Plasticity of airway cell proliferation and gene expression after acute naphthalene injury

Abstract

The goal of this study was to determine the temporal and spatial sequence of events that accompany lung injury and repair after parenteral administration of the Clara cell-specific cytotoxicant, naphthalene. Changes in airway epithelial cells were evaluated by measuring alterations in the expression of markers for differentiated Clara cells (CYPIIF and Clara cell 10-kDa secretory protein, CC10), distal airway/alveolar type II cells (surfactant protein B; SP-B) and for cycling/proliferating cells (cyclin dependent kinase 1;CDK1). Naphthalene-induced Clara cell cytotoxicity resulted in the exfoliation of epithelial cells containing CC10 protein. This was accompanied by a dramatic reduction in the abundance of mRNA for CC10 and CYPIIF. Large numbers of CDK1 mRNA-positive cells were identified in and around bronchioles and terminal bronchioles 48 h after treatment. This cellular proliferation resulted in the population of airways by immature epithelial cells lacking normal levels of CC10 mRNA but overexpressing SP-B mRNA. Seventy-two hours after naphthalene treatment a reduction in CDK1 mRNA-positive cells was noted within bronchioles and terminal bronchioles at all locations, with the exception of airway bifurcations. At airway bifurcations CDK1 mRNA appeared to be more abundant at the 72-h time point than at 48 h. Comparison of these sections with serial sections probed for CC10 mRNA demonstrated a correlation between the expression of CDK1 and CC10 mRNA at bifurcations. Temporal increases in the abundance of CC10 mRNA observed at later time points were largely accounted for by the processive maturation of newly repopulated cells neighboring bifurcations in bronchioles. These studies identify spatially distinct populations of cells that act in concert to repopulate naphthalene-injured airways and support the notion that branch point cells play an important role in the maturation of newly regenerated airway epithelial cells after acute injury.

Basal Cells Are a Multipotent Progenitor Capable of Renewing the Bronchial Epithelium

“…These findings are in contrast to our previous studies showing that renewal of bronchiolar airways is dependent on CE cells. 14,16,18 This disparity between bronchial and bronchiolar airways is consistent with a mechanism in which the activity of distinct progenitor cell pools accounts for regional differences in both lineage specification during lung development and in the cellular composition of tracheobronchial and bronchiolar airways. The tracheobronchial epithelium of the mouse forms a pseudostratified epithelium composed of ciliated, nonciliated secretory (CE, serous, and goblet) and basal cells.…”

“…The bronchial versus bronchiolar regenerative patterns observed within this transitional zone could be distinguished not only by the distribution of regenerative cells but also the kinetics with which regenerating CE cells were observed; basal cellderived CE cells observed in the present study appeared approximately 6 days after naphthalene-induced airway injury, whereas focal regeneration of bronchiolar epithelium re-establishes depleted CE cells as early as 48 hours post naphthalene-exposure. 18 Data from the present study also suggest a complex relationship among progenitor cell populations in bronchial airways involving multiple distinct cell types capable of functioning as a multipotent progenitor cell.…”

“…16 These data also implicate the basal cell as either a secondary progenitor or a multipotent stem cell for this airway location. Interestingly, intrapulmonary bronchi represent a transitional regenerative zone in which both the widespread basal-cell-dependent (present study) and focal NEB-associated regenerative processes 14,18 contribute to epithelial maintenance following naphthalene-induced ablation of the Clara cell progenitor pool. The bronchial versus bronchiolar regenerative patterns observed within this transitional zone could be distinguished not only by the distribution of regenerative cells but also the kinetics with which regenerating CE cells were observed; basal cellderived CE cells observed in the present study appeared approximately 6 days after naphthalene-induced airway injury, whereas focal regeneration of bronchiolar epithelium re-establishes depleted CE cells as early as 48 hours post naphthalene-exposure.…”

“…18 Groups of 4 to 6 mice were recovered for 1, 1.5, 2, 3, 6, or 9 days and injected i.p. with 50 mg/kg body weight of BrdU (Sigma) 2 hours before sacrifice.…”

Loss of GFI1 impairs pulmonary neuroendorine cell proliferation, but the neuroendocrine phenotype has limited impact on post-naphthalene airway repair

“…6,22 The present study used the naphthalene-induced lung injury model to evaluate the functional consequences of impaired NE phenotype upon Clara cell reconstitution. 35 Following naphthalene injury, PNEC undergo proliferation with concomitant increase in NE marker expression. 6 Although the levels of NE cells were lower in Gfi1 À/À mice, the post-naphthalene rate of change between the wt and Gfi1 À/À mice were similar.…”