Type 2 alveolar cells are stem cells in adult lung
Christina E. Barkauskas, … , Paul W. Noble, Brigid L.M. Hogan
Christina E. Barkauskas, … , Paul W. Noble, Brigid L.M. Hogan
Published July 1, 2013; First published June 10, 2013
Citation Information: J Clin Invest. 2013;123(7):3025-3036. https://doi.org/10.1172/JCI68782.
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Categories: Research Article Pulmonology

Type 2 alveolar cells are stem cells in adult lung

Abstract

Gas exchange in the lung occurs within alveoli, air-filled sacs composed of type 2 and type 1 epithelial cells (AEC2s and AEC1s), capillaries, and various resident mesenchymal cells. Here, we use a combination of in vivo clonal lineage analysis, different injury/repair systems, and in vitro culture of purified cell populations to obtain new information about the contribution of AEC2s to alveolar maintenance and repair. Genetic lineage-tracing experiments showed that surfactant protein C–positive (SFTPC-positive) AEC2s self renew and differentiate over about a year, consistent with the population containing long-term alveolar stem cells. Moreover, if many AEC2s were specifically ablated, high-resolution imaging of intact lungs showed that individual survivors undergo rapid clonal expansion and daughter cell dispersal. Individual lineage-labeled AEC2s placed into 3D culture gave rise to self-renewing “alveolospheres,” which contained both AEC2s and cells expressing multiple AEC1 markers, including HOPX, a new marker for AEC1s. Growth and differentiation of the alveolospheres occurred most readily when cocultured with primary PDGFRα+ lung stromal cells. This population included lipofibroblasts that normally reside close to AEC2s and may therefore contribute to a stem cell niche in the murine lung. Results suggest that a similar dynamic exists between AEC2s and mesenchymal cells in the human lung.

Authors

Christina E. Barkauskas, Michael J. Cronce, Craig R. Rackley, Emily J. Bowie, Douglas R. Keene, Barry R. Stripp, Scott H. Randell, Paul W. Noble, Brigid L.M. Hogan

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Figure 2

During repair after bleomycin, SCGB1A1 lineage–labeled cells account for most of the SFTPC lineage-negative AEC2s, and clones can arise in bronchioles.

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During repair after bleomycin, SCGB1A1 lineage–labeled cells account for...
Sftpc-CreER;Rosa-Tm and Scgb1a1-CreER;Sftpc-CreER;Rosa-Tm mice were dosed with Tmx (0.2 mg/g × 4) and exposed to bleomycin (1.25 U/kg). Controls received Tmx and intratracheal saline. Sections of 21-dpi lungs were stained for SFTPC. Confocal z-stack images (n ≥ 3 mice per point, 6 sections/mouse) were acquired and cells counted from fibrotic areas (high density of DAPI+ nuclei) or from random alveolar areas in controls. (A) Fibrotic region of Sftpc-CreER;Rosa-Tm lung showing clusters of SFTPC+ AECs that are not lineage labeled. By contrast, in a similar region of Scgb1a1-CreER;Sftpc-CreER;Rosa-Tm lung (B), significantly more AEC2 cells are lineage labeled. This is quantified in C. The smaller decline in value in the Scgb1a1-CreER;Sftpc-CreER;Rosa-Tm group compared with Sftpc-CreER;Rosa-Tm group suggests that there is no other important source of AEC2 precursors besides SCGB1A1+ cells. (D–F) Scgb1a1-CreER;Rosa-Confetti mice (n = 3) were dosed with Tmx (0.05 mg/g × 1) and sacrificed 21 days after bleomycin. Uninjured areas show random labeling of single cells in the bronchiolar epithelium (D), while injured areas display clones of labeled cells (E) especially in the BADJ (asterisks). (F) Clones occasionally extend from the BADJ (asterisks) into the alveoli, suggesting that at least some of the SCGB1A1+ lineage-labeled cells giving rise to AEC2s and AEC1s originate in the bronchioles. Scale bars: 100 μm. See also Supplemental Figure 2.