Activation of the neuregulin/ErbB system during physiological ventricular remodeling in pregnancy

Geroscience in heart failure: the search for therapeutic targets in the shared pathobiology of human aging and heart failure

Age is a major risk factor for heart failure, but one that has been historically viewed as non-modifiable. Emerging evidence suggests that the biology of aging is malleable, and can potentially be intervened upon to treat age-associated chronic diseases, such as heart failure. While aging biology represents a new frontier for therapeutic target discovery in heart failure, the challenges of translating Geroscience research to the clinic are multifold. In this review, we propose a strategy that prioritizes initial target discovery in human biology. We review the rationale for starting with human omics, which has generated important insights into the shared (patho)biology of human aging and heart failure. We then discuss how this knowledge can be leveraged to identify the mechanisms of aging biology most relevant to heart failure. Lastly, we provide examples of how this human-first Geroscience approach, when paired with rigorous functional assessments in preclinical models, is leading to early-stage clinical development of gerotherapeutic approaches for heart failure.

Guidelines for assessing maternal cardiovascular physiology during pregnancy and postpartum

Maternal mortality rates are at an all-time high across the world and are set to increase in subsequent years. Cardiovascular disease is the leading cause of death during pregnancy and postpartum, especially in the United States. Therefore, understanding the physiological changes in the cardiovascular system during normal pregnancy is necessary to understand disease-related pathology. Significant systemic and cardiovascular physiological changes occur during pregnancy that are essential for supporting the maternal-fetal dyad. The physiological impact of pregnancy on the cardiovascular system has been examined in both experimental animal models and in humans. However, there is a continued need in this field of study to provide increased rigor and reproducibility. Therefore, these guidelines aim to provide information regarding best practices and recommendations to accurately and rigorously measure cardiovascular physiology during normal and cardiovascular disease-complicated pregnancies in human and animal models.

Computational model captures cardiac growth in hypertensive pregnancies and in the postpartum period

Heart growth in the pregnant patient helps maintain cardiovascular function while supporting the growing fetus. However, in some cases, the cardiovascular demand of pregnancy can trigger life-threatening conditions, including hypertensive disorders of pregnancy and peripartum cardiomyopathy. The mechanisms that control heart growth throughout pregnancy are unclear, and treating these diseases remains elusive. We previously developed a computational model that accounts for hormonal and hemodynamic interactions throughout pregnancy and demonstrated its ability to capture realistic cardiac growth in normal rat pregnancy. In this study, we evaluated whether this model could capture heart growth beyond normal pregnancy. After further validation of our normal pregnancy predictions, we tested our model predictions of three rat studies of hypertensive pregnancies. We next simulated the postpartum period and examined the impact of lactation on cardiac growth in rats. We demonstrate that our multiscale model can capture cardiac growth associated with new-onset hypertension during pregnancy and lactation status in the postpartum period. We conclude by elaborating on the potential clinical utility of our model in the future.NEW & NOTEWORTHY Our multiscale model predicts appropriate heart growth beyond normal pregnancy, including elevated heart weights in rats with induced hypertension during pregnancy and in lactating mice and decreased heart weight in nonlactating mice. Our model captures distinct mechanisms that result in similar organ-level growth, highlighting its potential to distinguish healthy from diseased pregnancy-induced growth.

Endothelial cell dysfunction in cardiac disease: driver or consequence?

The vascular endothelium is a multifunctional cellular system which directly influences blood components and cells within the vessel wall in a given tissue. Importantly, this cellular interface undergoes critical phenotypic changes in response to various biochemical and hemodynamic stimuli, driving several developmental and pathophysiological processes. Multiple studies have indicated a central role of the endothelium in the initiation, progression, and clinical outcomes of cardiac disease. In this review we synthesize the current understanding of endothelial function and dysfunction as mediators of the cardiomyocyte phenotype in the setting of distinct cardiac pathologies; outline existing in vivo and in vitro models where key features of endothelial cell dysfunction can be recapitulated; and discuss future directions for development of endothelium-targeted therapeutics for cardiac diseases with limited existing treatment options.

Environmental enteric dysfunction: gut and microbiota adaptation in pregnancy and infancy

Environmental enteric dysfunction (EED) is a subclinical syndrome of intestinal inflammation, malabsorption and barrier disruption that is highly prevalent in low- and middle-income countries in which poverty, food insecurity and frequent exposure to enteric pathogens impair growth, immunity and neurodevelopment in children. In this Review, we discuss advances in our understanding of EED, intestinal adaptation and the gut microbiome over the 'first 1,000 days' of life, spanning pregnancy and early childhood. Data on maternal EED are emerging, and they mirror earlier findings of increased risks for preterm birth and fetal growth restriction in mothers with either active inflammatory bowel disease or coeliac disease. The intense metabolic demands of pregnancy and lactation drive gut adaptation, including dramatic changes in the composition, function and mother-to-child transmission of the gut microbiota. We urgently need to elucidate the mechanisms by which EED undermines these critical processes so that we can improve global strategies to prevent and reverse intergenerational cycles of undernutrition.

MOTS-c and aerobic exercise induce cardiac physiological adaptation via NRG1/ErbB4/CEBPβ modification in rats

AIMS

To determine the effects of the mitochondrial open reading frame of the 12S ribosomal RNA type-c (MOTS-c) and aerobic exercise on cardiac structure and function and explore the role of neuregulin-1 (NRG1)- ErbB2 receptor tyrosine kinase 4(ErbB4)- CCAAT-enhancer binding protein β (C/EBPβ) in cardiac physiological adaptation induced by MOTS-c and aerobic training.

MAIN METHODS

We used Hematoxylin-Eosin staining(HE)and Transmission Electron Microscope (TEM) to observe the cardiac myocardial structure, carotid artery catheterization to test cardiac function, and real-time quantitative polymerase chain reaction (qRT-PCR) and Western blotting to describe the changes of NRG1, ErbB4, C/EBPβ, and Gata in cardiac physiological adaptation.

KEY FINDINGS

MOTS-c and aerobic training significantly increased heart weight and heart weight index (HWI) (all p < 0.05). Aerobic exercise and MOTS-c treatment thickened myocardial fibers, with a tendency of hypertrophy. Heart rate (HR) (p < 0.001, p = 0.010, p = 0.011), the isovolumic diastolic time constant (Tau) (p < 0.001, p < 0.001, p < 0.001) in exercised (E), MOST-c treated (M) and their combination (ME) decreased significantly, while the dP/dt_max (p < 0.001, p < 0.001, p = 0.039) and dP/dt_min (p < 0.001, p < 0.001, p = 0.001) in groups E, M and ME were significantly higher than those in group C, but EDP (p = 0.903, p = 0.708, p = 0.744) remained unchanged. Moreover, C/EBPβ gene levels were significantly decreased in the differential gene expression between groups C and M transcriptomics sequencing. The levels of ErbB4 mRNA (p < 0.001, p < 0.001, p < 0.001) and Gata4 mRNA (p < 0.001, p < 0.001, p = 0.001) in groups E, M and ME increased significantly, while C/EBPβ mRNA expression decreased significantly (p < 0.001, p = 0.002, p = 0.001), which was consistent with the results of transcriptome sequencing. NRG1 mRNA in group E was significantly higher than that in group C (p = 0.003), but there was no significant difference between groups M and ME (p = 0.804, p = 0.320). The protein expression of NRG1 (p = 0.026, p < 0.001, p < 0.001), ErbB4 (p < 0.001, p < 0.001, p < 0.001) and Gata4 (p = 0.014, p < 0.001, p = 0.006) in groups E, M and ME increased significantly, while C/EBPβ decreased significantly (p < 0.001, p = 0.001, p = 0.002).

SIGNIFICANCE

Our findings suggest that MOTS-c and aerobic exercise had similar effects, improving myocardial morphology and structure and enhancing cardiac function through activation of the NRG1-ErbB4-C/EBPβ pathway.

Prolactin Inhibition in Peripartum Cardiomyopathy: Systematic Review and Meta-analysis

Heart failure (HF) is one of the leading causes of maternal mortality and morbidity in the United States. Peripartum cardiomyopathy (PPCM) constitutes up to 70% of all HF in pregnancy. Cardiac angiogenic imbalance caused by cleaved 16kDa prolactin has been hypothesized to contribute to the development of PPCM, fueling investigation of prolactin inhibitors for the management of PPCM. We conducted a systematic review and meta-analysis to assess the impact of prolactin inhibition on left ventricular (LV) function and mortality in patients with PPCM. We included English language articles from PubMed and EMBASE published upto March 2022. We pooled the mean difference (MD) for left ventricular ejection fraction (LVEF) at follow-up, odds ratio (OR) for LV recovery and risk ratio (RR) for all-cause mortality using random-effects meta-analysis. Among 548 studies screened, 10 studies (3 randomized control trials (RCTs), 2 retrospective and 5 prospective cohorts) were included in the systematic review. Patients in the Bromocriptine + standard guideline directed medical therapy (GDMT) group had higher LVEF% (pMD 12.56 (95% CI 5.84-19.28, I2=0%) from two cohorts and pMD 14.25 (95% CI 0.61-27.89, I2=88%) from two RCTs) at follow-up compared to standard GDMT alone group. Bromocriptine group also had higher odds of LV recovery (pOR 3.55 (95% CI 1.39-9.1, I2=62)). We did not find any difference in all-cause mortality between the groups. Our analysis demonstrates that the addition of Bromocriptine to standard GDMT was associated with a significant improvement in LVEF% and greater odds of LV recovery, without significant reduction in all-cause mortality.

