Human primary lung endothelial cells in culture

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.

Arterial stiffness induces remodeling phenotypes in pulmonary artery smooth muscle cells via YAP/TAZ-mediated repression of cyclooxygenase-2

Pulmonary arterial stiffness is an independent risk factor for mortality in pulmonary hypertension (PH) and plays a critical role in PH pathophysiology. Our laboratory has recently demonstrated arterial stiffening early in experimental PH, along with evidence for a mechanobiological feedback loop by which arterial stiffening promotes further cellular remodeling behaviors (Liu F, Haeger CM, Dieffenbach PB, Sicard D, Chrobak I, Coronata AM, Suárez Velandia MM, Vitali S, Colas RA, Norris PC, Marinković A, Liu X, Ma J, Rose CD, Lee SJ, Comhair SA, Erzurum SC, McDonald JD, Serhan CN, Walsh SR, Tschumperlin DJ, Fredenburgh LE. JCI Insight 1: e86987, 2016). Cyclooxygenase-2 (COX-2) and prostaglandin signaling have been implicated in stiffness-mediated regulation, with prostaglandin activity inversely correlated to matrix stiffness and remodeling behaviors in vitro, as well as to disease progression in rodent PH models. The mechanism by which mechanical signaling translates to reduced COX-2 activity in pulmonary vascular cells is unknown. The present work investigated the transcriptional regulators Yes-associated protein (YAP) and WW domain-containing transcription regulator 1 (WWTR1, a.k.a., TAZ), which are known drivers of downstream mechanical signaling, in mediating stiffness-induced changes in COX-2 and prostaglandin activity in pulmonary artery smooth muscle cells (PASMCs). We found that YAP/TAZ activity is increased in PAH PASMCs and experimental PH and is necessary for the development of stiffness-dependent remodeling phenotypes. Knockdown of YAP and TAZ markedly induces COX-2 expression and downstream prostaglandin production by approximately threefold, whereas overexpression of YAP or TAZ reduces COX-2 expression and prostaglandin production to near undetectable levels. Together, our findings demonstrate a stiffness-dependent YAP/TAZ-mediated positive feedback loop that drives remodeling phenotypes in PASMCs via reduced COX-2 and prostaglandin activity. The ability to interrupt this critical mechanobiological feedback loop and enhance local prostaglandin activity via manipulation of YAP/TAZ signaling presents a highly attractive novel strategy for the treatment of PH.

Genomic stability of pulmonary artery endothelial colony-forming cells in culture

Pulmonary vascular remodeling, including proliferation and migration of pulmonary artery endothelial cells (PAEC), is a pathologic hallmark of pulmonary arterial hypertension (PAH). Multiple studies have shown evidence of increased levels of DNA damage and lineage-specific genetic changes in PAH lung vascular cells, suggesting increased genomic instability. Highly proliferative endothelial colony-forming cell (ECFC) clones can be isolated from PAEC. Here we utilized ECFC to track chromosomal copy number of 20 PAH and eight control clones across serial passages using genome-wide microarrays. All PAH clones were genomically stable for at least 20–22 population doublings. At very late passages, ECFC developed a highly aneuploid karyotype, but this was generally associated with senescence and was common to both PAH and controls. We also utilized ECFC to isolate the chromosomally abnormal cells from a mixed population of PAH PAEC. Analysis of PAEC harboring two different changes affecting chromosomes 1 and X demonstrated that both abnormalities were present in the same clone, indicating they originated in a common ancestral cell. In a second case, with a partial duplication of chromosome 17, clones carrying the duplication were more frequent at later passages than chromosomally normal clones from the same PAEC culture, suggesting the rearrangement may confer a proliferative advantage. Overall, this small study suggests that endothelial cells from PAH lungs are stable in culture, but that when chromosome abnormalities do occur, they may confer a selective advantage that allows expansion of the abnormal cell population and could contribute to lung vascular remodeling in vivo.

Modulation of Endothelial Bone Morphogenetic Protein Receptor Type 2 Activity by Vascular Endothelial Growth Factor Receptor 3 in Pulmonary Arterial Hypertension

BACKGROUND

Bone morphogenetic protein (BMP) signaling has multiple roles in the development and function of the blood vessels. In humans, mutations in BMP receptor type 2 (BMPR2), a key component of BMP signaling, have been identified in the majority of patients with familial pulmonary arterial hypertension (PAH). However, only a small subset of individuals with BMPR2 mutation develops PAH, suggesting that additional modifiers of BMPR2 function play an important role in the onset and progression of PAH.

METHODS

We used a combination of studies in zebrafish embryos and genetically engineered mice lacking endothelial expression of Vegfr3 to determine the interaction between vascular endothelial growth factor receptor 3 (VEGFR3) and BMPR2. Additional in vitro studies were performed by using human endothelial cells, including primary lung endothelial cells from subjects with PAH.

RESULTS

Attenuation of Vegfr3 in zebrafish embryos abrogated Bmp2b-induced ectopic angiogenesis. Endothelial cells with disrupted VEGFR3 expression failed to respond to exogenous BMP stimulation. Mechanistically, VEGFR3 is physically associated with BMPR2 and facilitates ligand-induced endocytosis of BMPR2 to promote phosphorylation of SMADs and transcription of ID genes. Conditional, endothelial-specific deletion of Vegfr3 in mice resulted in impaired BMP signaling responses, and significantly worsened hypoxia-induced pulmonary hypertension. Consistent with these data, we found significant decrease in VEGFR3 expression in pulmonary arterial endothelial cells from human PAH subjects, and reconstitution of VEGFR3 expression in PAH pulmonary arterial endothelial cells restored BMP signaling responses.

CONCLUSIONS

Our findings identify VEGFR3 as a key regulator of endothelial BMPR2 signaling and a potential determinant of PAH penetrance in humans.

