Human primary lung endothelial cells in culture

Impact and mechanisms of drag-reducing polymers on shear stress regulation in pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is a refractory disease characterized by elevated pulmonary artery pressure and resistance. Drag-reducing polymers (DRPs) are blood-soluble macromolecules that reduce vascular resistance by altering the blood dynamics and rheology. Our previous work indicated that polyethylene oxide (PEO) can significantly reduce the medial wall thickness and vascular resistance of the pulmonary arteries, but the specific mechanism is still unclear.

METHODS

This study was designed to investigate the role and mechanism of PEO on intracellular calcium [Ca2 +] i and cytoskeletal proteins of endothelial cells (ECs) induced by low shear stress (LSS) in PH. Primary Pulmonary Artery Endothelial Cells (PAECs) were subjected to steady LSS (1 dyn/cm2) or physiological shear stress (SS) (10 dyn/cm2) for 20 h in a BioFlux 200 flow system. Calcium influx assays were conducted to evaluate the mechanisms of PEO on [Ca2 +] i. Subsequently, taking the key protein that induces cytoskeletal remodeling, the regulatory light chain (RLC) phosphorylation, as the breakthrough point, this study focused on the two key pathways of PEO that regulate phosphorylation of RLC: Myosin light chain kinase (MLCK) and Rho-associated kinase (ROCK) pathways.

RESULTS

Our current research revealed that PEO at LSS (1 dyn/cm2) significantly suppressed LSS-induced [Ca2 +] i and the expression level of transient receptor potential channel 1(TRPC1). In addition, ECs convert LSS stimuli into the upregulation of cytoskeletal proteins, including filamentous actin (F-actin), MLCK, ROCK, p-RLC, and pp-RLC. Further experiments using pharmacological inhibitors demonstrated that PEO at the LSS downregulated cytoskeleton-related proteins mainly through the ROCK and MLCK pathways.

CONCLUSIONS

This study considered intracellular calcium and cytoskeleton rearrangement as entry points to study the application of PEO in the biomedical field, which has important theoretical significance and practical application value for the treatment of PH.

Dysregulation of the Long Non-coding RNA Xist Expression in Male Patients with Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a sex-biased disease with female gender as a significant risk factor. Recently, we reported that increased expression of the long non-coding (lnc)RNA Xist, as induced by an intersectin-1s protein fragment with proliferative potential (EHITSN), may explain the sexual dimorphism of female pulmonary artery endothelial cells (ECs) and at least in part, the imbalance sex/ratio of PAH. Xist is essential for X-chromosome inactivation and dosage compensation of X-linked genes. Increased Xist expression was also detected in a subset of ECs and lung tissue samples of male PAH patients. The role of different Xist expression levels in ECs of male PAH patients (ECPAH) was studied in several lines of male ECPAH in conjunction with molecular, biochemical, morphological, and functional approaches. Male ECPAH showed on average 10.3-fold increase in high Xist vs. low Xist, a significant association between Xist levels and their proliferative potential, and a heterogeneous methylation of the Xist/Tsix locus. Interestingly, Xist up-regulation in male ECPAH decreases the expression of Klf2, via EHITSN interaction with EZH2, the catalytic subunit of the polycomb repressive complex 2. Moreover, the studies demonstrate that EHITSN-triggered p38/Elk1/c-Fos signaling is a pathological mechanism central to ECPAH proliferation and the dynamic crosstalk with cell cycle regulatory proteins ccna1/ccnd2, and Xist-EZH2-Klf2 interaction participate directly and differentially in establishing the proliferative profile of male ECPAH.

In vitro modelling of bacterial pneumonia: a comparative analysis of widely applied complex cell culture models

Bacterial pneumonia greatly contributes to the disease burden and mortality of lower respiratory tract infections among all age groups and risk profiles. Therefore, laboratory modelling of bacterial pneumonia remains important for elucidating the complex host-pathogen interactions and to determine drug efficacy and toxicity. In vitro cell culture enables for the creation of high-throughput, specific disease models in a tightly controlled environment. Advanced human cell culture models specifically, can bridge the research gap between the classical two-dimensional cell models and animal models. This review provides an overview of the current status of the development of complex cellular in vitro models to study bacterial pneumonia infections, with a focus on air-liquid interface models, spheroid, organoid, and lung-on-a-chip models. For the wide scale, comparative literature search, we selected six clinically highly relevant bacteria (Pseudomonas aeruginosa, Mycoplasma pneumoniae, Haemophilus influenzae, Mycobacterium tuberculosis, Streptococcus pneumoniae, and Staphylococcus aureus). We reviewed the cell lines that are commonly used, as well as trends and discrepancies in the methodology, ranging from cell infection parameters to assay read-outs. We also highlighted the importance of model validation and data transparency in guiding the research field towards more complex infection models.

Single-Cell Analysis Reveals Distinct Immune and Smooth Muscle Cell Populations that Contribute to Chronic Thromboembolic Pulmonary Hypertension

Rationale: Chronic thromboembolic pulmonary hypertension (CTEPH) is a sequela of acute pulmonary embolism (PE) in which the PE remodels into a chronic scar in the pulmonary arteries. This results in vascular obstruction, pulmonary microvasculopathy, and pulmonary hypertension. Objectives: Our current understanding of CTEPH pathobiology is primarily derived from cell-based studies limited by the use of specific cell markers or phenotypic modulation in cell culture. Therefore, our main objective was to identify the multiple cell types that constitute CTEPH thrombusy and to study their dysfunction. Methods: Here we used single-cell RNA sequencing of tissue removed at the time of pulmonary endarterectomy surgery from five patients to identify the multiple cell types. Using in vitro assays, we analyzed differences in phenotype between CTEPH thrombus and healthy pulmonary vascular cells. We studied potential therapeutic targets in cells isolated from CTEPH thrombus. Measurements and Main Results: Single-cell RNA sequencing identified multiple cell types, including macrophages, T cells, and smooth muscle cells (SMCs), that constitute CTEPH thrombus. Notably, multiple macrophage subclusters were identified but broadly split into two categories, with the larger group characterized by an upregulation of inflammatory signaling predicted to promote pulmonary vascular remodeling. CD4+ and CD8+ T cells were identified and likely contribute to chronic inflammation in CTEPH. SMCs were a heterogeneous population, with a cluster of myofibroblasts that express markers of fibrosis and are predicted to arise from other SMC clusters based on pseudotime analysis. Additionally, cultured endothelial, smooth muscle, and myofibroblast cells isolated from CTEPH fibrothrombotic material have distinct phenotypes from control cells with regard to angiogenic potential and rates of proliferation and apoptosis. Last, our analysis identified PAR1 (protease-activated receptor 1) as a potential therapeutic target that links thrombosis to chronic PE in CTEPH, with PAR1 inhibition decreasing SMC and myofibroblast proliferation and migration. Conclusions: These findings suggest a model for CTEPH similar to atherosclerosis, with chronic inflammation promoted by macrophages and T cells driving vascular remodeling through SMC modulation, and suggest new approaches for pharmacologically targeting this disease.

GEF-H1/RhoA signaling pathway mediates pro-inflammatory effects of NF-κB on CD40L-induced pulmonary endothelial cells

One of the key targets of the inflammatory response in acute lung injury (ALI) is the human pulmonary micro-vascular endothelial cells (HPMVECs). Owing to its role in the activation of endothelial cells (ECs), CD40L figures prominently in the pathogenesis of ALI. Increasing evidences have showed that CD40L mediates inflammatory effects on ECs, at least in part, by triggering NF-κB-dependent gene expression. However, the mechanisms of such signal transmission remain unknown. In this study, we found that CD40L stimulated the transactivation of NF-κB and expression of its downstream cytokines in a p38 MAPK-dependent mechanism in HPMVECs. In addition, CD40L-mediated inflammatory effects might be correlated with the activation of the IKK/IκB/NF-κB pathway and nuclear translocation of NF-κB, being accompanied by dynamic cytoskeletal changes. GEF-H1/RhoA signaling is best known for its role in regulating cytoskeletal rearrangements. An interesting finding was that CD40L induced the activation of p38 and IKK/IκB, and the subsequent transactivation of NF-κB via GEF-H1/RhoA signaling. The critical role of GEF-H1/RhoA in CD40L-induced inflammatory responses in the lung was further confirmed in GEF-H1 and RhoA knockout mouse models, both of which were established by adeno-associated virus (AAV)-mediated delivery of sgRNAs into mice with EC-specific Cas9 expression. These results taken together suggested that p38 and IKK/IκB-mediated signaling pathways, both of which lied downstream of GEF-H1/RhoA, may coordinately regulate the transactivation of NF-κB in CD40L-activated HPMVECs. These findings may help to determine key pharmacological targets of intervention for CD40L-activated inflammatory effects associated with ALI.

