Effects of interleukin-1 beta and nitric oxide on cardiac myocytes

IFN-γ-mediated control of SARS-CoV-2 infection through nitric oxide

Introduction

The COVID-19 pandemic has highlighted the need to identify mechanisms of antiviral host defense against SARS-CoV-2. One such mediator is interferon-g (IFN-γ), which, when administered to infected patients, is reported to result in viral clearance and resolution of pulmonary symptoms. IFN-γ treatment of a human lung epithelial cell line triggered an antiviral activity against SARS-CoV-2, yet the mechanism for this antiviral response was not identified.

Methods

Given that IFN-γ has been shown to trigger antiviral activity via the generation of nitric oxide (NO), we investigated whether IFN-γ induction of antiviral activity against SARS-CoV-2 infection is dependent upon the generation of NO in human pulmonary epithelial cells. We treated the simian epithelial cell line Vero E6 and human pulmonary epithelial cell lines, including A549-ACE2, and Calu-3, with IFN-γ and observed the resulting induction of NO and its effects on SARS-CoV-2 replication. Pharmacological inhibition of inducible nitric oxide synthase (iNOS) was employed to assess the dependency on NO production. Additionally, the study examined the effect of interleukin-1b (IL-1β) on the IFN-g-induced NO production and its antiviral efficacy.

Results

Treatment of Vero E6 cells with IFN-γ resulted in a dose-responsive induction of NO and an inhibitory effect on SARS-CoV-2 replication. This antiviral activity was blocked by pharmacologic inhibition of iNOS. IFN-γ also triggered a NO-mediated antiviral activity in SARS-CoV-2 infected human lung epithelial cell lines A549-ACE2 and Calu-3. IL-1β enhanced IFN-γ induction of NO, but it had little effect on antiviral activity.

Discussion

Given that IFN-g has been shown to be produced by CD8+ T cells in the early response to SARS-CoV-2, our findings in human lung epithelial cell lines, of an IFN-γ-triggered, NO-dependent, links the adaptive immune response to an innate antiviral pathway in host defense against SARS-CoV-2. These results underscore the importance of IFN-γ and NO in the antiviral response and provide insights into potential therapeutic strategies for COVID-19.

R. Tafazzin Mutation Affecting Cardiolipin Leads to Increased Mitochondrial Superoxide Anions and Mitophagy Inhibition in Barth Syndrome

Tafazzin is a phospholipid transacylase that catalyzes the remodeling of cardiolipin, a mitochondrial phospholipid required for oxidative phosphorylation. Mutations of the tafazzin gene cause Barth syndrome, which is characterized by mitochondrial dysfunction and dilated cardiomyopathy, leading to premature death. However, the molecular mechanisms underlying the cause of mitochondrial dysfunction in Barth syndrome remain poorly understood. We again highlight the fact that the tafazzin deficiency is also linked to defective oxidative phosphorylation associated with oxidative stress. All the mitochondrial events are positioned in a context where mitophagy is a key element in mitochondrial quality control. Here, we investigated the role of tafazzin in mitochondrial homeostasis dysregulation and mitophagy alteration. Using a HeLa cell model of tafazzin deficiency, we show that dysregulation of tafazzin in HeLa cells induces alteration of mitophagy. Our findings provide some additional insights into mitochondrial dysfunction associated with Barth syndrome, but also show that mitophagy inhibition is concomitant with apoptosis dysfunction through the inability of abnormal mitochondrial cardiolipin to assume its role in cytoplasmic signal transduction. Our work raises hope that pharmacological manipulation of the mitophagic pathway together with mitochondrially targeted antioxidants may provide new insights leading to promising treatment for these highly lethal conditions.

Interleukin-1 Receptor Antagonist Protects Newborn Mice Against Pulmonary Hypertension

