Important role of PLC-γ1 in hypoxic increase in intracellular calcium in pulmonary arterial smooth muscle cells

Cytotoxicity effect and transcriptome analysis of PCV3-infected cells revealed potential viral pathogenic mechanisms

Porcine circovirus type 3 (PCV3) has become an important pathogen in the global swine industry and poses a threat to pig health, but its pathogenic mechanism remains unknown. In this study, we constructed an innovative, linear infectious clone of PCV3 for rescuing the virus, and explored the transcriptome of infected cells to gain insights into its pathogenic mechanisms. Subsequently, an in vivo experiment was conducted to evaluate the pathogenicity of the rescued virus in pig. PCV3 nucleic acid was distributed across various organs, indicating systemic circulation via the bloodstream and viremia. Immunohistochemical staining also revealed a significant presence of PCV3 antigens in the spleen, lungs, and lymph nodes, indicating that PCV3 had tropism for these organs. Transcriptome analysis of infected ST cells revealed differential expression of genes associated with apoptosis, immune responses, and cellular metabolism. Notably, upregulation of genes related to the hypoxia-inducible factor-1 pathway, glycolysis, and the AGE/RAGE pathway suggests activation of inflammatory responses, ultimately leading to onset of disease. These findings have expanded our understanding of PCV3 pathogenesis, and the interplay between PCV3 and host factors.

Neuroprotective effect of chrysophanol in Alzheimer disease via modulating the Ca2+/EGFR-PLCγ pathway

Chrysophanol (CHR) is an anthraquinone compound found in rhubarb, and it possesses neuroprotective properties. The purpose of this study was to gain a better understanding of its role in Alzheimer's disease (AD). In vivo study, D-galactose combined with intracerebral injection of β-protein 25-35(Aβ25-35) were used to establish AD model rats. In vitro study, Aβ25-35 was used to induce AD model cells. Our results indicated that CHR improves learning and memory in AD model rats and provides protection against neuronal damage in both AD model rats and cells. Additionally, we observed that CHR suppressed the protein expression of p-tau, EGFR, PLCγ, IP3R, and CAM, as well as the mRNA levels of tau, EGFR, PLCγ, IP3R, and CAM. Furthermore, we have confirmed that CHR inhibited the fluorescence expression of calcium ions (Ca2+). In conclusion, the CHR may exert neuroprotective effects in AD by reducing tau phosphorylation through the Ca2+/EGFR-PLCγ pathway.

Role of ryanodine receptor 2 and FK506-binding protein 12.6 dissociation in pulmonary hypertension

Pulmonary hypertension (PH) is a devastating disease characterized by a progressive increase in pulmonary arterial pressure leading to right ventricular failure and death. A major cellular response in this disease is the contraction of smooth muscle cells (SMCs) of the pulmonary vasculature. Cell contraction is determined by the increase in intracellular Ca2+ concentration ([Ca2+]i), which is generated and regulated by various ion channels. Several studies by us and others have shown that ryanodine receptor 2 (RyR2), a Ca2+-releasing channel in the sarcoplasmic reticulum (SR), is an essential ion channel for the control of [Ca2+]i in pulmonary artery SMCs (PASMCs), thereby mediating the sustained vasoconstriction seen in PH. FK506-binding protein 12.6 (FKBP12.6) strongly associates with RyR2 to stabilize its functional activity. FKBP12.6 can be dissociated from RyR2 by a hypoxic stimulus to increase channel function and Ca2+ release, leading to pulmonary vasoconstriction and PH. More specifically, dissociation of the RyR2-FKBP12.6 complex is a consequence of increased mitochondrial ROS generation mediated by the Rieske iron-sulfur protein (RISP) at the mitochondrial complex III after hypoxia. Overall, RyR2/FKBP12.6 dissociation and the corresponding signaling pathway may be an important factor in the development of PH. Novel drugs and biologics targeting RyR2, FKBP12.6, and related molecules may become unique effective therapeutics for PH.

