The integrin-blocking peptide RGDS inhibits airway smooth muscle remodeling in a guinea pig model of allergic asthma

Membrane adhesion junctions regulate airway smooth muscle phenotype and function

The local environment surrounding airway smooth muscle (ASM) cells has profound effects on the physiological and phenotypic properties of ASM tissues. ASM is continually subjected to the mechanical forces generated during breathing and to the constituents of its surrounding extracellular milieu. The smooth muscle cells within the airways continually modulate their properties to adapt to these changing environmental influences. Smooth muscle cells connect to the extracellular cell matrix (ECM) at membrane adhesion junctions that provide mechanical coupling between smooth muscle cells within the tissue. Membrane adhesion junctions also sense local environmental signals and transduce them to cytoplasmic and nuclear signaling pathways in the ASM cell. Adhesion junctions are composed of clusters of transmembrane integrin proteins that bind to ECM proteins outside the cell and to large multiprotein complexes in the submembranous cytoplasm. Physiological conditions and stimuli from the surrounding ECM are sensed by integrin proteins and transduced by submembranous adhesion complexes to signaling pathways to the cytoskeleton and nucleus. The transmission of information between the local environment of the cells and intracellular processes enables ASM cells to rapidly adapt their physiological properties to modulating influences in their extracellular environment: mechanical and physical forces that impinge on the cell, ECM constituents, local mediators, and metabolites. The structure and molecular organization of adhesion junction complexes and the actin cytoskeleton are dynamic and constantly changing in response to environmental influences. The ability of ASM to rapidly accommodate to the ever-changing conditions and fluctuating physical forces within its local environment is essential for its normal physiological function.

Airway smooth muscle function in asthma

Known to have affected around 340 million people across the world in 2018, asthma is a prevalent chronic inflammatory disease of the airways. The symptoms such as wheezing, dyspnea, chest tightness, and cough reflect episodes of reversible airway obstruction. Asthma is a heterogeneous disease that varies in clinical presentation, severity, and pathobiology, but consistently features airway hyperresponsiveness (AHR)—excessive airway narrowing due to an exaggerated response of the airways to various stimuli. Airway smooth muscle (ASM) is the major effector of exaggerated airway narrowing and AHR and many factors may contribute to its altered function in asthma. These include genetic predispositions, early life exposure to viruses, pollutants and allergens that lead to chronic exposure to inflammatory cells and mediators, altered innervation, airway structural cell remodeling, and airway mechanical stress. Early studies aiming to address the dysfunctional nature of ASM in the etiology and pathogenesis of asthma have been inconclusive due to the methodological limitations in assessing the intrapulmonary airways, the site of asthma. The study of the trachealis, although convenient, has been misleading as it has shown no alterations in asthma and it is not as exposed to inflammatory cells as intrapulmonary ASM. Furthermore, the cartilage rings offer protection against stress and strain of repeated contractions. More recent strategies that allow for the isolation of viable intrapulmonary ASM tissue reveal significant mechanical differences between asthmatic and non-asthmatic tissues. This review will thus summarize the latest techniques used to study ASM mechanics within its environment and in isolation, identify the potential causes of the discrepancy between the ASM of the extra- and intrapulmonary airways, and address future directions that may lead to an improved understanding of ASM hypercontractility in asthma.

Pathobiology of Airway Remodeling in Asthma: The Emerging Role of Integrins

Airway remodeling is a complex clinical feature of asthma that involves long-term disruption and modification of airway architecture, which contributes significantly to airway hyperresponsiveness (AHR) and lung function decline. It is characterized by thickening of the airway smooth muscle layer, deposition of a matrix below the airway epithelium, resulting in subepithelial fibrosis, changes within the airway epithelium, leading to disruption of the barrier, and excessive mucous production and angiogenesis within the airway wall. Airway remodeling contributes to stiffer and less compliant airways in asthma and leads to persistent, irreversible airflow obstruction. Current asthma treatments aim to reduce airway inflammation and exacerbations but none are targeted towards airway remodeling. Inhibiting the development of airway remodeling or reversing established remodeling has the potential to dramatically improve symptoms and disease burden in asthmatic patients. Integrins are a family of transmembrane heterodimeric proteins that serve as the primary receptors for extracellular matrix (ECM) components, mediating cell-cell and cell-ECM interactions to initiate intracellular signaling cascades. Cells present within the lungs, including structural and inflammatory cells, express a wide and varying range of integrin heterodimer combinations and permutations. Integrins are emerging as an important regulator of inflammation, repair, remodeling, and fibrosis in the lung, particularly in chronic lung diseases such as asthma. Here, we provide a comprehensive summary of the current state of knowledge on integrins in the asthmatic airway and how these integrins promote the remodeling process, and emphasize their potential involvement in airway disease.

Basement membranes in obstructive pulmonary diseases

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Basement membrane composition is changed in the airways of patients with obstructive airway diseases.

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Basement membrane changes are linked to disease characteristics in patients.

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Mechanisms behind the altered BM composition remain to be elucidated.

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Laminin and collagen IV affect key pathological processes in obstructive airway diseases.

Increased and changed deposition of extracellular matrix proteins is a key feature of airway wall remodeling in obstructive pulmonary diseases, including asthma and chronic obstructive pulmonary disease. Studies have highlighted that the deposition of various basement membrane proteins in the lung tissue is altered and that these changes reflect tissue compartment specificity. Inflammatory responses in both diseases may result in the deregulation of production and degradation of these proteins. In addition to their role in tissue development and integrity, emerging evidence indicates that basement membrane proteins also actively modulate cellular processes in obstructive airway diseases, contributing to disease development, progression and maintenance. In this review, we summarize the changes in basement membrane composition in airway remodeling in obstructive airway diseases and explore their potential application as innovative targets for treatment development.

Effects of silver nanoparticles-polysaccharide on bleomycin-induced pulmonary fibrosis in rats

OBJECTIVES

The first goal of this study was to synthesize the silver nanoparticles Alcaligenes xylosoxidans exopolysaccharide (Ag-AXEPS). The second objective was to analyse the role of Ag-AXEPS nanoparticles (NPS) in treating bleomycin (BLM)-induced lung fibrosis.

METHODS

Intratracheal bleomycin (2.5 U/kg) was administered to prompt pulmonary fibrosis in rats, and pulmonary fibrosis was treated with Ag-AXEPS nanoparticles (100 ppm/twice a week for four weeks).

KEY FINDINGS

Ag-AXEPS nanoparticles significantly decreased the diversity of pulmonary inflammatory agents in rats with BLM-induced fibrosis. Reduced levels of respiratory tumor necrosis factor-alpha, monocyte chemotactic protein-1, matrix metalloproteinases (MMP-2 and MMP-9) were observed on treatment with synthesized Ag-AXEPS. Similarly, the treatment decreased IL-12, mRNA levels of BAX and plasma fibrosis markers like N-terminal procollagen III propeptide and transforming growth factor-β1. On the other hand, the treatment increased mRNA BCL2 and total antioxidant capacity. It also lowered the level of fibrosis, as was shown by a quantified pathologic study of hematoxylin-eosin-stained lung parts. The treatment, however, ensured that lung collagen was restored, as assessed by Masson's trichrome stain, and that overall survival was increased and enhanced.

CONCLUSIONS

Our work showed that nanoparticles could be obtained at 37°C and may be a possible pulmonary fibrosis therapeutic agent.

