms involved in vasoconstriction and remodeling are not clearly defined, but increased wall stress, especially in small pulmonary arteries, presumably plays an important role. Myogenic contraction may account for increased vascular tone and also indirectly stimulate remodeling of the vessel wall. Increased wall stress may also directly cause smooth muscle growth, migration, and intimal hyperplasia. Even long-standing and severe pulmonary hypertension (PH) usually abates with elimination of PVH, but PVH-PH is an important clinical problem, especially because PVH due to left ventricular noncompliance lacks definitive therapy. The role of targeted PH therapy in patients with PVH-PH is unclear at this time. Most prospective studies indicate that these medications are not helpful or worse, but there is ample reason to think that a subset of patients with PVH-PH may benefit from phosphodiesterase inhibitors or other agents. A different approach to evaluating possible pharmacologic therapy for PVH-PH may be required to better define its possible utility.

Nox2 and p47(phox) modulate compensatory growth of primary collateral arteries

The role of NADPH oxidase (Nox) in both the promotion and impairment of compensatory collateral growth remains controversial because the specific Nox and reactive oxygen species involved are unclear. The aim of this study was to identify the primary Nox and reactive oxygen species associated with early stage compensatory collateral growth in young, healthy animals. Ligation of the feed arteries that form primary collateral pathways in rat mesentery and mouse hindlimb was used to assess the role of Nox during collateral growth. Changes in mesenteric collateral artery Nox mRNA expression determined by real-time PCR at 1, 3, and 7 days relative to same-animal control arteries suggested a role for Nox subunits Nox2 and p47(phox). Administration of apocynin or Nox2ds-tat suppressed collateral growth in both rat and mouse models, suggesting the Nox2/p47(phox) interaction was involved. Functional significance of p47(phox) expression was assessed by evaluation of collateral growth in rats administered p47(phox) small interfering RNA and in p47(phox-/-) mice. Diameter measurements of collateral mesenteric and gracilis arteries at 7 and 14 days, respectively, indicated no significant collateral growth compared with control rats or C57BL/6 mice. Chronic polyethylene glycol-conjugated catalase administration significantly suppressed collateral development in rats and mice, implying a requirement for H2O2. Taken together, these results suggest that Nox2, modulated at least in part by p47(phox), mediates early stage compensatory collateral development via a process dependent upon peroxide generation. These results have important implications for the use of antioxidants and the development of therapies for peripheral arterial disease.

Endothelin-1 stimulates catalase activity through the PKCδ-mediated phosphorylation of serine 167

Our previous studies have shown that endothelin-1 (ET-1) stimulates catalase activity in endothelial cells and in lambs with acute increases in pulmonary blood flow (PBF), without altering gene expression. The purpose of this study was to investigate the molecular mechanism by which this occurs. Exposing pulmonary arterial endothelial cells to ET-1 increased catalase activity and decreased cellular hydrogen peroxide (H2O2) levels. These changes correlated with an increase in serine-phosphorylated catalase. Using the inhibitory peptide δV1.1, this phosphorylation was shown to be protein kinase Cδ (PKCδ) dependent. Mass spectrometry identified serine 167 as the phosphorylation site. Site-directed mutagenesis was used to generate a phospho-mimic (S167D) catalase. Activity assays using recombinant protein purified from Escherichia coli or transiently transfected COS-7 cells demonstrated that S167D catalase had an increased ability to degrade H2O2 compared to the wild-type enzyme. Using a phospho-specific antibody, we were able to verify that pS167 catalase levels are modulated in lambs with acute increases in PBF in the presence and absence of the ET receptor antagonist tezosentan. S167 is located on the dimeric interface, suggesting it could be involved in regulating the formation of catalase tetramers. To evaluate this possibility we utilized analytical gel filtration to examine the multimeric structure of recombinant wild-type and S167D catalase. We found that recombinant wild-type catalase was present as a mixture of monomers and dimers, whereas S167D catalase was primarily tetrameric. Further, the incubation of wild-type catalase with PKCδ was sufficient to convert wild-type catalase into a tetrameric structure. In conclusion, this is the first report indicating that the phosphorylation of catalase regulates its multimeric structure and activity.