Pulmonary hypertension secondary to bronchopulmonary dysplasia (BPD-PH) represents a major complication of BPD in extremely preterm infants for which there are currently no safe and effective interventions. The abundance of interleukin-1 (IL-1) is strongly correlated with the severity and long-term outcome of BPD infants and we have previously shown that IL-1 receptor antagonist (IL-1Ra) protects against murine BPD; therefore, we hypothesized that IL-1Ra may also be effective against BPD-PH. We employed daily injections of IL-1Ra in a murine model in which BPD/BPD-PH was induced by antenatal LPS and postnatal hyperoxia of 65% O₂. Pups reared in hyperoxia for 28 days exhibited a BPD-PH-like disease accompanied by significant changes in pulmonary vascular morphology: micro-CT revealed an 84% reduction in small vessels (4-5 μm diameter) compared to room air controls; this change was prevented by IL-1Ra. Pulmonary vascular resistance, assessed at day 28 of life by echocardiography using the inversely-related surrogate marker time-to-peak-velocity/right ventricular ejection time (TPV/RVET), increased in hyperoxic mice (0.27 compared to 0.32 in air controls), and fell significantly with daily IL-1Ra treatment (0.31). Importantly, in vivo cine-angiography revealed that this protection afforded by IL-1Ra treatment for 28 days is maintained at day 60 of life. Despite an increased abundance of mediators of pulmonary angiogenesis in day 5 lung lysates, namely vascular endothelial growth factor (VEGF) and endothelin-1 (ET-1), no difference was detected in ex vivo pulmonary vascular reactivity between air and hyperoxia mice as measured in precision cut lung slices, or by immunohistochemistry in alpha-smooth muscle actin (α-SMA) and endothelin receptor type-A (ET_A) at day 28. Further, on day 28 of life we observed cardiac fibrosis by Sirius Red staining, which was accompanied by an increase in mRNA expression of galectin-3 and CCL2 (chemokine (C-C motif) ligand 2) in whole hearts of hyperoxic pups, which improved with IL-1Ra. In summary, our findings suggest that daily administration of the anti-inflammatory IL-1Ra prevents the increase in pulmonary vascular resistance and the pulmonary dysangiogenesis of murine BPD-PH, thus pointing to IL-1Ra as a promising candidate for the treatment of both BPD and BPD-PH.

Cytokine Effects on Mechano-Induced Electrical Activity in Atrial Myocardium

The role of cytokines as regulators of stretch-related mechanisms is of special importance since mechano-sensitivity plays an important role in a wide variety of biological processes. Here, we elucidate the influence of cytokine application on mechano-sensitivity and mechano-transduction. The atrial myocardial stretch induces production of interleukin (IL)-2, IL-6, IL-13, IL-17A, and IL-18 with exception of tumor necrosis factor α (TNF-α), IL-1β, and vascular endothelial growth factor B (VEGF-B). Positive ionotropic effect was specific for VEGF-B, negative ionotropic effects were specific for TNF-α, IL-1β, IL-2, IL-6, IL-13, IL-17A and IL-18, while IL-1α doesn't show direct ionotropic effect. The IL-2, IL-6, IL-17A, IL-18, and VEGF-B cause elongation of the APD, in comparison with the reduced APD caused by the IL-13. The TNF-α, IL-1β, and IL-18 influences L-type Ca²⁺ channels, IL-2 has an inhibitory effect on the fast Na⁺ channels while IL-17A and VEGF-B were specific for Kir channels. With exception of the IL-1α, IL-2, and VEGF-B, all analyzed cytokines include nitric oxide dependent signaling with resultant combined effects on mechano-gated and Ca²⁺ channels. The relationships between these pathways and the time-dependence of their activation are of important considerations in the evaluation of cytokine-induced electrical abnormality, specific for cardiac dysfunctions. In general, the discussion presented in this review covers research devoted to counterbalance between different cytokines in the regulation of stretch-induced effects in rat atrial myocardium.

ABBREVIATIONS

APs: action potentials; APD25: action potential durations to 25% of re-polarization; APD50: action potential durations to 50% of repolarization; APD90: action potential durations to 90% of repolarization; MGCs: mechanically gated channels.

PGE2 reduces MMP-14 and increases plasminogen activator inhibitor-1 in cardiac fibroblasts

Prostaglandin E2 (PGE2) is elevated during cardiac injury and we have previously shown that mice lacking the PGE2 EP4 receptor display dilated cardiomyopathy (DCM) with increased expression of the membrane type matrix metalloproteinase, MMP-14. We thus hypothesized that PGE2 regulates expression of MMP-14 and also affects fibroblast migration. Primary cultures of neonatal rat ventricular fibroblasts (NVFs) were used to test the effects of PGE2. Gene and protein expression was assessed by real time RT-PCR and Western blot, MMP activity was determined by zymography and migration of NVF was assessed by motility in a transwell system. PGE2 reduced expression of MMP-14 and these effects were antagonized by an EP4 antagonist. An EP4 agonist mimicked the effect of PGE2. PGE2 also increased mRNA and protein levels of plasminogen activator inhibitor-1 (PAI-1), an inhibitor of MMP activation. However, PGE2-stimulation of PAI-1 was mediated by the EP1/EP3 receptor and not EP4. Migration of NVF was assessed by motility in a transwell system. Treatment of NVFs with PGE2 reduced the number of cells migrating toward 10% FCS. Treatment with the EP2 agonist also reduced migration but did not affect MMP-14 expression or PAI-1. Our results suggest that PGE2 utilizes different receptors and mechanisms to ultimately decrease MMP expression and NVF migration.

