Wound repair of human surface respiratory epithelium

Secretome Analysis of Human Nasal Fibroblast Identifies Proteins That Promote Wound Healing

Conditioned medium from cultured fibroblast cells is recognized to promote wound healing and growth through the secretion of enzymes, extracellular matrix proteins, and various growth factors and cytokines. The objective of this study was to profile the secreted proteins present in nasal fibroblast conditioned medium (NFCM). Nasal fibroblasts isolated from human nasal turbinates were cultured for 72 h in Defined Keratinocytes Serum Free Medium (DKSFM) or serum-free F12: Dulbecco's Modified Eagle's Medium (DMEM) to collect conditioned medium, denoted as NFCM_DKSFM and NFCM_FD, respectively. SDS-PAGE was performed to detect the presence of protein bands, followed by MALDI-TOF and mass spectrometry analysis. SignalP, SecretomeP, and TMHMM were used to identify the secreted proteins in conditioned media. PANTHER Classification System was performed to categorize the protein according to protein class, whereas STRING 10 was carried out to evaluate the predicted proteins interactions. SDS-PAGE results showed the presence of various protein with molecular weight ranging from ~10 kDa to ~260 kDa. Four protein bands were identified using MALDI-TOF. The analyses identified 104, 83, and 7 secreted proteins in NFCM_FD, NFCM_DKSFM, and DKSFM, respectively. Four protein classes involved in wound healing were identified, namely calcium-binding proteins, cell adhesion molecules, extracellular matrix proteins, and signaling molecules. STRING10 protein prediction successfully identified various pathways regulated by secretory proteins in NFCM. In conclusion, this study successfully profiled the secreted proteins of nasal fibroblasts and these proteins are predicted to play important roles in RECs wound healing through various pathways.

Regeneration in calcareous sponge relies on 'purse-string' mechanism and the rearrangements of actin cytoskeleton

The crucial step in any regeneration process is epithelization, i.e. the restoration of an epithelium structural and functional integrity. Epithelization requires cytoskeletal rearrangements, primarily of actin filaments and microtubules. Sponges (phylum Porifera) are early branching metazoans with pronounced regenerative abilities. Calcareous sponges have a unique step during regeneration: the formation of a temporary structure, called regenerative membrane which initially covers a wound. It forms due to the morphallactic rearrangements of exopinaco- and choanoderm epithelial-like layers. The current study quantitatively evaluates morphological changes and characterises underlying actin cytoskeleton rearrangements during regenerative membrane formation in asconoid calcareous sponge Leucosolenia variabilis through a combination of time-lapse imaging, immunocytochemistry, and confocal laser scanning microscopy. Regenerative membrane formation has non-linear stochastic dynamics with numerous fluctuations. The pinacocytes at the leading edge of regenerative membrane form a contractile actomyosin cable. Regenerative membrane formation either depends on its contraction or being coordinated through it. The cell morphology changes significantly during regenerative membrane formation. Exopinacocytes flatten, their area increases, while circularity decreases. Choanocytes transdifferentiate into endopinacocytes, losing microvillar collar and flagellum. Their area increases and circularity decreases. Subsequent redifferentiation of endopinacocytes into choanocytes is accompanied by inverse changes in cell morphology. All transformations rely on actin filament rearrangements similar to those characteristic of bilaterian animals. Altogether, we provide here a qualitative and quantitative description of cell transformations during reparative epithelial morphogenesis in a calcareous sponge.

Lung extracellular matrix modulates KRT5+ basal cell activity in pulmonary fibrosis

Aberrant expansion of KRT5+ basal cells in the distal lung accompanies progressive alveolar epithelial cell loss and tissue remodelling during fibrogenesis in idiopathic pulmonary fibrosis (IPF). The mechanisms determining activity of KRT5+ cells in IPF have not been delineated. Here, we reveal a potential mechanism by which KRT5+ cells migrate within the fibrotic lung, navigating regional differences in collagen topography. In vitro, KRT5+ cell migratory characteristics and expression of remodelling genes are modulated by extracellular matrix (ECM) composition and organisation. Mass spectrometry- based proteomics revealed compositional differences in ECM components secreted by primary human lung fibroblasts (HLF) from IPF patients compared to controls. Over-expression of ECM glycoprotein, Secreted Protein Acidic and Cysteine Rich (SPARC) in the IPF HLF matrix restricts KRT5+ cell migration in vitro. Together, our findings demonstrate how changes to the ECM in IPF directly influence KRT5+ cell behaviour and function contributing to remodelling events in the fibrotic niche.

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

Ursodeoxycholic acid ameliorates cell migration retarded by the SARS-CoV-2 spike protein in BEAS-2B human bronchial epithelial cells

BACKGROUND

Coronavirus disease 2019 (COVID-19) is caused by severe acute -respiratory syndrome coronavirus 2 (SARS- CoV-2) through interaction of the spike protein (SP) with the receptor-binding domain (RBD) and its receptor, angiotensin converting enzyme 2(ACE2). Repair mechanisms induced following virus infection can restore the protective barrier through wound healing. Then, cells from the epithelial basal layer repopulate the damaged area, followed by cell proliferation and differentiation, as well as changes in gene expression.

METHODS

Using Beas-2B cells and SP, we investigated whether ursodeoxycholic acid (UDCA) contributes to restoration of the bronchial epithelial layer. ACE2 expression was measured by RT-PCR and Western blotting. SP-ACE2 interaction was analyzed by flow cytometry and visualized through immunostaining. Cell migration was assessed using single cell path tracking and wound healing assay.

RESULTS

Upon ACE2 overexpression in HeLa, HEK293T, and Beas-2B cells following the transfection of pCMV-ACE2 plasmid DNA, SP binding on each cell was increased in the ACE2 overexpression group compared to pCMV-transfected control cells. SP treatment delayed the migration of BEAS-2B cells compared to the control. SP also reduced cell migration, even under ACE2 overexpression; SP binding was greater in ACE2-overexpressed cells than control cells. UDCA interfered significantly with the binding of SP to ACE2 under our experimental conditions. UDCA also restored the inhibitory migration of Beas-2B cells induced by SP treatment.

CONCLSION

Our data demonstrate that UDCA can contribute to the inhibition of abnormal airway epithelial cell migration. These results suggest that UDCA can enhance the repair mechanism, to prevent damage caused by SP-ACE2 interaction and enhance restoration of the epithelial basal layer.

Invasion and diversity in Pseudomonas aeruginosa urinary tract infections

Introduction.P. aeruginosa is an opportunistic Gram-negative pathogen frequently isolated in urinary tract infections (UTI) affecting elderly and catheterized patients and associated with ineffective antibiotic treatment and poor clinical outcomes.

Gap statement. Invasion has been shown to play an important role in UTI caused by E. coli but has only recently been studied with P. aeruginosa. The ability of P. aeruginosa to adapt and evolve in chronic lung infections is associated with resistance to antibiotics but has rarely been studied in P. aeruginosa UTI populations.

Aim. We sought to determine whether phenotypic and genotypic heterogeneity exists in P. aeruginosa UTI isolates and whether, like urinary pathogenic Escherichia coli, these could invade human bladder epithelial cells – two factors that could complicate antibiotic treatment.

Methodology.P. aeruginosa UTI samples were obtained from five elderly patients at the Royal Liverpool University Hospital as part of routine diagnostics. Fourty isolates from each patient sample were screened for a range of phenotypes. The most phenotypically diverse isolates were genome sequenced. Gentamicin protection assays and confocal microscopy were used to determine capacity to invade bladder epithelial cells.

