Bone marrow-derived angiogenic cells restore lung alveolar and vascular structure after neonatal hyperoxia in infant mice

Extracellular vesicle-mediated cellular crosstalk in lung repair, remodelling and regeneration

The unperturbed lung is highly quiescent, with a remarkably low level of cell turnover. However, once damaged, the lung shows an extensive regenerative capacity, with resident progenitor cell populations re-entering the cell cycle and differentiating to promote repair. This quick and dramatic repair response requires interactions among more than 40 different cell lineages in the lung, and defects in any of these processes can lead to various lung pathologies. Understanding the mechanisms of interaction in lung injury, repair and regeneration thus has considerable practical and therapeutic implications. Moreover, therapeutic strategies for replacing lung progenitor cells and their progeny through cell therapy have gained increasing attention. In the last decade, extracellular vesicles (EVs), including exosomes, have been recognised as paracrine mediators through the transfer of biological cargo. Recent work has revealed that EVs are involved in lung homeostasis and diseases. In addition, EVs derived from specific cells or tissues have proven to be a promising cell-free modality for the treatment of lung diseases. This review highlights the EV-mediated cellular crosstalk that regulates lung homeostasis and discusses the potential of EV therapeutics for lung regenerative medicine.

Application Prospects of Mesenchymal Stem Cell Therapy for Bronchopulmonary Dysplasia and the Challenges Encountered

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease in premature babies, especially affecting those with very low or extremely low birth weights. Survivors experience adverse lung and neurological defects including cognitive dysfunction. This impacts the prognosis of children with BPD and may result in developmental delays. The currently available options for the treatment of BPD are limited owing to low efficacy or several side effects; therefore, there is a lack of effective treatments for BPD. The treatment for BPD must help in the repair of damaged lung tissue and promote further growth of the lung tissue. In recent years, the emergence of stem cell therapy, especially mesenchymal stem cell (MSC) therapy, has improved the treatment of BPD to a great extent. This article briefly reviews the advantages, research progress, and challenges faced with the use of MSCs in the treatment of BPD. Stem cell therapy is beneficial as it repairs damaged tissues by reducing inflammation, fibrosis, and by acting against oxidative stress damage. Experimental trials have also proven that MSCs provide a promising avenue for BPD treatment. However, there are challenges such as the possibility of MSCs contributing to tumorous growths, the presence of heterogeneous cell populations resulting in variable efficacy, and the ethical considerations regarding the use of this treatment in humans. Therefore, more research must be conducted to determine whether MSC therapy can be approved as a treatment option for BPD.

Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension in preclinical models

Congenital diaphragmatic hernia (CDH)-related deaths are the largest contributor to in-hospital neonatal deaths in children with congenital malformations. Morbidity and mortality in CDH are directly related to the development of pulmonary hypertension (PH). Current treatment consists of supportive measures. To date, no pharmacotherapy has been shown to effectively reverse the hallmark finding of pulmonary vascular remodeling that is associated with pulmonary hypertension in CDH (CDH-PH). As such, there is a great need for novel therapies to effectively manage CDH-PH. Our review aims to evaluate emerging therapies, and specifically focuses on those that are still under investigation and not approved for clinical use by the Food and Drug Administration. Therapies were categorized into antenatal pharmacotherapies or antenatal regenerative therapies and assessed on their method of administration, safety profile, the effect on pulmonary vascular pathophysiology, and overall efficacy. In general, emerging antenatal pharmaceutical and regenerative treatments primarily aim to alleviate pulmonary vascular remodeling by restoring normal function and levels of key regulatory factors involved in pulmonary vascular development and/or in promoting angiogenesis. Overall, while these emerging therapies show great promise for the management of CDH-PH, most require further assessment of safety and efficacy in preclinical models before translation into the clinical setting. IMPACT: Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension (CDH-PH) show promise to effectively mitigate vascular remodeling in preclinical models. Further investigation is needed in preclinical and human studies to evaluate safety and efficacy prior to translation into the clinical arena. This review offers a comprehensive and up-to-date summary of emerging therapies currently under investigation in experimental animal models. There is no cure for CDH-PH. This review explores emerging therapeutic options for the treatment of CDH-PH and evaluates their impact on key molecular pathways and clinical markers of disease to determine efficacy in the preclinical stage.

Preconditioning the immature lung with enhanced Nrf2 activity protects against oxidant-induced hypoalveolarization in mice

Bronchopulmonary dysplasia (BPD) is a chronic disease of preterm babies with poor clinical outcomes. Nrf2 transcription factor is crucial for cytoprotective response, whereas Keap1—an endogenous inhibitor of Nrf2 signaling—dampens these protective responses. Nrf2-sufficient (wild type) newborn mice exposed to hyperoxia develop hypoalveolarization, which phenocopies human BPD, and Nrf2 deficiency worsens it. In this study, we used PND1 pups bearing bearing hypomorphic Keap1 floxed alleles (Keap1^f/f) with increased levels of Nrf2 to test the hypothesis that constitutive levels of Nrf2 in the premature lung are insufficient to mitigate hyperoxia-induced hypoalveolarization. Both wildtype and Keap1^f/f pups at PND1 were exposed to hyperoxia for 72 h and then allowed to recover at room air for two weeks (at PND18), sacrificed, and lung hypoalveolarization and inflammation assessed. Hyperoxia-induced lung hypoalveolarization was remarkably lower in Keap1^f/f pups than in wildtype counterparts (28.9% vs 2.4%, wildtype vs Keap1^f/f). Likewise, Keap1^f/f pups were protected against prolonged (96 h) hyperoxia-induced hypoalveolarization. However, there were no differences in hyperoxia-induced lung inflammatory response immediately after exposure or at PND18. Lack of hypoalveolarization in Keap1^f/f pups was accompanied by increased levels of expression of antioxidant genes and GSH as assessed immediately following hyperoxia. Keap1 knockdown resulted in upregulation of lung cell proliferation postnatally but had opposing effects following hyperoxia. Collectively, our study demonstrates that augmenting endogenous Nrf2 activation by targeting Keap1 may provide a physiological way to prevent hypoalveolarization associated with prematurity.

Present and Future of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is the most common respiratory disorder among infants born extremely preterm. The pathogenesis of BPD involves multiple prenatal and postnatal mechanisms affecting the development of a very immature lung. Their combined effects alter the lung's morphogenesis, disrupt capillary gas exchange in the alveoli, and lead to the pathological and clinical features of BPD. The disorder is ultimately the result of an aberrant repair response to antenatal and postnatal injuries to the developing lungs. Neonatology has made huge advances in dealing with conditions related to prematurity, but efforts to prevent and treat BPD have so far been only partially effective. Seeing that BPD appears to have a role in the early origin of chronic obstructive pulmonary disease, its prevention is pivotal also in long-term respiratory outcome of these patients. There is currently some evidence to support the use of antenatal glucocorticoids, surfactant therapy, protective noninvasive ventilation, targeted saturations, early caffeine treatment, vitamin A, and fluid restriction, but none of the existing strategies have had any significant impact in reducing the burden of BPD. New areas of research are raising novel therapeutic prospects, however. For instance, early topical (intratracheal or nebulized) steroids seem promising: they might help to limit BPD development without the side effects of systemic steroids. Evidence in favor of stem cell therapy has emerged from several preclinical trials, and from a couple of studies in humans. Mesenchymal stromal/stem cells (MSCs) have revealed a reparatory capability, preventing the progression of BPD in animal models. Administering MSC-conditioned media containing extracellular vesicles (EVs) have also demonstrated a preventive action, without the potential risks associated with unwanted engraftment or the adverse effects of administering cells. In this paper, we explore these emerging treatments and take a look at the revolutionary changes in BPD and neonatology on the horizon.

