ErbB Receptors Signaling Promote Endothelial Phenotype of Human Left Ventricular Epicardial Highly Proliferative Cells

Abstract

Despite a long history of heart‐specific ErbB signaling research, the role of ErbB receptors in cardiac non‐myocyte cells is largely unknown. We recently have shown that neuregulin‐1b (NRG‐1b) prevented transition of CD105posCD31neg cells obtained from mouse heart into myfibroblasts. These cells can form single‐cell derived colonies with high proliferative potential and capability to differentiate into different cell types. The present study examines the expression of ErbB receptors on highly proliferative cells (HiPC) obtained from human LV epicardium and the role of ErbB receptor subtypes in the regulation of CD31, VEGFR2 and Tie2 endothelial markers expression. Left ventricular free wall epicardial biopsies from human subjects undergoing open heart surgery were used to obtain myocytes‐depleted cardiac cell suspension. These cells were seeded at low cell density to produce colonies of HiPC. We found that human HiPC are characterized by expression of all four ErbB receptors. The level of ErbB receptors varied among HiPC obtained from different subjects. ErbB2 and ErbB3 showed highest level of inter‐individual variability compared to ErbB1 and ErbB4. Flow cytometric analysis revealed strong expression of CD105 (endoglin), CD73 (ecto‐5′‐nucleotidase) and CD29 (integrin β1), and lack of CD34, CD117 (c‐kit), CD11b, and CD45 on HiPC. In addition, we detected expression of CD49f (integrin alpha 6), CD90 (Thy‐1) and CD31 (PECAM‐1) on cell surface of HiPC. A strong positive correlation was found between CD31/PECAM‐1 and ErbB2 but not ErbB1, 3 or 4. To determine the role of ErbB receptors, we incubated HiPC in the absence or presence of EGF to stimulate ErbB1, and NRG‐1b to stimulate ErbB3 and ErbB4 receptor activation. We found that both EGF and NRG‐1b ligands promoted CD31 cell surface expression on HiPC which express high level of ErbB2 (ErbB2hi). In contrast, no effects of ErbB ligands were seen in ErbB2low/− HiPC. Only EGF but not NRG‐1b increased VEGFR2 expression on HiPC. No difference was found between ErbB2hi and ErbB2low/− HiPC, indicating that ErbB1 receptors are solely responsible for the upregulation of cell surface expression of VEGFR2. In addition, both EGF and NRG‐1b induced up‐regulation of Tie2 on HiPC to a similar degree, irrespective of the level of ErbB2 expression. Thus our data identified a novel role of ErbB signaling in promotion of endothelial phenotype of human HiPC.Support or Funding InformationSupported in part by Acorda therapeutics, Inc, U01 HL100398, and the Osher Cardiovascular Research Fund at Maine Medical Center