Induced pluripotent stem cell-derived lung alveolar epithelial type II cells reduce damage in bleomycin-induced lung fibrosis

Microvesicles derived from mesenchymal stem cells inhibit acute respiratory distress syndrome-related pulmonary fibrosis in mouse partly through hepatocyte growth factor

BACKGROUND

Pulmonary fibrosis is one of the main reasons for the high mortality rate among acute respiratory distress syndrome (ARDS) patients. Mesenchymal stromal cell-derived microvesicles (MSC-MVs) have been shown to exert antifibrotic effects in lung diseases.

AIM

To investigate the effects and mechanisms of MSC-MVs on pulmonary fibrosis in ARDS mouse models.

METHODS

MSC-MVs with low hepatocyte growth factor (HGF) expression (siHGF-MSC-MVs) were obtained via lentivirus transfection and used to establish the ARDS pulmonary fibrosis mouse model. Following intubation, respiratory mechanics-related indicators were measured via an experimental small animal lung function tester. Homing of MSC-MVs in lung tissues was investigated by near-infrared live imaging. Immunohistochemical, western blotting, ELISA and other methods were used to detect expression of pulmonary fibrosis-related proteins and to compare effects on pulmonary fibrosis and fibrosis-related indicators.

RESULTS

The MSC-MVs gradually migrated and homed to damaged lung tissues in the ARDS model mice. Treatment with MSC-MVs significantly reduced lung injury and pulmonary fibrosis scores. However, low expression of HGF (siHGF-MSC-MVs) significantly inhibited the effects of MSC-MVs (P < 0.05). Compared with the ARDS pulmonary fibrosis group, the MSC-MVs group exhibited suppressed expression of type I collagen antigen, type III collagen antigen, and the proteins transforming growth factor-β and α-smooth muscle actin, whereas the siHGF-MVs group exhibited significantly increased expression of these proteins. In addition, pulmonary compliance and the pressure of oxygen/oxygen inhalation ratio were significantly lower in the MSC-MVs group, and the effects of the MSC-MVs were significantly inhibited by low HGF expression (all P < 0.05).

CONCLUSION

MSC-MVs improved lung ventilation functions and inhibited pulmonary fibrosis in ARDS mice partly via HGF mRNA transfer.

Mechanisms of Bleomycin-induced Lung Fibrosis: A Review of Therapeutic Targets and Approaches

Pulmonary toxicity is a serious side effect of some specific anticancer drugs. Bleomycin is a well-known anticancer drug that triggers severe reactions in the lungs. It is an approved drug that may be prescribed for the treatment of testicular cancers, Hodgkin's and non-Hodgkin's lymphomas, ovarian cancer, head and neck cancers, and cervical cancer. A large number of experimental studies and clinical findings show that bleomycin can concentrate in lung tissue, leading to massive oxidative stress, alveolar epithelial cell death, the proliferation of fibroblasts, and finally the infiltration of immune cells. Chronic release of pro-inflammatory and pro-fibrotic molecules by immune cells and fibroblasts leads to pneumonitis and fibrosis. Both fibrosis and pneumonitis are serious concerns for patients who receive bleomycin and may lead to death. Therefore, the management of lung toxicity following cancer therapy with bleomycin is a critical issue. This review explains the cellular and molecular mechanisms of pulmonary injury following treatment with bleomycin. Furthermore, we review therapeutic targets and possible promising strategies for ameliorating bleomycin-induced lung injury.

Stem cell-based therapy for fibrotic diseases: mechanisms and pathways

Fibrosis is a pathological process, that could result in permanent scarring and impairment of the physiological function of the affected organ; this condition which is categorized under the term organ failure could affect various organs in different situations. The involvement of the major organs, such as the lungs, liver, kidney, heart, and skin, is associated with a high rate of morbidity and mortality across the world. Fibrotic disorders encompass a broad range of complications and could be traced to various illnesses and impairments; these could range from simple skin scars with beauty issues to severe rheumatologic or inflammatory disorders such as systemic sclerosis as well as idiopathic pulmonary fibrosis. Besides, the overactivation of immune responses during any inflammatory condition causing tissue damage could contribute to the pathogenic fibrotic events accompanying the healing response; for instance, the inflammation resulting from tissue engraftment could cause the formation of fibrotic scars in the grafted tissue, even in cases where the immune system deals with hard to clear infections, fibrotic scars could follow and cause severe adverse effects. A good example of such a complication is post-Covid19 lung fibrosis which could impair the life of the affected individuals with extensive lung involvement. However, effective therapies that halt or slow down the progression of fibrosis are missing in the current clinical settings. Considering the immunomodulatory and regenerative potential of distinct stem cell types, their application as an anti-fibrotic agent, capable of attenuating tissue fibrosis has been investigated by many researchers. Although the majority of the studies addressing the anti-fibrotic effects of stem cells indicated their potent capabilities, the underlying mechanisms, and pathways by which these cells could impact fibrotic processes remain poorly understood. Here, we first, review the properties of various stem cell types utilized so far as anti-fibrotic treatments and discuss the challenges and limitations associated with their applications in clinical settings; then, we will summarize the general and organ-specific mechanisms and pathways contributing to tissue fibrosis; finally, we will describe the mechanisms and pathways considered to be employed by distinct stem cell types for exerting anti-fibrotic events.

