IKKβ Activation in the Fetal Lung Mesenchyme Alters Lung Vascular Development but Not Airway Morphogenesis.

In the immature lung, inflammation and injury disrupt the epithelial-mesenchymal interactions required for normal development. Innate immune signaling and NF-κB activation disrupt the normal expression of multiple mesenchymal genes that play a key role in airway branching and alveolar formation. To test the role of the NF-κB pathway specifically in lung mesenchyme, we utilized the mesenchymal Twist2-Cre to drive expression of a constitutively active inhibitor of NF-κB kinase subunit β (IKKβca) mutant in developing mice. Embryonic Twist2-IKKβca mice were generated in expected numbers and appeared grossly normal. Airway branching also appeared normal in Twist2-IKKβca embryos, with airway morphometry, elastin staining, and saccular branching similar to those in control littermates. While Twist2-IKKβca lungs did not contain increased levels of Il1b, we did measure an increased expression of the chemokine-encoding gene Ccl2. Twist2-IKKβca lungs had increased staining for the vascular marker platelet endothelial cell adhesion molecule 1. In addition, type I alveolar epithelial differentiation appeared to be diminished in Twist2-IKKβca lungs. The normal airway branching and lack of Il1b expression may have been due to the inability of the Twist2-IKKβca transgene to induce inflammasome activity. While Twist2-IKKβca lungs had an increased number of macrophages, inflammasome expression remained restricted to macrophages without evidence of spontaneous inflammasome activity. These results emphasize the importance of cellular niche in considering how inflammatory signaling influences fetal lung development.