Increased circulating endothelial progenitor cells are associated with survival in acute lung injury

Mechanisms of pulmonary endothelial barrier dysfunction in acute lung injury and acute respiratory distress syndrome

Endothelial cells (ECs) form a semi-permeable barrier between the interior space of blood vessels and the underlying tissues. Pulmonary endothelial barrier integrity is maintained through coordinated cellular processes involving receptors, signaling molecules, junctional complexes, and protein-regulated cytoskeletal reorganization. In acute lung injury (ALI) or its more severe form acute respiratory distress syndrome (ARDS), the loss of endothelial barrier integrity secondary to endothelial dysfunction caused by severe pulmonary inflammation and/or infection leads to pulmonary edema and hypoxemia. Pro-inflammatory agonists such as histamine, thrombin, bradykinin, interleukin 1β, tumor necrosis factor α, vascular endothelial growth factor, angiopoietin-2, and platelet-activating factor, as well as bacterial toxins and reactive oxygen species, cause dynamic changes in cytoskeletal structure, adherens junction disorganization, and detachment of vascular endothelial cadherin (VE-cadherin) from the actin cytoskeleton, leading to an increase in endothelial permeability. Endothelial interactions with leukocytes, platelets, and coagulation enhance the inflammatory response. Moreover, inflammatory infiltration and the associated generation of pro-inflammatory cytokines during infection cause EC death, resulting in further compromise of the structural integrity of lung endothelial barrier. Despite the use of potent antibiotics and aggressive intensive care support, the mortality of ALI is still high, because the mechanisms of pulmonary EC barrier disruption are not fully understood. In this review, we summarized recent advances in the studies of endothelial cytoskeletal reorganization, inter-endothelial junctions, endothelial inflammation, EC death, and endothelial repair in ALI and ARDS, intending to shed some light on the potential diagnostic and therapeutic targets in the clinical management of the disease.

Worsening of lung perfusion to tissue density distributions during early acute lung injury

Lung perfusion magnitude and distribution are essential for oxygenation and, potentially, lung inflammation and protection during acute respiratory distress syndrome (ARDS). Yet, perfusion patterns and their relationship to inflammation are unknown pre-ARDS. We aimed to assess perfusion/density ratios and spatial perfusion-density distributions and associate these to lung inflammation, during early lung injury in large animals at different physiological conditions caused by different systemic inflammation and positive end-expiratory pressure (PEEP) levels. Sheep were protectively ventilated (16-24 h) and imaged for lung density, pulmonary capillary perfusion (13Nitrogen-saline), and inflammation (18F-fluorodeoxyglucose) using positron emission and computed tomography. We studied four conditions: permissive atelectasis (PEEP = 0 cmH2O); and ARDSNet low-stretch PEEP-setting strategy with supine moderate or mild endotoxemia, and prone mild endotoxemia. Perfusion/density heterogeneity increased pre-ARDS in all groups. Perfusion redistribution to density depended on ventilation strategy and endotoxemia level, producing more atelectasis in mild than moderate endotoxemia (P = 0.010) with the oxygenation-based PEEP-setting strategy. The spatial distribution of 18F-fluorodeoxyglucose uptake was related to local Q/D (P < 0.001 for Q/D group interaction). Moderate endotoxemia yielded markedly low/zero perfusion in normal-low density lung, with 13Nitrogen-saline perfusion indicating nondependent capillary obliteration. Prone animals' perfusion was remarkably homogeneously distributed with density. Lung perfusion redistributes heterogeneously to density during pre-ARDS protective ventilation in animals. This is associated with increased inflammation, nondependent capillary obliteration, and lung derecruitment susceptibility depending on endotoxemia level and ventilation strategy.NEW & NOTEWORTHY Perfusion redistribution does not follow lung density redistribution in the first 16-24 h of systemic endotoxemia and protective tidal volume mechanical ventilation. The same oxygenation-based positive end-expiratory pressure (PEEP)-setting strategy can lead at different endotoxemia levels to different perfusion redistributions, PEEP values, and lung aerations, worsening lung biomechanical conditions. During early acute lung injury, regional perfusion-to-tissue density ratio is associated with increased neutrophilic inflammation, and susceptibility to nondependent capillary occlusion and lung derecruitment, potentially marking and/or driving lung injury.

Endothelial progenitor cells in the host defense response

Extensive injury of endothelial cells in blood vasculature, especially in the microcirculatory system, frequently occurs in hosts suffering from sepsis and the accompanied systemic inflammation. Pathological factors, including toxic components derived from invading microbes, oxidative stress associated with tissue ischemia/reperfusion, and vessel active mediators generated during the inflammatory response, are known to play important roles in mediating endothelial injury. Collapse of microcirculation and tissue edema developed from the failure of endothelial barrier function in vital organ systems, including the lung, brain, and kidney, are detrimental, which often predict fatal outcomes. The host body possesses a substantial capacity for maintaining vascular homeostasis and repairing endothelial damage. Bone marrow and vascular wall niches house endothelial progenitor cells (EPCs). In response to septic challenges, EPCs in their niche environment are rapidly activated for proliferation and angiogenic differentiation. In the meantime, release of EPCs from their niches into the blood stream and homing of these vascular precursors to tissue sites of injury are markedly increased. The recruited EPCs actively participate in host defense against endothelial injury and repair of damage in blood vasculature via direct differentiation into endothelial cells for re-endothelialization as well as production of vessel active mediators to exert paracrine and autocrine effects on angiogenesis/vasculogenesis. In recent years, investigations on significance of EPCs in host defense and molecular signaling mechanisms underlying regulation of the EPC response have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches for effective prevention and treatment of sepsis-induced vascular injury as well as vital organ system failure.

Molecular mechanisms and roles of pyroptosis in acute lung injury

ABSTRACT

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which are characterized by excessive inflammation and accompanied by diffuse injury of alveoli, can result in severe respiratory failures. The morbidity and mortality of patients remain high because the major treatments for ALI/ARDS are mainly supportive due to the lack of effective therapies. Numerous studies have demonstrated that the aggravation of coronavirus disease 2019 (COVID-19) leads to severe pneumonia and even ARDS. Pyroptosis, a biological process identified as a type of programed cell death, is mainly triggered by inflammatory caspase activation and is directly meditated by the gasdermin protein family, as well as being associated with the secretion and release of pro-inflammatory cytokines. Clinical and experimental evidence corroborates that pyroptosis of various cells in the lung, such as immune cells and structural cells, may play an important role in the pathogenesis of "cytokine storms" in ALI/ARDS, including those induced by COVID-19. Here, with a focus on ALI/ARDS and COVID-19, we summarized the recent advances in this field and proposed the theory of an inflammatory cascade in pyroptosis to identify new targets and pave the way for new approaches to treat these diseases.

Stem-Cell Therapy for Bronchopulmonary Dysplasia (BPD) in Newborns

Premature newborns are at a higher risk for the development of respiratory distress syndrome (RDS), acute lung injury (ALI) associated with lung inflammation, disruption of alveolar structure, impaired alveolar growth, lung fibrosis, impaired lung angiogenesis, and development of bronchopulmonary dysplasia (BPD) with severe long-term developmental adverse effects. The current therapy for BPD is limited to supportive care including high-oxygen therapy and pharmacotherapy. Recognizing more feasible treatment options to improve lung health and reduce complications associated with BPD is essential for improving the overall quality of life of premature infants. There is a reduction in the resident stem cells in lungs of premature infants with BPD, which strongly suggests a critical role of stem cells in BPD pathogenesis; this warrants the exploration of the potential therapeutic use of stem-cell therapy. Stem-cell-based therapies have shown promise for the treatment of many pathological conditions including acute lung injury and BPD. Mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) including exosomes are promising and effective therapeutic modalities for the treatment of BPD. Treatment with MSCs and EVs may help to reduce lung inflammation, improve pulmonary architecture, attenuate pulmonary fibrosis, and increase the survival rate.

