Markers of extracellular matrix and epithelial cell maturation after fetal tracheal occlusion in newborn rabbits with lung hypoplasia induced by diaphragmatic hernia.

Background and aims: Tracheal occlusion (TO), a prenatal treatment promoting lung growth, improves defective elastogenesis in congenital diaphragmatic hernia (CDH). Because the transforming growth factor-ß (TGF-ß) regulates extracellular matrix (ECM) during late lung development, we hypothesized that the effects of TO on ECM would be mediated by the TGF-ß/Smad2 pathway. We therefore investigated the effects of TO on lung connective tissue composition and function, and on TGF-ß signaling expression in an experimental model of CDH. Methods: Rabbit fetuses were randomized twice during gestation: at day 23 (pseudoglandular phase), for a DH or a sham thoracotomy, and five days later (canalicular phase) for a tracheal ligation or a sham operation. Non-operated littermates served as controls. At term (day 31), live fetuses underwent an evaluation of global and peripheral lung mechanics, followed by pulmonary tissue sampling for morphometric and biological studies. Results: TO normalized the lung to body weight ratio and morphometry of airways in DH fetuses compared to controls. TO did not improve dynamic resistance and compliance in DH fetuses, and even resulted in worsening of lung function in sham DH fetuses. TO had no effect on peripheral lung mechanics assessed by forced oscillation technique. In DH fetuses, gene expressions for tropoelastin and lysyl-oxidase were downregulated (by 50%) and restored by TO. Besides, TO stimulates gene expressions for fibulin-5, types I and III procollagens, integrins (respectively by 700%, 180% and 200%), and the density of elastic fibers was increased. These effects on ECM composition co-occurred with an increase in gene and protein expressions for TGF-ß, and a rise of the phosphorylation of Smad2 (by 100%). Conclusions: In surgically induced CDH, sustained TO restores elastogenesis, but also enhances the synthesis of many ECM components, coinciding with an activation of the TGF-ß/Smad2 signaling pathway. These biological effects, together with decreased level of surfactant after TO, may contribute to the impairment of neonatal lung mechanics.