Junctional Adhesion Molecule A Expressed on Human CD34+ Cells Promotes Adhesion on Vascular Wall and Differentiation Into Endothelial Progenitor Cells
Objective— To investigate the role of junctional adhesion molecule A (JAM-A) on adhesion and differentiation of human CD34+ cells into endothelial progenitor cells.
Methods and Results— Tissue healing and vascular regeneration is a multistep process requiring firm adhesion of circulating progenitor cells to the vascular wall and their further differentiation into endothelial cells. The role of JAM-A in platelet-mediated adhesion of progenitor cells was investigated by adhesion assays in vitro and with the help of intravital fluorescence microscopy in mice. Preincubation of human CD34+ progenitor cells with soluble JAM-A-Fc (sJAM-A-Fc) resulted in significantly decreased adhesion over immobilized platelets or inflammatory endothelium under high shear stress in vitro and after carotid ligation in vivo or ischemia/reperfusion injury in the microcirculation of mice. Human CD34+ cells express JAM-A, as defined by flow cytometry and Western blot analysis. JAM-A mediates differentiation of CD34+ cells to endothelial progenitor cells and facilitates CD34+ cell-induced reendothelialization in vitro. Pretreatment of human CD34+ cells with sJAM-A-Fc resulted in increased neointima formation 3 weeks after endothelial denudation in the carotid arteries of nonobese diabetic/severe combined immunodeficient mice.
Conclusion— These results indicate that the expression of JAM-A on CD34+ cells mediates adhesion to the vascular wall after injury and differentiation into endothelial progenitor cells, a mechanism potentially involved in vascular regeneration. Human CD34+ cells express JAM-A, mediating their interaction with platelets and endothelial cells. Specifically, JAM-A expressed on human CD34+ progenitor cells regulates their adhesion over immobilized platelets or inflammatory endothelium under high shear stress in vitro and after carotid ligation in vivo or ischemia/reperfusion injury in the microcirculation of mice. Moreover, it mediates differentiation of CD34+ cells to endothelial progenitor cells and facilitates reendothelialization.
As early as 1997, Asahara and colleagues1 first reported that CD34+ cells isolated from human peripheral blood can differentiate into endothelial cells, contributing to neoangiogenesis. Since then, numerous experimental studies2–5 investigated and further supported the role of CD34+ stem cells in vascular regeneration and tissue healing. The mobilization of CD34+ cells expressing early cardiac, muscle, and endothelial markers into peripheral blood was reported in patients with acute myocardial infarction. After tissue ischemia, progenitor cells are mobilized from their bone marrow or peripheral niches into circulation, adhere at sites of the vascular lesion, and differentiate into a variety of mature cell types according to their origin and the local environment.6,7 Impairment in this pathophysiological process, as the result of either low numbers of circulating progenitor cells or dysfunctional progenitor cells, leads to inadequate vascular repair; on coexistence with different cardiovascular risk factors, this type of impairment leads to vascular injury and atherosclerosis. The level of circulating CD34+ progenitor cells predicts the occurrence of cardiovascular events and death from cardiovascular causes and correlates with cardiovascular risk factors in patients with coronary artery disease.8 Therefore, it is not surprising that a plethora of in vivo studies and clinical trials were raised to examine the therapeutic benefits of CD34+ cell transplantation in ischemic disease. The transplantation of CD34+ cells exhibited increased potency and safety for therapeutic neovascularization, cardiomyogenesis, neurogenesis, and functional regenerative recovery after myocardial infarction in vivo.9,10 However, a major part of the molecular mechanisms underlying progenitor cell-mediated repair has not yet been elaborated.
Vascular repair is a complex process that includes mobilization, chemotaxis, adhesion, proliferation, and differentiation of progenitor cells. Although homing of CD34+ progenitor cells into bone marrow has been extensively studied,11 domiciliation of CD34+ precursor cells into peripheral tissues and differentiation into endothelial cells is poorly understood. The role of platelets in domiciliation and subsequent differentiation of progenitor cells has been recently highlighted.12–17 Adherent platelets secrete a potent stem cell chemokine, the stromal cell–derived factor 1 (SDF-1); recruit circulating progenitor cells; and induce differentiation of the latter into endothelial cells.13,15 To our knowledge, the mechanisms responsible for platelet-mediated recruitment and differentiation of CD34+ cells have not been sufficiently elucidated.
