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. 2016 Apr 12;6(4):607-617.
doi: 10.1016/j.stemcr.2016.02.014. Epub 2016 Mar 24.

Wnt/β-Catenin Stimulation and Laminins Support Cardiovascular Cell Progenitor Expansion From Human Fetal Cardiac Mesenchymal Stromal Cells

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Wnt/β-Catenin Stimulation and Laminins Support Cardiovascular Cell Progenitor Expansion From Human Fetal Cardiac Mesenchymal Stromal Cells

Agneta Månsson-Broberg et al. Stem Cell Reports. .
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Abstract

The intrinsic regenerative capacity of human fetal cardiac mesenchymal stromal cells (MSCs) has not been fully characterized. Here we demonstrate that we can expand cells with characteristics of cardiovascular progenitor cells from the MSC population of human fetal hearts. Cells cultured on cardiac muscle laminin (LN)-based substrata in combination with stimulation of the canonical Wnt/β-catenin pathway showed increased gene expression of ISL1, OCT4, KDR, and NKX2.5. The majority of cells stained positive for PDGFR-α, ISL1, and NKX2.5, and subpopulations also expressed the progenitor markers TBX18, KDR, c-KIT, and SSEA-1. Upon culture of the cardiac MSCs in differentiation media and on relevant LNs, portions of the cells differentiated into spontaneously beating cardiomyocytes, and endothelial and smooth muscle-like cells. Our protocol for large-scale culture of human fetal cardiac MSCs enables future exploration of the regenerative functions of these cells in the context of myocardial injury in vitro and in vivo.

Figures

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Figure 1
Figure 1
Derivation of Multipotent MSCs from Human Fetal Hearts (A) Schematic representation of the experimental procedure used to generate and expand multipotent cardiac MSCs from the adherent cell fraction of human fetal hearts (gestational weeks 6–10). (B) The initial adherent MSC fraction was cultured under different conditions: Wnt-medium + Geltrex (green), Wnt-medium + plastic (red), medium without Wnt3a + Geltrex (blue), and medium without Wnt3a + plastic (gray). (C) mRNA expression levels of cardiogenic genes in response to the different culture conditions depicted in (B). Data are normalized against the cells cultured with Wnt3a + Geltrex and presented as mean ± SD of three independent experiments performed in quadruplicate. See also Figure S1. (D) Western blot analysis confirmed the activation of the Wnt/β-catenin pathway in the cultured human fetal cardiac MSCs (hfcMSC), demonstrating increased levels of both phosphorylated S1490-Lrp6 and Dvl3 (left panel) as well as active (dephosphorylated) β-catenin (ABC) (right panel) compared with the initial adherent cell fraction. β-Actin was used as a control of equal loading of protein. ∗∗p < 0.01; ∗∗∗p < 0.001.
Figure 2
Figure 2
Differentiation into Mesenchymal Lineages To confirm the mesenchymal origin of the fetal cardiac MSCs they were differentiated into the three mesenchymal lineages: bone (alkaline phosphatase, ALP), cartilage (Aggrecan), and adipose tissue (oil red O, ORO). See also Figure S2. Scale bars represent 100 μm.
Figure 3
Figure 3
Characterization of Cultured Cardiac MSCs (A) The gene-expression profile of key transcription factors related to mesodermal progenitors as well as markers of cardiovascular differentiation and pluripotency was analyzed with microarray in cultured cardiac MSCs at day 15, 27, and 48. Log2 transformation of signals is depicted as bar graphs. (B) Immunofluorescence staining (green) of ISL1, TBX18 (arrows), and NKX2.5 after 3 weeks in culture. (C) Flow cytometry analysis of cardiac MSCs from different human fetal hearts (gestational weeks 8 and 9, n = 6) gave a quantitative assessment of the proportions of cells expressing KDR, c-KIT, and SSEA-1 (mean ± SD). (D) Immunocytochemical staining of SSEA-1 (green) and PDGFR-α (green). Nuclei are stained with DAPI. In (B) and (D), scale bars represent 50 μm.
Figure 4
Figure 4
LN-Based Propagation and Differentiation of Cardiac MSCs (A) Immunohistochemical staining of laminin chains α2, α5, and γ1 (all red) in a human fetal heart (gestational week 9). Nuclei are stained with DAPI. Scale bars represent 200 μm. (B) Normalized mRNA levels ISL1 and TNNT2 from fetal cardiac MSCs cultured for 2 weeks on Geltrex, LN-511 or LN-521 in medium containing Wnt3a. (C) Normalized mRNA levels of ISL1, KDR, NKX2.5, and TNNT2 from cardiac MSCs expanded for 2 weeks on LN-521 followed by culture on LN-211 and Geltrex for 2 weeks in medium devoid of Wnt3a. Data presented as mean ± SD of three independent experiments performed in quadruplicate. ∗∗p < 0.001. (D) Normalized levels of TNNT2 expression in cells cultured on Geltrex (control) or LN-211 with or without blocking antibodies against α-DG and β1-integrins or corresponding isotype control antibodies. Data are presented as means ± SD of three independent experiments performed in duplicate. p = 0.05.
Figure 5
Figure 5
Cardiomyocyte Differentiation Potential of Human Fetal Cardiac MSCs (A) Upon exposure to cardiomyocyte differentiation medium, portions of the cardiac MSCs differentiated into elongated, striated TnT+ (green) cardiomyocytes. Scale bar represents 50 μm. (B) A zoom-in of the box in (A) demonstrating the striations in the cardiomyocytes. (C) All cardiac MSCs stained negative for TnT prior to initiation of the differentiation protocol. Scale bar represents 50 μm. (D) Primary cardiomyocytes isolated from a human fetal heart were used as a positive control. Nuclei are stained with DAPI (blue). Scale bar represents 50 μm. (E) Normalized mRNA levels of TNNT2 before and after differentiation on Matrigel and LN-211. (F) Numbers of TnT+ cells of human fetal cardiac MSCs differentiated on plastic, LN-211, and Matrigel. Numbers of positive cells are normalized against the total number of nuclei in the same well multiplied by a factor of 100,000. Data are presented as means ± SD of three independent experiments performed in triplicate. p < 0.05.
Figure 6
Figure 6
Differentiation into Endothelial and Smooth Muscle Cells The cardiac MSCs underwent differentiation into endothelial cells (left panel) expressing CD31 (red) and smooth muscle cells (right panel) expressing α-SMA (green). There was no CD31 expression before differentiation, whereas the majority of the cardiac MSCs expressed α-SMA in abundance before initiation of differentiation. The intensity of the α-SMA staining did not increase as a result of differentiation but rather appeared in a more polarized fashion similar to what can be found in contractile, adult vascular smooth muscle cells exposed to PDGF-BB and TGF-β1. Human aortic endothelial cells (HAEC) and smooth muscle cells from a human carotid artery (HCtSMC) were positive controls for endothelial cells and smooth muscle cells, respectively. Nuclei are stained blue with DAPI. Scale bars represent 50 μm.

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