TGF-beta isoform release and activation during in vitro bronchial epithelial wound repair

Immune Inhibitory Properties and Therapeutic Prospects of Transforming Growth Factor-Beta and Interleukin 10 in Autoimmune Hepatitis

Transforming growth factor-beta and interleukin 10 have diverse immune inhibitory properties that have restored homeostatic defense mechanisms in experimental models of autoimmune disease. The goals of this review are to describe the actions of each cytokine, review their investigational use in animal models and patients, and indicate their prospects as interventions in autoimmune hepatitis. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Transforming growth factor-beta expands the natural and inducible populations of regulatory T cells, limits the proliferation of natural killer cells, suppresses the activation of naïve CD8⁺ T cells, decreases the production of interferon-gamma, and stimulates fibrotic repair. Interleukin 10 selectively inhibits the CD28 co-stimulatory signal for antigen recognition and impairs antigen-specific activation of uncommitted CD4⁺ and CD8⁺ T cells. It also inhibits maturation of dendritic cells, suppresses Th17 cells, supports regulatory T cells, and limits production of diverse pro-inflammatory cytokines. Contradictory immune stimulatory effects have been associated with each cytokine and may relate to the dose and accompanying cytokine milieu. Experimental findings have not translated into successful early clinical trials. The recombinant preparation of each agent in low dosage has been safe in human studies. In conclusion, transforming growth factor-beta and interleukin 10 have powerful immune inhibitory actions of potential therapeutic value in autoimmune hepatitis. The keys to their therapeutic application will be to match their predominant non-redundant function with the pivotal pathogenic mechanism or cytokine deficiency and to avoid contradictory immune stimulatory actions.

Epithelial Cells and Inflammation in Pulmonary Wound Repair

Respiratory diseases are frequently characterised by epithelial injury, airway inflammation, defective tissue repair, and airway remodelling. This may occur in a subacute or chronic context, such as asthma and chronic obstructive pulmonary disease, or occur acutely as in pathogen challenge and acute respiratory distress syndrome (ARDS). Despite the frequent challenge of lung homeostasis, not all pulmonary insults lead to disease. Traditionally thought of as a quiescent organ, emerging evidence highlights that the lung has significant capacity to respond to injury by repairing and replacing damaged cells. This occurs with the appropriate and timely resolution of inflammation and concurrent initiation of tissue repair programmes. Airway epithelial cells are key effectors in lung homeostasis and host defence; continual exposure to pathogens, toxins, and particulate matter challenge homeostasis, requiring robust defence and repair mechanisms. As such, the epithelium is critically involved in the return to homeostasis, orchestrating the resolution of inflammation and initiating tissue repair. This review examines the pivotal role of pulmonary airway epithelial cells in initiating and moderating tissue repair and restitution. We discuss emerging evidence of the interactions between airway epithelial cells and candidate stem or progenitor cells to initiate tissue repair as well as with cells of the innate and adaptive immune systems in driving successful tissue regeneration. Understanding the mechanisms of intercellular communication is rapidly increasing, and a major focus of this review includes the various mediators involved, including growth factors, extracellular vesicles, soluble lipid mediators, cytokines, and chemokines. Understanding these areas will ultimately identify potential cells, mediators, and interactions for therapeutic targeting.

Hepatoprotective and antioxidant effects of Wu-Zi-Yuan-Chung-Wan against CCl4-induced oxidative damage in rats

This study was designed to investigate the hepatoprotective potentials of the Wu-Zi-Yuan-Chung-Wan (WZYCW) using an animal model of carbon tetrachloride (CCl4) induced liver injury. CCl4 induced chronic liver hepatotoxicity in adult Sprague-Dawley rats. Excluding the control group, all of the rats with chronic liver fibrosis received 0.4% CCl4 (1.5 mL/kg of body weight, ip) twice per week for 8 weeks. WZYCW (20, 100, and 500 mg/kg) and silymarin (200 mg/kg) were administered five times per week for 8 weeks. After 8 weeks, the rats were sacrificed, blood samples were obtained, and liver histological examinations were performed for subsequent assays. These results suggest that WZYCW considerably reduced Glutamic Oxaloacetic Transaminase (GOT), Glutamic Pyruvic Transaminase (GPT), Triglyceride (TG); and cholesterol activity; and the levels of malonaldehyde (MDA), nitric oxide (NO), and transforming growth factor-β1 (TGF-β1) in the liver. WZYCW also increased the level of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) in liver tissue. WZYCW produced hepatoprotective and antifibrotic effects. This is the first study to demonstrate that WZYCW expressed hepatoprotective activity against CCl4 induced acute hepatotoxicity in rat. In addition, the primary compound of WZCYW was analyzed using HPLC. The major peaks of WZCYW, including schizandrin. The results indicate that WZYCW not only enhances hepatic antioxidant enzyme activities and inhibits lipid peroxidation but also suppresses inflammatory responses in CCl4 induced liver damage. Our findings provide evidence that WZYCW possesses a hepatoprotective activity to ameliorate chronic liver injury.

Hyaluronan antagonizes the differentiation effect of TGF-β1 on nasal epithelial cells through down-regulation of TGF-β type I receptor

Although hyaluronan (HA)-based biomaterials have been proposed to promote mucociliary differentiation of nasal epithelial cells (NECs), the mechanism by which HA affects the growth and differentiation of NECs has not been thoroughly explored. This study investigates the effect and mechanism of HA on the differentiation of NECs. The experiment cultures human NECs in four conditions, namely controls, transforming growth factor (TGF)-β1, TGF-β1 + HA and HA groups. In the TGF group, the NECs become irregular shape without formation of tight junction and mucociliary differentiation of NECs is inhibited. Epithelial-mesenchymal transition (EMT) of NECs also occurs in the TGF group. However, with addition of HA in TGF groups, NECs reveal the mucociliary phenotypes of epithelial cells with tight junction expression. Incubation of TGF-β1 in an NEC culture leads to an increase in phosphorylated type 1 TGF-β receptors (p-TβRI). This increase is attenuated when NECs are cultured in the presence of HA. Similar expressions are observed in phosphorylated smad2/smad3. Additionally, HA-dependent inhibition of TGF-β1 signalling is inhibited by co-incubation with a blocking antibody to CD44. Experimental results indicate that HA can antagonize TGF-β1 effect on EMT and mucociliary differentiation of NECs by down-regulation of TβR I, which is via CD44.

MicroRNA-328 is involved in wound repair process in human bronchial epithelial cells

Our aim was to investigate the role of microRNA on epithelial wound repair by global microRNA silencing. We have also analysed the influence of five miRNAs (miR-328, miR-342, miR-411, miR-609, miR-888, previously identified) on wound repair in 16HBE14o-bronchial epithelial cell line. Cells were transfected with siRNAs against human DROSHA and DICER1 or miRNA mimics or inhibitors. Wounding assays were performed and the cells were observed using time-lapse microscopy. The area of damage was calculated at chosen time points, followed by data analysis. Cells with silenced global miRNA expression showed a significantly slower repair rate compared to the control cells (p=0.001). For miR-328, we observed significantly delayed repair in cells transfected with the inhibitor compared to control (p=0.02). Global microRNA silencing significantly decreased the repair rate of airway epithelial cells in vitro, indicating an important role of miRNA in the regulation of wound repair and that miR-328, possibly involved in actin pathway, may be a potent modifier of this process.

