Alteration of tight junctions in pulmonary microvascular endothelial cells in bleomycin-treated rats

Three-Dimensional Imaging of Pulmonary Fibrotic Foci at the Alveolar Scale Using Tissue-Clearing Treatment with Staining Techniques of Extracellular Matrix

Idiopathic pulmonary fibrosis is a progressive, chronic lung disease characterized by the accumulation of extracellular matrix proteins, including collagen and elastin. Imaging of extracellular matrix in fibrotic lungs is important for evaluating its pathological condition as well as the distribution of drugs to pulmonary focus sites and their therapeutic effects. In this study, we compared techniques of staining the extracellular matrix with optical tissue-clearing treatment for developing three-dimensional imaging methods for focus sites in pulmonary fibrosis. Mouse models of pulmonary fibrosis were prepared via the intrapulmonary administration of bleomycin. Fluorescent-labeled tomato lectin, collagen I antibody, and Col-F, which is a fluorescent probe for collagen and elastin, were used to compare the imaging of fibrotic foci in intact fibrotic lungs. These lung samples were cleared using the Clear^T2 tissue-clearing technique. The cleared lungs were two dimensionally observed using laser-scanning confocal microscopy, and the images were compared with those of the lung tissue sections. Moreover, three-dimensional images were reconstructed from serial two-dimensional images. Fluorescent-labeled tomato lectin did not enable the visualization of fibrotic foci in cleared fibrotic lungs. Although collagen I in fibrotic lungs could be visualized via immunofluorescence staining, collagen I was clearly visible only until 40 μm from the lung surface. Col-F staining facilitated the visualization of collagen and elastin to a depth of 120 μm in cleared lung tissues. Furthermore, we visualized the three-dimensional extracellular matrix in cleared fibrotic lungs using Col-F, and the images provided better visualization than immunofluorescence staining. These results suggest that Clear^T2 tissue-clearing treatment combined with Col-F staining represents a simple and rapid technique for imaging fibrotic foci in intact fibrotic lungs. This study provides important information for imaging various organs with extracellular matrix-related diseases.

[Intrapulmonary Pharmacokinetics and Drug Distribution Characteristics for the Treatment of Respiratory Diseases]

This study was designed to clarify the intrapulmonary pharmacokinetics and distribution characteristics of drugs in order to develop better therapies for respiratory diseases, including respiratory infections and pulmonary fibrosis. The distribution characteristics of three macrolide antimicrobial agents-clarithromycin, azithromycin, and telithromycin-in plasma, lung epithelial lining fluid (ELF), and alveolar macrophages (AMs), were examined for the optimization of antimicrobial therapy. The time course of the uptake of these agents in ELF and AMs, following oral administration to rats, resulted in markedly higher concentrations than that in plasma. The high concentration of the agents in AMs was due to their sustained distribution to ELF via multidrug resistance protein 1 and to high uptake by AMs themselves via active transport mechanisms and trapping and/or binding in acidic organelles. The intrapulmonary pharmacokinetics of aerosolized model compounds administered to animals with bleomycin-induced pulmonary fibrosis via aerosol formulations of model compounds (MicroSprayer) were then evaluated. The concentrations of these compounds in the plasma of pulmonary fibrotic rats were markedly higher than in that of control rats. The expression of epithelial tight junctions decreased in pulmonary fibrotic lesions. The accumulation of extracellular matrix inhibited the intrapulmonary distribution of aerosolized model compounds, indicating that aerosolized drugs are easily absorbed after leakage through damaged alveolar epithelia, but cannot become widely distributed in the lungs because of interruption by the extracellular matrix. This review provides useful findings for the development of therapies for respiratory infections and pulmonary fibrosis.

Feixian Recipe inhibits pulmonary fibrosis by targeting pulmonary microvascular endothelial cells and VEGF/VEGFR2 signaling pathway

Objective: To investigate the regulatory mechanism of PMVECs and vascular endothelial growth factor VEGF/vascular endothelial growth factor receptor 2 (VEGFR2) signaling pathway in pulmonary fibrosis and the inhibitory effect of Feixian Recipe (FXR) in pulmonary fibrosis by targeting VEGF/VEGFR2 signal pathway.

Methods: In this study, pulmonary microvascular endothelial cells (PMVECs) were successfully isolated from rats with pulmonary fibrosis. Cells were divided into six groups: model group, prednisone group, losartan group and three different concentrated (100[Formula: see text]ug/mL, 60[Formula: see text]ug/mL, 20[Formula: see text]ug/mL) FXR groups. The adhesion rate, migration and closed blood vessels of each PMVECs group were detected. The mRNA expression of VEGF, VEGFR2, phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinases 38 (P38 MAPK) and activin receptor-like kinase (ALK) were detected by SYBR Green I real-time fluorescence quantitative PCR.

