Blood outgrowth endothelial cells from cord blood and peripheral blood: angiogenesis-related characteristics in vitro: a rebuttal

Osteoprotegerin Induces CD34+ Differentiation in Endothelial Progenitor Cells

Endothelial progenitor cells (EPCs) are the main hypothetical cells that could give rise to vessels and in particular one subtype isolated from peripheral or cord bloods: endothelial colony forming cells (ECFCs). These ECFCs are clonogenic precursors committed to endothelial lineage and have robust vasculogenic properties. However, their low number and poor expansion properties when isolated from human adult bloods, currently limit their use as an autologous cell therapy product. We previously reported that osteoprotegerin (OPG), a well-characterized regulator of bone metabolism, contributes to ischemic tissue revascularization, tumor growth in vivo, and potentiates ECFCs proangiogenic properties through the secretion of SDF-1. The current study investigated the role of OPG in ECFCs differentiation and expansion from cord blood CD34⁺ cells. OPG increased the number of ECFCs after endothelial differentiation of CD34⁺ cells, enhancing the time of EPCs colonies initial appearance and the growth kinetic of endothelial cell progeny. OPG-exposed ECFCs expressed higher levels of CD34⁺ compared to control ECFCs. In conclusion, our findings provide novel insights into OPG in regulation of CD34⁺ progenitor cells. These results give new opportunities for ex vivo expansion of human ECFCs using OPG as a cell culture component for future ECFC product manufacture according to GMP.

Co-injection of mesenchymal stem cells with endothelial progenitor cells accelerates muscle recovery in hind limb ischemia through an endoglin-dependent mechanism

Endothelial colony-forming cells (ECFCs) are progenitor cells committed to endothelial lineages and have robust vasculogenic properties. Mesenchymal stem cells (MSCs) have been described to support ECFC-mediated angiogenic processes in various matrices. However, MSC-ECFC interactions in hind limb ischemia (HLI) are largely unknown. Here we examined whether co-administration of ECFCs and MSCs bolsters vasculogenic activity in nude mice with HLI. In addition, as we have previously shown that endoglin is a key adhesion molecule, we evaluated its involvement in ECFC/MSC interaction. Foot perfusion increased on day 7 after ECFC injection and was even better at 14 days. Co-administration of MSCs significantly increased vessel density and foot perfusion on day 7 but the differences were no longer significant at day 14. Analysis of mouse and human CD31, and in situ hybridization of the human ALU sequence, showed enhanced capillary density in ECFC+MSC mice. When ECFCs were silenced for endoglin, coinjection with MSCs led to lower vessel density and foot perfusion at both 7 and 14 days (p<0.001). Endoglin silencing in ECFCs did not affect MSC differentiation into perivascular cells or other mesenchymal lineages. Endoglin silencing markedly inhibited ECFC adhesion to MSCs. Thus, MSCs, when combined with ECFCs, accelerate muscle recovery in a mouse model of hind limb ischemia, through an endoglin-dependent mechanism.

Human Cord Blood-Derived CD133+/C-Kit+/Lin- Cells Have Bipotential Ability to Differentiate into Mesenchymal Stem Cells and Outgrowth Endothelial Cells

Recent evidence suggests that mononuclear cells (MNCs) derived from bone marrow and cord blood can differentiate into mesenchymal stem cells (MSCs) or outgrowth endothelial cells (OECs). However, controversy exists as to whether MNCs have the pluripotent capacity to differentiate into MSCs or OECs or are a mixture of cell lineage-determined progenitors of MSCs or OECs. Here, using CD133⁺/C-kit⁺/Lin⁻ mononuclear cells (CKL− cells) isolated from human umbilical cord blood using magnetic cell sorting, we characterized the potency of MNC differentiation. We first found that CKL− cells cultured with conditioned medium of OECs or MSCs differentiated into OECs or MSCs and this differentiation was also induced by cell-to-cell contact. When we cultured single CKL− cells on OEC- or MSC-conditioned medium, the cells differentiated morphologically and genetically into OEC- or MSC-like cells, respectively. Moreover, we confirmed that OECs or MSCs differentiated from CKL− cells had the ability to form capillary-like structures in Matrigel and differentiate into osteoblasts, chondrocytes, and adipocytes. Finally, using microarray analysis, we identified specific factors of OECs or MSCs that could potentially be involved in the differentiation fate of CKL− cells. Together, these results suggest that cord blood-derived CKL− cells possess at least bipotential differentiation capacity toward MSCs or OECs.

