Lung Stem Cells Research Articles

Lung Tissue Engineering: Toward a More Deliberate Approach.

Chronic lung disease remains a leading cause of morbidity and mortality. Given the dearth of definitive therapeutic options, there is an urgent need to augment the pool of donor organs for transplantation. One strategy entails building a lung ex vivo in the laboratory. The past decade of whole lung tissue engineering has laid a foundation of systems and strategies for this approach. Meanwhile, tremendous progress in lung stem cell biology is elucidating cues contributing to alveolar repair, and speaks to the potential of whole lung regeneration in the future. This perspective discusses the key challenges facing the field and highlights opportunities to combine insights from biology with engineering strategies to adopt a more deliberate, and ultimately successful, approach to lung engineering.

Telomere Dysfunction in Idiopathic Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis is an age-dependent progressive and fatal lung disease of unknown etiology, which is characterized by the excessive accumulation of extracellular matrix inside the interstitial layer of the lung parenchyma that leads to abnormal scar architecture and compromised lung function capacity. Recent genetic studies have attributed the pathological genes or genetic mutations associated with familial idiopathic pulmonary fibrosis (IPF) and sporadic IPF to telomere-related components, suggesting that telomere dysfunction is an important determinant of this disease. In this study, we summarized recent advances in our understanding of how telomere dysfunction drives IPF genesis. We highlighted the key role of alveolar stem cell dysfunction caused by telomere shortening or telomere uncapping, which bridged the gap between telomere abnormalities and fibrotic lung pathology. We emphasized that senescence-associated secretory phenotypes, innate immune cell infiltration, and/or inflammation downstream of lung stem cell dysfunction influenced the native microenvironment and local cell signals, including increased transforming growth factor-beta (TGF-β) signaling in the lung, to induce pro-fibrotic conditions. In addition, the failed regeneration of new alveoli due to alveolar stem cell dysfunction might expose lung cells to elevated mechanical tension, which could activate the TGF-β signaling loop to promote the fibrotic process, especially in a periphery-to-center pattern as seen in IPF patients. Understanding the telomere-related molecular and pathophysiological mechanisms of IPF would provide new insights into IPF etiology and therapeutic strategies for this fatal disease.

Total Lymphatic Irradiation as Part of Conditioning in Pediatric Hematopoietic Stem Cell Transplantation: A Single Institution Experience From a Radiation Oncology Perspective