The Potential Important Role of Mitochondrial Rieske Iron–Sulfur Protein as a Novel Therapeutic Target for Pulmonary Hypertension in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide, which is often due to pulmonary hypertension (PH). The underlying molecular mechanisms are poorly understood, and current medications are neither specific nor always effective. In this review, we highlight the recent findings on the roles of altered mitochondrial bioenergetics in PH in COPD. We also discuss the central role of mitochondrial reactive oxygen species (ROS) generation mediated by Rieske iron–sulfur protein (RISP) and review the contributions of RISP-dependent DNA damage and NF-κB-associated inflammatory signaling. Finally, the potential importance of mitochondrial RISP and its associated molecules as novel therapeutic targets for PH in COPD are meticulously discussed.

Overview on Interactive Role of Inflammation, Reactive Oxygen Species, and Calcium Signaling in Asthma, COPD, and Pulmonary Hypertension

Inflammatory signaling is a major component in the development and progression of many lung diseases, including asthma, chronic obstructive pulmonary disorder (COPD), and pulmonary hypertension (PH). This chapter will provide a brief overview of asthma, COPD, and PH and how inflammation plays a vital role in these diseases. Specifically, we will discuss the role of reactive oxygen species (ROS) and Ca²⁺ signaling in inflammatory cellular responses and how these interactive signaling pathways mediate the development of asthma, COPD, and PH. We will also deliberate the key cellular responses of pulmonary arterial (PA) smooth muscle cells (SMCs) and airway SMCs (ASMCs) in these devastating lung diseases. The analysis of the importance of inflammation will shed light on the key questions remaining in this field and highlight molecular targets that are worth exploring. The crucial findings will not only demonstrate the novel roles of essential signaling molecules such as Rieske iron-sulfur protein and ryanodine receptor in the development and progress of asthma, COPD, and PH but also offer advanced insight for creating more effective and new therapeutic targets for these devastating inflammatory lung diseases.

EGFR inhibitors regulate Ca2+ concentration and apoptosis after PM2.5 exposure based on a lung-mimic microfluidic system

Air pollution has side effects on human health. Epidemiology studies indicate a positive association between ambient fine particle (PM_2.5, or particles less than 2.5 μm in diameter) concentration and lung cancer. However, how fine particles affect lung cancer at the molecular level and related therapeutic methods to address these diseases are unclear. Here, the multi-omics analysis (DNA methylation and transcriptomic) was used to detect human bronchial epithelial cells (HBE), that were exposed to PM_2.5 using a quantified, small, portable, and organ-level air-liquid interface microfluidic system that mimics lung functions. The results indicate that 36,838 differentially methylated genes were detected. Of these 33,796 genes were hypomethylated (beta < 0), and 2862 genes were hypermethylated (beta > 0). RNA-Seq analysis demonstrated that 19,489 genes were upregulated (log₂FC > 0), and 16,659 were downregulated. Furthermore, the calcium and apoptosis pathways were activated according to multi-omics analysis. The change in EGFR gene expression after PM_2.5 exposure was the result of alterations of the cellular DNA methylome in the promoter. Inhibition or down-regulation of EGFR could result in the regulation of the downstream intracellular Ca²⁺ concentration and apoptosis via the EGFR/PLCγ and EGFR/STAT/Bcl-XL pathways after PM_2.5 exposure. EGFR inhibitors decrease the Ca²⁺ concentration of cells, thereby strengthening the effects of fine particles on apoptosis. In short, the Ca²⁺ concentration and the apoptosis of cells can be regulated via EGFR related pathway after PM_2.5 exposure. The EGFR may be a potentially promising therapeutic target for the treatment of air pollution-induced lung cancer through regulation of the intracellular Ca²⁺ concentration and apoptosis.

Up-regulation of nPKC contributes to proliferation of mice pulmonary artery smooth muscle cells in hypoxia-induced pulmonary hypertension

