Mesenchymal stromal cells from neonatal tracheal aspirates demonstrate a pattern of lung-specific gene expression

Mesenchymal stromal/stem cells and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common complication in preterm infants, leading to chronic respiratory disease. There has been an improvement in perinatal care, but many infants still suffer from impaired branching morphogenesis, alveolarization, and pulmonary capillary formation, causing lung function impairments and BPD. There is an increased risk of respiratory infections, pulmonary hypertension, and neurodevelopmental delays in infants with BPD, all of which can lead to long-term morbidity and mortality. Unfortunately, treatment options for Bronchopulmonary dysplasia are limited. A growing body of evidence indicates that mesenchymal stromal/stem cells (MSCs) can treat various lung diseases in regenerative medicine. MSCs are multipotent cells that can differentiate into multiple cell types, including lung cells, and possess immunomodulatory, anti-inflammatory, antioxidative stress, and regenerative properties. MSCs are regulated by mitochondrial function, as well as oxidant stress responses. Maintaining mitochondrial homeostasis will likely be key for MSCs to stimulate proper lung development and regeneration in Bronchopulmonary dysplasia. In recent years, MSCs have demonstrated promising results in treating and preventing bronchopulmonary dysplasia. Studies have shown that MSC therapy can reduce inflammation, mitochondrial impairment, lung injury, and fibrosis. In light of this, MSCs have emerged as a potential therapeutic option for treating Bronchopulmonary dysplasia. The article explores the role of MSCs in lung development and disease, summarizes MSC therapy's effectiveness in treating Bronchopulmonary dysplasia, and delves into the mechanisms behind this treatment.

CCR2 Mediates Chronic LPS-Induced Pulmonary Inflammation and Hypoalveolarization in a Murine Model of Bronchopulmonary Dysplasia

The histopathology of bronchopulmonary dysplasia (BPD) includes hypoalveolarization and interstitial thickening due to abnormal myofibroblast accumulation. Chorioamnionitis and sepsis are major risk factors for BPD development. The cellular mechanisms leading to these lung structural abnormalities are poorly understood. We used an animal model with repeated lipopolysaccharide (LPS) administration into the airways of immature mice to simulate prolonged airway exposure to gram-negative bacteria, focusing on the role of C-C chemokine receptor type 2-positive (CCR2+) exudative macrophages (ExMf). Repetitive LPS exposure of immature mice induced persistent hypoalveolarization observed at 4 and 18 days after the last LPS administration. LPS upregulated the expression of lung pro-inflammatory cytokines (TNF-α, IL-17a, IL-6, IL-1β) and chemokines (CCL2, CCL7, CXCL1, and CXCL2), while the expression of genes involved in lung alveolar and mesenchymal cell development (PDGFR-α, FGF7, FGF10, and SPRY1) was decreased. LPS induced recruitment of ExMf, including CCR2+ ExMf, as well as other myeloid cells like DCs and neutrophils. Lungs of LPS-exposed CCR2−/− mice showed preserved alveolar structure and normal patterns of α-actin and PDGFRα expression at the tips of the secondary alveolar crests. Compared to wild type mice, a significantly lower number of ExMf, including TNF-α+ ExMf were recruited to the lungs of CCR2−/− mice following repetitive LPS exposure. Further, pharmacological inhibition of TLR4 with TAK-242 also blocked the effect of LPS on alveolarization, α-SMA and PDGFRα expression. TNF-α and IL-17a induced α-smooth muscle actin expression in the distal airspaces of E16 fetal mouse lung explants. In human preterm lung mesenchymal stromal cells, TNF-α reduced mRNA and protein expression of PDGFR-α and decreased mRNA expression of WNT2, FOXF2, and SPRY1. Collectively, our findings demonstrate that in immature mice repetitive LPS exposure, through TLR4 signaling increases lung inflammation and impairs lung alveolar growth in a CCR2-dependent manner.

Cell therapy for the preterm infant: promise and practicalities

Recent decades have seen the rapid progress of neonatal intensive care, and the survival rates of the most preterm infants are improving. This improvement is associated with changing patterns of morbidity and new phenotypes of bronchopulmonary dysplasia and preterm brain injury are recognised. Inflammation and immaturity are known contributors to their pathogenesis. However, a new phenomenon, the exhaustion of progenitor cells is emerging as an important factor. Current therapeutic approaches do not adequately address these new mechanisms of injury. Cell therapy, that is the use of stem and stem-like cells, with its potential to both repair and prevent injury, offers a new approach to these challenging conditions. This review will examine the rationale for cell therapy in the extremely preterm infant, the preclinical and early clinical evidence to support its use in bronchopulmonary dysplasia and preterm brain injury. Finally, it will address the challenges in translating cell therapy from the laboratory to early clinical trials.