Isolation of vasa vasorum endothelial cells from pulmonary artery adventitia: Implementation to vascular biology research

Isolated endothelial cells are valuable in vitro model for vascular research. At present, investigation of disease-relevant changes in vascular endothelium at the molecular level requires established endothelial cell cultures, preserving vascular bed-specific phenotypic characteristics. Vasa vasorum (VV) form a microvascular network around large blood vessels, in both the pulmonary and systemic circulations, that are critically important for maintaining the integrity and oxygen supply of the vascular wall. However, despite the pathophysiological significance of the VV, methods for the isolation and culture of vasa vasorum endothelial cells (VVEC) have not yet been reported. In our prior studies, we demonstrated the presence of hypoxia-induced angiogenic expansion of the VV in the pulmonary artery (PA) of neonatal calves; an observation which has been followed by a series of in vitro studies on isolated PA VVEC. Here we present a detailed protocol for reproducible isolation, purification, and culture of PA VVEC. We show these cells to express generic endothelial markers, (vWF, eNOS, VEGFR2, Tie1, and CD31), as well as progenitor markers (CD34 and CD133), bind lectin Lycopersicon Esculentum, and incorporate acetylated low-density lipoproteins labeled with acetylated LDL (DiI-Ac-LDL). qPCR analysis additionally revealed the expression of CD105, VCAM-1, ICAM-1, MCAM, and NCAM. Ultrastructural electron microscopy and immunofluorescence staining demonstrated that VVEC are morphologically characterized by a developed actin and microtubular cytoskeleton, mitochondrial network, abundant intracellular vacuolar/secretory system, and cell-surface filopodia. VVEC exhibit exponential growth in culture and can be mitogenically activated by multiple growth factors. Thus, our protocol provides the opportunity for VVEC isolation from the PA, and potentially from other large vessels, enabling advances in VV research.

Obstructive sleep apnea-increased DEC1 regulates systemic inflammation and oxidative stress that promotes development of pulmonary arterial hypertension

Obstructive sleep apnea (OSA), characterized by chronic intermittent hypoxia (CIH), is a common risk factor for pulmonary arterial hypertension (PAH). As a hypoxia-induced transcription factor, differentially expressed in chondrocytes (DEC1) negatively regulates the transcription of peroxisome proliferative activated receptor-γ (PPARγ), a recognized protective factor of PAH. However, whether and how DEC1 is associated with PAH pathogenesis remains unclear. In the present study, we found that DEC1 was increased in lungs and pulmonary arterial smooth muscle cells (PASMCs) of rat models of OSA-associated PAH. Oxidative indicators and inflammatory cytokines were also elevated in the blood of the rats. Similarly, hypoxia-treated PASMCs displayed enhanced DEC1 expression and reduced PPARγ expression in vitro. Functionally, DEC1 overexpression exacerbated reactive oxygen species (ROS) production and the expression of pro-inflammatory cytokines (such as TNFα, IL-1β, IL-6, and MCP-1) in PASMCs. Conversely, shRNA knockdown of Dec1 increased PPARγ expression but attenuated hypoxia-induced oxidative stress and inflammatory responses in PASMCs. Additionally, DEC1 overexpression promoted PASMC proliferation, which was drastically attenuated by a PPARγ agonist rosiglitazone. Collectively, these results suggest that hypoxia-induced DEC1 inhibits PPARγ, and that this is a predominant mechanism underpinning oxidative stress and inflammatory responses in PASMCs during PAH. DEC1 could be used as a potential target to treat PAH.

Loss of lung microvascular endothelial Piezo2 expression impairs NO synthesis, induces EndMT, and is associated with pulmonary hypertension

Mechanical forces are translated into biochemical stimuli by mechanotransduction channels, such as the mechanically activated cation channel Piezo2. Lung Piezo2 expression has recently been shown to be restricted to endothelial cells. Hence, we aimed to investigate the role of Piezo2 in regulation of pulmonary vascular function and structure, as well as its contribution to development of pulmonary arterial hypertension (PAH). The expression of Piezo2 was significantly reduced in pulmonary microvascular endothelial cells (MVECs) from patients with PAH, in lung tissue from mice with a Bmpr2^+/R899X knock-in mutation commonly found in patients with pulmonary hypertension, and in lung tissue of monocrotaline (MCT) and sugen-hypoxia-induced PH (SuHx) PAH rat models, as well as from a swine model with pulmonary vein banding. In MVECs, Piezo2 expression was reduced in response to abnormal shear stress, hypoxia, and TGFβ stimulation. Functional studies in MVECs exposed to shear stress illustrated that siRNA-mediated Piezo2 knockdown impaired endothelial alignment, calcium influx, phosphorylation of AKT, and nitric oxide production. In addition, siPiezo2 reduced the expression of the endothelial marker PECAM-1 and increased the expression of vascular smooth muscle markers ACTA2, SM22a, and calponin. Thus, Piezo2 acts as a mechanotransduction channel in pulmonary MVECs, stimulating shear-induced production of nitric oxide and is essentially involved in preventing endothelial to mesenchymal transition. Its blunted expression in pulmonary hypertension could impair the vasodilator capacity and stimulate vascular remodeling, indicating that Piezo2 might be an interesting therapeutic target to attenuate progression of the disease.NEW & NOTEWORTHY The mechanosensory ion channel Piezo2 is exclusively expressed in lung microvascular endothelial cells (MVECs). Patient MVECs as well as animal models of pulmonary (arterial) hypertension showed lower expression of Piezo2 in the lung. Mechanistically, Piezo2 is required for calcium influx and NO production in response to shear stress, whereas stimuli known to induce endothelial to mesenchymal transition (EndMT) reduce Piezo2 expression in MVECs, and Piezo2 knockdown induces a gene and protein expression pattern consistent with EndMT.

Sourcing cells for in vitro models of human vascular barriers of inflammation

The vascular system plays a critical role in the progression and resolution of inflammation. The contributions of the vascular endothelium to these processes, however, vary with tissue and disease state. Recently, tissue chip models have emerged as promising tools to understand human disease and for the development of personalized medicine approaches. Inclusion of a vascular component within these platforms is critical for properly evaluating most diseases, but many models to date use "generic" endothelial cells, which can preclude the identification of biomedically meaningful pathways and mechanisms. As the knowledge of vascular heterogeneity and immune cell trafficking throughout the body advances, tissue chip models should also advance to incorporate tissue-specific cells where possible. Here, we discuss the known heterogeneity of leukocyte trafficking in vascular beds of some commonly modeled tissues. We comment on the availability of different tissue-specific cell sources for endothelial cells and pericytes, with a focus on stem cell sources for the full realization of personalized medicine. We discuss sources available for the immune cells needed to model inflammatory processes and the findings of tissue chip models that have used the cells to studying transmigration.

Substrate stiffness modulates migration and local intercellular membrane motion in pulmonary endothelial cell monolayers

The pulmonary artery endothelium forms a semipermeable barrier that limits macromolecular flux through intercellular junctions. This barrier is maintained by an intrinsic forward protrusion of the interacting membranes between adjacent cells. However, the dynamic interactions of these membranes have been incompletely quantified. Here, we present a novel technique to quantify the motion of the peripheral membrane of the cells, called paracellular morphological fluctuations (PMFs), and to assess the impact of substrate stiffness on PMFs. Substrate stiffness impacted large-length scale morphological changes such as cell size and motion. Cell size was larger on stiffer substrates, whereas the speed of cell movement was decreased on hydrogels with stiffness either larger or smaller than 1.25 kPa, consistent with cells approaching a jammed state. Pulmonary artery endothelial cells moved fastest on 1.25 kPa hydrogel, a stiffness consistent with a healthy pulmonary artery. Unlike these large-length scale morphological changes, the baseline of PMFs was largely insensitive to the substrate stiffness on which the cells were cultured. Activation of store-operated calcium channels using thapsigargin treatment triggered a transient increase in PMFs beyond the control treatment. However, in hypocalcemic conditions, such an increase in PMFs was absent on 1.25 kPa hydrogel but was present on 30 kPa hydrogel-a stiffness consistent with that of a hypertensive pulmonary artery. These findings indicate that 1) PMFs occur in cultured endothelial cell clusters, irrespective of the substrate stiffness; 2) PMFs increase in response to calcium influx through store-operated calcium entry channels; and 3) stiffer substrate promotes PMFs through a mechanism that does not require calcium influx.

Agonists for Bitter Taste Receptors T2R10 and T2R38 Attenuate LPS-Induced Permeability of the Pulmonary Endothelium in vitro

One of the hallmarks of acute respiratory distress syndrome (ARDS) is an excessive increase in pulmonary vascular permeability. In settings of ARDS, the loss of barrier integrity is mediated by cell-cell contact disassembly and actin remodelling. Studies into molecular mechanisms responsible for improving microvascular barrier function are therefore vital in the development of therapeutic targets for reducing vascular permeability seen in ARDS. Bitter taste receptors (T2Rs) belong to the superfamily of G-protein-coupled receptors found in several extraoral systems, including lung epithelial and smooth muscle cells. In the present study, we show for the first time that several T2Rs are expressed in human pulmonary arterial endothelial cells (HPAECs). Our results focus on those which are highly expressed as: T2R10, T2R14 and T2R38. Agonists for T2R10 (denatonium) and T2R38 (phenylthiourea), but not T2R14 (noscapine), significantly attenuated lipopolysaccharide (LPS)-induced permeability and VE-cadherin internalisation in HPAECs. In T2R10- or T2R38-siRNA knockdown cells, these endothelial-protective effects were abolished, indicating a direct effect of agonists in regulating barrier integrity. Our further findings indicate that T2R10 and T2R38 exert their barrier-protective function through cAMP but via Rac1-dependent and independent pathways, respectively. However, using an in vivo model of ARDS, the T2R38 agonist, phenylthiourea, was not able to protect against pulmonary edema formation. Taken together, these studies identify bitter taste sensing in the pulmonary endothelium to regulate barrier integrity in vitro through cAMP-Rac1 signalling.