Novel insights into the potential applications of stem cells in pulmonary hypertension therapy

Pulmonary hypertension (PH) refers to a group of deadly lung diseases characterized by vascular lesions in the microvasculature and a progressive increase in pulmonary vascular resistance. The prevalence of PH has increased over time. Currently, the treatment options available for PH patients have limited efficacy, and none of them can fundamentally reverse pulmonary vascular remodeling. Stem cells represent an ideal seed with proven efficacy in clinical studies focusing on liver, cardiovascular, and nerve diseases. Since the potential therapeutic effect of mesenchymal stem cells (MSCs) on PH was first reported in 2006, many studies have demonstrated the efficacy of stem cells in PH animal models and suggested that stem cells can help slow the deterioration of lung tissue. Existing PH treatment studies basically focus on the paracrine action of stem cells, including protein regulation, exosome pathway, and cell signaling; however, the specific mechanisms have not yet been clarified. Apoptotic and afunctional pulmonary microvascular endothelial cells (PMVECs) and alveolar epithelial cells (AECs) are two fundamental promoters of PH although they have not been extensively studied by researchers. This review mainly focuses on the supportive communication and interaction between PMVECs and AECs as well as the potential restorative effect of stem cells on their injury. In the future, more studies are needed to prove these effects and explore more radical cures for PH.

Unlocking the Future: Pluripotent Stem Cell-Based Lung Repair

The human respiratory system is susceptible to a variety of diseases, ranging from chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis to acute respiratory distress syndrome (ARDS). Today, lung diseases represent one of the major challenges to the health care sector and represent one of the leading causes of death worldwide. Current treatment options often focus on managing symptoms rather than addressing the underlying cause of the disease. The limitations of conventional therapies highlight the urgent clinical need for innovative solutions capable of repairing damaged lung tissue at a fundamental level. Pluripotent stem cell technologies have now reached clinical maturity and hold immense potential to revolutionize the landscape of lung repair and regenerative medicine. Meanwhile, human embryonic (HESCs) and human-induced pluripotent stem cells (hiPSCs) can be coaxed to differentiate into lung-specific cell types such as bronchial and alveolar epithelial cells, or pulmonary endothelial cells. This holds the promise of regenerating damaged lung tissue and restoring normal respiratory function. While methods for targeted genetic engineering of hPSCs and lung cell differentiation have substantially advanced, the required GMP-grade clinical-scale production technologies as well as the development of suitable preclinical animal models and cell application strategies are less advanced. This review provides an overview of current perspectives on PSC-based therapies for lung repair, explores key advances, and envisions future directions in this dynamic field.

Therapeutic approaches of cell therapy based on stem cells and terminally differentiated cells: Potential and effectiveness

Cell-based therapy, as a promising regenerative medicine approach, has been a promising and effective strategy to treat or even cure various kinds of diseases and conditions. Generally, two types of cells are used in cell therapy, the first is the stem cell, and the other is a fully differentiated cell. Initially, all cells in the body are derived from stem cells. Based on the capacity, potency and differentiation potential of stem cells, there are four types: totipotent (produces all somatic cells plus perinatal tissues), pluripotent (produces all somatic cells), multipotent (produces many types of cells), and unipotent (produces a particular type of cells). All non-totipotent stem cells can be used for cell therapy, depending on their potency and/or disease state/conditions. Adult fully differentiated cell is another cell type for cell therapy that is isolated from adult tissues or obtained following the differentiation of stem cells. The cells can then be transplanted back into the patient to replace damaged or malfunctioning cells, promote tissue repair, or enhance the targeted organ's overall function. With increasing science and knowledge in biology and medicine, different types of techniques have been developed to obtain efficient cells to use for therapeutic approaches. In this study, the potential and opportunity of use of all cell types, both stem cells and fully differentiated cells, are reviewed.

Lung Progenitor and Stem Cell Transplantation as a Potential Regenerative Therapy for Lung Diseases

Chronic lung diseases are debilitating illnesses ranking among the top causes of death globally. Currently, clinically available therapeutic options capable of curing chronic lung diseases are limited to lung transplantation, which is hindered by donor organ shortage. This highlights the urgent need for alternative strategies to repair damaged lung tissues. Stem cell transplantation has emerged as a promising avenue for regenerative treatment of the lung, which involves delivery of healthy lung epithelial progenitor cells that subsequently engraft in the injured tissue and further differentiate to reconstitute the functional respiratory epithelium. These transplanted progenitor cells possess the remarkable ability to self-renew, thereby offering the potential for sustained long-term treatment effects. Notably, the transplantation of basal cells, the airway stem cells, holds the promise for rehabilitating airway injuries resulting from environmental factors or genetic conditions such as cystic fibrosis. Similarly, for diseases affecting the alveoli, alveolar type II cells have garnered interest as a viable alveolar stem cell source for restoring the lung parenchyma from genetic or environmentally induced dysfunctions. Expanding upon these advancements, the use of induced pluripotent stem cells to derive lung progenitor cells for transplantation offers advantages such as scalability and patient specificity. In this review, we comprehensively explore the progress made in lung stem cell transplantation, providing insights into the current state of the field and its future prospects.

