Alexander Schuh

Double-Edged Role of the CXCL12/CXCR4 Axis in Experimental Myocardial Infarction

OBJECTIVES Here we assess the intrinsic functions of the chemokine receptor CXCR4 in remodeling after myocardial infarction (MI) using Cxcr4 heterozygous (Cxcr4(+/-)) mice. BACKGROUND Myocardial necrosis triggers complex remodeling and inflammatory changes. The chemokine CXCL12 has been implicated in protection and therapeutic regeneration after MI through recruiting angiogenic outgrowth cells, improving neovascularization and cardiac function, but the endogenous role of its receptor CXCR4 is unknown. METHODS MI was induced by ligation of the left descending artery. Langendoff perfusion, echocardiography, quantitative immunohistochemistry, flow cytometry, angiogenesis assays, and cardiomyocyte analysis were performed. RESULTS After 4 weeks, infarct size was reduced in Cxcr4(+/-) mice compared with wild-type mice and in respective bone marrow chimeras compared with controls. This was associated with altered inflammatory cell recruitment, decreased neutrophil content, delayed monocyte infiltration, and a predominance of Gr1(low) over classic Gr1(high) monocytes. Basal coronary flow and its recovery after MI were impaired in Cxcr4(+/-)mice, paralleled by reduced angiogenesis, myocardial vessel density, and endothelial cell count. Notably, no differences in cardiac function were seen in Cxcr4(+/-)mice compared with wild-type mice. Despite defective angiogenesis, Cxcr4(+/-) mouse hearts showed no difference in CXCL12, vascular endothelial growth factor or apoptosis-related gene expression. Electron microscopy revealed lipofuscin-like lipid accumulation in Cxcr4(+/-) mouse hearts and analysis of lipid extracts detected high levels of phosphatidylserine, which protect cardiomyocytes from hypoxic stress in vitro. CONCLUSIONS CXCR4 plays a crucial role in endogenous remodeling processes after MI, contributing to inflammatory/progenitor cell recruitment and neovascularization, whereas its deficiency limits infarct size and causes adaptation to hypoxic stress. This should be carefully scrutinized when devising therapeutic strategies involving the CXCL12/CXCR4 axis.

Transplantation of human umbilical vein endothelial cells improves left ventricular function in a rat model of myocardial infarction.

AbstractIntroductionAlthough cell–based therapy after myocardial infarction (MI) may be beneficial in improving cardiac dysfunction, the underlying mechanisms remain to be clarified. Since human umbilical vein endothelial cells (HUVEC) harbor the potential for transdifferentiation, we studied the functional effects of HUVEC transplantation in a rat model of MI.Methods and resultsHUVEC labeled with BrdU or medium alone were injected into the infarcted area and its margin 4 weeks after ligation of the left coronary artery in cyclosporine–treated rats. BrdU+ signals could be detected in the area of MI at two weeks and two months after injection only in hearts transplanted with HUVEC. While no signs of transdifferentiation into cardiomyocytes were evident, staining for the rat macrophage marker ED–1, adjacent to or colocalized with BrdU+ signals, revealed an in.ltration with macrophages and implied the phagocytosis of injected HUVEC. In the vicinity of BrdU+ signals, the density of CD31+ microvessels was significantly increased in HUVEC–transplanted as compared to medium–treated hearts after two months. HUVEC transplantation led to improved contractility as assessed by echocardiography and to higher coronary flow rates as well as to improved response to volume strain and catecholamine stress in Langendorff perfused hearts.ConclusionsAfter MI, transplanted HUVEC persist in the host myocardium and trigger an infiltration with macrophages. The ensuing increase in neovascularization and improvement in global left ventricular function may be attributable to the associated inflammatory response.

Transplantation of Fetal Cardiomyocytes into Infarcted Rat Hearts Results in Long-Term Functional Improvement

Studies have demonstrated the feasibility of transplanting cardiomyocytes after myocardial infarction (MI). However, persistence and effects on left ventricular (LV) function have not been elucidated in long-term studies. Ventricular fetal cardiomyocytes from embryos of both sexes were injected into marginal regions of MI 4 weeks after suture occlusion of the left anterior descending artery in adult female rats. Two and 6 months after transplantation (Tx), engrafted cells were traced by immunohistochemical in situ hybridization for Y chromosomes or bromodeoxyuridine (BrdU) staining, LV dimensions and function were assessed by echocardiography, and LV pressure was assessed ex vivo in a Langendorff perfusion system. Immunohistochemistry for alpha-sarcomeric actin and Y chromosomes revealed the presence of transplanted cells in infarcted host myocardium at both 2 and 6 months. End-diastolic LV diameter markedly decreased after Tx and fractional shortening gradually increased after Tx (31.3 +/- 4.5% before Tx, 45.4 +/- 4.2% at 6 months; p<0.005). Wall area fraction and MI size were unaffected by Tx. In hearts with MI, but not in normal hearts, Tx led to the development of higher pressures (87 +/- 18 versus 38 +/- 8 mmHg, 6 months post-Tx versus nontreated). After catecholamine stimulation, both infarcted and normal hearts developed higher pressures after Tx (p<0.005), ultimately associated with reduced mortality after Tx versus nontreated. Transplanted cardiomyocyte-rich graft cells persist in host myocardium and mediate continuous improvement of LV function and survival in a rat model of MI even during long-term follow-up, possibly involving a catecholamine-sensitive mechanism.

