Failure of bone marrow to reconstitute lung epithelium

Cell therapy: A beacon of hope in the battle against pulmonary fibrosis

Pulmonary fibrosis (PF) is a chronic and progressive interstitial lung disease characterized by abnormal activation of myofibroblasts and pathological remodeling of the extracellular matrix, with a poor prognosis and limited treatment options. Lung transplantation is currently the only approach that can extend the life expectancy of patients; however, its applicability is severely restricted due to donor shortages and patient-specific limitations. Therefore, the search for novel therapeutic strategies is imperative. In recent years, stem cells have shown great promise in the field of regenerative medicine due to their self-renewal capacity and multidirectional differentiation potential, and a growing body of literature supports the efficacy of stem cell therapy in PF treatment. This paper systematically summarizes the research progress of various stem cell types in the treatment of PF. Furthermore, it discusses the primary methods and clinical outcomes of stem cell therapy in PF, based on both preclinical and clinical data. Finally, the current challenges and key factors to consider in stem cell therapy for PF are objectively analyzed, and future directions for improving this therapy are proposed, providing new insights and references for the clinical treatment of PF patients.

Shh Signaling from the Injured Lung Microenvironment Drives BMSCs Differentiation into Alveolar Type II Cells for Acute Lung Injury Treatment in Mice

Alveolar type II (AT2) cells are key effector cells for repairing damaged lungs. Direct differentiation into AT2 cells from bone marrow mesenchymal stem cells (BMSCs) is a promising approach to treating acute lung injury (ALI). The mechanisms of BMSC differentiation into AT2 cells have not been determined. The Sonic Hedgehog (Shh) pathway is involved in regulating multiple differentiation of MSCs. However, the role of the Shh pathway in mediating the differentiation of BMSCs into AT2 cells remains to be explored. The results showed that BMSCs significantly ameliorated lung injury and improved pulmonary function in mice with ALI. These improvements were accompanied by a relatively high proportion of BMSCs differentiate into AT2 cells and an increase in the total number of AT2 cells in the lungs. Lung tissue extracts from mice with ALI (ALITEs) were used to mimic the injured lung microenvironment. The addition of ALITEs significantly improved the differentiation efficiency of BMSCs into AT2 cells along with activation of the Shh pathway. The inhibition of the Shh pathway not only reduced the differentiation rate of BMSCs but also failed to mitigate lung injury and regenerate AT2 cells. The results confirmed that promoting AT2 cell regeneration through the differentiation of BMSCs into AT2 cells is one of the important therapeutic mechanisms for the treatment of ALI with BMSCs. This differentiation process is highly dependent on Shh pathway activation in BMSCs in the injured lung microenvironment.

Lung repair and regeneration: Advanced models and insights into human disease

The respiratory system acts as both the primary site of gas exchange and an important sensor and barrier to the external environment. The increase in incidences of respiratory disease over the past decades has highlighted the importance of developing improved therapeutic approaches. This review will summarize recent research on the cellular complexity of the mammalian respiratory system with a focus on gas exchange and immunological defense functions of the lung. Different models of repair and regeneration will be discussed to help interpret human and animal data and spur the investigation of models and assays for future drug development.

Emerging delivery approaches for targeted pulmonary fibrosis treatment

Pulmonary fibrosis (PF) is a progressive, and life-threatening interstitial lung disease which causes scarring in the lung parenchyma and thereby affects architecture and functioning of lung. It is an irreversible damage to lung functioning which is related to epithelial cell injury, immense accumulation of immune cells and inflammatory cytokines, and irregular recruitment of extracellular matrix. The inflammatory cytokines trigger the differentiation of fibroblasts into activated fibroblasts, also known as myofibroblasts, which further increase the production and deposition of collagen at the injury sites in the lung. Despite the significant morbidity and mortality associated with PF, there is no available treatment that efficiently and effectively treats the disease by reversing their underlying pathologies. In recent years, many therapeutic regimens, for instance, rho kinase inhibitors, Smad signaling pathway inhibitors, p38, BCL-xL/ BCL-2 and JNK pathway inhibitors, have been found to be potent and effective in treating PF, in preclinical stages. However, due to non-selectivity and non-specificity, the therapeutic molecules also result in toxicity mediated severe side effects. Hence, this review demonstrates recent advances on PF pathology, mechanism and targets related to PF, development of various drug delivery systems based on small molecules, RNAs, oligonucleotides, peptides, antibodies, exosomes, and stem cells for the treatment of PF and the progress of various therapeutic treatments in clinical trials to advance PF treatment.

Intratracheally injected human-induced pluripotent stem cell-derived pneumocytes and endothelial cells engraft in the distal lung and ameliorate emphysema in a rat model

OBJECTIVES

Pulmonary emphysema is characterized by the destruction of alveolar units and reduced gas exchange capacity. In the present study, we aimed to deliver induced pluripotent stem cell-derived endothelial cells and pneumocytes to repair and regenerate distal lung tissue in an elastase-induced emphysema model.

METHODS

We induced emphysema in athymic rats via intratracheal injection of elastase as previously reported. At 21 and 35 days after elastase treatment, we suspended 80 million induced pluripotent stem cell-derived endothelial cells and 20 million induced pluripotent stem cell-derived pneumocytes in hydrogel and injected the mixture intratracheally. On day 49 after elastase treatment, we performed imaging, functional analysis, and collected lungs for histology.

RESULTS

Using immunofluorescence detection of human-specific human leukocyte antigen 1, human-specific CD31, and anti--green fluorescent protein for the reporter labeled pneumocytes, we found that transplanted cells engrafted in 14.69% ± 0.95% of the host alveoli and fully integrated to form vascularized alveoli together with host cells. Transmission electron microscopy confirmed the incorporation of the transplanted human cells and the formation of a blood-air barrier. Human endothelial cells formed perfused vasculature. Computed tomography scans revealed improved vascular density and decelerated emphysema progression in cell-treated lungs. Proliferation of both human and rat cell was higher in cell-treated versus nontreated controls. Cell treatment reduced alveolar enlargement, improved dynamic compliance and residual volume, and improved diffusion capacity.

CONCLUSIONS

Our findings suggest that human induced pluripotent stem cell-derived distal lung cells can engraft in emphysematous lungs and participate in the formation of functional distal lung units to ameliorate the progression of emphysema.

PGE2 Produced by Exogenous MSCs Promotes Immunoregulation in ARDS Induced by Highly Pathogenic Influenza A through Activation of the Wnt-β-Catenin Signaling Pathway

Acute respiratory distress syndrome is an acute respiratory failure caused by cytokine storms; highly pathogenic influenza A virus infection can induce cytokine storms. The innate immune response is vital in this cytokine storm, acting by activating the transcription factor NF-κB. Tissue injury releases a danger-associated molecular pattern that provides positive feedback for NF-κB activation. Exogenous mesenchymal stem cells can also modulate immune responses by producing potent immunosuppressive substances, such as prostaglandin E2. Prostaglandin E2 is a critical mediator that regulates various physiological and pathological processes through autocrine or paracrine mechanisms. Activation of prostaglandin E2 results in the accumulation of unphosphorylated β-catenin in the cytoplasm, which subsequently reaches the nucleus to inhibit the transcription factor NF-κB. The inhibition of NF-κB by β-catenin is a mechanism that reduces inflammation.

Stem cell therapies for neonatal lung diseases: Are we there yet?

