Connective tissue growth factor and vascular endothelial growth factor from airway smooth muscle interact with the extracellular matrix

Role of transforming growth factor-β in airway remodelling in bronchiolitis obliterans

Airway remodelling is the main pathological mechanism of bronchiolitis obliterans (BO). Several studies have found that transforming growth factor-β (TGF-β) expression is increased in BO during airway remodelling, where it plays an important role in various biological processes by binding to its receptor complex to activate multiple signalling proteins and pathways. This review examines the role of TGF-β in airway remodelling in BO and its potential as a therapeutic target, highlighting the mechanisms of TGF-β activation and signalling, cellular targets of TGF-β actions, and research progress in TGF-β signalling and TGF-β-mediated processes.

Hedgehog Signaling: Linking Embryonic Lung Development and Asthmatic Airway Remodeling

The development of the embryonic lung demands complex endodermal-mesodermal interactions, which are regulated by a variety of signaling proteins. Hedgehog (Hh) signaling is vital for lung development. It plays a key regulatory role during several morphogenic mechanisms, such as cell growth, differentiation, migration, and persistence of cells. On the other hand, abnormal expression or loss of regulation of Hh signaling leads to airway asthmatic remodeling, which is characterized by cellular matrix modification in the respiratory system, goblet cell hyperplasia, deposition of collagen, epithelial cell apoptosis, proliferation, and activation of fibroblasts. Hh also targets some of the pathogens and seems to have a significant function in tissue repairment and immune-related disorders. Similarly, aberrant Hh signaling expression is critically associated with the etiology of a variety of other airway lung diseases, mainly, bronchial or tissue fibrosis, lung cancer, and pulmonary arterial hypertension, suggesting that controlled regulation of Hh signaling is crucial to retain healthy lung functioning. Moreover, shreds of evidence imply that the Hh signaling pathway links to lung organogenesis and asthmatic airway remodeling. Here, we compiled all up-to-date investigations linked with the role of Hh signaling in the development of lungs as well as the attribution of Hh signaling in impairment of lung expansion, airway remodeling, and immune response. In addition, we included all current investigational and therapeutic approaches to treat airway asthmatic remodeling and immune system pathway diseases.

Engineering Functional Vasculature in Decellularized Lungs Depends on Comprehensive Endothelial Cell Tropism

Tissue engineering using decellularized whole lungs as matrix scaffolds began as a promise for creating autologous transplantable lungs for patients with end-stage lung disease and can also be used to study strategies for lung regeneration. Vascularization remains a critical component for all solid organ bioengineering, yet there has been limited success in generating functional re-endothelialization of most pulmonary vascular segments. We evaluated recellularization of the blood vessel conduits of acellular mouse scaffolds with highly proliferating, rat pulmonary microvascular endothelial progenitor cells (RMEPCs), pulmonary arterial endothelial cells (PAECs) or microvascular endothelial cells (MVECs). After 8 days of pulsatile perfusion, histological analysis showed that PAECs and MVECs possessed selective tropism for larger vessels or microvasculature, respectively. In contrast, RMEPCs lacked site preference and repopulated all vascular segments. RMEPC-derived endothelium exhibited thrombomodulin activity, expression of junctional genes, ability to synthesize endothelial signaling molecules, and formation of a restrictive barrier. The RMEPC phenotype described here could be useful for identifying endothelial progenitors suitable for efficient vascular organ and tissue engineering, regeneration and repair.

Fibroblast-to-myofibroblast transition in bronchial asthma

Bronchial asthma is a chronic inflammatory disease in which bronchial wall remodelling plays a significant role. This phenomenon is related to enhanced proliferation of airway smooth muscle cells, elevated extracellular matrix protein secretion and an increased number of myofibroblasts. Phenotypic fibroblast-to-myofibroblast transition represents one of the primary mechanisms by which myofibroblasts arise in fibrotic lung tissue. Fibroblast-to-myofibroblast transition requires a combination of several types of factors, the most important of which are divided into humoural and mechanical factors, as well as certain extracellular matrix proteins. Despite intensive research on the nature of this process, its underlying mechanisms during bronchial airway wall remodelling in asthma are not yet fully clarified. This review focuses on what is known about the nature of fibroblast-to-myofibroblast transition in asthma. We aim to consider possible mechanisms and conditions that may play an important role in fibroblast-to-myofibroblast transition but have not yet been discussed in this context. Recent studies have shown that some inherent and previously undescribed features of fibroblasts can also play a significant role in fibroblast-to-myofibroblast transition. Differences observed between asthmatic and non-asthmatic bronchial fibroblasts (e.g., response to transforming growth factor β, cell shape, elasticity, and protein expression profile) may have a crucial influence on this phenomenon. An accurate understanding and recognition of all factors affecting fibroblast-to-myofibroblast transition might provide an opportunity to discover efficient methods of counteracting this phenomenon.