Results. Despite significant within-patient phenotypic differences, no UTI patient was colonized by distinct strains of P. aeruginosa. Limited genotypic differences were identified in the form of non-synonymous SNPs. Gentamicin protection assays and confocal microscopy provided evidence of P. aeruginosa’s ability to invade bladder epithelial cells.

Conclusions. Phenotypic variation and cell invasion could further complicate antibiotic treatment in some patients. More work is needed to better understand P. aeruginosa UTI pathogenesis and develop more effective treatment strategies.

CrkII/Abl phosphorylation cascade is critical for NLRC4 inflammasome activity and is blocked by Pseudomonas aeruginosa ExoT

Type 3 Secretion System (T3SS) is a highly conserved virulence structure that plays an essential role in the pathogenesis of many Gram-negative pathogenic bacteria, including Pseudomonas aeruginosa. Exotoxin T (ExoT) is the only T3SS effector protein that is expressed in all T3SS-expressing P. aeruginosa strains. Here we show that T3SS recognition leads to a rapid phosphorylation cascade involving Abl / PKCδ / NLRC4, which results in NLRC4 inflammasome activation, culminating in inflammatory responses that limit P. aeruginosa infection in wounds. We further show that ExoT functions as the main anti-inflammatory agent for P. aeruginosa in that it blocks the phosphorylation cascade through Abl / PKCδ / NLRC4 by targeting CrkII, which we further demonstrate to be important for Abl transactivation and NLRC4 inflammasome activation in response to T3SS and P. aeruginosa infection.

Pseudomonas aeruginosa secretes the toxin ExoT, which is important for pathogenesis. Here, the authors show that ExoT inhibits NLRC4-dependent inflammatory responses during wound infection.

Primary Cilium by Polyinosinic:Polycytidylic Acid Regulates the Regenerative Migration of Beas-2B Bronchial Epithelial Cells

The airway epithelium is equipped with the ability to resist respiratory disease development and airway damage, including the migration of airway epithelial cells and the activation of TLR3, which recognizes double-stranded (ds) RNA. Primary cilia on airway epithelial cells are involved in the cell cycle and cell differentiation and repair. In this study, we used Beas-2B human bronchial epithelial cells to investigate the effects of the TLR3 agonist polyinosinic:polycytidylic acid [Poly(I:C)] on airway cell migration and primary cilia (PC) formation. PC formation increased in cells incubated under serum deprivation. Migration was faster in Beas-2B cells pretreated with Poly(I:C) than in control cells, as judged by a wound healing assay, single-cell path tracking, and a Transwell migration assay. No changes in cell migration were observed when the cells were incubated in conditioned medium from Poly(I:C)-treated cells. PC formation was enhanced by Poly(I:C) treatment, but was reduced when the cells were exposed to the ciliogenesis inhibitor ciliobrevin A (CilioA). The inhibition of Beas-2B cell migration by CilioA was also assessed and a slight decrease in ciliogenesis was detected in SARS-CoV-2 spike protein (SP)-treated Beas-2B cells overexpressing ACE2 compared to control cells. Cell migration was decreased by SP but restored by Poly(I:C) treatment. Taken together, our results demonstrate that impaired migration by SP-treated cells can be attenuated by Poly(I:C) treatment, thus increasing airway cell migration through the regulation of ciliogenesis.

Wound Healing of the Nasal and Paranasal Mucosa: A Review

Background

Wound healing is a highly coordinated process involving clot formation, inflammatory reaction, immune response, and, finally, tissue remodeling and maturation. Only few data regarding the specific healing of the nasal or sinusal mucosa are available.

Methods

After a short summary of the general principles of wound healing, the most important data regarding in vitro or in vivo models of wound healing of the nasal and paranasal mucosa are discussed. Attention is paid to clinical application.

Main Findings

First observations regarding the specific regulation of epithelial regeneration by growth factors have underlined the complex relationship between extracellular matrix and epithelium during the repair process. However, only poor and aspecific correlations can be described between endoscopically and histomorphologically defined postoperative phases.

Leukotriene B4 receptor 2 regulates the proliferation, migration, and barrier integrity of bronchial epithelial cells

The airway epithelium plays a crucial role in the pathogenesis of asthma. The functions of leukotriene B4 receptor 2 (BLT2) on the airway epithelial cells remains unknown. In our study, BLT2 expression in 16HBE bronchial epithelial cells were manipulated by transfection with BLT2 overexpression plasmid or BLT2 small interference RNA. 16HBE cells were then exposed to BLT2 antagonist (LY255283) or BLT2 agonist (12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid [12-HHT] or CAY10583). The results showed that BLT2 overexpression, 12-HHT stimulation, or CAY10583 treatment resulted in the enhanced proliferation and migration of 16HBE cells. In addition, BLT2 showed an inhibitory effect on epithelial permeability as illustrated by the measurement of transepithelial electrical resistance (TER) and epithelial permeability, and a promoting effect on the levels of tight junction proteins (occludin and claudin-4) and phosphorylated p38 as demonstrated by real-time PCR and Western blotting analyses. These results suggest BLT2 as a key determinant of airway epithelial barrier integrity. On the contrary, RNAi-mediated knockdown or LY255283 treatment had reversed effects on the proliferation, migration, and epithelial barrier integrity. Together, our findings suggest the critical roles of BLT2 on the functions of bronchial epithelial cells and that BLT2 agonists are potential therapeutic agents for asthma treatment.

Effect of a combination of mometasone furoate, levofloxacin, and retinyl palmitate with an in situ gel-forming nasal delivery system on nasal mucosa damage repair in an experimental rabbit model

BACKGROUND

In this study a combination of Mometasone Furoate (MF)+Levofloxacin hemihydrate (LH)+Retinyl palmitate (RP) with an in situ gel-forming delivery system was evaluated at different stages of nasal mucosal damage repair in a rabbit maxillary sinus model.

METHODS

In this study, 28 rabbits were included and assigned randomly to four groups. In all rabbits, a standard ostium was opened in the medial wall of the maxillary sinus by using a drill. Two different subsequently prepared gels with an in situ gel-forming delivery system were used. Of these 14 nasal cavities, combination 1 (active combination) was applied daily to 5, combination 2 (placebo) to 5, while 4 did not receive any pharmaceutical treatment. The diameter of the ostium was measured. Histopathological assessment was performed.

RESULTS

After 2, 3 and 4 weeks, the ostium diameter was significantly wider in the group where gel 1 had been applied compared to both the placebo group and control group. In the group treated with gel 1, after 2, 3 and 4 weeks the presence of superficial cilia was significantly greater, surface epithelium significantly less. In the 4th week, histologic scores for fibroblastic proliferation and vascular proliferation in the group treated with gel 1 were better than in either the control group or the placebo group. With gel 1, chronic inflammation parameters were also significantly lower than in the other groups.

CONCLUSION

The MF+LH+RP mixture with an in situ gel-forming nasal delivery system applied for wound healing after FESS prevents the formation of stenosis and is favorable for proper wound healing.

A heteromeric molecular complex regulates the migration of lung alveolar epithelial cells during wound healing

Alveolar type II epithelial cells (ATII) are instrumental in early wound healing in response to lung injury, restoring epithelial integrity through spreading and migration. We previously reported in separate studies that focal adhesion kinase-1 (FAK) and the chemokine receptor CXCR4 promote epithelial repair mechanisms. However, potential interactions between these two pathways were not previously considered. In the present study, we found that wounding of rat ATII cells promoted increased association between FAK and CXCR4. In addition, protein phosphatase-5 (PP5) increased its association with this heteromeric complex, while apoptosis signal regulating kinase-1 (ASK1) dissociated from the complex. Cell migration following wounding was decreased when PP5 expression was decreased using shRNA, but migration was increased in ATII cells isolated from ASK1 knockout mice. Interactions between FAK and CXCR4 were increased upon depletion of ASK1 using shRNA in MLE-12 cells, but unaffected when PP5 was depleted. Furthermore, we found that wounded rat ATII cells exhibited decreased ASK1 phosphorylation at Serine-966, decreased serine phosphorylation of FAK, and decreased association of phosphorylated ASK1 with FAK. These changes in phosphorylation were dependent upon expression of PP5. These results demonstrate a unique molecular complex comprising CXCR4, FAK, ASK1, and PP5 in ATII cells during wound healing.

