AI is a viable alternative to high throughput screening: a 318-target study

High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that our AtomNet® convolutional neural network successfully finds novel hits across every major therapeutic area and protein class. We address historical limitations of computational screening by demonstrating success for target proteins without known binders, high-quality X-ray crystal structures, or manual cherry-picking of compounds. We show that the molecules selected by the AtomNet® model are novel drug-like scaffolds rather than minor modifications to known bioactive compounds. Our empirical results suggest that computational methods can substantially replace HTS as the first step of small-molecule drug discovery.

Pathophysiology and clinical relevance of atrial myopathy

Atrial myopathy is a condition that consists of electrical, structural, contractile, and autonomic remodeling of the atria and is the substrate for development of atrial fibrillation, the most common arrhythmia. Pathophysiologic mechanisms driving atrial myopathy are inflammation, oxidative stress, atrial stretch, and neurohormonal signals, e.g., angiotensin-II and aldosterone. These mechanisms initiate the structural and functional remodeling of the atrial myocardium. Novel therapeutic strategies are being developed that target the pathophysiologic mechanisms of atrial myopathy. In this review, we will discuss the pathophysiology of atrial myopathy, as well as diagnostic and therapeutic strategies.

Peripheral Microvascular Dysfunction in Children and Adults with Congenital Heart Disease: A Literature Review

Although there is a continually growing number of patients with congenital heart disease (CHD) due to medical and surgical advances, these patients still have a poorer prognosis compared to healthy individuals of similar age. In patients with heart failure, microvascular dysfunction (MVD) has recently emerged as a crucial modulator of disease initiation and progression. Because of the substantial pathophysiological overlap between CHD and heart failure induced by other etiologies, MVD could be important in the pathophysiology of CHD as well. MVD is believed to be a systemic disease and may be manifested in several vascular beds. This review will focus on what is currently known about MVD in the peripheral vasculature in CHD. Therefore, a search on the direct assessment of the vasodilatory capacity of the peripheral microcirculation in patients with CHD was conducted in the PubMed database. Since there is little data available and the reported studies are also very heterogeneous, peripheral MVD in CHD is not sufficiently understood to date. Its exact extent and pathophysiological relevance remain to be elucidated in further research.

Fluorescent In Situ Hybridization for miRNA Combined with Staining of Proteins

The last decades have illustrated the importance of microRNAs (miRNAs) in various biological and pathological processes. The combined visualization of miRNAs using fluorescent in situ hybridization (FISH) and proteins using immunofluorescence (IF) can reveal their spatiotemporal distribution in relation to the cell and tissue morphology and can provide interesting insights into miRNA-protein interactions. However, standardized protocols for co-localization of miRNAs and proteins are currently lacking, and substantial technical obstacles still need to be addressed. In particular, the incompatibility of protein IF protocols with steps required for miRNA FISH, such as proteolytic pretreatments and ethylcarbodiimide post-fixation, as well as hurdles related to low signal intensity of low-copy miRNAs, remains challenging. Our technique may considerably enhance miRNA-based research, as current detection techniques lack the ability to elucidate cellular and subcellular localization. Here, we describe an optimized 2-day protocol for combined detection of low-abundant miRNAs and proteins in cryosections of cardiac tissue, without the need for protease-dependent pretreatment or post-fixation treatment. We successfully demonstrate endothelial-specific localization of low-abundant miR-181c-5p in cardiac tissue. © 2023 Wiley Periodicals LLC. Basic Protocol: Fluorescent in situ hybridization for miRNA combined with staining of proteins.

Endothelial Dysfunction at the Cellular Level in 3 Dimensions: Severity, Acuteness, and Distribution

Dysfunction or failure of the endothelial organ is a heterogenous and often ill-described feature of both cardiovascular and non-cardiovascular disorders. Although seldom recognized as a separate clinical condition, endothelial dysfunction (ECD) is an established catalyst of disease. However, even in recent pathophysiological studies, ECD is frequently oversimplified as a binary state without gradation, based on the assessment of a single function (e.g., synthesis or activity of nitric oxide) and without considering spatio-temporal dimensions (local vs. generalized-acute vs. chronic). In this paper, we suggest a simple scale to grade the severity of ECD and a definition of ECD in three dimensions: space, time, and severity. We also adopt a broader perspective on ECD by integrating and comparing gene expression data of endothelial cells from different organs and diseases, and propose a concept that links common pathophysiological mechanisms. We hope that this will enhance the understanding of the pathophysiology of ECD and stimulate discussion in this field.

Elevated oxidative stress in patients with congenital heart disease and the effect of cyanosis: a meta-analysis

Oxidative stress is an important pathophysiological mechanism in the development of numerous cardiovascular disorders. To improve therapy and preventive strategies, clinicians need a better understanding of the underlying pathophysiological mechanisms of congenital heart diseases (CHD). The objective of this meta-analysis was to determine whether oxidative stress is elevated in patients with CHD compared to healthy controls, and to evaluate whether a difference in oxidative stress parameters can be observed between patients with cyanotic (cCHD) and acyanotic CHD (aCHD). Therefore, 21 studies investigating oxidative stress in peripheral blood of both children and adults with CHD were reviewed. Different methods to assess the oxidant status were compared and divided into three categories: pro-oxidative or anti-oxidative stress markers and the ratio of pro-to-anti oxidative stress markers. This meta-analysis showed elevated oxidative stress levels in patients with CHD, and more specifically in patients with cCHD. Moreover, this indicates that there could be potential in oxidative stress measurements as a new biomarker of disease severity. Further research will be needed to clarify the exact role of oxidative stress and its contributors in CHD in order to get a better and more in-depth understanding of the underlying pathophysiology of CHD, especially the higher susceptibility of the right ventricle (RV) to progress to heart failure (HF). This could facilitate the development of antioxidant treatments and RV-specific HF therapies, which are necessary to improve survival in these patients and could be of particular importance in cCHD.

Circulating Reactive Oxygen Species in Adults with Congenital Heart Disease

Oxidative stress is an important pathophysiological mechanism in the development of numerous cardiovascular disorders, but few studies have examined the levels of oxidative stress in adults with congenital heart disease (CHD). The objective of this study was to investigate oxidative stress levels in adults with CHD and the association with inflammation, exercise capacity and endothelial function. To this end, 36 adults with different types of CHD and 36 age- and gender-matched healthy controls were enrolled. Blood cell counts, hs-CRP, NT-proBNP, fasting glucose, cholesterol levels, iron saturation and folic acid concentrations were determined in venous blood samples. Levels of superoxide anion radical in whole blood were determined using electron paramagnetic resonance spectroscopy in combination with the spin probe CMH. Physical activity was assessed with the IPAQ-SF questionnaire. Vascular function assessment (EndoPAT) and cardiopulmonary exercise testing were performed in the patient group. Superoxide anion radical levels were not statistically significantly different between adults with CHD and the matched controls. Moreover, oxidative stress did not correlate with inflammation, or with endothelial function or cardiorespiratory fitness in CHD; however, a significant negative correlation with iron saturation was observed. Overall, whole blood superoxide anion radical levels in adults with CHD were not elevated, but iron levels seem to play a more important role in oxidative stress mechanisms in CHD than in healthy controls. More research will be needed to improve our understanding of the underlying pathophysiology of CHD.

