Mechanical stress induces lung fibrosis by epithelial-mesenchymal transition

Diffuse tumors: Molecular determinants shared by different cancer types

Most cancer types have both diffuse and non-diffuse subtypes, which have rather distinct morphologies, namely scattered tiny tumors vs. one solid tumor, and different levels of aggressiveness. However, the causes for forming such distinct subtypes remain largely unknown. Using the diffuse and non-diffuse gastric cancers (GCs) as the illustrative example, we present a computational study based on the transcriptomic data from the TCGA and GEO databases, to address the following questions: (i) What are the key molecular determinants that give rise to the distinct morphologies between diffuse and non-diffuse cancers? (ii) What are the main reasons for diffuse cancers to be generally more aggressive than non-diffuse ones of the same cancer type? (iii) What are the reasons for their distinct immunoactivities? And (iv) why do diffuse cancers on average tend to take place in younger patients? The study is conducted using the framework we have previously developed for elucidation of general drivers cancer formation and development. Our main discoveries are: (a) the level of (poly-) sialic acids deployed on the surface of cancer cells is a significant factor contributing to questions (i) and (ii); (b) poly-sialic acids synthesized by ST8SIA4 are the key to question (iii); and (c) the circulating growth factors specifically needed by the diffuse subtype dictate the answer to question (iv). All these predictions are substantiated by published experimental studies. Our further analyses on breast, prostate, lung, liver, and thyroid cancers reveal that these discoveries generally apply to the diffuse subtypes of these cancer types, hence indicating the generality of our discoveries.

Excessive mechanical loading promotes osteoarthritis development by upregulating Rcn2

Exposure of articular cartilage to excessive mechanical loading is closely related to the pathogenesis of osteoarthritis (OA). However, the exact molecular mechanism by which excessive mechanical loading drives OA remains unclear. In vitro, primary chondrocytes were exposed to cyclic tensile strain at 0.5 Hz and 10 % elongation for 30 min to simulate excessive mechanical loading in OA. In vivo experiments involved mice undergoing anterior cruciate ligament transection (ACLT) to model OA, followed by interventions on Rcn2 expression through adeno-associated virus (AAV) injection and tamoxifen-induced gene deletion. 10 μL AAV2/5 containing AAV-Rcn2 or AAV-shRcn2 was administered to the mice by articular injection at 1 week post ACLT surgery, and Col2a1-creERT: Rcn2flox/flox mice were injected with tamoxifen intraperitoneally to obtain Rcn2-conditional knockout mice. Finally, we explored the mechanism of Rcn2 affecting OA. Here, we identified reticulocalbin-2 (Rcn2) as a mechanosensitive factor in chondrocytes, which was significantly elevated in chondrocytes under mechanical overloading. PIEZO type mechanosensitive ion channel component 1 (Piezo1) is a critical mechanosensitive ion channel, which mediates the effect of mechanical loading on chondrocytes, and we found that increased Rcn2 could be suppressed through knocking down Piezo1 under excessive mechanical loading. Furthermore, chondrocyte-specific deletion of Rcn2 in adult mice alleviated OA progression in the mice receiving the surgery of ACLT. On the contrary, articular injection of Rcn2-expressing adeno-associated virus (AAV) accelerated the progression of ACLT-induced OA in mice. Mechanistically, Rcn2 accelerated the progression of OA through promoting the phosphorylation and nuclear translocation of signal transducer and activator of transcription 3 (Stat3).

Collagen Tubular Airway-on-Chip for Extended Epithelial Culture and Investigation of Ventilation Dynamics

The lower respiratory tract is a hierarchical network of compliant tubular structures that are made from extracellular matrix proteins with a wall lined by an epithelium. While microfluidic airway-on-a-chip models incorporate the effects of shear and stretch on the epithelium, week-long air-liquid-interface culture at physiological shear stresses, the circular cross-section, and compliance of native airway walls have yet to be recapitulated. To overcome these limitations, a collagen tube-based airway model is presented. The lumen is lined with a confluent epithelium during two-week continuous perfusion with warm, humid air while presenting culture medium from the outside and compensating for evaporation. The model recapitulates human small airways in extracellular matrix composition and mechanical microenvironment, allowing for the first time dynamic studies of elastocapillary phenomena associated with regular breathing and mechanical ventilation, as well as their impacts on the epithelium. A case study reveales increasing damage to the epithelium during repetitive collapse and reopening cycles as opposed to overdistension, suggesting expiratory flow resistance to reduce atelectasis. The model is expected to promote systematic comparisons between different clinically used ventilation strategies and, more broadly, to enhance human organ-on-a-chip platforms for a variety of tubular tissues.

Suppression of Ventilation-Induced Diaphragm Fibrosis through the Phosphoinositide 3-Kinase-γ in a Murine Bleomycin-Induced Acute Lung Injury Model

Mechanical ventilation (MV), used in patients with acute lung injury (ALI), induces diaphragmatic myofiber atrophy and contractile inactivity, termed ventilator-induced diaphragm dysfunction. Phosphoinositide 3-kinase-γ (PI3K-γ) is crucial in modulating fibrogenesis during the reparative phase of ALI; however, the mechanisms regulating the interactions among MV, myofiber fibrosis, and PI3K-γ remain unclear. We hypothesized that MV with or without bleomycin treatment would increase diaphragm muscle fibrosis through the PI3K-γ pathway. Five days after receiving a single bolus of 0.075 units of bleomycin intratracheally, C57BL/6 mice were exposed to 6 or 10 mL/kg of MV for 8 h after receiving 5 mg/kg of AS605240 intraperitoneally. In wild-type mice, bleomycin exposure followed by MV 10 mL/kg prompted significant increases in disruptions of diaphragmatic myofibrillar organization, transforming growth factor-β1, oxidative loads, Masson's trichrome staining, extracellular collagen levels, positive staining of α-smooth muscle actin, PI3K-γ expression, and myonuclear apoptosis (p < 0.05). Decreased diaphragm contractility and peroxisome proliferator-activated receptor-γ coactivator-1α levels were also observed (p < 0.05). MV-augmented bleomycin-induced diaphragm fibrosis and myonuclear apoptosis were attenuated in PI3K-γ-deficient mice and through AS605240-induced inhibition of PI3K-γ activity (p < 0.05). MV-augmented diaphragm fibrosis after bleomycin-induced ALI is partially mediated by PI3K-γ. Therapy targeting PI3K-γ may ameliorate MV-associated diaphragm fibrosis.

Metabolic alterations and mitochondrial dysfunction in human airway BEAS-2B cells exposed to vanadium pentoxide

Vanadium pentoxide (V+5) is a hazardous material that has drawn considerable attention due to its wide use in industrial sectors and increased release into environment from human activities. It poses potential adverse effects on animals and human health, with pronounced impact on lung physiology and functions. In this study, we investigated the metabolic response of human bronchial epithelial BEAS-2B cells to low-level V+5 exposure (0.01, 0.1, and 1 ppm) using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Exposure to V+5 caused extensive changes to cellular metabolism in BEAS-2B cells, including TCA cycle, glycolysis, fatty acids, amino acids, amino sugars, nucleotide sugar, sialic acid, vitamin D3, and drug metabolism, without causing cell death. Altered mitochondrial structure and function were observed with as low as 0.01 ppm (0.2 μM) V+5 exposure. In addition, decreased level of E-cadherin, the prototypical epithelial marker of epithelial-mesenchymal transition (EMT), was observed following V+5 treatment, supporting potential toxicity of V+5 at low levels. Taken together, the present study shows that V+5 has adverse effects on mitochondria and the metabolome which may result in EMT activation in the absence of cell death. Furthermore, results suggest that high-resolution metabolomics could serve as a powerful tool to investigate metal toxicity at levels which do not cause cell death.

