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iPSC-derived Organoids Support the Study of Alveolar Cell Differentiation and Function

Review of “Directed induction of alveolar type 1 cells derived from pluripotent stem cells via Wnt signaling inhibition” from STEM CELLS by Stuart P. Atkinson

The gas exchange process occurring in the alveoli of the lungs depends on the differentiation of alveolar type II (AT2) into alveolar type I (AT1) cells [1, 2]; the recapitulation of this process in vitro, a difficult task, may provide clues regarding the pathological and physiological roles of human AT1 cells. Researchers led by Shimpei Gotoh (Kyoto University, Japan) previously reported the generation and expansion of human induced pluripotent stem cell (iPSC)‐derived AT2 (iAT2) cells in three-dimensional alveolar organoid culture [3, 4].

In their more recent study, the authors sought to employ this alveolar organoid culture system to define presumed iPSC‐derived AT1 (iAT1) cells and evaluate the potential of iAT2 cells to differentiate into iAT1 cells. As reported in STEM CELLS [5], Kanagaki et al. now demonstrate that iAT1 cells present in iPSC‐derived alveolar organoids closely resemble primary AT1 cells and establish the utility of iPSC‐derived alveolar organoids regarding the study of the AT2 to AT1 differentiation process.

Following the generation of alveolar organoids via the differentiation of iPSCs in the presence of fetal lung fibroblasts, single‐cell RNA sequencing analysis highlighted the presence of five independent cell types - pulmonary neuroendocrine cells, NKX2‐1-expressing cells, mitotic cells, surfactant protein B and C (SFTPC and SFTPB)-expressing iAT2 cells, and finally, iAT1 cells, identified on the basis of high expression of EpCAM and the presence of an AT1-like marker expression profile (high expression of advanced glycosylation end‐product specific receptor (AGER), podoplanin (PDPN), caveolin‐1 (CAV1)) and the lack of SFTPC expression. Overall, iAT1 cells derived from the fibroblast-dependent alveolar organoids displayed a transcriptomic profile remarkably similar to primary AT1 cells.

Interestingly, a comparison between alveolar organoids generated with and without the aid of fetal lung fibroblasts established the lack of the all-important iAT1 cells in the fibroblast‐free alveolar organoids. Further analysis then suggested that fetal lung fibroblast-dependent modulation of Wnt signaling represented one of the driving forces behind the generation of iAT1 cells from iAT2 cells in fibroblast-dependent alveolar organoids. With this knowledge in hand, the authors then demonstrated the ability to induce iAT1 cell differentiation from iAT2 cells via treatment with an inhibitor of the canonical Wnt signaling pathway.

In the future, the authors hope that the chemically-induced differentiation of iAT2 cells into iAT1 cells within alveolar organoids may serve as a highly utile means to dissect the molecular pathways regulating this all-important process.

For more on human iPSC-derived organoids and their vast potential, stay tuned to the Stem Cells Portal!

References

  1. Borok Z, Danto SI, Lubman RL, et al., Modulation of T1α expression with alveolar epithelial cell phenotype in vitro. American Journal of Physiology-Lung Cellular and Molecular Physiology 1998;275:L155-L164.
  2. Marconett CN, Zhou B, Sunohara M, et al., Cross-Species Transcriptome Profiling Identifies New Alveolar Epithelial Type I Cell–Specific Genes. American Journal of Respiratory Cell and Molecular Biology 2016;56:310-321.
  3. Yamamoto Y, Gotoh S, Korogi Y, et al., Long-term expansion of alveolar stem cells derived from human iPS cells in organoids. Nature Methods 2017;14:1097-1106.
  4. Gotoh S, Ito I, Nagasaki T, et al., Generation of Alveolar Epithelial Spheroids via Isolated Progenitor Cells from Human Pluripotent Stem Cells. Stem Cell Reports 2014;3:394-403.
  5. Kanagaki S, Ikeo S, Suezawa T, et al., Directed induction of alveolar type I cells derived from pluripotent stem cells via Wnt signaling inhibition. STEM CELLS 2021;39:156-169.