Exercise protects against chronic β-adrenergic remodeling of the heart by activation of endothelial nitric oxide synthase

Extensive data have shown that exercise training can provide cardio-protection against pathological cardiac hypertrophy. However, how long the heart can retain cardio-protective phenotype after the cessation of exercise is currently unknown. In this study, we investigated the time course of the loss of cardio-protection after cessation of exercise and the signaling molecules that are responsible for the possible sustained protection. Mice were made to run on a treadmill six times a week for 4 weeks and then rested for a period of 0, 1, 2 and 4 weeks followed by isoproterenol injection for 8 days. Morphological, echocardiographic and hemodynamic changes were measured, gene reactivation was determined by real-time PCR, and the expression and phosphorylation status of several cardio-protective signaling molecules were analyzed by Western-blot. HW/BW, HW/TL and LW/BW decreased significantly in exercise training (ER) mice. The less necrosis and lower fetal gene reactivation induced by isoproterenol injection were also found in ER mice. The echocardiographic and hemodynamic changes induced by β-adrenergic overload were also attenuated in ER mice. The protective effects can be sustained for at least 2 weeks after the cessation of the training. Western-blot analysis showed that the alterations in the phosphorylation status of endothelial nitric oxide synthase (eNOS) (increase in serine 1177 and decrease in threonine 495) continued for 2 weeks after the cessation of the training whereas increases of the phosphorylation of Akt and mTOR disappeared. Further study showed that L-NG-Nitroarginine methyl ester (L-NAME) treatment abolished the cardio-protective effects of ER. Our findings demonstrate that stimulation of eNOS in mice through exercise training provides acute and sustained cardioprotection against cardiac hypertrophy.

Fractalkine depresses cardiomyocyte contractility

Background

Our laboratory reported that male mice with cardiomyocyte-selective knockout of the prostaglandin E₂ EP4 receptor sub-type (EP4 KO) exhibit reduced cardiac function. Gene array on left ventricles (LV) showed increased fractalkine, a chemokine implicated in heart failure. We therefore hypothesized that fractalkine is regulated by PGE₂ and contributes to depressed contractility via alterations in intracellular calcium.

Methods

Fractalkine was measured in LV of 28–32 week old male EP4 KO and wild type controls (WT) by ELISA and the effect of PGE₂ on fractalkine secretion was measured in cultured neonatal cardiomyocytes and fibroblasts. The effect of fractalkine on contractility and intracellular calcium was determined in Fura-2 AM-loaded, electrical field-paced cardiomyocytes. Cardiomyocytes (AVM) from male C57Bl/6 mice were treated with fractalkine and responses measured under basal conditions and after isoproterenol (Iso) stimulation.

Results

LV fractalkine was increased in EP4 KO mice but surprisingly, PGE₂ regulated fractalkine secretion only in fibroblasts. Fractalkine treatment of AVM decreased both the speed of contraction and relaxation under basal conditions and after Iso stimulation. Despite reducing contractility after Iso stimulation, fractalkine increased the Ca²⁺ transient amplitude but decreased phosphorylation of cardiac troponin I, suggesting direct effects on the contractile machinery.

Conclusions

Fractalkine depresses myocyte contractility by mechanisms downstream of intracellular calcium.

Effect of lipopolysaccharide, cytokines, and catecholamines on brain natriuretic peptide release from human myocardium

BACKGROUND

During sepsis and septic shock, elevated plasma concentrations of brain natriuretic peptide (BNP) have been reported but may be related to several underlying mechanisms. The aim of the present experimental study was to investigate the effect of lipopolysaccharide (LPS), tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), interleukin 6 (IL-6), dobutamine (Dobu), epinephrine (Epi), and norepinephrine (Nor) on BNP synthesis by atrial human myocardium in vitro.