Junctional adhesion molecule A (JAM-A; also known as JAM-1 or F11 receptor) is a cell adhesion molecule expressed on a variety of cells, including platelets playing a crucial role in platelet adhesion and vascular inflammation.18 The role of platelet-derived JAM-A in adhesion and differentiation of human CD34+ cells has not been described.
The present study analyzes the role of JAM-A in the adhesion and differentiation of CD34+ cells into endothelial progenitor cells.
A detailed “Methods” section is given in the Supplemental Material (available online at http://atvb.ahajournals.org).
Isolation and Culture of Platelets, Human CD34+ Cells, and Human Arterial Endothelial Cells
Human platelets were isolated as previously described.13,15 Human CD34+ cells were isolated from either human cord blood or bone marrow and cultured as previously described.14,15 Human arterial endothelial cells (haECs) were isolated and passaged according to techniques previously described.15
Adhesion Assays Under Static and Dynamic Conditions and Flow Cytometry
Evaluation of CD34+ cell adhesion to immobilized platelets under static and dynamic conditions (flow chamber) and to immobilized JAM-A-Fc was performed as previously described.15
To evaluate JAM-A expression on isolated CD34+ cells and on isolated platelets, 1-color flow cytometry was applied as previously described.15 The expression of CD146, CD31, CD34, and CD45 was determined on isolated CD34+ cells, haECs, and endothelial progenitor cells (EPCs).
Detection of JAM-A Protein by Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis and Immunoblot Analysis, CFU Assay, and Reverse Transcription–Polymerase Chain Reaction
Protein detection of JAM-A on isolated platelets and human CD34+ cells was performed with a Western blotting detection system (Enhanced Chemiluminescence [ECL], Western Blotting Detection Kit; GE Healthcare, Buckinghamshire, UK).
To analyze the effect of JAM-A on CD34+ cell differentiation to endothelial progenitor cells, CD34+ cells were either seeded onto a monolayer of isolated platelets over a collagen matrix, 10 μg/ mL; or added onto immobilized JAM-A-Fc, as previously described.15
On differentiation of CD34+ progenitor cells to endothelial progenitor cell colonies, endothelial cells were further cultivated in culture flasks and analyzed for the expression of mRNA for endothelial nitric oxide synthase, CD45, platelet endothelial cellular adhesion molecule-1 (PECAM-1) (CD31), angioprotein receptor-2 (tie-2), vascular endothelial growth-1 (flk-1) (vascular endothelial growth factor-2 [VEGFR-2]), and β-actin by RT-PCR, as previously described.15
Endothelial Injury Assay and Intravital Fluorescence Microscopy
A wound-induced reendothelialization assay was performed as previously described.19
Dichlorofluorescin (DCF)-labeled CD34+ cells, 5×104/250 μL, were intravenously injected into C57BL/6J mice before carotid artery ligation or segmental intestinal ischemia by ligation of the supplying vessels. Before and after injury, the cell–vascular wall interactions were visualized by in vivo videomicroscopy. All images were recorded and evaluated off-line.
Evaluation of Neointima Formation
Wire-induced injury of the carotid artery was performed as previously described.27 In brief, male NOD.CB17-Prkdcscid/J mice were randomly assigned to receive either CD34+ stem cells, 5×105 cells/250 μL, preincubated for 30 minutes with JAM-A-Fc, 10 μg/mL (n=5); or control-Fc, 10 μg/mL (n=6), intravenously after denudation. After 3 weeks, the mice were euthanized and the left carotid arteries were removed, embedded in paraffin, and cut in sections. Staining with hematoxylin-eosin and elastica van Gieson reagent was performed according to standard protocols. The degree of stenosis was calculated from the neointimal area, and the original lumen area was defined as the area bounded by the internal elastic lamina.
Data Presentation and Statistical Analysis
Data are given as mean±SD, unless otherwise stated. For pairwise comparisons, we applied a 2-tailed unpaired t test. For multiple comparisons between 3 or more groups, we applied an ANOVA with a subsequent Scheffé post hoc analysis. All tests were 2-tailed, and P≤0.05 was considered statistically significant. All statistical analyses were performed using commercially available software (SPSS version 15 for Windows; SPSS Inc, Cary, NC).
Adhesion of Human CD34+ Progenitor Cells Over Immobilized Platelets Is Mediated Through JAM-A Under Static and Dynamic Conditions
Murine and human progenitor cells adhere to immobilized platelets in vitro13–15 and are recruited to arterial thrombi in vivo,12 involving the chemokine SDF-1 binding to chemokine CXC receptor-4 (CXCR4)15 and the adhesion receptors P-selectin/P-selectin glycoprotein ligand 112,13 and β2-integrin.13 Nevertheless, the counterreceptor for the β2-integrin on the surface of platelets has not been described until now.
