Human fetal aorta-derived vascular progenitor cells: identification and potential application in ischemic diseases

Abstract

Vasculogenesis, the formation of blood vessels in embryonic or fetal tissue mediated by immature vascular cells (i.e., angioblasts), is poorly understood. Here we report a summary of our recent studies on the identification of a population of vascular progenitor cells (VPCs) in human fetal aorta. These undifferentiated mesenchymal cells co-express endothelial and myogenic markers (CD133+, CD34+, KDR+, desmin+) and are localized in outer layer of the aortic stroma of 11-12 weeks old human fetuses. Under stimulation with VEGF-A or PDGF-BB, VPCs give origin to a mixed population of mature endothelial and mural cells, respectively. When embedded in a three-dimensional collagen gel, VPCs organize into cohesive cellular cords that resembled mature vascular structures. The therapeutic efficacy of a small number of VPCs transplanted into ischemic limb muscle was demonstrated in immunodeficient mice. Investigation of the effect of VPCs on experimental heart ischemia and on diabetic ischemic ulcers in mice is in progress and seems to confirm their efficacy. On the whole, fetal aorta represents an important source for the investigation of phenotypic and functional features of human vascular progenitor cells.

Fig. 1

Identification of VPCs in Human FA. a Micrographs of collagen gel culture of human fetal aorta explants: an example of outgrowths of branching capillary-like tubes after 72 h of culture. The cords grow haphazardly and divide into branches to form complex structures. b Immunohistochemistry of capillary-like structures arising from aortic rings paraffine-embedded after 72 h of culture in collagen gel matrix: cross-section of an aortic ring showing many CD31-positive cells organized into capillary-like structures. These outgrowths appear to arise from undifferentiated mesenchymal cells at the periphery of explants. c Immunohistochemistry of untreated fetal aorta. The tissues were immediately fixed after recovery and then embedded in paraffin and cross-sectioned. Left upper panel shows aortic ring stained with CD31, left lower and right upper panel stained with CD34, lower right panel stained with KDR. CD31 (mature endothelial marker) stained only pre-existing endothelial lining the aorta lumen it was absent in the parenchyma or at periphery of aorta. In contrast CD34 and KDR stained both mature ECs and a lot of mesenchymal immature cells present particularly in the outer layer of aorta stroma. d Immature sorted CD34+CD133+KDR+VPCs grow in culture as cells aggregates. When seeded in a collagen gel they start to form vascular-like structures that connect each other

Fig. 2

Therapeutic efficacy of VPCs treatment on experimental hind limb ischemia. a Immunohistochemical identification of VPCs injected locally in mouse hind limb ischemic muscle. VPCs colored in green appear localized in the vicinity of capillaries and arterioles colored in red (upper panel) and in muscle fibers colored in red (lower panel). b Immunohistochemistry of control muscle treated with control cells or medium. The absence of cells demonstrated the specificity of the antibodies (anti-human nuclei) used for VPCs identification. c Distribution of necrotic toes in the left foot of mice that were exposed to ipsilateral ischemia. Zero means absence of necrotic toes, 5 indicates all toes being necrotic or absent. One point was scored for each necrotic toe. Each circle is representative of a single mouse. Note that EPCs treatment (at the same dose of VPCs) did not significantly ameliorate the number of necrotic toes, whereas VPCs significantly reduced the necrotic toes. d A representative image of hindlimb region submitted to ischemia and treated with VPCs or control medium (CM). Note the absence of necrosis in the foot of mouse treated with VPCs