The effect of adoptive transferring myeloid-derived suppressor cells in ventilator-induced lung injury mice

The effects of adoptive transferring myeloid-derived suppressor cells (MDSCs) to mice with ventilator-induced lung injury (VILI) are unclear. Our objective was to investigate the effects of adoptively transferring MDSCs in VILI. The mouse model was created by introducing mechanical ventilation through a high tidal volume of 20 ml/kg for 4 h. Inflammation-induced MDSCs (iMDSCs) were collected from the bone marrow of mice with cecal ligation and puncture. iMDSCs were administrated through retrobulbar angular vein 1 h before the mechanical ventilation. The control group was anesthetized and maintained spontaneous respiration. After the termination of mechanical ventilation, bronchoalveolar lavage fluid (BALF) and lung samples 6 h were collected. The concentrations of BALF protein, levels of inflammatory mediators, and white blood cells were all significantly decreased in mice treated with iMDSCs. Histological examinations indicated reduced lung damage after iMDSCs treatment. Moreover, adoptive transfer of iMDSCs could reduce CD4+ T-cell counts and inhibit its inflammatory cytokine secretion. iMDSCs treatment was found to had no immunostimulatory effects or cause secondary infections in mice. In conclusion, MDSCs might be a potential targeted therapy for alleviating the inflammatory response of VILI mice in a T-cell dependent manner.

High Stretch Associated with Mechanical Ventilation Promotes Piezo1-Mediated Migration of Airway Smooth Muscle Cells

Ventilator-induced lung injury (VILI) during mechanical ventilation (MV) has been attributed to airway remodeling involving increased airway smooth muscle cells (ASMCs), but the underlying mechanism is not fully understood. Thus, we aimed to investigate whether MV-associated high stretch (>10% strain) could modulate mechanosensitive Piezo1 expression and thereby alter cell migration of ASMCs as a potential pathway to increased ASMCs in VILI. C57BL/6 mice and ASMCs were subjected to MV at high tidal volume (VT, 18 mL/kg, 3 h) and high stretch (13% strain, 0.5 Hz, 72 h), respectively. Subsequently, the mice or cells were evaluated for Piezo1 and integrin mRNA expression by immunohistochemical staining and quantitative PCR (qPCR), and cell migration and adhesion by transwell and cell adhesion assays. Cells were either treated or not with Piezo1 siRNA, Piezo1-eGFP, Piezo1 knockin, Y27632, or blebbistatin to regulate Piezo1 mRNA expression or inhibit Rho-associated kinase (ROCK) signaling prior to migration or adhesion assessment. We found that expression of Piezo1 in in situ lung tissue, mRNA expression of Piezo1 and integrin αVβ1 and cell adhesion of ASMCs isolated from mice with MV were all reduced but the cell migration of primary ASMCs (pASMCs) isolated from mice with MV was greatly enhanced. Similarly, cell line mouse ASMCs (mASMCs) cultured in vitro with high stretch showed that mRNA expression of Piezo1 and integrin αVβ1 and cell adhesion were all reduced but cell migration was greatly enhanced. Interestingly, such effects of MV or high stretch on ASMCs could be either induced or abolished/reversed by down/up-regulation of Piezo1 mRNA expression and inhibition of ROCK signaling. High stretch associated with MV appears to be a mechanical modulator of Piezo1 mRNA expression and can, thus, promote cell migration of ASMCs during therapeutic MV. This may be a novel mechanism of detrimental airway remodeling associated with MV, and, therefore, a potential intervention target to treat VILI.

Alveolar epithelial-to-mesenchymal transition in scleroderma interstitial lung disease: Technical challenges, available evidence and therapeutic perspectives

The alveolar epithelial-to-mesenchymal transition is the process of transformation of differentiated epithelial cells into mesenchymal-like cells through functional and morphological changes. A partial epithelial-to-mesenchymal transition process can indirectly contribute to lung fibrosis through a paracrine stimulation of the surrounding cells, while a finalized process could also directly enhance the pool of pulmonary fibroblasts and the extracellular matrix deposition. The direct demonstration of alveolar epithelial-to-mesenchymal transition in scleroderma-related interstitial lung disease is challenging due to technical pitfalls and the limited availability of lung tissue samples. Similarly, any inference on epithelial-to-mesenchymal transition occurrence driven from preclinical models should consider the limitations of cell cultures and animal models. Notwithstanding, while the occurrence or the relevance of this phenomenon in scleroderma-related interstitial lung disease have not been directly and conclusively demonstrated until now, pre-clinical and clinical evidence supports the potential role of epithelial-to-mesenchymal transition in the development and progression of lung fibrosis. Evidence consolidation on scleroderma-related interstitial lung disease epithelial-to-mesenchymal transition would pave the way for new therapeutic opportunities to prevent, slow or even reverse lung fibrosis, drawing lessons from current research lines in neoplastic epithelial-to-mesenchymal transition.

Signaling pathways and potential therapeutic targets in acute respiratory distress syndrome (ARDS)

Acute respiratory distress syndrome (ARDS) is a common condition associated with critically ill patients, characterized by bilateral chest radiographical opacities with refractory hypoxemia due to noncardiogenic pulmonary edema. Despite significant advances, the mortality of ARDS remains unacceptably high, and there are still no effective targeted pharmacotherapeutic agents. With the outbreak of coronavirus disease 19 worldwide, the mortality of ARDS has increased correspondingly. Comprehending the pathophysiology and the underlying molecular mechanisms of ARDS may thus be essential to developing effective therapeutic strategies and reducing mortality. To facilitate further understanding of its pathogenesis and exploring novel therapeutics, this review provides comprehensive information of ARDS from pathophysiology to molecular mechanisms and presents targeted therapeutics. We first describe the pathogenesis and pathophysiology of ARDS that involve dysregulated inflammation, alveolar-capillary barrier dysfunction, impaired alveolar fluid clearance and oxidative stress. Next, we summarize the molecular mechanisms and signaling pathways related to the above four aspects of ARDS pathophysiology, along with the latest research progress. Finally, we discuss the emerging therapeutic strategies that show exciting promise in ARDS, including several pharmacologic therapies, microRNA-based therapies and mesenchymal stromal cell therapies, highlighting the pathophysiological basis and the influences on signal transduction pathways for their use.

Mechanosensitive ion channel Piezo1 mediates mechanical ventilation-exacerbated ARDS-associated pulmonary fibrosis

INTRODUCTION

Pulmonary fibrosis is a major cause of the poor prognosis of acute respiratory distress syndrome (ARDS). While mechanical ventilation (MV) is an indispensable life-saving intervention for ARDS, it may cause the remodeling process in lung epithelial cells to become disorganized and exacerbate ARDS-associated pulmonary fibrosis. Piezo1 is a mechanosensitive ion channel that is known to play a role in regulating diverse physiological processes, but whether Piezo1 is necessary for MV-exacerbated ARDS-associated pulmonary fibrosis remains unknown.

OBJECTIVES

This study aimed to explore the role of Piezo1 in MV-exacerbated ARDS-associated pulmonary fibrosis.

METHODS

Human lung epithelial cells were stimulated with hydrochloric acid (HCl) followed by mechanical stretch for 48 h. A two-hitmodel of MV afteracidaspiration-inducedlunginjuryin mice was used. Mice were sacrificed after 14 days of MV. Pharmacological inhibition and knockout of Piezo1 were used to delineate the role of Piezo1 in MV-exacerbated ARDS-associated pulmonary fibrosis. In some experiments, ATP or the ATP-hydrolyzing enzyme apyrase was administered.

RESULTS

The stimulation of human lung epithelial cells to HCl resulted in phenotypes of epithelial-mesenchymal transition (EMT), which were enhanced by mechanical stretching. MV exacerbated pulmonary fibrosis in mice exposed to HCl. Pharmacologicalinhibitionorknockout of Piezo1 attenuated the MV-exacerbated EMT process and lung fibrosis in vivo and in vitro. Mechanistically, the observed effects were mediated by Piezo1-dependent Ca2+ influx and ATP release in lung epithelial cells.

CONCLUSIONS

Our findings identify a key role for Piezo1 in MV-exacerbated ARDS-associated pulmonary fibrosis that is mediated by increased ATP release in lung epithelial cells. Inhibiting Piezo1 may constitute a novelstrategyfor the treatment of MV-exacerbated ARDS-associated pulmonary fibrosis.

Hyperoxia but not high tidal volume contributes to ventilator-induced lung injury in healthy mice

BACKGROUND

Mechanical ventilation is a supportive therapy used to maintain respiratory function in several clinical and surgical cases but is always accompanied by lung injury risk due to improper treatment. We investigated how tidal volume and oxygen delivery would contribute independently or synergistically to ventilator-induced lung injury (VILI).

