Figure 1. Gli1+ mesenchymal cells promote metaplastic KRT5 differentiation in vivo.

(a,b) Current model of airway progenitors migrating into the alveoli to form endogenous SFTPC+ Type 2 cells or metaplastic KRT5+ basal cells after severe injury, as demonstrated by lineage tracing of Sox2 (Sox2 Lin+) airway progenitors after repetitive bleomycin fibrotic injury. This experiment was repeated four times independently with similar results.

(c,d) Histology of proximally-located Gli1-lineage traced (Gli1 Lin+) mesenchymal cells and SOX2+ airway progenitors during homeostasis (PBS treated) with cell-to-cell distance showing proximity of SOX2+ progenitors and SFTPC+ alveolar progenitors respectively to Gli1 Lin+ cells during homeostasis (n = 4,207 SOX2 cells, n = 11,945 SFTPC cells; each datapoint represents an individual distance measurement with all distance measurements for 3 animals plotted; one-tailed unpaired Student’s t-test). Data are expressed as mean ± SD.

(e,f) Histology and average cell-to-cell distance of Gli1 Lin+ mesenchymal cells in the alveoli relative to alveolar SOX2+ progenitors during fibrotic repair (n = 7,285 SOX2 cells, n = 11,710 SFTPC cells; each datapoint represents an individual distance measurement with all distance measurements for 3 animals plotted; one-tailed unpaired Student’s t-test). Data are expressed as mean ± SD.

(g,h) Histology quantification of areas of KRT5+ pods and percentage of SFTPC+ cells after genetic deletion of Gli1+ cells with bleomycin injury (n = 6 for control, n = 5 for Gli1-deleted; each data point represents one animal; one-tailed unpaired Student’s t-test). Data are expressed as mean ± SD. AW = airway. Scale bars, 100 µm.