0190 : Ephrin-B1 blocks adult cardiomyocyte proliferation and cardiac tissue regeneration

The possibility to reboot the proliferation of adult resident cardiomyocytes (CM) has recently emerged as a new promising avenue in cardiac regenerative medicine. For that purpose, there is an urgent need for identifying the molecular mechanisms involved in the natural blockage of adult CM proliferation.We recently identified ephrin-B1 as specific stabilizer of the CM rod-shape allowing the cardiac tissue cohesion. Interestingly, we found that ephrin-B1 knock-out mice (KO) compensate aging stress through a surprising CM hyperplasia, suggesting an atypical proliferation of adult CM. Cell cycle genes profiling performed by qRT-PCR showed that old KO CM significantly upregulated genes involved in all cell cycle phases. Progression of CM throughout the cell cycle was confirmed by flow cytometry and revealed the presence of the replicative S-phase only in old KO CM. Proliferation was next directly assessed on isolated 2 months-old CM stimulated or not with neuregulin- 1 growth factor. Remarkably, while this treatment resulted in 0.17% of BrdU uptake in WT CM, it increased up to 9.57% in KO. KO CM also exhibited significant higher mitotic (pH3+) and cytokinesis (AuroraB+) events compared to WT. Thus, the capacity for adult KO CM to proliferate is not restricted to aged CM but more likely an intrinsic potential of young KO CM. We next assessed the proliferative capacity of 2 month-old KO mice in vivo using the apectomy model. Remarkably, while WT mice developed a classical healing process (fibrosis/inflammation), KO mice almost completely regenerated the apex as indicated by the presence of mitotic (BrdU+, pH3+, AuroraB+) CM and significant reduced fibrosis (50%) in the resected zone.These results demonstrated that ephrin-B1 protein is a specific blocker of adult CM proliferation and its downregulation represents a huge interest for future therapeutic approaches in cardiac regenerative medicine