Genetic analysis of lung alveolar myofibroblasts

The lung is built as a system of branched tubes that terminate in alveoli with a large surface area to enable efficient gas exchange. In humans the development of alveoli occurs predominantly after birth by subdivision of air saccules into smaller compartments through the process of secondary septation. Very low birth weight premature infants are born with immature lungs and are at risk of developing bronchopulmonary dysplasia (BPD), a chronic lung condition characterized by enlarged airspaces as a result of arrested alveolar development and septation failure. Similarly, emphysema, a life-threatening respiratory disease commonly associated with tobacco smoking, involves damage and loss of alveolar walls. The development of therapeutic strategies to regenerate lung alveoli and replace lost or missing septa in patients with emphysema or BPD will require a deep understanding of the cellular and molecular mechanism of septation. Myofibroblasts appear to be involved in septa formation, potentially by generation of contractile forces to compartmentalize the terminal saccules, but the origin, identity and function of this lineage remain unclear. The proposed work aims to address these questions by generation of new and adaptation of existing genetic tools and imaging approaches to label and follow the fate of myofibroblasts at cellular resolution and in three dimensions during postnatal lung development in mice. First, comparative gene expression profiling of mesenchymal subpopulations purified from lung interstitium will identify a myofibroblast- specific marker that will be used to generate novel tools for labeling and tracking of myofibroblasts in the lung. The myofibroblast progenitors and their lineage relationship with smooth muscle cells and fibroblasts will then be elucidated by lineage tracing using conditional Cre-mediated recombination techniques. Finally, the role of myofibroblasts and their contractions in septation will be examined by diphtheria toxin-mediated specific ablation of myofibroblasts and selective inhibition of their contractile activity during alveolar development. This work will provide a detailed cellular level understanding of septa formation and open up opportunities to identify the molecular pathways controlling this process, which I hope will lead in the long run to new avenues for regeneration of alveoli and treatment of BPD, emphysema and other diseases associated with misregulation of myofibroblasts in the lung.