Circulating angiogenic precursors in idiopathic pulmonary arterial hypertension

Reversal of inflammatory reprogramming by vasodilator agents in pulmonary hypertension

Background

Pulmonary arterial hypertension (PAH) is a deadly disease without effective non-invasive diagnostic and prognostic testing. It remains unclear whether vasodilators reverse inflammatory activation, a part of PAH pathogenesis. Single-cell profiling of inflammatory cells in blood could clarify these PAH mechanisms.

Methods

We evaluated a University of Pittsburgh Medical Center cohort consisting of idiopathic PAH (iPAH) and systemic sclerosis-associated PAH (sscPAH) patients and non-PAH controls. We performed single-cell RNA sequencing of peripheral blood mononuclear cells (PBMCs) from controls (n=3) and from PAH patients (iPAH and sscPAH) naïve to treatment (n=4), PAH patients 3 months after phosphodiesterase-5 inhibitor (PDE5i) treatment (n=7) and PAH patients 3 months after PDE5i+macitentan treatment (n=6). We compared the transcriptomes of five PBMC subtypes from iPAH and sscPAH to observe their serial responses to treatments. Furthermore, we utilised network analysis to illuminate the altered connectivity of biological networks in this complex disease.

Results

We defined differential gene expression and perturbed network connectivity in PBMCs of PAH patients following treatment with PDE5i or PDE5i+macitentan. Importantly, we identified significant reversal of inflammatory transcripts and pathways in the combined PAH patient cohort after vasodilator therapy in every PBMC type assessed. The "glucagon signalling in metabolic regulation" pathway in monocytes was reversed after vasodilator therapy via two independent analysis modalities.

Conclusion

Via a systems-biology approach, we define inflammatory reprogramming in the blood of PAH patients and the anti-inflammatory activity of vasodilators. Such findings establish diagnostic and prognostic blood-based tools for tracking inflammatory progression of PAH and response to therapy.

Flow Cytometric Determination of Circulating Progenitor Cells in Patients With Pulmonary Arterial Hypertension: A Systematic Review

Pulmonary arterial hypertension (PAH) is characterized by progressive narrowing and obliteration of distal, pre-capillary pulmonary vessels. Yet, noninvasive biomarkers that reflect this disease-defining process are lacking. A systematic review of PAH studies that measured circulating progenitor cells (CPCs) or circulating endothelial cells (CECs) in PAH by flow cytometry was performed to understand how future studies, leveraging state-of-the-art single-cell analyses, can advance the field. The study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews. Of the 2422 studies identified, 20 met inclusion criteria. Nineteen studies measured CPCs by flow cytometry, only one study examined CECs. A total of 647 PAH patients were included across all 19 CPC studies. Marker schemes chosen to define CPCs, and the methods of flow cytometry used, varied significantly across studies. Meta-analysis of a subgroup of CPC studies (n = 8) similarly identified a significant amount of heterogeneity even amongst studies using the same marker scheme. In conclusion, a systematic review of CPC studies in PAH patients reveals the limitations of the current literature. Future studies should include contemporary risk assessments, disease duration, reporting of comorbid conditions, and serial sampling over time. Furthermore, methods that incorporate best practices for detecting rare cell populations by flow cytometry are essential and should be reported in sufficient detail in future publications. With the emergence of single-cell technologies, future studies of circulating progenitor and endothelial cells in PAH remain relevant and may incorporate several insights from the current review to build upon the existing literature.

Risk stratification and treatment goals in pulmonary arterial hypertension

Risk stratification has gained an increasing role in predicting outcomes and guiding the treatment of patients with pulmonary arterial hypertension (PAH). The most predictive prognostic factors are three noninvasive parameters (World Health Organization functional class, 6-min walk distance and natriuretic peptides) that are included in all currently validated risk stratification tools. However, suffering from limitations mainly related to reduced specificity of PAH severity, these variables may not always be adequate in isolation for guiding individualised treatment decisions. Moreover, with effective combination treatment regimens and emerging PAH therapies, markers associated with pulmonary vascular remodelling are expected to become of increasing relevance in guiding the treatment of patients with PAH. While reaching a low mortality risk, assessed with a validated risk tool, remains an important treatment goal, preliminary data suggest that invasive haemodynamics and cardiac imaging may add incremental value in guiding treatment decisions.

Cardiovascular Risk in Philadelphia-Negative Myeloproliferative Neoplasms: Mechanisms and Implications-A Narrative Review

Myeloproliferative neoplasms (MPNs), encompassing disorders like polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are characterized by clonal hematopoiesis without the Philadelphia chromosome. The JAK2 V617F mutation is prevalent in PV, ET, and PMF, while mutations in MPL and CALR also play significant roles. These conditions predispose patients to thrombotic events, with PMF exhibiting the lowest survival among MPNs. Chronic inflammation, driven by cytokine release from aberrant leukocytes and platelets, amplifies cardiovascular risk through various mechanisms, including atherosclerosis and vascular remodeling. Additionally, MPN-related complications like pulmonary hypertension and cardiac fibrosis contribute to cardiovascular morbidity and mortality. This review consolidates recent research on MPNs' cardiovascular implications, emphasizing thrombotic risk, chronic inflammation, and vascular stiffness. Understanding these associations is crucial for developing targeted therapies and improving outcomes in MPN patients.

Dysregulated VEGF/VEGFR-2 Signaling and Plexogenic Lesions in the Embryonic Lungs of Chickens Predisposed to Pulmonary Arterial Hypertension

Plexiform lesions are a hallmark of pulmonary arterial hypertension (PAH) in humans and are proposed to stem from dysfunctional angioblasts. Broiler chickens (Gallus gallus) are highly susceptible to PAH, with plexiform-like lesions observed in newly hatched individuals. Here, we reported the emergence of plexiform-like lesions in the embryonic lungs of broiler chickens. Lung samples were collected from broiler chickens at embryonic day 20 (E20), hatch, and one-day-old, with PAH-resistant layer chickens as controls. Plexiform lesions consisting of CD133+/vascular endothelial growth factor receptor type-2 (VEGFR-2)+ angioblasts were exclusively observed in broiler embryos and sporadically in layer embryos. Distinct gene profiles of angiogenic factors were observed between the two strains, with impaired VEGF-A/VEGFR-2 signaling correlating with lesion development and reduced arteriogenesis. Pharmaceutical inhibition of VEGFR-2 resulted in enhanced lesion development in layer embryos. Moreover, broiler embryonic lungs displayed increased activation of HIF-1α and nuclear factor erythroid 2-related factor 2 (Nrf2), indicating a hypoxic state. Remarkably, we found a negative correlation between lung Nrf2 activation and VEGF-A and VEGFR-2 expression. In vitro studies indicated that Nrf2 overactivation restricted VEGF signaling in endothelial progenitor cells. The findings from broiler embryos suggest an association between plexiform lesion development and impaired VEGF system due to aberrant activation of Nrf2.

Extrapulmonary manifestations of pulmonary arterial hypertension

INTRODUCTION

Extrapulmonary manifestations of pulmonary arterial hypertension (PAH) may play a critical pathobiological role and a deeper understanding will advance insight into mechanisms and novel therapeutic targets. This manuscript reviews our understanding of extrapulmonary manifestations of PAH.

AREAS COVERED

A group of experts was assembled and a complimentary PubMed search performed (October 2023 - March 2024). Inflammation is observed throughout the central nervous system and attempts at manipulation are an encouraging step toward novel therapeutics. Retinal vascular imaging holds promise as a noninvasive method of detecting early disease and monitoring treatment responses. PAH patients have gut flora alterations and dysbiosis likely plays a role in systemic inflammation. Despite inconsistent observations, the roles of obesity, insulin resistance and dysregulated metabolism may be illuminated by deep phenotyping of body composition. Skeletal muscle dysfunction is perpetuated by metabolic dysfunction, inflammation, and hypoperfusion, but exercise training shows benefit. Renal, hepatic, and bone marrow abnormalities are observed in PAH and may represent both end-organ damage and disease modifiers.

