Lung-specific TGFβ overexpression increases airway fibrosis and airway contractility in transgenic mice.

Transforming growth factor β1 (TGFβ1) is a pleiotropic cytokine implicated in the pathophysiology of chronic lung diseases such as asthma and chronic obstructive pulmonary disease. Epithelial TGFβ1 is released in response to injury, inflammatory stimuli, and during bronchoconstriction to induce fibrosis. We hypothesized that elevated expression of endogenous TGFβ1, localized to the lung, would elicit autocrine effects to alter airway responsiveness. We utilized a transgenic mouse model of doxycycline (Dox)-induced, lung-specific overexpression of active TGFβ1 by giving Dox (0.25 mg/mL in drinking water, 8 wk), or normal water as a control. Comparing Dox with control groups, levels of TGFβ1 were ∼30-fold higher in bronchoalveolar lavage fluid (BALF), but not in serum, as measured by ELISA. BALF cells, predominantly macrophages, were ∼3.5-fold higher, with no evidence of tissue inflammation in hematoxylin and eosin (H&E)-stained sections from Dox mice. Higher collagen deposition was evident around the airways in Masson's trichrome-stained sections [subepithelial thickness (µm): control 10.4 ± 10.9, = 9; Dox 25.8 ± 1.5, = 13, < 0.0001]. TGFβ1 overexpression increased baseline airway resistance and induced airway hyperresponsiveness (AHR) to methacholine (MCh) in vivo, as measured using in vivo plethysmography. Comparing precision-cut lung slices (PCLS) from separate Dox-treated and control mice, maximum contraction of intrapulmonary airways to MCh was increased ex vivo. Overall, elevated lung TGFβ1 levels resulted in localized airway fibrosis associated with increased airway contraction to MCh. These autocrine effects of endogenous TGFβ1 implicate its potential contribution to AHR, suggesting that targeting TGFβ1 may provide a novel approach to oppose excessive airway contraction in chronic lung diseases. TGFβ upregulation is common in respiratory diseases. Here, the authors have utilized for the first time a mouse model of lung-specific overexpression of active TGFβ to demonstrate the dual role of TGFβ1 in structural remodeling and dysregulation of airway contractility. Given these pathologies are common to asthma and COPD, this model provides a unique opportunity to identify essential novel therapeutics for the treatment of chronic lung diseases.