Are all stem cells equal? Systematic review, evidence map, and meta-analyses of preclinical stem cell-based therapies for bronchopulmonary dysplasia

Regenerative stem cell-based therapies for bronchopulmonary dysplasia (BPD), the most common preterm birth complication, demonstrate promise in animals. Failure to objectively appraise available preclinical data and identify knowledge gaps could jeopardize clinical translation. We performed a systematic review and network meta-analysis (NMA) of preclinical studies testing cell-based therapies in experimental neonatal lung injury. Fifty-three studies assessing 15 different cell-based therapies were identified: 35 studied the effects of mesenchymal stromal cells (MSCs) almost exclusively in hyperoxic rodent models of BPD. Exploratory NMAs, for select outcomes, suggest that MSCs are the most effective therapy. Although a broad range of promising cell-based therapies has been assessed, few head-to-head comparisons and unclear risk of bias exists. Successful clinical translation of cell-based therapies demands robust preclinical experimental design with appropriately blinded, randomized, and statistically powered studies, based on biological plausibility for a given cell product, in standardized models and endpoints with transparent reporting.

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.

Advanced pulmonary MRI to quantify alveolar and acinar duct abnormalities: Current status and future clinical applications

There are serious clinical gaps in our understanding of chronic lung disease that require novel, sensitive, and noninvasive in vivo measurements of the lung parenchyma to measure disease pathogenesis and progressive changes over time as well as response to treatment. Until recently, our knowledge and appreciation of the tissue changes that accompany lung disease has depended on ex vivo biopsy and concomitant histological and stereological measurements. These measurements have revealed the underlying pathologies that drive lung disease and have provided important observations about airway occlusion, obliteration of the terminal bronchioles and airspace enlargement, or fibrosis and their roles in disease initiation and progression. ex vivo tissue stereology and histology are the established gold standards and, more recently, micro-computed tomography (CT) measurements of ex vivo tissue samples has also been employed to reveal new mechanistic findings about the progression of obstructive lung disease in patients. While these approaches have provided important understandings using ex vivo analysis of excised samples, recently developed hyperpolarized noble gas MRI methods provide an opportunity to noninvasively measure acinar duct and terminal airway dimensions and geometry in vivo, and, without radiation burden. Therefore, in this review we summarize emerging pulmonary MRI morphometry methods that provide noninvasive in vivo measurements of the lung in patients with bronchopulmonary dysplasia and chronic obstructive pulmonary disease, among others. We discuss new findings, future research directions, as well as clinical opportunities to address current gaps in patient care and for testing of new therapies. Level of Evidence: 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2019;50:28-40.

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.

Stem cell biology and regenerative medicine for neonatal lung diseases

Lung diseases remain one of the main causes of morbidity and mortality in neonates. Cell therapy and regenerative medicine have the potential to revolutionize the management of life-threatening and debilitating lung diseases that currently lack effective treatments. Over the past decade, the repair capabilities of stem/progenitor cells have been harnessed to prevent/rescue lung damage in experimental neonatal lung diseases. Mesenchymal stromal cells and amnion epithelial cells exert pleiotropic effects and represent ideal therapeutic cells for bronchopulmonary dysplasia, a multifactorial disease. Endothelial progenitor cells are optimally suited to promote lung vascular growth and attenuate pulmonary hypertension in infants with congenital diaphragmatic hernia or a vascular bronchopulmonary dysplasia phenotype. Induced pluripotent stem cells (iPSCs) are one of the most exciting breakthroughs of the past decade. Patient-specific iPSCs can be derived from somatic cells and differentiated into any cell type. iPSCs can be capitalized upon to develop personalized regenerative cell products for surfactant protein deficiencies-lethal lung disorders without treatment-that affect a single gene in a single cell type and thus lend themselves to phenotype-specific cell replacement. While the clinical translation has begun, more needs to be learned about the biology of these repair cells to make this translation successful.

Fresh Noncultured Endothelial Progenitor Cells Improve Neonatal Lung Hyperoxia-Induced Alveolar Injury

Treatment of preterm human infants with high oxygen can result in disrupted lung alveolar and vascular development. Local or systemic administration of endothelial progenitor cells (EPCs) is reported to remedy such disruption in animal models. In this study, the effects of both fresh (enriched for KDR) and cultured bone marrow (BM)-derived cell populations with EPC characteristics were examined following hyperoxia in neonatal mouse lungs. Intraperitoneal injection of fresh EPCs into five-day-old mice treated with 90% oxygen resulted in full recovery of hyperoxia-induced alveolar disruption by 56 days of age. Partial recovery in septal number following hyperoxia was observed following injection of short-term cultured EPCs, yet aberrant tissue growths appeared following injection of long-term cultured cells. Fresh and long-term cultured cells had no impact on blood vessel development. Short-term cultured cells increased blood vessel number in normoxic and hyperoxic mice by 28 days but had no impact on day 56. Injection of fresh EPCs into normoxic mice significantly reduced alveolarization compared with phosphate buffered saline-injected normoxic controls. These results indicate that fresh BM EPCs have a higher and safer corrective profile in a hyperoxia-induced lung injury model compared with cultured BM EPCs but may be detrimental to the normoxic lung. The appearance of aberrant tissue growths and other side effects following injection of cultured EPCs warrants further investigation. Stem Cells Translational Medicine 2017;6:2094-2105.

Surfactant effects on the viability and function of human mesenchymal stem cells: in vitro and in vivo assessment

BACKGROUND

Surfactant therapy has become the standard of care for preterm infants with respiratory distress syndrome. Preclinical studies have reported the therapeutic benefits of mesenchymal stem cells (MSCs) in experimental bronchopulmonary dysplasia. This study investigated the effects of a surfactant on the in vitro viability and in vivo function of human MSCs.

METHODS

The viability, phenotype, and mitochondrial membrane potential (MMP) of MSCs were assessed through flow cytometry. The in vivo function was assessed after intratracheal injection of human MSCs (1 × 10⁵ cells) diluted in 30 μl of normal saline (NS), 10 μl of a surfactant diluted in 20 μl of NS, and 10 μl of a surfactant and MSCs (1 × 10⁵ cells) diluted in 20 μl of NS in newborn rats on postnatal day 5. The pups were reared in room air (RA) or an oxygen-enriched atmosphere (85% O₂) from postnatal days 1 to 14; eight study groups were examined: RA + NS, RA + MSCs, RA + surfactant, RA + surfactant + MSCs, O₂ + NS, O₂ + MSCs, O₂ + surfactant, and O₂ + surfactant + MSCs. The lungs were excised for histological and cytokine analysis on postnatal day 14.

