Exogenous mesenchymal stem cells affect the function of endogenous lung stem cells (club cells) in phosgene-induced lung injury

PTTG1 promotes CD34+CD45+ cells to repair the pulmonary vascular barrier via activating the VEGF-bFGF/PI3K/AKT/eNOS signaling pathway in rats with phosgene-induced acute lung injury

Accidental exposure to phosgene can cause acute lung injury (ALI), characterized by uncontrolled inflammation and impaired lung blood-gas barrier. CD34⁺CD45⁺ cells with high pituitary tumor transforming gene 1 (PTTG1) expression were identified around rat pulmonary vessels through single-cell RNA sequencing, and have been shown to attenuate P-ALI by promoting lung vascular barrier repair. As a transcription factor closely related to angiogenesis, whether PTTG1 plays a role in CD34⁺CD45⁺ cell repairing the pulmonary vascular barrier in rats with P-ALI remains unclear. This study provided compelling evidence that CD34⁺CD45⁺ cells possess endothelial differentiation potential. Rats with P-ALI were intratracheally administered with CD34⁺CD45⁺ cells transfected with or without PTTG1-overexpressing and sh-PTTG1 lentivirus. It was found that CD34⁺CD45⁺ cells reduced the pulmonary vascular permeability and mitigated the lung inflammation, which could be reversed by knocking down PTTG1. Although PTTG1 overexpression enhanced the ability of CD34⁺CD45⁺ cells to attenuate P-ALI, no significant difference was found. PTTG1 was found to regulate the endothelial differentiation of CD34⁺CD45⁺ cells. In addition, knocking down of PTTG1 significantly reduced the protein levels of VEGF and bFGF, as well as their receptors, which in turn inhibited the activation of the PI3K/AKT/eNOS signaling pathway in CD34⁺CD45⁺ cells. Moreover, LY294002 (PI3K inhibitor) treatment inhibited the endothelial differentiation of CD34⁺CD45⁺ cells, while SC79 (AKT activator) yielded the opposite effect. These findings suggest that PTTG1 can promote the endothelial differentiation of CD34⁺CD45⁺ cells by activating the VEGF-bFGF/PI3K/AKT/eNOS signaling pathway, leading to the repair of the pulmonary vascular barrier in rats with P-ALI.

Phosgene-Induced acute lung injury: Approaches for mechanism-based treatment strategies

Phosgene (COCl2) gas is a chemical intermediate of high-volume production with numerous industrial applications worldwide. Due to its high toxicity, accidental exposure to phosgene leads to various chemical injuries, primarily resulting in chemical-induced lung injury due to inhalation. Initially, the illness is mild and presents as coughing, chest tightness, and wheezing; however, within a few hours, symptoms progress to chronic respiratory depression, refractory pulmonary edema, dyspnea, and hypoxemia, which may contribute to acute respiratory distress syndrome or even death in severe cases. Despite rapid advances in medicine, effective treatments for phosgene-inhaled poisoning are lacking. Elucidating the pathophysiology and pathogenesis of acute inhalation toxicity caused by phosgene is necessary for the development of appropriate therapeutics. In this review, we discuss extant literature on relevant mechanisms and therapeutic strategies to highlight novel ideas for the treatment of phosgene-induced acute lung injury.

Antifibrotic effect of AD-1 on lipopolysaccharide-mediated fibroblast injury in L929 cells and bleomycin-induced pulmonary fibrosis in mice

