Norepinephrine-induced interleukin-6 increase in rat hearts: differential signal transduction in myocytes and non-myocytes

The Microenvironment of the Pathogenesis of Cardiac Hypertrophy

Pathological cardiac hypertrophy is a key risk factor for the development of heart failure and predisposes individuals to cardiac arrhythmia and sudden death. While physiological cardiac hypertrophy is adaptive, hypertrophy resulting from conditions comprising hypertension, aortic stenosis, or genetic mutations, such as hypertrophic cardiomyopathy, is maladaptive. Here, we highlight the essential role and reciprocal interactions involving both cardiomyocytes and non-myocardial cells in response to pathological conditions. Prolonged cardiovascular stress causes cardiomyocytes and non-myocardial cells to enter an activated state releasing numerous pro-hypertrophic, pro-fibrotic, and pro-inflammatory mediators such as vasoactive hormones, growth factors, and cytokines, i.e., commencing signaling events that collectively cause cardiac hypertrophy. Fibrotic remodeling is mediated by cardiac fibroblasts as the central players, but also endothelial cells and resident and infiltrating immune cells enhance these processes. Many of these hypertrophic mediators are now being integrated into computational models that provide system-level insights and will help to translate our knowledge into new pharmacological targets. This perspective article summarizes the last decades' advances in cardiac hypertrophy research and discusses the herein-involved complex myocardial microenvironment and signaling components.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Left ventricular depression and pulmonary edema in rats after short-term normobaric hypoxia: effects of adrenergic blockade and reduced fluid load

Acute normobaric hypoxia may induce pulmonary injury with edema (PE) and inflammation. Hypoxia is accompanied by sympathetic activation. As both acute hypoxia and high plasma catecholamine levels may elicit PE, we had originally expected that adrenergic blockade may attenuate the severity of hypoxic pulmonary injury. In particular, we investigated whether administration of drugs with reduced fluid load would be beneficial with respect to both cardiocirculatory and pulmonary functions in acute hypoxia. Rats were exposed to normobaric hypoxia (10% O₂) over 1.5 or 6 h and received 0.9% NaCl or adrenergic blockers either as infusion (1 ml/h, increased fluid load) or injection (0.5 ml, reduced fluid load). Control animals were kept in normoxia and received infusions or injections of 0.9% NaCl. After 6 h of hypoxia, LV inotropic function was maintained with NaCl injection but decreased significantly with NaCl infusion. Adrenergic blockade induced a similar LV depression when fluid load was low, but did not further deteriorate LV depression after 6 h of infusion. Reduced fluid load also attenuated pulmonary injury after 6 h of hypoxia. This might be due to an effective fluid drainage into the pleural space. Adrenergic blockade could not prevent PE. In general, increased fluid load and impaired LV inotropic function promote the development of PE in acute hypoxia. The main physiologic conclusion from this study is that fluid reduction under hypoxic conditions has a protective effect on cardiopulmonary function. Consequently, appropriate fluid management has particular importance to subjects in hypoxic conditions.

Immunometabolic cross-talk in the inflamed heart

Inflammatory processes underlie many diseases associated with injury of the heart muscle, including conditions without an obvious inflammatory pathogenic component such as hypertensive and diabetic cardiomyopathy. Persistence of cardiac inflammation can cause irreversible structural and functional deficits. Some are induced by direct damage of the heart muscle by cellular and soluble mediators but also by metabolic adaptations sustained by the inflammatory microenvironment. It is well established that both cardiomyocytes and immune cells undergo metabolic reprogramming in the site of inflammation, which allow them to deal with decreased availability of nutrients and oxygen. However, like in cancer, competition for nutrients and increased production of signalling metabolites such as lactate initiate a metabolic cross-talk between immune cells and cardiomyocytes which, we propose, might tip the balance between resolution of the inflammation versus adverse cardiac remodeling. Here we review our current understanding of the metabolic reprogramming of both heart tissue and immune cells during inflammation, and we discuss potential key mechanisms by which these metabolic responses intersect and influence each other and ultimately define the prognosis of the inflammatory process in the heart.

