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Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited cardiac disease. Up to 40% of cases are associated with heterozygous mutations in myosin binding protein C (cMyBP-C, MYBPC3). Most of these mutations lead to premature termination codons (PTC) and patients show reduction of functional cMyBP-C. This so-called haploinsufficiency most likely contributes to disease development. We analyzed mechanisms underlying haploinsufficiency using cardiac tissue from HCM-patients with truncation mutations in MYBPC3 (MYBPC3 trunc ). We compared transcriptional activity, mRNA and protein expression to donor controls. To differentiate between HCM-specific and general hypertrophy-induced mechanisms we used patients with left ventricular hypertrophy due to aortic stenosis (AS) as an additional control. We show that cMyBP-C haploinsufficiency starts at the mRNA level, despite hypertrophy-induced increased transcriptional activity. Gene set enrichment analysis (GSEA) of RNA-sequencing data revealed an increased expression of NMD-components. Among them, Up-frameshift protein UPF3B, a regulator of NMD was upregulated in MYBPC3 trunc patients and not in AS-patients. Strikingly, we show that in sarcomeres UPF3B but not UPF1 and UPF2 are localized to the Z-discs, the presumed location of sarcomeric protein translation. Our data suggest that cMyBP-C haploinsufficiency in HCM-patients is established by UPF3B-dependent NMD during the initial translation round at the Z-disc., Competing Interests: Declaration of Competing Interest None., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Cardiac levels of the signal transducer and activator of transcription factor-3 (STAT3) decline with age, and male but not female mice with a cardiomyocyte-specific STAT3 deficiency conditional knockout (CKO) display premature age-related heart failure associated with reduced cardiac capillary density. In the present study, isolated male and female CKO-cardiomyocytes exhibit increased prostaglandin (PG)-generating cyclooxygenase-2 (COX-2) expression. The PG-degrading hydroxyprostaglandin-dehydrogenase-15 (HPGD) expression is only reduced in male cardiomyocytes, which is associated with increased prostaglandin D2 (PGD2) secretion from isolated male but not female CKO-cardiomyocytes. Reduced HPGD expression in male cardiomyocytes derive from impaired androgen receptor (AR)-signaling due to loss of its cofactor STAT3. Elevated PGD2 secretion in males is associated with increased white adipocyte accumulation in aged male but not female hearts. Adipocyte differentiation is enhanced in isolated stem cell antigen-1 (SCA-1)+ cardiac progenitor cells (CPC) from young male CKO-mice compared with the adipocyte differentiation of male wild-type (WT)-CPC and CPC isolated from female mice. Epigenetic analysis in freshly isolated male CKO-CPC display hypermethylation in pro-angiogenic genes (Fgfr2, Epas1) and hypomethylation in the white adipocyte differentiation gene Zfp423 associated with up-regulated ZFP423 expression and a shift from endothelial to white adipocyte differentiation compared with WT-CPC. The expression of the histone-methyltransferase EZH2 is reduced in male CKO-CPC compared with male WT-CPC, whereas no differences in the EZH2 expression in female CPC were observed. Clonally expanded CPC can differentiate into endothelial cells or into adipocytes depending on the differentiation conditions. ZFP423 overexpression is sufficient to induce white adipocyte differentiation of clonal CPC. In isolated WT-CPC, PGD2 stimulation reduces the expression of EZH2, thereby up-regulating ZFP423 expression and promoting white adipocyte differentiation. The treatment of young male CKO mice with the COX inhibitor Ibuprofen or the PGD2 receptor (DP)2 receptor antagonist BAY-u 3405 in vivo increased EZH2 expression and reduced ZFP423 expression and adipocyte differentiation in CKO-CPC. Thus, cardiomyocyte STAT3 deficiency leads to age-related and sex-specific cardiac remodeling and failure in part due to sex-specific alterations in PGD2 secretion and subsequent epigenetic impairment of the differentiation potential of CPC. Causally involved is the impaired AR signaling in absence of STAT3, which reduces the expression of the PG-degrading enzyme HPGD., Competing Interests: The authors have declared that no competing interests exist.