Phenotype and Functional Features of Human Telomerase Reverse Transcriptase Immortalized Human Airway Smooth Muscle Cells from Asthmatic and Non-Asthmatic Donors

Asthma is an obstructive respiratory disease characterised by chronic inflammation with airway hyperresponsiveness. In asthmatic airways, there is an increase in airway smooth muscle (ASM) cell bulk, which differs from non-asthmatic ASM in characteristics. This study aimed to assess the usefulness of hTERT immortalisation of human ASM cells as a research tool. Specifically we compared proliferative capacity, inflammatory mediator release and extracellular matrix (ECM) production in hTERT immortalised and parent primary ASM cells from asthmatic and non-asthmatic donors. Our studies revealed no significant differences in proliferation, IL-6 and eotaxin-1 production, or CTGF synthesis between donor-matched parent and hTERT immortalised ASM cell lines. However, deposition of ECM proteins fibronectin and fibulin-1 was significantly lower in immortalised ASM cells compared to corresponding primary cells. Notably, previously reported differences in proliferation and inflammatory mediator release between asthmatic and non-asthmatic ASM cells were retained, but excessive ECM protein deposition in asthmatic ASM cells was lost in hTERT ASM cells. This study shows that hTERT immortalised ASM cells mirror primary ASM cells in proliferation and inflammatory profile characteristics. Moreover, we demonstrate both strengths and weaknesses of this immortalised cell model as a representation of primary ASM cells for future asthma pathophysiological research.

The BPD trio? Interaction of dysregulated PDGF, VEGF, and TGF signaling in neonatal chronic lung disease

The development of neonatal chronic lung disease (nCLD), i.e., bronchopulmonary dysplasia (BPD) in preterm infants, significantly determines long-term outcome in this patient population. Risk factors include mechanical ventilation and oxygen toxicity impacting on the immature lung resulting in impaired alveolarization and vascularization. Disease development is characterized by inflammation, extracellular matrix remodeling, and apoptosis, closely intertwined with the dysregulation of growth factor signaling. This review focuses on the causes and consequences of altered signaling in central pathways like transforming growth factor (TGF), platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) driving these above indicated processes, i.e., inflammation, matrix remodeling, and vascular development. We emphasize the shared and distinct role of these pathways as well as their interconnection in disease initiation and progression, generating important knowledge for the development of future treatment strategies.

The Effects of Tumstatin on Vascularity, Airway Inflammation and Lung Function in an Experimental Sheep Model of Chronic Asthma

Tumstatin, a protein fragment of the alpha-3 chain of Collagen IV, is known to be significantly reduced in the airways of asthmatics. Further, there is evidence that suggests a link between the relatively low level of tumstatin and the induction of angiogenesis and inflammation in allergic airway disease. Here, we show that the intra-segmental administration of tumstatin can impede the development of vascular remodelling and allergic inflammatory responses that are induced in a segmental challenge model of experimental asthma in sheep. In particular, the administration of tumstatin to lung segments chronically exposed to house dust mite (HDM) resulted in a significant reduction of airway small blood vessels in the diameter range 10⁺–20 μm compared to controls. In tumstatin treated lung segments after HDM challenge, the number of eosinophils was significantly reduced in parenchymal and airway wall tissues, as well as in the bronchoalveolar lavage fluid. The expression of VEGF in airway smooth muscle was also significantly reduced in tumstatin-treated segments compared to control saline-treated segments. Allergic lung function responses were not attenuated by tumstatin administration in this model. The data are consistent with the concept that tumstatin can act to suppress vascular remodelling and inflammation in allergic airway disease.

Differential deposition of fibronectin by asthmatic bronchial epithelial cells

Altered ECM protein deposition is a feature in asthmatic airways. Fibronectin (Fn), an ECM protein produced by human bronchial epithelial cells (HBECs), is increased in asthmatic airways. This study investigated the regulation of Fn production in asthmatic or nonasthmatic HBECs and whether Fn modulated HBEC proliferation and inflammatory mediator secretion. The signaling pathways underlying transforming growth factor (TGF)-β1-regulated Fn production were examined using specific inhibitors for ERK, JNK, p38 MAPK, phosphatidylinositol 3 kinase, and activin-like kinase 5 (ALK5). Asthmatic HBECs deposited higher levels of Fn in the ECM than nonasthmatic cells under basal conditions, whereas cells from the two groups had similar levels of Fn mRNA and soluble Fn. TGF-β1 increased mRNA levels and ECM and soluble forms of Fn but decreased cell proliferation in both cells. The rate of increase in Fn mRNA was higher in nonasthmatic cells. However, the excessive amounts of ECM Fn deposited by asthmatic cells after TGF-β1 stimulation persisted compared with nonasthmatic cells. Inhibition of ALK5 completely prevented TGF-β1-induced Fn deposition. Importantly, ECM Fn increased HBEC proliferation and IL-6 release, decreased PGE2 secretion, but had no effect on VEGF release. Soluble Fn had no effect on cell proliferation and inflammatory mediator release. Asthmatic HBECs are intrinsically primed to produce more ECM Fn, which when deposited into the ECM, is capable of driving remodeling and inflammation. The increased airway Fn may be one of the key driving factors in the persistence of asthma and represents a novel, therapeutic target.

Extracellular matrix composition is modified by β₂-agonists through cAMP in COPD

Long acting β₂-agonists (LABA) have been reported to modify the extracellular matrix (ECM) composition in the airway wall. Based on our earlier studies we here investigated the mechanism underlying the control of ECM modification by LABA in primary human airway smooth muscle cells. Cells were treated with formoterol or salmeterol (30 min) before TGF-β₁ stimulation (2-3 days) Using RT-PCT, immuno-blotting and ELISA the de novo synthesis and deposition of collagen type-I, -III, -IV and fibronectin were determined. Matrix metalloproteinases (MMP)-2 and -9 were analyzed by zymography. Both LABA activated cAMP and its corresponding transcription factor CREB within 60 min and thus partly reduced TGF-β₁-induced gene transcription of collagen type-I, -III, fibronectin and connective tissue growth factor (CTGF). The inhibitory effect of both LABA on collagen type-I and -III deposition involved a cAMP dependent mechanism, while the inhibitory effect of the two drugs on TGF-β1-induced fibronectin deposition and on CTGF secretion was independent of cAMP. Interestingly, none of the two LABA reduced CTGF-induced synthesis of collagen type-I or type-III deposition. In addition, none of the two LABA modified collagen type-IV deposition or the expression and activity of MMP-2 or MMP-9. Our results show that LABA can prevent de novo deposition of specific ECM components through cAMP dependent and independent signaling. However, they do not reduce all ECM components by the same mechanism and they do not reduce existing collagen deposits. This might explain some of the controversial reports on the anti-remodeling effect of LABA in chronic inflammatory lung diseases.