MicroRNA-98 reduces nerve growth factor expression in nicotine-induced airway remodeling

Evolving evidence suggests that nicotine may contribute to impaired asthma control by stimulating expression of nerve growth factor (NGF), a neurotrophin associated with airway remodeling and airway hyperresponsiveness. We explored the hypothesis that nicotine increases NGF by reducing lung fibroblast (LF) microRNA-98 (miR-98) and PPARγ levels, thus promoting airway remodeling. Levels of NGF, miR-98, PPARγ, fibronectin 1 (FN1), endothelin-1 (EDN1, herein referred to as ET-1), and collagen (COL1A1 and COL3A1) were measured in human LFs isolated from smoking donors, in mouse primary LFs exposed to nicotine (50 μg/ml), and in whole lung homogenates from mice chronically exposed to nicotine (100 μg/ml) in the drinking water. In selected studies, these pathways were manipulated in LFs with miR-98 inhibitor (anti-miR-98), miR-98 overexpression (miR-98 mimic), or the PPARγ agonist rosiglitazone. Compared with unexposed controls, nicotine increased NGF, FN1, ET-1, COL1A1, and COL3A1 expression in human and mouse LFs and mouse lung homogenates. In contrast, nicotine reduced miR-98 levels in LFs in vitro and in lung homogenates in vivo Treatment with anti-miR-98 alone was sufficient to recapitulate increases in NGF, FN1, and ET-1, whereas treatment with a miR-98 mimic significantly suppressed luciferase expression in cells transfected with a luciferase reporter linked to the putative seed sequence in the NGF 3'UTR and also abrogated nicotine-induced increases in NGF, FN1, and ET-1 in LFs. Similarly, rosiglitazone increased miR-98 and reversed nicotine-induced increases in NGF, FN1, and ET-1. Taken together, these findings demonstrate that nicotine-induced increases in NGF and other markers of airway remodeling are negatively regulated by miR-98.

Identification and Modulation of Microenvironment Is Crucial for Effective Mesenchymal Stromal Cell Therapy in Acute Lung Injury

Rationale: There are controversial reports on applications of mesenchymal stromal cells (MSCs) in patients with acute respiratory distress syndrome (ARDS). Objectives: We hypothesized that lung microenvironment was the main determinant of beneficial versus detrimental effects of MSCs during ARDS. Methods: Lung proteome was profiled in three models of injury induced by acid instillation and/or mechanical ventilation in mice. Human gene of glutathione peroxidase-1 was delivered before MSC administration; or MSCs carrying human gene of IL-10 or hepatocyte growth factor were administered after lung injury. An inhibitory cocktail against IL-6, fibronectin, and oxidative stress was used in in vitro studies using human small airway epithelial cells and human MSCs after exposure to plasma of patients with ARDS. Measurements and Main Results: Distinct proteomic profiles were observed in three lung injury models. Administration of MSCs protected lung from ventilator-induced injury, whereas it worsened acid-primed lung injuries associated with fibrotic development in lung environment that had high levels of IL-6 and fibronectin along with low antioxidant capacity. Correction of microenvironment with glutathione peroxidase-1, or treatment with MSCs carrying human gene of IL-10 or hepatocyte growth factor after acid-primed injury, reversed the detrimental effects of native MSCs. Proteomic profiles obtained in the mouse models were also similarly observed in human ARDS. Treatment with the inhibitory cocktail in samples of patients with ARDS retained protective effects of MSCs in small airway epithelial cells. Conclusions: MSCs can be beneficial or detrimental depending on microenvironment at the time of administration. Identification of potential beneficiaries seems to be crucial to guide MSC therapy in ARDS.

Laminin α4 contributes to airway remodeling and inflammation in asthma

Airway inflammation and remodeling are characteristic features of asthma, with both contributing to airway hyperresponsiveness (AHR) and lung function limitation. Airway smooth muscle (ASM) accumulation and extracellular matrix deposition are characteristic features of airway remodeling, which may contribute to persistent AHR. Laminins containing the α2-chain contribute to characteristics of ASM remodeling in vitro and AHR in animal models of asthma. The role of other laminin chains, including the laminin α4 and α5 chains, which contribute to leukocyte migration in other diseases, is currently unknown. The aim of the current study was to investigate the role of these laminin chains in ASM function and in AHR, remodeling, and inflammation in asthma. Expression of both laminin α4 and α5 was observed in the human and mouse ASM bundle. In vitro, laminin α4 was found to promote a pro-proliferative, pro-contractile, and pro-fibrotic ASM cell phenotype. In line with this, treatment with laminin α4 and α5 function-blocking antibodies reduced allergen-induced increases in ASM mass in a mouse model of allergen-induced asthma. Moreover, eosinophilic inflammation was reduced by the laminin α4 function-blocking antibody as well. Using airway biopsies from healthy subjects and asthmatic patients, we found inverse correlations between ASM α4-chain expression and lung function and AHR, whereas eosinophil numbers correlated positively with expression of laminin α4 in the ASM bundle. This study, for the first time, indicates a prominent role for laminin α4 in ASM function and in inflammation, AHR, and remodeling in asthma, whereas the role of laminin α5 is more subtle.

Complement-independent bystander injury in AQP4-IgG seropositive neuromyelitis optica produced by antibody-dependent cellular cytotoxicity

Cellular injury in AQP4-IgG seropositive neuromyelitis spectrum disorder (herein called NMO) involves AQP4-IgG binding to astrocytes, resulting in astrocyte injury by complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) mechanisms. The rapid disease progression, severe tissue damage, and abundant leukocyte infiltration seen in some NMO patients suggest a more direct mechanism for demyelination and neurologic deficit than secondary injury from astrocyte loss. Here, we report evidence for an ‘ADCC bystander mechanism’ in NMO involving injury to nearby cells by leukocytes following their activation by AQP4-bound AQP4-IgG on astrocytes. In model cocultures containing AQP4-expressing and null CHO cells, AQP4-IgG and complement killed bystander null cells to ~ 100 μm away from AQP4-expressing cells; AQP4-IgG and NK cells produced bystander killing to ~ 300 μm, with perforin deposition seen on injured null cells. Bystander cytotoxicity was also seen with neutrophil-mediated ADCC and in astrocyte-neuron cocultures. Mechanistic studies, including real-time imaging, suggested that leukocytes activated by an AQP4-dependent ADCC mechanism injure bystander cells by direct targeted exocytosis on neighboring cells and not by diffusion of soluble granule contents. In support of this conclusion, ADCC bystander injury was preferentially reduced by an RGDS peptide that inhibits integrin adhesion. Evidence for ADCC bystander injury to oligodendrocytes and neurons was also found in mice following intracerebral injection of AQP4-IgG and NK cells, which was inhibited by RGDS peptide. These results establish a novel cellular pathogenesis mechanism in AQP4-IgG seropositive NMO and provide evidence that inflammatory mechanisms can cause widespread tissue damage in NMO independently of the secondary effects from astrocyte loss.

Traffic-related air pollution induces non-allergic eosinophilic airway inflammation and cough hypersensitivity in guinea-pigs

BACKGROUND

The pathogenesis and pathophysiology of eosinophilia-related chronic cough such as non-asthmatic eosinophilic bronchitis and cough variant asthma are still not clear.

OBJECTIVE

This study is to examine the potential role of traffic-related air pollution (TRAP) in eosinophilic inflammation and cough responses.

