Mechanistic Insights into the Contribution of Epithelial Damage to Airway Remodeling. Novel Therapeutic Targets for Asthma

Abstract

It has been suggested that an inherent airway epithelial repair defect is the root cause of airway remodeling in asthma. However, the relationship between airway epithelial injury and repair, airway remodeling, and airway hyperresponsiveness (AHR) has not been directly examined. We investigated the contribution of epithelial damage and repair to the development of airway remodeling and AHR using a validated naphthalene (NA)-induced murine model of airway injury. In addition, we examined the endogenous versus exogenous role of the epithelial repair peptide trefoil factor 2 (TFF2) in disease pathogenesis. A single dose of NA (200 mg/kg in 10 ml/kg body weight corn oil [CO] vehicle, intraperitoneally) was administered to mice. Control mice were treated with CO (10 ml/kg body weight, intraperitoneally). At 12, 24, 48, and 72 hours after NA or CO injection, AHR and various measures of airway remodeling were examined by invasive plethysmography and morphometric analyses, respectively. TFF2-deficient mice and intranasal treatment were used to examine the role of the epithelial repair peptide. NA treatment induced denudation and apoptosis of airway epithelial cells, goblet cell metaplasia, elevated AHR, and increased levels of endogenous TFF2. Airway epithelial changes peaked at 12 hours after NA treatment, whereas airway remodeling changes were observed from 48 hours. TFF2 was protective against epithelial damage and induced remodeling and was found to mediate organ protection via a platelet-derived growth factor-associated mechanism. Our findings directly demonstrate the contribution of epithelial damage to airway remodeling and AHR and suggest that preventing airway epithelial damage and promoting epithelial repair may have therapeutic implications for asthma treatment.

Characterization of a novel model incorporating airway epithelial damage and related fibrosis to the pathogenesis of asthma

“…There was a significant increase in AHR in OVA-sensitized/challenged mice compared with that measured from saline-sensitized/challenged controls (Po0.05 vs saline group). In contrast, there was no significant difference in airway reactivity between NA-treated and CO-treated mice, consistent with previous studies 23 and reflecting the fact that NA-treated mice undergo reparative healing by 3 days post injury, which is not associated with increased AHR. In comparison, only OVA þ NA-treated mice exhibited significantly enhanced AHR compared with that measured from OVA-sensitized/challenged (Po0.05 vs OVA group) and NA-treated mice (Po0.001 vs NA group; Figure 5).…”

“…Characterization of a novel model of asthma SG Royce et al repair peptide, trefoil factor 2, 23,25 it can be suggested that epithelial damage alone can lead to subepithelial airway fibrosis (as demonstrated by the increased NA-induced subepithelial collagen thickness and total lung collagen concentration), similar to processes occurring in human asthma where repeated episodes of epithelial injury lead to prolonged activation of the epithelial mesenchymal trophic unit. 26,27 Previous studies have shown that epithelial damage results in epithelial cells releasing pro-inflammatory factors such as IL-1 and tumor necrosis factor-a.…”

“…23,25 Despite its significance, epithelial damage has been poorly addressed in current experimental models used to study the pathogenesis of asthma, and also by currently available therapies for asthma. Thus, establishing experimental models of AAD that better reflect the pathogenesis of human asthma and incorporate the contribution of epithelial damage with other features of AWR and AHR is warranted.…”

“…Immunohistochemistry Paraffin-embedded lung sections were immunohistochemically stained for annexin V (a marker of apoptosis) 23 and TGF-b1 23 as described before: utilizing polyclonal antibodies to annexin V (S0961; 1:100 dilution; Epitomics, Burlingame, CA, USA) and TGF-b1 (sc146; 1:800 dilution; Santa Cruz Biotechnology, Santa Cruz, CA, USA), respectively. Detection of antibody staining was completed using the Dako EnVision anti-rabbit kit (Dako, Carpinteria, CA, USA) and 3,3 0 -diaminobenzidine (Sigma-Aldrich), where sections were counterstained with hematoxylin.…”

“…The second largest lung lobe from each mouse was processed as described before 11,23 for the measurement of hydroxyproline content, which was determined from a standard curve of purified trans-4-hydroxy-L-proline (Sigma-Aldrich). Hydroxyproline values were multiplied by a factor of 6.94 (based on hydroxyproline representing B14.4% of the amino-acid composition of collagen in most mammalian Characterization of a novel model of asthma SG Royce et al tissues), 24 to extrapolate total collagen content, which in turn was divided by the dry weight of each corresponding tissue to yield percent collagen concentration.…”