A high-yield isolation and enrichment strategy for human lung microvascular endothelial cells

Vasculopathies, characterized by the formation of fragile and abnormal microvessels, are associated with the severity of many chronic lung diseases, including pulmonary fibrosis, emphysema/chronic obstructive pulmonary disease, systemic sclerosis, and hypertension. However, the study of human lung vasculature has been limited by the ability to isolate generous quantities of microvascular endothelial cells (MVEC) free from mesenchymal contamination. Expansion and passaging of primary human MVEC in vitro typically results in loss of a traditional phenotype in favor of an intermediate mesenchymal one, as early as passage five. Here we provide a detailed protocol for the selection of large quantities of enriched primary human lung MVEC based upon differential adherence from mesenchyme and simple magnetic separation, which decreases the need for excessive passaging, in order to obtain sufficient cell numbers to successfully freeze stock cultures. Additional protocols are provided for Ac-di-LDL selection, characterization, and a sandwich angiogenesis method of functional tube formation. The complete protocol including cell isolation and characterization takes approximately six weeks to complete.

Nicotinamide Phosphoribosyltransferase Promotes Pulmonary Vascular Remodeling and Is a Therapeutic Target in Pulmonary Arterial Hypertension

BACKGROUND

Pulmonary arterial hypertension is a severe and progressive disease, a hallmark of which is pulmonary vascular remodeling. Nicotinamide phosphoribosyltransferase (NAMPT) is a cytozyme that regulates intracellular nicotinamide adenine dinucleotide levels and cellular redox state, regulates histone deacetylases, promotes cell proliferation, and inhibits apoptosis. We hypothesized that NAMPT promotes pulmonary vascular remodeling and that inhibition of NAMPT could attenuate pulmonary hypertension.

METHODS

Plasma, mRNA, and protein levels of NAMPT were measured in the lungs and isolated pulmonary artery endothelial cells from patients with pulmonary arterial hypertension and in the lungs of rodent models of pulmonary hypertension. Nampt^+/- mice were exposed to 10% hypoxia and room air for 4 weeks, and the preventive and therapeutic effects of NAMPT inhibition were tested in the monocrotaline and Sugen hypoxia models of pulmonary hypertension. The effects of NAMPT activity on proliferation, migration, apoptosis, and calcium signaling were tested in human pulmonary artery smooth muscle cells.

RESULTS

Plasma and mRNA and protein levels of NAMPT were increased in the lungs and isolated pulmonary artery endothelial cells from patients with pulmonary arterial hypertension, as well as in lungs of rodent models of pulmonary hypertension. Nampt^+/- mice were protected from hypoxia-mediated pulmonary hypertension. NAMPT activity promoted human pulmonary artery smooth muscle cell proliferation via a paracrine effect. In addition, recombinant NAMPT stimulated human pulmonary artery smooth muscle cell proliferation via enhancement of store-operated calcium entry by enhancing expression of Orai2 and STIM2. Last, inhibition of NAMPT activity attenuated monocrotaline and Sugen hypoxia-induced pulmonary hypertension in rats.

CONCLUSIONS

Our data provide evidence that NAMPT plays a role in pulmonary vascular remodeling and that its inhibition could be a potential therapeutic target for pulmonary arterial hypertension.

Bone Morphogenic Protein Type 2 Receptor Mutation-Independent Mechanisms of Disrupted Bone Morphogenetic Protein Signaling in Idiopathic Pulmonary Arterial Hypertension

Altered bone morphogenic protein (BMP) signaling, independent of BMPR2 mutations, can result in idiopathic pulmonary arterial hypertension (IPAH). Glucose dysregulation can regulate multiple processes in IPAH. However, the role of glucose in BMP antagonist expression in IPAH has not been characterized. We hypothesized that glucose uptake regulates BMP signaling through stimulation of BMP antagonist expression in IPAH. Using human plasma, lung tissue, and primary pulmonary arterial smooth muscle cells (PASMCs), we examined the protein expression of BMP2, BMP-regulated Smads, and Smurf-1 in patients with IPAH and control subjects. Gremlin-1 levels were elevated in patients with IPAH compared with control subjects, whereas expression of BMP2 was not different. We demonstrate increased Smad polyubiquitination in IPAH lung tissue and PASMCs that was further enhanced with proteasomal inhibition. Examination of the Smad ubiquitin-ligase, Smurf-1, showed increased protein expression in IPAH lung tissue and localization in the smooth muscle of the pulmonary artery. Glucose dose dependently increased Smurf-1 protein expression in control PASMCs, whereas Smurf-1 in IPAH PASMCs was increased and sustained. Conversely, phospho-Smad1/5/8 levels were reduced in IPAH compared with control PASMCs at physiological glucose concentrations. Interestingly, high glucose concentrations decreased phosphorylation of Smad1/5/8 in control PASMCs. Blocking glucose uptake had opposing effects in IPAH PASMCs, and inhibition of Smurf-1 activity resulted in partial rescue of Smad1/5/8 activation and cell migration rates. Collectively, these data suggest that BMP signaling can be regulated through BMPR2 mutation-independent mechanisms. Gremlin-1 (synonym: induced-in-high-glucose-2 protein) and Smurf-1 may function to inhibit BMP signaling as a consequence of the glucose dysregulation described in IPAH.

Protective Roles of Endothelial AMP-Activated Protein Kinase Against Hypoxia-Induced Pulmonary Hypertension in Mice

Rationale:

Endothelial AMP-activated protein kinase (AMPK) plays an important role for vascular homeostasis, and its role is impaired by vascular inflammation. However, the role of endothelial AMPK in the pathogenesis of pulmonary arterial hypertension (PAH) remains to be elucidated.

Objective:

To determine the role of endothelial AMPK in the development of PAH.