Tropoelastin modulates TGF-β1-induced expression of VEGF and CTGF in airway smooth muscle cells

Elastin is predominantly comprised of crosslinked tropoelastin. For many years elastin was considered to serve a solely structural role but is now being increasingly identified as causal in cell signaling, development and repair. We introduced tropoelastin into an in vitro model in which airway smooth muscle cells (ASMCs) were stimulated with transforming growth factor (TGF)-β1 to examine the modulatory effect of this modular elastin sequence on release of angiogenic factors and matrix metalloproteinases (MMPs). Human ASMCs were presented to surfaces coated with tropoelastin or collagen and controls, then stimulated with TGF-β1. Transcript levels of vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF) were quantified 4 and 24 h after TGF-β1 stimulation. Protein VEGF release from cells and CTGF sequestered at cell surfaces were measured by ELISA at 24 and 48 h. TGF-β1 increased VEGF mRNA 2.4 fold at 4 h and 5 fold at 24 h, accompanied by elevated cognate protein release 3 fold at 24 h and 2.5 fold at 48 h. TGF-β1 stimulation increased CTGF mRNA 6.9 fold at 4 h and 11.8 fold at 24 h, accompanied by increased sequestering of its protein counterpart 1.2 fold at 24 h and 1.4 fold at 48 h. Pre-incubation of cells with tropoelastin did not modulate VEGF or CTGF mRNA expression, but combined with TGF-β1 stimulation it led to enhanced VEGF release 5.1-fold at 24h and 4.4-fold at 48 h. Pre-incubation with tropoelastin decreased CTGF sequestering 0.6-fold at 24 and 48 h, and increased MMP-2 production. Collagen pre-incubation under the same conditions displayed no effect on TGF-β1 stimulation apart from a slightly decreased (0.9 fold) sequestered CTGF at 48 h. As CTGF is known to anchor VEGF to the matrix and inhibit its angiogenic activity, a process which can be reversed by digestion with MMP-2, these findings reveal that elastin sequences can disrupt the balance of angiogenic factors, with implications for aberrant angiogenesis. The results suggest a model of molecular crosstalk and support an active role for elastin in vascular remodeling.

Functional phenotype of airway myocytes from asthmatic airways

In asthma, the airway smooth muscle (ASM) cell plays a central role in disease pathogenesis through cellular changes which may impact on its microenvironment and alter ASM response and function. The answer to the long debated question of what makes a 'healthy' ASM cell become 'asthmatic' still remains speculative. What is known of an 'asthmatic' ASM cell, is its ability to contribute to the hallmarks of asthma such as bronchoconstriction (contractile phenotype), inflammation (synthetic phenotype) and ASM hyperplasia (proliferative phenotype). The phenotype of healthy or diseased ASM cells or tissue for the most part is determined by expression of key phenotypic markers. ASM is commonly accepted to have different phenotypes: the contractile (differentiated) state versus the synthetic (dedifferentiated) state (with the capacity to synthesize mediators, proliferate and migrate). There is now accumulating evidence that the synthetic functions of ASM in culture derived from asthmatic and non-asthmatic donors differ. Some of these differences include an altered profile and increased production of extracellular matrix proteins, pro-inflammatory mediators and adhesion receptors, collectively suggesting that ASM cells from asthmatic subjects have the capacity to alter their environment, actively participate in repair processes and functionally respond to changes in their microenvironment.

Prostaglandins but not leukotrienes alter extracellular matrix protein deposition and cytokine release in primary human airway smooth muscle cells and fibroblasts

Eicosanoids are lipid-signaling mediators released by many cells in response to various stimuli. Increasing evidence suggests that eicosanoids such as leukotrienes and prostaglandins (PGs) may directly mediate remodeling. In this study, we assessed whether these substances could alter extracellular matrix (ECM) proteins and the inflammatory profiles of primary human airway smooth muscle cells (ASM) and fibroblasts. PGE(2) decreased both fibronectin and tenascin C in fibroblasts but only fibronectin in ASM. PGD(2) decreased both fibronectin and tenascin C in both ASM and fibroblasts, whereas PGF(2α) had no effect on ECM deposition. The selective PGI(2) analog, MRE-269, decreased fibronectin but not tenascin C in both cell types. All the PGs increased IL-6 and IL-8 release in a dose-dependent manner in ASM and fibroblasts. Changes in ECM deposition and cytokine release induced by prostaglandins in both ASM and fibroblasts were independent of an effect on cell number. Neither the acute nor repeated stimulation with leukotrienes had an effect on the deposition of ECM proteins or cytokine release from ASM or fibroblasts. We concluded that, collectively, these results provide evidence that PGs may contribute to ECM remodeling to a greater extent than leukotrienes in airway cells.

The presence and regulation of connective tissue growth factor in the human endometrium

BACKGROUND

The human endometrium efficiently repairs each month after menstruation. The mechanisms involved in this repair process remain undefined. Aberrations in endometrial repair may lead to the common disorder of heavy menstrual bleeding. We hypothesized that connective tissue growth factor (CTGF) is increased at the time of endometrial repair post-menses and that this increase is regulated by prostaglandins (PGs) and hypoxic conditions present during menstruation.