CD90+CD146+ identifies a pulmonary mesenchymal cell subtype with both immune modulatory and perivascular-like function in postnatal human lung

Our understanding of mesenchymal cell subsets and their function in human lung affected by aging and in certain disease settings remains poorly described. We use a combination of flow cytometry, prospective cell-sorting strategies, confocal imaging, and modeling of microvessel formation using advanced microfluidic chip technology to characterize mesenchymal cell subtypes in human postnatal and adult lung. Tissue was obtained from patients undergoing elective surgery for congenital pulmonary airway malformations (CPAM) and other airway abnormalities including chronic obstructive pulmonary disease (COPD). In microscopically normal postnatal human lung, there was a fivefold higher mesenchymal compared with epithelial (EpCAM⁺) fraction, which diminished with age. The mesenchymal fraction composed of CD90⁺ and CD90⁺CD73⁺ cells was enriched in CXCL12 and platelet-derived growth factor receptor-α (PDGFRα) and located in close proximity to EpCAM⁺ cells in the alveolar region. Surprisingly, alveolar organoids generated from EpCAM⁺ cells supported by CD90⁺ subset were immature and displayed dysplastic features. In congenital lung lesions, cystic air spaces and dysplastic alveolar regions were marked with an underlying thick interstitium composed of CD90⁺ and CD90⁺PDGFRα⁺ cells. In postnatal lung, a subset of CD90⁺ cells coexpresses the pericyte marker CD146 and supports self-assembly of perfusable microvessels. CD90⁺CD146⁺ cells from COPD patients fail to support microvessel formation due to fibrinolysis. Targeting the plasmin-plasminogen system during microvessel self-assembly prevented fibrin gel degradation, but microvessels were narrower and excessive contraction blocked perfusion. These data provide important new information regarding the immunophenotypic identity of key mesenchymal lineages and their change in a diverse setting of congenital lung lesions and COPD.

Consequences of early postnatal lipopolysaccharide exposure on developing lungs in mice

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of infants that is characterized by interrupted lung development. Postnatal sepsis causes BPD, yet the contributory mechanisms are unclear. To address this gap, studies have used lipopolysaccharide (LPS) during the alveolar phase of lung development. However, the lungs of infants who develop BPD are still in the saccular phase of development, and the effects of LPS during this phase are poorly characterized. We hypothesized that chronic LPS exposure during the saccular phase disrupts lung development by mechanisms that promote inflammation and prevent optimal lung development and repair. Wild-type C57BL6J mice were intraperitoneally administered 3, 6, or 10 mg/kg of LPS or a vehicle once daily on postnatal days (PNDs) 3-5. The lungs were collected for proteomic and genomic analyses and flow cytometric detection on PND6. The impact of LPS on lung development, cell proliferation, and apoptosis was determined on PND7. Finally, we determined differences in the LPS effects between the saccular and alveolar lungs. LPS decreased the survival and growth rate and lung development in a dose-dependent manner. These effects were associated with a decreased expression of proteins regulating cell proliferation and differentiation and increased expression of those mediating inflammation. While the lung macrophage population of LPS-treated mice increased, the T-regulatory cell population decreased. Furthermore, LPS-induced inflammatory and apoptotic response and interruption of cell proliferation and alveolarization was greater in alveolar than in saccular lungs. Collectively, the data support our hypothesis and reveal several potential therapeutic targets for sepsis-mediated BPD in infants.

Gene Expression Signatures Point to a Male Sex-Specific Lung Mesenchymal Cell PDGF Receptor Signaling Defect in Infants Developing Bronchopulmonary Dysplasia

Male sex is a risk factor for development of bronchopulmonary dysplasia (BPD), a common chronic lung disease following preterm birth. We previously found that tracheal aspirate mesenchymal stromal cells (MSCs) from premature infants developing BPD show reduced expression of PDGFRα, which is required for normal lung development. We hypothesized that MSCs from male infants developing BPD exhibit a pathologic gene expression profile deficient in PDGFR and its downstream effectors, thereby favoring delayed lung development. In a discovery cohort of 6 male and 7 female premature infants, we analyzed the tracheal aspirate MSCs transcriptome. A unique gene signature distinguished MSCs from male infants developing BPD from all other MSCs. Genes involved in lung development, PDGF signaling and extracellular matrix remodeling were differentially expressed. We sought to confirm these findings in a second cohort of 13 male and 12 female premature infants. mRNA expression of PDGFRA, FGF7, WNT2, SPRY1, MMP3 and FOXF2 were significantly lower in MSCs from male infants developing BPD. In female infants developing BPD, tracheal aspirate levels of proinflammatory CCL2 and profibrotic Galectin-1 were higher compared to male infants developing BPD and female not developing BPD. Our findings support a notion for sex-specific differences in the mechanisms of BPD development.

