Endothelial Progenitor Cells Attenuate Ventilator-Induced Lung Injury with Large-Volume Ventilation

Mechanisms of pulmonary endothelial barrier dysfunction in acute lung injury and acute respiratory distress syndrome

Endothelial cells (ECs) form a semi-permeable barrier between the interior space of blood vessels and the underlying tissues. Pulmonary endothelial barrier integrity is maintained through coordinated cellular processes involving receptors, signaling molecules, junctional complexes, and protein-regulated cytoskeletal reorganization. In acute lung injury (ALI) or its more severe form acute respiratory distress syndrome (ARDS), the loss of endothelial barrier integrity secondary to endothelial dysfunction caused by severe pulmonary inflammation and/or infection leads to pulmonary edema and hypoxemia. Pro-inflammatory agonists such as histamine, thrombin, bradykinin, interleukin 1β, tumor necrosis factor α, vascular endothelial growth factor, angiopoietin-2, and platelet-activating factor, as well as bacterial toxins and reactive oxygen species, cause dynamic changes in cytoskeletal structure, adherens junction disorganization, and detachment of vascular endothelial cadherin (VE-cadherin) from the actin cytoskeleton, leading to an increase in endothelial permeability. Endothelial interactions with leukocytes, platelets, and coagulation enhance the inflammatory response. Moreover, inflammatory infiltration and the associated generation of pro-inflammatory cytokines during infection cause EC death, resulting in further compromise of the structural integrity of lung endothelial barrier. Despite the use of potent antibiotics and aggressive intensive care support, the mortality of ALI is still high, because the mechanisms of pulmonary EC barrier disruption are not fully understood. In this review, we summarized recent advances in the studies of endothelial cytoskeletal reorganization, inter-endothelial junctions, endothelial inflammation, EC death, and endothelial repair in ALI and ARDS, intending to shed some light on the potential diagnostic and therapeutic targets in the clinical management of the disease.

Electroacupuncture Attenuates Ventilator-Induced Lung Injury by Modulating the Nrf2/HO-1 Pathway

INTRODUCTION

Ventilator-induced lung injury (VILI) is the most common complication associated with mechanical ventilation. Electroacupuncture (EA) has shown potent anti-inflammatory effects. This study aimed to investigate the effects of EA on VILI and explore the underlying mechanisms.

METHODS

Male C57BL/6 mice were subjected to high tidal volume ventilation to induce VILI. Prior to mechanical ventilation, mice received treatment with EA, nonacupoint EA, or EA combined with zinc protoporphyrin.

RESULTS

EA treatment significantly improved oxygenation, as indicated by increased PaO2 levels in VILI mice. Moreover, EA reduced lung injury score, lung wet/dry weight ratio, and protein concentration in bronchoalveolar lavage fluid. EA also decreased the expression of pro-inflammatory cytokines including interleukin (IL)-1β, IL-6, tumor necrosis factor-α, IL-18, chemokine keratinocyte chemoattractant, macrophage inflammatory protein 2, and malondialdehyde. Furthermore, EA increased the activities of antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase in VILI mice. At the molecular level, EA upregulated the expression of Nrf2 (nucleus) and heme oxygenase -1, while down-regulating the expression of p-NF-κB p65, NLR Family Pyrin Domain Containing 3, Cleaved Caspase-1, and ASC in VILI mice. Notably, the effects of EA were reversed by zinc protoporphyrin treatment, nonacupoint EA did not affect the aforementioned indicators of VILI.

CONCLUSIONS

EA alleviates VILI by inhibiting the NLR Family Pyrin Domain Containing three inflammasome through activation of the Nrf2/HO-1 pathway.

Aggressive alternative splicing events discovered in cecum ligation and puncture induced lung injury

AIMS

Acute lung injury (ALI) induced by sepsis and its complications have high morbidity and mortality rates globally. The objective of this study was to enhance our understanding of the underlying mechanism of ALI by identifying potential splicing events that are regulated in this condition.

MATERIALS AND METHODS

The CLP mouse model was utilized for mRNA sequencing, and the expression and splicing data were analyzed. Verification of the changes in expression and splicing induced by CLP was conducted using qPCR and RT-PCR.

RESULTS

Our results showed that splicing-related genes were regulated, suggesting that splicing regulation may be a key mechanism in ALI. We also found that more than 2900 genes displayed alternative splicing in the lungs of mice with sepsis. Using RT-PCR, we verified that TLR4 and other genes had differential splicing isoforms in the lungs of mice with sepsis. We confirmed the presence of TLR4-s in the lungs of mice with sepsis using RNA-fluorescence in situ hybridization.