JTE-013 Alleviates Inflammatory Injury and Endothelial Dysfunction Induced by Sepsis In Vivo and In Vitro

BACKGROUND

Nowadays, there is no approved targeted agent for lung injury induced by sepsis. S1PR2 is confirmed to be a promising diagnosis and treatment target. JTE-013 as S1PR2 antagonists may be an agent of great potential. In this research, we sought to determine the functional role of JTE-013 in lung injury induced by sepsis.

MATERIALS AND METHODS

Seventy-two rats were assigned into normal group, sepsis model group and JTE-013 group. The animal model of lung injury induced by sepsis was constructed by cecal ligation and puncture. The human pulmonary microvascular endothelial cells (HPMECs) were divided into control, LPS and LPS + JTE-013 group. HPMECs induced by LPS served as the cell model of lung injury induced by sepsis. HE staining assay was performed for assessment of the pathological condition and Evans blue was applied for assessment of pulmonary tissue permeability. Wet/dry ratio was measured as indicators of pulmonary edema degree and neutrophil count was measured as indicators of infection status. The levels of inflammatory factors were detected by corresponding kits, cell survival by CCK-8 assay and protein expression level by western blot.

RESULTS

S1PR2 was highly expressed in vivo model of lung injury induced by sepsis. It was observed that JTE-013 as antagonist of S1PR2 alleviated the lung tissue injury, endothelial dysfunction and pulmonary edema induced by sepsis. In addition, JTE-013 reduced neutrophil count and levels of inflammatory factors. Moreover, results confirmed that JTE-013 enhanced cell viability and mitigated inflammatory response in cell model of sepsis.

CONCLUSIONS

Overall, JTE-013 as an antagonist of S1PR2 could relieve inflammatory injury and endothelial dysfunction induced by sepsis in vivo and vitro, resulting in attenuation of lung injury. These findings elucidated that JTE-013 may be a promising targeted agent for lung injury induced by sepsis.

Mesenchymal stem cell and endothelial progenitor cells coinjection improves LPS-induced lung injury via Tie2 activation and downregulation of the TLR4/MyD88 pathway

Sepsis is one of the most important complications of infection with a high mortality rate. Recently, cell therapy has been widely used to reduce the symptoms of sepsis. It has been previously reported that mesenchymal stem cell (MSC) and endothelial progenitor cells (EPC) therapy have beneficial effects in experimental models of sepsis. The effects of coculture of MSC and EPC have not yet been used to treat sepsis. Therefore, the aim of this study was to investigate the therapeutic potential of EPC + MSC coculture on the residual effects of sepsis in a lipopolysaccharide (LPS)-induced mice model. Coinjections of EPC + MSC significantly enhanced the survival rate of LPS-induced mice, decreased concentrations of pro-inflammatory cytokines, and increased the level of anti-inflammatory cytokine. The LPS-induced mice that were treated with EPC + MSC showed a notable reduction in pulmonary edema, hepatic enzymes, and C-reactive protein level compared with the control group. Our results showed that coinjection of EPC + MSC up and downregulates Tie2 and TLR4/MyD88 signaling pathways in LPS-induced mice, respectively. Also, in vitro study showed that viability, adhesion, and migration in coculture cells is significantly decreased after being induced with 10 μg/ml LPS. Our results showed that LPS impaired the functional activity of the cocultured EPC + MSC via upregulation of the TLR4/MyD88 signaling pathway, which may be associated with decreased pTie2/Tie2 expression. In conclusion, coinjection of EPC and MSC modulated the TLR4/MyD88 signaling pathway that leads to reduce the inflammatory response. This study may provide promising results for the introduction of cocultured cells to manage infectious diseases and balance the immune response through immune regulatory function.

Therapeutic Potential of Endothelial Progenitor Cells in Pulmonary Diseases

Compromised alveolar development and pulmonary vascular remodeling are hallmarks of pediatric lung diseases such as bronchopulmonary dysplasia (BPD) and alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Although advances in surfactant therapy, corticosteroids, and anti-inflammatory drugs have improved clinical management of preterm infants, still those who suffer with severe vascular complications lack viable treatment options. Paucity of the alveolar capillary network in ACDMPV causes respiratory distress and leads to mortality in a vast majority of ACDMPV infants. The discovery of endothelial progenitor cells (EPCs) in 1997 brought forth the paradigm of postnatal vasculogenesis and hope for promoting vascularization in fragile patient populations, such as those with BPD and ACDMPV. The identification of diverse EPC populations, both hematopoietic and nonhematopoietic in origin, provided a need to identify progenitor cell selective markers which are linked to progenitor properties needed to develop cell-based therapies. Focusing to the future potential of EPCs for regenerative medicine, this review will discuss various aspects of EPC biology, beginning with the identification of hematopoietic, nonhematopoietic, and tissue-resident EPC populations. We will review knowledge related to cell surface markers, signature gene expression, key transcriptional regulators, and will explore the translational potential of EPCs for cell-based therapy for BPD and ACDMPV. The ability to produce pulmonary EPCs from patient-derived induced pluripotent stem cells (iPSCs) in vitro, holds promise for restoring vascular growth and function in the lungs of patients with pediatric pulmonary disorders.

Fucoidan inhibits LPS-induced acute lung injury in mice through regulating GSK-3β-Nrf2 signaling pathway

The purpose of this study was to investigate the protective effects of fucoidan on Lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. The mice were divided into the control, LPS, and LPS + fucoidan (20, 40, or 80 mg/kg) groups. LPS was given by intracheal instillation and fucoidan was given 1 h before LPS treatment. Myeloperoxidase (MPO) activity, malondialdehyde (MDA), superoxide dismutase (SOD), reactive oxygen species (ROS), glutathione (GSH) contents, and inflammatory cytokine production were detected. The results showed that LPS-induced TNF-α, IL-1β, and IL-6 production, lung wet/dry (W/D) ratio, ROS, MDA content, and MPO activity were suppressed by fucoidan. The levels of SOD and GSH were increased by fucoidan. Meanwhile, LPS-induced nuclear factor kappa-B (NF-κB) activation was dose-dependently attenuated by fucoidan. Furthermore, fucoidan increased the expression of nuclear factor erythroid-2 related factor 2 (Nrf2), Glycogen synthase kinase3β (GSK-3β), and heme oxygenase (HO-1). In vitro, the results demonstrated that fucoidan or GSK-3β inhibitor significantly inhibited LPS-induced TNF-α production in A549 cells. And the inhibition of fucoidan on TNF-α production was blocked by Nrf2 siRNA. This study showed fucoidan protected mice against LPS-induced ALI through inhibiting inflammatory and oxidative responses via regulating GSK-3β-Nrf2 signaling pathway.

Increased mobilization of mesenchymal stem cells in patients with acute respiratory distress syndrome undergoing extracorporeal membrane oxygenation

Background

The acute respiratory distress syndrome (ARDS) is characterized by pulmonary epithelial and endothelial barrier dysfunction and injury. In severe forms of ARDS, extracorporeal membrane oxygenation (ECMO) is often the last option for life support. Endothelial progenitor (EPC) and mesenchymal stem cells (MSC) can regenerate damaged endothelium and thereby improve pulmonary endothelial dysfunction. However, we still lack sufficient knowledge about how ECMO might affect EPC- and MSC-mediated regenerative pathways in ARDS. Therefore, we investigated if ECMO impacts EPC and MSC numbers in ARDS patients.