Chitosan promotes aquaporin formation and inhibits mucociliary differentiation of nasal epithelial cells through increased TGF-β1 production

Although endoscopic sinus surgery is the mainstay surgical treatment for chronic rhinosinusitis, over 15% of patients require a repeat operation wherein postoperative adhesion formation is one of the main causes of failure. Several recently proposed chitosan-based biomaterials promote mucosal healing, reduce postoperative adhesion formation and restore mucociliary function of sinonasal mucosa. However, the effects of chitosan on cellular morphology, re-epithelization, and mucociliary differentiation of nasal epithelial cells (NECs) during the wound healing process have not been thoroughly investigated. The present study investigates the direct effects of chitosan on cellular growth, cellular migration, mucociliary differentiation and aquaporin (AQP) formation of NECs to elucidate the role of chitosan in sinonasal applications. Wound healing assay reveals that proliferation and migration of NECs are inhibited by incubation of chitosan. The NECs become irregular in shape without formation of tight junction and mucociliary differentiation of NECs is inhibited during a culture period with incubation of chitosan. However, AQP3 and AQP5 formation in NECs is significantly higher in chitosan groups than in control groups. Further, expressions of transforming growth factor (TGF)-β1, Smad2, and Smad3 are significantly higher in the chitosan groups compared with controls. The results of the comparison indicate that chitosan inhibits proliferation, migration and mucociliary differentiation of NECs through increasing production of TGF-β1. Copyright © 2016 John Wiley & Sons, Ltd.

Reduced transforming growth factor β1 (TGF-β1) in the repair of airway epithelial cells of children with asthma

BACKGROUND AND OBJECTIVE

Evidence into the role of TGF-β1 in airway epithelial repair in asthma is still controversial. This study tested the hypothesis that the reduced TGF-β1 levels previously observed in paediatric asthmatic airway epithelial cells directly contribute to the dysregulated repair seen in these cells.

METHODS

Primary airway epithelial cells (pAEC) from children with asthma (n = 16) and non-asthmatic subjects (n = 20) were isolated, and subcultured for investigation of TGF-β1 gene and protein via quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Expression of other associated genes such as integrins αvβ6, αvβ8 and MT1-MMP were also tested. Small interfering RNA (siRNA) was employed to assess the role of TGF-β1 during wound repair.

RESULTS

TGF-β1 gene and protein expression were significantly downregulated in asthmatic pAEC over the course of repair, compared with cells from non-asthmatic children. Messenger RNA (mRNA) expression of TGF-β1 was also directly implicated in non-asthmatic and asthmatic pAEC proliferation over their quiescent counterparts. Small interfering RNA-mediated knockdown of TGF-β1 compromised repair in non-asthmatic pAEC and exacerbated the dysregulated repair seen in asthmatic pAEC. Expression of major TGF-β1 activators of epithelial cells, integrin αvβ6 and αvβ8 was also measured and there was no difference in αvβ6 gene expression between the two cohorts. Although integrin αvβ8 gene expression was significantly higher in asthmatic pAEC, the expression of MT1-MMP (MMP14) which facilitates the αvβ8 mediated TGF-β1 activation was significantly downregulated.

CONCLUSION

Our data has highlighted the importance of TGF-β1 in pAEC wound repair in vitro. The significantly lower levels seen in asthmatic pAEC subsequently contributes to the dysregulated repair observed in these cells.

Mechanical Strain Causes Adaptive Change in Bronchial Fibroblasts Enhancing Profibrotic and Inflammatory Responses

Asthma is characterized by periodic episodes of bronchoconstriction and reversible airway obstruction; these symptoms are attributable to a number of factors including increased mass and reactivity of bronchial smooth muscle and extracellular matrix (ECM) in asthmatic airways. Literature has suggested changes in cell responses and signaling can be elicited via modulation of mechanical stress acting upon them, potentially affecting the microenvironment of the cell. In this study, we hypothesized that mechanical strain directly affects the (myo)fibroblast phenotype in asthma. Therefore, we characterized responses of bronchial fibroblasts, from 6 normal and 11 asthmatic non-smoking volunteers, exposed to cyclical mechanical strain using flexible silastic membranes. Samples were analyzed for proteoglycans, α-smooth muscle actin (αSMA), collagens I and III, matrix metalloproteinase (MMP) 2 & 9 and interleukin-8 (IL-8) by qRT-PCR, Western blot, zymography and ELISA. Mechanical strain caused a decrease in αSMA mRNA but no change in either αSMA protein or proteoglycan expression. In contrast the inflammatory mediator IL-8, MMPs and interstitial collagens were increased at both the transcriptional and protein level. The results demonstrate an adaptive response of bronchial fibroblasts to mechanical strain, irrespective of donor. The adaptation involves cytoskeletal rearrangement, matrix remodelling and inflammatory cytokine release. These results suggest that mechanical strain could contribute to disease progression in asthma by promoting inflammation and remodelling responses.

Protocadherin-1 binds to SMAD3 and suppresses TGF-β1-induced gene transcription

Genetic studies have identified Protocadherin-1 (PCDH1) and Mothers against decapentaplegic homolog-3 (SMAD3) as susceptibility genes for asthma. PCDH1 is expressed in bronchial epithelial cells and has been found to interact with SMAD3 in yeast two-hybrid (Y2H) overexpression assays. Here, we test whether PCDH1 and SMAD3 interact at endogenous protein levels in bronchial epithelial cells and evaluate the consequences thereof for transforming growth factor-β1 (TGF-β1)-induced gene transcription. We performed Y2H screens and coimmunoprecipitation (co-IP) experiments of PCDH1 and SMAD3 in HEK293T and 16HBE14o(-) (16HBE) cell lines. Activity of a SMAD3-driven luciferase reporter gene in response to TGF-β1 was measured in BEAS-2B cells transfected with PCDH1 and in 16HBE cells transfected with PCDH1-small-interfering RNA (siRNA). TGF-β1-induced gene expression was quantified in BEAS-2B clones overexpressing PCDH1 and in human primary bronchial epithelial cells (PBECs) transfected with PCDH1-siRNA. We confirm PCDH1 and SMAD3 interactions by Y2H and by co-IP in HEK293T cells overexpressing both proteins, and at endogenous protein levels in 16HBE cells. TGF-β-induced activation of a SMAD3-driven reporter was reduced by exogenous PCDH1 in BEAS2B cells, whereas it was increased by siRNA-mediated knockdown of endogenous PCDH1 in 16HBE cells. Overexpression of PCDH1 suppressed expression of TGF-β target genes in BEAS-2B cells, whereas knockdown of PCDH1 in human PBECs increased TGF-β-induced gene expression. In conclusion, we demonstrate that PCDH1 binds to SMAD3 and regulates its activation by TGF-β signaling in bronchial epithelial cells. We propose that PCDH1 and SMAD3 act in a single pathway in asthma susceptibility that affects sensitivity of the airway epithelium to TGF-β.

PRMT1 Upregulated by Epithelial Proinflammatory Cytokines Participates in COX2 Expression in Fibroblasts and Chronic Antigen-Induced Pulmonary Inflammation

Protein arginine methyltransferase (PRMT)1, methylating both histones and key cellular proteins, has emerged as a key regulator of various cellular processes. This study aimed to identify the mechanism that regulates PRMT1 in chronic Ag-induced pulmonary inflammation (AIPI) in the E3 rat asthma model. E3 rats were challenged with OVA for 1 or 8 wk to induce acute or chronic AIPI. Expression of mRNAs was detected by real-time quantitative PCR. PRMT1, TGF-β, COX2, and vascular endothelial growth factor protein expression in lung tissues was determined by immunohistochemistry staining and Western blotting. In the in vitro study, IL-4-stimulated lung epithelial cell (A549) medium (ISEM) with or without anti-TGF-β Ab was applied to human fibroblasts from lung (HFL1). The proliferation of HFL1 was determined by MTT. AMI-1 (pan-PRMT inhibitor) was administered intranasally to chronic AIPI rats to determine PRMT effects on asthmatic parameters. In lung tissue sections, PRMT1 expression was significantly upregulated, mainly in epithelial cells, in acute AIPI lungs, whereas it was significantly upregulated mainly in fibroblasts in chronic AIPI lungs. The in vitro study revealed that ISEM elevates PRMT1, COX2, and vascular endothelial growth factor expressions, and it promoted fibroblast proliferation. The application of anti-TGF-β Ab suppressed COX2 upregulation by ISEM. AMI-1 inhibited the expression of COX2 in TGF-β-stimulated cells. In the in vivo experiment, AMI-1 administered to AIPI rats reduced COX2 production and humoral immune response, and it abrogated mucus secretion and collagen generation. These findings suggested that TGF-β-induced PRMT1 expression participates in fibroblast proliferation and chronic airway inflammation in AIPI.