Bone-marrow-derived very small embryonic-like stem cells in patients with critical leg ischaemia: evidence of vasculogenic potential

Very small embryonic-like stem cells (VSELs) are multipotent stem cells localised in adult bone marrow (BM) that may be mobilised into peripheral blood (PB) in response to tissue injury. We aimed to quantify VSELs in BM and PB of patients with critical limb ischaemia (CLI) and to test their angiogenic potential in vitro as well as their therapeutic capacity in mouse model of CLI. We isolated BM VSELs from patients with CLI and studied their potential to differentiate into vascular lineages. Flow and imaging cytometry showed that VSEL counts were lower in BM (p< 0.001) and higher (p< 0.001) in PB from CLI patients compared to healthy controls, suggesting that ischaemia may trigger VSELs mobilisation in this patient population. Sorted BM-VSELs cultured in angiogenic media acquired a mesenchymal phenotype (CD90+, Thy-1 gene positive expression). VSEL-derived cells had a pattern of secretion similar to that of endothelial progenitor cells, as they released low levels of VEGF-A and inflammatory cytokines. Noteworthy, VSELs triggered post-ischaemic revascularisation in immunodeficient mice (p< 0.05 vs PBS treatment), and acquired an endothelial phenotype either in vitro when cultured in the presence of VEGF-B (Cdh-5 gene positive expression), or in vivo in Matrigel implants (human CD31+ staining in neo-vessels from plug sections). In conclusion, VSELs are a potential new source of therapeutic cells that may give rise to cells of the endothelial lineage in humans.

Uterine vasculature remodeling in human pregnancy involves functional macrochimerism by endothelial colony forming cells of fetal origin

The potency of adult-derived circulating progenitor endothelial colony forming cells (ECFCs) is drastically surpassed by their fetal counterparts. Human pregnancy is associated with robust intensification of blood flow and vascular expansion in the uterus, crucial for placental perfusion and fetal supply. Here, we investigate whether fetal ECFCs transmigrate to maternal bloodstream and home to locations of maternal vasculogenesis, primarily the pregnant uterus. In the first instance, endothelial-like cells, originating from mouse fetuses expressing paternal eGFP, were identified within uterine endothelia. Subsequently, LacZ or enhanced green fluorescent protein (eGFP)-labeled human fetal ECFCs, transplanted into immunodeficient (NOD/SCID) fetuses on D15.5 pregnancy, showed similar integration into the mouse uterus by term. Mature endothelial controls (human umbilical vein endothelial cells), similarly introduced, were unequivocally absent. In humans, SRY was detected in 6 of 12 myometrial microvessels obtained from women delivering male babies. The copy number was calculated at 175 [IQR 149-471] fetal cells per millimeter square endothelium, constituting 12.5% of maternal vessel lumina. Cross-sections of similar human vessels, hybridized for Y-chromosome, positively identified endothelial-associated fetal cells. It appears that through ECFC donation, fetuses assist maternal uterine vascular expansion in pregnancy, potentiating placental perfusion and consequently their own fetal supply. In addition to fetal growth, this cellular mechanism holds implications for materno-fetal immune interactions and long-term maternal vascular health.

Imbalance of circulating endothelial cells and progenitors in idiopathic pulmonary fibrosis

BACKGROUND

Fibrogenesis during idiopathic pulmonary fibrosis (IPF) is strongly associated with abnormal vascular remodeling. Respective abundance of circulating endothelial cells (CEC) and endothelial progenitor cells (EPC) might reflect the balance between vascular injury and repair and potentially serve as biomarkers of the disease.

OBJECTIVES AND METHODS

We postulated that CEC and EPC subtypes might be differently modulated in IPF. Sixty-four consecutive patients with newly diagnosed IPF were prospectively enrolled and compared to thirteen healthy volunteers. CEC were counted with immunomagnetic CD146-coated beads; progenitors CD34+45(dim)/CD34+133+/CD34+KDR+were assessed through flow cytometry and EPC (colony-forming-units-Endothelial Cells, CFU-EC, and endothelial colonies forming cells, ECFC) were quantified by cell culture assays.

RESULTS

IPF patients were characterized by a marked increase in CEC associated to an EPC defect: both CD34(+)KDR(+) cells and CFU-EC were decreased versus controls. Moreover, in IPF subjects with a low diffusing capacity of the lung for carbon monoxide (DL(CO)) < 40 %, CFU-EC and ECFC were higher compared to those with DL(CO) > 40 %. Finally, ECFC were negatively correlated with DL(CO). During an 18 month follow up, CEC levels increased in patients with exacerbation, including those who died during follow up. Finally, ECFC from patients with exacerbation proliferative potential was strongly increased.

CONCLUSION

IPF is basically associated with both a vascular injury and a repair defect. This study highlights an adaptative process of EPC mobilization in the most severe forms of IPF, that could reflect enhanced homing to the pulmonary vasculature, which clinical consequences remain to be determined.