Purpose/Objective(s)Total lymphatic irradiation (TLI) is a procedure in which a patient's major lymph nodes and spleen are treated with low doses of radiation for recipient immunosuppression as part of multi-agent conditioning for cardiac, lung or hematopoietic stem cell transplantation, to facilitate engraftment and to decrease the risk of rejection. TLI is considered an attractive option instead of total body irradiation (TBI) to mitigate side effects of radiation exposure to normal tissues. There are no established guidelines on technique and dose fractionation. Herein, we share our experience.Materials/MethodsRetrospective review of children who received TLI for hematopoietic stem cell transplants at the hospital was done.ResultsTwenty-two patients who had TLI from 2004 to 2020, with a median age of 7.5 years (range 0.9-19.0) were included. Twelve had benign conditions and 10 had malignant conditions. Eighteen had haploidentical grafts, 2 had matched sibling and 2 had unrelated donors. Four patients had previously failed engraftment prior to TLI. Conditioning included multi-agent chemotherapy for all including rabbit-ATG for 12 patients. All patients had computer-tomographic scans simulation except for 2 patients who were treated in the earlier years when only orthogonal XR was available. Dose fractionation was single prior to 2017 (5-7Gy/1#) and in recent times more fractionated (6-7.5Gy/3#). The treatment targets were the spleen and the following nodal stations: cervical, axillary, mediastinal, hilar, paraaortic, pelvic, inguinal and femoral. Normal organs including the medial thyroid, heart, lungs, and abdominal organs were shielded with multi-leaf collimators using three-dimensional conformal technique (Figure 1, 2). Of 12 patients with benign conditions, all are alive at last follow up. Of 10 patients with malignant conditions, 3 are dead from disease. Five out of 12 patients who had haploidentical grafts, 0/2 matched sibling graft and 1/2 unrelated grafts experienced rejection. The median follow up is 14.0 months (IQR 6-41.5). None developed acute pneumonitis. One patient developed thyroid cancer 14 years after TLI.ConclusionHerein we describe our TLI experience and technique. More studies should be undertaken to evaluate the safety and efficacy of TLI compared to TBI. Going forward, a consensus on technique and dose should be developed. Total lymphatic irradiation (TLI) is a procedure in which a patient's major lymph nodes and spleen are treated with low doses of radiation for recipient immunosuppression as part of multi-agent conditioning for cardiac, lung or hematopoietic stem cell transplantation, to facilitate engraftment and to decrease the risk of rejection. TLI is considered an attractive option instead of total body irradiation (TBI) to mitigate side effects of radiation exposure to normal tissues. There are no established guidelines on technique and dose fractionation. Herein, we share our experience. Retrospective review of children who received TLI for hematopoietic stem cell transplants at the hospital was done. Twenty-two patients who had TLI from 2004 to 2020, with a median age of 7.5 years (range 0.9-19.0) were included. Twelve had benign conditions and 10 had malignant conditions. Eighteen had haploidentical grafts, 2 had matched sibling and 2 had unrelated donors. Four patients had previously failed engraftment prior to TLI. Conditioning included multi-agent chemotherapy for all including rabbit-ATG for 12 patients. All patients had computer-tomographic scans simulation except for 2 patients who were treated in the earlier years when only orthogonal XR was available. Dose fractionation was single prior to 2017 (5-7Gy/1#) and in recent times more fractionated (6-7.5Gy/3#). The treatment targets were the spleen and the following nodal stations: cervical, axillary, mediastinal, hilar, paraaortic, pelvic, inguinal and femoral. Normal organs including the medial thyroid, heart, lungs, and abdominal organs were shielded with multi-leaf collimators using three-dimensional conformal technique (Figure 1, 2). Of 12 patients with benign conditions, all are alive at last follow up. Of 10 patients with malignant conditions, 3 are dead from disease. Five out of 12 patients who had haploidentical grafts, 0/2 matched sibling graft and 1/2 unrelated grafts experienced rejection. The median follow up is 14.0 months (IQR 6-41.5). None developed acute pneumonitis. One patient developed thyroid cancer 14 years after TLI. Herein we describe our TLI experience and technique. More studies should be undertaken to evaluate the safety and efficacy of TLI compared to TBI. Going forward, a consensus on technique and dose should be developed.

Therapeutic Targeting of Cancer Stem Cells in Lung, Head and Neck, and Bladder Cancers

Simple SummaryEffective cancer treatment hinges upon overcoming therapeutic resistance mechanisms that allow for the continued proliferation of cancer cell subpopulations. Exposure to pharmacotherapy invariably leads to resistance as tumor cells with selected advantageous features evade destruction and alter the tumor composition. Cancer stem cells (CSCs) with features of plasticity that allow for regeneration and differentiation are particularly responsible for this phenomenon. Advances in tumor biology and molecular signaling have highlighted their role in neoplastic initiation, invasion, and maintenance. Novel strategies to direct therapy against these tumor cell subpopulations have the potential to dramatically alter tumor response and change the course of cancer care. Resistance to cancer therapy remains a significant obstacle in treating patients with various solid malignancies. Exposure to current chemotherapeutics and targeted agents invariably leads to therapy resistance, heralding the need for novel agents. Cancer stem cells (CSCs)—a subpopulation of tumor cells with capacities for self-renewal and multi-lineage differentiation—represent a pool of therapeutically resistant cells. CSCs often share physical and molecular characteristics with the stem cell population of the human body. It remains challenging to selectively target CSCs in therapeutically resistant tumors. The generation of CSCs and induction of therapeutic resistance can be attributed to several deregulated critical growth regulatory signaling pathways such as WNT/β-catenin, Notch, Hippo, and Hedgehog. Beyond growth regulatory pathways, CSCs also change the tumor microenvironment and resist endogenous immune attack. Thus, CSCs can interfere with each stage of carcinogenesis from malignant transformation to the onset of metastasis to tumor recurrence. A thorough review of novel targeted agents to act against CSCs is fundamental for advancing cancer treatment in the setting of both intrinsic and acquired resistance.