Advances in mechanisms of allergic disease in 2017

This review highlights advances in mechanisms of allergic disease, particularly type 2 innate lymphoid cells, T_H2 lymphocytes, B cells, dendritic cells, microbiome and barrier function, eosinophils, and mast cells. During the last year, considerable progress has been made in the further characterization of type 2 inflammation controlled by both adaptive (T_H2) and type 2 innate lymphoid effector cells. New pathways of lymphocyte activation, trafficking, and recruitment and effector cell mechanisms have been discovered. The plasticity of lymphocyte effector cell responses is another area in which major progress has been achieved. Accumulating evidence will influence both our understanding of allergic disease and our efforts for allergy prevention and treatment.

Lung omics signatures in a bronchopulmonary dysplasia and pulmonary hypertension-like murine model

Bronchopulmonary dysplasia (BPD), the most common chronic lung disease in infants, is associated with long-term morbidities, including pulmonary hypertension (PH). Importantly, hyperoxia causes BPD and PH; however, the underlying mechanisms remain unclear. Herein, we performed high-throughput transcriptomic and proteomic studies using a clinically relevant murine model of BPD with PH. Neonatal wild-type C57BL6J mice were exposed to 21% oxygen (normoxia) or 70% oxygen (hyperoxia) during postnatal days (PNDs) 1-7. Lung tissues were collected for proteomic and genomic analyses on PND 7, and selected genes and proteins were validated by real-time quantitative PCR and immunoblotting analysis, respectively. Hyperoxia exposure dysregulated the expression of 344 genes and 21 proteins. Interestingly, hyperoxia downregulated genes involved in neuronal development and maturation in lung tissues. Gene set enrichment and gene ontology analyses identified apoptosis, oxidoreductase activity, plasma membrane integrity, organ development, angiogenesis, cell proliferation, and mitophagy as the predominant processes affected by hyperoxia. Furthermore, selected deregulated proteins strongly correlated with the expression of specific genes. Collectively, our results identified several potential therapeutic targets for hyperoxia-mediated BPD and PH in infants.

Alveolar capillary dysplasia with misalignment of the pulmonary veins: clinical, histological, and genetic aspects

Alveolar capillary dysplasia with misalignment of the pulmonary veins (ACD/MPV) is a rare and lethal disorder mainly involving the vascular development of the lungs. Since its first description, significant achievements in research have led to a better understanding of the underlying molecular mechanism of ACD/MPV and genetic studies have identified associations with genomic alterations in the locus of the transcription factor FOXF1. This in turn has increased the awareness among clinicians resulting in over 200 cases reported so far, including genotyping of patients in most recent reports. Collectively, this promoted a better stratification of the patient group, leading to new perspectives in research on the pathogenesis. Here, we provide an overview of the clinical aspects of ACD/MPV, including guidance for clinicians, and review the ongoing research into the complex molecular mechanism causing this severe lung disorder.

Activation of the NF-κB pathway alters the phenotype of MSCs in the tracheal aspirates of preterm infants with severe BPD

Mesenchymal stromal cells (MSCs) are released into the airways of preterm infants following lung injury. These cells display a proinflammatory phenotype and are associated with development of severe bronchopulmonary dysplasia (BPD). We aimed to characterize the functional properties of MSCs obtained from tracheal aspirates of 50 preterm infants who required invasive ventilation. Samples were separated by disease severity. The increased proliferative capacity of MSCs was associated with longer duration of mechanical ventilation and higher severity of BPD. Augmented growth depended on nuclear accumulation of NFκBp65 and was accompanied by reduced expression of cytosolic α-smooth muscle actin (α-SMA). The central role of NF-κB signaling was confirmed by inhibition of IκBα phosphorylation. The combined score of proliferative capacity, accumulation of NFκBp65, and expression of α-SMA was used to predict the development of severe BPD with an area under the curve (AUC) of 0.847. We mimicked the clinical situation in vitro, and stimulated MSCs with IL-1β and TNF-α. Both cytokines induced similar and persistent changes as was observed in MSCs obtained from preterm infants with severe BPD. RNA interference was employed to investigate the mechanistic link between NFκBp65 accumulation and alterations in phenotype. Our data indicate that determining the phenotype of resident pulmonary MSCs represents a promising biomarker-based approach. The persistent alterations in phenotype, observed in MSCs from preterm infants with severe BPD, were induced by the pulmonary inflammatory response. NFκBp65 accumulation was identified as a central regulatory mechanism. Future preclinical and clinical studies, aimed to prevent BPD, should focus on phenotype changes in pulmonary MSCs.