Binding of the β2-integrin lymphocyte function–associated antigen 1 (LFA-1) to JAM-A20 has been shown to enhance leukocyte interaction with platelets and endothelial cells. Because JAM-A plays a central role in cell adhesion, we investigated whether platelet-bound JAM-A plays a role in the recruitment of circulating CD34+ progenitor cells. At the beginning, we tested the adhesion of CD34+ cells on immobilized platelets under static conditions. As previously described,13,15 human CD34+ cells adhere onto immobilized platelets, but hardly adhere to immobilized collagen type I alone, which represents the major extracellular matrix component of the injured arterial wall (P≤0.05) (Figure 1A–G). Adhesion of CD34+ cells onto immobilized platelets was significantly attenuated in the presence of soluble JAM-A-Fc, but not in the presence of control-Fc protein (P≤0.05) (Figure 1A). In a similar manner, neutralizing monoclonal antibodies to JAM-A and to LFA-1 (CD11a), but not a respective isotype control IgG, inhibited the adhesion of CD34+ cells onto immobilized platelets (P≤0.05) (Figure 1A–G). Parallel adhesion assays with anti–SDF-1 and anti–JAM-A showed a possible synergistic role of these 2 platelet receptors in the adhesion of human CD34+ cells to immobilized platelets (Figure 1A–G).
To verify our findings under high shear conditions, similar to arterial flow, we conducted perfusion experiments of CD34+ cells over adherent platelets in a parallel plate flow chamber at a wall shear rate of 2000/s (2 Pa) (Figure 1H). A remarkable number of perfused CD34+ cells quickly turned into rolling and later into firm adherent cells (Figure 1H and I and Supplemental Video). Preincubation of immobilized platelets with soluble JAM-A-Fc, but not with control-Fc, attenuated rolling of CD34+ cells under high shear stress (Figure 1I). Moreover, significantly decreased firm adhesion of CD34+ cells over immobilized platelets was observed after preincubation with soluble JAM-A-Fc (90.00±8.69 versus 37.22±6.20 for control-Fc versus JAM-A-Fc; P≤0.05; n=3) (Figure 1I and Supplemental Video). The present results indicate that JAM-A regulates adhesion of CD34+ cells onto immobilized platelets (Figure 1). The binding characteristics of JAM-A-Fc on CD34+ cells are depicted in Supplemental Figure 1A.
Human CD34+ Progenitor Cells Express JAM-A
JAM-A has been described to be expressed on murine hematopoietic precursors only recently.21 However, the presence of JAM-A and its functional role on human CD34+ progenitor cells are not elucidated, encouraging us to investigate their possible expression on human CD34+ cells. Platelets constitutively express on their surface JAM-A (Figure 2A), as previously reported.18,22 Flow cytometric analysis of JAM-A expression on CD34+ cells revealed that high levels of JAM-A are expressed on their surface (Figure 2B). The presence of JAM-A in CD34+ cells was also verified by immunoblotting (Figure 2C). JAM-A expression levels remained unaltered under high shear stress or inflammatory conditions (Supplemental Figure 1B and C). JAM-A expression was also investigated in different CD34+ cell sources and subpopulations (Supplemental Figures 1D and Figure 2).
CD34+ Progenitor Cell Adhesion Is Mediated Through JAM-A Binding to JAM-A and LFA-1
JAM-A supports both homophilic and heterophilic interactions. JAM-A interacts with both JAM-A and the integrin LFA-1 or CD11a. In the present study, we showed that JAM-A is also present in human CD34+ progenitor cells. Because JAM-A binds to both JAM-A (homophilic interaction) and LFA-1 (heterophilic interaction), we asked whether a homophilic (JAM-JAM) or a heterophilic (JAM-integrin) interaction primarily regulates CD34+ cell adhesion. By using a static adhesion assay, we observed that CD34+ cells firmly adhered to immobilized JAM-A (P≤0.05; n=3) (Figure 2E). The adhesion of CD34+ cells to immobilized JAM-A was substantially reduced in the presence of soluble JAM-A-Fc or of a neutralizing monoclonal antibody to JAM-A (Figure 2D and E). In a similar manner, preincubation of CD34+ cells with a blocking anti–LFA-1 monoclonal antibody resulted in decreased CD34+ cell adhesion over immobilized JAM-A (Figure 2D and E). This indicates that both JAM-A and LFA-1 play a role in immobilized JAM-A–mediated CD34+ cell adhesion. Most of the circulating CD34+ cells are also positive for CD45, and both CD34+/CD45+ and CD34+/CD45− populations were highly positive for JAM-A in healthy subjects and in patients with stable coronary artery disease (Supplemental Figure 2A and B). Pretreatment of platelets or CD34+ cells with JAM-A-Fc resulted in similar inhibition levels of adherent CD34+ cells over immobilized platelets (Supplemental Figure 3A).