Neuraminidase (NEU)1 forms a multienzyme complex with beta-galactosidase (β-GAL) and protective-protein/cathepsin (PPC) A, which cleaves sialic-acids from cell surface glycoconjugates. We investigated the role of NEU1 in the myocardium after ischemia/reperfusion (I/R). Three days after inducing I/R, left ventricles (LV) of male mice (3 months-old) displayed upregulated neuraminidase activity and increased NEU1, β-GAL and PPCA expression. Mice hypomorphic for neu1 (hNEU1) had less neuraminidase activity, fewer pro-inflammatory (Lin - CD11b + F4/80 + Ly-6C high ), and more anti-inflammatory macrophages (Lin - CD11b + F4/80 + Ly-6C low ) 3 days after I/R, and less LV dysfunction 14 days after I/R. WT mice transplanted with hNEU1-bone marrow (BM) and hNEU1 mice with WT-BM showed significantly better LV function 14 days after I/R compared with WT mice with WT-BM. Mice with a cardiomyocyte-specific NEU1 overexpression displayed no difference in inflammation 3 days after I/R, but showed increased cardiomyocyte hypertrophy, reduced expression and mislocalization of Connexin-43 in gap junctions, and LV dysfunction despite a similar infarct scar size to WT mice 14 days after I/R. The upregulation of NEU1 after I/R contributes to heart failure by promoting inflammation in invading monocytes/macrophages, enhancing cardiomyocyte hypertrophy, and impairing gap junction function, suggesting that systemic NEU1 inhibition may reduce heart failure after I/R.

Duchenne muscular dystrophy (DMD) is an X-linked progressive muscle degenerative disease, caused by mutations in the dystrophin gene and resulting in death because of respiratory or cardiac failure. To investigate the cardiac cellular manifestation of DMD, we generated induced pluripotent stem cells (iPSCs) and iPSC-derived cardiomyocytes (iPSC-CMs) from two DMD patients: a male and female manifesting heterozygous carrier. Dystrophin mRNA and protein expression were analysed by qRT-PCR, RNAseq, Western blot and immunofluorescence staining. For comprehensive electrophysiological analysis, current and voltage clamp were used to record transmembrane action potentials and ion currents, respectively. Microelectrode array was used to record extracellular electrograms. X-inactive specific transcript (XIST) and dystrophin expression analyses revealed that female iPSCs underwent X chromosome reactivation (XCR) or erosion of X chromosome inactivation, which was maintained in female iPSC-CMs displaying mixed X chromosome expression of wild type (WT) and mutated alleles. Both DMD female and male iPSC-CMs presented low spontaneous firing rate, arrhythmias and prolonged action potential duration. DMD female iPSC-CMs displayed increased beat rate variability (BRV). DMD male iPSC-CMs manifested decreased I f density, and DMD female and male iPSC-CMs showed increased I Ca,L density. Our findings demonstrate cellular mechanisms underlying electrophysiological abnormalities and cardiac arrhythmias in DMD., (© 2019 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Peripartum cardiomyopathy (PPCM) and dilated cardiomyopathy (DCM) show similarities in clinical presentation. However, although DCM patients do not recover and slowly deteriorate further, PPCM patients show either a fast cardiac deterioration or complete recovery. The aim of this study was to assess if underlying cellular changes can explain the clinical similarities and differences in the two diseases. We, therefore, assessed sarcomeric protein expression, modification, titin isoform shift, and contractile behavior of cardiomyocytes in heart tissue of PPCM and DCM patients and compared these with nonfailing controls. Heart samples from ischemic heart disease (ISHD) patients served as heart failure control samples. Passive force was only increased in PPCM samples compared with controls, whereas PPCM, DCM, and ISHD samples all showed increased myofilament Ca 2+ sensitivity. Length-dependent activation was significantly impaired in PPCM compared with controls, no impairment was observed in ISHD samples, and DCM samples showed an intermediate response. Contractile impairments were caused by impaired protein kinase A (PKA)-mediated phosphorylation because exogenous PKA restored all parameters to control levels. Although DCM samples showed reexpression of EH-myomesin, an isoform usually only expressed in the heart before birth, PPCM