Beyond cardiomyocytes: Cellular diversity in the heart's response to exercise

Cardiomyocytes comprise ∼70% to 85% of the total volume of the adult mammalian heart but only about 25% to 35% of its total number of cells. Advances in single cell and single nuclei RNA sequencing have greatly facilitated investigation into and increased appreciation of the potential functions of non-cardiomyocytes in the heart. While much of this work has focused on the relationship between non-cardiomyocytes, disease, and the heart's response to pathological stress, it will also be important to understand the roles that these cells play in the healthy heart, cardiac homeostasis, and the response to physiological stress such as exercise. The present review summarizes recent research highlighting dynamic changes in non-cardiomyocytes in response to the physiological stress of exercise. Of particular interest are changes in fibrotic pathways, the cardiac vasculature, and immune or inflammatory cells. In many instances, limited data are available about how specific lineages change in response to exercise or whether the changes observed are functionally important, underscoring the need for further research.

Neuregulin-1, a potential therapeutic target for cardiac repair

NRG1 (Neuregulin-1) is an effective cardiomyocyte proliferator, secreted and released by endothelial vascular cells, and affects the cardiovascular system. It plays a major role in heart growth, proliferation, differentiation, apoptosis, and other cardiovascular processes. Numerous experiments have shown that NRG1 can repair the heart in the pathophysiology of atherosclerosis, myocardial infarction, ischemia reperfusion, heart failure, cardiomyopathy and other cardiovascular diseases. NRG1 can connect related signaling pathways through the NRG1/ErbB pathway, which form signal cascades to improve the myocardial microenvironment, such as regulating cardiac inflammation, oxidative stress, necrotic apoptosis. Here, we summarize recent research advances on the molecular mechanisms of NRG1, elucidate the contribution of NRG1 to cardiovascular disease, discuss therapeutic approaches targeting NRG1 associated with cardiovascular disease, and highlight areas for future research.

Multiscale model of heart growth during pregnancy: integrating mechanical and hormonal signaling

Pregnancy stands at the interface of mechanics and biology. The growing fetus continuously loads the maternal organs as circulating hormone levels surge, leading to significant changes in mechanical and hormonal cues during pregnancy. In response, maternal soft tissues undergo remarkable growth and remodeling to support the mother and baby for a healthy pregnancy. We focus on the maternal left ventricle, which increases its cardiac output and mass during pregnancy. This study develops a multiscale cardiac growth model for pregnancy to understand how mechanical and hormonal cues interact to drive this growth process. We coupled a cell signaling network model that predicts cell-level hypertrophy in response to hormones and stretch to a compartmental model of the rat heart and circulation that predicts organ-level growth in response to hemodynamic changes. We calibrated this multiscale model to data from experimental volume overload and hormonal infusions of angiotensin 2 (AngII), estrogen (E2), and progesterone (P4). We then validated the model's ability to capture interactions between inputs by comparing model predictions against published observations for the combinations of VO + E2 and AngII + E2. Finally, we simulated pregnancy-induced changes in hormones and hemodynamics to predict heart growth during pregnancy. Our model produced growth consistent with experimental data. Overall, our analysis suggests that the rise in P4 during the first half of gestation is an important contributor to heart growth during pregnancy. We conclude with suggestions for future experimental studies that will provide a better understanding of how hormonal and mechanical cues interact to drive pregnancy-induced heart growth.

Metabolic Signatures of Pregnancy-Induced Cardiac Growth

The goal of this study was to develop an atlas of the metabolic, transcriptional, and proteomic changes that occur with pregnancy in the maternal heart. Timed pregnancy studies in FVB/NJ mice revealed significant increases in heart size by day 8 of pregnancy (mid-pregnancy; MP), which was sustained throughout the rest of the term compared with non-pregnant controls. Cardiac hypertrophy and myocyte cross-sectional area were highest 7 d after birth (post-birth; PB) and were associated with significant increases in end-diastolic and end-systolic left ventricular volumes and cardiac output. Metabolomics analyses revealed that, by day 16 of pregnancy (late pregnancy; LP), metabolites associated with nitric oxide production as well as acylcholines, sphingomyelins, and fatty acid species were elevated, which coincided with a lower activation state of phosphofructokinase and higher levels of pyruvate dehydrogenase kinase 4 (Pdk4). In the postpartum period, urea cycle metabolites, polyamines, and phospholipid levels were markedly elevated in the maternal heart. Cardiac transcriptomics in LP revealed significant increases in not only Pdk4, but also genes that regulate glutamate and ketone body oxidation, which were preceded in MP by higher expression of transcripts controlling cell proliferation and angiogenesis. Proteomics analysis of the maternal heart in LP and PB revealed significant reductions in several contractile filaments and mitochondrial complex subunits. Collectively, these findings describe the coordinated molecular changes that occur in the maternal heart during and after pregnancy.

Targeting Myadm to Intervene Pulmonary Hypertension on Rats Before Pregnancy Alleviates the Effect on Their Offspring's Cardiac-Cerebral Systems

Pregnancy with pulmonary hypertension (PH) seriously threatens the life and safety of mothers and infants. Here, the long-term effect of maternal PH on the postpartum growth of rat offspring was focused for the first time, as well as explored the role of Myadm in PH rats before pregnancy based upon the previous findings. Patients with PH are prone to hypoxemia, leading to insufficient placental structure and function, which affects the organ function of fetuses, followed by evidence that differently expressed genes (DEGs) existed in the heart of maternal PH newborn rats and enriched in pathways related to cardiac and nerve development on human infants with similar birth outcome: low birth weight (LBW). LBW was one of the possible birth outcomes of pregnancy with PH, especially severe PH, accompanied by evidence that offspring derived from mothers with PH presented lower birth weights and slower growth rates than those derived from normal control mothers in a rat model. Besides, maternal PH rat offspring showed cardiac remodeling and a significant elevation of the expression levels of hypoxia- and inflammation-related markers in the cerebral cortex at both 10 and 14 weeks of age, respectively. What is more, the previous studies found that the overexpression of Myadm could result in the remodeling of the pulmonary artery. And targeting Myadm to intervene PH before pregnancy could alleviate sustained low weight growth in maternal PH rat offspring, and the pathological changes of the cardiac–cerebral system caused by maternal PH, including enlarged right heart cavity, loss of cardiomyocytes, abnormal heart index, as well as cerebral cortex hypoxia and the inflammatory state as they grew up to a certain extent. The findings show the pathological significance of maternal PH on offspring growth and the cardiac–cerebral development in a rat model, as well as point out the potential treatment target, which may provide a further reference for pregnancy outcomes in women with PH and healthy development of offspring to some extent.

The Potential of Gamma Secretase as a Therapeutic Target for Cardiac Diseases

Heart diseases are some of the most common and pressing threats to human health worldwide. The American Heart Association and the National Institute of Health jointly work to annually update data on cardiac diseases. In 2018, 126.9 million Americans were reported as having some form of cardiac disorder, with an estimated direct and indirect total cost of USD 363.4 billion. This necessitates developing therapeutic interventions for heart diseases to improve human life expectancy and economic relief. In this review, we look into gamma-secretase as a potential therapeutic target for cardiac diseases. Gamma-secretase, an aspartyl protease enzyme, is responsible for the cleavage and activation of a number of substrates that are relevant to normal cardiac development and function as found in mutation studies. Some of these substrates are involved in downstream signaling processes and crosstalk with pathways relevant to heart diseases. Most of the substrates and signaling events we explored were found to be potentially beneficial to maintain cardiac function in diseased conditions. This review presents an updated overview of the current knowledge on gamma-secretase processing of cardiac-relevant substrates and seeks to understand if the modulation of gamma-secretase activity would be beneficial to combat cardiac diseases.

ERBB4 and Multiple MicroRNAs That Target ERBB4 Participate in Pregnancy-Related Cardiomyopathy

BACKGROUND

Peripartum cardiomyopathy (PPCM) is a life-threatening disease in women without previously known cardiovascular disease. It is characterized by a sudden onset of heart failure before or after delivery. Previous studies revealed that the generation of a 16-kDa PRL (prolactin) metabolite, the subsequent upregulation of miR-146a, and the downregulation of the target gene Erbb4 is a common driving factor of PPCM.