Vascular smooth muscle ROCK1 contributes to hypoxia-induced pulmonary hypertension development in mice

Rho kinase (ROCK) is implicated in the development of pulmonary arterial hypertension (PAH) in which abnormal pulmonary vascular smooth muscle (VSM) contractility and remodeling lead to right heart failure. Pharmacologic ROCK inhibitors block experimental pulmonary hypertension (PH) development in rodents but can have off-target effects and do not distinguish between the two ROCK forms, ROCK1 and ROCK2, encoded by separate genes. An earlier study using gene knock out (KO) in mice indicated that VSM ROCK2 is required for experimental PH development, but the role of ROCK1 is not well understood. Here we investigated the in vivo role of ROCK1 in PH development by generating a VSM-targeted homozygous ROCK1 gene KO mouse strain. Adult control mice exposed to Sugen5416 (Su)/hypoxia treatment to induce PH had significantly increased right ventricular systolic pressures (RVSP) and RV hypertrophy versus normoxic controls. In contrast, Su/hypoxia-exposed VSM ROCK1 KO mice did not exhibit significant RVSP elevation, and RV hypertrophy was blunted. Su/hypoxia-induced pulmonary small vessel muscularization was similarly elevated in both control and VSM ROCK1 KO animals. siRNA-mediated ROCK1 knock-down (KD) in human PAH pulmonary arterial SM cells (PASMC) did not affect cell growth. However, ROCK1 KD led to reduced AKT and MYPT1 signaling in serotonin-treated PAH PASMC. The findings suggest that like VSM ROCK2, VSM ROCK1 actively contributes to PH development, but in distinction acts via nonproliferative pathways to promote hypoxemia, and thus may be a distinct therapeutic target in PH.

Histone 2B Facilitates Plasminogen-Enhanced Endothelial Migration through Protease-Activated Receptor 1 (PAR1) and Protease-Activated Receptor 2 (PAR2)

Plasminogen and its multiple receptors have been implicated in the responses of many different cell types. Among these receptors, histone 2B (H2B) has been shown to play a prominent role in macrophage responses. The contribution of H2B to plasminogen-induced endothelial migration, an event relevant to wound healing and angiogenesis, is unknown. Plasminogen enhanced the migration of endothelial cells, which was inhibited by both Protease-Activated Receptor-1 (PAR1) and 2 (PAR2) antagonists. H2B was detected on viable endothelial cells of venous and arterial origin, and an antibody to H2B that blocks plasminogen binding also inhibited the plasminogen-dependent migration by these cells. The antibody blockade was as effective as PAR1 or PAR2 antagonists in inhibiting endothelial cell migration. In pull-down experiments, H2B formed a complex with both PAR1 and PAR2 but not β3 integrin, another receptor implicated in endothelial migration in the presence of plasminogen. H2B was found to be associated with clathrin adapator protein, AP2µ (clathrin AP2µ) and β-arrestin2, which are central to the internationalization/signaling machinery of the PARs. These associations with PAR1-clathrin adaptor AP2µ- and PAR2-β-arrestin2-dependent internalization/signaling pathways provide a mechanism to link plasminogen to responses such as wound healing and angiogenesis.

Epigenetic Modification of the VWF Promotor Drives Platelet Aggregation on the Pulmonary Endothelium in Chronic Thromboembolic Pulmonary Hypertension

RATIONALE

Von Willebrand Factor (VWF) mediates platelet adhesion during thrombosis. While chronic thromboembolic pulmonary hypertension (CTEPH) is associated with increased plasma levels of VWF, the role of this protein in CTEPH has remained enigmatic.

OBJECTIVE

To identify the role of VWF in CTEPH.

METHODS

CTEPH-specific patient plasma and pulmonary endarterectomy material from CTEPH patients were used to study the relationship between inflammation, VWF expression and pulmonary thrombosis. Cell culture findings were validated in human tissue and proteomics and chromatin immunoprecipitation were used to investigate the underlying mechanism of CTEPH.

MEASUREMENTS AND MAIN RESULTS

VWF is increased in plasma and in the pulmonary endothelium of CTEPH patients. In vitro, the increase in VWF gene expression and the higher release of VWF protein upon endothelial activation resulted in elevated platelet adhesion to CTEPH endothelium. Proteomic analysis revealed that Nuclear Factor κB 2 (NFκB2) was significantly increased in CTEPH. We demonstrate reduced histone tri-methylation and increased histone acetylation of the VWF promotor in CTEPH endothelium, facilitating binding of NFκB2 to the VWF promotor and driving VWF transcription. Genetic interference of NFκB2 normalized the high VWF RNA expression levels and reversed the pro-thrombotic phenotype observed in CTEPH-PAEC.

CONCLUSION

Epigenetic regulation of the VWF promotor contributes to the creation of a local environment that favors in situ thrombosis in the pulmonary arteries. It reveals a direct molecular link between inflammatory pathways and platelet adhesion in the pulmonary vascular wall, emphasizing a possible role of in situ thrombosis in the development or progression of CTEPH.

Isolation of Primary Mouse Pulmonary Microvascular Endothelial Cells and Generation of an Immortalized Cell Line to Obtain Sufficient Extracellular Vesicles

Pulmonary microvascular endothelial cells (PMECs) and the extracellular vesicles (EVs) derived from PMECs participate in maintaining pulmonary homeostasis and mediating the inflammatory response. However, obtaining a high-purity population of PMECs and their EVs from mouse is still notoriously difficult. Herein we provide a method to isolate primary mouse PMECs (pMPMECs) and to transduce SV40 lentivirus into pMPMECs to establish an immortalized cell line (iMPMECs), which provides sufficient quantities of EVs for further studies. pMPMECs and iMPMECs can be identified using morphologic criteria, a phenotypic expression profile (e.g., CD31, CD144, G. simplicifolia lectin binding), and functional properties (e.g., Dil-acetylated low-density protein uptake, Matrigel angiogenesis). Furthermore, pMPMEC-EVs and iMPMEC-EVs can be identified and compared. The characteristics of pMPMEC-EVs and iMPMEC-EVs are ascertained by transmission electron microscopy, nanoparticle tracking analysis, and specific protein markers. iMPMECs produce far more EVs than pMPMECs, while their particle size distribution is similar. Our detailed protocol to isolate and immortalize MPMECs will provide researchers with an in vitro model to investigate the specific roles of EVs in pulmonary physiology and diseases.

Endothelial Dec1-PPARγ Axis Impairs Proliferation and Apoptosis Homeostasis Under Hypoxia in Pulmonary Arterial Hypertension

Background: The hypoxia-induced pro-proliferative and anti-apoptotic characteristics of pulmonary arterial endothelial cells (PAECs) play critical roles in pulmonary vascular remodeling and contribute to hypoxic pulmonary arterial hypertension (PAH) pathogenesis. However, the mechanism underlying this hypoxic disease has not been fully elucidated.

Methods: Bioinformatics was adopted to screen out the key hypoxia-related genes in PAH. Gain- and loss-function assays were then performed to test the identified hypoxic pathways in vitro. Human PAECs were cultured under hypoxic (3% O₂) or normoxic (21% O₂) conditions. Hypoxia-induced changes in apoptosis and proliferation were determined by flow cytometry and Ki-67 immunofluorescence staining, respectively. Survival of the hypoxic cells was estimated by cell counting kit-8 assay. Expression alterations of the target hypoxia-related genes, cell cycle regulators, and apoptosis factors were investigated by Western blot.

Results: According to the Gene Expression Omnibus dataset (GSE84538), differentiated embryo chondrocyte expressed gene 1-peroxisome proliferative-activated receptor-γ (Dec1-PPARγ) axis was defined as a key hypoxia-related signaling in PAH. A negative correlation was observed between Dec1 and PPARγ expression in patients with hypoxic PAH. In vitro observations revealed an increased proliferation and a decreased apoptosis in PAECs under hypoxia. Furthermore, hypoxic PAECs exhibited remarkable upregulation of Dec1 and downregulation of PPARγ. Dec1 was confirmed to be crucial for the imbalance of proliferation and apoptosis in hypoxic PAECs. Furthermore, the pro-surviving effect of hypoxic Dec1 was mediated through PPARγ inhibition.

Conclusion: For the first time, Dec1-PPARγ axis was identified as a key determinant hypoxia-modifying signaling that is necessary for the imbalance between proliferation and apoptosis of PAECs. These novel endothelial signal transduction events may offer new diagnostic and therapeutic options for patients with hypoxic PAH.

Integrated Single-Cell Atlas of Endothelial Cells of the Human Lung

BACKGROUND

Cellular diversity of the lung endothelium has not been systematically characterized in humans. We provide a reference atlas of human lung endothelial cells (ECs) to facilitate a better understanding of the phenotypic diversity and composition of cells comprising the lung endothelium.