Lung diseases are a main cause of mortality and morbidity in neonates. Despite major breakthroughs, therapies remain supportive and, in some instances, contribute to lung injury. Because the neonatal lung is still developing, the ideal therapy should be capable of preventing/repairing lung injury while at the same time, promoting lung growth. Cell-based therapies hold high hopes based on laboratory experiments in animal models of neonatal lung injury. Mesenchymal stromal cells and amnion epithelial cells are now in early phase clinical trials to test the feasibility, safety and early signs of efficacy in preterm infants at risk of developing bronchopulmonary dysplasia. Other cell-based therapies are being explored in experimental models of congenital diaphragmatic hernia and alveolar capillary dysplasia. This review will summarize current evidence that has lead to the clinical translation of cell-based therapies and highlights controversies and the numerous questions that remain to be addressed to harness the putative repair potential of cell-based therapies.

Overexpression of FoxM1 optimizes the therapeutic effect of bone marrow mesenchymal stem cells on acute respiratory distress syndrome

BACKGROUND

Injury of alveolar epithelial cells and capillary endothelial cells is crucial in the pathogenesis of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Mesenchymal stem cells (MSCs) are a promising cell source for ALI/ARDS treatment. Overexpression of Fork head box protein M1 (FoxM1) facilitates MSC differentiation into alveolar type II (AT II) cells in vitro. Moreover, FoxM1 has been shown to repair the endothelial barrier. Therefore, this study explored whether overexpression of FoxM1 promotes the therapeutic effect of bone marrow-derived MSCs (BMSCs) on ARDS by differentiation of BMSCs into AT II cells or a paracrine mechanism.

METHODS

A septic ALI model was established in mice by intraperitoneal administration of lipopolysaccharide. The protective effect of BMSCs-FoxM1 on ALI was explored by detecting pathological variations in the lung, total protein concentration in bronchoalveolar lavage fluid (BALF), wet/dry (W/D) lung weight ratio, oxidative stress levels, cytokine levels, and retention of BMSCs in the lung. In addition, we assessed whether FoxM1 overexpression promoted the therapeutic effect of BMSCs on ALI/ARDS by differentiating into AT II cells using SPC-/- mice. Furthermore, the protective effect of BMSCs-FoxM1 on lipopolysaccharide-induced endothelial cell (EC) injury was explored by detecting EC proliferation, apoptosis, scratch wounds, tube formation, permeability, and oxidative stress, and analyzing whether the Wnt/β-catenin pathway contributes to the regulatory mechanism in vitro using a pathway inhibitor.

RESULTS

Compared with BMSCs-Vector, treatment with BMSCs-FoxM1 significantly decreased the W/D lung weight ratio, total BALF protein level, lung injury score, oxidative stress, and cytokine levels. With the detected track of BMSCs-FoxM1, we observed a low residency rate and short duration of residency in the lung. Notably, SPC was not expressed in SPC-/- mice injected with BMSCs-FoxM1. Furthermore, BMSCs-FoxM1 enhanced EC proliferation, migration, and tube formation; inhibited EC apoptosis and inflammation; and maintained vascular integrity through activation of the Wnt/β-catenin pathway, which was partially reversed by XAV-939.

CONCLUSION

Overexpression of FoxM1 enhanced the therapeutic effect of BMSCs on ARDS, possibly through a paracrine mechanism rather than by promoting BMSC differentiation into AT II cells in vivo, and prevented LPS-induced EC barrier disruption partially through activating the Wnt/β-catenin signaling pathway in vitro.

What is the need and why is it time for innovative models for understanding lung repair and regeneration?

Advances in tissue engineering continue at a rapid pace and have provided novel methodologies and insights into normal cell and tissue homeostasis, disease pathogenesis, and new potential therapeutic strategies. The evolution of new techniques has particularly invigorated the field and span a range from novel organ and organoid technologies to increasingly sophisticated imaging modalities. This is particularly relevant for the field of lung biology and diseases as many lung diseases, including chronic obstructive pulmonary disease (COPD) and idiopathic fibrosis (IPF), among others, remain incurable with significant morbidity and mortality. Advances in lung regenerative medicine and engineering also offer new potential avenues for critical illnesses such as the acute respiratory distress syndrome (ARDS) which also continue to have significant morbidity and mortality. In this review, an overview of lung regenerative medicine with focus on current status of both structural and functional repair will be presented. This will serve as a platform for surveying innovative models and techniques for study, highlighting the need and timeliness for these approaches.

Stem cell-based therapy for pulmonary fibrosis

Pulmonary fibrosis (PF) is a chronic and relentlessly progressive interstitial lung disease in which the accumulation of fibroblasts and extracellular matrix (ECM) induces the destruction of normal alveolar structures, ultimately leading to respiratory failure. Patients with advanced PF are unable to perform physical labor and often have concomitant cough and dyspnea, which markedly impair their quality of life. However, there is a paucity of available pharmacological therapies, and to date, lung transplantation remains the only possible treatment for patients suffering from end-stage PF; moreover, the complexity of transplantation surgery and the paucity of donors greatly restrict the application of this treatment. Therefore, there is a pressing need for alternative therapeutic strategies for this complex disease. Due to their capacity for pluripotency and paracrine actions, stem cells are promising therapeutic agents for the treatment of interstitial lung disease, and an extensive body of literature supports the therapeutic efficacy of stem cells in lung fibrosis. Although stem cell transplantation may play an important role in the treatment of PF, some key issues, such as safety and therapeutic efficacy, remain to be resolved. In this review, we summarize recent preclinical and clinical studies on the stem cell-mediated regeneration of fibrotic lungs and present an analysis of concerning issues related to stem cell therapy to guide therapeutic development for this complex disease.

Proceedings of the ISCT scientific signature series symposium, "Advances in cell and gene therapies for lung diseases and critical illnesses": International Society for Cell & Gene Therapy, Burlington VT, US, July 16, 2021

The ISCT Scientific Signature Series Symposium "Advances in Cell and Gene Therapies for Lung Diseases and Critical Illnesses" was held as an independent symposium in conjunction with the biennial meeting, "Stem Cells, Cell Therapies, and Bioengineering in Lung Biology and Diseases," which took place July 12-15, 2021, at the University of Vermont. This is the third Respiratory System-based Signature Series event; the first 2, "Tracheal Bioengineering, the Next Steps" and "Cellular Therapies for Pulmonary Diseases and Critical Illnesses: State of the Art of European Science," took place in 2014 and 2015, respectively. Cell- and gene-based therapies for respiratory diseases and critical illnesses continue to be a source of great promise and opportunity. This reflects ongoing advancements in understanding of the mechanisms by which cell-based therapies, particularly those using mesenchymal stromal cells (MSCs), can mitigate different lung injuries and the increasing sophistication with which preclinical data is translated into clinical investigations. This also reflects continuing evolution in gene transfer vectors, including those designed for in situ gene editing in parallel with those targeting gene or cell replacement. Therefore, this symposium convened global thought leaders in a forum designed to catalyze communication and collaboration to bring the greatest possible innovation and value of cell- and gene-based therapies for patients with respiratory diseases and critical illnesses.

Mesenchymal Stromal Cell Therapy for Acute Respiratory Distress Syndrome due to COVID-19

Background aims

The acute respiratory distress syndrome (ARDS) resulting from coronavirus disease 2019 (COVID-19) is associated with a massive release of inflammatory cytokines and high mortality. Mesenchymal stromal cells (MSCs) have anti-inflammatory properties and have shown activity in treating acute lung injury. Here the authors report a case series of 11 patients with COVID-19-associated ARDS (CARDS) requiring mechanical ventilation who were treated with remestemcel-L, an allogeneic MSC product, under individual patient emergency investigational new drug applications.

Methods

Patients were eligible if they were mechanically ventilated for less than 72 h prior to the first infusion. Patients with pre-existing lung disease requiring supplemental oxygen or severe liver or kidney injury were excluded. Each patient received two infusions of remestemcel-L at a dose of 2 million cells/kg per infusion given 48–120 h apart.

