Donor Mesenchymal Stromal Cells (MSCs) Undergo Variable Cardiac Reprogramming in Vivo and Predominantly Co-Express Cardiac and Stromal Determinants after Experimental Acute Myocardial Infarction
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We previously showed the emergence of predominantly non-fused murine cells co-expressing cardiac and stromal determinants in co-cultures of murine mesenchymal stromal cells (MSCs) and rat embryonic cardiomyocytes. To determine whether a similar phenotype is detectable in vivo in ischemic myocardium, we infused green fluorescence protein (GFP)-marked MSCs intravenously into wild-type mice in an acute myocardial infarction (AMI) model generated by ischemia/reperfusion (I/R) or fixed coronary artery ligation. We found that infused GFP+ cells were confined strictly to ischemic areas and represented approximately 10 % of total cellularity. We showed that over 60 % of the cells co-expressed collagen type IV and troponin T or myosin heavy chain, characteristic of MSCs and cardiomyocytes, respectively, and were CD45(-). Nonetheless, up to 25 % of the GFP+ donor cells expressed one of two cardiomyocyte markers, either myosin heavy chain or troponin T, in the absence of MSC determinants. We also observed a marked reduction in OCT4 expression in MSCs pre-infusion compared with those lodged in the myocardium, suggesting reduced stem cell properties. Despite the low frequency of lodged donor MSCs, left-ventricular end-diastolic pressure was significantly better in experimental versus saline animals for both AMI (12.10 ± 1.81 vs. 20.50 ± 1.53 mmHg, p < 0.001) and I/R models (8.75 ± 2.95 vs. 17.53 ± 3.85 mmHg, p = 0.004) when measured 21 days after MSC infusion and is consistent with a paracrine effect. Our data indicate that donor MSCs undergo variable degrees of cardiomyocyte reprogramming with the majority co-expressing cardiomyocyte and stromal markers. Further studies are needed to elucidate the factors mediating the extent of cardiomyocyte reprogramming and importance of the cellular changes on tissue repair.
KeywordsMesenchymal stromal cells Cardiomyocyte reprograming Acute myocardial infarction
We are grateful to Huijie Xiang, University Health Network for outstanding technical assistance, to Qi-Long Yi (Biostatistics Department, Princess Margaret Hospital/Ontario Cancer Institute) for assistance in statistical analysis and to Ye Yang, Department of Pathology, University Health Network for technical assistance in preparation of histological sections. A.K holds the Gloria and Seymour Epstein Chair in Cell Therapy and Transplantation at the University Health Network and the University of Toronto.
Conceived and designed the experiments: GY, JNT, AK. Performed the experiments: GY, JNT, JFD, XHW, AP. Analyzed the data: GY, JNT. Contributed reagents/materials/analysis tools: SV, TGP, AK. Wrote the paper: GY, JNT, SV, AK.
Conflict of Interest
The authors declare that they have no competing interests.
This work was supported by the Orsino Translational Research Laboratory, PMH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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