β-Catenin Dosage Is a Critical Determinant of Tracheal Basal Cell Fate Determination

Abstract

The purpose of this study was to determine whether β-catenin regulates basal cell fate determination in the mouse trachea. Analysis of TOPGal transgene reporter activity and Wnt/β-catenin pathway gene expression suggested a role for β-catenin in basal cell proliferation and differentiation after naphthalene-mediated Clara-like and ciliated cell depletion. However, these basal cell activities occurred simultaneously, limiting precise determination of the role(s) played by β-catenin. This issue was overcome by analysis of β-catenin signaling in tracheal air-liquid interface cultures. The cultures could be divided into two phases: basal cell proliferation and basal cell differentiation. A role for β-catenin in basal cell proliferation was indicated by activation of the TOPGal transgene on proliferation days 3 to 5 and by transient expression of Myc (alias c-myc). Another peak of TOPGal transgene activity was detected on differentiation days 2 to 10 and was associated with the expression of Axin 2. These results suggest a role for β-catenin in basal to ciliated and basal to Clara-like cell differentiation. Genetic stabilization of β-catenin in basal cells shortened the period of basal cell proliferation but had a minor effect on this process. Persistent β-catenin signaling regulated basal cell fate by driving the generation of ciliated cells and preventing the production of Clara-like cells.

Lung Epithelial Healing: A Modified Seed and Soil Concept

“…On Recovery Day 13, most of the tracheal epithelial surface was normal (19), whereas approximately 20% of the epithelium showed basal and ciliated cell hyperplasia, and Clara-like hypoplasia. We reported similar results for male or female C57Bl/6 mice that were exposed to 275 mg/kg naphthalene (38). These data showed that naphthalene exposure resulted in acute injury that was rapidly resolved.…”

“…We and others have shown that air-liquid-interface (ALI) cultures of primary mouse tracheal epithelial cells can be used to evaluate the cellular and molecular mechanisms regulating FBP function (20,29,38,39,(48)(49)(50). We showed that FBP initiate ALI cultures and that K5/K15/K14 triple-positive basal cells comprise 98% of the ALI culture on Culture Day 2 (38).…”

“…Since each FBP generates only one of several possible cell types, it is not a TSC. The molecular signals that regulate FBP differentiation involve direct and indirect cell-cell interactions that function through b-catenin (38,39). A summary of these results is presented in the Vermont Stem Cell Meeting Report (manuscript in preparation).…”

Stem Cells and Cell Therapies in Lung Biology and Diseases: Conference Report

“…Susan Reynolds then focused on a specific subset of basal epithelial progenitor cells, the facultative basal progenitor (FBP), and roles for b-catenin in regulation of FBP proliferation and differentiation (30). Using tracheal airliquid interface cultures, Reynolds showed that these cultures could be divided into two phases: basal cell proliferation, which results in expansion of the basal cell population, and basal cell differentiation into ciliated or Club-like cells.…”

The Wnt/β-catenin pathway regulates self-renewal of cancer stem-like cells in human gastric cancer

“…The reason for this may be that axin 2 acts as a negative regulator of the Wnt/β-catenin pathway, and a negative feedback loop inhibits the expression of axin 2 during the active course of the pathway. Our explanation has been tested previously: Axin 2 mRNA was not detected, whereas other Wnt/β-catenin target genes were reactivated (36). Rough surface topography increases Wnt/β-catenin target genes but decreases axin 2 expression without affecting β-catenin mRNA levels (37).…”