RESULTS

Compared with the controls, surfactant-treated MSCs showed significantly reduced viability and MMP after exposure to 1:1 and 1:2 of surfactant:MSCs for 15 and 60 minutes. All human MSC samples exhibited similar percentages of CD markers, regardless of surfactant exposure. The rats reared in hyperoxia and treated with NS exhibited a significantly higher mean linear intercept (MLI) than did those reared in RA and treated with NS, MSCs, surfactant, or surfactant + MSCs. Treatment with MSCs, surfactant, or surfactant + MSCs significantly reduced the hyperoxia-induced increase in MLI. The O₂ + surfactant + MSCs group exhibited a significantly higher MLI than did the O₂ + MSCs group. Furthermore, treatment with MSCs and MSCs + surfactant significantly reduced the hyperoxia-induced increase in apoptotic cells.

CONCLUSIONS

Combination therapy involving a surfactant and MSCs does not exert additive effects on lung development in hyperoxia-induced lung injury.

Effects of human umbilical cord blood mononuclear cells on respiratory system mechanics in a murine model of neonatal lung injury

BACKGROUND

Mononuclear cells (MNCs) have well-documented beneficial effects in a wide range of adult pulmonary diseases. The effects of human umbilical cord blood-derived MNCs on neonatal lung injury, highly relevant for potential autologous application in preterm newborns at risk for bronchopulmonary dysplasia (BPD), remain incompletely established. The aim of this study was to determine the long-term morphologic and functional effects of systemically delivered MNCs in a murine model of neonatal lung injury.

MATERIALS AND METHODS

MNCs from cryopreserved cord blood (1 × 10⁶ cells per pup) were given intravenously to newborn mice exposed to 90% O₂ from birth; controls received cord blood total nucleated cells (TNCs) or granular cells, or equal volume vehicle buffer (sham controls). In order to avoid immune rejection, we used SCID mice as recipients. Lung mechanics (flexiVent™), engraftment, growth, and alveolarization were evaluated eight weeks postinfusion.

RESULTS

Systemic MNC administration to hyperoxia-exposed newborn mice resulted in significant attenuation of methacholine-induced airway hyperreactivity, leading to reduction of central airway resistance to normoxic levels. These bronchial effects were associated with mild improvement of alveolarization, lung compliance, and elastance. TNCs had no effects on alveolar remodeling and were associated with worsened methacholine-induced bronchial hyperreactivity. Granular cell administration resulted in a marked morphologic and functional emphysematous phenotype, associated with high mortality. Pulmonary donor cell engraftment was sporadic in all groups.

CONCLUSIONS

These results suggest that cord blood MNCs may have a cell type-specific role in therapy of pulmonary conditions characterized by increased airway resistance, such as BPD and asthma. Future studies need to determine the active MNC subtype(s), their mechanisms of action, and optimal purification methods to minimize granular cell contamination.

Preclinical evaluation of cell-based strategies to prevent or treat bronchopulmonary dysplasia in animal models: a systematic review

Bronchopulmonary dysplasia (BPD) remains the most common complication of extreme prematurity as no effective treatment is available to date. This calls for the exploration of new therapeutic options like cell therapy, which is already effective for various human (lung) disorders. We systematically searched the MEDLINE, Embase, and Web of Science databases from the earliest date till January 2017 and included original studies on the perinatal use of cell-based therapies (i.e. cells and/or cell-derivatives) to treat BDP in animal models. Fourth publications describing 47 interventions were retrieved. Newborn mice/rats raised in a hyperoxic environment were studied in most interventions. Different cell types - either intact cells or their conditioned medium - were administered, but bone marrow and umbilical cord blood derived mesenchymal stem cells were most prevalent. All studies reported positive effects on outcome parameters including alveolar and vascular morphometry, lung function, and inflammation. Cell homing to the lungs was demonstrated in some studies, but the therapeutic effects seemed to be mostly mediated via paracrine modulation of inflammation, fibrosis and angiogenesis.

CONCLUSION

Multiple rat/mouse studies show promise for cell therapy for BPD. Yet careful study of action mechanisms and side effects in large animal models is imperative before clinical translation can be achieved.

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.

Cell Therapy for Bronchopulmonary Dysplasia: Promises and Perils

Despite great achievements in neonatal and perinatal medicine over the past decades, the immature lung remains the most critical organ to care for after premature birth. As a consequence, bronchopulmonary dysplasia (BPD) remains the most common complication of extreme prematurity. BPD impairs normal development and may cause lifelong morbidities. At present, there is no effective treatment for BPD - including preventing premature birth. Recent insights into the biology of stem and progenitor cells have ignited the hope of protecting the immature lung, and even regenerating an already damaged lung by using exogenous stem- or progenitor cells as therapeutics. These therapies are still experimental, and knowledge on the exact mechanisms behind the beneficial effects seen in various animal models of BPD is limited. Nevertheless, early phase clinical trials have started, and encouraging steps towards the therapeutic use of these cells are being made. This review aims to (I) provide an overview of the role of stem/progenitor cells in development and therapy of BPD for the practicing clinician, (II) discuss the potential clinical applications of cell products as therapeutic agents to prevent neonatal lung injury and (III) examine potential obstacles towards the manufacturing of clinical grade cell products for use in the care for premature infants.

Hepatocyte growth factor as a downstream mediator of vascular endothelial growth factor-dependent preservation of growth in the developing lung

Impaired vascular endothelial growth factor (VEGF) signaling contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). We hypothesized that the effects of VEGF on lung structure during development may be mediated through its downstream effects on both endothelial nitric oxide synthase (eNOS) and hepatocyte growth factor (HGF) activity, and that, in the absence of eNOS, trophic effects of VEGF would be mediated through HGF signaling. To test this hypothesis, we performed an integrative series of in vitro (fetal rat lung explants and isolated fetal alveolar and endothelial cells) and in vivo studies with normal rat pups and eNOS(-/-) mice. Compared with controls, fetal lung explants from eNOS(-/-) mice had decreased terminal lung bud formation, which was restored with recombinant human VEGF (rhVEGF) treatment. Neonatal eNOS(-/-) mice were more susceptible to hyperoxia-induced inhibition of lung growth than controls, which was prevented with rhVEGF treatment. Fetal alveolar type II (AT2) cell proliferation was increased with rhVEGF treatment only with mesenchymal cell (MC) coculture, and these effects were attenuated with anti-HGF antibody treatment. Unlike VEGF, HGF directly stimulated isolated AT2 cells even without MC coculture. HGF directly stimulates fetal pulmonary artery endothelial cell growth and tube formation, which is attenuated by treatment with JNJ-38877605, a c-Met inhibitor. rHGF treatment preserves alveolar and vascular growth after postnatal exposure to SU-5416, a VEGF receptor inhibitor. We conclude that the effects of VEGF on AT2 and endothelial cells during lung development are partly mediated through HGF-c-Met signaling and speculate that reciprocal VEGF-HGF signaling between epithelia and endothelia is disrupted in infants who develop BPD.