Social defeat stimulates local glucocorticoid regeneration in lymphoid organs

Stress is an important risk factors for human diseases. It activates the hypothalamic-pituitary-adrenal (HPA) axis and increases plasma glucocorticoids, which are powerful regulators of immune system. The response of the target cells to glucocorticoids depends not only on the plasma concentrations of cortisol and corticosterone but also on their local metabolism. This metabolism is catalyzed by 11β-hydroxysteroid dehydrogenases type 1 and 2, which interconvert glucocorticoid hormones cortisol and corticosterone and their 11-oxo metabolites cortisone and 11-dehydrocorticosterone. The goal of this study was to determine whether stress modulates glucocorticoid metabolism within lymphoid organs - the structures where immune cells undergo development and activation. Using the resident-intruder paradigm, we studied the effect of social stress on glucocorticoid metabolism in primary and secondary lymphoid organs of Fisher 344 (F344) and Lewis (LEW) rats, which exhibit marked differences in their HPA axis response to social stressors and inflammation. We show that repeated social defeat increased the regeneration of corticosterone from 11-dehydrocorticosterone in the thymus, spleen and mesenteric lymphatic nodes (MLN). Compared with the F344 strain, LEW rats showed higher corticosterone regeneration in splenocytes of unstressed rats and in thymic and MLN mobile cells after stress but corticosterone regeneration in the stroma of all lymphoid organs was similar in both strains. Inactivation of corticosterone to 11-dehydrocorticosterone was found only in the stroma of lymphoid organs but not in mobile lymphoid cells and was not upregulated by stress. Together, our findings demonstrate the tissue- and strain-dependent regeneration of glucocorticoids following social stress.

IDH2 deficiency promotes mitochondrial dysfunction and cardiac hypertrophy in mice

Cardiac hypertrophy, a risk factor for heart failure, is associated with enhanced oxidative stress in the mitochondria, resulting from high levels of reactive oxygen species (ROS). The balance between ROS generation and ROS detoxification dictates ROS levels. As such, disruption of these processes results in either increased or decreased levels of ROS. In previous publications, we have demonstrated that one of the primary functions of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDH2) is to control the mitochondrial redox balance, and thereby mediate the cellular defense against oxidative damage, via the production of NADPH. To explore the association between IDH2 expression and cardiac function, we measured myocardial hypertrophy, apoptosis, and contractile dysfunction in IDH2 knockout (idh2(-/-)) and wild-type (idh2(+/+)) mice. As expected, mitochondria from the hearts of knockout mice lacked IDH2 activity and the hearts of IDH2-deficient mice developed accelerated heart failure, increased levels of apoptosis and hypertrophy, and exhibited mitochondrial dysfunction, which was associated with a loss of redox homeostasis. Our results suggest that IDH2 plays an important role in maintaining both baseline mitochondrial function and cardiac contractile function following pressure-overload hypertrophy, by preventing oxidative stress.

Influence of gestational overfeeding on myocardial proinflammatory mediators in fetal sheep heart

Maternal overnutrition is associated with predisposition of offspring to cardiovascular disease in later life. Since maternal overnutrition may promote fetal and placental inflammatory responses, we hypothesized that maternal overnutrition/obesity increases expression of fetal cardiac proinflammatory mediators and alter cardiac morphometry. Multiparous ewes were fed either 150% of National Research Council (NRC) nutrient recommendations (overfed) or 100% of NRC requirement (control) from 60 days prior to mating to gestation Day 75 (D75), when ewes were euthanized. An additional cohort of overfed and control ewes were necropsied on D135. Cardiac morphometry, histology, mRNA and protein expression of toll-like receptor 4, iNOS, IL-1a, IL-1b, IL-6, IL-18, CD-14, CD-68, M-CSF and protein levels of phosphorylated I-κB and nuclear factor κB (NF-κB) were examined. Immunohistochemistry was performed to assess neutrophil and monocyte infiltration. Crown rump length, left and right ventricular free wall weights as well as left and right ventricular wall thickness were significantly increased in D75 fetuses of overfed mothers. Hematoxylin and eosin staining revealed irregular myofiber orientation and increased interstitial space in fetal ventricular tissues born to overfed mothers. Oil red O staining exhibited marked lipid droplet accumulation in the overfed fetuses. Overfeeding significantly enhanced TLR4, IL-1a, IL-1b IL-6 expression, promoted phosphorylation of IκB, decreased cytoplasmic NF-κB levels and increased neutrophil and monocyte infiltration. Collectively, these data suggest that maternal overfeeding prior to and throughout gestation leads to inflammation in the fetal heart and alters fetal cardiac morphometry.

p42/p44-MAPK and PI3K are sufficient for IL-6 family cytokines/gp130 to signal to hypertrophy and survival in cardiomyocytes in the absence of JAK/STAT activation