Methods

Peripheral blood mononuclear cells from ARDS patients undergoing ECMO (n = 16) and without ECMO support (n = 12) and from healthy volunteers (n = 16) were isolated. The number and presence of circulating EPC and MSC was detected by flow cytometry. Serum concentrations of vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang2) were determined.

Results

In the ECMO group, MSC subpopulations were higher by 71% compared to the non-ECMO group. Numbers of circulating EPC were not significantly altered. During ECMO, VEGF and Ang2 serum levels remained unchanged compared to the non-ECMO group (p = 0.16), but Ang2 serum levels in non-survivors of ARDS were significantly increased by 100% (p = 0.02) compared to survivors.

Conclusions

ECMO support in ARDS is specifically associated with an increased number of circulating MSC, most likely due to enhanced mobilization, but not with a higher numbers of EPC or serum concentrations of VEGF and Ang2.

Therapeutic potential of mesenchymal stem/stromal cell-derived secretome and vesicles for lung injury and disease

Introduction: The acute respiratory distress syndrome (ARDS) is a devastating clinical condition common in patients with respiratory failure. Based largely on numerous preclinical studies and recent Phase I/II clinical trials, administration of stem cells, specifically mesenchymal stem or stromal cells (MSC), as a therapeutic for acute lung injury (ALI) holds great promise. However, concern for the use of stem cells, specifically the risk of iatrogenic tumor formation, remains unresolved. Accumulating evidence now suggest that stem cell-derived conditioned medium (CM) and/or extracellular vesicles (EV) might constitute compelling alternatives.Areas covered: The current review focuses on the preclinical studies testing MSC CM and/or EV as treatment for ALI and other inflammatory lung diseases.Expert opinion: Clinical application of MSC or their secreted CM may be limited by the cost of growing enough cells, the logistic of MSC storage, and the lack of standardization of what constitutes MSC CM. However, the clinical application of MSC EV remains promising, primarily due to the ability of EV to maintain the functional phenotype of the parent cell as a therapeutic. However, utilization of MSC EV will also require large-scale production, the cost of which may be prohibitive unless the potency of the EV can be increased.

Erythropoietin treatment is associated with a reduction in moderate to severe bronchopulmonary dysplasia in preterm infants. A regional retrospective study

Erythropoietin treatment is associated with a reduction in moderate to severe bronchopulmonary dysplasia in preterm infants. A regional retrospective study.

OBJECTIVE

To determine whether premature infants treated with erythropoietin (Epo) in the neonatal period for anemia had a lower incidence of bronchopulmonary dysplasia (BPD), defined as oxygen need at 36 weeks postmenstrual age, and lower rehospitalization rates in the first year of life than infants not exposed.

METHODS

Retrospective study of a population of infants born at 23 to 32 weeks gestational age, between January 2009 and December 2014, with birthweight ≤1500 g. Patient characteristics, and risk factors for BPD were compared between patients who received erythropoietin, and those not exposed. To examine the association between the outcomes of BPD at 36 weeks PMA, rehospitalization, and erythropoietin treatment, we performed a propensity score (PS) analysis using inverse probability of treatment weighted (IPTW) approach. For comparison, we conducted a logistic regression adjusting for the same covariates used to generate PS using the original population.

RESULTS

The study population included 1821 preterm infants: 928 received Epo and 893 did not. Epo treatment was associated with a reduction in BPD (18.8% versus 25.9%, p < 0.01) at 36 weeks PMA and reduced median length of stay with lowest BPD rate with Epo initiation before 2 weeks of age. There was no difference in rehospitalization rates in the first year of life.

CONCLUSION

Erythropoietin treatment was associated with a reduction in BPD but not in rehospitalization rate in the first year of life.

Early Prediction of Persistent Organ Failure by Circulating Endothelial Progenitor Cells in Patients With Acute Pancreatitis

INTRODUCTION

Increased circulating endothelial progenitor cells (cEPC) have been observed in patients with vascular injury associated with sepsis and acute lung injury. However, a role for cEPC in severe acute pancreatitis (SAP) remains unclear. We therefore conducted a prospective study to study whether the quantities of cEPC can predict persistent organ failure (POF) in patients with predicted SAP.

METHODS

A total of 42 predicted SAP patients who were admitted within 24 h after symptom onset and 10 healthy control subjects were enrolled in our study. The proportions of cEPC were analyzed based on flow cytometry simultaneously. Vascular endothelial growth factor (VEGF) levels were measured by enzyme-linked immunosorbent assay.

RESULTS

The percentage of cEPC was significantly higher in patients with predicted SAP compared with healthy controls. Similarly, the levels of VEGF in peripheral blood were also significantly higher in predicted SAP patients than in the controls. Notably, patients with POF had lower proportion of cEPC compared with patients with transient organ failure (TOF). In contrast, patients with POF had a significantly higher level of VEGF compared with TOF. Of note, the percentages of cEPC were significantly inversely correlated with disease severity scores. More importantly, cEPC showed an excellent discriminative power for predicting POF among predicted SAP patients, whereas plasma VEGF and disease severity scores showed moderate accuracy in predicting future POF.

CONCLUSIONS

Peripheral EPC as a novel biomarker is elevated and may aid to predict the development of POF in patients with predicted SAP.

Reverse-D-4F improves endothelial progenitor cell function and attenuates LPS-induced acute lung injury

Background

Patients with acute lung injury (ALI) have increased levels of pro-inflammatory mediators, which impair endothelial progenitor cell (EPC) function. Increasing the number of EPC and alleviating EPC dysfunction induced by pro-inflammatory mediators play important roles in suppressing ALI development. Because the high density lipoprotein reverse-D-4F (Rev-D4F) improves EPC function, we hypothesized that it might repair lipopolysaccharide (LPS)-induced lung damage by improving EPC numbers and function in an LPS-induced ALI mouse model.

Methods

LPS was used to induce ALI in mice, and then the mice received intraperitoneal injections of Rev-D4F. Immunohistochemical staining, flow cytometry, MTT, transwell, and western blotting were used to assess the effect of Rev-D4F on repairment of lung impairment, and improvement of EPC numbers and function, as well as the signaling pathways involved.

Results

Rev-D4F inhibits LPS-induced pulmonary edema and decreases plasma levels of the pro-inflammatory mediators TNF-α and ET-1 in ALI mice. Rev-D4F inhibited infiltration of red and white blood cells into the interstitial space, reduced lung injury-induced inflammation, and restored injured pulmonary capillary endothelial cells. In addition, Rev-D4F increased numbers of circulating EPC, stimulated EPC differentiation, and improved EPC function impaired by LPS. Rev-D4F also acted via a PI3-kinase-dependent mechanism to restore levels of phospho-AKT, eNOS, and phospho-eNOS suppressed by LPS.

Conclusions

These findings indicate that Rev-D4F has an important vasculoprotective role in ALI by improving the EPC numbers and functions, and Rev-D4F reverses LPS-induced EPC dysfuncion partially through PI3K/AKT/eNOS signaling pathway.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1099-6) contains supplementary material, which is available to authorized users.

Intravenous delivery of granulocyte-macrophage colony stimulating factor impairs survival in lipopolysaccharide-induced sepsis

Background

Cell-based therapies with bone marrow-derived progenitor cells (BMDPC) lead to an improved clinical outcome in animal sepsis models. In the present study we evaluated the ability of granulocyte macrophage-colony stimulating factor (GM-CSF) to mobilize BMDPC in a lipopolysaccharide (LPS)-induced sepsis model and thereby its potential as a novel treatment strategy.