Density and duration of pneumococcal carriage is maintained by transforming growth factor β1 and T regulatory cells

RATIONALE

Nasopharyngeal carriage of Streptococcus pneumoniae is a prerequisite for invasive disease, but the majority of carriage episodes are asymptomatic and self-resolving. Interactions determining the development of carriage versus invasive disease are poorly understood but will influence the effectiveness of vaccines or therapeutics that disrupt nasal colonization.

OBJECTIVES

We sought to elucidate immunological mechanisms underlying noninvasive pneumococcal nasopharyngeal carriage.

METHODS

Pneumococcal interactions with human nasopharyngeal and bronchial fibroblasts and epithelial cells were investigated in vitro. A murine model of nasopharyngeal carriage and an experimental human pneumococcal challenge model were used to characterize immune responses in the airways during carriage.

MEASUREMENTS AND MAIN RESULTS

We describe the previously unknown immunological basis of noninvasive carriage and highlight mechanisms whose perturbation may lead to invasive disease. We identify the induction of active transforming growth factor (TGF)-β1 by S. pneumoniae in human host cells and highlight the key role for TGF-β1 and T regulatory cells in the establishment and maintenance of nasopharyngeal carriage in mice and humans. We identify the ability of pneumococci to drive TGF-β1 production from nasopharyngeal cells in vivo and show that an immune tolerance profile, characterized by elevated TGF-β1 and high nasopharyngeal T regulatory cell numbers, is crucial for prolonged carriage of pneumococci. Blockade of TGF-β1 signaling prevents prolonged carriage and leads to clearance of pneumococci from the nasopharynx.

CONCLUSIONS

These data explain the mechanisms by which S. pneumoniae colonize the human nasopharynx without inducing damaging host inflammation and provide insight into the role of bacterial and host constituents that allow and maintain carriage.

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.

HMGB1 accelerates alveolar epithelial repair via an IL-1β- and αvβ6 integrin-dependent activation of TGF-β1

High mobility group box 1 (HMGB1) protein is a danger-signaling molecule, known to activate an inflammatory response via TLR4 and RAGE. HMGB1 can be either actively secreted or passively released from damaged alveolar epithelial cells. Previous studies have shown that IL-1β, a critical mediator acute lung injury in humans that is activated by HMGB1, enhances alveolar epithelial repair, although the mechanisms are not fully understood. Herein, we tested the hypothesis that HMGB1 released by wounded alveolar epithelial cells would increase primary rat and human alveolar type II cell monolayer wound repair via an IL-1β-dependent activation of TGF-β1. HMGB1 induced in primary cultures of rat alveolar epithelial cells results in the release of IL-1β that caused the activation of TGF-β1 via a p38 MAPK-, RhoA- and αvβ6 integrin-dependent mechanism. Furthermore, active TGF-β1 accelerated the wound closure of primary rat epithelial cell monolayers via a PI3 kinase α-dependent mechanism. In conclusion, this study demonstrates that HMGB1 released by wounded epithelial cell monolayers, accelerates wound closure in the distal lung epithelium via the IL-1β-mediated αvβ6-dependent activation of TGF-β1, and thus could play an important role in the resolution of acute lung injury by promoting repair of the injured alveolar epithelium.

Matrix metalloproteinase-9, transforming growth factor-β1, and tumor necrosis factor-α plasma levels in chronic pancreatitis

OBJECTIVE

The aim of the study was to investigate the plasma levels of matrix metalloproteinase-9 (MMP-9), transforming growth factor-β 1 (TGF-β1), and tumor necrosis factor-α (TNF-α) in chronic pancreatitis (CP).

METHODS

Blood samples were obtained from 71 patients with CP and 100 control subjects, and plasma levels of MMP-9, TGF-β1, and TNF-α were determined by enzyme-linked immunosorbent assay.

RESULTS

The plasma levels of MMP-9 (18.3 ± 3.0 ng/mL, p < 0.0001), TGF-β1 (215.4 ± 178.1 ng/mL, p = 0.0301), and TNF-α (111.2 ± 69.3 ng/mL, p < 0.001) were significantly elevated in CP compared to the control group.

CONCLUSION

The role of elevated plasma MMP-9, TGF-β1, and TNF-α in CP requires further evaluation.

Regulation of a disintegrin and metalloprotease-33 expression by transforming growth factor-β

The asthma susceptibility gene, a disintegrin and metalloprotease-33 (ADAM33), is selectively expressed in mesenchymal cells, and the activity of soluble ADAM33 has been linked to angiogenesis and airway remodeling. Transforming growth factor (TGF)-β is a profibrogenic growth factor, the expression of which is increased in asthma, and recent studies show that it enhances shedding of soluble ADAM33. In this study, we hypothesized that TGF-β also affects ADAM33 expression in bronchial fibroblasts in asthma. Primary fibroblasts were grown from bronchial biopsies from donors with and those without asthma, and treated with TGF-β(2) to induce myofibroblast differentiation. ADAM33 expression was assessed using quantitative RT-PCR and Western blotting. To examine the mechanisms whereby TGF-β(2) affected ADAM33 expression, quantitative methylation-sensitive PCR, chromatin immunoprecipitation, and nuclear accessibility assays were conducted on the ADAM33 promoter. We found that TGF-β(2) caused a time- and concentration-dependent reduction in ADAM33 mRNA expression in normal and asthmatic fibroblasts, affecting levels of splice variants similarly. TGF-β(2) also induced ADAM33 protein turnover and appearance of a cell-associated C-terminal fragment. TGF-β(2) down-regulated ADAM33 mRNA expression by causing chromatin condensation around the ADAM33 promoter with deacetylation of histone H3, demethylation of H3 on lysine-4, and hypermethylation of H3 on lysine-9. However, the methylation status of the ADAM33 promoter did not change. Together, these data suggest that TGF-β(2) suppresses expression of ADAM33 mRNA in normal or asthmatic fibroblasts. This occurs by altering chromatin structure, rather than by gene silencing through DNA methylation as in epithelial cells. This may provide a mechanism for fine regulation of levels of ADAM33 expression in fibroblasts, and may self-limit TGF-β(2)-induced ectodomain shedding of ADAM33.

Integrin αvβ5-mediated TGF-β activation by airway smooth muscle cells in asthma

Severe asthma is associated with airway remodeling, characterized by structural changes including increased smooth muscle mass and matrix deposition in the airway, leading to deteriorating lung function. TGF-β is a pleiotropic cytokine leading to increased synthesis of matrix molecules by human airway smooth muscle (HASM) cells and is implicated in asthmatic airway remodeling. TGF-β is synthesized as a latent complex, sequestered in the extracellular matrix, and requires activation for functionality. Activation of latent TGF-β is the rate-limiting step in its bioavailability. This study investigated the effect of the contraction agonists LPA and methacholine on TGF-β activation by HASM cells and its role in the development of asthmatic airway remodeling. The data presented show that LPA and methacholine induced TGF-β activation by HASM cells via the integrin αvβ5. Our findings highlight the importance of the β5 cytoplasmic domain because a polymorphism in the β5 subunit rendered the integrin unable to activate TGF-β. To our knowledge, this is the first description of a biologically relevant integrin that is unable to activate TGF-β. These data demonstrate that murine airway smooth muscle cells express αvβ5 integrins and activate TGF-β. Finally, these data show that inhibition, or genetic loss, of αvβ5 reduces allergen-induced increases in airway smooth muscle thickness in two models of asthma. These data highlight a mechanism of TGF-β activation in asthma and support the hypothesis that bronchoconstriction promotes airway remodeling via integrin mediated TGF-β activation.