Lung Cancer Stem Cells and Their Clinical Implications.

It is now widely accepted that stem cells exist in various cancers, including lung cancer, which are referred to as cancer stem cells (CSCs). CSCs are defined in this context as the subset of tumor cells with the ability to form tumors in serial transplantation and cloning assays and form tumors at metastatic sites. Mouse models of lung cancer have shown that lung CSCs reside in niches that are essential for the maintenance of stemness, plasticity, enable antitumor immune evasion, and provide metastatic potential. Similar to normal lung stem cells, Notch, Wnt, and the Hedgehog signaling cascades have been recruited by the CSCs to regulate stemness and also provide therapy-driven resistance in lung cancer. Compounds targeting β-catenin and Sonic hedgehog (Shh) activity have shown promising anti-CSC activity in preclinical murine models of lung cancer. Understanding CSCs and their niches in lung cancer can answer fundamental questions pertaining to tumor maintenance and associated immune regulation and escape that appear important in the quest to develop novel lung cancer therapies and enhance sensitivity to currently approved chemo-, targeted-, and immune therapeutics.

Lentiviral vectors transduce lung stem cells without disrupting plasticity

Life-long expression of a gene therapy agent likely requires targeting stem cells. Here we ask the question: does viral vector transduction or ectopic expression of a therapeutic transgene preclude airway stem cell function? We used a lentiviral vector containing a GFP or cystic fibrosis transmembrane conductance regulator (CFTR) transgene to transduce primary airway basal cells from human cystic fibrosis (CF) or non-CF lung donors and monitored expression and function after differentiation. Ussing chamber measurements confirmed CFTR-dependent chloride channel activity in CF donor cells. Immunostaining, quantitative real-time PCR, and single-cell sequencing analysis of cell-type markers indicated that vector transduction or CFTR expression does not alter the formation of pseudostratified, fully differentiated epithelial cell cultures or cell type distribution. These results have important implications for use of gene addition or gene editing strategies as life-long curative approaches for lung genetic diseases.

VEGF receptor 2 (KDR) protects airways from mucus metaplasia through a Sox9-dependent pathway.

Mucus-secreting goblet cells are the dominant cell type in pulmonary diseases, e.g., asthma and cystic fibrosis (CF), leading to pathologic mucus metaplasia and airway obstruction. Cytokines including IL-13 are the major players in the transdifferentiation of club cells into goblet cells. Unexpectedly, we have uncovered a previously undescribed pathway promoting mucous metaplasia that involves VEGFa and its receptor KDR. Single-cell RNA sequencing analysis coupled with genetic mouse modeling demonstrates that loss of epithelial VEGFa, KDR, or MEK/ERK kinase promotes excessive club-to-goblet transdifferentiation during development and regeneration. Sox9 is required for goblet cell differentiation following Kdr inhibition in both mouse and human club cells. Significantly, airway mucous metaplasia in asthmatic and CF patients is also associated with reduced KDR signaling and increased SOX9 expression. Together, these findings reveal an unexpected role for VEGFa/KDR signaling in the defense against mucous metaplasia, offering a potential therapeutic target for this common airway pathology.

In silico analysis suggests the RNAi-enhancing antibiotic enoxacin as a potential inhibitor of SARS-CoV-2 infection

