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Cardiac Mesenchymal Stem Cells Proliferate Early in the Ischemic Heart

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.