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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.

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 ERBB4/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 weeks. 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 weeks following TAC both myocardial hypertrophy and fibrosis were attenuated by EC-specific Erbb4 deletion, albeit these responses were normalized after 20 weeks. Similarly, 4 weeks after Ang II treatment myocardial fibrosis was less pronounced compared to 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 spatio-temporal heterogeneity of myocardial autocrine and paracrine responses following cardiac injury.

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.

Background: MiR-181c-5p is described to induce heart failure (HF), while its role in renal pathology is undetermined. Renal dysfunction is present in 40-60% of HF patients and associated with poor prognosis. This study is the first of its kind to investigate the role of miR-181c-5p in a mouse model of cardiorenal disease (CRD). Our hypothesis states a protective effect of miR-181c-5p inhibition on HF development. 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) 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, 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, with 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, hypertrophy/atrophy, mesangial matrix expansion, reduced podocyte number). CRD+INH animals had comparable cardiac phenotype to CRD (p>0.05). 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). qPCR analysis identified Vegf as potential target of miR-181c-5p. 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. Cardiac function was unaffected.

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Introduction: Heart failure is a complex syndrome with a poor prognosis. The neuregulin-1 (NRG1)/ERBB4 axis has been shown to be cardioprotective and is a possible target for heart failure therapy. Clinical trials with NRG1 are ongoing, but require intravenous administration. Our aim is to develop a small-molecule ERBB4 agonist with cardioprotective properties. Methods: A high-throughput diversity screening (HTS) of 10,240 compounds was performed on a cellular ERBB4/ERBB4 dimerization assay. Ligand binding of hit compounds was tested in co-administration studies with NRG1 (0.1 μM) and competition binding assays with fluorescently labeled NRG1 (0.03 μM). Selectivity, post-receptor phosphorylation, and cell toxicity of hit compounds were determined using Luminex® RTK phosphoprotein, U2OS ERBB2/ERBB3 dimerization and adenylate kinase assays. Biological effects were studied in vitro in different doses (4-32 μM) on TGF-β-induced collagen synthesis by human dermal and atrial fibroblasts, and on angiotensin II (AngII, 1000 ng/kg/min)-induced left ventricular (LV) remodeling in mice with 2 selected hit compounds (83 μg/kg/h), administrated through osmotic pumps (N=4-5/group). After 28 days, left ventricular myocardial fibrosis and cardiomyocyte cross sectional area (CSA) were analyzed. Results: The HTS resulted in 8 similar pyrimidine derivatives inducing ERBB4/ERBB4 but not ERBB2/ERBB3 dimerization (Emax 9 to 33% relative to NRG1, and EC50 6x10 -6 M to 2x10 -7 M). Two compounds were excluded due to in vitro toxicity. The other 6 compounds were non-toxic and induced ERBB4, but not ERBB1, ERBB2 or ERBB3 phosphorylation in EFO-21 cells. Competition assays showed allosteric binding, and co-administration studies with NRG1 revealed that compounds potentiated NRG1-induced ERBB4 receptor dimerization up to 2.5 fold. Selected compounds showed significant dose-dependent antifibrotic effects in cultured human atrial and dermal fibroblasts and significantly attenuated AngII-induced LV myocardial fibrosis by 76%±26%, whereas cardiomyocyte CSA was not affected. Conclusions: We identified novel pyrimidine derivative small-molecule ERBB4 agonists with antifibrotic properties, both in vitro and in a mouse model of AngII-induced LV fibrosis.