METHODS

We reprocessed human control single-cell RNA sequencing (scRNAseq) data from 6 datasets. EC populations were characterized through iterative clustering with subsequent differential expression analysis. Marker genes were validated by fluorescent microscopy and in situ hybridization. scRNAseq of primary lung ECs cultured in vitro was performed. The signaling network between different lung cell types was studied. For cross-species analysis or disease relevance, we applied the same methods to scRNAseq data obtained from mouse lungs or from human lungs with pulmonary hypertension.

RESULTS

Six lung scRNAseq datasets were reanalyzed and annotated to identify >15 000 vascular EC cells from 73 individuals. Differential expression analysis of EC revealed signatures corresponding to endothelial lineage, including panendothelial, panvascular, and subpopulation-specific marker gene sets. Beyond the broad cellular categories of lymphatic, capillary, arterial, and venous ECs, we found previously indistinguishable subpopulations; among venous EC, we identified 2 previously indistinguishable populations: pulmonary-venous ECs (COL15A1neg) localized to the lung parenchyma and systemic-venous ECs (COL15A1pos) localized to the airways and the visceral pleura; among capillary ECs, we confirmed their subclassification into recently discovered aerocytes characterized by EDNRB, SOSTDC1, and TBX2 and general capillary EC. We confirmed that all 6 endothelial cell types, including the systemic-venous ECs and aerocytes, are present in mice and identified endothelial marker genes conserved in humans and mice. Ligand-receptor connectome analysis revealed important homeostatic crosstalk of EC with other lung resident cell types. scRNAseq of commercially available primary lung ECs demonstrated a loss of their native lung phenotype in culture. scRNAseq revealed that endothelial diversity is maintained in pulmonary hypertension. Our article is accompanied by an online data mining tool (www.LungEndothelialCellAtlas.com).

CONCLUSIONS

Our integrated analysis provides a comprehensive and well-crafted reference atlas of ECs in the normal lung and confirms and describes in detail previously unrecognized endothelial populations across a large number of humans and mice.

Single-cell transcriptomic profile of human pulmonary artery endothelial cells in health and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an insidious disease characterized by severe remodeling of the pulmonary vasculature caused in part by pathologic changes of endothelial cell functions. Although heterogeneity of endothelial cells across various vascular beds is well known, the diversity among endothelial cells in the healthy pulmonary vascular bed and the pathologic diversity among pulmonary arterial endothelial cells (PAEC) in PAH is unknown and previously unexplored. Here single-cell RNA sequencing technology was used to decipher the cellular heterogeneity among PAEC in the human pulmonary arteries isolated from explanted lungs from three patients with PAH undergoing lung transplantation and three healthy donor lungs not utilized for transplantation. Datasets of 36,368 PAH individual endothelial cells and 36,086 healthy cells were analyzed using the SeqGeq bioinformatics program. Total population differential gene expression analyses identified 629 differentially expressed genes between PAH and controls. Gene Ontology and Canonical Ingenuity analysis revealed pathways that are known to be involved in pathogenesis, as well as unique new pathways. At the individual cell level, dimensionality reduction followed by density based clustering revealed the presence of eight unique PAEC clusters that were typified by proliferative, angiogenic or quiescent phenotypes. While control and PAH harbored many similar subgroups of endothelial cells, PAH had greater proportions of angiogenic and proliferative subsets. These findings identify that only specific subgroups of PAH PAEC have gene expression different than healthy PAEC, and suggest these subpopulations lead to the pathologic functions leading to remodeling.

CDC2 Is an Important Driver of Vascular Smooth Muscle Cell Proliferation via FOXM1 and PLK1 in Pulmonary Arterial Hypertension

A key feature of pulmonary arterial hypertension (PAH) is the hyperplastic proliferation exhibited by the vascular smooth muscle cells from patients (HPASMC). The growth inducers FOXM1 and PLK1 are highly upregulated in these cells. The mechanism by which these two proteins direct aberrant growth in these cells is not clear. Herein, we identify cyclin-dependent kinase 1 (CDK1), also termed cell division cycle protein 2 (CDC2), as having a primary role in promoting progress of the cell cycle leading to proliferation in HPASMC. HPASMC obtained from PAH patients and pulmonary arteries from Sugen/hypoxia rats were investigated for their expression of CDC2. Protein levels of CDC2 were much higher in PAH than in cells from normal donors. Knocking down FOXM1 or PLK1 protein expression with siRNA or pharmacological inhibitors lowered the cellular expression of CDC2 considerably. However, knockdown of CDC2 with siRNA or inhibiting its activity with RO-3306 did not reduce the protein expression of FOXM1 or PLK1. Expression of CDC2 and FOXM1 reached its maximum at G1/S, while PLK1 reached its maximum at G2/M phase of the cell cycle. The expression of other CDKs such as CDK2, CDK4, CDK6, CDK7, and CDK9 did not change in PAH HPASMC. Moreover, inhibition via Wee1 inhibitor adavosertib or siRNAs targeting Wee1, Myt1, CDC25A, CDC25B, or CDC25C led to dramatic decreases in CDC2 protein expression. Lastly, we found CDC2 expression at the RNA and protein level to be upregulated in pulmonary arteries during disease progression Sugen/hypoxia rats. In sum, our present results illustrate that the increased expression of FOXM1 and PLK1 in PAH leads directly to increased expression of CDC2 resulting in potentiated growth hyperactivity of PASMC from patients with pulmonary hypertension. Our results further suggest that the regulation of CDC2, or associated regulatory proteins, will prove beneficial in the treatment of this disease.

Cystic Fibrosis Human Organs-on-a-Chip

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane regulator (CFTR) gene: the gene product responsible for transporting chloride and bicarbonate ions through the apical membrane of most epithelial cells. Major clinical features of CF include respiratory failure, pancreatic exocrine insufficiency, and intestinal disease. Many CF animal models have been generated, but some models fail to fully capture the phenotypic manifestations of human CF disease. Other models that better capture the key characteristics of the human CF phenotype are cost prohibitive or require special care to maintain. Important differences have been reported between the pathophysiology seen in human CF patients and in animal models. These limitations present significant limitations to translational research. This review outlines the study of CF using patient-derived organs-on-a-chip to overcome some of these limitations. Recently developed microfluidic-based organs-on-a-chip provide a human experimental model that allows researchers to manipulate environmental factors and mimic in vivo conditions. These chips may be scaled to support pharmaceutical studies and may also be used to study organ systems and human disease. The use of these chips in CF discovery science enables researchers to avoid the barriers inherent in animal models and promote the advancement of personalized medicine.

ACTRIIA-Fc rebalances activin/GDF versus BMP signaling in pulmonary hypertension

Human genetics, biomarker, and animal studies implicate loss of function in bone morphogenetic protein (BMP) signaling and maladaptive transforming growth factor-β (TGFβ) signaling as drivers of pulmonary arterial hypertension (PAH). Although sharing common receptors and effectors with BMP/TGFβ, the function of activin and growth and differentiation factor (GDF) ligands in PAH are less well defined. Increased expression of GDF8, GDF11, and activin A was detected in lung lesions from humans with PAH and experimental rodent models of pulmonary hypertension (PH). ACTRIIA-Fc, a potent GDF8/11 and activin ligand trap, was used to test the roles of these ligands in animal and cellular models of PH. By blocking GDF8/11- and activin-mediated SMAD2/3 activation in vascular cells, ACTRIIA-Fc attenuated proliferation of pulmonary arterial smooth muscle cells and pulmonary microvascular endothelial cells. In several experimental models of PH, prophylactic administration of ACTRIIA-Fc markedly improved hemodynamics, right ventricular (RV) hypertrophy, RV function, and arteriolar remodeling. When administered after the establishment of hemodynamically severe PH in a vasculoproliferative model, ACTRIIA-Fc was more effective than vasodilator in attenuating PH and arteriolar remodeling. Potent antiremodeling effects of ACTRIIA-Fc were associated with inhibition of SMAD2/3 activation and downstream transcriptional activity, inhibition of proliferation, and enhancement of apoptosis in the vascular wall. ACTRIIA-Fc reveals an unexpectedly prominent role of GDF8, GDF11, and activin as drivers of pulmonary vascular disease and represents a therapeutic strategy for restoring the balance between SMAD1/5/9 and SMAD2/3 signaling in PAH.

NEDD9 Is a Novel and Modifiable Mediator of Platelet-Endothelial Adhesion in the Pulmonary Circulation

Rationale: Data on the molecular mechanisms that regulate platelet-pulmonary endothelial adhesion under conditions of hypoxia are lacking, but may have important therapeutic implications. Objectives: To identify a hypoxia-sensitive, modifiable mediator of platelet-pulmonary artery endothelial cell adhesion and thrombotic remodeling. Methods: Network medicine was used to profile protein-protein interactions in hypoxia-treated human pulmonary artery endothelial cells. Data from liquid chromatography-mass spectrometry and microscale thermophoresis informed the development of a novel antibody (Ab) to inhibit platelet-endothelial adhesion, which was tested in cells from patients with chronic thromboembolic pulmonary hypertension (CTEPH) and three animal models in vivo. Measurements and Main Results: The protein NEDD9 was identified in the hypoxia thrombosome network in silico. Compared with normoxia, hypoxia (0.2% O2) for 24 hours increased HIF-1α (hypoxia-inducible factor-1α)-dependent NEDD9 upregulation in vitro. Increased NEDD9 was localized to the plasma-membrane surface of cells from control donors and patients with CTEPH. In endarterectomy specimens, NEDD9 colocalized with the platelet surface adhesion molecule P-selectin. Our custom-made anti-NEDD9 Ab targeted the NEDD9-P-selectin interaction and inhibited the adhesion of activated platelets to pulmonary artery endothelial cells from control donors in vitro and from patients with CTEPH ex vivo. Compared with control mice, platelet-pulmonary endothelial aggregates and pulmonary hypertension induced by ADP were decreased in NEDD9-/- mice or wild-type mice treated with the anti-NEDD9 Ab, which also decreased chronic pulmonary thromboembolic remodeling in vivo. Conclusions: The NEDD9-P-selectin protein-protein interaction is a modifiable target with which to inhibit platelet-pulmonary endothelial adhesion and thromboembolic vascular remodeling, with potential therapeutic implications for patients with disorders of increased hypoxia signaling pathways, including CTEPH.