METHODS

After the approval of local ethics committee, right atrial appendages were obtained during cannulation for cardiac surgery and pinned in a isolated organ bath containing 15 ml of Tyrode's modified solution. Preparations were oxygenated, maintained at 36 ± 0.5°C and stimulated at a frequency of 1 Hz. A 60-min equilibration period was followed by 180-min exposure to 1 μM endothelin 1 (ET-1; n = 9), 20,000 pg/ml TNF-α (n = 10), 1000 pg/ml IL-1β (n = 10), 5000 pg/ml IL-6 (n = 10), 10,000 pg/ml LPS (n = 10), 100 μM Epi (n = 9), 100 μM Nor (n = 10), and 100 μM Dobu (n = 8). No product was added in Control group (n = 10). Two BNP dosages were performed: the first after 60 min of stabilization and the second after 180 min of stimulation. Absolute and relative changes in BNP concentration were compared between groups.

RESULTS

Exposure to ET-1 significantly increased BNP release as compared with Control group. Dobu, Epi, Nor, and LPS significantly increased BNP concentration but not TNF-α, IL-1β, or IL-6.

CONCLUSIONS

In vitro, LPS, Dobu, Epi, and Nor induced BNP synthesis by human atrial myocardium.

Prostaglandin E2 increases cardiac fibroblast proliferation and increases cyclin D expression via EP1 receptor

PGE(2) affects growth of many cell types. Thus, we hypothesized that PGE(2) would stimulate growth of cardiac fibroblasts. To test our hypothesis we used neonatal rat ventricular fibroblasts (NVF). RT-PCR demonstrated the presence of all 4 PGE(2) receptor (EPs) mRNAs in NVF. Using flow cytometry, we found that PGE(2) decreased the percentage of cells in G0/G1 and increased the number of cells in S phase. PGE(2) also increased expression of cyclin D3, a known regulator of the cell cycle and this effect was mimicked by the EP1/EP3 agonist sulprostone. Next, we found that treatment of NVF with PGE(2) increased phosphorylation of p42/44 MAPK and Akt and that PGE(2)-stimulation of cyclin D3 was antagonized with both a MEK inhibitor and a PI3 kinase inhibitor. In conclusion, PGE(2) stimulates cardiac fibroblast proliferation via EP1 and/or EP3, p42/44 MAPK and Akt-regulation of cyclin D3. These results may be relevant to cardiac fibrosis.

Tafazzin knockdown causes hypertrophy of neonatal ventricular myocytes

Mutation of the mitochondrial protein tafazzin causes dilated cardiomyopathy in Barth syndrome. We employed an adenovirus as a vector to transfer tafazzin small hairpin RNA (shRNA) into neonatal ventricular myocytes (NVMs) to investigate the effects of tafazzin knockdown. The tafazzin shRNA adenovirus consistently knocked down tafazzin mRNA and lowered cardiolipin while significantly decreasing the production of ATP by the mitochondria. The phosphorylation of AMP-activated protein kinase and mitochondrial density were both increased in tafazzin knockdown NVMs compared with scrambled shRNA controls. When we tested whether tafazzin knockdown causes hypertrophy in vitro, we found that the surface area of NVMs infected with tafazzin shRNA adenovirus was significantly increased, as were the protein synthesis and expression of the hypertrophic marker gene, brain natriuretic peptide. Taken together, our data support the concept that a decreased tafazzin expression causes cardiomyocyte hypertrophy in vitro.

Both cGMP and peroxynitrite mediate chronic interleukin-6-induced negative inotropy in adult rat ventricular myocytes

We previously showed that chronic exposure to interleukin (IL)-6 decreases contractile and sarcoplasmic reticular (SR) function assessed by postrest potentiation (PRP) via a nitric oxide (NO)-dependent mechanism in adult rat ventricular myocytes (ARVM). Cyclic GMP (cGMP) has been associated with NO-associated negative inotropic effects of IL-6 during acute exposure; however, its role in chronic cardiac effects of IL-6 remains unclear. The present study examined the roles of cGMP and peroxynitrite (ONOO-) in chronic IL-6-induced negative inotropy in ARVM. After ARVM were exposed to IL-6 for 2-24 h, intracellular cGMP contents were time dependently increased; this was mimicked by a NO donor and abolished by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase (sGC), or Rp-8-Br-cGMP, an inhibitor of cGMP-dependent protein kinase G (PKG). Meanwhile, the IL-6-induced decrease in PRP at 2 h was blocked by ODQ or Rp-8-Br-cGMP. By contrast, ODQ or Rp-8-Br-cGMP only attenuated the inhibition of PRP induced by IL-6 after 24 h exposure. Furthermore, IL-6 time dependently increased superoxide anion production and ONOO- formation; the latter was abolished by 5,10,15,20-tetrakis-(4-sulphonatophenyl)-porphyrinato iron (III) (FeTPPS), an ONOO- decomposition catalyst. Interestingly, FeTPPS had no effect on the IL-6-elicited decrease in PRP at 2 h, but attenuated it after 24 h exposure. Moreover, inhibition of sGC/cGMP/PKG, but not ONOO- formation, abolished the IL-6-induced inhibition of kinetics of myocyte contraction during 24 h exposure. We conclude that while the sGC/cGMP/PKG pathway was the primary mechanism for chronic IL-6-induced negative inotropy at 2 h, both sGC/cGMP/PKG and ONOO-, at least in part, mediate the IL-6-induced inhibition of SR function after 24 h exposure.