Shear-induced endothelial mechanotransduction: the interplay between reactive oxygen species (ROS) and nitric oxide (NO) and the pathophysiological implications

Hemodynamic shear stress, the blood flow-generated frictional force acting on the vascular endothelial cells, is essential for endothelial homeostasis under normal physiological conditions. Mechanosensors on endothelial cells detect shear stress and transduce it into biochemical signals to trigger vascular adaptive responses. Among the various shear-induced signaling molecules, reactive oxygen species (ROS) and nitric oxide (NO) have been implicated in vascular homeostasis and diseases. In this review, we explore the molecular, cellular, and vascular processes arising from shear-induced signaling (mechanotransduction) with emphasis on the roles of ROS and NO, and also discuss the mechanisms that may lead to excessive vascular remodeling and thus drive pathobiologic processes responsible for atherosclerosis. Current evidence suggests that NADPH oxidase is one of main cellular sources of ROS generation in endothelial cells under flow condition. Flow patterns and magnitude of shear determine the amount of ROS produced by endothelial cells, usually an irregular flow pattern (disturbed or oscillatory) producing higher levels of ROS than a regular flow pattern (steady or pulsatile). ROS production is closely linked to NO generation and elevated levels of ROS lead to low NO bioavailability, as is often observed in endothelial cells exposed to irregular flow. The low NO bioavailability is partly caused by the reaction of ROS with NO to form peroxynitrite, a key molecule which may initiate many pro-atherogenic events. This differential production of ROS and RNS (reactive nitrogen species) under various flow patterns and conditions modulates endothelial gene expression and thus results in differential vascular responses. Moreover, ROS/RNS are able to promote specific post-translational modifications in regulatory proteins (including S-glutathionylation, S-nitrosylation and tyrosine nitration), which constitute chemical signals that are relevant in cardiovascular pathophysiology. Overall, the dynamic interplay between local hemodynamic milieu and the resulting oxidative and S-nitrosative modification of regulatory proteins is important for ensuing vascular homeostasis. Based on available evidence, it is proposed that a regular flow pattern produces lower levels of ROS and higher NO bioavailability, creating an anti-atherogenic environment. On the other hand, an irregular flow pattern results in higher levels of ROS and yet lower NO bioavailability, thus triggering pro-atherogenic effects.

Effects of dinuclear berenil-platinum(II) complexes on fibroblasts redox status

PURPOSE

Platinum(II) complex anticarcinogenic mechanisms are associated with changes in the cellular redox status of cancer as well as healthy cells. Therefore, the goal of the present study was to investigate oxidative modifications in cellular components following fibroblast exposure to novel dinuclear berenil-platinum(II) complexes.

MATERIAL AND METHOD

ROS levels, antioxidant parameters level/activity, and damage to DNA, lipids, and proteins, including pro-apoptotic and anti-apoptotic factors in human skin fibroblasts following berenil-platinum(II) complex treatments i.e. Pt2(isopropylamine)4(berenil)2, Pt2(piperazine)4(berenil)4, Pt2(2-picoline)4(berenil)2, Pt2(3-picoline)4(berenil)2, and Pt2(4- picoline)4(berenil)2 were examined.

RESULTS

Treatment of fibroblasts with platinum(II) complexes has shown that all compounds enhance total ROS and superoxide anion generation as well as change the activity of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase and decrease in the level of non-enzymatic antioxidants (GSH, vitamin C, E and A). Such a situation is conducive to oxidative stress formation and oxidative modifications of cellular macromolecules and to increase in the expression of proapoptotic proteins. Pt2(isopropylamine)4(berenil)2 elicited the most damage, which resulted in oxidative modification of cellular components. The therapeutic use of this complex would cause considerable side effects in patients, therefore the agent lacks drug potential; however Pt2(piperazine)4(berenil)2 and Pt2(2-picoline)4(berenil)2 exhibited reduced redox and increased apoptotic profiles compared to cisplatin.

