Vasculogenic and Osteogenesis-Enhancing Potential of Human Umbilical Cord Blood Endothelial Colony-Forming Cells

Abstract

Umbilical cord blood‐derived endothelial colony‐forming cells (UCB‐ECFC) show utility in neovascularization, but their contribution to osteogenesis has not been defined. Cocultures of UCB‐ECFC with human fetal‐mesenchymal stem cells (hfMSC) resulted in earlier induction of alkaline phosphatase (ALP) (Day 7 vs. 10) and increased mineralization (1.9×; p < .001) compared to hfMSC monocultures. This effect was mediated through soluble factors in ECFC‐conditioned media, leading to 1.8–2.2× higher ALP levels and a 1.4–1.5× increase in calcium deposition (p < .01) in a dose‐dependent manner. Transcriptomic and protein array studies demonstrated high basal levels of osteogenic (BMPs and TGF‐βs) and angiogenic (VEGF and angiopoietins) regulators. Comparison of defined UCB and adult peripheral blood ECFC showed higher osteogenic and angiogenic gene expression in UCB‐ECFC. Subcutaneous implantation of UCB‐ECFC with hfMSC in immunodeficient mice resulted in the formation of chimeric human vessels, with a 2.2‐fold increase in host neovascularization compared to hfMSC‐only implants (p = .001). We conclude that this study shows that UCB‐ECFC have potential in therapeutic angiogenesis and osteogenic applications in conjunction with MSC. We speculate that UCB‐ECFC play an important role in skeletal and vascular development during perinatal development but less so in later life when expression of key osteogenesis and angiogenesis genes in ECFC is lower. Stem Cells2012;30:1911–1924

CXCL12/Stromal-Cell-Derived Factor-1 Effectively Replaces Endothelial Progenitor Cells to Induce Vascularized Ectopic Bone

“…When we combined EPCs and MSCs in our hybrid constructs, we observed more luminal-vessel-like structures as well as elaborate interconnected vessel networks when compared with constructs containing the single growth factor SDF-1a, EPCs alone, or the combination of SDF-1a and EPCs. This is in accordance to our previous experiments [7] and other reports [9,12,14]. In addition, the formed vessel networks had a significantly higher mean length when compared with the single EPC or SDF-1a constructs.…”

“…It has been proven that the use of endothelial cells (ECs) or their progenitors (EPCs) improves vascularization by inducing the formation of blood vessel networks that connect to the host circulation [7]. Moreover, when ECs are combined with multipotent stromal cells (MSCs), communication between both cell types positively influences osteogenic differentiation in vitro [7][8][9][10][11] as well as bone formation in vivo [5][6][7][8]. To this end, an optimal ratio of both cell types leads to higher efficiency in the formation of tubular structures [7,9,12,13] and mineralization [7,9,10] in vitro, when compared with single-cell-type cultures.…”

“…Moreover, when ECs are combined with multipotent stromal cells (MSCs), communication between both cell types positively influences osteogenic differentiation in vitro [7][8][9][10][11] as well as bone formation in vivo [5][6][7][8]. To this end, an optimal ratio of both cell types leads to higher efficiency in the formation of tubular structures [7,9,12,13] and mineralization [7,9,10] in vitro, when compared with single-cell-type cultures. When implanted in vivo, ectopic implantations show that combined constructs contain higher density of vasculature than the seeding of MSCs alone [9,12,14] and that bone formation is positively affected by the addition of ECs or EPCs [8][9][10].…”

“…To this end, an optimal ratio of both cell types leads to higher efficiency in the formation of tubular structures [7,9,12,13] and mineralization [7,9,10] in vitro, when compared with single-cell-type cultures. When implanted in vivo, ectopic implantations show that combined constructs contain higher density of vasculature than the seeding of MSCs alone [9,12,14] and that bone formation is positively affected by the addition of ECs or EPCs [8][9][10]. At orthotopic locations, some studies claim that there is no beneficial effect on total vessel formation after implantation [6,15], while other results show significantly higher early vascularization using EPCs in combination with MSCs [5,6].…”

Platelet-Derived Growth Factor and Spatiotemporal Cues Induce Development of Vascularized Bone Tissue by Adipose-Derived Stem Cells

“…While vasculature plays a necessary and intimate role in bone development, inducing the formation of vascularized bone tissues in vitro remains a challenge because the factors that promote each lineage may be detrimental to the other. [1][2][3] This incompatibility has led researchers to develop various methods to encourage vasculature to form concurrently or in a sequential manner with osteogenic differentiation, including precise dosing regimens of induction factors, [4][5][6] various cocktail media, 7,8 and pretreating multiple cell types separately followed by a recombination in a unified graft. 5,6,[9][10][11] Yet, each of these approaches relies on mitigating competing factors, resulting in an imbalance with suboptimal results for one or both of the tissue components.…”