METHODS

Under general anesthesia and tracheal intubation, healthy female C57BL/6 N mice (9 weeks old) were randomly ventilated for 2 h by standard (7 ml/kg) or high (14 ml/kg) tidal volume at positive end-expiratory pressure (PEEP) of 2 cmH2O, with room air, 50% O2 (moderate hyperoxia), or 100% O2 (severe hyperoxia); respectively. Mice were sacrificed 4 h after mechanical ventilation, and lung tissues were collected for experimental assessments on lung injury.

RESULTS

Compared with the healthy control, severe hyperoxia ventilation by either standard or high tidal volume resulted in significantly higher wet-to-dry lung weight ratio and higher levels of IL-1β and 8-OHdG in the lungs. However, moderate hyperoxia ventilation, even by high tidal volume did not significantly increase the levels of IL-1β and 8-OHdG in the lungs. Western blot analysis showed that the expression of RhoA, ROCK1, MLC2, and p-MLC2 was not significantly induced in the ventilated lungs, even by high tidal volume at 2 cmH2O PEEP.

CONCLUSION

Severe hyperoxia ventilation causes inflammatory response and oxidative damage in mechanically ventilated lungs, while high tidal volume ventilation at a reasonable PEEP possibly does not cause VILI.

COVID-19 and interstitial lung diseases: A multifaceted look at the relationship between the two diseases

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although it has been a fatal disease for many patients, the development of treatment strategies and vaccines have progressed over the past 3 years, and our society has become able to accept COVID-19 as a manageable common disease. However, as COVID-19 sometimes causes pneumonia, post-COVID pulmonary fibrosis (PCPF), and worsening of preexisting interstitial lung diseases (ILDs), it is still a concern for pulmonary physicians. In this review, we have selected several topics regarding the relationships between ILDs and COVID-19. The pathogenesis of COVID-19-induced ILD is currently assumed based mainly on the evidence of other ILDs and has not been well elucidated specifically in the context of COVID-19. We have summarized what has been clarified to date and constructed a coherent story about the establishment and progress of the disease. We have also reviewed clinical information regarding ILDs newly induced or worsened by COVID-19 or anti-SARS-CoV-2 vaccines. Inflammatory and profibrotic responses induced by COVID-19 or vaccines have been thought to be a risk for de novo induction or worsening of ILDs, and this has been supported by the evidence obtained through clinical experience over the past 3 years. Although COVID-19 has become a mild disease in most cases, it is still worth looking back on the above-reviewed information to broaden our perspectives regarding the relationship between viral infection and ILD. As a representative etiology for severe viral pneumonia, further studies in this area are expected.

Glucocorticoid Alleviates Mechanical Stress-Induced Airway Inflammation and Remodeling in COPD via Transient Receptor Potential Canonical 1 Channel

Background

Increased airway resistance and hyperinflation in chronic obstructive pulmonary disease (COPD) are associated with increased mechanical stress that modulate many essential pathophysiological functions including airway remodeling and inflammation. Our present study aimed to investigate the role of transient receptor potential canonical 1 (TRPC1), a mechanosensitive cation channel in airway remodeling and inflammation in COPD and the effect of glucocorticoid on this process.

Methods

In patients, we investigated the effect of pathological high mechanical stress on the expression of airway remodeling-related cytokines transforming growth factor β1 (TGF-β1), matrix metalloproteinase-9 (MMP9) and the count of inflammatory cells in endotracheal aspirates (ETAs) by means of different levels of peak inspiratory pressure (PIP) under mechanical ventilation, and analyzed their correlation with TRPC1. Based on whether patients regularly used inhaled corticosteroid (ICS), COPD patients were further divided into ICS group (n = 12) and non-ICS group (n=15). The ICS effect on the expression of TRPC1 was detected by Western blot. In vitro, we imitated the mechanical stress using cyclic stretch and examined the levels of TGF-β1 and MMP-9. The role of TRPC1 was further explored by siRNA transfection and dexamethasone administration.

Results

Our results revealed that the TRPC1 level and the inflammatory cells counts were significantly higher in COPD group. After mechanical ventilation, the expression of TGF-β1 and MMP-9 in all COPD subgroups was significantly increased, while in the control group, only high PIP subgroup increased. Meanwhile, TRPC1 expression was positively correlated with the counts of inflammatory cells and the levels of TGF-β1 and MMP-9. In vitro, mechanical stretch significantly increased TGF-β1 and MMP-9 levels and such increase was greatly attenuated by TRPC1 siRNA transfection and dexamethasone administration.

Conclusion

Our results suggest that the increased TRPC1 may play a role in the airway inflammation and airway remodeling in COPD under high airway pressure. Glucocorticoid could in some degree alleviate airway remodeling via inhibition of TRPC1.

Fibrotic extracellular vesicles contribute to mechanical ventilation-induced pulmonary fibrosis development by activating lung fibroblasts via JNK signalling pathway: an experimental study

Recent research has revealed that mechanical ventilation (MV) could initiate ventilator-induced lung injury along with the initiation of the process of pulmonary fibrosis (PF), leading to MV-induced PF (MVPF). However, the underlying mechanism remains unclear. This study aimed to explore the role of MV-induced extracellular vesicles (MV-EVs) and the c-Jun N-terminal kinase (JNK) signalling pathway in the pathogenesis of MVPF in vivo and in vitro. The process of MV is accompanied by the secretion of MV-EVs, which could induce lung fibroblast activation. Furthermore, single-cell RNA-sequencing analysis revealed that the JNK pathway in lung fibroblasts was activated after MV initiation. Inhibiting the JNK pathway could both restrain MV-EV-induced lung fibroblast activation in vitro or reduce the severity of MVPF in vivo. In conclusion, this study demonstrated that MV-EVs contribute to MVPF progression by activating lung fibroblasts via the JNK signalling pathway and that inhibiting the secretion of EV and the activation of the JNK signalling pathway is a promising strategy for treating MVPF.

mRNA Levels of Epithelial and Mesenchymal Markers in Lung Epithelial Cell Lines

Background

Epithelial-mesenchymal transition (EMT) is an important physiologic process that determines the outcome of lung tissue healing after injury. Stimuli and molecular cascades inducing EMT lead to up-regulation of the mesenchymal-specific genes in the alveolar epithelial cells and to down-regulation of the genes coding for epithelial markers. Alveolar epithelial cell lines are commonly used as in vitro models to study processes occurring in the lung tissue. The aim of this study is to quantify and compare mRNA expression levels of epithelial and mesenchymal markers in a number of lung epithelial cell lines.

Methods

Lung epithelial cell lines L2, R3/1 and RLE-6TN were cultured. Repeated mRNA isolation, reverse transcription, and quantitative PCR with primers to epithelial (E-cadherin, occludin, and ZO-2) and mesenchymal (α-SMA, collagen III, and vimentin) markers were performed.

Results

First, our study revealed a higher level of epithelial transcripts in the RLE-6TN cell line compared to L2 and R3/1 cells. Secondly, we have found simultaneous mRNA expression of both epithelial (E-cadherin, occludin and ZO-2) and mesenchymal (α-SMA, collagen III and vimentin) markers in all cell lines studied.

Conclusions

Our data indicate that at the transcriptional level the L2, R3/1, and RLE-6TN cell lines are at one of the intermediate stages of EMT, which opens new possibilities for the study of EMT on cell lines. Determination of the direction of changes in epithelial and mesenchymal markers will make it possible to establish the factors responsible for both EMT and reverse mesenchymal-epithelial transition.

Role of Epithelial-to-Mesenchymal Transition of Retinal Pigment Epithelial Cells in Glaucoma Cupping

Optic nerve head (ONH) cupping is a clinical feature of glaucoma associated with extracellular matrix (ECM) remodelling and lamina cribrosa (LC) fibrosis. Peripapillary atrophy (PPA) occurs commonly in glaucoma, and is characterised by the loss of retinal pigment epithelium (RPE) adjacent to the ONH. Under pro-fibrotic conditions, epithelial cells throughout the body can differentiate into fibroblast-like cells through epithelial-to-mesenchymal transition (EMT) and contribute to ECM fibrosis. This is investigated here in the context of glaucoma and PPA. Human-donor ONH sections were assessed for the presence of the RPE cell-specific marker RPE65 using immunofluorescence. We examined the EMT response of ARPE-19 cells to the following glaucoma-related stimuli: cyclic mechanical stretch, mechanical stiffness, transforming growth factor beta (TGFβ), and tumour necrosis factor alpha (TNFα). The gene expression was measured using the PCR of the epithelial tight junction marker zona occludens 1 (ZO-1) and the mesenchymal markers alpha smooth muscle actin (αSMA) and vimentin. A scratch assay was used to assess the ARPE-19 migration. Significant RPE-65 staining was demonstrated in the glaucomatous ONH. The cyclic stretching and substrate stiffness of the ARPE-19 cells caused a significant decrease in ZO-1 (p = 0.04), and an increase in αSMA (p = 0.04). The scratch assays demonstrated increased migration of ARPE19 in the presence of TNFα (p = 0.02). Furthermore, ARPE-19 cells undergo an EMT-like transition (gain of αSMA, loss of ZO-1 and increased migration) in response to glaucomatous stimuli. This suggests that during PPA, RPE cells have the potential to migrate into the ONH and differentiate into fibroblast-like cells, contributing to glaucomatous ONH cupping.