and ISHD did not. The lack of EH-myomesin, combined with low PKA-mediated phosphorylation of myofilament proteins and increased compliant titin isoform, may explain the increase in passive force and blunted length-dependent activation of myofilaments in PPCM samples., (Copyright © 2017 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Aims: Peripartum cardiomyopathy (PPCM) is a systolic left ventricular dysfunction developing in the peripartum phase in previously healthy women. Relaxin-2 is a pregnancy hormone with potential beneficial effects in heart failure patients. We evaluated Relaxin-2 as a potential diagnostic marker and/or a therapeutic agent in PPCM., Methods and Results: In healthy peripartum women, serum Relaxin-2 levels (measured by ELISA in the second half of pregnancy) were elevated showing a decreasing trend in the first postpartum week and returned to non-pregnant levels thereafter. In PPCM patients diagnosed in the first postpartum week, serum Relaxin-2 levels were lower compared to healthy postpartum stage-matched controls. In PPCM patients diagnosed later (0.5-10 months postpartum) Relaxin-2 levels were in the range of non-pregnant controls and not different from healthy postpartum stage-matched controls. In mice, serum Relaxin-1 (functional equivalent of human Relaxin-2) was increased late in pregnancy and rapidly cleared in the first postpartum week. In mice with PPCM due to a cardiomyocyte-specific knockout of STAT3 (CKO) neither low nor high dose of recombinant Relaxin-2 (serelaxin, sRlx-LD: 30 µg/kg/day; sRlx-HD: 300 µg/kg/day) affected cardiac fibrosis, inflammation and heart failure but sRlx-HD increased capillary/cardiomyocyte ratio. sRlx-HD significantly increased heart/body weight ratio and cardiomyocyte cross-sectional area in postpartum CKO and wild-type mice without changing the foetal gene expression program (ANP or β-MHC). sRlx-HD augmented plasma Prolactin levels in both genotypes, which induced cardiac activation of STAT5. In vitro analyses showed that Prolactin induces cardiomyocyte hypertrophy via activation of STAT5., Conclusion: Although Relaxin-2 levels seemed lower in PPCM patients diagnosed early postpartum, we observed a high pregnancy-related variance of serum Relaxin-2 levels peripartum making it unsuitable as a biomarker for this condition. Supplementation with sRlx may contribute to angiogenesis and compensatory hypertrophy in the diseased heart, but the effects are not sufficient to prevent heart failure in an experimental PPCM model., (© The Author 2017. Published by Oxford University Press on behalf of the European Society of Cardiology.)

As previously reported, the cardiac phosphodiesterase PDE3A hydrolyzes cUMP. Moreover, cUMP-degrading activity was detected in cow and dog hearts several decades ago. Our aim was to characterize the enzyme kinetic parameters of PDE3A-mediated cUMP hydrolysis and to investigate whether cUMP and cUMP-hydrolyzing PDEs are present in cardiomyocytes. PDE3A-mediated cUMP hydrolysis was characterized in time course, inhibitor, and Michaelis-Menten kinetics experiments. Intracellular cyclic nucleotide (cNMP) concentrations and the mRNAs of cUMP-degrading PDEs were quantitated in neonatal rat cardiomyocytes (NRCMs) and murine HL-1 cardiomyogenic cells. Moreover, we investigated cUMP degradation in HL-1 cell homogenates and intact cells. Educts (cNMPs) and products (NMPs) of the PDE reactions were detected by HPLC-coupled tandem mass spectrometry. PDE3A degraded cUMP (measurement of UMP formation) with a K M value of ~143 μM and a V max value of ~42 μmol/min/mg. PDE3A hydrolyzed cAMP with a K M value of ~0.7 μM and a V max of ~1.2 μmol/min/mg (determination of AMP formation). The PDE3 inhibitor milrinone inhibited cUMP hydrolysis (determination of UMP formation) by PDE3A (K i  = 57 nM). Significant amounts of cUMP as well as of PDE3A mRNA (in addition to PDE3B and PDE9A transcripts) were detected in HL-1 cells and NRCMs. Although HL-1 cell homogenates contain a milrinone-sensitive cUMP-hydrolyzing activity, intact HL-1 cells may use additional PDE3-independent mechanisms for cUMP disposal. PDE3A is a low-affinity and high-velocity PDE for cUMP. Future studies should investigate biological effects of cUMP in cardiomyocytes and the role of PDE3A in detoxifying high intracellular cUMP concentrations under pathophysiological conditions.