Glycogen Synthase Kinase-3 Inhibition by CHIR99021 Promotes Alveolar Epithelial Cell Proliferation and Lung Regeneration in the Lipopolysaccharide-Induced Acute Lung Injury Mouse Model

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury that currently lacks effective clinical treatments. Evidence highlights the potential role of glycogen synthase kinase-3 (GSK-3) inhibition in mitigating severe inflammation. The inhibition of GSK-3α/β by CHIR99021 promoted fetal lung progenitor proliferation and maturation of alveolar epithelial cells (AECs). The precise impact of CHIR99021 in lung repair and regeneration during acute lung injury (ALI) remains unexplored. This study intends to elucidate the influence of CHIR99021 on AEC behaviour during the peak of the inflammatory phase of ALI and, after its attenuation, during the repair and regeneration stage. Furthermore, a long-term evaluation was conducted post CHIR99021 treatment at a late phase of the disease. Our results disclosed the role of GSK-3α/β inhibition in promoting AECI and AECII proliferation. Later administration of CHIR99021 during ALI progression contributed to the transdifferentiation of AECII into AECI and an AECI/AECII increase, suggesting its contribution to the renewal of the alveolar epithelial population and lung regeneration. This effect was confirmed to be maintained histologically in the long term. These findings underscore the potential of targeted therapies that modulate GSK-3α/β inhibition, offering innovative approaches for managing acute lung diseases, mostly in later stages where no treatment is available.

Lung regeneration with rat fetal lung implantation and promotion of alveolar stem cell differentiation by corticosteroids

Introduction

The lung is a difficult organ to regenerate, and the development of functional lungs has still not been achieved. In this study, we investigated lung regeneration using a rat fetal lung tissue-implanted model. This study aimed to evaluate the functioning of the implanted fetal lung tissue and investigate the graft differentiation and maturation mechanism, focusing on alveolar stem cells.

Methods

Fetal lung tissue fragments were obtained from Lewis rats on day 17 and implanted into adult lungs. Animals were divided into the following three groups: group 1, injection into the adult left lung parenchyma; group 2, injection with post-caval lobectomy; and group 3, injection with post-caval lobectomy and corticosteroid administration. Computed tomography was performed on weeks 1, 2, 4, and 8. The presence of alveolar pore, CD31 expression, and bipotential progenitor cell (podoplanin+/surfactant protein C+) localization were histologically evaluated. MiRNA expression was comprehensively compared among the three groups.

Results

The grafts comprised type I and type II alveolar cells connected to the recipient lungs with alveolar pores and capillary networks in the interstitial tissue. The alveolar space was the largest and the computed tomography value was the lowest in the grafts of the corticosteroid-administered group. The number of bipotential progenitor cells was the lowest in the corticosteroid administration group on day 7. Moreover, microRNA-487-3p, 374-5p, and 20b-5p expression was changed by more than 2-fold between the post-caval lobectomy and corticosteroid administration groups.

Conclusions

Implanted fetal lung tissues established airway and capillary communication with the recipient lungs, and corticosteroids accelerated their maturation by promoting the differentiation of progenitor cells. The study findings provide new insights into lung regeneration research.

Induced pluripotent stem cells modulate the Wnt pathway in the bleomycin-induced model of idiopathic pulmonary fibrosis

BACKGROUND

The Wnt signaling pathway has been implicated in the pathogenesis of fibrotic disorders and malignancies. Hence, we aimed to assess the potential of the induced pluripotent stem cells (IPS) in modulating the expression of the cardinal genes of the Wnt pathway in a mouse model of idiopathic pulmonary fibrosis (IPF).

METHODS

C57Bl/6 mice were randomly divided into three groups of Control, Bleomycin (BLM), and BLM + IPS; the BLM mice received intratracheal instillation of bleomycin, BLM + IPS mice received tail vein injection of IPS cells 48 h post instillation of the BLM; The Control group received Phosphate-buffered saline instead. After 3 weeks, the mice were sacrificed and Histologic assessments including hydroxy proline assay, Hematoxylin and Eosin, and Masson-trichrome staining were performed. The expression of the genes for Wnt, β-Catenin, Lef, Dkk1, and Bmp4 was assessed utilizing specific primers and SYBR green master mix.

RESULTS

Histologic assessments revealed that the fibrotic lesions and inflammation were significantly alleviated in the BLM + IPS group. Besides, the gene expression analyses demonstrated the upregulation of Wnt, β-Catenin, and LEF along with the significant downregulation of the Bmp4 and DKK1 in response to bleomycin treatment; subsequently, it was found that the treatment of the IPF mice with IPS cells results in the downregulation of the Wnt, β-Catenin, and Lef, as well as upregulation of the Dkk1, but not the Bmp4 gene (P values < 0.05).

CONCLUSION

The current study highlights the therapeutic potential of the IPS cells on the IPF mouse model in terms of regulating the aberrant expression of the factors contributing to the Wnt signaling pathway.

Induced pluripotent stem cell-based therapies for organ fibrosis

Fibrotic diseases result in organ remodelling and dysfunctional failure and account for one-third of all deaths worldwide. There are no ideal treatments that can halt or reverse progressive organ fibrosis, moreover, organ transplantation is complicated by problems with a limited supply of donor organs and graft rejection. The development of new approaches, especially induced pluripotent stem cell (iPSC)-based therapy, is becoming a hot topic due to their ability to self-renew and differentiate into different cell types that may replace the fibrotic organs. In the past decade, studies have differentiated iPSCs into fibrosis-relevant cell types which were demonstrated to have anti-fibrotic effects that may have the potential to inform new effective precision treatments for organ-specific fibrosis. In this review, we summarize the potential of iPSC-based cellular approaches as therapeutic avenues for treating organ fibrosis, the advantages and disadvantages of iPSCs compared with other types of stem cell-based therapies, as well as the challenges and future outlook in this field.