Methods and Results:

Immunostaining showed that endothelial AMPK is downregulated in the pulmonary arteries of patients with PAH and hypoxia mouse model of pulmonary hypertension (PH). To elucidate the role of endothelial AMPK in PH, we used endothelial-specific AMPK-knockout mice ( eAMPK –/– ), which were exposed to hypoxia. Under normoxic condition, eAMPK –/– mice showed the normal morphology of pulmonary arteries compared with littermate controls ( eAMPK flox/flox ). In contrast, development of hypoxia-induced PH was accelerated in eAMPK –/– mice compared with controls. Furthermore, the exacerbation of PH in eAMPK –/– mice was accompanied by reduced endothelial function, upregulation of growth factors, and increased proliferation of pulmonary artery smooth muscle cells. Importantly, conditioned medium from endothelial cells promoted pulmonary artery smooth muscle cell proliferation, which was further enhanced by the treatment with AMPK inhibitor. Serum levels of inflammatory cytokines, including tumor necrosis factor-α and interferon-γ were significantly increased in patients with PAH compared with healthy controls. Consistently, endothelial AMPK and cell proliferation were significantly reduced by the treatment with serum from patients with PAH compared with controls. Importantly, long-term treatment with metformin, an AMPK activator, significantly attenuated hypoxia-induced PH in mice.

Conclusions:

These results indicate that endothelial AMPK is a novel therapeutic target for the treatment of PAH.

Distal vessel stiffening is an early and pivotal mechanobiological regulator of vascular remodeling and pulmonary hypertension

Pulmonary arterial (PA) stiffness is associated with increased mortality in patients with pulmonary hypertension (PH); however, the role of PA stiffening in the pathogenesis of PH remains elusive. Here, we show that distal vascular matrix stiffening is an early mechanobiological regulator of experimental PH. We identify cyclooxygenase-2 (COX-2) suppression and corresponding reduction in prostaglandin production as pivotal regulators of stiffness-dependent vascular cell activation. Atomic force microscopy microindentation demonstrated early PA stiffening in experimental PH and human lung tissue. Pulmonary artery smooth muscle cells (PASMC) grown on substrates with the stiffness of remodeled PAs showed increased proliferation, decreased apoptosis, exaggerated contraction, enhanced matrix deposition, and reduced COX-2-derived prostanoid production compared with cells grown on substrates approximating normal PA stiffness. Treatment with a prostaglandin I₂ analog abrogated monocrotaline-induced PA stiffening and attenuated stiffness-dependent increases in proliferation, matrix deposition, and contraction in PASMC. Our results suggest a pivotal role for early PA stiffening in PH and demonstrate the therapeutic potential of interrupting mechanobiological feedback amplification of vascular remodeling in experimental PH.

Phosphorylation inactivation of endothelial nitric oxide synthesis in pulmonary arterial hypertension

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

Isolation and analysis of sugar nucleotides using solid phase extraction and fluorophore assisted carbohydrate electrophoresis

The building blocks of simple and complex oligosaccharides, termed sugar nucleotides, are often overlooked for their role in metabolic diseases and may hold the key to the underlying disease pathogenesis. Multiple reasons may account for the lack of analysis and quantitation of these sugar nucleotides, including the difficulty in isolation and purification as well as the required expensive instrumentation such as a high performance liquid chromatography (HPLC), mass spectrometer, or capillary electrophoresis. We have established a simple yet effective way to purify and quantitate sugar nucleotides using solid phase extraction (SPE) chromatography combined with fluorophore assisted carbohydrate electrophoresis (FACE). The simplicity of use, combined with the ability to run multiple samples at one time, give this technique a distinct advantage over the established methods for isolation and analysis of sugar nucleotides from cell culture models.

•

Sugar nucleotides can be easily purified with solid phase extraction chromatography.

•

FACE can be used to analyze multiple nucleotide sugar extracts with a single run.

•

The proposed method is simple, affordable, and uses common everyday research labware.

Increased Mutagen Sensitivity and DNA Damage in Pulmonary Arterial Hypertension

RATIONALE

Pulmonary arterial hypertension (PAH) is a serious lung condition characterized by vascular remodeling in the precapillary pulmonary arterioles. We and others have demonstrated chromosomal abnormalities and increased DNA damage in PAH lung vascular cells, but their timing and role in disease pathogenesis is unknown.

OBJECTIVES

We hypothesized that if DNA damage predates PAH, it might be an intrinsic cell property that is present outside the diseased lung.

METHODS

We measured DNA damage, mutagen sensitivity, and reactive oxygen species (ROS) in lung and blood cells from patients with Group 1 PAH, their relatives, and unrelated control subjects.

MEASUREMENTS AND MAIN RESULTS

Baseline DNA damage was significantly elevated in PAH, both in pulmonary artery endothelial cells (P < 0.05) and peripheral blood mononuclear cells (PBMC) (P < 0.001). Remarkably, PBMC from unaffected relatives showed similar increases, indicating this is not related to PAH treatments. ROS levels were also higher (P < 0.01). DNA damage correlated with ROS production and was suppressed by antioxidants (P < 0.001). PBMC from patients and relatives also showed markedly increased sensitivity to two chemotherapeutic drugs, bleomycin and etoposide (P < 0.001). Results were consistent across idiopathic, heritable, and associated PAH groups.

CONCLUSIONS

Levels of baseline and mutagen-induced DNA damage are intrinsically higher in PAH cells. Similar results in PBMC from unaffected relatives suggest this may be a genetically determined trait that predates disease onset and may act as a risk factor contributing to lung vascular remodeling following endothelial cell injury. Further studies are required to fully characterize mutagen sensitivity, which could have important implications for clinical management.