METHODS

Non-sensitized guinea-pigs were exposed to TRAP in an urban traffic tunnel or kept in a filtered air environment for 7 or 14 days. Reflexive cough was measured using citric acid and allyl isothiocyanate (AITC) challenges, respectively. Spontaneous cough counting was determined using audio recording and a waveform analysis. Airway inflammation was evaluated using differential cells in bronchoalveolar lavage fluid (BALF) and lung histopathology. To further elucidate the relationship between airway inflammation and cough hypersensitivity, a subgroup of those exposed for 14 days received a dexamethasone treatment.

RESULTS

Compared to reflexive cough count (mean (95% confidence interval) in 10 minutes) provoked by the AITC challenge for the unexposed animals (3.1 (1.7-4.5)), those were increased significantly following both the 7-day (12.0 (6.8-17.2), P < 0.01) and the 14-day (12.0 (6.4-17.6), P < 0.01) TRAP exposure. The effect provoked by the citric acid challenge was more profound following the 14-day exposure (26.0 (19.5-32.5) vs 3.8 (1.5-6.0) for the control, P < 0.001). TRAP exposures enhanced spontaneous cough events, caused a significant increase of eosinophils and neutrophils in BALF and resulted in a dramatic eosinophilic infiltration in submucosal layer of trachea and bronchus, which can be inhibited significantly by dexamethasone treatment.

CONCLUSIONS & CLINICAL RELEVANCE

TRAP exposures induced cough hypersensitivity and non-allergic eosinophilic inflammation of airways in guinea-pigs. This study highlights the potential mechanisms of eosinophilia-related chronic cough that can be induced by traffic-related air pollution.

The Dynamic Actin Cytoskeleton in Smooth Muscle

Smooth muscle contraction requires both myosin activation and actin cytoskeletal remodeling. Actin cytoskeletal reorganization facilitates smooth muscle contraction by promoting force transmission between the contractile unit and the extracellular matrix (ECM), and by enhancing intercellular mechanical transduction. Myosin may be viewed to serve as an "engine" for smooth muscle contraction whereas the actin cytoskeleton may function as a "transmission system" in smooth muscle. The actin cytoskeleton in smooth muscle also undergoes restructuring upon activation with growth factors or the ECM, which controls smooth muscle cell proliferation and migration. Abnormal smooth muscle contraction, cell proliferation, and motility contribute to the development of vascular and pulmonary diseases. A number of actin-regulatory proteins including protein kinases have been discovered to orchestrate actin dynamics in smooth muscle. In particular, Abelson tyrosine kinase (c-Abl) is an important molecule that controls actin dynamics, contraction, growth, and motility in smooth muscle. Moreover, c-Abl coordinates the regulation of blood pressure and contributes to the pathogenesis of airway hyperresponsiveness and vascular/airway remodeling in vivo. Thus, c-Abl may be a novel pharmacological target for the development of new therapy to treat smooth muscle diseases such as hypertension and asthma.

Cyclic peptide *CRRETAWAC* attenuates fibronectin-induced cytokine secretion of human airway smooth muscle cells by inhibiting FAK and p38 MAPK

α5β1 integrin is highly expressed in airway smooth muscle cells and mediate the adhesion of airway smooth muscle cells to fibronectin to regulate airway remodelling in asthma. This study aimed to investigate the effects of synthetic cyclic peptide *CRRETAWAC* on fibronectin‐induced cytokine secretion of airway smooth muscle cells and the underlying mechanism. Human airway smooth muscle cells were isolated and treated with fibronectin, IL‐13, *CRRETAWAC* peptide, α5β1 integrin‐blocking antibody, FAK inhibitor or p38 MAPK inhibitor. The transcription and secretion of eotaxin‐1 and RANTES were detected by real‐time PCR and ELISA, respectively. The phosphorylation of FAK and MAPKs including p38, ERK1/2 and JNK1/2 was detected by Western blot analysis. The transcription and secretion of eotaxin‐1 and RANTES increased in airway smooth muscle cells cultured in fibronectin‐coated plates. However, α5β1 integrin‐blocking antibody, *CRRETAWAC* peptide, FAK inhibitor or p38 MAPK inhibitor significantly reduced mRNA levels and the secretion of eotaxin‐1 and RANTES in airway smooth muscle cells cultured in fibronectin‐coated plates. In addition, the phosphorylation of FAK and p38 MAPK was significantly increased in airway smooth muscle cells cultured in fibronectin‐coated plates compared to the cells cultured in uncoated plates and was significantly reduced in airway smooth muscle cells treated with *CRRETAWAC* peptide. Fibronectin induces cytokine synthesis and secretion of airway smooth muscle cells. Peptide *CRRETAWAC* antagonizes fibronectin‐induced cytokine synthesis and secretion of airway smooth muscle cells via the inhibition of FAK and p38 MAPK, and is a potential agent for the therapy of asthma.

The roles and regulation of the actin cytoskeleton, intermediate filaments and microtubules in smooth muscle cell migration

Smooth muscle cell migration has been implicated in the development of respiratory and cardiovascular systems; and airway/vascular remodeling. Cell migration is a polarized cellular process involving a protrusive cell front and a retracting trailing rear. There are three cytoskeletal systems in mammalian cells: the actin cytoskeleton, the intermediate filament network, and microtubules; all of which regulate all or part of the migrated process. The dynamic actin cytoskeleton spatially and temporally regulates protrusion, adhesions, contraction, and retraction from the cell front to the rear. c-Abl tyrosine kinase plays a critical role in regulating actin dynamics and migration of airway smooth muscle cells and nonmuscle cells. Recent studies suggest that intermediate filaments undergo reorganization during migration, which coordinates focal adhesion dynamics, cell contraction, and nucleus rigidity. In particular, vimentin intermediate filaments undergo phosphorylation and reorientation in smooth muscle cells, which may regulate cell contraction and focal adhesion assembly/disassembly. Motile cells are characterized by a front-rear polarization of the microtubule framework, which regulates all essential processes leading to cell migration through its role in cell mechanics, intracellular trafficking, and signaling. This review recapitulates our current knowledge how the three cytoskeletal systems spatially and temporally modulate the migratory properties of cells. We also summarize the potential role of migration-associated biomolecules in lung and vascular diseases.

Suppression of Eosinophil Integrins Prevents Remodeling of Airway Smooth Muscle in Asthma

Background: Airway smooth muscle (ASM) remodeling is an important component of the structural changes to airways seen in asthma. Eosinophils are the prominent inflammatory cells in asthma, and there is some evidence that they contribute to ASM remodeling via released mediators and direct contact through integrin-ligand interactions. Eosinophils express several types of outer membrane integrin, which are responsible for cell-cell and cell-extracellular matrix interactions. In our previous study we demonstrated that asthmatic eosinophils show increased adhesion to ASM cells and it may be important factor contributing to ASM remodeling in asthma. According to these findings, in the present study we investigated the effects of suppression of eosinophil integrin on eosinophil-induced ASM remodeling in asthma. Materials and Methods: Individual combined cell cultures of immortalized human ASM cells and eosinophils from peripheral blood of 22 asthmatic patients and 17 healthy controls were prepared. Eosinophil adhesion was evaluated using eosinophil peroxidase activity assay. Genes expression levels in ASM cells and eosinophils were measured using quantitative real-time PCR. ASM cell proliferation was measured using alamarBlue® solution. Eosinophil integrins were blocked by incubating with Arg-Gly-Asp-Ser peptide. Results: Eosinophils from the asthma group showed increased outer membrane α4β1 and αMβ2 integrin expression, increased adhesion to ASM cells, and overexpression of TGF-β1 compared with eosinophils from the healthy control group. Blockade of eosinophil RGD-binding integrins by Arg-Gly-Asp-Ser peptide significantly reduced adhesion of eosinophils to ASM cells in both groups. Integrin-blocking decreased the effects of eosinophils on TGF-β1, WNT-5a, and extracellular matrix protein gene expression in ASM cells and ASM cell proliferation in both groups. These effects were more pronounced in the asthma group compared with the control group. Conclusion: Suppression of eosinophil-ASM interaction via RGD-binding integrins attenuates eosinophil-induced ASM remodeling in asthma. Trial Registration: ClinicalTrials.gov Identifier: NCT02648074.