EXPERT OPINION

Insights into systemic manifestations of PAH will illuminate disease mechanisms and novel therapeutic targets. Additional study is needed to understand whether extrapulmonary manifestations are a cause or effect of PAH and how manipulation may affect outcomes.

Tm4sf1-marked Endothelial Subpopulation Is Dysregulated in Pulmonary Arterial Hypertension

The identification and role of endothelial progenitor cells in pulmonary arterial hypertension (PAH) remain controversial. Single-cell omics analysis can shed light on endothelial progenitor cells and their potential contribution to PAH pathobiology. We aim to identify endothelial cells that may have stem/progenitor potential in rat lungs and assess their relevance to PAH. Differential expression, gene set enrichment, cell-cell communication, and trajectory reconstruction analyses were performed on lung endothelial cells from single-cell RNA sequencing of Sugen-hypoxia, monocrotaline, and control rats. Relevance to human PAH was assessed in multiple independent blood and lung transcriptomic data sets. Rat lung endothelial cells were visualized by immunofluorescence in situ, analyzed by flow cytometry, and assessed for tubulogenesis in vitro. A subpopulation of endothelial cells (endothelial arterial type 2 [EA2]) marked by Tm4sf1 (transmembrane 4 L six family member 1), a gene strongly implicated in cancer, harbored a distinct transcriptomic signature enriched for angiogenesis and CXCL12 signaling. Trajectory analysis predicted that EA2 has a less differentiated state compared with other endothelial subpopulations. Analysis of independent data sets revealed that TM4SF1 is downregulated in lungs and endothelial cells from patients and PAH models, is a marker for hematopoietic stem cells, and is upregulated in PAH circulation. TM4SF1+CD31+ rat lung endothelial cells were visualized in distal pulmonary arteries, expressed hematopoietic marker CD45, and formed tubules in coculture with lung fibroblasts. Our study uncovered a novel Tm4sf1-marked subpopulation of rat lung endothelial cells that may have stem/progenitor potential and demonstrated its relevance to PAH. Future studies are warranted to further elucidate the role of EA2 and Tm4sf1 in PAH.

Aberration in myeloid-derived pro-angiogenic cells in type-2 diabetes mellitus; implication for diabetic retinopathy?

Purpose

Diabetic retinopathy (DR) is a major microvascular complication of type 2 diabetes mellitus (T2DM). Myelomonocytic proangiogenic cells (PAC) have been implicated in DR pathogenesis, but their functional and developmental abnormalities are unclear. In this study we assessed PAC characteristics from healthy controls, T2DM patients with DR (DR) and without (NoDR) in order to determine the consequence of the diabetic condition on PAC phenotype and function, and whether these differ between DR and NoDR patients.

Methods

PAC were generated by culturing PBMC on fibronectin coating and then immunophenotyped using flow cytometry. Furthermore, cells were sorted based on CD14, CD105, and CD133 expression and added to an in vitro 3-D endothelial tubule formation assay, containing GFP-expressing human retinal endothelial cells (REC), pericytes, and pro-angiogenic growth factors. Tubule formation was quantified by fluorescence microscopy and image analysis. Moreover, sorted populations were analyzed for angiogenic mediator production using a multiplex assay.

Results

The expression of CD16, CD105 and CD31, but not CD133, was lower in PAC from T2DM patients with or without DR. Myeloid and non-myeloid T2DM-derived sorted populations increased REC angiogenesis in vitro as compared to control cultures. They also showed increased S100A8 secretion, decreased VEGF-A secretion, and similar levels of IL-8, HGF, and IL-3 as compared to healthy control (HC)-derived cell populations.

Conclusion

T2DM PAC are phenotypically and functionally altered compared to PAC from HC. Differences between DR and NoDR PAC are limited. We propose that impaired T2DM PAC provide inadequate vascular support and promote compensatory, albeit pathological, retinal neovascularization.

Blood-Derived Progenitor Cells Are Depleted in Older Adults with Cognitive Impairment: A Role for Vascular Resilience?

BACKGROUND

Depletion of blood-derived progenitor cells, including so called "early endothelial progenitor cells", has been observed in individuals with early stage Alzheimer's disease relative to matched older control subjects. These findings could implicate the loss of angiogenic support from hematopoietic progenitors or endothelial progenitors in cognitive dysfunction.

OBJECTIVE

To investigate links between progenitor cell proliferation and mild levels of cognitive dysfunction.

METHODS

We conducted in vitro studies of blood-derived progenitor cells using blood samples from sixty-five older adults who were free of stroke or dementia. Peripheral blood mononuclear cells from venous blood samples were cultured in CFU-Hill media and the number of colony forming units were counted after 5 days in vitro. Neuropsychological testing was administered to all participants.

RESULTS

Fewer colony forming units were observed in samples from older adults with a Clinical Dementia Rating global score of 0.5 versus 0. Older adults whose samples developed fewer colony forming units exhibited worse performance on neuropsychological measures of memory, executive functioning, and language ability.

CONCLUSION

These data suggest blood progenitors may represent a vascular resilience marker related to cognitive dysfunction in older adults.

Pulmonary hypertension is associated with poor cardiovascular and hematologic outcomes in patients with myeloproliferative neoplasms and cardiovascular disease

Cardiovascular events and hematologic progression to myelofibrosis or leukemia are leading causes of morbidity and mortality among patients with myeloproliferative neoplasms (MPN). Pulmonary hypertension (PH) is also associated with MPN and cardiovascular disease (CVD), though its prognostic significance in MPN is not well characterized. Our primary objective was to investigate the effect of PH, defined as right-ventricular systolic pressure (RVSP) ≥ 50 mmHg on echocardiogram or mean pulmonary artery pressure (mPAP) ≥ 20 on right heart catheterization, on cardiovascular and all-cause mortality and hematologic progression in patients with MPN and CVD (atrial fibrillation, heart failure hospitalization, and myocardial infarction after MPN diagnosis). Of the 197 patients included (86 ET, 80 PV, 31 PMF), 92 (47%) had PH and 98 (50%) were male. All-cause mortality (58 vs 37%, p = 0.004), cardiovascular death (35 vs 9%, p < 0.0001), and hematologic progression (23 vs 11%, p = 0.037) occurred more frequently in patients with PH. Multivariable competing-risk and proportional hazards regression showed that PH was associated with increased risk of all-cause death (adjusted hazard ratio [HR], 1.80, 95% CI 1.10-2.93), CV death (adjusted subdistribution HR 3.71, 95% CI 1.58-8.73), and hematologic progression (adjusted subdistribution HR 1.99, 95% CI 1.21-3.27).

Potential contribution of early endothelial progenitor cell (eEPC)-to-macrophage switching in the development of pulmonary plexogenic lesion

Background

Plexiform lesions, which have a dynamic appearance in structure and cellular composition, are the histological hallmark of severe pulmonary arterial hypertension in humans. The pathogenesis of the lesion development remains largely unknown, although it may be related to local inflammation and dysfunction in early progenitor endothelial cells (eEPCs). We tested the hypothesis that eEPCs contribute to the development of plexiform lesions by differentiating into macrophages in the setting of chronic inflammation.

Methods

The eEPC markers CD133 and VEGFR-2, macrophage lineage marker mannose receptor C-type 1 (MRC1), TNFα and nuclear factor erythroid 2-related factor 2 (Nrf2) in plexiform lesions in a broiler model were determined by immunohistochemistry. eEPCs derived from peripheral blood mononuclear cells were exposed to TNFα, and macrophage differentiation and angiogenic capacity of the cells were evaluated by phagocytotic and Matrigel plug assays, respectively. The role of Nrf2 in eEPC-to-macrophage transition as well as in MRC1 expression was also evaluated. Intratracheal installation of TNFα was conducted to determine the effect of local inflammation on the formation of plexiform lesions.