Exploring m6A-RNA methylation as a potential therapeutic strategy for acute lung injury and acute respiratory distress syndrome

N6-methyladenosine (m6A) is the most common methylation modification in mammalian messenger RNA (mRNA) and noncoding RNAs. m6A modification plays a role in the regulation of gene expression and deregulation of m6A methylation has been implicated in many human diseases. Recent publications suggest that exploitation of this methylation process may possess utility against acute lung injury (ALI). ALI and its more severe form, acute respiratory distress syndrome (ARDS) are acute, inflammatory clinical syndromes characterized by poor oxygenation and diffuse pulmonary infiltrates. This syndrome is associated with microvascular endothelial dysfunction, subsequent pulmonary hypertension and may ultimately lead to mortality without rigorous and acute clinical intervention. Over the years, many attempts have been made to detect novel therapeutic avenues for research without much success. The urgency for the discovery of novel therapeutic agents has become more pronounced recently given the current pandemic infection of coronavirus disease 2019 (COVID-2019), still ongoing at the time that this review is being written. We review the current landscape of literature regarding ALI and ARDS etiology, pathophysiology, and therapeutics and present a potential role of m6A methylation. Additionally, we will establish the axiomatic principles of m6A methylation to provide a framework. In conclusion, METTL3, or methyltransferase-like 3, the selective RNA methyltransferase for m6A, is a hub of proinflammatory gene expression regulation in ALI, and using a modern drug discovery strategy will identify new and effective ALI drug candidates targeting METTTL3.

Non-coding RNA alterations in extracellular vesicles from bronchoalveolar lavage fluid contribute to mechanical ventilation-induced pulmonary fibrosis

Objective

For respiratory failure patients, mechanical ventilation (MV) is a life-saving therapy to maintain respiratory function. However, MV could also cause damage to pulmonary structures, result in ventilator-induced lung injury (VILI) and eventually progress to mechanical ventilation-induced pulmonary fibrosis (MVPF). Mechanically ventilated patients with MVPF are closely related to increased mortality and poor quality of life in long-term survival. Thus, a thorough understanding of the involved mechanism is necessary.

Methods

We used next-generation sequencing to identify differentially expressed non-coding RNAs (ncRNAs) in BALF EVs which were isolated from Sham and MV mice. Bioinformatics analysis was conducted to identify the engaged ncRNAs and related signaling pathways in the process of MVPF.

Results

We found 1801 messenger RNAs (mRNA), 53 micro RNAs (miRNA), 273 circular RNAs (circRNA) and 552 long non-coding RNAs (lncRNA) in mice BALF EVs of two groups, which showed significant differential expression. TargetScan predicted that 53 differentially expressed miRNAs targeted 3105 mRNAs. MiRanda revealed that 273 differentially expressed circRNAs were associated with 241 mRNAs while 552 differentially expressed lncRNAs were predicated to target 20528 mRNAs. GO, KEGG pathway analysis and KOG classification showed that these differentially expressed ncRNA-targeted mRNAs were enriched in fibrosis related signaling pathways and biological processes. By taking the intersection of miRNAs target genes, circRNAs target genes and lncRNAs target genes, we found 24 common key genes and 6 downregulated genes were confirmed by qRT-PCR.

Conclusions

Changes in BALF-EV ncRNAs may contribute to MVPF. Identification of key target genes involved in the pathogenesis of MVPF could lead to interventions that slow or reverse fibrosis progression.

Post-COVID Interstitial Lung Disease and Other Lung Sequelae

As the world emerges from the COVID-19 pandemic, clinicians and researchers across the world are trying to understand the sequelae in patients recovered from COVID-19 infection. In this article, the authors review post-acute sequelae of SARS-COV-2, interstitial lung disease, and other lung sequelae in patients recovering from COVID-19 infection.

Post-COVID Interstitial Lung Disease—The Tip of the Iceberg

The proportion of symptomatic patients with post-coronavirus 2019 (COVID-19) condition (long COVID) represents a significant burden on the individual as well as on the health care systems. A greater understanding of the natural evolution of symptoms over a longer period and the impacts of interventions will improve our understanding of the long-term impacts of the COVID-19 disease. This review will discuss the emerging evidence for the development of post-COVID interstitial lung disease focusing on the pathophysiological mechanisms, incidence, diagnosis, and impact of this potentially new and emerging respiratory disease.

Effectiveness of losartan on infrapatellar fat pad/synovial fibrosis and pain behavior in the monoiodoacetate-induced rat model of osteoarthritis pain

Infrapatellar fat pad (IFP)/ synovial fibrosis is closely associated with the clinical symptoms of joint pain and stiffness, which contribute to locomotor restriction in osteoarthritis (OA) patients. Hence, this study was designed to gain insight on whether losartan, a selective angiotensin II type 1 receptor (AT1R) antagonist, has therapeutic benefit to reverse IFP/synovial fibrosis and secondarily to attenuate pain behavior. In male Wistar rats with monoiodoacetic acid (MIA)-induced IFP/synovial fibrosis, a possible role for increased AT1R expression in the pathogenesis of IFP/synovial fibrosis was assessed over an 8-week period. Pain behavior comprised static weight bearing and von Frey paw withdrawal thresholds (PWTs), which were assessed once or twice weekly, respectively. Groups of MIA-rats received oral losartan (30-mg/kg; n = 8 or 100-mg/kg; n = 9) or vehicle (n = 9) for 28-days according to a prevention protocol. Animals were euthanized on day 28 and various tissues (IFP/synovium, cartilage and lumbar dorsal root ganglia (DRGs)) were collected for histological, immunohistochemical and western blot analyses. Administration of once-daily losartan for 28-days dose-dependently attenuated the development of static weight bearing. This was accompanied by reduced IFP/synovial fibrosis and suppression of TGF-β1 expression. Chronic treatment of MIA-rats with losartan had an anti-fibrotic effect and it attenuated pain behavior in this animal model.

Metabolomics of V2O5 nanoparticles and V2O5 nanofibers in human airway epithelial BEAS-2B cells

Vanadium is a toxic metal listed by the IARC as possibly carcinogenic to humans. Manufactured nanosize vanadium pentoxide (V2O5) materials are used in a wide range of industrial sectors and recently have been developed as nanomedicine for cancer therapeutics, yet limited information is available to evaluate relevant nanotoxicity. In this study we used high-resolution metabolomics to assess effects of two V2O5 nanomaterials, nanoparticles and nanofibers, at exposure levels (0.01, 0.1, and 1 ppm) that did not cause cell death (i.e., non-cytotoxic) in a human airway epithelial cell line, BEAS-2B. As prepared, V2O5 nanofiber exhibited a fibrous morphology, with a width approximately 63 ± 12 nm and length in average 420 ± 70 nm; whereas, V2O5 nanoparticles showed a typical particle morphology with a size 36 ± 2 nm. Both V2O5 nanoparticles and nanofibers had dose-response effects on aminosugar, amino acid, fatty acid, carnitine, niacin and nucleotide metabolism. Differential effects of the particles and fibers included dibasic acid, glycosphingolipid and glycerophospholipid pathway associations with V2O5 nanoparticles, and cholesterol and sialic acid metabolism associations with V2O5 nanofibers. Examination by transmission electron microscopy provided evidence for mitochondrial stress and increased lysosome fusion by both nanomaterials, and these data were supported by effects on mitochondrial membrane potential and lysosomal activity. The results showed that non-cytotoxic exposures to V2O5 nanomaterials impact major metabolic pathways previously associated with human lung diseases and suggest that toxico-metabolomics may be useful to evaluate health risks from V2O5 nanomaterials.