Isolation and Characterization of Human Lung Lymphatic Endothelial Cells

Characterization of lymphatic endothelial cells from the respiratory system may be crucial to investigate the role of the lymphatic system in the normal and diseased lung. We describe a simple and inexpensive method to harvest, isolate, and expand lymphatic endothelial cells from the human lung (HL-LECs). Fifty-five samples of healthy lung selected from patients undergoing lobectomy were studied. A two-step purification tool, based on paramagnetic sorting with monoclonal antibodies to CD31 and Podoplanin, was employed to select a pure population of HL-LECs. The purity of HL-LECs was assessed by morphologic criteria, immunocytochemistry, flow cytometry, and functional assays. Interestingly, these cells retain in vitro several receptor tyrosine kinases (RTKs) implicated in cell survival and proliferation. HL-LECs represent a clinically relevant cellular substrate to study lymphatic biology, lymphoangiogenesis, interaction with microbial agents, wound healing, and anticancer therapy.

Loss of microRNA-17∼92 in smooth muscle cells attenuates experimental pulmonary hypertension via induction of PDZ and LIM domain 5

RATIONALE

Recent studies suggest that microRNAs (miRNAs) play important roles in regulation of pulmonary artery smooth muscle cell (PASMC) phenotype and are implicated in pulmonary arterial hypertension (PAH). However, the underlying molecular mechanisms remain elusive.

OBJECTIVES

This study aims to understand the mechanisms regulating PASMC proliferation and differentiation by microRNA-17∼92 (miR-17∼92) and to elucidate its implication in PAH.

METHODS

We generated smooth muscle cell (SMC)-specific miR-17∼92 and PDZ and LIM domain 5 (PDLIM5) knockout mice and overexpressed miR-17∼92 and PDLIM5 by injection of miR-17∼92 mimics or PDLIM5-V5-His plasmids and measured their responses to hypoxia. We used miR-17∼92 mimics, inhibitors, overexpression vectors, small interfering RNAs against PDLIM5, Smad, and transforming growth factor (TGF)-β to determine the role of miR-17∼92 and its downstream targets in PASMC proliferation and differentiation.

MEASUREMENTS AND MAIN RESULTS

We found that human PASMC (HPASMC) from patients with PAH expressed decreased levels of the miR-17∼92 cluster, TGF-β, and SMC markers. Overexpression of miR-17∼92 increased and restored the expression of TGF-β3, Smad3, and SMC markers in HPASMC of normal subjects and patients with idiopathic PAH, respectively. Knockdown of Smad3 but not Smad2 prevented miR-17∼92-induced expression of SMC markers. SMC-specific knockout of miR-17∼92 attenuated hypoxia-induced pulmonary hypertension (PH) in mice, whereas reconstitution of miR-17∼92 restored hypoxia-induced PH in these mice. We also found that PDLIM5 is a direct target of miR-17/20a, and hypertensive HPASMC and mouse PASMC expressed elevated PDLIM5 levels. Suppression of PDLIM5 increased expression of SMC markers and enhanced TGF-β/Smad2/3 activity in vitro and enhanced hypoxia-induced PH in vivo, whereas overexpression of PDLIM5 attenuated hypoxia-induced PH.

CONCLUSIONS

We provided the first evidence that miR-17∼92 inhibits PDLIM5 to induce the TGF-β3/SMAD3 pathway, contributing to the pathogenesis of PAH.

Targeting receptor tyrosine kinases and their downstream signaling with cell-penetrating peptides in human pulmonary artery smooth muscle and endothelial cells

Cell-penetrating peptide (CPP) intracellular delivery of receptor signaling motifs provides an opportunity to regulate specific receptor tyrosine kinase signal transductions. We targeted tyrosine residues Y740 and Y751 of the PDGF receptor β (PDGFRβ) and Y1175 of the VEGF receptor 2 (VEGFR2). The Y740 and Y751 motifs activated ERK and Akt, while the Y1175 motif activated ERK. Targeting either Y740 or Y751 of the PDGFRβ in human pulmonary artery smooth muscle cells (HPASMC) effectively inhibited PDGF activation of ERK or Akt. Interfering with the Y751 region of the PDGFRβ proved more effective than targeting the Y740 region. The phosphorylation of Y751 of the CPP and the length and exact sequence of the mimicking peptide proved crucial. On the other hand, in human pulmonary artery endothelial cell phosphorylation of the VEGFR2 Y1175 CPP was not a determinant in blockage of ERK activation. Likewise, the length of the peptide mimic was not crucial with a very small sequence containing the Y1175 remaining effective. Physiologic proof of concept for the effectiveness of the CPP was confirmed by blockage of HPASMC migration in response to PDGF following culture injury. Thus targeted blockage of tyrosine kinase receptor signaling can be very effective.

Hyperplastic Growth of Pulmonary Artery Smooth Muscle Cells from Subjects with Pulmonary Arterial Hypertension Is Activated through JNK and p38 MAPK

Smooth muscle in the pulmonary artery of PAH subjects, both idiopathic and hereditary, is characterized by hyperplasia. Smooth muscle cells (HPASMC) isolated from subjects with or without PAH retain their in vivo phenotype as illustrated by their expression of alpha-smooth muscle actin and expression of H-caldesmon. Both non PAH and PAH HPASMC display a lengthy, approximately 94h, cell cycle. The HPASMC from both idiopathic and hereditary PAH display an abnormal proliferation characterized by continued growth under non-proliferative, non-growth stimulated conditions. This effector independent proliferation is JNK and p38 MAP kinase dependent. Blocking the activation of either abrogates the HPASMC growth. HPASMC from non PAH donors under quiescent conditions display negligible proliferation but divide upon exposure to growth factors such as PDGF-BB or FGF2 but not EGF. This growth does not involve the MAP kinases. Instead it routes via the tyrosine kinase receptor through mTOR and then 6SK. In the PAH cells PDGF-BB and FGF2 augment the dysregulated cell proliferation, also through mTOR/6SK. Additionally, blocking the activation of mTOR also modulates the MAP kinase promoted dysregulated growth. These results highlight key alterations in the growth of HPASMC from subjects with PAH which contribute to the etiology of the disease and can clearly be targeted at various regulatory points for future therapies.

