Abstract
Recent evidence has shown that cardiac progenitor cells (CPCs) can fuse with existing cardiomyocytes (CMs). The fusion frequency significantly increases during heart injury or drug treatment, but the role of CPC-CM fusion in heart regeneration is largely unknown. In this study, we investigate CM-CPC fusion in vivo and its effects on CM proliferation in vitro using genetic lineage tracing and isolated cardiac cells from adult mice. To distinguish between nuclear fusion and membrane fusion, we utilized double fluorescent nuclear reporter mice. After one month of tamoxifen chow treatment, as many as 78% (n=4) of fused CMs displayed cytoplasm fusion, but not nuclear fusion. To further study the role of cytoplasm fusion in CM proliferation, we designed in vitro experiments where we either induce partial fusion or co-culture freshly isolated CMs with previously isolated c-kit+ cells. We find that 52% (387 of 741 cells, n=10) of the fused CMs maintain rod-shape morphology for over two months during culture, while all CMs ball up and dedifferentiate in co-culture controls (n=10) within 24 hours. Next, EdU was added to the culture media to assess DNA replication. EdU+ CMs were observed in both rod-shape and rounded CMs in 7 days. Finally, we monitored cell division of rod-shaped CMs fused with c-kit+ CPCs using intermittent live-cell imaging. We identified 2 cell division events from 20 randomly monitored rod-shape CMs in two months after fusion. These results demonstrate that fusion of c-kit+ cells with CMs are typically partial fusion events, that may play a role in regulating CM proliferation.
Published Version
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