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. 2015 Mar 10;4(3):473-88.
doi: 10.1016/j.stemcr.2015.01.007. Epub 2015 Feb 13.

Comparative Quantification of the Surfaceome of Human Multipotent Mesenchymal Progenitor Cells

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Free PMC article

Comparative Quantification of the Surfaceome of Human Multipotent Mesenchymal Progenitor Cells

Rebecca J Holley et al. Stem Cell Reports. .
Free PMC article

Abstract

Mesenchymal progenitor cells have great therapeutic potential, yet incomplete characterization of their cell-surface interface limits their clinical exploitation. We have employed subcellular fractionation with quantitative discovery proteomics to define the cell-surface interface proteome of human bone marrow mesenchymal stromal/stem cells (MSCs) and human umbilical cord perivascular cells (HUCPVCs). We compared cell-surface-enriched fractions from MSCs and HUCPVCs (three donors each) with adult mesenchymal fibroblasts using eight-channel isobaric-tagging mass spectrometry, yielding relative quantification on >6,000 proteins with high confidence. This approach identified 186 upregulated mesenchymal progenitor biomarkers. Validation of 10 of these markers, including ROR2, EPHA2, and PLXNA2, confirmed upregulated expression in mesenchymal progenitor populations and distinct roles in progenitor cell proliferation, migration, and differentiation. Our approach has delivered a cell-surface proteome repository that now enables improved selection and characterization of human mesenchymal progenitor populations.