Results

Remestemcel-L infusions were well tolerated in all 11 patients. At the end of the 28-day follow-up period, 10 (91%, 95% confidence interval [CI], 59–100%) patients were extubated, nine (82%, 95% CI, 48–97%) patients remained liberated from mechanical ventilation and were discharged from the intensive care unit and two (18%, 95 CI%, 2–52%) patients died. The median time to extubation was 10 days. Eight (73%, 95% CI, 34–100%) patients were discharged from the hospital. C-reactive protein levels significantly declined within 5 days of MSC infusion.

Conclusions

The authors demonstrate in this case series that remestemcel-L infusions to treat moderate to severe CARDS were safe and well tolerated and resulted in improved clinical outcomes.

Wnt/β-Catenin Participates in the Repair of Acute Respiratory Distress Syndrome-Associated Early Pulmonary Fibrosis via Mesenchymal Stem Cell Microvesicles

Purpose

The main aim of the present study was to establish whether mesenchymal stem cell microvesicles (MSC MVs) exert anti-fibrotic effects and investigate the mechanisms underlying these effects in a mouse model of acute respiratory distress syndrome (ARDS)-associated early pulmonary fibrosis.

Methods

An ARDS-associated pulmonary fibrosis model was established in mice by an intratracheal injection of lipopolysaccharide (LPS). At 1, 3, and 7 days after LPS-mediated injury, the lungs of mice treated with MSC MVs and untreated controls were carefully excised and fibrosis was assessed based on the extent of collagen deposition. In addition, the development of epithelial–mesenchymal transition (EMT) was evaluated based on loss of E-cadherin and zona occludens-1 (ZO-1) along with the acquisition of α-smooth muscle actin (α-SMA) and N-cadherin. Nuclear translocation and β-catenin expression analyses were also used to evaluate activation of the Wnt/β-catenin signaling pathway.

Results

Blue-stained collagen fibers were evident as early as 7 days after LPS injection. Treatment with MSC MVs suppressed pathological progression to a significant extent. MSC MVs markedly reversed the upregulation of N-cadherin and α-SMA and attenuated the downregulation of E-cadherin and ZO-1. The expression and nuclear translocation of β-catenin were clearly decreased on day 7 after MSC MV treatment.

Conclusion

Analyses indicated that MSC MVs could ameliorate ARDS-associated early pulmonary fibrosis via the suppression of EMT and might be related to Wnt/β-catenin transition signaling.

Stem Cell Therapy for COPD: Hope and Exploitation

COPD is a chronic inflammatory and destructive disease characterized by progressive decline in lung function that can accelerate with aging. Preclinical studies suggest that mesenchymal stem cells (MSCs) may provide a therapeutic option for this incurable disease because of their antiinflammatory, reparative, and immunomodulatory properties. To date, clinical trials using MSCs demonstrate safety in patients with COPD. However, because of the notable absence of large, multicenter randomized trials, no efficacy or evidence exists to support the possibility that MSCs can restore lung function in patients with COPD. Unfortunately, the investigational status of cell-based interventions for lung diseases has not hindered the propagation of commercial businesses, exploitation of the public, and explosion of medical tourism to promote unproven and potentially harmful cell-based interventions for COPD in the United States and worldwide. Patients with COPD constitute the largest group of patients with lung disease flocking to these unregulated clinics. This review highlights the numerous questions and concerns that remain before the establishment of cell-based interventions as safe and efficacious treatments for patients with COPD.

HSCs transdifferentiate primarily to pneumonocytes in radiation-induced lung damage repair

Accumulative radiation exposure leads to hematopoietic or tissue aging. Whether hematopoietic stem cells (HSCs) are involved in lung damage repair in response to radiation remains controversial. The aim of this study is to identify if HSC can transdifferentiate to pneumonocytes for radiation-induced damage repair. To this end, HSCs from male Rosa^mT/mG mice were isolated by fluorescence-activated cell sorting (FACS) and transplanted into lethally irradiated female CD45.1 mice. 4 months after transplantation, transplanted HSC was shown to repair the radiation-induced tissue damage, and donor-derived tdTomato (phycoerythrin, PE) red fluorescence cells and Ddx3y representing Y chromosome were detected exclusively in female recipient lung epithelial and endothelial cells. Co-localization of donor-derived cells and recipient lung tissue cells were observed by laser confocal microscopy and image flow cytometry. Furthermore, the results showed HSC transplantation replenished radiation-induced lung HSC depletion and the PE positive repaired lung epithelial cells were identified as donor HSC origin. The above data suggest that donor HSC may migrate to the injured lung of the recipient and some of them can be transdifferentiated to pneumonocytes to repair the injury caused by radiation.

Epithelial Stem and Progenitor Cells in Lung Repair and Regeneration

The mammalian lung epithelium is composed of a wide array of specialized cells that have adapted to survive environmental exposure and perform the tasks necessary for respiration. Although the majority of these cells are remarkably quiescent during adult lung homeostasis, a growing body of literature has demonstrated the capacity of these epithelial lineages to proliferate in response to injury and regenerate lost or damaged cells. In this review, we focus on the regionally distinct lung epithelial cell types that contribute to repair after injury, and we address current controversies regarding whether elite stem cells or frequent facultative progenitors are the predominant participants. We also shed light on the newly emerging approaches for exogenously generating similar lung epithelial lineages from pluripotent stem cells.

Allogeneic human umbilical cord-derived mesenchymal stem cells reduce lipopolysaccharide-induced inflammation and acute lung injury

Acute lung injury (ALI) is the clinical disorder of acute hypoxemic respiratory deficiency and it is associated with a high mortality rate. Increased lung permeability, infiltration of inflammatory cells, secretion of inflammatory cytokines, and pulmonary edema are hallmarks of ALI. Currently, there is no effective pharmacological agent approved for ALI, and the treatment regimens available are mostly supportive. Mesenchymal stem cells (MSCs) are multipotent stromal cells with immunomodulating potential, which therefore hold great promise for the treatment of ALI. We established an LPS-induced ALI mouse model by intratracheal injection of lipopolysaccharide (LPS). Human umbilical cord-derived MSCs (hUC-MSCs) were delivered through the tail vein to assess the effects of MSCs on relieving LPS-induced ALI. Intratracheal injection of LPS increased the infiltration of neutrophils and enhanced the expression of pro-inflammatory cytokines, such as IL-6, IL-1β and TNF-α. Administration of hUC-MSCs decreased pathological signs of inflammation, as well as reduced ALI scores. The levels of IL-6, IL-1β and TNF-α were also dose-dependently inhibited in the bronchoalveolar lavage fluids from damaged lung tissues. Moreover, MPO and BAX levels were decreased by the hUC-MSC treatment, suggesting hUC-MSCs may play the role in inhibiting ROS production and apoptotic death in ALI repair. These results highlight the potential of hUC-MSCs to alleviate bacterial endotoxin-induced inflammation, and may represent an effective modality for the treatment of ALI in clinical settings.

