Reactive oxygen species induced Ca2+ influx via TRPV4 and microvascular endothelial dysfunction in the SU5416/hypoxia model of pulmonary arterial hypertension

Deficiency of Endothelial Piezo2 Impairs Pulmonary Vascular Angiogenesis and Predisposes Pulmonary Hypertension

BACKGROUND

Mechanosensitive Piezo1 (Piezo Type Mechanosensitive Ion Channel Component 1) channel plays a key role in pulmonary hypertension (PH). However, the role of Piezo2 in PH remains unclear.

METHODS

Endothelial cell (EC)-specific Piezo2 knockout (Piezo2flox/flox, Tek-Cre+; Piezo2EC-/-) rats and primarily cultured pulmonary microvascular ECs were used to determine the role of Piezo2 in PH.

RESULTS

Data analysis of publicly accessible single-cell RNA-sequencing data sets uncovered significant downregulation of Piezo2 in lung ECs from patients with idiopathic pulmonary arterial hypertension, which was verified in the lungs/ECs from PH rat models induced by hypoxia or monocrotaline. Comparing to wild-type rats, Piezo2EC-/- rats exhibited exacerbated PH in both hypoxia-induced PH and monocrotaline-induced PH, characterized by the worsened hemodynamical and histological changes. Piezo2EC-/- rats showed dramatic loss of pulmonary microvessels, in association with the decreased intracellular free calcium concentration ([Ca2+]i) and downregulation of VEGFR2 (vascular endothelial growth factor receptor 2) and phosphorylated SRF (serum response factor) in pulmonary microvascular ECs. Knockout of Piezo2 or treatment with a calcium chelator, EDTA, impaired the ability of tube formation and migration in pulmonary microvascular ECs, which was restored by supplementation of extra calcium. A safflower oil diet rich in linoleic acid, which can enhance the stability and function of Piezo2, effectively alleviated PH development in a hypoxia-induced PH rat model.

CONCLUSIONS

This study demonstrates that EC-specific knockout of Piezo2 exacerbates PH pathogenesis, at least partially, through the suppression of [Ca2+]i/phosphorylated SRF/VEGFR2 signaling axis in pulmonary vascular ECs. Targeted activation of Piezo2 could be a novel effective strategy for the treatment of PH.

Mechanotransduction in Development: A Focus on Angiogenesis

Cells respond to external mechanical cues and transduce these forces into biological signals. This process is known as mechanotransduction and requires a group of proteins called mechanosensors. This peculiar class of receptors include extracellular matrix proteins, plasma membrane proteins, the cytoskeleton and the nuclear envelope. These cell components are responsive to a wide spectrum of physical cues including stiffness, tensile force, hydrostatic pressure and shear stress. Among mechanotransducers, the Transient Receptor Potential (TRP) and the PIEZO family members are mechanosensitive ion channels, coupling force transduction with intracellular cation transport. Their activity contributes to embryo development, tissue remodeling and repair, and cell homeostasis. In particular, vessel development is driven by hemodynamic cues such as flow direction and shear stress. Perturbed mechanotransduction is involved in several pathological vascular phenotypes including hereditary hemorrhagic telangiectasia. This review is conceived to summarize the most recent findings of mechanotransduction in development. We first collected main features of mechanosensitive proteins. However, we focused on the role of mechanical cues during development. Mechanosensitive ion channels and their function in vascular development are also discussed, with a focus on brain vessel morphogenesis.

Roles for TRPV4 in disease: A discussion of possible mechanisms

The transient receptor potential vanilloid 4 (TRPV4) ion channel is a ubiquitously expressed Ca2+-permeable ion channel that controls intracellular calcium ([Ca2+]i) homeostasis in various types of cells. The physiological roles for TRPV4 are tissue specific and the mechanisms behind this specificity remain mostly unclarified. It is noteworthy that mutations in the TRPV4 channel have been associated to a broad spectrum of congenital diseases, with most of these mutations mainly resulting in gain-of-function. Mutations have been identified in human patients showing a variety of phenotypes and symptoms, mostly related to skeletal and neuromuscular disorders. Since TRPV4 is so widely expressed throughout the body, it comes as no surprise that the literature is growing in evidence linking this protein to malfunction in systems other than the skeletal and neuromuscular. In this review, we summarize the expression patterns of TRPV4 in several tissues and highlight findings of recent studies that address critical structural and functional features of this channel, particularly focusing on its interactions and signaling pathways related to Ca2+ entry. Moreover, we discuss the roles of TRPV4 mutations in some diseases and pinpoint some of the mechanisms underlying pathological states where TRPV4's malfunction is prominent.

Fatty acid metabolism promotes TRPV4 activity in lung microvascular endothelial cells in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a morbid disease characterized by significant lung endothelial cell (EC) dysfunction. Prior work has shown that microvascular endothelial cells (MVECs) isolated from animals with experimental PAH and patients with PAH exhibit significant abnormalities in metabolism and calcium signaling. With regards to metabolism, we and others have shown evidence of increased aerobic glycolysis and evidence of increased utilization of alternate fuel sources (such as fatty acids) in PAH EC. In the realm of calcium signaling, our prior work linked increased activity of the transient receptor potential vanilloid-4 (TRPV4) channel to increased proliferation of MVECs isolated from the Sugen/Hypoxia rat model of PAH (SuHx-MVECs). However, the relationship between metabolic shifts and calcium abnormalities was not clear. Specifically, whether shifts in metabolism were responsible for increasing TRPV4 channel activity in SuHx-MVECs was not known. In this study, using human data, serum samples from SuHx rats, and SuHx-MVECs, we describe the consequences of increased MVEC fatty acid oxidation in PAH. In human samples, we observed an increase in long-chain fatty acid levels that was associated with PAH severity. Next, using SuHx rats and SuHx-MVECs, we observed increased intracellular levels of lipids. We also show that increasing intracellular lipid content increases TRPV4 activity, whereas inhibiting fatty acid oxidation normalizes basal calcium levels in SuHx-MVECs. By exploring the fate of fatty acid-derived carbons, we observed that the metabolite linking increased intracellular lipids to TRPV4 activity was β-hydroxybutyrate (BOHB), a product of fatty acid oxidation. Finally, we show that BOHB supplementation alone is sufficient to sensitize the TRPV4 channel in rat and mouse MVECs. Returning to humans, we observe a transpulmonary BOHB gradient in human patients with PAH. Thus, we establish a link between fatty acid oxidation, BOHB production, and TRPV4 activity in MVECs in PAH. These data provide new insight into metabolic regulation of calcium signaling in lung MVECs in PAH.NEW & NOTEWORTHY In this paper, we explore the link between metabolism and intracellular calcium levels in microvascular endothelial cells (MVECs) in pulmonary arterial hypertension (PAH). We show that fatty acid oxidation promotes sensitivity of the transient receptor potential vanilloid-4 (TRPV4) calcium channel in MVECs isolated from a rodent model of PAH.

Contribution of Mitochondrial Reactive Oxygen Species to Chronic Hypoxia-Induced Pulmonary Hypertension

Pulmonary hypertension (PH) resulting from chronic hypoxia (CH) occurs in patients with chronic obstructive pulmonary diseases, sleep apnea, and restrictive lung diseases, as well as in residents at high altitude. Previous studies from our group and others demonstrate a detrimental role of reactive oxygen species (ROS) in the pathogenesis of CH-induced PH, although the subcellular sources of ROS are not fully understood. We hypothesized that mitochondria-derived ROS (mtROS) contribute to enhanced vasoconstrictor reactivity and PH following CH. To test the hypothesis, we exposed rats to 4 weeks of hypobaric hypoxia (PB ≈ 380 mmHg), with control rats housed in ambient air (PB ≈ 630 mmHg). Chronic oral administration of the mitochondria-targeted antioxidant MitoQ attenuated CH-induced decreases in pulmonary artery (PA) acceleration time, increases in right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary arterial remodeling. In addition, endothelium-intact PAs from CH rats exhibited a significantly greater basal tone compared to those from control animals, as was eliminated via MitoQ. CH also augmented the basal tone in endothelium-disrupted PAs, a response associated with increased mtROS production in primary PA smooth muscle cells (PASMCs) from CH rats. However, we further uncovered an effect of NO synthase inhibition with Nω-nitro-L-arginine (L-NNA) to unmask a potent endothelial vasoconstrictor influence that accentuates mtROS-dependent vasoconstriction following CH. This basal tone augmentation in the presence of L-NNA disappeared following combined endothelin A and B receptor blockade with BQ123 and BQ788. The effects of using CH to augment vasoconstriction and PASMC mtROS production in exogenous endothelin 1 (ET-1) were similarly prevented by MitoQ. We conclude that mtROS participate in the development of CH-induced PH. Furthermore, mtROS signaling in PASMCs is centrally involved in enhanced pulmonary arterial constriction following CH, a response potentiated by endogenous ET-1.

