Endogenous distal airway progenitor cells, lung mechanics, and disproportionate lobar growth following long-term postpneumonectomy in mice

Using a model of postpneumonectomy (PNY) compensatory lung growth in mice, we previously observed an increase in numbers of a putative endogenous distal airway progenitor cell population (CCSPpos/pro-SPCpos cells located at bronchoalveolar duct junctions [BADJs]), at 3, 7, and 14 days after pneumonectomy, returning to baseline at 28 days post-PNY. As the origin of these cells is poorly understood, we evaluated whether bone marrow cells contributed to the pool of these or other cells during prolonged post-PNY lung regrowth. Na?̈ve and sexmismatched chimeric mice underwent left PNY and were evaluated at 1, 2, and 3 months for numbers of BADJ CCSPpos/pro-SPCpos cells and presence of donor-derived marrow cells engrafted as airway or alveolar epithelium. Nonchimeric mice were also examined at 12 months after PNY for numbers of BADJ CCSPpos/pro-SPCpos cells. Notably, the right accessory lobe (RAL) continued to grow disproportionately over 12 months, a novel finding not previously described. Assessment of lung mechanics demonstrated an increase in lung stiffness following PNY, which significantly diminished over 1 year, but remained elevated relative to 1-year-old na?̈ve controls. However, the number of CCSPpos/pro-SPCpos BADJ cells 1-month following PNY was equivalent to that found in na?̈ve controls even after 12 months of continued RAL growth. Notably, no donor bone marrow-derived cells engrafted as airway or alveolar epithelial cells, including those at the BADJ, up to 3 months after PNY. These studies suggest that lung epithelial cells, including CCSPpos/pro-SPCpos cells, are not replenished from marrow-derived cells during post-PNY lung growth in mice.