20(R)-25-methoxyl-dammarane-3β,12β,20-triol (25-OCH₃-PPD, AD-1) is a dammarane ginsenoside that is isolated from Panax notoginseng. The present study aimed to explore its anti-pulmonary fibrosis (PF) effect in vitro and in vivo. L929 cells were treated with 10 μg mL^-1 lipopolysaccharide (LPS) to establish a PF model in vitro and mice were administered with 3.5 mg kg^-1 bleomycin (BLM) by endotracheal intubation to establish a PF model in vivo for investigating the anti-PF effect and its potential mechanism. The results demonstrated that AD-1 reduced the injury, extracellular matrix (ECM) buildup and α-smooth muscle actin (α-SMA) protein expression levels of L929 induced by LPS. Oral administration of AD-1 downregulated the expression of interleukins (such as IL-1β, IL-6 and IL-18), increased the expression of superoxide dismutase (SOD) and glutathione (GSH), reduced the lung coefficient and the content of hydroxyproline (HYP), and mediated the Bax/Bcl-2 protein ratio and P-p53, β-catenin and SIRT3 expression in the lung tissue of mice. Furthermore, AD-1 inhibited the expression levels of TGF-β1, TIMP-1 and α-SMA and reduced inflammatory cell infiltration and collagen deposition in the lung tissue of PF mice. These results indicated that AD-1 could alleviate PF both in vitro and in vivo, and the underlying mechanism may be related to the decrease in ECM deposition and inflammation, the enhancement of antioxidant capacity, and the mediation of lung cell apoptosis and the TGF-β1/TIMP-1/α-SMA signaling pathway, which provide a theoretical basis for the rehabilitation treatment of PF.

Hypoxia pretreatment enhances the therapeutic potential of mesenchymal stem cells (BMSCs) on ozone-induced lung injury in rats

Ozone (O₃) gas is a double-sided weapon. It provides a shield that protects life on earth from the harmful ultraviolet (UV) rays, but ground-level O₃ is considered an urban air pollutant. So, a rat model of chronic O₃ inhalation was established to assess the biochemical and morphological alterations in the lung tissue and to investigate the ameliorative effects of bone marrow-derived mesenchymal stem cells (BMSCs) with or without hypoxia pre-treatment. Forty-two adult male albino rats were divided into four groups: control, ozone-exposed, normoxic BMSC-treated, and hypoxic BMSC-treated groups. Lung tissue sections were processed for light and electron microscope examination, immunohistochemical staining for caspase 3, and iNOS. Quantitative real-time PCR for IL-1α, IL-17, TNF-α, and Nrf2 mRNA gene expression were also performed. Chronic O₃ exposure caused elevated inflammatory cytokines and decreased antioxidant Nrf2 mRNA expression. Marked morphological alterations with increased collagen deposition and elevated apoptotic markers and iNOS were evident. BMSC treatment showed immunomodulatory (decreased inflammatory cytokine gene expression), antioxidant (increased Nrf2 expression and decreased iNOS), and anti-apoptotic (decreased caspase3 expression) effects. Consequently, ameliorated lung morphology with diminished collagen deposition was observed. Hypoxia pretreatment enhanced BMSC survival by MTT assay. It also augmented the previously mentioned effects of BMSCs on the lung tissue as proved by statistical analysis. Lung morphology was similar to that of control group. In conclusion, hypoxia pretreatment represents a valuable intervention to enhance the effects of MSCs on chronic lung injury.

Mechanism of Phosgene-Induced Acute Lung Injury and Treatment Strategy

Phosgene (COCl₂) was once used as a classic suffocation poison and currently plays an essential role in industrial production. Due to its high toxicity, the problem of poisoning caused by leakage during production, storage, and use cannot be ignored. Phosgene mainly acts on the lungs, causing long-lasting respiratory depression, refractory pulmonary edema, and other related lung injuries, which may cause acute respiratory distress syndrome or even death in severe cases. Due to the high mortality, poor prognosis, and frequent sequelae, targeted therapies for phosgene exposure are needed. However, there is currently no specific antidote for phosgene poisoning. This paper reviews the literature on the mechanism and treatment strategies to explore new ideas for the treatment of phosgene poisoning.

