Repair of naphthalene-induced acute tracheal injury by basal cells depends on ß-catenin.

ABSTRACT

OBJECTIVES: Little is known about the role of Wnt/ß-catenin in postnatal airway homeostasis and basal cell function. This study aimed to investigate the role of Wnt signaling in the self-renewal of basal cells and the involvement of ß-catenin in tracheal repair after naphthalene-induced injury. METHODS: Mice were treated with naphthalene and injected with 4-hydroxytamoxifen. Injury and repair of the tracheal epithelium after naphthalene-mediated secretory cell depletion was assessed by a immunohistochemical study. The involvement of Wnt and ß-catenin signaling in basal cell proliferation was investigated during in vitro expansion. RESULTS: Immunohistochemical analysis of tracheal epithelium in wild-type mice showed a reduction in the number of Clara cell secretory protein (CCSP+) and forkhead box transcription factor (Fox-J1+) cells on days 2 to 5 after naphthalene-induced injury; this cell population was regenerated by day 10. After flush labeling, bromodeoxyuridine-positive (BrdU+) cells and Ki67+ cells were observed in tracheal epithelium on days 2 to 5 but not on days 10 and 21. Confocal microscopy visualizing K5+ and BrdU+ cells showed that Wnt3a promotes proliferation of K5+ cells. Immunohistochemical analysis of K5+ and CCSP+ in tracheal epithelial cells from wild-type littermate and K5-Cre-mediated ß-catenin knock-out mice showed that on day 3, the number of CCSP+ cells was decreased in all mice. On day 10, CCSP+ cells were present in wild-type littermate mice but absent in conditional knock-out mice. CONCLUSIONS: Basal cells serve as stem cells in the tracheal epithelium, regenerating and maintaining tracheal epithelial cells in a mouse model of tracheal injury. ß-Catenin is required for proliferation and self-renewal of tracheal epithelial cells.