Vimentin-Induced Cardiac Mesenchymal Stem Cells Proliferate in the Acute Ischemic Myocardium

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.