Healing of the nasal septal mucosa in an experimental rabbit model of mucosal injury

Objective

The aim of this study was to investigate the regeneration process of the nasal mucosa after a surgically created mucosal defect in the rabbit nasal septum, and to evaluate the effects of different interventions.

Methods

A 7 mm-diameter circular mucosal defect was made in the septum of forty New Zealand white rabbits. The rabbits were divided into four groups (ten rabbits in each group) according to the type of intervention; no treatment (control), silastic sheet (SS), hyaluronic acid (HA), and silastic sheet and hyaluronic acid (SS + HA) group. The diameter of the defect, mucosal thickness, epithelial thickness, and ciliated cell count were evaluated every week for five weeks.

Results

The average diameter of the defect in the control group were 5.1, 3.65, 1.2, 0.75, and 0.05 mm at postoperative 1, 2, 3, 4, and 5 weeks. In the SS group, the diameter decreased to 4.35, 2.1, 0.35, 0.15, and 0 mm at postoperative 1, 2, 3, 4, and 5 weeks, respectively, in which the mean diameter of the postoperative week 2 was significantly smaller compared to control (3.65 mm vs. 2.1 mm, P = 0.039). For the HA group and SS + HA group, the diameter of the defect did not show a significant difference from the control group during the five weeks. The mucosal thickness, epithelial thickness, and ciliated cell count of the regenerated mucosa were not significantly different among the groups.

Conclusion

The regeneration process of the nasal septal mucosa was identified using a novel rabbit model. Mucosal regeneration can be accelerated by applying silastic sheets.

Pseudomonas aeruginosa ExoT Induces Mitochondrial Apoptosis in Target Host Cells in a Manner That Depends on Its GTPase-activating Protein (GAP) Domain Activity

Pseudomonas aeruginosa is the most common cause of hospital-acquired pneumonia and a killer of immunocompromised patients. We and others have demonstrated that the type III secretion system (T3SS) effector protein ExoT plays a pivotal role in facilitating P. aeruginosa pathogenesis. ExoT possesses an N-terminal GTPase-activating protein (GAP) domain and a C-terminal ADP-ribosyltransferase (ADPRT) domain. Because it targets multiple non-overlapping cellular targets, ExoT performs several distinct virulence functions for P. aeruginosa, including induction of apoptosis in a variety of target host cells. Both the ADPRT and the GAP domain activities contribute to ExoT-induced apoptosis. The ADPRT domain of ExoT induces atypical anoikis by transforming an innocuous cellular protein, Crk, into a cytotoxin, which interferes with integrin survival signaling. However, the mechanism underlying the GAP-induced apoptosis remains unknown. In this study, we demonstrate that the GAP domain activity is both necessary and sufficient to induce mitochondrial (intrinsic) apoptosis. We show that intoxication with GAP domain results in: (i) JNK1/2 activation; (ii) substantial increases in the mitochondrial levels of activated pro-apoptotic proteins Bax and Bid, and to a lesser extent Bim; (iii) loss of mitochondrial membrane potential and cytochrome c release; and (iv) activation of initiator caspase-9 and executioner caspase-3. Further, GAP-induced apoptosis is partially mediated by JNK1/2, but it is completely dependent on caspase-9 activity. Together, the ADPRT and the GAP domains make ExoT into a highly versatile and potent cytotoxin, capable of inducing multiple forms of apoptosis in target host cells.

Murine ciliotoxicity and rabbit sinus mucosal healing by polyhydrated ionogen

OBJECTIVES

Determine the toxicity and efficacy of a novel antiprotease topical irrigation, polyhydrated ionogen (PHI) ± MgBr2, in improving sinonasal remucosalization following surgery.

STUDY DESIGN

Blinded, randomized controlled study. Setting. Academic.

SUBJECTS AND METHODS

Ciliary beat frequency (CBF) of murine nasal septal explants was continuously recorded before and after addition of PHI solution to asses for ciliotoxicity. To evaluate for efficacy in remucosalization, 9 New Zealand white rabbits underwent bilateral medial-wall maxillary mucosal stripping followed by placement of an indwelling irrigation catheter. In a randomized fashion one side received 3 mL of normal saline (NS) daily, whereas the contralateral side received PHI ± MgBr2. Following a 14-day therapeutic trial, remucosalization was assessed by hematoxylin and eosin staining and immunohistochemistry for β-tubulin, a marker of cilia. A semiquantitative grading of ciliated remucosalization was applied with a chi-square test to compare the saline with the PHI ± MgBr2 treatment.

RESULTS

Safety evaluation of the PHI solutions demonstrated no evidence of ciliotoxicity. Histologic semiquantitative analysis of maxillary sinus remucosalization demonstrated significantly more ciliated epithelium (>60%) in the majority of PHI (n = 4) and PHI with MgBr2 (n = 5) treatment compared with the saline treatment (<30%) (n = 9). This was confirmed with immunohistochemical staining for type IV β-tubulin a marker of respiratory cilia.

CONCLUSIONS

Success of functional endoscopic sinus surgery depends on restoration of normal mucociliary clearance. Topical PHI application has previously been demonstrated to significantly increase dermal wound healing. PHI solution is not ciliotoxic, and daily topical PHI or PHI MgBr2 irrigation enhances ciliated remucosalization compared with saline.

Physiological impact of abnormal lipoxin A₄ production on cystic fibrosis airway epithelium and therapeutic potential

Lipoxin A4 has been described as a major signal for the resolution of inflammation and is abnormally produced in the lungs of patients with cystic fibrosis (CF). In CF, the loss of chloride transport caused by the mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel gene results in dehydration, mucus plugging, and reduction of the airway surface liquid layer (ASL) height which favour chronic lung infection and neutrophil based inflammation leading to progressive lung destruction and early death of people with CF. This review highlights the unique ability of LXA4 to restore airway surface hydration, to stimulate airway epithelial repair, and to antagonise the proinflammatory program of the CF airway, circumventing some of the most difficult aspects of CF pathophysiology. The report points out novel aspects of the cellular mechanism involved in the physiological response to LXA4, including release of ATP from airway epithelial cell via pannexin channel and subsequent activation of and P2Y11 purinoreceptor. Therefore, inadequate endogenous LXA4 biosynthesis reported in CF exacerbates the ion transport abnormality and defective mucociliary clearance, in addition to impairing the resolution of inflammation, thus amplifying the vicious circle of airway dehydration, chronic infection, and inflammation.

Pulmonary preconditioning, injury, and inflammation modulate expression of the candidate tumor suppressor gene ECRG4 in lung

PURPOSE

The human c2orf40 gene encodes a candidate tumor suppressor called Esophageal Cancer-Related Gene-4 (ECRG4) that is a cytokine-like epigenetically-regulated protein that is characteristically downregulated in cancer, injury, inflammation, and infection. Here, we asked whether ECRG4 gene expression is detectable in lung epithelial cells and if its expression changes with inflammation, infection, and/or protective preconditioning.