The effect of differential signalling by IL-6 and leukaemia inhibitory factor (LIF) which signal by gp130 homodimerisation or LIFRβ/gp130 heterodimerisation on survival and hypertrophy was studied in neonatal rat cardiomyocytes. Both LIF and IL-6 [in the absence of soluble IL-6 receptor (sIL-6Rα)] activated Erk1/2, JNK1/2, p38-MAPK and PI3K signalling peaking at 20 min and induced cytoprotection against simulated ischemia-reperfusion injury which was blocked by the MEK1/2 inhibitor PD98059 but not the p38-MAPK inhibitor SB203580. In the absence of sIL-6R, IL-6 did not induce STAT1/3 phosphorylation, whereas IL-6/sIL-6R and LIF induced STAT1 and STAT3 phosphorylation. Furthermore, IL-6/sIL-6R induced phosphorylation of STAT1 Tyr⁷⁰¹ and STAT3 Tyr⁷⁰⁵ were enhanced by SB203580. IL-6 and pheneylephrine (PE), but not LIF, induced cardiomyocyte iNOS expression and nitric oxide (NO) production. IL-6, LIF and PE induced cardiomyocyte hypertrophy, but with phenotypic differences in ANF and SERCA2 expression and myofilament organisation with IL-6 more resembling PE than LIF. Transfection of cardiomyocytes with full length or truncated chimaeric gp130 cytoplasmic domain/Erythropoietin receptor (EpoR) extracellular domain fusion constructs showed that the membrane proximal Box 1 and Box 2 containing region of gp130 was necessary and sufficient for MAPK and PI3K activation; hypertrophy; SERCA2 expression and iNOS/NO induction in the absence of JAK/STAT activation. In conclusion, IL-6 can signal in cardiomyocytes independent of sIL-6R and STAT1/3 and furthermore, that Erk1/2 and PI3K activation by IL-6 are both necessary and sufficient for induced cardioprotection. In addition, p38-MAPK may act as a negative feedback regulator of JAK/STAT activation in cardiomyocytes.

Contribution of α - and β -Adrenergic Mechanisms to the Development of Pulmonary Edema

Endogenous or exogenous catecholamines can induce pulmonary edema (PE). This may occur in human pathologic conditions such as in pheochromocytoma or in neurogenic pulmonary edema (NPE) but can also be provoked after experimental administration of adrenergic agonists. PE can result from stimulation with different types of adrenergic stimulation. With α-adrenergic treatment, it develops more rapidly, is more severe with abundant protein-rich fluid in the alveolar space, and is accompanied by strong generalized inflammation in the lung. Similar detrimental effects of α-adrenergic stimulation have repeatedly been described and are considered to play a pivotal role in NPE or in PE in patients with pheochromocytoma. Although β-adrenergic agonists have often been reported to prevent or attenuate PE by enhancing alveolar fluid clearance, PE may also be induced by β-adrenergic treatment as can be observed in tocolysis. In experimental models, infusion of β-adrenergic agonists induces less severe PE than α-adrenergic stimulation. The present paper addresses the current understanding of the possible contribution of α- and β-adrenergic pathways to the development of PE.

Rad GTPase inhibits cardiac fibrosis through connective tissue growth factor

AIMS

Our previous studies documented that Rad (Ras associated with diabetes), a member of the RGK (Rad, Gem, and Kir) family of Ras-related small G protein, is significantly decreased in human failing hearts and plays an important role in attenuating cardiac hypertrophy. The goal of this study is to identify the effect of Rad on cardiac fibrosis and the underlying mechanisms.

METHODS AND RESULTS

Rad knockout (KO) mice showed more severe cardiac fibrosis compared with wild-type littermate controls as detected by Sirius Red staining. Western blot analyses demonstrated that the expression of connective tissue growth factor (CTGF), a key mediator of fibrosis, increased dramatically in Rad KO mice. Overexpression of Rad in cultured neonatal cardiomyocytes suppressed both basal and transforming growth factor-β1-induced CTGF expression. Elevated CTGF expression was observed in cardiomyocytes when Rad was reduced by RNA interference. Moreover, cardiac fibroblasts produced greater extracellular matrix (ECM) when stimulated with conditioned medium from Rad-knockdown cardiomyocytes. ECM production was completely abolished by adding a CTGF-neutralizing antibody into the medium. CCAAT/enhancer-binding protein δ (C/EBP-δ) was demonstrated to activate CTGF in cardiomyocytes. Chromatin immunoprecipitation assay and co-immunoprecipitation further demonstrated that Rad inhibited the binding of C/EBP-δ to the CTGF promoter via direct interaction with C/EBP-δ.