Mitochondria in hypoxic pulmonary hypertension, roles and the potential targets

Mitochondria are the centrol hub for cellular energy metabolisms. They regulate fuel metabolism by oxygen levels, participate in physiological signaling pathways, and act as oxygen sensors. Once oxygen deprived, the fuel utilizations can be switched from mitochondrial oxidative phosphorylation to glycolysis for ATP production. Notably, mitochondria can also adapt to hypoxia by making various functional and phenotypes changes to meet the demanding of oxygen levels. Hypoxic pulmonary hypertension is a life-threatening disease, but its exact pathgenesis mechanism is still unclear and there is no effective treatment available until now. Ample of evidence indicated that mitochondria play key factor in the development of hypoxic pulmonary hypertension. By hypoxia-inducible factors, multiple cells sense and transmit hypoxia signals, which then control the expression of various metabolic genes. This activation of hypoxia-inducible factors considered associations with crosstalk between hypoxia and altered mitochondrial metabolism, which plays an important role in the development of hypoxic pulmonary hypertension. Here, we review the molecular mechanisms of how hypoxia affects mitochondrial function, including mitochondrial biosynthesis, reactive oxygen homeostasis, and mitochondrial dynamics, to explore the potential of improving mitochondrial function as a strategy for treating hypoxic pulmonary hypertension.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Pathophysiological Roles of the TRPV4 Channel in the Heart

The transient receptor potential vanilloid 4 (TRPV4) channel is a non-selective cation channel that is mostly permeable to calcium (Ca²⁺), which participates in intracellular Ca²⁺ handling in cardiac cells. It is widely expressed through the body and is activated by a large spectrum of physicochemical stimuli, conferring it a role in a variety of sensorial and physiological functions. Within the cardiovascular system, TRPV4 expression is reported in cardiomyocytes, endothelial cells (ECs) and smooth muscle cells (SMCs), where it modulates mitochondrial activity, Ca²⁺ homeostasis, cardiomyocytes electrical activity and contractility, cardiac embryonic development and fibroblast proliferation, as well as vascular permeability, dilatation and constriction. On the other hand, TRPV4 channels participate in several cardiac pathological processes such as the development of cardiac fibrosis, hypertrophy, ischemia-reperfusion injuries, heart failure, myocardial infarction and arrhythmia. In this manuscript, we provide an overview of TRPV4 channel implications in cardiac physiology and discuss the potential of the TRPV4 channel as a therapeutic target against cardiovascular diseases.

Transient Receptor Potential Vanilloid (TRPV4) channel inhibition: A novel promising approach for the treatment of lung diseases

Research on transient receptor potential vanilloid-4 (TRPV4) can provide a promising potential therapeutic target in the development of novel medicines for lung disorders. TRPV4 expresses in lung tissue and plays an important role in the maintenance of respiratory homeostatic function. TRPV4 is upregulated in life-threatening respiratory diseases like pulmonary hypertension, asthma, cystic fibrosis, and chronic obstructive pulmonary diseases. TRPV4 is linked to several proteins that have physiological functions and are sensitive to a wide variety of stimuli, such as mechanical stimulation, changes in temperature, and hypotonicity, and responds to a variety of proteins and lipid mediators, including anandamide (AA), the arachidonic acid metabolite, 5,6-epoxyeicosatrienoic acid (5,6-EET), a plant dimeric diterpenoid called bisandrographolide A (BAA), and the phorbol ester 4-alpha-phorbol-12,13-didecanoate (4α-PDD). This study focused on relevant research evidence of TRPV4 in lung disorders and its agonist and antagonist effects. TRPV4 can be a possible target of discovered molecules that exerts high therapeutic potential in the treatment of respiratory diseases by inhibiting TRPV4.

Oxidative Stress and Antioxidant Therapy in Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive disease characterized by elevated artery pressures and pulmonary vascular resistance. Underlying mechanisms comprise endothelial dysfunction, pulmonary artery remodeling and vasoconstriction. Several studies have shown evidence of the critical role of oxidative stress in PH pathophysiology. Alteration of redox homeostasis produces excessive generation of reactive oxygen species, inducing oxidative stress and the subsequent alteration of biological molecules. Exacerbations in oxidative stress production can lead to alterations in nitric oxide signaling pathways, contributing to the proliferation of pulmonary arterial endothelial cells and smooth muscle cells, inducing PH development. Recently, antioxidant therapy has been suggested as a novel therapeutic strategy for PH pathology. However, the favorable outcomes observed in preclinical studies have not been consistently reproduced in clinical practice. Therefore, targeting oxidative stress as a therapeutic intervention for PH is an area that is still being explored. This review summarizes the contribution of oxidative stress to the pathogenesis of the different types of PH and suggests antioxidant therapy as a promising strategy for PH treatment.

Natural Products for the Treatment of Pulmonary Hypertension: Mechanism, Progress, and Future Opportunities

Pulmonary hypertension (PH) is a lethal disease due to the remodeling of pulmonary vessels. Its pathophysiological characteristics include increased pulmonary arterial pressure and pulmonary vascular resistance, leading to right heart failure and death. The pathological mechanism of PH is complex and includes inflammation, oxidative stress, vasoconstriction/diastolic imbalance, genetic factors, and ion channel abnormalities. Currently, many clinical drugs for the treatment of PH mainly play their role by relaxing pulmonary arteries, and the treatment effect is limited. Recent studies have shown that various natural products have unique therapeutic advantages for PH with complex pathological mechanisms owing to their multitarget characteristics and low toxicity. This review summarizes the main natural products and their pharmacological mechanisms in PH treatment to provide a useful reference for future research and development of new anti-PH drugs and their mechanisms.

ABCB5+ mesenchymal stromal cells therapy protects from hypoxia by restoring Ca2+ homeostasis in vitro and in vivo

BACKGROUND

Hypoxia in ischemic disease impairs Ca²⁺ homeostasis and may promote angiogenesis. The therapeutic efficacy of mesenchymal stromal cells (MSCs) in peripheral arterial occlusive disease is well established, yet its influence on cellular Ca²⁺ homeostasis remains to be elucidated. We addressed the influence of ATP-binding cassette subfamily B member 5 positive mesenchymal stromal cells (ABCB5⁺ MSCs) on Ca²⁺ homeostasis in hypoxic human umbilical vein endothelial cells (HUVECs) in vitro and in vivo.

METHODS

Hypoxia was induced in HUVECs by Cobalt (II) chloride (CoCl₂) or Deferoxamine (DFO). Dynamic changes in the cytosolic- and endoplasmic reticulum (ER) Ca²⁺ and changes in reactive oxygen species were assessed by appropriate fluorescence-based sensors. Metabolic activity, cell migration, and tube formation were assessed by standard assays. Acute-on-chronic ischemia in Apolipoprotein E knock-out (ApoE^-/-) mice was performed by double ligation of the right femoral artery (DFLA). ABCB5⁺ MSC cells were injected into the ischemic limb. Functional recovery after DFLA and histology of gastrocnemius and aorta were assessed.

RESULTS

Hypoxia-induced impairment of cytosolic and ER Ca²⁺ were restored by ABCB5⁺ MSCs or their conditioned medium. Similar was found for changes in intracellular ROS production, metabolic activity, migratory ability and tube formation. The restoration was paralleled by an increased expression of the Ca²⁺ transporter Sarco-/endoplasmic reticulum ATPase 2a (SERCA2a) and the phosphorylation of Phospholamban (PLN). In acute-on-chronic ischemia, ABCB5⁺ MSCs treated mice showed a higher microvascular density, increased SERCA2a expression and PLN phosphorylation relative to untreated controls.

CONCLUSIONS

ABCB5⁺ MSCs therapy can restore cellular Ca²⁺ homeostasis, which may beneficially affect the angiogenic function of endothelial cells under hypoxia in vitro and in vivo.