Up-Regulation of the Long Noncoding RNA X-Inactive-Specific Transcript and the Sex Bias in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a sex-biased disease. Increased expression and activity of the long-noncoding RNA X-inactive-specific transcript (Xist), essential for X-chromosome inactivation and dosage compensation of X-linked genes, may explain the sex bias of PAH. The present studies used a murine model of plexiform PAH, the intersectin-1s (ITSN) heterozygous knockout (KOITSN+/-) mouse transduced with an ITSN fragment (EHITSN) possessing endothelial cell proliferative activity, in conjunction with molecular, cell biology, biochemical, morphologic, and functional approaches. The data demonstrate significant sex-centered differences with regard to EHITSN-induced alterations in pulmonary artery remodeling, lung hemodynamics, and p38/ETS domain containing protein/c-Fos signaling, altogether leading to a more severe female lung PAH phenotype. Moreover, the long-noncoding RNA-Xist is up-regulated in the lungs of female EHITSN-KOITSN+/- mice compared with that in female wild-type mice, leading to sex-specific modulation of the X-linked gene ETS domain containing protein and its target, two molecular events also characteristic to female human PAH lung. More importantly, cyclin A1 expression in the S and G2/M phases of the cell cycle of synchronized pulmonary artery endothelial cells of female PAH patients is greater versus controls, suggesting functional hyperproliferation. Thus, Xist up-regulation leading to female pulmonary artery endothelial cell sexual dimorphic behavior may provide a better understanding of the origin of sex bias in PAH. Notably, the EHITSN-KOITSN+/- mouse is a unique experimental animal model of PAH that recapitulates most of the sexually dimorphic characteristics of human disease.

Sphingosine 1 Phosphate (S1P) Receptor 1 Is Decreased in Human Lung Microvascular Endothelial Cells of Smokers and Mediates S1P Effect on Autophagy

Destruction of alveoli by apoptosis induced by cigarette smoke (CS) is a major driver of emphysema pathogenesis. However, when compared to cells isolated from non-smokers, primary human lung microvascular endothelial cells (HLMVECs) isolated from chronic smokers are more resilient when exposed to apoptosis-inducing ceramide. Whether this adaptation restores homeostasis is unknown. To better understand the phenotype of HLMVEC in smokers, we interrogated a major pro-survival pathway supported by sphingosine-1-phosphate (S1P) signaling via S1P receptor 1 (S1P1). Primary HLMVECs from lungs of non-smoker or smoker donors were isolated and studied in culture for up to five passages. S1P1 mRNA and protein abundance were significantly decreased in HLMVECs from smokers compared to non-smokers. S1P1 was also decreased in situ in lungs of mice chronically exposed to CS. Levels of S1P1 expression tended to correlate with those of autophagy markers, and increasing S1P (via S1P lyase knockdown with siRNA) stimulated baseline macroautophagy with lysosomal degradation. In turn, loss of S1P1 (siRNA) inhibited these effects of S1P on HLMVECs autophagy. These findings suggest that the anti-apoptotic phenotype of HLMVECs from smokers may be maladaptive, since it is associated with decreased S1P1 expression that may impair their autophagic response to S1P.

Noncanonical scaffolding of Gαi and β-arrestin by G protein-coupled receptors

Heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) are common drug targets and canonically couple to specific G_α protein subtypes and β-arrestin adaptor proteins. G protein-mediated signaling and β-arrestin-mediated signaling have been considered separable. We show here that GPCRs promote a direct interaction between G_αi protein subtype family members and β-arrestins regardless of their canonical G_α protein subtype coupling. G_αi:β-arrestin complexes bound extracellular signal-regulated kinase (ERK), and their disruption impaired both ERK activation and cell migration, which is consistent with β-arrestins requiring a functional interaction with G_αi for certain signaling events. These results introduce a GPCR signaling mechanism distinct from canonical G protein activation in which GPCRs cause the formation of G_αi:β-arrestin signaling complexes.

Comprehensive phenotyping of endothelial cells using flow cytometry 2: Human

In vascular research, clinical samples and samples from animal models are often used together to foster translation of preclinical findings to humans. General concepts of endothelia and murine-specific endothelial phenotypes were discussed in part 1 of this two part series. Here, in part 2, we present a comprehensive overview of human-specific endothelial phenotypes. Pan-endothelial cell markers, organ specific endothelial antigens, and flow cytometric immunophenotyping of blood-borne endothelial cells are reviewed.

Pulmonary-arterial-hypertension (PAH)-on-a-chip: fabrication, validation and application

Currently used animal and cellular models for pulmonary arterial hypertension (PAH) only partially recapitulate its pathophysiology in humans and are thus inadequate in reproducing the hallmarks of the disease, inconsistent in portraying the sex-disparity, and unyielding to combinatorial study designs. Here we sought to deploy the ingenuity of microengineering in developing and validating a tissue chip model for human PAH. We designed and fabricated a microfluidic device to emulate the luminal, intimal, medial, adventitial, and perivascular layers of a pulmonary artery. By growing three types of pulmonary arterial cells (PACs)-endothelial, smooth muscle, and adventitial cells, we recreated the PAH pathophysiology on the device. Diseased (PAH) PACs, when grown on the chips, moved of out their designated layers and created phenomena similar to the major pathologies of human PAH: intimal thickening, muscularization, and arterial remodeling and show an endothelial to mesenchymal transition. Flow-induced stress caused control cells, grown on the chips, to undergo morphological changes and elicit arterial remodeling. Our data also suggest that the newly developed chips can be used to elucidate the sex disparity in PAH and to study the therapeutic efficacy of existing and investigational anti-PAH drugs. We believe this miniaturized device can be deployed for testing various prevailing and new hypotheses regarding the pathobiology and drug therapy in human PAH.

Sex differences in the proliferation of pulmonary artery endothelial cells: implications for plexiform arteriopathy

The sex-biased disease pulmonary arterial hypertension (PAH) is characterized by the proliferation and overgrowth of dysfunctional pulmonary artery endothelial cells (PAECs). During inflammation associated with PAH, granzyme B cleaves intersectin-1 to produce N-terminal (EH_ITSN) and C-terminal (SH3A-E_ITSN) protein fragments. In a murine model of PAH, EH_ITSN triggers plexiform arteriopathy via p38-ELK1-c-Fos signaling. The SH3A-E_ITSN fragment also influences signaling, having dominant-negative effects on ERK1 and ERK2 (also known as MAPK3 and MAPK1, respectively). Using PAECs engineered to express tagged versions of EH_ITSN and SH3A-E_ITSN, we demonstrate that the two ITSN fragments increase both p38-ELK1 activation and the ratio of p38 to ERK1 and ERK2 activity, leading to PAEC proliferation, with female cells being more responsive than male cells. Furthermore, expression of EH_ITSN substantially upregulates the expression and activity of the long non-coding RNA Xist in female PAECs, which in turn upregulates the X-linked gene ELK1 and represses expression of krüppel-like factor 2 (KLF2). These events are recapitulated by the PAECs of female idiopathic PAH patients, and may account for their proliferative phenotype. Thus, upregulation of Xist could be an important factor in explaining sexual dimorphism in the proliferative response of PAECs and the imbalanced sex ratio of PAH.

Lung regeneration: a tale of mice and men

The respiratory system is the main site of gas exchange with the external environment in complex terrestrial animals. Within the trachea and lungs are multiple different tissue niches each consisting of a myriad of cells types with critical roles in air conduction, gas exchange, providing important niche specific cell-cell interactions, connection to the cardiovascular system, and immune surveillance. How the respiratory system responds to external insults and executes the appropriate regenerative response remains challenging to study given the plethora of cell and tissue interactions for this to occur properly. This review will examine the various cell types and tissue niches found within the respiratory system and provide a comparison between mouse and human lungs and trachea to highlight important similarities and differences. Defining the critical gaps in knowledge in human lung and tracheal regeneration is critical for future development of therapies directed towards respiratory diseases.

Vascular Endothelial Growth Factor Receptor 3 Regulates Endothelial Function Through β-Arrestin 1

BACKGROUND

Receptor signaling is central to vascular endothelial function and is dysregulated in vascular diseases such as atherosclerosis and pulmonary arterial hypertension (PAH). Signaling pathways involved in endothelial function include vascular endothelial growth factor receptors (VEGFRs) and G protein-coupled receptors, which classically activate distinct intracellular signaling pathways and responses. The mechanisms that regulate these signaling pathways have not been fully elucidated and it is unclear what nodes for cross talk exist between these diverse signaling pathways. For example, multifunctional β-arrestin (ARRB) adapter proteins are best known as regulators of G protein-coupled receptor signaling, but their role at other receptors and their physiological importance in the setting of vascular disease are unclear.