Results

Cells composed of the early lesions have a typical eEPC phenotype whereas those in more mature lesions display molecular and morphological characteristics of macrophages. Increased TNFα production in plexiform lesions was observed with lesion progression. In vitro studies showed that chronic TNFα challenge directed eEPCs to macrophage differentiation accompanied by hyperactivation of Nrf2, a stress-responsive transcription factor. Nrf2 activation (Keap1 knockdown) caused a marked downregulation in CD133 but upregulation in MRC1 mRNA. Dual luciferase reporter assay demonstrated that Nrf2 binds to the promoter of MRC1 to trigger its expression. In good agreement with the in vitro observation, TNFα exposure induced macrophage differentiation of eEPCs in Matrigel plugs, resulting in reduced neovascularization of the plugs. Intratracheal installation of TNFα resulted in a significant increase in plexiform lesion density.

Conclusions

This work provides evidence suggesting that macrophage differentiation of eEPCs resulting from chronic inflammatory stimulation contributes to the development of plexiform lesions. Given the key role of Nrf2 in the phenotypic switching of eEPCs to macrophages, targeting this molecular might be beneficial for intervention of plexiform lesions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02210-7.

Radiation-induced cardiac side-effects: The lung as target for interacting damage and intervention

Radiotherapy is part of the treatment for many thoracic cancers. During this treatment heart and lung tissue can often receive considerable doses of radiation. Doses to the heart can potentially lead to cardiac effects such as pericarditis and myocardial fibrosis. Common side effects after lung irradiation are pneumonitis and pulmonary fibrosis. It has also been shown that lung irradiation has effects on cardiac function. In a rat model lung irradiation caused remodeling of the pulmonary vasculature increasing resistance of the pulmonary vascular bed, leading to enhanced pulmonary artery pressure, right ventricle hypertrophy and reduced right ventricle performance. Even more pronounced effects are observed when both, lung and heart are irradiated.

The effects observed after lung irradiation show striking similarities with symptoms of pulmonary arterial hypertension. In particular, the vascular remodeling in lung tissue seems to have similar underlying features. Here, we discuss the similarities and differences of vascular remodeling observed after thoracic irradiation compared to those in pulmonary arterial hypertension patients and research models. We will also assess how this knowledge of similarities could potentially be translated into interventions which would be beneficial for patients treated for thoracic tumors, where dose to lung tissue is often unavoidable.

Cardiovascular Disease in Myeloproliferative Neoplasms: JACC: CardioOncology State-of-the-Art Review

Myeloproliferative neoplasms are associated with increased risk for thrombotic complications. These conditions most commonly involve somatic mutations in genes that lead to constitutive activation of the Janus-associated kinase signaling pathway (eg, Janus kinase 2, calreticulin, myeloproliferative leukemia protein). Acquired gain-of-function mutations in these genes, particularly Janus kinase 2, can cause a spectrum of disorders, ranging from clonal hematopoiesis of indeterminate potential, a recently recognized age-related promoter of cardiovascular disease, to frank hematologic malignancy. Beyond thrombosis, patients with myeloproliferative neoplasms can develop other cardiovascular conditions, including heart failure and pulmonary hypertension. The authors review the pathophysiologic mechanisms of cardiovascular complications of myeloproliferative neoplasms, which involve inflammation, prothrombotic and profibrotic factors (including transforming growth factor-beta and lysyl oxidase), and abnormal function of circulating clones of mutated leukocytes and platelets from affected individuals. Anti-inflammatory therapies may provide cardiovascular benefit in patients with myeloproliferative neoplasms, a hypothesis that requires rigorous evaluation in clinical trials.

"NOVEL MECHANISMS TARGETED BY DRUG TRIALS IN PULMONARY ARTERIAL HYPERTENSION"

Pulmonary arterial hypertension (PAH) is a rare disease associated with abnormally elevated pulmonary pressures and right heart failure resulting in high morbidity and mortality. While PAH prognosis has improved with the introduction of pulmonary vasodilators, disease progression remains a major problem. Given that available therapies are inadequate for preventing small vessel loss and obstruction, there is an active interest in identifying drugs capable of targeting angiogenesis and mechanisms involved in regulation of cell growth and fibrosis. Among the mechanisms linked to PAH pathogenesis, recent preclinical studies have identified promising compounds that are currently being tested in clinical trials. These drugs target seven of the major mechanisms associated with PAH pathogenesis: BMP signaling, tyrosine kinase receptors, estrogen metabolism, extracellular matrix, angiogenesis, epigenetics, and serotonin metabolism. In this review, we will discuss the preclinical studies that led to prioritization of these mechanisms and will discuss recently completed and ongoing phase 2/3 trials using novel interventions such as sotatercept, anastrozole, rodatristat ethyl, tyrosine kinase inhibitors, and endothelial progenitor cells among others. We anticipate that the next generation of compounds will build upon the success of the current standard of care and improve clinical outcomes and quality of life of patients afflicted with PAH.

Progenitor/Stem Cells in Vascular Remodeling during Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by an important occlusive vascular remodeling with the production of new endothelial cells, smooth muscle cells, myofibroblasts, and fibroblasts. Identifying the cellular processes leading to vascular proliferation and dysfunction is a major goal in order to decipher the mechanisms leading to PAH development. In addition to in situ proliferation of vascular cells, studies from the past 20 years have unveiled the role of circulating and resident vascular in pulmonary vascular remodeling. This review aims at summarizing the current knowledge on the different progenitor and stem cells that have been shown to participate in pulmonary vascular lesions and on the pathways regulating their recruitment during PAH. Finally, this review also addresses the therapeutic potential of circulating endothelial progenitor cells and mesenchymal stem cells.

Mice with a specific deficiency of Pfkfb3 in myeloid cells are protected from hypoxia-induced pulmonary hypertension

BACKGROUND AND PURPOSE

Macrophage infiltration into the lungs is a characteristic of pulmonary hypertension (PH). Glycolysis is the main metabolic pathway for macrophage activation. However, the effect of macrophage glycolysis on the development of PH remains unknown. We investigated the effect of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKBF3), a critical enzyme of macrophage glycolysis, on PH development.

EXPERIMENTAL APPROACH

Lung tissues from PH patients were examined by immunostaining with macrophage markers. PH was induced in Wistar rats with SU5416/hypoxia and in mice with hypoxia. Lungs and macrophages were isolated for analysis by RT-PCR, western blot, flow cytometry, and immunostaining.

KEY RESULTS

Expression of glycolytic molecules was increased in circulating peripheral blood mononuclear cells (PBMCs) and lung macrophages of PH patients. These results were also found in lung macrophages of SU5416/hypoxia (Su/Hx)-induced PH rats and hypoxia-induced PH mice. PH was ameliorated in myeloid-specific Pfkfb3-deficient mice (Pfkfb3ΔMϕ ) or mice treated with the PFKFB3 inhibitor 3PO, compared with their controls. Alveolar macrophages of PH Pfkfb3ΔMϕ mice produced lower levels of growth factors and pro-inflammatory cytokines than those of control mice. Circulating myeloid cells and lung myeloid cells were much fewer in PH Pfkfb3ΔMϕ mice than controls. Mechanistically, overexpression of Hif1a or Hif2a in bone marrow-derived macrophages (BMDMs) cultured with bone marrow of Pfkfb3ΔMϕ mice restored the decreased expression of pro-inflammatory cytokines and growth factors.

CONCLUSIONS AND IMPLICATIONS

Myeloid Pfkfb3 deficiency protects mice from PH, thereby suggesting that myeloid PFKFB3 is one of the important targets in the therapeutic effect of PFKFB3 inhibition in PH treatment.

Metabolism in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is characterized by impaired regulation of pulmonary hemodynamics and vascular growth. Alterations of metabolism and bioenergetics are increasingly recognized as universal hallmarks of PAH, as metabolic abnormalities are identified in lungs and hearts of patients, animal models of the disease, and cells derived from lungs of patients. Mitochondria are the primary organelle critically mediating the complex and integrative metabolic pathways in bioenergetics, biosynthetic pathways, and cell signaling. Here, we review the alterations in metabolic pathways that are linked to the pathologic vascular phenotype of PAH, including abnormalities in glycolysis and glucose oxidation, fatty acid oxidation, glutaminolysis, arginine metabolism, one-carbon metabolism, the reducing and oxidizing cell environment, and the tricarboxylic acid cycle, as well as the effects of PAH-associated nuclear and mitochondrial mutations on metabolism. Understanding of the metabolic mechanisms underlying PAH provides important knowledge for the design of new therapeutics for treatment of patients.