Methods

Male Wistar rats received LPS (25μg/kg/h for 4 days) intravenously and were subsequently treated with GM-CSF 12.5μg/kg (0h,24h,48h,72h). As control groups, rats were infused with sodium chloride or GM-CSF only. Clinical and laboratory parameters, proinflammatory plasma cytokines as well as BMDPC counts were analyzed. Cytokine release by isolated peripheral blood mononuclear cells from rat spleen upon incubation with LPS, GM-CSF and a combination of both were investigated in vitro.

Results

In vivo, rats receiving both LPS and GM-CSF, showed a reduced weight loss and increased mobilization of BMDPC. At the same time, this regime resulted in an increased release of proinflammatory cytokines (IL-6, IL-8) and a significantly increased mortality. In vitro, the combination of LPS and GM-CSF showed a significantly increased IL-6 release upon incubation compared to incubation with LPS or GM-CSF alone.

Conclusions

GM-CSF did not have a beneficial effect on the clinical course in our LPS-induced sepsis model. It synergistically promoted inflammation with LPS and probably thereby impaired survival.

Mesenchymal stromal cells and TGF-β1 in tracheal aspirate of premature infants: early predictors for bronchopulmonary dysplasia?

Background The pathogenesis of bronchopulmonary dysplasia (BPD) includes arrest of alveolar septation and enhanced fibrosis. We hypothesized that mesenchymal stromal cells (MSC) and transforming growth factor-β1 (TGF-β1) in tracheal aspirates of mechanically ventilated premature infants differ in BPD and non-BPD infants. Methods Tracheal aspirates were collected during the first week of life. Mononuclear cells were separated, cultured and immunophenotyped by flow cytometry. MSCs colony/cluster ratio was calculated as an index for dysplastic potentials. TGF-β1 was assessed by enzyme-linked immunosorbent assay (ELISA). Setting: Neonatal intensive care unit. Patients Premature infants at risk for BPD. Results A total of 121 preterm infants were enrolled; 27 of them died and among the 94 survivors 23 infants had BPD. MSCs were identified in younger [gestational age (GA): 30.9±1.7 vs. 31.8±1.8, P=0.025] and smaller [birth weight (BW): 1.3±0.28 vs. 1.44±0.37 kg, P=0.04] infants with lower Apgar scores. The recovery rate of MSCs in BPD and non-BPD groups did not differ. BPD group had significantly smaller colony/cluster ratio compared to non-BPD (0.97 vs. 4.25, P=0.002). TGF-β1 was significantly greater in BPD infants (4173.9±864.3 vs. 3705.8±540.5 pg/mL, P=0.021). Conclusion Infants with BPD had different MSCs morphology and greater TGF-β1 expression. The pathogenesis for these morphological changes of resident lung MSCs needs further studying.

Endothelial Progenitor and Mesenchymal Stromal Cells in Newborns With Congenital Diaphragmatic Hernia Undergoing Extracorporeal Membrane Oxygenation

Background: Endothelial progenitor (EPC) and mesenchymal stromal cells (MSC) can regenerate damaged endothelium and thereby improve pulmonary endothelial dysfunction. We do not know, how extracorporeal membrane oxygenation (ECMO) might affect EPC- and MSC-mediated regenerative pathways in patients with congenital diaphragmatic hernia (CDH). Therefore, we investigated, if ECMO support impacts EPC and MSC numbers in CDH patients. Methods: Peripheral blood mononuclear cells from newborns with ECMO-dependent (n = 18) and ECMO-independent CDH (n = 12) and from healthy controls (n = 12) were isolated. The numbers of EPC and MSC were identified by flowcytometry. Serum levels of vascular endothelial growth factor (VEGF) and angiopoietin (Ang)-2 were determined. Results: EPC and MSC were elevated in newborns with CDH. ECMO-dependent infants had higher EPC subpopulation counts (2,1-7,6-fold) before treatment compared to ECMO-independent infants. In the disease course, EPC and MSC subpopulation counts in ECMO-dependent infants were lower than before ECMO initiation. During ECMO, VEGF serum levels were significantly reduced (by 90.5%) and Ang2 levels significantly increased (by 74.8%). Conclusions: Our data suggest that ECMO might be associated with a rather impaired mobilization of EPC and MSC and with a depression of VEGF serum levels in newborns with CDH.

Stem cells therapy: a review on approaches that can be used for treatment of respiratory failures in sulfur mustard-injured patients

Sulfur mustard (SM) is a toxic agent which causes severe abnormalities in an airway system such as necrosis and inflammation, oxidative stress, chronic bronchitis, shortness of breath, and chronic obstructive pulmonary disease. Although possible mechanisms of SM toxicity have been extensively considered, there is still need to find an appropriate clinical treatment to decrease chronic lung injuries caused by SM. Due to extensive progresses and achievement in tissue repairing through stem cells therapy, the importance of cell therapy for the treatment of lung injuries has been increased. However, several factors such as types of stem cells, necessary conditions for growth and proliferation of stem cells, and their homing into the target tissues are considered as the most important problems in this issue. Mesenchymal stem cells (MSCs) are a class of multipotent stem cells with proliferative and self-renewal capacity which are able to differentiate into different cell lines such as lung epithelial cells. They have a potential repairing and immune modulatory properties which make them as a good candidate for the regeneration of bronchioles tract in SM-exposed patients. Unlike chemical drugs, the differentiation and high-level safety properties of MSCs can be considered as a new strategy for the treatment of SM-injured patients with pulmonary complications. This review aims to consider the therapeutic effects of MSCs in the treatment of SM-induced pulmonary injuries in both animals and humans.

Cell therapy in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is driven by a severe pro-inflammatory response resulting in lung damage, impaired gas exchange and severe respiratory failure. There is no specific treatment that effectively improves outcome in ARDS. However, in recent years, cell therapy has shown great promise in preclinical ARDS studies. A wide range of cells have been identified as potential candidates for use, among these are mesenchymal stromal cells (MSCs), which are adult multi-lineage cells that can modulate the immune response and enhance repair of damaged tissue. The therapeutic potential of MSC therapy for sepsis and ARDS has been demonstrated in multiple in vivo models. The therapeutic effect of these cells seems to be due to two different mechanisms; direct cellular interaction, and paracrine release of different soluble products such as extracellular vesicles (EVs)/exosomes. Different approaches have also been studied to enhance the therapeutic effect of these cells, such as the over-expression of anti-inflammatory or pro-reparative molecules. Several clinical trials (phase I and II) have already shown safety of MSCs in ARDS and other diseases. However, several translational issues still need to be addressed, such as the large-scale production of cells, and their potentiality and variability, before the therapeutic potential of stem cells therapies can be realized.

Glutamine Administration Modulates Endothelial Progenitor Cell and Lung Injury in Septic Mice

This study investigated the effects of glutamine (GLN) administration on circulating endothelial progenitor cells (EPCs) and lung angiopoietin (Ang) gene expressions in polymicrobial sepsis. Mice were randomly assigned to a normal control group (NC), septic saline group (SS), and septic GLN group (SG). All mice were fed with a chow diet. Sepsis was induced by cecal ligation and puncture (CLP). The mice in SS group were injected with saline, whereas SG group administered 0.75 g GLN/kg body weight once via tail vein 1 h after CLP. Mice were killed 24 and 48 h after CLP. Their blood and lungs were collected for further analysis. The results showed that, compared with normal mice, sepsis resulted in higher C-X-C motif chemokine-12, vascular endothelial growth factor, nitric oxide levels, and a higher circulating EPC percentage. In addition, inflammatory cytokine concentrations and Ang-2 gene expression were upregulated in lung tissues. GLN administration enhanced the mobilization of EPC, and downregulated inflammatory cytokine production and the Ang-2 gene expressions in lungs. Histopathological findings showed that the extent of inflammatory lesions of the lung alveolar was less severe in the SG group than the SS group after CLP. Our results suggest that a single dose of intravenous GLN administration after initiation of sepsis promotes the mobilization of circulating EPC, and modulates the balance of Ang-Tie2 axis that may improve the vascular function, ameliorate inflammation, and protect lung injury against polymicrobial sepsis.