Therapeutic potential of mesenchymal stem cells for pulmonary complications associated with preterm birth

Preterm infants frequently suffer from pulmonary complications resulting in significant morbidity and mortality. Physiological and structural lung immaturity impairs perinatal lung transition to air breathing resulting in respiratory distress. Mechanical ventilation and oxygen supplementation ensure sufficient oxygen supply but enhance inflammatory processes which might lead to the establishment of a chronic lung disease called bronchopulmonary dysplasia (BPD). Current therapeutic options to prevent or treat BPD are limited and have salient side effects, highlighting the need for new therapeutic approaches. Mesenchymal stem cells (MSCs) have demonstrated therapeutic potential in animal models of BPD. This review focuses on MSC-based therapeutic approaches to treat pulmonary complications and critically compares results obtained in BPD models. Thereby bottlenecks in the translational systems are identified that are preventing progress in combating BPD. Notably, current animal models closely resemble the so-called "old" BPD with profound inflammation and injury, whereas clinical improvements shifted disease pathology towards a "new" BPD in which arrest of lung maturation predominates. Future studies need to evaluate the utility of MSC-based therapies in animal models resembling the "new" BPD though promising in vitro evidence suggests that MSCs do possess the potential to stimulate lung maturation. Furthermore, we address the mode-of-action of MSC-based therapies with regard to lung development and inflammation/fibrosis. Their therapeutic efficacy is mainly attributed to an enhancement of regeneration and immunomodulation due to paracrine effects. In addition, we discuss current improvement strategies by genetic modifications or precondition of MSCs to enhance their therapeutic efficacy which could also prove beneficial for BPD therapies.

Regeneration of the lung: Lung stem cells and the development of lung mimicking devices

Inspired by the increasing burden of lung associated diseases in society and an growing demand to accommodate patients, great efforts by the scientific community produce an increasing stream of data that are focused on delineating the basic principles of lung development and growth, as well as understanding the biomechanical properties to build artificial lung devices. In addition, the continuing efforts to better define the disease origin, progression and pathology by basic scientists and clinicians contributes to insights in the basic principles of lung biology. However, the use of different model systems, experimental approaches and readout systems may generate somewhat conflicting or contradictory results. In an effort to summarize the latest developments in the lung epithelial stem cell biology, we provide an overview of the current status of the field. We first describe the different stem cells, or progenitor cells, residing in the homeostatic lung. Next, we focus on the plasticity of the different cell types upon several injury-induced activation or repair models, and highlight the regenerative capacity of lung cells. Lastly, we summarize the generation of lung mimics, such as air-liquid interface cultures, organoids and lung on a chip, that are required to test emerging hypotheses. Moreover, the increasing collaboration between distinct specializations will contribute to the eventual development of an artificial lung device capable of assisting reduced lung function and capacity in human patients.

Impact of bronchopulmonary dysplasia on brain and retina

Many premature newborns develop bronchopulmonary dysplasia (BPD), a chronic lung disease resulting from prolonged mechanical ventilation and hyperoxia. BPD survivors typically suffer long-term injuries not only to the lungs, but also to the brain and retina. However, currently it is not clear whether the brain and retinal injuries in these newborns are related only to their prematurity, or also to BPD. We investigated whether the hyperoxia known to cause histologic changes in the lungs similar to BPD in an animal model also causes brain and retinal injuries. Sprague Dawley rat pups were exposed to hyperoxia (95% O₂, ‘BPD’ group) or room air (21% O₂, ‘control’ group) from postnatal day 4–14 (P4–14); the rat pups were housed in room air between P14 and P28. At P28, they were sacrificed, and their lungs, brain, and eyes were extracted. Hematoxylin and eosin staining was performed on lung and brain sections; retinas were stained with Toluidine Blue. Hyperoxia exposure resulted in an increased mean linear intercept in the lungs (P<0.0001). This increase was associated with a decrease in some brain structures [especially the whole-brain surface (P=0.02)], as well as a decrease in the thickness of the retinal layers [especially the total retina (P=0.0008)], compared to the room air control group. In addition, a significant negative relationship was observed between the lung structures and the brain (r=−0.49, P=0.02) and retina (r=−0.70, P=0.0008) structures. In conclusion, hyperoxia exposure impaired lung, brain, and retina structures. More severe lung injuries correlated with more severe brain and retinal injuries. This result suggests that the same animal model of chronic neonatal hyperoxia can be used to simultaneously study lung, brain and retinal injuries related to hyperoxia.

Summary: Our results suggest that the same animal model of chronic neonatal hyperoxia can be used to simultaneously study lung, brain and retinal injuries related to hyperoxia.

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.

Mesenchymal stem cell treatment in hyperoxia-induced lung injury in newborn rats

BACKGROUND

The aim of this study was to evaluate the effectiveness of tracheally delivered mesenchymal stem cells (MSC) on lung pathology in a hyperoxia-induced lung injury (HILI) model in neonatal rats.

METHODS

For the HILI model, rat pups were exposed to 85-95% oxygen during the first 10 days of life. Rats were divided into six groups: room-air normoxia (n = 11); room air, sham (n = 11); hyperoxia exposed with normal saline as placebo (n = 9); hyperoxia exposed with culture medium of MSC (n = 10); hyperoxia exposed with medium remaining after harvesting of MSC (n = 8); and hyperoxia exposed with MSC (n = 17). Pathologic changes, number and diameter of alveoli, α-smooth muscle actin (α-SMA) expression and localization of MSC in the lungs were assessed.

RESULTS

Number of alveoli increased and alveolar diameter decreased in the mesenchymal stem cell group so that there were no differences when compared with the normoxia group (P = 0.126 and P = 0.715, respectively). Expression of α-SMA decreased significantly in the mesenchymal stem cell group compared with the placebo group (P < 0001). Green fluorescent protein-positive cells were found in lung tissue from all rats given MSC. Some green fluorescent protein-positive MSC also expressed surfactant protein-C.

CONCLUSION

Mesenchymal stem cells became localized in damaged lung tissue, and recovery approximated the room air control.

Human mesenchymal stem cells attenuate experimental bronchopulmonary dysplasia induced by perinatal inflammation and hyperoxia

BACKGROUND

Systemic maternal inflammation and neonatal hyperoxia arrest alveolarization in neonates. The aims were to test whether human mesenchymal stem cells (MSCs) reduce lung inflammation and improve lung development in perinatal inflammation- and hyperoxia-induced experimental bronchopulmonary dysplasia.

METHODS

Pregnant Sprague-Dawley rats were intraperitoneally injected with lipopolysaccharide (LPS, 0.5 mg/kg/day) on Gestational Days 20 and 21. Human MSCs (3×10(5) and 1×10(6) cells) in 0.03 ml normal saline (NS) were administered intratracheally on Postnatal Day 5. Pups were reared in room air (RA) or an oxygen-enriched atmosphere (O2) from Postnatal Days 1 to 14, and six study groups were obtained: LPS+RA+NS, LPS+RA+MSC (3×10(5) cells), LPS+RA+MSC (1×10(6) cells), LPS+O2+NS, LPS+O2+MSC (3×10(5) cells), and LPS+O2+MSC (1×10(6) cells). The lungs were excised for cytokine, vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF) expression, and histological analyses on Postnatal Day 14.

RESULTS

Body weight was significantly lower in rats reared in hyperoxia than in those reared in RA. The LPS+O2+NS group exhibited a significantly higher mean linear intercept (MLI) and collagen density and a significantly lower vascular density than the LPS+RA+NS group did. Administering MSC to hyperoxia-exposed rats improved MLI and vascular density and reduced tumor necrosis factor-α and interleukin-6 levels and collagen density to normoxic levels. This improvement in lung development and fibrosis was accompanied by an increase and decrease in lung VEGF and CTGF expression, respectively.