Cobalt protoporphyrin-induced nano-self-assembly for CT imaging, magnetic-guidance, and antioxidative protection of stem cells in pulmonary fibrosis treatment

Mesenchymal stem cells (MSCs) transplantation is a promising approach for pulmonary fibrosis (PF), however it is impeded by several persistent challenges, including the lack of long-term tracking, low retention, and poor survival of MSCs, as well as the low labeling efficiency of nanoprobes. Herein, a cobalt protoporphyrin IX (CoPP) aggregation-induced strategy is applied to develop a multifunctional nano-self-assembly (ASCP) by combining gold nanoparticle (AuNPs), superparamagnetic iron oxide nanoparticles (SPIONs), and CoPP through a facile solvent evaporation-driven approach. Since no additional carrier materials are employed during the synthesis, high loading efficiency of active ingredients and excellent biocompatibility are achieved. Additionally, facile modification of the ASCPs with bicyclo[6.1.0]nonyne (BCN) groups (named as ASCP-BCN) enables them to effectively label MSCs through bioorthogonal chemistry. The obtained ASCP-BCN could not only help to track MSCs with AuNP-based computed tomography (CT) imaging, but also achieve an SPIONs-assisted magnetic field based improvement in the MSCs retention in lungs as well as promoted the survival of MSCs via the sustained release of CoPP. The in vivo results demonstrated that the labeled MSCs improved the lung functions and alleviated the fibrosis symptoms in a bleomycin–induced PF mouse model. Collectively, a novel ASCP-BCN multifunctional nanoagent was developed to bioorthogonally-label MSCs with a high efficiency, presenting a promising potential in the high-efficient MSC therapy for PF.

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Cobalt protoporphyrin IX induces the formation of multifunctional nanoagent by self-assembly without additional carriers.

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Bioorthogonal reaction increases the stem cell labeling efficiency of nanoagents.

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Gold nanoparticles-based CT imaging enables stem cell tracking in vivo.

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Magnetic guidance and cytoprotection functions improve the therapeutic effect of stem cell therapy for pulmonary fibrosis.

Pulmonary endogenous progenitor stem cell subpopulation: Physiology, pathogenesis, and progress

Lungs are structurally and functionally complex organs consisting of diverse cell types from the proximal to distal axis. They have direct contact with the external environment and are constantly at risk of various injuries. Capable to proliferate and differentiate, pulmonary endogenous progenitor stem cells contribute to the maintenance of lung structure and function both under homeostasis and following injuries. Discovering candidate pulmonary endogenous progenitor stem cell types and underlying regenerative mechanisms provide insights into therapeutic strategy development for lung diseases. In this review, we reveal their compositions, roles in lung disease pathogenesis and injury repair, and the underlying mechanisms. We further underline the advanced progress in research approach and potential therapy for lung regeneration. We also demonstrate the feasibility and prospects of pulmonary endogenous stem cell transplantation for lung disease treatment.

iPSC-Derived Airway Epithelial Cells: Progress, Promise, and Challenges

Induced pluripotent stem cells (iPSCs) generated from somatic cell sources are pluripotent and capable of indefinite expansion in vitro. They provide an unlimited source of cells that can be differentiated into lung progenitor cells for potential clinical use in pulmonary regenerative medicine. This review gives a comprehensive overview of recent progress toward the use of iPSCs to generate proximal and distal airway epithelial cells and mix lung organoids. Furthermore, their potential applications and future challenges for the field are discussed, with a focus on the technological hurdles that must be cleared before stem cell therapeutics can be used for clinical treatment.

Efficacy of Alveolar Type II Epithelial Cell Transplantation for Pulmonary Fibrosis: A Meta-Analysis

Background

Cell transplantation is a promising therapeutic strategy for pulmonary fibrosis. In order to clarify the alveolar type II epithelial cell potential utility in the treatment of lung disease, we conducted a meta-analysis, to evaluate alveolar type II epithelial cells in animal models of lung injury and pulmonary fibrosis.

Methods

This review followed the recommendations from the PRISMA statements, Comprehensive retrieval method was used to search Embase, PubMed, Cochrane, Chinese Knowledge Infrastructure, VIP and Wanfang databases. A total of 7 studies and 286 model rats were included. Two researchers independently screened the identified studies, based on inclusion and exclusion criteria. All analyses were conducted using Review Manager V.5.3 software. The combined standard mean difference (SMD) and 95% confidence interval (CI) of data from the included studies were calculated using fixed or random-effects models.

Results

The analysis of three outcome indexes showed that the heterogeneity of the oxygen saturation group was high (I²=85%), the lung weight group (I²=64%) was close to moderate heterogeneity, and the lung hydroxyproline content group (I²=0) was not heterogeneous.

Conclusion

Meta-analysis showed that transplantation of alveolar type II epithelial cells has beneficial effects, and no obvious adverse reactions. Alveolar type II epithelial cell transplantation can significantly reduce the intervention group and lung hydroxyproline content weight, improve the blood oxygen saturation, lung histo-pathology showed significant improvement in pulmonary fibrosis.

