Recruitment and entrapment of bone marrow-derived endothelial progenitor cells (EPCs)
is important in vascular endothelial growth factor (VEGF)-induced angiogenesis. EPC
mobilization and differentiation are modulated by stromal-derived factor-1alpha (SDF-1alpha/CXCL12),
another important chemokine. In this study, we investigated the hypothesis that SDF-1alpha
and VEGF might act synergistically on EPC-mediated vasculogenesis.
EPCs were isolated and cultured from human peripheral blood, then transduced with
retroviral vectors pBabe containing human VEGF(165) complimentary DNA (Td/V-EPCs)
and pBabe wild-type (Td/p-EPCs). EPC migration activity was investigated with a modified
Boyden chamber assay. EPC apoptosis induced by serum starvation was studied by annexin
V assays. The combined effect of local administration of SDF-1alpha and Td/V-EPC transplantation
on neovascularization was investigated in a murine model of hind limb ischemia.
Over-expression of hVEGF(165) increased SDF-1alpha-mediated EPC migration. SDF-1alpha-mediated
migration was significantly increased when EPCs were modified with VEGF (Td/V-EPCs)
vs when VEGF was not present (Td/p-EPCs) or when VEGF alone was present (Td/V-EPCs;
196.8 +/- 15.2, 81.2 +/- 9.8, and 67.4 +/- 7.4/mm(2), respectively P < .001). SDF-1alpha
combined with VEGF reduced serum starvation-induced apoptosis of EPCs more than SDF-1alpha
or VEGF alone (P < .001). To determine the effect of this combination in vivo, SDF-1alpha
was locally injected alone into the ischemic hind limb muscle of nude mice or combined
with systemically injected Td/V-EPCs. The SDF-1alpha plus VEGF group showed significantly
increased local accumulation of EPCs, blood-flow recovery, and capillary density compared
with the other groups. The ratio of ischemic/normal blood flow in Td/V-EPCs plus SDF-1alpha
group was significantly higher (P < .01), as was capillary density (capillaries/mm(2)),
an index of neovascularization (Td/V-EPCs plus SDF-1alpha group, 863 +/- 31; no treatment,
395 +/-13; SDF-1alpha, 520 +/- 29; Td/p-EPCs, 448 +/- 28; Td/p-EPCs plus SDF-1alpha,
620 +/- 29; Td/V-EPCs, 570 +/- 30; P < .01). To investigate a possible mechanistic
basis, we showed that VEGF up-regulated the receptor for SDF-1alpha, CXCR4, on EPCs
in vitro.
The combination of SDF-1alpha and VEGF greatly increases EPC-mediated angiogenesis.
The use VEGF and SDF-1alpha together, rather than alone, will be a novel and efficient
angiogenesis strategy to provide therapeutic neovascularization.