CONCLUSION

Human MSCs attenuated perinatal inflammation- and hyperoxia-induced defective alveolarization and angiogenesis and reduced lung fibrosis, likely through increased VEGF and decreased CTGF expression.

Lung parenchymal development in premature infants without bronchopulmonary dysplasia

RATIONALE

While infants who are born extremely premature and develop bronchopulmonary dysplasia (BPD) have impaired alveolar development and decreased pulmonary diffusion (DLCO), it remains unclear whether infants born less premature and do not develop BPD, healthy premature (HP), have impaired parenchymal development. In addition, there is increasing evidence that pro-angiogenic cells are important for vascular development; however, there is little information on the relationship of pro-angiogenic cells to lung growth and development in infants.

OBJECTIVE

and Methods Determine among healthy premature (HP) and fullterm (FT) infants, whether DLCO and alveolar volume (VA) are related to gestational age at birth (GA), respiratory support during the neonatal period (mechanical ventilation [MV], supplemental oxygen [O2], continuous positive airway pressure [CPAP]), and pro-angiogenic circulating hematopoietic stem/progenitor cells (CHSPCs). We measured DLCO, VA, and CHSPCs in infants between 3-33 months corrected-ages; HP (mean GA = 31.7 wks; N = 48,) and FT (mean GA = 39.3 wks; N =88).

RESULT

DLCO was significantly higher in HP than FT subjects, while there was no difference in VA , after adjusting for body length, gender, and race. DLCO and VA were not associated with GA, MV and O2; however, higher values were associated with higher CHSPCs, as well as treatment with CPAP.

CONCLUSION

Our findings suggest that in the absence of extreme premature birth, as well as BPD, prematurity per se, does not impair lung parenchymal development.

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.

Neonatal exposure to mild hyperoxia causes persistent increases in oxidative stress and immune cells in the lungs of mice without altering lung structure

Preterm infants often require supplemental oxygen due to lung immaturity, but hyperoxia can contribute to an increased risk of respiratory illness later in life. Our aim was to compare the effects of mild and moderate levels of neonatal hyperoxia on markers of pulmonary oxidative stress and inflammation and on lung architecture; both immediate and persistent effects were assessed. Neonatal mice (C57BL6/J) were raised in either room air (21% O2), mild (40% O2), or moderate (65% O2) hyperoxia from birth until postnatal day 7 (P7d). The mice were killed at either P7d (immediate effects) or lived in air until adulthood (P56d, persistent effects). We enumerated macrophages in lung tissue at P7d and immune cells in bronchoalveolar lavage fluid (BALF) at P56d. At P7d and P56d, we assessed pulmonary oxidative stress [heme oxygenase-1 (HO-1) and nitrotyrosine staining] and lung architecture. The data were interrogated for sex differences. At P7d, HO-1 gene expression was greater in the 65% O2 group than in the 21% O2 group. At P56d, the area of nitrotyrosine staining and number of immune cells were greater in the 40% O2 and 65% O2 groups relative to the 21% O2 group. Exposure to 65% O2, but not 40% O2, led to larger alveoli and lower tissue fraction in the short term and to persistently fewer bronchiolar-alveolar attachments. Exposure to 40% O2 or 65% O2 causes persistent increases in pulmonary oxidative stress and immune cells, suggesting chronic inflammation within the adult lung. Unlike 65% O2, 40% O2 does not affect lung architecture.

Combined iNO and endothelial progenitor cells improve lung alveolar and vascular structure in neonatal rats exposed to prolonged hyperoxia

BACKGROUND

Stem cells or inhaled nitric oxide (iNO) are reported to improve lung structures in bronchopulmonary dysplasia (BPD) models. We hypothesized that combined iNO and transplanted endothelial progenitor cells (EPCs) might restore lung structure in rats after neonatal hyperoxia.

METHODS

Litters were separated into eight groups: room air, hyperoxia, hyperoxia + iNO, hyperoxia + iNO + L-NAME, hyperoxia + EPCs, hyperoxia + EPCs + L-NAME, hyperoxia + EPCs + iNO, and hyperoxia + EPCs + iNO + L-NAME. Litters were exposed to hyperoxia from the 21st day, then, sacrificed. EPCs were injected on the 21st day. L-NAME was injected daily for 7 d from the 21st day. Serum vascular endothelial growth factor (VEGF), radial alveolar count (RAC), VIII factor, EPCs engraftment, lung VEGF, VEGFR2, endothelial nitric oxide (eNOS) and SDF-1 expression, and NO production were examined.

RESULTS

Hyperoxia exposure led to air space enlargement, loss of lung capillaries, and low expression of VEGF and eNOS. Transplanted EPCs, when combined with iNO, had significantly increased engraftment in lungs, compared to EPCs alone, upon hyperoxia exposure. There was improvement in alveolarization, microvessel density, and upregulation of VEGF and eNOS proteins in the hyperoxia-exposed EPCs with iNO group, compared to hyperoxia alone.

CONCLUSION

Combined EPCs and iNO improved lung structures after neonatal hyperoxia. This was associated with the upregulation of VEGF and eNOS expression.

Cell type-dependent variation in paracrine potency determines therapeutic efficacy against neonatal hyperoxic lung injury

BACKGROUND AIMS

The aim of this study was to determine the optimal cell type for transplantation to protect against neonatal hyperoxic lung injury. To this end, the in vitro and in vivo therapeutic efficacies and paracrine potencies of human umbilical cord blood-derived mesenchymal stromal cells (HUMs), human adipose tissue-derived mesenchymal stromal cells (HAMs) and human umbilical cord blood mononuclear cells (HMNs) were compared.

METHODS

Hyperoxic injury was induced in vitro in A549 cells by challenge with H2O2. Alternatively, hyperoxic injury was induced in newborn Sprague-Dawley rats in vivo by exposure to hyperoxia (90% oxygen) for 14 days. HUMs, HAMs or HMNs (5 × 10(5) cells) were given intratracheally at postnatal day 5.

RESULTS

Hyperoxia-induced increases in in vitro cell death and in vivo impaired alveolarization were significantly attenuated in both the HUM and HAM groups but not in the HMN group. Hyperoxia impaired angiogenesis, increased the cell death and pulmonary macrophages and elevated inflammatory cytokine levels. These effects were significantly decreased in the HUM group but not in the HAM or HMN groups. The levels of human vascular endothelial growth factor and hepatocyte growth factor produced by donor cells were highest in HUM group, followed by HAM group and then HMN group.

CONCLUSIONS

HUMs exhibited the best therapeutic efficacy and paracrine potency than HAMs or HMNs in protecting against neonatal hyperoxic lung injury. These cell type-dependent variations in therapeutic efficacy might be associated or mediated with the paracrine potency of the transplanted donor cells.

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.

Advances in paediatric pulmonary vascular disease associated with bronchopulmonary dysplasia

Pulmonary hypertension (PH) is a common finding in infants with bronchopulmonary dysplasia (BPD). The aim of this review is to describe recent advances in the diagnosis and treatment of PH and discuss whether they will benefit infants and children with BPD related PH. Echocardiography remains the mainstay of diagnosis but has limitations, further developments in diagnostic techniques and identification of biomarkers are required. There are many potential therapies for PH associated with BPD. Inhaled nitric oxide has been shown to improve short term outcomes only. Sidenafil in resource limited settings was shown in three randomized trials to significantly reduce mortality. The efficacy of other therapies including prostacyclin, PDE3 inhibitors and endothelin receptor blockers has only been reported in case reports or case series. Randomized controlled trials with long term follow up are required to appropriately assess the efficacy of therapies aimed at improving the outcome of children with PH.