Epigenetic regulation of miR-181c-5p in a cardiorenal mouse model with co-occurring thrombotic microangiopathy

Background

MiR-181c-5p is described to induce heart failure (HF), while its role in renal pathology and healthy mice is rather undetermined. Renal dysfunction is present in 40–60% of HF patients and associated with high morbidity and mortality rate.

Purpose

This study aims to investigate the role of miR-181c-5p in a new mouse model of metabolic cardiorenal disease (CRD). Our hypothesis states a protective effect of miR-181c-5p inhibition on HF development by regulation of Tgfbr1.

Methods

CRD was induced by feeding male C57BL/6J mice (n=20) a high-fat diet (HFD) and L-NAME in drinking water (5g/L) for 6 weeks, angiotensin-II was co-administered via osmotic minipumps (1000ng/kg/min) during the final 2 weeks. Healthy controls (n=16) were given normal chow and drinking water, and underwent sham-surgery. Mice were randomly assigned to weekly injections (40mg/kg) with miR-181c-5p antagomiR (INH) or scrambled control for the duration of the study. We assessed cardiac function (echocardiography, invasive hemodynamics), renal function (plasma creatinine), target expression (RT-qPCR), and histology.

Results

CRD animals showed mild systolic and diastolic cardiac dysfunction compared to healthy controls characterized by reduced dP/dt min (−4795±1164 vs −7728±1693 mmHg/s; p=0.01) and dP/dt max (6222±1069 vs 8706±1739 mmHg/s; p=0.038), and increased tau (9.88±3.09 vs 6.07±0.73 ms; p=0.02) with preserved ejection fraction (45±21 vs 51±8%; p=0.53). Histology shows cardiac fibrosis (2.5±0.3 vs 1.8±0.2% area; p=0.0004) and hypertrophy (0.11±0.03 vs 0.08±0.01g/cm; p=0.005). Renal dysfunction presents with kidney atrophy (0.07±0.006 vs 0.09±0.01g/cm; p=0.02), increased plasma creatinine (21±6 vs 10±5; p=0.01), renal fibrosis (0.26±0.22 vs 0.005±0.21% area; p=0.036) and glomerular abnormalities (glomerulosclerosis, hyperfiltration, mesangial matrix expansion, reduced podocyte number). CRD+INH animals had comparable cardiac phenotype to CRD (p>0.05), except a significantly reduced cardiac output compared to healthy controls (6±3 vs 18±3 μl/s; p=0.035). Their renal phenotype was exacerbated with elevated glomerular damage (26±3 vs 18±9; p=0.04) and significantly increased mortality rate (50%) (Kaplan-Meier p=0.01) compared to healthy controls (0%) or CRD (20%), associated with increased occurrence of tubular atrophy, endothelial swelling and systemic thrombotic microangiopathy (TMA) that manifested in kidney and the heart. RT-qPCR analysis identified Vegf as potential target of miR-181c-5p in kidney and showed significantly reduced levels of Tgfbr1 in cardiac tissue of CRD+INH mice.

Conclusion

This study demonstrates a detrimental effect of miR-181c-5p inhibition on renal function in a CRD mouse model, driven by glomerular damage and TMA through Vegf signaling. Despite identification of Tgfbr1 as potential target of miR-181c-5p in the heart, cardiac function was rather unaffected.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): University of Antwerp

Cardiac electrophysiology studies in mice via the transjugular route: a comprehensive practical guide

Cardiac arrhythmias are associated with cardiovascular morbidity and mortality. Cardiac electrophysiology studies (EPS) use intracardiac catheter recording and stimulation for profound evaluation of the heart's electrical properties. The main clinical application is investigation and treatment of rhythm disorders. These techniques have been translated to the murine setting to open opportunities for detailed evaluation of the impact of different characteristics (including genetics) and interventions on cardiac electrophysiology and -pathology. Currently, a detailed description of the technique of murine transjugular EPS (which is the standard route of catheter introduction) is lacking. This article provides detailed information on EPS in mice via the transjugular route. This includes catheter placement, stimulation protocols, intracardiac tracing interpretation, artefact reduction and surface ECG recording. In addition, reference values as obtained in C57BL/6N mice are presented for common electrophysiological parameters. This detailed methodological description aims to increase accessibility and standardisation of EPS in mice. Ultimately, also human research and patient care may benefit from translation of the knowledge obtained in preclinical models using this technique.

Intracoronary Lithotripsy in Calcified Coronary Lesions: A Multicenter Observational Study

OBJECTIVES

The aim of this study was to evaluate the feasibility, effectiveness, and safety of coronary intravascular lithotripsy (IVL; Shockwave Medical) in the treatment of severe coronary artery calcification (CAC) in a real-world setting.

BACKGROUND

Severe CAC can be an arduous obstacle in interventional cardiology, often leading to suboptimal results of percutaneous coronary interventions (PCI). Coronary IVL is a novel technique that modulates severe CAC, thereby facilitating stent implantation.

METHODS AND RESULTS

In this multicenter observational study, data from 134 IVL procedures in 5 Belgian hospitals were prospectively obtained. Successful delivery of the IVL catheter was achieved in all cases but 1 (99.3%). The primary endpoint was final overall procedural success, which was obtained in 88.1% of cases, an aggregate of 92.6% in de novo lesions and 77.5% in stent underexpansion or in-stent restenosis (ISR). IVL therapy effect was considered successful by the operators in 94% of cases, with 68.7% achieving optimal and 25.3% achieving suboptimal results. The 1-month major adverse cardiovascular event rate was 3%, including 2 cardiovascular deaths (1 in-stent thrombosis and 1 coronary artery perforation).

CONCLUSIONS

This real-world experience suggests that Shockwave IVL is a feasible, effective, and safe technique for the treatment of heavily calcified coronary lesions.

