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Background Increased airway smooth muscle mass is a prominent feature of asthmatic airway remodeling. Airway smooth muscle hyperplasia occurs in rodent models of experimental asthma, but the relevance of such finding to spontaneously occurring disease in large mammals is unknown. Objective We examined horses with heaves, a naturally occurring equine asthma related to sensitization and exposure to moldy hay. We hypothesized that airway remodeling occurs in heaves and shares disease mechanisms with asthma. Methods We quantified the airway smooth muscle mass and the numbers of proliferating and apoptotic airway smooth muscle cells in 5 horses with heaves and 5 control horses using morphometric techniques. Cell proliferation was detected in tissue sections by immunostaining for proliferating cell nuclear antigen, and apoptotic cells were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling of fragmented DNA. Both signals were colocalized with smooth muscle specific α-actin. Results Horses with heaves had a significant increase in the amount of smooth muscle in the airways (nearly triple that of the controls) associated with increased myocyte proliferation (7-fold proliferating cell nuclear antigen–positive airway myocytes) and apoptosis (6-fold). Conclusion Heaves involves airway smooth muscle growth associated with myocyte hyperplasia, which may contribute to the growth, and increased myocyte apoptosis that may reflect a compensatory mechanism serving to limit the abnormal smooth muscle growth. Clinical implications Airway smooth muscle remodeling in heaves may be involved in the mechanism of airway hyperresponsiveness and chronic lung function impairment in a way comparable to human asthma.

Airway remodeling is a major change responsible for irreversible asthmatic airflow restriction. The Th-2 cytokines-dominant eosinophilic inflammatory mechanism cannot fully explain the progressive subepithelial fibrosis and structural changes in the extracellular matrix (ECM). Matrix metalloproteinases (MMPs) are the key enzymes responsible for ECM degradation. MMPs are normally produced and secreted under the tight regulation of, at least, 3 different levels: the gene transcriptional level, the activation of the latent form of enzyme, and the inactivation by specific endogenous inhibitors. In asthmatic condition, as shown by the large amount of accumulated evidence in this review, MMP-9 is the most relevant among the 23 kinds of human MMPs at present detected. Although the mechanism is still under investigation and not accurately known, the imbalance between MMP-9 and tissue inhibitor of metalloproteinase-1 is considered a major theory to explain the progression of asthmatic airway remodeling. Various inflammatory cytokines including TGF beta and growth factors play a pivotal role in MMP-9 production and secretion. This review mainly focuses upon the pivotal role of MMP-9 in airway remodeling, and also upon major cellular source of MMP-9 in asthma such as eosinophils, neutrophils, epithelial cells and alveolar macrophages. This review also refers to the partial contribution of nitric oxide to MMP-9 in asthma.

Airway hyperresponsiveness and remodeling are defining features of asthma. We hypothesized that impaired superoxide dismutase (SOD) antioxidant defense is a primary event in the pathophysiology of hyperresponsiveness and remodeling that induces apoptosis and shedding of airway epithelial cells. Mechanisms leading to apoptosis were studied in vivo and in vitro. Asthmatic lungs had increased apoptotic epithelial cells compared to controls as determined by terminal dUTP nick-end labeling-positive cells. Apoptosis was confirmed by the finding that caspase-9 and -3 and poly (ADP-ribose) polymerase were cleaved. On the basis that SOD inactivation triggers cell death and low SOD levels occur in asthma, we tested whether SOD inactivation plays a role in airway epithelial cell death. SOD inhibition increased cell death and cleavage/activation of caspases in bronchial epithelial cells in vitro. Furthermore, oxidation and nitration of MnSOD were identified in the asthmatic airway, correlating with physiological parameters of asthma severity. These findings link oxidative and nitrative stress to loss of SOD activity and downstream events that typify asthma, including apoptosis and shedding of the airway epithelium and hyperresponsiveness.