CD34+ Cell Differentiation Into Endothelial Progenitor Cells Is Mediated Through JAM-A
Adherent platelets cause CD34+ cell differentiation into endothelial cells.13,15 To further evaluate the molecular requirements of platelet-dependent differentiation of progenitor cells, CD34+ cells were allowed to adhere onto immobilized platelets or collagen (negative control) and were cultivated in endothelial cell growth medium, as previously described.15 Where indicated, sJAM-A-Fc or control-Fc was added in the cell culture system. Platelet-mediated formation of endothelial colonies of CD34+ cells was significantly reduced in the presence of sJAM-A-Fc, but not in the presence of control-Fc (number of colonies, 11.0±1.4 versus 3.5±0.7 for control-Fc versus sJAM-A-Fc; P≤0.05; n=3) (Figure 3A and B). To define the role of JAM-A on differentiation of CD34+ cells into endothelial progenitor cells, similar CFU assays were performed. Specifically, CD34+ cells were allowed to adhere onto immobilized fibronectin (positive control), control-Fc (negative control), and immobilized JAM-A-Fc; and the endothelial colonies were measured, as previously described.15 Immobilized JAM-A promoted the formation of endothelial colonies derived from CD34+ cells, when compared with control-Fc (number of endothelial colonies, 0.3±0.6 versus 8.0±2.0 for immobilized control-Fc versus immobilized JAM-A-Fc; P≤0.05; n=3) (Figure 3B). Interestingly, immobilized JAM-A-Fc induced the differentiation of CD34+ cells into endothelial colonies at a similar level to immobilized fibronectin, SDF-1, and P-selectin, indicating that differentiation of CD34+ cells relies first on firm adhesion (Supplemental Figure 3B). Parallel CFU assays with anti–SDF-1 and anti–JAM-A showed a significant role of these 2 platelet receptors in the platelet-mediated differentiation of human CD34+ cells to EPCs (Figure 3C).
Next, we studied the capacity of EPCs to integrate into vascular structures through Matrigel angiogenesis assays. Incubation of EPCs and haECs, but not of monocytes and CD34+ cells, on Matrigel led to the formation of extensive tube formation (Figure 3D and E). Furthermore, the proliferation capacity of CD34+ cells, haECs, CFU-derived EPCs (derived from CD34+ cells incubated on immobilized JAM-A-Fc) over a 3-day period was studied. EPCs reached a significantly higher proliferation capacity after 3 days of culture when compared with mature haECs (Figure 3F). Verification of CD34+ cell differentiation into endothelial progenitor cells was further performed with flow cytometry and determination of specific mRNA. The surface expression of CD146, PECAM-1 (CD31), CD34, and CD45 was tested on CD34+ cells, haECs, and platelet- or JAM-A–induced endothelial colonies by flow cytometry, as described in the Supplemental Online Methods section. CFU-derived EPCs exhibit similar endothelial surface markers (eg, CD146, CD144, or CD31) compared with primary endothelial cell cultures cultivated from human arteries (Figure 4A and Supplemental Figure 4). After 5 days, the morphology of initially round CD34+ cells on immobilized platelets and on JAM-A turned into adherent spindle-shaped cells, which were positive for von Willebrand factor, as shown by immunofluorescence microscopy (Figure 4B). Next, we analyzed whether EPCs can be activated to express activation-dependent surface markers, such as intercellular adhesion molecule-1 (CD54) and CD106. We found that stimulation of immobilized JAM-A–induced CD34+ cell-derived endothelial colonies with tumor necrosis factor α or interferon γ cytokines showed enhanced expression of CD54 and CD106, similar to the activation profile obtained when haECs were used or when cells were cultivated on immobilized platelets (Figure 4C). PCR analysis showed that EPCs cultivated on immobilized JAM-A exhibit positive signals for endothelial nitric oxide synthase, endothelial angiopoietin receptor (Tie-2), and vascular endothelial growth factor receptor 2 (VEGFR-2, or flk-1), similar to those signals obtained from haECs or CD34+ cell-derived endothelial progenitor cells cultivated on immobilized platelets (Figure 4D).