CONCLUSION

Results of this paper and preliminary data show that Pt2(2-picoline)4(berenil)2 is less dangers than cisplatin to fibroblasts and more disruptive than cisplatin to breast cancer cell metabolism, and therefore it is a promising candidate for use in future anticancer drug strategies.

Tezosentan increases nitric oxide signaling via enhanced hydrogen peroxide generation in lambs with surgically induced acute increases in pulmonary blood flow

We have previously shown that acute increases in pulmonary blood flow (PBF) are limited by a compensatory increase in pulmonary vascular resistance (PVR) via an endothelin-1 (ET-1) dependent decrease in nitric oxide synthase (NOS) activity. The mechanisms underlying the reduction in NO signaling are unresolved. Thus, the purpose of this study was to elucidate mechanisms of this ET-1-NO interaction. Pulmonary arterial endothelial cells were acutely exposed to shear stress in the presence or absence of tezosentan, a combined ET(A) /ET(B) receptor antagonist. Shear increased NO(x) , eNOS phospho-Ser1177, and H(2) O(2) and decreased catalase activity; tezosentan enhanced, while ET-1 attenuated all of these changes. In addition, ET-1 increased eNOS phospho-Thr495 levels. In lambs, 4 h of increased PBF decreased H(2) O(2) , eNOS phospho-Ser1177, and NO(X) levels, and increased eNOS phospho-Thr495, phospho-catalase, and catalase activity. These changes were reversed by tezosentan. PEG-catalase reversed the positive effects of tezosentan on NO signaling. In all groups, opening the shunt resulted in a rapid increase in PBF by 30 min. In vehicle- and tezosentan/PEG-catalase lambs, PBF did not change further over the 4 h study period. PVR fell by 30 min in vehicle- and tezosentan-treated lambs, and by 60 min in tezosentan/PEG-catalase-treated lambs. In vehicle- and tezosentan/PEG-catalase lambs, PVR did not change further over the 4 h study period. In tezosentan-treated lambs, PBF continued to increase and LPVR to decrease over the 4 h study period. We conclude that acute increases in PBF are limited by an ET-1 dependent decrease in NO production via alterations in catalase activity, H(2) O(2) levels, and eNOS phosphorylation.

Endothelial microparticles increase in mitral valve disease and impair mitral valve endothelial function

Mitral valve endothelial cells are important for maintaining lifelong mitral valve integrity and function. Plasma endothelial microparticles (EMPs) increased in various pathological conditions related to activation of endothelial cells. However, whether EMPs will increase in mitral valve disease and their relationship remains unclear. Here, 81 patients with mitral valve disease and 45 healthy subjects were analyzed for the generation of EMPs by flow cytometry. Human mitral valve endothelial cells (HMVECs) were treated with EMPs. The phosphorylation of Akt and endothelial nitric oxide synthase (eNOS), the association of eNOS and heat shock protein 90 (HSP90), and the generation of nitric oxide (NO) and superoxide anion (O(2)(∙-)) were measured. EMPs were increased significantly in patients with mitral valve disease compared with those in healthy subjects. EMPs were negatively correlated with mitral valve area in patients with isolated mitral stenosis. EMPs were significantly higher in the group with severe mitral regurgitation than those in the group with mild and moderate mitral regurgitation. Furthermore, EMPs were decreased dramatically in both Akt and eNOS phosphorylation and the association of HSP90 with eNOS in HMVECs. EMPs decreased NO production but increased O(2)(∙-) generation in HMVECs. Our data demonstrated that EMPs were significantly increased in patients with mitral valve disease. The increase of EMPs can in turn impair HMVEC function by inhibiting the Akt/eNOS-HSP90 signaling pathway. These findings suggest that EMPs may be a therapeutic target for mitral valve disease.

