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We investigated the influence of syngeneic cardiomyocyte transplantation after myocardial infarction (MI) on the immune response and cardiac function. Methods and Results: We show for the first time that the immune response is altered as a result of syngeneic neonatal cardiomyocyte transplantation after MI leading to improved cardiac pump function as observed by magnetic resonance imaging in C57BL/6J mice. Interestingly, there was no improvement in the capillary density as well as infarct area as observed by CD31 and Sirius Red staining, respectively. Flow cytometric analysis revealed a significantly different response of monocyte-derived macrophages and regulatory T cells after cell transplantation. Interestingly, the inhibition of monocyte infiltration accompanied by cardiomyocyte transplantation diminished the positive effect of cell transplantation alone. The number of CD68+ macrophages in the remote area of the heart observed after four weeks was also different between the groups. Transcriptome analysis showed several changes in the gene expression involving circadian regulation, mitochondrial metabolism and immune responses after cardiomyocyte transplantation. Conclusion: Our work shows that cardiomyocyte transplantation alters the immune response after myocardial infarction with the recruited monocytes playing a role in the beneficial effect of cell transplantation. It also paves the way for further optimization of the efficacy of cardiomyocyte transplantation and their successful translation in the clinic.

Ischemic heart failure is the leading cause of mortality worldwide. An early boost of intracardiac regenerative key mechanisms and angiogenetic niche signaling in cardiac mesenchymal stem cells (MSCs) could improve myocardial infarction (MI) healing. Epicardial erythropoietin (EPO; 300 U kg -1 ) was compared with intraperitoneal and intramyocardial EPO treatments after acute MI in rats ( n =156). Real-time PCR and confocal microscopy revealed that epicardial EPO treatment enhanced levels of intracardiac regenerative key indicators (SDF-1, CXCR4, CD34, Bcl-2, cyclin D1, Cdc2 and MMP2), induced transforming growth factor β (TGF-β)/WNT signaling in intramyocardial MSC niches through the direct activation of AKT and upregulation of upstream signals FOS and Fzd7, and augmented intracardiac mesenchymal proliferation 24 h after MI. Cardiac catheterization and tissue analysis showed superior cardiac functions, beneficial remodeling and increased capillary density 6 weeks after MI. Concomitant fluorescence-activated cell sorting, co-cultures with neonatal cardiomyocytes, angiogenesis assays, ELISA, western blotting and RAMAN spectroscopy demonstrated that EPO could promote cardiomyogenic differentiation that was specific of tissue origin and enhance paracrine angiogenetic activity in cardiac CD45 - CD44 + DDR2 + MSCs. Epicardial EPO delivery might be the optimal route for efficient upregulation of regenerative key signals after acute MI. Early EPO-mediated stimulation of mesenchymal proliferation, synergistic angiogenesis with cardiac MSCs and direct induction of TGF-β/WNT signaling in intramyocardial cardiac MSCs could initiate an accelerated healing process that enhances cardiac recovery., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

In-depth knowledge of the mechanisms induced by early postischemic cardiac endogenous mesenchymal stem cells (MSCs) in the acutely ischemic heart could advance our understanding of cardiac regeneration. Herein, we aimed to identify, isolate, and initially characterize the origin, kinetics and fate of cardiac MSCs. This was facilitated by in vivo genetic cell fate mapping through green fluorescent protein (GFP) expression under the control of vimentin induction after acute myocardial infarction (MI). Following permanent ligation of the left anterior descending coronary artery in CreER+ mTom/mGFP+ mice, vimentin/GFP+ cells revealed ischemia-responsive activation, survival, and local enrichment inside the peri-infarction border zone. Fluorescence-activated cell sorting (FACS)-isolated vimentin/GFP+ cells could be strongly expanded in vitro with clonogenic precursor formation and revealed MSC-typical cell morphology. Flow-cytometric analyses demonstrated an increase in cardiac vimentin/GFP+ cells in the ischemic heart, from a 0.6% cardiac mononuclear cell (MNC) fraction at 24 h to 1.6% at 72 h following MI. Sca-1+CD45- cells within the vimentin/GFP+ subtype of this MNC fraction increased from 35.2% at 24 h to 74.6% at 72 h after MI. The cardiac postischemic vimentin/GFP+ MNC subtype showed multipotent adipogenic, chondrogenic, and osteogenic differentiation potential, which is distinctive for MSCs. In conclusion, we demonstrated a seemingly proliferative first response of vimentin- induced cardiac endogenous MSCs in the acutely ischemic heart. Genetically, GFP-targeted in vivo cell tracking, isolation, and in vitro expansion of this cardiac MSC subtype could help to clarify their reparative status in inflammation, fibrogenesis, cell turnover, tissue homeostasis, and myocardial regeneration., (© 2019 S. Karger AG, Basel.)