O-linked β-N-acetylglucosamine transferase directs cell proliferation in idiopathic pulmonary arterial hypertension

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is a cardiopulmonary disease characterized by cellular proliferation and vascular remodeling. A more recently recognized characteristic of the disease is the dysregulation of glucose metabolism. The primary link between altered glucose metabolism and cell proliferation in IPAH has not been elucidated. We aimed to determine the relationship between glucose metabolism and smooth muscle cell proliferation in IPAH.

METHODS AND RESULTS

Human IPAH and control patient lung tissues and pulmonary artery smooth muscle cells (PASMCs) were used to analyze a specific pathway of glucose metabolism, the hexosamine biosynthetic pathway. We measured the levels of O-linked β-N-acetylglucosamine modification, O-linked β-N-acetylglucosamine transferase (OGT), and O-linked β-N-acetylglucosamine hydrolase in control and IPAH cells and tissues. Our data suggest that the activation of the hexosamine biosynthetic pathway directly increased OGT levels and activity, triggering changes in glycosylation and PASMC proliferation. Partial knockdown of OGT in IPAH PASMCs resulted in reduced global O-linked β-N-acetylglucosamine modification levels and abrogated PASMC proliferation. The increased proliferation observed in IPAH PASMCs was directly impacted by proteolytic activation of the cell cycle regulator, host cell factor-1.

CONCLUSIONS

Our data demonstrate that hexosamine biosynthetic pathway flux is increased in IPAH and drives OGT-facilitated PASMC proliferation through specific proteolysis and direct activation of host cell factor-1. These findings establish a novel regulatory role for OGT in IPAH, shed a new light on our understanding of the disease pathobiology, and provide opportunities to design novel therapeutic strategies for IPAH.

Modulating the dysregulated migration of pulmonary arterial hypertensive smooth muscle cells with motif mimicking cell permeable peptides

Migration of vascular smooth muscle cells is a key element in remodeling during pulmonary arterial hypertension (PAH). We are observing key alterations in the migratory characteristics of human pulmonary artery smooth muscle cells (HPASMC) isolated from transplanted lungs of subjects with PAH. Using wound migration and barrier removal assays, we demonstrate that the PAH cells migrate under quiescent growth conditions and in the absence of pro-migratory factors such as platelet derived growth factor (PDGF). Under the same conditions, in the absence of PDGF, non-PAH HPASMC show negligible migration. The dysregulated migration initiates, in part, through phosphorylation events signaled through the unstimulated PDGF receptor via focal adhesion kinase (FAK) whose total basal expression and phosphorylation at tyrosine 391 is markedly increased in the PAH cells and is inhibited by a motif mimicking cell-permeable peptide (MMCPP) targeting the Tyr751 region of the PDGF receptor and by imatinib. However, exposure of the PAH cells to PDGF further promotes migration. Inhibition of p21 activated kinases (PAK), LIM kinases (LIMK), c-Jun N-terminal kinases (JNK) and p38 mitogen-activated protein kinases (MAPK) reduces both the dysregulated and the PDGF-stimulated migration. Immunofluorescence microscopy confirms these observations showing activated JNK and p38 MAPK at the edge of the wound but not in the rest of the culture in the PAH cells. The upstream inhibitors FAK (PF-573228) and imatinib block this activation of JNK and p38 at the edge of the site of injury and correspondingly inhibit migration. MMCPP which inhibit the activation of downstream effectors of migration, cofilin and caldesmon, also limit the dysregulated migration. These results highlight key pathways which point to potential targets for future therapies of pulmonary hypertension with MMCPP.

Restoration of impaired endothelial myocyte enhancer factor 2 function rescues pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary arterioles, characterized by increased pulmonary arterial pressure and right ventricular failure. The cause of PAH is complex, but aberrant proliferation of the pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells is thought to play an important role in its pathogenesis. Understanding the mechanisms of transcriptional gene regulation involved in pulmonary vascular homeostasis can provide key insights into potential therapeutic strategies.

METHODS AND RESULTS

We demonstrate that the activity of the transcription factor myocyte enhancer factor 2 (MEF2) is significantly impaired in the PAECs derived from subjects with PAH. We identified MEF2 as the key cis-acting factor that regulates expression of a number of transcriptional targets involved in pulmonary vascular homeostasis, including microRNAs 424 and 503, connexins 37, and 40, and Krűppel Like Factors 2 and 4, which were found to be significantly decreased in PAH PAECs. The impaired MEF2 activity in PAH PAECs was mediated by excess nuclear accumulation of 2 class IIa histone deacetylases (HDACs) that inhibit its function, namely HDAC4 and HDAC5. Selective, pharmacological inhibition of class IIa HDACs led to restoration of MEF2 activity in PAECs, as demonstrated by increased expression of its transcriptional targets, decreased cell migration and proliferation, and rescue of experimental pulmonary hypertension models.

CONCLUSIONS

Our results demonstrate that strategies to augment MEF2 activity hold potential therapeutic value in PAH. Moreover, we identify selective HDAC IIa inhibition as a viable alternative approach to avoid the potential adverse effects of broad spectrum HDAC inhibition in PAH.

