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

The Impact of Natriuretic Peptides on Heart Development, Homeostasis, and Disease

During mammalian heart development, the clustered genes encoding peptide hormones, Natriuretic Peptide A (NPPA; ANP) and B (NPPB; BNP), are transcriptionally co-regulated and co-expressed predominately in the atrial and ventricular trabecular cardiomyocytes. After birth, expression of NPPA and a natural antisense transcript NPPA-AS1 becomes restricted to the atrial cardiomyocytes. Both NPPA and NPPB are induced by cardiac stress and serve as markers for cardiovascular dysfunction or injury. NPPB gene products are extensively used as diagnostic and prognostic biomarkers for various cardiovascular disorders. Membrane-localized guanylyl cyclase receptors on many cell types throughout the body mediate the signaling of the natriuretic peptide ligands through the generation of intracellular cGMP, which interacts with and modulates the activity of cGMP-activated kinase and other enzymes and ion channels. The natriuretic peptide system plays a fundamental role in cardio-renal homeostasis, and its potent diuretic and vasodilatory effects provide compensatory mechanisms in cardiac pathophysiological conditions and heart failure. In addition, both peptides, but also CNP, have important intracardiac actions during heart development and homeostasis independent of the systemic functions. Exploration of the intracardiac functions may provide new leads for the therapeutic utility of natriuretic peptide-mediated signaling in heart diseases and rhythm disorders. Here, we review recent insights into the regulation of expression and intracardiac functions of NPPA and NPPB during heart development, homeostasis, and disease.

Atrial natriuretic peptide signaling co-regulates lipid metabolism and ventricular conduction system gene expression in the embryonic heart

It has been shown that atrial natriuretic peptide (ANP) and its high affinity receptor (NPRA) are involved in the formation of ventricular conduction system (VCS). Inherited genetic variants in fatty acid oxidation (FAO) genes are known to cause conduction abnormalities in newborn children. Although the effect of ANP on energy metabolism in noncardiac cell types is well documented, the role of lipid metabolism in VCS cell differentiation via ANP/NPRA signaling is not known. In this study, histological sections and primary cultures obtained from E11.5 mouse ventricles were analyzed to determine the role of metabolic adaptations in VCS cell fate determination and maturation. Exogenous treatment of E11.5 ventricular cells with ANP revealed a significant increase in lipid droplet accumulation, FAO and higher expression of VCS marker Cx40. Using specific inhibitors, we further identified PPARγ and FAO as critical downstream regulators of ANP-mediated regulation of metabolism and VCS formation.

Developmental roles of natriuretic peptides and their receptors

Natriuretic peptides and their receptors are implicated in the physiological control of blood pressure, bone growth, and cardiovascular and renal homeostasis. They mediate their action through the modulation of intracellular levels of cGMP and cAMP, two second-messengers that have broad biological roles. In this review, we briefly describe the major players of this signaling pathway and their physiological roles in the adult, and discuss several reports describing their activity in the control of various aspects of embryonic development in several species. While the core components of this signaling pathway are well conserved, their functions have diverged in the embryo and the adult to control a diverse array of biological processes.

Application of Three-Dimensional Culture Method in the Cardiac Conduction System Research

Congenital heart defects (CHD) are the most common type of birth defects. Several human case studies and genetically altered animal models have identified abnormalities in the development of ventricular conduction system (VCS) in the heart. While cell-based therapies hold promise for treating CHDs, translational efforts are limited by the lack of suitable in vitro models for feasibility and safety studies. A better understanding of cell differentiation pathways can lead to development of cell-based therapies for individuals living with CHD/VCS disorders. Here, we describe a new and reproducible 3-D cell culture method for studying cardiac cell lineage differentiation in vitro. We used primary ventricular cells isolated from embryonic day 11.5 (E11.5) mouse embryos, which can differentiate into multiple cardiac cell types including VCS cells. We compared 3-D cultures with three types of basement membrane extracts (BME) for their abilities to support E11.5 ventricular cell differentiation. In addition, the effects of atrial natriuretic peptide (ANP) and an inhibitor for its high affinity receptor were tested on cell differentiation in 3-D cultures. Following the cell culture, protocols for immunofluorescence imaging, cell extraction and protein isolation from the 3-D culture matrix and in-cell western methods are described. Further, these approaches can be used to study the effects of various ligands and genetic interventions on VCS cell development. We propose that these methodologies may also be extended for differentiation studies using other sources of stem cells such as induced pluripotent stem cells.

