Adult bone marrow-derived stem cells for the lung: implications for pediatric lung diseases

Bone marrow stem cells accelerate lung maturation and prevent the LPS-induced delay of morphological and functional fetal lung development in the presence of ErbB4

ErbB4 is a regulator in lung development and disease. Prenatal infection is an important risk factor for the delay of morphologic lung development, while promoting the maturation of the surfactant system. Bone marrow-derived mesenchymal stem cells (BMSCs) have the potential to prevent lung injury. We hypothesized that BMSCs in comparison with hematopoietic control stem cells (HPSCs) minimize the lipopolysaccharide (LPS)-induced lung injury only when functional ErbB4 receptor is present. We injected LPS and/or murine green fluorescent protein-labeled BMSCs or HPSCs into the amniotic cavity of transgenic ErbB4^heart mothers at gestational day 17. Fetal lungs were analyzed 24 h later. BMSCs minimized significantly LPS-induced delay in morphological lung maturation consisting of a stereologically measured increase in mesenchyme and septal thickness and a decrease of future airspace and septal surface. This effect was more prominent and significant in the ErbB4^heart+/- lungs, suggesting that the presence of functioning ErbB4 signaling is required. BMSC also diminished the LPS induced increase in surfactant protein (Sftp)a mRNA and decrease in Sftpc mRNA is only seen if ErbB4 is present. The reduction of morphological delay of lung development and of levels of immune-modulating Sftp was more pronounced in the presence of the ErbB4 receptor. Thus, ErbB4 may be required for the protective signaling of BMSCs.

Therapeutic potential of mesenchymal stem cell transplantation in a nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

The aim of this study was to evaluate the efficacy of mesenchymal stem cells (MSCs) in a nitrofen-induced congenital diaphragmatic hernia (CDH) rat model.

METHODS

Pregnant rats were exposed to nitrofen on embryonic day 9.5 (E9.5). MSCs were isolated from the enhanced green fluorescent protein (eGFP) transgenic rat lungs. The MSCs were transplanted into the nitrofen-induced E12.5 rats via the uterine vein, and the E21 lung explants were harvested. The study animals were divided into three: the control group, the nitrofen-induced left CDH (CDH group), and the MSC-treated nitrofen-induced left CDH (MSC-treated CDH group). The specimens were morphologically analyzed using HE and immunohistochemical staining with proliferating cell nuclear antigen (PCNA), surfactant protein-C (SP-C), and α-smooth muscle actin.

RESULTS

The alveolar and medial walls of the pulmonary arteries were significantly thinner in the MSC-treated CDH group than in the CDH group. The alveolar air space areas were larger, while PCNA and the SP-C positive cells were significantly higher in the MSC-treated CDH group, than in the CDH group. MSC engraftment was identified on immunohistochemical staining of the GFP in the MSC-treated CDH group.

CONCLUSIONS

MSC transplantation potentially promotes alveolar and pulmonary artery development, thereby reducing the severity of pulmonary hypoplasia.

Bone marrow-derived c-kit+ cells attenuate neonatal hyperoxia-induced lung injury

Recent studies suggest that bone marrow (BM)-derived stem cells have therapeutic efficacy in neonatal hyperoxia-induced lung injury (HILI). c-kit, a tyrosine kinase receptor that regulates angiogenesis, is expressed on several populations of BM-derived cells. Preterm infants exposed to hyperoxia have decreased lung angiogenesis. Here we tested the hypothesis that administration of BM-derived c-kit(+) cells would improve angiogenesis in neonatal rats with HILI. To determine whether intratracheal (IT) administration of BM-derived c-kit(+) cells attenuates neonatal HILI, rat pups exposed to either normobaric normoxia (21% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to P15 were randomly assigned to receive either IT BM-derived green fluorescent protein (GFP)(+) c-kit(-) cells (PL) or BM-derived GFP(+) c-kit(+) cells on P8. The effect of cell therapy on lung angiogenesis, alveolarization, pulmonary hypertension, vascular remodeling, cell proliferation, and apoptosis was determined at P15. Cell engraftment was determined by GFP immunostaining. Compared to PL, the IT administration of BM-derived c-kit(+) cells to neonatal rodents with HILI improved alveolarization as evidenced by increased lung septation and decreased mean linear intercept. This was accompanied by an increase in lung vascular density, a decrease in lung apoptosis, and an increase in the secretion of proangiogenic factors. There was no difference in pulmonary vascular remodeling or the degree of pulmonary hypertension. Confocal microscopy demonstrated that 1% of total lung cells were GFP(+) cells. IT administration of BM-derived c-kit(+) cells improves lung alveolarization and angiogenesis in neonatal HILI, and this may be secondary to an improvement in the lung angiogenic milieu.