Role of carnitine acetyl transferase in regulation of nitric oxide signaling in pulmonary arterial endothelial cells

Congenital heart defects with increased pulmonary blood flow (PBF) result in pulmonary endothelial dysfunction that is dependent, at least in part, on decreases in nitric oxide (NO) signaling. Utilizing a lamb model with left-to-right shunting of blood and increased PBF that mimics the human disease, we have recently shown that a disruption in carnitine homeostasis, due to a decreased carnitine acetyl transferase (CrAT) activity, correlates with decreased bioavailable NO. Thus, we undertook this study to test the hypothesis that the CrAT enzyme plays a major role in regulating NO signaling through its effect on mitochondrial function. We utilized the siRNA gene knockdown approach to mimic the effect of decreased CrAT activity in pulmonary arterial endothelial cells (PAEC). Our data indicate that silencing the CrAT gene disrupted cellular carnitine homeostasis, reduced the expression of mitochondrial superoxide dismutase-and resulted in an increase in oxidative stress within the mitochondrion. CrAT gene silencing also disrupted mitochondrial bioenergetics resulting in reduced ATP generation and decreased NO signaling secondary to a reduction in eNOS/Hsp90 interactions. Thus, this study links the disruption of carnitine homeostasis to the loss of NO signaling observed in children with CHD. Preserving carnitine homeostasis may have important clinical implications that warrant further investigation.

Pulmonary blood flow and pulmonary hypertension: Is the pulmonary circulation flowophobic or flowophilic?

Increased pulmonary blood flow (PBF) is widely thought to provoke pulmonary vascular obstructive disease (PVO), but the impact of wall shear stress in the lung is actually poorly defined. We examined information from patients having cardiac lesions which impact the pulmonary circulation in distinct ways, as well as experimental studies, asking how altered hemodynamics impact the risk of developing PVO. Our results are as follows: (1) with atrial septal defect (ASD; increased PBF but low PAP), shear stress may be increased but there is little tendency to develop PVO; (2) with normal PBF but increased pulmonary vascular resistance (PVR; mitral valve disease) shear stress may also be increased but risk of PVO still low; (3) with high PVR and PBF (e.g., large ventricular septal defect), wall shear stress is markedly increased and the likelihood of developing PVO is much higher than with high PBF or PAP only; and (4) with ASD, experimental and clinical observations suggest that increased PBF plus another stimulus (e.g., endothelial inflammation) may be required for PVO. We conclude that modestly increased wall shear stress (e.g., ASD) infrequently provokes PVO, and likely requires other factors to be harmful. Likewise, increased PAP seldom causes PVO. Markedly increased wall shear stress may greatly increase the likelihood of PVO, but we cannot discriminate its effect from the combined effects of increased PAP and PBF. Finally, the age of onset of increased PAP may critically impact the risk of PVO. Some implications of these observations for future investigations are discussed.

Lipoteichoic acid from Staphylococcus aureus induces lung endothelial cell barrier dysfunction: role of reactive oxygen and nitrogen species

Tunneled central venous catheters (TCVCs) are used for dialysis access in 82% of new hemodialysis patients and are rapidly colonized with Gram-positive organism (e.g. Staphylococcus aureus) biofilm, a source of recurrent infections and chronic inflammation. Lipoteichoic acid (LTA), a cell wall ribitol polymer from Gram-positive organisms, mediates inflammation through the Toll-like receptor 2 (TLR2). The effect of LTA on lung endothelial permeability is not known. We tested the hypothesis that LTA from Staphylococcus aureus induces alterations in the permeability of pulmonary microvessel endothelial monolayers (PMEM) that result from activation of TLR2 and are mediated by reactive oxygen/nitrogen species (RONS). The permeability of PMEM was assessed by the clearance rate of Evans blue-labeled albumin, the activation of the TLR2 pathway was assessed by Western blot, and the generation of RONS was measured by the fluorescence of oxidized dihydroethidium and a dichlorofluorescein derivative. Treatment with LTA or the TLR2 agonist Pam₍₃₎CSK₍₄₎ induced significant increases in albumin permeability, IκBα phosphorylation, IRAK1 degradation, RONS generation, and endothelial nitric oxide synthase (eNOS) activation (as measured by the p-eNOS^ser1177:p-eNOS^thr495 ratio). The effects on permeability and RONS were effectively prevented by co-administration of the superoxide scavenger Tiron, the peroxynitrite scavenger Urate, or the eNOS inhibitor L-NAME and these effects as well as eNOS activation were reduced or prevented by pretreatment with an IRAK1/4 inhibitor. The results indicate that the activation of TLR2 and the generation of ROS/RNS mediates LTA-induced barrier dysfunction in PMEM.