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.

Wound-induced TGF-β1 and TGF-β2 enhance airway epithelial repair via HB-EGF and TGF-α

The abundance of transforming growth factor-beta (TGF-β) in normal airway epithelium suggests its participation in physiological processes to maintain airway homeostasis. The current study was designed to address the hypothesis that TGF-β1 and TGF-β2 might contribute to normal reparative response of airway epithelial cells (AECs). Treatments with exogenous TGF-β1 or TGF-β2 significantly enhanced wound repair of confluent AEC monolayers. Mechanical injury of AEC monolayers induced production of both TGF-β1 and TGF-β2. Wound repair of AECs was significantly reduced by a specific inhibitor of TGF-β type I receptor kinase activity. We investigated whether the TGF-β-enhanced repair required epidermal growth factor receptor (EGFR) transactivation and secretion of EGFR ligands. Both TGF-β1 and TGF-β2 enhanced EGFR phosphorylation and induced production of heparin-binding EGF-like growth factor (HB-EGF) and transforming growth factor-alpha (TGF-α) in AECs. Moreover, treatment with a broad-spectrum metalloproteinase inhibitor or anti-HB-EGF and anti-TGF-α antibodies inhibited the wound repair and the EGFR phosphorylation by TGF-β1 and TGF-β2, indicating that the TGF-β1 and TGF-β2 effects on wound repair required the release of HB-EGF and TGF-α. Our data, for the first time, have shown that both TGF-β1 and TGF-β2 play a stimulatory role in airway epithelial repair through EGFR phosphorylation following autocrine production of HB-EGF and TGF-α. These findings highlight an important collaborative mechanism between TGF-β and EGFR in maintaining airway epithelial homeostasis.

Epithelial cells modulate genes associated with NF kappa B activation in co-cultured human macrophages

Macrophages located in airways and the alveolar space are continually exposed to different signals from the respiratory mucosa. In this respect, epithelial cells represent an important source of cytokines and mediators modulating the state of activation and/or differentiation of mononuclear phagocytes. Many of the proinflammatory genes induced in macrophages during immune and immunopathological reactions are regulated by transcription factor NF kappa B. The aim of our study was to characterize changes in the expression of genes associated with NF kappa B activation and signalling in THP-1 human macrophages co-cultured with A549 respiratory epithelial cells. At least 4-fold upregulation of mRNA level was found in 29 of 84 tested genes including genes for multiple cytokines and chemokines, membrane antigens and receptors, and molecules associated with NF kappa B signalling. The mRNA induction was confirmed at the level of protein expression by evaluating the release of IL-6 and IL-8 and by ICAM-1 expression. Blocking of one NFκB subunit by p65 siRNA inhibited the production of IL-6 in both cell types while IL-8 release from THP-1 cells did not seem to be affected. We conclude from our data that unstimulated respiratory epithelial cells regulate genes associated with NF kappa B dependent immune responses in human macrophages and that these interactions may play a key role in immediate responses in the respiratory mucosa.

Hot Water ExtractedLycium BarbarumandRehmannia GlutinosaInhibit Liver Inflammation and Fibrosis in Rats

Polysaccharide-rich Lycium barbarum and Rehmannia glutinosa have been considered to have immune-modulating activity. This study investigated the effects of water extracted Lycium barbarum and Rehmannia glutinosa (HE) on carbon tetrachloride ( CCl4)-induced liver injury in rats. Male Sprague-Dawley rats were randomly divided into: normal diet + peritoneal injection of olive oil (control), normal diet + CCl4injection ( CCl4), 1 × HE (0.05% HE for each) + CCl4(1 × HE), and 3 × HE (0.15% HE for each) + CCl4(3 × HE) groups. Rats were injected with 40% CCl4at a dose of 0.75 ml/kg body weight once a week for seven weeks, one week after herbal extract treatment. After eight week herbal extract treatment, pathohistological examination showed that both 1× and 3 × HE treatments diminished necrotic hepatocytes, chemoattraction of inflammatory cells, and liver fibrosis. Both 1× and 3 × HE treatments decreased plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, and reduced hepatic levels of pro-inflammatory cytokines — tumor necrosis factor-α and interleukin-1β — compared to CCl4treatment alone. The 1 × HE treatment increased hepatic anti-inflammatory cytokine IL-10 levels. Both the 1× and 3 × HE treatments suppressed liver fibrosis biomarkers — transforming growth factor-β1 and hydroxyproline. Therefore, treatment with water extracted Lycium barbarum and Rehmannia glutinosa (0.05% and 0.15% for each) for eight weeks protects against necrotic damage, indicated by decreases in plasma ALT and AST activities, and suppresses liver fibrosis by down-regulation of liver inflammation in rats with CCl4-induced liver injury.

Curcumin and saikosaponin a inhibit chemical-induced liver inflammation and fibrosis in rats

Curcumin and saikosaponin A as antioxidants improve antioxidant status. This study investigated the anti-inflammatory and antifibrotic actions of curcumin and saikosaponin A on CCl(4)-induced liver damage. Sprague-Dawley rats were randomly divided into control, CCl(4), CCl(4)+ curcumin (0.005%; CU), CCl(4) + saikosaponin A (0.004%; SS), and CCl(4) + curcumin + saikosaponin A (0.005% + 0.004%; CU + SS) groups. Carbon tetrachloride (40% in olive oil) at a dose of 0.75 ml/kg was injected intraperitoneally once a week. Curcumin and saikosaponin A were supplemented alone or in combination with diet 1 week before CCl(4) injection for 8 weeks. After 8-week supplementation, histopathological results showed hepatic collagen deposition was significantly reduced in the CU and SS groups, and activated nuclear factor-kappa B expression induced by CCl(4) in the liver was significantly inhibited by curcumin and/or saikosaponin A. Hepatic proinflammatory cytokines tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 were significantly inhibited, and anti-inflammatory cytokine interleukin-10 was significantly increased by supplementation with curcumin and/or saikosaponin A. Additionally, curcumin and/or saikosaponin A significantly reduced the increased levels of hepatic transforming growth factor-beta1 and hydroxyproline after CCl(4) treatment. Therefore, supplementation with curcumin and/or saikosaponin A suppress inflammation and fibrogenesis in rats with CCl(4)-induced liver injury. However, the combination has no additive effects on anti-inflammation and antifibrosis.

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.

Cell cycle arrest by transforming growth factor beta1 enhances replication of respiratory syncytial virus in lung epithelial cells

Respiratory syncytial virus (RSV) is a common respiratory viral infection in children which is associated with immune dysregulation and subsequent induction and exacerbations of asthma. We recently reported that treatment of primary human epithelial cells (PHBE cells) with transforming growth factor beta (TGF-beta) enhanced RSV replication. Here, we report that the enhancement of RSV replication is mediated by induction of cell cycle arrest. These data were confirmed by using pharmacologic inhibitors of cell cycle progression, which significantly enhanced RSV replication. Our data also showed that RSV infection alone resulted in cell cycle arrest in A549 and PHBE cells. Interestingly, our data showed that RSV infection induced the expression of TGF-beta in epithelial cells. Blocking of TGF-beta with anti-TGF-beta antibody or use of a specific TGF-beta receptor signaling inhibitor resulted in rescue of the RSV-induced cell cycle arrest, suggesting an autocrine mechanism. Collectively, our data demonstrate that RSV regulates the cell cycle through TGF-beta in order to enhance its replication. These findings identify a novel pathway for upregulation of virus replication and suggest a plausible mechanism for association of RSV with immune dysregulation and asthma.