Circulating nerve growth factor receptor positive cells are associated with severity and prognosis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) remains a disease with a poor prognosis, so early detection and treatment are very important. Sensitive and non-invasive markers for PAH are urgently required. This study was performed to identify sensitive markers of the clinical severity and prognosis of PAH. Patients diagnosed with PAH (n = 30) and control participants (n = 15) were enrolled in this observational study. Major EPC and MSC markers (including CD34, CD133, VEGFR2, CD90, PDGFRα, and NGFR) in peripheral blood mononuclear cells (PBMNCs) were assessed by flow cytometry. Associations of these markers with hemodynamic parameters (e.g. mean pulmonary arterial pressure, pulmonary vascular resistance, and cardiac index) were assessed. Patients with PAH were followed up for 12 months to assess the incidence of major adverse events, defined as death or lung transplantation. Levels of circulating EPC and MSC markers in PBMNCs were higher in patients with PAH than in control participants. Among the studied markers, nerve growth factor receptor (NGFR) was significantly positively correlated with hemodynamic parameters. During the 12-month follow-up period, major-event-free survival was significantly higher in patients with PAH who had relatively low frequencies of NGFR positive cells than patients who had higher frequencies. These results suggested that the presence of circulating NGFR positive cells among PBMNCs may be a novel biomarker for the severity and prognosis of PAH.

Iron (III)-Quercetin Complex: Synthesis, Physicochemical Characterization, and MRI Cell Tracking toward Potential Applications in Regenerative Medicine

In cell therapy, contrast agents T1 and T2 are both needed for the labeling and tracking of transplanted stem cells over extended periods of time through magnetic resonance imaging (MRI). Importantly, the metal-quercetin complex via coordination chemistry has been studied extensively for biomedical applications, such as anticancer therapies and imaging probes. Herein, we report on the synthesis, characterization, and labeling of the iron (III)-quercetin complex, "IronQ," in circulating proangiogenic cells (CACs) and also explore tracking via the use of a clinical 1.5 Tesla (T) MRI scanner. Moreover, IronQ had a paramagnetic T1 positive contrast agent property with a saturation magnetization of 0.155 emu/g at 1.0 T and longitudinal relaxivity (r1) values of 2.29 and 3.70 mM-1s-1 at 1.5 T for water and human plasma, respectively. Surprisingly, IronQ was able to promote CAC growth in conventional cell culture systems without the addition of specific growth factors. Increasing dosages of IronQ from 0 to 200 μg/mL led to higher CAC uptake, and maximum labeling time was achieved in 10 days. The accumulated IronQ in CACs was measured by two methodologies, an inductively coupled plasma optical emission spectrometry (ICP-EOS) and T1-weighted MRI. In our research, we confirmed that IronQ has excellent dual functions with the use of an imaging probe for MRI. IronQ can also act as a stimulating agent by favoring circulating proangiogenic cell differentiation. Optimistically, IronQ is considered beneficial for alternative labeling and in the tracking of circulation proangiogenic cells and/or other stem cells in applications of cell therapy through noninvasive magnetic resonance imaging in both preclinical and clinical settings.

Evidence of Accumulated Endothelial Progenitor Cells in the Lungs of Rats with Pulmonary Arterial Hypertension by 89Zr-oxine PET Imaging

Endothelial progenitor cells (EPCs) play a major role in regulating pulmonary vascular remodeling during pulmonary arterial hypertension (PAH) development. Several preclinical and clinical trials of EPCs transplantation have been performed for the treatment of PAH. However, there is no reliable method to monitor real-time cell trafficking and quantify transplanted EPCs. Here in this paper we isolated EPCs from human peripheral blood, identified their functional integrity, and efficiently labeled the EPCs with ⁸⁹Zr-oxine and DiO. Labeled EPCs were injected into the tail vein of normal and PAH rats to be tracked in vivo. From the microPET/CT images, we found EPCs were distributed primarily in the lung at 1 h and then migrated to the liver and spleen. We could observe the 3,3′ dioctadecyloxacarbocyanine perchlorate (DiO)-labeled EPCs binding in the pulmonary vasculature by CellVizio confocal. The result of quantitative analysis revealed significantly higher accumulation of EPCs in the lungs of PAH rats than in those of healthy rats. The distribution and higher accumulation of EPCs in the lungs of PAH rats could help to evaluate the safety and provide evidence of effectiveness of EPC therapy.

The hallmarks of severe pulmonary arterial hypertension: the cancer hypothesis-ten years later

Severe forms of pulmonary arterial hypertension (PAH) are most frequently the consequence of a lumen-obliterating angiopathy. One pathobiological model is that the initial pulmonary vascular endothelial cell injury and apoptosis is followed by the evolution of phenotypically altered, apoptosis-resistant, proliferating cells and an inflammatory vascular immune response. Although there may be a vasoconstrictive disease component, the increased pulmonary vascular shear stress in established PAH is caused largely by the vascular wall pathology. In this review, we revisit the "quasi-malignancy concept" of severe PAH and examine to what extent the hallmarks of PAH can be compared with the hallmarks of cancer. The cancer model of severe PAH, based on the growth of abnormal vascular and bone marrow-derived cells, may enable the emergence of novel cell-based PAH treatment strategies.

Pluripotent hematopoietic stem cells augment α-adrenergic receptor-mediated contraction of pulmonary artery and contribute to the pathogenesis of pulmonary hypertension

Pulmonary hypertension (PH) is a multicellular and progressive disease with a high mortality rate. Among many cell types, hematopoietic stem cells (HSCs) are incriminated in the pathogenesis of PH. However, our understanding of the mechanisms that increase HSCs in blood and lungs of hypertensive animals or patients and the role played by HSCs in the pathogenesis of PH remains elusive. Studies suggest that glycolysis is critical for the survival and growth of HSCs. In various cell types from hypertensive lungs of animals and patients, glycolysis and the glucose-6-phosphate dehydrogenase (G6PD) activity are increased. Herein, we demonstrated in mice that chronic hypoxia increased HSCs (CD34+, CD117+, CD133+, CD34+/CD117+, and CD34+/CD133+) in bone marrow and blood and around hypertensive pulmonary arteries in a time-dependent manner. Intriguingly, we found fewer CD133+ cells in the bone marrow of C57BL/6 mice compared with Sv129J mice, and C57BL mice developed less severe chronic hypoxia-elicited PH and heart failure than Sv129J mice. Similarly, the numbers of CD34+ and CD117+ cells in blood of patients with pulmonary arterial hypertension (PAH) were higher (>3-fold) compared with healthy individuals. By allogeneic bone marrow transplantation, we found that GFP+ bone marrow cells infiltrated the lungs and accumulated around the pulmonary arteries in lungs of hypoxic mice, and these cells contributed to increased α-adrenergic receptor-mediated contraction of the pulmonary artery cultured in hypoxia. Inhibition of G6PD activity with (3β,5α)-3,21-dihydroxypregnan-20-one, a novel and potent G6PD inhibitor, decreased HSCs in bone marrow, blood, and lungs of hypoxic mice and reduced α-agonist-induced contraction of the pulmonary artery and established hypoxia-induced PH. We did not observe CD133+ cells around the pulmonary arteries in the lungs of chronically hypoxic G6PD-deficient mice. Furthermore, knockdown of G6PD and inhibition of G6PD activity: 1) downregulated canonical and noncanonical Wnt and Fzd receptors genes; 2) upregulated Bmpr1a; 3) decreased Cxcl12, and 4) reduced HSC (CD117+ and CD133+) numbers. In all, our findings demonstrate unexpected function for bone marrow-derived HSCs in augmenting α-adrenergic receptor-mediated contraction of pulmonary arteries and remodeling of pulmonary arteries that contribute to increase pulmonary vascular resistance in PAH patients and hypoxic mice and suggest that G6PD, by regulating expression of genes in the WNT and BMPR signaling, contributed to increase and release of HSCs from the bone marrow in response to hypoxic stimuli.