METHODS AND RESULTS

Examination of 41 endometrial biopsies from 5 stages of the menstrual cycle revealed maximal CTGF mRNA expression (using quantitative RT-PCR) at menstruation and peak protein levels during the proliferative phase. CTGF was immunolocalized to epithelial and stromal cells, with intense staining of occasional stromal cells during the proliferative phase. Dual immunohistochemistry identified these cells as macrophages. Treatment of endometrial epithelial cells with 100 nM PGE(2), PGF(2α) or hypoxia (0.5% O(2)) revealed a significant increase in CTGF mRNA expression (P < 0.01 for all, versus vehicle control). Cells treated simultaneously with PGE(2) and hypoxia revealed a synergistic increase in CTGF expression (P < 0.05 versus PGE(2) or hypoxia alone) and maximal secreted CTGF protein levels (P < 0.05 versus control).

CONCLUSIONS

CTGF is increased in the human endometrium at the time of endometrial repair post-menses. The increase in CTGF may be mediated by PG production and the transient hypoxic episode observed in the endometrium at menstruation.

Elastin in asthma

Extracellular matrix is generally increased in asthma, causing thickening of the airways which may either increase or decrease airway responsiveness, depending on the mechanical requirements of the deposited matrix. However, in vitro studies have shown that the altered extracellular matrix produced by asthmatic airway smooth muscle cells is able to induce increased proliferation of non-asthmatic smooth muscle cells, which is a process believed to contribute to airway hyper-responsiveness in asthma. Elastin is an extracellular matrix protein that is altered in asthmatic airways, but there has been no systematic investigation of the functional effect of these changes. This review reveals divergent reports of the state of elastin in the airway wall in asthma. In some layers of the airway it has been described as increased, decreased and/or fragmented, or unchanged. There is also considerable evidence for an imbalance of matrix metalloproteinases, which degrade elastin, and their respective inhibitors the tissue inhibitors of metalloproteinases, which collectively help to explain observations of both increased elastin and elastin fragments. A loss of lung elastic recoil in asthma suggests a mechanical role for disordered elastin in the aetiology of the disease, but extensive studies of elastin in other tissues show that elastin fragments elicit cellular effects such as increased proliferation and inflammation. This review summarises the current understanding of the role of elastin in the asthmatic airway.

Combined Beta-agonists and corticosteroids do not inhibit extracellular matrix protein production in vitro

Background. Persistent asthma is characterized by airway remodeling. Whereas we have previously shown that neither β(2)-agonists nor corticosteroids inhibit extracellular matrix (ECM) protein release from airway smooth muscle (ASM) cells, the effect of their combination is unknown and this forms the rationale for the present study. Methods. ASM cells from people with and without asthma were stimulated with TGFβ1 (1 ng/ml) with or without budesonide (10(-8) M) and formoterol (10(-10) and 10(-8) M), and fibronectin expression and IL-6 release were measured by ELISA. Bronchial rings from nonasthmatic individuals were incubated with TGFβ1 (1 ng/ml) with or without the drugs, and fibronectin expression was measured using immunohistochemistry. Results. Budesonide stimulated fibronectin deposition, in the presence or absence of TGFβ1, and this was partially reversed by formoterol (10(-8) M) in both asthmatic and nonasthmatic cells. Budesonide and formoterol in combination failed to inhibit TGFβ-induced fibronectin in either cell type. A similar pattern of expression of fibronectin was seen in bronchial rings. TGFβ1-induced IL-6 release was inhibited by the combination of drugs. Conclusion. Current combination asthma therapies are unable to prevent or reverse remodeling events regulated by ASM cells.

The effect of cathepsin K deficiency on airway development and TGF-β1 degradation

BACKGROUND

Cathepsin K, a cysteine protease predominantly expressed in osteoclasts, is a major drug target for the treatment of osteoporosis. Recent findings, however, indicate that cathepsin K is also involved in non-skeletal metabolism. The development of fibrotic phenotypes in lung and skin is a concern for cathepsin K inhibitors presently evaluated in clinical trials. Cathepsin K is expressed in lung tissue and has been implicated in lung fibrosis. However, little is known about the role of cathepsin K in airway development and its effect on TGF-β1 degradation.

METHODS

We investigated the effects of cathepsin K-deficiency on alterations in airway integrity, extracellular matrix composition, and TGF-β1 expression and degradation. Lung homogenates of wild-type and cathepsin K-deficient mice were used to evaluate their contents of collagen, glycosaminoglycans, and TGF-β1. The accessibility of TGF-β1 to cathepsin K-mediated degradation was determined in vitro and lung fibroblast proliferations in wild-type and cathepsin K-deficient cells were evaluated.

RESULTS

Lung airway cathepsin K expression in wild-type mice remained constant between 1 and 6 months of age and the airway integrity was maintained. In contrast, after 2 months of age, all Ctsk-/- mice demonstrated increased airway epithelium thickness by 16-28%, a lower structural airway integrity (1-2 score units lower), elevated cytokeratin expression of 12%, increased α-actin and vimentin expression by 50% and 70%, increased area of smooth muscle cells by 15%, elevated hydroxyproline and GAGs content by 20% and 25%, and increased TGF-β1 expression by 25%. TGF-β1 proved an efficient substrate of cathepsin K and TGF-β1 protein content in lung was increased by a potent cathepsin inhibitor. Lung fibroblasts from Ctsk-/- mice after TGF-β1 treatment showed increased proliferation rates, increased levels of TGF-β1 by 30%, and increased ECM secretion.