Myocardial regeneration by transplantation of modified endothelial progenitor cells expressing SDF-1 in a rat model

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.

Administration of vascular endothelial growth factor adjunctive to fetal cardiomyocyte transplantation and improvement of cardiac function in the rat model.

Background: The functional impact of cellular transplantation and the potential role of the addition of angiogenic factors for survival of engrafts remain controversial. Methods: Vascular endothelial growth factor (VEGF) (25 ng/mL) was added to cultured fetal cardiomyocytes labeled with bromodeoxyuridine (BrDU), which was injected into the border zones of myocardial infarction 4 weeks after coronary occlusion in rat hearts. Group 1 (n = 12) received cells plus VEGF protein (100 ng), group 2 (n = 12) received cells without VEGF, group 3 (n = 10) received VEGF without cells, and group 4 (n = 12) received pure culture medium. Cardiac function was then assessed by transthoracic two-dimensional echocardiography and Langendorff perfusion system. In situ hybridization for Y chromosomes of transplanted cells, detection of BrDU-labeled cells, and platelet/endothelial cell adhesion molecule-1 (PECAM-1) staining for endothelial cells was performed. Results: Echocardiography revealed smaller end-diastolic left ventricular dimensions in transplanted hearts in group 1 (0.83 ± 0.13 cm 4 weeks after coronary occlusion before transplantation and 0.69 ± 0.14 cm 2 months after transplantation, P < .05) and in group 2 (0.88 ± 0.09 cm after coronary occlusion before transplantation and 0.76 ± 0.08 cm 2 months after transplant), and increases in fractional shortening (34.2% ± 8.53% before transplant and 45.3% ± 10.9% after [P < .05] in group 1; 26.9% ± 6.02% before transplant and 37.15% ± 8.08% after [P < .005] in group 2), whereas groups 3 and 4 showed a decrease in fractional shortening. Transplanted hearts developed higher pressures at rest (group 1, 96.8 ± 20.8 mm Hg; group 2, 98.6 ± 21.9 mm Hg) compared with controls (group 4, 70.9 ± 25 mm Hg) (P < .05) and during inotropic stimulation (group 1, 111 ± 19.5 mm Hg and group 2, 113.3 ± 32.6 vs group 4, 80.7 ± 31.6 mm Hg, P < .05). Histologic analysis demonstrated the presence of transplanted cells in border zones of infarcted host myocardium with neovascularization in all transplanted hearts. Conclusion: Transplantation of fetal cardiomyocytes results in improvement of left ventricular function. The addition of VEGF does not contribute to further improvement of left ventricular function and angiogenesis in the present model.

Novel insights into the mechanism of cell-based therapy after chronic myocardial infarction

Cell transplantation therapy is considered a novel and promising strategy in regenerative medicine. Recent studies point out that paracrine effects and inflammation induced by transplanted cells are key factors for the improvement of myocardial function. The present study aims at differentiating paracrine effects from inflammatory reactions after cell transplantation. Therefore, in vitro induced apoptotic bodies were transplanted after myocardial infarction in a rat model. Eight weeks after transplantation, the functional results showed no improvement in left ventricular function. Histological analysis revealed no significant differences in the amount of infiltrated cells and collagen content did not differ among the four groups, which sustains the functional data. Surprisingly, angiogenesis increased in groups with apoptotic bodies derived from HUVEC and endothelial progenitor cells, but not from fibroblasts. A complex genetic analysis of apoptotic bodies indicated that miRNAs could be responsible for these changes. Our study demonstrates that inflammatory reaction is critical for scar remodelling and improvement of the heart function after late cell therapy, while neoangiogenesis alone is not sufficient to improve heart function.