The coronary and microcirculatory measurements in patients with aortic valve stenosis study: rationale and design

Although concomitant coronary artery disease (CAD) is frequent in patients with severe aortic stenosis (AS), hemodynamic assessment of CAD severity in patients undergoing valve replacement for severe AS is challenging. Myocardial hypertrophic remodeling interferes with coronary blood flow and may influence the values of fractional flow reserve (FFR) and nonhyperemic pressure ratios (NHPRs). The aim of the current study is to investigate the effect of the AS and its treatment on current indices used for evaluation of CAD. We will compare intracoronary hemodynamics before, immediately after, and 6 mo after aortic valve replacement (AVR) when it is expected that microvascular function has improved. Furthermore, we will compare FFR and resting full-cycle ratio (RFR) with myocardial perfusion single-photon emission-computed tomography (SPECT) as indicators of myocardial ischemia in patients with AS and CAD. One-hundred consecutive patients with AS and intermediate CAD will be prospectively included. Patients will undergo pre-AVR SPECT and intracoronary hemodynamic assessment at baseline, immediately after valve replacement [if transcatheter AVR (TAVR) is chosen], and 6 mo after AVR. The primary end point is the change in FFR 6 mo after AVR. Secondary end points include the acute change of FFR after TAVR, the diagnostic accuracy of FFR versus RFR compared with SPECT for the assessment of ischemia, changes in microvascular function as assessed by the index of microcirculatory resistance (IMR), and the effect of these changes on FFR. The present study will evaluate intracoronary hemodynamic parameters before, immediately after, and 6 mo after AVR in patients with AS and intermediate coronary stenosis. The understanding of the impact of AVR on the assessment of FFR, NHPR, and microvascular function may help guide the need for revascularization in patients with AS and CAD planned for AVR.

Sterile Pericarditis in Aachener Minipigs As a Model for Atrial Myopathy and Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia caused by structural remodeling of the atria, also called atrial myopathy. Current therapies only target the electrical abnormalities and not the underlying atrial myopathy. For the development of novel therapies, a reproducible large animal model of atrial myopathy is necessary. This paper presents a model of sterile pericarditis-induced atrial myopathy in Aachener minipigs. Sterile pericarditis was induced by spraying sterile talcum and leaving a layer of sterile gauze over the atrial epicardial surface. This led to inflammation and fibrosis, two crucial components of the pathophysiology of atrial myopathy, making the atria susceptible to the induction of AF. Two pacemaker electrodes were positioned epicardially on each atrium and connected to two pacemakers from different manufacturers. This strategy allowed for repeated non-invasive atrial programmed stimulation to determine the inducibility of AF at specified time points after surgery. Different protocols to test AF inducibility were used. The advantages of this model are its clinical relevance, with AF inducibility and the rapid induction of inflammation and fibrosis-both present in atrial myopathy-and its reproducibility. The model will be useful in the development of novel therapies targeting atrial myopathy and AF.

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.

Autocrine Signaling in Cardiac Remodeling: A Rich Source of Therapeutic Targets

The myocardium consists of different cell types, of which endothelial cells, cardiomyocytes, and fibroblasts are the most abundant. Communication between these different cell types, also called paracrine signaling, is essential for normal cardiac function, but also important in cardiac remodeling and heart failure. Systematic studies on the expression of ligands and their corresponding receptors in different cell types showed that for 60% of the expressed ligands in a particular cell, the receptor is also expressed. The fact that many ligand-receptor pairs are present in most cells, including the major cell types in the heart, indicates that autocrine signaling is a widespread phenomenon. Autocrine signaling in cardiac remodeling and heart failure is involved in all pathophysiological mechanisms generally observed: hypertrophy, fibrosis, angiogenesis, cell survival, and inflammation. Herein, we review ligand-receptor pairs present in the major cardiac cell types based on RNA-sequencing expression databases, and we review current literature on extracellular signaling proteins with an autocrine function in the heart; these include C-type natriuretic peptide, fibroblast growth factors 2, F21, and 23, macrophage migration inhibitory factor, heparin binding-epidermal growth factor, angiopoietin-like protein 2, leptin, adiponectin, follistatin-like 1, apelin, neuregulin 1, vascular endothelial growth factor, transforming growth factor β, wingless-type integration site family, member 1-induced secreted protein-1, interleukin 11, connective tissue growth factor/cellular communication network factor, and calcitonin gene‒related peptide. The large number of autocrine signaling factors that have been studied in the literature supports the concept that autocrine signaling is an essential part of myocardial biology and disease.

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.

INSPIRE: A European training network to foster research and training in cardiovascular safety pharmacology

Safety pharmacology is an essential part of drug development aiming to identify, evaluate and investigate undesirable pharmacodynamic properties of a drug primarily prior to clinical trials. In particular, cardiovascular adverse drug reactions (ADR) have halted many drug development programs. Safety pharmacology has successfully implemented a screening strategy to detect cardiovascular liabilities, but there is room for further refinement. In this setting, we present the INSPIRE project, a European Training Network in safety pharmacology for Early Stage Researchers (ESRs), funded by the European Commission's H2020-MSCA-ITN programme. INSPIRE has recruited 15 ESR fellows that will conduct an individual PhD-research project for a period of 36 months. INSPIRE aims to be complementary to ongoing research initiatives. With this as a goal, an inventory of collaborative research initiatives in safety pharmacology was created and the ESR projects have been designed to be complementary to this roadmap. Overall, INSPIRE aims to improve cardiovascular safety evaluation, either by investigating technological innovations or by adding mechanistic insight in emerging safety concerns, as observed in the field of cardio-oncology. Finally, in addition to its hands-on research pillar, INSPIRE will organize a number of summer schools and workshops that will be open to the wider community as well. In summary, INSPIRE aims to foster both research and training in safety pharmacology and hopes to inspire the future generation of safety scientists.

The role of ErbB4 in cancer

BACKGROUND

The epidermal growth factor receptor family consists of four members, ErbB1 (epidermal growth factor receptor-1), ErbB2, ErbB3, and ErbB4, which all have been found to play important roles in tumor development. ErbB4 appears to be unique among these receptors, because it is the only member with growth inhibiting properties. ErbB4 plays well-defined roles in normal tissue development, in particular the heart, the nervous system, and the mammary gland system. In recent years, information on the role of ErbB4 in a number of tumors has emerged and its general direction points towards a tumor suppressor role for ErbB4. However, there are some controversies and conflicting data, warranting a review on this topic.

CONCLUSIONS

Here, we discuss the role of ErbB4 in normal physiology and in breast, lung, colorectal, gastric, pancreatic, prostate, bladder, and brain cancers, as well as in hepatocellular carcinoma, cholangiocarcinoma, and melanoma. Understanding the role of ErbB4 in cancer is not only important for the treatment of tumors, but also for the treatment of other disorders in which ErbB4 plays a major role, e.g. cardiovascular disease.