Intranasal versus intraperitoneal delivery of human umbilical cord tissue-derived cultured mesenchymal stromal cells in a murine model of neonatal lung injury

Clinical trials investigating mesenchymal stromal cell (MSC) therapy for bronchopulmonary dysplasia have been initiated; however, the optimal delivery route and functional effects of MSC therapy in newborns remain incompletely established. We studied the morphologic and functional effects of intranasal versus i.p. MSC administration in a rodent model of neonatal lung injury. Cultured human cord tissue MSCs (0.1, 0.5, or 1 × 10(6) cell per pup) were given intranasally or i.p. to newborn severe combined immunodeficiency-beige mice exposed to 90% O2 from birth; sham controls received an equal volume of phosphate-buffered saline. Lung mechanics, engraftment, lung growth, and alveolarization were evaluated 8 weeks after transplantation. High-dose i.p. MSC administration to newborn mice exposed to 90% O2 resulted in the restoration of normal lung compliance, elastance, and pressure-volume loops (tissue recoil). Histologically, high-dose i.p. MSC administration was associated with alveolar septal widening, suggestive of interstitial matrix modification. Intranasal MSC or lower-dose i.p. administration had no significant effects on lung function or alveolar remodeling. Pulmonary engraftment was rare in all the groups. These findings suggest that high-dose systemic administration of human cultured MSCs can restore normal compliance in neonatally injured lungs, possibly by paracrine modulation of the interstitial matrix. Intranasal delivery had no obvious pulmonary effects.

Concise review: current status of stem cells and regenerative medicine in lung biology and diseases

Lung diseases remain a significant and devastating cause of morbidity and mortality worldwide. In contrast to many other major diseases, lung diseases notably chronic obstructive pulmonary diseases (COPDs), including both asthma and emphysema, are increasing in prevalence and COPD is expected to become the third leading cause of disease mortality worldwide by 2020. New therapeutic options are desperately needed. A rapidly growing number of investigations of stem cells and cell therapies in lung biology and diseases as well as in ex vivo lung bioengineering have offered exciting new avenues for advancing knowledge of lung biology as well as providing novel potential therapeutic approaches for lung diseases. These initial observations have led to a growing exploration of endothelial progenitor cells and mesenchymal stem (stromal) cells in clinical trials of pulmonary hypertension and COPD with other clinical investigations planned. Ex vivo bioengineering of the trachea, larynx, diaphragm, and the lung itself with both biosynthetic constructs as well as decellularized tissues have been used to explore engineering both airway and vascular systems of the lung. Lung is thus a ripe organ for a variety of cell therapy and regenerative medicine approaches. Current state-of-the-art progress for each of the above areas will be presented as will discussion of current considerations for cell therapy-based clinical trials in lung diseases.

MSC microvesicles for the treatment of lung disease: a new paradigm for cell-free therapy

SIGNIFICANCE

Bronchopulmonary dysplasia (BPD), also known as chronic lung disease of infancy, is a major complication of preterm birth that, despite improvements in neonatal respiratory support and perinatal care, remains an important cause of morbidity and mortality, often with severe adverse neurodevelopmental sequelae. Even with major advances in our understanding of the pathogenesis of this disease, BPD remains essentially without adequate treatment.

RECENT ADVANCES

Cell-based therapies arose as a promising treatment for acute and chronic lung injury in many experimental models of disease. Currently, more than 3000 human clinical trials employing cell therapy for the treatment of diverse diseases, including cardiac, neurologic, immune, and respiratory conditions, are ongoing or completed. Among the treatments, mesenchymal stem cells (MSCs) are the most studied and have been extensively tested in experimental models of BPD, pulmonary hypertension, pulmonary fibrosis, and acute lung injury.

CRITICAL ISSUES

Despite the promising potential, MSC therapy for human lung disease still remains at an experimental stage and optimal transplantation conditions need to be determined. Although the mechanism of MSC action can be manifold, accumulating evidence suggests a predominant paracrine, immunomodulatory, and cytoprotective effect.

FUTURE DIRECTIONS

The current review summarizes the effect of MSC treatment in models of lung injury, including BPD, and focuses on the MSC secretome and, specifically, MSC-derived microvesicles as potential key mediators of therapeutic action that can be the focus of future therapies.

Stem cell therapy for neonatal diseases associated with preterm birth

In the last decades, the prevention and treatment of neonatal respiratory distress syndrome with antenatal steroids and surfactant replacement allowed the survival of infants born at extremely low gestational ages. These extremely preterm infants are highly vulnerable to the detrimental effects of oxidative stress and infection, and are prone to develop lung and brain diseases that eventually evolve in severe sequelae: The so-called new bronchopulmonary dysplasia (BPD) and the noncystic, diffuse form of periventricular leukomalacia (PVL). Tissue simplification and developmental arrest (larger and fewer alveoli and hypomyelination in the lungs and brain, respectively) appears to be the hallmark of these emerging sequelae, while fibrosis is usually mild and contributes to a lesser extent to their pathogenesis. New data suggest that loss of stem/progenitor cell populations in the developing brain and lungs may underlie tissue simplification. These observations constitute the basis for the application of stem cell-based protocols following extremely preterm birth. Transplantation of different cell types (including, but not limited to, mesenchymal stromal cells, endothelial progenitor cells, human amnion epithelial cells) could be beneficial in preterm infants for the prevention and/or treatment of BPD, PVL and other major sequelae of prematurity. However, before this new knowledge can be translated into clinical practice, several issues still need to be addressed in preclinical in vitro and in vivo models.

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.

Sustained hyperoxia-induced NF-κB activation improves survival and preserves lung development in neonatal mice

Oxygen toxicity contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). Neonatal mice exposed to hyperoxia develop a simplified lung structure that resembles BPD. Sustained activation of the transcription factor NF-κB and increased expression of protective target genes attenuate hyperoxia-induced mortality in adults. However, the effect of enhancing hyperoxia-induced NF-κB activity on lung injury and development in neonatal animals is unknown. We performed this study to determine whether sustained NF-κB activation, mediated through IκBβ overexpression, preserves lung development in neonatal animals exposed to hyperoxia. Newborn wild-type (WT) and IκBβ-overexpressing (AKBI) mice were exposed to hyperoxia (>95%) or room air from day of life (DOL) 0-14, after which all animals were kept in room air. Survival curves were generated through DOL 14. Lung development was assessed using radial alveolar count (RAC) and mean linear intercept (MLI) at DOL 3 and 28 and pulmonary vessel density at DOL 28. Lung tissue was collected, and NF-κB activity was assessed using Western blot for IκB degradation and NF-κB nuclear translocation. WT mice demonstrated 80% mortality through 14 days of exposure. In contrast, AKBI mice demonstrated 60% survival. Decreased RAC, increased MLI, and pulmonary vessel density caused by hyperoxia in WT mice were significantly attenuated in AKBI mice. These findings were associated with early and sustained NF-κB activation and expression of cytoprotective target genes, including vascular endothelial growth factor receptor 2. We conclude that sustained hyperoxia-induced NF-κB activation improves neonatal survival and preserves lung development. Potentiating early NF-κB activity after hyperoxic exposure may represent a therapeutic intervention to prevent BPD.