The changing face of pulmonary hypertension diagnosis: a historical perspective on the influence of diagnostics and biomarkers

Pulmonary hypertension is a complex, multifactorial disease that results in right heart failure and premature death. Since the initial reports of pulmonary hypertension in the late 1800s, the diagnosis of pulmonary hypertension has evolved with respect to its definition, screening tools, and diagnostic techniques. This historical perspective traces the earliest roots of pulmonary hypertension detection and diagnosis through to the current recommendations for classification. We highlight the diagnostic tools used in the past and present, and end with a focus on the future directions of early detection. Early detection of pulmonary hypertension and pulmonary arterial hypertension and the proper determination of etiology are vital for the early therapeutic intervention that can prolong life expectancy and improve quality of life. The search for a non-invasive screening tool for the identification and classification of pulmonary hypertension is ongoing, and we discuss the role of animal models of the disease in this search.

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.

Bone Marrow-Derived Proangiogenic Cells Mediate Pulmonary Arteriole Stiffening via Serotonin 2B Receptor Dependent Mechanism

RATIONALE

Pulmonary arterial hypertension is a deadly disease of the pulmonary vasculature for which no disease-modifying therapies exist. Small-vessel stiffening and remodeling are fundamental pathological features of pulmonary arterial hypertension that occur early and drive further endovascular cell dysfunction. Bone marrow (BM)-derived proangiogenic cells (PACs), a specialized heterogeneous subpopulation of myeloid lineage cells, are thought to play an important role in pathogenesis.

OBJECTIVE

To determine whether BM-derived PACs directly contributed to experimental pulmonary hypertension (PH) by promoting small-vessel stiffening through 5-HT_2B (serotonin 2B receptor)-mediated signaling.

METHODS AND RESULTS

We performed BM transplants using transgenic donor animals expressing diphtheria toxin secondary to activation of an endothelial-specific tamoxifen-inducible Cre and induced experimental PH using hypoxia with SU5416 to enhance endovascular injury and ablated BM-derived PACs, after which we measured right ventricular systolic pressures in a closed-chest procedure. BM-derived PAC lineage tracing was accomplished by transplanting BM from transgenic donor animals with fluorescently labeled hematopoietic cells and treating mice with a 5-HT_2B antagonist. BM-derived PAC ablation both prevented and reversed experimental PH with SU5416-enhanced endovascular injury, reducing the number of muscularized pulmonary arterioles and normalizing arteriole stiffness as measured by atomic force microscopy. Similarly, treatment with a pharmacological antagonist of 5-HT_2B also prevented experimental PH, reducing the number and stiffness of muscularized pulmonary arterioles. PACs accelerated pulmonary microvascular endothelial cell injury response in vitro, and the presence of BM-derived PACs significantly correlated with stiffer pulmonary arterioles in pulmonary arterial hypertension patients and mice with experimental PH. RNA sequencing of BM-derived PACs showed that 5-HT_2B antagonism significantly altered biologic pathways regulating cell proliferation, locomotion and migration, and cytokine production and response to cytokine stimulus.

CONCLUSIONS

Together, our findings illustrate that BM-derived PACs directly contribute to experimental PH with SU5416-enhanced endovascular injury by mediating small-vessel stiffening and remodeling in a 5-HT_2B signaling-dependent manner.

Endoglin is a conserved regulator of vasculogenesis in zebrafish - implications for hereditary haemorrhagic telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is a progressive vascular disease with high mortality and prevalence. There is no effective treatment of HHT due to the lack of comprehensive knowledge of its underlying pathological mechanisms. The majority of HHT1 patients carry endoglin (ENG) mutations. Here, we used Danio rerio (zebrafish) as an in vivo model to investigate the effects of endoglin knockdown on vascular development. According to phylogenetic analyses and amino acid sequence similarity analyses, we confirmed that endoglin is conserved in vertebrates and descended from a single common ancestor. Endoglin is highly expressed in the vasculature beginning at the segmentation period in zebrafish. Upon endoglin knockdown by morpholinos, we observed disruption in the intersegmental vessels (ISVs) and decreased expression of several vascular markers. RNA sequencing (RNA-Seq) results implied that the BMP-binding endothelial regulator (bmper) is a gene affected by endoglin knockdown. Rescue experiments demonstrated that overexpression of bmper significantly increased the number of endothelial cells (ECs) and reduced the defects at ISVs in zebrafish. Moreover, there was enhanced tube formation in ENG mutant ECs derived from a HHT patient after human recombinant BMPER (hrBMPER) stimulation. Taken together, our results suggest that bmper, a potential downstream gene of ENG, could be targeted to improve vascular integrity in HHT.

Blood Outgrowth and Proliferation of Endothelial Colony Forming Cells are Related to Markers of Disease Severity in Patients with Pulmonary Arterial Hypertension

In pulmonary arterial hypertension (PAH), lung-angioproliferation leads to increased pulmonary vascular resistance, while simultaneous myocardial microvessel loss contributes to right ventricular (RV) failure. Endothelial colony forming cells (ECFC) are highly proliferative, angiogenic cells that may contribute to either pulmonary vascular obstruction or to RV microvascular adaptation. We hypothesize ECFC phenotypes (outgrowth, proliferation, tube formation) are related to markers of disease severity in a prospective cohort-study of 33 PAH and 30 healthy subjects. ECFC were transplanted in pulmonary trunk banded rats with RV failure. The presence of ECFC outgrowth in PAH patients was associated with low RV ejection fraction, low central venous saturation and a shorter time to clinical worsening (5.4 months (0.6–29.2) vs. 36.5 months (7.4–63.4), p = 0.032). Functionally, PAH ECFC had higher proliferative rates compared to control in vitro, although inter-patient variability was high. ECFC proliferation was inversely related to RV end diastolic volume (R² = 0.39, p = 0.018), but not pulmonary vascular resistance. Tube formation-ability was similar among donors. Normal and highly proliferative PAH ECFC were transplanted in pulmonary trunk banded rats. While no effect on hemodynamic measurements was observed, RV vascular density was restored. In conclusion, we found that ECFC outgrowth associates with high clinical severity in PAH, suggesting recruitment. Transplantation of highly proliferative ECFC restored myocardial vascular density in pulmonary trunk banded rats, while RV functional improvements were not observed.

Dysfunction and Therapeutic Potential of Endothelial Progenitor Cells in Diabetes Mellitus

Diabetes mellitus (DM) is a chronic, multifactorial metabolic disease whereby insulin deficiency or resistance results in hyperglycemia. Endothelial cells (ECs) form the innermost layer of the blood vessel and produce and release a variety of vasoactive substances and growth factors to regulate vascular homeostasis and angiogenesis. Hyperglycemia and insulin resistance can cause endothelial dysfunction, leading to vascular complications such as coronary artery disease, peripheral arterial disease, diabetic nephropathy, neuropathy and retinopathy. The detrimental effect exerted on ECs by hyperglycemia and insulin resistance underlines the importance of reparatory mechanisms in DM. Endothelial progenitor cells (EPCs), derived from bone marrow, have been recognized as endogenous cells involved in endothelial repair and new blood vessel formation. Initially isolated from a subset of circulating CD34+ mononuclear cells, EPCs were found to possess the ability to differentiate into ECs when cultured in vitro and incorporate into newly formed vessels upon transplantation in animal models of ischemia. Due to the low frequency of CD34+ cells in circulation, the vast majority of studies investigating EPC actions have used cells that are generated through the culture of peripheral blood mononuclear cells (PBMNCs) for 4 - 7 days in endothelial selective medium. These cells, mainly of myeloid hematopoietic cell origin, were termed “Early EPCs,” of which, few expressed stem/progenitor-cell markers. Therefore, early EPCs were also termed “myeloid angiogenic cells” (MACs). When PBMNCs are cultured for over 2 weeks, early EPCs gradually diminish while so-called late EPCs appear. Late EPCs share phenotypic features with mature ECs and are therefore also termed blood-derived ECs; they will not be addressed in this review. MAC dysfunction has been observed in a variety of disease conditions including DM. In this article we review the activities and therapeutic potential of MACs in DM. We will interchangeably use “EPCs” and “MACs” to refer to the cells procured by culture of PBMNCs in EC selective medium for approximately 7 days.