CONCLUSION

Our results suggest that sepsis-induced ALI can significantly alter splicing in the lungs of mice. The list of DASGs and splicing factors is valuable for further study in the search for new treatment approaches for sepsis-induced ALI.

Transplantation of Endothelial Progenitor Cells: Summary and prospect

Endothelial Progenitor Cells (EPCs) are precursor cells of endothelial cells (ECs), which can differentiate into vascular ECs, protect from endothelial dysfunction and tissue ischemia, and reduce vascular hyperplasia. Due to these functions, EPCs are used as a candidate cell source for transplantation strategies. In recent years, a great progress was achieved in EPCs biology research, and EPCs transplantation has become a research hotspot. At present, transplanted EPCs have been used to treat ischemic diseases due to their powerful vasculogenesis and beneficial paracrine effects. Although EPCs transplantation has been proved to play an important role, the clinical application of EPCs still faces many challenges. This review briefly summarized the basic characteristics of EPCs, the process of EPCs transplantation promoting the healing of ischemic tissue, and the ways to improve the efficiency of EPCs transplantation. In addition, the application of EPCs in neurological improvement, cardiovascular and respiratory diseases and the challenges and problems in clinical application of EPCs were also discussed. In the end, the application of EPCs transplantation in regenerative medicine and tissue engineering was discussed.

A Review Into the Insights of the Role of Endothelial Progenitor Cells on Bone Biology

In addition to its important transport functions, the skeletal system is involved in complex biological activities for the regulation of blood vessels. Endothelial progenitor cells (EPCs), as stem cells of endothelial cells (ECs), possess an effective proliferative capacity and a powerful angiogenic capacity prior to their differentiation. They demonstrate synergistic effects to promote bone regeneration and vascularization more effectively by co-culturing with multiple cells. EPCs demonstrate a significant therapeutic potential for the treatment of various bone diseases by secreting a combination of growth factors, regulating cellular functions, and promoting bone regeneration. In this review, we retrospect the definition and properties of EPCs, their interaction with mesenchymal stem cells, ECs, smooth muscle cells, and immune cells in bone regeneration, vascularization, and immunity, summarizing their mechanism of action and contribution to bone biology. Additionally, we generalized their role and potential mechanisms in the treatment of various bone diseases, possibly indicating their clinical application.

SARS-CoV-2 Infection and Lung Regeneration

The lung is the primary site of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced immunopathology whereby the virus enters the host cells by binding to angiotensin-converting enzyme 2 (ACE2). Sophisticated regeneration and repair programs exist in the lungs to replenish injured cell populations. However, known resident stem/progenitor cells have been demonstrated to express ACE2, raising a substantial concern regarding the long-term consequences of impaired lung regeneration after SARS-CoV-2 infection. Moreover, clinical treatments may also affect lung repair from antiviral drug candidates to mechanical ventilation. In this review, we highlight how SARS-CoV-2 disrupts a program that governs lung homeostasis. We also summarize the current efforts of targeted therapy and supportive treatments for COVID-19 patients. In addition, we discuss the pros and cons of cell therapy with mesenchymal stem cells or resident lung epithelial stem/progenitor cells in preventing post-acute sequelae of COVID-19. We propose that, in addition to symptomatic treatments being developed and applied in the clinic, targeting lung regeneration is also essential to restore lung homeostasis in COVID-19 patients.

Paracrine mechanisms of endothelial progenitor cells in vascular repair

Endothelial progenitor cells (EPCs) play an important role in repairing damaged blood vessels and promoting neovascularization. However, the specific mechanism of EPCs promoting vascular repair is still unclear. Currently, there are two different views on the repair of damaged vessels by EPCs, one is that EPCs can directly differentiate into endothelial cells (ECs) and integrate into injured vessels, the other is that EPCs act on cells and blood vessels by releasing paracrine substances. But more evidence now supports the latter. Therefore, the paracrine mechanisms of EPCs are worth further study. This review describes the substances secreted by EPCs, some applications based on paracrine effects of EPCs, and the studies of paracrine mechanisms in cardiovascular diseases--all of these are to support the view that EPCs repair blood vessels through paracrine effects rather than integrating directly into damaged vessels.

The Elk1/MMP-9 axis regulates E-cadherin and occludin in ventilator-induced lung injury

Background

Ventilator-induced lung injury (VILI) is a common complication in the treatment of respiratory diseases with high morbidity and mortality. ETS-domain containing protein (Elk1) and Matrix metalloproteinase (MMP) 9 are involved in VILI, but the roles have not been fully elucidated. This study examined the mechanisms of the activation of MMP-9 and Elk1 regulating barrier function in VILI in vitro and in vivo.

