Tiam Mana Saffari

163 STEM CELLS, VASCULARITY, AND NERVE 8 Figure 1. Schematic drawing of interaction between stem cells, vascularity, and nerve regen - eration. After a nerve injury, paracrine cues are provided to stem cells to produce trophic and angiogenic factors that enhance nerve regeneration and angiogenesis, respectively. Blood supply mobilizes stem cells and delivers nutrients and trophic factors to the site of injury to improve nerve regeneration. Blood supply is not only important for the survivability of stem cells but also precedes nerve regeneration after nerve trauma. Copyrighted and used with permission of the Mayo Founda- tion for Medical Education and Research; all rights reserved. Stem cells and revascularization of nerve Blood vessels have been postulated to be a systemic source of stem cells in regenerating hematopoietic cells secondary to their vascular origin. Embryologically, hematopoietic stem cells emerge closely in the vicinity of vascular endothelial cells 25,26 . The subendothelial zone, located in the tunica intima of blood vessels, has been specifically implicated as a source of endothelial progenitor cells (EPC) 27 . Evidence has demonstrated that other structural layers also serve as niches for stem cells that are