Impaired myofibroblast proliferation is a central feature of pathologic post-natal alveolar simplification
- Division of Neonatology, Department of Pediatrics, UCSF, United States
- Cardiovascular Research Institute, UCSF, United States
- Division of Pulmonary, Critical Care, Allergy, and Sleep, UCSF, United States
- Department of Medicine, UCSF, United States
Figures
Figure 1
Neonatal hyperoxia treatment and loss of epithelial TGFβ signaling both cause alveolar simplification.
(A) Wildtype C57BL/6 mice were treated in 75% hyperoxia versus normoxia from P0-P10 and recovered in room air until harvest at P40 for analysis by either histology or lung physiology. (B) H&E sections of representative lungs from (A) harvested at P40 (left) with quantification of mean linear intercept (right). (C) Mice treated as in (A) and harvested for lung physiology measurements of compliance, elastance and lung capacity. (D) Tgfbr2F/F and Tgfbr2F/F;Nkx2.1-cre littermates were treated in hyperoxia versus normoxia from P0-P10 and recovered in room air until harvest at P40 for analysis by histology. (E) H&E sections of representative lungs from (D) harvested at P40 (left) with quantification of mean linear intercept (right). (F) Normoxia cohort treated as in (D) and harvested for lung physiology measurements of compliance, elastance and lung capacity. Data in (B), (C), and (F) compared by two-tailed unpaired Student’s t-test. Data in (E) compared by ANOVA with Fisher’s post hoc test. Error bars depict mean ± SEM. **p<0.01, ***p<0.001, ****p<0.0001. Scale bars = 100 μm.
Figure 2
Loss of PDGFRα+ Cells with neonatal hyperoxia treatment and loss of epithelial TGFβ signaling.
(A) Wildtype C57BL/6 mice were treated in 75% hyperoxia versus normoxia from P0-P10 and harvested on P10 for analysis by flow cytometry. Graph on right shows total cells per left lung as quantified by flow cytometry. (B) Representative flow cytometry plots of the lung mesenchyme (live, CD45-, CD31-, and Epcam-) with gates depicting PDGFRα+ cells (left). Major cell populations of the lung were defined by the indicated cell surface markers and shown as either a percentage of all cells (top) or as absolute number (bottom). (C) Tgfb2F/F and Tgfbr2F/F;Nkx2.1-cre littermates were maintained in normoxic conditions from P0-P10 and harvested on P10 for analysis by flow cytometry. Graph on right shows total cells per left lung as quantified by flow cytometry. (D) Flow cytometry plots for (C) using the same gating strategy as described above. Data in (A–D) analyzed by two-tailed unpaired Student’s t-test. Error bars depict mean ± SEM. *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001.
Figure 3 with 3 supplements
scRNA-seq reveals loss of myofibroblasts in both models of alveolar simplification.
(A) Schematic of scRNA-seq project showing CTRL (Tgfbr2F/F) and cKO (Tgfbr2F/F;Nkx2.1-cre) littermates treated in 75% hyperoxia versus normoxia from P0-P10 and harvested on P7 or P14 for FACS-purification and analysis by scRNA-seq. n=2 mice harvested for each genotype, treatment condition and timepoint. (B) Venn-diagram depicting strategy to compare these two models to identify shared features of alveolar simplification. (C) UMAP projection of mesenchymal cells from scRNA-seq as outlined in (A). (D) Bar graphs depicting the frequency of each cell type by treatment condition, genotype, and timepoint. (E) The frequency of alveolar and ductal myofibroblasts within the mesenchyme as depicted in (D) with each data point representing either a biologic or technical replicate. Because the data depicts both biologic and technical replicates, no statistics were performed on this data set. (F) Differentially expressed genes in myofibroblasts were identified by comparing either CTRL RA vs O2 cells or RA CTRL vs cKO cells. These lists were subsequently analyzed by Qiagen IPA to identify predicted upstream regulators for each comparison. The Venn-diagram on left depicts the number of overlapping predicted upstream regulators with z-score >1.5 (upregulated), while the table on right lists these 32 shared upstream regulators. Blue = TGFβ signaling, red = inhibitors of cell cycle, green = Wnt signaling.