Results: Compared with the model group, the adhesion rate, migration and angiogenesis of PMVECs were decreased in FXR groups ([Formula: see text]). Compared with prednisone and losartan groups, the mRNA expressions of VEGF, VEGFR2, PI3K and P38 MAPK were down-regulated significantly by FXR ([Formula: see text]).

Conclution: FXR can inhibit the migration, adhesion and angiogenesis of PMVECs in rats with pulmonary fibrosis by targeting VEGF/VEGFR2 signal pathway, and inhibit the progress of pulmonary fibrosis.

The expression levels of Notch-related signaling molecules in pulmonary microvascular endothelial cells in bleomycin-induced rat pulmonary fibrosis

Previous studies have suggested that the Notch signaling pathway plays a very important role in the proliferation and differentiation of pulmonary microvascular endothelial cells (PMVECs). Therefore, we aimed to investigate the expression level of Notch-related signaling molecules in PMVECs in bleomycin (BLM)-induced rat pulmonary fibrosis. Immunohistochemistry, immunofluorescence, Western blotting, and real-time PCR were used to analyze the differences in protein and mRNA expression levels of Notch-related signaling molecules, i.e. Notch1, Jagged1, Delta-like ligand 4 (Dll4), and hairy and enhancer of split homolog 1 (Hes1), between a control group treated with intratracheal instillation of saline and a study group treated with intratracheal instillation of BLM solution. Expression levels of the receptor Notch1 and one of its ligands, Jagged1, were upregulated, while the expression levels of the ligand Dll4 and the target molecule of the Notch signaling pathway, Hes1, were downregulated. The differences in protein and mRNA expression levels between the control and study groups were significant (p<0.001). The Jagged1/Notch1 signaling pathway is activated in the pathogenesis of BLM-induced rat pulmonary fibrosis, while the Dll4/Notch1 signaling pathway is inhibited, which inhibits the suppressive effect of Dll4/Notch1 signaling on PMVEC overproliferation, further causing PMVEC dysfunction in cell sprouting and maturation as well as abnormal differentiation of the cell phenotype. Conversely, the down-expression of Hes1 indicates that the Jagged1/Notch1 signaling pathway could be a non-canonical Notch signaling pathway independent of Hes1 activation, which differs from the canonical Dll4/Notch1 signaling pathway.

Lung fibrosis: drug screening and disease biomarker identification with a lung slice culture model and subtracted cDNA Library

Pulmonary fibrosis is a progressive and irreversible disorder with no appropriate cure. A practical and effective experimental model that recapitulates the disease will greatly benefit the research community and, ultimately, patients. In this study, we tested the lung slice culture (LSC) system for its potential use in drug screening and disease biomarker identification. Fibrosis was induced by treating rat lung slices with 1ng/ml TGF-β1 and 2.5μM CdCl2, quantified by measuring the content of hydroxyproline, and confirmed by detecting the expression of collagen type III alpha 1 (Col3α1) and connective tissue growth factor (CTGF) genes. The anti-fibrotic effects of pirfenidone, spironolactone and eplerenone were assessed by their capability to reduce hydroxyproline content. A subtractive hybridisation technique was used to create two cDNA libraries (subtracted and unsubtracted) from lung slices. The housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was employed to assess the subtraction efficiency of the subtracted cDNA library. Clones from the two libraries were sequenced and the genes were identified by performing a BLAST search on the NCBI GenBank database. Furthermore, the relevance of the genes to fibrosis formation was verified. The results presented here show that fibrosis was effectively induced in cultured lung slices, which exhibited significantly elevated levels of hydroxyproline and Col3α1/CTGF gene expression. Several inhibitors have demonstrated their anti-fibrotic effects by significantly reducing hydroxyproline content. The subtracted cDNA library, which was enriched for differentially expressed genes, was used to successfully identify genes associated with fibrosis. Collectively, the results indicate that our LSC system is an effective model for the screening of drug candidates and for disease biomarker identification.

Isoflurane Ameliorates Acute Lung Injury by Preserving Epithelial Tight Junction Integrity

BACKGROUND

Isoflurane may be protective in preclinical models of lung injury, but its use in patients with lung injury remains controversial and the mechanism of its protective effects remains unclear. The authors hypothesized that this protection is mediated at the level of alveolar tight junctions and investigated the possibility in a two-hit model of lung injury that mirrors human acute respiratory distress syndrome.

METHODS

Wild-type mice were treated with isoflurane 1 h after exposure to nebulized endotoxin (n = 8) or saline control (n = 9) and then allowed to recover for 24 h before mechanical ventilation (MV; tidal volume, 15 ml/kg, 2 h) producing ventilator-induced lung injury. Mouse lung epithelial cells were similarly treated with isoflurane 1 h after exposure to lipopolysaccharide. Cells were cyclically stretched the following day to mirror the MV protocol used in vivo.