MATERIALS AND METHODS

We used immunoblotting, PCR, and quantitative PCR to measure ECRG4 and either inhalation anesthesia preconditioning, lipopolysaccharide injection, or laparotomy to modulate lung inflammation.

RESULTS

Immunoblotting establishes the presence of the full-length 14 kDa ECRG4 peptide in mouse lung. Immunohistochemistry localizes ECRG4 to type l alveolar epithelial cells. Basal ECRG4 mRNA is greater than TNF-α, IL-1β, and IL-6 but following inflammatory lung injury, TNF-α, IL-1β, IL-6, and IL-10 are upregulated while ECRG4 gene expression is decreased. Similar findings are observed after an intravenous administration of lipopolysaccharide. In contrast, lung preconditioning with isoflurane anesthesia increases lung ECRG4 gene expression. Over-expression of ECRG4 in human lung epithelial cells in vitro decreases cell proliferation implying that a loss of ECRG4 in vivo would be permissive to cell growth.

CONCLUSIONS

This study supports the hypothesis that ECRG4 acts as a sentinel growth inhibitor in lung alveolar epithelial cells. Its downregulation by injury, infection, and inflammation and upregulation by preconditioning supports a role for ECRG4 in regulating the alveolar epithelium response to injury and inflammation. By extension, the findings support a functional consequence to its inhibition by promoter hypermethylation (i.e. lung cancer) and suggest potential benefits to its upregulation.

Ets homologous factor regulates pathways controlling response to injury in airway epithelial cells

Ets homologous factor (EHF) is an Ets family transcription factor expressed in many epithelial cell types including those lining the respiratory system. Disruption of the airway epithelium is central to many lung diseases, and a network of transcription factors coordinates its normal function. EHF can act as a transcriptional activator or a repressor, though its targets in lung epithelial cells are largely uncharacterized. Chromatin immunoprecipitation followed by deep sequencing (ChIP-seq), showed that the majority of EHF binding sites in lung epithelial cells are intergenic or intronic and coincide with putative enhancers, marked by specific histone modifications. EHF occupies many genomic sites that are close to genes involved in intercellular and cell–matrix adhesion. RNA-seq after EHF depletion or overexpression showed significant alterations in the expression of genes involved in response to wounding. EHF knockdown also targeted genes in pathways of epithelial development and differentiation and locomotory behavior. These changes in gene expression coincided with alterations in cellular phenotype including slowed wound closure and increased transepithelial resistance. Our data suggest that EHF regulates gene pathways critical for epithelial response to injury, including those involved in maintenance of barrier function, inflammation and efficient wound repair.

Polyhydrated ionogen with MgBr2 accelerates in vitro respiratory epithelial healing

BACKGROUND

Remucoslization of the sinonasal cavity after sinus surgery is critical for successful outcomes. Recently, a novel antiprotease and antifibroblast compound, polyhydrated ionogen (PHI) with MgBr2, showed improved wound healing in a rabbit maxillary sinus mucosal wound model. We set out to determine if this effect was reproducible in an in vitro respiratory epithelial culture system.

METHODS

Fully differentiated mature murine nasal septal air-liquid interface cultures were injured by creating a full-thickness 400-mM-wide scratch through the monolayer. Cultures were then treated with nothing, saline, or PHI with MgBr2 for 1 hour on the apical surface. Twenty-four hours after the injury cultures were fixed and processed for immunofluorescence with type IV beta-tubulin and Hoechst stain.

RESULTS

Initial injury resulted in a wound of 394 micromolar (377-411 micromoler; 95% CI; n = 8). After 24 hours with no intervention the wound closed to 161 micromolar (138-184 micromolar; 95% CI; n = 9) and treatment with saline resulted in a residual gap of 88 micromolar (60-116 micromolar; 95% CI; n = 9; p < 0.05) and treatment with PHI with MgBr2 resulted in a gap of only 30 micromolar (14-46 micromolar; 95% CI; n = 9; p < 0.05).

CONCLUSION

Poor healing of the sinonasal mucosa after surgery with loss of ciliary function results in adverse clinical outcomes. In an in vitro sinonasal respiratory epithelial injury model, a one-time treatment with PHI with MgBr2 showed significantly improved wound healing compared with saline or nothing. This is a viable model to further investigate the mechanism by which PHI with MgBr2 improves sinonasal remucosolization.

[Regeneration of airway epithelium]

INTRODUCTION

Epithelial regeneration is a complex process. It can lead to the remodeling of the airway epithelium as in asthma, COPD or cystic fibrosis.

BACKGROUND

The development of in vivo and in vitro models has allowed the analysis of remodeling mechanisms and showed the role of components of extracellular matrix, proteases, cytokines and growth factors. Airway epithelial progenitors and stems cells have been studied in these models. However, their identification remains difficult.

CONCLUSION

Identification and characterization of airway epithelial progenitor/stem-cells, and a better knowledge of the regeneration process may allow the development of new therapeutic strategies for airway epithelial reconstitution.

The role of Lipoxin A4 in Cystic Fibrosis Lung Disease

In Cystic Fibrosis (CF), mutations of the CFTR gene result in defective Cl(-) secretion and Na(+) hyperabsorption by epithelia which leads to airway lumen dehydration and mucus plugging and favours chronic bacterial colonization, persistent inflammation and progressive lung destruction. Beyond this general description, the pathogenesis of CF lung disease remains obscure due to an incomplete understanding of normal innate airway defense. This mini-review aims to highlight the role of the pro-resolution lipid mediator, Lipoxin A4, which is inadequately produced in CF, on several aspects of innate immunity that are altered in CF airway disease.

Altered microRNA expression profile during epithelial wound repair in bronchial epithelial cells

BACKGROUND

Airway epithelial cells provide a protective barrier against environmental particles including potential pathogens. Epithelial repair in response to tissue damage is abnormal in asthmatic airway epithelium in comparison to the repair of normal epithelium after damage. The complex mechanisms coordinating the regulation of the processes involved in wound repair requires the phased expression of networks of genes. Small non-coding RNA molecules termed microRNAs (miRNAs) play a critical role in such coordinated regulation of gene expression. We aimed to establish if the phased expression of specific miRNAs is correlated with the repair of mechanically induced damage to the epithelium.

METHODS

To investigate the possible involvement of miRNA in epithelial repair, we analyzed miRNA expression profiles during epithelial repair in a cell culture model using TaqMan-based quantitative real-time PCR in a TaqMan Low Density Array format. The expression of 754 miRNA genes at seven time points in a 48-hour period during the wound repair process was profiled using the bronchial epithelial cell line 16HBE14o- growing in monolayer.

RESULTS

The expression levels of numerous miRNAs were found to be altered during the wound repair process. These miRNA genes were clustered into 3 different patterns of expression that correlate with the further regulation of several biological pathways involved in wound repair. Moreover, it was observed that expression of some miRNA genes were significantly altered only at one time point, indicating their involvement in a specific stage of the epithelial wound repair.

CONCLUSIONS

In summary, miRNA expression is modulated during the normal repair processes in airway epithelium in vitro suggesting a potential role in regulation of wound repair.