Repairing Mechanisms for Distal Airway Injuries and Related Targeted Therapeutics for Chronic Lung Diseases

Chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF), involve progressive and irreversible destruction and pathogenic remodeling of airways and have become the leading health care burden worldwide. Pulmonary tissue has extensive capacities to launch injury-responsive repairing programs (IRRPs) to replace the damaged or dead cells upon acute lung injuries. However, the IRRPs are frequently compromised in chronic lung diseases. In this review, we aim to provide an overview of somatic stem cell subpopulations within distal airway epithelium and the underlying mechanisms mediating their self-renewal and trans-differentiation under both physiological and pathological circumstances. We also compared the differences between humans and mice on distal airway structure and stem cell composition. At last, we reviewed the current status and future directions for the development of targeted therapeutics on defective distal airway regeneration and repairment in chronic lung diseases.

Forthcoming complications in recovered COVID-19 patients with COPD and asthma; possible therapeutic opportunities

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been growing swiftly worldwide. Patients with background chronic pulmonary inflammations such as asthma or chronic obstructive pulmonary diseases (COPD) are likely to be infected with this virus. Of note, there is an argument that COVID-19 can remain with serious complications like fibrosis or other pathological changes in the pulmonary tissue of patients with chronic diseases. Along with conventional medications, regenerative medicine, and cell-based therapy could be alternative approaches to compensate for organ loss or restore injured sites using different stem cell types. Owing to unique differentiation capacity and paracrine activity, these cells can accelerate the healing procedure. In this review article, we have tried to scrutinize different reports related to the harmful effects of SARS-CoV-2 on patients with asthma and COPD, as well as the possible therapeutic effects of stem cells in the alleviation of post-COVID-19 complications. Video abstract.

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.

Characterization of circRNA–miRNA–mRNA networks regulating oxygen utilization in type II alveolar epithelial cells of Tibetan pigs

Understanding the signaling pathway regulatory mechanisms in type II alveolar epithelial (ATII) cells, the progenitor cells responsible for proliferating and regenerating type I alveolar epithelial (ATI) and ATII cells, in Tibetan pigs is beneficial for exploring methods of preventing and repairing cellular damage during hypoxia. We simulated a hypoxic environment (2% O2) for culture ATII cells of Tibetan pigs and Landrace pigs, with cells cultured under normoxic conditions (21% O2) as a control group, and performed integrated analysis of circular RNA (circRNA)–microRNA (miRNA)–messenger RNA (mRNA) regulatory axes by whole-transcriptome sequencing. Functional enrichment analysis indicated that the source genes of the differential expressed circRNAs (DEcircRNAs) were primarily involved in cell proliferation, cellular processes, and cell killing. A series of DEcircRNAs were derived from inhibitors of apoptosis proteins and led to a key autonomous effect as modulators of cell repair in Tibetan pigs under hypoxia. The significant higher expression of COL5A1 in TL groups may inhibited apoptosis of ATII cells in Tibetan pigs under lower oxygen concentration, and may lead their better survive in the hypoxia environment. In addition, a competing endogenous RNA (ceRNA) network of functional interactions was constructed that included novel_circ_000898-ssc-miR-199a-5p-CAV1 and novel_circ_000898-ssc-miR-378-BMP2, based on the node genes ssc-miR-199a-5p and ssc-miR-378, which may regulate multiple miRNAs and mRNAs that mediate endoplasmic reticulum (ER) stress-induced apoptosis and inflammation and attenuate hypoxia-induced injury in ATII cells under hypoxic conditions. These results broaden our knowledge of circRNAs, miRNAs, and mRNAs associated with hypoxia and provide new insights into the hypoxic response of ATII cells in Tibetan pigs.

Alternative splicing signature of alveolar type II epithelial cells of Tibetan pigs under hypoxia-induced

Alternative splicing (AS) allows the generation of multiple transcript variants from a single gene and affects biological processes by generating protein diversity in organisms. In total, 41,642 AS events corresponding to 9,924 genes were identified, and SE is the most abundant alternatively spliced type. The analysis of functional categories demonstrates that alternatively spliced differentially expressed genes (DEGs) were enriched in the MAPK signaling pathway and hypoxia-inducible factor 1 (HIF-1) signaling pathway. Proteoglycans in cancer between the normoxic (21% O2, TN and LN) and hypoxic (2% O2, TL and LL) groups, such as SLC2A1, HK1, HK2, ENO3, and PFKFB3, have the potential to rapidly proliferate alveolar type II epithelial (ATII) cells by increasing the intracellular levels of glucose and quickly divert to anabolic pathways by glycolysis intermediates under hypoxia. ACADL, EHHADH, and CPT1A undergo one or two AS types with different frequencies in ATII cells between TN and TL groups (excluding alternatively spliced DEGs shared between normoxic and hypoxic groups), and a constant supply of lipids might be obtained either from the circulation or de novo synthesis for better growth of ATII cells under hypoxia condition. MCM7 and MCM3 undergo different AS types between LN and LL groups (excluding alternatively spliced DEGs shared between normoxic and hypoxic groups), which may bind to the amino-terminal PER-SIM-ARNT domain and the carboxyl terminus of HIF-1α to maintain their stability. Overall, AS and expression levels of candidate mRNAs between Tibetan pigs and Landrace pigs revealed by RNA-seq suggest their potential involvement in the ATII cells grown under hypoxia conditions.