Modeling the lung: Design and development of tissue engineered macro- and micro-physiologic lung models for research use

Respiratory tract specific cell populations, or tissue engineered in vitro grown human lung, have the potential to be used as research tools to mimic physiology, toxicology, pathology, as well as infectious diseases responses of cells or tissues. Studies related to respiratory tract pathogenesis or drug toxicity testing in the past made use of basic systems where single cell populations were exposed to test agents followed by evaluations of simple cellular responses. Although these simple single-cell-type systems provided good basic information related to cellular responses, much more can be learned from cells grown in fabricated microenvironments which mimic in vivo conditions in specialized microfabricated chambers or by human tissue engineered three-dimensional (3D) models which allow for more natural interactions between cells. Recent advances in microengineering technology, microfluidics, and tissue engineering have provided a new approach to the development of 2D and 3D cell culture models which enable production of more robust human in vitro respiratory tract models. Complex models containing multiple cell phenotypes also provide a more reasonable approximation of what occurs in vivo without the confounding elements in the dynamic in vivo environment. The goal of engineering good 3D human models is the formation of physiologically functional respiratory tissue surrogates which can be used as pathogenesis models or in the case of 2D screening systems for drug therapy evaluation as well as human toxicity testing. We hope that this manuscript will serve as a guide for development of future respiratory tract model systems as well as a review of conventional models.

Vascular targeting of nanocarriers: perplexing aspects of the seemingly straightforward paradigm

Targeted nanomedicine holds promise to find clinical use in many medical areas. Endothelial cells that line the luminal surface of blood vessels represent a key target for treatment of inflammation, ischemia, thrombosis, stroke, and other neurological, cardiovascular, pulmonary, and oncological conditions. In other cases, the endothelium is a barrier for tissue penetration or a victim of adverse effects. Several endothelial surface markers including peptidases (e.g., ACE, APP, and APN) and adhesion molecules (e.g., ICAM-1 and PECAM) have been identified as key targets. Binding of nanocarriers to these molecules enables drug targeting and subsequent penetration into or across the endothelium, offering therapeutic effects that are unattainable by their nontargeted counterparts. We analyze diverse aspects of endothelial nanomedicine including (i) circulation and targeting of carriers with diverse geometries, (ii) multivalent interactions of carrier with endothelium, (iii) anchoring to multiple determinants, (iv) accessibility of binding sites and cellular response to their engagement, (v) role of cell phenotype and microenvironment in targeting, (vi) optimization of targeting by lowering carrier avidity, (vii) endocytosis of multivalent carriers via molecules not implicated in internalization of their ligands, and (viii) modulation of cellular uptake and trafficking by selection of specific epitopes on the target determinant, carrier geometry, and hydrodynamic factors. Refinement of these aspects and improving our understanding of vascular biology and pathology is likely to enable the clinical translation of vascular endothelial targeting of nanocarriers.

Rho-kinase inhibitor prevents bleomycin-induced injury in neonatal rats independent of effects on lung inflammation

Bleomycin-induced lung injury is characterized in the neonatal rat by inflammation dominated by neutrophils and macrophages, inhibited distal airway and vascular development, and pulmonary hypertension, similar to human infants with severe bronchopulmonary dysplasia. Rho-kinase (ROCK) is known to mediate lung injury in adult animals via stimulatory effects on inflammation. We therefore hypothesized that inhibition of ROCK may ameliorate bleomycin-induced lung injury in the neonatal rat. Pups received daily intraperitoneal bleomycin or saline from Postnatal Days 1 through 14 with or without Y-27632, a ROCK inhibitor. Treatment with Y-27632 prevented bleomycin-induced pulmonary hypertension, as evidenced by normalized pulmonary vascular resistance, decreased right-ventricular hypertrophy, and attenuated remodeling of pulmonary resistance arteries. Bleomycin-induced changes in distal lung architecture, including septal thinning, inhibited alveolarization, and decreased numbers of peripheral arteries and capillaries, were partially or completely normalized by Y-27632. Treatment with Y-27632 or a CXCR2 antagonist, SB265610, also abrogated tissue neutrophil influx, while having no effect on macrophages. However, treatment with SB265610 did not prevent bleomycin-induced lung injury. Lung content of angiostatic thrombospondin-1 (TSP1) was increased significantly in the lungs of bleomycin-exposed animals, and was completely attenuated by treatment with Y-27632. Thrombin-stimulated TSP1 production by primary cultured rat pulmonary artery endothelial cells was also attenuated by Y-27632. Taken together, our findings suggest a preventive effect of Y-27632 on bleomycin-mediated injury by a mechanism unrelated to inflammatory cells. Our data suggest that improvements in lung morphology may have been related to indirect stimulatory effects on angiogenesis via down-regulation of TSP1.

Nitrosation-dependent caveolin 1 phosphorylation, ubiquitination, and degradation and its association with idiopathic pulmonary arterial hypertension

In the present study, we tested the hypothesis that chronic inflammation and oxidative/nitrosative stress induce caveolin 1 (Cav-1) degradation, providing an underlying mechanism of endothelial cell activation/dysfunction and pulmonary vascular remodeling in patients with idiopathic pulmonary arterial hypertension (IPAH). We observed reduced Cav-1 protein despite increased Cav-1 messenger RNA expression and also endothelial nitric oxide synthase (eNOS) hyperphosphorylation in human pulmonary artery endothelial cells (PAECs) from patients with IPAH. In control human lung endothelial cell cultures, tumor necrosis factor α-induced nitric oxide (NO) production and S-nitrosation (SNO) of Cav-1 Cys-156 were associated with Src displacement and activation, Cav-1 Tyr-14 phosphorylation, and destabilization of Cav-1 oligomers within 5 minutes that could be blocked by eNOS or Src inhibition. Prolonged stimulation (72 hours) with NO donor DETANONOate reduced oligomerized and total Cav-1 levels by 40%-80%, similar to that observed in IPAH patient-derived PAECs. NO donor stimulation of endothelial cells for >72 hours, which was associated with sustained Src activation and Cav-1 phosphorylation, ubiquitination, and degradation, was blocked by NOS inhibitor L-NAME, Src inhibitor PP2, and proteosomal inhibitor MG132. Thus, chronic inflammation, sustained eNOS and Src signaling, and Cav-1 degradation may be important causal factors in the development of IPAH by promoting PAEC dysfunction/activation via sustained oxidative/nitrosative stress.

