(J) Quantitation of Masson's staining of the lungs of WT and Lyn mice in I (original magnification, ×200, ** p<0.05). (I) Masson's trichrome staining of collagen in the lungs of WT and Lyn −/− mice. (H) The fluorescent intensity per micrometer of peribronchial collagen type I in 10 random basement membrane fields in G and presented as the mean ± SEM, * p<0.01. (G) Immunohistochemistry of collagen type I (Col I) in the lungs of WT and Lyn −/− mice exposed to dust mite or PBS. (F) Quantification of PAS positive cells percentage in 10 random airway epithelial cells fields in E (original magnification, ×200, * p<0.01). (E) PAS staining of epithelial goblet cells in the lungs of WT and Lyn −/− mice exposed to dust mite or PBS. (D) MUC5AC protein was also determined in Lyn −/− mice and WT mice using ELISPOT assay. GAPDH was measured for internal controls. (C) MUC5AC mRNA expression was determined in the lungs of Lyn −/− mice and WT mice using RT-PCR. Positive cells were counted in 10 random airway epithelial cells fields and presented as the mean ± SEM. ( B) Percentages of cells staining positive for MUC5AC in A. Arrow shows MUC5AC positive cells in airway in A (the markers similarly indicated below). (A) Immunohistochemistry of MUC5AC in the lungs of WT and Lyn −/− mice exposed to dust mite or PBS (merged images). Collectively, these findings revealed that Lyn regulates TGF-β3 isoform and modulates the development of airway remodeling, which may have therapeutic implications for severe chronic asthma. Finally, Lyn may critically regulate airway remodeling by directly interacting with TGF-β3. Further examination of chronic asthma patients showed that a decreased Lyn correlated with the severity of airway inflammation and mucus hypersecretion. In addition, both recombinant and adenoviral TGF-β3 significantly promoted epithelial-to-mesenchymal transition and intensified collagen I production and MUC5AC expression. Furthermore, TGF-β3 neutralizing Abs not only inhibited the expression of STAT6 and Smad2/3 but also decreased phosphorylation of Smad2 and NF-κB in Lyn(-/-) mouse lungs. Strikingly, a significant increase in TGF-β3 rather than TGF-β1 was observed in Lyn(-/-) mouse lungs compared with lungs in wild-type mice. Using Lyn(-/-) mice, we show that continual exposure (for 8 wk) of house dust mite extracts induced a severe phenotype of chronic airway remodeling, including exacerbated mucus production, collagen deposition, dysregulated cytokine secretion, and elevated inflammation. Despite versatile functions, the role of Lyn in chronic airway remodeling remains undefined. Chronic airway remodeling is a serious consequence of asthma, which is caused by complex but largely unknown mechanisms.
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