CONCLUSION

Our data reveal that Rad deficiency can lead to cardiac fibrosis. Rad inhibits CTGF expression through binding with C/EBP-δ, thus regulating ECM production in the heart. This study suggests a potential link between decreased Rad levels and increased cardiac fibrosis in human failing hearts.

Stress hormones increase cell proliferation and regulates interleukin-6 secretion in human oral squamous cell carcinoma cells

Patients with oral cancer can have high psychological distress levels, but the effects of stress-related hormones on oral cancer cells and possible mechanisms underlying these relationships are unknown. In this study, we have investigated the effects of stress-related hormones on interleukin-6 (IL-6) secretion and proliferation of oral squamous cell carcinoma (OSCC) cells. The effects of norepinephrine (NE), and cortisol were studied in SCC9, SCC15, and SCC25 cells and effects of isoproterenol in SCC9 and SCC25 cells. Real-time PCR studies revealed constitutive β1- and β2-adrenergic receptors (β-ARs) expression in the SCC9, SCC15, and SCC25 cells. The results showed that NE and isoproterenol significantly enhanced IL-6 mRNA expression and protein production in supernatants of SCC9 and SCC25 cells. Physiological stress levels of NE and isoproterenol (10 μM) at 1 h elicited the most robust IL-6 increase. Regarding IL-6 secretion, 10 μM NE induced a 5-fold increase at 1 h, 3.7-fold increase at 6 h, and 3.2-fold at 24 h in SCC9 cells. These effects were blocked by the β-adrenergic antagonist propranolol, supporting a role for β-ARs in IL-6 secretion. The effects of cortisol varied according to the hormone concentration. Pharmacological concentrations of cortisol (1000 nM) inhibited IL-6 production by SCC9 and SCC25 cells. Cortisol dose that simulates stress conditions (10 nM) tended to increase IL-6 expression in SCC9 cells. Hormonal doses that simulate stress conditions (10 μM NE, at 6 h in SCC9 and SCC15 cells and 10 nM cortisol, at 48 h in SCC15 cells) stimulated increased cell proliferation. Treatment of SCC9 cells with IL-6 neutralizing ab (10 μg/mL) partially inhibited NE-induced proliferation. Finally, 20 OSCC biopsies were shown to express β1- and β2-ARs. These findings suggest that stress hormones can affect oral cancer cells behavior.

TGF-beta, IL-6, IL-17 and CTGF direct multiple pathologies of chronic cardiac allograft rejection

Cardiac transplantation is an effective treatment for heart failure refractive to therapy. Although immunosuppressive therapeutics have increased first year survival rates, chronic rejection remains a significant barrier to long-term graft survival. Chronic rejection manifests as patchy interstitial fibrosis, vascular occlusion and progressive loss of graft function. Recent evidence from experimental and patient studies suggests that the development of cardiomyocyte hypertrophy is another hallmark of chronic cardiac allograft rejection. This pathologic hypertrophy is tightly linked to the immune cytokine IL-6, which promotes facets of chronic rejection in concert with TGF-beta and IL-17. These factors potentiate downstream mediators, such as CTGF, which promote the fibrosis associated with the disease. In this article, we summarize contemporary findings that have revealed several elements involved in the induction and progression of chronic rejection of cardiac allografts. Further efforts to elucidate the interplay between these factors may direct the development of targeted therapies for this disease.

Computational identification of gene-social environment interaction at the human IL6 locus

To identify genetic factors that interact with social environments to impact human health, we used a bioinformatic strategy that couples expression array-based detection of environmentally responsive transcription factors with in silico discovery of regulatory polymorphisms to predict genetic loci that modulate transcriptional responses to stressful environments. Tests of one predicted interaction locus in the human IL6 promoter (SNP rs1800795) verified that it modulates transcriptional response to beta-adrenergic activation of the GATA1 transcription factor in vitro. In vivo validation studies confirmed links between adverse social conditions and increased transcription of GATA1 target genes in primary neural, immune, and cancer cells. Epidemiologic analyses verified the health significance of those molecular interactions by documenting increased 10-year mortality risk associated with late-life depressive symptoms that occurred solely for homozygous carriers of the GATA1-sensitive G allele of rs1800795. Gating of depression-related mortality risk by IL6 genotype pertained only to inflammation-related causes of death and was associated with increased chronic inflammation as indexed by plasma C-reactive protein. Computational modeling of molecular interactions, in vitro biochemical analyses, in vivo animal modeling, and human molecular epidemiologic analyses thus converge in identifying beta-adrenergic activation of GATA1 as a molecular pathway by which social adversity can alter human health risk selectively depending on individual genetic status at the IL6 locus.