Methods

For the in vitro study, Mouse lung epithelial cells (MLE-12) were pre-treated with Elk1 siRNA or MMP-9 siRNA for 48 h prior to cyclic stretch at 20% for 4 h. For the in vivo study, C57BL/6 mice were pre-treated with Elk1 siRNA or MMP-9 siRNA for 72 h prior to 4 h of mechanical ventilation. The expressions of Elk1, MMP-9, Tissue inhibitor of metalloproteinase 1 (TIMP-1), E-cadherin, and occludin were measured by Western blotting. The intracellular distribution of E-cadherin and occludin was shown by immunofluorescence. The degree of pulmonary edema and lung injury were evaluated by Hematoxylin–eosin (HE) staining, lung injury scores, Wet/Dry (W/D) weight ratio, total cell counts, and Evans blue dye.

Results

20% cyclic stretch and high tidal volume increases the expressions of Elk1, MMP-9, and TIMP-1, increases the ratio of MMP-9/TIMP-1, decreases the E-cadherin and occludin level. Elk1 siRNA or MMP-9 siRNA reverses the degradations of E-cadherin, occludin, and the ratio of MMP-9/TIMP-1 caused by cyclic stretch. Elk1 siRNA decreases the MMP-9 level with or not 20% cyclic stretch and high tidal volume.

Conclusions

The results demonstrate mechanical stretch damages the tight junctions and aggravates the permeability in VILI, Elk1 plays an important role in affecting the tight junctions and permeability by regulating the balance of MMP-9 and TIMP-1, thus indicating the therapeutic potential of Elk1 to treat VILI.

Identification of significant alteration genes, pathways and TFs induced by LPS in ARDS via bioinformatical analysis

Background and aims

Acute respiratory distress syndrome (ARDS) or acute lung injury (ALI) is one of the most common acute thoracopathy with complicated pathogenesis in ICU. The study is to explore the differentially expressed genes (DEGs) in the lung tissue and underlying altering mechanisms in ARDS.

Methods

Gene expression profiles of GSE2411 and GSE130936 were available from GEO database, both of them included in GPL339. Then, an integrated analysis of these genes was performed, including gene ontology (GO) and KEGG pathway enrichment analysis in DAVID database, protein–protein interaction (PPI) network construction evaluated by the online database STRING, Transcription Factors (TFs) forecasting based on the Cytoscape plugin iRegulon, and their expression in varied organs in The Human Protein Atlas.

Results

A total of 39 differential expressed genes were screened from the two datasets, including 39 up-regulated genes and 0 down-regulated genes. The up-regulated genes were mainly enriched in the biological process, such as immune system process, innate immune response, inflammatory response, and also involved in some signal pathways, including cytokine–cytokine receptor interaction, Salmonella infection, Legionellosis, Chemokine, and Toll-like receptor signal pathway with an integrated analysis. GBP2, IFIT2 and IFIT3 were identified as hub genes in the lung by PPI network analysis with MCODE plug-in, as well as GO and KEGG re-enrichment. All of the three hub genes were regulated by the predictive common TFs, including STAT1, E2F1, IRF1, IRF2, and IRF9.

Conclusions

This study implied that hub gene GBP2, IFIT2 and IFIT3, which might be regulated by STAT1, E2F1, IRF1, IRF2, or IRF9, played significant roles in ARDS. They could be potential diagnostic or therapeutic targets for ARDS patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06578-7.

Effect and Mechanism Study of Sodium Houttuyfonate on Ventilator-Induced Lung Injury by Inhibiting ROS and Inflammation

PURPOSE

Ventilator-induced lung injury (VILI) is a serious complication of mechanical ventilation (MV) that increases morbidity and mortality of patients receiving ventilator treatment. This study aimed to reveal the molecular mechanism of sodium houttuyfonate (SH) on VILI.

MATERIALS AND METHODS

The male mice VILI model was established by high tidal volume ventilation. The cell model was established by performing cell stretch (CS) experiments on murine respiratory epithelial cells MLE-15. In addition, the JNK activator Anisomycin and JNK inhibitor SP600125 were used on VILI mice and CS-treated cells.

RESULTS

VILI modeling damaged the structural integrity, increased apoptosis and wet-to-dry (W/D) ratio, enhanced the levels of inflammatory factors, reactive oxygen species (ROS) and malonaldehyde (MDA), and activated JNK pathway in lung tissues. SH gavage alleviated lung injury, decreased apoptosis and W/D ratio, and reduced levels of inflammatory factors, ROS and MDA, and p-JNK/JNK expression of lung tissues in VILI mice. However, activation of JNK wiped the protective effect of SH on VILI. Contrary results were found in experiments with JNK inhibitor SP600125.