Translating Basic Research into Safe and Effective Cell-based Treatments for Respiratory Diseases

Respiratory diseases, such as chronic obstructive pulmonary disease and pulmonary fibrosis, result in severely impaired quality of life and impose significant burdens on healthcare systems worldwide. Current disease management involves pharmacologic interventions, oxygen administration, reduction of infections, and lung transplantation in advanced disease stages. An increasing understanding of mechanisms of respiratory epithelial and pulmonary vascular endothelial maintenance and repair and the underlying stem/progenitor cell populations, including but not limited to airway basal cells and type II alveolar epithelial cells, has opened the possibility of cell replacement-based regenerative approaches for treatment of lung diseases. Further potential for personalized therapies, including in vitro drug screening, has been underscored by the recent derivation of various lung epithelial, endothelial, and immune cell types from human induced pluripotent stem cells. In parallel, immunomodulatory treatments using allogeneic or autologous mesenchymal stromal cells have shown a good safety profile in clinical investigations for acute inflammatory conditions, such as acute respiratory distress syndrome and septic shock. However, as yet, no cell-based therapy has been shown to be both safe and effective for any lung disease. Despite the investigational status of cell-based interventions for lung diseases, businesses that market unproven, unlicensed and potentially harmful cell-based interventions for respiratory diseases have proliferated in the United States and worldwide. The current status of various cell-based regenerative approaches for lung disease as well as the effect of the regulatory environment on clinical translation of such approaches are presented and critically discussed in this review.

Cell-based Therapy for Chronic Obstructive Pulmonary Disease. Rebuilding the Lung

As the prevalence and impact of lung diseases continue to increase worldwide, new therapeutic strategies are desperately needed. Advances in lung-regenerative medicine, a broad field encompassing stem cells, cell-based therapies, and a range of bioengineering approaches, offer new insights into and new techniques for studying lung physiology and pathophysiology. This provides a platform for the development of novel therapeutic approaches. Applicability to chronic obstructive pulmonary disease of recent advances and applications in cell-based therapies, predominantly those with mesenchymal stromal cell-based approaches, and bioengineering approaches for lung diseases are reviewed.

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

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

Mesenchymal stem cells for the prevention of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in preterm infants who have been treated with supplemental oxygen and mechanical ventilation. Despite major advances in perinatal and neonatal medicine, limited progress has been made in reducing BPD rates. The use of mesenchymal stem cells (MSC) is a promising and innovative therapy for several diseases because they are easy to extract and they have low immunogenicity, anti-inflammatory properties, and regenerative ability. According to several pre-clinical studies that have used BPD animal models, one mechanism of action for MSC in BPD is mainly due to the paracrine effects of MSC-derived humoral factors, such as interleukin (IL)-6, IL-8, vascular endothelial growth factor, collagen, and elastin, rather than the multilineage and regenerative capacities of MSC. Cell-free preparations derived from MSC, including conditioned media and exosomes, remain a pre-clinical technology despite their great clinical potential. A first-in-human clinical trial of MSC treatment for BPD was performed as a phase I dose-escalation trial using umbilical cord blood-derived MSC. That trial demonstrated the short- and long-term safety and feasibility of MSC, given that significantly reduced inflammatory marker expression was observed in tracheal aspirates. As of recently, several clinical trials of MSC use for BPD are ongoing or are planned in some countries to investigate the efficacy of MSC in the prevention or treatment of BPD in premature infants. Many clinicians are currently awaiting the results from these trials so that MSC can be used clinically for human BPD.

CXCR4-Overexpressing Umbilical Cord Mesenchymal Stem Cells Enhance Protection against Radiation-Induced Lung Injury

Less quantity of transplanted mesenchymal stem cells (MSCs) influences the therapeutic effects on radiation-induced lung injury (RILI). Previous studies have demonstrated that MSCs overexpressing Chemokine (C-X-C motif) receptor 4 (CXCR4) could increase the quantity of transplanted cells to local tissues. In the present study, we conducted overexpressing CXCR4 human umbilical cord mesenchymal stem cell (HUMSC) therapy for RILI. C57BL mice received single dose of thoracic irradiation with 13 Gy of X-rays and then were administered saline, control HUMSCs, or CXCR4-overexpressing HUMSCs via tail vein. Transfection with CXCR4 enhanced the quantity of transplanted HUMSCs in the radiation-induced injured lung tissues. CXCR4-overexpressing HUMSCs not only improved histopathological changes but also decreased the radiation-induced expression of SDF-1, TGF-β1, α-SMA, and collagen I and inhibited the radiation-induced decreased expression of E-cadherin. Transplanted CXCR4-overexpressing HUMSCs also could express pro-SP-C, indicated adopting the feature of ATII. These finding suggests that CXCR4-overexpressing HUMSCs enhance the protection against RILI and may be a promising strategy for RILI treatment.

Therapeutic effects of human mesenchymal stem cell microvesicles in an ex vivo perfused human lung injured with severe E. coli pneumonia

BACKGROUND

We previously reported that microvesicles (MVs) released by human mesenchymal stem cells (MSC) were as effective as the cells themselves in both Escherichia coli lipopolysaccharide and live bacteria-induced acute lung injury (ALI) mice models. However, it remained unclear whether the biological effect of MSC MV can be applied to human ALI.

METHODS

In the current study, we tested the therapeutic effects of MSC MVs in a well-established ex vivo perfused human model of bacterial pneumonia. Using human donor lungs not used for transplantation, we instilled E. coli bacteria intrabronchially and, 1 hour later, administered MSC MVs into the perfusate as therapy.

RESULTS

After 6 hours, instillation of E. coli bacteria caused influx of inflammatory cells, which resulted in significant inflammation, lung protein permeability and pulmonary oedema formation. Administration of MSC MV significantly increased alveolar fluid clearance and reduced protein permeability and numerically lowered the bacterial load in the injured alveolus. The beneficial effect on bacterial killing was more pronounced with pretreatment of MSCs with a Toll-like receptor 3 agonist, polyinosinic:polycytidylic acid (Poly (I:C)), prior to the isolation of MVs. Isolated human alveolar macrophages had increased antimicrobial activity with MSC MV treatment in vitro as well. Although oxygenation and lung compliance levels were similar between injury and treatment groups, administration of MSC MVs numerically decreased median pulmonary artery pressure at 6 hours.

CONCLUSIONS

In summary, MSC MVs increased alveolar fluid clearance and reduced lung protein permeability, and pretreatment with Poly (I:C) enhanced the antimicrobial activity of MVs in an ex vivo perfused human lung with severe bacteria pneumonia.

Stem cell-based therapies in neonatology: a new hope

Despite progress made in neonatal intensive care, complications of extreme preterm birth still contribute as the main cause of death to children below 5 years of age. Stem cell-based therapies-mesenchymal stromal cells in particular-offer a new hope in preventing and/or restoring organ damage in extreme preterm infants. Early phase clinical trials, fueled by promising preclinical studies on lung and brain injury, have begun. While the enthusiasm in the neonatal community is palpable, much more needs to be learnt about cell-based therapies. Maintaining the balance between temptation and a cautious, evidence-based approach will be critical for cell therapies to fulfil their promise in substantially improving the outcome of extreme preterm infants.

Nanotherapies for micropreemies: Stem cells and the secretome in bronchopulmonary dysplasia

Improved survival of extreme preterm infants has made the task of protecting the ever more immature lung from injury more challenging. As a consequence, the incidence of bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, has remained unchanged. The multifactorial disease pathogenesis of BPD - including amongst others inflammation, oxidative stress and excessive lung stretch - adds further complexity to finding effective therapies that would prevent lung injury and promote lung growth. Mesenchymal stromal cells and the discovery of their pleiotropic effects represent an appealing approach for the prevention of BPD. Mesenchymal stromal cells do not engraft but exert their therapeutic benefit through paracrine effects. These paracrine effects seem to be mediated through the release of nanosized extra-cellular vesicles used for cell-cell communication. This review will summarize our current knowledge on these potential nanotherapies for micropreemies.