JAM-A Is Involved in the CD34+ Cell–Induced Reendothelialization Process In Vitro
Endothelial progenitor cells promote neoendothelialization of the injured endothelial monolayer. Thus, we asked whether JAM-A mediates reendothelialization of an injured endothelial monolayer in a “scratch-wounded assay,” as previously described.19 Primary cultures of haECs were cultivated to confluence. After scratch-induced injury of the monolayer, CD34+ cells, CD34+ cells and platelets, or platelets alone were added and the coculture was further incubated for 13.5±2.6 hours (n=6) (Figure 5A). CD34+ cells promoted neoendothelialization of the injured zone compared with experiments in which CD34+ cells were absent (P≤0.05) (Figure 5A). Moreover, the addition of platelets, but not of platelets alone, in our coculture system after scratch-induced injury resulted in significantly enhanced reendothelialization compared with CD34+ cells alone (P≤0.05) (Figure 5A).
In the presence of soluble JAM-A-Fc, CD34+ cell–induced reendothelialization of the injured zone was significantly reduced compared with Fc control experiments (P≤0.05; n=6). In a similar manner, the reendothelialization induced by a combination of CD34+ cells and platelets was significantly inhibited through sJAM-A-Fc (P≤0.05; n=6) (Figure 5B and C). By using rhodamine fluorescence, we could detect that JAM-A-Fc mainly inhibited the adhesion of CD34+ cells to endothelial cells or endothelial cells and platelets; therefore, less reendothelialization capacity was observed (Supplemental Figure 5A and B).
The interaction of circulating progenitor cells with the endothelial monolayer of the vasculature of peripheral organs is critical for homing. Previously, we showed that JAM-A-Fc reduced the reendothelialization capability in a coculture system of endothelial cells and CD34+ cells. Thus, we asked whether JAM-A is involved in the interaction of CD34+ cells with cultured haECs under dynamic shear conditions. As expected, cultured nonactivated endothelial cells do not support firm adhesion of CD34+ cells under arterial flow conditions (Figure 5E). However, when monolayers of haECs were activated with tumor necrosis factor α or interferon γ, the adhesion of CD34+ cells was significantly enhanced (P≤0.05). In the presence of soluble JAM-A-Fc, but not of control-Fc, a significant reduction of firm adhesion of CD34+ cells to the endothelial surface was observed (P≤0.05) (Figure 5D and E).
JAM-A Is Critical for CD34+ Cell Adhesion on Vascular Wall and Neointima Formation After Vascular Injury In Vivo
To verify our experimental results in vivo, the common carotid artery of C57BL/6J mice was injured by ligation; and DCF-stained CD34+ progenitor cells were injected intravenously. Preincubation of CD34+ cells with JAM-A-Fc resulted in decreased adhesion of progenitor cells to the injured vessel wall (P≤0.05) (Figure 6A and B). The role of JAM-A in the CD34+ cell-endothelium interaction was investigated in the microcirculation of the small intestine of mice after ischemia/reperfusion injury using intravital fluorescence microscopy. Enhanced platelet/endothelium adhesion occurs in the microcirculation of inflamed tissue and during reperfusion of ischemic organs.23 The preincubation of CD34+ cells with JAM-A-Fc, but not of control-Fc, resulted in decreased adhesion of progenitor cells in the microvasculature (P≤0.05) (Figure 6C and D).
To evaluate the role of CD34+ cells and especially of JAM-A in neointima formation and in reendothelialization, we preincubated human CD34+ cells with either JAM-A-Fc (n=5 mice) or control-Fc (n=6 mice) and injected them into nonobese diabetic/severe combined immunodeficient mice after carotid endothelial denudation. Three weeks after denudation, the mice were euthanized; and the carotid arteries and aortic arches were analyzed by histomorphometry and histochemistry. Hematoxylin-eosin and elastica von Gieson stainings at lesion sites show a lumen-narrowing neointima formation in all Fc-treated mice, which was significantly increased in JAM-A-Fc–treated mice (P≤0.05) (Figure 6E and F). With respect to media area, there was no significant difference between the groups.