Transpulmonary amino acid metabolism in the sugen hypoxia model of pulmonary hypertension

In pulmonary artery hypertension (PAH), emerging evidence suggests that metabolic abnormalities may be contributing to cellular dysfunction in PAH. Metabolic abnormalities such as glycolytic shift have been observed intracellularly in several cell types in PAH, including microvacular endothelial cells (MVECs). Concurrently, metabolomics of human PAH samples has also revealed a variety of metabolic abnormalities; however the relationship between the intracellular metabolic abnormalities and the serum metabolome in PAH remains under investigation. In this study, we utilize the sugen/hypoxia (SuHx) rodent model of PAH to examine the RV, LV and MVEC intracellular metabolome (using targeted metabolomics) in normoxic and SuHx rats. We additionally validate key findings from our metabolomics experiments with data obtained from cell culture of normoxic and SuHx MVECs, as well as metabolomics of human serum samples from two different PAH patient cohorts. Taken together, our data, spanning rat serum, human serum and primary isolated rat MVECs reveal that: (1) key classes of amino acids (specifically, branched chain amino acids-BCAA) are lower in the pre-capillary (i.e., RV) serum of SuHx rats (and humans); (2) intracellular amino acid levels (in particular BCAAs) are increased in SuHx-MVECs; (3) there may be secretion rather than utilization of amino acids across the pulmonary microvasculature in PAH and (4) an oxidized glutathione gradient is present across the pulmonary vasculature, suggesting a novel fate for increased glutamine uptake (i.e., as a source of glutathione). in MVECs in PAH. In summary, these data reveal new insight into the shifts in amino acid metabolism occurring across the pulmonary circulation in PAH.

Transient Receptor Potential (TRP) Channels in Airway Toxicity and Disease: An Update

Our respiratory system is exposed to toxicants and pathogens from both sides: the airways and the vasculature. While tracheal, bronchial and alveolar epithelial cells form a natural barrier in the airways, endothelial cells protect the lung from perfused toxic compounds, particulate matter and invading microorganism in the vascular system. Damages induce inflammation by our immune response and wound healing by (myo)fibroblast proliferation. Members of the transient receptor potential (TRP) superfamily of ion channel are expressed in many cells of the respiratory tract and serve multiple functions in physiology and pathophysiology. TRP expression patterns in non-neuronal cells with a focus on TRPA1, TRPC6, TRPM2, TRPM5, TRPM7, TRPV2, TRPV4 and TRPV6 channels are presented, and their roles in barrier function, immune regulation and phagocytosis are summarized. Moreover, TRP channels as future pharmacological targets in chronic obstructive pulmonary disease (COPD), asthma, cystic and pulmonary fibrosis as well as lung edema are discussed.

Potential of the TRPM7 channel as a novel therapeutic target for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an intractable vascular disease characterized by a progressive increase in pulmonary vascular resistance caused by pulmonary vascular remodeling, which ultimately leads to right-sided heart failure. PAH remains incurable, despite the development of PAH-targeted therapeutics centered on pulmonary artery relaxants. It is necessary to identify the target molecules that contribute to pulmonary artery remodeling. Transient receptor potential (TRP) channels have been suggested to modulate pulmonary artery remodeling. Our study focused on the transient receptor potential ion channel subfamily M, member 7, or the TRPM7 channel, which modulates endothelial-to-mesenchymal transition and smooth muscle proliferation in the pulmonary artery. In this review, we summarize the role and expression profile of TRPM7 channels in PAH progression and discuss TRPM7 channels as possible therapeutic targets. In addition, we discuss the therapeutic effect of a Chinese herbal medicine, Ophiocordyceps sinensis (OCS), on PAH progression, which partly involves TRPM7 inhibition.

The Novel Regulatory Role of the lncRNA–miRNA–mRNA Axis in Chronic Inflammatory Airway Diseases

Chronic inflammatory airway diseases, characterized by airway inflammation and airway remodelling, are increasing as a cause of morbidity and mortality for all age groups and races across the world. The underlying molecular mechanisms involved in chronic inflammatory airway diseases have not been fully explored. MicroRNAs (miRNAs) and long noncoding RNAs (lncRNAs) have recently attracted much attention for their roles in the regulation of a variety of biological processes. A number of studies have confirmed that both lncRNAs and miRNAs can regulate the initiation and progression of chronic airway diseases by targeting mRNAs and regulating different cellular processes, such as proliferation, apoptosis, inflammation, migration, and epithelial–mesenchymal transition (EMT). Recently, accumulative evidence has shown that the novel regulatory mechanism underlying the interaction among lncRNAs, miRNAs and messenger RNAs (mRNAs) plays a critical role in the pathophysiological processes of chronic inflammatory airway diseases. In this review, we comprehensively summarized the regulatory roles of the lncRNA–miRNA–mRNA network in different cell types and their potential roles as biomarkers, indicators of comorbidities or therapeutic targets for chronic inflammatory airway diseases, particularly chronic obstructive pulmonary disease (COPD) and asthma.

Small molecule compound M12 reduces vascular permeability in obese mice via blocking endothelial TRPV4-Nox2 interaction

Transient receptor potential channel TRPV4 and nicotinamide adenine dinucleotide phosphate oxidase (Nox2) are involved in oxidative stress that increases endothelial permeability. It has been shown that obesity enhances the physical association of TRPV4 and Nox2, but the role of TRPV4-Nox2 association in obesity has not been clarified. In this study we investigated the function of TRPV4-Nox2 complex in reducing oxidative stress and regulating abnormal vascular permeability in obesity. Obesity was induced in mice by feeding a high-fat diet (HFD) for 14 weeks. The physical interaction between TRPV4 and Nox2 was measured using FRET, co-immunoprecipitation and GST pull-down assays. The functional interaction was measured by rhodamine phalloidin, CM-H₂DCFDA in vitro, the fluorescent dye dihydroethidium (DHE) staining assay, and the Evans blue permeability assay in vivo. We demonstrated that TRPV4 physically and functionally associated with Nox2, and this physical association was enhanced in aorta of obese mice. Furthermore, we showed that interrupting TRPV4-Nox2 coupling by TRPV4 knockout, or by treatment with a specific Nox2 inhibitor Nox2 dstat or a specific TRPV4 inhibitor HC067046 significantly attenuated obesity-induced ROS overproduction in aortic endothelial cells, and reversed the abnormal endothelial cytoskeletal structure. In order to discover small molecules disrupting the over-coupling of TPRV4 and Nox2 in obesity, we performed molecular docking analysis and found that compound M12 modulated TRPV4-Nox2 association, reduced ROS production, and finally reversed disruption of the vascular barrier in obesity. Together, this study, for the first time, provides evidence for the TRPV4 physically interacting with Nox2. TRPV4-Nox2 complex is a potential drug target in improving oxidative stress and disruption of the vascular barrier in obesity. Compound M12 targeting TRPV4-Nox2 complex can improve vascular barrier function in obesity.

Calcium–Permeable Channels and Endothelial Dysfunction in Acute Lung Injury

The increased permeability of the lung microvascular endothelium is one critical initiation of acute lung injury (ALI). The disruption of vascular-endothelium integrity results in leakiness of the endothelial barrier and accumulation of protein-rich fluid in the alveoli. During ALI, increased endothelial-cell (EC) permeability is always companied by high frequency and amplitude of cytosolic Ca²⁺ oscillations. Mechanistically, cytosolic calcium oscillations include calcium release from internal stores and calcium entry via channels located in the cell membrane. Recently, numerous publications have shown substantial evidence that calcium-permeable channels play an important role in maintaining the integrity of the endothelium barrier function of the vessel wall in ALI. These novel endothelial signaling pathways are future targets for the treatment of lung injury. This short review focuses on the up-to-date research and provide insight into the contribution of calcium influx via ion channels to the disruption of lung microvascular endothelial-barrier function during ALI.

Cross-talk between TRPC-1, mTOR, PGC-1α and PPARδ in the dystrophic muscle cells treated with tempol

Background Ca2+ dysregulation and oxidative damage appear to have a central role in Duchenne muscular dystrophy (DMD) progression. The current study provides muscle cell-specific insights into the effect of Tempol on the TRPC 1 channel; on the positive and negative regulators of muscle cell differentiation; on the antioxidant enzymatic system; on the activators of mitochondrial biogenesis; and on the inflammatory process in the dystrophic primary muscle cells in culture.