Generation of IL10 and TGFB1 coexpressed mice displaying resistance to ovalbumin-induced asthma

Asthma is a common chronic inflammatory disease in the airways with wide prevalence, and it is thought to be caused by the combinational factors in environment and genetics. A large body of studies has suggested that cell immunity played a vital role in regulating the airway hyperreactivity (AHR) and inflammation. Therefore, we here developed a mouse model of asthma by microinjecting the pronucleus with a vector spontaneously coding human IL10 and TGFB1 gene to explore the possible interaction between these two potent molecules during asthma progression. From the total 35 newborn mice, we successfully obtained 3 founders expressing exogenous genes. In the transgenic mice, we observed profoundly enhanced expression of IL10 and TGFB1. In the condition of ovalbumin challenge, transgenic mice displayed a 1.9-fold higher MCh50 score than wild-type counterparts, indicating reminiscent AHR. Meanwhile, a three-fold decrease of cell counts in bronchoalveolar lavage fluid (BALF) was recorded as well. These results suggested that IL10 and TGFB1 cooperatively protected the respiratory system in response to antigenic stimulus. To interrogate the respective behaviors of the two genes, we quantified the expression of downstream genes in IL10 signaling or TGFB1 signaling. We observed that the examined genes in IL10 signaling were significantly repressed, especially IL5, which showed 5.4-fold decreased expression. Most genes were not altered in TGFB1 signaling, and the production of endogenous TGFB1 was significantly inhibited. These evidences collectively proved that the activation of IL0 and TGFB1 protected the host from antigen-induced asthma, possibly through IL10 signaling. This study shed some light on the modulations of IL10 and TGFB1, and related networks to asthma progression.

Interstitial collagen turnover during airway remodeling in acute and chronic experimental asthma

Asthma airway remodeling is characterized by the thickening of the basement membrane (BM) due to an increase in extracellular matrix (ECM) deposition, which contributes to the irreversibility of airflow obstruction. Interstitial collagens are the primary ECM components to be increased during the fibrotic process. The aim of the present study was to examine the interstitial collagen turnover during the course of acute and chronic asthma, and 1 month after the last exposure to the allergen. Guinea pigs sensitized to ovalbumin (OVA) and exposed to 3 further OVA challenges (acute model) or 12 OVA challenges (chronic model) were used as asthma experimental models. A group of animals from either model was sacrificed 1 h or 1 month after the last OVA challenge. Collagen distribution, collagen content, interstitial collagenase activity and matrix metalloproteinase (MMP)-1, MMP-13 and tissue inhibitor of metalloproteinase (TIMP)-1 protein expression levels were measured in the lung tissue samples from both experimental models. The results revealed that collagen deposit in bronchiole BM, adventitial and airway smooth muscle layers was increased in both experimental models as well as lung tissue collagen concentration. These structural changes persisted 1 month after the last OVA challenge. In the acute model, a decrease in collagenase activity and in MMP-1 concentration was observed. Collagenase activity returned to basal levels, and an increase in MMP-1 and MMP-13 expression levels along with a decrease in TIMP-1 expression levels were observed in animals sacrificed 1 month after the last OVA challenge. In the chronic model, there were no changes in collagenase activity or in MMP-13 concentration, although MMP-1 expression levels increased. One month later, an increase in collagenase activity was observed, although MMP-1 and TIMP-1 levels were not altered. The results of the present study suggest that even when the allergen challenges were discontinued, and collagenase activity and MMP-1 expression increased, fibrosis remained, contributing to the irreversibility of bronchoconstriction.

Critical role of actin-associated proteins in smooth muscle contraction, cell proliferation, airway hyperresponsiveness and airway remodeling

Asthma is characterized by airway hyperresponsiveness and airway remodeling, which are largely attributed to increased airway smooth muscle contractility and cell proliferation. It is known that both chemical and mechanical stimulation regulates smooth muscle contraction. Recent studies suggest that contractile activation and mechanical stretch induce actin cytoskeletal remodeling in smooth muscle. However, the mechanisms that control actin cytoskeletal reorganization are not completely elucidated. This review summarizes our current understanding regarding how actin-associated proteins may regulate remodeling of the actin cytoskeleton in airway smooth muscle. In particular, there is accumulating evidence to suggest that Abelson tyrosine kinase (Abl) plays a critical role in regulating airway smooth muscle contraction and cell proliferation in vitro, and airway hyperresponsiveness and remodeling in vivo. These studies indicate that Abl may be a novel target for the development of new therapy to treat asthma.

Microfibrillar-associated protein 4 modulates airway smooth muscle cell phenotype in experimental asthma

BACKGROUND

Recently, several proteins of the extracellular matrix have been characterised as active contributors to allergic airway disease. Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein abundant in the lung, whose biological functions remain poorly understood. In the current study we investigated the role of MFAP4 in experimental allergic asthma.

METHODS

MFAP4-deficient mice were subjected to alum/ovalbumin and house dust mite induced models of allergic airway disease. In addition, human healthy and asthmatic primary bronchial smooth muscle cell cultures were used to evaluate MFAP4-dependent airway smooth muscle responses.

RESULTS

MFAP4 deficiency attenuated classical hallmarks of asthma, such as eosinophilic inflammation, eotaxin production, airway remodelling and hyperresponsiveness. In wild-type mice, serum MFAP4 was increased after disease development and correlated with local eotaxin levels. MFAP4 was expressed in human bronchial smooth muscle cells and its expression was upregulated in asthmatic cells. Regarding the underlying mechanism, we showed that MFAP4 interacted with integrin αvβ5 and promoted asthmatic bronchial smooth muscle cell proliferation and CCL11 release dependent on phosphatidyloinositol-3-kinase but not extracellular signal-regulated kinase pathway.

CONCLUSIONS

MFAP4 promoted the development of asthmatic airway disease in vivo and pro-asthmatic functions of bronchial smooth muscle cells in vitro. Collectively, our results identify MFAP4 as a novel contributor to experimental asthma, acting through modulation of airway smooth muscle cells.