Bone marrow mesenchymal stem cells tune the differentiation of myeloid-derived suppressor cells in bleomycin-induced lung injury

Background

Bone marrow mesenchymal stem cells (BMSC) transfer has been attempted as a therapeutic strategy in experimental lung injury and fibrosis. Reduction of neutrophilic infiltration is one of the mechanisms involved in this effect. However, the mechanisms by which BMSC modulate neutrophil remains unknown.

Methods and results

Exposure of mice to bleomycin (BLM) resulted in significant accumulation of cells that express neutrophilic markers Gr-1^HighCD11b⁺Ly-6G^HighF4/80^―CD115^―CD49d^―. These cells lacked immunosuppressive activity and could not be defined as myeloid-derived suppressor cells (MDSC). When BMSC were administrated to BLM-treated mice, they tuned the differentiation of Gr-1^HighCD11b⁺ toward Gr-1^LowCD11b⁺ cells. Gr-1^LowCD11b⁺ cells exhibited unsegmented nuclei and expressed F4/80, Ly-6C, CD49d, and CD115 markers. These cells had potent immunosuppressive activity and thus could be defined as monocytic MDSC. As a result of such immunoregulation, BMSC mediated a decrease of pro-inflammatory products and amelioration of lung injury in BLM-treated mice. Further study using antibody array showed increased expression of macrophage colony-stimulating factor (M-CSF) in BMSC-treated mice. Accumulation of Gr-1^LowCD11b⁺ cells in BMSC-treated mice was abrogated in M-CSF neutralizing mice. The beneficial effect of BMSC was independent of the ability of the cells to engraft in lung and in vitro coculture study of BMSC with Gr-1⁺CD11b⁺ cells showed that the induction of Gr-1^LowCD11b⁺ cells by BMSC was independent of cell-cell contact.

Conclusions

These results document the generation of Gr-1^HighCD11b⁺ cells in BLM-treated mice, and suggest that BMSC tune the differentiation of Gr-1^HighCD11b⁺ toward Gr-1^LowCD11b⁺ cells and therefore inhibit the progression of BLM-induced lung injury.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0983-1) contains supplementary material, which is available to authorized users.

Interrupted reprogramming of alveolar type II cells induces progenitor-like cells that ameliorate pulmonary fibrosis

We describe here an interrupted reprogramming strategy to generate “induced progenitor-like (iPL) cells” from alveolar epithelial type II (AEC-II) cells. A carefully defined period of transient expression of reprogramming factors (Oct4, Sox2, Klf4, and c-Myc (OSKM)) is able to rescue the limited in vitro clonogenic capacity of AEC-II cells, potentially by activation of a bipotential progenitor-like state. Importantly, our results demonstrate that interrupted reprogramming results in controlled expansion of cell numbers yet preservation of the differentiation pathway to the alveolar epithelial lineage. When transplanted to the injured lungs, AEC-II-iPL cells are retained in the lung and ameliorate bleomycin-induced pulmonary fibrosis. Interrupted reprogramming can be used as an alternative approach to produce highly specified functional therapeutic cell populations and may lead to significant advances in regenerative medicine.

A modified reprogramming strategy helps expand populations of surfactant-producing lung cells in a dish without altering their cellular function. A team led by Thomas Waddell and Andras Nagy from the University of Toronto, Canada isolated alveolar type II cells from the lungs of mice. They transiently induced expression of four reprogramming factors in these cells for a defined period of time. Before this “interrupted” reprogramming, the lung cells had limited ability to continue replicating themselves. Afterwards, the cells could expand their numbers dramatically without entering a pluripotent state. Rather, the cells maintained their original function while also expressing genes associated with lung precursor cells, which could explain their proliferative ability. The cells, when transplanted into the injured lungs, helped ameliorate pulmonary fibrosis in a mouse model, suggesting that a similar cell-based therapy may be useful in people.

Novel mechanisms regulating endothelial barrier function in the pulmonary microcirculation

The pulmonary epithelial and vascular endothelial cell layers provide two sequential physical and immunological barriers that together form a semi-permeable interface and prevent alveolar and interstitial oedema formation. In this review, we focus specifically on the continuous endothelium of the pulmonary microvascular bed that warrants strict control of the exchange of gases, fluid, solutes and circulating cells between the plasma and the interstitial space. The present review provides an overview of emerging molecular mechanisms that permit constant transcellular exchange between the vascular and interstitial compartment, and cause, prevent or reverse lung endothelial barrier failure under experimental conditions, yet with a clinical perspective. Based on recent findings and at times seemingly conflicting results we discuss emerging paradigms of permeability regulation by altered ion transport as well as shifts in the homeostasis of sphingolipids, angiopoietins and prostaglandins.

Rationale and design of the Clinical and Histologic Analysis of Mesenchymal Stromal Cells in AmPutations (CHAMP) trial investigating the therapeutic mechanism of mesenchymal stromal cells in the treatment of critical limb ischemia

OBJECTIVE

Currently, there are no accepted nonsurgical therapies that improve the delivery of blood-derived nutrients to patients with critical limb ischemia. Here, we describe the ongoing phase 1/2 Clinical and Histologic Analysis of Mesenchymal Stromal Cells in AmPutations (CHAMP) trial, which will provide crucial evidence of the safety profile of mesenchymal stromal cells (MSCs) and explore their therapeutic mechanisms in the setting of critical limb ischemia requiring below-knee amputation (BKA).

METHODS

In the CHAMP and the parallel marrowCHAMP trials (hereafter grouped together as CHAMP), a total of 32 extremities with rest pain or tissue loss requiring BKA will be enrolled to receive intramuscular injections of allogeneic MSCs (CHAMP; n = 16) or autogenous concentrated bone marrow aspirate (marrowCHAMP; n = 16) along the distribution of the BKA myocutaneous flap and proximal tibialis anterior. After treatment, subjects are randomized to BKA at four time points after injection (days 3, 7, 14, and 21). At the time of amputation, skeletal muscle is collected at 2-cm increments from the tibialis injection site and used to determine proangiogenic cytokine description, MSC retention, quantification of proangiogenic hematopoietic progenitor cells, and histologic description. Clinical limb perfusion before and after treatment will be quantified using transcutaneous oximetry, toe-brachial index, ankle-brachial index, and indocyanine angiography. Additional clinical end points include all-cause mortality, need for amputation revision, and gangrene incidence during the 6-month post-treatment follow-up.

RESULTS

Enrollment is under way, with 10 patients treated per protocol thus far. We anticipate full conclusion of follow-up within the next 24 months.

CONCLUSIONS

CHAMP will be pivotal in characterizing the safety, efficacy, and, most important, therapeutic mechanism of allogeneic MSCs and autogenous concentrated bone marrow aspirate in ischemic skeletal muscle.

Stem cells in lung repair and regeneration: Current applications and future promise

Lung diseases are major cause of morbidity and mortality worldwide. The progress in regenerative medicine and stem cell research in the lung are currently a fast-growing research topic that can provide solutions to these major health problems. Under normal conditions, the rate of cellular proliferation is relatively low in the lung in vivo, compared to other major organ systems. Lung injury leads to the activation of stem/progenitor cell populations that re-enter the cell cycle. Yet, little is known about stem cells in the lung, despite common thoughts that these cells could play a critical role in the repair of lung injuries. Nor do we fully understand the cellular and architectural complexity of the respiratory tract, and the diverse stem/progenitor cells that are involved in the lung repair and regeneration. In this review, we discuss the conceptual framework of lung stem/progenitor cell biology, and describe lung diseases, in which stem cell manipulations may be physiologically significant. In addition, we highlight the challenges of lung stem cell-based therapy.