Muco-ciliary differentiation of nasal epithelial cells is decreased after wound healing in vitro

BACKGROUND

Epithelial damage and modifications of cell differentiation are frequent in airway diseases with chronic inflammation, in which transforming growth factor-beta1 (TGF-beta1) plays an important role. The aim of this study was to evaluate the differentiation of human nasal epithelial cells (HNEC) after wound healing and the potential effects of TGF-beta1.

METHODS

Basal, mucus, and ciliated cells were characterized by cytokeratin-14, MUC5AC, and betaIV tubulin immunodetection, respectively. Their expression was evaluated in situ in nasal polyps and in an in vitro model of wound healing in primary cultures of HNEC after wound closure, under basal conditions and after TGF-beta1 supplementation. Using RT-PCR, the effects of TGF-beta1 on MUC5AC and DNAI1 genes, specifically transcribed in mucus and ciliated cells, were evaluated.

RESULTS

In situ, high TGF-beta1 expression was associated with low MUC5AC and betaIV tubulin expression. In vitro, under basal conditions, MUC5AC expression remained stable, cytokeratin-14 expression was strong and decreased with time, while betaIV tubulin expression increased. Transforming growth factor-beta1 supplementation downregulated MUC5AC and betaIV tubulin expression as well as MUC5AC and DNAI1 transcripts.

CONCLUSION

After a wound, differentiation into mucus and ciliated cells was possible and partially inhibited in vitro by TGF-beta1, a cytokine that may be involved in epithelial remodeling observed in chronic airway diseases.

Non-allergic Eosinophilic Inflammation

Much is known about the eosinophilic processes associated with antigens, tumors, and infection, yet data on other causes of eosinophilic inflammation are scarce. This paper investigates the locations and causes of other nonrespiratory eosinophilic inflammation. Although eosinophilic inflammation can involve locomotor, urinary, cardiovascular, nervous, gastrointestinal, and other mucosal surfaces, such inflammation also can accompany tissue trauma, foreign-body reactions, and necrotic or granulomatous processes. Despite their cytolytic/histolytic effects, eosinophil leukocytes are a component of tissue remodeling, can be antigen-presenting cells, and have a role in the reproductive system and in blood coagulation. The study of various types of eosinophilic inflammation may increase our understanding of the biological responses of eosinophil leukocytes to different inflammatory stimuli.

A dynamic reinfection hypothesis of latent tuberculosis infection

BACKGROUND

It has been traditionally postulated that individuals, once infected by Mycobacterium tuberculosis, will retain throughout their entire lifetime latent bacilli which will remain dormant in old lesions. This bacillus would then be the source of a later reactivation of active tuberculosis (TB), with the aid of resuscitation factors. Unfortunately, the presence of these bacilli can only be predicted by indirect immunological methods, such as the tuberculin skin test (TST) or T cell interferon-gamma release assays. Other evidence shows that a 9-month isoniazid treatment of TST+ individuals converting to TB reduces the incidence of TB by approximately 90%.

QUESTIONS

Taking into account this widely accepted framework, I suggest that there are at least three relevant questions to answer: (1) How can dormant bacilli remain in the lungs for an entire lifetime, taking into account constant cellular turnover and the healing of damaged tissues? (2) What provides the resuscitation factor to dormant bacilli, assuming that these latent bacilli are indeed present inside old lesions? (3) Why can a 9-month treatment with isoniazid eliminate dormant bacilli? As isoniazid is active only against growing bacilli, and thus is only able to destroy them after reactivation of latent bacilli, this treatment should have to be provided for life if the traditionally accepted postulate is correct.

HYPOTHESIS

For a better understanding of latent TB infection. I propose a hypothesis that describes a dynamic scenario of constant endogenous reinfection with M. tuberculosis which explains the efficacy of the current standard of treatment. If this hypothesis is true, new strategies for the management of TB may arise.

17beta-estradiol regulates the secretion of TGF-beta by cultured human dermal fibroblasts

Estrogen plays an important role in skin homeostasis, as demonstrated by the changes seen in the skin of post-menopausal women, changes reversed by HRT. Estrogen also has a role in wound healing, since estrogen deficiency as occurs post-menopausally and in ovariectomised animals, is associated with a reduced rate of wound healing. Estrogen appears to modulate all phases of wound healing with effects on inflammatory cells, epithelialization, angiogenesis, extracellular matrix deposition and tissue remodelling. This study was designed to investigate the effects of 17beta-estradiol on cultured human dermal fibroblasts using an in vitro wound-healing assay. The end points investigated were cell migration, proliferation, total collagen secretion and active TGF-beta1 secretion. 17beta-estradiol significantly increased the migration and proliferation of cultured dermal fibroblasts following mechanical wounding, although the secretion of total soluble collagen was not altered. An increase in TGF-beta1 was demonstrated by unwounded confluent dermal fibroblast monolayers in response to 17beta-estradiol, but paradoxically, a decrease in the secretion of TGF-beta1 was demonstrated in the mechanically wounded dermal fibroblasts. These results identify human dermal fibroblasts as estrogen target cells and provide further evidence for a role by which estrogen regulates this particular cell type as part of the wound-healing process. However, the paradoxical nature of the effect of estrogen on TGF-beta1 secretion following mechanical wounding suggests that the cellular mechanism of action is complex. A greater understanding of the cell-specific action of estrogen may help to develop therapies that will improve cutaneous wound healing in the future.

Arsenic upregulates MMP-9 and inhibits wound repair in human airway epithelial cells

As part of the innate immune defense, the polarized conducting lung epithelium acts as a barrier to keep particulates carried in respiration from underlying tissue. Arsenic is a metalloid toxicant that can affect the lung via inhalation or ingestion. We have recently shown that chronic exposure of mice or humans to arsenic (10-50 ppb) in drinking water alters bronchiolar lavage or sputum proteins consistent with reduced epithelial cell migration and wound repair in the airway. In this report, we used an in vitro model to examine effects of acute exposure of arsenic (15-290 ppb) on conducting airway lung epithelium. We found that arsenic at concentrations as low as 30 ppb inhibits reformation of the epithelial monolayer following scrape wounds of monolayer cultures. In an effort to understand functional contributions to epithelial wound repair altered by arsenic, we showed that acute arsenic exposure increases activity and expression of matrix metalloproteinase (MMP)-9, an important protease in lung function. Furthermore, inhibition of MMP-9 in arsenic-treated cells improved wound repair. We propose that arsenic in the airway can alter the airway epithelial barrier by restricting proper wound repair in part through the upregulation of MMP-9 by lung epithelial cells.

Airway smooth muscle in asthma

Airway smooth muscle plays a multifaceted role in the pathogenesis of asthma. We review the current understanding of the contribution of airway myocytes to airway inflammation, airway wall remodeling, and airflow obstruction in this prevalent disease syndrome. Together, these roles make airway smooth muscle an attractive target for asthma therapy.

Interleukin-13 acts as an apoptotic effector on lung epithelial cells and induces pro-fibrotic gene expression in lung fibroblasts

BACKGROUND

IL-13 promotes acute allergic asthma and is discussed to play a role in late asthmatic features such as fibrotic processes and airway remodelling. The contributions of IL-13-mediated mechanisms to subepithelial events related to fibrosis are not yet settled.

OBJECTIVE

We investigated the impact of IL-13 on lung epithelial cells as apoptotic effector and on lung fibroblasts as inducer of pro-fibrotic gene expression.

METHODS

Using the two lung epithelial cell lines A549 and BEAS-2B as well as primary lung epithelial cells, we investigated the capability of IL-13 to induce apoptosis by both flow-cytometry and ELISA. The ability of IL-13 to increase the expression of pro-fibrotic genes and to exert influence on the expression of its own receptor was investigated by real-time quantitative PCR measurement of mRNAs encoding collagen I, collagen III, basic fibroblast growth factor (bFGF), alpha-smooth muscle actin (alpha-SMA) and the IL-13 receptor alpha1 (IL-13Ralpha1) chain in human primary lung fibroblasts. The specificity of IL-13-mediated cellular responses was confirmed by means of an inhibitory monoclonal antibody directed to the IL-13 receptor.

