Abstract 123: Erythropoietin Enhances Abundance of Cardiomyogenic Precursors in vitro and in vivo

Abstract

Recent data suggest that erythropoietin (Epo) can improve cardiac function following ischemia reperfusion injury. We found EpoR to be prominently expressed in embryonic rather than adult mouse heart. In the latter EpoR expression was confined to interstitial cells. We isolated the non-myocyte fraction of adult mouse hearts by enzymatic digestion and straining (pore size: 30 µm) and found a 4-fold higher EpoR expression compared to unselected cardiac cells (n=3). Flow cytometry (FC) revealed that 24±3% of this heterogeneous cell pool expressed EpoR (n=3) and 11±2% co-expressed αMHC. Half of the αMHC+ cells stained positive for Ki67, consistent with FC showing that 49±7% αMHC+/EpoR+ cells were in S and G2 phase (n=3; vs. 13±3% in αMHC-/EpoR-; n=3). Interestingly, co-culture with neonatal rat cardiomyocytes yielded EGFP+ cardiomyocyte-like cells. Since αMHC+ proliferated and differentiated in vitro we termed them cardiomyogenic precursors (CMPs). Epo treatment of the non-myocyte pool enhanced Akt phosphorylation (n=6/group) and increased CMP abundance in vitro (2-fold; n=3). Cell cycle arrest abrogated the aforementioned effect, suggesting that Epo influenced CMP proliferation. Finally, we tested the potential of Epo to protect against ischemia by enhancing CMP numbers in a model of myocardial infarction (MI). Following MI mice were treated twice with 2,000 U/kg Epo (i.p.). Ten weeks post MI echocardiography revealed blunted myocardial deterioration in mice receiving Epo (ΔEF=-11.18%, n=5) compared to control (ΔEF=-20.82%, n=6). FC revealed an enhanced αMHC+/cTnT+ cell pool in the Epo treated group (20.3±1.9% vs. 10.6±2.3% in control, n=8/6) 4 weeks post MI. In conclusion, we found that EpoR is expressed in a putative cardiomyogenic precursor cell pool in the adult heart. CMPs appear to proliferate in vitro and in vivo; with further enhanced proliferation under Epo administration. This may contribute to Epo mediated protection after MI and highlights the therapeutic effect of Epo upon ischemic cardiac injury. Whether these cells remain from embryogenesis or just constitute an immature myocyte population in the adult heart deriving from cardiomyocyte dedifferentiation needs to be further investigated.