Correction of nonsense BMPR2 and SMAD9 mutations by ataluren in pulmonary arterial hypertension

Heritable pulmonary arterial hypertension (HPAH) is a serious lung vascular disease caused by heterozygous mutations in the bone morphogenetic protein (BMP) pathway genes, BMPR2 and SMAD9. One noncanonical function of BMP signaling regulates biogenesis of a subset of microRNAs. We have previously shown that this function is abrogated in patients with HPAH, making it a highly sensitive readout of BMP pathway integrity. Ataluren (PTC124) is an investigational drug that permits ribosomal readthrough of premature stop codons, resulting in a full-length protein. It exhibits oral bioavailability and limited toxicity in human trials. Here, we tested ataluren in lung- or blood-derived cells from patients with HPAH with nonsense mutations in BMPR2 (n = 6) or SMAD9 (n = 1). Ataluren significantly increased BMP-mediated microRNA processing in six of the seven cases. Moreover, rescue was achieved even for mutations exhibiting significant nonsense-mediated mRNA decay. Response to ataluren was dose dependent, and complete correction was achieved at therapeutic doses currently used in clinical trials for cystic fibrosis. BMP receptor (BMPR)-II protein levels were normalized and ligand-dependent phosphorylation of downstream target Smads was increased. Furthermore, the usually hyperproliferative phenotype of pulmonary artery endothelial and smooth muscle cells was reversed by ataluren. These results indicate that ataluren can effectively suppress a high proportion of BMPR2 and SMAD9 nonsense mutations and correct BMP signaling in vitro. Approximately 29% of all HPAH mutations are nonsense point mutations. In light of this, we propose ataluren as a potential new personalized therapy for this significant subgroup of patients with PAH.

A novel p38 mitogen-activated protein kinase/Elk-1 transcription factor-dependent molecular mechanism underlying abnormal endothelial cell proliferation in plexogenic pulmonary arterial hypertension

Plexiform lesions (PLs), the hallmark of plexogenic pulmonary arterial hypertension (PAH), contain phenotypically altered, proliferative endothelial cells (ECs). The molecular mechanism that contributes to EC proliferation and formation of PLs is poorly understood. We now show that a decrease in intersectin-1s (ITSN-1s) expression due to granzyme B (GrB) cleavage during inflammation associated with PAH and the high p38/Erk1/2(MAPK) activity ratio caused by the GrB/ITSN cleavage products lead to EC proliferation and selection of a proliferative/plexiform EC phenotype. We used human pulmonary artery ECs of PAH subjects (EC(PAH)), paraffin-embedded and frozen human lung tissue, and animal models of PAH in conjunction with microscopy imaging, biochemical, and molecular biology approaches to demonstrate that GrB cleaves ITSN-1s, a prosurvival protein of lung ECs, and generates two biologically active fragments, an N-terminal fragment (GrB-EH(ITSN)) with EC proliferative potential and a C-terminal product with dominant negative effects on Ras/Erk1/2. The proliferative potential of GrB-EH(ITSN) is mediated via sustained phosphorylation of p38(MAPK) and Elk-1 transcription factor and abolished by chemical inhibition of p38(MAPK). Moreover, lung tissue of PAH animal models and human specimens and EC(PAH) express lower levels of ITSN-1s compared with controls and the GrB-EH(ITSN) cleavage product. Moreover, GrB immunoreactivity is associated with PLs in PAH lungs. The concurrent expression of the two cleavage products results in a high p38/Erk1/2(MAPK) activity ratio, which is critical for EC proliferation. Our findings identify a novel GrB-EH(ITSN)-dependent pathogenic p38(MAPK)/Elk-1 signaling pathway involved in the poorly understood process of PL formation in severe PAH.

Production and assessment of decellularized pig and human lung scaffolds

The authors have previously shown that acellular (AC) trachea-lung scaffolds can (1) be produced from natural rat lungs, (2) retain critical components of the extracellular matrix (ECM) such as collagen-1 and elastin, and (3) be used to produce lung tissue after recellularization with murine embryonic stem cells. The aim of this study was to produce large (porcine or human) AC lung scaffolds to determine the feasibility of producing scaffolds with potential clinical applicability. We report here the first attempt to produce AC pig or human trachea-lung scaffold. Using a combination of freezing and sodium dodecyl sulfate washes, pig trachea-lungs and human trachea-lungs were decellularized. Once decellularization was complete we evaluated the structural integrity of the AC lung scaffolds using bronchoscopy, multiphoton microscopy (MPM), assessment of the ECM utilizing immunocytochemistry and evaluation of mechanics through the use of pulmonary function tests (PFTs). Immunocytochemistry indicated that there was loss of collagen type IV and laminin in the AC lung scaffold, but retention of collagen-1, elastin, and fibronectin in some regions. MPM scoring was also used to examine the AC lung scaffold ECM structure and to evaluate the amount of collagen I in normal and AC lung. MPM was used to examine the physical arrangement of collagen-1 and elastin in the pleura, distal lung, lung borders, and trachea or bronchi. MPM and bronchoscopy of trachea and lung tissues showed that no cells or cell debris remained in the AC scaffolds. PFT measurements of the trachea-lungs showed no relevant differences in peak pressure, dynamic or static compliance, and a nonrestricted flow pattern in AC compared to normal lungs. Although there were changes in content of collagen I and elastin this did not affect the mechanics of lung function as evidenced by normal PFT values. When repopulated with a variety of stem or adult cells including human adult primary alveolar epithelial type II cells both pig and human AC scaffolds supported cell attachment and cell viability. Examination of scaffolds produced using a variety of detergents indicated that detergent choice influenced human immune response in terms of T cell activation and chemokine production.