Biomarkers to Predict Cardiovascular Death

This article reviews biomarkers that have been shown to identify subjects at increased risk for cardiovascular death within the general population, in those with established coronary artery disease, and in those with heart failure. Use of biomarkers for risk stratification for sudden cardiac death continues to evolve. It seems that a multimarker strategy for risk stratification using simple measures of circulating proteins and usual clinical risk factors, particularly in patients with known coronary artery disease, can be used to identify patients at near-term risk of death. Whether similar strategies in the general population will prove to be cost-effective needs to be investigated.

Alpha-Klotho Enrichment in Induced Pluripotent Stem Cell Secretome Contributes to Antioxidative Protection in Acute Lung Injury

Induced pluripotent stem cells (iPSCs) have been reported to alleviate organ injury, although the mechanisms of action remain unclear and administration of intact cells faces many limitations. We hypothesized that cell-free conditioned media (CM) containing the secretome of iPSCs possess antioxidative constituents that can alleviate pulmonary oxidant stress damage. We derived iPSCs from human dermal fibroblasts and harvested the CM. Addition of iPSC CM to cultured human alveolar type-1 epithelial cells mitigated hyperoxia-induced depletion of endogenous total antioxidant capacity while tracheal instillation of iPSC CM into adult rat lungs enhanced hyperoxia-induced increase in TAC. In both the in vitro and in vivo models, iPSC CM ameliorated oxidative damage to DNA, lipid, and protein, and activated the nuclear factor (erythroid 2)-related factor 2 (Nrf2) network of endogenous antioxidant proteins. Compared with control fibroblast-conditioned or cell-free media, iPSC CM is highly enriched with αKlotho at a concentration up to more than 10-fold of that in normal serum. αKlotho is an essential antioxidative cell maintenance and protective factor and an activator of the Nrf2 network. Immunodepletion of αKlotho reduced iPSC CM-mediated cytoprotection by ∼50%. Thus, the abundant αKlotho content significantly contributes to iPSC-mediated antioxidation and cytoprotection. Results uncover a major mechanism of iPSC action, suggest a fundamental role of αKlotho in iPSC maintenance, and support the translational potential of airway delivery of cell-free iPSC secretome for protection against lung injury. The targeted cell-free secretome-based approach may also be applicable to the amelioration of injury in other organs. Stem Cells 2018;36:616-625.

Toll‑like receptor 4 is expressed and functional in late endothelial progenitor cells

It has been previously demonstrated that lipopolysaccharides (LPS) inhibit the viability, migration, adhesion and in vitro angiogenesis of late endothelial progenitor cells (EPCs). However, the mechanisms underlying this LPS‑induced impairment of late EPC functional activity are unknown. The aim of the present study was to investigate whether Toll‑like receptor 4 (TLR4) is expressed and functional on late EPCs, using late EPCs of 3‑5 passages. Cells were deprived of serum for 24 h prior to experiments and incubated with 10 µg/ml LPS for 24 h with or without pretreatment with 2 µg/ml TLR4 signaling inhibitor CLI‑095 for 30 min. The viability, migration, adhesion and in vitro angiogenesis, as well as the expression of silent information regulator 1 (SIRT1), in late EPCs were evaluated. Treatment with 10 µg/ml LPS decreased the viability, migration and adhesion abilities, and in vitro angiogenesis of late EPCs. Pretreatment with the TLR4 signaling inhibitor reversed this LPS‑induced dysfunction of late EPCs. LPS downregulated the expression of SIRT1 protein, however, blocking TLR4 attenuated the effect of LPS on SIRT1 expression. Therefore, the results of the present study indicate that LPS impaired the functional activity of late EPCs via TLR4, which may be associated with decreased SIRT1 expression.

Inhibition of Murine Pulmonary Microvascular Endothelial Cell Apoptosis Promotes Recovery of Barrier Function under Septic Conditions

Sepsis is characterized by injury of the pulmonary microvasculature and the pulmonary microvascular endothelial cells (PMVEC), leading to barrier dysfunction and acute respiratory distress syndrome (ARDS). Our recent work identified a strong correlation between PMVEC apoptosis and microvascular leak in septic mice in vivo, but the specific role of apoptosis in septic PMVEC barrier dysfunction remains unclear. Thus, we hypothesize that PMVEC apoptosis is likely required for PMVEC barrier dysfunction under septic conditions in vitro. Septic stimulation (mixture of tumour necrosis factor α, interleukin 1β, and interferon γ [cytomix]) of isolated murine PMVEC resulted in a significant loss of barrier function as early as 4 h after stimulation, which persisted until 24 h. PMVEC apoptosis, as reflected by caspase activation, DNA fragmentation, and loss of membrane polarity, was first apparent at 8 h after cytomix. Pretreatment of PMVEC with the pan-caspase inhibitor Q-VD significantly decreased septic PMVEC apoptosis and was associated with reestablishment of PMVEC barrier function at 16 and 24 h after stimulation but had no effect on septic PMVEC barrier dysfunction over the first 8 h. Collectively, our data suggest that early septic murine PMVEC barrier dysfunction driven by proinflammatory cytokines is not mediated through apoptosis, but PMVEC apoptosis contributes to late septic PMVEC barrier dysfunction.

Umbilical Cord Blood Circulating Progenitor Cells and Endothelial Colony-Forming Cells Are Decreased in Preeclampsia

Preeclampsia (PE) is a pregnancy-specific disease characterized by the new onset of hypertension and proteinuria. Mothers with PE are known to develop endothelial dysfunction, but its effect on infants has been understudied, as newborns are often asymptomatic. Recent studies indicate that infants born from preeclamptic pregnancies develop endothelial dysfunction including higher blood pressure during childhood and an increased risk of stroke later in life. We hypothesize that PE reduces the number and function of fetal angiogenic progenitor cells and may contribute to this increased risk. We quantified 2 distinct types of angiogenic progenitors, pro-angiogenic circulating progenitor cells (CPCs) and endothelial colony-forming cells (ECFCs), from the umbilical cord blood of preeclamptic pregnancies and normotensive controls. Pro-angiogenic and nonangiogenic CPCs were enumerated via flow cytometry and ECFCs by cell culture. Additionally, we studied the growth, migration, and tube formation of ECFCs from PE and gestational age-matched normotensive control pregnancies. We found that PE resulted in decreased cord blood pro-angiogenic CPCs and ECFCs. Nonangiogenic CPCs were also decreased. Preeclamptic ECFCs demonstrated decreased growth and migration but formed tube-like structures in vitro similar to controls. Our results suggest that the preeclamptic environment alters the number and function of angiogenic progenitor cells and may increase the risk of later vascular disease.

Stem cell therapy for acute respiratory distress syndrome: a promising future?

PURPOSE OF REVIEW

Acute respiratory distress syndrome (ARDS) is a devastating disease process with a 40% mortality rate, and for which there is no therapy. Stem cells are an exciting potential therapy for ARDS, and are currently the subject of intensive ongoing research efforts. We review data concerning the therapeutic promise of cell-based therapies for ARDS.