Promises and Challenges of Cell-Based Therapies to Promote Lung Regeneration in Idiopathic Pulmonary Fibrosis

The lung epithelium is constantly exposed to harmful agents present in the air that we breathe making it highly susceptible to damage. However, in instances of injury to the lung, it exhibits a remarkable capacity to regenerate injured tissue thanks to the presence of distinct stem and progenitor cell populations along the airway and alveolar epithelium. Mechanisms of repair are affected in chronic lung diseases such as idiopathic pulmonary fibrosis (IPF), a progressive life-threatening disorder characterized by the loss of alveolar structures, wherein excessive deposition of extracellular matrix components cause the distortion of tissue architecture that limits lung function and impairs tissue repair. Here, we review the most recent findings of a study of epithelial cells with progenitor behavior that contribute to tissue repair as well as the mechanisms involved in mouse and human lung regeneration. In addition, we describe therapeutic strategies to promote or induce lung regeneration and the cell-based strategies tested in clinical trials for the treatment of IPF. Finally, we discuss the challenges, concerns and limitations of applying these therapies of cell transplantation in IPF patients. Further research is still required to develop successful strategies focused on cell-based therapies to promote lung regeneration to restore lung architecture and function.

Effects of transplanted mesenchymal stem cells on repair of the lung tissue of rats with experimental pulmonary fibrosis

Pulmonary fibrosis is one of the commonest forms of interstitial lung diseases with poorly studied methods of its treatment in both human and veterinary medicines. Therefore, this paper focused on seeking alternative methods of its diagnostics and treatment. The article provides the results of the study of bronchoalveolar lavage fluid of rats with experimental lung fibrosis and influence of transplanted allogeneic mesenchymal stem cells of the bone marrow on stimulation of regenerative processes in damaged lung tissues. The studies were conducted on female Wistar rats with pulmonary fibrosis modeled using single transthoracic injection of solution of bleomycin hydrochloride. For the purpose of treatment, we used allogeneic mesenchymal stem cells introduced by various methods and the traditional treatment. We determined that best normalization of the parameters of the studied brochoalveolar lavage occurred in animals that received mesenchymal stem cells. The most active repair processes were in the experimental group that received the mesenchymal stem cells directly to the lung tissue. The animals that received intravenous injection of mesenchymal stemm cells were observed to have lower clinical parameters of the brochoalveolar lavage, but still better than such in the group treated traditionally. The lowest parameters were in animals that received the traditional treatment; they were greater than the phisological parameters, but significantly exceeded them in animals of the control group, indicating presence of inflammatory process in the lung tissue. The conducted cytological assays of the samples of the brochoalveolar lavage revealed that experimental animals with experimental pulmonary fibrosis had development of macrophage and lymphocytic reactions under the influence of transplanted mesenchymal stemm cells. We observed no atypical cells in all the experimental groups. This allows us to draw a conclusion that using stem cells by various methods of transplantation does not stimulate the onset of negative reactons (formation of atypical cells, metastatic processes, etc). Thus, the results of the study of the influence of transplanted mesenchymal stem cells demonstrate that in the conditions of experimental pulmonary fibrosis, the activity of regenerative processes in pathologically altered lung tissue may be an effective method of treatment of animals with this kind of pathology.

Regeneration or Repair? The Role of Alveolar Epithelial Cells in the Pathogenesis of Idiopathic Pulmonary Fibrosis (IPF)

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease (ILD) with unknown etiology in which gradual fibrotic scarring of the lungs leads to usual interstitial pneumonia (UIP) and, ultimately, to death. IPF affects three million people worldwide, and the only currently available treatments include the antifibrotic drugs nintedanib and pirfenidone, which effectively reduce fibrosis progression are, unfortunately, not effective in curing the disease. In recent years, the paradigm of IPF pathogenesis has shifted from a fibroblast-driven disease to an epithelium-driven disease, wherein, upon recurrent microinjuries, dysfunctional alveolar type II epithelial cells (ATII) are not only unable to sustain physiological lung regeneration but also promote aberrant epithelial–mesenchymal crosstalk. This creates a drift towards fibrosis rather than regeneration. In the context of this review article, we discuss the most relevant mechanisms involved in IPF pathogenesis with a specific focus on the role of dysfunctional ATII cells in promoting disease progression. In particular, we summarize the main causes of ATII cell dysfunction, such as aging, environmental factors, and genetic determinants. Next, we describe the known mechanisms of physiological lung regeneration by drawing a parallel between embryonic lung development and the known pathways involved in ATII-driven alveolar re-epithelization after injury. Finally, we review the most relevant interventional clinical trials performed in the last 20 years with the aim of underlining the urgency of developing new therapies against IPF that are not only aimed at reducing disease progression by hampering ECM deposition but also boost the physiological processes of ATII-driven alveolar regeneration.