METHODS

Mdx myotubes were treated with Tempol (5 mM) for 24 h. Untreated mdx myotubes and C57BL/10 myotubes were used as controls.

RESULTS

The Trypan Blue, MTT and Live/Dead Cell assays showed that Tempol (5 mM) presented no cytotoxic effect on the dystrophic muscle cells. The Tempol treated-mdx muscle cells showed significantly lower levels in the fluorescence intensity of intracellular calcium; TRPC-1 channel; MyoD; H₂O₂ and O₂^•- production; 4-HNE levels; SOD2, CAT and GPx levels; and TNF levels. On the other hand, SOD, CAT and GR mRNA relative expression were significantly higher in Tempol treated-mdx muscle cells. In addition, higher levels of Myogenin, MHC-Slow, mTOR, PGC-1α and PPARδ were also observed in Tempol treated-mdx muscle cells.

CONCLUSION

Our findings demonstrated that Tempol decreased intracellular calcium and oxidative stress in primary dystrophic muscle cells, promoting a cross-talk between TRPC-1, mTOR, PGC-1α and PPARδ.

VPO1/HOCl/ERK pathway mediates the right ventricular remodeling in rats with hypoxic pulmonary hypertension

Right ventricular (RV) remodeling is a major feature of pulmonary arterial hypertension (PAH). Vascular peroxidase 1 (VPO1) is reported to participate in the process of PAH. This study aims to explore whether VPO1 contributes to hypoxia-induced cardiac hypertrophy and the underlying mechanisms. SD rats were exposure to continuous hypoxia (10% O₂) for 3 weeks, which showed RV hypertrophy (increases in the ratio of RV weight to tibia length, cardiac cell size and hypertrophic markers), concomitant with upregulation of VPO1, elevation in hypochlorous acid (HOCl) production and ERK phosphorylation. In hypoxia (3% O₂)-induced hypertrophic H9c2 cells, similar characteristics of cardiac hypertrophy to that of hypoxia-treated rats were observed. Administration of VPO1 siRNA or NaHS (the HOCl inhibitor) suppressed HOCl production, ERK phosphorylation, and cardiac hypertrophy. Replacement of hypoxia with NaClO (exogenous HOCl) could also induce cardiac cell hypertrophy and activate ERK signaling pathway. In addition, hypoxia-induced cardiac hypertrophy could be blocked by PD98059 (the ERK-specific inhibitor). Based on these observations, we conclude that VPO1 promotes RV remodeling in PAH rats through catalyzing HOCl production, leading to the activation of ERK signaling. Thus, VPO1 may have the potential as a therapeutic target for PAH.

Signal Transduction during Metabolic and Inflammatory Reprogramming in Pulmonary Vascular Remodeling

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by (mal)adaptive remodeling of the pulmonary vasculature, which is associated with inflammation, fibrosis, thrombosis, and neovascularization. Vascular remodeling in PAH is associated with cellular metabolic and inflammatory reprogramming that induce profound endothelial and smooth muscle cell phenotypic changes. Multiple signaling pathways and regulatory loops act on metabolic and inflammatory mediators which influence cellular behavior and trigger pulmonary vascular remodeling in vivo. This review discusses the role of bioenergetic and inflammatory impairments in PAH development.

Tanreqing Injection Regulates Cell Function of Hypoxia-Induced Human Pulmonary Artery Smooth Muscle Cells (HPASMCs) through TRPC1/CX3CL1 Signaling Pathway

Hypoxia-induced pulmonary arterial hypertension (HPAH) is due to hypoxia caused by vascular endothelial cell remolding and damage. Previous studies have suggested that CX3CL1 plays an important role in HPAH which is affected by oxidative stress. Ca²⁺ channel activation correlated with increasing NF-κB levels induced by ROS. Tanreqing injection (TRQ) is a traditional Chinese medicine (TCM) for acute upper respiratory tract infection and acute pneumonia. In the present study, we explored the effect of TRQ on human pulmonary artery smooth muscle cells (HPASMCs) undergoing hypoxia and feasible molecular mechanisms involved in. Cell proliferation was assayed using CCK8 kits. Immunofluorescence and western blotting along with ELISA assay were performed to investigate the effect of TRQ on hypoxia-induced ROS, Ca²⁺, hydroxyl free radicals, and the expression of Ca²⁺ channel protein TRPC1, CX3CR1, HIF-1α, NF-κBp65, and p-NF-κBp65 in HPASMCs. Human CX3CL1 and the inhibitor of TRPC1 as SKF96365 were used for further investigation. TRQ inhibited hypoxia-induced increasing cell adhesion, ROS, Ca²⁺, hydroxyl free radicals, CX3CR1, HIF-1α, NF-κBp65 activation, and even on TRPC1 expression in HPASMC which tended to be attenuated even reversed by CX3CL1. Our results suggested that TRQ might help to attenuate remodeling of HPASMC through inhibiting the ROS and TRPC1/CX3CL1 signaling pathway.

Endothelial TRPV4 channels in lung edema and injury

The alveolo-capillary barrier is relatively impermeable, and facilitates gas exchange via the large alveolar surface in the lung. Disruption of alveolo-capillary barrier leads to accumulation of edema fluid in lung injury. Studies in animal models of various forms of lung injury provide evidence that TRPV4 channels play a critical role in disruption of the alveolo-capillary barrier and pathogenesis of lung injury. TRPV4 channels from capillary endothelial cells, alveolar epithelial cells, and immune cells have been implicated in the pathogenesis of lung injury. Recent studies in endothelium-specific TRPV4 knockout mice point to a central role for endothelial TRPV4 channels in lung injury. In this chapter, we review the findings on the pathological roles of endothelial TRPV4 channels in different forms of lung injury and future directions for further investigation.

Upregulation of Aquaporin 1 Mediates Increased Migration and Proliferation in Pulmonary Vascular Cells From the Rat SU5416/Hypoxia Model of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disorder characterized by exuberant vascular remodeling leading to elevated pulmonary arterial pressure, maladaptive right ventricular remodeling, and eventual death. The factors controlling pulmonary arterial smooth muscle cell (PASMC) and endothelial cell hyperplasia and migration, hallmark features of the vascular remodeling observed in PAH, remain poorly understood. We previously demonstrated that hypoxia upregulates the expression of aquaporin 1 (AQP1), a water channel, in PASMCs, and that this upregulation was required for hypoxia-induced migration and proliferation. However, whether the same is true in a model of severe PAH and in pulmonary microvascular endothelial cells (MVECs) is unknown. In this study, we used the SU5416 plus hypoxia (SuHx) rat model of severe pulmonary hypertension, which mimics many of the features of human PAH, to determine whether AQP1 levels were altered in PASMCs and MVECs and contributed to a hyperproliferative/hypermigratory phenotype. Rats received a single injection of SU5416 (20 mg/kg) and then were placed in 10% O2 for 3 weeks, followed by a return to normoxic conditions for an additional 2 weeks. We found that AQP1 protein levels were increased in both PASMCs and MVECs from SuHx rats, even in the absence of sustained hypoxic exposure, and that in MVECs, the increase in protein expression was associated with upregulation of AQP1 mRNA levels. Silencing of AQP1 had no significant effect on PASMCs from control animals but normalized enhanced migration and proliferation observed in cells from SuHx rats. Loss of AQP1 also reduced migration and proliferation in MVECs from SuHx rats. Finally, augmenting AQP1 levels in MVECs from control rats using forced expression was sufficient to increase migration and proliferation. These results demonstrate a key role for enhanced AQP1 expression in mediating abnormal migration and proliferation in pulmonary vascular cells from a rodent model that reflects many of the features of human PAH.

NF-κB/p65 Competes With Peroxisome Proliferator-Activated Receptor Gamma for Transient Receptor Potential Channel 6 in Hypoxia-Induced Human Pulmonary Arterial Smooth Muscle Cells

Objective: Peroxisome proliferator-activated receptor gamma (PPARγ) has an anti-proliferation effect on pulmonary arterial smooth muscle cells (PASMCs) via the transient receptor potential channel (TRPC) and protects against pulmonary artery hypertension (PAH), whereas nuclear factor-kappa B (NF-κB) has pro-proliferation and pro-inflammation effects, which contributes to PAH. However, the association between them in PAH pathology remains unclear. Therefore, this study aimed to investigate this association and the mechanisms underlying TRPC1/6 signaling-mediated PAH.