Angiogenesis in the lung

Both systemic (tracheal and bronchial) and pulmonary circulations perfuse the lung. However, documentation of angiogenesis of either is complicated by the presence of the other. Well-documented angiogenesis of the systemic circulations have been identified in asthma, cystic fibrosis, chronic thromboembolism and primary carcinomas. Angiogenesis of the vasa vasorum, which are branches of bronchial arteries, is seen in the walls of large pulmonary vessels after a period of chronic hypoxia. Documentation of increased pulmonary capillaries has been shown in models of chronic hypoxia, after pneumonectomy and in some carcinomas. Although endothelial cell proliferation may occur as part of the repair process in several pulmonary diseases, it is separate from the unique establishment of new functional perfusing networks defined as angiogenesis. Identification of the mechanisms driving the expansion of new vascular beds in the adult needs further investigation. Yet the growth factors and molecular mechanisms of lung angiogenesis remain difficult to separate from underlying disease sequelae.

Myeloid-Derived Suppressor Cells and Pulmonary Hypertension

Myeloid–derived suppressor cells (MDSCs) comprised a heterogeneous subset of bone marrow–derived myeloid cells, best studied in cancer research, that are increasingly implicated in the pathogenesis of pulmonary vascular remodeling and the development of pulmonary hypertension. Stem cell transplantation represents one extreme interventional strategy for ablating the myeloid compartment but poses a number of translational challenges. There remains an outstanding need for additional therapeutic targets to impact MDSC function, including the potential to alter interactions with innate and adaptive immune subsets, or alternatively, alter trafficking receptors, metabolic pathways, and transcription factor signaling with readily available and safe drugs. In this review, we summarize the current literature on the role of myeloid cells in the development of pulmonary hypertension, first in pulmonary circulation changes associated with myelodysplastic syndromes, and then by examining intrinsic myeloid cell changes that contribute to disease progression in pulmonary hypertension. We then outline several tractable targets and pathways relevant to pulmonary hypertension via MDSC regulation. Identifying these MDSC-regulated effectors is part of an ongoing effort to impact the field of pulmonary hypertension research through identification of myeloid compartment-specific therapeutic applications in the treatment of pulmonary vasculopathies.

Pentose Shunt, Glucose-6-Phosphate Dehydrogenase, NADPH Redox, and Stem Cells in Pulmonary Hypertension

Redox signaling plays a critical role in the pathophysiology of cardiovascular diseases. The pentose phosphate pathway is a major source of NADPH redox in the cell. The activities of glucose-6-phosphate dehydrogenase (the rate-limiting enzyme in the pentose shunt) and glucose flux through the shunt pathway is increased in various lung cells including, the stem cells, in pulmonary hypertension. This chapter discusses the importance of the shunt pathway and glucose-6-phosphate dehydrogenase in the pathogenesis of pulmonary artery remodeling and occlusive lesion formation within the hypertensive lungs.

Desmosine and Isodesmosine as a Novel Biomarker for Pulmonary Arterial Hypertension: A Pilot Study

Delayed diagnosis is common in patients with pulmonary arterial hypertension (PAH). Right-sided heart catheterization, the gold standard for diagnosis, is invasive and cannot be applied for routine screening. Some biomarkers have been looked into; however, due to the lack of a clear pathological mechanism linking the marker to PAH, the search for an ideal one is still ongoing. Elastin is a significant structural constituent of blood vessels. Its synthesis involves cross-linking of monomers by 2 amino acids, desmosine and isodesmosine (D&I). Being extremely stable, elastin undergoes little metabolic turnover in healthy individuals resulting in very low levels of D&I amino acids in the human plasma, urine, or sputum. We hypothesized that in PAH patients, the elastin turnover is high; which in turn should result in elevated levels of D&I in plasma and urine. Using mass spectrometry, plasma and urine levels of D&I were measured in 20 consecutive patients with PAH confirmed by cardiac catheterization. The levels were compared with 13 healthy controls. The mean level of total plasma D&I in patients with PAH was 0.47 ng/mL and in controls was 0.19 ng/mL (P = 0.001). The mean levels of total D&I in the urine of PAH patients was 20.55 mg/g creatinine and in controls was 12.78 mg/g creatinine (P = 0.005). The mean level of free D&I in the urine of PAH patients was 10.34 mg/g creatinine and in controls was 2.52 mg/g creatinine (P < 0.001). This is the first study highlighting that the serum and urine D&I has a potential to be a novel screening biomarker for patients with PAH. It paves the way for larger studies to analyze its role in assessing for disease severity and response to treatment.

Hallmarks of Pulmonary Hypertension: Mesenchymal and Inflammatory Cell Metabolic Reprogramming

SIGNIFICANCE

The molecular events that promote the development of pulmonary hypertension (PH) are complex and incompletely understood. The complex interplay between the pulmonary vasculature and its immediate microenvironment involving cells of immune system (i.e., macrophages) promotes a persistent inflammatory state, pathological angiogenesis, and fibrosis that are driven by metabolic reprogramming of mesenchymal and immune cells. Recent Advancements: Consistent with previous findings in the field of cancer metabolism, increased glycolytic rates, incomplete glucose and glutamine oxidation to support anabolism and anaplerosis, altered lipid synthesis/oxidation ratios, increased one-carbon metabolism, and activation of the pentose phosphate pathway to support nucleoside synthesis are but some of the key metabolic signatures of vascular cells in PH. In addition, metabolic reprogramming of macrophages is observed in PH and is characterized by distinct features, such as the induction of specific activation or polarization states that enable their participation in the vascular remodeling process.

CRITICAL ISSUES

Accumulation of reducing equivalents, such as NAD(P)H in PH cells, also contributes to their altered phenotype both directly and indirectly by regulating the activity of the transcriptional co-repressor C-terminal-binding protein 1 to control the proliferative/inflammatory gene expression in resident and immune cells. Further, similar to the role of anomalous metabolism in mitochondria in cancer, in PH short-term hypoxia-dependent and long-term hypoxia-independent alterations of mitochondrial activity, in the absence of genetic mutation of key mitochondrial enzymes, have been observed and explored as potential therapeutic targets.

FUTURE DIRECTIONS

For the foreseeable future, short- and long-term metabolic reprogramming will become a candidate druggable target in the treatment of PH. Antioxid. Redox Signal. 28, 230-250.

Targeting Hypoxia Inducible Factors-1α As a Novel Therapy in Fibrosis

Fibrosis, characterized by increased extracellular matrix (ECM) deposition, and widespread vasculopathy, has the prominent trait of chronic hypoxia. Hypoxia inducible factors-1α (HIF-1α), a key transcriptional factor in response to this chronic hypoxia, is involved in fibrotic disease, such as Systemic sclerosis (SSc). The implicated function of HIF-1α in fibrosis include stimulation of excessive ECM, vascular remodeling, and futile angiogenesis with further exacerbation of chronic hypoxia and deteriorate pathofibrogenesis. This review will focus on the molecular biological behavior of HIF-1α in regulating progressive fibrosis. Better understanding of the role for HIF-1α-regulated pathways in fibrotic disease will accelerate development of novel therapeutic strategies that target HIF-1α. Such new therapeutic strategies may be particularly effective for treatment of the prototypic, multisystem fibrotic, autoimmune disease SSc.