METHODS

miRNA profiling was performed in plasma of PPCM patients (n=33) and postpartum-matched healthy CTRLs (controls; n=36). Elevated miRNAs in PPCM plasma, potentially targeting ERBB4 (erythroblastic leukemia viral oncogene homolog 4), were overexpressed in cardiomyocytes using lentiviral vectors. Next, cardiac function, cardiac morphology, and PPCM phenotype were investigated after recurrent pregnancies of HZ (heterozygous) cardiomyocyte-specific Erbb4 mice (Erbb4^F/+ αMHC-Cre⁺, n=9) with their age-matched nonpregnant CTRLs (n=9-10).

RESULTS

Here, we identify 9 additional highly conserved miRNAs (miR-199a-5p and miR-199a-3p, miR-145a-5p, miR-130a-3p, miR-135a-5p, miR-221-3p, miR-222-3p, miR-23a-3p, and miR19b-3p) that target tyrosine kinase receptor ERBB4 and are over 4-fold upregulated in plasma of PPCM patients at the time of diagnosis. We confirmed that miR-146a, miR-199a-5p, miR-221-3p, miR-222-3p, miR-23a-3p, miR-130a-5p, and miR-135-3p overexpression decreases ERBB4 expression in cardiomyocytes (-29% to -50%; P<0.05). In addition, we demonstrate that genetic cardiomyocyte-specific downregulation of Erbb4 during pregnancy suffices to induce a variant of PPCM in mice, characterized by left ventricular dilatation (postpartum second delivery: left ventricular internal diameter in diastole, +19±7% versus HZ-CTRL; P<0.05), increased atrial natriuretic peptide (ANP) levels (4-fold increase versus HZ-CTRL mice, P<0.001), decreased VEGF (vascular endothelial growth factor) and VE-cadherin levels (-33±17%, P=0.07; -27±20%, P<0.05 versus HZ-CTRL), and histologically enlarged cardiomyocytes (+20±21%, versus HZ-CTRL, P<0.05) but without signs of myocardial apoptosis and inflammation.

CONCLUSIONS

ERBB4 is essential to protect the maternal heart from peripartum stress. Downregulation of ERBB4 in cardiomyocytes induced by multiple miRNAs in the peripartum period may be crucial in PPCM pathophysiology. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT00998556.

Neuregulin-1 compensates for endothelial nitric oxide synthase deficiency

Endothelial cells (ECs) secrete different paracrine signals that modulate the function of adjacent cells; two examples of these paracrine signals are nitric oxide (NO) and neuregulin-1 (NRG1), a cardioprotective growth factor. Currently, it is undetermined whether one paracrine factor can compensate for the loss of another. Herein, we hypothesized that NRG1 can compensate for endothelial NO synthase (eNOS) deficiency. We characterized eNOS null and wild-type (WT) mice by cardiac ultrasound and histology and we determined circulating NRG1 levels. In a separate experiment, eight groups of mice were divided into four groups of eNOS null mice and WT mice; half of the mice received angiotensin II (ANG II) to induce a more severe phenotype. Mice were randomized to daily injections with NRG1 or vehicle for 28 days. eNOS deficiency increased NRG1 plasma levels, indicating that ECs increase their NRG1 expression when NO production is deleted. eNOS deficiency also increased blood pressure, lowered heart rate, induced cardiac fibrosis, and affected diastolic function. In eNOS null mice, ANG II administration not only increased cardiac fibrosis but also induced cardiac hypertrophy and renal fibrosis. NRG1 administration prevented cardiac and renal hypertrophy and fibrosis caused by ANG II infusion and eNOS deficiency. Moreover, Nrg1 expression in the myocardium is shown to be regulated by miR-134. This study indicates that administration of endothelium-derived NRG1 can compensate for eNOS deficiency in the heart and kidneys.NEW & NOTEWORTHY ECs compensate for eNOS deficiency by increasing the secretion of NRG1. NRG1 administration prevents cardiac and renal hypertrophy and fibrosis caused by ANG II infusion and eNOS deficiency. NRG1 expression is regulated by miR-134.

Neuregulins: protective and reparative growth factors in multiple forms of cardiovascular disease

Neuregulins (NRGs) are protein ligands that act through ErbB receptor tyrosine kinases to regulate tissue morphogenesis, plasticity, and adaptive responses to physiologic needs in multiple tissues, including the heart and circulatory system. The role of NRG/ErbB signaling in cardiovascular biology, and how it responds to physiologic and pathologic stresses is a rapidly evolving field. While initial concepts focused on the role that NRG may play in regulating cardiac myocyte responses, including cell survival, growth, adaptation to stress, and proliferation, emerging data support a broader role for NRGs in the regulation of metabolism, inflammation, and fibrosis in response to injury. The constellation of effects modulated by NRGs may account for the findings that two distinct forms of recombinant NRG-1 have beneficial effects on cardiac function in humans with systolic heart failure. NRG-4 has recently emerged as an adipokine with similar potential to regulate cardiovascular responses to inflammation and injury. Beyond systolic heart failure, NRGs appear to have beneficial effects in diastolic heart failure, prevention of atherosclerosis, preventing adverse effects on diabetes on the heart and vasculature, including atherosclerosis, as well as the cardiac dysfunction associated with sepsis. Collectively, this literature supports the further examination of how this developmentally critical signaling system functions and how it might be leveraged to treat cardiovascular disease.

Qiliqiangxin alleviates Ang II-induced CMECs apoptosis by downregulating autophagy via the ErbB2-AKT-FoxO3a axis

Our previous work revealed the protective effect of Qiliqiangxin (QLQX) on cardiac microvascular endothelial cells (CMECs), but the underlying mechanisms remain unclear. We aimed to investigate whether QLQX exerts its protective effect against high-concentration angiotensin II (Ang II)-induced CMEC apoptosis through the autophagy machinery. CMECs were cultured in high-concentration Ang II (1 μM) medium in the presence or absence of QLQX for 48 h. We found that QLQX obviously inhibited Ang II-triggered autophagosome synthesis and apoptosis in cultured CMECs. QLQX-mediated protection against Ang II-induced CMEC apoptosis was reversed by the autophagy activator rapamycin. Specifically, deletion of ATG7 in cultured CMECs indicated a detrimental role of autophagy in Ang II-induced CMEC apoptosis. QLQX reversed Ang II-mediated ErbB2 phosphorylation impairment. Furthermore, inhibition of ErbB2 phosphorylation with lapatinib in CMECs revealed that QLQX-induced downregulation of Ang II-activated autophagy and apoptosis was ErbB2 phosphorylation-dependent via the AKT-FoxO3a axis. Activation of ErbB2 phosphorylation by Neuregulin-1β achieved a similar CMEC-protective effect as QLQX in high-concentration Ang II medium, and this effect was also abolished by autophagy activation. These results show that the CMEC-protective effect of QLQX under high-concentration Ang II conditions could be partly attributable to QLQX-mediated ErbB2 phosphorylation-dependent downregulation of autophagy via the AKT-FoxO3a axis.

Human endothelial colony-forming cells provide trophic support for pluripotent stem cell-derived cardiomyocytes via distinctively high expression of neuregulin-1

The search for a source of endothelial cells (ECs) with translational therapeutic potential remains crucial in regenerative medicine. Human blood-derived endothelial colony-forming cells (ECFCs) represent a promising source of autologous ECs due to their robust capacity to form vascular networks in vivo and their easy accessibility from peripheral blood. However, whether ECFCs have distinct characteristics with translational value compared to other ECs remains unclear. Here, we show that vascular networks generated with human ECFCs exhibited robust paracrine support for human pluripotent stem cell-derived cardiomyocytes (iCMs), significantly improving protection against drug-induced cardiac injury and enhancing engraftment at ectopic (subcutaneous) and orthotopic (cardiac) sites. In contrast, iCM support was notably absent in grafts with vessels lined by mature-ECs. This differential trophic ability was due to a unique high constitutive expression of the cardioprotective growth factor neuregulin-1 (NRG1). ECFCs, but not mature-ECs, were capable of actively releasing NRG1, which, in turn, reduced apoptosis and increased the proliferation of iCMs via the PI3K/Akt signaling pathway. Transcriptional silencing of NRG1 abrogated these cardioprotective effects. Our study suggests that ECFCs are uniquely suited to support human iCMs, making these progenitor cells ideal for cardiovascular regenerative medicine.