METHODS

We used a combination of human samples from PAH, human microvascular endothelial cells from lung, and Arrb knockout mice to determine the role of ARRB1 in endothelial VEGFR3 signaling. In addition, a number of biochemical analyses were performed to determine the interaction between ARRB1 and VEGFR3, signaling mediators downstream of VEGFR3, and the internalization of VEGFR3.

RESULTS

Expression of ARRB1 and VEGFR3 was reduced in human PAH, and the deletion of Arrb1 in mice exposed to hypoxia led to worse PAH with a loss of VEGFR3 signaling. Knockdown of ARRB1 inhibited VEGF-C-induced endothelial cell proliferation, migration, and tube formation, along with reduced VEGFR3, Akt, and endothelial nitric oxide synthase phosphorylation. This regulation was mediated by direct ARRB1 binding to the VEGFR3 kinase domain and resulted in decreased VEGFR3 internalization.

CONCLUSIONS

Our results demonstrate a novel role for ARRB1 in VEGFR regulation and suggest a mechanism for cross talk between G protein-coupled receptors and VEGFRs in PAH. These findings also suggest that strategies to promote ARRB1-mediated VEGFR3 signaling could be useful in the treatment of pulmonary hypertension and other vascular disease.

O-GlcNAc Transferase Regulates Angiogenesis in Idiopathic Pulmonary Arterial Hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is considered a vasculopathy characterized by elevated pulmonary vascular resistance due to vasoconstriction and/or lung remodeling such as plexiform lesions, the hallmark of the PAH, as well as cell proliferation and vascular and angiogenic dysfunction. The serine/threonine hydroxyl-linked N-Acetylglucosamine (O-GlcNAc) transferase (OGT) has been shown to drive pulmonary arterial smooth muscle cell (PASMC) proliferation in IPAH. OGT is a cellular nutrient sensor that is essential in maintaining proper cell function through the regulation of cell signaling, proliferation, and metabolism. The aim of this study was to determine the role of OGT and O-GlcNAc in vascular and angiogenic dysfunction in IPAH. Primary isolated human control and IPAH patient PASMCs and pulmonary arterial endothelial cells (PAECs) were grown in the presence or absence of OGT inhibitors and subjected to biochemical assessments in monolayer cultures and tube formation assays, in vitro vascular sprouting 3D spheroid co-culture models, and de novo vascularization models in NODSCID mice. We showed that knockdown of OGT resulted in reduced vascular endothelial growth factor (VEGF) expression in IPAH primary isolated vascular cells. In addition, specificity protein 1 (SP1), a known stimulator of VEGF expression, was shown to have higher O-GlcNAc levels in IPAH compared to control at physiological (5 mM) and high (25 mM) glucose concentrations, and knockdown resulted in decreased VEGF protein levels. Furthermore, human IPAH PAECs demonstrated a significantly higher degree of capillary tube-like structures and increased length compared to control PAECs. Addition of an OGT inhibitor, OSMI-1, significantly reduced the number of tube-like structures and tube length similar to control levels. Assessment of vascular sprouting from an in vitro 3D spheroid co-culture model using IPAH and control PAEC/PASMCs and an in vivo vascularization model using control and PAEC-embedded collagen implants demonstrated higher vascularization in IPAH compared to control. Blocking OGT activity in these experiments, however, altered the vascular sprouting and de novo vascularization in IPAH similar to control levels when compared to controls. Our findings in this report are the first to describe a role for the OGT/O-GlcNAc axis in modulating VEGF expression and vascularization in IPAH. These findings provide greater insight into the potential role that altered glucose uptake and metabolism may have on the angiogenic process and the development of plexiform lesions. Therefore, we believe that the OGT/O-GlcNAc axis may be a potential therapeutic target for treating the angiogenic dysregulation that is present in IPAH.

Integrative proteomics and phosphoproteomics in pulmonary arterial hypertension

Pulmonary arterial endothelial cells (PAEC) are mechanistically linked to origins of pulmonary arterial hypertension (PAH). Here, global proteomics and phosphoproteomics of PAEC from PAH (n = 4) and healthy lungs (n = 5) were performed using LC-MS/MS to confirm known pathways and identify new areas of investigation in PAH. Among PAH and control cells, 170 proteins and 240 phosphopeptides were differentially expressed; of these, 45 proteins and 18 phosphopeptides were located in the mitochondria. Pathologic pathways were identified with integrative bioinformatics and human protein-protein interactome network analyses, then confirmed with targeted proteomics in PAH PAEC and non-targeted metabolomics and targeted high-performance liquid chromatography of metabolites in plasma from PAH patients (n = 30) and healthy controls (n = 12). Dysregulated pathways in PAH include accelerated one carbon metabolism, abnormal tricarboxylic acid (TCA) cycle flux and glutamate metabolism, dysfunctional arginine and nitric oxide pathways, and increased oxidative stress. Functional studies in cells confirmed abnormalities in glucose metabolism, mitochondrial oxygen consumption, and production of reactive oxygen species in PAH. Altogether, the findings indicate that PAH is typified by changes in metabolic pathways that are primarily found in mitochondria.

An Optimized Method to Isolate Human Fibroblasts from Tissue for ex vivo Analysis

Despite their involvement in many physiological and pathological processes, fibroblasts remain a poorly-characterized cell type. Analysis of primary fibroblasts while maintaining their in vivo phenotype is challenging: standard methods for fibroblast isolation require cell culture in vitro, which is known to alter phenotypes. Previously-described protocols for the dissociation of primary tissues fail to extract sufficient numbers of fibroblasts, instead largely yielding immune cells. Here, we describe an optimized method for generating a fibroblast-enriched single-cell suspension from human tissues using combined mechanical and enzymatic dissociation. This allows analysis of ex vivo fibroblasts without the need for culture in vitro.

New artery of knowledge: 3D models of angiogenesis

Angiogenesis and vasculogenesis are complex processes by which new blood vessels are formed and expanded. They play a pivotal role not only in physiological development and growth and tissue and organ repair, but also in a range of pathological conditions, from tumour formation to chronic inflammation and atherosclerosis. Understanding the multistep cell-differentiation programmes and identifying the key molecular players of physiological angiogenesis/vasculogenesis are critical to tackle pathological mechanisms. While many questions are yet to be answered, increasingly sophisticated in vitro, in vivo and ex vivo models of angiogenesis/vasculogenesis, together with cutting-edge imaging techniques, allowed for recent major advances in the field. This review aims to summarise the three-dimensional models available to study vascular network formation and to discuss advantages and limitations of the current systems.

A novel molecular dynamics study of CO2 permeation through aquaporin-5

Aquaporins (AQPs) are protein channels which facilitate rapid water permeation across cell membrane. The AQPs are very vital for biological organs, as their malfunction causes severe diseases in human body. A particular family of AQPs, that is AQP5, has a significant role in lung fluid transport due to submucosal glands structure. However, it has not been yet well understood whether these protein channels can conduct gas molecules. Here, Molecular Dynamics (MD) simulations are used to investigate the CO₂ permeability and diffusion in AQP5 during a 40-nanosecond period. For the first time, equilibrium and Steered MD (SMD) are used to simulate self and force-induced diffusion of CO₂ molecules across AQP5 and POPE lipid bilayer. According to PMFs profile associated to CO₂ permeation, the hydrophobic central pore provides a more suitable pathway for gas molecules compared to other AQP5 channels. Although CO₂ molecules can also permeate across AQP5 water channels, the rate of CO₂ permeation through four channels of the AQP5 monomers is much lower than the central pore. The rate of CO₂ permeation through four AQP5 water channels is even lower than CO₂ diffusion through POPE lipid membrane. The results reported in this investigation demonstrate that MD simulations of human AQP5 provide valuable insights into the gas permeation mechanism for both the equilibrium self-diffusion, and quasi-equilibrium condition.

Selenoprotein P Promotes the Development of Pulmonary Arterial Hypertension: Possible Novel Therapeutic Target

BACKGROUND

Excessive proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs) are key mechanisms of pulmonary arterial hypertension (PAH). Despite the multiple combination therapy, a considerable number of patients develop severe pulmonary hypertension (PH) because of the lack of diagnostic biomarker and antiproliferative therapies for PASMCs.

METHODS

Microarray analyses were used to identify a novel therapeutic target for PAH. In vitro experiments, including lung and serum samples from patients with PAH, cultured PAH-PASMCs, and high-throughput screening of 3336 low-molecular-weight compounds, were used for mechanistic study and exploring a novel therapeutic agent. Five genetically modified mouse strains, including PASMC-specific selenoprotein P (SeP) knockout mice and PH model rats, were used to study the role of SeP and therapeutic capacity of the compounds for the development of PH in vivo.