This study is designed to investigate the role of novel protein kinases C (nPKC) in mediating pulmonary artery smooth muscle cells (PASMCs) proliferation in pulmonary hypertension (PH) and the underlying mechanisms. Mouse PASMCs was isolated using magnetic separation technology. The PASMCs were divided into 24 h group, 48 h group and 72 h group according to different hypoxia treatment time, then detected cell proliferation rate and nPKC expression level in each group. We treated PASMCs with agonists or inhibitors of PKCdelta (PKCδ) and PKCepsilon (PKCε) and exposed them to hypoxia or normoxia for 72 h, then measured the proliferation of PASMCs. We also constructed a lentiviral vector containing siRNA fragments for inhibiting PKCδ and PKCε to transfected PASMCs, then examined their proliferation. PASMCs isolated successfully by magnetic separation method and were in good condition. Hypoxia promoted the proliferation of PASMCs, and the treatment for 72 h had the most significant effect. Hypoxia upregulated the expression of PKCδ and PKCε in mouse PASMCs, leading to PASMCs proliferation. Moreover, Our study demonstrated that hypoxia induced upregulation of PKCδ and PKCε expression resulting to the proliferation of PASMCs via up-regulating the phosphorylation of AKT and ERK. Our study provides clear evidence that increased nPKC expression contributes to PASMCs proliferation and uncovers the correlation between AKT and ERK pathways and nPKC-mediated proliferation of PASMCs. These findings may provide novel targets for molecular therapy of pulmonary hypertension.

Rieske iron-sulfur protein induces FKBP12.6/RyR2 complex remodeling and subsequent pulmonary hypertension through NF-κB/cyclin D1 pathway

Ca2+ signaling in pulmonary arterial smooth muscle cells (PASMCs) plays an important role in pulmonary hypertension (PH). However, the underlying specific ion channel mechanisms remain largely unknown. Here, we report ryanodine receptor (RyR) channel activity and Ca2+ release both are increased, and association of RyR2 by FK506 binding protein 12.6 (FKBP12.6) is decreased in PASMCs from mice with chronic hypoxia (CH)-induced PH. Smooth muscle cell (SMC)-specific RyR2 knockout (KO) or Rieske iron-sulfur protein (RISP) knockdown inhibits the altered Ca2+ signaling, increased nuclear factor (NF)-κB/cyclin D1 activation and cell proliferation, and CH-induced PH in mice. FKBP12.6 KO or FK506 treatment enhances CH-induced PH, while S107 (a specific stabilizer of RyR2/FKBP12.6 complex) produces an opposite effect. In conclusion, CH causes RISP-dependent ROS generation and FKBP12.6/RyR2 dissociation, leading to PH. RISP inhibition, RyR2/FKBP12.6 complex stabilization and Ca2+ release blockade may be potentially beneficial for the treatment of PH.

Important Role of Sarcoplasmic Reticulum Ca2+ Release via Ryanodine Receptor-2 Channel in Hypoxia-Induced Rieske Iron-Sulfur Protein-Mediated Mitochondrial Reactive Oxygen Species Generation in Pulmonary Artery Smooth Muscle Cells

Aims: It is known that mitochondrial reactive oxygen species generation ([ROS]_m) causes the release of Ca²⁺via ryanodine receptor-2 (RyR2) on the sarcoplasmic reticulum (SR) in pulmonary artery smooth muscle cells (PASMCs), playing an essential role in hypoxic pulmonary vasoconstriction (HPV). In this study, we sought to determine whether hypoxia-induced RyR2-mediated Ca²⁺ release may in turn promote [ROS]_m in PASMCs and the underlying signaling mechanism. Results: Our data reveal that application of caffeine or norepinephrine to induce Ca²⁺ release increased [ROS]_m in PASMCs. Likewise, exogenous Ca²⁺ augmented ROS generation in isolated mitochondria and at complex III from PASMCs. Inhibition of mitochondrial Ca²⁺ uniporter (MCU) with Ru360 attenuated agonist-induced [ROS]_m. Ru360 produced a similar inhibitory effect on hypoxia-induced [ROS]_m. Rieske iron-sulfur protein (RISP) gene knockdown inhibited Ca²⁺- and caffeine-induced [ROS]_m. Inhibition of RyR2 by tetracaine or RyR2 gene knockout suppressed hypoxia-induced [ROS]_m as well. Innovation: In this article, we present convincing evidence that Ca²⁺ release following hypoxia or RyR simulation causes a significant increase in MCU, and the increased MCU subsequently RISP-dependent [ROS]_m, which provides a positive feedback mechanism to enhance hypoxia-initiated [ROS]_m in PASMCs. Conclusion: Our findings demonstrate that hypoxia-induced mitochondrial ROS-dependent SR RyR2-mediated Ca²⁺ release increases MCU and then RISP-dependent [ROS]_m in PASMCs, which may make significant contributions to HPV and associated pulmonary hypertension.