Innate Immunity Effector Cells as Inflammatory Drivers of Cardiac Fibrosis

Despite relevant advances made in therapies for cardiovascular diseases (CVDs), they still represent the first cause of death worldwide. Cardiac fibrosis and excessive extracellular matrix (ECM) remodeling are common end-organ features in diseased hearts, leading to tissue stiffness, impaired myocardial functional, and progression to heart failure. Although fibrosis has been largely recognized to accompany and complicate various CVDs, events and mechanisms driving and governing fibrosis are still not entirely elucidated, and clinical interventions targeting cardiac fibrosis are not yet available. Immune cell types, both from innate and adaptive immunity, are involved not just in the classical response to pathogens, but they take an active part in "sterile" inflammation, in response to ischemia and other forms of injury. In this context, different cell types infiltrate the injured heart and release distinct pro-inflammatory cytokines that initiate the fibrotic response by triggering myofibroblast activation. The complex interplay between immune cells, fibroblasts, and other non-immune/host-derived cells is now considered as the major driving force of cardiac fibrosis. Here, we review and discuss the contribution of inflammatory cells of innate immunity, including neutrophils, macrophages, natural killer cells, eosinophils and mast cells, in modulating the myocardial microenvironment, by orchestrating the fibrogenic process in response to tissue injury. A better understanding of the time frame, sequences of events during immune cells infiltration, and their action in the injured inflammatory heart environment, may provide a rationale to design new and more efficacious therapeutic interventions to reduce cardiac fibrosis.

The role of endothelial autocrine NRG1/ERBB4 signaling in cardiac remodeling

Neuregulin-1 (NRG1) is a paracrine growth factor, secreted by cardiac endothelial cells (ECs) in conditions of cardiac overload/injury. The current concept is that the cardiac effects of NRG1 are mediated by activation of erythroblastic leukemia viral oncogene homolog (ERBB)4/ERBB2 receptors on cardiomyocytes. However, recent studies have shown that paracrine effects of NRG1 on fibroblasts and macrophages are equally important. Here, we hypothesize that NRG1 autocrine signaling plays a role in cardiac remodeling. We generated EC-specific Erbb4 knockout mice to eliminate endothelial autocrine ERBB4 signaling without affecting paracrine NRG1/ERBB4 signaling in the heart. We first observed no basal cardiac phenotype in these mice up to 32 wk. We next studied these mice following transverse aortic constriction (TAC), exposure to angiotensin II (ANG II), or myocardial infarction in terms of cardiac performance, myocardial hypertrophy, myocardial fibrosis, and capillary density. In general, no major differences between EC-specific Erbb4 knockout mice and control littermates were observed. However, 8 wk following TAC both myocardial hypertrophy and fibrosis were attenuated by EC-specific Erbb4 deletion, albeit these responses were normalized after 20 wk. Similarly, 4 wk after ANG II treatment, myocardial fibrosis was less pronounced compared with control littermates. These observations were supported by RNA-sequencing experiments on cultured endothelial cells showing that NRG1 controls the expression of various hypertrophic and fibrotic pathways. Overall, this study shows a role of endothelial autocrine NRG1/ERBB4 signaling in the modulation of hypertrophic and fibrotic responses during early cardiac remodeling. This study contributes to understanding the spatiotemporal heterogeneity of myocardial autocrine and paracrine responses following cardiac injury.NEW & NOTEWORTHY The role of NRG1/ERBB signaling in endothelial cells is not completely understood. Our study contributes to the understanding of spatiotemporal heterogeneity of myocardial autocrine and paracrine responses following cardiac injury and shows a role of endothelial autocrine NRG1/ERBB4 signaling in the modulation of hypertrophic and fibrotic responses during early cardiac remodeling.

Angiogenesis and angiocrines regulating heart growth

Endothelial cells (ECs) line the inner surface of all blood and lymphatic vessels throughout the body, making endothelium one of the largest tissues. In addition to its transport function, endothelium is now appreciated as a dynamic organ actively participating in angiogenesis, permeability and vascular tone regulation, as well as in the development and regeneration of tissues. The identification of endothelial-derived secreted factors, angiocrines, has revealed non-angiogenic mechanisms of endothelial cells in both physiological and pathological tissue remodeling. In the heart, ECs play a variety of important roles during cardiac development as well as in growth, homeostasis and regeneration of the adult heart. To date, several angiocrines affecting cardiomyocyte growth in response to physiological or pathological stimuli have been identified. In this review, we discuss the effects of angiogenesis and EC-mediated signaling in the regulation of cardiac hypertrophy. Identification of the molecular and metabolic signals from ECs during physiological and pathological cardiac growth could provide novel therapeutic targets to treat heart failure, as endothelium is emerging as one of the potential target organs in cardiovascular and metabolic diseases.

Pregnancy-associated cardiac dysfunction and the regulatory role of microRNAs

Many crucial cardiovascular adaptations occur in the body during pregnancy to ensure successful gestation. Maladaptation of the cardiovascular system during pregnancy can lead to complications that promote cardiac dysfunction and may lead to heart failure (HF). About 12% of pregnancy-related deaths in the USA have been attributed to HF and the detrimental effects of cardiovascular complications on the heart can be long-lasting, pre-disposing the mother to HF later in life. Indeed, cardiovascular complications such as gestational diabetes mellitus, preeclampsia, gestational hypertension, and peripartum cardiomyopathy have been shown to induce cardiac metabolic dysfunction, oxidative stress, fibrosis, apoptosis, and diastolic and systolic dysfunction in the hearts of pregnant women, all of which are hallmarks of HF. The exact etiology and cardiac pathophysiology of pregnancy-related complications is not yet fully deciphered. Furthermore, diagnosis of cardiac dysfunction in pregnancy is often made only after clinical symptoms are already present, thus necessitating the need for novel diagnostic and prognostic biomarkers. Mounting data demonstrates an altered expression of maternal circulating miRNAs during pregnancy affected by cardiovascular complications. Throughout the past decade, miRNAs have become of growing interest as modulators and biomarkers of pathophysiology, diagnosis, and prognosis in cardiac dysfunction. While the association between pregnancy-related cardiovascular complications and cardiac dysfunction or HF is becoming increasingly evident, the roles of miRNA-mediated regulation herein remain poorly understood. Therefore, this review will summarize current reports on pregnancy-related cardiovascular complications that may lead to cardiac dysfunction and HF during and after pregnancy in previously healthy women, with a focus on the pathophysiological role of miRNAs.

Neuregulin-1 triggers GLUT4 translocation and enhances glucose uptake independently of insulin receptor substrate and ErbB3 in neonatal rat cardiomyocytes

During stress conditions such as pressure overload and acute ischemia, the myocardial endothelium releases neuregulin-1β (NRG-1), which acts as a cardioprotective factor and supports recovery of the heart. Recently, we demonstrated that recombinant human (rh)NRG-1 enhances glucose uptake in neonatal rat ventricular myocytes via the ErbB2/ErbB4 heterodimer and PI3Kα. The present study aimed to further elucidate the mechanism whereby rhNRG-1 activates glucose uptake in comparison to the well-established insulin and to extend the findings to adult models. Combinations of rhNRG-1 with increasing doses of insulin did not yield any additive effect on glucose uptake measured as ³H-deoxy-d-glucose incorporation, indicating that the mechanisms of the two stimuli are similar. In c-Myc-GLUT4-mCherry-transfected neonatal rat cardiomyocytes, rhNRG-1 increased sarcolemmal GLUT4 by 16-fold, similar to insulin. In contrast to insulin, rhNRG-1 did not phosphorylate IRS-1 at Tyr⁶¹², indicating that IRS-1 is not implicated in the signal transmission. Treatment of neonatal rats with rhNRG-1 induced a signaling response comparable with that observed in vitro, including increased ErbB4-pTyr¹²⁸⁴, Akt-pThr³⁰⁸ and Erk1/2-pThr²⁰²/Tyr²⁰⁴. In contrast, in adult cardiomyocytes rhNRG-1 only increased the phosphorylation of Erk1/2 without having any significant effect on Akt and AS160 phosphorylation and glucose uptake, suggesting that rhNRG-1 function in neonatal cardiomyocytes differs from that in adult cardiomyocytes. In conclusion, our results show that similar to insulin, rhNRG-1 can induce glucose uptake by activating the PI3Kα-Akt-AS160 pathway and GLUT4 translocation. Unlike insulin, the rhNRG-1-induced effect is not mediated by IRS proteins and is observed in neonatal, but not in adult rat cardiomyocytes.