L-thyroxine promotes a proliferative airway smooth muscle phenotype in the presence of TGF-β1

Hypothyroidism may reduce, whereas hyperthyroidism may aggravate, asthma symptoms. The mechanisms underlying this relationship are largely unknown. Since thyroid hormones have central roles in cell growth and differentiation, we hypothesized that airway remodeling, in particular increased airway smooth muscle (ASM) mass, may be involved. To address this hypothesis, we investigated the effects of triiodothyronine (T3) and l-thyroxine (T4) in the absence and presence of the profibrotic transforming growth factor (TGF)-β1 on human ASM cell phenotype switching. T3 (1-100 nM) and T4 (1-100 nM) did not affect basal ASM proliferation. However, when combined with TGF-β1 (2 ng/ml), T4 synergistically increased the proliferative response, whereas only a minor effect was observed for T3. In line with a switch from a contractile to a proliferative ASM phenotype, T4 reduced the TGF-β1-induced contractile protein expression by ∼50%. Cotreatment with T3 reduced TGF-β1-induced contractile protein expression by ∼25%. The synergistic increase in proliferation was almost fully inhibited by the integrin αvβ3 antagonist tetrac (100 nM), whereas no significant effects of the thyroid receptor antagonist 1-850 (3 μM) were observed. Inhibition of MEK1/2, downstream of the integrin αvβ3, also inhibited the T4- and TGF-β1-induced proliferative responses. Collectively, the results indicate that T4, and to a lesser extent T3, promotes a proliferative ASM phenotype in the presence of TGF-β1, which is predominantly mediated by the membrane-bound T4 receptor αvβ3. These results indicate that thyroid hormones may enhance ASM remodeling in asthma, which could be of relevance for hyperthyroid patients with this disease.

Integrins: therapeutic targets in airway hyperresponsiveness and remodelling?

Integrins are a group of transmembrane heterodimeric proteins that mediate cell-cell and cell-extracellular matrix (ECM) interactions. Integrins have been under intense investigation for their role in inflammation in asthma. Clinical trials investigating integrin antagonists, however, have shown that these compounds are relatively ineffective. Airway remodelling is another pathological feature of asthma that is thought to make an important contribution to airway hyperresponsiveness (AHR) and lung function decline. Recent studies have identified integrins as important players in this process, with a particular role for β1 and αv integrins. Here we review the role of these integrins in airway remodelling and hyperresponsiveness in obstructive airway disease and their potential as pharmacological targets for future treatment.

Transforming growth factor β and severe asthma: a perfect storm

Asthma is a chronic inflammatory airway disease involving complex interplay between resident and infiltrative cells, which in turn are regulated by a wide range of host mediators. Identifying useful biomarkers correlating with clinical symptoms and degree of airway obstruction remain important to effective future asthma treatments. Transforming growth factor β (TGF-β) is a major mediator involved in pro-inflammatory responses and fibrotic tissue remodeling within the asthmatic lung. Its role however, as a therapeutic target remains controversial. The aim of this review is to highlight its role in severe asthma including interactions with adaptive T-helper cells, cytokines and differentiation through regulatory T-cells. Associations between TGF-β and eosinophils will be addressed and the effects of genetic polymorphisms of the TGF-β1 gene explored in the context of asthma. We highlight TGF-β1 as a potential future therapeutic target in severe asthma including its importance in identifying emerging clinical phenotypes in asthmatic subjects who may be suitable for individualized therapy through TGF-β modulation.

Beyond TGFβ--novel ways to target airway and parenchymal fibrosis

Within the lungs, fibrosis can affect both the parenchyma and the airways. Fibrosis is a hallmark pathological change in the parenchyma in patients with idiopathic pulmonary fibrosis (IPF), whilst in asthma or chronic obstructive pulmonary disease (COPD) fibrosis is a component of the remodelling of the airways. In the past decade, significant advances have been made in understanding the disease behaviour and pathogenesis of parenchymal and airway fibrosis and as a result a variety of novel therapeutic targets for slowing or preventing progression of these fibrotic changes have been identified. This review highlights a number of these targets and discusses the potential for treating parenchymal or airway fibrosis through these mediators/pathways in the future.

c-Abl tyrosine kinase regulates cytokinesis of human airway smooth muscle cells

Cytokinesis is a critical step of airway smooth muscle cell division that plays an essential role in the development and homeostasis of the respiratory system, as well as the progression of airway remodeling. The mechanisms that regulate smooth muscle cytokinesis are not fully understood. c-Abl (c-Abelson tyrosine kinase) is a nonreceptor protein tyrosine kinase that has a role in regulating actin dynamics and smooth muscle contraction. The role of c-Abl in cytokinesis has not been investigated. Here, c-Abl was found in the contractile ring, as evidenced by immunofluorescent microscopy. In addition, cortactin is a phosphorylatable protein that has been implicated in actin filament assembly. In this report, phosphorylated cortactin was also found in the contractile ring. Knockdown of c-Abl by RNA interference attenuated cortactin phosphorylation in the midzone and contractile ring formation. c-Abl knockdown decreased the number of cells undergoing cytokinesis, but increased the quantity of cells in metaphase/anaphase and the number of multinucleate cells. Treatment with the c-Abl pharmacological inhibitors, imatinib and GNF-5, had similar effects. Furthermore, the expression of a nonphosphorylatable cortactin mutant diminished cytokinesis. Finally, inhibition of actin filament assembly by latrunculin A attenuated c-Abl recruitment to the midzone. Thus, we propose a novel mechanism that regulates smooth muscle cell cytokinesis. c-Abl is recruited to the equator during cytokinesis, which may mediate cortactin phosphorylation. Phosphorylated cortactin may promote actin filament assembly, which facilitates contractile ring formation and cytokinesis. In addition, actin filament polymerization may facilitate the positioning of c-Abl to the contractile ring.

Synthetic RGDS peptide attenuated lipopolysaccharide/D-galactosamine-induced fulminant hepatic failure in mice

BACKGROUND AND AIM

Fulminant hepatic failure (FHF) is a serious clinic syndrome with extremely poor prognosis and no effective treatment except for liver transplantation. Synthetic RGDS peptide, an inhibitor of integrins, was proved to suppress integrin signals. In this study, we investigated the protection effects of RGDS peptide on lipopolysaccharide/D-galactosamine (LPS/D-GalN)-induced FHF and the underlying molecular mechanisms.

METHODS

Synthetic RGDS peptide was given intraperitoneally 30 min before LPS/D-GalN injection. Liver function and the extent of liver injury were analyzed biochemically and pathologically respectively. Enzyme-linked immunosorbent assay, real-time polymerase chain reaction and Western blotting were used to detect effectors and signaling molecules.

RESULTS

Pretreatment with synthetic RGDS peptide significantly improved LPS/D-GalN-induced mortality, and liver injury as determined by alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, as well as pathological analysis. In addition, RGDS peptide significantly reduced tumor necrosis factor (TNF)-α and macrophage inflammatory protein (MIP)-2 production, and decreased myeloperoxidase (MPO) and NF-κB activity. Furthermore, Western blotting indicated that the levels of phospho-integrin β3, phospho-focal adhesion kinase (FAK) and phospho-p38 mitogen-activated protein kinases (MAPK) decreased with RGDS peptide pretreatment.

CONCLUSION

Together, these data suggest that synthetic RGDS peptide protect against LPS/D-GalN-induced FHF by inhibiting inflammatory cells migration and blocking the integrin αVβ3-FAK-p38 MAPK and NF-κB signaling.