CONCLUSION

This study suggests that airway development is partly regulated by cathepsin K and that its expression contributes to the maintenance of the airway structural integrity. The anticipated use of therapeutic cathepsin K inhibitors needs to take potential changes in human lungs into consideration.

Phosphatidylinositol 3-kinase isoform-specific effects in airway mesenchymal cell function

The phosphatidylinositol 3-kinase (PI3K) signal transduction pathway is implicated in the airway remodeling associated with asthma. The class IA PI3K isoforms are known to be activated by growth factors and cytokines. Because this pathway is a possible site of pharmacological intervention for treating the disease, it is important to know which isoforms contribute to this process. Therefore, we used a pharmacological approach to investigate the roles of the three class IA PI3K isoforms (p110α, p110β, and p110δ) in airway remodeling using airway smooth muscle (ASM) cells derived from asthmatic subjects and ASM cells and lung fibroblasts from nonasthmatic subjects. These studies used the inhibitors N'-[(E)-(6-bromoimidazo[1,2-a]pyridin-3-yl)methylidene]-N,2-dimethyl-5-nitrobenzenesulfonohydrazide (PIK75) (which selectively inhibits p110α), 7-methyl-2-(4-morpholinyl)-9-[1-(phenylamino)ethyl]-4H-pyrido[1,2-a]pyrimidin-4-one (TGX221) (which selectively inhibits p110β), and 2-[(6-amino-9H-purin-9-yl)methyl]-5-methyl-3-(2-methylphenyl)-4(3H)-quinazolinone (IC87114) (which selectively inhibits p110δ). Cells were stimulated with transforming growth factor-β (TGFβ) and/or 10% fetal bovine serum in the presence or absence of inhibitor or vehicle control (dimethyl sulfoxide). PIK75, but not TGX221 or IC87114, attenuated TGFβ-induced fibronectin deposition in all cell types tested. PIK75 and TGX221 each decreased secretion of vascular endothelial growth factor and interleukin-6 in nonasthmatic ASM cells and lung fibroblasts, whereas TGX221 was not as effective in asthmatic ASM cells. In addition, PIK75 decreased cell survival in TGFβ-stimulated asthmatic, but not nonasthmatic, ASM cells. In conclusion, specific PI3K isoforms may play a role in pathophysiological events relevant to airway wall remodeling.

Vascular endothelial growth factor overexpression in induced sputum of children with bronchial asthma

Vascular endothelial growth factor (VEGF) induces angiogenesis and increases vascular permeability participating in narrowing of the airway lumen that follows lung injury. We sought to investigate the expression of VEGF in induced sputum during and after recovery from acute episodes of bronchial asthma in children. Eighteen asthmatic children with acute attacks of varying severity were subjected to VEGF estimation by an enzymatic immunoassay in induced sputum. They were followed up till complete remission of symptoms and signs and were then retested. VEGF was also estimated in sputum induced from age 34 and sex-matched healthy children enrolled as a control group. The sputum VEGF levels during acute asthma [median = 71 ng/ml; mean (s.d.) = 114.6 (121.8) ng/ml] were significantly higher than the levels estimated during remission [median = 50 ng/ml; mean (s.d.) = 45.7 (24.2) ng/ml] and both were higher than the corresponding levels of the control group [median = 36 ng/ml; mean (s.d.) = 31.3 (17.2) ng/ml]. VEGF levels during asthmatic episodes correlated positively to the recovery levels (r = 0.6, p = 0.009). The patients' VEGF expression did not vary with asthma severity, serum total IgE concentration, peripheral blood eosinophil count, or erythrocyte sedimentation rate of patients. Children on corticosteroids inhalation therapy at enrollment had sputum VEGF levels that were comparable to those on other therapies. The increased expression of sputum VEGF in asthmatic children reinforces the concept that it might have a pathogenetic role in bronchial asthma and may represent a biomarker of airway inflammation.

The role of the extracellular matrix and specific growth factors in the regulation of inflammation and remodelling in asthma

Asthma is a disease characterised by persistent inflammation and structural changes in the airways, referred to as airway remodelling. The mechanisms underlying these processes may be interdependent or they may be separate processes that are driven by common factors. The levels of a variety of growth factors (including transforming growth factor beta, granulocyte macrophage colony stimulating factor, and vascular endothelial growth factor) are known to be changed in the asthmatic airway. These and other growth factors can contribute to the development and persistence of inflammation and remodelling. One of the prominent features of the structural changes of the airways is the increased deposition and alterations in the composition of the extracellular matrix proteins. These proteins include fibronectin, many different collagen types and hyaluronan. There is a dynamic relationship between the extracellular matrix proteins and the airway mesenchymal cells such that the changes in the extracellular matrix proteins can also contribute to the persistence of inflammation and the airway remodelling. This review aims to summarise the role growth factors and extracellular matrix proteins play in the regulation of inflammation and airway remodelling in the asthmatic airway.