Regenerative pulmonary medicine: potential and promise, pitfalls and challenges

BACKGROUND

Chronic lung diseases contribute significantly to the morbidity and mortality of the population. There are few effective treatments for many chronic lung diseases, and even fewer therapies that can arrest or reverse the progress of the disease.

DESIGN

In this review, we present the current state of regenerative therapies for the treatment of chronic lung diseases. We focus on endothelial progenitor cells, mesenchymal stem cells, and endogenous lung stem/progenitor cells; summarize the work to date in models of lung diseases for each of these therapies; and consider their potential benefits and risks as viable therapies for patients with lung diseases.

CONCLUSIONS

Cell-based regenerative therapies for lung diseases offer great promise, with preclinical studies suggesting that the next decade should provide the evidence necessary for their ultimate application to our therapeutic armamentarium.

[Lung development and mesenchymal stem cells]

The survival of extremely premature newborns has increased because of improvements in perinatal care. These infants however, are at high risk for chronic lung disease of prematurity or bronchopulmonary dysplasia (BPD). BPD, the most common complication in infants born before 28 weeks of gestation, is a multifactorial disease characterized by an arrest in alveolar development. Current preventive and curative therapies show limited efficacy. Cell-based therapies hold tremendous promise in regenerative medicine. Recent evidence suggests the therapeutic benefit of mesenchymal stem (or stromal) cells (MSC) in various diseases, including among others neurodegenerative, cardiovascular and respiratory disorders. Moreover, in an oxygen-induced BPD model, we and others recently demonstrated that bone marrow (BM) derived-MSCs efficiently prevent the arrest in lung development. In this review, we summarize the current knowledge regarding the therapeutic properties and mechanisms of action, specifically paracrine, of MSCs.

Targeting inflammation to prevent bronchopulmonary dysplasia: can new insights be translated into therapies?

Bronchopulmonary dysplasia (BPD) frequently complicates preterm birth and leads to significant long-term morbidity. Unfortunately, few therapies are known to effectively prevent or treat BPD. Ongoing research has been focusing on potential therapies to limit inflammation in the preterm lung. In this review we highlight recent bench and clinical research aimed at understanding the role of inflammation in the pathogenesis of BPD. We also critically assess currently used therapies and promising developments in the field.

Roles of Wnt/beta-catenin signaling in epithelial differentiation of mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) have been demonstrated to be able to differentiate into epithelial lineage, but the precise mechanisms controlling this process are unclear. Our aim is to explore the roles of Wnt/beta-catenin in the epithelial differentiation of MSCs. Using indirect co-culture of rat MSCs with rat airway epithelial cells (RTE), MSCs expressed several airway epithelial markers (cytokeratin 18, tight junction protein occudin, cystic fibrosis transmembrance regulator). The protein levels of some important members in Wnt/beta-catenin signaling were determined, suggested down-regulation of Wnt/beta-catenin with epithelial differentiation of MSCs. Furthermore, Wnt3alpha can inhibit the epithelial differentiation of MSCs. A loss of beta-catenin induced by Dickkopf-1 can enhance MSCs differentiation into epithelial cells. Lithium chloride transiently activated beta-catenin expression and subsequently decreased beta-catenin level and at last inhibited MSCs to differentiate into airway epithelium. Taken together, our study indicated that RTE cells can trigger epithelial differentiation of MSCs. Blocking Wnt/beta-catenin signaling may promote MSCs to differentiate towards airway epithelial cells.

