Evidence for Vasculogenic Potential and Endothelial Differentiation of Bone-Marrow-Derived Very Small Embryonic-like Stem Cells

Objective: Very small embryonic-like stem cells (VSELs) are multipotent stem cells localized in adult bone marrow (BM) that may be mobilized into peripheral blood (PB) in response to tissue injury. We aimed to quantify VSELs in BM and PB of patients with critical limb ischemia (CLI) and to test their angiogenic potential in vitro as well as their therapeutic capacity in mouse model of CLI.

Approach and Results: 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 ischemia may trigger VSELs mobilization 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-ischemic revascularization 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).

Conclusions: VSELs are a potential new source of therapeutic cells that may give rise to cells of the endothelial lineage in humans.