Peripartum cardiomyopathy: basic mechanisms and hope for new therapies

Peripartum cardiomyopathy (PPCM) is a life-threatening cardiomyopathy characterized by acute or slow progression of left ventricular (LV) systolic dysfunction (LV ejection fraction of &lt;45%) late in pregnancy, during delivery, or in the first postpartum months, in women with no other identifiable causes of heart failure. PPCM patients display variable phenotypes and risk factor profiles, pointing to involvement of multiple mechanisms in the pathogenesis of the disease. The higher risk for PPCM in women with African ancestry, the prevalence of gene variants associated with cardiomyopathies, and the high variability in onset and disease progression in PPCM patients also indicate multiple mechanisms at work. Experimental data have shown that different factors can induce and drive PPCM, including inflammation and immunity, pregnancy hormone impairment, catecholamine stress, defective cAMP-PKA, and G-protein-coupled-receptor signalling, and genetic variants. However, several of these mechanisms may merge into a common major pathway, which includes unbalanced oxidative stress and the cleavage of the nursing hormone prolactin (PRL) into an angiostatic, pro-apoptotic, and pro-inflammatory 16 kDa-PRL fragment, resulting in subsequent vascular damage and heart failure. Based on this common pathway, potential disease-specific biomarkers and therapies have emerged. Despite commonalities, the variation in aetiology and mechanisms poses challenges for the diagnosis, treatment, and management of the disease. This review summarizes current knowledge on the clinical presentation of PPCM in the context of recent experimental research. It discusses the challenge to develop disease-specific biomarkers in the context of rapid changing physiology in the peripartum phase, and outlines possible future treatment and management strategies for PPCM patients.

Mechanisms of the Multitasking Endothelial Protein NRG-1 as a Compensatory Factor During Chronic Heart Failure

Heart failure is a complex syndrome whose phenotypic presentation and disease progression depends on a complex network of adaptive and maladaptive responses. One of these responses is the endothelial release of NRG (neuregulin)-1—a paracrine growth factor activating ErbB2 (erythroblastic leukemia viral oncogene homolog B2), ErbB3, and ErbB4 receptor tyrosine kinases on various targets cells. NRG-1 features a multitasking profile tuning regenerative, inflammatory, fibrotic, and metabolic processes. Here, we review the activities of NRG-1 on different cell types and organs and their implication for heart failure progression and its comorbidities. Although, in general, effects of NRG-1 in heart failure are compensatory and beneficial, translation into therapies remains unaccomplished both because of the complexity of the underlying pathways and because of the challenges in the development of therapeutics (proteins, peptides, small molecules, and RNA-based therapies) for tyrosine kinase receptors. Here, we give an overview of the complexity to be faced and how it may be tackled.

Metabolic Coordination of Physiological and Pathological Cardiac Remodeling

Metabolic pathways integrate to support tissue homeostasis and to prompt changes in cell phenotype. In particular, the heart consumes relatively large amounts of substrate not only to regenerate ATP for contraction but also to sustain biosynthetic reactions for replacement of cellular building blocks. Metabolic pathways also control intracellular redox state, and metabolic intermediates and end products provide signals that prompt changes in enzymatic activity and gene expression. Mounting evidence suggests that the changes in cardiac metabolism that occur during development, exercise, and pregnancy as well as with pathological stress (eg, myocardial infarction, pressure overload) are causative in cardiac remodeling. Metabolism-mediated changes in gene expression, metabolite signaling, and the channeling of glucose-derived carbon toward anabolic pathways seem critical for physiological growth of the heart, and metabolic inefficiency and loss of coordinated anabolic activity are emerging as proximal causes of pathological remodeling. This review integrates knowledge of different forms of cardiac remodeling to develop general models of how relationships between catabolic and anabolic glucose metabolism may fortify cardiac health or promote (mal)adaptive myocardial remodeling. Adoption of conceptual frameworks based in relational biology may enable further understanding of how metabolism regulates cardiac structure and function.

Neuregulin-1 attenuates stress-induced vascular senescence

Aims

Cardiovascular ageing is a key determinant of life expectancy. Cellular senescence, a state of irreversible cell cycle arrest, is an important contributor to ageing due to the accumulation of damaged cells. Targeting cellular senescence could prevent age-related cardiovascular diseases. In this study, we investigated the effects of neuregulin-1 (NRG-1), an epidermal growth factor with cardioprotective and anti-atherosclerotic effects, on cellular senescence.

Methods and results

Senescence was induced in cultured rat aortic endothelial cells (ECs) and aortic smooth muscle cells (SMCs) by 2 h exposure to 30 µM hydrogen peroxide (H2O2). Cellular senescence was confirmed after 72 h using senescence-associated-β-galactosidase staining (SA-β-gal), cell surface area, and western blot analyses of SA pathways (acetyl-p53, p21). Recombinant human NRG-1 (rhNRG-1, 20 ng/mL) significantly reduced H2O2-induced senescence, as shown by a lower number of SA-β-gal positive cells, smaller surface area and lower expression of acetyl-p53. In C57BL/6 male mice rendered diabetic with streptozotocin (STZ), rhNRG-1 attenuated cellular senescence in aortic ECs and SMCs. Next, we created mice with SMC-specific knockdown of the NRG-1 receptor ErbB4. Aortic SMCs isolated from SMC-specific ErbB4 deficient mice (ErbB4f/+ SM22α-Cre+) showed earlier cellular senescence in vitro compared with wild-type (ErbB4+/+ SM22α-Cre+) SMCs. Furthermore, when rendered diabetic with STZ, ErbB4f/+ SM22α-Cre+ male mice showed significantly more vascular senescence than their diabetic wild-type littermates and had increased mortality.

Conclusions

This study is the first to explore the role of NRG-1 in vascular senescence. Our data demonstrate that NRG-1 markedly inhibits stress-induced premature senescence in vascular cells in vitro and in the aorta of diabetic mice in vivo. Consistently, deficiency in the NRG-1 receptor ErbB4 provokes cellular senescence in vitro as well as in vivo.

Matrix Metalloproteinases System and Types of Fibrosis in Rat Heart during Late Pregnancy and Postpartum

Background and objectives: Cardiac remodeling in pregnancy and postpartum is poorly understood. The aim of this study was to evaluate changes in cardiac fibrosis (pericardial, perivascular, and interstitial), as well as the expression of matrix metalloproteinases (MMP-1, MMP-2, and MMP-9) and their inhibitors (Tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-4) during late pregnancy and postpartum in rat left ventricle. Materials and Methods: Female Sprague–Dawley rats were used for this study. Rats were divided three groups: non-pregnant, late pregnancy, and postpartum. The heart was weighed and cardiac fibrosis was studied by conventional histological procedures. The expression and transcript level of target proteins were evaluated using immunoblot techniques and quantitative PCR. Results: The experiments showed an increase of perivascular, pericardial, and interstitial fibrosis in heart during pregnancy and its reversion in postpartum. Moreover, in late pregnancy, MMP-1, MMP-2, and MMP-9 metalloproteinases were downregulated and TIMP-1 and TIMP-4 were upregulated in left ventricle. Conclusions: Our data suggest that the metalloproteinases system is involved in the cardiac extracellular matrix remodeling during pregnancy and its reversion in postpartum, this improves the knowledge of the adaptive cardiac remodeling in response to a blood volume overload present during pregnancy.

Mechanotransduction, immunoregulation, and metabolic functions of CD31 in cardiovascular pathophysiology

Biomechanical changes in the heart and vessels drive rapid and dynamic regulation of blood flow, a vital process for meeting the changing metabolic needs of the peripheral tissues at any given point in time. The fluid movement of the blood exerts haemodynamic stress upon the solid elements of the cardiovascular system: the heart, vessels, and cellular components of the blood. Cardiovascular diseases can lead to prolonged mechanical stress, such as cardiac remodelling during heart failure or vascular stiffening in atherosclerosis. This can lead to a significantly reduced or increasingly turbulent blood supply, inducing a shift in cellular metabolism that, amongst other effects, can trigger the release of reactive oxygen species and initiate a self-perpetuating cycle of inflammation and oxidative stress. CD31 is the most abundant constitutive co-signalling receptor glycoprotein on endothelial cells, which line the cardiovascular system and form the first-line of cellular contact with the blood. By associating with most endothelial receptors involved in mechanosensing, CD31 regulates the response to biomechanical stimuli. In addition, by relocating in the lipid rafts of endothelial cells as well as of cells stably interacting with the endothelium, including leucocytes and platelets, CD31–CD31 trans-homophilic engagement guides and restrains platelet and immune cell accumulation and activation and at sites of damage. In this way, CD31 is at the centre of mediating mechanical, metabolic, and immunological changes within the circulation and provides a single target that may have pleiotropic beneficial effects.

Endothelial cell-cardiomyocyte crosstalk in heart development and disease

The crosstalk between endothelial cells and cardiomyocytes has emerged as a requisite for normal cardiac development, but also a key pathogenic player during the onset and progression of cardiac disease. Endothelial cells and cardiomyocytes are in close proximity and communicate through the secretion of paracrine signals, as well as through direct cell-to-cell contact. Here, we provide an overview of the endothelial cell-cardiomyocyte interactions controlling heart development and the main processes affecting the heart in normal and pathological conditions, including ischaemia, remodelling and metabolic dysfunction. We also discuss the possible role of these interactions in cardiac regeneration and encourage the further improvement of in vitro models able to reproduce the complex environment of the cardiac tissue, in order to better define the mechanisms by which endothelial cells and cardiomyocytes interact with a final aim of developing novel therapeutic opportunities.