Rho-associated protein kinase inhibition enhances airway epithelial Basal-cell proliferation and lentivirus transduction

The identification of factors that regulate airway epithelial cell proliferation and differentiation are essential for understanding the pathophysiology of airway diseases. Rho-associated protein kinases (ROCKs) are downstream effector proteins of RhoA GTPase that direct the functions of cell cytoskeletal proteins. ROCK inhibition with Y27632 has been shown to enhance the survival and cloning of human embryonic stem cells and pluripotent cells in other tissues. We hypothesized that Y27632 treatment exerts a similar effect on airway epithelial basal cells, which function as airway epithelial progenitor cells. Treatment with Y27632 enhanced basal-cell proliferation in cultured human tracheobronchial and mouse tracheal epithelial cells. ROCK inhibition accelerated the maturation of basal cells, characterized by a diminution of the cell size associated with cell compaction and the expression of E-cadherin at cell-cell junctions. Transient treatment of cultured basal cells with Y27632 did not affect subsequent ciliated or mucous cell differentiation under air-liquid interface conditions, and allowed for the initial use of lower numbers of human or mouse primary airway epithelial cells than otherwise possible. Moreover, the use of Y27632 during lentivirus-mediated transduction significantly improved posttransduction efficiency and the selection of a transduced cell population, as determined by reporter gene expression. These findings suggest an important role for ROCKs in the regulation of proliferation and maturation of epithelial basal cells, and demonstrate that the inhibition of ROCK pathways using Y27632 provides an adjunctive tool for the in vitro genetic manipulation of airway epithelial cells by lentivirus vectors.

The growing role of eicosanoids in tissue regeneration, repair, and wound healing

Tissue repair and regeneration are essential processes in maintaining tissue homeostasis, especially in response to injury or stress. Eicosanoids are ubiquitous mediators of cell proliferation, differentiation, and angiogenesis, all of which are important for tissue growth. Eicosanoids regulate the induction and resolution of inflammation that accompany the tissue response to injury. In this review, we describe how this diverse group of molecules is a key regulator of tissue repair and regeneration in multiple organ systems and biologic contexts.

Lipoxin A₄-mediated KATP potassium channel activation results in cystic fibrosis airway epithelial repair

The main cause of morbidity and mortality in cystic fibrosis (CF) is progressive lung destruction as a result of persistent bacterial infection and inflammation, coupled with reduced capacity for epithelial repair. Levels of the anti-inflammatory mediator lipoxin A₄ (LXA₄) have been reported to be reduced in bronchoalveolar lavages of patients with CF. We investigated the ability of LXA₄ to trigger epithelial repair through the initiation of proliferation and migration in non-CF (NuLi-1) and CF (CuFi-1) airway epithelia. Spontaneous repair and cell migration were significantly slower in CF epithelial cultures (CuFi-1) compared with controls (NuLi-1). LXA₄ triggered an increase in migration, proliferation, and wound repair of non-CF and CF airway epithelia. These responses to LXA₄ were completely abolished by the ALX/FPR2 receptor antagonist, Boc2 and ALX/FPR2 siRNA. The KATP channel opener pinacidil mimicked the LXA₄ effect on migration, proliferation, and epithelial repair, whereas the KATP channel inhibitor, glibenclamide, blocked the responses to LXA₄. LXA₄ did not affect potassium channel expression but significantly upregulated glibenclamide-sensitive (KATP) currents through the basolateral membrane of NuLi-1 and CuFi-1 cells. MAP kinase (ERK1/2) inhibitor, PD98059, also inhibited the LXA₄-induced proliferation of NuLi-1 and CuFi-1 cells. Finally, both LXA₄ and pinacidil stimulated ERK-MAP kinase phosphorylation, whereas the effect of LXA₄ on ERK phosphorylation was inhibited by glibenclamide. Taken together, our results provided evidence for a role of LXA₄ in triggering epithelial repair through stimulation of the ALX/FPR2 receptor, KATP potassium channel activation, and ERK phosphorylation. This work suggests exogenous delivery of LXA₄, restoring levels in patients with CF, perhaps as a potential therapeutic strategy.

A novel human antimicrobial factor targets Pseudomonas aeruginosa through its type III secretion system

Pseudomonas aeruginosa is an important opportunistic bacterial pathogen. Despite its metabolic and virulence versatility, it has not been shown to infect articular joints, which are areas that are rarely infected with bacteria in general. We hypothesized that articular joints possess antimicrobial activity that limits bacterial survival in these environments. We report that cartilages secrete a novel antimicrobial factor, henceforth referred to as the cartilage-associated antimicrobial factor (CA-AMF), with potent antimicrobial activity. Importantly, CA-AMF exhibited significantly more antimicrobial activity against P. aeruginosa strains with a functional type III secretion system (T3SS). We propose that CA-AMF represents a new class of human antimicrobial factors in innate immunity, one which has evolved to selectively target pathogenic bacteria among the beneficial and commensal microflora. The T3SS is the first example, to the best of our knowledge, of a pathogen-specific molecular target in this antimicrobial defence system.

Therapeutic potential of growth factors in pulmonary emphysematous condition

Pulmonary emphysema is a major manifestation of chronic obstructive pulmonary disease (COPD), which is characterized by progressive destruction of alveolar parenchyma with persistent inflammation of the small airways. Such destruction in the distal respiratory tract is irreversible and irreparable. All-trans-retinoic acid was suggested as a novel therapy for regeneration of lost alveoli in emphysema. However, profound discrepancies were evident between studies. At present, no effective therapeutic options are available that allow for the regeneration of lost alveoli in emphysematous human lungs. Recently, some reports on rodent's models have suggested the beneficial effects of various growth factors toward alveolar maintenance and repair processes.

Polyhydrated ionogen enhances postoperative sinonasal ciliated remucosalization

BACKGROUND

Mucosalization of the sinonasal cavity following surgery is critical for successful outcomes. Recently a novel anti-protease compound, polyhydrated-ionogen (PHI) with Mg(2+)/Br(-), demonstrated improved dermal wound healing. We set out to investigate the effect of PHI Mg(2+)/Br(-) on sinus remucosalization following surgery.

METHODS

A total of 24 rabbits underwent bilateral medial-wall maxillary mucosal stripping followed by placement of an indwelling irrigation catheter. In a randomized fashion 1 side received 3 cc normal saline (NS) daily, while the contralateral side received PHI Mg(2+)/Br(-). Following a 14-day therapeutic trial, remucosalization was assessed by hematoxylin and eosin (H&E) staining and immunohistochemistry for β-tubulin, a marker of cilia. A semiquantitative grading of ciliated remucosalization was applied with a chi-square test used to compare distributions for each treatment.

RESULTS

H&E staining comparison demonstrated NS treated sinuses (n = 24) had substantial bare areas with predominant ciliation scores under 30%. The PHI Mg(2+)/Br(-)-treated group (n = 24) achieved a statistically significant improvement in reciliation (>60%) when compared with NS (p < 0.01). These results were confirmed with Type IV β-tubulin staining (p < 0.01).

CONCLUSION

Poor postsurgical sinonasal mucosa healing results in adverse clinical outcomes. In a rabbit model of sinonasal mucosal healing, daily irrigation for 14 days with PHI Mg(2+)/Br(-)-enhanced ciliated remucosalization compared to saline.