COVID-19 has currently become the biggest challenge in the world. There is still no specific medicine for COVID-19, which leaves a critical gap for the identification of new drug candidates for the disease. Recent studies have reported that the small-molecule enoxacin exerts an antiviral activity by enhancing the RNAi pathway. The aim of this study is to analyze if enoxacin can exert anti-SARS-CoV-2 effects. We exploit multiple computational tools and databases to examine (i) whether the RNAi mechanism, as the target pathway of enoxacin, could act on the SARS-CoV-2 genome, and (ii) microRNAs induced by enoxacin might directly silence viral components as well as the host cell proteins mediating the viral entry and replication. We find that the RNA genome of SARS-CoV-2 might be a suitable substrate for DICER activity. We also highlight several enoxacin-enhanced microRNAs which could target SARS-CoV-2 components, pro-inflammatory cytokines, host cell components facilitating viral replication, and transcription factors enriched in lung stem cells, thereby promoting their differentiation and lung regeneration. Finally, our analyses identify several enoxacin-targeted regulatory modules that were critically associated with exacerbation of the SARS-CoV-2 infection. Overall, our analysis suggests that enoxacin could be a promising candidate for COVID-19 treatment through enhancing the RNAi pathway.

Club Cell Functions As A Wnt‐responsible Progenitor For Tissue Repair In COPD

Introduction Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide that is characterized by progressive loss of alveolar tissue. Endogenous lung stem cells and tissue repair pathways are thought be dysfunctional and their reactivation is a promising therapeutic approach for COPD. Wnt/β-catenin signaling is critical for stem cell function and is reduced in human COPD lungs. We have previously demonstrated that therapeutic Wnt/β-catenin initiated tissue repair in COPD patient-derived lung tissue ex vivo. Recently, we identified an epithelial progenitor population, which were activated by Wnt/β-catenin signaling to form alveolar organoids. Thus, we hypothesize that club cells represent a novel Wnt-responsive epithelial progenitor for tissue repair in COPD. Methods Single cell RNA sequencing (scRNA seq), organoid assay, fate tracing studies, flow cytometry, immunofluorescence, FACS sorting, porcine pancreatic elastase (PPE) induced mouse COPD model. Results First, using scRNA seq, we identified club cells as the major progenitor cells in the Wnt-responsive epithelial progenitor cell population. Further, we perform fate tracing studies using a Scgb1a1Cre-ERT;Rosa-Tomato;TCF/Lef:H2B-GFP mouse line combined with lung organoid assays to further demonstrate that activation of the Wnt/β-catenin signaling using the GSK3β inhibitor CHIR9920 increased the number of alveolar organoids formed by club cells. Finally, in a PPE-induced mouse COPD model, we identified an impaired organoid forming capacity of club cells, which could be restored by activation of the Wnt/β-catenin signaling. Conclusion Our study reveals a novel mechanism of club cell activation by Wnt/β-catenin signaling in COPD.

Antenatal Thymosin β4: a New Tool for Accelerating Fetal Development in Preterms? Thymosin Beta-4: a Breakthrough in the “Physiological” Regenerative Medicine in Preterm Newborns

To prevent the health risks related to prematurity, multiple drugs have been introduced in clinical practice in recent years. This paper focuses on a new "physiological" regenerative approach to be started in the perinatal period, particularly on very low birth weight preterm infants. This new preventive approach underlined the necessity to start regenerative medicine very early after birth, a period in which kidney, brain, pancreas, and lung stem cells maintain their proliferative and differentiating abilities. Among the multiple factors proposed in the literature as potential growth promoters for preterm neonates, thymosin beta-4 (Tβ4) has been indicated as one of the most important candidates for regenerative medicine.

Stem cells in pulmonary alveolar regeneration.

The lungs are constantly exposed to the external environment and are therefore vulnerable to insults that can cause infection and injury. Maintaining the integrity and barrier function of the lung epithelium requires complex interactions of multiple cell lineages. Elucidating the cellular players and their regulation mechanisms provides fundamental information to deepen understanding about the responses and contributions of lung stem cells. This Review focuses on advances in our understanding of mammalian alveolar epithelial stem cell subpopulations and discusses insights about the regeneration-specific cell status of alveolar epithelial stem cells. We also consider how these advances can inform our understanding of post-injury lung repair processes and lung diseases.

Stem Cell-derived Respiratory Epithelial Cell Cultures as Human Disease Models.