Mitochondrial Rieske iron-sulfur protein in pulmonary artery smooth muscle: A key primary signaling molecule in pulmonary hypertension

Rieske iron-sulfur protein (RISP) is a catalytic subunit of the complex III in the mitochondrial electron transport chain. Studies for years have revealed that RISP is essential for the generation of intracellular reactive oxygen species (ROS) via delicate signaling pathways associated with many important molecules such as protein kinase C-ε, NADPH oxidase, and ryanodine receptors. More significantly, mitochondrial RISP-mediated ROS production has been implicated in the development of hypoxic pulmonary vasoconstriction, leading to pulmonary hypertension, right heart failure, and death. Investigations have also shown the involvement of RISP in ROS-dependent cardiac ischemic/reperfusion injuries. Further research may provide novel and valuable information that can not only enhance our understanding of the functional roles of RISP and the underlying molecular mechanisms in the pulmonary vasculature and other systems, but also elucidate whether RISP targeting can act as preventative and restorative therapies against pulmonary hypertension, cardiac diseases, and other disorders.

Reactive oxygen species as mediators of oxygen signaling during fetal-to-neonatal circulatory transition

Reactive oxygen species (ROS) are frequently seen as pathological agents of oxidative stress. However, ROS are not always deleterious and can also act as cell signaling molecules. Vascular oxygen sensing and signaling during fetal-to-neonatal circulatory transition is a remarkable example of the physiological regulatory actions of ROS. The fetal relative hypoxic environment induces hypoxic pulmonary vasoconstriction (HPV) and ductus arteriosus (DA) relaxation favoring the presence of high pulmonary vascular resistance and right-to-left ductal shunt. At birth, the increase in oxygen tension causes relaxation of pulmonary arteries (PAs) and normoxic DA vasoconstriction (NDAV), thus diverting blood flow to the lungs. Although the response to changes in oxygen tension is diametrically opposite, the mechanisms responsible for HPV and NDAV appear to be the result of a similar interaction between triggering and modulating factors that lead to an increase in cytosolic Ca²⁺ concentration and Ca²⁺ sensitization of the contractile apparatus. Growing evidence points to an increase in ROS (mitochondria- and/or NADPH-derived superoxide and/or H₂O₂), leading to inhibition of voltage-gated K⁺ channels, membrane depolarization, and activation of voltage-gated L-type Ca²⁺ channels as critical events in the signaling pathway of both HPV and NDAV. Several groups of investigators have completed this pathway adding other elements such as neutral sphingomyelinase-derived ceramide, the sarcoplasmic/endoplasmic reticulum (through ryanodine and inositol 1,4,5-trisphosphate receptors), Rho kinase-mediated Ca²⁺ sensitization, or transient receptor potential channels. The present review focus on the role of ROS as mediators of the homeostatic oxygen sensing system during fetal and neonatal life not only in the PAs and DA but also in systemic arteries.

Quantum Blue Reduces the Severity of Woody Breast Myopathy via Modulation of Oxygen Homeostasis-Related Genes in Broiler Chickens