Background: Magnetic activated cell sorting (MACS ® ) is routinely used to isolate stem cell subpopulations intended for the treatment of cardiovascular diseases. In strong contrast, studies examining the amount, effect and intramyocardial distribution of iron nanoparticles used for magnetic cell labelling are missing, although iron excess can cause functional disorders in the heart., Methods and Results: CD133 + haematopoietic and CD271 + mesenchymal stem cells were purified from bone marrow using automatically and manually MACS ® based systems. Flow cytometric measurements demonstrated a rapid loss of MACS ® MicroBeads from cells under culture conditions, while storage under hypothermic conditions decelerated their detachment. Moreover, an average loading of ∼11 fg iron/cell caused by magnetic labelling was determined in magnetic particle spectroscopy. Importantly, hemodynamic measurements as well as histological examinations using a myocardial ischemia/reperfusion mouse model showed no influence of MACS ® MicroBeads on cardiac regeneration, while the transplantation of stem cells caused a significant improvement. Furthermore, immunostainings demonstrated the clearance of co-injected iron nanoparticles from stem cells and the surrounding heart tissue within 48 h post transplantation., Conclusions: Our results indicate that iron amounts typically co-injected with MACS ® purified stem cells do not harm cardiac functions and are cleared from heart tissue within a few hours. Therefore, we conclude that MACS ® MicroBeads exhibit a good compatibility in the cardiac environment., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background/purpose: Cardiac mesenchymal stem cells (MSCs) could stimulate cell-specific regenerative mechanisms after myocardial infarction (MI) depending on spatial origin, distribution, and niche regulation. We aimed at identifying and isolating tissue-specific cardiac MSCs that could contribute to regeneration., Methods: Following permanent ligation of the left anterior descending coronary artery in rats (n = 16), early cardiac tissues and cardiac mononuclear cells (MNCs) were analyzed by immunohistology, confocal laser scanning microscopy, and flow cytometry, respectively. Early postischemic specific MSCs were purified by fluorescence-activated cell sorting, cultivated under standardized culture conditions, and tested for multipotent differentiation in functional identification kits., Results: Cardiac MSC niches were detected intramyocardially in cell clusters after MI and characterized by positive expression for vimentin, CD29, CD44, CD90, CD105, PDGFRα, and DDR2. Following myocardial ischemia, proliferation was induced early and proliferation density was approximately 11% in intramyocardial MSC clusters of the peri-infarction border zone. Cluster sizes increased by 157 and 64% in the peri-infarction and noninfarcted areas of infarcted hearts compared with noninfarcted hearts 24 h following MI, respectively. Coincidentally, flow cytometry analyses illustrated postischemic moderate enrichments of CD45-CD44+ and CD45-DDR2+ cardiac MNCs. We enabled isolation of early postischemic culturable cardiac CD45-CD44+DDR2+ MSCs that demonstrated typical clonogenicity with colony-forming unit-fibroblast formation as well as adipogenic, chondrogenic, and osteogenic differentiation., Conclusions: MI triggered early proliferation in specific cardiac MSC niches that were organized in intramyocardial clusters. Following targeted isolation, early postischemic cardiac CD45-CD44+DDR2+ MSCs exhibited typical characteristics with multipotent differentiation capacity and clonogenic expansion., (© 2017 S. Karger AG, Basel.)