LNGFR(+)THY-1(+)VCAM-1(hi+) cells reveal functionally distinct subpopulations in mesenchymal stem cells

Abstract

Human mesenchymal stem cells (hMSCs), which conventionally are isolated based on their adherence to plastic, are heterogeneous and have poor growth and differentiation, limiting our ability to investigate their intrinsic characteristics. We report an improved prospective clonal isolation technique and reveal that the combination of three cell-surface markers (LNGFR, THY-1, and VCAM-1) allows for the selection of highly enriched clonogenic cells (one out of three isolated cells). Clonal characterization of LNGFR(+)THY-1(+) cells demonstrated cellular heterogeneity among the clones. Rapidly expanding clones (RECs) exhibited robust multilineage differentiation and self-renewal potency, whereas the other clones tended to acquire cellular senescence via P16INK4a and exhibited frequent genomic errors. Furthermore, RECs exhibited unique expression of VCAM-1 and higher cellular motility compared with the other clones. The combination marker LNGFR(+)THY-1(+)VCAM-1(hi+) (LTV) can be used selectively to isolate the most potent and genetically stable MSCs.

Graphical abstract

Figure 1

Screening of Putative Surface Markers for Prospective Identification of hMSCs (A) Human bone fragments were washed with PBS (BM cells) or treated with collagenase (CR cells). (B) Expression ratio of the indicated surface markers in the CD45⁻ and GPA⁻ cell populations. The data are shown as the ratio of the expression of a given marker on CR cells versus BM cells (mean ± SEM, n = 5; ^∗p < 0.1). (C) Colony-forming assay of a single marker population (2,000 cells) in CR cells at 14 days (mean ± SEM, n = 6 per group; ^∗p < 0.05). (D) Assay measuring the negative linear relationship between the numbers of seeded cells (BM, CR, and CD45⁻GPA⁻ CR cells) and sorted cells, using a surface marker in CR cells. (E) Clonogenic assay of single cells seeded into 96-well plates and cultured for 14 days (BM-MNC POIETICS were used in this assay; mean ± SEM, n = 3; ^∗p < 0.05). See also Figure S1.

Figure 2

The LNGFR⁺THY-1⁺ Population Is Significantly Enriched for CFU-Fs with Potent Differentiation Potential (A) Representative flow-cytometric profiles of human BM stained for LNGFR and THY-1. (B) Numbers of CFU-Fs detected 14 days after plating 5,000 cells from each of the following groups: LNGFR⁺THY-1⁺, +/−, −/+, and −/− cells (mean ± SEM, n = 12 per group; ^∗∗p < 0.01). (C) Assay of the negative linear relationship between the numbers of seeded LNGFR⁺THY-1⁺ and LNGFR⁺THY-1⁻ cells. (D) Phase-contrast micrographs of a colony of LNGFR⁺THY-1⁺ cells (phase), showing the potential of a LNGFR⁺THY-1⁺ colony to differentiate into osteoblasts, chondrocytes, and adipocytes. Scale bar = 100 μm. (E) Phase-contrast micrographs of LNGFR⁺THY-1⁺ and LNGFR⁺THY-1⁻ colonies (passage 1). Arrows point to cells with larger amounts of cytoplasm. Scale bar = 100 μm. (F) Secondary CFU-Fs assays were performed with single cells sorted from LNGFR⁺THY-1⁺ and LNGFR⁺THY-1⁻ colonies after one passage (mean ± SEM, n = 3; ^∗∗p < 0.01). (G) Flow-cytometric analysis of surface markers on LNGFR⁺THY-1⁺ cells, showing the percentage of cells that express the antigen (red line) versus a matched isotype control (gray). Lineage cocktail: CD3, CD14, CD16, CD19, CD20, and CD56. (H) Phase-contrast image of cultures of LNGFR⁺THY-1⁺ and LNGFR⁻THY-1⁺ cells after 14 days of culture in MethoCult medium (CFU-C assay). Scale bar = 100 μm. (I) Total numbers of CFU-Cs counted on day 14 (mean ± SEM, n = 3; ^∗∗p < 0.01). BM-MNC POIETICS were used for all experiments in this figure. See also Figures S2 and S3.