The role of endothelial miRNAs in myocardial biology and disease

The myocardium is a highly structured pluricellular tissue which is governed by an intricate network of intercellular communication. Endothelial cells are the most abundant cell type in the myocardium and exert crucial roles in both healthy myocardium and during myocardial disease. In the last decade, microRNAs have emerged as new actors in the regulation of cellular function in almost every cell type. Here, we review recent evidence on the regulatory function of different microRNAs expressed in endothelial cells, also called endothelial microRNAs, in healthy and diseased myocardium. Endothelial microRNA emerged as modulators of angiogenesis in the myocardium, they are implicated in the paracrine role of endothelial cells in regulating cardiac contractility and homeostasis, and interfere in the crosstalk between endothelial cells and cardiomyocytes.

P3507Heterozygous cardiomyocyte-specific deletion of ErbB4 sensitizes to development of pregnancy-related cardiomyopathy

Background

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening disease in women without known cardiovascular disease; PPCM is characterized by left ventricular (LV) systolic dysfunction towards the end of pregnancy and/or in the first months postpartum. The underlying mechanisms of PPCM are incompletely understood, but there is recent evidence that impaired cardiomyocyte expression of the tyrosine kinase ErbB4 receptor plays a role. ErbB4 is the main receptor of neuregulin-1, a protective and regenerative paracrine factor in the heart. Homozygous deletion of ErbB4 is lethal.

Purpose

To test the hypothesis that mice with heterozygous (HZ) cardiomyocyte-specific deletion of ErbB4 (ErbB4+/−) are more susceptible to PPCM.

Methods

Cardiac morphology and function was evaluated by echocardiography with a Vevo 2100 Imaging System during 2 pregnancies and 6 weeks postpartum (n=7–9) or during non-pregnant control conditions in HZ (ErbB4+/−) and wild type controls (n=9–10). Then, hearts were excised for analyses of myocardial fibrosis, macrophage infiltration, capillary density and cardiomyocyte cross sectional area.

Results

When compared to pregnant wild type controls, pregnant ErbB4+/− mice developed significant LV dilatation (2 weeks after the 2nd delivery: LVIDd +16% ± 2%, p<0.05) and dysfunction (6 weeks after the 2nd delivery: EF −23% ± 3%, p<0.001), increased heart to body weight ratio (+7% ± 4%, p<0.05) and increased cardiomyocyte cross sectional area (+28% ± 7%, p<0.01). Non-pregnant ErbB4+/− mice also developed LV dilatation and dysfunction, albeit slower than pregnant ErbB4+/− mice. On histology, however, myocardial tissue of pregnant ErbB4+/− mice did not show macrophage infiltration, neither fibrosis, nor reduced capillary density.

Conclusions

Heterozygous cardiomyocyte-specific deletion of ErbB4 sensitizes to peripartum LV dilatation and cardiomyocyte hypertrophy and systolic dysfunction without profound cardiac injury, features that are frequently present in PPCM patients and may explain their high chance for recovery. These data reinforce a compensatory role for neuregulin-ErbB4 signaling during hemodynamic overload, and confirm that this signaling pathway is important to protect the maternal heart during peripartum stress.

Acknowledgement/Funding

Fund scientific research Flanders; University Antwerp

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.

P316The cardiac endothelial cell transcriptome in neonatal, adult, and remodeling hearts

Background

Cardiac microvascular endothelial cells (CMVECs) are the most numerous cells in the myocardium and orchestrate cardiogenesis during development, regulate adult cardiac function, and modulate pathophysiology of heart failure. It has been shown that the transcriptome of CMVECs differs from other endothelial cell types, but transcriptomic changes in cardiac endothelial cells during cardiac maturation and cardiac remodeling have not been studied earlier.

Purpose

To study changes in the transcriptome of CMVECs during cardiac maturation and cardiac remodeling, and to test the hypothesis that the fetal gene program is reactivated during cardiac remodeling in CVMECs.

Methods

CMVECs were isolated from rat hearts based on CD31 expression and were immediately processed for RNA sequencing, without an in vitro propagation step. We compared gene expression levels from primary CMVECs of neonatal hearts, normal adult hearts, and infarcted-hearts (4 weeks post LAD ligation).

Results

Between neonatal and adult CMVECs, 6838 genes were differentially expressed indicating that CMVECs undergo a substantial transformation during postnatal cardiac growth. A large fraction of genes upregulated in neonatal CMVECs are part of mitosis pathways, whereas a large fraction of genes upregulated in adult CMVECs are part of cellular response, secretory, signaling, and cell adhesion pathways. Between CMVECs of normal adult hearts and infarcted hearts, 159 genes were differentially expressed. We found a limited degree of overlap (55 genes) between the differentially expressed genes in neonatal and infarcted-hearts. Of 46 significantly upregulated genes in the infarcted heart, 46% were also upregulated in neonatal hearts relative to sham. Of 113 significantly downregulated genes in the infarcted-hearts, 30% were also downregulated in neonatal hearts relative to sham.

Conclusion

These data demonstrate that CMVECs undergo dramatic changes from neonatal to adult and more subtle changes between normal state and cardiac remodeling. During cardiac remodeling, a small part of the fetal gene program is reactivated in CMVECs.

Acknowledgement/Funding

IOF/SBO research grant (PID34923), Fund for Scientific Research Flanders (Application numbers 1501118N and 1842219N).

Coronary-subclavian steal syndrome, an easily overlooked entity in interventional cardiology

Coronary-subclavian steal syndrome (CSSS) is a severe complication of coronary artery bypass graft (CABG) surgery with internal mammary artery grafting. It is caused by functional graft failure due to a hemodynamically significant proximal subclavian artery stenosis. In this manuscript, we provide a comprehensive review of literature and we report a series of five consecutive CSSS cases. This case series illustrates the variable clinical presentation, thereby emphasizing the importance of raised awareness concerning this pathology in CABG patients.

Epigenetic regulation of intercellular communication in the heart

The myocardium is a highly structured tissue consisting of different cell types including cardiomyocytes, endothelial cells, fibroblasts, smooth muscle cells, inflammatory cells, and stem cells. Microvascular endothelial cells are the most abundant cell type in the myocardium and play crucial roles during cardiac development, in normal adult myocardium, and during myocardial diseases such as heart failure. In the last decade, epigenetic changes have been described regulating cellular function in almost every cell type in the organism. Here, we review recent evidence on different epigenetic changes that regulate intercellular communication in normal myocardium and during myocardial diseases, including cardiac remodeling. Epigenetic changes influence many intercellular communication signaling systems, including the nitric oxide, angiotensin, and endothelin signaling systems. In this review, we go beyond discussing classic endothelial function (for instance nitric oxide secretion) and will discuss epigenetic regulation of intercellular communication.