Cyp2c44 gene disruption is associated with increased hematopoietic stem cells: implication in chronic hypoxia-induced pulmonary hypertension

We have recently demonstrated that disruption of the murine cytochrome P-450 2c44 gene (Cyp2c44) exacerbates chronic hypoxia-induced pulmonary artery remodeling and hypertension in mice. Subsequently, we serendipitously found that Cyp2c44 gene disruption also increases hematopoietic stem cell (HSC) numbers in bone marrow and blood. Therefore, the objective of the present study was to investigate whether CYP2C44-derived eicosanoids regulate HSC proliferation/cell growth and whether increased HSCs contribute to chronic hypoxia-induced remodeling of pulmonary arteries in Cyp2c44 knockout mice. Our findings demonstrated that lack of CYP2C44 epoxygenase, which catalyzed the oxidation of arachidonic acid to epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic (HETE) acids, increases the numbers of 1) HSCs (CD34⁺, CD117⁺, and CD133⁺), 2) proangiogenic (CD34⁺CD133⁺ and CD34⁺CD117⁺CD133⁺) cells, and 3) immunogenic/inflammatory (CD34⁺CD11b⁺, CD133⁺CD11b⁺, F4/80⁺, CD11b⁺, and F4/80⁺CD11b⁺) macrophages in bone marrow and blood compared with wild-type mice. Among the various CYP2C44-derived arachidonic acids, only 15-HETE decreased CD117⁺ cell numbers when applied to bone marrow cell cultures. Interestingly, CD133⁺ and von Willebrand factor-positive cells, which are derived from proangiogenic stem cells, are increased in the bone marrow, blood, and lungs of mice exposed to chronic hypoxia and in remodeled and occluded pulmonary arteries of CYP2C44-deficient mice. In conclusion, our results demonstrate that CYP2C44-derived 15-HETE plays a critical role in downregulating HSC proliferation and growth, because disruption of the Cyp2c44 gene increased HSCs that potentially contribute to chronic hypoxia-induced pulmonary arterial remodeling and occlusion.NEW & NOTEWORTHY This study demonstrates that cytochrome P-450 2C44 plays a critical role in controlling the phenotype of hematopoietic stem cells and that when this enzyme is knocked out, stem cells are differentiated. These stem cells give rise to increased circulating monocytes and macrophages and contribute to the pathogenesis of chronic hypoxia-induced pulmonary artery remodeling and hypertension.

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.

Bone Marrow Endothelial Progenitor Cells Are the Cellular Mediators of Pulmonary Hypertension in the Murine Monocrotaline Injury Model

The role of bone marrow (BM) cells in modulating pulmonary hypertensive responses is not well understood. Determine if BM‐derived endothelial progenitor cells (EPCs) induce pulmonary hypertension (PH) and if this is attenuated by mesenchymal stem cell (MSC)‐derived extracellular vesicles (EVs). Three BM populations were studied: (a) BM from vehicle and monocrotaline (MCT)‐treated mice (PH induction), (b) BM from vehicle‐, MCT‐treated mice that received MSC‐EV infusion after vehicle, MCT treatment (PH reversal, in vivo), (c) BM from vehicle‐, MCT‐treated mice cultured with MSC‐EVs (PH reversal, in vitro). BM was separated into EPCs (sca‐1+/c‐kit+/VEGFR2+) and non‐EPCs (sca‐1‐/c‐kit‐/VEGFR2‐) and transplanted into healthy mice. Right ventricular (RV) hypertrophy was assessed by RV‐to‐left ventricle+septum (RV/LV+S) ratio and pulmonary vascular remodeling by blood vessel wall thickness‐to‐diameter (WT/D) ratio. EPCs but not non‐EPCs from mice with MCT‐induced PH (MCT‐PH) increased RV/LV+S, WT/D ratios in healthy mice (PH induction). EPCs from MCT‐PH mice treated with MSC‐EVs did not increase RV/LV+S, WT/D ratios in healthy mice (PH reversal, in vivo). Similarly, EPCs from MCT‐PH mice treated with MSC‐EVs pre‐transplantation did not increase RV/LV+S, WT/D ratios in healthy mice (PH reversal, in vitro). MSC‐EV infusion reversed increases in BM‐EPCs and increased lung tissue expression of EPC genes and their receptors/ligands in MCT‐PH mice. These findings suggest that the pulmonary hypertensive effects of BM are mediated by EPCs and those MSC‐EVs attenuate these effects. These findings provide new insights into the pathogenesis of PH and offer a potential target for development of novel PH therapies. Stem Cells Translational Medicine2017;6:1595–1606

Effect of targeted therapy on circulating progenitor cells in precapillary pulmonary hypertension

BACKGROUND

Endothelial dysfunction is key in the development of pulmonary hypertension (PH) and is associated with reduced number of circulating progenitor cells. Studies to date evaluating levels of circulating progenitor cells in PH have provided conflicting results. Current treatment of pulmonary arterial hypertension (PAH) and medical treatment of chronic thromboembolic pulmonary hypertension (CTEPH) targets endothelium dependent signalling pathways. The effect of PAH-targeted therapy on circulating progenitor cells has not been clearly established.

OBJECTIVES

To investigate whether levels of circulating progenitor cells in treatment-naïve patients with PAH or CTEPH differ from healthy subjects and to assess the effect of PAH-targeted therapy on the circulating levels of these progenitors.

METHODS

Thirty controls, 33 PAH and 11 CTEPH treatment-naïve patients were studied. Eighteen patients with PAH and 9 with CTEPH were re-evaluated 6-12months after starting PAH-targeted therapy. Levels of progenitors were measured by flow cytometry as CD45⁺CD34⁺ and CD45⁺CD34⁺CD133⁺ cells.

RESULTS

Compared with controls, the number of circulating progenitor cells was reduced in PAH but not in CTEPH. After 6-12months of treatment, levels of circulating progenitors increased in PAH and remained unchanged in CTEPH. Patients with lower exercise tolerance presented lower levels of circulating progenitors. No other relation was found between levels of progenitors and clinical or hemodynamic parameters.

CONCLUSIONS

Patients with PAH, but not those with CTEPH, present reduced levels of circulating progenitor cells. PAH-targeted therapy increases levels of progenitors in PAH but not in CTEPH, suggesting different involvement of progenitor cells in the pathobiology of these pulmonary hypertensive disorders.

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.

[Pulmonary arterial hypertension, bone marrow, endothelial cell precursors and serotonin]

Serotonin and bone-marrow-derived stem cells participate together in triggering pulmonary hypertension. Our work has shown that the absence of 5-HT2B receptors generates permanent changes in the composition of the blood and bone-marrow in the myeloid lineages, particularly in endothelial cell progenitors. The initial functions of 5-HT2B receptors in pulmonary arterial hypertension (PAH) are restricted to bone-marrow cells. They contribute to the differentiation/proliferation/mobilization of endothelial progenitor cells from the bone-marrow. Those bone-marrow-derived cells have a critical role in the development of pulmonary hypertension and pulmonary vascular remodeling. These data indicate that bone-marrow derived endothelial progenitors play a key role in the pathogenesis of PAH and suggest that interactions involving serotonin and bone morphogenic protein type 2 receptor (BMPR2) could take place at the level of the bone-marrow.