CONCLUSION

SH relieved VILI by inhibiting the ROS-mediated JNK pathway.

Lipoxin A4 Reduces Ventilator-Induced Lung Injury in Rats with Large-Volume Mechanical Ventilation

Ventilator-induced lung injury (VILI) is a severe and inevitable complication in patients who require mechanical ventilation (MV) for respiratory support. Lipoxin A4 is an endogenous anti-inflammatory and antioxidant mediator. The present study determined the effects of lipoxin A4 on VILI. Twenty-four rats were randomized to the sham, VILI, and lipoxin A4 (LX4) groups. The rats in the VILI and LX4 groups received large-volume MV for 4 hours to simulate VILI. Capillary permeability was evaluated using the PaO₂/FiO₂ ratio, lung wet/dry weight ratio, and protein level in the lung. VILI-induced inflammation was assessed by measuring cytokines in serum and lung tissue, the expression and activity of NF-κB, and phosphorylated myosin light chain. The oxidative stress response, lung tissue injury, and apoptosis in lung tissue were also estimated, and the expression of apoptotic proteins was examined. MV worsened all of the indices compared to the sham group. Compared to the VILI group, the LX4 group showed significantly improved alveolar-capillary permeability (increased PaO₂/FiO₂ and decreased wet/dry weight ratios and protein levels), ameliorated histological injury, and reduced local and systemic inflammation (downregulated proinflammatory factors and NF-κB expression and activity). Lipoxin A4 notably inhibited the oxidative stress response and apoptosis and balanced apoptotic protein levels in lung tissue. Lipoxin A4 protects against VILI via anti-inflammatory, antioxidant, and antiapoptotic effects.

Evidence of Accumulated Endothelial Progenitor Cells in the Lungs of Rats with Pulmonary Arterial Hypertension by 89Zr-oxine PET Imaging

Endothelial progenitor cells (EPCs) play a major role in regulating pulmonary vascular remodeling during pulmonary arterial hypertension (PAH) development. Several preclinical and clinical trials of EPCs transplantation have been performed for the treatment of PAH. However, there is no reliable method to monitor real-time cell trafficking and quantify transplanted EPCs. Here in this paper we isolated EPCs from human peripheral blood, identified their functional integrity, and efficiently labeled the EPCs with ⁸⁹Zr-oxine and DiO. Labeled EPCs were injected into the tail vein of normal and PAH rats to be tracked in vivo. From the microPET/CT images, we found EPCs were distributed primarily in the lung at 1 h and then migrated to the liver and spleen. We could observe the 3,3′ dioctadecyloxacarbocyanine perchlorate (DiO)-labeled EPCs binding in the pulmonary vasculature by CellVizio confocal. The result of quantitative analysis revealed significantly higher accumulation of EPCs in the lungs of PAH rats than in those of healthy rats. The distribution and higher accumulation of EPCs in the lungs of PAH rats could help to evaluate the safety and provide evidence of effectiveness of EPC therapy.

Propofol alleviates ventilator-induced lung injury through regulating the Nrf2/NLRP3 signaling pathway

Ventilator-induced lung injury (VILI) causes problems during acute lung injury treatment, and propofol is a well-known drug to prevent VILI. Herein, we discussed how propofol protects against VILI-induced inflammation with the interaction of nuclear factor E2-related factor 2 (Nrf2)/NOD-like receptor protein 3 (NLRP3). We established VILI mouse models for collecting lung tissues, and these mice were later treated with propofol and Nrf2/NLRP3 activator or inhibitor to observe their effects on VILI with inflammatory factors, 8-hydroxy-2 deoxyguanosine, malondialchehyche level, mitochondrial reactive oxygen species production rate, lung wet/dry weight ratio, lung permeability index measured. Propofol treatment improved VILI, alleviated pulmonary inflammation induced by mechanical ventilation. Propofol up-regulated Nrf2 and down-regulated NLRP3 in VILI model. Activating Nrf2 or inhibiting NLRP3 downregulated pro-inflammatory factors in lung tissues in VILI mice. Above all, we can conclude that propofol exerts it protective function against VILI and the subsequent inflammatory responses through activating Nrf2 and inhibiting NLRP3 expression. Therefore, Nrf2 activator and NLRP3 inhibitor might be latent targets in the VILI prevention.