Cardiac endothelial cell transcriptome in neonatal, adult, and remodeling hearts

Cardiac microvascular endothelial cells (CMVECs) are the most numerous cells in the myocardium and orchestrate cardiogenesis during development, regulate adult cardiac function, and modulate pathophysiology of heart failure. It has been shown that the transcriptome of CMVECs differs from other endothelial cell types, but transcriptomic changes in cardiac endothelial cells during cardiac maturation and cardiac remodeling have not been studied. CMVECs were isolated from rat hearts based on CD31 expression and were immediately processed for RNA sequencing. We compared gene expression levels from primary CMVECs of neonatal hearts, normal adult hearts, and infarcted hearts. Between neonatal and adult CMVECs, 6,838 genes were differentially expressed, indicating that CMVECs undergo a substantial transformation during postnatal cardiac growth. A large fraction of genes upregulated in neonatal CMVECs are part of mitosis pathways, whereas a large fraction of genes upregulated in adult CMVECs are part of cellular response, secretory, signaling, and cell adhesion pathways. Between CMVECs of normal adult hearts and infarcted hearts, 159 genes were differentially expressed. We found a limited degree of overlap (55 genes) between the differentially expressed genes in neonatal and infarcted-hearts. Of 46 significantly upregulated genes in the infarcted heart, 46% were also upregulated in neonatal hearts relative to sham. Of 113 significantly downregulated genes in the infarcted-hearts, 30% were also downregulated in neonatal hearts relative to sham. These data demonstrate that CMVECs undergo dramatic changes from neonatal to adult and more subtle changes between normal state and cardiac remodeling.

Short-Term Angiotensin II Treatment Affects Large Artery Biomechanics and Function in the Absence of Small Artery Alterations in Mice

Induction of hypertension by angiotensin II (AngII) is a widely used experimental stimulus to study vascular aging in mice. It is associated with large artery stiffness, a hallmark of arterial aging and a root cause of increased cardiovascular risk. We reported earlier that long term (4 week) AngII treatment in mice altered the active, contractile properties of the arteries in a vascular bed-specific manner and that, in healthy mice aorta, active contractile properties of the aortic wall determine isobaric aortic stiffness. Given the huge physiological relevance of large artery stiffening, we aimed to characterize the early (1 week) changes in the active properties of the aorta of AngII-treated mice. We were not able to detect a significant effect of AngII treatment on anesthetized blood pressure or abdominal aorta pulse wave velocity. Ex vivo biomechanical and functional studies of the aorta revealed increased arterial stiffness and altered vascular smooth muscle cell (VSMC) and endothelial cell reactivity. Interestingly, the AngII-associated changes in the aorta could be largely attributed to alterations in basal VSMC tone and basal nitric oxide efficacy, indicating that, besides structural remodeling of the arterial wall, dysfunctional active components of the aorta play a crucial role in the pathophysiological mechanisms by which AngII treatment induces arterial stiffness.

Cellular senescence links aging and diabetes in cardiovascular disease

Aging is a powerful independent risk factor for cardiovascular diseases such as atherosclerosis and heart failure. Concomitant diabetes mellitus strongly reinforces this effect of aging on cardiovascular disease. Cellular senescence is a fundamental mechanism of aging and appears to play a crucial role in the onset and prognosis of cardiovascular disease in the context of both aging and diabetes. Senescent cells are in a state of cell cycle arrest but remain metabolically active by secreting inflammatory factors. This senescence-associated secretory phenotype is a trigger of chronic inflammation, oxidative stress, and decreased nitric oxide bioavailability. A complex interplay between these three mechanisms results in age- and diabetes-associated cardiovascular damage. In this review, we summarize current knowledge on cellular senescence and its secretory phenotype, which might be the missing link between aging and diabetes contributing to cardiovascular disease.

Cardiac Remodeling: Endothelial Cells Have More to Say Than Just NO

The heart is a highly structured organ consisting of different cell types, including myocytes, endothelial cells, fibroblasts, stem cells, and inflammatory cells. This pluricellularity provides the opportunity of intercellular communication within the organ, with subsequent optimization of its function. Intercellular cross-talk is indispensable during cardiac development, but also plays a substantial modulatory role in the normal and failing heart of adults. More specifically, factors secreted by cardiac microvascular endothelial cells modulate cardiac performance and either positively or negatively affect cardiac remodeling. The role of endothelium-derived small molecules and peptides—for instance NO or endothelin-1—has been extensively studied and is relatively well defined. However, endothelial cells also secrete numerous larger proteins. Information on the role of these proteins in the heart is scattered throughout the literature. In this review, we will link specific proteins that modulate cardiac contractility or cardiac remodeling to their expression by cardiac microvascular endothelial cells. The following proteins will be discussed: IL-6, periostin, tenascin-C, thrombospondin, follistatin-like 1, frizzled-related protein 3, IGF-1, CTGF, dickkopf-3, BMP-2 and−4, apelin, IL-1β, placental growth factor, LIF, WISP-1, midkine, and adrenomedullin. In the future, it is likely that some of these proteins can serve as markers of cardiac remodeling and that the concept of endothelial function and dysfunction might have to be redefined as we learn more about other factors secreted by ECs besides NO.

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.

The future of pleiotropic therapy in heart failure. Lessons from the benefits of exercise training on endothelial function

A novel generation of drugs is introduced in the treatment of heart failure (HF). These drugs, including phosphodiesterase-5 inhibitors, guanylate cyclase stimulators and activators, share the feature that their action is either endothelial-mediated or substitutes for endothelial pathways, in particular the nitric oxide-cyclic guanosine monophosphate pathway, thereby influencing homeostatic balances in virtually each organ system in a pleiotropic fashion. Unfortunately, recent clinical trials with some of these drugs have shown disappointing results, at least in the setting of HF with a preserved ejection fraction. This suggests that their clinical use may require approaches that diverge from traditional pharmacological approaches, the latter often titrated on the effects of drugs on haemodynamic parameters or single biomarkers. In this paper we preconize that HF drugs with an endothelial profile should be applied conform to principles of endothelial physiology and systems pharmacology. This type of drug therapy should be viewed as a systems physio-pharmacological intervention and its clinical use accustomed to systems pharmacological principles, comparable to the systemic endothelial-mediated benefits induced by exercise training in HF. We will review the actions of these drugs and define criteria to which trials with these drugs should comply in order to increase chances of success.

