Contribution of stem cells to neointimal formation of decellularized vessel grafts in a novel mouse model.

Artificial vessel grafts are often used for the treatment of occluded blood vessels, but neointimal lesions commonly occur. To both elucidate and quantify which cell types contribute to the developing neointima, we established a novel mouse model of restenosis by grafting a decellularized vessel to the carotid artery. Typically, the graft developed neointimal lesions after 2 weeks, resulting in lumen closure within 4 weeks. Immunohistochemical staining revealed the presence of endothelial and smooth muscle cells, monocytes, and stem/progenitor cells at 2 weeks after implantation. Explanted cultures of neointimal tissues displayed heterogeneous outgrowth in stem cell medium. These lesional cells expressed a panel of stem/progenitor markers, including c-kit, stem cell antigen-1 (Sca-1), and CD34. Furthermore, these cells showed clonogenic and multilineage differentiation capacities. Isolated Sca-1(+) cells were able to differentiate into endothelial and smooth muscle cells in response to vascular endothelial growth factor (VEGF) or platelet-derived growth factor (PDGF)-BB stimulation in vitro. In vivo, local application of VEGF to the adventitial side of the decellularized vessel increased re-endothelialization and reduced neointimal formation in samples at 4 weeks after implantation. A population of stem/progenitor cells exists within developing neointima, which displays the ability to differentiate into both endothelial and smooth muscle cells and can contribute to restenosis. Our findings also indicate that drugs or cytokines that direct cell differentiation toward an endothelial lineage may be effective tools in the prevention or delay of restenosis.