A mouse model of inherited choline kinase β-deficiency presents with specific cardiac abnormalities and a predisposition to arrhythmia

The CHKB gene encodes choline kinase β, which catalyzes the first step in the biosynthetic pathway for the major phospholipid phosphatidylcholine. Homozygous loss-of-function variants in human CHKB are associated with a congenital muscular dystrophy. Dilated cardiomyopathy is present in some CHKB patients and can cause heart failure and death. Mechanisms underlying a cardiac phenotype due to decreased CHKB levels are not well characterized. We determined that there is cardiac hypertrophy in Chkb^−/− mice along with a decrease in left ventricle size, internal diameter, and stroke volume compared with wildtype and Chkb^+/− mice. Unlike wildtype mice, 60% of the Chkb^+/− and all Chkb^−/− mice tested displayed arrhythmic events when challenged with isoproterenol. Lipidomic analysis revealed that the major change in lipid level in Chkb^+/− and Chkb^−/− hearts was an increase in the arrhythmogenic lipid acylcarnitine. An increase in acylcarnitine level is also associated with a defect in the ability of mitochondria to use fatty acids for energy and we observed that mitochondria from Chkb^−/− hearts had abnormal cristae and inefficient electron transport chain activity. Atrial natriuretic peptide (ANP) is a hormone produced by the heart that protects against the development of heart failure including ventricular conduction defects. We determined that there was a decrease in expression of ANP, its receptor NPRA, as well as ventricular conduction system markers in Chkb^+/− and Chkb^−/− mice.

Regulation of Transplanted Cell Homing by FGF1 and PDGFB after Doxorubicin Myocardial Injury

There is no effective treatment for the total recovery of myocardial injury caused by an anticancer drug, doxorubicin (Dox). In this study, using a Dox-induced cardiac injury model, we compared the cardioprotective effects of ventricular cells harvested from 11.5-day old embryonic mice (E11.5) with those from E14.5 embryos. Our results indicate that tail-vein-infused E11.5 ventricular cells are more efficient at homing into the injured adult myocardium, and are more angiogenic, than E14.5 ventricular cells. In addition, E11.5 cells were shown to mitigate the cardiomyopathic effects of Dox. In vitro, E11.5 ventricular cells were more migratory than E14.5 cells, and RT-qPCR analysis revealed that they express significantly higher levels of cytokine receptors Fgfr1, Fgfr2, Pdgfra, Pdgfrb and Kit. Remarkably, mRNA levels for Fgf1, Fgf2, Pdgfa and Pdgfb were also found to be elevated in the Dox-injured adult heart, as were the FGF1 and PDGFB protein levels. Addition of exogenous FGF1 or PDGFB was able to enhance E11.5 ventricular cell migration in vitro, and, whereas their neutralizing antibodies decreased cell migration. These results indicate that therapies raising the levels of FGF1 and PDGFB receptors in donor cells and or corresponding ligands in an injured heart could improve the efficacy of cell-based interventions for myocardial repair.

Selective recognition of a cyclic peptide hormone in human plasma by hydrazone bond-oriented surface imprinted nanoparticles

As a kind of artificial recognition material, molecularly imprinted polymers (MIPs) offer a promising perspective to be developed as synthetic chemical binders capable of selectively recognize biomacromolecules. However, owing to the large size and conformational flexibility of proteins and peptides, imprinting of these biomacromolecules remains a challenge. Novel imprinting strategies still need exploration for the improvement of recognition performance of MIPs. Herein, we developed a hydrazone bond-oriented surface imprinting strategy for an endogenous peptide hormone, human atrial natriuretic peptide (ANP). Surface-oriented imprinting of peptide via reversible covalent bond anchoring approach increased the orientation homogeneity of imprinted cavities as well as the utility of templates. The prepared nanoparticles exhibited high selectivity and fast recognition kinetics for ANP epitope. The dissociation constant between ANP epitope and MIP was measured as 5.3 μM. The applicability of the material in real samples was verified by the selective magnetic extraction of ANP from human plasma samples. This hydrazone bond-oriented surface imprinting strategy provides an alternative approach for the separation of peptides or proteins in complex bio-samples.

Characterization of primary adult mouse cardiac fibroblast cultures

The role of cardiac fibroblasts (CFs) in disease states has been a focus of cardiovascular research over the past decade. Here, we briefly describe methods for isolation and characterization of CFs from adult mouse ventricles. Primary cultures were stained using antibodies for several marker proteins such as α-smooth muscle actin (αSMA), vimentin, and discoidin domain receptor 2 (DDR2) to confirm the identity of CFs or cardiac myofibroblasts (CMFs). Most cells in primary cultures consisted of CFs, with very low frequencies of endothelial cells, cardiomyocytes, and smooth muscle cells. We compared marker expression between cultures that were not passaged (P0) or passaged for few times (P1-3). When compared with P1-3 cultures, P0 cultures consistently displayed a lower percentage of cells positive for αSMA and DDR2, whereas vimentin expression was significantly higher in P0 cultures compared with P1-3 cultures. P0 cells were also smaller in area than P1-3 cells. Further, P1-3 mouse CFs were found to express both β1 and β2 adrenergic receptors (ARs) and β1ARs were more readily detected on the cell surface compared with β2ARs. In summary, mouse CF cultures underwent phenotype conversion into CMFs after passaging, consistent with what is seen with CF cultures from other species.