Regulation of hypertrophic and apoptotic signaling pathways by reactive oxygen species in cardiac myocytes

Increasing evidence suggests that oxidative and nitrosative stress play an important role in regulation of cardiac myocyte growth and survival. The cardiovascular system is continuously exposed to both reactive oxygen species (ROS) and nitrogen species (RNS), collectively termed reactive inflammatory species (RIS), and imbalances between the enzymes that regulate their bioavailability are associated with cardiac hypertrophy and the pathogenesis of cardiomyopathies, myocardial infarction and heart failure. It is now clear that RIS act as critical regulators of cardiac myocyte hypertrophy and apoptosis through control of redox-sensitive signaling cascades, such as tyrosine kinases and phosphatases, protein kinase C, and mitogen-activated protein kinases. This review will focus on the mechanisms by which ROS/RNS modulate cardiac myocyte growth and apoptosis induced by neurohormones and cytokines, and will discuss evidence for a role in the pathophysiology of heart failure.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Overexpression of endothelial nitric oxide synthase attenuates cardiac hypertrophy induced by chronic isoproterenol infusion

Endogenous nitric oxide (NO) inhibits the contractile response to beta-adrenergic stimulation, but its effect on cardiac hypertrophy mediated by beta-adrenoceptors remains unclear. The present study was designed to determine whether overproduction of endothelial NO synthase (eNOS) could inhibit cardiac hypertrophy induced by chronic isoproterenol (ISO) infusion (30mg/kg per day) using eNOS overexpressing (eNOS-Tg) mice and wild-type (WT) mice. In a separate group, WT mice were treated with ISO and hydralazine to decrease blood pressure to the same levels in eNOS-Tg mice. The eNOS expression, NOS activity, and cGMP levels in the heart were remarkably higher in eNOS-Tg mice than in WT mice. ISO increased both heart weight and the heart/body weight ratio, which were significantly attenuated in eNOS-Tg mice compared with WT or hydralazine-treated WT mice. Histological examination revealed that the extent of fibrosis was not significantly different among the 3 groups, and that the increase in myocyte size was more than 10% lower in eNOS-Tg than in the other groups. In addition, up-regulated expression of atrial natriuretic peptide mRNA associated with cardiac hypertrophy was significantly inhibited in eNOS-Tg mice during ISO infusion. These results indicate that endogenous NO might act as a negative modulator for the hypertrophic response to beta-adrenergic stimulation.

Phorbol ester stimulates cyclooxygenase-2 expression and prostanoid production in cardiac myocytes

Phorbol-12-myristate- 13-acetate (PMA) has been shown to induce hypertrophy of cardiac myocytes. The prostaglandin endoperoxide H synthase isoform 2 (cyclooxygenase-2, COX-2) has been associated with enhanced growth and/or proliferation of several types of cells. Thus we studied whether PMA induces COX-2 and prostanoid products PGE(2) and PGF(2alpha) in neonatal ventricular myocytes and whether endogenous COX-2 products participate in their growth. In addition, we examined whether PMA affects interleukin-1beta (IL-1beta) stimulation of COX-2 and PGE(2) production. PMA (0.1 micromol/l) stimulated growth, as indicated by a 1.6-fold increase in [(3)H]leucine incorporation. PMA increased COX-2 protein levels 2. 8-fold, PGE(2) 3.7-fold, and PGF(2alpha) 2.9-fold. Inhibition of either p38 kinase or protein kinase C (PKC) prevented PMA-stimulated COX-2. Inhibition of COX-2 with either indomethacin or NS-398 had no effect on PMA-stimulated [(3)H]leucine incorporation. Exogenous administration of PGF(2alpha), but not PGE(2), stimulated protein synthesis. Treatment with IL-1beta (5 ng/ml) increased COX-2 protein levels 42-fold, whereas cotreatment with IL-1beta and PMA stimulated COX-2 protein only 32-fold. IL-1beta did not affect control or PMA-stimulated protein synthesis. These findings indicate that: 1) PMA, acting through PKC and p38 kinase, enhances COX-2 expression, but chronic treatment with PMA partially inhibits IL-1beta stimulation of COX-2; and 2) exogenous PGF(2alpha) is involved in neonatal ventricular myocyte growth but endogenous COX-2 products are not.

