The airway epithelium of the mammalian lung develops in the presence of exogenous fluid forces exerted from fetal breathing movements and peristaltic contraction of the surrounding smooth muscle. Defects in the mechanical environment of the thoracic cavity, including those due to congenital diaphragmatic hernia or oligohydramnios, can lead to pulmonary hypoplasia and respiratory failure after birth. Although several major biochemical signals, including fibroblast growth factor 10 (FGF10), have been identified in the control of airway branching morphogenesis, the signaling defects resulting from mechanical perturbations are unclear. Here, we propose to use microfluidic approaches to replicate the mechanical environment of the fetal chest cavity and explore effects from fluid pressure, volume, and flow on development of embryonic mouse lung explants. We will combine these microfluidic approaches with timelapse imaging of lungs explanted from transgenic reporter mice, particle imaging velocimetry analysis of the fluid flow within the airways, and molecular analysis of mechanotransductive signaling in the regulation of the FGF10 signaling axis.
In Specific Aim 1, we will determine how static transmural pressure and luminal fluid volume regulate branching of the airway epithelium, development of the mesenchyme, and expression of FGF10 and its known regulators. We will also quantify mechanical regulation of proliferation, apoptosis, and cell shape changes in the epithelium, mesenchyme, and mesothelium.
In Specific Aim 2, we will mimic the pressure changes that result from fetal breathing movements and quantify the effects of these dynamic changes on morphogenesis, gene expression, and fluid transport within the developing lung. This work will isolate the effects of pressure, volume, and flow and define precisely how each contributes to morphogenesis of the airways and their surrounding mesenchyme at both the cellular and molecular levels. We expect that this model system will open new avenues of investigation for identifying medical treatments to combat pressure-induced diseases such as fetal pulmonary hypoplasia.
Development of the lung requires precisely tuned signaling to ensure breathing of air immediately after birth. Practice fetal breathing movements are necessary for proper lung development, and defects in these mechanical changes lead to pulmonary hypoplasia, the most common cause of neonatal death in the first week after birth. Here we present an innovative model system to replicate the mechanical changes induced within the developing lungs of embryonic mice in order to define how mechanical stresses regulate molecular signaling to affect lung development, which will enable future definition of therapeutic targets to treat fetal lung disease.