The therapeutic effect of B-type natriuretic peptides in acute decompensated heart failure

B-type natriuretic peptide (BNP) exhibits roles in natriuresis and diuresis, making it an ideal drug that may aid in diuresing a fluid-overloaded patient with poor or worsening renal function. Several randomized clinical trials have tested the hypothesis that infusions of pharmacological doses of BNP to acute heart failure (HF) patients may enhance decongestion and preserve renal function in this clinical setting. Unfortunately, none of these have demonstrated beneficial outcomes. The current challenge for BNP research in acute HF lies in addressing a failure of concept and a reluctance to abandon an ineffective research model. Future success will necessitate a detailed understanding of the mechanism of action of BNP, as well as better integration of basic and clinical science.

Fractionation of embryonic cardiac progenitor cells and evaluation of their differentiation potential

Mid-gestation mouse ventricles (E11.5) contain a larger number of Nkx2.5⁺ cardiac progenitor cells (CPCs). The proliferation rates are consistently higher in CPCs compared to myocyte population of developing ventricles. Recent studies suggested that CPCs are an ideal donor cell type for replacing damaged tissue in diseased hearts. Thus, the ability to isolate and expand CPCs from embryos or stem cell cultures could be useful for cell fate studies and regenerative therapies. Since embryonic CPCs possess fewer mitochondria compared to cardiomyocytes, we reasoned that CPCs can be fractionated using a fluorescent mitochondrial membrane potential dye (TMRM) and these cells may retain cardiomyogenic potential even in the absence of cardiomyocytes (CMs). FACS sorting of TMRM stained embryonic ventricular cells indicated that over 99% of cells in TMRM high fraction stained positive for sarcomeric myosin (MF20) and all of them expressed Nkx2.5. Although majority of cells present in TMRM low fraction expressed Nkx2.5, very few cells (~1%) stained positive for MF20. Further culturing of TMRM low cells over a period of 48 h showed a progressive increase in MF20 positive cells. Additional analyses revealed that MF20 negative cells in TMRM low fraction do not express markers for endothelial cells (vWF, CD31) or smooth muscle cells (SM myosin). Treatment of TMRM low cells with known cardiogenic factors DMSO and dynorphin B significantly increased the percentage of MF20⁺ cells compared to untreated cultures. Collectively, these studies suggest that embryonic CPCs can be separated as a TMRM low fraction and their differentiation potential can be enhanced by exogenous addition of known cardiomyogenic factors.

Characterizing the role of atrial natriuretic peptide signaling in the development of embryonic ventricular conduction system

Patients born with congenital heart defects frequently encounter arrhythmias due to defects in the ventricular conduction system (VCS) development. Although recent studies identified transcriptional networks essential for the heart development, there is scant information on the mechanisms regulating VCS development. Based on the association of atrial natriuretic peptide (ANP) expression with VCS forming regions, it was reasoned that ANP could play a critical role in differentiation of cardiac progenitor cells (CPCs) and cardiomyocytes (CMs) toward a VCS cell lineage. The present study showed that treatment of embryonic ventricular cells with ANP or cell permeable 8-Br-cGMP can induce gene expression of important VCS markers such as hyperpolarization-activated cyclic nucleotide-gated channel-4 (HCN4) and connexin 40 (Cx40). Inhibition of protein kinase G (PKG) via Rp-8-pCPT-cGMPS further confirmed the role of ANP/NPRA/cGMP/PKG pathway in the regulation of HCN4 and Cx40 gene expression. Additional experiments indicated that ANP may regulate VCS marker gene expression by modulating levels of miRNAs that are known to control the stability of transcripts encoding HCN4 and Cx40. Genetic ablation of NPRA revealed significant decreases in VCS marker gene expression and defects in Purkinje fiber arborisation. These results provide mechanistic insights into the role of ANP/NPRA signaling in VCS formation.

