Dissecting the Role of Mechanical Forces in the Branching Morphogenesis of the Mouse Bronchial Tree

About This Grant

PROJECT SUMMARY Lung development requires a tight interplay between the pulmonary epithelium and the surrounding mechanical environment, including the airway smooth muscle (ASM) and the thoracic cavity. Defects in the mechanical environment of the embryonic lung, such as congenital diaphragmatic hernia (CDH), are associated with pulmonary hypoplasia leading to significant mortality and morbidity. Therefore, it is necessary to investigate the role of the mechanics on lung development. The central objective of this proposal is to characterize the effects of the mechanical environment on the spatial and temporal patterns of branching morphogenesis in the lung. Mechanical forces have been thought to play a role in branching morphogenesis of the embryonic lung for decades, but a detailed understanding has been limited by the experimental challenge of simultaneously manipulating and observing lung development in a physiologically relevant setting: studies in vivo are limited by the inaccessibility of the lung in the embryo, while those in culture restrict lung explant growth to a non- physiological, flat surface. Nonetheless, recent innovations in microfluidic approaches support physiologically relevant lung development ex vivo and enable tracking of branching morphogenesis under various applied pressures. Studies using these approaches have revealed a tight coupling between transpulmonary pressure, ASM contractions, and the rate of lung branching. The overall hypothesis of this proposal is that branching in the lung is driven by a pressure-dependent ‘clock’ of ASM contractions. To test this hypothesis, I will combine a mouse model of CDH, whole-mount immunostaining, quantitative imaging and analysis, and a microfluidic culture model to track the development of lungs under various mechanical perturbations. First, I will determine whether the mechanical stimulus of ASM contraction is sufficient for inducing lung branching events. Second, I will define the progression of lung development in a mouse model of CDH and assess the role of local changes in pressure on branching rates in lungs cultured ex vivo. Collectively, the findings of this proposal will provide detailed insight into the function of ASM contractions and compressive forces in a physiologically relevant setting amenable to fine perturbations. These results will have a broad impact on understanding the physical forces that sculpt lung development and will provide original insights that will help guide strategies for treatment of prenatal lung hypoplasia. The activities proposed here will enhance my ability to conduct experiments and data analysis and to communicate research to a broader audience. These activities will also offer opportunities to teach and mentor emerging scientists. I will leverage the analytic skills acquired during my undergraduate training and expand my aptitude in bioengineering and mechanobiology by making use of the world-class expertise and extensive resources that my supervisor (Dr. Celeste Nelson) and Princeton University have to offer. These activities will help me become an independent researcher and will provide a robust foundation for establishing my own research direction investigating the determinants of multiscale coordination in tissue morphogenesis.