Effects of ß-adrenergic receptor drugs on embryonic ventricular cell proliferation and differentiation and their impact on donor cell transplantation.

ß-Adrenergic receptors (ß-ARs) and catecholamines are present in rodents as early as embryonic day (E)10.5. However, it is not known whether ß-AR signaling plays any role in the proliferation and differentiation of ventricular cells in the embryonic heart. Here, we characterized expression profiles of ß-AR subtypes and established dose-response curves for the nonselective ß-AR agonist isoproterenol (ISO) in the developing mouse ventricular cells. Furthermore, we investigated the effects of ISO on cell cycle activity and differentiation of cultured E11.5 ventricular cells. ISO treatment significantly reduced tritiated thymidine incorporation and cell proliferation rates in both cardiac progenitor cell and cardiomyocyte populations. The ISO-mediated effects on DNA synthesis could be abolished by cotreatment of E11.5 cultures with either metoprolol (a ß1-AR antagonist) or ICI-118,551 (a ß2-AR antagonist). In contrast, ISO-mediated effects on cell proliferation could be abolished only by metoprolol. Furthermore, ISO treatment significantly increased the percentage of differentiated cardiomyocytes compared with that in control cultures. Additional experiments revealed that ß-AR stimulation leads to downregulation of Erk and Akt phosphorylation followed by significant decreases in cyclin D1 and cyclin-dependent kinase 4 levels in E11.5 ventricular cells. Consistent with in vitro results, we found that chronic stimulation of recipient mice with ISO after intracardiac cell transplantation significantly decreased graft size, whereas metoprolol protected grafts from the inhibitory effects of systemic catecholamines. Collectively, these results underscore the effects of ß-AR signaling in cardiac development as well as graft expansion after cell transplantation.NEW & NOTEWORTHY ß-Adrenergic receptor (ß-AR) stimulation can decrease the proliferation of embryonic ventricular cells in vitro and reduce the graft size after intracardiac cell transplantation. In contrast, ß1-AR antagonists can abrogate the antiproliferative effects mediated by ß-AR stimulation and increase graft size. These results highlight potential interactions between adrenergic drugs and cell transplantation.

Atrial natriuretic peptide inhibits cell cycle activity of embryonic cardiac progenitor cells via its NPRA receptor signaling axis.

The biological effects of atrial natriuretic peptide (ANP) are mediated by natriuretic peptide receptors (NPRs), which can either activate guanylyl cyclase (NPRA and NPRB) or inhibit adenylyl cyclase (NPRC) to modulate intracellular cGMP or cAMP, respectively. During cardiac development, ANP serves as an early maker of differentiating atrial and ventricular chamber myocardium. As development proceeds, expression of ANP persists in the atria but declines in the ventricles. Currently, it is not known whether ANP is secreted or the ANP-NPR signaling system plays any active role in the developing ventricles. Thus the primary aims of this study were to 1) examine biological activity of ANP signaling systems in embryonic ventricular myocardium, and 2) determine whether ANP signaling modulates proliferation/differentiation of undifferentiated cardiac progenitor cells (CPCs) and/or cardiomyocytes. Here, we provide evidence that ANP synthesized in embryonic day (E)11.5 ventricular myocytes is actively secreted and processed to its biologically active form. Notably, NPRA and NPRC were detected in E11.5 ventricles and exogenous ANP stimulated production of cGMP in ventricular cell cultures. Furthermore, we showed that exogenous ANP significantly decreased cell number and DNA synthesis of CPCs but not cardiomyocytes and this effect could be reversed by pretreatment with the NPRA receptor-specific inhibitor A71915. ANP treatment also led to a robust increase in nuclear p27 levels in CPCs compared with cardiomyocytes. Collectively, these data provide evidence that in the developing mammalian ventricles ANP plays a local paracrine role in regulating the balance between CPC proliferation and differentiation via NPRA/cGMP-mediated signaling pathways.