Contribution of bone marrow-derived endothelial progenitor cells to neovascularization and astrogliosis following spinal cord injury.

Spinal cord injury causes initial mechanical damage, followed by ischemia-induced, secondary degeneration, worsening the tissue damage. Although endothelial progenitor cells (EPCs) have been reported to play an important role for pathophysiological neovascularization in various ischemic tissues, the EPC kinetics following spinal cord injury have never been elucidated. In this study, we therefore assessed the in vivo kinetics of bone marrow-derived EPCs by EPC colony-forming assay and bone marrow transplantation from Tie2/lacZ transgenic mice into wild-type mice with spinal cord injury. The number of circulating mononuclear cells and EPC colonies formed by the mononuclear cells peaked at day 3 postspinal cord injury. Bone marrow transplantation study revealed that bone marrow-derived EPCs recruited into the injured spinal cord markedly increased at day 7, when neovascularization and astrogliosis drastically occurred in parallel with axon growth in the damaged tissue. To elucidate further the contribution of EPCs to recovery after spinal cord injury, exogenous EPCs were systemically infused immediately after the injury. The administered EPCs were incorporated into the injured spinal cord and accelerated neovascularization and astrogliosis. These findings suggest that bone marrow-derived EPCs may contribute to the tissue repair by augmenting neovascularization and astrogliosis following spinal cord injury.