The major findings of the present study are as follows: (1) platelet-mediated adhesion of human CD34+ progenitor cells is mediated via JAM-A, (2) JAM-A is expressed on human CD34+ cells, (3) JAM-A interactions are mediated through progenitor cell–expressed JAM-A and β2-integrin LFA-1, (4) JAM-A promotes the differentiation of human CD34+ cells into endothelial progenitor cells, (5) JAM-A plays a role in CD34+ cell-mediated reendothelialization in vitro through interaction with nearby endothelial cells, (6) JAM-A is important for the adhesion of human CD34+ cells on the vascular wall after injury in vivo, and (7) pretreatment of CD34+ cells with JAM-A-Fc results in increased neointima formation after endothelial denudation in vivo.
Domiciliation of progenitor cells in peripheral tissue is a multistep cascade, including initial adhesion to the vascular wall and differentiation to vascular cells. Platelets are the first circulating blood cells that adhere to vascular lesions and that accumulate in the microcirculation within ischemic tissue,24 supporting angiogenesis25 and vascular regeneration through interaction with progenitor cells.12,15,16 Researchers12–17 recently demonstrated that platelets influence progenitor cell recruitment and differentiation toward an endothelial phenotype. However, the underlying mechanisms are poorly elucidated.
JAM-A/JAM-1/F11R is a cell adhesion molecule expressed in epithelial, endothelial, and hematopoietic cells, such as leukocytes, platelets, and erythrocytes.26 JAM-A plays a role in platelet aggregation, secretion, adhesion, and spreading.18,22 The role of platelet-bound JAM-A in platelet interaction with progenitor cells has not been studied until recently. To our knowledge, we show for the first time that platelet-bound JAM-A mediates the adhesion and differentiation of human CD34+ cells toward an endothelial phenotype. Moreover, in accordance with the recent finding that JAM-A is expressed on murine hematopoietic stem cells,21 we could verify the expression of JAM-A on the surface of human CD34+ progenitor cells. To enlighten the ligand-receptor interactions involved on JAM-A–mediated platelet interaction with progenitor cells, we performed a series of adhesion assays showing that JAM-A binds to both CD34+ cell-derived JAM-A and integrin LFA-1. Moreover, immobilized JAM-A not only supported the adhesion of human CD34+ cells, but also promoted their differentiation to endothelial progenitor cells in a similar manner to fibronectin. Endothelial progenitor cells were positive for CD34, tie-2, endothelial nitric oxide synthase, and VEGFR-2 mRNA; however, CD34 protein was not detectable on their surface. Moreover, 2 endothelial markers (CD144 and CD146) were present on the surface of EPCs; however, intercellular adhesion molecule-1 and CD106 expression was further enhanced under inflammatory conditions, indicating that our CFU-derived EPCs present with a mature functional endothelial phenotype.
Previously, we showed that platelet-derived SDF-1 regulates the adhesion and differentiation of CD34+ cells to EPCs.27 The Rap1 pathway is involved in both SDF-1–stimulated integrin activation and JAM-A downregulation, indicating a possible link between these 2 important receptors.28,29 In accordance with these findings, the present study results indicated parallel adhesion and CFU assays with SDF-1; JAM-A showed a possible synergistic role of these 2 platelet receptors in the platelet-mediated adhesion and differentiation of human CD34+ cells to EPCs.
Hematopoietic and endothelial progenitor cells are recruited to ischemic regions that modulate vasculogenesis, accelerating reendothelialization and limiting atherosclerotic lesion formation.6,30–32 Clinical trials33,34 indicate a beneficial effect of intracoronary infusion of progenitor cells on myocardial function in patients with ischemic heart disease. However, the potential determinants and receptors involved in reendothelialization are still unknown.35 In the present study, we showed that soluble JAM-A-Fc could inhibit the CD34+ cell–induced reendothelialization in vitro and enhance neointima formation in vivo, indicating that JAM-A may play a critical role in reendothelialization.
The present findings imply that JAM-A mediates recruitment of circulating CD34+ cells toward the injured vessel wall (vascular lesion and inflamed endothelium) and that JAM-A induces differentiation of CD34+ cells into endothelial progenitor cells and supports reendothelialization.
We thank Jadwiga Kwiatkowska, MTA and Christina Neff, MTA for their technical assistance; and Dorothea Siegel-Axel, PhD for the isolation of the haECs.
Sources of Funding
This study was supported by the German Research Foundation (DFG Sonderforschungsbereich Transregio 19) “Inflammatory Cardiomyopathy–Molecular Pathogenesis and Therapy” (Drs Stellos and Gawaz) and DFG 849/3/1 (Dr Lindemann); and by the Fortune Project 1795–1-0 of the Eberhard-Karls Universität Tübingen (Dr Stellos).
Received on: February 5, 2009; final version accepted on: March 12, 2010.
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