Sleep and biomarkers of atherosclerosis in elderly Alzheimer caregivers and controls

BACKGROUND

Perturbed sleep might contribute to cardiovascular disease by accelerating atherosclerosis. Sleep is poor in Alzheimer caregivers who are also a group at increased cardiovascular risk.

OBJECTIVE

To test the hypothesis that impaired sleep relates to elevated levels of biomarkers of atherosclerosis in community-dwelling elderly and that this association would possibly be stronger in caregivers than in non-caregiving controls.

METHODS

We studied 97 Alzheimer caregivers and 48 non-caregiving controls (mean age 71 +/- 8 years, 72% women) who underwent wrist actigraphy at their homes. Measures of objective sleep were averaged across 3 consecutive nights. The Pittsburgh Sleep Quality Index was administered by an interviewer to rate subjective sleep quality. Morning fasting blood samples were collected to determine measures of inflammation, coagulation and endothelial dysfunction.

RESULTS

There were independent associations between decreased subjective sleep quality and increased levels of fibrin D-dimer (p = 0.022, DeltaR(2) = 0.029) and von Willebrand factor antigen (p = 0.029, DeltaR(2) = 0.034) in all participants. Percent sleep (p = 0.025) and subjective sleep quality (p = 0.017) were lower in caregivers than in controls. In caregivers, the correlation between decreased percent sleep and elevated levels of interleukin-6 (p = 0.042, DeltaR(2) = 0.039) and C-reactive protein (p < 0.10, DeltaR(2) = 0.027) was significantly stronger than in controls.

CONCLUSION

Perceived impairment in sleep related to increased coagulation activity and endothelial dysfunction in all participants, whereas objectively impaired sleep related to inflammation activity in caregivers. The findings provide one explanation for the increased cardiovascular risk in elderly poor sleepers and dementia caregivers in particular.

Suppression of collagen production in norepinephrine stimulated cardiac fibroblasts culture: differential effect of alpha and beta-adrenoreceptor antagonism

OBJECTIVES

Prolonged sympathetic activation is damaging to the heart and experimental norepinephrine (NE) infusion induces the deposition of myocardial collagen. This study investigated the effects of NE on collagen and transforming growth factor-beta1 (TGF-beta1) gene expression in rat cardiac fibroblasts (CF) culture, and compared the anti-fibrotic effect of alpha and beta (both selective and non-selective adrenergic receptor antagonists) receptors.

METHODS AND RESULTS

Rat CF were cultured in the presence of NE (0.01 to 100 muM) for 24 hours. Procollagen types I and III as well as TGF-beta1 gene expressions were measured by real-time quantitative PCR method. Collagen protein level was measured by Sirius red-based colorimetric method and Western blot analysis. The optimal dose of NE on fibrogenesis was 0.1 muM. Incubation for 24 hours increased procollagen I, III and TGF-beta1 gene expression by 1.35 +/- 0.23, 1.26 +/- 0.16 and 1.35 +/- 0.21 fold, respectively (all p < 0.05). The collagen protein was increased by both Sirius-red assay (0.120 +/- 0.03 vs 0.093 +/- 0.04 microg/total microg of protein, p < 0.05) and Western blot analysis (1.29 +/- 0.26 fold, p < 0.05), when compared with the control group. Addition of carvedilol (a non-selective beta-blocker with alpha-blockage activity) inhibited the effect of NE on procollagen I (0.64 +/- 0.17 vs 1.28 +/- 0.08 fold, p < 0.01), procollagen III gene (0.47 +/- 0.16 vs 1.45 +/- 0.29 fold, p < 0.01) and collagen protein expressions (0.99 +/- 0.12 vs 1.26 +/- 0.31 fold, p < 0.05, respectively). Doxazosin (an alpha-blocker) also inhibited the effect of NE on procollagen I (0.88 +/- 0.30 vs 1.28 +/- 0.08 fold, p < 0.01), procollagen III gene (0.64 +/- 0.13 vs 1.45 +/- 0.29 fold, p < 0.01) and collagen protein expression (0.90 +/- 0.11 vs 1.26 +/- 0.31 fold, p < 0.01 respectively). Such inhibitory effects were not seen in metoprolol (a beta1-selective blocker) and propranolol (a non-selective beta blocker). Furthermore, all the 4 drugs were unable to inhibit the NE induced TGF-beta1 gene over-expression.