The Potentials and Caveats of Mesenchymal Stromal Cell-Based Therapies in the Preterm Infant

Preponderance of proinflammatory signals is a characteristic feature of all acute and resulting long-term morbidities of the preterm infant. The proinflammatory actions are best characterized for bronchopulmonary dysplasia (BPD) which is the chronic lung disease of the preterm infant with lifelong restrictions of pulmonary function and severe consequences for psychomotor development and quality of life. Besides BPD, the immature brain, eye, and gut are also exposed to inflammatory injuries provoked by infection, mechanical ventilation, and oxygen toxicity. Despite the tremendous progress in the understanding of disease pathologies, therapeutic interventions with proven efficiency remain restricted to a few drug therapies with restricted therapeutic benefit, partially considerable side effects, and missing option of applicability to the inflamed brain. The therapeutic potential of mesenchymal stromal cells (MSCs)—also known as mesenchymal stem cells—has attracted much attention during the recent years due to their anti-inflammatory activities and their secretion of growth and development-promoting factors. Based on a molecular understanding, this review summarizes the positive actions of exogenous umbilical cord-derived MSCs on the immature lung and brain and the therapeutic potential of reprogramming resident MSCs. The pathomechanistic understanding of MSC actions from the animal model is complemented by the promising results from the first phase I clinical trials testing allogenic MSC transplantation from umbilical cord blood. Despite all the enthusiasm towards this new therapeutic option, the caveats and outstanding issues have to be critically evaluated before a broad introduction of MSC-based therapies.

"Good things come in small packages": application of exosome-based therapeutics in neonatal lung injury

Infants born at very low gestational age contribute disproportionately to neonatal morbidity and mortality. Advancements in antenatal steroid therapies and surfactant replacement have favored the survival of infants with ever-more immature lungs. Despite such advances in medical care, cardiopulmonary and neurological impairment prevail in constituting the major adverse outcomes for neonatal intensive care unit survivors. With no single effective therapy for either the prevention or treatment of such neonatal disorders, the need for new tools to treat and reduce risk of further complications associated with extreme preterm birth is urgent. Mesenchymal stem/stromal cell (MSC)-based approaches have shown promise in numerous experimental models of lung injury relevant to neonatology. Recent studies have highlighted that the therapeutic potential of MSCs is harnessed in their secretome, and that the therapeutic vector therein is represented by the exosomes released by MSCs. In this review, we summarize the development and significance of stem cell-based therapies for neonatal diseases, focusing on preclinical models of neonatal lung injury. We emphasize the development of MSC exosome-based therapeutics and comment on the challenges in bringing these promising interventions to clinic.

Mesenchymal stem cells in the pathogenesis and treatment of bronchopulmonary dysplasia: a clinical review

Advances in neonatal medicine have led to increased survival of infants born at the limits of viability, resulting in an increased incidence of bronchopulmonary dysplasia (BPD). BPD is a chronic lung disease of premature infants characterized by the arrest of alveolarization, fibroblast activation, and inflammation. BPD leads to significant morbidity and mortality in the neonatal period and is one of the leading causes of chronic lung disease in children. The past decade has brought a surge of trials investigating cellular therapies for the treatment of pulmonary diseases. Mesenchymal stem cells (MSCs) are of particular interest because of their ease of isolation, low immunogenicity, and anti-inflammatory and reparative properties. Clinical trials of MSCs have demonstrated short-term safety and tolerability; however, studies have also shown populations of MSCs with adverse pro-inflammatory and myofibroblastic characteristics. Cell-based therapies may represent the next breakthrough therapy for the treatment of BPD, however, there remain barriers to implementation as well as gaps in knowledge of the role of endogenous MSCs in the pathogenesis of BPD. Concurrent high-quality basic science, translational, and clinical studies investigating the fundamental pathophysiology underlying BPD, therapeutic mechanisms of exogenous MSCs, and logistics of translating cellular therapies will be important areas of future research.

Cellular and humoral biomarkers of Bronchopulmonary Dysplasia

The pathogenesis of Bronchopulmonary Dysplasia (BPD) is multifactorial and the clinical phenotype of BPD is extremely variable. Predicting BPD is difficult, as it is a disease with a clinical operational definition but many clinical phenotypes and endotypes. Most biomarkers studied over the years have low predictive accuracy, and none are currently used in routine clinical care or shown to be useful for predicting longer-term respiratory outcome. Targeted cellular and humoral biomarkers and novel systems biology 'omic' based approaches including genomic and microbiomic analyses are described in this review.

Lethal lung hypoplasia and vascular defects in mice with conditional Foxf1 overexpression

FOXF1 heterozygous point mutations and genomic deletions have been reported in newborns with the neonatally lethal lung developmental disorder, alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). However, no gain-of-function mutations in FOXF1 have been identified yet in any human disease conditions. To study the effects of FOXF1 overexpression in lung development, we generated a Foxf1 overexpression mouse model by knocking-in a Cre-inducible Foxf1 allele into the ROSA26 (R26) locus. The mice were phenotyped using micro-computed tomography (micro-CT), head-out plethysmography, ChIP-seq and transcriptome analyses, immunohistochemistry, and lung histopathology. Thirty-five percent of heterozygous R26-Lox-Stop-Lox (LSL)-Foxf1 embryonic day (E)15.5 embryos exhibit subcutaneous edema, hemorrhages and die perinatally when bred to Tie2-cre mice, which targets Foxf1 overexpression to endothelial and hematopoietic cells. Histopathological and micro-CT evaluations revealed that R26Foxf1; Tie2-cre embryos have immature lungs with a diminished vascular network. Neonates exhibited respiratory deficits verified by detailed plethysmography studies. ChIP-seq and transcriptome analyses in E18.5 lungs identified Sox11, Ghr, Ednrb, and Slit2 as potential downstream targets of FOXF1. Our study shows that overexpression of the highly dosage-sensitive Foxf1 impairs lung development and causes vascular abnormalities. This has important clinical implications when considering potential gene therapy approaches to treat disorders of FOXF1 abnormal dosage, such as ACDMPV.