Existence, functional impairment, and lung repair potential of endothelial colony-forming cells in oxygen-induced arrested alveolar growth

BACKGROUND

Bronchopulmonary dysplasia and emphysema are life-threatening diseases resulting from impaired alveolar development or alveolar destruction. Both conditions lack effective therapies. Angiogenic growth factors promote alveolar growth and contribute to alveolar maintenance. Endothelial colony-forming cells (ECFCs) represent a subset of circulating and resident endothelial cells capable of self-renewal and de novo vessel formation. We hypothesized that resident ECFCs exist in the developing lung, that they are impaired during arrested alveolar growth in experimental bronchopulmonary dysplasia, and that exogenous ECFCs restore disrupted alveolar growth.

METHODS AND RESULTS

Human fetal and neonatal rat lungs contain ECFCs with robust proliferative potential, secondary colony formation on replating, and de novo blood vessel formation in vivo when transplanted into immunodeficient mice. In contrast, human fetal lung ECFCs exposed to hyperoxia in vitro and neonatal rat ECFCs isolated from hyperoxic alveolar growth-arrested rat lungs mimicking bronchopulmonary dysplasia proliferated less, showed decreased clonogenic capacity, and formed fewer capillary-like networks. Intrajugular administration of human cord blood-derived ECFCs after established arrested alveolar growth restored lung function, alveolar and lung vascular growth, and attenuated pulmonary hypertension. Lung ECFC colony- and capillary-like network-forming capabilities were also restored. Low ECFC engraftment and the protective effect of cell-free ECFC-derived conditioned media suggest a paracrine effect. Long-term (10 months) assessment of ECFC therapy showed no adverse effects with persistent improvement in lung structure, exercise capacity, and pulmonary hypertension.

CONCLUSIONS

Impaired ECFC function may contribute to arrested alveolar growth. Cord blood-derived ECFC therapy may offer new therapeutic options for lung diseases characterized by alveolar damage.

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.

Disrupted pulmonary artery cyclic guanosine monophosphate signaling in mice with hyperoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) occurs in 25 to 35% of premature infants with significant bronchopulmonary dysplasia (BPD). Neonatal mice exposed to 14 days of hyperoxia develop BPD-like lung injury and PH. To determinne the impact of hyperoxia on pulmonary artery (PA) cyclic guanosine monophosphate (cGMP) signaling in a murine model of lung injury and PH, neonatal C57BL/6 mice were placed in room air, 75% O2 for 14 days (chronic hyperoxia [CH]) or 75% O2 for 24 hours, followed by 13 days of room air (acute hyperoxia with recovery [AHR]) with or without sildenafil. At 14 days, mean alveolar area, PA medial wall thickness (MWT), right ventricular hypertrophy (RVH), and vessel density were assessed. PA protein was analyzed for cGMP, soluble guanylate cyclase, and PDE5 activity. CH and AHR mice had RVH, but only CH mice had increased alveolar area and MWT and decreased vessel density. In CH and AHR PAs, soluble guanylate cyclase activity was decreased, and PDE5 activity was increased. In CH mice, sildenafil attenuated MWT and RVH but did not improve mean alveolar area or vessel density. In CH and AHR PAs, sildenafil decreased PDE5 activity and increased cGMP. Our results indicate that prolonged hyperoxia leads to lung injury, PH, RVH, and disrupted PA cGMP signaling. Furthermore, 24 hours of hyperoxia causes RVH and disrupted PA cGMP signaling that persists for 13 days. Sildenafil reduced RVH and restored vascular cGMP signaling but did not attenuate lung injury. Thus, hyperoxia can rapidly disrupt PA cGMP signaling in vivo with sustained effects, and concurrent sildenafil therapy can be protective.

Lung stem and progenitor cells in tissue homeostasis and disease

The mammalian lung is a complex organ containing numerous putative stem/progenitor cell populations that contribute to region-specific tissue homeostasis and repair. In this review, we discuss recent advances in identifying and studying these cell populations in the context of lung homeostasis and disease. Genetically engineered mice now allow for lineage tracing of several lung stem and progenitor cell populations in vivo during different types of lung injury repair. Using specific sets of cell surface markers, these cells can also be isolated from murine and human lung and tested in 3D culture systems and in vivo transplant assays. The pathology of devastating lung diseases, including lung cancers, is likely in part due to dysregulation and dysfunction of lung stem cells. More precise characterization of stem cells with identification of new, unique markers; improvement in isolation and transplant techniques; and further development of functional assays will ultimately lead to new therapies for a host of human lung diseases. In particular, lung cancer biology may be greatly informed by findings in normal lung stem cell biology as evidence suggests that lung cancer is a disease that begins in, and may be driven by, neoplastic lung stem cells.

Stem cell-based therapy for neonatal lung disease: it is in the juice

Bronchopulmonary dysplasia, the chronic lung disease of prematurity, is the most common complication in extremely premature infants (born before 28 wk gestation). Despite advances in perinatal care, modern clinical management remains devoid of therapies specifically promoting lung repair and lung growth. Recent progress in stem cell biology has uncovered the promise of stem/progenitor cells to repair damaged organs. Contrary to the original theory that stem cells engraft and repopulate the damaged organ, evidence suggests that stem cells act via a paracrine mechanism. This review highlights the preclinical evidence for the therapeutic potential of cell-based therapies in animal models of neonatal chronic lung injury and the multiple therapeutic avenues offered by soluble stem cell-derived factors.

Neural differentiation and support of neuroregeneration of non-neural adult stem cells

Although it is well established that neural stem cells (NSCs) or neural stem/progenitor cells differentiated from pluripotent stem cells can generate neurons, astrocytes, and oligodendrocytes, a number of other cell populations are also being considered for therapy of central nervous system disorders. Here, we describe the potential of (stem) cells from other postnatal tissues, including bone marrow, (umbilical cord) blood, fat tissue, or dental pulp, which themselves do not (robustly) generate neural progeny. However, these non-neuroectoderm derived cell populations appear to capable of inducing endogenous neurogenesis and angiogenesis. As these "trophic" effects are also, at least partly, responsible for some of the beneficial effects seen when NSC are grafted in the brain, these non-neuroectodermal cells may exert beneficial effects when used to treat neurodegenerative disorders.

Human amniotic fluid stem cells protect rat lungs exposed to moderate hyperoxia

BACKGROUND

Treatment of bronchopulmonary dysplasia (BPD) remains as yet an unmet clinical need and recently stem cells have been proposed as a therapeutic tool in animal models. We investigated the role of amniotic fluid stem cells (AFS) in an adult rat model of hyperoxia lung injury.

METHODS

Fifty Sprague-Dawley rats were, at birth, randomly exposed to moderate hyperoxia or room air for 14 days and a single dose of human amniotic fluid stem (hAFS) or human Fibroblasts (hF), cells was delivered intratracheally (P21). At P42 animals were euthanized and lung tissue examined using histology, immunohistochemistry, PCR, and ELISA. hAFS cells characterization and homing were studied by immunofluorescence.