Methods: Human pulmonary arterial smooth muscle cells (hPASMCs) were transfected with p65 overexpressing (pcDNA-p65) and interfering plasmids (shp65) and incubated in normal and hypoxic conditions (4% O₂ and 72 h). The effects of hypoxia and p65 expression on cell proliferation, invasion, apoptosis, [Ca²⁺]i, PPARγ, and TRPC1/6 expression were determined using Cell Counting Kit-8 (CCK-8), Transwell, Annexin V/PI, Fura-2/AM, and western blotting, respectively. In addition, the binding of p65 or PPARγ proteins to the TRPC6 promoter was validated using a dual-luciferase report assay, chromatin-immunoprecipitation-polymerase chain reaction (ChIP-PCR), and electrophoretic mobility shift assay (EMSA).

Results: Hypoxia inhibited hPASMC apoptosis and promoted cell proliferation and invasion. Furthermore, it increased [Ca²⁺]i and the expression of TRPC1/6, p65, and Bcl-2 proteins. Moreover, pcDNA-p65 had similar effects on hypoxia treatment by increasing TRPC1/6 expression, [Ca²⁺]i, hPASMC proliferation, and invasion. The dual-luciferase report and ChIP-PCR assays revealed three p65 binding sites and two PPARγ binding sites on the promoter region of TRPC6. In addition, hypoxia treatment and shPPARγ promoted the binding of p65 to the TRPC6 promoter, whereas shp65 promoted the binding of PPARγ to the TRPC6 promoter.

Conclusion: Competitive binding of NF-κB p65 and PPARγ to TRPC6 produced an anti-PAH effect.

Acetazolamide prevents hypoxia-induced reactive oxygen species generation and calcium release in pulmonary arterial smooth muscle

Upon sensing a reduction in local oxygen partial pressure, pulmonary vessels constrict, a phenomenon known as hypoxic pulmonary vasoconstriction. Excessive hypoxic pulmonary vasoconstriction can occur with ascent to high altitude and is a contributing factor to the development of high-altitude pulmonary edema. The carbonic anhydrase inhibitor, acetazolamide, attenuates hypoxic pulmonary vasoconstriction through stimulation of alveolar ventilation via modulation of acid-base homeostasis and by direct effects on pulmonary vascular smooth muscle. In pulmonary arterial smooth muscle cells (PASMCs), acetazolamide prevents hypoxia-induced increases in intracellular calcium concentration ([Ca²⁺]_i), although the exact mechanism by which this occurs is unknown. In this study, we explored the effect of acetazolamide on various calcium-handling pathways in PASMCs. Using fluorescent microscopy, we tested whether acetazolamide directly inhibited store-operated calcium entry or calcium release from the sarcoplasmic reticulum, two well-documented sources of hypoxia-induced increases in [Ca²⁺]_i in PASMCs. Acetazolamide had no effect on calcium entry stimulated by store-depletion, nor on calcium release from the sarcoplasmic reticulum induced by either phenylephrine to activate inositol triphosphate receptors or caffeine to activate ryanodine receptors. In contrast, acetazolamide completely prevented Ca²⁺-release from the sarcoplasmic reticulum induced by hypoxia (4% O₂). Since these results suggest the acetazolamide interferes with a mechanism upstream of the inositol triphosphate and ryanodine receptors, we also determined whether acetazolamide might prevent hypoxia-induced changes in reactive oxygen species production. Using roGFP, a ratiometric reactive oxygen species-sensitive fluorescent probe, we found that hypoxia caused a significant increase in reactive oxygen species in PASMCs that was prevented by 100 μM acetazolamide. Together, these results suggest that acetazolamide prevents hypoxia-induced changes in [Ca²⁺]_i by attenuating reactive oxygen species production and subsequent activation of Ca²⁺-release from sarcoplasmic reticulum stores.

The involvement of TRPV4 on the hypoxia-induced oxidative neurotoxicity and apoptosis in a neuronal cell line: Protective role of melatonin

The hypoxia (HYPX)-mediated excessive generation of mitochondrial free reactive oxygen species (mROS) and the overload Ca²⁺ influx via the inhibition of TRPV4 are controlled by the treatment of antioxidants. However, the molecular mechanisms underlying melatonin (MLT)'s neuroprotection remains elusive. We investigated the role of MLT via modulation of TRPV4 on oxidative neurodegeneration and death in SH-SY5Y neuronal cells. The SH-SY5Y cells were divided into five groups as follows: control, MLT (1 mM for 2 h), HYPX (200 μM CoCl₂ for 24 h), HYPX + MLT, and HYPX + TRPV4 blockers (ruthenium red-1 μM for 30 min). The HYPX caused to the increase of TRPV4 current density and overload Ca²⁺ influx with an increase of mitochondrial membrane potential and mROS generation. The changes were not observed in the absence of TRPV4. When HYPX exposure and TRPV4 agonist (GSK1016790A)-induced TRPV4 activity were inhibited by the treatment of ruthenium red or MLT, the increase of mROS, lipid peroxidation, apoptosis, Zn²⁺ concentrations, TRPV4, caspase -3, caspase -9, Bax, and Bcl-2 expressions were restored via upregulation of reduced glutathione, glutathione peroxidase, and total antioxidant status. The levels of apoptosis and cell death in the cells were enriched with increases of caspase -3 and -9 activations, although they were decreased by MLT treatment. In conclusion, the treatment of MLT modulates HYPX-mediated mROS, apoptosis, and TRPV4-mediated overload Ca²⁺ influx and may provide an avenue for protecting HYPX-mediated neurological diseases associated with the increase of mROS, Ca²⁺, and Zn²⁺ concentration.

Mechanosensitivity in Pulmonary Circulation: Pathophysiological Relevance of Stretch-Activated Channels in Pulmonary Hypertension

A variety of cell types in pulmonary arteries (endothelial cells, fibroblasts, and smooth muscle cells) are continuously exposed to mechanical stimulations such as shear stress and pulsatile blood pressure, which are altered under conditions of pulmonary hypertension (PH). Most functions of such vascular cells (e.g., contraction, migration, proliferation, production of extracellular matrix proteins, etc.) depend on a key event, i.e., the increase in intracellular calcium concentration ([Ca²⁺]_i) which results from an influx of extracellular Ca²⁺ and/or a release of intracellular stored Ca²⁺. Calcium entry from the extracellular space is a major step in the elevation of [Ca²⁺]_i, involving a variety of plasmalemmal Ca²⁺ channels including the superfamily of stretch-activated channels (SAC). A common characteristic of SAC is that their gating depends on membrane stretch. In general, SAC are non-selective Ca²⁺-permeable cation channels, including proteins of the TRP (Transient Receptor Potential) and Piezo channel superfamily. As membrane mechano-transducers, SAC convert physical forces into biological signals and hence into a cell response. Consequently, SAC play a major role in pulmonary arterial calcium homeostasis and, thus, appear as potential novel drug targets for a better management of PH.

Reactive Oxygen Species and Endothelial Ca2+ Signaling: Brothers in Arms or Partners in Crime?

An increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) controls virtually all endothelial cell functions and is, therefore, crucial to maintain cardiovascular homeostasis. An aberrant elevation in endothelial can indeed lead to severe cardiovascular disorders. Likewise, moderate amounts of reactive oxygen species (ROS) induce intracellular Ca²⁺ signals to regulate vascular functions, while excessive ROS production may exploit dysregulated Ca²⁺ dynamics to induce endothelial injury. Herein, we survey how ROS induce endothelial Ca²⁺ signals to regulate vascular functions and, vice versa, how aberrant ROS generation may exploit the Ca²⁺ handling machinery to promote endothelial dysfunction. ROS elicit endothelial Ca²⁺ signals by regulating inositol-1,4,5-trisphosphate receptors, sarco-endoplasmic reticulum Ca²⁺-ATPase 2B, two-pore channels, store-operated Ca²⁺ entry (SOCE), and multiple isoforms of transient receptor potential (TRP) channels. ROS-induced endothelial Ca²⁺ signals regulate endothelial permeability, angiogenesis, and generation of vasorelaxing mediators and can be exploited to induce therapeutic angiogenesis, rescue neurovascular coupling, and induce cancer regression. However, an increase in endothelial [Ca²⁺]_i induced by aberrant ROS formation may result in endothelial dysfunction, inflammatory diseases, metabolic disorders, and pulmonary artery hypertension. This information could pave the way to design alternative treatments to interfere with the life-threatening interconnection between endothelial ROS and Ca²⁺ signaling under multiple pathological conditions.