Stem/progenitor cells and obstructive sleep apnea syndrome - new insights for clinical applications

Obstructive sleep apnea syndrome (OSAS) is a widespread disorder, characterized by recurrent upper airway obstruction during sleep, mostly as a result of complete or partial pharyngeal obstruction. Due to the occurrence of frequent and regular hypoxic events, patients with OSAS are at increased risk of cardiovascular disease, stroke, metabolic disorders, occupational errors, motor vehicle accidents and even death. Thus, OSAS has severe consequences and represents a significant economic burden. However, some of the consequences, as well as their costs can be reduced with appropriate detection and treatment. In this context, the recent advances that were made in stem cell biology knowledge and stem cell - based technologies hold a great promise for various medical conditions, including respiratory diseases. However, the investigation of the role of stem cells in OSAS is still recent and rather limited, requiring further studies, both in animal models and humans. The goal of this review is to summarize the current state of knowledge regarding both lung resident as well as circulating stem/progenitor cells and discuss existing controversies in the field in order to identify future research directions for clinical applications in OSAS. Also, the paper highlights the requisite for inter-institutional, multi-disciplinary research collaborations in order to achieve breakthrough results in the field.

Cell-based therapies for neonatal lung disease

Preterm birth occurs in approximately 11 % of all births worldwide. Advances in perinatal care have enabled the survival of preterm infants born as early as 23-24 weeks of gestation. However, many are affected by bronchopulmonary dysplasia (BPD)-a common respiratory complication of preterm birth, which has life-long consequences for lung health. Currently, there is no specific treatment for BPD. Recent advances in stem cell research have opened new therapeutic avenues for prevention/repair of lung damage. This review summarizes recent pre-clinical data and early clinical translation of cell-based therapies for BPD.

Age dictates a steroid-resistant cascade of Wnt5a, transglutaminase 2, and leukotrienes in inflamed airways

BACKGROUND

Airway remodeling is a detrimental and refractory process showing age-dependent clinical manifestations that are mechanistically undefined. The leukotriene (LT) and wingless/integrase (Wnt) pathways have been implicated in remodeling, but age-specific expression profiles and common regulators remained elusive.

OBJECTIVE

We sought to study the activation of the LT and Wnt pathways during early- or late-onset allergic airway inflammation and to address regulatory mechanisms and clinical relevance in normal human bronchial epithelial cells (NHBEs) and nasal polyp tissues.

METHODS

Mice were sensitized with house dust mite (HDM) allergens from days 3, 15, or 60 after birth. Remodeling factors in murine bronchoalveolar lavage fluid, lung tissue, or human nasal polyp tissue were analyzed by means of Western blotting, immunoassays, or histology. Regulatory mechanisms were studied in cytokine/HDM-stimulated NHBEs and macrophages.

RESULTS

Bronchoalveolar lavage fluid LT levels were increased in neonatal and adult but reduced in juvenile HDM-sensitized mice. Lungs of neonatally sensitized mice showed increased 5-lipoxygenase levels, whereas adult mice expressed more group 10 secretory phospholipase A₂, Wnt5a, and transglutaminase 2 (Tgm2). Older mice showed colocalization of Wnt5a and LT enzymes in the epithelium, a pattern also observed in human nasal polyps. IL-4 promoted epithelial Wnt5a secretion, which upregulated macrophage Tgm2 expression, and Tgm2 inhibition in turn reduced LT release. Tgm2, group 10 secretory phospholipase A₂, and LT enzymes in NHBEs and nasal polyps were refractory to corticosteroids.

CONCLUSION

Our findings reveal age differences in LT and Wnt pathways during airway inflammation and identify a steroid-resistant cascade of Wnt5a, Tgm2, and LTs, which might represent a therapeutic target for airway inflammation and remodeling.

Stem cell-based therapies for the newborn lung and brain: Possibilities and challenges

There have been substantial advances in neonatal medical care over the past 2 decades that have resulted in the increased survival of very low birth weight infants, survival that in some centers extends to 22 weeks gestational age. Despite these advances, there continues to be significant morbidity associated with extreme preterm birth that includes both short-term and long-term pulmonary and neurologic consequences. No single therapy has proven to be effective in preventing or treating either developmental lung and brain injuries in preterm infants or the hypoxic-ischemic injury that can be inflicted on the full-term brain as a result of in utero or perinatal complications. Stem cell-based therapies are emerging as a potential paradigm-shifting approach for such complex diseases with multifactorial etiologies, but a great deal of work is still required to understand the role of stem/progenitor cells in normal development and in the repair of injured tissue. This review will summarize the biology of the various stem/progenitor cells, their effects on tissue repair in experimental models of lung and brain injury, the recent advances in our understanding of their mechanism of action, and the challenges that remain to be addressed before their eventual application to clinical care.