Effect of SDF-1 α on Endogenous Mobilized and Transplanted Stem Cells in Regeneration after Myocardial Infarction

Aim of the presented study was to investigate the role of stromal derived factor 1 (SDF-1α) in mobilizing stem cells in combination with endothelial progenitor cell (EPC) transplantation in a regenerative strategy for myocardial infarction therapy in a murine ischemia/reperfusion model. Initially bone marrow was eradicated and reconstituted with the use of green fluorescent protein (GFP) labelled allogenic cells. After reconstitution, myocardial ischemia was induced by temporary ligation of the left anterior descending coronary artery (LAD) in C57/B16 mice and maintained for 1h. After reperfusion, EPCs (1 x 10(6) cells) or medium were injected directly into the border zones of the infarcted areas. In addition, the animals were divided in groups treated or not with specific antibodies against SDF-1α. 4 weeks after transplantation, echocardiography revealed a significantly decreased left ventricular function after application of EPCs in anti-SDF-1α treated animals compared to untreated groups. Histology revealed that EPC transplantation and anti-SDF-1α treatment diminished the amount of intramyocardially attracted GFP positive bone marrow cells. Interestingly, no significant changes in the density of CD31+ vessel structures compared to EPC transplantation alone were detectable in anti-SDF-1α treated groups. Anti-SDF-1α treatment also increased numbers of inflammatory cells (monocytes and neutrophiles) in infarcted areas. Rate of apoptotic cells and proliferation after transplantation did not differ. In conclusion, transplanted endothelial progenitor cells as well as SDF-1α are key factors in mobilization of endogenous bone marrow cells towards infarcted myocardium. Anti-SDF-1α treatment leads to a significant decreased left ventricular function, alters the inflammatory processes, but does not lead to significant alterations in neovascularization or collagen content of infarcted areas.

Chemokine Contribution in Stem Cell Engraftment into the Infarcted Myocardium

Modern life styles have made cardiovascular disease the leading cause of morbidity and mortality worldwide. Although current treatments substantially ameliorate patients’ prognosis after MI, they cannot restore the affected tissue or entirely re-establish organ function. Therefore, the main goal of modern cardiology should be to design strategies to reduce myocardial necrosis and optimize cardiac repair following MI. Cell-based therapy was considered a novel and potentially new strategy in regenerative medicine; however, its clinical implementation has not yielded the expected results. Chemokines seem to increase the efficiency of cell-therapy and may represent a reliable method to be exploited in the future. This review surveys current knowledge of cell therapy and highlights key insights into the role of chemokines in stem cell engraftment in infarcted myocardium and their possible clinical implications.

Hemocompatibility of plasma electrolytic oxidation (PEO) coated Mg-RE and Mg-Zn-Ca alloys for vascular scaffold applications

Percutaneous transluminal coronary angioplasty and subsequent vascular scaffold implantation remains the prevalent invasive treatment of coronary heart disease. In-stent restenosis remained a problem with bare metal stents, until drug-eluting stents were introduced. The inhibition of the healing process by the antimitotic drug coating and the permanent metallic remnant can promote sub-acute and delayed stent thrombosis. Thus, the development of biodegradable stents emerged as a subject of research. Magnesium-based bioabsorbable devices can provide sufficient radial force in the acute phase of vessel-treatment and degrade thoroughly in aqueous environment, making them potential new candidates for vascular scaffold applications. Magnesium alloys tend to degrade very quickly due to their high electrochemical corrosion potential. Plasma Electrolytic Oxidation modification of magnesium alloys improves interface and degradadation properties and may therefore enhance the performance and suitability for vascular scaffold applications of these materials. Assuring the hemocompatibility and foremost assessing the thrombogenicity of new biomaterials prior to their use is essential in order to avoid adverse effects. The goal was to assess thrombocyte adhesion on coated Mg-RE and Mg-Zn-Ca alloys. Static experiments with human blood were carried out on the plasma-electrolytically treated or corresponding untreated Mg alloy in order to assess quantity and quality of thrombocyte adhesion via standardized SEM imaging. In a second step, a parallel plate flow chamber was designed in order to examine thrombocyte adhesion under dynamic flow conditions. During flow chamber experiments the test-materials were exposed to human thrombocyte concentrate and the number of adherent thrombocytes was assessed. The flow chamber was additionally perfused with human blood and thrombocyte adhesion was semiquantitatively and qualitatively assessed via SEM imaging and subsequent scoring. In conclusion, a new parallel plate flow chamber design simulating blood-circulation was successfully established, enabling the further assessment of platelet adhesion on bioabsorbable materials under dynamic flow conditions. Static and dynamic experiments showed, that plasma-electrolytically treated specimens showed low thrombocyte adhesion on both alloys, proposing their potential use in vascular scaffolds. The uncoated magnesium alloys showed rapid degradation along with gas formation due to the chemically active surface and therefore give concern regarding their safety and suitability for vascular applications.

Corrigendum: FGF23 in Cardiovascular Disease: Innocent Bystander or Active Mediator?

[This corrects the article DOI: 10.3389/fendo.2018.00351.].