RESULTS

Microarray analysis revealed a 32-fold increase in SeP in PAH-PASMCs compared with control PASMCs. SeP is a widely expressed extracellular protein maintaining cellular metabolism. Immunoreactivity of SeP was enhanced in the thickened media of pulmonary arteries in PAH. Serum SeP levels were also elevated in patients with PH compared with controls, and high serum SeP predicted poor outcome. SeP-knockout mice ( SeP^-/-) exposed to chronic hypoxia showed significantly reduced right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary artery remodeling compared with controls. In contrast, systemic SeP-overexpressing mice showed exacerbation of hypoxia-induced PH. Furthermore, PASMC-specific SeP^-/- mice showed reduced hypoxia-induced PH compared with controls, whereas neither liver-specific SeP knockout nor liver-specific SeP-overexpressing mice showed significant differences with controls. Altogether, protein levels of SeP in the lungs were associated with the development of PH. Mechanistic experiments demonstrated that SeP promotes PASMC proliferation and resistance to apoptosis through increased oxidative stress and mitochondrial dysfunction, which were associated with activated hypoxia-inducible factor-1α and dysregulated glutathione metabolism. It is important to note that the high-throughput screening of 3336 compounds identified that sanguinarine, a plant alkaloid with antiproliferative effects, reduced SeP expression and proliferation in PASMCs and ameliorated PH in mice and rats.

CONCLUSIONS

These results indicate that SeP promotes the development of PH, suggesting that it is a novel biomarker and therapeutic target of the disorder.

Participation of PLK1 and FOXM1 in the hyperplastic proliferation of pulmonary artery smooth muscle cells in pulmonary arterial hypertension

Vascular smooth muscle cells from the pulmonary arteries (HPASMC) of subjects with pulmonary arterial hypertension (PAH) exhibit hyperplastic growth. The PAH HPASMC display an increased sensitivity to fetal bovine serum (FBS) and undergo growth at a very low, 0.2%, FBS concentration. On the other hand, normal HPASMC (obtained from non-PAH donors) do not proliferate at low FBS (0.2%). A previous genomic study suggested that the nuclear factor, FOXM1 and the polo like kinase 1 (PLK1) are involved in promoting this hyperplastic growth of the PAH HPASMC. Here we find that limiting the action of FOXM1 or PLK1 not only restricts the hyperplastic proliferation of the PAH HPASMC but also modulates the FBS stimulated growth of normal HPASMC. The PAH HPASMC exhibit significantly elevated PLK1 and FOXM1 expression and decreased p27 (quiescence protein) levels compared to normal HPASMC. Regulation of the expression of FOXM1 and PLK1 is accompanied by the regulation of downstream expression of cell cycle components, Aurora B, cyclin B1 and cyclin D1. Expression of these cell cycle components is reversed by the knockdown of FOXM1 or PLK1 expression/activity. Furthermore, the knockdown of PLK1 expression lowers the protein level of FOXM1. On the other hand, inhibiting the action of FOXO1, a growth inhibitor, further increases the expression of FOXM1 in PAH HPASMC. Although PLK1 and FOXM1 clearly participate in PAH HPASMC hyperplasia, at this time it is not clear whether their increased activity is the primary driver of the hyperplastic behavior of the PAH HPASMC or merely a component of the pathway(s) leading to this response.

The ex vivo human lung: research value for translational science

Respiratory diseases are among the leading causes of death and disability worldwide. However, the pathogenesis of both acute and chronic lung diseases remains incompletely understood. As a result, therapeutic options for important clinical problems, including acute respiratory distress syndrome and chronic obstructive pulmonary disease, are limited. Research efforts have been held back in part by the difficulty of modeling lung injury in animals. Donor human lungs that have been rejected for transplantation offer a valuable alternative for understanding these diseases. In 2007, our group developed a simple preparation of an ex vivo-perfused single human lung. In this Review, we discuss the availability of donor human lungs for research, describe the ex vivo-perfused lung preparation, and highlight how this preparation can be used to study the mechanisms of lung injury, to isolate primary cells, and to test novel therapeutics.

Isolating pulmonary microvascular endothelial cells ex vivo: Implications for pulmonary arterial hypertension, and a caution on the use of commercial biomaterials

Transcriptomic analysis of pulmonary microvascular endothelial cells from experimental models offers insight into pulmonary arterial hypertension (PAH) pathobiology. However, culturing may alter the molecular profile of endothelial cells prior to analysis, limiting the translational relevance of results. Here we present a novel and validated method for isolating RNA from pulmonary microvascular endothelial cells (PMVECs) ex vivo that does not require cell culturing. Initially, presumed rat PMVECs were isolated from rat peripheral lung tissue using tissue dissociation and enzymatic digestion, and cells were cultured until confluence to assess endothelial marker expression. Anti-CD31, anti-von Willebrand Factor, and anti-α-smooth muscle actin immunocytochemistry/immunofluorescence signal was detected in presumed rat PMVECs, but also in non-endothelial cell type controls. By contrast, flow cytometry using an anti-CD31 antibody and isolectin 1-B4 (from Griffonia simplicifolia) was highly specific for rat PMVECs. We next developed a strategy in which the addition of an immunomagnetic selection step for CD31+ cells permitted culture-free isolation of rat PMVECs ex vivo for RNA isolation and transcriptomic analysis using fluorescence-activated cell sorting. Heterogeneity in the validity and reproducibility of results using commercial antibodies against endothelial surface markers corresponded to a substantial burden on laboratory time, labor, and scientific budget. We demonstrate a novel protocol for the culture-free isolation and transcriptomic analysis of rat PMVECs with translational relevance to PAH. In doing so, we highlight wide variability in the quality of commonly used biological reagents, which emphasizes the importance of investigator-initiated validation of commercial biomaterials.

Epsin15 Homology Domains: Role in the Pathogenesis of Pulmonary Arterial Hypertension

Intersectin-1s (ITSN) deficiency and expression of a biologically active ITSN fragment, result of granzyme B cleavage under inflammatory conditions associated with pulmonary arterial hypertension (PAH), are characteristics of lung tissue of human and animal models of PAH. Recently, we have shown that this ITSN fragment comprising two Epsin15 homology domains (EH_ITSN) triggers endothelial cell (EC) proliferation and the plexiform arteriopathy in PAH. Limited evidence also indicates that the EH domains of endocytic proteins such as ITSN, upregulate compensatory endocytic pathways in cells with impaired vesicular trafficking. Thus, we sought to investigate whether the EH_ITSN may be involved in this compensatory mechanism for improving the EC endocytic dysfunction induced by ITSN deficiency and possibly contribute to PAH pathogenesis. We used stably-transfected human pulmonary artery ECs expressing the Myc-EH_ITSN (EC_EH-ITSN) and ITSN knockout heterozygous mice (K0^ITSN+/-) transduced with the Myc-EH_ITSN, in conjunction with functional assays: the biotin assay for caveolae internalization and 8 nm gold (Au)- and dinitrophenylated (DNP)-albumin perfusion of murine lung microvasculature. Pulmonary artery ECs of PAH patients (EC_PAH), ITSN knockdown ECs (EC_KD-ITSN), the monocrotaline (MCT)-induced mouse and rat models of PAH, as well as untreated animals, served as controls. ELISA via streptavidin-HRP or anti-DNP antibody (Ab), applied on ECs and lung lysates indicated greater than 30% increase in biotin internalization in EC_EH-ITSN compared to EC_Ctrl. Despite their endocytic deficiency, EC_PAH internalized biotin similar to EC_Ctrl which is twofold higher compared to EC_KD-ITSN. Moreover, the lung microvascular bed of Myc-EH_ITSN-transduced mice and MCT-treated animals showed greater than twofold increase in DNP-BSA transendothelial transport, all compared to untreated controls. Electron microscopy (EM) revealed the increased occurrence of non-conventional endocytic/transcytotic structures (i.e., caveolae clusters, tubulo-vesicular and enlarged endocytic structures, membranous rings), usually underrepresented. Most of these structures were labeled by Au-BSA, consistent with their involvement in the transendothelial transport. Furthermore, ITSN deficiency and EH_ITSN expression alter the subcellular localization of the EH-binding protein 1 (EHBP1) and cortical actin organization, altogether supporting the increase occurrence/trafficking of the alternative endocytic structures. Thus, the EH_ITSN by shifting the physiological vesicular (caveolae) transport toward the alternative endocytic pathways is a significant contributor to the dysfunctional molecular phenotype of EC_PAH.

Brain-Derived Glia Maturation Factor β Participates in Lung Injury Induced by Acute Cerebral Ischemia by Increasing ROS in Endothelial Cells

Brain damage can cause lung injury. To explore the mechanism underlying the lung injury induced by acute cerebral ischemia (ACI), we established a middle cerebral artery occlusion (MCAO) model in male Sprague-Dawley rats. We focused on glia maturation factor β (GMFB) based on quantitative analysis of the global rat serum proteome. Polymerase chain reaction, western blotting, and immunofluorescence revealed that GMFB was over-expressed in astrocytes in the brains of rats subjected to MCAO. We cultured rat primary astrocytes and confirmed that GMFB was also up-regulated in primary astrocytes after oxygen-glucose deprivation (OGD). We subjected the primary astrocytes to Gmfb RNA interference before OGD and collected the conditioned medium (CM) after OGD. We then used the CM to culture pulmonary microvascular endothelial cells (PMVECs) acquired in advance and assessed their status. The viability of the PMVECs improved significantly when Gmfb was blocked. Moreover, ELISA assays revealed an elevation in GMFB concentration in the medium after OGD. Cell cultures containing recombinant GMFB showed increased levels of reactive oxygen species and a deterioration in the state of the cells. In conclusion, GMFB is up-regulated in astrocytes after ACI, and brain-derived GMFB damages PMVECs by increasing reactive oxygen species. GMFB might thus be an initiator of the lung injury induced by ACI.