RESULTS

IL-13 induces apoptosis in lung epithelial cell lines as well as in primary lung epithelial cells. Furthermore, IL-13 increases the expression of mRNA for alpha-SMA and collagen III, but not for bFGF in human primary lung fibroblasts. The susceptibility of lung fibroblasts to IL-13-induced up-regulation of pro-fibrotic genes is associated with the regulation of IL-13 receptor expression. IL-13-dependent fibrosis-associated effects could be inhibited by antibody-mediated blockade of the IL-13Ralpha1 subunit.

CONCLUSION

Our findings indicate a function of IL-13 as a mediator in fibrotic processes leading to loss of functional airway tissue in asthma. They also highlight the therapeutic potential of specifically targeting the interaction between IL-13 and its receptor.

Fibrin formation by wounded bronchial epithelial cell layers in vitro is essential for normal epithelial repair and independent of plasma proteins

BACKGROUND

The bronchial epithelium is in contact with, and continually damaged by, the environment. Animal models have indicated that normal epithelial repair is rapid and supported by the formation of a provisional fibrin matrix that is exclusively plasma-derived.

OBJECTIVES

Our objectives were to demonstrate the ability of normal human bronchial epithelial (NHBE) cells to produce coagulation cascade proteins and form fibrin in response to damage, independently of plasma proteins, and to show that formation of a cross-linked fibrin matrix is essential for normal epithelial repair in vitro.

METHODS

Primary NHBE cells and cells of the 16HBE 14o- bronchial epithelial cell line were grown and maintained in vitro prior to mechanical wounding of confluent monolayers in serum-free media. Tissue factor (TF) and factor XIII (FXIII) were visualized on 16HBE 14o- monolayers using immunohistochemistry. The time-dependent expression of TF, factor VII (FVII), factor X (FX), fibrinogen, soluble fibrin, FXIII subunit A (FXIIIA) and D-dimers following wounding of confluent 16HBE 14o- monolayers was investigated using immunoassays. TF and FVII expression at the mRNA level was investigated by RT-PCR. The role of coagulation cascade proteins in the repair response of NHBE and 16HBE 14o- monolayers was investigated using neutralizing antibodies.

RESULTS

Active TF was constitutively expressed in 16HBE 14o- cells. Levels of FVII, FX, fibrinogen, soluble fibrin, FXIIIA and D-dimers in culture supernatants increased rapidly and were maximal 20 min after wounding the monolayers. Expression of TF and FVII mRNA was significantly increased 10 and 4 h, respectively, after wounding. Neutralizing antibodies to TF, fibrinogen and FXIIIA significantly inhibited repair of NHBE and 16HBE 14o- cell layers.

CONCLUSIONS

The bronchial epithelium has the potential to respond rapidly to mechanical damage by forming a cross-linked fibrin matrix that is essential for normal epithelial repair, independently of plasma proteins.

Transforming growth factor beta enhances respiratory syncytial virus replication and tumor necrosis factor alpha induction in human epithelial cells

Asthma is characterized as a chronic inflammatory disease associated with significant tissue remodeling. Patients with asthma are more susceptible to virus-induced exacerbation, which subsequently can lead to increased rates of hospitalization and mortality. While the most common cause of asthma-related deaths is respiratory viral infections, the underlying factors in the lung environment which render asthmatic subjects more susceptible to viral exacerbation are not yet identified. Since transforming growth factor beta (TGF-beta) is a critical cytokine for lung tissue remodeling and asthma phenotype, we have focused on the effects of TGF-beta on viral replication and virus-induced inflammation. Treatment of human epithelial cells with TGF-beta increased respiratory syncytial virus (RSV) replication by approximately fourfold. Tumor necrosis factor alpha (TNF-alpha) mRNA and protein expression were also significantly increased above levels with RSV infection alone. The increase in RSV replication and TNF-alpha expression after TGF-beta treatment was concomitant with an increase in virus-induced p38 mitogen-activated protein kinase activation. Our data reveal a novel effect for TGF-beta on RSV replication and provide a potential mechanism for the exaggerated inflammatory response observed in asthmatic subjects during respiratory viral infections.

Epithelial repair is inhibited by an alpha(1,6)-fucose binding lectin

The effective repair of damage to the airway epithelium is essential to maintain the ability to exclude airborne particulates and protect against potential pathogens. Carbohydrates on the cell surface have an important role in cell-cell and cell substrate interactions. Using a model of repair with airway epithelial-derived cells of the 16HBE 14o(-) cell line, we have examined the effect of the Aleuria aurantia lectin (AAL), which binds very selectively to alpha(1,6)-linked fucose residues. Addition of unconjugated or FITC-labeled AAL reduced the rate of epithelial repair to approximately one-third of control values as measured by image analysis while cell viability was maintained. Pulse labeling with AAL-FITC for 30 min followed by incubation in AAL-free medium caused similar inhibition of repair but could be reversed by addition of fucose up to 7 h after AAL removal. By confocal microscopy, AAL binding was found to be on the apical, but not basolateral, surfaces of cells, and internalization of the labeled lectin was seen. Preincubation of the lectin with fucose prevented this effect. Ulex europeaus I lectin, which is also fucose specific, resulted in similar binding to the cells and internalization, but it did not affect the speed of the repair process. We conclude that alpha(1,6)-fucose binding sites play an important role in epithelial repair. Better understanding of this process will provide a deeper insight into the crucial mechanisms of epithelial repair.

Intrinsic biochemical and functional differences in bronchial epithelial cells of children with asthma

RATIONALE

Convincing evidence of epithelial damage and aberrant repair exists in adult asthmatic airways, even in the absence of inflammation. However, comparable studies in children have been limited by access and availability of clinical samples.

OBJECTIVES

To determine whether bronchial epithelial cells from children with asthma are inherently distinct from those obtained from children without asthma.

METHODS

Epithelial cells were obtained by nonbronchoscopic bronchial brushing of children with mild asthma (n = 7), atopic children without asthma (n = 9), and healthy children (n = 12). Cells were subject to morphologic, biochemical, molecular, and functional assessment. Responses were also compared with commercially available epithelial cultures and the transformed cell line 16HBE140.

RESULTS

All epithelial cells exhibited a "cobblestone" morphology, which was maintained throughout culture and repeated passage. Expression of cytokeratin 19 varied, with disease phenotype being greatest in healthy nonatopics and lowest in asthmatics. In contrast, expression of cytokeratin 5/14 was greatest in asthmatic samples and least in healthy nonatopic samples. Asthmatic epithelial cells also spontaneously produced significantly greater amounts of interleukin (IL)-6, prostaglandin E2, and epidermal growth factor, and equivalent amounts of IL-1beta and soluble intracellular adhesion molecule-1, but significantly lower amounts of transforming growth factor beta1. This profile was maintained through successive passages. Asthmatic epithelial cells also exhibited greater rates of proliferation than nonasthmatic cells.

CONCLUSIONS

This study has shown that epithelial cells from children with mild asthma are intrinsically different both biochemically and functionally compared with epithelial cells from children without asthma. Importantly, these differences are maintained over successive passages, suggesting that they are not dependent on an in vivo environment.

Physiologic and pathologic abnormalities in severe asthma

Severe asthma remains poorly understood and frustrating to treat, partly because it is a heterogeneous disease. Recent improvements in the definition of severe asthma have allowed better characterization of the phenotypes of severe asthma and the related physiologic and pathologic abnormalities. Early-onset severe asthma is a more allergy-associated disease than late-onset asthma. Persistent eosinophilia is more commonly seen in patients who have late-onset disease but is associated with a more symptomatic disease in both early- and late-onset disease. Recent studies suggest that response to therapy in severe asthma may depend on the phenotype.