Stem Cells and Their Mediators - Next Generation Therapy for Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) remains a major complication of premature birth. Despite great achievements in perinatal medicine over the past decades, there is no treatment for BPD. Recent insights into the biology of stem/progenitor cells have ignited the hope of regenerating damaged organs. Animal experiments revealed promising lung protection/regeneration with stem/progenitor cells in experimental models of BPD and led to first clinical studies in infants. However, these therapies are still experimental and knowledge on the exact mechanisms of action of these cells is limited. Furthermore, heterogeneity of the therapeutic cell populations and missing potency assays currently limit our ability to predict a cell product’s efficacy. Here, we review the therapeutic potential of mesenchymal stromal, endothelial progenitor, and amniotic epithelial cells for BPD. Current knowledge on the mechanisms behind the beneficial effects of stem cells is briefly summarized. Finally, we discuss the obstacles constraining their transition from bench-to-bedside and present potential approaches to overcome them.

Genomic and Epigenetic Complexity of the FOXF1 Locus in 16q24.1: Implications for Development and Disease

The FOXF1 (Forkhead box F1) gene, located on chromosome 16q24.1 encodes a member of the FOX family of transcription factors characterized by a distinct forkhead DNA binding domain. FOXF1 plays an important role in epithelium-mesenchyme signaling, as a downstream target of Sonic hedgehog pathway. Heterozygous point mutations and genomic deletions involving FOXF1 have been reported in newborns with a lethal lung developmental disorder, Alveolar Capillary Dysplasia with Misalignment of Pulmonary Veins (ACDMPV). In addition, genomic deletions upstream to FOXF1 identified in ACDMPV patients have revealed that FOXF1 expression is tightly regulated by distal tissue-specific enhancers. Interestingly, FOXF1 has been found to be incompletely paternally imprinted in human lungs; characterized genomic deletions arose de novo exclusively on maternal chromosome 16, with most of them being Alu-Alu mediated. Regulation of FOXF1 expression likely utilizes a combination of chromosomal looping, differential methylation of an upstream CpG island overlapping GLI transcription factor binding sites, and the function of lung-specific long non-coding RNAs (lncRNAs). FOXF1 knock-out mouse models demonstrated its critical role in mesoderm differentiation and in the development of pulmonary vasculature. Additionally, epigenetic inactivation of FOXF1 has been reported in breast and colorectal cancers, whereas overexpression of FOXF1 has been associated with a number of other human cancers, e.g. medulloblastoma and rhabdomyosarcoma. Constitutional duplications of FOXF1 have recently been reported in congenital intestinal malformations. Thus, understanding the genomic and epigenetic complexity at the FOXF1 locus will improve diagnosis, prognosis, and treatment of ACDMPV and other human disorders associated with FOXF1 alterations.

Stem cells for the prevention of neonatal lung disease

Preterm birth affects approximately 11% of all newborns worldwide and is a major risk factor for infant mortality and morbidity. A common complication of preterm birth is the chronic lung disease of prematurity called bronchopulmonary dysplasia (BPD). Due to the lack of a specific treatment for BPD, preterm infants surviving with BPD face a lifelong risk of poor lung health. The therapeutic potential of stem cells in regenerative medicine is being harnessed for many diseases, including BPD. Compelling preclinical data using stem cells to prevent/repair lung damage in animal models of experimental BPD has built the basis for its translation into the clinic in preterm infants. This review highlights the exciting translation from bench to bedside that will hopefully lead in the near future to improved pulmonary outcomes in preterm infants.

Lung mesenchymal stromal cells in development and disease: to serve and protect?

SIGNIFICANCE

Bronchopulmonary dysplasia (BPD) is a disease of the developing lung that afflicts extreme preterm infants in the neonatal intensive care unit. Follow-up studies into adulthood show that BPD is not merely a problem of the neonatal period, as it also may predispose to early-onset emphysema and poor lung function in later life.

RECENT ADVANCES

The increasing promise of bone marrow- or umbilical cord-derived mesenchymal stromal cells (MSCs) to repair neonatal and adult lung diseases may for the first time offer the chance to make substantial strides in improving the outcome of extreme premature infants at risk of developing BPD. As more knowledge has been obtained on MSCs over the past decades, it has become clear that each organ has its own reservoir of endogenous MSCs, including the lung.