Airway remodeling is a main pathological characteristic of asthma, and strongly associated with migration and proliferation of airway smooth muscle cells. E-prostanoid (EP) receptor can regulate airway remodeling. This study established a rat model of asthma and evaluated EP changes in airway smooth muscle cells under the asthmatic state so as to provide theoretical evidence for developing EP drugs to treat airway remodeling in asthma. A total of 20 clean Sprague-Dawley rats were randomly assigned to asthma group and control group. 28 days later, they were sacrificed for histological examination. Airway smooth muscle cells were isolated, cultured and measured using quantitative fluorescent PCR. Histopathological examination revealed that rat models of asthma were in accordance with the manifestations of asthmatic airway remodeling. After reverse transcription, real-time quantitative fluorescent PCR was performed using miRNA Q-PCR diagnostic kit. GAPDH was considered the internal reference. Relative expressions of E-prostanoid 1–4 (EP1–4) (2-△△Ct) in the control and asthma groups were respectively as follows: EP1: 4.35±0.18, 6.55±1.21; EP2: 3.64±0.12, 1.35±1.06; EP3: 4.59±1.14, 5.89±1.74; EP4: 2.89±1.85, 1.69±0.44. EP2/4 significantly decreased, but EP1 significantly increased in the asthma group (P < 0.01). These results suggested that the reduced EP2/4 and increased EP1 expressions in airway smooth muscle cells of rat models of asthma were probably important factors for asthmatic airway remodeling.

Asthma continues to challenge physicians and scientists. After declining for years, the prevalence, morbidity and mortality of asthma have increased over the last two decades. In keeping with the importance of this “epidemic,” significant attention has been focused on the pathogenesis of this disorder. These investigations have revised our concepts of the abnormalities that underlie the asthmatic diathesis and our understanding of crucial aspects of its natural history. They have also provided exciting insights into the cellular and molecular events that regulate airway inflammation and inflammation in other tissues. It is clear from these studies that a genetic predisposition plus an appropriate life event(s) conspire to generate the asthmatic diathesis and that often early life (and possibly in utero) events play a crucial role in disease pathogenesis. It is also clear that inflammation is the cornerstone of asthma and that, in the majority of cases, Th2 dominated tissue responses are responsible for this disorder. Recently, the non-inflammatory structural alterations in the asthmatic airway have received renewed attention and the roles these structural changes may play in generating symptomatology and altering natural history have begun to be elucidated. The first Perspective in this series, by Gern, Lemanske and Busse, deals with the early life origins of the asthmatic diathesis, and the second article, by Oettgen and Geha, highlights recent insights into the importance of IgE and new anti-IgE-based therapies in atopy and the asthmatic response. The third article by Ray and Cohn highlights the large body of data that has now been generated regarding the cellular and molecular events that regulate and the effector functions of Th2 inflammatory responses, and the fourth article by Lukacs and colleagues describes the organized chemokine network that is involved in the generation of airway inflammation. The last article in the series by Elias et al. deals with the structural changes and the concept of asthmatic airway remodeling, highlighting both our level of knowledge and the challenges for the future. When the information presented in this series is looked at in composite, one can easily be impressed by the depth and breadth of our knowledge. It is also easy to see how these studies will serve as a springboard for future investigations and the foundation upon which new and powerful therapeutic interventions for asthma can be developed. It is important to keep in mind, however, that the relationship between atopy and asthma and the cause of the asthmatic epidemic are still poorly understood despite significant investigation. Perspective is also provided by the fact that William Osler stated in 1892 that asthma “in many cases is a special form of inflammation of the smaller bronchioles.” It has taken us almost a century to fully embrace this concept and begin to carefully dissect this airway response. Although we have made impressive progress, we still have a long way to go.