RECENT FINDINGS

Recent experimental studies suggest that cell-based therapies, particularly mesenchymal stem/stromal cells (MSCs), endothelial progenitor cells, and embryonic or induced pluripotent stem cells all offer considerable promise for ARDS. Of these cell types, mesenchymal stromal cells offer the greatest potential for allogeneic therapy, given the large body of preclinical data supporting their use, and the advanced state of our understanding of their diverse mechanisms of action. Although other stem cells such as EPCs also have therapeutic potential, greater barriers exist, particularly the requirement for autologous EPC therapy. Other stem cells, such as ESCs and iPSCs, are at an earlier stage in the translational process, but offer the hope of directly replacing injured lung tissue. Ultimately, lung-derived stem cells may offer the greatest hope for lung diseases, given their homeostatic role in replacing and repairing damaged native lung tissues.MSCs are currently in early phase clinical trials, the results of which will be of critical importance to subsequent translational efforts for MSCs in ARDS. A number of translational challenges exist, including minimizing variability in cell batches, developing standard tests for cell potency, and producing large amounts of clinical-grade cells for use in patients.

SUMMARY

Cell-based therapies, particularly MSCs, offer considerable promise for the treatment of ARDS. Overcoming translational challenges will be important to fully realizing their therapeutic potential for ARDS.

Autologous endothelial progenitor cells improve allograft survival in porcine lung transplantation with prolonged ischemia

BACKGROUND

As endothelial progenitor cells (EPCs) attenuated acute lung injury (ALI) in rabbit model, we hypothesized that autologous EPCs preserved lung graft function during the acute reperfusion period of lung transplantation and tested the therapeutic potential of EPCs in a porcine model of lung transplantation with prolonged graft ischemia.

METHODS

Day-7 EPCs isolated from the recipient subjects or plain culture media were administered into the left pulmonary artery immediately before restoration of pulmonary blood flow in a porcine lung allotransplantation model, with the transplantation surgeons blinded to the content of injection. Hemodynamics and arterial blood gas were recorded, and the right pulmonary artery was occluded 30 min after reperfusion to evaluate the lung graft function. The lung grafts were sectioned for histological examination at the end of experiments. The total ischemic time for lung graft was approximately 14 h.

RESULTS

All animals receiving plain medium died within 40 min after reperfusion, but 3 out of 5 (60%) piglets receiving EPCs survived up to 4 h after diversion of the entire cardiac output into the lung graft (P<0.01). The donor body weight, recipient body weight, cold ischemic time, and time for anastomosis were comparable between the EPC and control group (P=0.989, 0.822, 0.843, and 0.452, respectively). The mean aortic pressure decreased, and the cardiac output and mean pulmonary artery pressure elevated after right pulmonary artery occlusion. All these parameters were gradually compensated in the EPC group but decompensated in the control group. Better preservation of gas exchange function, reduced thrombi formation in the terminal pulmonary arterioles, and attenuated interstitial hemorrhage of the lung graft were observed in the EPC group.

CONCLUSIONS

We concluded autologous EPCs significantly enhanced the function of lung allograft and improved survival in a porcine model of lung transplantation with prolonged ischemia.

Therapeutic strategies in pneumonia: going beyond antibiotics

Dysregulation of the innate immune system drives lung injury and its systemic sequelae due to breakdown of vascular barrier function, harmful hyperinflammation and microcirculatory failure, which contribute to the unfavourable outcome of patients with severe pneumonia. A variety of promising therapeutic targets have been identified and numerous innovative therapeutic approaches demonstrated to improve lung injury in experimental preclinical studies. However, at present specific preventive or curative strategies for the treatment of lung failure in pneumonia in addition to antibiotics are still missing. The aim of this mini-review is to give a short overview of some, but not all, adjuvant therapeutic strategies for pneumonia and its most important complications, sepsis and acute respiratory distress syndrome, and briefly discuss future perspectives.

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.

Endothelial-to-mesenchymal transition in lipopolysaccharide-induced acute lung injury drives a progenitor cell-like phenotype

Pulmonary vascular endothelial function may be impaired by oxidative stress in endotoxemia-derived acute lung injury. Growing evidence suggests that endothelial-to-mesenchymal transition (EndMT) could play a pivotal role in various respiratory diseases; however, it remains unclear whether EndMT participates in the injury/repair process of septic acute lung injury. Here, we analyzed lipopolysaccharide (LPS)-treated mice whose total number of pulmonary vascular endothelial cells (PVECs) transiently decreased after production of reactive oxygen species (ROS), while the population of EndMT-PVECs significantly increased. NAD(P)H oxidase inhibition suppressed EndMT of PVECs. Most EndMT-PVECs derived from tissue-resident cells, not from bone marrow, as assessed by mice with chimeric bone marrow. Bromodeoxyuridine-incorporation assays revealed higher proliferation of capillary EndMT-PVECs. In addition, EndMT-PVECs strongly expressed c-kit and CD133. LPS loading to human lung microvascular endothelial cells (HMVEC-Ls) induced reversible EndMT, as evidenced by phenotypic recovery observed after removal of LPS. LPS-induced EndMT-HMVEC-Ls had increased vasculogenic ability, aldehyde dehydrogenase activity, and expression of drug resistance genes, which are also fundamental properties of progenitor cells. Taken together, our results demonstrate that LPS induces EndMT of tissue-resident PVECs during the early phase of acute lung injury, partly mediated by ROS, contributing to increased proliferation of PVECs.

Cord blood-derived endothelial colony-forming cell function is disrupted in congenital diaphragmatic hernia

Vascular growth is necessary for normal lung development. Although endothelial progenitor cells (EPCs) play an important role in vascularization, little is known about EPC function in congenital diaphragmatic hernia (CDH), a severe neonatal condition that is associated with pulmonary hypoplasia. We hypothesized that the function of endothelial colony-forming cells (ECFCs), a type of EPC, is impaired in CDH. Cord blood (CB) was collected from full-term CDH patients and healthy controls. We assessed CB progenitor cell populations as well as plasma vascular endothelial growth factor (VEGF) and stromal cell-derived factor 1α (SDF1α) levels. CB ECFC clonogenicity; growth kinetics; migration; production of VEGF, SDF1α, and nitric oxide (NO); vasculogenic capacity; and mRNA expression of VEGF-A, fms-related tyrosine kinase 1 (FLT1), kinase insert domain receptor (KDR), nitric oxide synthase (NOS) 1-3, SDF1, and chemokine (C-X-C motif) receptor 4 (CXCR4) were also assessed. Compared with controls, CB ECFCs were decreased in CDH. CDH ECFCs had reduced potential for self-renewal, clonogenicity, proliferation, and migration. Their capacity for NO production was enhanced but their response to VEGF was blunted in CDH ECFCs. In vivo potential for de novo vasculogenesis was reduced in CDH ECFCs. There was no difference in CB plasma VEGF and SDF1α concentrations, VEGF and SDF1α production by ECFCs, and ECFC mRNA expression of VEGF-A, FLT1, KDR, NOS1-3, SDF1, and CXCR4 between CDH and control subjects. In conclusion, CB ECFC function is disrupted in CDH, but these changes may be caused by mechanisms other than alteration of VEGF-NO and SDF1-CXCR4 signaling.

Endothelial Progenitor Cells Predict Long-Term Mortality in Hemodialysis Patients

BACKGROUND

The endothelial progenitor cells (EPCs) dysfunction is a critical event in the initiation of atherosclerotic plaque development and the level of circulating EPCs can be considered a biomarker of cardiovascular events. The level and functional change in EPCs has been investigated in hemodialysis patients, but the effect of absolute number of EPCs on risk of death has not yet been explored. We hypothesized that the number of EPCs predicted death from cardiovascular and all-cause mortality in hemodialysis patients.