The lysosomal inhibitor, chloroquine, increases cell surface BMPR-II levels and restores BMP9 signalling in endothelial cells harbouring BMPR-II mutations

Pulmonary arterial hypertension (PAH) is characterized by dysregulated pulmonary artery endothelial cell (PAEC) proliferation, apoptosis and permeability. Loss-of-function mutations in the bone morphogenetic protein receptor type-II (BMPR-II) are the most common cause of heritable PAH, usually resulting in haploinsufficiency. We previously showed that BMPR-II expression is regulated via a lysosomal degradative pathway. Here, we show that the antimalarial drug, chloroquine, markedly increased cell surface expression of BMPR-II protein independent of transcription in PAECs. Inhibition of protein synthesis experiments revealed a rapid turnover of cell surface BMPR-II, which was inhibited by chloroquine treatment. Chloroquine enhanced PAEC expression of BMPR-II following siRNA knockdown of the BMPR-II transcript. Using blood outgrowth endothelial cells (BOECs), we confirmed that signalling in response to the endothelial BMPR-II ligand, BMP9, is compromised in BOECs from patients harbouring BMPR-II mutations, and in BMPR-II mutant PAECs. Chloroquine significantly increased gene expression of BMP9-BMPR-II signalling targets Id1, miR21 and miR27a in both mutant BMPR-II PAECs and BOECs. These findings provide support for the restoration of cell surface BMPR-II with agents such as chloroquine as a potential therapeutic approach for heritable PAH.

Altered expression and signal transduction of endothelin-1 receptors in heritable and idiopathic pulmonary arterial hypertension

Human pulmonary arterial smooth muscle cells (PASMC) were isolated from elastic pulmonary arteries dissected from lungs of individuals with and without pulmonary arterial hypertension (PAH). Reflecting increased smooth muscle constriction in cells from PAH subject, Ca(2+) influx in response to endothelin-1 (ET-1) increased in all the PAH PASMC populations relative to the normal donor control cells. The ETA receptor mRNA levels remained unchanged, whereas the ETB receptor mRNA levels decreased in both heritable and idiopathic PAH-derived PASMC. All the PASMC populations expressed considerably higher ETA compared to ETB receptor number. Both ETA and ETB receptor numbers were reduced in bone morphogenetic protein receptor type II (BMPR2) mutation PAH. ETB receptors showed a particular reduction in number. Phospho-antibody array analysis of normal and BMPR2 deletion PASMC illustrated ERK and Akt activation to be the most prominent and to be taking place principally through ETB receptors in normal PASMC, but primarily through ETA receptors in PASMC from BMPR2 PAH subjects. Additionally in the PAH cells the total relative ET-1 signal response was markedly reduced. Western analysis from the BMPR2 PASMC duplicated the array results, whereas PASMC from iPAH subjects showed variability with most samples continuing to signal through ETB. In sum, these results indicate that generally both receptors are reduced in PAH particularly ETB, and that ETB signaling through protein kinases becomes markedly reduced in BMPR2 PASMC, while it continues in IPAH. Importantly, the data suggest that caution must be taken when applying ET-1 receptor antagonist therapy to PAH patients.

An endothelial apelin-FGF link mediated by miR-424 and miR-503 is disrupted in pulmonary arterial hypertension

Pulmonary arterial hypertension is characterized by vascular remodeling associated with obliteration of pulmonary arterioles and formation of plexiform lesions comprised of hyperproliferative endothelial and vascular smooth muscle cells. Here, we describe a novel, microRNA-dependent association between APLN and FGF2 pathways in the pulmonary artery endothelial cells (PAECs), where disruption of APLN signaling results in a robust increase in FGF2 expression. We show that this link is mediated by two microRNAs, miR-424 and miR-503, that are regulated by APLN and significantly downregulated in PAH. MiR-424 and miR-503 exert anti-proliferative effects by targeting FGF2 and FGFR1. Overexpression of miR-424 and miR-503 in PAECs promoted cellular quiescence and inhibited the capacity of PAEC conditioned media to induce proliferation of pulmonary artery smooth muscle cells. We show that reconstitution of miR-424 and miR-503 can ameliorate pulmonary hypertension in experimental models. These studies demonstrate the importance of APLN-miR-424/503-FGF axis in maintaining pulmonary vascular homeostasis.

Enhancing and limiting endothelin-1 signaling with a cell-penetrating peptide mimicking the third intracellular loop of the ETB receptor

TAT (a 13-mer derived from the HIV-1 Tat protein)-linked cell-permeable peptides deliver plasma membrane impermeable cargos into the cell. We investigated the effect of a TAT-linked intracellular third loop of the endothelin-1 type B receptor on endothelin-1 activation of ERK. The effect of this peptide on ERK activation was determined in ETB receptor cDNA-transfected Chinese hamster ovary cells and in ETA- and ETB-expressing human pulmonary artery smooth muscle cells obtained from a normal and a bone morphogenetic protein-2 receptor, exon 1-8 deletion subject, with pulmonary hypertension. In the Chinese hamster ovary cells the peptide, at optimum 10 μm concentration, suppressed endothelin-1 activation. In the normal human pulmonary artery smooth muscle cells, the peptide marginally enhanced endothelin-1 activation of ERK. However, it markedly enhanced the endothelin-1 activation of ERK in the bone morphogenetic protein-2 receptor human pulmonary artery smooth muscle cells. While the effective concentration for endothelin-1 activation of ERK remained unchanged in the bone morphogenetic protein-2 receptor human pulmonary artery smooth muscle cells, the number of ETB receptors declined by 2/3. These data point to the intracellular third loop peptide as having variable receptor interactive effects with both signal repressive and enhancing capabilities. Peptides that can alter endothelin-1 signal capabilities are potentially important in the study and treatment of pulmonary hypertension.