Fig. 4: Activation of TRβ constrains the metaplasia and hyperplasia of AT2 cells in fibrosis.

a The uniform manifold approximation and projection (UMAP) plot displays cells colored by cell type identity in scRNA-seq. b UMAP visualization of Thrb regulon activity. c GO enrichment analysis of GC-1-regulated genes in differential expression between BLM and PBS groups in mouse lung bulk RNA-seq (n = 3). d Immunochemistry staining for SFTPC and KRT8 in lung sections of mice, same as Fig. 3. Arrows indicate normal AT2 cells, and arrowheads indicate elongated or hypertrophic AT2 cells. Scale bar, 100 μm. e Protein analysis in lung homogenates for M-AT2 cell marker CLDN4. f, g Workflow, representative IF images, and quantification of Ki67-positive AT2 cells in lineage-labeled mice lungs with or without GC-1 after BLM challenge. Arrowheads indicate basaloid cells from lineage-labeled cells (indicated by arrows) (n = 3). Scale bar, 50 μm. h Representative pictures and quantification of EdU assay (n = 12, images from four experiments) in A549. GC-1 15 nM for 36 h. Scale bar, 100 μm. i–l AT2 cells isolated from different groups were used to stimulate normal primary fibroblasts for 48 h. The activation of lung fibroblasts was assayed by the 3D-collagen gel contraction (j, n = 3), expression of a-SMA (k, Scale bar, 20 μm), COL1A1, and FN1 (l). The value of n indicates biologically independent samples (c, g, j). Data of different views from four biologically independent samples (h). Similar results were repeated in two biologically independent experiments. Significant differences were assessed using two-tailed unpaired Student’s t test (h) and one-way ANOVA with Tukey test (g, j). Results are presented as mean ± SEM.