From bedside to bench to clinic trials: identifying new treatments for severe asthma

Asthmatics with a severe form of the disease are frequently refractory to standard medications such as inhaled corticosteroids, underlining the need for new treatments to prevent the occurrence of potentially life-threatening episodes. A major obstacle in the development of new treatments for severe asthma is the heterogeneous pathogenesis of the disease, which involves multiple mechanisms and cell types. Furthermore, new therapies might need to be targeted to subgroups of patients whose disease pathogenesis is mediated by a specific pathway. One approach to solving the challenge of developing new treatments for severe asthma is to use experimental mouse models of asthma to address clinically relevant questions regarding disease pathogenesis. The mechanistic insights gained from mouse studies can be translated back to the clinic as potential treatment approaches that require evaluation in clinical trials to validate their effectiveness and safety in human subjects. Here, we will review how mouse models have advanced our understanding of severe asthma pathogenesis. Mouse studies have helped us to uncover the underlying inflammatory mechanisms (mediated by multiple immune cell types that produce Th1, Th2 or Th17 cytokines) and non-inflammatory pathways, in addition to shedding light on asthma that is associated with obesity or steroid unresponsiveness. We propose that the strategy of using mouse models to address clinically relevant questions remains an attractive and productive research approach for identifying mechanistic pathways that can be developed into novel treatments for severe asthma.

Role of Abl in airway hyperresponsiveness and airway remodeling

BACKGROUND

Asthma is a chronic disease that is characterized by airway hyperresponsiveness and airway remodeling. The underlying mechanisms that mediate the pathological processes are not fully understood. Abl is a non-receptor protein tyrosine kinase that has a role in the regulation of smooth muscle contraction and smooth muscle cell proliferation in vitro. The role of Abl in airway hyperresponsiveness and airway remodeling in vivo is largely unknown.

METHODS

To evaluate the role of Abl in asthma pathology, we assessed the expression of Abl in airway tissues from the ovalbumin sensitized and challenged mouse model, and human asthmatic airway smooth muscle cells. In addition, we generated conditional knockout mice in which Abl expression in smooth muscle was disrupted, and then evaluated the effects of Abl conditional knockout on airway resistance, smooth muscle mass, cell proliferation, IL-13 and CCL2 in the mouse model of asthma. Furthermore, we determined the effects of the Abl pharmacological inhibitors imatinib and GNF-5 on these processes in the animal model of asthma.

RESULTS

The expression of Abl was upregulated in airway tissues of the animal model of asthma and in airway smooth muscle cells of patients with severe asthma. Conditional knockout of Abl attenuated airway resistance, smooth muscle mass and staining of proliferating cell nuclear antigen in the airway of mice sensitized and challenged with ovalbumin. Interestingly, conditional knockout of Abl did not affect the levels of IL-13 and CCL2 in bronchoalveolar lavage fluid of animals treated with ovalbumin. However, treatment with imatinib and GNF-5 inhibited the ovalbumin-induced increase in IL-13 and CCL2 as well as airway resistance and smooth muscle growth in animals.

CONCLUSIONS

These results suggest that the altered expression of Abl in airway smooth muscle may play a critical role in the development of airway hyperresponsiveness and airway remodeling in asthma. Our findings support the concept that Abl may be a novel target for the development of new therapy to treat asthma.

Cross-talk between transforming growth factor-β₁ and muscarinic M₂ receptors augments airway smooth muscle proliferation

Transforming growth factor-β₁ (TGF-β₁) is a central mediator in tissue remodeling processes, including fibrosis and airway smooth muscle (ASM) hyperplasia, as observed in asthma. The mechanisms underlying this response, however, remain unclear because TGF-β₁ exerts only weak mitogenic effects on ASM cells. In this study, we hypothesized that the mitogenic effect of TGF-β₁ on ASM is indirect and requires prolonged exposure to allow for extracellular matrix (ECM) deposition. To address this hypothesis, we investigated the effects of acute and prolonged treatment with TGF-β₁, alone and in combination with the muscarinic receptor agonist methacholine, on human ASM cell proliferation. Acutely, TGF-β₁ exerted no mitogenic effect. However, prolonged treatment (for 7 d) with TGF-β₁ increased ASM cell proliferation and potentiated the platelet-derived growth factor-induced mitogenic response. Muscarinic receptor stimulation with methacholine synergistically enhanced the effect of TGF-β₁. Interestingly, the integrin-blocking peptide Arg-Gly-Asp-Ser, as well as integrin α5β1 function-blocking antibodies, inhibited the effects of TGF-β₁ and its combination with methacholine on cell proliferation. Accordingly, prolonged treatment with TGF-β₁ increased fibronectin expression, which was also synergistically enhanced by methacholine. The synergistic effects of methacholine on TGF-β₁-induced proliferation were reduced by the long-acting muscarinic receptor antagonist tiotropium and the M₂ receptor subtype-selective antagonist gallamine, but not the M₃-selective antagonist DAU5884. In line with these findings, the irreversible Gi protein inhibitor pertussis toxin also prevented the potentiation of TGF-β₁-induced proliferation by methacholine. We conclude that prolonged exposure to TGF-β₁ enhances ASM cell proliferation, which is mediated by extracellular matrix-integrin interactions, and which can be enhanced by muscarinic M₂ receptor stimulation.

Focal adhesion kinase regulates collagen I-induced airway smooth muscle phenotype switching

Increased extracellular matrix (ECM) deposition and airway smooth muscle (ASM) mass are major contributors to airway remodeling in asthma. Recently, we demonstrated that the ECM protein collagen I, which is increased surrounding asthmatic ASM, induces a proliferative, hypocontractile ASM phenotype. Little is known, however, about the signaling pathways involved. Using bovine tracheal smooth muscle, we investigated the role of focal adhesion kinase (FAK) and downstream signaling pathways in collagen I-induced ASM phenotype modulation. Phosphorylation of FAK was increased during adhesion to both uncoated and collagen I-coated culture dishes, without differences between these matrices. Nor were any differences found in cellular adhesion. Inhibition of FAK activity by overexpression of the FAK deletion mutants FAT (focal adhesion targeting domain) and FRNK (FAK-related nonkinase) attenuated adhesion. After attachment, FAK phosphorylation increased in a time-dependent manner in cells cultured on collagen I, whereas no activation was found on an uncoated plastic matrix. In addition, collagen I increased in a time- and concentration-dependent manner the cell proliferation, which was fully inhibited by FAT and FRNK. Similarly, the specific pharmacologic FAK inhibitor PF-573228 [6-((4-((3-(methanesulfonyl)benzyl)amino)-5-trifluoromethylpyrimidin-2-yl) amino)-3,4-dihydro-1H-quinolin-2-one] as well as specific inhibitors of p38 mitogen-activated protein kinase (MAPK) and Src also fully inhibited collagen I-induced proliferation, whereas partial inhibition was observed by inhibition of phosphatidylinositol-3-kinase (PI3-kinase) and mitogen-activated protein kinase kinase (MEK). The inhibition of cell proliferation by these inhibitors was associated with attenuation of the collagen I-induced hypocontractility. Collectively, the results indicate that induction of a proliferative, hypocontractile ASM phenotype by collagen I is mediated by FAK and downstream signaling pathways.