Prominin-1/CD133 expression as potential tissue-resident vascular endothelial progenitor cells in the pulmonary circulation

Pulmonary vascular endothelial cells could contribute to maintain homeostasis in adult lung vasculature. "Tissue-resident" endothelial progenitor cells (EPCs) play pivotal roles in postnatal vasculogenesis, vascular repair, and tissue regeneration; however, their local pulmonary counterparts remain to be defined. To determine whether prominin-1/CD133 expression can be a marker of tissue-resident vascular EPCs in the pulmonary circulation, we examined the origin and characteristics of prominin-1/CD133-positive (Prom1(+)) PVECs considering cell cycle status, viability, histological distribution, and association with pulmonary vascular remodeling. Prom1(+) PVECs exhibited high steady-state transit through the cell cycle compared with Prom1(-) PVECs and exhibited homeostatic cell division as assessed using the label dilution method and mice expressing green fluorescent protein. In addition, Prom1(+) PVECs showed more marked expression of putative EPC markers and drug resistance genes as well as highly increased activation of aldehyde dehydrogenase compared with Prom1(-) PVECs. Bone marrow reconstitution demonstrated that tissue-resident cells were the source of >98% of Prom1(+) PVECs. Immunofluorescence analyses revealed that Prom1(+) PVECs preferentially resided in the arterial vasculature, including the resistant vessels of the lung. The number of Prom1(+) PVECs was higher in developing postnatal lungs. Sorted Prom1(+) PVECs gave rise to colonies and formed fine vascular networks compared with Prom1(-) PVECs. Moreover, Prom1(+) PVECs increased in the monocrotaline and the Su-5416 + hypoxia experimental models of pulmonary vascular remodeling. Our findings indicated that Prom1(+) PVECs exhibited the phenotype of tissue-resident EPCs. The unique biological characteristics of Prom1(+) PVECs predominantly contribute to neovasculogenesis and maintenance of homeostasis in pulmonary vascular tissues.

Prolyl-4 Hydroxylase 2 (PHD2) Deficiency in Endothelial Cells and Hematopoietic Cells Induces Obliterative Vascular Remodeling and Severe Pulmonary Arterial Hypertension in Mice and Humans Through Hypoxia-Inducible Factor-2α

BACKGROUND

Vascular occlusion and complex plexiform lesions are hallmarks of the pathology of severe pulmonary arterial hypertension (PAH) in patients. However, the mechanisms of obliterative vascular remodeling remain elusive; hence, current therapies have not targeted the fundamental disease-modifying mechanisms and result in only modest improvement in morbidity and mortality.

METHODS AND RESULTS

Mice with Tie2Cre-mediated disruption of Egln1 (encoding prolyl-4 hydroxylase 2 [PHD2]; Egln1(Tie2)) in endothelial cells and hematopoietic cells exhibited spontaneous severe PAH with extensive pulmonary vascular remodeling, including vascular occlusion and plexiform-like lesions, resembling the hallmarks of the pathology of clinical PAH. As seen in patients with idiopathic PAH, Egln1(Tie2) mice exhibited unprecedented right ventricular hypertrophy and failure and progressive mortality. Consistently, PHD2 expression was diminished in lung endothelial cells of obliterated pulmonary vessels in patients with idiopathic PAH. Genetic deletions of both Egln1 and Hif1a or Egln1 and Hif2a identified hypoxia-inducible factor-2α as the critical mediator of the severe PAH seen in Egln1(Tie2) mice. We also observed altered expression of many pulmonary hypertension-causing genes in Egln1(Tie2) lungs, which was normalized in Egln1(Tie2)/Hif2a(Tie2) lungs. PHD2-deficient endothelial cells promoted smooth muscle cell proliferation in part through hypoxia-inducible factor-2α-activated CXCL12 expression. Genetic deletion of Cxcl12 attenuated PAH in Egln1(Tie2) mice.

CONCLUSIONS

These studies defined an unexpected role of PHD2 deficiency in the mechanisms of severe PAH and identified the first genetically modified mouse model with obliterative vascular remodeling and pathophysiology recapitulating clinical PAH. Thus, targeting PHD2/hypoxia-inducible factor-2α signaling is a promising strategy to reverse vascular remodeling for treatment of severe PAH.

CD133+ cells in pulmonary arterial hypertension

Circulating mononuclear cells may play an important role for the vascular remodelling in pulmonary arterial hypertension (PAH), but studies addressing multiple progenitor populations are rare and inconsistent.

We used a comprehensive fluorescence-activated cell sorting analysis of circulating mononuclear cells in 20 PAH patients and 20 age- and sex-matched controls, and additionally analysed CD133+ cells in the lung tissue of five PAH transplant recipients and five healthy controls (donor lungs).

PAH patients were characterised by increased numbers of circulating CD133+ cells and lymphopenia as compared with control. In PAH, CD133+ subpopulations positive for CD117 or CD45 were significantly increased, whereas CD133+CD309+, CD133+CXCR2+ and CD133+CD31+ cells were decreased. In CD133+ cells, SOX2, Nanog, Ki67 and CXCR4 were not detected, but Oct3/4 mRNA was present in both PAH and controls. In the lung tissue, CD133+ cells included three main populations: type 2 pneumocytes, monocytes and undifferentiated cells without significant differences between PAH and controls.

In conclusion, circulating CD133+ progenitor cells are elevated in PAH and consist of phenotypically different subpopulations that may be up- or downregulated. This may explain the inconsistent results in the literature. CD133+ type 2 pneumocytes in the lung tissue are not associated with circulating CD133+ mononuclear cells.

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.

Vascular Repair by Tissue-Resident Endothelial Progenitor Cells in Endotoxin-Induced Lung Injury

Vascular disruption is one of the pathological hallmarks in acute respiratory distress syndrome. Bone marrow (BM)-derived circulating endothelial progenitor cells (EPCs) and lung tissue-resident EPCs have been considered to play a pivotal role in pulmonary vascular repair; however, which population is predominant in local pulmonary vasculogenesis remains to be clarified. We therefore examined the origin of EPCs participating in the regenerative process of pulmonary vascular endothelial cells (PVECs) in experimental acute respiratory distress syndrome. Lung samples from mice administered LPS intratracheally were investigated for cell dynamics and EPC functions. Quantitative flow cytometric analysis demonstrated that the number of PVECs decreased by roughly 20% on Day 1 and then recovered on Day 7 of LPS challenge. Bromodeoxyuridine-incorporation assays and immunofluorescence microscopy demonstrated that proliferating PVECs preferentially located in the capillary vessels. Experiments using BM chimera mice revealed that most of the regenerating PVECs were tissue-resident cells, and BM-derived cells hardly engrafted as PVECs. The population of circulating putative phenotypical EPCs decreased during the first week after LPS challenge. The regenerating PVECs were characterized by high colony-forming and vasculogenic capacities, intracellular reactive oxygen species scavenging and aldehyde dehydrogenase activites, and enhanced gene expression of Abcb1b (a drug-resistant gene), suggesting that the population of PVECs included tissue-resident EPCs activated during regenerative process of PVECs. The proliferating PVECs expressed CD34, Flk-1/KDR, and c-kit more strongly and Prom1/CD133 less strongly on the surface than nonproliferating PVECs. Our findings indicated that lung tissue-resident EPCs predominantly contribute to pulmonary vascular repair after endotoxin-induced injury.

Novel Targets of Drug Treatment for Pulmonary Hypertension

Biomedical advances over the last decade have identified the central role of proliferative pulmonary arterial smooth muscle cells (PASMCs) in the development of pulmonary hypertension (PH). Furthermore, promoters of proliferation and apoptosis resistance in PASMCs and endothelial cells, such as aberrant signal pathways involving growth factors, G protein-coupled receptors, kinases, and microRNAs, have also been described. As a result of these discoveries, PH is currently divided into subgroups based on the underlying pathology, which allows focused and targeted treatment of the condition. The defining features of PH, which subsequently lead to vascular wall remodeling, are dysregulated proliferation of PASMCs, local inflammation, and apoptosis-resistant endothelial cells. Efforts to assess the relative contributions of these factors have generated several promising targets. This review discusses recent novel targets of therapies for PH that have been developed as a result of these advances, which are now in pre-clinical and clinical trials (e.g., imatinib [phase III]; nilotinib, AT-877ER, rituximab, tacrolimus, paroxetine, sertraline, fluoxetine, bardoxolone methyl [phase II]; and sorafenib, FK506, aviptadil, endothelial progenitor cells (EPCs) [phase I]). While substantial progress has been made in recent years in targeting key molecular pathways, PH still remains without a cure, and these novel therapies provide an important conceptual framework of categorizing patients on the basis of molecular phenotype(s) for effective treatment of the disease.