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.

Ethanol induces vascular relaxation via redox-sensitive and nitric oxide-dependent pathways

We investigated the role of reactive oxygen species (ROS) and nitric oxide (NO) in ethanol-induced relaxation. Vascular reactivity experiments showed that ethanol (0.03-200 mmol/L) induced relaxation in endothelium-intact and denuded rat aortic rings isolated from male Wistar rats. Pre-incubation of intact or denuded rings with l-NAME (non selective NOS inhibitor, 100 μmol/L), 7-nitroindazole (selective nNOS inhibitor, 100 μmol/L), ODQ (selective inhibitor of guanylyl cyclase enzyme, 1 μmol/L), glibenclamide (selective blocker of ATP-sensitive K(+) channels, 3 μmol/L) and 4-aminopyridine (selective blocker of voltage-dependent K(+) channels, 4-AP, 1 mmol/L) reduced ethanol-induced relaxation. Similarly, tiron (superoxide anion (O(2)(-)) scavenger, 1 mmol/L) and catalase (hydrogen peroxide (H(2)O(2)) scavenger, 300 U/mL) reduced ethanol-induced relaxation to a similar extent in both endothelium-intact and denuded rings. Finally, prodifen (non-selective cytochrome P450 enzymes inhibitor, 10 μmol/L) and 4-methylpyrazole (selective alcohol dehydrogenase inhibitor, 10 μmol/L) reduced ethanol-induced relaxation. In cultured aortic vascular smooth muscle cells (VSMCs), ethanol stimulated generation of NO, which was significantly inhibited by l-NAME. In endothelial cells, flow cytometry studies showed that ethanol increased cytosolic Ca(2+) concentration ([Ca(2+)]c), O(2)(-) and cytosolic NO concentration ([NO]c). Tiron inhibited ethanol-induced increase in [Ca(2+)]c and [NO]c. The major new finding of this work is that ethanol induces relaxation via redox-sensitive and NO-cGMP-dependent pathways through direct effects on ROS production and NO signaling. These findings identify putative molecular mechanisms whereby ethanol, at pharmacological concentrations, influences vascular reactivity.

The toxic effect of fluoride on MG-63 osteoblast cells is also dependent on the production of nitric oxide