CONCLUSIONS

In conclusion, NE increased collagen gene and protein expressions in CF culture. This effect is likely mediated through alpha-receptor as they were normalized by pretreatment with carvedilol and doxazosin, but not beta-blockers such as propranolol and metoprolol. Also, TGF-beta1 doesn't seem to play a role in carvedilol inhibition of NE induced fibrogenesis.

Critical role for IL-6 in hypertrophy and fibrosis in chronic cardiac allograft rejection

Chronic cardiac allograft rejection is the major barrier to long term graft survival. There is currently no effective treatment for chronic rejection except re-transplantation. Though neointimal development, fibrosis, and progressive deterioration of graft function are hallmarks of chronic rejection, the immunologic mechanisms driving this process are poorly understood. These experiments tested a functional role for IL-6 in chronic rejection by utilizing serial echocardiography to assess the progression of chronic rejection in vascularized mouse cardiac allografts. Cardiac allografts in mice transiently depleted of CD4+ cells that develop chronic rejection were compared with those receiving anti-CD40L therapy that do not develop chronic rejection. Echocardiography revealed the development of hypertrophy in grafts undergoing chronic rejection. Histologic analysis confirmed hypertrophy that coincided with graft fibrosis and elevated intragraft expression of IL-6. To elucidate the role of IL-6 in chronic rejection, cardiac allograft recipients depleted of CD4+ cells were treated with neutralizing anti-IL-6 mAb. IL-6 neutralization ameliorated cardiomyocyte hypertrophy, graft fibrosis, and prevented deterioration of graft contractility associated with chronic rejection. These observations reveal a new paradigm in which IL-6 drives development of pathologic hypertrophy and fibrosis in chronic cardiac allograft rejection and suggest that IL-6 could be a therapeutic target to prevent this disease.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

alpha1-Adrenergic receptor stimulates interleukin-6 expression and secretion through both mRNA stability and transcriptional regulation: involvement of p38 mitogen-activated protein kinase and nuclear factor-kappaB

Our previous studies have demonstrated that activation of alpha(1)-adrenergic receptors (ARs) increased interleukin-6 (IL-6) mRNA expression and protein secretion, which is probably an important yet unknown mechanism contributing to the regulation of cardiac function. Using Rat-1 fibroblasts stably transfected with the alpha(1A)-AR subtype and primary mouse neonatal cardiomyocytes, we elucidated the basic molecular mechanisms responsible for the alpha(1)-AR modulation of IL-6 expression. IL-6 mRNA production mediated by alpha(1)-AR peaked at 1 to 2 h. Studies of the mRNA decay rate indicated that alpha(1)-AR activation enhanced IL-6 mRNA stability. Analysis of IL-6 promoter activity using a series of deletion constructs indicated that alpha(1)-ARs enhanced IL-6 transcription through several transcriptional elements, including nuclear factor kappaB (NF-kappaB). Inhibition of alpha(1)-AR mediated IL-6 production and secretion by actinomycin D and the increase of intracellular IL-6 levels by alpha(1)-AR activation suggest that alpha(1)-AR mediated IL-6 secretion through de novo synthesis. Both IL-6 transcription and protein secretion mediated by alpha(1)-ARs were significantly reduced by chemical inhibitors for p38 mitogen-activated protein kinase (MAPK) and NF-kappaB and by a dominant-negative construct of p38 MAPK. Serum level of IL-6 was elevated in transgenic mice expressing a constitutively active mutant of the alpha(1A)-AR subtype but not in a similar mouse model expressing the alpha(1B)-AR subtype. Our results indicate that alpha(1)-ARs stimulated IL-6 expression and secretion through regulating both mRNA transcription and stability, involving p38 MAPK and NF-kappaB pathways.

