Receptor agonist of NFκB signaling ligand directs lung epithelial cell expansion through RANK signaling

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally, with progressive emphysema driven by repeated epithelial damage and impaired repair. Recently, we found that secretion of cytokine receptor agonist of nuclear factor κB signaling ligand (RANKL) is higher from lung fibroblasts of patients with COPD compared with control and that RANKL reduces lung epithelial cell death. However, the underlying mechanisms, their conservation across species, and the specific epithelial cell types involved remain unclear. To investigate how RANKL affects lung epithelial cells, we used in vitro and in vivo models. Primary lung organoids from human and mouse epithelial cells assessed progenitor activation and expansion. Furthermore, we used a murine model of elastase-induced alveolar injury to examine which epithelial cell types were affected by RANKL in vivo and whether this was altered upon lung damage. RANKL supplementation increased alveolar organoid formation in both murine and human cultures compared with vehicle-treated controls. In elastase-treated mice, RANKL administration during the early repair phase enhanced the proportion of EpCAM⁺ epithelial cells and increased transitional epithelial cell states characterized by keratin 8 (Krt8) and major histocompatibility complex II (MHCII) expression following elastase-induced injury. RANKL signaling promoted epithelial regeneration by expanding alveolar progenitor and transitional epithelial cell populations, with consistent effects across human and murine models. These findings identify RANKL as a novel modulator of epithelial repair and suggest that controlled activation of this pathway could enhance lung regeneration in diseases such as COPD.NEW & NOTEWORTHY This study describes for the first time a role for bone cytokine RANKL in lung epithelial repair following lung damage. Using both murine and human models, we describe how RANKL-mediated signaling promotes epithelial expansion by acting on epithelial transitional cell states. For diseases with substantial lung damage, modulating RANKL signaling during the early repair phase following lung injury could represent a strategy to enhance epithelial regeneration.