Wnt Signaling Dynamics in the Airway: Regeneration, Aging, and Cancer

The proximal airway plays a vital role in host defense via a specialized mucociliary epithelium that arises from airway basal stem cells (ABSCs). The subepithelial intercartilaginous zone (ICZ) of the airway harbors diverse cell types that comprise an intricate ABSC niche. However, our understanding of dynamic interactions between ABSCs and their niches in homeostasis, upon injury, and during aging remains elusive. Using several transgenic mouse models and pharmacologic studies, we found that β-catenin within ABSCs was essential for proliferation post-injury in vivo, mediated by β-catenin phosphorylated at tyrosine 489 (p-β-cateninY489). ABSC-derived Wnt production was dispensable for epithelial proliferation following injury. Instead, the PDGFRα+ lineage in the ICZ niche was activated to transiently secrete Wnt ligand necessary for ABSC proliferation in vivo. Strikingly, an intra-epithelial niche emerged during the differentiation phase of repair; ABSC-derived Wnt ligand secretion drove a switch that facilitated early progenitor differentiation to ciliated cells. We discovered additional niche changes during aging, as glandular-like epithelial invaginations (GLEIs) derived from ABSCs emerged exclusively in the ICZ of aged mice and contributed to repair. Further, ABSC-derived Wnt ligand secretion was necessary for GLEI formation during aging and ectopic, constitutive activation of β-catenin in young mice induced their formation in vivo. We next observed that this signaling network was dysregulated in disease contexts, as nuclear p-β-cateninY489 emerged during human squamous lung cancer (SqLC) progression. This led us to develop an in vitro model of ABSC hyperproliferation concomitant with loss of ciliated cell differentiation by driving Wnt/β-catenin signaling. To identify small molecules that could reverse this, we performed high-throughput drug screening for inhibitors of Wnt/β-catenin signaling. Our studies unveiled Wnt Inhibitor Compound 1 (WIC1), a novel compound that decreased nuclear p-β-cateninY489, reduced ABSC proliferation, and induced ciliated cell differentiation to an extent similar to known Wnt inhibitors with less toxicity. Collectively, our work underscores multiple, spatiotemporally dynamic Wnt-secreting niches that regulate functionally distinct phases of airway regeneration and aging. We also identify a dysregulated Wnt/p-β-cateninY489 signaling network in lung premalignancy and a novel inhibitor that promotes airway homeostasis. Our studies have implications for regenerative medicine, informing future efforts towards promoting airway homeostasis