The promise of mesenchymal stem cell therapy for acute respiratory distress syndrome

This review describes the current state of the science on mesenchymal stem cell (MSC) treatment for acute lung injury (ALI). The general characteristics, regenerative potential, and mechanism of action of MSCs are first presented. Next, particular emphasis is placed on the application of MSCs for the treatment of acute respiratory distress syndrome (ARDS) in preclinical and clinical studies. Finally, we discuss current challenges and future directions in the field presented from a clinician-researcher perspective. The objective of this work is to provide the readership with a current review of the literature discussing the hurdles and overall promise of MSCs as therapeutic interventions for the treatment of ARDS.

The Therapeutic Potential of Stem Cells for Bronchopulmonary Dysplasia: "It's About Time" or "Not so Fast" ?

OBJECTIVE

While the survival of extremely premature infants has improved over the past decades, the rate of complications - especially for bronchopulmonary dysplasia (BPD) - remains unacceptably high. Over the past 50 years, no safe therapy has had a substantial impact on the incidence and severity of BPD.

METHODS

This may stem from the multifactorial disease pathogenesis and the increasing lung immaturity. Mesenchymal Stromal Cells (MSCs) display pleiotropic effects and show promising results in neonatal rodents in preventing or rescuing lung injury without adverse effects. Early phase clinical trials are now underway to determine the safety and efficacy of this therapy in extremely premature infants.

RESULTS AND CONCLUSION

This review summarizes our current knowledge about MSCs, their mechanism of action and the results of preclinical studies that provide the rationale for early phase clinical trials and discuss remaining gaps in our knowledge.

Bone Marrow Stem Cells Do Not Contribute to Endometrial Cell Lineages in Chimeric Mouse Models

Studies from five independent laboratories conclude that bone marrow stem cells transdifferentiate into endometrial stroma, epithelium, and endothelium. We investigated the nature of bone marrow-derived cells in the mouse endometrium by reconstituting irradiated wild type recipients with bone marrow containing transgenic mTert-green fluorescent protein (GFP) or chicken β-actin (Ch β-actin)-GFP reporters. mTert-GFP is a telomerase marker identifying hematopoietic stem cells and subpopulations of epithelial, endothelial, and immune cells in the endometrium. Ch β-actin-GFP is a ubiquitous reporter previously used to identify bone marrow-derived cells in the endometrium. Confocal fluorescence microscopy for GFP and markers of endometrial and immune cells were used to characterize bone marrow-derived cells in the endometrium of transplant recipients. No evidence of GFP⁺ bone marrow-derived stroma, epithelium, or endothelium was observed in the endometrium of mTert-GFP or Ch β-actin-GFP recipients. All GFP⁺ cells detected in the endometrium were immune cells expressing the pan leukocyte marker CD45, including CD3⁺ T cells and F4/80⁺ macrophages. Further examination of the Ch β-actin-GFP transplant model revealed that bone marrow-derived F4/80⁺ macrophages immunostained weakly for CD45. These macrophages were abundant in the stroma, infiltrated the epithelial and vascular compartments, and could easily be mistaken for bone marrow-derived endometrial cells. We conclude that it is unlikely that bone marrow cells are able to transdifferentiate into endometrial stroma, epithelium, and endothelium. This result has important therapeutic implications, as the expectation that bone marrow stem cells contribute directly to endometrial regeneration is shaping strategies designed to regenerate endometrium in Asherman's syndrome and to control aberrant endometrial growth in endometriosis. Stem Cells 2018;36:91-102.

When Is an Alveolar Type 2 Cell an Alveolar Type 2 Cell? A Conundrum for Lung Stem Cell Biology and Regenerative Medicine

Generating mature, differentiated, adult lung cells from pluripotent cells, such as induced pluripotent stem cells and embryonic stem cells, offers the hope of both generating disease-specific in vitro models and creating definitive and personalized therapies for a host of debilitating lung parenchymal and airway diseases. With the goal of advancing lung-regenerative medicine, several groups have developed and reported on protocols using defined media, coculture with mesenchymal components, or sequential treatments mimicking lung development, to obtain distal lung epithelial cells from stem cell precursors. However, there remains significant controversy about the degree of differentiation of these cells compared with their primary counterparts, coupled with a lack of consistency or uniformity in assessing the resultant phenotypes. Given the inevitable, exponential expansion of these approaches and the probable, but yet-to-emerge second and higher generation techniques to create such assets, we were prompted to pose the question, what makes a lung epithelial cell a lung epithelial cell? More specifically for this Perspective, we also posed the question, what are the minimum features that constitute an alveolar type (AT) 2 epithelial cell? In addressing this, we summarize a body of work spanning nearly five decades, amassed by a series of "lung epithelial cell biology pioneers," which carefully describes well characterized molecular, functional, and morphological features critical for discriminately assessing an AT2 phenotype. Armed with this, we propose a series of core criteria to assist the field in confirming that cells obtained following a differentiation protocol are indeed mature and functional AT2 epithelial cells.

Stem Cell Markers Describe a Transition From Somatic to Pluripotent Cell States in a Rat Model of Endometriosis

OBJECTIVE

To study Thy1 as a fibroblast marker, SSEA1 as a marker of intermediate pluripotency, and Oct4 as a marker of established pluripotency in rat model of endometriosis.

DESIGN

In vivo animal study.

MATERIALS AND METHODS

Endometriosis was induced in 20 albino female rats through autologous transplantation of one uterine horn to mesentery of intestine. Other 20 rats had their horn removed without transplantation (controls). Rats were sacrificed 4 weeks after induction surgery. Ectopic, eutopic, and control endometria were harvested from endometriosis and control animals respectively. Quantitative syber green based RT-PCR was used to detect expression of Thy-1 (CD90), FUT4 (SSEA1), and POU5F1 (Oct4) genes in tissues. Relative expression was normalized to that of β actin. Thy1, SSEA1, and Oct4 protein expression were detected by immunohistochemistry.

RESULTS

Ectopic endometrium expressed significantly higher mRNA of Oct4 and SSEA1 as compared to control endometrium. Expression levels of Oct4 and SSEA1 were comparable between ectopic and eutopic endometria and between eutopic and control endometria. Thy1 (CD90) gene expression level was comparable among ectopic, eutopic, and control endometria. Oct4 immunoscore were significantly higher in ectopic (6.6±0.91) than eutopic (2.5±0.78) or control endometrium (3.7±0.1) (P value 0.02). Thy1 and SSEA1 immunoscores were comparable among all three types of endometria.

CONCLUSIONS

Using rat model of endometriosis, ectopic endometrium showed significantly higher Oct4, and SSEA1, but similar Thy1 gene expression to that of control endometrium. This indicates increased transition from somatic to pluripotent cell states in ectopic endometrium which may play a role in endometriosis pathogenesis.

Mesenchymal Stem Cells Adopt Lung Cell Phenotype in Normal and Radiation-induced Lung Injury Conditions

Lung tissue exposure to ionizing irradiation can invariably occur during the treatment of a variety of cancers leading to increased risk of radiation-induced lung disease (RILD). Mesenchymal stem cells (MSCs) possess the potential to differentiate into epithelial cells. However, cell culture methods of primary type II pneumocytes are slow and cannot provide a sufficient number of cells to regenerate damaged lungs. Moreover, effects of ablative radiation doses on the ability of MSCs to differentiate in vitro into lung cells have not been investigated yet. Therefore, an in vitro coculture system was used, where MSCs were physically separated from dissociated lung tissue obtained from either healthy or high ablative doses of 16 or 20 Gy whole thorax irradiated rats. Around 10±5% and 20±3% of cocultured MSCs demonstrated a change into lung-specific Clara and type II pneumocyte cells when MSCs were cocultured with healthy lung tissue. Interestingly, in cocultures with irradiated lung biopsies, the percentage of MSCs changed into Clara and type II pneumocytes cells increased to 40±7% and 50±6% at 16 Gy irradiation dose and 30±5% and 40±8% at 20 Gy irradiation dose, respectively. These data suggest that MSCs to lung cell differentiation is possible without cell fusion. In addition, 16 and 20 Gy whole thorax irradiation doses that can cause varying levels of RILD, induced different percentages of MSCs to adopt lung cell phenotype compared with healthy lung tissue, providing encouraging outlook for RILD therapeutic intervention for ablative radiotherapy prescriptions.