Airway delivery of mesenchymal stem cells prevents arrested alveolar growth in neonatal lung injury in rats

RATIONALE

Bronchopulmonary dysplasia (BPD) and emphysema are characterized by arrested alveolar development or loss of alveoli; both are significant global health problems and currently lack effective therapy. Bone marrow-derived mesenchymal stem cells (BMSCs) prevent adult lung injury, but their therapeutic potential in neonatal lung disease is unknown.

OBJECTIVES

We hypothesized that intratracheal delivery of BMSCs would prevent alveolar destruction in experimental BPD.

METHODS

In vitro, BMSC differentiation and migration were assessed using co-culture assays and a modified Boyden chamber. In vivo, the therapeutic potential of BMSCs was assessed in a chronic hyperoxia-induced model of BPD in newborn rats.

MEASUREMENTS AND MAIN RESULTS

In vitro, BMSCs developed immunophenotypic and ultrastructural characteristics of type II alveolar epithelial cells (AEC2) (surfactant protein C expression and lamellar bodies) when co-cultured with lung tissue, but not with culture medium alone or liver. Migration assays revealed preferential attraction of BMSCs toward oxygen-damaged lung versus normal lung. In vivo, chronic hyperoxia in newborn rats led to air space enlargement and loss of lung capillaries, and this was associated with a decrease in circulating and resident lung BMSCs. Intratracheal delivery of BMSCs on Postnatal Day 4 improved survival and exercise tolerance while attenuating alveolar and lung vascular injury and pulmonary hypertension. Engrafted BMSCs coexpressed the AEC2-specific marker surfactant protein C. However, engraftment was disproportionately low for cell replacement to account for the therapeutic benefit, suggesting a paracrine-mediated mechanism. In vitro, BMSC-derived conditioned medium prevented O(2)-induced AEC2 apoptosis, accelerated AEC2 wound healing, and enhanced endothelial cord formation.

CONCLUSIONS

BMSCs prevent arrested alveolar and vascular growth in part through paracrine activity. Stem cell-based therapies may offer new therapeutic avenues for lung diseases that currently lack efficient treatments.

Stem cells as a potential future treatment of pediatric intestinal disorders

All surgical disciplines encounter planned and unplanned ischemic events that may ultimately lead to cellular dysfunction and death. Stem cell therapy has shown promise for the treatment of a variety of ischemic and inflammatory disorders where tissue damage has occurred. As stem cells have proven beneficial in many disease processes, important opportunities in the future treatment of gastrointestinal disorders may exist. Therefore, this article will serve to review the different types of stem cells that may be applicable to the treatment of gastrointestinal disorders, review the mechanisms suggesting that stem cells may work for these conditions, discuss current practices for harvesting and purifying stem cells, and provide a concise summary of a few of the pediatric intestinal disorders that could be treated with cellular therapy.

Bone marrow-derived cells participate in stromal remodeling of the lung following acute bacterial pneumonia in mice

Bone marrow-derived cells (BMDC) have been shown to graft injured tissues, differentiate in specialized cells, and participate in repair. The importance of these processes in acute lung bacterial inflammation and development of fibrosis is unknown. The goal of this study was to investigate the temporal sequence and lineage commitment of BMDC in mouse lungs injured by bacterial pneumonia. We transplanted GFP-tagged BMDC into 5-Gy-irradiated C57BL/6 mice. After 3 months of recovery, mice were subjected to LD(50) intratracheal instillation of live E. coli (controls received saline) which produced pneumonia and subsequent areas of fibrosis. Lungs were investigated by immunohistology for up to 6 months. At the peak of lung inflammation, the predominant influx of BMDC were GFP(+) leukocytes. Postinflammatory foci of lung fibrosis were evident after 1-2 months. The fibrotic foci in lung stroma contained clusters of GFP(+) CD45(+) cells, GFP(+) vimentin-positive cells, and GFP(+) collagen I-positive fibroblasts. GFP(+) endothelial or epithelial cells were not identified. These data suggest that following 5-Gy irradiation and acute bacterial pneumonia, BMDC may temporarily participate in lung postinflammatory repair and stromal remodeling without long-term engraftment as specialized endothelial or epithelial cells.