ASK1-ER stress pathway-mediated fibrotic-EV release contributes to the interaction of alveolar epithelial cells and lung fibroblasts to promote mechanical ventilation-induced pulmonary fibrosis

Recent clinical research has revealed that mechanical ventilation (MV) can initiate pulmonary fibrosis and induce mechanical ventilation-induced pulmonary fibrosis (MVPF). However, the underlying mechanism remains largely uncharacterized. Based on a mouse model of MVPF and an alveolar epithelial cell cyclic strain model, the present study explores the possible mechanism of MVPF. Single-cell RNA-sequencing and EV RNA-sequencing analysis revealed that MV promoted apoptosis signal-regulating kinase 1 (ASK1)-mediated endoplasmic reticulum (ER) stress pathway activation and extracellular vesicle (EV) release from alveolar epithelial cells. Furthermore, the ASK1-ER stress pathway was shown to mediate mechanical stretch (MS)- or MV-induced EV release and lung fibroblast activation in vivo and in vitro. These processes were suppressed by ER stress inhibitors or by silencing ASK1 with ASK1- short hairpin RNA (shRNA). In addition, MVPF was suppressed by inhibiting ASK1 and ER stress in vivo. Therefore, the present study demonstrates that ASK1-ER stress pathway-mediated fibrotic-EV release from alveolar epithelial cells contributes to fibroblast activation and the initiation of pulmonary fibrosis during MV. The inhibited release of EVs targeting the ASK1-ER stress pathway might be a promising treatment strategy for MVPF.

Fibrotic-like abnormalities notably prevalent one year after hospitalization with COVID-19

BACKGROUND

We investigated whether COVID-19 leads to persistent impaired pulmonary function, fibrotic-like abnormalities or psychological symptoms 12 months after discharge and whether severely ill patients (ICU admission) recover differently than moderately ill patients.

METHODS

This single-centre cohort study followed adult COVID-19 survivors for a period of one year after discharge. Patients underwent pulmonary function tests 6 weeks, 3 months and 12 months after discharge and were psychologically evaluated at 6 weeks and 12 months. Computed tomography (CT) was performed after 3 months and 12 months.

RESULTS

66 patients were analysed, their median age was 60.5 (IQR: 54-69) years, 46 (70%) patients were male. 38 (58%) patients had moderate disease and 28 (42%) patients had severe disease. Most patients had spirometric values within normal range after 12 months of follow-up. 12 (23%) patients still had an impaired lung diffusion after 12 months. Impaired pulmonary diffusion capacity was associated with residual CT abnormalities (OR 5.1,CI-95: 1.2-22.2), shortness of breath (OR 7.0, CI-95: 1.6-29.7) and with functional limitations (OR 5.8, CI-95: 1.4-23.8). Ground-glass opacities resolved in most patients during follow-up. Resorption of reticulation, bronchiectasis and curvilinear bands was rare and independent of disease severity. 81% of severely ill patients and 37% of moderately ill patients showed residual abnormalities after 12 months (OR 8.1, CI-95: 2.5-26.4). A minority of patients had symptoms of post-traumatic stress disorder, anxiety, depression and cognitive failure during follow-up.

CONCLUSION

Some patients still had impaired lung diffusion 12 months after discharge and fibrotic-like residual abnormalities were notably prevalent, especially in severely ill patients.

P311 promotes type II transforming growth factor-β receptor mediated fibroblast activation and granulation tissue formation in wound healing

Background

P311, a highly conserved 8 kDa intracellular protein, has recently been reported to play an important role in aggravating hypertrophic scaring by promoting the differentiation and secretion of fibroblasts. Nevertheless, how P311 regulates the differentiation and function of fibroblasts to affect granulation tissue formation remains unclear. In this work, we studied the underlying mechanisms via which P311 affects fibroblasts and promotes acute skin wound repair.

Methods

To explore the role of P311, both in vitro and in vivo wound-healing models were used. Full-thickness skin excisional wounds were made in wild-type and P311^-/- C57 adult mice. Wound healing rate, re-epithelialization, granulation tissue formation and collagen deposition were measured at days 3, 6 and 9 after skin injury. The biological phenotypes of fibroblasts, the expression of target proteins and relevant signaling pathways were examined both in vitro and in vivo.

Results

P311 could promote the proliferation and differentiation of fibroblasts, enhance the ability of myofibroblasts to secrete extracellular matrix and promote cell contraction, and then facilitate the formation of granulation tissue and eventually accelerate skin wound closure. Importantly, we discovered that P311 acts via up-regulating the expression of type II transforming growth factor-β receptor (TGF-βRII) in fibroblasts and promoting the activation of the TGF-βRII-Smad signaling pathway. Mechanistically, the mammalian target of rapamycin signaling pathway is closely implicated in the regulation of the TGF-βRII-Smad pathway in fibroblasts mediated by P311.

Conclusions

P311 plays a critical role in activation of the TGF-βRII-Smad pathway to promote fibroblast proliferation and differentiation as well as granulation tissue formation in the process of skin wound repair.

The Role of Circadian Clock Genes in Critical Illness: The Potential Role of Translational Clock Gene Therapies for Targeting Inflammation, Mitochondrial Function, and Muscle Mass in Intensive Care

The Earth's 24-h planetary rotation, with predictable light and heat cycles, has driven profound evolutionary adaptation, with prominent impacts on physiological mechanisms important for surviving critical illness. Pathways of interest include inflammation, mitochondrial function, energy metabolism, hypoxic signaling, apoptosis, and defenses against reactive oxygen species. Regulation of these by the cellular circadian clock (BMAL-1 and its network) has an important influence on pulmonary inflammation; ventilator-associated lung injury; septic shock; brain injury, including vasospasm; and overall mortality in both animals and humans. Whether it is cytokines, the inflammasome, or mitochondrial biogenesis, circadian medicine represents exciting opportunities for translational therapy in intensive care, which is currently lacking. Circadian medicine also represents a link to metabolic determinants of outcome, such as diabetes and cardiovascular disease. More than ever, we are appreciating the problem of circadian desynchrony in intensive care. This review explores the rationale and evidence for the importance of the circadian clock in surviving critical illness.

Advances in the Regulation of Macrophage Polarization by Mesenchymal Stem Cells and Implications for ALI/ARDS Treatment

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a common condition with high mortality. ALI/ARDS is caused by multiple etiologies, and the main clinical manifestations are progressive dyspnea and intractable hypoxemia. Currently, supportive therapy is the main ALI/ARDS treatment, and there remains a lack of targeted and effective therapeutic strategies. Macrophages are important components of innate immunity. M1 macrophages are pro-inflammatory, while M2 macrophages are anti-inflammatory and promote tissue repair. Mesenchymal stem cells (MSCs) are stem cells with broad application prospects in tissue regeneration due to their multi-directional differentiation potential along with their anti-inflammatory and paracrine properties. MSCs can regulate the balance of M1/M2 macrophage polarization to improve the prognosis of ALI/ARDS. In this paper, we review the mechanisms by which MSCs regulate macrophage polarization and the signaling pathways associated with polarization. This review is expected to provide new targets for the treatment of ALI/ARDS.

Management of BMI Is a Potential New Approach for the Prevention of Idiopathic Pulmonary Fibrosis

Aims: Current idiopathic pulmonary fibrosis (IPF) therapies usually show a poor outcome or treatment efficacy. The search for new risk factors has significant implications in preventing, delaying, and treating IPF. The association between obesity and the risk of IPF is not clear. This study aimed to investigate the role of different obesity types in IPF risk, which provides the possibility of weight loss as a new approach for IPF prevention.

Methods: We conducted a two-sample Mendelian randomization (MR) analysis to assess the causal effect of obesity on IPF risk. We collected summary data of genetically determined obesity-related traits, including body mass index (BMI), waist circumference (WC), and waist-to-hip ratio (WHR) from large-scale consortia (the sample size ranging from 232,101 to 681,275), and genetic association with IPF from one of the largest meta-analyses including 2,668 cases. A total of 35–469 single nucleotide polymorphisms were selected as instrumental variables for obesity-related traits. We further performed multivariable MR to estimate the independent effect of BMI and WC on the risk of IPF.