Isoproterenol and cAMP regulation of the human brain natriuretic peptide gene involves Src and Rac

Brain natriuretic peptide (BNP) gene expression and chronic activation of the sympathetic nervous system are characteristics of the development of heart failure. We studied the role of the beta-adrenergic signaling pathway in regulation of the human BNP (hBNP) promoter. An hBNP promoter (-1818 to +100) coupled to a luciferase reporter gene was transferred into neonatal cardiac myocytes, and luciferase activity was measured as an index of promoter activity. Isoproterenol (ISO), forskolin, and cAMP stimulated the promoter, and the beta(2)-antagonist ICI 118,551 abrogated the effect of ISO. In contrast, the protein kinase A (PKA) inhibitor H-89 failed to block the action of cAMP and ISO. Pertussis toxin (PT), which inactivates Galpha(i), inhibited ISO- and cAMP-stimulated hBNP promoter activity. The Src tyrosine kinase inhibitor PP1 and a dominant-negative mutant of the small G protein Rac also abolished the effect of ISO and cAMP. Finally, we studied the involvement of M-CAT-like binding sites in basal and inducible regulation of the hBNP promoter. Mutation of these elements decreased basal and cAMP-induced activity. These data suggest that beta-adrenergic regulation of hBNP is PKA independent, involves a Galpha(i)-activated pathway, and targets regulatory elements in the proximal BNP promoter.

Wnt-1 regulation of connexin43 in cardiac myocytes

Gap junction channels composed of connexin43 (Cx43) are essential for normal heart formation and function. We studied the potential role of the Wnt family of secreted polypeptides as regulators of Cx43 expression and gap junction channel function in dissociated myocytes and intact hearts. Neonatal rat cardiomyocytes responded to Li(+), which mimics Wnt signaling, by accumulating the effector protein beta-catenin and by inducing Cx43 mRNA and protein markedly. Induction of Cx43 expression was also observed in cardiomyocytes cocultured with Rat-2 fibroblasts or N2A neuroblastoma cells programmed to secrete bioactive Wnt-1. By transfecting a Cx43 promoter-reporter gene construct into cardiomyocytes, we demonstrated that the inductive effect of Wnt signaling was transcriptionally mediated. Enhanced expression of Cx43 increased cardiomyocyte cell coupling, as determined by Lucifer Yellow dye transfer and by calcium wave propagation. Conversely, in a transgenic cardiomyopathic mouse model that exhibits ventricular arrhythmias and gap junctional remodeling, beta-catenin and Cx43 expression were downregulated concordantly. In response to Wnt signaling, the accumulating Cx43 colocalized with beta-catenin in the junctional membrane; moreover, forced expression of Cx43 in cardiomyocytes reduced the transactivation potential of beta-catenin. These findings demonstrate that Wnt signaling is an important modulator of Cx43-dependent intercellular coupling in the heart, and they support the hypothesis that dysregulated signaling contributes to altered impulse propagation and arrhythmia in the myopathic heart.

Effect of interleukin-1 beta on cardiac hypertrophy and production of natriuretic peptides in rat cardiocyte culture

This study was designed to examine the effects of interleukin-1 beta (IL-1 beta) on myocyte (MC) hypertrophy and the production of A-type natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in rat ventricular cardiocyte culture, and to investigate the role of nonmyocyte (NMC) in this process. We examined the effects of IL-1 beta on the production of ANP and BNP in comparison with the effects of endothelin-1 (ET-1) by using two types of neonatal rat cardiocyte culture; MC-enriched culture and MC-NMC coculture. In the MC-enriched culture, the increase in secretion of ANP and BNP was small in treatment with IL-1 beta (1000 pg/ml), while ET-1 (10 nM) markedly augmented the secretion of ANP and BNP. In the MC-NMC coculture, IL-1 beta and ET-1 each significantly augmented the secretion of ANP and BNP. The degree of the increase of ANP and BNP was equivalent between IL-1 beta and ET-1. As for the morphological changes of MCs, IL-1 beta induced the star-shaped MC hypertrophy characterized by elongation and pointed edges only in the MC-NMC coculture, while ET-1 induced the MC hypertrophy characterized by shapes of squares, triangles or circles in both cultures. This study shows that IL-1 beta induces unique cardiac hypertrophy and the marked secretion of ANP and BNP, and that NMC is indispensable when treated with IL-1 beta.