Tissue and matrix influences on airway smooth muscle function

Asthma is characterized by structural changes in the airways - airway remodelling. These changes include an increase in the bulk of the airway smooth muscle (ASM) and alterations in the profile of extracellular matrix (ECM) proteins in the airway wall. The mechanisms leading to airway remodelling are not well understood. ASM cells have the potential to play a key role in these processes through the production and release of ECM proteins. The ASM cells and ECM proteins are each able to influence the behaviour and characteristics of the other. The modified ECM profile in the asthmatic airway may contribute to the altered behaviour of the ASM cells, such responses to ECM proteins are modulated through the cell surface expression of integrin receptors. ASM cells from asthmatic individuals express different levels of some integrin subunits compared to nonasthmatic ASM cells, which have the potential to further influence their responses to the ECM proteins in the airways. ECM homeostasis requires the presence and activation of matrix metalloproteinases and their tissue inhibitors, which in turn modulate the interaction of the ASM cells and the ECM proteins. Furthermore, the complex interactions of the ASM cells and the ECM in the asthmatic airways and the role played by external stimuli, such as viral infections, to modulate airway remodelling are currently unknown. This review summarises our current understanding of the influence of the ECM on ASM function.

The effect of asthma therapeutics on signalling and transcriptional regulation of airway smooth muscle function

SCOPE OF THE REVIEW

Our knowledge of the multifunctional nature of airway smooth muscle (ASM) has expanded rapidly in the last decade, but the underlying molecular mechanisms and how current therapies for obstructive airway diseases, such as asthma and chronic obstructive pulmonary disease (COPD), affect these are still being elucidated. Our current knowledge has built on the pharmacology of human ASM contraction and relaxation established prior to that and which is reviewed in detail elsewhere in this issue. The advent of methods to isolate and culture ASM cells, especially human ASM cells, has made it possible to study how they may contribute to airway remodelling through their synthetic, proliferative, and migratory capacities. Now the underlying molecular mechanisms of ASM growth factor secretion, extracellular matrix (ECM) production, proliferation and migration, as well as contraction and relaxation, are being determined. A complex network of signalling pathways leading to gene transcription in ASM cells permits this functional plasticity in healthy and diseased airways. This review is an overview of the effects of current therapies, and some of those in development, on key signalling pathways and transcription factors involved in these ASM functions.

Induction of angiogenesis by airway smooth muscle from patients with asthma

RATIONALE

Airway remodeling in asthma involves accumulation of airway smooth muscle (ASM) and increased vascularity due to angiogenesis. Bronchial blood vessels and ASM are found in close proximity, and ASM releases multiple proinflammatory mediators, including vascular endothelial growth factor (VEGF).

OBJECTIVES

We examined whether release of proangiogenic mediators is increased in ASM from subjects with asthma and whether this is translated to induction of angiogenesis.

METHODS

Biopsy-derived ASM cells were cultured from 12 subjects with mild asthma, 8 with moderate asthma, and 9 healthy control subjects. Angiogenesis induced by cell-conditioned medium (CM) from ASM was evaluated in a tubule formation assay. Anti-CD31-labeled tubules were quantified by image analysis. Angiogenic factors in CM were quantified by antibody arrays and by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Induction of angiogenesis by CM from unstimulated ASM was increased in subjects with mild asthma (twofold) and moderate asthma (threefold), compared with healthy CM (P < 0.001). Levels of angiogenic factors (VEGF, angiopoietin [Ang]-1, angiogenin) were similarly elevated in CM from subjects with asthma compared with that from healthy subjects (P < 0.05), whereas antiangiogenic factors (endostatin, Ang-2) were unchanged. VEGF, Ang-1, and angiogenin in combination increased vascularity (twofold, P < 0.01) in cultured intact biopsies. Selective VEGF immunodepletion abolished enhanced tubule formation by CM from asthmatic ASM (P < 0.01), but CM depletion of Ang-1 or angiogenin had no effect.

CONCLUSIONS

ASM cultured from subjects with mild or moderate asthma, but not from healthy control subjects, promotes angiogenesis in vitro. This proangiogenic capacity resides in elevated VEGF release and suggests that ASM regulates airway neovascularization in asthma.

Vasoactive peptides upregulate mRNA expression and secretion of vascular endothelial growth factor in human airway smooth muscle cells

Airway remodeling and associated angiogenesis are documented features of asthma, of which the molecular mechanisms are not fully understood. Angiotensin (ANG)II and endothelin (ET)-1 are potent vasoconstricting circulatory hormones implicated in asthma. We investigated the effects of ANG II and ET-1 on human airway smooth muscle (ASM) cells proliferation and growth and examined the mRNA expression and release of the angiogenic peptide, vascular endothelial growth factor (VEGF). Serum deprived (48 h) human ASM cells were incubated with ANG II (100 nM) or ET-1 (10 nM) for 30 min, 1, 2, 4, 8, 16, and 24 h and the endogenous synthesis of VEGF was examined in relation to control cells receiving serum free culture medium. ET-1 induced time dependent DNA biosynthesis as determined by [3H]-thymidine incorporation assay. Using northern blot hybridization, we detected two mRNA species of 3.9 and 1.7 kb encoding VEGF in the cultured smooth muscle cells. Both ANG II and ET-1 induced the mRNA expression (two- to threefold) and secretion (1.8- to 2.8-fold) of VEGF reaching maximal levels between 4-8 h of incubation. Induced expression and release of VEGF declined after 8 h of ANG II incubation while levels remained elevated in the case of ET-1. The conditioned medium derived from ET-1-treated ASM cells induced [3H]-thymidine incorporation and cell number in porcine pulmonary artery endothelial as well as human umbilical vein endothelial cells. Moreover, the VEGF tyrosine kinase receptor inhibitor blocked the conditioned medium induced mitogenesis in endothelial cells. Our results suggest a potential role for ANG II and ET-1 in ASM cell growth and upregulation of VEGF that may participate in endothelial cell proliferation via paracrine mechanisms and thus causing pathological angiogenesis and vascular remodelling seen during asthma.