Neuregulin-1 attenuates development of nephropathy in a type 1 diabetes mouse model with high cardiovascular risk

Neuregulin-1 (NRG-1) is an endothelium-derived growth factor with cardioprotective and antiatherosclerotic properties and is currently being tested in clinical trials as a treatment for systolic heart failure. In clinical practice, heart failure often coexists with renal failure, sharing an overlapping pathophysiological background. In this study, we hypothesized that NRG-1 might protect against cardiomyopathy, atherosclerosis, and nephropathy within one disease process. We tested this hypothesis in a hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)) type 1 diabetes mouse model prone to the development of cardiomyopathy, atherosclerosis, and nephropathy and compared the effects of NRG-1 with insulin. Upon onset of hyperglycemia induced by streptozotocin, apoE(-/-)mice were treated with vehicle, insulin, or recombinant human (rh)NRG-1 for 14 wk and were compared with nondiabetic apoE(-/-)littermates. Vehicle-treated diabetic apoE(-/-)mice developed left ventricular (LV) dilatation and dysfunction, dense atherosclerotic plaques, and signs of nephropathy. Nephropathy was characterized by abnormalities including hyperfiltration, albuminuria, increased urinary neutrophil gelatinase-associated lipocalin (NGAL), upregulation of renal fibrotic markers, and glomerulosclerosis. rhNRG-1 treatment induced systemic activation of ErbB2 and ErbB4 receptors in both heart and kidneys and prevented LV dilatation, improved LV contractile function, and reduced atherosclerotic plaque size. rhNRG-1 also significantly reduced albuminuria, NGALuria, glomerular fibrosis, and expression of fibrotic markers. Regarding the renal effects of rhNRG-1, further analysis showed that rhNRG-1 inhibited collagen synthesis of glomerular mesangial cells in vitro but did not affect AngII-induced vasoconstriction of glomerular arterioles. In conclusion, systemic administration of rhNRG-1 in hypercholesterolemic type 1 diabetic mice simultaneously protects against complications in the heart, arteries and kidneys.

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.

Pathophysiology of diastolic dysfunction in chronic heart failure

Chronic heart failure is a disease with high morbidity and mortality, and its incidence is increasing rapidly worldwide. New therapies are needed that can halt or even reverse the progression of heart failure, but little progress has been made in the last 20 years. This is partly due to the fact that chronic heart failure is a heterogeneous disease with many different etiologies and clinical phenotypes. At present, a pathophysiological concept to unify these different phenotypes is missing. A prominent pathophysiological feature of chronic heart failure is diastolic dysfunction, which is almost universally present in heart failure patients. This review will examine the role and mechanisms of diastolic dysfunction in heart failure. We will study diastolic dysfunction at different levels of complexity of organization: the cardiovascular system, the heart as an organ, the myocardium as a tissue, the myocyte as a cell and the molecular aspects of diastolic dysfunction.

Protease-resistant stromal cell-derived factor-1 for the treatment of experimental peripheral artery disease

BACKGROUND

Peripheral artery disease is a potentially incapacitating disease for which pharmacological options are limited. Stromal cell-derived factor-1 (SDF-1) is a chemokine that attracts endothelial progenitor cells and promotes angiogenesis. Therapeutic use of SDF-1 in hindlimb ischemia may be challenged by proteolytic degradation. We hypothesized that protease-resistant variants of SDF-1 can increase blood flow in an experimental model of hindlimb ischemia.

METHODS AND RESULTS

We screened a peptide library for mutations in SDF-1 that provide resistance to matrix metalloproteinase cleavage. Recombinant SDF-1 proteins carrying the mutations were designed, expressed, and purified, and activity of mutant proteins was tested with receptor activation assays and in vivo Matrigel plug assays. SSDF-1(S4V), which is resistant to both dipeptidylpeptidase IV/CD26 and matrix metalloproteinase-2 cleavage, was active in vitro and induced angiogenesis in vivo. We then designed and purified fusion proteins of SSDF-1 and SSDF-1(S4V) with the sequence of self-assembling peptide nanofibers for incorporation into nanofibers. In a blinded and randomized hindlimb ischemia mouse study, SSDF-1(S4V) delivery by nanofibers improved blood flow as measured by laser Doppler from 23.1±1.9% (untreated control) to 55.1±5.7% 6 weeks after surgery (P<0.001). Nanofibers alone or SSDF-1 delivered by nanofibers did not improve blood flow. Furthermore, SSDF-1(S4V) delivered by nanofibers increased formation of new arterioles. In vitro, SSDF-1(S4V) attracts smooth muscle cells but does not induce mitosis.

CONCLUSIONS

SDF-1 engineered to be resistant to dipeptidylpeptidase IV/CD26 and matrix metalloproteinase-2 cleavage and delivered by nanofibers improves blood flow in a model of peripheral artery disease.

Protein therapeutics for cardiac regeneration after myocardial infarction

Although most medicines have historically been small molecules, many newly approved drugs are derived from proteins. Protein therapies have been developed for treatment of diseases in almost every organ system, including the heart. Great excitement has now arisen in the field of regenerative medicine, particularly for cardiac regeneration after myocardial infarction. Every year, millions of people suffer from acute myocardial infarction, but the adult mammalian myocardium has limited regeneration potential. Regeneration of the heart after myocardium infarction is therefore an exciting target for protein therapeutics. In this review, we discuss different classes of proteins that have therapeutic potential to regenerate the heart after myocardial infarction. Protein candidates have been described that induce angiogenesis, including fibroblast growth factors and vascular endothelial growth factors, although thus far clinical development has been disappointing. Chemotactic factors that attract stem cells, e.g., hepatocyte growth factor and stromal cell-derived factor-1, may also be useful. Finally, neuregulins and periostin are proteins that induce cell-cycle reentry of cardiomyocytes, and growth factors like IGF-1 can induce growth and differentiation of stem cells. As our knowledge of the biology of regenerative processes and the role of specific proteins in these processes increases, the use of proteins as regenerative drugs could develop as a cardiac therapy.

Cardiac progenitor cells and biotinylated insulin-like growth factor-1 nanofibers improve endogenous and exogenous myocardial regeneration after infarction

BACKGROUND

Cardiac progenitor cells (CPCs) possess the insulin-like growth factor-1 (IGF-1)-IGF-1 receptor system, and IGF-1 can be tethered to self-assembling peptide nanofibers (NF-IGF-1), leading to prolonged release of this growth factor to the myocardium. Therefore, we tested whether local injection of clonogenic CPCs and NF-IGF-1 potentiates the activation and differentiation of delivered and resident CPCs enhancing cardiac repair after infarction.

METHODS AND RESULTS

Myocardial infarction was induced in rats, and untreated infarcts and infarcts treated with CPCs or NF-IGF-1 only and CPCs and NF-IGF-1 together were analyzed. With respect to infarcts exposed to CPCs or NF-IGF-1 alone, combination therapy resulted in a greater increase in the ratio of left ventricular mass to chamber volume and a better preservation of +dP/dt, -dP/dt, ejection fraction, and diastolic wall stress. Myocardial regeneration was detected in all treated infarcts, but the number of newly formed myocytes with combination therapy was 32% and 230% higher than with CPCs and NF-IGF-1, respectively. Corresponding differences in the volume of regenerated myocytes were 48% and 115%. Similarly, the length density of newly formed coronary arterioles with both CPCs and NF-IGF-1 was 73% and 83% greater than with CPCs and NF-IGF-1 alone, respectively. Importantly, activation of resident CPCs by paracrine effects contributed to cardiomyogenesis and vasculogenesis. Collectively, CPCs and NF-IGF-1 therapy reduced infarct size more than CPCs and NF-IGF-1 alone.