Impaired Alveolar Re-Epithelialization in Pulmonary Emphysema

Alveolar type II (ATII) cells are progenitors in alveoli and can repair the alveolar epithelium after injury. They are intertwined with the microenvironment for alveolar epithelial cell homeostasis and re-epithelialization. A variety of ATII cell niches, transcription factors, mediators, and signaling pathways constitute a specific environment to regulate ATII cell function. Particularly, WNT/β-catenin, YAP/TAZ, NOTCH, TGF-β, and P53 signaling pathways are dynamically involved in ATII cell proliferation and differentiation, although there are still plenty of unknowns regarding the mechanism. However, an imbalance of alveolar cell death and proliferation was observed in patients with pulmonary emphysema, contributing to alveolar wall destruction and impaired gas exchange. Cigarette smoking causes oxidative stress and is the primary cause of this disease development. Aberrant inflammatory and oxidative stress responses result in loss of cell homeostasis and ATII cell dysfunction in emphysema. Here, we discuss the current understanding of alveolar re-epithelialization and altered reparative responses in the pathophysiology of this disease. Current therapeutics and emerging treatments, including cell therapies in clinical trials, are addressed as well.

Abnormal respiratory progenitors in fibrotic lung injury

Recent advances in single-cell RNA sequencing (scRNA-seq) and epithelium lineage labeling have yielded identification of multiple abnormal epithelial progenitor populations during alveolar type 2 (ATII) cell differentiation into alveolar type 1 (ATI) cells during regenerative lung post-fibrotic injury. These abnormal cells include basaloid/basal-like cells, ATII transition cells, and persistent epithelial progenitors (PEPs). These cells occurred and accumulated during the regeneration of distal airway and alveoli in response to both chronic and acute pulmonary injury. Among the alveolar epithelial progenitors, PEPs express a distinct Krt8+ phenotype that is rarely found in intact alveoli. However, post-injury, the Krt8+ phenotype is seen in dysplastic epithelial cells. Fully understanding the characteristics and functions of these newly found, injury-induced abnormal behavioral epithelial progenitors and the signaling pathways regulating their phenotype could potentially point the way to unique therapeutic targets for fibrosing lung diseases. This review summarizes recent advances in understanding these epithelial progenitors as they relate to uncovering regenerative mechanisms.

Application of the Pluripotent Stem Cells and Genomics in Cardiovascular Research-What We Have Learnt and Not Learnt until Now

Personalized regenerative medicine and biomedical research have been galvanized and revolutionized by human pluripotent stem cells in combination with recent advances in genomics, artificial intelligence, and genome engineering. More recently, we have witnessed the unprecedented breakthrough life-saving translation of mRNA-based vaccines for COVID-19 to contain the global pandemic and the investment in billions of US dollars in space exploration projects and the blooming space-tourism industry fueled by the latest reusable space vessels. Now, it is time to examine where the translation of pluripotent stem cell research stands currently, which has been touted for more than the last two decades to cure and treat millions of patients with severe debilitating degenerative diseases and tissue injuries. This review attempts to highlight the accomplishments of pluripotent stem cell research together with cutting-edge genomics and genome editing tools and, also, the promises that have still not been transformed into clinical applications, with cardiovascular research as a case example. This review also brings to our attention the scientific and socioeconomic challenges that need to be effectively addressed to see the full potential of pluripotent stem cells at the clinical bedside.

Evolution of Diploid Progenitor Lung Cell Applications: From Optimized Biotechnological Substrates to Potential Active Pharmaceutical Ingredients in Respiratory Tract Regenerative Medicine

The objective of this review is to describe the evolution of lung tissue-derived diploid progenitor cell applications, ranging from historical biotechnological substrate functions for vaccine production and testing to current investigations around potential therapeutic use in respiratory tract regenerative medicine. Such cell types (e.g., MRC-5 or WI-38 sources) were extensively studied since the 1960s and have been continuously used over five decades as safe and sustainable industrial vaccine substrates. Recent research and development efforts around diploid progenitor lung cells (e.g., FE002-Lu or Walvax-2 sources) consist in qualification for potential use as optimal and renewed vaccine production substrates and, alternatively, for potential therapeutic applications in respiratory tract regenerative medicine. Potentially effective, safe, and sustainable cell therapy approaches for the management of inflammatory lung diseases or affections and related symptoms (e.g., COVID-19 patients and burn patient severe inhalation syndrome) using local homologous allogeneic cell-based or cell-derived product administrations are considered. Overall, lung tissue-derived progenitor cells isolated and produced under good manufacturing practices (GMP) may be used with high versatility. They can either act as key industrial platforms optimally conforming to specific pharmacopoeial requirements or as active pharmaceutical ingredients (API) for potentially effective promotion of lung tissue repair or regeneration.

LncRNA MEG3 Involved in NiO NPs-Induced Pulmonary Fibrosis via Regulating TGF-β1-Mediated PI3K/AKT Pathway

