Naphthalene as a model to study repair processes of the murine tracheal epithelium in vivo

Abstract

The naphthalene model of damage and repair of the small intrapulmonary airway epithelium is well established. We aimed to determine if naphthalene can also be used to study repair processes in murine tracheal epithelium. Explanted mouse tracheae were kept in Hepes-Ringer solution at 37°C and were incubated with naphthalene (200µg/ml) for 2h. In mice, a dose of 300mg/kg naphthalene or vehicle was injected intraperitoneally. Tracheae were explanted and fixed at 12h, 24h, 48h, 60h, 72h, 4d, 5d, 6d and 15d and examined using semi-thin sections, scanning electron microscopy, immunohistochemistry, real-time RT-PCR and high speed video microscopy. Lungs were obtained as positive control. Ex vivo application of naphthalene resulted in detachment of secretory cells from the basement membrane leaving islets of ciliated cells. In vivo after 12h, the detachment of few secretory as well as ciliated cells was observed. After 24h, the epithelium was destroyed with the majority of secretory and ciliated cells being lost. After 48h, no ciliated and secretory cells were found. However, basal cells still covered the basement membrane. Cell proliferation in the remaining cells increased from less than 1% to >20% and remained high until 4d. After 60h a continuous epithelium with short cilia was observed. Ciliary beat frequency was nearly normal at 4d but cilia-driven transport was impaired. Transcripts for CK5 (expressed in basal cells) remained constant throughout. In contrast, transcripts for CC10 (expressed in secretory cells) were significantly increased at 60h, 72h, 4d and 6d and returned to baseline at 15d. However, CC10-immunoreactivity was detectable only from day 5 on. After 15d, repair of the epithelium was completed and cilia reached their initial length.