Results: Increased BMI and WC were associated with higher risk of IPF [odds ratio (OR) = 1.51, 95% confidence interval (CI) (1.22–1.87), p = 1.27 × 10^–4, and OR = 1.71, 95% CI (1.08–2.72), p = 2.33 × 10^–2, respectively]. Similar results for the BMI and WC were obtained in the replicated analysis. Subsequently, only the result for BMI survived following the multiple testing correction and showed good consistency with the weighted median estimator. Sensitivity analyses indicated that there was no heterogeneity or horizontal pleiotropy for MR estimations. Further multivariable MR suggested that the BMI showed the same direction and similar magnitude with that in the univariable MR analysis. There was little evidence to support the causal role of WHR on the risk of IPF in this study.

Conclusion: Genetically determined BMI demonstrates a causal risk for IPF, which offers a novel insight into probing potential mechanisms. Meanwhile, these results also suggest that weight loss may be beneficial to IPF prevention.

The effect of N6-methyladenosine (m6A) factors on the development of acute respiratory distress syndrome in the mouse model

Acute respiratory distress syndrome (ARDS) can cause loss of alveolar-capillary membrane integrity and life-threatening immune responses. The underlying molecular mechanisms of ARDS remain unclear. N6-methyladenosine (m6A)-RNA modification plays an important part in many biological processes. However, it is not clear whether ARDS alters RNA methylation in lung tissue. We tried to investigate the changes of m6A-RNA methylation in lung tissues of lipopolysaccharide (LPS)-induced ARDS mice. Lung tissue samples were collected to detect the expression of m6A factors through hematoxylin and eosin (HE) staining, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), immunohistochemical analysis and western blot. The overall m6A levels in lung tissue of ARDS in mouse were detected by UPLC-UV-MS. HE staining showed that the degree of the inflammatory response was more severe in the LPS-3 h group. The mRNA expression of YTHDF1, YTHDC1 and IGFBP3 was remarkably up-regulated at, respectively, 6, 6 and 12 h after LPS treatment. The mRNA expression of METTL16, FTO, METTL3, KIAA1429, RBM15, ALKBH5, YTHDF2, YTHDF3, YTHDC2 and IGFBP2 was significantly down-regulated at 24 h after LPS treatment. The protein expression of METTL16 and FTO increased, YTHDC1, IGFBP3 YTHDF1 and YTHDF3 showed a down-regulation trend after LPS induction. Overall m6A-RNA methylation levels were significantly increased at 6 h after LPS induction. In ARDS mice, LPS-induced m6A methylation may be involved in the expression regulation of inflammatory factors and may play important roles in the occurrence and development of lung tissue. It is suggested that m6A modification may be a promising therapeutic target for ARDS.

Ventilator-Associated Lung Injury

Ventilatory support, while life saving, can also cause or aggravate lung injury through several mechanisms which are encompassed within ventilator-associated lung injury (VALI). The important realizationin the acute respiratory distress syndrome that the “baby” lung resided in non-dependent areas led to the conceptualization of “lung rest” to reduce stress and strain to exposed alveolar units. We discuss concepts and mechanisms within VALI that ultimately induce maladaptive lung responses, as well as, current and future management strategies to detect and mitigate VALI at the bedside.

Emerging roles of mechanosensitive ion channels in acute lung injury/acute respiratory distress syndrome

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a devastating respiratory disorder with high rates of mortality and morbidity, but the detailed underlying mechanisms of ALI/ARDS remain largely unknown. Mechanosensitive ion channels (MSCs), including epithelial sodium channel (ENaC), Piezo channels, transient receptor potential channels (TRPs), and two-pore domain potassium ion (K2P) channels, are highly expressed in lung tissues, and the activity of these MSCs can be modulated by mechanical forces (e.g., mechanical ventilation) and other stimuli (e.g., LPS, hyperoxia). Dysfunction of MSCs has been found in various types of ALI/ARDS, and MSCs play a key role in regulating alveolar fluid clearance, alveolar epithelial/endothelial barrier function, the inflammatory response and surfactant secretion in ALI/ARDS lungs. Targeting MSCs exerts therapeutic effects in the treatment of ALI/ARDS. In this review, we summarize the structure and functions of several well-recognized MSCs, the role of MSCs in the pathogenesis of ALI/ARDS and recent advances in the pharmacological and molecular modulation of MSCs in the treatment of ALI/ARDS. According to the current literature, targeting MSCs might be a very promising therapeutic approach against ALI/ARDS.

Mechanical overloading induces GPX4-regulated chondrocyte ferroptosis in osteoarthritis via Piezo1 channel facilitated calcium influx

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Our study proved that mechanical overloading induces ferroptosis of chondrocyte, which might be a potential therapeutic target for mechanical damage of chondrocyte and OA.

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Our study demonstrated Piezo1 facilitated calcium influx leads to reduction of GSH, decrease of Gpx4 and activation of oxidative stress in chondrocyte under high strain mechanical stimulation.

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Mechanical signals were converted into ferroptosis-associated signals through Piezo1 channel induced calcium influx, which might shed light on therapeutic interventions for treatment of OA and other diseases associated with ferroptosis.

Introductions

Excessive mechanical stress is closely associated with cell death in various conditions. Exposure of chondrocytes to excessive mechanical loading leads to a catabolic response as well as exaggerated cell death. Ferroptosis is a recently identified form of cell death during cell aging and degeneration. However, it's potential association with mechanical stress remains to be illustrated.

Objectives

To identify whether excessive mechanical stress can cause ferroptosis. To explore the role of mechanical overloading in chondrocyte ferroptosis.

Methods

Chondrocytes were collected from loading and unloading zones of cartilage in patients with osteoarthritis (OA), and the ferroptosis phenotype was analyzed through transmission electron microscope and microarray. Moreover, the relationship between ferroptosis and OA was analyzed by GPX4-conditional knockout (Col2a1-CreERT: GPX4^flox/flox) mice OA model and chondrocytes cultured with high strain mechanical stress. Furthermore, the role of Piezo1 ion channel in chondrocyte ferroptosis and OA development was explored by using its inhibitor (GsMTx4) and agonist (Yoda1). Additionally, chondrocyte was cultured in calcium-free medium with mechanical stress, and ferroptosis phenotype was tested.

Results

Human cartilage and mouse chondrocyte experiments revealed that mechanical overloading can induce GPX4-associated ferroptosis. Conditional knockout of GPX4 in cartilage aggravated experimental OA process, while additional treatment with ferroptosis suppressor protein (FSP-1) and coenzyme Q10 (CoQ10) abated OA development in GPX4-CKO mice. In mouse OA model and chondrocyte experiments, inhibition of Piezo1 channel activity increased GPX4 expression, attenuated ferroptosis phenotype and reduced the severity of osteoarthritis. Additionally, high strain mechanical stress induced ferroptosis damage in chondrocyte was largely abolished by blocking calcium influx through calcium-free medium.

Conclusions

Our findings show that mechanical overloading induces ferroptosis through Piezo1 activation and subsequent calcium influx in chondrocytes, which might provide a potential target for OA treatment.

Transcriptomic-Based Quantification of the Epithelial-Hybrid-Mesenchymal Spectrum across Biological Contexts

Epithelial-mesenchymal plasticity (EMP) underlies embryonic development, wound healing, and cancer metastasis and fibrosis. Cancer cells exhibiting EMP often have more aggressive behavior, characterized by drug resistance, and tumor-initiating and immuno-evasive traits. Thus, the EMP status of cancer cells can be a critical indicator of patient prognosis. Here, we compare three distinct transcriptomic-based metrics-each derived using a different gene list and algorithm-that quantify the EMP spectrum. Our results for over 80 cancer-related RNA-seq datasets reveal a high degree of concordance among these metrics in quantifying the extent of EMP. Moreover, each metric, despite being trained on cancer expression profiles, recapitulates the expected changes in EMP scores for non-cancer contexts such as lung fibrosis and cellular reprogramming into induced pluripotent stem cells. Thus, we offer a scoring platform to quantify the extent of EMP in vitro and in vivo for diverse biological applications including cancer.

Ventilator-induced lung-injury in mouse models: Is there a trap?

