Novel Porcine Model Reveals Two Distinct LGR5 Cell Types during Lung Development and Homeostasis

Cells expressing leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) play a pivotal role in homeostasis, repair, and regeneration in multiple organs, including skin and gastrointestinal tract, but little is known about their role in the lung. Findings from mice, a widely used animal model, suggest that lung LGR5 expression differs from that of humans. In this work, using a new transgenic pig model, we identify two main populations of LGR5⁺ cells in the lung that are conserved in human but not mouse lungs. Using RNA sequencing, three-dimensional imaging, and organoid models, we determine that in the fetal lung, epithelial LGR5 expression is transient in a subpopulation of SOX9⁺/ETV5⁺/SFTPC⁺ progenitor lung tip cells. In contrast, epithelial LGR5 expression is absent from postnatal lung but is reactivated in bronchioalveolar organoids derived from basal airway cells. We also describe a separate population of mesenchymal LGR5⁺ cells that surrounds developing and mature airways, lies adjacent to airway basal cells, and is closely associated with nerve fibers. Transcriptionally, mesenchymal LGR5⁺ cells include a subset of peribronchial fibroblasts that express unique patterns of <i>SHH</i>, <i>FGF</i>, <i>WNT</i>, and <i>TGF-β</i> signaling pathway genes. These results support distinct roles for LGR5⁺ cells in the lung and describe a physiologically relevant animal model for further studies on the function of these cells in repair and regeneration.