TGF-β activation and lung fibrosis

Lung fibrosis can affect the parenchyma and the airways, classically giving rise to idiopathic pulmonary fibrosis (IPF) in the parenchyma or airway remodeling in asthma and chronic obstructive pulmonary disease. TGF-β activation has been implicated in the fibrosis of both IPF and airway remodeling. However, the mechanisms of TGF-β activation appear to differ depending on the cellular and anatomical compartments, with implications on disease pathogenesis. Although it appears that epithelial cell activation of TGF-β by the αvβ6 integrin is central in IPF, mesenchymal activation of TGF-β by the αvβ5 and αvβ8 integrins appears to predominate in airway remodeling. Interestingly, the mechanism of TGF-β by the integrins αvβ6 and αvβ5 is shared, relying on cytoskeletal changes, whereas activation of TGF-β by the αvβ8 integrin is distinct, relying on proteolytic cleavage of the latency-associated peptide of TGF-β by matrix metalloproteinase 14. This article describes the mechanisms through which epithelial cells activate TGF-β by the αvβ6 integrin and mesenchymal cells activate TGF-β by the αvβ5 integrin, and highlights their roles in lung fibrosis.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Integrin and GPCR Crosstalk in the Regulation of ASM Contraction Signaling in Asthma

Airway hyperresponsiveness (AHR) is one of the cardinal features of asthma. Contraction of airway smooth muscle (ASM) cells that line the airway wall is thought to influence aspects of AHR, resulting in excessive narrowing or occlusion of the airway. ASM contraction is primarily controlled by agonists that bind G protein-coupled receptor (GPCR), which are expressed on ASM. Integrins also play a role in regulating ASM contraction signaling. As therapies for asthma are based on symptom relief, better understanding of the crosstalk between GPCRs and integrins holds good promise for the design of more effective therapies that target the underlying cellular and molecular mechanism that governs AHR. In this paper, we will review current knowledge about integrins and GPCRs in their regulation of ASM contraction signaling and discuss the emerging concept of crosstalk between the two and the implication of this crosstalk on the development of agents that target AHR.

Airway contractility and remodeling: links to asthma symptoms

Respiratory symptoms are largely caused by obstruction of the airways. In asthma, airway narrowing mediated by airway smooth muscle (ASM) contraction contributes significantly to obstruction. The spasmogens produced following exposure to environmental triggers, such as viruses or allergens, are initially responsible for ASM activation. However, the extent of narrowing of the airway lumen due to ASM shortening can be influenced by many factors and it remains a real challenge to decipher the exact role of ASM in causing asthmatic symptoms. Innovative tools, such as the forced oscillation technique, continue to develop and have been proven useful to assess some features of ASM function in vivo. Despite these technologic advances, it is still not clear whether excessive narrowing in asthma is driven by ASM abnormalities, by other alterations in non-muscle factors or simply because of the overexpression of spasmogens. This is because a multitude of forces are acting on the airway wall, and because not only are these forces constantly changing but they are also intricately interconnected. To counteract these limitations, investigators have utilized in vitro and ex vivo systems to assess and compare asthmatic and non-asthmatic ASM contractility. This review describes: 1- some muscle and non-muscle factors that are altered in asthma that may lead to airway narrowing and asthma symptoms; 2- some technologies such as the forced oscillation technique that have the potential to unveil the role of ASM in airway narrowing in vivo; and 3- some data from ex vivo and in vitro methods that probe the possibility that airway hyperresponsiveness is due to the altered environment surrounding the ASM or, alternatively, to a hypercontractile ASM phenotype that can be either innate or acquired.

Models to study airway smooth muscle contraction in vivo, ex vivo and in vitro: implications in understanding asthma

Asthma is a chronic obstructive airway disease characterised by airway hyperresponsiveness (AHR) and airway wall remodelling. The effector of airway narrowing is the contraction of airway smooth muscle (ASM), yet the question of whether an inherent or acquired dysfunction in ASM contractile function plays a significant role in the disease pathophysiology remains contentious. The difficulty in determining the role of ASM lies in limitations with the models used to assess contraction. In vivo models provide a fully integrated physiological response but ASM contraction cannot be directly measured. Ex vivo and in vitro models can provide more direct assessment of ASM contraction but the loss of factors that may modulate ASM responsiveness and AHR, including interaction between multiple cell types and disruption of the mechanical environment, precludes a complete understanding of the disease process. In this review we detail key advantages of common in vivo, ex vivo and in vitro models of ASM contraction, as well as emerging tissue engineered models of ASM and whole airways. We also highlight important findings from each model with respect to the pathophysiology of asthma.

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.

Functional consequences of human airway smooth muscle phenotype plasticity

BACKGROUND AND PURPOSE

Airway smooth muscle (ASM) phenotype plasticity, characterized by reversible switching between contractile and proliferative phenotypes, is considered to contribute to increased ASM mass and airway hyper-responsiveness in asthma. Further, increased expression of collagen I has been observed within the ASM bundle of asthmatics. Previously, we showed that exposure of intact bovine tracheal smooth muscle (BTSM) to collagen I induces a switch from a contractile to a hypocontractile, proliferative phenotype. However, the functional relevance of this finding for intact human ASM has not been established.

EXPERIMENTAL APPROACH

We investigated the effects of exposure of human tracheal smooth muscle (HTSM) strips to monomeric collagen I and PDGF on contractile responses to methacholine and KCl. Expression of contractile proteins sm-α-actin and sm-MHC was assessed by Western blot analysis. The proliferation of HTSM cells was assessed by cell counting, measuring mitochondrial activity (Alamarblue conversion) and [(3) H]-thymidine incorporation. Proliferation of intact tissue slices was assessed by [(3) H]-thymidine incorporation.

KEY RESULTS

Culturing HTSM strips in the presence of collagen I or PDGF for 4 days reduced maximal contractile responses to methacholine or KCl and the expression of contractile proteins. Conversely, collagen I and PDGF increased proliferation of HTSM cells and proliferative responses in tissue slices. PDGF additively increased the proliferation of HTSM cells cultured on collagen I; this additive effect was not observed on contractility, contractile protein expression or proliferation of intact tissue.

CONCLUSION AND IMPLICATIONS

These findings indicate that collagen I and PDGF induce a functionally hypocontractile, proliferative phenotype of human ASM, which may contribute to airway remodelling in asthma.

Glucocorticosteroids and β₂-adrenoceptor agonists synergize to inhibit airway smooth muscle remodeling

Airway remodeling, including increased airway smooth muscle (ASM) mass and contractility, contributes to increased airway narrowing in asthma. Increased ASM mass may be caused by exposure to mitogens, including platelet-derived growth factor (PDGF) and collagen type I, which induce a proliferative, hypocontractile ASM phenotype. In contrast, prolonged exposure to insulin induces a hypercontractile phenotype. Glucocorticosteroids and β₂-adrenoceptor agonists synergize to increase glucocorticosteroid receptor translocation in ASM cells; however, the impact of this synergism on phenotype modulation is unknown. Using bovine tracheal smooth muscle, we investigated the effects of the glucocorticosteroids fluticasone (10 nM), budesonide (30 nM), and dexamethasone (0.1-1 μM) and the combination of low concentrations of fluticasone (3-100 pM) and fenoterol (10 nM) on ASM phenotype switching in response to PDGF (10 ng/ml), collagen type I (50 μg/ml), and insulin (1 μM). All glucocorticosteroids inhibited PDGF- and collagen I-induced proliferation and hypocontractility, with the effects of collagen I being less susceptible to glucocorticosteroid action. At 100-fold lower concentrations, fluticasone (100 pM) synergized with fenoterol to prevent PDGF- and collagen I-induced phenotype switching. This inhibition of ASM phenotype switching was associated with a normalization of the PDGF-induced decrease in the cell cycle inhibitors p21(WAF1/CIP1) and p57(KIP2). At this concentration, fluticasone also prevented the insulin-induced hypercontractile phenotype. At even lower concentrations, fluticasone (3 pM) synergized with fenoterol to inhibit this phenotype switch. Collectively, these findings indicate that glucocorticosteroids and β₂-agonists synergistically inhibit ASM phenotype switching, which may contribute to the increased effectiveness of combined treatment with glucocorticosteroids and β₂-agonists in asthma.

