Transgenic porcine model reveals two roles for LGR5 during lung development and homeostasis

Stem cells play a pivotal role in lung homeostasis, repair, and regeneration, and yet the mechanisms underlying these processes are unknown. Furthermore, species-specific differences make certain findings from mice, a widely used animal model, difficult to translate into humans. In this work, we address these limitations by using a transgenic pig model and identify two populations of LGR5+ cells in the lung. Interestingly, we found similar populations in human lungs but not in mice. Using RNA sequencing, 3D imaging, organoid models, and differentiation assays, we determine that in the fetal lung, epithelial LGR5 expression is transient in a subpopulation of developing lung bud tips, co-expresses bud tip markers SOX9 and SFTPC. While epithelial LGR5 expression is absent from postnatal lung, it is reactivated in bronchioalveolar organoids derived from basal airway cells. A separate population of LGR5+ cells is mesenchymal, surrounds developing and mature airways, lies adjacent to airway basal cells, is closely associated with nerve fibers, and acts as a multipotent progenitor cell capable of supporting the airway basal cell niche. Transcriptionally, mesenchymal LGR5+ cells are analogous to stromal stem cell populations and express unique patterns of WNT and TGFbeta signaling pathway genes. These results point to two roles for LGR5 in orchestrating stem and progenitor cell dynamics and provide a physiologically relevant model for further studies on the role of these populations in repair and regeneration.