METHODS

We evaluate the association between endothelial progenitor cells and clinical outcome in 154 patients on maintenance hemodialysis. The blood sample was drawn at the time of patient enrollment and EPCs were identified by flow cytometry using triple staining for CD34/CD133/KDR.

RESULTS

The median duration of follow-up was 4.19 years. There were 79 (51.3%) deaths during the follow-up period, 41 of whom died due to a confirmed cardiovascular cause. The cumulative survival was greater in the high-EPC group than the low-EPC group for all-cause and cardiovascular mortality. Decreased EPCs levels were associated with a significant increase in the risk of cardiovascular and all-cause mortality after adjusting for age, gender, current smokers, diabetes mellitus, and hypertension.

CONCLUSIONS

The level of circulating EPCs independently predicts the clinical outcome in patients on maintenance hemodialysis. Thus, the EPCs levels may be a useful predictive tool for evaluating the risk of death in maintenance hemodialysis patients.

Significance and therapeutic implications of endothelial progenitor cells in angiogenic-mediated tumour metastasis

Cancer conveys profound social and economic consequences throughout the world. Metastasis is responsible for approximately 90% of cancer-associated mortality and, when it occurs, cancer becomes almost incurable. During metastatic dissemination, cancer cells pass through a series of complex steps including the establishment of tumour-associated angiogenesis. The human endothelial progenitor cells (hEPCs) are a cell population derived from the bone marrow which are required for endothelial tubulogenesis and neovascularization. They also express abundant inflammatory cytokines and paracrine angiogenic factors. Clinically hEPCs are highly correlated with relapse, disease progression, metastasis and treatment response in malignancies such as breast cancer, ovarian cancer and non-small-cell lung carcinoma. It has become evident that the hEPCs are involved in the angiogenesis-required progression and metastasis of tumours. However, it is not clear in what way the signalling pathways, controlling the normal cellular function of human BM-derived EPCs, are hijacked by aggressive tumour cells to facilitate tumour metastasis. In addition, the actual roles of hEPCs in tumour angiogenesis-mediated metastasis are not well characterised. In this paper we reviewed the clinical relevance of the hEPCs with cancer diagnosis, progression and prognosis. We further summarised the effects of tumour microenvironment on the hEPCs and underlying mechanisms. We also hypothesized the roles of altered hEPCs in tumour angiogenesis and metastasis. We hope this review may enhance our understanding of the interaction between hEPCs and tumour cells thus aiding the development of cellular-targeted anti-tumour therapies.

Accumulation of Multipotent Progenitor Cells on Polymethylpentene Membranes During Extracorporeal Membrane Oxygenation

Multipotent progenitor cells were mobilized during pediatric extracorporeal membrane oxygenation (ECMO). We hypothesize that these cells also adhered onto polymethylpentene (PMP) fibers within the membrane oxygenator (MO) during adult ECMO support. Mononuclear cells were removed from the surface of explanted PMP-MOs (n = 16). Endothelial-like outgrowth and mesenchymal-like cells were characterized by flow cytometric analysis using different surface markers. Spindle-shaped attaching cells were identified early, but without proliferative activity. After long-term cultivation palisading type or cobblestone-type outgrowth cells with high proliferative activity appeared and were characterized as (i) leukocytoid CD45+/CD31+ (CD133+/VEGFR-II+/CD90+/CD14+/CD146dim/CD105dim); (ii) endothelial-like CD45-/CD31+ (VEGF-RII+/CD146+/CD105+/CD133-/CD14-/CD90-); and (iii) mesenchymal-like cells CD45-/CD31- (CD105+/CD90+/CD133dim/VEGFR-II-/CD146-/CD14-). The distribution of the cell populations depended on the MO and cultivation time. Endothelial-like cells formed capillary-like structures and did uptake Dil-acetylated low-density lipoprotein. Endothelial- and mesenchymal-like cells adhered on the surface of PMP-MOs. Further research is needed to identify the clinical relevance of these cells.

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.

Effects of Vascular Endothelial Growth Factor in Recovery Phase of Acute Lung Injury in Mice

AIM

To test the hypothesis that exogenous administration of vascular endothelial growth factor (VEGF) promotes lung repair in acute lung injury (ALI).

METHODS

ALI was induced by intranasal lipopolysaccharide (LPS) administration in mice, followed by different treatment protocols for 7 days in 3 groups (n = 6, each) including the LPS, the VEGF and the anti-VEGF group. At day 7, peripheral blood and lungs were collected. Lung wet-to-dry (W/D) ratio and lung injury score were measured. Immunohistochemistry assay was employed to detect the number of pulmonary vessels. Circulating endothelial progenitor cells (EPCs) was detected using flow cytometric analysis, and the apoptosis of lung cells was determined by TUNEL staining.

RESULTS

VEGF treatment reduced W/D ratio and pulmonary neutrophil infiltration in the VEGF group compared with the LPS group. The treatment of VEGF increased the number of pulmonary vessels, and significantly increased the number of circulating EPC cells. Moreover, administration of VEGF decreased the percentage of apoptotic cells in the VEGF group.

CONCLUSIONS

Our results suggest that VEGF may contribute to vascular endothelial repair and function as a protective factor against ALI.

Stem cells for respiratory failure

PURPOSE OF REVIEW

The prognosis of patients with respiratory failure in the ICU remains poor, while current therapeutic approaches are aimed at minimizing ventilator-induced lung injury. Stem cell-based therapies have the potential to transform respiratory failure treatment by achieving lung repair. The purpose of this article is to critically review the large body of clinical and experimental work performed with respect to the use of stem/progenitor cells in respiratory failure, and to discuss current challenges and future directions.

RECENT FINDINGS

Since the initial report of cell therapy for lung injury in 2005, numerous preclinical and clinical studies have been performed that support the ability of various stem cell populations to improve physiologic lung function and reduce inflammation in both infective and sterile acute respiratory distress syndrome. Nevertheless, many important issues (e.g., mechanism of action, long-term engraftment, optimal cell type, dose, route of administration) remain to be resolved.

SUMMARY

Cell-based therapeutics hold promise, particularly for acute respiratory distress syndrome, and early preclinical testing has been encouraging. To advance clinical testing of cell therapies in respiratory failure, and to help ensure that this approach will facilitate bench-to-bedside and bedside-to-bench discoveries, parallel paths of basic and clinical research are needed, including measures of cell therapy effectiveness in vivo and in vitro.

Preconditioning allows engraftment of mouse and human embryonic lung cells, enabling lung repair in mice

Repair of injured lungs represents a longstanding therapeutic challenge. We show that human and mouse embryonic lung tissue from the canalicular stage of development (20-22 weeks of gestation for humans, and embryonic day 15-16 (E15-E16) for mouse) are enriched with progenitors residing in distinct niches. On the basis of the marked analogy to progenitor niches in bone marrow (BM), we attempted strategies similar to BM transplantation, employing sublethal radiation to vacate lung progenitor niches and to reduce stem cell competition. Intravenous infusion of a single cell suspension of canalicular lung tissue from GFP-marked mice or human fetal donors into naphthalene-injured and irradiated syngeneic or SCID mice, respectively, induced marked long-term lung chimerism. Donor type structures or 'patches' contained epithelial, mesenchymal and endothelial cells. Transplantation of differentially labeled E16 mouse lung cells indicated that these patches were probably of clonal origin from the donor. Recipients of the single cell suspension transplant exhibited marked improvement in lung compliance and tissue damping reflecting the energy dissipation in the lung tissues. Our study provides proof of concept for lung reconstitution by canalicular-stage human lung cells after preconditioning of the pulmonary niche.