Extracellular matrix and airway smooth muscle interactions: a target for modulating airway wall remodelling and hyperresponsiveness?

The airway smooth muscle from asthmatic airways produces increased amounts and an altered composition of extracellular matrix proteins. The extracellular matrix can in turn influence the phenotype and function of airway smooth muscle cells, affecting the biochemical, geometric, and mechanical properties of the airway wall. This review provides a brief overview of the current understanding of the biology associated with airway smooth muscle interactions with the extracellular matrix. We present future directions needed for the study of cellular and molecular mechanisms that determine the outcomes of extracellular matrix - airway smooth muscle interactions, and discuss their possible importance as determinants of airway function in asthma.

IL-4 stimulates the expression of CXCL-8, E-selectin, VEGF, and inducible nitric oxide synthase mRNA by equine pulmonary artery endothelial cells

Little is known concerning the possible contribution of T helper 2 (Th2)-type cytokines to the recruitment of neutrophils into the lung tissue. In the present study, endothelial cells from equine pulmonary arteries were cultured in the presence of recombinant equine (re) IL-4 and reIL-5, and the cytokine mRNA expression of molecules implicated in the chemotaxis and migration of neutrophils was studied using real-time RT-PCR. The functional response of reIL-4-induced endothelial cell stimulation on neutrophil migration was also studied using a chemotaxis chamber. ReIL-4 either increased the expression of CXCL-8, E-selectin, vascular endothelial growth factor (VEGF), and inducible nitric oxide synthase (iNOS), or potentiated the coeffects of lipopolysaccharide (LPS) and tumor necrosis factor-alpha (TNF-alpha) on CXCL-8. Supernatants collected from cultured endothelial cells stimulated with reIL-4 significantly promoted neutrophil migration in a dose-dependent manner. Dexamethasone (DXM) decreased the expression of CXCL-8, VEGF, and iNOS induced by reIL-4, while 1400W dihydrochloride (1400W), a selective inhibitor of iNOS, decreased the expression of E-selectin, VEGF, and iNOS. DXM and 1400W attenuated the mRNA expression of E-selectin and iNOS induced by the costimulation of reIL-4, reTNF-alpha, and LPS. Neither equine nor human recombinant IL-5 influenced the mRNA expression of CXCL-8, E-selectin, or VEGF. These findings suggest that Th2-type cytokines may contribute to pulmonary neutrophilia during allergic inflammation by the increased expression of neutrophil chemokines and adhesion molecules by endothelial cells. DXM and the iNOS inhibitors may decrease pulmonary neutrophilia due, in part, to a direct inhibition of some of these factors.

Functional characteristics of connective tissue growth factor on vitreoretinal cells

Connective tissue growth factor (CTGF) level is elevated in eyes with proliferative vitreoretinal diseases, such as proliferative diabetic retinopathy and proliferative vitreoretinopathy (PVR), as we previously reported, but its functional characteristics on vitreoretinal cells are yet to be clarified. In this study, we demonstrated a growth-promoting effect of CTGF on cultured hyalocytes and bovine retinal pigment epithelial cells (BRPEs) with the induction of p44/p42 mitogen-activated protein kinase phosphorylation and [(3)H]thymidine incorporation. CTGF also stimulated the synthesis of fibronectin by hyalocytes and BRPEs without significant effect on collagen gel contraction by these cells. On the other hand, CTGF had no direct effects on the proliferation, migration, or in vitro tube formation by vascular endothelial cells. Nevertheless, CTGF promoted vascular endothelial growth factor (VEGF) gene expression by hyalocytes and BRPEs. Although the concentrations of both CTGF and VEGF in the human vitreous samples with proliferative vitreoretinal diseases were elevated, there was no significant correlation between these concentrations. These findings indicate that CTGF appears to be involved in the formation of proliferative membranes without direct regulation of their cicatricial contraction in the pathogenesis of proliferative vitreoretinal diseases. Whereas CTGF might have no direct effects or minimal effects, if any, on retinal neovascularization, it is possible that CTGF has indirect effects by modulating the expression of VEGF.

Connective tissue growth factor expression is regulated by histamine in lung fibroblasts: potential role of histamine in airway remodeling

BACKGROUND

In the inflamed lung of allergic asthma, an aberrant injury-repair response is accompanied by structural changes in the airway, known as airway remodeling. TGF-beta and its downstream mediator connective tissue growth factor (CTGF) are playing a key role in these processes, resulting in irreversible airway remodelling.

OBJECTIVE

As histamine is a key mediator of allergic reactions, we investigated whether histamine is involved in airway remodeling.

METHODS

The effect of histamine and TGF-beta1 on proliferation of lung fibroblast cells IMR-90 was studied by [(3)H]-thymidine proliferation assay. The regulation of CTGF by histamine and TGF-beta1 in lung fibroblasts was analyzed by RT-PCR, real-time PCR, Western blot analysis, and promoter analysis and characterized by specific histamine-receptor antagonists.

RESULTS

Histamine and TGF-beta1 enhanced proliferation of lung fibroblast cells IMR-90. Both induced CTGF mRNA and protein expression with different time kinetics. Whereas TGF-beta1 induced maximal CTGF expression after 12 hours (347% +/- 23%), histamine-induced maximal CTGF expression was lower and delayed (maximum expression of 204% +/- 11% after 48 hours). Histamine and TGF-beta1 stimulated the CTGF promoter and the TGF-beta-response element in the CTGF promoter. The histamine-induced CTGF expression was mediated through the histamine receptor (HR1) and could be completely abolished by TNF-alpha.