Advances in stem cell biology and the understanding of factors that determine lung stem cell self-renewal have enabled long-term in vitro culture of human lung cells derived from airway basal and alveolar type II cells. Improved capability to expand and study primary cells long term, including in clonal cultures that are recently derived from a single cell, will allow experiments that address fundamental questions about lung homeostasis and repair, as well as translational questions in asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, and lung cancer research. Here, we provide a brief history of postnatal lung epithelial cell culture and describe recent methodological advances. We further discuss the applications of primary cultures in defining "normal" epithelium, in modeling lung disease, and in future cell therapies.

Benzo[a]pyrene induces fibrotic changes and impairs differentiation in lung stem cells

Human activities have generated air pollution, with extremely small particles (PM 2.5, particulate matter less than 2.5 µm in diameter) and liquid droplets, which become a menace to human health. Among the pollutants, polycyclic aromatic hydrocarbons (PAHs), which enhance the risks of pulmonary dysfunction and cancer development, have been extensively studied. Numerous studies have addressed the effects of PAHs on the respiratory system, whereas the effects on lung stem/progenitor cells remain unknown. Here, we provide evidence that benzo[a]pyrene (BaP), a major toxic PAH, induces fibrotic changes with a loss of α-1,6-fucosylation in CD54+CD157+CD45− cells (lung stem cells). In studies with aryl hydrocarbon receptor (AHR) antagonist, we found that these effects by BaP are independent of the canonical AHR pathway. In addition, these BaP-induced fibrotic changes are reduced by TGF-β antagonist, suggesting an alternative pathway of BaP toxicity is different from other PAH/AHR signaling pathways. Finally, it was observed that BaP impairs the spheroid formation and the podoplanin expression of CD54+CD157+CD45− cells, indicating that BaP suppresses the differentiation of lung stem cells. Taken together, our findings reveal specific BaP-induced injuries in CD54+CD157+CD45− cells.

Optimizing the in vitro colony-forming assay for more efficient delineation of the interaction between lung epithelial stem cells and their niche.

The use of in vitro 3D organoid/colony forming assay (CFA); which mimics the in vivo environment have provided insight into the mechanisms by which lung stem cells maintain and repair the lung. In recent years, the use of CFA has markedly expanded. However, variations among laboratories in lung cell isolation methods, media used, type, origin, and processing methods of mesenchymal cells used as feeders for the epithelial colonies, and terms utilized to describe and quantify the growing colonies, have caused difficulty in reproducing results among different labs. In this study, we compared several previously described methods for lung cell isolation and culture media, to identify their influence on retrieved cells and growing colonies. We also characterized the effect of freeze/thaw, and propagation of fibroblasts on their ability to support epithelial colonies. Importantly, we suggested markers to identify fibroblast subtypes that offer the best support to alveolar stem cell proliferation. Then, we used our optimized assay to confirm the in vitro identity of recently described epithelial progenitors. We also tested the effect of hyperoxia on lung stem cells, and examined the expression of the receptors for the SARS-COV-2 virus's entry into epithelial cells, on our organoids. In summary, our findings facilitate CFA standardization, help understand how niche cell variations influence growing colonies, and confirm some of the recently described lung stem cells.

Stem Cells, Cell Therapies, and Bioengineering in Lung Biology and Disease 2019.

A workshop entitled “Stem Cells, Cell Therapies and Bioengineering in Lung Biology and Diseases” was hosted by the University of Vermont Larner College of Medicine in collaboration with the National Heart, Lung and Blood Institute, the Alpha-1 Foundation, the Cystic Fibrosis Foundation, the International Society for Cell and Gene Therapy and the Pulmonary Fibrosis Foundation. The event was held from July 15 to 18, 2019 at the University of Vermont, Burlington, Vermont. The objectives of the conference were to review and discuss the current status of the following active areas of research: 1) technological advancements in the analysis and visualisation of lung stem and progenitor cells; 2) evaluation of lung stem and progenitor cells in the context of their interactions with the niche; 3) progress toward the application and delivery of stem and progenitor cells for the treatment of lung diseases such as cystic fibrosis; 4) progress in induced pluripotent stem cell models and application for disease modelling; and 5) the emerging roles of cell therapy and extracellular vesicles in immunomodulation of the lung. This selection of topics represents some of the most dynamic research areas in which incredible progress continues to be made. The workshop also included active discussion on the regulation and commercialisation of regenerative medicine products and concluded with an open discussion to set priorities and recommendations for future research directions in basic and translation lung biology.