Lung Epithelial Cells Induce Endodermal Differentiation in Mouse Mesenchymal Bone Marrow Stem Cells by Paracrine Mechanism

Mesenchymal stem cells (MSCs) from bone marrow are a potential source for reconstructive therapy. In vitro, MSCs differentiate into cells of mesodermal and ectodermal lineages but rarely into cells of endodermal lineage. We developed an in vitro model to study the endodermal differentiation of MSCs using co-culture of MSCs and transformed lung epithelial (A-549) cells. The cells were separated using a cell-impermeable membrane to eliminate the possibility of cell fusion. Under these conditions, MSCs expressed several lung epithelial markers (cytokeratins 5, 8, 14, 18, 19, pro-surfactant protein C, zonula occludens-1), detected using quantitative reverse transcriptase polymerase chain reaction and Western blot, and beta-catenin signaling was activated in MSCs. Treatment of MSCs with 10 to 20 mM lithium chloride activated the beta-catenin pathway and enhanced expression of epithelial markers, although this activation was transient. We conclude that A-549 cells can trigger epithelial differentiation of MSCs by a paracrine mechanism that may include activation of beta-catenin signaling.

Lung cells from neonates show a mesenchymal stem cell phenotype

RATIONALE

Mesenchymal stem cells have been isolated from adult bone marrow, peripheral blood, adipose tissue, trabecular bone, articular synovium, and bronchial submucosa.

OBJECTIVES

We hypothesized that the lungs of premature infants undergoing mechanical ventilation contain fibroblast-like cells with features of mesenchymal stem cells.

METHODS

Tracheal aspirate fluid from mechanically ventilated, premature (< 30 wk gestation) infants 7 days old or younger was obtained from routine suctioning and plated on plastic culture dishes.

MEASUREMENTS AND MAIN RESULTS

A total of 11 of 20 patients studied demonstrated fibroblast-like cells, which were identified as early as 6 hours after plating. Cells were found to express the mesenchymal stem cell markers STRO-1, CD73, CD90, CD105, and CD166, as well as CCR2b, CD13, prolyl 4-hydroxylase, and alpha-smooth muscle actin. Cells were negative for the hematopoietic and endothelial cell markers CD11b, CD31, CD34, or CD45. Tracheal aspirate monocyte chemoattractant protein-1/CCL2 levels were ninefold higher in aspirates in which fibroblast-like cells were found, and cells demonstrated chemotaxis in response to monocyte chemoattractant protein. Placement of cells into appropriate media resulted in adipogenic, osteogenic, and myofibroblastic differentiation. Patients from whom mesenchymal stem cells were isolated tended to require more days of mechanical ventilation and supplemental oxygen.

CONCLUSIONS

Together, these data demonstrate that tracheal aspirate fluid from premature, mechanically ventilated infants contains fibroblasts with cell markers and differentiation potential typically found in mesenchymal stem cells.

New Insights into the Pathogenesis and Treatment of Idiopathic Pulmonary Fibrosis: A Potential Role for Stem Cells in the Lung Parenchyma and Implications for Therapy

