This study aimed to analyze the role of endothelial progenitor cell (EPC)-derived angiogenic factors and chemokines in the multistep process driving angiogenesis with a focus on the recently discovered macrophage migration inhibitory factor (MIF)/chemokine receptor axis. Primary murine and murine embryonic EPCs (eEPCs) were analyzed for the expression of angiogenic/chemokines and components of the MIF/CXC chemokine receptor axis, focusing on the influence of hypoxic versus normoxic stimulation. Hypoxia induced an upregulation of CXCR2 and CXCR4 but not CD74 on EPCs and triggered the secretion of CXCL12, CXCL1, MIF, and vascular endothelial growth factor (VEGF). These factors stimulated the transmigration activity and adhesive capacity of EPCs, with MIF and VEGF exhibiting the strongest effects under hypoxia. MIF-, VEGF-, CXCL12-, and CXCL1-stimulated EPCs enhanced tube formation, with MIF and VEGF exhibiting again the strongest effect following hypoxia. Tube formation following in vivo implantation utilizing angiogenic factor-loaded Matrigel plugs was only promoted by VEGF. Coloading of plugs with eEPCs led to enhanced tube formation only by CXCL12, whereas MIF was the only factor which induced differentiation towards an endothelial and smooth muscle cell (SMC) phenotype, indicating an angiogenic and differentiation capacity in vivo. Surprisingly, CXCL12, a chemoattractant for smooth muscle progenitor cells, inhibited SMC differentiation. We have identified a role for EPC-derived proangiogenic MIF, VEGF and MIF receptors in EPC recruitment following hypoxia, EPC differentiation and subsequent tube and vessel formation, whereas CXCL12, a mediator of early EPC recruitment, does not contribute to the remodeling process. By discerning the contributions of key angiogenic chemokines and EPCs, these findings offer valuable mechanistic insight into mouse models of angiogenesis and help to define the intricate interplay between EPC-derived angiogenic cargo factors, EPCs, and the angiogenic target tissue.

Objectives Here we aimed to clarify the role of CXCR2 in the macrophage migration inhibitory factor (MIF)-mediated effects after myocardial ischemia and reperfusion (I/R). As a pleiotropic chemokine-like cytokine, MIF has been identified to activate multiple receptors including CD74 and CXCR2. In models of myocardial infarction (MI), MIF exerts both pro-inflammatory effects and protective effects in cardiomyocytes. Likewise, CXCR2 displays opposing effects in resident versus circulating cells. Approach and results Using bone marrow (BM) transplantation, we generated chimeric mice with CXCR2−/− BM-derived inflammatory cells and wild-type resident cells (wt/CXCR2−/−), with CXCR2−/− cardiomyocytes and wild-type BM-derived cells (CXCR2−/−/wt) and wild-type controls reconstituted with wild-type BM (wt/wt). All groups were treated with anti-MIF or isotype control antibody before they underwent myocardial I/R. Blocking MIF increased infarction size and impaired cardiac function in wt/wt and wt/CXCR2−/− mice but ameliorated functional parameters in CXCR2−/−/wt mice, as analyzed by echocardiography and Langendorff perfusion. Neutrophil infiltration and angiogenesis were unaltered by MIF blockade or CXCR2 deficiency. Monocyte infiltration was blunted in wt/CXCR2−/− mice and reduced by MIF blockade in wt/wt and CXCR2−/−/wt mice. Moreover, MIF blockade attenuated collagen content in all groups in a CXCR2-independent manner. Conclusions The compartmentalized and opposing effects of MIF after myocardial I/R are largely mediated by CXCR2. Whereas MIF confers protective effects improving myocardial healing and function through CXCR2 in resident cells, complementing paracrine effects through CD74/AMPK, it exerts detrimental effects on CXCR2-bearing inflammatory cells, increasing monocyte infiltration and impairing heart function. These dichotomous findings should be considered, when developing novel therapeutic strategies to treat MI.

Cell based therapy has been shown to attenuate myocardial dysfunction after myocardial infarction (MI) in different acute and chronic animal models. It has been further shown that stromal-cell derived factor-1α (SDF-1α) facilitates proliferation and migration of endogenous progenitor cells into injured tissue. The aim of the present study was to investigate the role of exogenously applied and endogenously mobilized cells in a regenerative strategy for MI therapy. Lentivirally SDF-1α-infected endothelial progenitor cells (EPCs) were injected after 90 min. of ligation and reperfusion of the left anterior descending artery (LAD) intramyocardial and intracoronary using a new rodent catheter system. Eight weeks after transplantation, echocardiography and isolated heart studies revealed a significant improvement of LV function after intramyocardial application of lentiviral with SDF-1 infected EPCs compared to medium control. Intracoronary application of cells did not lead to significant differences compared to medium injected control hearts. Histology showed a significantly elevated rate of apoptotic cells and augmented proliferation after transplantation of EPCs and EPCs + SDF-1α in infarcted myocardium. In addition, a significant increased density of CD31+ vessel structures, a lower collagen content and higher numbers of inflammatory cells after transplantation of SDF-1 transgenic cells were detectable. Intramyocardial application of lentiviral-infected EPCs is associated with a significant improvement of myocardial function after infarction, in contrast to an intracoronary application. Histological results revealed a significant augmentation of neovascularization, lower collagen content, higher numbers of inflammatory cells and remarkable alterations of apoptotic/proliferative processes in infarcted areas after cell transplantation.