Generation of alveolar epithelial spheroids via isolated progenitor cells from human pluripotent stem cells

Abstract

No methods for isolating induced alveolar epithelial progenitor cells (AEPCs) from human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have been reported. Based on a study of the stepwise induction of alveolar epithelial cells (AECs), we identified carboxypeptidase M (CPM) as a surface marker of NKX2-1(+) "ventralized" anterior foregut endoderm cells (VAFECs) in vitro and in fetal human and murine lungs. Using SFTPC-GFP reporter hPSCs and a 3D coculture system with fetal human lung fibroblasts, we showed that CPM(+) cells isolated from VAFECs differentiate into AECs, demonstrating that CPM is a marker of AEPCs. Moreover, 3D coculture differentiation of CPM(+) cells formed spheroids with lamellar-body-like structures and an increased expression of surfactant proteins compared with 2D differentiation. Methods to induce and isolate AEPCs using CPM and consequently generate alveolar epithelial spheroids would aid human pulmonary disease modeling and regenerative medicine.

Graphical abstract

Figure 1

Identification of CPM as a Candidate Marker of NKX2-1⁺ VAFECs (A) Stepwise differentiation to AECs from hPSCs. (B) Gene-expression levels of transcription factors from day 0 to day 25 (n = 3). Each value was normalized to the level of β-ACTIN. The relative expression level was scored with the maximum value set to 1.0. (C) Induction efficiency of VAFECs analyzed by scoring the number of FOXA2⁺ and NKX2-1⁺ cells relative to the total number of nuclei in an average of ten randomly selected images (n = 3). (D) FOXA2⁺NKX2-1⁺ VAFECs derived from 201B7 hiPSCs. (E) Scatterplots comparing the global gene-expression profiles of AFECs (day 10) and VAFECs (day 14). CPM (arrows) and NKX2-1 (arrowheads) are noted. The lines beside the diagonal line indicate a 2-fold cutoff change between the AFECs and VAFECs. (F) Simultaneous increases of CPM and NKX2-1 detected by IF staining of AFECs (day 10) and VAFECs (day 14). (G) CPM detected in NKX2-1⁺, SOX9⁺, SFTPB⁺, SFTPC⁺, and SCGB3A2⁺ cells, but not in KRT5⁺ cells, on day 25. (H) CPM detected in NKX2-1⁺ lung epithelial cells in fetal human lung. (I) CPM in E12.5, E15.5, and E17.5 murine lungs. Error bars show SEM. Scale bars, 100 μm. See also Figure S1 and Tables S1 and S2.

Figure 2

Isolation of CPM⁺ VAFECs Using Anti-CPM Antibody (A) Flow cytometry of VAFECs. EPCAM⁺CPM⁺ (Q2) and EPCAM⁺CPM⁻ cells (Q4) were isolated on day 14 (n = 3). (B) Hierarchical clustering heatmaps of 336 genes with differences of >2-fold (FDR-adjusted p < 0.05) comparing EPCAM⁺CPM⁺ cells with EPCAM⁺CPM⁻ cells. The cluster of genes increased as the greatest fold change was magnified. (C) Flow cytometry of MACS-sorted CPM⁺ and CPM⁻ cells from VAFECs (n = 3). (D) NKX2-1⁺ cells in FACS-sorted CPM⁺ and CPM⁻ cells derived from VAFECs analyzed by scoring the number of NKX2-1⁺ cells relative to the total number of nuclei in an average of five randomly selected images (n = 3). (E) Levels of CPM and NKX2-1 on day 14 before and after MACS-based purification of CPM⁺ cells on qRT-PCR (n = 5). (F) Levels of AEC and club-cell markers and NGFR, a proximal airway stem cell marker, on day 25 before and after MACS-based purification of CPM⁺ cells (n = 5). The gene-expression level observed in the fetal lungs was set at one. Values are presented as the mean ± SEM. Error bars show SEM. #p < 0.05, ^∗p < 0.01. Scale bars, 100 μm. See also Figure S2 and Tables S1 and S2.

Figure 3

Generation of SFTPC-GFP Knockin hPSC Lines (A) Strategy for BAC-based gene targeting to produce SFTPC-GFP knockin hPSC lines. (B) Screening of knockin hPSC lines using TaqMan qPCR. Positive clones with candidate heterozygous deletion of the endogenous SFTPC gene are shown in white bars. Only clones that were initially suspected to be positive were tested independently three times. (C) Genomic PCR to confirm the removal of the pgk-NeoR cassette by Cre-recombinase in the A17-14 and B2-3 SFTPC-GFP reporter hPSCs. (D) SNP array analysis of the SFTPC-GFP knockin hPSC lines. The copy number of SFTPC gene loci was analyzed in A17-13, A17-14, and B2-3 clones. The A17-14 and B2-3 clones have two copies of the SFTPC gene loci, whereas the A17-13 clone has three copies of the loci. The red dots and y axis represent the normalized signal intensity of each SNP. (E) Isolation of SFTPC⁻GFP⁺ and GFP⁻ cells via FACS after sorting CPM⁺ cells via MACS on day 25. (F) RT-PCR analyses of GFP⁺ and GFP⁻ sorted cells in the A17-14 and B2-3 SFTPC-GFP reporter hPSC lines. (G) Representative images of GFP detected in SFTPC⁺, SFTPB⁺, and NKX2-1⁺ cells. Error bars show SEM. Scale bars, 100 μm. See also Figure S3 and Tables S1 and S2.

Figure 4

Alveolar Differentiation from CPM⁺ VAFECs in 3D Coculture (A) Strategy for inducing AECs via 3D coculture with FHLFs. (B) SFTPC-GFP⁺ cells detected in spheroids derived from isolated CPM⁺ VAFECs. (C) Transmission electron microscopy of lamellar-body-like structures observed in 3D coculture differentiation of CPM⁺ cells compared with those observed in the adult and fetal murine lungs. Lu, lumen. (D) IF staining of spheroids derived from CPM⁺ VAFECs. (E) Flow cytometry of SFTPC-GFP⁺ cells in 3D coculture differentiation of CPM⁺ cells or CPM⁻ cells (n = 3). (F) GFP⁺ and GFP⁻ cells isolated via FACS, spun down onto slides, and stained by anti-GFP and anti-SFTPC antibodies. (G) qRT-PCR comparing the 2D and 3D differentiation into AECs in H9 hESCs and 201B7 (parental), 604A1, and 585A1 hiPSCs. Each value of the gene expression was normalized to the level of β-ACTIN. The levels of the fetal lungs were set at one. Values are presented as the mean ± SEM. Error bars show SEM. #p < 0.05, ^∗p < 0.01. Scale bars, 100 μm unless otherwise indicated. See also Figure S4 and Tables S1 and S2.