Sera From Children After Cardiopulmonary Bypass Reduces Permeability of Capillary Endothelial Cell Barriers

OBJECTIVES

Children undergoing cardiopulmonary bypass develop clinically impactful capillary leak of unclear etiology. A widely held hypothesis that exposure of circulating cells to the cardiopulmonary bypass circuit induces the release of inflammatory mediators that act to disrupt intercellular junctions of capillary endothelial cells inducing paracellular capillary leak either directly or through new gene expression.

DESIGN

Cohort study.

SETTING

Tertiary pediatric hospital.

PATIENTS

Twenty children undergoing surgery with cardiopulmonary bypass for congenital heart disease. Serum was collected before cardiopulmonary bypass, 2 hours after cardiopulmonary bypass, and 18 hours after cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We analyzed the effects of 10% patient sera on the "function, structure, and gene expression" of cultured human dermal and pulmonary microvascular endothelial cells. Changes in barrier "function" were measured using transendothelial electrical resistance. Associations between changes in transendothelial electrical resistance and subject characteristics were analyzed using linear mixed effects model with area under the resistance curve as outcome. Changes in junctional "structure" were assessed by analyzing the organization of the endothelial cell junctional proteins claudin-5 and VE-cadherin using immunofluorescence microscopy. Changes in inflammatory "gene expression" were measured using real-time quantitative reverse transcription-polymerase chain reaction. All serum samples induced a transient, 120-minute increase in transendothelial electrical resistance followed by persistent loss of barrier function. Unexpectedly, sera collected postcardiopulmonary bypass-induced significantly less loss of barrier function in both dermal and pulmonary capillary endothelial cell compared with precardiopulmonary bypass sera. Consistent with the transendothelial electrical resistance results, claudin-5 and vascular endothelial-cadherin junctional staining showed less disruption in cultures treated with postcardiopulmonary bypass sera. Expression of genes commonly associated with inflammation was largely unaffected by patient sera.

CONCLUSIONS

Contrary to the hypothesis, sera taken from children after cardiopulmonary bypass induces less capillary barrier disruption relative to sera taken from children before cardiopulmonary bypass, and none of the sera induced significant changes in expression of inflammatory genes.

Activation of Anoctamin-1 Limits Pulmonary Endothelial Cell Proliferation via p38-Mitogen-activated Protein Kinase-Dependent Apoptosis

Hyperproliferative endothelial cells (ECs) play an important role in the pathogenesis of pulmonary arterial hypertension (PAH). Anoctamin (Ano)-1, a calcium-activated chloride channel, can regulate cell proliferation and cell cycle in multiple cell types. However, the expression and function of Ano1 in the pulmonary endothelium is unknown. We examined whether Ano1 was expressed in pulmonary ECs and if altering Ano1 activity would affect EC survival. Expression and localization of Ano1 in rat lung microvascular ECs (RLMVECs) was assessed using immunoblot, immunofluorescence, and subcellular fractionation. Cell counts, flow cytometry, and caspase-3 activity were used to assess changes in cell number and apoptosis in response to the small molecule Ano1 activator, Eact. Changes in mitochondrial membrane potential and mitochondrial reactive oxygen species (mtROS) were assessed using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine, iodide (mitochondrial membrane potential dye) and mitochondrial ROS dye, respectively. Ano1 is expressed in RLMVECs and is enriched in the mitochondria. Activation of Ano1 with Eact reduced RLMVEC counts through increased apoptosis. Ano1 knockdown blocked the effects of Eact. Ano1 activation increased mtROS, reduced mitochondrial membrane potential, increased p38 phosphorylation, and induced release of apoptosis-inducing factor. mtROS inhibition attenuated Eact-mediated p38 phosphorylation. Pulmonary artery ECs isolated from patients with idiopathic PAH (IPAH) had higher expression of Ano1 and increased cell counts compared with control subjects. Eact treatment reduced cell counts in IPAH cells, which was associated with increased apoptosis. In summary, Ano1 is expressed in lung EC mitochondria. Activation of Ano1 promotes apoptosis of pulmonary ECs and human IPAH-pulmonary artery ECs, likely via increased mtROS and p38 phosphorylation, leading to apoptosis.

Unraveling endothelin-1 induced hypercontractility of human pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension

Contraction of human pulmonary artery smooth muscle cells (HPASMC) isolated from pulmonary arterial hypertensive (PAH) and normal (non-PAH) subject lungs was determined and measured with real-time electrical impedance. Treatment of HPASMC with vasoactive peptides, endothelin-1 (ET-1) and bradykinin (BK) but not angiotensin II, induced a temporal decrease in the electrical impedance profile mirroring constrictive morphological change of the cells which typically was more robust in PAH as opposed to non-PAH cells. Inhibition with LIMKi3 and a cofilin targeted motif mimicking cell permeable peptide (MMCPP) had no effect on ET-1 induced HPASMC contraction indicating a negligible role for these actin regulatory proteins. On the other hand, a MMCPP blocking the activity of caldesmon reduced ET-1 promoted contraction pointing to a regulatory role of this protein and its activation pathway in HPASMC contraction. Inhibition of this MEK/ERK/p90RSK pathway, which is an upstream regulator of caldesmon phosphorylation, reduced ET-1 induced cell contraction. While the regulation of ET-1 induced cell contraction was found to be similar in PAH and non-PAH cells, a key difference was the response to pharmacological inhibitors and to siRNA knockdown of Rho kinases (ROCK1/ROCK2). The PAH cells required much higher concentrations of inhibitors to abrogate ET-1 induced contractions and their contraction was not affected by siRNA against either ROCK1 or ROCK2. Lastly, blocking of L-type and T-type Ca2+ channels had no effect on ET-1 or BK induced contraction. However, inhibiting the activity of the sarcoplasmic reticulum Ca2+ ATPase blunted ET-1 and BK induced HPASMC contraction in both PAH and non-PAH derived HPASMC. In summary, our findings here together with previous communications illustrate similarities and differences in the regulation PAH and non-PAH smooth muscle cell contraction relating to calcium translocation, RhoA/ROCK signaling and the activity of caldesmon. These findings may provide useful tools in achieving the regulation of the vascular hypercontractility taking place in PAH.

Establishment and long-term culture of human cystic fibrosis endothelial cells

Endothelial cell (EC) dysfunction has been reported in cystic fibrosis (CF) patients. Thus, the availability of CF EC is paramount to uncover mechanisms of endothelial dysfunction in CF. Using collagenase digestion, we isolated cells from small fragments of pulmonary artery dissected from non-CF lobes or explanted CF lungs. These cells were a heterogeneous mixture, containing variable percentages of EC. To obtain virtually pure pulmonary artery endothelial cells (PAEC), we developed an easy, inexpensive, and reliable method, based on the differential adhesion time of pulmonary artery cells collected after collagenase digestion. With this method, we obtained up to 95% pure non-CF and CF-PAEC. Moreover, we also succeed at immortalizing both PAEC and CF-PAEC, which remained viable and with unchanged phenotype and proliferation rate over the 30th passage. These cells recapitulated cystic fibrosis transmembrane conductance regulator expression and functions of the parental cells. Thus, we isolated for the first time endothelial cells from CF patients, providing a valuable tool to define the emerging role of EC in CF lung and vascular disease.

Generation of a Close-to-Native In Vitro System to Study Lung Cells-Extracellular Matrix Crosstalk

Extracellular matrix (ECM) is an essential component of the tissue microenvironment, actively shaping cellular behavior. In vitro culture systems are often poor in ECM constituents, thus not allowing for naturally occurring cell-ECM interactions. This study reports on a straightforward and efficient method for the generation of ECM scaffolds from lung tissue and its subsequent in vitro application using primary lung cells. Mouse lung tissue was subjected to decellularization with 0.2% sodium dodecyl sulfate, hypotonic solutions, and DNase. Resultant ECM scaffolds were devoid of cells and DNA, whereas lung ECM architecture of alveolar region and blood and airway networks were preserved. Scaffolds were predominantly composed of core ECM and ECM-associated proteins such as collagens I-IV, nephronectin, heparan sulfate proteoglycan core protein, and lysyl oxidase homolog 1, among others. When homogenized and applied as coating substrate, ECM supported the attachment of lung fibroblasts (LFs) in a dose-dependent manner. After ECM characterization and biocompatibility tests, a novel in vitro platform for three-dimensional (3D) matrix repopulation that permits live imaging of cell-ECM interactions was established. Using this system, LFs colonized the ECM scaffolds, displaying a close-to-native morphology in intimate interaction with the ECM fibers, and showed nuclear translocation of the mechanosensor yes-associated protein (YAP), when compared with cells cultured in two dimensions. In conclusion, we developed a 3D-like culture system, by combining an efficient decellularization method with a live-imaging culture platform, to replicate in vitro native lung cell-ECM crosstalk. This is a valuable system that can be easily applied to other organs for ECM-related drug screening, disease modeling, and basic mechanistic studies.