Figures

Figure 1
Figure 1
Method to Identify Mesenchymal Progenitor Cell-Specific Markers at the Stem Cell Niche Interface (A) Flow cytometry for known MSC markers in HDFs (black), MSCs (green), and HUCPVCs (blue). Plots shown are representative of results from three different donor MSC, HUCPVC, and HDF cultures (n = 3). Red filled, isotype control; black line, antibody as indicated. (B) Immunofluorescence staining for indicated markers (green) after differentiation under adipogenic (16 days), chondrogenic (21 days), and osteogenic (18 days) conditions. DAPI (blue, nuclear); F-actin (red, cytoskeleton). Images are representative of results from three donors (n = 3), with magnified inserts. (C) Immunoblotting for neuropilin 1, PDGFRβ, ATPase, and β-actin in whole-cell lysate and membrane-enriched (PM) protein samples. Results are representative of three different donor preparations. (D) Quantification of immunoblot results shown in (C). (E) Phase images of MSCs pre-denudation and post-denudation. (F) Fibronectin (green) and DAPI (blue) staining of pre-denuded and post-denuded MSCs. (G) Coomassie stained gels of whole-cell lysates and matrix-enriched protein samples. (H) Immunoblotting for fibronectin, fibrillin-1, and β-actin in whole-cell lysates and matrix-enriched protein samples. (I) Schematic of experimental proteomic workflow. HDF1 and HDF2 represent biological internal replicates with proteins isolated from two donors. Protein samples from three different MSC and HUCPVC donor populations were used. See also Figure S1.
Figure 2
Figure 2
Identification of Mesenchymal Progenitor Cell-Specific Markers Using Eight-Plex Isobaric Tagging and LC-MS/MS (A and B) Histograms showing the distribution of (log) quantification protein ratios for individual MSC donors versus HDF (A) or HUCPVC donors versus HDF (B) in membrane-enriched fractions. MSC2 was excluded as ITRAQ labeling of this sample was inefficient. Error bars are + SD. (C) Histogram comparing the distribution (log) of the average protein ratios for MSCs versus HDF and HUCPVCs versus HDF in membrane-enriched fractions. Error bars are + SD. (D) Venn diagram for membrane-enriched protein fractions illustrating overlapping protein changes seen when comparing all individual MSC cultures versus HDF (MSC up or MSC down) and individual HUCPVC cultures versus HDF (HUCPVC up or HUCPVC down). (E) Heatmap illustrating clustering of changing genes in membrane-enriched fractions. (F) Venn diagram for changes seen in matrix-enriched protein fractions. (G) Heatmap illustrating clustering of changing genes in matrix-enriched fractions. See also Figure S2.
Figure 3
Figure 3
Validation of Mesenchymal Progenitor Cell Targets (A) Flow cytometry for known mesenchymal progenitor cell markers identified as being enriched within both MSCs and HUCPVCs in the eight-plex iTRAQ LC-MS/MS experiment. Plots are representative profiles from MSC, HUCPVC, and HDF cultures (n = 3–4 donors of each cell type). (B) Flow cytometry for CD54 and BST1 in MSC, HUCPVC, and HDF cultures. Plots are representative profiles (n = 3–4 donors of each cell type). (C) Flow cytometry validation of EPHA2, TEK, CDH13, and CD98 identified to be enriched within mesenchymal progenitor populations by MS. Plots are representative profiles (n = 3–4 donors of each cell type). (D) Immunoblot validation of new markers identified to be enriched within mesenchymal progenitor populations by MS. Blots show protein extracts from HDF, two MSC donors, two HUCPVC donors, human coronary artery, and aortic SMC and HUVEC cultures. (E) qRT-PCR for markers identified to be enriched within mesenchymal progenitor populations. Results are averages with error bars representing SEM. Expression was normalized relative to housekeeper genes TBP and β2M, using averages from three individual HDF, four MSC, and four HUCPVC donors. (F) Immunoblots showing expression of new markers by MSC cultured under normal growth conditions (MSC) or under adipogenic conditions (adipo, 21 days) in pellet chondrogenic conditions (chondro, 24 days) or osteogenic conditions (osteo, 24 days). Blots are representative of results from two donor MSCs. See also Figure S3.
Figure 4
Figure 4
Expression of Markers by Freshly Isolated HUCPVCs, Bone Marrow MSCs, and MSCs from Adipose Tissue (A) Flow cytometry for the indicated markers using freshly isolated HUCPVCs, at passage 0, after cell release from perivascular regions of the umbilical cord with collagenase. Plots are representative profiles (n = 2 donors). Red filled, isotype control; black line, antibody as indicated. (B) Flow cytometry for the indicated markers using freshly isolated bone marrow MSCs, at passage 0, after plating of bone marrow cells on tissue culture plastic, analyzing adherent populations. Plots are representative profiles (n = 2 technical repeats). Red filled, isotype control; black line, antibody as indicated. Plots from two further MSC donors at passage 0 are given in Figure S4. (C) Flow cytometry for the indicated markers using freshly isolated adipose-derived MSCs, at passage 0, after plating of isolated cells from subcutaneous fat on tissue culture plastic, analyzing adherent populations. Plots are representative profiles (n = 2 technical repeats). Red filled, isotype control; black line, antibody as indicated. Plots from two further adipose-derived MSC donors at passage 0 are given in Figure S4. See also Figure S4.
Figure 5
Figure 5
siRNA against Newly Identified Mesenchymal Progenitor Markers Reveals Functional Roles (A–G) Validation of knockdown using siRNA. (Left) qRT-PCR results for the indicated gene after 24 hr treatment with each siRNA. (Right) Flow cytometry or immunoblots for the protein indicated after 7 days of siRNA treatment (n = 3 independent experiments using two different donor-derived MSC cultures; error bars represent + SD.). Cells were transfected at days 0, 2, and 5. (H) Phase-contrast images of cells at day 7 after siRNA additions (representative images from three independent experiments all with two different donor-derived MSC cultures). Cells were transfected at days 0, 2, and 5. (I) Cell proliferation assay results. Cells were plated at 1,800 cells per cm2 and incubated with specific siRNAs for the indicated time periods before assessing cell numbers. Cells were transfected with siRNAs at days 0, 2, 5, and 7. Plots show error bars + SD (n = 4 independent experiments using two different donor-derived MSC cultures). p < 0.05 compared with control siRNA. (J) Cell wound assay migration results. Cells were grown to confluency for 5 days with siRNA addition (transfected day 0, 2, and 5) before a single wound was made and wound closure was monitored for 24 hr. Data are represented as percentage wound coverage at 12 and 24 hr after injury. Plots show error bars +SD (n = 4 independent experiments using two different donor-derived MSC cultures). p < 0.05 compared with control siRNA.
Figure 6
Figure 6
Mesenchymal Progenitor Cell Marker siRNAs Affect Focal Adhesion Formation, Cell Shape, and Gene Expression Profiles of MSCs (A) Representative immunofluorescence staining for vinculin (green), F-actin (red), and nuclei (DAPI, blue) after siRNA treatment for 7 days (n = 3 independent experiments using two different donor-derived MSC cultures). Cells were plated at equivalent densities 48 hr prior to imaging. (B–G) Cell image processing to determine the size and shape measurements of MSCs after staining with wheat germ agglutinin, F-actin, and DAPI on day 7 of siRNA-treated cultures plated at equivalent densities 24 hr prior to imaging (B). Processed CellProfiler output files determining cell boundaries are shown. Full images are shown in Figure S5A. Representative length and width measurements (C), length to width ratios (D), cytoplasm and nuclei measurements (E), nucleus to cytoplasm ratios (F) and two distinct shape features, eccentricity, extent, and form factor (G) taken from six to ten processed images from two independent experiments both using two different MSC cultures (n = 4). Plots show error bars + SEM. p < 0.05 compared with control siRNA. (H–M) qRT-PCR to define the changes in expression of adiopogenic (H), osteogenic (I), chondrogenic (J), ectodermal (K), endodermal (L), and mesodermal (M) markers after siRNA treatment for 12 days under multipotent growth conditions relative to control siRNA treated cultures (n = 4 from two independent experiments using two different donor-derived MSCs). Plots show error bars + SD. (N and O) Expression of CD9, ROR2, EPHA2, PLXNA2, and CDH13 after treatment with the indicated siRNA for 6 hr (N) or 12 days (O) relative to control siRNA. Expression is normalized to housekeeper genes TBP and β2M. Error bars + SEM (n = 4 from two independent experiments using two different donor-derived MSCs); p < 0.05 compared with control siRNA. See also Figure S5.

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