CONCLUSIONS

These findings demonstrate that histamine plays a potential role in the induction of airway remodeling mediated by the induction of lung fibroblasts proliferation and CTGF expression.

CLINICAL IMPLICATIONS

This mechanism could be important for prophylactic strategies aiming at airway remodeling and could be a new indication for antihistamine treatment.

Genetic polymorphisms in transforming growth factor beta-1 (TGFB1) and childhood asthma and atopy

Transforming growth factor beta-1 (TGFB1) may influence asthma by modulating allergic airway inflammation and airway remodeling. The role of single nucleotide polymorphisms (SNPs) of TGFB1 in asthma remains inconclusive. We examined TGFB1 SNPs in relation to asthma risk and degree of atopy among 546 case-parent triads, consisting of asthmatics aged 4-17 years and their parents in Mexico City. Atopy to 24 aeroallergens was determined by skin prick tests. We genotyped five TGFB1 SNPs, including two known functional SNPs [C-509T (rs1800469), T869C (rs1982073)] and three others (rs7258445, rs1800472, rs8179181), using TaqMan and Masscode assays. We analyzed the data using log-linear and polytomous logistic methods. Three associated SNPs, including the two known functional SNPs, were statistically significantly related to asthma risk. Individuals carrying the T allele of C-509T had an increased risk of asthma [relative risk (RR)=1.42, 95% confidence interval (CI)=1.08-1.87 for one copy; RR (95%CI)=1.95 (1.36-2.78) for two copies]. For T869C, the RRs (95%CI) were 1.47 (1.09-1.98) for one and 2.00 (1.38-2.90) for two copies of the C allele. Similar results were found for rs7258445. The haplotype containing all three risk alleles conferred an increased risk of asthma (RR=1.48, 95% CI=1.11-1.95 for one copy; RR=1.77, 95% CI=1.22-2.57 for two copies). These three SNPs were also related to the degree of atopy. This largest study to date of genetic variation in TGFB1 and asthma and atopy adds to increasing evidence for a role in these disorders.

The regulatory role of TGF-beta in airway remodeling in asthma

Both structural and inflammatory cells are capable of secreting transforming growth factor (TGF)-beta and expressing TGF-beta receptors. TGF-beta can induce multiple cellular responses including differentiation, apoptosis, survival and proliferation, and has been implicated in the development of several pathogenic conditions including cancer and asthma. Elevated levels of TGF-beta have been reported in the asthmatic airway. TGF-beta binds to its receptor complex and activates multiple pathways involving proteins such as Sma and Mad homologues, phosphatidylinositol-3 kinase and the mitogen-activated protein kinases, leading to the transcription of several genes. Cell type, cellular condition, and microenvironment, all play a role in determining which pathway is activated, which, in turn, is an indication of which gene is to be transcribed. TGF-beta has been shown to induce apoptosis in airway epithelial cells. A possible role for TGF-beta in the regulation of epithelial cell adhesion properties has also been reported. Enhancement of goblet cell proliferation by TGF-beta suggests a role in mucus hyper-secretion. Elevated levels of TGF-beta correlate with subepithelial fibrosis. TGF-beta induces proliferation of fibroblast cells and their differentiation into myofibroblasts and extracellular matrix (ECM) protein synthesis during the development of subepithelial fibrosis. TGF-beta also induces proliferation and survival of and ECM secretion in airway smooth muscle cells (ASMCs), suggesting a possible cause of increased thickness of airway tissues. TGF-beta also induces the production and release of vascular endothelial cell growth factor and plasminogen activator inhibitor, contributing to the vascular remodeling in the asthmatic airway. Blocking TGF-beta activity inhibits epithelial shedding, mucus hyper-secretion, angiogenesis, ASMC hypertrophy and hyperplasia in an asthmatic mouse model. Reduction of TGF-beta production and control of TGF-beta effects would be beneficial in the development of therapeutic intervention for airway remodeling in chronic asthma.

Antenatal inflammation induced TGF-beta1 but suppressed CTGF in preterm lungs

Chorioamnionitis is frequently associated with preterm birth and increases the risk of adverse outcomes such as bronchopulmonary dysplasia (BPD). Transforming growth factor (TGF)-beta1 is a key regulator of lung development, airway remodeling, lung fibrosis, and regulation of inflammation, and all these processes contribute to the development of BPD. Connective tissue growth factor (CTGF) is a downstream mediator of some of the profibrotic effects of TGF-beta1, vascular remodeling, and angiogenesis. TGF-beta1-induced CTGF expression can be blocked by TNF-alpha. We asked whether chorioamnionitis-associated antenatal inflammation would regulate TGF-beta1, the TGF-beta1 signaling pathway, and CTGF in preterm lamb lungs. Fetal sheep were exposed to 4 mg of intra-amniotic endotoxin or saline for 5 h, 24 h, 72 h, or 7 days before preterm delivery at 125 days gestation (full term = 150 days). Intra-amniotic endotoxin increased lung TGF-beta1 mRNA and protein expression. Elevated TGF-beta1 levels were associated with TGF-beta1-induced phosphorylation of Smad2. CTGF was selectively expressed in lung endothelial cells in control lungs, and intra-amniotic endotoxin caused CTGF expression to decrease to 30% of control values and TNF-alpha protein to increase. The antenatal inflammation-induced TGF-beta1 expression and Smad signaling in the fetal lamb lung may contribute to impaired lung alveolarization and reduced lung inflammation. Decreased CTGF expression may inhibit vascular development or remodeling and limit lung fibrosis during remodeling. These effects may contribute to the impaired alveolar and pulmonary vascular development that is the hallmark of the new form of BPD.