Ventilator-induced lung injury (VILI) is a serious acute injury to the lung tissue that can develop during mechanical ventilation of patients. Due to the mechanical strain of ventilation, damage can occur in the bronchiolar and alveolar epithelium resulting in a cascade of events that may be fatal to the patients. Patients requiring mechanical ventilation are often critically ill, which limits the possibility of obtaining patient samples, making VILI research challenging. In vitro models are very important for VILI research, but the complexity of the cellular interactions in multi-organ animals, necessitates in vivo studies where the mouse model is a common choice. However, the settings and duration of ventilation used to create VILI in mice vary greatly, causing uncertainty in interpretation and comparison of results. This review examines approaches to induce VILI in mouse models for the last 10 years, to our best knowledge, summarizing methods and key parameters presented across the studies. The results imply that a more standardized approach is warranted.

Noninvasive respiratory support and patient self-inflicted lung injury in COVID-19: a narrative review

COVID-19 pneumonia is associated with hypoxaemic respiratory failure, ranging from mild to severe. Because of the worldwide shortage of ICU beds, a relatively high number of patients with respiratory failure are receiving prolonged noninvasive respiratory support, even when their clinical status would have required invasive mechanical ventilation. There are few experimental and clinical data reporting that vigorous breathing effort during spontaneous ventilation can worsen lung injury and cause a phenomenon that has been termed patient self-inflicted lung injury (P-SILI). The aim of this narrative review is to provide an overview of P-SILI pathophysiology and the role of noninvasive respiratory support in COVID-19 pneumonia. Respiratory mechanics, vascular compromise, viscoelastic properties, lung inhomogeneity, work of breathing, and oesophageal pressure swings are discussed. The concept of P-SILI has been widely investigated in recent years, but controversies persist regarding its mechanisms. To minimise the risk of P-SILI, intensivists should better understand its underlying pathophysiology to optimise the type of noninvasive respiratory support provided to patients with COVID-19 pneumonia, and decide on the optimal timing of intubation for these patients.

Post-COVID-19 Pulmonary Fibrosis: Novel Sequelae of the Current Pandemic

Since the initial identification of the novel coronavirus SARS-CoV-2 in December 2019, the COVID-19 pandemic has become a leading cause of morbidity and mortality worldwide. As effective vaccines and treatments begin to emerge, it will become increasingly important to identify and proactively manage the long-term respiratory complications of severe disease. The patterns of imaging abnormalities coupled with data from prior coronavirus outbreaks suggest that patients with severe COVID-19 pneumonia are likely at an increased risk of progression to interstitial lung disease (ILD) and chronic pulmonary vascular disease. In this paper, we briefly review the definition, classification, and underlying pathophysiology of interstitial lung disease (ILD). We then review the current literature on the proposed mechanisms of lung injury in severe COVID-19 infection, and outline potential viral- and immune-mediated processes implicated in the development of post-COVID-19 pulmonary fibrosis (PCPF). Finally, we address patient-specific and iatrogenic risk factors that could lead to PCPF and discuss strategies for reducing risk of pulmonary complications/sequelae.

D-Limonene Is a Potential Monoterpene to Inhibit PI3K/Akt/IKK-α/NF-κB p65 Signaling Pathway in Coronavirus Disease 2019 Pulmonary Fibrosis

At the time of the prevalence of coronavirus disease 2019 (COVID-19), pulmonary fibrosis (PF) related to COVID-19 has become the main sequela. However, the mechanism of PF related to COVID (COVID-PF) is unknown. This study aimed to explore the key targets in the development of COVID-PF and the mechanism of d-limonene in the COVID-PF treatment. The differentially expressed genes of COVID-PF were downloaded from the GeneCards database, and their pathways were analyzed. d-Limonene was molecularly docked with related proteins to screen its pharmacological targets, and a rat lung fibrosis model was established to verify d-limonene's effect on COVID-PF-related targets. The results showed that the imbalance between collagen breakdown and metabolism, inflammatory response, and angiogenesis are the core processes of COVID-PF; and PI3K/AKT signaling pathways are the key targets of the treatment of COVID-PF. The ability of d-limonene to protect against PF induced by bleomycin in rats was reported. The mechanism is related to the binding of PI3K and NF-κB p65, and the inhibition of PI3K/Akt/IKK-α/NF-κB p65 signaling pathway expression and phosphorylation. These results confirmed the relationship between the PI3K–Akt signaling pathway and COVID-PF, showing that d-limonene has a potential therapeutic value for COVID-PF.

Spontaneous Breathing and Evolving Phenotypes of Lung Damage in Patients with COVID-19: Review of Current Evidence and Forecast of a New Scenario

The mechanisms of acute respiratory failure other than inflammation and complicating the SARS-CoV-2 infection are still far from being fully understood, thus challenging the management of COVID-19 patients in the critical care setting. In this unforeseen scenario, the role of an individual's excessive spontaneous breathing may acquire critical importance, being one potential and important driver of lung injury and disease progression. The consequences of this acute lung damage may impair lung structure, forecasting the model of a fragile respiratory system. This perspective article aims to analyze the progression of injured lung phenotypes across the SARS-CoV-2 induced respiratory failure, pointing out the role of spontaneous breathing and also tackling the specific respiratory/ventilatory strategy required by the fragile lung type.

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.

Healing after COVID-19: are survivors at risk for pulmonary fibrosis?

The novel SARS-CoV-2 coronavirus, which is responsible for COVID-19 disease, was first reported in Wuhan, China, in December of 2019. The virus rapidly spread, and the World Health Organization declared a pandemic by March 2020. With millions of confirmed cases worldwide, there is growing concern and considerable debate regarding the potential for coronavirus infection to contribute to an appreciable burden of chronic respiratory symptoms or fibrotic disease among recovered individuals. Because the first case of COVID-19 was documented less than one year ago, data regarding long-term clinical outcomes are not yet available, and predictions for long-term outcome are speculative at best. However, due to the staggering number of cases and the severity of disease in many individuals, there is a critical need to consider the potential long-term implications of COVID-19. This review examines current basic and clinical data regarding fibrogenic mechanisms of viral injury in the context of SARS-CoV-2. Several intersecting mechanisms between coronavirus infection and fibrotic pathways are discussed to highlight factors and processes that may be targetable to improve patient outcome. Reports of post-infection sequelae from previous coronavirus outbreaks are presented toward the goal of improved recognition of potential contributing risk factors for fibrotic disease.

A Potential Bioelectromagnetic Method to Slow Down the Progression and Prevent the Development of Ultimate Pulmonary Fibrosis by COVID-19

Introduction

Right now, we are facing a global pandemic caused by the coronavirus SARS-CoV-2 that causes the highly contagious human disease COVID-19. The number of COVID-19 cases is increasing at an alarming rate, more and more people suffer from it, and the death toll is on the rise since December 2019, when COVID-19 has presumably appeared. We need an urgent solution for the prevention, treatment, and recovery of the involved patients.

Methods

Modulated electro-hyperthermia (mEHT) is known as an immuno-supportive therapy in oncology. Our proposal is to apply this method to prevent the progression of the disease after its identification, to provide treatment when necessary, and deliver rehabilitation to diminish the fibrotic-often fatal-consequences of the infection.

Hypothesis

The effects of mEHT, which are proven for oncological applications, could be utilized for the inactivation of the virus or for treating the fibrotic consequences. The hypothesized mEHT effects, which could have a role in the antiviral treatment, it could be applied for viral-specific immune-activation and for anti-fibrotic treatments.

Fibrotic Changes Depicted by Thin-Section CT in Patients With COVID-19 at the Early Recovery Stage: Preliminary Experience

Objectives: To analyze follow-up CTs of patients recovering from COVID-19 in Wuhan, focusing on fibrotic change and its relevant risk factors.

Methods: From January 13 to February 27, 2020, 166 hospitalized patients meeting our criteria were included. The scores of fibrotic patterns on follow-up CT were evaluated. Patients were designated as group 1 (with CT evidence of fibrotic pattern) and group 2 (without CT evidence of fibrotic pattern). Multivariate logistic regression was performed to explore risk factors for fibrotic change in patients with COVID-19.

Results: The follow-up CTs were obtained on 56 days (median, IQR 51–63 days) after symptom onset. Of the 166 patients (mean age, 57 ± 15 years; 69/166 male), 46% (76/166) had CT evidence of fibrotic change and 77% (127/166) were severe or critical cases. Among patients with fibrotic change on CT, 84% (64/76) got a minimal or mild score of fibrosis. The high total score on peak CT, peak eosinophils, erythrocyte sedimentation rate (ESR) and advancing age were related to lung fibrotic change in patients with COVID-19.