The ultimate goal of tissue engineering is the generation of implants similar to native tissue. Thus, it is essential to utilize physiological stimuli to improve the quality of engineered constructs. Numerous publications reported that mechanical stimulation of small-sized, non-perfusable, tissue engineered cardiac constructs leads to a maturation of immature cardiomyocytes like neonatal rat cardiomyocytes or induced pluripotent stem cells/embryonic stem cells derived self-contracting cells. The aim of this study was to investigate the impact of mechanical stimulation and perfusion on the maturation process of large-scale (2.5×4.5cm), implantable cardiac patches based on decellularized porcine small intestinal submucosa (SIS) or Biological Vascularized Matrix (BioVaM) and a 3-dimensional construct containing neonatal rat heart cells. Application of cyclic mechanical stretch improved contractile function, cardiomyocyte alignment along the stretch axis and gene expression of cardiomyocyte markers. The development of a complex network formed by endothelial cells within the cardiac construct was enhanced by cyclic stretch. Finally, the utilization of BioVaM enabled the perfusion of the matrix during stimulation, augmenting the beneficial influence of cyclic stretch. Thus, this study demonstrates the maturation of cardiac constructs with clinically relevant dimensions by the application of cyclic mechanical stretch and perfusion of the starter matrix., Statement of Significance: Considering the poor endogenous regeneration of the heart, engineering of bioartificial cardiac tissue for the replacement of infarcted myocardium is an exciting strategy. Most techniques for the generation of cardiac tissue result in relative small-sized constructs insufficient for clinical applications. Another issue is to achieve cardiomyocytes and tissue maturation in culture. Here we report, for the first time, the effect of mechanical stimulation and simultaneous perfusion on the maturation of cardiac constructs of clinical relevant dimensions, which are based on a perfusable starter matrix derived from porcine small intestine. In response to these stimuli superior organization of cardiomyocytes and vascular networks was observed in contrast to untreated controls. The study provides substantial progress towards the generation of implantable cardiac patches., (Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

The failing heart is characterized by complex tissue remodelling involving increased cardiomyocyte death, and impairment of sarcomere function, metabolic activity, endothelial and vascular function, together with increased inflammation and interstitial fibrosis. For years, therapeutic approaches for heart failure (HF) relied on vasodilators and diuretics which relieve cardiac workload and HF symptoms. The introduction in the clinic of drugs interfering with beta-adrenergic and angiotensin signalling have ameliorated survival by interfering with the intimate mechanism of cardiac compensation. Current therapy, though, still has a limited capacity to restore muscle function fully, and the development of novel therapeutic targets is still an important medical need. Recent progress in understanding the molecular basis of myocardial dysfunction in HF is paving the way for development of new treatments capable of restoring muscle function and targeting specific pathological subsets of LV dysfunction. These include potentiating cardiomyocyte contractility, increasing cardiomyocyte survival and adaptive hypertrophy, increasing oxygen and nutrition supply by sustaining vessel formation, and reducing ventricular stiffness by favourable extracellular matrix remodelling. Here, we consider drugs such as omecamtiv mecarbil, nitroxyl donors, cyclosporin A, SERCA2a (sarcoplasmic/endoplasmic Ca(2 +) ATPase 2a), neuregulin, and bromocriptine, all of which are currently in clinical trials as potential HF therapies, and discuss novel molecular targets with potential therapeutic impact that are in the pre-clinical phases of investigation. Finally, we consider conceptual changes in basic science approaches to improve their translation into successful clinical applications., (© 2014 The Authors. European Journal of Heart Failure © 2014 European Society of Cardiology.)