Effects of endotoxin on human myocardial contractility involvement of nitric oxide and peroxynitrite

OBJECTIVES

This study examined the effects of endotoxin on cardiac contractility in human myocardium.

BACKGROUND

In animal myocardium, endotoxin and cytokine treatment led to enhanced inducible nitric oxide synthase (iNOS) expression and contractile dysfunction. Effects in human myocardium are unknown.

METHODS

Left ventricular myocardial preparations from failing (n = 18) and nonfailing (n = 5) human hearts were incubated for 6 and 12 h in tyrode solution or in tyrode plus lipopolysaccharides (LPS), with LPS plus N(G)-mono-methyl-L-arginine (L-NMMA), with LPS plus hemoglobin or with LPS plus the superoxide scavenger 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron). Force of contraction in response to isoprenaline (0.001 to 3 micromol/liter) was determined in electrically stimulated muscle preparations. The iNOS mRNA expression was examined by in situ hybridization and by polymerase chain reaction. The cyclic guanosine monophosphate (cGMP) levels were determined by radioimmunoassay.

RESULTS

Isoprenaline concentration dependently increased force of contraction. Six and 12 hours of LPS treatment of failing myocardium decreased maximum inotropic response to isoprenaline by 54% (p = 0.009) and by 69% (p = 0.0023), respectively. In nonfailing myocardium, 12 h of LPS treatment decreased maximum inotropic effect of isoprenaline by 66% (p < 0.001). The LPS effects were attenuated by L-NMMA, hemoglobin and also Tiron. The iNOS mRNA was expressed in all LPS-treated preparations but also in most control myocardial preparations. In situ hybridization revealed iNOS expression within cardiac myocytes. There was no increase in myocardial cGMP content in response to endotoxin.

CONCLUSIONS

Endotoxin exposure of human myocardium leads to a depression of cardiac contractility, which is mediated by enhanced iNOS activity and release of nitric oxide (NO). Consecutive reaction of NO with superoxide and formation of peroxynitrite may contribute to the decrease in force of contraction.

Cardiac fibroblasts arrest at the G1/S restriction point in response to interleukin (IL)-1beta. Evidence for IL-1beta-induced hypophosphorylation of the retinoblastoma protein

Although responsible for only approximately one-third of the overall myocardial mass, the interstitial fibroblasts of the heart serve a fundamental role in establishing the functional integrity of myocardium and are the major source of myocardial extracellular matrix production. Their importance in clinical medicine is underscored by the observation that fibroblast numbers increase in response to several pathologic circumstances that are associated with an increase in extracellular matrix production, such as long standing hypertension and myocardial injury/infarction. Up to the present time, however, there has been little information available on either the kinetics of the cardiac fibroblast cell cycle, or the fundamental mechanisms that regulate its entry into and exit from the cell cycle. Previous work from our laboratory examining the effects of interleukin (IL)-1beta on myocardial growth and gene expression in culture indicated that cardiac fibroblasts have a diminished capacity to synthesize DNA in response to mitogen in the presence of this cytokine. The mechanism of IL-1beta action was not clear, however, and could have resulted from action at several different points in the cell cycle. The investigations described in this report indicate that IL-1beta exerts its effect on the fibroblast cell cycle at multiple levels through altering the expression of cardiac fibroblast cyclins, cyclin-dependent kinases, and their inhibitors, which ultimately affect the phosphorylation of the retinoblastoma gene product.

Angiotensin II-induced hypertrophy of adult rat cardiomyocytes is blocked by nitric oxide

The aim of the present study was to test the hypothesis that bradykinin-stimulated release of nitric oxide (NO) and/or prostacyclin from endothelium blocks myocyte hypertrophy in vitro. Angiotensin II increased [3H]phenylalanine incorporation by 21 +/- 2% in myocytes cocultured with endothelial cells; this was abolished by bradykinin in the presence of endothelial cells. Bradykinin increased cytosolic concentrations of cGMP by 29 +/- 4% in myocytes cocultured with endothelial cells. This was abolished by inhibition of NO synthase and by a cyclooxygenase inhibitor. Angiotensin II also increased [3H]phenylalanine incorporation by 28 +/- 3% in myocytes cultured in the absence of endothelial cells. This effect of angiotensin II in monoculture was abolished by donors of NO but not by bradykinin. Neither the stable analog of prostacyclin (iloprost) nor the prostacyclin second messanger analog 8-bromo-cAMP (8-BrcAMP) blocked the effect of angiotensin II. Furthermore, 8-BrcAMP and iloprost individually increased [3H]phenylalanine incorporation. The antihypertrophic effects of bradykinin are critically dependent on endothelium-derived NO.