Cytoskeletal drugs prevent posterior capsular opacification in human lens capsule in vitro

BACKGROUND

To determine whether the cytoskeletal drugs H-7 and Latrunculin B (LAT-B) inhibit posterior capsular opacification (PCO) in the cultured human lens capsular bag.

METHODS

Following extracapsular cataract (lens) extraction in human donor eyes, the capsular bag was prepared and cultured by standard techniques. Forty-eight capsular bags were studied, of which 13 were treated with H-7 (50, 100 or 300 μM), 12 with 1% BSS (vehicle of H-7), 11 with LAT-B (2, 5 or 10 μM), and 12 with 0.25% DMSO (vehicle of LAT-B). Forty out of the 48 capsular bags were from paired eyes of 20 donors, with one bag being treated with H-7/LAT-B and the other with BSS/DMSO for each pair, including 20 for the H-7-BSS protocol and 20 for the LAT-B-DMSO protocol. The medium with the cytoskeletal drug/vehicle was replaced every 3-4 days for 4 weeks. PCO was assessed daily using inverted phase-contrast microscopy, and scored on a 4-point scale.

RESULTS

In all cultures with BSS or DMSO, residual lens epithelial cells (LECs) on the anterior capsule migrated to and proliferated on the posterior capsule by 3-7 days, and apparent LEC growth on the posterior capsule with severe capsular wrinkling (PCO Grade 3) was seen by 2-3 weeks. When treated continuously with H-7 or LAT-B, the migration and proliferation of LECs and the capsular wrinkling were inhibited in a dose-dependent manner, with the inhibition being complete (PCO Grade 0) in the 300 μM H-7 (n = 8, p < 0.001) or 10 μM LAT-B culture (n = 3, p = 0.002).

CONCLUSION

H-7 and LAT-B dose-dependently inhibited PCO formation in the cultured human lens capsular bags, suggesting that cytoskeletal drugs might prevent PCO formation after surgery in the human eye.

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.

β-Catenin signaling is required for TGF-β1-induced extracellular matrix production by airway smooth muscle cells

Chronic inflammatory airway diseases like asthma and chronic obstructive pulmonary disease (COPD) are characterized by airway remodeling with altered extracellular matrix (ECM) deposition. Transforming growth factor-β(1) (TGF-β(1)) is upregulated in asthma and COPD and contributes to tissue remodeling in the airways by driving ECM production by structural cells, including airway smooth muscle. In this study, we investigated the activation of β-catenin signaling and its contribution to ECM production by airway smooth muscle cells in response to TGF-β(1). Stimulation of airway smooth muscle cells with TGF-β(1) resulted in a time-dependent increase of total and nonphosphorylated β-catenin protein expression via induction of β-catenin mRNA and inhibition of GSK-3. In addition, the TGF-β(1)-induced β-catenin activated TCF/LEF-dependent gene transcription, as determined by the β-catenin sensitive TOP-flash luciferase reporter assay. Furthermore, TGF-β(1) stimulation increased mRNA expression of collagen Iα1, fibronectin, versican, and PAI-1. Pharmacological inhibition of β-catenin by PKF115-584 or downregulation of β-catenin expression by specific small interfering RNA (siRNA) substantially inhibited TGF-β(1)-induced expression of the ECM genes. Fibronectin protein deposition by airway smooth muscle cells in response to TGF-β(1) was also inhibited by PKF115-584 and β-catenin siRNA. Moreover, transfection of airway smooth muscle cells with a nondegradable β-catenin mutant (S33Y β-catenin) was sufficient for inducing fibronectin protein expression. Collectively, these findings indicate that β-catenin signaling is activated in response to TGF-β(1) in airway smooth muscle cells, which is required and sufficient for the regulation of ECM protein production. Targeting β-catenin-dependent gene transcription may therefore hold promise as a therapeutic intervention in airway remodeling in both asthma and COPD.

The laminin β1-competing peptide YIGSR induces a hypercontractile, hypoproliferative airway smooth muscle phenotype in an animal model of allergic asthma

Background

Fibroproliferative airway remodelling, including increased airway smooth muscle (ASM) mass and contractility, contributes to airway hyperresponsiveness in asthma. In vitro studies have shown that maturation of ASM cells to a (hyper)contractile phenotype is dependent on laminin, which can be inhibited by the laminin-competing peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). The role of laminins in ASM remodelling in chronic asthma in vivo, however, has not yet been established.

Methods

Using an established guinea pig model of allergic asthma, we investigated the effects of topical treatment of the airways with YIGSR on features of airway remodelling induced by repeated allergen challenge, including ASM hyperplasia and hypercontractility, inflammation and fibrosis. Human ASM cells were used to investigate the direct effects of YIGSR on ASM proliferation in vitro.

Results

Topical administration of YIGSR attenuated allergen-induced ASM hyperplasia and pulmonary expression of the proliferative marker proliferating cell nuclear antigen (PCNA). Treatment with YIGSR also increased both the expression of sm-MHC and ASM contractility in saline- and allergen-challenged animals; this suggests that treatment with the laminin-competing peptide YIGSR mimics rather than inhibits laminin function in vivo. In addition, treatment with YIGSR increased allergen-induced fibrosis and submucosal eosinophilia. Immobilized YIGSR concentration-dependently reduced PDGF-induced proliferation of cultured ASM to a similar extent as laminin-coated culture plates. Notably, the effects of both immobilized YIGSR and laminin were antagonized by soluble YIGSR.

Conclusion

These results indicate that the laminin-competing peptide YIGSR promotes a contractile, hypoproliferative ASM phenotype in vivo, an effect that appears to be linked to the microenvironment in which the cells are exposed to the peptide.

Effect of H-7 on secondary cataract after phacoemulsification in the live rabbit eye

PURPOSE

This study is aimed to determine if the serine-threonine kinase inhibitor H-7 inhibits secondary cataract after phacoemulsification in the live rabbit eye.

METHODS

Eighteen rabbits underwent extracapsular lens extraction by phacoemulsification in 1 eye. The eye was treated with intravitreal H-7 (300 or 1,200 μM; n = 6 or 5) or balanced salt solution (BSS) (n = 7) immediately after the surgery and twice weekly for 10 weeks. Each eye received slit lamp biomicroscopy once a week, during which posterior capsule opacification (PCO) was evaluated. The eye was then enucleated and the lens capsule was prepared, fixed, and imaged. PCO was evaluated again on the isolated lens capsule under a phase microscope. Soemmering's ring area (SRA) and the entire lens capsule area were measured from capsule images on a computer and the percentage of SRA (PSRA) in the entire capsule area was calculated. Wet weight of the capsule (WW) was determined on a balance.

RESULTS

No significant difference in PCO was observed in any comparison. No significant differences in SRA, PSRA, and WW were observed between the 300 μM H-7-treated eye and the BSS-treated eye. However, SRA, PSRA, and WW in the 1,200 μM H-7-treated eye were significantly smaller than those in the BSS-treated eye [28.3 ± 16.2 vs. 61.4 ± 8.86 mm(2) (P = 0.001), 33% ± 20% vs. 65% ± 15% (P = 0.01), and 65.6 ± 27.9 vs. 127.0 ±37.3 mg (P = 0.01)].

CONCLUSIONS

Intravitreal H-7 (1,200 μM) significantly inhibits Soemmering's ring formation in the live rabbit eye, suggesting that agents that inhibit the actomyosin system in cells may prevent secondary cataract after phacoemulsification.