Effects of neuregulin-1 on autonomic nervous system remodeling post-myocardial infarction in a rat model

Sympathetic nerve and vagus nerve remodeling play an important part in cardiac function post-myocardial infarction (MI). Increasing evidence indicates that neuregulin-1 (NRG-1) improves cardiac function following heart failure. Since its impact on cardiac function and neural remodeling post-MI is poorly understood, we aimed to investigate the role of NRG-1 in autonomic nervous system remodeling post-MI. Forty-five Sprague-Dawley rats were equally randomized into three groups: sham (with the left anterior descending coronary artery exposed but without ligation), MI (left anterior descending coronary artery ligation), and MI plus NRG-1 (left anterior descending coronary artery ligation followed by intraperitoneal injection of NRG-1 (10 μg/kg, once daily for 7 days)). At 4 weeks after MI, echocardiography was used to detect the rat cardiac function by measuring the left ventricular end-systolic inner diameter, left ventricular diastolic diameter, left ventricular end-systolic volume, left ventricular end-diastolic volume, left ventricular ejection fraction, and left ventricular fractional shortening. mRNA and protein expression levels of tyrosine hydroxylase, growth associated protein-43 (neuronal specific protein), nerve growth factor, choline acetyltransferase (vagus nerve marker), and vesicular acetylcholine transporter (cardiac vagal nerve fiber marker) in ischemic myocardia were detected by real-time PCR and western blot assay to assess autonomous nervous remodeling. After MI, the rat cardiac function deteriorated significantly, and it was significantly improved after NRG-1 injection. Compared with the MI group, mRNA and protein levels of tyrosine hydroxylase and growth associated protein-43, as well as choline acetyltransferase mRNA level significantly decreased in the MI plus NRG-1 group, while mRNA and protein levels of nerve growth factor and vesicular acetylcholine transporters, as well as choline acetyltransferase protein level slightly decreased. Our results indicate that NRG-1 can improve cardiac function and regulate sympathetic and vagus nerve remodeling post-MI, thus reaching a new balance of the autonomic nervous system to protect the heart from injury.

PDK4 Inhibits Cardiac Pyruvate Oxidation in Late Pregnancy

RATIONALE

Pregnancy profoundly alters maternal physiology. The heart hypertrophies during pregnancy, but its metabolic adaptations, are not well understood.

OBJECTIVE

To determine the mechanisms underlying cardiac substrate use during pregnancy.

METHODS AND RESULTS

We use here ¹³C glucose, ¹³C lactate, and ¹³C fatty acid tracing analyses to show that hearts in late pregnant mice increase fatty acid uptake and oxidation into the tricarboxylic acid cycle, while reducing glucose and lactate oxidation. Mitochondrial quantity, morphology, and function do not seem altered. Insulin signaling seems intact, and the abundance and localization of the major fatty acid and glucose transporters, CD36 (cluster of differentiation 36) and GLUT4 (glucose transporter type 4), are also unchanged. Rather, we find that the pregnancy hormone progesterone induces PDK4 (pyruvate dehydrogenase kinase 4) in cardiomyocytes and that elevated PDK4 levels in late pregnancy lead to inhibition of PDH (pyruvate dehydrogenase) and pyruvate flux into the tricarboxylic acid cycle. Blocking PDK4 reverses the metabolic changes seen in hearts in late pregnancy.

CONCLUSIONS

Taken together, these data indicate that the hormonal environment of late pregnancy promotes metabolic remodeling in the heart at the level of PDH, rather than at the level of insulin signaling.

Inhibitory actions of the NRG-1/ErbB4 pathway in macrophages during tissue fibrosis in the heart, skin, and lung

The neuregulin-1 (NRG-1)/receptor tyrosine-protein kinase erbB (ErbB) system is an endothelium-controlled paracrine system modulating cardiac performance and adaptation. Recent studies have indicated that NRG-1 has antifibrotic effects in the left ventricle, which were explained by direct actions on cardiac fibroblasts. However, the NRG-1/ErbB system also regulates the function of macrophages. In this study, we hypothesized that the antifibrotic effect of NRG-1 in the heart is at least partially mediated through inhibitory effects on macrophages. We also hypothesized that the antifibrotic effect of NRG-1 may be active in other organs, such as the skin and lung. First, in a mouse model of angiotensin II (ANG II)-induced myocardial hypertrophy and fibrosis, NRG-1 treatment (20 µg·kg^-1·day^-1 ip) significantly attenuated myocardial hypertrophy and fibrosis and improved passive ventricular stiffness (4 wk). Interestingly, 1 wk after exposure to ANG II, NRG-1 already attenuated myocardial macrophage infiltration and cytokine expression. Furthermore, mice with myeloid-specific deletion of the ErbB4 gene (ErbB4^F/FLysM-Cre^+/-) showed an intensified myocardial fibrotic response to ANG II. Consistently, NRG-1 activated the ErbB4 receptor in isolated macrophages, inhibited phosphatidylinositide 3-kinase/Akt and STAT3 signaling pathways, and reduced the release of inflammatory cytokines. Further experiments showed that the antifibrotic and anti-inflammatory effects of NRG-1 were reproducible in mouse models of bleomycin-induced dermal and pulmonary fibrosis. Overall, this study demonstrates that the antifibrotic effect of NRG-1 in the heart is linked to anti-inflammatory activity NRG-1/ErbB4 signaling in macrophages. Second, this study shows that NRG-1 has antifibrotic and anti-inflammatory effects in organs other than the heart, such as the skin and lung.NEW & NOTEWORTHY Our study contributes to the understanding of the antifibrotic effect of neuregulin-1 during myocardial remodeling. Here, we show that the antifibrotic effect of neuregulin-1 is at least partially mediated through anti-inflammatory activity, linked to receptor tyrosine-protein kinase erbB-4 activation in macrophages. Furthermore, we show that this effect is also present outside the heart.

ERBB signaling attenuates proinflammatory activation of nonclassical monocytes

Immune activation in chronic systolic heart failure (HF) correlates with disease severity and prognosis. Recombinant neuregulin-1 (rNRG-1) is being developed as a possible therapy for HF, based on the activation of ERBB receptors in cardiac cells. Work in animal models of HF led us to hypothesize that there may be direct effects of NRG-1 on immune system activation and inflammation. We investigated the expression of ERBB receptors and the effect of rNRG-1 isoform glial growth factor 2 (GGF2) in subpopulations of peripheral blood mononuclear cells (PB MNCs) in subjects with HF. We found that human monocytes express both ERBB2 and ERBB3 receptors, with high interindividual variability among subjects. Monocyte surface ERBB3 and TNF-α mRNA expression were inversely correlated in subjects with HF but not in human subjects without HF. GGF2 activation of ERBB signaling ex vivo inhibited LPS-induced TNF-α production, specifically in the CD14^lowCD16⁺ population of monocytes in a phosphoinositide 3-kinase-dependent manner. GGF2 suppression of TNF-α correlated directly with the expression of ERBB3. In vivo, a single dose of intravenous GGF2 reduced TNF-α expression in PB MNCs of HF subjects participating in a phase I safety study of GGF2. These results support a role for ERBB3 signaling in the regulation of TNF-α production from CD14^lowCD16⁺ monocytes and a need for further investigation into the clinical significance of NRG-1/ERBB signaling as a modulator of immune system function.NEW & NOTEWORTHY This study identified a novel role of neuregulin-1 (NRG-1)/ERBB signaling in the control of proinflammatory activation of monocytes. These results further improve our fundamental understanding of cardioprotective effects of NRG-1 in patients with heart failure.

RETRACTED: The receptor tyrosine kinase AXL mediates nuclear translocation of the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a therapeutic target in patients with various cancers. Unfortunately, resistance to EGFR-targeted therapeutics is common. Previous studies identified two mechanisms of resistance to the EGFR monoclonal antibody cetuximab. Nuclear translocation of EGFR bypasses the inhibitory effects of cetuximab, and the receptor tyrosine kinase AXL mediates cetuximab resistance by maintaining EGFR activation and downstream signaling. Thus, we hypothesized that AXL mediated the nuclear translocation of EGFR in the setting of cetuximab resistance. Cetuximab-resistant clones of non-small cell lung cancer in culture and patient-derived xenografts in mice had increased abundance of AXL and nuclear EGFR (nEGFR). Cellular fractionation analysis, super-resolution microscopy, and electron microscopy revealed that genetic loss of AXL reduced the accumulation of nEGFR. SRC family kinases (SFKs) and HER family ligands promote the nuclear translocation of EGFR. We found that AXL knockdown reduced the expression of the genes encoding the SFK family members YES and LYN and the ligand neuregulin-1 (NRG1). AXL knockdown also decreased the interaction between EGFR and the related receptor HER3 and accumulation of HER3 in the nucleus. Overexpression of LYN and NRG1 in cells depleted of AXL resulted in accumulation of nEGFR, rescuing the deficit induced by lack of AXL. Collectively, these data uncover a previously unrecognized role for AXL in regulating the nuclear translocation of EGFR and suggest that AXL-mediated SFK and NRG1 expression promote this process.