Figure 3

Clonal Assay of LNGFR⁺THY-1⁺ Cells (A) Single-cell assay in a LNGFR⁺THY-1⁺ population. Representative image of a typical 96-well culture plate (day 21 after initial seeding) shows colony-forming wells. (B) Single-cell sorting and in vitro expansion reveals three distinct MSC subpopulations of rapidly, moderately, or slowly expanding MSC clones (RECs, MECs, and SECs, respectively). Growth curves of representative RECs, MECs, and SECs, and the percentage of each colony type present are shown. (C) Phase-contrast micrograph showing the cellular morphologies of RECs, MECs, and SECs. The arrows point to larger MECs and SECs with larger nuclei. Scale bar = 100 μm. (D) Differentiation of each colony type into adipocytes and osteoblasts. Scale bar = 100 μm. (E) Quantitative analysis of the differentiation capacity of each colony type (differentiation cells / nuclei; mean ± SEM, n = 6; ^∗p < 0.05). (F) Average number of secondary CFU-Fs in wells for each cell type at 6 weeks (mean ± SEM, n = 3; ^∗p < 0.05). BM-MNC POIETICS were used for all experiments in this figure. See also Table S1.

Figure 4

Heterogeneity in the MSC Compartment (A) SA-β-gal assay of RECs, MECs, and SECs cultured in a glass chamber (at 6 weeks). Scale bar = 50 μm. (B) Quantitative analysis of SA-β-gal⁺ cells in RECs, MECs, and SECs (mean ± SEM, n = 3 per group; ^∗∗p < 0.01). (C) Relative expression of P14ARF, P16INK4a, and P21 in 6-week cultured cells by real-time RT-PCR (mean ± SEM, n = 3; ^∗p < 0.1, ^∗∗p < 0.01; n.s., not significant). See also Figure S4 and Table S2.

Figure 5

VCAM-1 Identifies Rapidly Dividing MSCs (A) Expression of the indicated surface markers in RECs, MECs, and SECs (6 weeks in culture). Shown is the percentage of cells that express the antigen (line) versus a matched isotype control (gray). (B) Immunocytochemistry of MSC subpopulation with VCAM-1 (green), Ki67 (red), and nuclei (blue). Scale bar = 100 μm. (C) Quantitative analysis of Ki67⁺ cells in RECs, MECs, and SECs (mean ± SEM, n = 3 per group; ^∗∗p < 0.01). (D) Relative expression of VCAM-1 marker in cultured cells (6 weeks) by real-time RT-PCR (mean ± SEM, n = 3; ^∗p < 0.05, ^∗∗p < 0.01). See also Figure S5.

Figure 6

Expression of VCAM-1 and CD49d Correlated with the Migration Ability of MSCs (A) Migration assay in vitro. A total of 1.5 × 10⁴ cells (RECs, MECs, and SECs) were resuspended in DMEM containing 1% FBS and 10 μg/ml aphidicolin, and allowed to migrate toward the culture medium supplemented with 20% FBS in the lower chamber. (B) Migration assay of RECs, MECs, and SECs with or without blocking antibody (“Normal” indicates no antibody treatment). The cells were incubated with each antibody (isotype control [mouse IgG1], anti-VCAM-1 [51-10C9], anti-CD49d [9F10], each at 10 μg/ml) for 30 min prior to assay (mean ± SEM, n = 3 per group; ^∗p < 0.05, ^∗∗p < 0.01). (C) The distribution of the indicated F-actin (green) and α-tubulin (red) was monitored by immunofluorescence and microscopy (after 4 days). The small box represents a high-resolution image. Scale bar = 100 μm. (D) Quantitative analysis of F-actin⁺ cells (mean ± SEM, n = 3 per group; ^∗∗p < 0.01). (E) Quantitative analysis of cell width (n = 30) in RECs, MECs, and SECs (^∗∗p < 0.01). (F) Imaging of transplanted cultured MSCs in vivo. A Luciferase image of cell migration in the recipient animals at 1 day postinjection of 1 × 10⁵ cultured cells (infected with Venus-ffLuc lentivirus) is shown. (G) Quantitation of luciferase activity in recipient animals. Luminescent intensity was significantly increased after injection of the cultured MSCs and MECs/SECs in lung regions (mean ± SEM, n = 3 per group; ^∗∗p < 0.01).

Figure 7

Isolation of Functional MSCs in Culture and Fresh BM Cells (A) Culture-dependent reduction in the frequency of VCAM-1⁺ cells in the LNGFR⁺THY-1⁺ cell population. (B) Colony-forming potential of cultured VCAM-1⁺ or VCAM-1⁻ cells derived from the LNGFR⁺THY-1⁺ cell population after 4 weeks and 8 weeks (mean ± SEM, n = 5; ^∗∗p < 0.01). (C) Direct isolation of RECs from fresh BM cells. (D) Colony-forming potential of low-positive or high-positive VCAM-1 cells in the LNGFR⁺THY-1⁺ cell population (mean ± SEM, n = 3; ^∗p < 0.05).