Rationale Genistein is a dietary isoflavone and a broad-spectrum tyrosine kinase inhibitor contained in soy products. An epidemiologic study of asthma revealed that subjects with high consumption of dietary soy isoflavones had better lung function than those with lower intake. In a guinea pig model of allergic asthma, genistein reduced methacholine-induced bronchoconstriction. To explore the mechanisms underlying these observations, we tested genistein9s ability to block lung myofibroblast differentiation, a key phenotypic change in asthmatic airway remodeling. Methods Human fetal lung fibroblasts (IMR-90) were grown to subconfluence in DMEM containing 10% FBS, serum-deprived for 24 hours, and treated with genistein (10 μM) for an additional 24 hurs. Cells were then stimulated with TGF-b1 (2 ng/mL) for 24 hours, and a-smooth muscle actin (aSMA) expression, a marker of the myofibroblast phenotype, was assessed by both immunoblot and immunofluorescence microscopy. To determine the intracellular mechanism of inhibitory actions by genistein, we also assessed phosphorylation of Smad2 by immunoblot in the presence and absence of genistein after 30-minute stimulation with TGF-b1. Results Treatment with genistein resulted in 54.9 ± 17.1% reduction in TGF-b1 induced expression of aSMA. Immunofluorescence microscopy revealed a decrease in aSMA staining intensity and stress fiber formation in genistein-treated cells. In addition, Smad2 phosphorylation was inhibited by 71.1 ± 16.7% in genistein-treated cells. Conclusions These results demonstrate that genistein interferes with TGF-b1-stimulated myofibroblast differentiation and suggest that tyrosine kinase inhibition may have a role in modulation of asthmatic airway remodeling. Funded by NIH RO1HL072891, T32HL076139, The CHEST Foundation-GSK Clinical Research Trainee Award.

Background : The pathological features in asthmatic airway remodeling are diverse. The aim of this study was to examine the degree of airway vascularity in relation to the other remodeling parameters in asthmatics. Methods : Bronchial biopsies were done in 34 asthmatic patients, and 6control subjects. The basement membrane thickness and the subepithelial thickness were measured in the hematoxylin-eosin stained tissue, and the degree of vascularity was measured using type IV collagen immunostaining. Results : 1) Compared to the control subjects, the asthmatics showed a significant increase in the basement membrane thickness (6.92±2.01μm vs 9.67±2.84μm, p

Background Airway remodeling is a proposed mechanism that underlies the persistent loss of lung function associated with childhood asthma. Previous studies have demonstrated that human lung fibroblasts (HLFs) co-cultured with primary human bronchial epithelial cells (BECs) from asthmatic children exhibit greater expression of extracellular matrix (ECM) components compared to co-culture with BECs derived from healthy children. Myofibroblasts represent a population of differentiated fibroblasts that have greater synthetic activity. We hypothesized co-culture with asthmatic BECs would lead to greater fibroblast to myofibroblast transition (FMT) compared to co-culture with healthy BECs. Methods BECs were obtained from well-characterized asthmatic and healthy children and were proliferated and differentiated at an air-liquid interface (ALI). BEC-ALI cultures were co-cultured with HLFs for 96 hours. RT-PCR was performed in HLFs for alpha smooth muscle actin (α-SMA) and flow cytometry was used to assay for α-SMA antibody labeling of HLFs. RT-PCR was also preformed for the expression of tropomyosin-I as an additional marker of myofibroblast phenotype. In separate experiments, we investigated the role of TGFβ2 in BEC-HLF co-cultures using monoclonal antibody inhibition. Results Expression of α-SMA by HLFs alone was greater than by HLFs co-cultured with healthy BECs, but not different than α-SMA expression by HLFs co-cultured with asthmatic BECs. Flow cytometry also revealed significantly less α-SMA expression by healthy co-co-cultures compared to asthmatic co-cultures or HLF alone. Monoclonal antibody inhibition of TGFβ2 led to similar expression of α-SMA between healthy and asthmatic BEC-HLF co-cultures. Expression of topomyosin-I was also significantly increased in HLF co-cultured with asthmatic BECs compared to healthy BEC-HLF co-cultures or HLF cultured alone. Conclusion These findings suggest dysregulation of FMT in HLF co-cultured with asthmatic as compared to healthy BECs. Our results suggest TGFβ2 may be involved in the differential regulation of FMT by asthmatic BECs. These findings further illustrate the importance of BEC-HLF cross-talk in asthmatic airway remodeling.