CRITICAL ISSUES

We have only barely scratched the surface on what resident lung MSCs exactly are and what their role and function in lung development may be. Moreover, what happens to these putative repair cells in BPD when alveolar development goes awry and why do their counterparts from the bone marrow and umbilical cord succeed in restoring normal alveolar development when they themselves do not?

FUTURE DIRECTIONS

Much work remains to be carried out to validate lung MSCs, but with the high potential of MSC-based treatment for BPD and other lung diseases, a thorough understanding of the endogenous lung MSC will be pivotal to get to the bottom of these diseases.

Stem cells, cell therapies, and bioengineering in lung biology and diseases. Comprehensive review of the recent literature 2010-2012

A conference, "Stem Cells and Cell Therapies in Lung Biology and Lung Diseases," was held July 25 to 28, 2011 at the University of Vermont to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy and ex vivo bioengineering approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, to discuss and debate current controversies, and to identify future research directions and opportunities for basic and translational research in cell-based therapies for lung diseases. The goal of this article, which accompanies the formal conference report, is to provide a comprehensive review of the published literature in lung regenerative medicine from the last conference report through December 2012.

Amniotic fluid derived mesenchymal stromal cells augment fetal lung growth in a nitrofen explant model

PURPOSE

Recent experimental work suggests the therapeutic role of mesenchymal stromal cells (MSCs) during lung morphogenesis. The purpose of this study was to investigate the potential paracrine effects of amniotic fluid-derived MSCs (AF-MSCs) on fetal lung growth in a nitrofen explant model.

METHODS

Pregnant Sprague-Dawley dams were gavage fed nitrofen on gestational day 9.5 (E9.5). E14.5 lung explants were subsequently harvested and cultured ex vivo for three days on filter membranes in conditioned media from rat AF-MSCs isolated from control (AF-Ctr) or nitrofen-exposed (AF-Nitro) dams. The lungs were analyzed morphometrically and by quantitative gene expression.

RESULTS

Although there were no significant differences in total lung surface area among hypoplastic lungs, there were significant increases in terminal budding among E14.5+3 nitrofen explants exposed to AF-Ctr compared to explants exposed to medium alone (58.8±8.4 vs. 39.0±10.0 terminal buds, respectively; p<0.05). In contrast, lungs cultured in AF-Nitro medium failed to augment terminal budding. Nitrofen explants exposed to AF-Ctr showed significant upregulation of surfactant protein C to levels observed in normal fetal lungs.

CONCLUSIONS

AF-MSCs can augment branching morphogenesis and lung epithelial maturation in a fetal explant model of pulmonary hypoplasia. Cell therapy using donor-derived AF-MSCs may represent a novel strategy for the treatment of fetal congenital diaphragmatic hernia.

Progenitor cells of the distal lung and their potential role in neonatal lung disease

Bronchopulmonary dysplasia (BPD) is the most common adverse outcome in extreme preterm neonates (born before 28 weeks gestation). BPD is characterized by interrupted lung growth and may predispose to early-onset emphysema and poor lung function in later life. At present, there is no treatment for BPD. Recent advances in stem/progenitor cell biology have enabled the exploration of endogenous lung progenitor populations in health and disease. In parallel, exogenous stem/progenitor cell administration has shown promise in protecting the lung from injury in the experimental setting. This review will provide an outline of the progenitor populations that have currently been identified in all tissue compartments of the distal lung and how they may be affected in BPD. A thorough understanding of the lung's endogenous progenitor populations during normal development, injury and repair may one day allow us to harness their regenerative capacity.

The promise of stem cells in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of prematurity, which affects very preterm infants. Advances in perinatal care have enabled the survival of infants born as early as 23-24 weeks of gestation, but make the task more challenging of protecting injury to an ever more immature lung. Currently, there is no specific treatment for BPD. Recent advances in our understanding of stem/progenitor cells and their potential to repair damaged organs offer the possibility of cell-based treatments for neonatal lung injury. This review summarizes the recent advances in our understanding of lung stem cells during normal and impaired lung growth and the exciting pre-clinical data using mesenchymal stromal cells to prevent/repair impaired alveolar growth in experimental models of BPD.

Lung stem and progenitor cells

Over the past few years, new insights have been added to the study of stem cells in the adult lung. The exploration of endogenous lung progenitors as well as the study of exogenously delivered stem cell populations holds promise for advancing our understanding of the biology of lung repair mechanisms. Moreover, it opens new possibilities for the use of stem cell therapy for the development of regenerative medicine approaches for the treatment of lung disease. Here, we discuss the main types of lung epithelial progenitor populations; the potential of endothelial progenitors, mesenchymal stem cells and embryonic stem cells for lung therapy, as well as summarize the cellular mechanisms involved.

Mechanisms of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease affecting premature infants with long term effect on lung function into adulthood. Multiple factors are involved in the development of BPD. This review will summarize the different mechanisms leading to this disease and highlight recent bench and clinical research targeted at understanding the role of the mesenchyme (both its cellular and extracellular components) in the pathogenesis of BPD.