Dynamic Tracking Human Mesenchymal Stem Cells Tropism following Smoke Inhalation Injury in NOD/SCID Mice

Multiple preclinical evidences have supported the potential value of mesenchymal stem cells (MSCs) for treatment of acute lung injury (ALI). However, few studies focus on the dynamic tropism of MSCs in animals with acute lung injury. In this study, we track systemically transplanted human bone marrow-derived mesenchymal stem cells (hBMSCs) in NOD/SCID mice with smoke inhalation injury (SII) through bioluminescence imaging (BLI). The results showed that hBMSCs systemically delivered into healthy NOD/SCID mouse initially reside in the lungs and then partially translocate to the abdomen after 24 h. Compared with the uninjured control group treated with hBMSCs, higher numbers of hBMSCs were found in the lungs of the SII NOD/SCID mice. In both the uninjured and SII mice, the BLI signals in the lungs steadily decreased over time and disappeared by 5 days after treatment. hBMSCs significantly attenuated lung injury, elevated the levels of KGF, decreased the levels of TNF-α in BALF, and inhibited inflammatory cell infiltration in the mice with SII. In conclusion, our findings demonstrated that more systemically infused hBMSCs localized to the lungs in mice with SII. hBMSC xenografts repaired smoke inhalation-induced lung injury in mice. This repair was maybe due to the effect of anti-inflammatory and secreting KGF of hMSCs but not associated with the differentiation of the hBMSCs into alveolar epithelial cells.

Hepatocyte Growth Factor Is Required for Mesenchymal Stromal Cell Protection Against Bleomycin-Induced Pulmonary Fibrosis

: The incidence of idiopathic pulmonary fibrosis is on the rise and existing treatments have failed to halt or reverse disease progression. Mesenchymal stromal cells (MSCs) have potent cytoprotective effects, can promote tissue repair, and have demonstrated efficacy in a range of fibrotic lung diseases; however, the exact mechanisms of action remain to be elucidated. Chemical antagonists and short hairpin RNA knockdown were used to identify the mechanisms of action used by MSCs in promoting wound healing, proliferation, and inhibiting apoptosis. Using the bleomycin induced fibrosis model, the protective effects of early or late MSC administration were examined. The role for hepatocyte growth factor (HGF) in MSC protection against bleomycin lung injury was examined using HGF knockdown MSC. Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling assay was performed on ex vivo lung sections to examine the effects of MSC on apoptosis. MSC conditioned media (CM) enhanced wound closure and inhibited apoptosis of pulmonary cells in vitro. HGF was required for MSC CM enhancement of epithelial cell proliferation and inhibition of apoptosis. In contrast, MSC required COX-2 for CM to inhibit fibroblast proliferation. In a murine model, early administration of MSC protected against bleomycin induced lung fibrosis and correlated with reduced levels of the proinflammatory cytokine interleukin-1β, reduced levels of apoptosis, and significantly increased levels of HGF. These protective effects were in part mediated by MSC derived HGF as HGF knockdown MSC were unable to protect against fibrosis in vivo. These findings delineate the mechanisms of MSC protection in a preclinical model of fibrotic lung disease.

SIGNIFICANCE

The mechanisms used by mesenchymal stromal cells (MSCs) in mediating protective effects in chronic models of lung disease are not understood and remain to be elucidated. These findings from in vitro studies highlight an important role for the MSC-derived soluble factors hepatocyte growth factor (HGF) and prostaglandin E₂ in promoting wound healing and inhibiting apoptosis. Furthermore, this study translates these findings demonstrating an important role for HGF in the protective effects mediated by MSC in vivo in the bleomycin model. These findings support a targeted approach to enhancing MSC therapy for fibrotic disease and highlight the importance of timing of MSC therapy.

Mesenchymal stem cells ameliorate inflammatory cytokine-induced impairment of AT-II cells through a keratinocyte growth factor-dependent PI3K/Akt/mTOR signaling pathway

Lung epithelium restoration subsequent to injury is of concern in association with the outcomes of diverse inflammatory lung diseases. Previous studies have demonstrated that mesenchymal stem cells (MSCs) may promote epithelial repair subsequent to inflammatory injury, however the mechanism that mediates this effect remains unclear. The current study examined the role of MSCs in alveolar type II epithelial cell (AT-II cell) restoration subsequent to an inflammatory insult. AT-II cells were firstly exposed to inflammatory cytokines including tumor necrosis factor-α, interleukin (IL)-6 and IL-1β, then were co-cultured with MSCs in Transwell for 72 h. Cell proliferation, expression of surfactant protein A (SP-A) and expression of the α1 subunit were evaluated respectively by the Cell Counting Kit-8 assay, western blotting and semiquantitative reverse transcription-polymerase chain reaction. Keratinocyte growth factor (KGF) small interfering RNA (siRNA) was applied to knockdown the main cytoprotective factors in the MSCs. Subsequent to an inflammatory insult, AT-II cells were observed to be impaired, exhibiting the characteristics of injured cell morphology, reduced cell proliferation and reduced expression of SP-A and the α1 subunit. Co-culture with MSCs significantly ameliorated these cell impairments, while these benefits were weakened by the application of KGF siRNA. Simultaneously, expression levels of phosphorylated (p-) protein kinase B (AKT) and p-mammalian target of rapamycin (mTOR) in AT-II cells were upregulated by MSCs, suggesting activation of the phosphoinositide 3-kinase (PI3K) pathway. These data demonstrate that administration of MSCs to the inflammation-insulted AT-II cells may ameliorate the impairments through a KGF-dependent PI3K/AKT/mTOR signaling pathway.

Mesenchymal Stem Cells Induce Suppressive Macrophages Through Phagocytosis in a Mouse Model of Asthma

Mesenchymal stem cell (MSC) immunosuppressive functions make them attractive candidates for anti-inflammatory therapy in allergic asthma. However, the mechanisms by which they ensure therapeutic effects remain to be elucidated. In an acute mouse model of house dust mite (Der f)-induced asthma, one i.v. MSC injection was sufficient to normalize and stabilize lung function in Der f-sensitized mice as compared to control mice. MSC injection decreased in vivo airway responsiveness and decreased ex vivo carbachol-induced bronchial contraction, maintaining bronchial expression of the inhibitory type 2 muscarinic receptor. To evaluate in vivo MSC survival, MSCs were labeled with PKH26 fluorescent marker prior to i.v. injection, and 1 to 10 days later total lungs were digested to obtain single-cell suspensions. 91.5 ± 2.3% and 86.6 ± 6.3% of the recovered PKH26(+) lung cells expressed specific macrophage markers in control and Der f mice, respectively, suggesting that macrophages had phagocyted in vivo the injected MSCs. Interestingly, only PKH26(+) macrophages expressed M2 phenotype, while the innate PKH26(-) macrophages expressed M1 phenotype. Finally, the remaining 0.5% PKH26(+) MSCs expressed 10- to 100-fold more COX-2 than before injection, suggesting in vivo MSC phenotype modification. Together, the results of this study indicate that MSCs attenuate asthma by being phagocyted by lung macrophages, which in turn acquire a M2 suppressive phenotype. Stem Cells 2016;34:1836-1845.