Chronic L-arginine treatment increases cardiac cyclic guanosine 5'-monophosphate in rats with aortic stenosis: effects on left ventricular mass and beta-adrenergic contractile reserve

OBJECTIVES

We tested the hypothesis that nitric oxide (NO) cyclic guanosine 5'-monophosphate (GMP) signaling is deficient in pressure overload hypertrophy due to ascending aortic stenosis, and that long-term L-arginine treatment will increase cardiac cyclic GMP production and modify left ventricular (LV) pressure overload hypertrophy and beta-adrenergic contractile response.

BACKGROUND

Nitric oxide cyclic GMP signaling is postulated to depress vascular growth, but its effects on cardiac hypertrophic growth are controversial.

METHODS

Forty control rats and 40 rats with aortic stenosis left ventricular hypertrophy ([LVH] group) were randomized to receive either L-arginine (0.40 g/kg/day) or no drug for 6 weeks.

RESULTS

The dose of L-arginine did not alter systemic blood pressure. Animals with LVH had similar LV constitutive nitric oxide synthase (cNOS) mRNA and protein levels, and LV cyclic GMP levels as compared with age-matched controls. In rats with LVH L-arginine treatment led to a 35% increase in cNOS protein levels (p = 0.09 vs untreated animals with LVH) and a 1.7-fold increase in LV cyclic GMP levels (p < 0.05 vs untreated animals with LVH). However, L-arginine treatment did not suppress LVH in the animals with aortic stenosis. In contrast, in vivo LV systolic pressure was depressed in L-arginine treated versus untreated rats with LVH (163 +/- 16 vs 198 +/- 10 mm Hg, p < 0.05). In addition, the contractile response to isoproterenol was blunted in both isolated intact hearts and isolated myocytes from L-arginine treated rats with LVH compared with untreated rats with LVH. This effect was mediated by a blunted increase in peak systolic intracellular calcium in response to beta-adrenergic stimulation.

CONCLUSIONS

Left ventricular hypertrophy due to chronic mechanical systolic pressure overload is not characterized by a deficiency of LV cNOS and cyclic GMP levels. In rats with aortic stenosis, L-arginine treatment increased cardiac levels of cyclic GMP, but it did not modify cardiac mass in rats with aortic stenosis. However, long-term stimulation of NO-cyclic GMP signaling depressed in vivo LV systolic function in LVH rats and markedly blunted the contractile response to beta-adrenergic stimulation.

Nitric oxide, atrial natriuretic peptide, and cyclic GMP inhibit the growth-promoting effects of norepinephrine in cardiac myocytes and fibroblasts

This study tested the hypothesis that nitric oxide (NO) and atrial natriuretic peptide (ANP) can attenuate the effects of adrenergic agonists on the growth of cardiac myocytes and fibroblasts. In ventricular cells cultured from neonatal rat heart, ANP and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) caused concentration-dependent decreases in the norepinephrine (NE)-stimulated incorporation of [3H]leucine in myocytes and [3H]thymidine in fibroblasts. In myocytes, the NO synthase inhibitor NG-monomethyl-L-arginine potentiated NE-stimulated [3H]leucine incorporation. In both cell types, ANP and SNAP increased intracellular cGMP levels, and their growth-suppressing effects were mimicked by the cGMP analogue 8-bromo-cGMP. Furthermore, in myocytes, 8-bromo-cGMP attenuated the alpha1-adrenergic receptor-stimulated increases in c-fos. Likewise, ANP and 8-bromo-cGMP attenuated the alpha1-adrenergic receptor- stimulated increase in prepro-ANP mRNA and the alpha1-adrenergic receptor-stimulated decrease in sarcoplasmic reticulum calcium ATPase mRNA. The L-type Ca2+ channel blockers verapamil and nifedipine inhibited NE-stimulated incorporation of [3H]leucine in myocytes and [3H]thymidine in fibroblasts, and these effects were not additive with those of ANP, SNAP, or 8-bromo-cGMP. In myocytes, the Ca2+ channel agonist BAY K8644 caused an increase in [3H]leucine incorporation which was inhibited by ANP. These findings indicate that NO and ANP can attenuate the effects of NE on the growth of cardiac myocytes and fibroblasts, most likely by a cGMP-mediated inhibition of NE-stimulated Ca2+ influx.