Small GTPase RAB6 deficiency promotes alveolar progenitor cell renewal and attenuates PM2.5-induced lung injury and fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease characterized by chronic non-specific inflammation of the interstitial lung and extensive deposition of collagen fibers leading to destruction of lung function. Studies have demonstrated that exposure to fine particulate matter (PM2.5) increases the risk of IPF. In order to recover from PM2.5-induced lung injury, alveolar epithelial cells need to be repaired and regenerated to maintain lung function. Type 2 alveolar epithelial cells (AEC2) are stem cells in the adult lung that contribute to the lung repair process through complex signaling. Our previous studies demonstrated that RAB6, a RAS family member lowly expressed in lung cancer, inhibited lung cancer stem cell self-renewal, but it is unclear whether or not and how RAB6 may regulate AEC2 cell proliferation and self-renewal in PM2.5-induced pulmonary fibrosis. Here, we demonstrated that knockout of RAB6 inhibited pulmonary fibrosis, oxidative stress, and AEC2 cell death in PM2.5-injured mice. In addition, knockout of RAB6 decreased Dickkopf 1(DKK1) autocrine and activated proliferation, self-renewal, and wnt/β-catenin signaling of PM2.5-injured AEC2 cells. RAB6 overexpression increased DKK1 autocrine and inhibited proliferation, self-renewal and wnt/β-catenin signaling in AEC2 cells in vitro. Furthermore, DKK1 inhibitors promoted proliferation, self-renewal and wnt/β-catenin signaling of RAB6 overexpressing AEC2 cells, and attenuated PM2.5-induced pulmonary fibrosis in mice. These data establish RAB6 as a regulator of DKK1 autocrine and wnt/β-catenin signal that serves to regulate AEC2 cell proliferation and self-renewal, and suggest a mechanism that RAB6 disruption may promote AEC2 cell proliferation and self-renewal to enhance lung repair following PM2.5 injury.

Radiation Induces Pulmonary Fibrosis by Promoting the Fibrogenic Differentiation of Alveolar Stem Cells.

The lung is a radiosensitive organ, which imposes limits on the therapeutic dose in thoracic radiotherapy. Irradiated alveolar epithelial cells promote radiation-related pneumonitis and fibrosis. However, the role of lung stem cells (LSCs) in the development of radiation-induced lung injury is still unclear. In this study, we found that both LSCs and LSC-derived type II alveolar epithelial cells (AECII) can repair radiation-induced DNA double-strand breaks, but the irradiated LSCs underwent growth arrest and cell differentiation faster than the irradiated AECII cells. Moreover, radiation drove LSCs to fibrosis as shown with the elevated levels of markers for epithelial-mesenchymal transition and myofibroblast (α-smooth muscle actin (α-SMA)) differentiation in in vitro and ex vivo studies. Increased gene expressions of connective tissue growth factor and α-SMA were found in both irradiated LSCs and alveolar cells, suggesting that radiation could induce the fibrogenic differentiation of LSCs. Irradiated LSCs showed an increase in the expression of surfactant protein C (SP-C), the AECII cell marker, and α-SMA, and irradiated AECII cells expressed SP-C and α-SMA. These results indicated that radiation induced LSCs to differentiate into myofibroblasts and AECII cells; then, AECII cells differentiated further into either myofibroblasts or type I alveolar epithelial cells (AECI). In conclusion, our results revealed that LSCs are sensitive to radiation-induced cell damage and may be involved in radiation-induced lung fibrosis.