The incidence of woody breast (WB) is increasing on a global scale representing a significant welfare problem and economic burden to the poultry industry and for which there is no effective treatment due to its unknown etiology. In this study, using diffuse reflectance spectroscopy (DRS) coupled with iSTAT portable clinical analyzer, we provide evidence that the circulatory- and breast muscle-oxygen homeostasis is dysregulated [low oxygen and hemoglobin (HB) levels] in chickens with WB myopathy compared to healthy counterparts. Molecular analysis showed that blood HB subunit Mu (HBM), Zeta (HBZ), and hephaestin (HEPH) expression were significantly down regulated; however, the expression of the subunit rho of HB beta (HBBR) was upregulated in chicken with WB compared to healthy counterparts. The breast muscle HBBR, HBE, HBZ, and hypoxia-inducible factor prolyl hydroxylase 2 (PHD2) mRNA abundances were significantly down regulated in WB-affected compared to normal birds. The expression of HIF-1α at mRNA and protein levels was significantly induced in breasts of WB-affected compared to unaffected birds confirming a local hypoxic status. The phosphorylated levels of the upstream mediators AKT at Ser473 site, mTOR at Ser2481 site, and PI3K P85 at Tyr458 site, as well as their mRNA levels were significantly increased in breasts of WB-affected birds. In attempt to identify a nutritional strategy to reduce WB incidence, male broiler chicks (Cobb 500, n = 576) were randomly distributed into 48 floor pens and subjected to six treatments (12 birds/pen; 8 pens/treatment): a nutrient adequate control group (PC), the PC supplemented with 0.3% myo-inositol (PC + MI), a negative control (NC) deficient in available P and Ca by 0.15 and 0.16%, respectively, the NC fed with quantum blue (QB) at 500 (NC + 500 FTU), 1,000 (NC + 1,000 FTU), or 2,000 FTU/kg of feed (NC + 2,000 FTU). Although QB-enriched diets did not affect growth performances (FCR and FE), it did reduce the severity of WB by 5% compared to the PC diet. This effect is mediated by reversing the expression profile of oxygen homeostasis-related genes; i.e., significant down regulation of HBBR and upregulation of HBM, HBZ, and HEPH in blood, as well as a significant upregulation of HBA1, HBBR, HBE, HBZ, and PHD2 in breast muscle compared to the positive control.

Arabidopsis PLDs with C2-domain function distinctively in hypoxia

Hypoxia (oxygen deprivation) causes metabolic disturbances at physiological, biochemical and genetic levels and results in decreased plant growth and development. Phospholipase D (PLD)-mediated signaling was reported for abiotic and biotic stress signaling events in plants. To investigate the participatory role of PLDs also in hypoxia signaling, we used wild type of Arabidopsis thaliana and 10 pld isoform mutants containing C2-domain. Hypoxia-induced changes in three major signaling players, namely, cytosolic free calcium (Ca²⁺ _cyt ), reactive oxygen species (ROS) and phosphatidic acid (PA), were determined in mesophyll protoplasts. The Ca²⁺ _cyt and ROS levels were monitored by fluorescence microscopy and confocal imaging, while PA levels were quantified by an enzymatic method. Our findings reveal that the elevations of cytosolic calcium and PA are reduced in all the 10 mutants dysfunctional in PLD isoforms. The hypoxia-related changes in both calcium and ROS show different kinetic patterns depending on the type of PLD studied. Pharmacological experiments confirm that both external and internal sources contribute to calcium and ROS accumulation under hypoxia. PLDα1-3, PLDβ1 and PLDγ1-3 are likely involved in calcium signaling under hypoxia as well as in PA production, while all investigated PLDs, except for PLDγ3, take part in ROS elevation.

Mitochondrial Rieske iron-sulfur protein in pulmonary artery smooth muscle: A key primary signaling molecule in pulmonary hypertension

Rieske iron-sulfur protein (RISP) is a catalytic subunit of the complex III in the mitochondrial electron transport chain. Studies for years have revealed that RISP is essential for the generation of intracellular reactive oxygen species (ROS) via delicate signaling pathways associated with many important molecules such as protein kinase C-ε, NADPH oxidase, and ryanodine receptors. More significantly, mitochondrial RISP-mediated ROS production has been implicated in the development of hypoxic pulmonary vasoconstriction, leading to pulmonary hypertension, right heart failure, and death. Investigations have also shown the involvement of RISP in ROS-dependent cardiac ischemic/reperfusion injuries. Further research may provide novel and valuable information that can not only enhance our understanding of the functional roles of RISP and the underlying molecular mechanisms in the pulmonary vasculature and other systems, but also elucidate whether RISP targeting can act as preventative and restorative therapies against pulmonary hypertension, cardiac diseases, and other disorders.