Activation of transforming growth factor-beta by the integrin alphavbeta8 delays epithelial wound closure

Transforming growth factor (TGF)-beta family members regulate multiple aspects of wound repair through effects on cell proliferation, matrix production, and tissue inflammation, but the effects of TGF-beta on wound closure itself have been controversial. We found that blocking antibodies to TGF-beta enhanced the degree of closure of scratch wounds in primary airway epithelial monolayers, while addition of exogenous TGF-beta1 inhibited the degree of closure, suggesting that endogenous activation of TGF-beta normally serves as a brake on the degree of wound closure. Although these cells secreted large amounts of TGF-beta2 and small amounts of TGF-beta1, blockade of TGF-beta1 enhanced the degree of wound closure, whereas blockade of TGF-beta2 had no effect. TGF-beta1 (but not TGF-beta2) can be activated by two members of the integrin family, alphavbeta6 and alphavbeta8, which are both expressed on airway epithelial cells. Wounding induced activation of TGF-beta through effects of both integrins, but antibodies against alphavbeta8 enhanced the degree of wound closure, whereas antibodies against alphavbeta6 did not.

Transforming growth factor-beta1 increases airway wound repair via MMP-2 upregulation: a new pathway for epithelial wound repair?

In vivo, transforming growth factor (TGF)-beta1 and matrix metalloproteinases (MMPs) present at the site of airway injury are thought to contribute to epithelial wound repair. As TGF-beta1 can modulate MMP expression and MMPs play an important role in wound repair, we hypothesized that TGF-beta1 may enhance airway epithelial repair via MMPs secreted by epithelial cells. We evaluated the in vitro influence of TGF-beta1 on wound repair in human airway epithelial cells cultured under conditions allowing differentiation. The results showed that TGF-beta1 accelerated in vitro airway wound repair, whereas MMP inhibitors prevented this acceleration. In parallel, we examined the effect of TGF-beta1 on the expression of MMP-2 and MMP-9. TGF-beta1 induced a dramatic increase of MMP-2 expression with an increased steady-state level of MMP-2 mRNA, contrasting with a slight increase in MMP-9 expression. To confirm the role of MMP-2, we subsequently evaluated the effect of MMP-2 on in vitro airway wound repair and demonstrated that the addition of MMP-2 reproduced the acceleration of wound repair induced by TGF-beta1. These results strongly suggest that TGF-beta1 increases in vitro airway wound repair via MMP-2 upregulation. It also raises the issue of a different in vivo biological role of MMP-2 and MMP-9 depending on the cytokine microenvironment.

Severe Asthma in Adults

Severe asthma remains poorly understood and frustrating to care for, partly because it is a heterogeneous disease. Patients with severe asthma disproportionately consume health care resources related to asthma. Severe asthma may develop over time, or shortly after onset of the disease. The genetic and environmental elements that may be most important in the development of severe disease are poorly understood, but likely include both allergic and nonallergic elements. Physiologically, these patients often have air trapping, airway collapsibility, and a high degree of methacholine hyperresponsiveness. Specific phenotypes of severe asthma are only beginning to be defined. However, describing severe asthma by age at onset (early- vs. late-onset) appears to describe two phenotypes that differ at immunologic, physiologic, epidemiologic, and pathologic levels. In particular, early-onset severe asthma is a more allergic-associated disease than late-onset severe asthma. In addition, patients with severe asthma can be defined on the basis of presence and type of inflammation. Severe asthma with persistent eosinophilia (of either early or late onset) is more symptomatic and has more near-fatal events. However, at least 50% of patients with severe asthma have very little identifiable inflammation. Thus, "steroid resistance" may occur at numerous levels, not all of which are caused by a lack of effect of steroids on inflammation. Treatment remains problematic, with corticosteroids remaining the most effective therapy. However, 5-lipoxygenase inhibitors, anti-IgE, and immunomodulatory drugs are also likely to have a place in treatment. Improving therapy in this disease will require a better understanding of the phenotypes involved.

Chemokine-mediated angiogenesis: an essential link in the evolution of airway fibrosis?

Angiogenesis may be an important factor in the development of fibrotic lung disease. Prior studies have strongly suggested a role for angiogenic vascular remodeling in pulmonary fibrosis, and emerging evidence indicates that new vessel formation is critical in airway fibrosis. Bronchiolitis obliterans syndrome is a fibrotic occlusion of distal airways that is largely responsible for the morbidity and mortality of patients after lung transplantation. In this issue, Belperio et al. demonstrate a role for CXC chemokine receptor 2 in the regulation of angiogenesis-mediated airway fibroproliferation. By integrating an understanding of neovascularization into the study of events that occur between inflammation and fibrosis, it becomes increasingly possible to rationally design therapies that can halt conditions of maladaptive fibrosis.

Multiple rows of cells behind an epithelial wound edge extend cryptic lamellipodia to collectively drive cell-sheet movement

The mechanism by which epithelial, endothelial and other strongly cell-cell adhesive cells migrate collectively as continuous sheets is not clear, even though this process is crucial for embryonic development and tissue repair in virtually all multicellular animals. Wound closure in Madin-Darby canine kidney (MDCK) epithelial cell monolayers involves Rac GTPase-dependent migration of cells both at and behind the wound edge. We report here for the first time that cells behind the margin of wounded MDCK cell monolayers, even hundreds of microns from the edge, extend 'cryptic' lamellipodia against the substratum beneath cells in front of them, toward the wound, as determined by confocal, two-photon and transmission electron microscopy. These so-called submarginal cells nevertheless strictly maintain their more apical cell-cell contacts when they migrate as part of a coherent cell sheet, hiding their basal protrusions from conventional microscopy. The submarginal protrusions display the hallmarks of traditional lamellipodia based on morphology and dynamics. Cells behind the margin therefore actively crawl, instead of just moving passively when cells at the margin pull on them. The rate of migration is inversely proportional to the distance from the margin, and cells move co-ordinately, yet still in part autonomously, toward the wound area. We also clarify the ancillary role played by nonprotrusive contractile actin bundles that assemble in a Rho GTPase-dependent manner at the margin after wounding. In addition, some cell proliferation occurs at a delay after wounding but does not contribute to closure. Instead, it apparently serves to replace damaged cells so that intact spread cells can revert to their normal cuboidal morphology and the original cell density of the unbroken sheet can be restored.

Transforming growth factor-beta2 induces bronchial epithelial mucin expression in asthma

The transforming growth factor (TGF)-beta family is important for tissue repair in pathological conditions including asthma. However, little is known about the impact of either TGF-beta1 or TGF-beta2 on asthmatic airway epithelial mucin expression. We evaluated bronchial epithelial TGF-beta1 and TGF-beta2 expression and their effects on mucin expression, and the role of TGF-beta1 or TGF-beta2 in interleukin (IL)-13-induced mucin expression. Epithelial TGF-beta1, TGF-beta2, and mucin expression were evaluated in endobronchial biopsies from asthmatics and normal subjects. The effects of TGF-beta1 or TGF-beta2 on mucin MUC5AC protein and mRNA expression, and the impact of IL-13 on epithelial TGF-beta1, TGF-beta2, and MUC5AC were determined in cultured bronchial epithelial cells from endobronchial brushings of both subject groups. In biopsy tissue, epithelial TGF-beta2 expression levels were higher than TGF-beta1 in both asthmatics and normals. TGF-beta2, but not TGF-beta1, was increased in asthmatics compared with normals, and significantly correlated with mucin expression. TGF-beta2, but not TGF-beta1, increased mucin expression in cultured epithelial cells from both subject groups. IL-13 increased the release of TGF-beta2, but not TGF-beta1, from epithelial cells. A neutralizing TGF-beta2 antibody partially inhibited IL-13-induced mucin expression. These data suggest that TGF-beta2 production by asthmatic bronchial epithelial cells may increase airway mucin expression. IL-13-induced mucin expression may occur in part through TGF-beta2 up-regulation.