DNA repair enzyme OGG1 promotes alveolar progenitor cell renewal and relieves PM2.5-induced lung injury and fibrosis

Fine particulate matter (PM2.5) airborne pollution increases the risk of chronic respiratory diseases, such as idiopathic pulmonary fibrosis (IPF), which is characterized by non-specific inflammation of the interstitial lung and extensive deposition of collagen fibers. Type 2 alveolar epithelial cells (AEC2s) are alveolar stem cells in the adult lung that contribute to the lung repair process through complex signaling. Our previous studies demonstrated that OGG1, a kind of DNA repair enzyme, have a critical role in protecting cells from oxidative damage and apoptosis induced by PM2.5, but the contribution of OGG1 in proliferation and self-renewal of AEC2s is not known. Here, we constructed OGG1−/−mice to test the effect and mechanism of OGG1 on PM2.5-induced pulmonary fibrosis and injury in vivo. We detected proliferation and self-renewal of OGG1 overexpression or OGG1 knockout AEC2s after PM2.5 injury by flow cytometry and clone formation. We observed that knockout of OGG1 aggravated pulmonary fibrosis, oxidative stress, and AEC2 cell death in PM2.5-injured mice. In addition, OGG1 is required for the proliferation and renewal of AEC2s after PM2.5 injury. Overexpression of OGG1 promotes the proliferation and self-renewal of AEC2s by inhibiting PM2.5-mediated oxidative stress and NF-κB signaling hyperactivation in vitro. Furthermore, NF-κB inhibitors promoted proliferation and self-renewal of OGG1-deficient AEC2s cells after PM2.5 injury, and attenuated PM2.5-induced pulmonary fibrosis and injury in mice. These data establish OGG1 as a regulator of NF-κB signal that serves to regulate AEC2 cell proliferation and self-renewal, and suggest a mechanism that inhibition of the NF-κB signaling pathway may represent a potential therapeutic strategy for IPF patients with low-expression of OGG1.

Regulation of JAM2 Expression in the Lungs of Streptozotocin-Induced Diabetic Mice and Human Pluripotent Stem Cell-Derived Alveolar Organoids.

Hyperglycemia is a causative factor in the pathogenesis of respiratory diseases, known to induce fibrosis and inflammation in the lung. However, little attention has been paid to genes related to hyperglycemic-induced lung alterations and stem cell applications for therapeutic use. In this study, our microarray data revealed significantly increased levels of junctional adhesion molecule 2 (JAM2) in the high glucose (HG)-induced transcriptional profile in human perivascular cells (hPVCs). The elevated level of JAM2 in HG-treated hPVCs was transcriptionally and epigenetically reversible when HG treatment was removed. We further investigated the expression of JAM2 using in vivo and in vitro hyperglycemic models. Our results showed significant upregulation of JAM2 in the lungs of streptozotocin (STZ)-induced diabetic mice, which was greatly suppressed by the administration of conditioned medium obtained from human mesenchymal stem cell cultures. Furthermore, JAM2 was found to be significantly upregulated in human pluripotent stem cell-derived multicellular alveolar organoids by exposure to HG. Our results suggest that JAM2 may play an important role in STZ-induced lung alterations and could be a potential indicator for predicting the therapeutic effects of stem cells and drugs in diabetic lung complications.

Stem cells and lung regeneration.

The ability to replace defective cells in an airway with cells that can engraft, integrate, and restore a functional epithelium could potentially cure a number of lung diseases. Progress toward the development of strategies to regenerate the adult lung by either in vivo or ex vivo targeting of endogenous stem cells or pluripotent stem cell derivatives is limited by our fundamental lack of understanding of the mechanisms controlling human lung development, the precise identity and function of human lung stem and progenitor cell types, and the genetic and epigenetic control of human lung fate. In this review, we intend to discuss the known stem/progenitor cell populations, their relative differences between rodents and humans, their roles in chronic lung disease, and their therapeutic prospects. Additionally, we highlight the recent breakthroughs that have increased our understanding of these cell types. These advancements include novel lineage-traced animal models and single-cell RNA sequencing of human airway cells, which have provided critical information on the stem cell subtypes, transition states, identifying cell markers, and intricate pathways that commit a stem cell to differentiate or to maintain plasticity. As our capacity to model the human lung evolves, so will our understanding of lung regeneration and our ability to target endogenous stem cells as a therapeutic approach for lung disease.