Conclusion: Forty six percentages of patients (mainly severe or critical cases) with COVID-19 showed fibrotic change on follow-up CT at early recovery phase, while the extent of fibrosis was not large. The advancing age, high total score on peak CT, peak eosinophils and ESR were associated with fibrotic change depicted by CT in patients recovering from COVID-19. An extended follow up by CT imaging and pulmonary function testing is necessary to fully assess the sequela of COVID-19.

The prophylaxis and treatment potential of supplements for COVID-19

The global impact of the new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), infection that caused COVID-19 has been evident in the last few months from the unprecedented socioeconomic disruption to more than 600,000 deaths. The lack of vaccine and effective therapeutic agents for the disease prompted world-wide effort to test those antiviral therapeutics already in use for other diseases. Another interesting approach has been based on the pathological sequel of the disease that involve severe inflammatory reaction (or the cytokine storm) associated with pneumonia in critically ill patients. This article outlines the prophylaxis therapeutic potential of supplements vitamins and micronutrients in COVID-19. By ameliorating the inflammatory and oxidative stress associated with the disease and some direct antiviral effects, the application of these agents as adjuvants and other alternative approaches are discussed. Available clinical trials including those currently registered on these supplements are scrutinized.

Alveolar cells under mechanical stressed niche: critical contributors to pulmonary fibrosis

Pulmonary fibrosis arises from the repeated epithelial mild injuries and insufficient repair lead to over activation of fibroblasts and excessive deposition of extracellular matrix, which result in a mechanical stretched niche. However, increasing mechanical stress likely exists before the establishment of fibrosis since early micro injuries increase local vascular permeability and prompt cytoskeletal remodeling which alter cellular mechanical forces. It is noteworthy that COVID-19 patients with severe hypoxemia will receive mechanical ventilation as supportive treatment and subsequent pathology studies indicate lung fibrosis pattern. At advanced stages, mechanical stress originates mainly from the stiff matrix since boundaries between stiff and compliant parts of the tissue could generate mechanical stress. Therefore, mechanical stress has a significant role in the whole development process of pulmonary fibrosis. The alveoli are covered by abundant capillaries and function as the main gas exchange unit. Constantly subject to variety of damages, the alveolar epithelium injuries were recently recognized to play a vital role in the onset and development of idiopathic pulmonary fibrosis. In this review, we summarize the literature regarding the effects of mechanical stress on the fundamental cells constituting the alveoli in the process of pulmonary fibrosis, particularly on epithelial cells, capillary endothelial cells, fibroblasts, mast cells, macrophages and stem cells. Finally, we briefly review this issue from a more comprehensive perspective: the metabolic and epigenetic regulation.

New Perspectives on the Aberrant Alveolar Repair of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease of unknown etiology and high mortality. Current therapeutic strategies have limited efficacy and the prognosis remains poor. Based on the histological observations of IPF lung tissues and experimental studies using lung fibrosis animal models, it is gradually accepted that impaired epithelial regeneration after lung injury is a critical mechanism underlying the pathogenesis of pulmonary fibrosis. The central role of AEC2 in this process has been well-elucidated, while the contribution of other lung progenitor/stem cells is less discussed. Recently, increasing studies have identified several non-AEC2 epithelial progenitor/stem cells with great plasticity to transform into mature AECs and reconstitute alveolar epithelium after lung injury. However, why these cells do not function as alternate stem cells to regenerate alveolar epithelium in IPF is still unknown. In this review, we discuss the contribution of lung epithelial progenitor/stem cells in the aberrant alveolar regeneration, and provide a novel perspective on the mechanism of IPF pathogenesis, in which non-AEC2 progenitors may play an essential role.

Ma Xing Shi Gan Decoction Protects against PM2.5-Induced Lung Injury through Suppression of Epithelial-to-Mesenchymal Transition (EMT) and Epithelial Barrier Disruption

This research was designed to explore the effect of Ma Xing Shi Gan decoction (MXD) in alleviating particulate matter less than 2.5 μm in diameter (PM2.5) induced lung injury from the perspective of epithelial barrier protection and inhibition of epithelial-to-mesenchymal transition (EMT). Rats were exposed to PM2.5 to establish a lung injury model in vivo, and a PM2.5-stimulated primary cultured type II alveolar epithelial cell model was introduced in vitro. Our results indicated that MXD alleviated the weight loss and pathologic changes and improved the epithelial barrier dysfunction. MXD also significantly inhibited the TGF-β/Smad3 pathway, increased the level of ZO-1 and claudin-5, and reversed the EMT process. Notably, the protection of MXD was abolished by TGF-β in vitro. Our results indicated that MXD has a protection against PM2.5-induced lung injury. The proposed mechanism is reversing PM2.5-induced EMT through inhibiting TGF-β/Smad3 pathway and then upregulating the expression of tight-junction proteins.

Transient receptor potential canonical 1 channel mediates the mechanical stress‑induced epithelial‑mesenchymal transition of human bronchial epithelial (16HBE) cells

Airway remodeling is a central event in the pathology of chronic obstructive pulmonary disease (COPD) that leads to airway narrowing and subsequently, to increased mechanical pressure. High mechanical pressure can exacerbate airway remodeling. Thus, a treatment regimen aimed at disrupting this high‑pressure airway remodeling vicious cycle may improve the prognosis of patients with COPD. Recent studies have demonstrated that mechanical stress induces lung epithelial‑mesenchymal transition (EMT), which is commonly present in airway epithelial cells of patients with COPD. As TRPC1 functions as a mechanosensitive channel that mediates non‑selective cation entry in response to increased membrane stretch, the present study investigated the role of TRPC1 in the occurrence of EMT induced by mechanical stress. In the present study, the expression of TRPC1 in the bronchial epithelium was examined in vivo by immunohistochemistry. In vitro, human bronchial epithelial (16HBE) cells were subjected to mechanical stretching for up to 48 h, and TRPC1 expression was then examined by RT‑qPCR and western blot analysis. In addition, TRPC1 receptor function was assessed by Ca2+ imaging and siRNA transfection. EMT was identified using immunofluorescence, western blot analysis and RT‑qPCR. It was found that TRPC1 expression was upregulated in patients with COPD and in 16HBE cells subjected to mechanical stretch. The mechanical stress‑induced activation of TRPC1 in 16HBE cells increased the intracellular calcium concentration and subsequently decreased the expression of cytokeratin 8 and E‑cadherin, and increased the expression of α‑smooth muscle actin, indicating the occurrence of EMT. On the whole, the findings of the present study demonstrate that TRPC1 plays a key role in the occurrence of EMT in human lung epithelial cells in response to mechanical stretch; thus, this protein may serve as a novel therapeutic target for progressive airway remodeling in COPD.

TRIM72 promotes alveolar epithelial cell membrane repair and ameliorates lung fibrosis

Background

Chronic tissue injury was shown to induce progressive scarring in fibrotic diseases such as idiopathic pulmonary fibrosis (IPF), while an array of repair/regeneration and stress responses come to equilibrium to determine the outcome of injury at the organ level. In the lung, type I alveolar epithelial (ATI) cells constitute the epithelial barrier, while type II alveolar epithelial (ATII) cells play a pivotal role in regenerating the injured distal lungs. It had been demonstrated that eukaryotic cells possess repair machinery that can quickly patch the damaged plasma membrane after injury, and our previous studies discovered the membrane-mending role of Tripartite motif containing 72 (TRIM72) that expresses in a limited number of tissues including the lung. Nevertheless, the role of alveolar epithelial cell (AEC) repair in the pathogenesis of IPF has not been examined yet.

Method

In this study, we tested the specific roles of TRIM72 in the repair of ATII cells and the development of lung fibrosis. The role of membrane repair was accessed by saponin assay on isolated primary ATII cells and rat ATII cell line. The anti-fibrotic potential of TRIM72 was tested with bleomycin-treated transgenic mice.

Results

We showed that TRIM72 was upregulated following various injuries and in human IPF lungs. However, TRIM72 expression in ATII cells of the IPF lungs had aberrant subcellular localization. In vitro studies showed that TRIM72 repairs membrane injury of immortalized and primary ATIIs, leading to inhibition of stress-induced p53 activation and reduction in cell apoptosis. In vivo studies demonstrated that TRIM72 protects the integrity of the alveolar epithelial layer and reduces lung fibrosis.

Conclusion

Our results suggest that TRIM72 protects injured lungs and ameliorates fibrosis through promoting post-injury repair of AECs.