Objectives-As SDF-1 and its cognate receptor CXCR4 play a key role in the survival and mobilization of immature cells, we examined whether preconditioning of endothelial progenitor cells (EPCs) with SDF-1 could further promote their capacity to enhance angiogenesis. Methods and Results-EPC exposure to 100 ng/mL SDF-1 for 30 min induced a proangiogenic phenotype, with cell migration and differentiation into vascular cords in Matrigel and increased their therapeutic potential in a nude mouse model of hindlimb ischemia. This pretreatment enhanced EPC adhesion to activated endothelium in physiological conditions of blood flow by stimulating integrin-mediated EPCs binding to endothelial cells. Pretreated EPCs showed significantly upregulated surface ␣4 and ␣M integrin subunit expression involved in the homing of immature cells to a neovasculature and enhanced FGF-2 and promatrix metalloproteinase (MMP)-2 secretion. All these effects were significantly attenuated by EPC incubation with AMD-3100, a CXCR4 antagonist, by prior HSPGs disruption and by HUVEC incubation with anti-intercellular adhesion molecule1 (ICAM-1) and anti-vascular cell adhesion molecule (VCAM) blocking antibodies. Pretreated EPCs adhered very rapidly (within minutes) and were resistant to shear stresses of up to 2500s Ϫ1 . Key Words: endothelial progenitor cells Ⅲ SDF-1 Ⅲ ischemia Ⅲ HSPGs Ⅲ adhesion T he discovery of bone marrow-derived endothelial progenitor cells (EPCs) in peripheral blood prompted an intensive search for new ways of inducing neovascularization in patients with heart and limb ischemia, based on transplantation of bone marrow-or peripheral blood-derived EPCs. 1,2 Several studies indicated that local implantation of ex vivoexpanded EPCs improved neovascularization of damaged tissues in animal models of hindlimb ischemia. [2][3][4][5] Contrary to differentiated endothelial cells, administration of EPCs led to increased blood flow in ischemic limbs of nude mice. These immature cells promote neovascularization by differentiating in situ into endothelial cells and by secreting growth factors, cytokines, and proteases that support angiogenic and vasculogenic processes. 6 -8 However, transplantation of autologous EPCs has several limitations, including the limited supply of expanded progenitors, the time required to harvest, expand, and reinject autologous EPCs, and poor graft efficiency. In addition, EPCs appear to undergo unfavorable functional changes during the expansion procedure. 9 This may explain why the capacity of injected EPCs to promote neovascularization is highly variable and depends on the experimental model. 1,10 The yield is currently so low that very large blood volumes would have to be processed to obtain sufficient EPCs for therapeutic use. The required number of EPCs can be reduced by using local infusion 3,5,11 or by concomitant infusion of proangiogenic proteins. 4,12 In addition, EPCs can be activated before their injection 3,5,10 or mobilized into the circulation by cytokines. 7,13 Cytokines released by damaged ti...

Because cells are sensitive to mechanical forces, weightlessness might act on stress-dependent cell changes. We hypothesized that the integration of environmental factors might induce specific cytoskeletal architecture patterns, characterized by quantitative image analysis. Human breast cancer cells MCF-7, flown in space in a photon capsule, were fixed after 1.5, 22, and 48 h in orbit. Cells subjected to weightlessness were compared with 1g in-flight and ground controls. Postflight, fluorescent labelings were performed to visualize cell proliferation (Ki-67), signal transduction (phosphotyrosine), three cytoskeleton components (microtubules, microfilaments, and intermediate filaments), and chromatin structure. Confocal microscopy and image analysis were used to quantify cycling cells and mitosis, modifications of the cytokeratin network, and chromatin structure. In weightlessness, phosphotyrosine signal transduction was lower, more cells were cycling, and mitosis was prolonged. Finally, cell proliferation was reduced as a consequence of a cell-cycle blockade. Microtubules were altered in many cells. The perinuclear cytokeratin network was more loosely 'woven', and chromatin structure was modified. The prolongaion of mitosis can be explained by an alteration of microtubule self-organization in weightlessness, involving reaction-diffusion processes. The loosening of the perinuclear cytokeratin network and modification of chromatin distribution are in agreement with basic predictions of cellular tensegrity.