Figure 3—figure supplement 1
scRNA-seq of murine lungs with neonatal hyperoxia treatment or loss of epithelial TGFβ Signaling.
(A) UMAP projection of all scRNA-seq data. Outlined in red are the mesenchymal cell populations. (B) UMAP plots showing expression levels of canonical markers for epithelial, endothelial, hematopoietic, mesenchymal, and mesothelial populations. (C) Total cell number within each of the indicated major lung populations. (D) Differentially expressed genes in myofibroblasts were identified by comparing either CTRL RA vs O2 cells or RA CTRL vs cKO cells. These lists were subsequently analyzed by Qiagen IPA to identify predicted upstream regulators for each comparison. The Venn-diagram on left depicts the number of overlapping predicted upstream regulators with z-score <−1.5 (upregulated), while the table on right lists these 40 shared upstream regulators.
Figure 3—figure supplement 2
Characterization of mesenchymal cell clusters by scRNA-seq.
(A) UMAP projection of mesenchymal cells from scRNA-seq data as outlined in Figure 3—figure supplement 1. (B) Heatmap of the top 10 most differentially expressed genes across mesenchymal clusters. The intensity of expression is indicated as specified by the color legend. (C) UMAP plots showing expression levels of select canonical markers for alveolar myofibroblast, ductal myofibroblast, Col13a1 fibroblast, and Col14a1 fibroblast populations as depicted by recent work by Hurskainen et al. and Narvaez Del Pilar et al. (D) Dot plot showing selected markers for each cluster within the mesenchyme.
Figure 3—figure supplement 3
Re-analysis of published data confirms loss of myofibroblasts with neonatal hyperoxia treatment.
(A) Hurskainen et al. treated C57BL/6 wildtype mice with 85% hyperoxia versus normoxia from P0-P14 and analyzed the lungs by scRNA-seq at P3, P7, and P14 (Hurskainen et al., 2021). The Seurat object used for publication was provided by the authors. UMAP projection shows the mesenchymal populations as defined by Hurskainen et al. (B) By using metadata within the Seurat object, we graphed the frequency of each mesenchymal population by treatment condition and time point. (C) The frequency of myofibroblasts within the mesenchyme as depicted in (B). (D) Xia et al. treated C57BL/6 wildtype mice with 85% hyperoxia versus normoxia from P0-P14 and analyzed the lungs by scRNA-seq at P14 (Xia et al., 2023). The Seurat object used for publication was provided by the authors. UMAP projection shows the mesenchymal populations as defined by Xia et al. (E) By using metadata within the Seurat object, we graphed the frequency of each mesenchymal population by treatment condition and time point. (F) The frequency of alveolar and ductal myofibroblasts within the mesenchyme as depicted in (E). Graphs in (C) and (F) depict one value for each condition because we were unable to extract replicate values from the data provided.
Figure 4
NicheNet ligand-receptor analysis of epithelial-mesenchymal crosstalk in both models of alveolar simplification.
scRNA-seq data was analyzed using the NicheNet software package. (A) Alveolar epithelial clusters were pooled to define sender population and myofibroblast clusters were pooled to define receiver population. By analyzing differential expression of ligands, receptors, and downstream gene expression changes in myofibroblasts, NicheNet predicted increased (left) or decreased (right) ligand-receptor signaling in each comparison of interest. Gray boxes show ligands expressed on the epithelium and the purple-shaded boxes indicate the corresponding receptors expressed on myofibroblasts. Upper panels compare hyperoxia versus normoxia in CTRL cells. Lower panels compare CTRL versus cKO cells in normoxia. (B) List of ligand-receptor pairs predicted to be increased in both injury models. Tgfb1-Tgfbr2 pairings highlighted in blue. (C) List of ligand-receptor pairs predicted to be decreased in both injury models. Pdgfa-Pdgfra and Pdgfb-Pdgfrb pairings highlighted in red.
Figure 5
Inhibiting TGFβ disrupts alveolar development and exacerbates hyperoxia-induced injury.
