A change in the number of CCSPpos/SPCpos cells in mouse lung during development, growth, and repair

Abstract

Putative resident stem/progenitor cells have been identified in the bronchoalveolar duct junction (BADJ) of the murine lung. However, the contribution of stem cells expressing both Clara cell secretory protein (CCSP) and pro-surfactant protein C (SP-C) to the repair and maintenance of normal homeostasis is still unclear. In this study, we identified and then quantified CD45(neg)/CCSP(pos)/SP-C(pos) cell numbers in normal and lung-injured mice. Normal lung tissues of fetal, newborn, and adult mice were used to evaluate lung progenitor cells during development and growth. Mice treated with naphthalene were used for the bronchiolar epithelium injury model, and mice treated with bleomycin were used for the alveolar epithelium injury model. These lung tissues were stained with CD45, CCSP, and SP-C antibodies by immunofluorescence. The number of lung progenitor cells was counted as CD45(neg)/CCSP(pos)/SP-C(pos) cells by flow cytometry. CCSP(pos)/SP-C(pos) epithelial cells in the BADJ were identified from E18 to 7 months after birth. The percentage of CD45(neg)/CCSP(pos)/SP-C(pos) cells was relatively stable to 7 months (between 0.3±0.04% and 1.28±0.11%). When lungs were treated with naphthalene, the proliferation of CCSP(pos)/SP-C(pos) cells was observed as patches of double-positive cells and preceded the recovery of bronchioles. In contrast, when lungs were treated with bleomycin, the proliferation of CCSP(pos)/SP-C(pos) cells was observed, but the type II alveolar epithelial cells never recovered to baseline. CCSP(pos)/SP-C(pos) lung cells were stable until 7 months after birth. These cells in the BADJ primarily regenerate bronchiolar epithelial cells and not alveolar epithelial cells.