RESULTS

Mice treated with isoflurane following exposure to inhaled endotoxin and before MV exhibited significantly less physiologic lung dysfunction. These effects appeared to be mediated by decreased vascular leak, but not altered inflammatory indices. Mouse lung epithelial cells treated with lipopolysaccharide and cyclic stretch and lungs harvested from mice after treatment with lipopolysaccharide and MV had decreased levels of a key tight junction protein (i.e., zona occludens 1) that was rescued by isoflurane treatment.

CONCLUSIONS

Isoflurane rescued lung injury induced by a two-hit model of endotoxin exposure followed by MV by maintaining the integrity of the alveolar-capillary barrier possibly by modulating the expression of a key tight junction protein.

Cytoskeletal mechanisms regulating vascular endothelial barrier function in response to acute lung injury

Endothelial cells (EC) form a semi-permeable barrier between the interior space of blood vessels and the underlying tissues. In acute lung injury (ALI) the EC barrier is weakened leading to increased vascular permeability. It is widely accepted that EC barrier integrity is critically dependent upon intact cytoskeletal structure and cell junctions. Edemagenic agonists, like thrombin or endotoxin lipopolysaccharide (LPS), induced cytoskeletal rearrangement, and EC contractile responses leading to disruption of intercellular contacts and EC permeability increase. The highly clinically-relevant cytoskeletal mechanisms of EC barrier dysfunction are currently under intense investigation and will be described and discussed in the current review.

Hyperoxia arrests pulmonary development in newborn rats via disruption of endothelial tight junctions and downregulation of Cx40

This study investigated changes in vascular endothelial cell tight junction structure and the expression of the gene encoding connexin 40 (Cx40) at the early pneumonedema stage of hyperoxia‑induced bronchopulmonary dysplasia (BPD) in a newborn rat model. A total of 96 newborn rats were randomly assigned to one of the following two groups, the hyperoxia group (n=48) and the control group (n=48). A hyperoxia-induced BPD model was established for the first group, while rats in the control group were maintained under normoxic conditions. Extravasation of Evans Blue (EB) was measured; the severity of lung injury was assessed; a transmission electron microscope (TEM) was used to examine the vascular endothelial cell tight junction structures, and immunohistochemical assay, western blotting and reverse transcription-polymerase chain reaction (RT-PCR) were used to evaluate the expression of Cx40 at the mRNA and protein level. Our findings showed that injuries due to BPD are progressively intensified during the time-course of exposure to hyperoxic conditions. Pulmonary vascular permeability in the hyperoxia group reached the highest level at day 5, and was significantly higher compared to the control group. TEM observations demonstrated tight junctions between endothelial cells were extremely tight. In the hyperoxia group, no marked changes in the tight junction structure were found at days 1 and 3; paracellular gaps were visible between endothelial cells at days 5 and 7. Immunohistochemical staining revealed that the Cx40 protein is mainly expressed in the vascular endothelial cells of lung tissue. Western blotting and RT-PCR assays showed a gradual decrease in Cx40 expression, depending on the exposure time to hyperoxic conditions. However, the Cx40 mRNA level reached a trough at 5 days. Overall, our study demonstrated that exposure to hyperoxia damages the tight junction structures between vascular endothelial cells and downregulates Cx40. We therefore conclude that hyperoxia may participate in the regulation of pulmonary vascular endothelial permeability.

Proliferative phenotype of pulmonary microvascular endothelial cells plays a critical role in the overexpression of CTGF in the bleomycin-injured rat

The pathogenesis of idiopathic pulmonary fibrosis (IPF) is not very clear, with evidence for the involvement of both inflammation and aberrant vascular remodeling (associated with angiogenesis). Pulmonary microvascular endothelial cells (PMVECs), which play a major role in inflammation, secrete cytokines that promote the transformation and collagen synthesis of fibroblasts. Moreover, angiogenesis is characterized by PMVEC proliferation. The main aim of this study was to confirm the role of PMVECs in pulmonary fibrosis. Accordingly, we observed the functional changes in PMVECs in bleomycin (BLM)-treated rats (pulmonary fibrosis model) in vivo, and compared them with those of rats with pneumonia. The proliferation phenotype and intracellular ionized calcium concentration ([Ca(2+)]i) of PMVECs from BLM-treated rats were also investigated. The functioning of PMVECs was abnormal in BLM-injured rats, particularly with regard to their proliferation and secretion of connective tissue growth factor (CTGF). [Ca(2+)]i was increased in the proliferated PMVECs from BLM-treated rats. The findings suggest that dysfunction of PMVECs characterized by overexpression of CTGF is critical in rat pulmonary injury induced by BLM, and is probably related with the proliferative phenotype and [Ca(2+)]i overload. It can be concluded from the results that proliferation of PMVECs plays an important role in the pathogenesis of BLM-induced PF.