(A) Wildtype C57BL/6 mice were injected every other day from P2-P10 with PBS or 1D11 (pan- TGFβ-blocking antibody), treated in 75% hyperoxia treatment versus normoxia from P0-P10, and recovered in room air until harvest at P40 for analysis by either histology or lung physiology. (B) H&E sections of representative lungs from (A) harvested at P40 (left). Images shown are from PBS and 30 mg/kg 1D11 treatment groups. Mean linear intercepts calculated for all treatment groups (right). (C) PBS- and 30 mg/kg 1D11-treated mice treated in normoxic conditions as in (A) and harvested for lung physiology measurements of compliance, elastance and lung capacity at P40. Data in (B) compared by ANOVA with Fisher’s post hoc test; for readability and limitations of graphing, only the statistical significance values within normoxia or hyperoxia cohorts are plotted. Data in (C) compared by two-tailed unpaired Student’s t-test. Error bars depict mean ± SEM. *p<0.05, **p<0.01, ****p<0.0001. Scale bars = 100 μm.
Figure 6 with 2 supplements
Deletion of αv-integrins in lung mesenchyme impairs alveolar development and worsens hyperoxia-induced injury.
(A) ItgavF/F and ItgavF/F;Gli1-CreERT2 littermates were injected with tamoxifen on P2 and P4, treated in 75% hyperoxia versus normoxia from P0-P10, and recovered in room air until harvest at P40 for analysis by either histology or lung physiology. (B) H&E sections of representative lungs from (A) harvested at P40 (left). Mean linear intercepts calculated for all treatment groups (right). (C) Normoxia cohort treated as in (A) and harvested for lung physiology measurements of compliance, elastance and lung capacity. Data in (B) compared by ANOVA with Fisher’s post hoc test. Data in (C) compared by two-tailed unpaired Student’s t-test. Error bars depict mean ± SEM. *p<0.05, **p<0.01, ****p<0.0001. Scale bars = 100 μm.
Figure 6—figure supplement 1
Gli1-CreERT2 allele does not disrupt alveolar development, but Pdgfra-CreERT2 allele worsens hyperoxia-induced injury.
(A) Either Gli1-CreERT2 or Pdgfra-CreERT2 mice and their cre-negative littermates were injected with tamoxifen on P2 and P4, treated in 75% hyperoxia versus normoxia from P0-P10, and recovered in room air until harvest at P40 for analysis by histology. (B) Mean linear intercepts of Gli1CreER/+ and Gli1+/+ mice treated as outlined in (A) and harvested at P40. (C) Mean linear intercepts of PdgfraCreER/+ and Pdgfra+/+ mice treated as outlined in (A) and harvested at P40. Data compared by ANOVA with Fisher’s post hoc test. Error bars depict mean ± SEM. ***p<0.001, ****p<0.0001.
Figure 6—figure supplement 2
Loss of TGFβ signaling to lung mesenchyme causes worse disease in hyperoxia while Itgb6 plays no role in alveolar development.
(A) Tgfbr2F/F and Tgfbr2F/F;Gli1-CreERT2 littermates were injected with tamoxifen on P2 and P4, treated in 75% hyperoxia versus normoxia from P0-P10, and recovered in room air until harvest at P40 for analysis by histology. (B) H&E sections of representative lungs from (A) harvested at P40 (left). Mean linear intercepts calculated for all treatment groups (right). (C) Itgb6F/F and Itgb6F/F;Nkx2.1-cre littermates were treated in 75% hyperoxia versus normoxia from P0-P10, and recovered in room air until harvest at P40 for analysis by histology (D) H&E sections of representative lungs from (C) harvested at P40 (left). Mean linear intercepts calculated for all treatment groups (right). Data compared by ANOVA with Fisher’s post hoc test. Error bars depict mean ± SEM. *p<0.05, ***p<0.001, ****p<0.0001. Scale bars = 100 μm.
Figure 7
Impaired proliferation of PDGFRα+ fibroblasts with neonatal hyperoxia treatment.
(A) Wildtype C57BL/6 mice were treated in 75% hyperoxia versus normoxia from P0-P10 and recovered in room air until indicated timepoints for analysis. Mice were injected with EdU 24 hr prior to each analysis timepoint. (B) Flow cytometry plots of lung mesenchyme (CD45-, CD31-, Epcam-, MCAM-) show gating of PDGFRα+ cells (upper panels) and subsequent identification of EdU+/PDGFRα+ cells (lower panels). Panels on far-right show an EdU-untreated littermate used to define EdU + gate. (C) Time course graphs showing indicated populations of the lung as percent of lung (top), total cells in left lung (middle), and percent EdU + cells (bottom). Data graphed as mean ± with exception of EdU + panel in which each animal is plotted individually. Data compared by two-tailed unpaired Student’s t-test. *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001.