SDF1 gradient associates with the distribution of c-Kit+ cardiac cells in the heart

Identification of the adult cardiac stem cells (CSCs) has offered new therapeutic possibilities for treating ischemic myocardium. CSCs positive for the cell surface antigen c-Kit are known as the primary source for cardiac regeneration. Accumulating evidence shows that chemokines play important roles in stem cell homing. Here we investigated molecular targets to be utilized in modulating the mobility of endogenous CSCs. In a four week follow-up after experimental acute myocardial infarction (AMI) with ligation of the left anterior descending (LAD) coronary artery of Sprague-Dawley rats c-Kit+ CSCs redistributed in the heart. The number of c-Kit+ CSCs in the atrial c-Kit niche was diminished, whereas increased amount was observed in the left ventricle and apex. This was associated with increased expression of stromal cell-derived factor 1 alpha (SDF1α), and a significant positive correlation was found between c-Kit+ CSCs and SDF1α expression in the heart. Moreover, the migratory capacity of isolated c-Kit+ CSCs was induced by SDF1 treatment in vitro. We conclude that upregulation of SDF1α after AMI associates with increased expression of endogenous c-Kit+ CSCs in the injury area, and show induced migration of c-Kit+ cells by SDF1.

ANP promotes proliferation and inhibits apoptosis of ovarian granulosa cells by NPRA/PGRMC1/EGFR complex and improves ovary functions of PCOS rats

Polycystic ovary syndrome (PCOS) is a complicated reproductive endocrine disease characterized by polycystic ovaries, hyperandrogenism and anovulation. It is one of the main causes of infertility. RU486 is an antagonist of progesterone receptor, and most commonly used as a contraceptive. However, whether RU486 is correlated with PCOS remains unclear. Atrial natriuretic peptide (ANP) is a small peptide with natriuretic and diuretic functions, and its availability to be used in PCOS treatment is unknown. Here, we showed that the serum ANP level was lower in PCOS patients than that in healthy women, and it was also decreased in the serum and ovarian tissues of RU486-induced PCOS rats compared with the control rats. We also found that RU486 inhibited the proliferation and promoted the apoptosis of human KGN ovarian granulosa cells by downregulating progesterone receptor membrane component 1 (PGRMC1). Meantime, ANP promoted the proliferation and inhibited the apoptosis of KGN cells through upregulating ANP receptor A (NPRA). The promotive effects of ANP on ovarian functions were mediated through the formation of an NPRA/PGRMC1/EGFR complex, which further activated MAPK/ERK signaling and transcription factor AP1. Moreover, ANP treatment reversed the PCOS symptoms, and improved the fertility of RU486-induced PCOS rats. Collectively, these findings highlight that RU486 is associated with the pathogenesis of PCOS, and ANP treatment may be a promising therapeutic option for PCOS.

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

β-Adrenergic receptors (β-ARs) and catecholamines are present in rodents as early as embryonic day (E)10.5. However, it is not known whether β-AR signaling plays any role in the proliferation and differentiation of ventricular cells in the embryonic heart. Here, we characterized expression profiles of β-AR subtypes and established dose-response curves for the nonselective β-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 β₁-AR antagonist) or ICI-118,551 (a β₂-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 β-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 β-AR signaling in cardiac development as well as graft expansion after cell transplantation.NEW & NOTEWORTHY β-Adrenergic receptor (β-AR) stimulation can decrease the proliferation of embryonic ventricular cells in vitro and reduce the graft size after intracardiac cell transplantation. In contrast, β₁-AR antagonists can abrogate the antiproliferative effects mediated by β-AR stimulation and increase graft size. These results highlight potential interactions between adrenergic drugs and cell transplantation.

Atrial natriuretic peptide regulates adipose tissue accumulation in adult atria

The abundance of epicardial adipose tissue (EAT) is associated with atrial fibrillation (AF), the most frequent cardiac arrhythmia. However, both the origin and the factors involved in EAT expansion are unknown. Here, we found that adult human atrial epicardial cells were highly adipogenic through an epithelial-mesenchymal transition both in vitro and in vivo. In a genetic lineage tracing the WT1^CreERT2+/-Rosa^tdT+/- mouse model subjected to a high-fat diet, adipocytes of atrial EAT derived from a subset of epicardial progenitors. Atrial myocardium secretome induces the adipogenic differentiation of adult mesenchymal epicardium-derived cells by modulating the balance between mesenchymal Wingless-type Mouse Mammary Tumor Virus integration site family, member 10B (Wnt10b)/β-catenin and adipogenic ERK/MAPK signaling pathways. The adipogenic property of the atrial secretome was enhanced in AF patients. The atrial natriuretic peptide secreted by atrial myocytes is a major adipogenic factor operating at a low concentration by binding to its natriuretic peptide receptor A (NPRA) receptor and, in turn, by activating a cGMP-dependent pathway. Hence, our data indicate cross-talk between EAT expansion and mechanical function of the atrial myocardium.