Normoxic cyclic GMP-independent oxidative signaling by nitrite enhances airway epithelial cell proliferation and wound healing

The airway epithelium provides important barrier and host defense functions. Recent studies reveal that nitrite is an endocrine reservoir of nitric oxide (NO) bioactivity that is converted to NO by enzymatic reductases along the physiological oxygen gradient. Nitrite signaling has been described as NO dependent activation mediated by reactions with deoxygenated redox active hemoproteins, such as hemoglobin, myoglobin, neuroglobin, xanthine oxidoreductase (XO) and NO synthase at low pH and oxygen tension. However, nitrite can also be readily oxidized to nitrogen dioxide (NO(2)·) via heme peroxidase reactions, suggesting the existence of alternative oxidative signaling pathways for nitrite under normoxic conditions. In the present study, we examined normoxic signaling effects of sodium nitrite on airway epithelial cell wound healing. In an in vitro scratch injury model under normoxia, we exposed cultured monolayers of human airway epithelial cells to various concentrations of sodium nitrite and compared responses to NO donor. We found sodium nitrite potently enhanced airway epithelium wound healing at physiological concentrations (from 1 μM). The effect of nitrite was blocked by the NO and NO(2)· scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO). Interestingly, nitrite treatment did not increase cyclic guanosine monophosphate (cGMP) levels under these normoxic conditions, even in the presence of a phosphodiesterase 5 inhibitor, suggesting cGMP independent signaling. Consistent with an oxidative signaling pathway requiring hydrogen peroxide (H(2)O(2))/heme-peroxidase/NO(2)· signaling, the effects of nitrite were potentiated by superoxide dismutase (SOD) and low concentration H(2)O(2), whereas inhibited completely by catalase, followed by downstream extracellular-signal-regulated kinase (ERK) 1/2 activation. Our data represent the first description of normoxic nitrite signaling on lung epithelial cell proliferation and wound healing and suggest novel oxidative signaling pathways involving nitrite-H(2)O(2) reactions, possibly via the intermediary, NO(2)·.

Pathogenesis and disease mechanisms of occupational asthma

Occupational asthma (OA) is one of the most common forms of work-related lung disease in all industrialized nations. The clinical management of patients with OA depends on an understanding of the multifactorial pathogenetic mechanisms that can contribute to this disease. This article discusses the various immunologic and nonimmunologic mechanisms and genetic susceptibility factors that drive the inflammatory processes of OA.

Analysis of airway epithelial regeneration and repair following endobronchial brush biopsy in sheep

Understanding the fundamental processes involved in repairing the airway wall following injury is fundamental to understanding the way in which these processes are perturbed during disease pathology. Indeed complex diseases such as asthma and chronic obstructive pulmonary disease (COPD) have at their core evidence of airway wall remodeling processes that play a crucial functional role in these diseases. The authors sought to understand the dynamic cellular events that occur during bronchial airway epithelial repair in sheep. The injury was induced by endobronchial brush biopsy (BBr), a process that causes epithelial débridement and induces a consequential repair process. In addition, the current experimental protocol allowed for the time-dependent changes in airway wall morphology to be studied both within and between animals. The initial débridement was followed by evidence of dedifferentiation in the intact epithelium at the wound margins, followed by proliferation of cells both within the epithelium and in the deeper wall structures, notably in association with the submucosal glands and smooth muscle bundles. Seven days after injury, although the airway wall was thickened at the site of damage, the epithelial layer was intact, with evidence of redifferentiation. These studies, in demonstrating broad agreement with previous studies in small animals, indicate the wider relevance of this system as a comparative model and should provide a solid basis upon which to further characterize the critical cellular and molecular interactions that underlie both effective restitution and pathological repair.

Vimentin is sufficient and required for wound repair and remodeling in alveolar epithelial cells

The physiological and pathophysiological implications of the expression of vimentin, a type III intermediate filament protein, in alveolar epithelial cells (AECs) are unknown. We provide data demonstrating that vimentin is regulated by TGFβ1, a major cytokine released in response to acute lung injury and that vimentin is required for wound repair and remodeling of the alveolar epithelium. Quantitative real-time PCR shows a 16-fold induction of vimentin mRNA in TGFβ1-treated transformed AECs. Luciferase assays identify a Smad-binding element in the 5' promoter of vimentin responsible for TGFβ1-induced transcription. Notably, TGFβ1 induces vimentin protein expression in AECs, which is associated with a 2.5-fold increase in cell motility, resulting in increased rates of migration and wound closure. These effects are independent of cell proliferation. TGFβ1-mediated vimentin protein expression, cell migration, and wound closure are prevented by a pharmacological inhibitor of the Smad pathway and by expression of Ad-shRNA against vimentin. Conversely, overexpression of mEmerald-vimentin is sufficient for increased cell-migration and wound-closure rates. These results demonstrate that vimentin is required and sufficient for increased wound repair in an in vitro model of lung injury.

Subversion of mucosal barrier polarity by pseudomonas aeruginosa

The lumenal surfaces of human body are lined by a monolayer of epithelia that together with mucus secreting cells and specialized immune cells form the mucosal barrier. This barrier is one of the most fundamental components of the innate immune system, protecting organisms from the vast environmental microbiota. The mucosal epithelium is comprised of polarized epithelial cells with distinct apical and basolateral surfaces that are defined by unique set of protein and lipid composition and are separated by tight junctions. The apical surface serves as a barrier to the outside world and is specialized for the exchange of materials with the lumen. The basolateral surface is adapted for interaction with other cells and for exchange with the bloodstream. A wide network of proteins and lipids regulates the formation and maintenance of the epithelium polarity. Many human pathogens have evolved virulence mechanisms that target this network and interfere with epithelial polarity to enhance binding to the apical surface, enter into cells, and/or cross the mucosal barrier. This review highlights recent advances in our understanding of how Pseudomonas aeruginosa, an important opportunistic human pathogen that preferentially infects damaged epithelial tissues, exploits the epithelial cell polarization machinery to enhance infection.

Epithelial Repair and Regeneration

Contact with the environment positions the respiratory epithelium at risk for acute and chronic injury from infectious pathogens, noxious agents, and inflammatory processes. Thus, to protect gas transfer within the lung the epithelium is programmed for routine maintenance and repair. Programs for repair are directed by epithelial, mesenchymal, and inflammatory signals that collectively constitute highly regulated networks. Principal components of the repair network are developmental morphogens, integrin and growth factor signaling molecules, and transcription factors. The epithelium responds to these signals with a remarkable plasticity and is bulwarked by a population of lung progenitor cells to ensure maintenance and repair for fluid balance and host defense functions.

Epithelial repair mechanisms in the lung

The recovery of an intact epithelium following lung injury is critical for restoration of lung homeostasis. The initial processes following injury include an acute inflammatory response, recruitment of immune cells, and epithelial cell spreading and migration upon an autologously secreted provisional matrix. Injury causes the release of factors that contribute to repair mechanisms including members of the epidermal growth factor and fibroblast growth factor families (TGF-alpha, KGF, HGF), chemokines (MCP-1), interleukins (IL-1beta, IL-2, IL-4, IL-13), and prostaglandins (PGE(2)), for example. These factors coordinate processes involving integrins, matrix materials (fibronectin, collagen, laminin), matrix metalloproteinases (MMP-1, MMP-7, MMP-9), focal adhesions, and cytoskeletal structures to promote cell spreading and migration. Several key signaling pathways are important in regulating these processes, including sonic hedgehog, Rho GTPases, MAP kinase pathways, STAT3, and Wnt. Changes in mechanical forces may also affect these pathways. Both localized and distal progenitor stem cells are recruited into the injured area, and proliferation and phenotypic differentiation of these cells leads to recovery of epithelial function. Persistent injury may contribute to the pathology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis. For example, dysregulated repair processes involving TGF-beta and epithelial-mesenchymal transition may lead to fibrosis. This review focuses on the processes of epithelial restitution, the localization and role of epithelial progenitor stem cells, the initiating factors involved in repair, and the signaling pathways involved in these processes.

Decreased fibronectin production significantly contributes to dysregulated repair of asthmatic epithelium

RATIONALE

Damage to airway epithelium is followed by deposition of extracellular matrix (ECM) and migration of adjacent epithelial cells. We have shown that epithelial cells from children with asthma fail to heal a wound in vitro.

OBJECTIVES

To determine whether dysregulated ECM production by the epithelium plays a role in aberrant repair in asthma.