Figure 8
Impaired PDGFRα+ cell proliferation is a conserved feature across multiple models of alveolar simplification.
(A) Tgfb2F/F and Tgfbr2F/F;Nkx2.1-cre littermates were maintained in normoxic conditions from P0-P7, injected with EdU on P6, and harvested 24 hr later on P7 for flow cytometry. (B) Flow cytometry plots of lung mesenchyme (CD45-, CD31-, Epcam-, MCAM-) show gating of PDGFRα+ cells (left panels) and subsequent identification of EdU+/PDGFRα+ cells (right panels). Graphs on far right show major cell populations of the lung by percentage (upper graphs) and percent EdU-positive within each of these populations (lower graphs). (C) Wildtype C57BL/6 mice were injected every other day from P2-P8 with PBS or 30 mg/kg 1D11 (pan-TGFβ-blocking antibody) in normoxic conditions, injected with EdU on P9, and harvested 24 hr later on P10 for flow cytometry. (D) Flow cytometry plots of lung mesenchyme (CD45-, CD31-, Epcam-, MCAM-) show gating of PDGFRα+ cells (left panels) and subsequent identification of EdU+/PDGFRα+ cells (right panels). Graphs on far right show major cell populations of the lung by percentage (upper graphs) and percent EdU-positive within each of these populations (lower graphs). Data in analyzed by two-tailed unpaired Student’s t-test. Error bars depict mean ± SEM. *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001.
Figure 9 with 1 supplement
Blocking proliferation of PDGFRα+ fibroblasts is sufficient to cause alveolar simplification.
(A) Ect2F/F and Ect2F/F;Pdgfra-CreERT2 littermates were injected with tamoxifen on P2 and P4 in normoxic conditions. Mice were analyzed by flow cytometry on P14 or aged until P40 for analysis by either histology or lung physiology. (B) Representative flow cytometry plots of the lung mesenchyme (live, CD45-, CD31-, and Epcam-) with gates depicting PDGFRα+ cells (left). Major cell populations of the lung were defined by the indicated cell surface markers and shown as either a percentage of all cells (top) or as absolute number (bottom). (C) H&E sections of representative lungs from (A) harvested at P40 (left). Mean linear intercepts calculated for all treatment groups (right). (D) Mice treated as in (A) and harvested for lung physiology measurements of compliance, elastance and lung capacity. Data in (B) compared by two-tailed unpaired Student’s t-test. Data in (C) compared by ANOVA with Fisher’s post hoc test. Error bars depict mean ± SEM. **p<0.01, ***p<0.001, ****p<0.0001. Scale bars = 100 μm.
Figure 9—figure supplement 1
Decreased PDGFRα mean fluorescence intensity across multiple models of alveolar simplification.
(A) Mean fluorescence intensity (geometric mean, MFI) of PDGFRα antibody staining on MCAM-negative mesenchymal cells (CD45-, CD31-, Epcam-) and PDGFRa + cells (CD45-, CD31-, Epcam-, MCAM-, PDGFRα+) as quantified by flow cytometry. Each column represents an experiment shown earlier in this study: normoxia vs hyperoxia at P10 (Figure 2), Tgfbr2F/F vs Tgfbr2F/F;Nkx2.1-cre at P10 (Figure 2), PBS vs 1D11 at P10 (Figure 8), Ect2F/F vs Ect2F/F;Pdgfra-CreERT2 at P14 (Figure 9). To compare values across multiple experiments, MFI’s were normalized to the control condition within each experiment. Data compared by ANOVA with Fisher’s post hoc test. Error bars depict mean ± SEM. ***p<0.001, ****p<0.0001.
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Alveolar myoFB.
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Ductal myoFB.
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Impaired myofibroblast proliferation is a central feature of pathologic post-natal alveolar simplification
eLife 13:RP94425.
https://doi.org/10.7554/eLife.94425.3