From Physiological Redox Signalling to Oxidant Stress

Oxidant stress is strongly associated with cardiovascular disease, including pulmonary hypertension, but antioxidant therapies have so far proven ineffective. This is partly due to a lack of understanding of the key role played by reactive oxygen species (ROS) in physiological cell signalling, and partly to the complex interrelationships between generators of ROS (e.g. mitochondria and NADPH oxidases, NOX), cellular antioxidant systems and indeed Ca²⁺ signalling. At physiological levels ROS reversibly affect the function of numerous enzymes and transcription factors, most often via oxidation of specific protein thiols. Importantly, they also affect pathways that promote ROS generation by NOX or mitochondria (ROS-induced ROS release), which has an inherent propensity for positive feedback and uncontrolled oxidant production. The reason this does not occur under normal conditions reflects in part a high level of compartmentalisation of ROS signalling within the cell, akin to that for Ca²⁺. This article considers the physiological processes which regulate NOX and mitochondrial ROS production and degradation and their interactions with each other and Ca²⁺ signalling pathways, and discusses how loss of spatiotemporal constraints and activation of positive feedback pathways may impact on their dysregulation in pulmonary hypertension.

PLCγ1-PKCε-IP3R1 signaling plays an important role in hypoxia-induced calcium response in pulmonary artery smooth muscle cells

Hypoxia-induced pulmonary vasoconstriction (HPV) is attributed to an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) in pulmonary artery smooth muscle cells (PASMCs). We have reported that phospholipase C-γ1 (PLCγ1) plays a significant role in the hypoxia-induced increase in [Ca²⁺]_i in PASMCs and attendant HPV. In this study, we intended to determine molecular mechanisms for hypoxic Ca²⁺ and contractile responses in PASMCs. Our data reveal that hypoxic vasoconstriction occurs in pulmonary arteries, but not in mesenteric arteries. Hypoxia caused a large increase in [Ca²⁺]_i in PASMCs, which is diminished by the PLC inhibitor U73122 and not by its inactive analog U73433 . Hypoxia augments PLCγ1-dependent inositol 1,4,5-trisphosphate (IP₃) generation. Exogenous ROS, hydrogen peroxide (H₂O₂), increases PLCγ1 phosphorylation at tyrosine-783 and IP₃ production. IP₃ receptor-1 (IP₃R1) knock-down remarkably diminishes hypoxia- or H₂O₂-induced increase in [Ca²⁺]_i. Hypoxia or H₂O₂ increases the activity of IP₃Rs, which is significantly reduced in protein kinase C-ε (PKCε) knockout PASMCs. A higher PLCγ1 expression, activity, and basal [Ca²⁺]_i are found in PASMCs, but not in mesenteric artery smooth muscle cells from mice exposed to chronic hypoxia (CH) for 21 days. CH enhances H₂O₂- and ATP-induced increase in [Ca²⁺]_i in PASMCs and PLC-dependent, norepinephrine-evoked pulmonary vasoconstriction. In conclusion, acute hypoxia uniquely causes ROS-dependent PLCγ1 activation, IP₃ production, PKCε activation, IP₃R1 opening, Ca²⁺ release, and contraction in mouse PASMCs; CH enhances PASM PLCγ1 expression, activity, and function, playing an essential role in pulmonary hypertension in mice.

Prostanoid EP4 agonist L-902,688 activates PPARγ and attenuates pulmonary arterial hypertension

Prostacyclin agonists that bind the prostacyclin receptor (IP) to stimulate cAMP synthesis are effective vasodilators for the treatment of idiopathic pulmonary arterial hypertension (IPAH), but this signaling may occur through nuclear peroxisome proliferator-activated receptor-γ (PPARγ). There is evidence of scant IP and PPARγ expression but stable prostanoid EP₄ receptor (EP₄) expression in IPAH patients. Both IP and EP₄ functionally couple with stimulatory G protein (G_s), which activates signal transduction. We investigated the effect of an EP₄-specific agonist on pulmonary arterial remodeling and its regulatory mechanisms in pulmonary arterial smooth muscle cells (PASMCs). Immunoblotting evealed IP, EP₄, and PPARγ expression in human pulmonary arterial hypertension (PAH) and monocrotaline (MCT)-induced PAH rat lung tissue. Isolated PASMCs from MCT-induced PAH rats (MCT-PASMCs) were treated with L-902,688, a selective EP₄ agonist, to investigate the anti-vascular remodeling effect. Scant expression of IP and PPARγ but stable expression of EP₄ was observed in IPAH patient lung tissues and MCT-PASMCs. L-902,688 inhibited IP-insufficient MCT-PASMC proliferation and migration by activating PPARγ in a time- and dose-dependent manner, but these effects were reversed by AH-23848 (an EP₄ antagonist) and H-89 [a protein kinase A (PKA) inhibitor], highlighting the crucial role of PPARγ in the activity of this EP₄ agonist. L-902,688 attenuated pulmonary arterial remodeling in hypoxic PAH mice and MCT-induced PAH rats; therefore, we conclude that the selective EP₄ agonist L-902,688 reverses vascular remodeling by activating PPARγ. This study identified a novel EP₄-PKA-PPARγ pathway, and we propose EP₄ as a potential therapeutic target for PAH.