Idiopathic Pulmonary Fibrosis (IPF) is a chronic, progressive, and often fatal form of interstitial lung disease. It is characterized by injury with loss of lung epithelial cells and abnormal tissue repair, resulting in replacement of normal functional tissue, abnormal accumulation of fibroblasts and myofibroblasts, deposition of extracellular matrix, and distortion of lung architecture which results in respiratory failure. Despite improvements in the diagnostic approach to IPF and active research in recent years, the molecular mechanisms of the disease remain poorly understood. This highly lethal lung disorder continues to pose major clinical challenges since an effective therapeutic regimen has yet to be identified and developed. For example, a treatment modality has been based on the assumption that IPF is a chronic inflammatory disease, yet most available anti-inflammatory drugs are not effective in treating it. Hence researchers are now focusing on understanding alternative underlying mechanisms involved in the pathogenesis of IPF in the hope of discovering potentially new pharmaceutical targets. This paper will focus on lung tissue repair, regeneration, remodeling, and cell types that may be important to consider in therapeutic interventions and includes a more detailed discussion of the potential targets of current therapeutic attack in pulmonary fibrosis. The discovery that adult bone marrow stem cells can contribute to the formation of differentiated cell types in other tissues, especially after injury, implies that they have the potential to participate in tissue remodeling, and perhaps regeneration. The current promise of the use of adult stem cells for tissue regeneration, and the belief that once irreversibly damaged tissue could be restored to a normal functional capacity using stem cell-based therapy, suggests a novel approach for treatment of diverse chronic diseases. However this optimism is tempered by current evidence that the pathogenesis of pulmonary fibrosis may involve the recruitment of bone marrow-derived fibroblasts, which are the key contributors to the pathogenesis of this chronic progressive disorder. Nevertheless, stem cell-related therapies are widely viewed as promising treatment options for patients suffering from various types of pulmonary diseases. Gender mismatched bone marrow or lung transplant recipients serve as natural populations in which to study the role of bone marrow-derived stem cells in recovery from pulmonary diseases. Understanding the mechanism of recruitment of stem cells to sites of injury, and their involvement in tissue repair, regeneration, and remodeling may offer a novel therapeutic target for developing more effective treatments against this fatal disorder. This article reviews the new concepts in the pathogenesis, current and future treatment options of pulmonary fibrosis, and the recent advances regarding the roles of stem cells in lung tissue repair, regeneration, and remodeling.

Microchimerism and Stem Cell Transplantation in Multiple Sclerosis

Scientific advances have demonstrated that autoreactive cells are a component of the healthy immune repertoire. If we define autoimmunity as an active induction of autoreaction, the solution should be an active induction of self-tolerance, and may indicate the direction to explore the future therapies. Microchimerism (MC) refers to the presence of a limited number of nonhost cells in the body of an individual. These cells can enter via blood transfusion and organ transplantation or naturally through pregnancy. Chimeric cells engraft in the host body, develop, proliferate, and are accepted by the immune system as self. These include stem cells that enter the maternal body during fetal stages. These stem cells are also postulated to be helpful reservoirs in protecting the host body. MC has been considered a risk factor in autoimmune disease induction. However, today we know it is a natural phenomenon. MC can be considered a natural model of successful transplantation, the earliest engrafting cells being fetal mesenchymal stem cells (MSCs). MSCs have two notable features. They have an immunosuppressive quality when encountering the adoptive immune system and they display repair-inducing potential within damaged tissues. For the fetus, MC appears to be an effective factor in maternal tolerance induction toward the fetal graft and for the mother; these novel fetal cells might be useful in disease conditions occurring after pregnancy. Hematopoietic stem cell transplantation has become an accepted treatment option for both malignant and nonmalignant diseases and this unique procedure is now being investigated as a potential therapy for multiple sclerosis (MS). Due to the dichotomous properties of MSC, suppressing aggressive immune dysfunction while promoting damaged tissue repair, they may be appropriate therapy for MS.

Evidence of Temporary Airway Epithelial Repopulation and Rare Clonal Formation by BM-derived Cells Following Naphthalene Injury in Mice

The goal of the study was to investigate participation of bone marrow (BM) cells in the process of airway epithelial restoration after naphthalene-induced injury. We transplanted sex-mismatched green fluorescent protein (GFP) -tagged BM-derived cultured plastic-adherent mesenchymal stem cells into 5Gy-irradiated C57BL/6 recipients. After 1 month of recovery, experimental animals were subjected to 250 mg/kg naphthalene IP. Animals were killed at 2-30 days after naphthalene. By immunofluorescence, immunohistochemistry, and by in situ hybridization for the Y-chromosome, we observed patches of donor-derived cells in the large and small conducting airways, mostly at 2-6 days after injury. GFP(+) cells in the epithelium of airways were positive for pancytokeratin and some other epithelial markers. Although rare, GFP(+) cells formed clear isolated patches of the bronchial epithelium, consistent with clonal formation; as some cells were also positive for proliferating cell nuclear antigen, a marker of proliferating cells. After day 12, only occasional GFP(+) cells were present in the epithelium. These data confirm that bone marrow-derived cultured mesenchymal cells can participate in the recovery of the injured airway epithelium after naphthalene-induced injury with minimal long-term engraftment.