ErbB2 signaling at the crossing between heart failure and cancer

The dual role of ErbB2 (or HER-2) in tumor growth and in physiological adaptive reactions of the heart positions ErbB2 at the intersection between cancer and chronic heart failure. Accordingly, ErbB2-targeted inhibitory therapy of cancer may lead to ventricular dysfunction, and activation of ErbB2 for heart failure therapy may induce malignancy. The molecular processes leading to the activation of ErbB2 in tumors and cardiac cells are, however, fundamentally different from each other. Thus, it must be feasible to design drugs that specifically target either physiological or malignant ErbB2 signaling, to activate ErbB2 signaling in heart failure with no increased risk for cancer, and to inhibit ErbB2 signaling in cancer with no increased risk for heart failure. In this review, we present a state-of-the-art on how ErbB2 is regulated in physiological conditions and in tumor cells and how this knowledge translates into smart drug design. This leads to a new generation of drugs interfering with ErbB2 in a unique way tailored for a specific clinical goal. These exciting developments at the crossing between cancer and heart failure are an elegant example of interdisciplinary collaborations between clinicians, physiologists, pharmacologists, and molecular biologists.

Neuregulin-1β promotes glucose uptake via PI3K/Akt in neonatal rat cardiomyocytes

Nrg1β is critically involved in cardiac development and also maintains function of the adult heart. Studies conducted in animal models showed that it improves cardiac performance under a range of pathological conditions, which led to its introduction in clinical trials to treat heart failure. Recent work also implicated Nrg1β in the regenerative potential of neonatal and adult hearts. The molecular mechanisms whereby Nrg1β acts in cardiac cells are still poorly understood. In the present study, we analyzed the effects of Nrg1β on glucose uptake in neonatal rat ventricular myocytes and investigated to what extent mTOR/Akt signaling pathways are implicated. We show that Nrg1β enhances glucose uptake in cardiomyocytes as efficiently as IGF-I and insulin. Nrg1β causes phosphorylation of ErbB2 and ErbB4 and rapidly induces the phosphorylation of FAK (Tyr(861)), Akt (Thr(308) and Ser(473)), and its effector AS160 (Thr(642)). Knockdown of ErbB2 or ErbB4 reduces Akt phosphorylation and blocks the glucose uptake. The Akt inhibitor VIII and the PI3K inhibitors LY-294002 and Byl-719 abolish Nrg1β-induced phosphorylation and glucose uptake. Finally, specific mTORC2 inactivation after knockdown of rictor blocks the Nrg1β-induced increases in Akt-p-Ser(473) but does not modify AS160-p-Thr(642) or the glucose uptake responses to Nrg1β. In conclusion, our study demonstrates that Nrg1β enhances glucose uptake in cardiomyocytes via ErbB2/ErbB4 heterodimers, PI3Kα, and Akt. Furthermore, although Nrg1β activates mTORC2, the resulting Akt-Ser(473) phosphorylation is not essential for glucose uptake induction. These new insights into pathways whereby Nrg1β regulates glucose uptake in cardiomyocytes may contribute to the understanding of its regenerative capacity and protective function in heart failure.

Cardiac Physiology of Pregnancy

Although the physiology of the heart and vascular system has not changed, there are many things we have learned and are still learning today. Research related to heart adaptations during pregnancy has been performed since the 1930s. Since the mid-1950s, researchers began to look at changes in the maternal cardiovascular system during exercise while pregnant. Research related to exercise during pregnancy and offspring heart development began and has continued since the 1970s. We will review the normal female cardiovascular system adaptations to pregnancy in general. Additionally, topics related to maternal cardiac adaptations to pregnancy during acute exercise, as well as the chronic conditioning response from exercise training will be explored. Since physical activity during pregnancy influences fetal development, the fetal cardiac development will be discussed in regards to acute and chronic maternal exercise. Similarly, the influence of various types of maternal exercise on acute and chronic fetal heart responses will be described. Briefly, the topics related to how and if there is maternal-fetal synchrony will be explained. Lastly, the developmental changes of the fetal cardiovascular system that persist after birth will be explored. Overall, the article will discuss maternal cardiac physiology related to changes with normal pregnancy, and exercise during pregnancy, as well as fetal cardiac physiology related to changes with normal development, and exercise during pregnancy as well as developmental changes in offspring after birth.

NRG1 and KITL Signal Downstream of Retinoic Acid in the Germline to Support Soma-Free Syncytial Growth of Differentiating Spermatogonia

Defined culture systems supporting spermatogonial differentiation will provide experimental platforms to study spermatogenesis. However, germline-intrinsic signaling mechanisms sufficient to support spermatogonial differentiation without somatic cells remain largely undefined. Here, we analyzed EGF superfamily receptor and ligand diversity in rat testis cells, and delineated germline-intrinsic signaling via an ERBB3 co-transducer, ERBB2, as essential for retinoic acid-induced syncytial growth by differentiating spermatogonia. Like the ERBB2/3 agonist NRG1, we found KIT Ligand (KITL) robustly supported spermatogonial differentiation without serum or somatic cells. ERBB2 inhibitors failed to disrupt KITL-dependent spermatogonial development, and, KITL prevented ERBB3-deficient spermatogonial degeneration upon differentiation. Thus, we report NRG1 and KITL activate alternative pathways downstream of retinoic acid signaling in the germline that are essential for stem cells to undergo pre-meiotic steps of spermatogenesis in culture. Robust serum/soma-free spermatogonial differentiation opens new doors to study mammalian germ cell biology in culture, which will facilitate the discovery of spermatogenic factors that can drive meiotic progression in vitro.

Cardiac endothelium-myocyte interaction: clinical opportunities for new heart failure therapies regardless of ejection fraction

Heart failure (HF) is an important global health problem with great socioeconomic burden. Outcomes remain sub-optimal. Endothelium-cardiomyocyte interactions play essential roles in cardiovascular homeostasis, and deranged endothelium-related signalling pathways have been implicated in the pathophysiology of HF. In particular, disturbances in nitric oxide (NO)-mediated pathway and neuregulin-mediated pathway have been shown to contribute to the development of HF. These signalling pathways hold the potential as pathophysiological targets for new HF therapies, and may aid in patient selection for future HF trials.

The roles of neuregulin-1 in cardiac development, homeostasis, and disease

Neuregulin-1 (NRG-1) and its signaling receptors, erythroblastic leukemia viral oncogene homologs (ErbB) 2, 3, and 4, have been implicated in both cardiomyocyte development and disease, as well as in homeostatic cardiac function. NRG-1/ErbB signaling is involved in a multitude of cardiac processes ranging from myocardial and cardiac conduction system development to angiogenic support of cardiomyocytes, to cardioprotective effects upon injury. Numerous studies of NRG-1 employ a variety of platforms, including in vitro assays, animal models, and human clinical trials, with equally varying and, sometimes, contradictory outcomes. NRG-1 has the potential to be used as a therapeutic tool in stem cell therapies, tissue engineering applications, and clinical diagnostics and treatment. This review presents a concise summary of the growing body of literature to highlight the temporally persistent significance of NRG-1/ErbB signaling throughout development, homeostasis, and disease in the heart, specifically in cardiomyocytes.

Differential effects of short- and long-term antipsychotic treatment on the expression of neuregulin-1 and ErbB4 receptors in the rat brain

Neuregulin-1 (NRG1) and ErbB4 genes have been identified as candidate genes for schizophrenia. Post-mortem studies indicated that NRG1-ErbB4 signalling is impaired in schizophrenia subjects. This study investigated whether short- or long-term antipsychotic treatment has different effects on the expression of NRG1 and ErbB4 receptors. Female Sprague-Dawley rats were treated orally with either aripiprazole (0.75 mg/kg), haloperidol (0.1 mg/kg), olanzapine (0.5 mg/kg), or vehicle, 3 times/day for 1 or 12 weeks. Western blotting was performed to examine the expression of NRG1 isoforms (135 kDa, 70 kDa and 40 kDa) and ErbB4 receptors. Both 1-week haloperidol and olanzapine treatment increased NRG1-70kDa expression in the hippocampus; haloperidol also up-regulated ErbB4 levels in the prefrontal cortex (PFC). In the 12-week group, aripiprazole decreased the expression of all three NRG1 isoforms and ErbB4 receptors in the PFC, NRG1-70 kDa and -40 kDa in the cingulate cortex (Cg), and NRG1-135 kDa, -70 kDa and ErbB4 receptors in the hippocampus; haloperidol reduced NRG1-135 kDa in the PFC, NRG1-40 kDa in all three brain regions, and ErbB4 receptor levels in the PFC and hippocampus; NRG1-40 kDa in the PFC and Cg was also down-regulated by olanzapine. These results suggest that the time-dependent and region-specific effects of antipsychotics on NRG1-ErbB4 signalling may contribute to the efficacy of antipsychotics to treat schizophrenia.