Phospholipase Cγ1 Mediates Intima Formation Through Akt-Notch1 Signaling Independent of the Phospholipase Activity

Background

Vascular smooth muscle cell proliferation, migration, and dedifferentiation are critical for vascular diseases. Recently, it was demonstrated that Notch receptors have opposing effects on intima formation after vessel injury. Therefore, it is important to investigate the specific regulatory pathways that activate the different Notch receptors.

Methods and Results

There was a time‐ and dose‐dependent activation of Notch1 by angiotensin II and platelet‐derived growth factor in vascular smooth muscle cells. When phospholipase Cγ1 (PLCγ1) expression was reduced by small interfering RNA, Notch1 activation and Hey2 expression (Notch target gene) induced by angiotensin II or platelet‐derived growth factor were remarkably inhibited, while Notch2 degradation was not affected. Mechanistically, we observed an association of PLCγ1 and Akt, which increased after angiotensin II or platelet‐derived growth factor stimulation. PLCγ1 knockdown significantly inhibited Akt activation. Importantly, PLCγ1 phospholipase site mutation (no phospholipase activity) did not affect Akt activation. Furthermore, PLCγ1 depletion inhibited platelet‐derived growth factor–induced vascular smooth muscle cell proliferation, migration, and dedifferentiation, while it increased apoptosis. In vivo, PLCγ1 and control small interfering RNA were delivered periadventitially in pluronic gel and complete carotid artery ligation was performed. Morphometric analysis 21 days after ligation demonstrated that PLCγ1 small interfering RNA robustly attenuated intima area and intima/media ratio compared with the control group.

Conclusions

PLCγ1‐Akt–mediated Notch1 signaling is crucial for intima formation. This effect is attributable to PLCγ1‐Akt interaction but not PLCγ1 phospholipase activity. Specific inhibition of the PLCγ1 and Akt interaction will be a promising therapeutic strategy for preventing vascular remodeling.

Single-cell resolution of intracellular T cell Ca2+ dynamics in response to frequency-based H2O2 stimulation

Adaptive immune cells, such as T cells, integrate information from their extracellular environment through complex signaling networks with exquisite sensitivity in order to direct decisions on proliferation, apoptosis, and cytokine production. These signaling networks are reliant on the interplay between finely tuned secondary messengers, such as Ca2+ and H2O2. Frequency response analysis, originally developed in control engineering, is a tool used for discerning complex networks. This analytical technique has been shown to be useful for understanding biological systems and facilitates identification of the dominant behaviour of the system. We probed intracellular Ca2+ dynamics in the frequency domain to investigate the complex relationship between two second messenger signaling molecules, H2O2 and Ca2+, during T cell activation with single cell resolution. Single-cell analysis provides a unique platform for interrogating and monitoring cellular processes of interest. We utilized a previously developed microfluidic device to monitor individual T cells through time while applying a dynamic input to reveal a natural frequency of the system at approximately 2.78 mHz stimulation. Although our network was much larger with more unknown connections than previous applications, we are able to derive features from our data, observe forced oscillations associated with specific amplitudes and frequencies of stimuli, and arrive at conclusions about potential transfer function fits as well as the underlying population dynamics.