Small noncoding differentially methylated copy-number variants, including lncRNA genes, cause a lethal lung developmental disorder

An unanticipated and tremendous amount of the noncoding sequence of the human genome is transcribed. Long noncoding RNAs (lncRNAs) constitute a significant fraction of non-protein-coding transcripts; however, their functions remain enigmatic. We demonstrate that deletions of a small noncoding differentially methylated region at 16q24.1, including lncRNA genes, cause a lethal lung developmental disorder, alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV), with parent-of-origin effects. We identify overlapping deletions 250 kb upstream of FOXF1 in nine patients with ACD/MPV that arose de novo specifically on the maternally inherited chromosome and delete lung-specific lncRNA genes. These deletions define a distant cis-regulatory region that harbors, besides lncRNA genes, also a differentially methylated CpG island, binds GLI2 depending on the methylation status of this CpG island, and physically interacts with and up-regulates the FOXF1 promoter. We suggest that lung-transcribed 16q24.1 lncRNAs may contribute to long-range regulation of FOXF1 by GLI2 and other transcription factors. Perturbation of lncRNA-mediated chromatin interactions may, in general, be responsible for position effect phenomena and potentially cause many disorders of human development.

Comparison of epithelial differentiation and immune regulatory properties of mesenchymal stromal cells derived from human lung and bone marrow

Mesenchymal stromal cells (MSCs) reside in many organs including lung, as shown by their isolation from fetal lung tissues, bronchial stromal compartment, bronchial-alveolar lavage and transplanted lung tissues. It is still controversial whether lung MSCs can undergo mesenchymal-to-epithelial-transition (MET) and possess immune regulatory properties. To this aim, we isolated, expanded and characterized MSCs from normal adult human lung (lung-hMSCs) and compared with human bone marrow-derived MSCs (BM-hMSCs). Our results show that lung-MSCs reside at the perivascular level and do not significantly differ from BM-hMSCs in terms of immunophenotype, stemness gene profile, mesodermal differentiation potential and modulation of T, B and NK cells. However, lung-hMSCs express higher basal level of the stemness-related marker nestin and show, following in vitro treatment with retinoic acid, higher epithelial cell polarization, which is anyway partial when compared to a control epithelial bronchial cell line. Although these results question the real capability of acquiring epithelial functions by MSCs and the feasibility of MSC-based therapeutic approaches to regenerate damaged lung tissues, the characterization of this lung-hMSC population may be useful to study the involvement of stromal cell compartment in lung diseases in which MET plays a role, such as in chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis.

Stem cells and regenerative medicine in lung biology and diseases

A number of novel approaches for repair and regeneration of injured lung have developed over the past several years. These include a better understanding of endogenous stem and progenitor cells in the lung that can function in reparative capacity as well as extensive exploration of the potential efficacy of administering exogenous stem or progenitor cells to function in lung repair. Recent advances in ex vivo lung engineering have also been increasingly applied to the lung. The current status of these approaches as well as initial clinical trials of cell therapies for lung diseases are reviewed below.

Neonatal periostin knockout mice are protected from hyperoxia-induced alveolar simplication

In bronchopulmonary dysplasia (BPD), alveolar septae are thickened with collagen and α-smooth muscle actin, transforming growth factor (TGF)-β-positive myofibroblasts. Periostin, a secreted extracellular matrix protein, is involved in TGF-β-mediated fibrosis and myofibroblast differentiation. We hypothesized that periostin expression is required for hypoalveolarization and interstitial fibrosis in hyperoxia-exposed neonatal mice, an animal model for this disease. We also examined periostin expression in neonatal lung mesenchymal stromal cells and lung tissue of hyperoxia-exposed neonatal mice and human infants with BPD. Two-to-three day-old wild-type and periostin null mice were exposed to air or 75% oxygen for 14 days. Mesenchymal stromal cells were isolated from tracheal aspirates of premature infants. Hyperoxic exposure of neonatal mice increased alveolar wall periostin expression, particularly in areas of interstitial thickening. Periostin co-localized with α-smooth muscle actin, suggesting synthesis by myofibroblasts. A similar pattern was found in lung sections of infants dying of BPD. Unlike wild-type mice, hyperoxia-exposed periostin null mice did not show larger air spaces or α-smooth muscle-positive myofibroblasts. Compared to hyperoxia-exposed wild-type mice, hyperoxia-exposed periostin null mice also showed reduced lung mRNA expression of α-smooth muscle actin, elastin, CXCL1, CXCL2 and CCL4. TGF-β treatment increased mesenchymal stromal cell periostin expression, and periostin treatment increased TGF-β-mediated DNA synthesis and myofibroblast differentiation. We conclude that periostin expression is increased in the lungs of hyperoxia-exposed neonatal mice and infants with BPD, and is required for hyperoxia-induced hypoalveolarization and interstitial fibrosis.