Background: Peripartum cardiomyopathy (PPCM) is a pregnancy-associated cardiomyopathy in previously healthy women. Mice with a cardiomyocyte-restricted deletion of signal transducer and activator of transcription-3 (STAT3, CKO) develop PPCM. PI3K-Akt signalling is thought to promote cardiac hypertrophy and protection during pregnancy. We evaluated the role of activated Akt signalling in the maternal heart postpartum., Methods and Results: CKO mice were bred to mice harbouring an Akt transgene, specifically expressed in cardiomyocytes (CAkt(tg)) generating CKO; CAkt(tg), CAkt(tg), CKO, and wild-type sibling mice. CAkt(tg) and CKO;CAkt(tg) female mice developed PPCM with systolic dysfunction. Both genotypes displayed cardiac hypertrophy and lower capillary density, showed increased phosphorylation of p66 Src homology 2 domain containing protein and FoxO3A, and reduced expression of manganese superoxide dismutase as well as increased cathepsin D activity and increased miR-146a levels [indicative for generation of the anti-angiogenic 16 kDa prolactin (PRL)]. Cardiac inflammation and fibrosis was accelerated in CKO;CAkt(tg) and associated with high postpartum mortality. The PRL blocker, bromocriptine (BR), prevented heart failure and the decrease in capillary density in CKO;CAkt(tg) and CAkt(tg) mice. BR attenuated high mortality, up-regulation of CCL2, and cardiac inflammation as well as fibrosis in CKO;CAkt(tg). PRL infusion induced cardiac inflammation in CKO;CAkt(tg) independent of pregnancy. In neonatal rat cardiomyocytes, PRL and interferon γ (IFNγ) induced the expression of CCL2 via activation of Akt., Conclusion: Postpartum Akt activation is detrimental for the peripartum heart as it lowers anti-oxidative defence and in combination with low STAT3 conditions, accelerate cardiac inflammation and fibrosis. PRL and its cleaved 16 kDa form are central for Akt-induced PPCM as indicated by the protection from the disease by PRL blockade.

The small molecule EMD 57033 has been shown to stimulate the actomyosin ATPase activity and contractility of myofilaments. Here, we show that EMD 57033 binds to an allosteric pocket in the myosin motor domain. EMD 57033-binding protects myosin against heat stress and thermal denaturation. In the presence of EMD 57033, ATP hydrolysis, coupling between actin and nucleotide binding sites, and actin affinity in the presence of ATP are increased more than 10-fold. Addition of EMD 57033 to heat-inactivated β-cardiac myosin is followed by refolding and reactivation of ATPase and motile activities. In heat-stressed cardiomyocytes expression of the stress-marker atrial natriuretic peptide is suppressed by EMD 57033. Thus, EMD 57033 displays a much wider spectrum of activities than those previously associated with small, drug-like compounds. Allosteric effectors that mediate refolding and enhance enzymatic function have the potential to improve the treatment of heart failure, myopathies, and protein misfolding diseases. DOI: http://dx.doi.org/10.7554/eLife.01603.001.

Background: β1-2-adrenergic receptors (AR) are key regulators of cardiac contractility and remodeling in response to catecholamines. β3-AR expression is enhanced in diseased human myocardium, but its impact on remodeling is unknown., Methods and Results: Mice with cardiac myocyte-specific expression of human β3-AR (β3-TG) and wild-type (WT) littermates were used to compare myocardial remodeling in response to isoproterenol (Iso) or Angiotensin II (Ang II). β3-TG and WT had similar morphometric and hemodynamic parameters at baseline. β3-AR colocalized with caveolin-3, endothelial nitric oxide synthase (NOS) and neuronal NOS in adult transgenic myocytes, which constitutively produced more cyclic GMP, detected with a new transgenic FRET sensor. Iso and Ang II produced hypertrophy and fibrosis in WT mice, but not in β3-TG mice, which also had less re-expression of fetal genes and transforming growth factor β1. Protection from Iso-induced hypertrophy was reversed by nonspecific NOS inhibition at low dose Iso, and by preferential neuronal NOS inhibition at high-dose Iso. Adenoviral overexpression of β3-AR in isolated cardiac myocytes also increased NO production and attenuated hypertrophy to Iso and phenylephrine. Hypertrophy was restored on NOS or protein kinase G inhibition. Mechanistically, β3-AR overexpression inhibited phenylephrine-induced nuclear factor of activated T-cell activation., Conclusions: Cardiac-specific overexpression of β3-AR does not affect cardiac morphology at baseline but inhibits the hypertrophic response to neurohormonal stimulation in vivo and in vitro, through a NOS-mediated mechanism. Activation of the cardiac β3-AR pathway may provide future therapeutic avenues for the modulation of hypertrophic remodeling.