Contribution of non-selective membrane channels and receptors in epilepsy

Overcoming refractory epilepsy's resistance to the combination of antiepileptic drugs (AED), mitigating side effects, and preventing sudden unexpected death in epilepsy are critical goals for therapy of this disorder. Current therapeutic strategies are based primarily on neurocentric mechanisms, overlooking the participation of astrocytes and microglia in the pathophysiology of epilepsy. This review is focused on a set of non-selective membrane channels (permeable to ions and small molecules), including channels and ionotropic receptors of neurons, astrocytes, and microglia, such as: the hemichannels formed by Cx43 and Panx1; the purinergic P2X7 receptors; the transient receptor potential vanilloid (TRPV1 and TRPV4) channels; calcium homeostasis modulators (CALHMs); transient receptor potential canonical (TRPC) channels; transient receptor potential melastatin (TRPM) channels; voltage-dependent anion channels (VDACs) and volume-regulated anion channels (VRACs), which all have in common being activated by epileptic activity and the capacity to exacerbate seizure intensity. Specifically, we highlight evidence for the activation of these channels/receptors during epilepsy including neuroinflammation and oxidative stress, discuss signaling pathways and feedback mechanisms, and propose the functions of each of them in acute and chronic epilepsy. Studying the role of these non-selective membrane channels in epilepsy and identifying appropriate blockers for one or more of them could provide complementary therapies to better alleviate the disease.

Oct4-dependent FoxC1 activation improves the survival and neovascularization of mesenchymal stem cells under myocardial ischemia

Background

The administration of mesenchymal stem cells (MSCs) remains the most promising approach for cardiac repair after myocardial infarct (MI). However, their poor survival and potential in the ischemic environment limit their therapeutic efficacy for heart repair after MI. The purpose of this study was to investigate the influence of FoxC1-induced vascular niche on the activation of octamer-binding protein 4 (Oct4) and the fate of MSCs under hypoxic/ischemic conditions.

Methods

Vascular microenvironment/niche was induced by efficient delivery of FoxC1 transfection into hypoxic endothelial cells (ECs) or infarcted hearts. MSCs were cultured or injected into this niche by utilizing an in vitro coculture model and a rat MI model. Survival and neovascularization of MSCs regulated by Oct4 were explored using gene transfer and functional studies.

Results

Here, using gene expression heatmap, we demonstrated that cardiac ECs rapidly upregulated FoxC1 after acute ischemic cardiac injury, contributing to an intrinsic angiogenesis. In vitro, FoxC1 accelerated tube-like structure formation and increased survival of ECs, resulting in inducing a vascular microenvironment. Overexpression of FoxC1 in ECs promoted survival and neovascularization of MSCs under hypoxic coculture. Overexpression of Oct4, a FoxC1 target gene, in MSCs enhanced their mesenchymal-to-endothelial transition (MEndoT) while knockdown of Oct4 by siRNA altering vascularization. In a rat MI model, overexpression of FoxC1 in ischemic hearts increased post-infarct vascular density and improved cardiac function. The transplantation of adOct4-pretreated MSCs into these ischemic niches augments MEndoT, enhanced vascularity, and further improved cardiac function. Consistently, these cardioprotective effects of FoxC1 was abrogated when Oct4 was depleted in the MSCs and was mimicked by overexpression of Oct4.

Conclusions

Together, these studies demonstrate that the FoxC1/Oct4 axis is an essential aspect for survival and neovascularization of MSCs in the ischemic conditions and represents a potential therapeutic target for enhancing cardiac repair.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02553-w.

Hypoxia and the integrated stress response promote pulmonary hypertension and preeclampsia: Implications in drug development

Chronic hypoxia is a common cause of pulmonary hypertension, preeclampsia, and intrauterine growth restriction (IUGR). The molecular mechanisms underlying these diseases are not completely understood. Chronic hypoxia may induce the generation of reactive oxygen species (ROS) in mitochondria, promote endoplasmic reticulum (ER) stress, and result in the integrated stress response (ISR) in the pulmonary artery and uteroplacental tissues. Numerous studies have implicated hypoxia-inducible factors (HIFs), oxidative stress, and ER stress/unfolded protein response (UPR) in the development of pulmonary hypertension, preeclampsia and IUGR. This review highlights the roles of HIFs, mitochondria-derived ROS and UPR, as well as their interplay, in the pathogenesis of pulmonary hypertension and preeclampsia, and their implications in drug development.

Thermosensory Transient Receptor Potential Ion Channels and Asthma

Asthma is a widespread chronic disease of the bronchopulmonary system with a heterogeneous course due to the complex etiopathogenesis. Natural-climatic and anthropogenic factors play an important role in the development and progression of this pathology. The reception of physical and chemical environmental stimuli and the regulation of body temperature are mediated by thermosensory channels, members of a subfamily of transient receptor potential (TRP) ion channels. It has been found that genes encoding vanilloid, ankyrin, and melastatin TRP channels are involved in the development of some asthma phenotypes and in the formation of exacerbations of this pathology. The review summarizes modern views on the role of high and low temperatures in airway inflammation in asthma. The participation of thermosensory TRP channels (vanilloid, ankyrin, and melastatin TRP channels) in the reaction to high and low temperatures and air humidity as well as in the formation of bronchial hyperreactivity and respiratory symptoms accompanying asthma is described. The genetic aspects of the functioning of thermosensory TRP channels are discussed. It is shown that new methods of treatment of asthma exacerbations caused by the influence of temperature and humidity should be based on the regulation of channel activity.

Hydrogen Sulfide Metabolism and Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe and multifactorial disease characterized by a progressive elevation of pulmonary arterial resistance and pressure due to remodeling, inflammation, oxidative stress, and vasoreactive alterations of pulmonary arteries (PAs). Currently, the etiology of these pathological features is not clearly understood and, therefore, no curative treatment is available. Since the 1990s, hydrogen sulfide (H₂S) has been described as the third gasotransmitter with plethoric regulatory functions in cardiovascular tissues, especially in pulmonary circulation. Alteration in H₂S biogenesis has been associated with the hallmarks of PH. H₂S is also involved in pulmonary vascular cell homeostasis via the regulation of hypoxia response and mitochondrial bioenergetics, which are critical phenomena affected during the development of PH. In addition, H₂S modulates ATP-sensitive K⁺ channel (K_ATP) activity, and is associated with PA relaxation. In vitro or in vivo H₂S supplementation exerts antioxidative and anti-inflammatory properties, and reduces PA remodeling. Altogether, current findings suggest that H₂S promotes protective effects against PH, and could be a relevant target for a new therapeutic strategy, using attractive H₂S-releasing molecules. Thus, the present review discusses the involvement and dysregulation of H₂S metabolism in pulmonary circulation pathophysiology.

Role of TRPV4 channel in vasodilation and neovascularization

The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca²⁺ -permeable nonselective cation channel, is widely distributed in the circulatory system, particularly in vascular endothelial cells (ECs) and smooth muscle cells (SMCs). The TRPV4 channel is activated by various endogenous and exogenous stimuli, including shear stress, low intravascular pressure, and arachidonic acid. TRPV4 has a role in mediating vascular tone and arterial blood pressure. The activation of the TRPV4 channel induces Ca²⁺ influx, thereby resulting in endothelium-dependent hyperpolarization and SMC relaxation through SK_Ca and IK_Ca activation on ECs or through BK_Ca activation on SMCs. Ca²⁺ binds to calmodulin, which leads to the production of nitric oxide, causing vasodilation. Furthermore, the TRPV4 channel plays an important role in angiogenesis and arteriogenesis and is critical for tumor angiogenesis and growth, since it promotes or inhibits the development of various types of cancer. The TRPV4 channel is involved in the active growth of collateral arteries induced by flow shear stress, which makes it a promising therapeutic target in the occlusion or stenosis of the main arteries. In this review, we explore the role and the potential mechanism of action of the TRPV4 channel in the regulation of vascular tone and in the induction of neovascularization to provide a reference for future research.