Activation of AP-1 contributes to the beta-adrenoceptor-mediated myocardial induction of interleukin-6

The induction of proinflammatory cytokines in stressed myocardium is considered an innate immune response, but the role of beta-adrenergic signaling in this proinflammatory response and the mechanisms of cardioprotection by beta-blockers are not fully understood. In the present study, we analyzed interleukin-6 (IL-6) formation and promoter activation in beta-adrenoceptor-stimulated neonatal rat cardiomyocytes, in transgenic mice with cardiac overexpression of beta1-adrenoceptors, and in failing human myocardium. IL-6 formation and release in cultured cardiomyocytes under beta-adrenoceptor stimulation requires the activation of activating protein-1 (AP-1) binding sites and of cAMP response elements (CRE) in the IL-6 promoter, but this release (140 +/- 6 pg/mL medium under 10(-6) M isoproterenol vs. 81 +/- 3 pg/mL unstimulated, P < 0.05) is moderate compared with that under inflammatory stimulation (855 +/- 44 pg/mL, endotoxin 0.1microg/mL). Similarly, IL-6 is induced together with CRE- and AP-1 activation in the left ventricle (LV) of beta1-transgenic mice before the onset of failure. However, we observed IL-6 induction with activation of NF-kappaB in addition to CRE and AP-1 in beta1-transgenic mice at the age of 22 weeks and in explanted human LV after full development of failure. Treatment with beta-blockers lowered myocardial IL-6 as well as AP-1, NF-kappaB, and CRE activation. Therefore, the activation of AP-1 and CRE is part of beta-adrenergic signal transduction for IL-6 induction in nonfailing and failing cardiomyocytes, whereas NF-kappaB activation contributes only in overloaded failing myocardium.

Stress hormones regulate interleukin-6 expression by human ovarian carcinoma cells through a Src-dependent mechanism

Recent studies have demonstrated that chronic stress promotes tumor growth, angiogenesis, and metastasis. In ovarian cancer, levels of the pro-angiogenic cytokine, interleukin 6 (IL-6), are known to be elevated in individuals experiencing chronic stress, but the mechanism(s) by which this cytokine is regulated and its role in tumor growth remain under investigation. Here we show that stress hormones such as norepinephrine lead to increased expression of IL-6 mRNA and protein levels in ovarian carcinoma cells. Furthermore, we demonstrate that norepinephrine stimulation activates Src tyrosine kinase and this activation is required for increased IL-6 expression. These results demonstrate that stress hormones activate signaling pathways known to be critical in ovarian tumor progression.

Classic interleukin-6 receptor signaling and interleukin-6 trans-signaling differentially control angiotensin II-dependent hypertension, cardiac signal transducer and activator of transcription-3 activation, and vascular hypertrophy in vivo

Interleukin (IL)-6 acts via a receptor complex consisting of the cognate IL-6 receptor (IL-6R) or the soluble IL-6 receptor (sIL-6R) and glycoprotein 130 (gp130). Here, we investigated the role of these IL-6R components in hypertension and vascular hypertrophy in mice. Angiotensin (Ang) II (1.1 mg/kg/day) caused hypertension and cardiac/aortic hypertrophy in wild-type, but not IL-6(-/-), mice throughout 7 days. A recombinant dimeric soluble gp130 (sgp130Fc; 50 to 100 microg, i.p.) blocked Ang II hypertension but not hypertrophy in wild-type mice. Cognate IL-6R was detected in aortic smooth muscle, but its levels and those of plasma sIL-6R were approximately 50% decreased in IL-6(-/-) mice. Ang II infusion activated signal transducer and activator of transcription-3 in heart of WT and decreased Ang II receptor 1 (ATR1) expression in aorta. Both responses were unaffected by sgp130Fc and absent in IL-6(-/-) mice. In summary, we show that IL-6 trans-signaling is required for Ang II-dependent hypertension, but that hypertrophy, down-regulation of AT1R, and cardiac signal transducer and activator of transcription-3 activation are mediated via cognate IL-6R. These data show that IL-6 responses in a single disease context are governed by both modes of IL-6 signaling, with each pathway eliciting different outcomes. Inhibition of IL-6 signaling is suggested as a potential therapy for hypertension and cardiac hypertrophy.

Survival pathways in hypertrophy and heart failure: the gp130-STAT3 axis

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.