Synergism of MSC-secreted HGF and VEGF in stabilising endothelial barrier function upon lipopolysaccharide stimulation via the Rac1 pathway

Background

Mesenchymal stem cells (MSCs) stabilise endothelial barrier function in acute lung injury via paracrine hepatocyte growth factor (HGF). Vascular endothelial growth factor (VEGF), which is secreted by MSCs, is another key regulator of endothelial permeability; however, its role in adjusting permeability remains controversial. In addition, whether an interaction occurs between HGF and VEGF, which are secreted by MSCs, is not completely understood.

Methods

We introduced a co-cultured model of human pulmonary microvascular endothelial cells (HPMECs) and MSC conditioned medium (CM) collected from MSCs after 24 h of hypoxic culture. The presence of VEGF and HGF in the MSC-CM was neutralised by anti-VEGF and anti-HGF antibodies, respectively. To determine the roles and mechanisms of MSC-secreted HGF and VEGF, we employed recombinant humanised HGF and recombinant humanised VEGF to co-culture with HPMECs. Additionally, we employed the RhoA inhibitor C3 transferase and the Rac1 inhibitor NSC23766 to inhibit the activities of RhoA and Rac1 in HPMECs treated with MSC-CM or VEGF/HGF with the same dosage as in the MSC-CM. Then, endothelial paracellular and transcellular permeability was detected. VE-cadherin, occludin and caveolin-1 protein expression in HPMECs was measured by western blot. Adherens junction proteins, including F-actin and VE-cadherin, were detected by immunofluorescence.

Results

MSC-CM treatment significantly decreased lipopolysaccharide-induced endothelial paracellular and transcellular permeability, which was significantly inhibited by pretreatment with HGF antibody or with both VEGF and HGF antibodies. Furthermore, MSC-CM treatment increased the expression of the endothelial intercellular adherence junction proteins VE-cadherin and occludin and decreased the expression of caveolin-1 protein. MSC-CM treatment also decreased endothelial apoptosis and induced endothelial cell proliferation; however, the effects of MSC-CM treatment were inhibited by pretreatment with HGF antibody or with both HGF and VEGF antibodies. Additionally, the effects of MSC-CM and VEGF/HGF on reducing endothelial paracellular and transcellular permeability were weakened when HPMECs were pretreated with the Rac1 inhibitor NSC23766.

Conclusion

HGF secreted by MSCs protects the endothelial barrier function; however, VEGF secreted by MSCs may synergize with HGF to stabilise endothelial cell barrier function. Rac1 is the pathway by which MSC-secreted VEGF and HGF regulate endothelial permeability.

Endometrial stem/progenitor cells: the first 10 years

BACKGROUND

The existence of stem/progenitor cells in the endometrium was postulated many years ago, but the first functional evidence was only published in 2004. The identification of rare epithelial and stromal populations of clonogenic cells in human endometrium has opened an active area of research on endometrial stem/progenitor cells in the subsequent 10 years.

METHODS

The published literature was searched using the PubMed database with the search terms ‘endometrial stem cells and menstrual blood stem cells' until December 2014.

RESULTS

Endometrial epithelial stem/progenitor cells have been identified as clonogenic cells in human and as label-retaining or CD44⁺ cells in mouse endometrium, but their characterization has been modest. In contrast, endometrial mesenchymal stem/stromal cells (MSCs) have been well characterized and show similar properties to bone marrow MSCs. Specific markers for their enrichment have been identified, CD146⁺PDGFRβ⁺ (platelet-derived growth factor receptor beta) and SUSD2⁺ (sushi domain containing-2), which detected their perivascular location and likely pericyte identity in endometrial basalis and functionalis vessels. Transcriptomics and secretomics of SUSD2⁺ cells confirm their perivascular phenotype. Stromal fibroblasts cultured from endometrial tissue or menstrual blood also have some MSC characteristics and demonstrate broad multilineage differentiation potential for mesodermal, endodermal and ectodermal lineages, indicating their plasticity. Side population (SP) cells are a mixed population, although predominantly vascular cells, which exhibit adult stem cell properties, including tissue reconstitution. There is some evidence that bone marrow cells contribute a small population of endometrial epithelial and stromal cells. The discovery of specific markers for endometrial stem/progenitor cells has enabled the examination of their role in endometrial proliferative disorders, including endometriosis, adenomyosis and Asherman's syndrome. Endometrial MSCs (eMSCs) and menstrual blood stromal fibroblasts are an attractive source of MSCs for regenerative medicine because of their relative ease of acquisition with minimal morbidity. Their homologous and non-homologous use as autologous and allogeneic cells for therapeutic purposes is currently being assessed in preclinical animal models of pelvic organ prolapse and phase I/II clinical trials for cardiac failure. eMSCs and stromal fibroblasts also exhibit non-stem cell-associated immunomodulatory and anti-inflammatory properties, further emphasizing their desirable properties for cell-based therapies.

CONCLUSIONS

Much has been learnt about endometrial stem/progenitor cells in the 10 years since their discovery, although several unresolved issues remain. These include rationalizing the terminology and diagnostic characteristics used for distinguishing perivascular stem/progenitor cells from stromal fibroblasts, which also have considerable differentiation potential. The hierarchical relationship between clonogenic epithelial progenitor cells, endometrial and decidual SP cells, CD146⁺PDGFR-β⁺ and SUSD2⁺ cells and menstrual blood stromal fibroblasts still needs to be resolved. Developing more genetic animal models for investigating the role of endometrial stem/progenitor cells in endometrial disorders is required, as well as elucidating which bone marrow cells contribute to endometrial tissue. Deep sequencing and epigenetic profiling of enriched populations of endometrial stem/progenitor cells and their differentiated progeny at the population and single-cell level will shed new light on the regulation and function of endometrial stem/progenitor cells.

Mesenchymal stromal cells are more effective than the MSC secretome in diminishing injury and enhancing recovery following ventilator-induced lung injury

Background

The potential for mesenchymal stem cells (MSCs) to reduce the severity of experimental lung injury has been established in several pre-clinical studies. We have recently demonstrated that MSCs, and MSC-secreted factors (secretome), enhance lung repair and regeneration at 48 h following ventilation-induced lung injury (VILI). We wished to determine the potential for MSC therapy to exert beneficial effects in the early recovery phase following VILI when ongoing injury coexists with processes of repair, and to compare the efficacy of MSC therapy to the use of the secretome alone.

Methods

Male Sprague–Dawley rats were anesthetized, oro-tracheally intubated, and subjected to high stretch mechanical ventilation until lung compliance had declined by 50 % of baseline. Animals were then weaned from mechanical ventilation, and anesthesia discontinued. Once awake and spontaneously ventilating, animals received an intravenous injection of either rodent MSCs (10 million/kg), MSC-conditioned medium, fibroblasts (10 million/kg), or vehicle. Thereafter, the animals were allowed to recover and the extent of lung injury/repair was determined after 4 h.

Results

Treatment with MSCs diminished injury and enhanced recovery following VILI to a greater extent compared to MSC-conditioned medium, with fibroblasts proving ineffective. MSCs, but not their conditioned medium, attenuated indices of lung injury including oxygenation, respiratory compliance, and lung edema. Total lung water as assessed by wet:dry ratio, bronchoalveolar lavage total inflammatory cell, neutrophil counts, and alveolar IL-6 concentrations were reduced in the animals that received MSC therapy.

Conclusions

The immunomodulating and/or reparative effect of MSCs is evident early after VILI in this model. MSC-conditioned medium was not as effective as the cells themselves in diminishing injury and restoring lung structure and function.