Bioinformatic analysis and validation of microRNA-508-3p as a protective predictor by targeting NR4A3/MEK axis in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) featured a debilitating progressive disorder. Here, we intend to determine diagnosis‐valuable biomarkers for PAH and decode the fundamental mechanisms of the biological function of these markers. Two mRNA microarray profiles (GSE70456 and GSE117261) and two microRNA microarray profiles (GSE55427 and GSE67597) were mined from the Gene Expression Omnibus platform. Then, we identified the differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs), respectively. Besides, we investigated online miRNA prediction tools to screen the target gene of DEMs. In this study, 185 DEGs and three common DEMs were screened as well as 1266 target genes of the three DEMs were identified. Next, 16 overlapping dysregulated genes from 185 DEGs and 1266 target gene were obtained. Meanwhile, we constructed the miRNA gene regulatory network and determined miRNA‐508‐3p‐NR4A3 pair for deeper exploring. Experiment methods verified the functional expression of miR‐508‐3p in PAH and its signalling cascade. We observed that ectopic miR‐508‐3p expression promotes proliferation and migration of pulmonary artery smooth muscle cell (PASMC). Bioinformatic, dual‐luciferase assay showed NR4A3 represents directly targeted gene of miR‐508‐3p. Mechanistically, we demonstrated that down‐regulation of miR‐508‐3p advances PASMC proliferation and migration via inducing NR4A3 to activate MAPK/ERK kinase signalling pathway. Altogether, our research provides a promising diagnosis of predictor and therapeutic avenues for patients in PAH.

Endothelial Transient Receptor Potential V4 Channels Mediate Lung Ischemia-Reperfusion Injury

BACKGROUND

Lung ischemia-reperfusion injury (IRI), involving severe inflammation and edema, is a major cause of primary graft dysfunction following transplant. Activation of transient receptor potential vanilloid 4 (TRPV4) channels modulates vascular permeability. Thus, this study tests the hypothesis that endothelial TRPV4 channels mediate lung IRI.

METHODS

C57BL/6 wild-type (WT), TRPV4^-/-, tamoxifen-inducible endothelial TRPV4 knockout (TRPV4_EC^-/-), and tamoxifen-treated control (TRPV4^fl/fl) mice underwent lung IR using a left lung hilar-ligation model (n≥6 mice/group). WT mice were also treated with a TRPV4-specific inhibitor (GSK2193874; 1mg/kg) (WT+GSK219). Partial pressure of oxygen (PaO₂), edema (wet-to-dry weight ratio), compliance, neutrophil infiltration, and cytokine concentrations in bronchioalveolar lavage fluid were assessed. Pulmonary microvascular endothelial cells (PMVECs) were characterized in vitro following exposure to hypoxia-reoxygenation.

RESULTS

Compared to WT, PaO₂ following IR was significantly improved in TRPV4^-/- mice (133.1±43.9 vs 427.8±83.1 mmHg, p<0.001) and WT+GSK219 mice (133.1±43.9 vs 447.0±67.6 mmHg, p<0.001). Pulmonary edema and neutrophil infiltration were also significantly reduced after IR in TRPV4^-/- and WT+GSK219 mice versus WT. TRPV4_EC^-/- mice following IR demonstrated significantly improved oxygenation versus control (109.2±21.6 vs 405.3±41.4 mmHg, p<0.001) as well as significantly improved compliance, and significantly less edema, neutrophil infiltration and proinflammatory cytokine production (TNF-α, CXCL1, IL-17, IFN-γ). Hypoxia-reoxygenation-induced permeability and CXCL1 expression by PMVECs was significantly attenuated by TRPV4 inhibitors.

CONCLUSIONS

Endothelial TRPV4 plays a key role in vascular permeability and lung inflammation following IR. TRPV4 channels may be a promising therapeutic target to mitigate lung IRI and decrease the incidence of primary graft dysfunction following transplant. (Word Count: 249/250).

Cyanidin‑3‑O‑β‑glucoside protects against pulmonary artery hypertension induced by monocrotaline via the TGF‑β1/p38 MAPK/CREB signaling pathway

Pulmonary artery hypertension (PAH) is a disease with high morbidity and mortality. Cyanidin‑3‑O‑β‑glucoside (Cy‑3‑g), a classical anthocyanin, has a variety of biological effects. The present study evaluated whether Cy‑3‑g attenuated PAH, and explored the potential mechanism of action. Rats were injected with monocrotaline (MCT; 60 mg per kg of body weight) and then treated with Cy‑3‑g (200 or 400 mg per kg of body weight) for 4 weeks. Protein expression was determined in vitro in transforming growth factor‑β1 (TGF‑β1)‑mediated human pulmonary arterial smooth muscle cells (SMCs). The results indicated that Cy‑3‑g significantly inhibited the mean pulmonary artery pressure, right ventricular systolic pressure and right ventricular hypertrophy index, as well as vascular remodeling induced by MCT in PAH rats. Further experiments showed that Cy‑3‑g suppressed the expression of pro‑-inflammatory factors and enhanced the levels of anti‑inflammatory factors. Cy‑3‑g blocked oxidative stress and improved vascular endothelial injury. Cy‑3‑g also reduced the proliferation of SMCs. Furthermore, the MCT‑ and TGF‑β1‑induced increase in TGF‑β1, phosphorylated (p)‑p38 mitogen‑activated protein kinase (MAPK) and p‑cAMP‑response element binding protein (CREB) expression was blocked by Cy‑3‑g treatment in vivo and in vitro. These results indicated that Cy‑3‑g could prevent vascular remodeling in PAH via inhibition of the TGF‑β1/p38 MAPK/CREB axis.

Caveolar peroxynitrite formation impairs endothelial TRPV4 channels and elevates pulmonary arterial pressure in pulmonary hypertension

Recent studies have focused on the contribution of capillary endothelial TRPV4 channels to pulmonary pathologies, including lung edema and lung injury. However, in pulmonary hypertension (PH), small pulmonary arteries are the focus of the pathology, and endothelial TRPV4 channels in this crucial anatomy remain unexplored in PH. Here, we provide evidence that TRPV4 channels in endothelial cell caveolae maintain a low pulmonary arterial pressure under normal conditions. Moreover, the activity of caveolar TRPV4 channels is impaired in pulmonary arteries from mouse models of PH and PH patients. In PH, up-regulation of iNOS and NOX1 enzymes at endothelial cell caveolae results in the formation of the oxidant molecule peroxynitrite. Peroxynitrite, in turn, targets the structural protein caveolin-1 to reduce the activity of TRPV4 channels. These results suggest that endothelial caveolin-1-TRPV4 channel signaling lowers pulmonary arterial pressure, and impairment of endothelial caveolin-1-TRPV4 channel signaling contributes to elevated pulmonary arterial pressure in PH. Thus, inhibiting NOX1 or iNOS activity, or lowering endothelial peroxynitrite levels, may represent strategies for restoring vasodilation and pulmonary arterial pressure in PH.

Role of Transient Receptor Potential Vanilloid 4 in Vascular Function

Transient receptor potential vanilloid 4 (TRPV4) channels are widely expressed in systemic tissues and can be activated by many stimuli. TRPV4, a Ca²⁺-permeable cation channel, plays an important role in the vasculature and is implicated in the regulation of cardiovascular homeostasis processes such as blood pressure, vascular remodeling, and pulmonary hypertension and edema. Within the vasculature, TRPV4 channels are expressed in smooth muscle cells, endothelial cells, and perivascular nerves. The activation of endothelial TRPV4 contributes to vasodilation involving nitric oxide, prostacyclin, and endothelial-derived hyperpolarizing factor pathways. TRPV4 activation also can directly cause vascular smooth muscle cell hyperpolarization and vasodilation. In addition, TRPV4 activation can evoke constriction in some specific vascular beds or under some pathological conditions. TRPV4 participates in the control of vascular permeability and vascular damage, particularly in the lung capillary endothelial barrier and lung injury. It also participates in vascular remodeling regulation mainly by controlling vasculogenesis and arteriogenesis. This review examines the role of TRPV4 in vascular function, particularly in vascular dilation and constriction, vascular permeability, vascular remodeling, and vascular damage, along with possible mechanisms, and discusses the possibility of targeting TRPV4 for therapy.