The involvement of erythropoietin in cardiac adaptation to acute and chronic (CHx) hypoxia was investigated in erythropoietin deficient transgenic (Epo-TAg(h)) and wild-type (WT) mice. Left (LV) and right ventricular functions were assessed by echocardiography and hemodynamics. HIF-1α, VEGF and Epo pathways were explored through RT-PCR, ELISA, Western blot and immunocytochemistry. Epo gene and protein were expressed in cardiomyocytes of WT mice in normoxia and hypoxia. Increase in blood hemoglobin, angiogenesis and functional cardiac adaptation occurred in CHx in WT mice, allowing a normal oxygen delivery (O2T). Epo deficiency induced LV hypertrophy, increased cardiac output (CO) and angiogenesis, but O2T remained lower than in WT mice. In CHx Epo-TAg(h) mice, LV hypertrophy, CO and O2T decreased. HIF-1α and Epo receptor pathways were depressed, suggesting that Epo-TAg(h) mice could not adapt to CHx despite activation of cardioprotective pathways (increased P-STAT-5/STAT-5). HIF/Epo pathway is activated in the heart of WT mice in hypoxia. Chronic hypoxia induced cardiac adaptive responses that were altered with Epo deficiency, failing to maintain oxygen delivery to tissues., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Aims: Mice with a cardiomyocyte (CM)-restricted knockout of signal transducer and activator of transcription 3 (STAT3-KO) develop spontaneous heart failure. We investigated the impact of STAT3-mediated regulation of microRNAs for pathophysiological alterations in the heart., Methods and Results: MicroRNAchip and qRT-PCR analysis revealed elevated cardiac expression of miR-199a in STAT3-KO mice. Lentiviral shRNA-mediated STAT3-knock-down in neonatal rat CMs markedly increased miR-199a promoter activity and miR-199a levels indicative of a suppressive effect of STAT3 on miR-199a transcription. Up-regulated miR-199a in CM by pre-miR-199a transfection (pre-miR-199a-CM) reduced expression of components of the ubiquitin-proteasome system (UPS), i.e. the ubiquitin-conjugating enzymes Ube2g1 (mRNA and protein) and Ube2i (protein). Pre-miR-199a-CM or CM with siRNA-mediated down-regulation of Ube2i and Ube2g1 (siRNA-Ube2i/2g1-CM) displayed massive down-regulation of α- and β-myosin heavy chain expression associated with disrupted sarcomere structures. In addition, protein arginine methyltransferase I (PRMT-I) expression and asymmetric dimethylarginine (ADMA) synthesis were increased in pre-miR-199a-CM or in siRNA-Ube2i/2g1-CM. Increased ADMA in cell culture supernatant (SN) from pre-miR-199a-CM or siRNA-Ube2i/2g1-CM lowered nitric oxide (NO) bioavailability of rat cardiac endothelial cells while lowering ADMA concentration in CM SNs by the PRMT inhibitor arginine methyltransferase inhibitor 1 (AMI-1) (100 µM) improved NO bioavailability. In STAT3-KO hearts Ube2i and Ube2g1 expression were markedly reduced. Human terminal failing hearts harbouring low STAT3 protein levels displayed increased miR-199a levels and decreased Ube2g1 expression., Conclusion: This study identifies a novel pathophysiological circuit in the heart between reduced STAT3 protein levels, increased miR-199a expression, and subsequent impairment of the UPS that disrupts CM sarcomere structure and impairs via the release of ADMA endothelial cell function.