RESULTS

In rats treated with hAFS and hF cells 16S human rRNA fragment was detected. Despite a low level of pulmonary hAFS cell retention (1.43 ± 0.2% anti-human-mitochondria-positive cells), the lungs of the treated animals revealed higher secondary crest numbers and lower mean linear intercept and alveolar size, than those exposed to hyperoxia, those left untreated or treated with hF cells. Except for those treated with hAFS cells, moderate hyperoxia induced an increase in protein content of IL-6, IL-1β, as well as IF-γ and TGF-1β in lung tissues. High VEGF expression and arrangement of capillary architecture in hAFS cell group were also detected.

CONCLUSIONS

Treatment with hAFS cells has a reparative potential through active involvement of cells in alveolarization and angiogenesis. A downstream paracrine action was also taken into account, in order to understand the immunodulatory response.

Isolation of pulmonary artery smooth muscle cells from neonatal mice

Pulmonary hypertension is a significant cause of morbidity and mortality in infants. Historically, there has been significant study of the signaling pathways involved in vascular smooth muscle contraction in PASMC from fetal sheep. While sheep make an excellent model of term pulmonary hypertension, they are very expensive and lack the advantage of genetic manipulation found in mice. Conversely, the inability to isolate PASMC from mice was a significant limitation of that system. Here we described the isolation of primary cultures of mouse PASMC from P7, P14, and P21 mice using a variation of the previously described technique of Marshall et al. that was previously used to isolate rat PASMC. These murine PASMC represent a novel tool for the study of signaling pathways in the neonatal period. Briefly, a slurry of 0.5% (w/v) agarose + 0.5% iron particles in M199 media is infused into the pulmonary vascular bed via the right ventricle (RV). The iron particles are 0.2 μM in diameter and cannot pass through the pulmonary capillary bed. Thus, the iron lodges in the small pulmonary arteries (PA). The lungs are inflated with agarose, removed and dissociated. The iron-containing vessels are pulled down with a magnet. After collagenase (80 U/ml) treatment and further dissociation, the vessels are put into a tissue culture dish in M199 media containing 20% fetal bovine serum (FBS), and antibiotics (M199 complete media) to allow cell migration onto the culture dish. This initial plate of cells is a 50-50 mixture of fibroblasts and PASMC. Thus, the pull down procedure is repeated multiple times to achieve a more pure PASMC population and remove any residual iron. Smooth muscle cell identity is confirmed by immunostaining for smooth muscle myosin and desmin.

Soluble guanylate cyclase modulates alveolarization in the newborn lung

Nitric oxide (NO) regulates lung development through incompletely understood mechanisms. NO controls pulmonary vascular smooth muscle cell (SMC) differentiation largely through stimulating soluble guanylate cyclase (sGC) to produce cGMP and increase cGMP-mediated signaling. To examine the role of sGC in regulating pulmonary development, we tested whether decreased sGC activity reduces alveolarization in the normal and injured newborn lung. For these studies, mouse pups with gene-targeted sGC-α1 subunit truncation were used because we determined that they have decreased pulmonary sGC enzyme activity. sGC-α1 knockout (KO) mouse pups were observed to have decreased numbers of small airway structures and lung volume compared with wild-type (WT) mice although lung septation and body weights were not different. However, following mild lung injury caused by breathing 70% O2, the sGC-α1 KO mouse pups had pronounced inhibition of alveolarization, as evidenced by an increase in airway mean linear intercept, reduction in terminal airway units, and decrease in lung septation and alveolar openings, as well as reduced somatic growth. Because cGMP regulates SMC phenotype, we also tested whether decreased sGC activity reduces lung myofibroblast differentiation. Cellular markers revealed that vascular SMC differentiation decreased, whereas myofibroblast activation increased in the hyperoxic sGC-α1 KO pup lung. These results indicate that lung development, particularly during hyperoxic injury, is impaired in mouse pups with diminished sGC activity. These studies support the investigation of sGC-targeting agents as therapies directed at improving development in the newborn lung exposed to injury.

Circulating hematopoietic and endothelial progenitor cells in newborn infants: effects of gestational age, postnatal age and clinical stress in the first 3 weeks of life

INTRODUCTION

Circulating endothelial progenitor cells (EPC) are bone marrow derived progenitors that can be mobilized by erythropoietin or in response to tissue injury, and participate in vascular repair. EPC are understudied in human neonates. Whether EPC frequency in newborn infants may be influenced by gestational age or postnatal stress is unknown.

METHODS

Blood samples were collected on day 1 of life and weekly for 3 weeks from hospitalized neonates for plasma erythropoietin and flow cytometry analysis for CD34+, CD34+CD45-, CD34+VEGFR2+ and CD34+CD45-VEGFR2+ cells (EPC). Associations between CD34+ cell subsets and clinical parameters were studied.

RESULTS

Forty five patients were enrolled. An inverse correlation with gestational age was observed for CD34+ and CD34+ VEGFR2+ cell frequencies in whole blood (WB) on day 1 (p<0.05). In preterm infants, CD34+ cell frequency decreased with increased postnatal age (p=0.0001) and CD34+VEGFR2+ cell frequency was higher at week 3 than on day 1 in WB (p=0.0002). On day one, CD34+ and CD34+CD45- cell frequencies in the mononuclear cell fraction (MNC) were higher in preterm than term infants (p=0.035 and p=0.049, respectively) but CD34+CD45-VEGFR2+ cell frequency (median 2.2/million MNC versus 3.8/million MNC) and erythropoietin levels were not significantly different. Transient increases in EPC were observed in five infants with infection. Four preterm infants who developed bronchopulmonary dysplasia had undetectable or low EPC through the first 3 weeks of life.

CONCLUSIONS

Gestational age and postnatal age influenced circulating CD34+ and CD34+VEGFR2+ but not CD34+CD45-VEGFR2+ (EPC) cell frequencies. Circulating EPC in neonates may be influenced by clinical stress.

Pulmonary vascular disease in bronchopulmonary dysplasia: pulmonary hypertension and beyond

PURPOSE OF REVIEW

Pulmonary hypertension contributes significantly to morbidity and mortality of chronic lung disease of infancy, or bronchopulmonary dysplasia (BPD). Advances in pulmonary vascular biology over the past few decades have led to new insights into the pathogenesis of BPD; however, many unique issues persist regarding our understanding of pulmonary vascular development and disease in preterm infants at risk for chronic lung disease.

RECENT FINDINGS

Recent studies have highlighted the important contribution of the developing pulmonary circulation to lung growth in the setting of preterm birth. These studies suggest that there is a spectrum of pulmonary vascular disease (PVD) in BPD rather than a simple question of whether or not pulmonary hypertension is present. Epidemiological studies underscore gaps in our understanding of PVD in the context of BPD, including universally accepted definitions, approaches to diagnosis and treatment, and patient outcomes. Unfortunately, therapeutic strategies for pulmonary hypertension in BPD are based on small observational studies with poorly defined endpoints and rely on results from older children and adult studies. Yet, unique characteristics of this population create other potential risks for the adoption of these strategies.

SUMMARY

Despite many recent advances, PVD remains an important contributor to poor outcomes in preterm infants with BPD. Substantial challenges persist, especially with regard to understanding mechanisms and the clinical approach to PVD. Future studies are needed to develop evidence-based definitions and clinical endpoints through which the pathophysiology can be investigated and potential therapeutic interventions evaluated.

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.