Platelet endothelial cell adhesion molecule-1 mediates endothelial-cardiomyocyte communication and regulates cardiac function

Background

Dilated cardiomyopathy is characterized by impaired contractility of cardiomyocytes, ventricular chamber dilatation, and systolic dysfunction. Although mutations in genes expressed in the cardiomyocyte are the best described causes of reduced contractility, the importance of endothelial‐cardiomyocyte communication for proper cardiac function is increasingly appreciated. In the present study, we investigate the role of the endothelial adhesion molecule platelet endothelial cell adhesion molecule (PECAM‐1) in the regulation of cardiac function.

Methods and Results

Using cell culture and animal models, we show that PECAM‐1 expressed in endothelial cells (ECs) regulates cardiomyocyte contractility and cardiac function via the neuregulin‐ErbB signaling pathway. Conscious echocardiography revealed left ventricular (LV) chamber dilation and systolic dysfunction in PECAM‐1^−/− mice in the absence of histological abnormalities or defects in cardiac capillary density. Despite deficits in global cardiac function, cardiomyocytes isolated from PECAM‐1^−/− hearts displayed normal baseline and isoproterenol‐stimulated contractility. Mechanistically, absence of PECAM‐1 resulted in elevated NO/ROS signaling and NRG‐1 release from ECs, which resulted in augmented phosphorylation of its receptor ErbB2. Treatment of cardiomyocytes with conditioned media from PECAM‐1^−/− ECs resulted in enhanced ErbB2 activation, which was normalized by pre‐treatment with an NRG‐1 blocking antibody. To determine whether normalization of increased NRG‐1 levels could correct cardiac function, PECAM‐1^−/− mice were treated with the NRG‐1 blocking antibody. Echocardiography showed that treatment significantly improved cardiac function of PECAM‐1^−/− mice, as revealed by increased ejection fraction and fractional shortening.

Conclusions

We identify a novel role for PECAM‐1 in regulating cardiac function via a paracrine NRG1‐ErbB pathway. These data highlight the importance of tightly regulated cellular communication for proper cardiac function.

Neuregulin as a heart failure therapy and mediator of reverse remodeling

The beta isoform of Neuregulin-1 (NRG-1β), along with its receptors (ErbB2-4), is required for cardiac development. NRG-1β, as well as the ErbB2 and ErbB4 receptors, is also essential for maintenance of adult heart function. These observations have led to its evaluation as a therapeutic for heart failure. Animal studies and ongoing clinical trials have demonstrated beneficial effects of two forms of recombinant NRG-1β on cardiac function. In addition to the possible role for recombinant NRG-1βs as heart failure therapies, endogenous NRG-1β/ErbB signaling appears to play a role in restoring cardiac function after injury. The potential mechanisms by which NRG-1β may act as both a therapy and a mediator of reverse remodeling remain incompletely understood. In addition to direct effects on cardiac myocytes NRG-1β acts on the vasculature, interstitium, cardiac fibroblasts, and hematopoietic and immune cells, which, collectively, may contribute to NRG-1β's role in maintaining cardiac structure and function, as well as mediating reverse remodeling.

Neuregulin-1/erbB activities with focus on the susceptibility of the heart to anthracyclines

Neuregulin-1 (NRG1) signaling through the tyrosine kinase receptors erbB2 and erbB4 is required for cardiac morphogenesis, and it plays an essential role in maintaining the myocardial architecture during adulthood. The tyrosine kinase receptor erbB2 was first linked to the amplification and overexpression of erbb2 gene in a subtype of breast tumor cells, which is indicative of highly proliferative cells and likely a poor prognosis following conventional chemotherapy. The development of targeted therapies to block the survival of erbB2-positive cancer cells revealed that impaired NRG1 signaling through erbB2/erbB4 heterodimers combined with anthracycline chemotherapy may lead to dilated cardiomyopathy in a subpopulation of treated patients. The ventricular-specific deletion of either erbb2 or erbb4 manifested dilated cardiomyopathy, which is aggravated by the administration of doxorubicin. Based on the exacerbated toxicity displayed by the combined treatment, it is expected that the relevant pathways would be affected in a synergistic manner. This review examines the NRG1 activities that were monitored in different model systems, focusing on the emerging pathways and molecular targets, which may aid in understanding the acquired dilated cardiomyopathy that occurs under the conditions of NRG1-deficient signaling.

Pregnancy differentially regulates the collagens types I and III in left ventricle from rat heart

The pathologic cardiac remodeling has been widely documented; however, the physiological cardiac remodeling induced by pregnancy and its reversion in postpartum are poorly understood. In the present study we investigated the changes in collagen I (Col I) and collagen III (Col III) mRNA and protein levels in left ventricle from rat heart during pregnancy and postpartum. Col I and Col III mRNA expression in left ventricle samples during pregnancy and postpartum were analyzed by using quantitative PCR. Data obtained from gene expression show that Col I and Col III in left ventricle are upregulated during pregnancy with reversion in postpartum. In contrast to gene expression, the protein expression evaluated by western blot showed that Col I is downregulated and Col III is upregulated in left ventricle during pregnancy. In conclusion, the pregnancy differentially regulates collagens types I and III in heart; this finding could be an important molecular mechanism that regulates the ventricular stiffness in response to blood volume overload present during pregnancy which is reversed in postpartum.

Signalling between microvascular endothelium and cardiomyocytes through neuregulin

Heterocellular communication in the heart is an important mechanism for matching circulatory demands with cardiac structure and function, and neuregulins (Nrgs) play an important role in transducing this signal between the hearts' vasculature and musculature. Here, we review the current knowledge regarding Nrgs, explaining their roles in transducing signals between the heart's microvasculature and cardiomyocytes. We highlight intriguing areas being investigated for developing new, Nrg-mediated strategies to heal the heart in acquired and congenital heart diseases, and note avenues for future research.

Pregnancy as a cardiac stress model

Cardiac hypertrophy occurs during pregnancy as a consequence of both volume overload and hormonal changes. Both pregnancy- and exercise-induced cardiac hypertrophy are generally thought to be similar and physiological. Despite the fact that there are shared transcriptional responses in both forms of cardiac adaptation, pregnancy results in a distinct signature of gene expression in the heart. In some cases, however, pregnancy can induce adverse cardiac events in previously healthy women without any known cardiovascular disease. Peripartum cardiomyopathy is the leading cause of non-obstetric mortality during pregnancy. To understand how pregnancy can cause heart disease, it is first important to understand cardiac adaptation during normal pregnancy. This review provides an overview of the cardiac consequences of pregnancy, including haemodynamic, functional, structural, and morphological adaptations, as well as molecular phenotypes. In addition, this review describes the signalling pathways responsible for pregnancy-induced cardiac hypertrophy and angiogenesis. We also compare and contrast cardiac adaptation in response to disease, exercise, and pregnancy. The comparisons of these settings of cardiac hypertrophy provide insight into pregnancy-associated cardiac adaptation.

STAT3, a key regulator of cell-to-cell communication in the heart

The signal transducer and activator of transcription 3 (STAT3) is fundamental for physiological homeostasis and stress-induced remodelling of the heart as deregulated STAT3 circuits are sufficient to induce dilated and peripartum cardiomyopathy and adverse remodelling after myocardial infarction. STAT3 activity depends on multiple post-translational modifications (phosphorylation, acetylation, and dimerization). It is regulated by multiple receptor systems, which are coupled to positive and negative feedback loops to ensure physiological and beneficial action. Its intracellular functions are diverse as it acts as a signalling protein, a transcription factor but also participates in mitochondria energy production and protection. STAT3 modulates proliferation, differentiation, survival, oxidative stress, and/or metabolism in cardiomyocytes, fibroblasts, endothelial cells, progenitor cells, and various inflammatory cells. By regulating the secretome of these cardiac cells, STAT3 influences a broad range of intercellular communication systems. It thereby impacts on the communication between cardiomyocytes, the plasticity of the cardiac microenvironment, the vasculature, the extracellular matrix, and the inflammation in response to physiological and pathophysiological stress. Here, we sum up current knowledge on STAT3-mediated intra- and intercellular communication within the heterogeneous cellular network of the myocardium to co-ordinate complex biological processes and discuss STAT3-dependent targets as novel therapeutic concepts to treat various forms of heart disease.