CONCLUSIONS

The addition of nanofiber-mediated IGF-1 delivery to CPC therapy improved in part the recovery of myocardial structure and function after infarction.

Self-assembling peptide nanofibers and skeletal myoblast transplantation in infarcted myocardium

Cell transplantation is currently limited by poor graft retention and survival in the postinfarction scar. Because this issue could potentially be addressed by embedding cells in bioinjectable scaffolds and boosting cell survival pathways, we induced a myocardial infarction in 72 rats to assess the effects of different self-assembling peptides with or without platelet-derived growth factor (PDGF-BB) on survival of transplanted skeletal myoblasts. Two weeks after coronary artery ligation, rats were randomized to receive in-scar injections of culture medium (controls, n = 11), self-assembling peptide (RAD16-I) nanofibers (NF, n = 9), skeletal myoblasts (n = 12), or skeletal myoblasts in combination with NF (n = 8). In separate experiments with different self-assembling peptides (RAD16-II), rats received in-scar injections of culture medium (controls, n = 6), skeletal myoblasts (n = 10), PDGF-loaded peptides (n = 7), or skeletal myoblasts (5 x 10(6)) in combination with PDGF-loaded peptides (n = 9). After 1 month, left ventricular function, as assessed by echocardiography, was not improved in either of the experimental groups compared with controls. This correlated with the failure of RAD16-I peptides or PDGF-loaded RAD16-II peptides to improve myoblast survival despite a greater angiogenesis. In vitro experiments confirmed that the number of myoblasts decreased over time when seeded on nanofiber gels. These data suggest that the optimal use of biomaterial scaffolds for survival of transplanted cells will require specific tailoring of the biomaterial to the cell type.

Engineering insulin-like growth factor-1 for local delivery

Insulin-like growth factor-1 (IGF-1) is a small protein that promotes cell survival and growth, often acting over long distances. Although for decades IGF-1 has been considered to have therapeutic potential, systemic side effects of IGF-1 are significant, and local delivery of IGF-1 for tissue repair has been a long-standing challenge. In this study, we designed and purified a novel protein, heparin-binding IGF-1 (Xp-HB-IGF-1), which is a fusion protein of native IGF-1 with the heparin-binding domain of heparin-binding epidermal growth factor-like growth factor. Xp-HB-IGF-1 bound selectively to heparin as well as the cell surfaces of 3T3 fibroblasts, neonatal cardiac myocytes and differentiating ES cells. Xp-HB-IGF-1 activated the IGF-1 receptor and Akt with identical kinetics and dose response, indicating no compromise of biological activity due to the heparin-binding domain. Because cartilage is a proteoglycan-rich environment and IGF-1 is a known stimulus for chondrocyte biosynthesis, we then studied the effectiveness of Xp-HB-IGF-1 in cartilage. Xp-HB-IGF-1 was selectively retained by cartilage explants and led to sustained chondrocyte proteoglycan biosynthesis compared to IGF-1. These data show that the strategy of engineering a "long-distance" growth factor like IGF-1 for local delivery may be useful for tissue repair and minimizing systemic effects.

Local delivery of protease-resistant stromal cell derived factor-1 for stem cell recruitment after myocardial infarction

BACKGROUND

Local delivery of chemotactic factors represents a novel approach to tissue regeneration. However, successful chemokine protein delivery is challenged by barriers including the rapid diffusion of chemokines and cleavage of chemokines by proteases that are activated in injured tissues. Stromal cell-derived factor-1 (SDF-1) is a well-characterized chemokine for attracting stem cells and thus a strong candidate for promoting regeneration. However, SDF-1 is cleaved by exopeptidases and matrix metalloproteinase-2, generating a neurotoxin implicated in some forms of dementia.

METHODS AND RESULTS

We designed a new chemokine called S-SDF-1(S4V) that is resistant to matrix metalloproteinase-2 and exopeptidase cleavage but retains chemotactic bioactivity, reducing the neurotoxic potential of native SDF-1. To deliver S-SDF-1(S4V), we expressed and purified fusion proteins to tether the chemokine to self-assembling peptides, which form nanofibers and allow local delivery. Intramyocardial delivery of S-SDF-1(S4V) after myocardial infarction recruited CXCR4+/c-Kit+ stem cells (46+/-7 to 119+/-18 cells per section) and increased capillary density (from 169+/-42 to 283+/-27 per 1 mm2). Furthermore, in a randomized, blinded study of 176 rats with myocardial infarction, nanofiber delivery of the protease-resistant S-SDF-1(S4V) improved cardiac function (ejection fraction increased from 34.0+/-2.5% to 50.7+/-3.1%), whereas native SDF-1 had no beneficial effects.

CONCLUSIONS

The combined advances of a new, protease-resistant SDF-1 and nanofiber-mediated delivery promoted recruitment of stem cells and improved cardiac function after myocardial infarction. These data demonstrate that driving chemotaxis of stem cells by local chemokine delivery is a promising new strategy for tissue regeneration.

Evidence from a genetic fate-mapping study that stem cells refresh adult mammalian cardiomyocytes after injury

An emerging concept is that the mammalian myocardium has the potential to regenerate, but that regeneration might be too inefficient to repair the extensive myocardial injury that is typical of human disease. However, the degree to which stem cells or precursor cells contribute to the renewal of adult mammalian cardiomyocytes remains controversial. Here we report evidence that stem cells or precursor cells contribute to the replacement of adult mammalian cardiomyocytes after injury but do not contribute significantly to cardiomyocyte renewal during normal aging. We generated double-transgenic mice to track the fate of adult cardiomyocytes in a 'pulse-chase' fashion: after a 4-OH-tamoxifen pulse, green fluorescent protein (GFP) expression was induced only in cardiomyocytes, with 82.7% of cardiomyocytes expressing GFP. During normal aging up to one year, the percentage of GFP+ cardiomyocytes remained unchanged, indicating that stem or precursor cells did not refresh uninjured cardiomyocytes at a significant rate during this period of time. By contrast, after myocardial infarction or pressure overload, the percentage of GFP+ cardiomyocytes decreased from 82.8% in heart tissue from sham-treated mice to 67.5% in areas bordering a myocardial infarction, 76.6% in areas away from a myocardial infarction, and 75.7% in hearts subjected to pressure overload, indicating that stem cells or precursor cells had refreshed the cardiomyocytes.