Smad and p38-MAPK signaling mediates apoptotic effects of transforming growth factor-beta1 in human airway epithelial cells

Transforming growth factor-beta1 (TGF-beta1) belongs to a family of multifunctional cytokines that regulate a variety of biological processes, including cell differentiation, proliferation, and apoptosis. The effects of TGF-beta1 are cell context and cell cycle specific and may be signaled through several pathways. We examined the effect of TGF-beta1 on apoptosis of primary human central airway epithelial cells and cell lines. TGF-beta1 protected human airway epithelial cells from apoptosis induced by either activation of the Fas death receptor (CD95) or by corticosteroids. This protective effect was blocked by inhibition of the Smad pathway via overexpression of inhibitory Smad7. The protective effect is associated with an increase in the cyclin-dependent kinase inhibitor p21 and was blocked by the overexpression of key gatekeeper cyclins for the G1/S interface, cyclins D1 and E. Blockade of the Smad pathway by overexpression of the inhibitory Smad7 permitted demonstration of a TGF-beta-mediated proapoptotic pathway. This proapoptotic effect was blocked by inhibition of the p38 MAPK kinase signaling with the inhibitor SB-203580 and was associated with an increase in p38 activity as measured by a kinase assay. Here we demonstrate dual signaling pathways involving TGF-beta1, an antiapoptotic pathway mediated by the Smad pathway involving p21, and an apoptosis-permissive pathway mediated in part by p38 MAPK.

The airway epithelium: structural and functional properties in health and disease

The major function of the respiratory epithelium was once thought to be that of a physical barrier. However, it constitutes the interface between the internal milieu and the external environment as well as being a primary target for inhaled respiratory drugs. It also responds to changes in the external environment by secreting a large number of molecules and mediators that signal to cells of the immune system and underlying mesenchyme. Thus, the epithelium is in a unique position to translate gene-environment interactions. Normally, the epithelium has a tremendous capacity to repair itself following injury. However, evidence is rapidly accumulating to show that the airway epithelium of asthmatics is abnormal and has increased susceptibility to injury compared to normal epithelium. Areas of detachment and fragility are a characteristic feature not observed in other inflammatory diseases such as COPD. In addition to being more susceptible to damage, normal repair processes are also compromised. Failure of appropriate growth and differentiation of airway epithelial cells will cause persistent mucosal injury. The response to traditional therapy such as glucocorticoids may also be compromised. However, whether the differences observed in asthmatic epithelium are a cause of or secondary to the development of the disease remains unanswered. Strategies to address this question include careful examination of the ontogeny of the disease in children and use of gene array technology should provide some important answers, as well as allow a better understanding of the critical role that the epithelium plays under normal conditions and in diseases such as asthma.

Differentiation-dependent responsiveness of bronchial epithelial cells to IL-4/13 stimulation

The Th2 cytokines interleukin (IL)-4 and IL-13 are thought to play critical roles in the airway inflammation and hyperresponsiveness that characterize asthma. Recent evidence indicates that IL-13 can mediate these effects by acting directly on airway epithelial cells. Here we evaluated early [signal transducer and activator of transcription (STAT)6 phosphorylation] and delayed [granulocyte/macrophage colony-stimulating factor (GM-CSF) and transforming growth factor-beta(2) (TGF-beta(2)) secretion] responses of airway epithelial cells to IL-4 and IL-13 stimulation and the dependence of these responses on the culture technique employed. As expected, normal human bronchial epithelial cells grown on microporous inserts at an air-liquid interface (ALI) expressed a well-differentiated mucociliary phenotype; in contrast, cells grown on plastic in submerged cultures were poorly differentiated. When stimulated with IL-4 or IL-13, the magnitude and duration of STAT6 phosphorylation under the differing culture conditions were statistically indistinguishable. In contrast, cytokine secretion responses to IL-4 and IL-13 were highly dependent on the culture technique; cells cultured on plastic exhibited significant concentration-dependent increases in GM-CSF and TGF-beta(2) secretion, whereas cells grown at ALI showed no statistically significant response. These results demonstrate that the coupling between early signal transduction responses to IL-4 and IL-13 and downstream functions such as cytokine secretion may be critically dependent on the cell culture technique employed and the resulting differentiation status of bronchial epithelial cells.

Mechanisms of severe asthma

The mechanisms behind the development of severe asthma are poorly understood. However, these patients disproportionately consume healthcare resources related to asthma. Severe asthma may develop over time, or may develop shortly after onset of the disease. The genetic and environmental elements that may be most important in the development of severe disease are poorly understood. Physiologically, these patients often have air trapping and airway collapsibility. The pathology demonstrates a heterogeneity of findings, including continued eosinophilic inflammation, an apparently different pathology, structural changes likely to be remodelling related, and predominant distal disease. Treatment remains problematic and likely will remain so until a better understanding of this disease develops.

Effector ExoU from the type III secretion system is an important modulator of gene expression in lung epithelial cells in response to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an important pathogen in immunocompromised patients and secretes a diverse set of virulence factors that aid colonization and influence host cell defenses. An important early step in the establishment of infection is the production of type III-secreted effectors translocated into host cells by the bacteria. We used cDNA microarrays to compare the transcriptomic response of lung epithelial cells to P. aeruginosa mutants defective in type IV pili, the type III secretion apparatus, or in the production of specific type III-secreted effectors. Of the 18,000 cDNA clones analyzed, 55 were induced or repressed after 4 h of infection and could be classified into four different expression patterns. These include (i) host genes that are induced or repressed in a type III secretion-independent manner (32 clones), (ii) host genes induced specifically by ExoU (20 clones), and (iii) host genes induced in an ExoU-independent but type III secretion dependent manner (3 clones). In particular, ExoU was essential for the expression of immediate-early response genes, including the transcription factor c-Fos. ExoU-dependent gene expression was mediated in part by early and transient activation of the AP1 transcription factor complex. In conclusion, the present study provides a detailed insight into the response of epithelial cells to infection and indicates the significant role played by the type III virulence mechanism in the initial host response.

TGF-beta down-regulates IL-6 signaling in intestinal epithelial cells: critical role of SMAD-2

Interleukin-6 (IL-6) is a pro-inflammatory cytokine that plays an important role in the pathogenesis of inflammatory bowel disease. TGF-beta, a multifunctional cytokine, is a potent negative regulator of mucosal inflammation in the intestine. The aim of the present study is to determine possible cross-talk between IL-6 and TGF-beta signaling pathways. Model intestinal epithelial cell lines, Caco2-BBE were used. We show that TGF-beta receptor Type II is predominantly present in the basolateral membrane of intestinal epithelial cells. TGF-beta1 induces a time-dependent phosphorylation of Smad2 and co-immunoprecipitation of SMAD-2 with Smad-4 and its subsequently translocation to the nucleus. We show that pretreatment of cells with TGF-beta1 is associated with a down-regulation of IL-6 induced tyrosine phosphorylation of STAT1 and STAT3 and suppression of ICAM-1 expression. Furthermore, TGF-beta1 pretreatment resulted in a significant inhibition of IL-6 induced ICAM-1 promoter activity. TGF-beta mediated inhibition of IL-6 induced ICAM-1 expression was reversed by transfection with dominant negative Smad2 constructs. In conclusion, we show that: 1) TGF-beta receptor Type II is predominantly located on basolateral membrane and receptor stimulation activates Smad pathway; 2) TGF-beta1 down-regulates IL-6-induced tyrosine phoshorylation of STAT1 and STAT3 and ICAM-1 expression; and 3) Smad2 is required for the down-regulation of IL-6 signaling by TGF-beta. Collectively, our data demonstrate a cross-talk between TGF-beta and IL-6, and TGF-beta may play a role in the negative regulation of IL-6 signaling in intestinal epithelial cells.