Circulating levels of interleukin (IL)-6 and related cytokines are elevated in patients with congestive heart failure and after myocardial infarction. Serum IL-6 concentrations are related to decreasing functional status of these patients and provide important prognostic information.Moreover, in the failing human heart, multiple components of the IL-6- glycoprotein (gp)130 receptor system are impaired, implicating an important role of this system in cardiac pathophysiology.Experimental studies have shown that the common receptor subunit of IL-6 cytokines is phosphorylated in response to pressure overload and myocardial infarction and that it subsequently activates at least three different downstream signaling pathways, the signal transducers and activators of transcription 1 and 3 (STAT1/3), the Src-homology tyrosine phosphatase 2 (SHP2)-Ras-ERK, and the PI3K-Akt system. Gp130 receptor mediated signaling promotes cardiomyocyte survival, induces hypertrophy, modulates cardiac extracellular matrix and cardiac function. In this regard, the gp130 receptor system and its main downstream mediator STAT3 play a key role in cardioprotection. This review summarizes the current knowledge of IL-6 cytokines, gp130 receptor and STAT3 signaling in the heart exposed to physiological (aging, pregnancy) and pathophysiological stress (ischemia, pressure overload, inflammation and cardiotoxic agents) with a special focus on the potential role of individual IL-6 cytokines.

Objective: Mice deficient for the AP-1 transcription factor JunD, the only Jun protein constitutively expressed and clearly detectable in the mammalian heart, develop enhanced cardiac hypertrophy in response to chronic pressure overload. Catecholamines inducing alpha-adrenergic receptor-mediated signaling have been implicated in the neurohumoral response to pressure overload and the development of left ventricular hypertrophy. In the present study we analyzed the mechanistic role of JunD in cardiomyocyte hypertrophy in vitro in response to alpha-adrenergic agonist phenylephrine (PE)., Methods: Cardiomyocytes were isolated from 1- to 3-day-old rats and transfected with adenoviruses expressing LacZ or wild-type JunD, or with expression vectors encoding LacZ, wild-type JunD, mutated JunD forming only JunD homodimers (JunDeb1), mutated JunD lacking the JNK site (JunD-Delta 162), or c-Jun. After stimulation with PE (10(-5) mol/L), hypertrophic growth of cardiomyocytes (cross-sectional area and [3H]-leucine incorporation) and mRNA expression of JunD, c-Jun, c-Fos, and atrial natriuretic peptide (ANP) were analyzed. Transcriptional activation was determined by luciferase activity in cardiomyocytes transfected with AP-1 or ANP luciferase reporter plasmids. Gel shift assays with an AP-1 consensus oligonucleotide were performed to analyze AP-1 DNA binding activities., Results: PE augmented mRNA levels of c-Jun and c-Fos, but decreased JunD transcript levels. Adenoviral over-expression of wild-type JunD blunted PE-induced hypertrophic growth and expression of ANP mRNA. Over-expression of JunD in cardiomyocytes caused enhanced AP-1 protein-DNA binding, without increasing the transcriptional response from AP-1 or ANP luciferase reporter plasmids at baseline or upon PE stimulation. Moreover, over-expression of JunDeb1 attenuated transcription from AP-1 or ANP luciferase reporter plasmids and blunted c-Jun-mediated acceleration of AP-1 transcriptional activity at baseline and in response to PE., Conclusions: Our observations establish a novel role for JunD as a negative regulator of cardiomyocyte hypertrophy in response to hypertrophic stimuli by inhibiting AP-1 transcriptional activity.

The transcription factor signal transducer and activator of transcription 3 (STAT3) participates in a wide variety of physiological processes and directs seemingly contradictory responses such as proliferation and apoptosis. To elucidate its role in the heart, we generated mice harboring a cardiomyocyte-restricted knockout of STAT3 using Cre/loxP-mediated recombination. STAT3-deficient mice developed reduced myocardial capillary density and increased interstitial fibrosis within the first 4 postnatal months, followed by dilated cardiomyopathy with impaired cardiac function and premature death. Conditioned medium from STAT3-deficient cardiomyocytes inhibited endothelial cell proliferation and increased fibroblast proliferation, suggesting the presence of paracrine factors attenuating angiogenesis and promoting fibrosis in vitro. STAT3-deficient mice showed enhanced susceptibility to myocardial ischemia/reperfusion injury and infarction with increased cardiac apoptosis, increased infarct sizes, and reduced cardiac function and survival. Our study establishes a novel role for STAT3 in controlling paracrine circuits in the heart essential for postnatal capillary vasculature maintenance, interstitial matrix deposition balance, and protection from ischemic injury and heart failure.