METHODS

Airway epithelial cells (AEC) from children with asthma (n = 36), healthy atopic control subjects (n = 23), and healthy nonatopic control subjects (n = 53) were investigated by microarray, gene expression and silencing, transcript regulation analysis, and ability to close mechanical wounds.

MEASUREMENTS AND MAIN RESULTS

Time to repair a mechanical wound in vitro by AEC from healthy and atopic children was not significantly different and both were faster than AEC from children with asthma. Microarray analysis revealed differential expression of multiple gene sets associated with repair and remodeling in asthmatic AEC. Fibronectin (FN) was the only ECM component whose expression was significantly lower in asthmatic AEC. Expression differences were verified by quantitative polymerase chain reaction and ELISA, and reduced FN expression persisted in asthmatic cells over passage. Silencing of FN expression in nonasthmatic AEC inhibited wound repair, whereas addition of FN to asthmatic AEC restored reparative capacity. Asthmatic AEC failed to synthesize FN in response to wounding or cytokine/growth factor stimulation. Exposure to 5', 2'deoxyazacytidine had no effect on FN expression and subsequent analysis of the FN promoter did not show evidence of DNA methylation.

CONCLUSIONS

These data show that the reduced capacity of asthmatic epithelial cells to secrete FN is an important contributor to the dysregulated AEC repair observed in these cells.

Laminin gamma2 fragments are increased in the circulation of patients with early phase acute lung injury

Objective

Laminin-5, a cell adhesive molecule expressed solely by epithelium, is known to enhance epithelial cell migration and repair of injured epithelium, after its essential component γ2-chain is processed proteolytically. Our previous study revealed circulating levels of amino-terminal fragment of laminin γ2-chain (G2F) reflect epithelial tumor invasiveness in carcinoma patients, but its physiological role in alveolar epithelial injury remains unknown.

Design

Sampling of epithelial lining fluids or pulmonary edema fluids from patients with acute lung injury (ALI) or related diseases was performed. Plasma samples were obtained from them at the time of disease onset or later. G2F concentrations were determined by immunoassay constructed by ourselves.

Results

We found a significantly higher amount of G2F in pulmonary edema and epithelial lining fluids of patients with ALI, as compared with those with the other respiratory diseases. Their plasma levels were also elevated significantly early at the onset of ALI (mean ± SD; 147 ± 82 ng/ml in non-surviving and 90 ± 56 in surviving patients) as compared with those in the patients with cardiogenic pulmonary edema (59 ± 36) or idiopathic pulmonary fibrosis (37 ± 17), indicating alveolar epithelium rapidly secrete laminin-5 in ALI. At 5 days after onset, non-surviving patients maintained higher plasma concentrations (152 ± 84), but in contrast, the levels in surviving patients declined (71 ± 35), suggesting secretion of laminin-5 was suppressed, associated with recovery from ALI.

Conclusion

Circulating G2F may be a biomarker for alveolar laminin-5 secreted early at disease onset in ALI, potentially regulating alveolar re-epithelialization.

MMP7 shedding of syndecan-1 facilitates re-epithelialization by affecting alpha(2)beta(1) integrin activation

Background

Lung injury promotes the expression of matrix metalloproteinase-7 (MMP7, matrilysin), which is required for neutrophil recruitment and re-epithelialization. MMP7 governs the lung inflammatory response through the shedding of syndecan-1. Because inflammation and repair are related events, we evaluated the role of syndecan-1 shedding in lung re-epithelialization.

Methodology/Principal Finding

Epithelial injury induced syndecan-1 shedding from wild-type epithelium but not from Mmp7^−/− mice in vitro and in vivo. Moreover, cell migration and wound closure was enhanced by MMP7 shedding of syndecan-1. Additionally, we found that syndecan-1 augmented cell adhesion to collagen by controlling the affinity state of the α₂β₁ integrin.

Conclusion/Significance

MMP7 shedding of syndecan-1 facilitates wound closure by causing the α₂β₁ integrin to assume a less active conformation thereby removing restrictions to migration. MMP7 acts in the lungs to regulate inflammation and repair, and our data now show that both these functions are controlled through the shedding of syndecan-1.

Ultrastructure of tracheal epithelial cells migrating in an in vivo environment

The tracheal epithelium can be induced to move as a cellular sheet by heterotopic transplantation, which offers the opportunity to observe migrating cells as a group in an in vivo environment. We therefor investigated the ultrastructural characteristics of migrating tracheal epithelial cells with special reference to the moving front using this transplantation. The migrating epithelial cells underwent squamous metaplasia and lost their differentiated characteristics such as cilia or secretory granules. Several unique observations were made concerning the mechanism of mobility: one is that epithelial cells in the front were elongated in a direction perpendicular to the course of movement, different from previous reports in vitro. The second is that lamellipodia, which are regarded as the major locomotive machinery in the adult wound epithelium, did not make up the major part of the front; the major portion of the anterior fringe of the moving front was usually smooth and gently curved, and actin cables parallel to the elongated cells were observed by confocal laser microscopy, indicating that the purse-string mechanism of epithelial wound healing takes place. The third finding is that the cells in the front had irregular bleb-like structures on their antero-basal surface, which were formed even in the portion where the cells did not attach to the matrix. Few organelles were recognized in these structures. From their location, one might propose that these bleb-like structures play a role in the recognition of the substrate and thus the movement of the cell sheet.

Aspects on pathophysiological mechanisms in COPD

Chronic obstructive pulmonary disease (COPD) is a condition which is characterized by irreversible airway obstruction due to narrowing of small airways, bronchiolitis, and destruction of the lung parenchyma, emphysema. It is the fourth most common cause of mortality in the world and is expected to be the third most common cause of death by 2020. The main cause of COPD is smoking but other exposures may be of importance. Exposure leads to airway inflammation in which a variety of cells are involved. Besides neutrophil granulocytes, macrophages and lymphocytes, airway epithelial cells are also of particular importance in the inflammatory process and in the development of emphysema. Cell trafficking orchestrated by chemokines and other chamoattractants, the proteinase-antiproteinase system, oxidative stress and airway remodelling are central processes associated with the development of COPD. Recently systemic effects of COPD have attracted attention and the importance of systemic inflammation has been recognized. This seems to have direct therapeutic implications as treatment with inhaled glucocorticosteroids has been shown to influence mortality. The increasing body of knowledge regarding the inflammatory mechanism in COPD will most likely have implications for future therapy and new drugs, specifically aimed at interaction with the inflammatory processes, are currently being developed.

[Injury and epithelial wound healing: a pathophysiologic hypothesis for nasal and sinus polyposis]

Nasal polyposis (NP), asthma, and chronic bronchitis are chronic inflammatory diseases of the upper airways. They may be caused by injury to the respiratory epithelium in a chronic inflammatory environment. Several studies show that during NP nasal epithelial cells are involved in the overexpression of cytokines and growth factors. Among these, transforming growth factor beta1 (TGF-beta1) appears to play a major role in the genesis of NP. Differentiated respiratory epithelium, obtained from in vivo or in vitro models, is used to study wound healing in inflammatory environments, to elucidate the pathophysiology of NP, and to improve understanding and management of upper airway inflammatory diseases.

