Alveolar epithelial disintegrity in pulmonary fibrosis

3D pulmospheres serve as a personalized and predictive multicellular model for assessment of antifibrotic drugs

Idiopathic pulmonary fibrosis (IPF) is a fatal progressive fibrotic lung disease characterized by the presence of invasive myofibroblasts in the lung. Currently, there are only two FDA-approved drugs (pirfenidone and nintedanib) for the treatment of IPF. There are no defined criteria to guide specific drug therapy. New methodologies are needed not only to predict personalized drug therapy, but also to screen novel molecules that are on the horizon for treatment of IPF. We have developed a model system that exploits the invasive phenotype of IPF lung tissue. This ex vivo 3D model uses lung tissue from patients to develop pulmospheres. Pulmospheres are 3D spheroids composed of cells derived exclusively from primary lung biopsies and inclusive of lung cell types reflective of those in situ, in the patient. We tested the pulmospheres of 20 subjects with IPF and 9 control subjects to evaluate the responsiveness of individual patients to antifibrotic drugs. Clinical parameters and outcomes were also followed in the same patients. Our results suggest that pulmospheres simulate the microenvironment in the lung and serve as a personalized and predictive model for assessing responsiveness to antifibrotic drugs in patients with IPF.

Epithelial disruption of Gab1 perturbs surfactant homeostasis and predisposes mice to lung injuries

GRB2-associated-binding protein 1 (Gab1) belongs to Gab adaptor family, which integrates multiple signals in response to the epithelial growth factors. Recent genetic studies identified genetic variants of human Gab1 gene as potential risk factors of asthmatic inflammation. However, the functions of Gab1 in lungs remain largely unknown. Alveolar type-II cells (AT-IIs) are responsible for surfactant homeostasis and essentially regulate lung inflammation following various injuries (3). In this study, in vitro knockdown of Gab1 was shown to decrease the surfactant proteins (SPs) levels in AT-IIs. We further examined in vivo Gab1 functions through alveolar epithelium-specific Gab1 knockout mice (Gab1^Δ/Δ). In vivo Gab1 deficiency leads to a decrease in SP synthesis and the appearance of disorganized lamellar bodies. Histological analysis of the lung sections in Gab1^Δ/Δ mice shows no apparent pathological alterations or inflammation. However, Gab1^Δ/Δ mice demonstrate inflammatory responses during the LPS-induced acute lung injury. Similarly, in mice challenged with bleomycin, fibrotic lesions were found to be aggravated in Gab1^Δ/Δ These observations suggest that the abolishment of Gab1 in AT-IIs impairs SP homeostasis, predisposing mice to lung injuries. In addition, we observed that the production of surfactants in AT-IIs overexpressing Gab1 mutants, in which Shp2 phosphatase and PI3K kinase binding sites have been mutated (Gab1^ΔShp2, Gab1^ΔPI3K), has been considerably attenuated. Together, these findings provide the direct evidence about the roles of docking protein Gab1 in lungs, adding to our understanding of acute and interstitial lung diseases caused by the disruption of alveolar SP homeostasis.