Erythropoietin promotes the protective properties of transplanted endothelial progenitor cells against acute lung injury via PI3K/Akt pathway

INTRODUCTION

Accumulating evidences have indicted the participation and repairing effects of endothelial progenitor cells (EPCs) on acute lung injury (ALI). Researchers have also revealed that erythropoietin (EPO) may exert multiple effects on EPCs including proliferative and adhesive properties. The present study was designed to investigate whether EPO can promote the healing efficiency of transplanted EPCs against ALI and the potential mechanism.

METHODS

Endothelial progenitor cells were derived from bone marrow mononuclear cells of BALB/c mice. In our in vitro studies, we tested the proproliferative and antiapoptotic effects of EPO on cultured EPCs. In our in vivo studies, we induced BALB/c mice ALI model by intratracheal instillation of lipopolysaccharide and treated with/without intravenous injection of enhanced green fluorescent protein-EPCs harvested from enhanced green fluorescent protein-BALB/c mice. Mice that received EPC transplantation either underwent EPO administration or not. The effects of EPO and EPC treatment on promoting pulmonary endothelial repair, decreasing pulmonary capillary permeability, alleviating pulmonary inflammation, improving gas exchange, and promoting pulmonary vessel angiogenesis were tested. The potential mechanisms that mediate EPO functions on EPC were also investigated.

RESULTS

Our studies revealed a significant antiapoptotic property of EPO on cultured EPCs as well as its promotion on EPC proliferation. We also found the severity of ALI was reduced by EPC therapy, and the protective effects of EPCs were highly enhanced when combined with EPO administration. However, all these stimulating effects of EPO on EPCs were consisted with the expression of phospho-Akt and were abrogated by PI3K inhibitors.

CONCLUSIONS

Transplanted EPCs directly incorporated into the injured pulmonary vessels and maintain the integrity of pulmonary endothelium. Erythropoietin improved the survival and proliferation of transplanted EPCs and recruited them to the injured sites to exert their repairing functions. PI3K/Akt pathway mediated EPO's functions on EPCs. The combination of EPO and EPC treatment may be a promising cell-based therapy for ALI patients.

Resident Endothelial Cells and Endothelial Progenitor Cells Restore Endothelial Barrier Function After Inflammatory Lung Injury

OBJECTIVE

Disruption of endothelial barrier integrity is a characteristic of many inflammatory conditions. However, the origin and function of endothelial cells (ECs) restoring endothelial barrier function remain unknown. This study defined the roles of resident ECs (RECs) and bone marrow-derived endothelial progenitor cells (BMDEPCs) in endothelial barrier restoration after endotoxemic lung injury.

APPROACH AND RESULTS

We generated mice that enable to quantify proliferating RECs or BMDEPCs and also to study the causal link between REC or BMDEPC proliferation and endothelial barrier restoration. Using these mouse models, we showed that endothelial barrier restoration was associated with increased REC and BMDEPC proliferation. RECs and BMDEPCs participate in barrier repair. Immunofluorescence staining demonstrated that RECs proliferate in situ on endothelial layer and that BMDEPCs are engrafted into endothelial layer of lung microvessels at the active barrier repair phase. In lungs, 8 weeks after lipopolysaccharide-induced injury, the number of REC-derived ECs (CD45(-)/CD31(+)/BrdU(+)/rtTA(+)) or BMDEPC-derived ECs (CD45(-)/CD31(+)/eNOS(+)/GFP(+)) increased by 22- or 121-fold, respectively. The suppression of REC or BMDEPC proliferation by blocking REC or BMDEPC intrinsic nuclear factor-κB at the barrier repair phase was associated with an augmented endothelial permeability and impeded endothelial barrier recovery. RECs and BMDEPCs contributed differently to endothelial barrier repair. In lungs, 8 weeks after lipopolysaccharide-induced injury, REC-derived ECs constituted 22%, but BMDEPC-derived ECs constituted only 3.7% of the total new ECs.

CONCLUSIONS

REC is a major and BMDEPC is a complementary source of new ECs in endothelial barrier restoration. RECs and BMDEPCs play important roles in endothelial barrier restoration after inflammatory lung injury.

Endothelial FoxM1 mediates bone marrow progenitor cell-induced vascular repair and resolution of inflammation following inflammatory lung injury

Adult stem cell treatment is a potential novel therapeutic approach for acute respiratory distress syndrome. Given the extremely low rate of cell engraftment, it is believed that these cells exert their beneficial effects via paracrine mechanisms. However, the endogenous mediator(s) in the pulmonary vasculature remains unclear. Using the mouse model with endothelial cell (EC)-restricted disruption of FoxM1 (FoxM1 CKO), here we show that endothelial expression of the reparative transcriptional factor FoxM1 is required for the protective effects of bone marrow progenitor cells (BMPC) against LPS-induced inflammatory lung injury and mortality. BMPC treatment resulted in rapid induction of FoxM1 expression in wild type (WT) but not FoxM1 CKO lungs. BMPC-induced inhibition of lung vascular injury, resolution of lung inflammation, and survival, as seen in WT mice, were abrogated in FoxM1 CKO mice following LPS challenge. Mechanistically, BMPC treatment failed to induce lung EC proliferation in FoxM1 CKO mice, which was associated with impaired expression of FoxM1 target genes essential for cell cycle progression. We also observed that BMPC treatment enhanced endothelial barrier function in WT but not in FoxM1-deficient EC monolayers. Restoration of β-catenin expression in FoxM1-deficient ECs normalized endothelial barrier enhancement in response to BMPC treatment. These data demonstrate the requisite role of endothelial FoxM1 in the mechanism of BMPC-induced vascular repair to restore vascular integrity and accelerate resolution of inflammation, thereby promoting survival following inflammatory lung injury.

Evaluation of endothelial damage in sepsis-related ARDS using circulating endothelial cells

PURPOSE

Endothelial cell activation and dysfunction are involved in the pathophysiology of ARDS. Circulating endothelial cells (CECs) may be a useful marker of endothelial dysfunction and damage but have been poorly studied in ARDS. We hypothesized that the CEC count may be elevated in patients with sepsis-related ARDS compared to those with sepsis without ARDS.

METHODS

ARDS was defined according to the Berlin consensus definition. The study population included 17 patients with moderate or severe ARDS, 9 with mild ARDS, 13 with sepsis and no ARDS, 13 non-septic patients, and 12 healthy volunteers. Demographic, hemodynamic, and prognostic variables, including PaO(2)/FiO(2) ratio, 28-day survival, blood lactate, APACHE II, and SOFA score, were recorded. CECs were counted in arterial blood samples using the reference CD146 antibody-based immunomagnetic isolation and UEA1-FITC staining method. Measurements were performed 12-24 h after diagnosis of ARDS and repeated daily for 3 days.

RESULTS

The median day-1 CEC count was significantly higher in patients with moderate or severe ARDS than in mild ARDS or septic-control patients [27.2 (18.3-49.4) vs. 17.4 (11-24.5) cells/ml (p < 0.034), and 18.4 (9.1-31) cells/ml (p < 0.035), respectively]. All septic patients (with or without ARDS) had higher day-1 CEC counts than the non-septic patients [19.6 (14.2-30.6) vs. 10.8 (5.7-13.2) cells/ml, p = 0.002].

CONCLUSION

The day-1 CEC count was significantly higher in ARDS patients than in other critically ill patients, and in moderate or severe ARDS patients compared to those with milder disease, making it a potentially useful marker of ARDS severity.