Pseudomonas lipopolysaccharide accelerates wound repair via activation of a novel epithelial cell signaling cascade

The surface of the airway epithelium represents a battleground in which the host intercepts signals from pathogens and activates epithelial defenses to combat infection. Wound repair is an essential function of the airway epithelium in response to injury in chronic airway diseases, and inhaled pathogens such as Pseudomonas bacteria are implicated in the pathobiology of several of these diseases. Because epidermal growth factor receptor (EGFR) activation stimulates wound repair and because LPS activates EGFR, we hypothesized that LPS accelerates wound repair via a surface signaling cascade that causes EGFR phosphorylation. In scrape wounds of NCI-H292 human airway epithelial cells, high concentrations of LPS were toxic and decreased wound repair. However, lower concentrations of LPS accelerated wound repair. This effect was inhibited by treatment with a selective inhibitor of EGFR phosphorylation (AG 1478) and by an EGFR neutralizing Ab. Metalloprotease inhibitors and TNF-alpha-converting enzyme (TACE) small interfering RNA inhibited wound repair, implicating TACE. Additional studies implicated TGF-alpha as the active EGFR ligand cleaved by TACE during wound repair. Reactive oxygen species scavengers, NADPH oxidase inhibitors, and importantly small interfering RNA of dual oxidase 1 inhibited LPS-induced wound repair. Inhibitors of protein kinase C isoforms alphabeta and a TLR-4 neutralizing Ab also inhibited LPS-induced wound repair. Normal human bronchial epithelial cells responded similarly. Thus, LPS accelerates wound repair in airway epithelial cells via a novel TLR-4-->protein kinase C alphabeta-->dual oxidase 1-->reactive oxygen species-->TACE-->TGF-alpha-->EGFR phosphorylation pathway.

Repair of the injury to respiratory epithelial cells characteristic of asthma is stimulated by Allomyrina dichotoma agglutinin specific serum glycoproteins

BACKGROUND

The airway epithelium acts as a protective barrier, separating the external environment from the underlying tissue. Daily challenges result in damage to the epithelium that, in normal individuals, is quickly and effectively repaired. In respiratory diseases, such as asthma, this repair is compromised. Following injury to the epithelium, plasma leaks into the airway lumen acting as a protective protein cap. Carbohydrates are mediators of epithelial repair, however, the associated regulatory proteins remain unknown.

OBJECTIVE

To identify mediators of epithelial repair based on their carbohydrate moieties using an in vitro wound repair culture model of human airway epithelial cells (1HAEo(-)).

METHODS

Using the lectin Allomyrina dichotoma agglutinin (AlloA) as a tool, ligands essential in the repair of damaged epithelium were characterized. AlloA was subsequently used to purify and identify a glycoprotein associated with epithelial repair.

RESULTS

The addition of AlloA to the media of mechanically wounded monolayers inhibited repair. Fetuin, a highly glycosylated serum protein, was identified as a glycoprotein bound by AlloA. The addition of fetuin to serum starved monolayers stimulated wound closure.

CONCLUSION

These results indicate that following mechanical injury to the epithelium, serum glycoproteins, not only provide a protective barrier, but also are involved in the initiation of wound closure.

Effects of corticosteroid-induced apoptosis on airway epithelial wound closure in vitro

Damage to the airway epithelium is common in asthma. Corticosteroids induce apoptosis in and suppress proliferation of airway epithelial cells in culture. Whether apoptosis contributes to impaired epithelial cell repair after injury is not known. We examined whether corticosteroids would impair epithelial cell migration in an in vitro model of wound closure. Wounds (approximately 0.5-1.3 mm2) were created in cultured 1HAEo- human airway epithelial cell monolayers, after which cells were treated with up to 10 microM dexamethasone or budesonide for 24 h. Cultured cells were pretreated for 24 or 48 h with dexamethasone to observe the effect of long-term exposure on wound closure. After 12 h, the remaining wound area in monolayers pretreated for 48 h with 10 microM dexamethasone was 43+/-18% vs. 10+/-8% for untreated control monolayers. The addition of either corticosteroid immediately after injury did not slow closure significantly. After 12 h the remaining wound area in monolayers treated with 10 microM budesonide was 39+/-4% vs. 43+/-3% for untreated control monolayers. The proportion of apoptotic epithelial cells as measured by terminal deoxynucleotidyltransferase-mediated dUTP biotin nick end labeling both at and away from the wound edge was higher in monolayers treated with budesonide compared with controls. However, wound closure in the apoptosis-resistant 1HAEo-.Bcl-2+ cell line was not different after dexamethasone treatment. We demonstrate that corticosteroid treatment before mechanical wounding impairs airway epithelial cell migration. The addition of corticosteroids after injury does not slow migration, despite their ability to induce apoptosis in these cells.

alpha3alpha5beta2-Nicotinic acetylcholine receptor contributes to the wound repair of the respiratory epithelium by modulating intracellular calcium in migrating cells

Nicotinic acetylcholine receptors (nAChRs), present in human bronchial epithelial cells (HBECs), have been shown in vitro to modulate cell shape. Because cell spreading and migration are important mechanisms involved in the repair of the bronchial epithelium, we investigated the potential role of nAChRs in the wound repair of the bronchial epithelium. In vivo and in vitro, alpha3alpha5beta2-nAChRs accumulated in migrating HBECs involved in repairing a wound, whereas alpha7-nAChRs were predominantly observed in stationary confluent cells. Wound repair was improved in the presence of nAChR agonists, nicotine, and acetylcholine, and delayed in the presence of alpha3beta2 neuronal nAChR antagonists, mecamylamine, alpha-conotoxin MII, and kappa-bungarotoxin; alpha-bungarotoxin, an antagonist of alpha7-nAChR, had no effect. Addition of nicotine to a repairing wound resulted in a dose-dependent transient increase of intracellular calcium in migrating cells that line the wound edge. Mecamylamine and kappa-bungarotoxin inhibited both the cell-migration speed and the nicotine-induced intracellular calcium increase in wound-repairing migrating cells in vitro. On the contrary alpha-bungarotoxin had no significant effect on migrating cells. These results suggest that alpha3alpha5beta2-nAChRs actively contribute to the wound repair process of the respiratory epithelium by modulating intracellular calcium in wound-repairing migrating cells.

CXCR3 chemokine receptor-induced chemotaxis in human airway epithelial cells: role of p38 MAPK and PI3K signaling pathways

Human airway epithelial cells (HAEC) constitutively express the CXC chemokine receptor CXCR3, which regulates epithelial cell movement. In diseases such as chronic obstructive pulmonary disease and asthma, characterized by denudation of the epithelial lining, epithelial cell migration may contribute to airway repair and reconstitution. This study compared the potency and efficacy of three CXCR3 ligands, I-TAC/CXCL11, IP-10/CXCL10, and Mig/CXCL9, as inducers of chemotaxis in HAEC and examined the underlying signaling pathways involved. Studies were performed in cultured HAEC from normal subjects and the 16-HBE cell line. In normal HAEC, the efficacy of I-TAC-induced chemotaxis was 349 +/- 88% (mean +/- SE) of the medium control and approximately one-half the response to epidermal growth factor, a highly potent chemoattractant. In normal HAEC, Mig, IP-10, and I-TAC induced chemotaxis with similar potency and a rank order of efficacy of I-TAC = IP-10 > Mig. Preincubation with pertussis toxin completely blocked CXCR3-induced migration. Of interest, intracellular [Ca(2+)] did not rise in response to I-TAC, IP-10, or Mig. I-TAC induced a rapid phosphorylation (5-10 min) of two of the three MAPKs, i.e., p38 and ERK1/2. Pretreatment of HAEC with the p38 inhibitor SB 20358 or the PI3K inhibitor wortmannin dose-dependently inhibited the chemotactic response to I-TAC. In contrast, the ERK1/2 inhibitor U0126 had no effect on chemotaxis. These data indicate that in HAEC, CXCR3-mediated chemotaxis involves a G protein, which activates both the p38 MAPK and PI3K pathways in a calcium-independent fashion.