Activation of transient receptor potential vanilloid channel 4 contributes to the development of ethanol-induced gastric injury in mice

The transient receptor potential vanilloid channel 4 (TRPV4) is associated with the development of several pathologies, particularly gastric disorders. However, there are no studies associating this receptor with the pathophysiology of gastric erosions. The aim of this study was to investigate the role of TRPV4 in the development of ethanol-induced gastric damage in vivo. Gastric lesions were induced by ethanol in Swiss mice pretreated with TRPV4 antagonists, GSK2193874 (0.1; 0.3 and 0.9 mg/kg) or Ruthenium red (0.03; 0.1 or 0.3 mg/kg) or its agonist, GSK1016790A (0.9 mg/kg). Gastric mucosal samples were taken for histopathology, immunohistochemistry, atomic force microscopy and evaluation of antioxidant parameters. The gastric mucus content and TRPV4 mRNA expression were analyzed. Ethanol exposure induced upregulation of gastric mRNA and protein expression of TRPV4. TRPV4 blockade promoted gastroprotection against ethanol-induced injury on macro- and microscopic levels, leading to reduced hemorrhage, cell loss and edema and enhanced gastric mucosal integrity. Moreover, an increase in superoxide dismutase (SOD) and glutathione (GSH) activity was observed, followed by a decrease in malondialdehyde (MDA) levels. TRPV4 blockade during alcohol challenge reestablished gastric mucus content. The combination of TRPV4 agonist and ethanol revealed macroscopic exacerbation of gastric damage area. Our results confirmed the association of TRPV4 with the development of gastric injury, showing the importance of this receptor for further investigations in the field of gastrointestinal pathophysiology and pharmacology.

Ca2+ Signaling by TRPV4 Channels in Respiratory Function and Disease

Members of the transient receptor potential (TRP) superfamily are broadly expressed in our body and contribute to multiple cellular functions. Most interestingly, the fourth member of the vanilloid family of TRP channels (TRPV4) serves different partially antagonistic functions in the respiratory system. This review highlights the role of TRPV4 channels in lung fibroblasts, the lung endothelium, as well as the alveolar and bronchial epithelium, during physiological and pathophysiological mechanisms. Data available from animal models and human tissues confirm the importance of this ion channel in cellular signal transduction complexes with Ca²⁺ ions as a second messenger. Moreover, TRPV4 is an excellent therapeutic target with numerous specific compounds regulating its activity in diseases, like asthma, lung fibrosis, edema, and infections.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

Selenium and Neurological Diseases: Focus on Peripheral Pain and TRP Channels

Pain is a complex physiological process that includes many components. Growing evidence supports the idea that oxidative stress and Ca2+ signaling pathways participate in pain detection by neurons. The main source of endogenous reactive oxygen species (ROS) is mitochondrial dysfunction induced by membrane depolarization, which is in turn caused by Ca2+ influx into the cytosol of neurons. ROS are controlled by antioxidants, including selenium. Selenium plays an important role in the nervous system, including the brain, where it acts as a cofactor for glutathione peroxidase and is incorporated into selenoproteins involved in antioxidant defenses. It has neuroprotective effects through modulation of excessive ROS production, inflammation, and Ca2+ overload in several diseases, including inflammatory pain, hypersensitivity, allodynia, diabetic neuropathic pain, and nociceptive pain. Ca2+ entry across membranes is mediated by different channels, including transient receptor potential (TRP) channels, some of which (e.g., TRPA1, TRPM2, TRPV1, and TRPV4) can be activated by oxidative stress and have a role in the induction of peripheral pain. The results of recent studies indicate the modulator roles of selenium in peripheral pain through inhibition of TRP channels in the dorsal root ganglia of experimental animals. This review summarizes the protective role of selenium in TRP channel regulation, Ca2+ signaling, apoptosis, and mitochondrial oxidative stress in peripheral pain induction.

NDUFA4L2 in smooth muscle promotes vascular remodeling in hypoxic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascular resistance and obliterative pulmonary vascular remodelling (PVR). The imbalance between the proliferation and apoptosis of pulmonary artery smooth muscle cells (PASMCs) is an important cause of PVR leading to PAH. Mitochondria play a key role in the production of hypoxia-induced pulmonary hypertension (HPH). However, there are still many issues worth studying in depth. In this study, we demonstrated that NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 like 2 (NDUFA4L2) was a proliferation factor and increased in vivo and in vitro through various molecular biology experiments. HIF-1α was an upstream target of NDUFA4L2. The plasma levels of 4-hydroxynonene (4-HNE) were increased both in PAH patients and hypoxic PAH model rats. Knockdown of NDUFA4L2 decreased the levels of malondialdehyde (MDA) and 4-HNE in human PASMCs in hypoxia. Elevated MDA and 4-HNE levels might be associated with excessive ROS generation and increased expression of 5-lipoxygenase (5-LO) in hypoxia, but this effect was blocked by siNDUFA4L2. Further research found that p38-5-LO was a downstream signalling pathway of PASMCs proliferation induced by NDUFA4L2. Up-regulated NDUFA4L2 plays a critical role in the development of HPH, which mediates ROS production and proliferation of PASMCs, suggesting NDUFA4L2 as a potential new therapeutic target for PAH.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Vasoconstrictor Mechanisms in Chronic Hypoxia-Induced Pulmonary Hypertension: Role of Oxidant Signaling

Elevated resistance of pulmonary circulation after chronic hypoxia exposure leads to pulmonary hypertension. Contributing to this pathological process is enhanced pulmonary vasoconstriction through both calcium-dependent and calcium sensitization mechanisms. Reactive oxygen species (ROS), as a result of increased enzymatic production and/or decreased scavenging, participate in augmentation of pulmonary arterial constriction by potentiating calcium influx as well as activation of myofilament sensitization, therefore mediating the development of pulmonary hypertension. Here, we review the effects of chronic hypoxia on sources of ROS within the pulmonary vasculature including NADPH oxidases, mitochondria, uncoupled endothelial nitric oxide synthase, xanthine oxidase, monoamine oxidases and dysfunctional superoxide dismutases. We also summarize the ROS-induced functional alterations of various Ca2+ and K+ channels involved in regulating Ca2+ influx, and of Rho kinase that is responsible for myofilament Ca2+ sensitivity. A variety of antioxidants have been shown to have beneficial therapeutic effects in animal models of pulmonary hypertension, supporting the role of ROS in the development of pulmonary hypertension. A better understanding of the mechanisms by which ROS enhance vasoconstriction will be useful in evaluating the efficacy of antioxidants for the treatment of pulmonary hypertension.

Endoplasmic reticulum Ca2+ release causes Rieske iron-sulfur protein-mediated mitochondrial ROS generation in pulmonary artery smooth muscle cells

Mitochondrial reactive oxygen species (ROS) cause Ca²⁺ release from the endoplasmic reticulum (ER) via ryanodine receptors (RyRs) in pulmonary artery smooth muscle cells (PASMCs), playing an essential role in hypoxic pulmonary vasoconstriction (HPV). Here we tested a novel hypothesis that hypoxia-induced RyR-mediated Ca²⁺ release may, in turn, promote mitochondrial ROS generation contributing to hypoxic cellular responses in PASMCs. Our data reveal that application of caffeine to elevate intracellular Ca²⁺ concentration ([Ca²⁺]_i) by activating RyRs results in a significant increase in ROS production in cytosol and mitochondria of PASMCs. Norepinephrine to increase [Ca²⁺]_i due to the opening of inositol 1,4,5-triphosphate receptors (IP3Rs) produces similar effects. Exogenous Ca²⁺ significantly increases mitochondrial-derived ROS generation as well. Ru360 also inhibits the hypoxic ROS production. The RyR antagonist tetracaine or RyR2 gene knockout (KO) suppresses hypoxia-induced responses as well. Inhibition of mitochondrial Ca²⁺ uptake with Ru360 eliminates N- and Ca²⁺-induced responses. RISP KD abolishes the hypoxia-induced ROS production in mitochondria of PASMCs. Rieske iron–sulfur protein (RISP) gene knockdown (KD) blocks caffeine- or NE-induced ROS production. Taken together, these findings have further demonstrated that ER Ca²⁺ release causes mitochondrial Ca²⁺ uptake and RISP-mediated ROS production; this novel local ER/mitochondrion communication-elicited, Ca²⁺-mediated, RISP-dependent ROS production may play a significant role in hypoxic cellular responses in PASMCs.