Some soda-lime-phospho-silicate glasses, such as Hench's Bioglass(®) 45S5, form bone-like apatite on their surface when bound to living bone. To improve their osteointegration for clinical purposes, the fluoride insertion in their structure has been proposed, but we recently showed that fluoride causes oxidative damage in human MG-63 osteoblasts, via inhibition of pentose phosphate oxidative pathway (PPP) and its key enzyme glucose 6-phosphate dehydrogenase (G6PD). In the same cells we have now investigated the role of nitric oxide (NO) in these effects. Fluoride-containing bioactive glasses and NaF caused, as expected, release of lactate dehydrogenase in the extracellular medium, accumulation of intracellular malonyldialdehyde, inhibition of PPP and G6PD: we have now observed that these effects were significantly reverted not only by superoxide dismutase (SOD) plus catalase (scavengers of reactive oxygen species), but also by N-monomethyl l-arginine (l-NMMA, a NOS inhibitor) and 2-phenyl-4,4,5,5,-tetramethylimidazoline-1oxyl 3-oxide (PTIO, a NO scavenger). Moreover the two highest concentrations of both fluoride-containing bioglasses and NaF caused increase of nitrite (a stable derivative of NO) levels in the culture supernatant, which was inhibited by l-NMMA, erythrocytes, PTIO and SOD/catalase, and increase of intracellular NO synthase (NOS) activity. The incubation with bioglasses or NaF increased also the phosphorylation of Ser(1177) in the endothelial NOS isoform. Furthermore, the NO donor spermine NONOate was able to inhibit G6PD activity in vitro, and this effect was partly reverted by PTIO. Therefore our results suggest that most cytotoxic effects of fluoride are mediated by the production of NO: reactive oxygen species are important, causing NOS phosphorylation. We also observed, for the first time, that Tempol, but not SOD/catalase, besides inhibiting the oxidative stress induced by fluoride, also scavenges fluoride ions. For this reason it is not a selective inhibitor of the oxidative effects of fluoride.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Shear stress increases nitric oxide production in thick ascending limbs

We showed that luminal flow stimulates nitric oxide (NO) production in thick ascending limbs. Ion delivery, stretch, pressure, and shear stress all increase when flow is enhanced. We hypothesized that shear stress stimulates NO in thick ascending limbs, whereas stretch, pressure, and ion delivery do not. We measured NO in isolated, perfused rat thick ascending limbs using the NO-sensitive dye DAF FM-DA. NO production rose from 21 ± 7 to 58 ± 12 AU/min (P < 0.02; n = 7) when we increased luminal flow from 0 to 20 nl/min, but dropped to 16 ± 8 AU/min (P < 0.02; n = 7) 10 min after flow was stopped. Flow did not increase NO in tubules from mice lacking NO synthase 3 (NOS 3). Flow stimulated NO production by the same extent in tubules perfused with ion-free solution and physiological saline (20 ± 7 vs. 24 ± 6 AU/min; n = 7). Increasing stretch while reducing shear stress and pressure lowered NO generation from 42 ± 9 to 17 ± 6 AU/min (P < 0.03; n = 6). In the absence of shear stress, increasing pressure and stretch had no effect on NO production (2 ± 8 vs. 8 ± 8 AU/min; n = 6). Similar results were obtained in the presence of tempol (100 μmol/l), a O(2)(-) scavenger. Primary cultures of thick ascending limb cells subjected to shear stresses of 0.02 and 0.55 dyne/cm(2) produced NO at rates of 55 ± 10 and 315 ± 93 AU/s, respectively (P < 0.002; n = 7). Pretreatment with the NOS inhibitor l-NAME (5 mmol/l) blocked the shear stress-induced increase in NO production. We concluded that shear stress rather than pressure, stretch, or ion delivery mediates flow-induced stimulation of NO by NOS 3 in thick ascending limbs.

Vascular Nitric Oxide: Formation and Function

Nitric oxide (NO) is a structurally simple, highly versatile molecule that was originally discovered over 30 years ago as an endothelium-derived relaxing factor. In addition to its vasorelaxing effects, NO is now recognized as a key determinant of vascular health, exerting antiplatelet, antithrombotic, and anti-inflammatory properties within the vasculature. This short-lived molecule exerts its inhibitory effect on vascular smooth muscle cells and platelets largely through cyclic guanosine monophosphate-dependent mechanisms, resulting in a multitude of molecular effects by which platelet activation and aggregation are prevented. The biosynthesis of NO occurs via the catalytic activity of NO synthase, an oxidoreductase found in many cell types. NO insufficiency can be attributed to limited substrate/cofactor availability as well as interactions with reactive oxygen species. Impaired NO bioavailability represents the central feature of endothelial dysfunction, a common abnormality found in many vascular diseases. In this review, we present an overview of NO synthesis and biochemistry, discuss the mechanisms of action of NO in regulating platelet and endothelial function, and review the effects of vascular disease states on NO bioavailability.