Targeted Isolation of Regenerative Cardiac Mesenchymal Stem Cells from Ischemic Myocardium

Objectives: Early after acute myocardial infarction (MI) cardiac mesenchymal stem cells (MSCs) might stimulate cell-specific regenerative mechanisms depending on origin, distribution and niche regulation.

Methods: Following permanent ligation of left anterior descending coronary artery in wild-type rats (n = 16) and tamoxifen-inducible Vimentin-CreER⁺ mTom/mGFP⁺ mice (n = 10), cardiac tissues, cardiac mononuclear cells (MNCs) and Vimentin/GFP⁺ cells were analyzed by immunohistology, confocal laser-scanning microscopy or flow cytometry. Early post-ischemic Vimentin-induced cardiac MSCs were purified by fluorescence-activated cell sorting using surface markers in rats and genetically-targeted GFP expression in mice. Cells were tested for multipotent differentiation in functional identification kits. In co-cultures with cardiomyocytes and in Matrigel assays with human umbilical cord vein endothelial cells (HUVECs) cardiomyogenic differentiation and angiogenesis were examined, respectively.

Results: Post-ischemic intramyocardial MSC clusters were characterized by induced expression for Vimentin in parallel to positive expressions for CD29, CD44, CD90, CD105, PDGFRa, DDR2 or Sca-1. Proliferation in cardiac MSCs was induced 24 hours after MI. Proliferation density was 11% in the peri-infarction border zone. Coincidentally, flow cytometry analyses of cardiac MNCs illustrated post-ischemic moderate enrichments of CD45^-CD44⁺ and CD45^-DDR2⁺ subfractions in rats as well as augmentation of the Vimentin/GFP⁺Sca1⁺CD45^- MNC subtype from 44.6% at 24 hours to 56.8% at 72 hours after MI in mice. Following purification, early post-ischemic rat cardiac Vimentin⁺CD45^-CD44⁺DDR2⁺ MSCs and mouse cardiac Vimentin/GFP⁺ MSCs demonstrated typical adipogenic, chondrogenic and osteogenic differentiation. Moreover, early post-ischemic Vimentin-induced cardiac MSCs showed a strong paracrine angiogenetic effect on HUVECs and cardiomyogenic differentiation potential by increased expressions of GATA4 and Nkx 2.5.

Conclusion: Acute MI triggered early proliferation in tissue-specific intramyocardial Vimentin-induced MSCs. Following targeted isolation these MSCs revealed multipotent differentiation capacity, paracrine angiogenesis and cardiomyogenic differentiation potential. Prospectively, genetic cell fate mapping of early post-ischemic Vimentin-induced cardiac MSCs could advance cell-specific signaling analysis while tracking their origin, kinetics and fate.

No conflict of interest has been declared by the author(s).