Hypoxia-induced pulmonary hypertension in type 2 diabetic mice

Hypoxia-induced pulmonary hypertension (HPH) is a progressive disease that is mainly caused by chronic exposure to high altitude, chronic obstructive lung disease, and obstructive sleep apnea. The increased pulmonary vascular resistance and increased pulmonary arterial pressure result in increased right ventricular afterload, leading to right heart failure and increased morbidity. There are several clinical reports suggesting a link between PH and diabetes, insulin resistance, or obesity; however, it is unclear whether HPH is associated with diabetes as a progressive complication in diabetes. The major goal of this study is to examine the effect of diabetic "preconditioning" or priming effect on the progression of HPH and define the molecular mechanisms that explain the link between diabetes and HPH. Our data show that HPH is significantly enhanced in diabetic mice, while endothelium-dependent relaxation in pulmonary arteries is significantly attenuated in chronically hypoxic diabetic mice (DH). In addition, we demonstrate that mouse pulmonary endothelial cells (MPECs) isolated from DH mice exhibit a significant increase in mitochondrial reactive oxygen species (ROS) concentration and decreased SOD2 protein expression. Finally, scavenging mitochondrial ROS by mitoTempol restores endothelium-dependent relaxation in pulmonary arteries that is attenuated in DH mice. These data suggest that excessive mitochondrial ROS production in diabetic MPECs leads to the development of severe HPH in diabetic mice exposed to hypoxia.

Mitochondria dysfunction: A novel therapeutic target in pathological lung remodeling or bystander?

The renascence in mitochondrial research has fueled breakthroughs in our understanding of mitochondrial biology identifying major roles in biological processes ranging from cellular oxygen sensing and regulation of intracellular calcium levels through to initiation of apoptosis or a shift in cell phenotype. Chronic respiratory diseases are no exception to the resurgent interest in mitochondrial biology. Microscopic observations of lungs from patients with chronic respiratory diseases such as pulmonary arterial hypertension, asthma and COPD show accumulation of dysmorphic mitochondria and provide the first evidence of mitochondrial dysfunction in diseased lungs. Recent mechanistic insights have established links between mitochondrial dysfunction or aberrant biogenesis and the pathogenesis of chronic respiratory diseases through playing a causative role in structural remodeling of the lung. The aim here is to discuss the case for a mitochondrial basis of lung remodeling in patients with chronic respiratory diseases. The present article will focus on the question of whether currently available data supports mitochondrial mechanisms as a viable point of therapeutic intervention in respiratory diseases and suggestions for future avenues of research in this rapidly evolving field.

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Linking phospholipase C isoforms with differentiation function in human vascular smooth muscle cells

The phosphoinositol-phospholipase C (PLC) family of enzymes consists of a number of isoforms, each of which has different cellular functions. PLCγ1 is primarily linked to tyrosine kinase transduction pathways, whereas PLCδ1 has been associated with a number of regulatory proteins, including those controlling the cell cycle. Recent studies have shown a central role of PLC in cell organisation and in regulating a wide array of cellular responses. It is of importance to define the precise role of each isoform, and how this changes the functional outcome of the cell. Here we investigated differences in PLC isoform levels and activity in relation to differentiation of human and rat vascular smooth muscle cells. Using Western blotting and PLC activity assay, we show that PLCδ1 and PLCγ1 are the predominant isoforms in randomly cycling human vascular smooth muscle cells (HVSMCs). Growth arrest of HVSMCs for seven days of serum deprivation was consistently associated with increases in PLCδ1 and SM α-actin, whereas there were no changes in PLCγ1 immuno-reactivity. Organ culture of rat mesenteric arteries in serum free media (SFM), a model of de-differentiation, led to a loss of contractility as well as a loss of contractile proteins (SM α-actin and calponin) and PLCδ1, and no change in PLCγ1 immuno-reactivity. Taken together, these data indicate that PLCδ1 is the predominant PLC isoform in vascular smooth muscle, and confirm that PLCδ1 expression is affected by conditions that affect the cell cycle, differentiation status and contractile function.

Oxidative stress mediates the disruption of airway epithelial tight junctions through a TRPM2-PLCγ1-PKCα signaling pathway

Oxidative stress has been implicated as an important contributing factor in the pathogenesis of several pulmonary inflammatory diseases. Previous studies have indicated a relationship between oxidative stress and the attenuation of epithelial tight junctions (TJs). In Human Bronchial Epithelial-16 cells (16HBE), we demonstrated the degradation of zonula occludens-1 (ZO-1), and claudin-2 exhibited a great dependence on the activation of the transient receptor potential melastatin (TRPM) 2 channel, phospholipase Cγ1 (PLCγ1) and the protein kinase Cα (PKCα) signaling cascade.