Long noncoding RNA maternally expressed gene 3 (MEG3) involves in fibrotic diseases, but its role in nickel oxide nanoparticles (NiO NPs)-induced pulmonary fibrosis remains unclear. The present study aimed to explore the relationships among MEG3, transforming growth factor-β1 (TGF-β1) and phosphoinositide 3-kinase (PI3K)/AKT pathway in NiO NPs-induced pulmonary fibrosis. Wistar rats were intratracheally instilled with NiO NPs twice a week for 9 weeks, and human lung adenocarcinoma epithelial cells (A549 cells) were exposed to NiO NPs for 24 h. The pathological alterations and increased hydroxyproline indicated that NiO NPs caused pulmonary fibrosis in rats. The up-regulated type I collagen (Col-I) suggested that NiO NPs-induced collagen deposition in A549 cells. Meanwhile, NiO NPs could significantly down-regulate MEG3, up-regulate TGF-β1 and activate PI3K/AKT signaling pathway both in vivo and in vitro. However, we found that the PI3K/AKT pathway activated by NiO NPs could be suppressed by 10 μM TGF-β1 inhibitor (SB431542) in A549 cells. The protein markers (Col-I, Fibronectin, and alpha-smooth muscle actin) of collagen deposition up-regulated by NiO NPs were reduced by 10 μM PI3K inhibitor (LY294002). Furthermore, we further found that overexpressed MEG3 inhibited the expression of TGF-β1, resulting in the inactivation of PI3K/AKT pathway and the reduction of collagen formation. In summary, our results validated that MEG3 could arrest NiO NPs-induced pulmonary fibrosis via inhibiting TGF-β1-mediated PI3K/AKT pathway.

COVID-19 and graft-versus-host disease: a tale of two diseases (and why age matters)

Disorders involving injury to tissue stem cells that ensure normal tissue homeostasis and repair have potential to show unusually devastating clinical consequences. Acute graft-versus-host disease (aGVHD) is one condition where relatively few cytotoxic immune cells target skin stem cells to produce significant morbidity and mortality. By analogy, SARS-CoV-2 is a vector that initially homes to pulmonary stem cells that preferentially express the ACE2 receptor, thus potentially incurring similarly robust pathological consequences. In older individuals, stem cell number and/or function become depleted due to pathways independent of disease-related injury to these subpopulations. Accordingly, pathologic targeting of stem cells in conditions like aGVHD and COVID-19 infection where these cells are already deficient due to the aging process may have dire consequences in elderly individuals. A hypothesis is herein advanced that, as with aGVHD, lung stem cell targeting is a potential co-factor in explaining age-related severity of COVID-19 infection.

Improved Alveolar Dynamics and Structure After Alveolar Epithelial Type II Cell Transplantation in Bleomycin Induced Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressively and ultimately fatal lung disease. Previously it has been shown that intratracheal administration of alveolar epithelial type II cells (AE2C) in the animal model of bleomycin-induced pulmonary fibrosis is able to reverse fibrosis and restore surfactant protein levels. However, to date, it has not been evaluated whether these changes involve any improvement in alveolar dynamics. Consequently, the aim of the present work was to study lung physiology after AE2C transplantation at different time points during the development of injury and fibrosis. Lung fibrosis was induced by intratracheal instillation of bleomycin (4U/kg) in rat lungs. The animals were transplanted with AE2C (2.5 × 10⁶ cells/animal) 3 or 7 days after bleomycin instillation. Assessments were done at day 7 and 14 after the induction of fibrosis to plot time dependent changes in lung physiology and mechanics. To assess the pressures and rates at which closed alveoli reopens invasive pulmonary tests using a small-animal mechanical ventilator (Flexivent®, Scireq, Canada) including de-recruitability tests and forced oscillation technique as well as quasi-static pressure volume loops were performed. Afterwards lungs were fixed by vascular perfusion and subjected to design-based stereological evaluation at light and electron microscopy level. AE2C delivered during the lung injury phase (3 days) of the disease are only able to slightly recover the volume of AE2C and volume fraction of LB in AE2C. However, it did not show either positive effects regarding ventilated alveolar surface nor any increase of lung compliance. On the other hand, when AE2C are delivered at the beginning of the fibrotic phase (7 days after bleomycin instillation), an increased ventilated alveolar surface to control levels and reduced septal wall thickness can be observed. Moreover, transplanted animals showed better lung performance, with increased inspiratory capacity and compliance. In addition, a detailed analysis of surfactant active forms [mainly tubular myelin, lamellar body (LB)-like structures and multilamellar vesicles (MLV)], showed an effective recovery during the pro-fibrotic phase due to the healthy AE2C transplantation. In conclusion, AE2C transplantation during fibrogenic phases of the disease improves lung performance, structure and surfactant ultrastructure in bleomycin-induced lung fibrosis.

Alveolar Type II Cells or Mesenchymal Stem Cells: Comparison of Two Different Cell Therapies for the Treatment of Acute Lung Injury in Rats

The use of cell therapies has recently increased for the treatment of pulmonary diseases. Mesenchymal stem/stromal cells (MSCs) and alveolar type II cells (ATII) are the main cell-based therapies used for the treatment of acute respiratory distress syndrome (ARDS). Many pre-clinical studies have shown that both therapies generate positive outcomes; however, the differences in the efficiency of MSCs or ATII for reducing lung damage remains to be studied. We compared the potential of both cell therapies, administering them using the same route and dose and equal time points in a sustained acute lung injury (ALI) model. We found that the MSCs and ATII cells have similar therapeutic effects when we tested them in a hydrochloric acid and lipopolysaccharide (HCl-LPS) two-hit ALI model. Both therapies were able to reduce proinflammatory cytokines, decrease neutrophil infiltration, reduce permeability, and moderate hemorrhage and interstitial edema. Although MSCs and ATII cells have been described as targeting different cellular and molecular mechanisms, our data indicates that both cell therapies are successful for the treatment of ALI, with similar beneficial results. Understanding direct cell crosstalk and the factors released from each cell will open the door to more accurate drugs being able to target specific pathways and offer new curative options for ARDS.