Abstract 910: Highly Purified Hematopoietic Stem Cells Generate Cardiomyocytes via Myeloid Progenitors through Cell Fusion
[Introduction] Recent reports demonstrating the ability of bone marrow (BM) cells to regenerate cardiomyocytes (CMs) have prompted clinical as well as basic studies for the treatment of ischemic and non-ischemic cardiomyopathies. However, the responsible BM cells and underlying mechanism of regeneration remain unclear. In this study, we checked the cardiomyogenic potential of BM cells in vivo, to identify the cell populations in BM that possess the capacity to give rise to CMs and clarify whether cardiomyogenic potential of BM-derived cells require cell fusion with host CMs.
[Method and Result] BM cells of mice constitutively expressing green fluorescent protein (GFP) was intravenously injected into irradiated syngeneic newborn C57BL/6 mouse within 48hours after the birth. At 4–5weeks after transplantation, the cardiac tissue of recipients was analyzed for the number of GFP+ CMs per 40 sections. We first separated Linaege antigen− BM cells to CD45+ cells (Lin−CD45+) and CD45− cells (Lin−CD45−) and transplanted each. In the recipients of Lin−CD45+, 37.0±23.9 GFP+ CMs were detected (n=6). While no GFP+ CM was detected in the recipients of Lin−CD45− (n=4). Since hematopoietic cells generated CMs, we next transplanted limiting numbers of purified HSCs and hematopoietic progenitors by cell sorting. Both HSCs and hematopoietic progenitors generated CMs dose-dependently, suggested that HSC can generate CMs via hematopoietic progenitors. To explore the hematopoietic lineage, we further transplanted purified myeloid progenitors and common lymphoid progenitors by cell sorting. The number of GFP+ CMs were 12.8±10.7 and 0.91±1.20 in the recipients of myeloid progenitors (n=7) and common lymphoid progenitors (n=10) respectively (p<0.005), suggested that myeloid lineage is more strongly involved in the generation of CMs than lymphoid lineage. Finally, we transplanted GFP+ HSCs and myeloid progenitors into cyan fluorescent protein (CFP) transgenic mouse. Linear unmixing analysis using confocal microscopy revealed that donor-derived GFP+ CMs coexpressed CFP, indicated cell fusion had occurred.
[Conclusion] Our results suggested that HSC can contribute to the post-natal generation of CMs via myeloid progenitors through cell fusion.