Tight junctions in skin: new perspectives

Tight junctions (TJs) are intercellular contacts that seal the space between the individual cells of an epithelial sheet or stratifying epithelia, such as the epidermis, so that they can collectively separate tissue compartments. Intercellular junctions, such as adherens and TJs, play a crucial role in the formation and maintenance of epithelial and endothelial barriers. A variety of components including claudins, occludin, tricellulin, zonula occluden proteins and junctional adhesion molecules have been identified in complex localization patterns in mammalian epidermis. In several skin diseases that are characterized by impaired skin barrier function, altered proliferation/differentiation of the epidermis and/or infiltration of inflammatory cells, altered expression patterns of TJ proteins have been observed. This review is aimed at providing an insight into the molecular composition, tools for identification and understanding the role of TJs in skin diseases and barrier function regulation.

Comparing the differential effects of LPA on the barrier function of human pulmonary endothelial cells

Lysophosphatidic acid (LPA) is a class of bioactive lyso-phospholipid that mediates most of its biological effects through a family of G protein-coupled receptors of which six have been identified. The role of the LPA pathway in driving chronic lung diseases such as idiopathic pulmonary fibrosis (IPF) has gained considerable academic and industry attention. Modulation of the pulmonary artery endothelial barrier function by the LPA1 receptor has been shown to drive pulmonary fibrosis in murine models of disease. The purpose of this study was (i) to assess the effect of LPA on the barrier function of human pulmonary arterial (HPAEC) and microvascular (HMVEC) endothelial cells and (ii) to identify the LPA receptor subtype(s) responsible for changes in human pulmonary endothelial cell permeability using LPA receptor antagonists and siRNA technology. Analysis of the LPA receptor subtype expression demonstrated predominant expression of LPA2 and LPA6 receptor subtypes in both HPAECs and HMVECs. HPAECs also exhibit low expression of LPA1, LPA3, and LPA4 receptor subtypes. Treatment of cells with increasing concentrations of LPA caused loss of barrier function in HPAECs but not HMVECs, despite both cell types exhibiting very similar LPA receptor expression profiles. The LPA-mediated loss of barrier function in HPAECs appears to be independent of the LPA1 receptor and likely to be mediated via the LPA6 receptor although we cannot exclude an additional role for the LPA2 and LPA4 receptors in mediating these effects. These results suggest cell-specific mechanisms exist in human pulmonary endothelial cells to permit regulation of barrier function downstream of LPA receptors. More importantly, our data indicate that selective LPA1 receptor antagonism may be insufficient for therapeutic use in pulmonary diseases where impaired endothelial barrier function is related to disease initiation and progression.

Thiol-redox antioxidants protect against lung vascular endothelial cytoskeletal alterations caused by pulmonary fibrosis inducer, bleomycin: comparison between classical thiol-protectant, N-acetyl-L-cysteine, and novel thiol antioxidant, N,N'-bis-2-mercaptoethyl isophthalamide

Lung vascular alterations and pulmonary hypertension associated with oxidative stress have been reported to be involved in idiopathic lung fibrosis (ILF). Therefore, here, we hypothesize that the widely used lung fibrosis inducer, bleomycin, would cause cytoskeletal rearrangement through thiol-redox alterations in the cultured lung vascular endothelial cell (EC) monolayers. We exposed the monolayers of primary bovine pulmonary artery ECs to bleomycin (10 µg) and studied the cytotoxicity, cytoskeletal rearrangements, and the macromolecule (fluorescein isothiocyanate-dextran, 70,000 mol. wt.) paracellular transport in the absence and presence of two thiol-redox protectants, the classic water-soluble N-acetyl-L-cysteine (NAC) and the novel hydrophobic N,N'-bis-2-mercaptoethyl isophthalamide (NBMI). Our results revealed that bleomycin induced cytotoxicity (lactate dehydrogenase leak), morphological alterations (rounding of cells and filipodia formation), and cytoskeletal rearrangement (actin stress fiber formation and alterations of tight junction proteins, ZO-1 and occludin) in a dose-dependent fashion. Furthermore, our study demonstrated the formation of reactive oxygen species, loss of thiols (glutathione, GSH), EC barrier dysfunction (decrease of transendothelial electrical resistance), and enhanced paracellular transport (leak) of macromolecules. The observed bleomycin-induced EC alterations were attenuated by both NAC and NBMI, revealing that the novel hydrophobic thiol-protectant, NBMI, was more effective at µM concentrations as compared to the water-soluble NAC that was effective at mM concentrations in offering protection against the bleomycin-induced EC alterations. Overall, the results of the current study suggested the central role of thiol-redox in vascular EC dysfunction associated with ILF.