Lung Multipotent Stem Cells of Mesenchymal Nature: Cellular Basis, Clinical Relevance, and Implications for Stem Cell Therapy

Significance: Tissue-resident stem cells are essential for normal organ homeostasis as well as for functional tissue regeneration after severe injury. Herein, mesenchymal stem cells, also designated as mesenchymal stromal cells (MSCs), contribute to the maintenance of organ integrity by their ability to replace dysfunctional cells or secrete cytokines locally and thus support the repair and healing processes of affected tissues. Recent Advances: Besides epithelial stem and progenitor cells, substantial evidence exists that tissue-resident multipotent stem cells of mesenchymal nature also exist in adult human lungs. These lung MSCs may function to regulate pulmonary tissue repair and/or regeneration, inflammation, fibrosis, and tumor formation. Critical Issues: Although therapeutically applied MSCs turned out to be a valuable therapeutic option for the prevention of lung diseases and/or the regeneration of diseased lung tissue, the true function of tissue-resident MSCs within the lung, and identification of their niche, which presumably dictates function, remain elusive. Future Directions: A detailed understanding of lung MSC localization (in the potential vascular stem cell niche) as well as of the signaling pathways controlling stem cell fate is prerequisite to unravel how (i) endogenous MSCs contribute to lung diseases, (ii) exogenous MSCs affect the proliferation of endogenous stem cells to repair damaged tissue, and (iii) a potential on-site manipulation of these cells directly within their endogenous niche could be used for therapeutic benefits. This review focuses on the central role of lung-resident MSCs, which are closely associated with the pulmonary vasculature, in a variety of chronic and acute lung diseases. Antioxid. Redox Signal. 35, 204-216.

Hypoxia-inducible Factor 2α Exerts Neuroprotective Effects by Promoting Angiogenesis via the VEGF/Notch Pathway after Intracerebral Hemorrhage Injury in Rats

Angiogenesis after intracerebral hemorrhage (ICH) injury can effectively alleviate brain damage and improve neurological function. Hypoxia-inducible factor 2α (HIF-2α) is an important angiogenic regulator and exhibits protective effects in several neurological diseases; however, its role in ICH has not yet been reported. Hence, in the present study, we explored whether HIF-2α reduces ICH injury by promoting angiogenesis. In addition, we explored the role of the vascular endothelial growth factor (VEGF)/Notch pathway in HIF-2α-mediated angiogenesis. We injected 50 μL of autologous blood taken from the femoral artery into the right striatum of healthy male adult Sprague-Dawley rats to create an autologous-blood-induced rat model of ICH. Lentiviral vectors were injected to both overexpress and knock down HIF-2α expression. VEGF receptor 2 (VEGFR2) and Notch-specific inhibitors were injected intraperitoneally to block VEGFR2- and Notch-mediated signaling after lentiviral injections. Our data showed that HIF-2α overexpression reduced neurological-damage scores and brain-water content, suggesting it had a protective effect on ICH injury. In addition, overexpression of HIF-2α promoted angiogenesis, increased focal cerebral blood flow (CBF), and reduced neuronal damage, whereas HIF-2α knockdown resulted in the opposite effects. Furthermore, we found that HIF-2α-mediated angiogenesis was blocked by a Notch-specific inhibitor. Likewise, the HIF-2α-mediated increase in phospho-VEGFR-2, cleaved-Notch1 and Notch1 expression was reversed via a VEGFR2-specific inhibitor. Taken together, our results indicate that HIF-2α promotes angiogenesis via the VEGF/Notch pathway to attenuate ICH injury. Moreover, our findings may contribute to the development of a novel strategy for alleviating ICH injury via HIF-2α-mediated upregulation of angiogenesis.

Stem cell therapy: a potential approach for treatment of influenza virus and coronavirus-induced acute lung injury

Acute lung injury (ALI), an increasingly devastating human disorder, is characterized by a multitude of lung changes arising from a wide variety of lung injuries. Viral infection is the main cause of morbidity and mortality in ALI and acute respiratory distress syndrome (ARDS) patients. In particular, influenza virus, coronavirus, and other respiratory viruses circulate in nature in various animal species and can cause severe and rapidly spread human infections. Although scientific advancements have allowed for rapid progress to be made to understand the pathogenesis and develop therapeutics after each viral pandemic, few effective methods to treat virus-induced ALI have been described. Recently, stem cell therapy has been widely used in the treatment of various diseases, including ALI. In this review, we detail the present stem cell-based therapeutics for lung injury caused by influenza virus and the outlook for the future state of stem cell therapy to deal with emerging influenza and coronaviruses.