Regulation of epithelial transitional states in murine and human pulmonary fibrosis
Fa Wang, … , M. Bishr Omary, Rachel L. Zemans
Fa Wang, … , M. Bishr Omary, Rachel L. Zemans
Published September 28, 2023
Citation Information: J Clin Invest. 2023;133(22):e165612. https://doi.org/10.1172/JCI165612.
View: Text | PDF
Research Article Pulmonology Article has an altmetric score of 18

Regulation of epithelial transitional states in murine and human pulmonary fibrosis

Abstract

Idiopathic pulmonary fibrosis (IPF) is a progressive scarring disease arising from impaired regeneration of the alveolar epithelium after injury. During regeneration, type 2 alveolar epithelial cells (AEC2s) assume a transitional state that upregulates multiple keratins and ultimately differentiate into AEC1s. In IPF, transitional AECs accumulate with ineffectual AEC1 differentiation. However, whether and how transitional cells cause fibrosis, whether keratins regulate transitional cell accumulation and fibrosis, and why transitional AECs and fibrosis resolve in mouse models but accumulate in IPF are unclear. Here, we show that human keratin 8 (KRT8) genetic variants were associated with IPF. Krt8–/– mice were protected from fibrosis and accumulation of the transitional state. Keratin 8 (K8) regulated the expression of macrophage chemokines and macrophage recruitment. Profibrotic macrophages and myofibroblasts promoted the accumulation of transitional AECs, establishing a K8-dependent positive feedback loop driving fibrogenesis. Finally, rare murine transitional AECs were highly senescent and basaloid and may not differentiate into AEC1s, recapitulating the aberrant basaloid state in human IPF. We conclude that transitional AECs induced and were maintained by fibrosis in a K8-dependent manner; in mice, most transitional cells and fibrosis resolved, whereas in human IPF, transitional AECs evolved into an aberrant basaloid state that persisted with progressive fibrosis.

Authors

Fa Wang, Christopher Ting, Kent A. Riemondy, Michael Douglas, Kendall Foster, Nisha Patel, Norihito Kaku, Alexander Linsalata, Jean Nemzek, Brian M. Varisco, Erez Cohen, Jasmine A. Wilson, David W.H. Riches, Elizabeth F. Redente, Diana M. Toivola, Xiaofeng Zhou, Bethany B. Moore, Pierre A. Coulombe, M. Bishr Omary, Rachel L. Zemans

×

Figure 7

Murine transitional cells include a highly senescent, basaloid subset.

Options: View larger image (or click on image) Download as PowerPoint
Murine transitional cells include a highly senescent, basaloid subset. B...
Bleomycin, LPS, and organoid scRNA-Seq data sets were integrated. (A) Expression of senescence markers. p16 (Cdkn2a) was exclusively expressed in cluster 7. (B) Pseudotime analysis suggested cells in cluster 7 may not have an AEC1 fate. (C) Top DEGs in cluster 7. (D) Cultured primary murine AEC2s upregulated cluster 7 markers and p16 (Cdkn2a) and were highly senescent. Human IPF transitional cells expressed high levels of cluster 7 markers, as shown by scRNA-Seq (E) and immunostaining or FISH (F). (G) The top DEGs in the human IPF transitional (KRT5–KRT17+) state (58) were differentially expressed in murine cluster 7. (H) scRNA-Seq data sets from IPF (57, 58), normal human lung (86), or human organoids (60) were interrogated. Mature basal cell genes found among the top 100 DEGs of the human IPF transitional state were upregulated in cluster 7 of the murine AECs (H and J) and in cultured murine AECs (I). (K) K17 was occasionally expressed in lineage-labeled cells in bleomycin-treated SftpcCreERT2 mTmG mice. (L) Compared with AEC2s, human “transitional AEC2s” from IPF (58), ABI1s from human organoids (60), and murine transitional cells in cluster 1 downregulated AEC2 markers and upregulated classic transitional state markers. KRT5–KRT17+ AECs from IPF (58), ABI2s from human organoids (60), and murine transitional cells in cluster 7 upregulated basaloid genes. (J and M) Transitional cells expressing cluster 7 markers were rare in the single bleomycin model but common in the repetitive bleomycin model. (N) Transitional cells in human IPF but not ARDS expressed basaloid markers and p16/CDKN2A. (D and I) Data represent the mean (n = 3). **P < 0.01 compared with day 0, by 1-way ANOVA with post hoc Bonferroni’s test. (D) P < 0.05 for all genes at day 7 compared with day 0. Scale bars: 50 μm. Original magnification, ×20 (enlarged insets in F, K, M, and N). Arrowheads indicate transitional cells expressing a marker of interest. For immunostaining, n = 3 mice/group.