Local delivery of proteins and the use of self-assembling peptides

Self-assembling peptides are members of a new class of molecules designed for tissue engineering and protein delivery. Upon injection in a physiological environment, self-assembling peptides form stable nanofiber hydrogels. Such biocompatible nanofibers can support three-dimensional growth and differentiation of many cell types. Self-assembling peptides are promising candidates for protein delivery, because they allow non-covalent binding of proteins, tethering of proteins, or incorporation of fusion proteins. Self-assembling peptides can be designed to deliver individual proteins or multiple factors, because the building blocks comprising self-assembling peptides can be designed with great flexibility.

Endogenous inhibitors of hypertrophy in concentric versus eccentric hypertrophy

Left ventricular (LV) hypertrophy (LVH) is an adaptive response to hemodynamic overload, but also contributes to the pathogenesis of heart failure. LVH can be concentric (cLVH) but subsequent dilatation and progression to eccentric hypertrophy (eLVH) may lead to global pump failure. Recently, several endogenous molecular inhibitors of hypertrophy have been identified. Using real-time PCR, we compared the myocardial mRNA expression of these inhibitors in pressure-overload induced cLVH (severe aortic stenosis) and in volume overload-induced eLVH (severe mitral regurgitation) in patients, and during the progression from cLVH to eLVH in pressure overload in rat. Each of these genes showed a unique temporal expression profile. Strikingly, except for SOCS-3, changes in gene expression of these negative regulators in rat cLVH and eLVH vs sham were recapitulated in human cLVH and eLVH. In particular, VDUP-1 and MCIP-1 were high in cLVH but expression levels were normal in eLVH, both in rat and human. These data indicate that during the progression of LVH, both in pressure and volume overload, expression levels of endogenous inhibitors of hypertrophy are modified and that these changes may have pathophysiological significance. In particular, MCIP-1 (the endogenous calcineurin inhibitor) and VDUP-1 (the endogenous inhibitor of thioredoxin) are potential molecular switches in the progression of LV hypertrophy.

Role of neuregulin-1/ErbB2 signaling in endothelium-cardiomyocyte cross-talk

Neuregulin-1 (NRG-1), a cardioactive growth factor released from endothelial cells, has been shown to be indispensable for the normal function of the adult heart by binding to ErbB4 receptors on cardiomyocytes. In the present study, we have investigated to what extent ErbB2, the favored co-factor of ErbB4 for heterodimerization, participates in the cardiac effects of endothelium-derived NRG-1. In addition, in view of our previously described anti-adrenergic effects of NRG-1, we have studied which neurohormonal stimuli affect endothelial NRG-1 expression and release and how this may fit into a broader frame of cardiovascular physiology. Immunohistochemical staining of rat heart and aorta showed that NRG-1 expression was restricted to the endocardial endothelium and the cardiac microvascular endothelium (CMVE); by contrast, NRG-1 expression was absent in larger coronary arteries and veins and in aortic endothelium. In rat CMVE in culture, NRG-1 mRNA and protein expression was down-regulated by angiotensin II and phenylephrine and up-regulated by endothelin-1 and mechanical strain. CMVE-derived NRG-1 was shown to phosphorylate cardiomyocyte ErbB2, an event prevented by a 24-h preincubation of myocytes with monoclonal ErbB2 antibodies. Pretreating cardiomyocytes with these inhibitory anti-ErbB2 antibodies significantly attenuated CMVE-induced cardiomyocyte hypertrophy and abolished the protective actions of CMVE against cardiomyocyte apoptosis. Accordingly, ErbB2 signaling participated in the paracrine survival and growth controlling effects of NRG-1 on cardiomyocytes in vitro, explaining the cardiotoxicity of ErbB2 antibodies in patients. Cardiac NRG-1 synthesis occurs in endothelial cells adjacent to cardiac myocytes and is sensitive to factors related to the regulation of blood pressure.

Mesenchymal stem cell adhesion to cardiac microvascular endothelium: activators and mechanisms

Circulating stem cells home within the myocardium, probably as the first step of a tissue regeneration process. This step requires adhesion to cardiac microvascular endothelium (CMVE). In this study, we studied mechanisms of adhesion between CMVE and mesenchymal stem cells (MSCs). Adhesion was studied in vitro and in vivo. Isolated 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-labeled rat MSCs were allowed to adhere to cultured CMVE in static and dynamic conditions. Either CMVE or MSCs were pretreated with cytokines [IL-1beta, IL-3, IL-6, stem cell factor, stromal cell-derived factor-1, or TNF-alpha, 10 ng/ml]. Control or TNF-alpha-treated MSCs were injected intracavitarily in rat hearts in vivo. In baseline in vitro conditions, the number of MSCs that adhered to CMVE was highly dependent on the flow rate of the superfusing medium but remained significant at venous and capillary shear stress amplitudes. Activation of both CMVE and MSCs with TNF-alpha or IL-1beta before adhesion concentration dependently increased adhesion of MSCs at each studied level of shear stress. Consistently, in vivo, activation of MSCs with TNF-alpha before injection significantly enhanced cardiac homing of MSCs. TNF-alpha-induced adhesion could be completely blocked by pretreating either CMVE or MSCs with anti-VCAM-1 monoclonal antibodies but not by anti-ICAM-1 antibodies. Adhesion of circulating MSCs in the heart appears to be an endothelium-dependent process and is sensitive to modulation by activators of both MSCs and endothelium. Inflammation and the expression of VCAM-1 but not ICAM-1 on both cell types have a regulatory effect on MSC homing in the heart.

Inhibition of heme oxygenase?1 impairs cardiac muscle sensitivity to beta?adrenergic stimulation

Heme oxygenase-1 (HO-1) is the inducible isoform of heme oxygenase and plays a role in defense against cellular stress. The effects of HO-1 on cardiac muscle contractility, however, are unknown.

METHODS

HO-1 was induced by intraperitoneal injection of hemin in rabbits 24 and 48 h before isolating right ventricular papillary muscles for mechanical in vitro analysis at baseline and during stimulation with isoprenalin. Western blotting and activity measurement con.rmed upregulation of HO-1 in ventricular tissue, and immunohistochemical stainings showed localization in the cardiac endothelium.

RESULTS

Baseline mechanical performance of papillary muscles and maximal inotropic response to ISO was not significantly affected by HO-1 induction. Also, the log(EC50) of the ISO concentration-response curve was not affected by HO-1 induction. Inhibition of heme oxygenase with stanneous mesoporphyrin or chromium mesoporphyrin in muscles with induced HO-1, however, shifted the log(EC50) of the ISO concentration-response curve from -6.9 +/- 0.2 to -6.0 +/- 0.2 (p = 0.008).

CONCLUSION

These results indicate that induction of cardiac HO-1 has no direct effect on baseline contractility. Pharmacological inhibition of HO-1 upon induction, however, diminishes cardiac muscle sensitivity to beta-adrenergic stimulation. These results caution against pharmacologically targeting HO-1 when an activated adrenergic system is important for hemodynamic stability.