Crosstalk between signaling pathways of adrenoreceptors and signal transducers and activators of transcription 3 (STAT3) in heart

Recently, there have been important advancements in our understanding of the signaling mechanisms of adrenoreceptors (AR) and signal transducers and activators of transcription 3 (STAT3). While their crucial roles in the pathological processes of the heart are well established, accumulating evidence suggests there is a complex pattern of crosstalk between these 2 signaling pathways. Moreover, the potential for crosstalk occurs at multiple levels in each signaling cascade and involves receptor transactivation, G proteins, small GTPases, cyclic adenosine 3',5'-monophosphate/protein kinase A, protein kinase C, scaffold/adaptor proteins, protein tyrosine kinases, and mitogen-activated protein kinases. In addition, post-translational modification (eg acetylation) of STAT3 may provide a link between STAT3 and AR signaling. In particular, crosstalk between these 2 systems in the heart would appear to be dependent upon the species/tissue studied, developmental stage, and eliciting stimulus. This at least partly accounts for the epigenetic effects on biological function that is mediated by the 2 signaling pathways. Elucidation of these mechanisms will provide new targets in the development of novel clinical strategies for heart disorders.

Jak/STAT/SOCS signaling circuits and associated cytokine-mediated inflammation and hypertrophy in the heart

Cytokines are important mediators of cardiac disease. Accumulating evidence indicates that members of the interleukin-6 family of cytokines promote cardiac hypertrophy through the activation of the Janus kinase-signal transducer and activator of transcription (Jak/STAT) pathway. Aberrant Jak/STAT signaling may promote progression from hypertrophy to heart failure. Suppressor of cytokine signaling (SOCS) proteins are underexplored, negative regulators of Jak/STAT signaling. SOCS proteins may also interact with other inflammatory pathways known to affect cardiac function. A better understanding of the therapeutic potential of these proteins may lead to the controlled progression of heart failure and the limitation of myocardial depression. This review summarizes the cardiophysiological effect of the IL-6 cytokine family, outlines the mechanistic pathway of Jak/STAT signaling, explores the regulatory role of SOCS proteins in the heart, and discusses the potential of using SOCS proteins clinically.

Interactions between cardiac cells enhance cardiomyocyte hypertrophy and increase fibroblast proliferation

In cardiac hypertrophy, both excessive enlargement of cardiac myocytes (CMs) and progressive fibrosis are known to occur simultaneously. To investigate the nature of interactions between ventricular CMs and cardiac fibroblasts (CFs) in these conditions, we have established a "dedifferentiated model" of adult murine CMs in coculture with CFs. In such a model, which is recognized to study cardiac cell hypertrophy in vitro, dedifferentiated CMs in culture and in coculture were characterized by immunopositive staining to ANP (atrial natriuretic peptide) and beta-myosin heavy chain (beta-MHC). The results confirm that ANP secretion by CMs was significantly increased during the cultures. The increase size of cultured CMs was significantly higher in CM/CF cocultures than in CM cultures which was also observed when CMs were cultured with fibroblast conditioned medium (FCM). In addition, fibroblast proliferation studies showed that CMs favored fibroblast adhesion and/or growth at the beginning of the coculture and fibroblast proliferation throughout the time course of the coculture. Furthermore, a significant level of interleukin-6 (IL-6) production was detected by ELISA in CM/CF cocultures. A similar higher increase was observed when CMs were cultured in the presence of FCM. These results demonstrate that CFs enhance myocyte hypertrophy and that CMs regulate fibroblast adhesion and/or proliferation, suggesting a paracrine interaction between CMs and CFs which could involve IL-6.

Psychological stress induces chemoresistance in breast cancer by upregulating mdr1

Psychological distress reduces the efficacy of chemotherapy in breast cancer patients. The mechanism may be related to the altered neuronal or hormonal secretions during stress. Here, we reported that adrenaline, a hormone mediating the biological activities of stress, upregulates mdr1 gene expression in MCF-7 breast cancer cells via alpha(2)-adrenergic receptors in a dose-dependent manner. Mdr1 upregulation can be specifically inhibited by pretreatment with mdr1-siRNA. Consequently, adrenergic stimulation enhances the pump function of P-glycoprotein and confers resistance of MCF-7 cells to paclitaxel. In vivo, restraint stress increases mdr1 gene expression in the MCF-7 cancers that are inoculated subcutaneously into the SCID mice and provokes resistance to doxorubicin in the implanted tumors. The effect can be blocked by injection of yohimbine, an alpha(2)-adrenergic inhibitor, but not by metyrapone, a corticosterone synthesis blocker. Therefore, we conclude that breast cancers may develop resistance against chemotherapeutic drugs under psychological distress by over-expressing mdr1 via adrenergic stimulation.