Chemokine stromal derived factor 1 (SDF-1) is involved in trafficking of hematopoietic stem cells (HSCs) from the bone marrow (BM) to peripheral blood (PB) and has been found to enhance postischemia angiogenesis. This study was aimed at investigating whether SDF-1 plays a role in differentiation of BM-derived c-kit ؉ stem cells into endothelial progenitor cells (EPCs) and in ischemia-induced trafficking of stem cells from PB to ischemic tissues. We found that SDF-1 enhanced EPC number by promoting ␣ 2 , ␣ 4 , and ␣ 5 integrinmediated adhesion to fibronectin and collagen I. EPC differentiation was reduced in mitogen-stimulated c-kit ؉ cells, while cytokine withdrawal or the overexpression of the cyclin-dependent kinase (CDK) inhibitor p16 INK4 restored such differentiation, suggesting a link between control of cell cycle and EPC differentiation. We also analyzed the time course of SDF-1 expression in a mouse model of hind-limb ischemia. Shortly after femoral artery dissection, plasma SDF-1 levels were up-regulated, while SDF-1 expression in the bone marrow was down-regulated in a timely fashion with the increase in the percentage of PB progenitor cells. An increase in ischemic tissue expression of SDF-1 at RNA and protein level was also observed. Finally, using an in vivo assay such as injection of matrigel plugs, we found that SDF IntroductionIt has been shown that endothelial progenitor cells (EPCs) play a role in vascular repair following ischemic injury. 1 EPCs give rise to endothelial-like cells in culture, growing as spindleshaped cells attaching to culture dishes coated with extracellular matrix (ECM) components. 2 However, the mechanisms driving EPC differentiation are largely unknown. Stromal-derived factor 1 (SDF-1) regulates adhesion/chemotaxis of bone marrow hematopoietic progenitor cells through activation/regulation of specific integrin molecules. [3][4][5] This factor is, therefore, suggested to play a major role in successful hematopoietic stem cell (HSC) engraftment in the bone marrow. 6 In vivo gene inactivation of SDF-1 and its receptor C-X-C chemokine receptor 4 in mice led to early embryonic lethality due to abnormal cerebellar, gastrointestinal vasculature, and hematopoiesis development. [7][8][9] A role for SDF-1 in HSC/EPC recruitment from bone marrow (BM) to peripheral blood (PB) has been proposed, based on the evidence that granulocyte colony stimulating factor (G-CSF)-mediated HSC/EPC mobilization causes an imbalance between the expression of BM SDF-1 and CXCR4 in HSCs, 10 and that SDF-1␣ adenovirus gene transfer enhances the number of circulating HSCs/EPCs. [11][12][13] Recently, overexpression of SDF-1 in ischemic tissues has been found to enhance EPC recruitment from PB and to induce neoangiogenesis. 14,15 In this paper, we show that SDF-1 increases EPC number through enhancement of (BM) c-kit ϩ stem cell adhesion onto extracellular matrix components by integrin receptors. Further, we show that treatment of c-kit ϩ cells with mitogenic cytokines abolished SDF-1-mediated EPC differen...

Leukocyte recruitment to sites of infection or inflammation requires multiple adhesive events. While numerous players promoting leukocyte-endothelial interactions have been characterized, functionally important endogenous inhibitors of leukocyte adhesion have not been identified. Here, we describe the endothelial-derived secreted molecule, developmental endothelial locus-1 (Del-1), as an anti-adhesive factor that interferes with the integrin LFA-1-dependent leukocyte-endothelial adhesion. Endothelial Del-1-deficiency increased LFA-1-dependent leukocyte adhesion in vitro and in vivo. Del-1-/-mice displayed significantly higher neutrophil accumulation in LPS-induced lung inflammation in vivo, which was reversed in Del-1/LFA-1-double deficient mice. Thus, Del-1 is an endogenous inhibitor of inflammatory cell recruitment and could provide a basis for targeting leukocyte-endothelial interactions in disease.Leukocyte extravasation is integral to the response to infection or injury and to inflammation and autoimmunity. Leukocyte recruitment comprises a well coordinated cascade of adhesive events including selectin-mediated rolling, firm adhesion of leukocytes to endothelial cells and & This manuscript has been accepted for publication in Science. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/. The manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the Copyright Act without the prior, written permission of AAAS. †To whom correspondence should be addressed chavakist@mail.nih.gov. * EYC and EC contributed equally # MAC and HL contributed equally NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript their subsequent transendothelial migration. The interaction between LFA-1 (αLβ2, CD11a/ CD18) and endothelial ICAM-1 is crucial during firm endothelial adhesion of leukocytes (1-5). Whereas numerous adhesion receptors promoting inflammatory cell recruitment have been identified, very little information exists about endogenous inhibitors of the leukocyte adhesion cascade (1-7). Developmental endothelial locus-1 (Del-1) is a glycoprotein that is secreted by endothelial cells and can associate with the endothelial cell surface and the extracellular matrix (8-10). Del-1 is regulated upon hypoxia or vascular injury and has been implicated in vascular remodelling during angiogenesis (10-12). Here, we sought to determine whether endothelial-derived Del-1 participates in leukocyte-endothelial interactions. RT-PCR analysis revealed Del-1 mRNA predominantly in the brain and lung, with no expression in liver, spleen, or whole blood (Fig. 1A and fig. S1A). Del-1 was expressed in WT but not in Del-1-/-murine lung endothelial cells (Fig. 1B, 9). Immunohistochemistry of lung tissues demonstrated the presence of Del-1 in vessels, as observed by co-staining with the endothelial marker PECAM-1 ( fig. S1B).To determine whether Del-1 participates in leukocyte recruitmen...

Abstract-Human umbilical cord blood (UCB) contains high numbers of endothelial progenitors cells (EPCs) characterized by coexpression of CD34 and CD133 markers. Prior studies have shown that CD34 ϩ /CD133 ϩ EPCs from the cord or peripheral blood (PB) can give rise to endothelial cells and induce angiogenesis in ischemic tissues. In the present study, it is shown that freshly isolated human cord blood CD34 ϩ cells injected into ischemic adductor muscles gave rise to endothelial and, unexpectedly, to skeletal muscle cells in mice. In fact, the treated limbs exhibited enhanced arteriole length density and regenerating muscle fiber density. Under similar experimental conditions, CD34-cells did not enhance the formation of new arterioles and regenerating muscle fibers. In nonischemic limbs CD34 ϩ cells increased arteriole length density but did not promote formation of new muscle fibers. Endothelial and myogenic differentiation ability was maintained in CD34 ϩ cells after ex vivo expansion.