Cardiotrophin-1 activates a distinct form of cardiac muscle cell hypertrophy. Assembly of sarcomeric units in series VIA gp130/leukemia inhibitory factor receptor-dependent pathways

Neurohormonal regulation of myocardial cell apoptosis during the development of heart failure

Adult cardiac myocytes are terminally differentiated cells that are no longer able to divide. Accumulating data support the idea that apoptosis in these cells is involved in the transition from cardiac compensation to decompensated heart failure. Since a number of neurohormonal factors are activated in this state, these factors may be involved in the positive and negative regulation of apoptosis in cardiac myocytes. beta1-Adrenergic receptor and angiotensin type 1 receptor pathways, nitric oxide and natriuretic peptides are involved in the induction of apoptosis in these cells, while alpha1- and beta2-adrenergic receptor and endothelin-1 type A receptor pathways and gp130-related cytokines are antiapoptotic. The myocardial protection of the latter is mediated, at least in part, through mitogen-activated protein kinase-dependent pathways, compatible with the findings in other cell types. In contrast, signaling pathways leading to apoptosis in cardiac myocytes are distinct from those in other cell types. The cAMP/PKA pathway induces apoptosis in cardiac myocytes and blocks apoptosis in other cell types. The p300 protein, a coactivator of p53, mediates apoptosis in fibroblasts but appears to play a protective role in differentiated cardiac myocytes. The inhibition of myocardial cell apoptosis in heart failure may be achieved by directly blocking apoptosis signaling pathways or by modulating neurohormonal factors involved in their regulation. These may provide novel therapeutic strategies in some forms of heart failure.

The heart is a source of circulating cardiotrophin-1 in humans

Cardiotrophin-1 (CT-1) is a new member of the interleukin (IL)-6 family of cytokines and one of the endogenous ligands for gp130 signaling pathways in the heart, which has potent hypertrophic and survival effects on cardiac myocytes. However, the clinical significance of CT-1 is poorly understood, mainly because there is no widely applicable specific and sensitive assay system for measuring plasma levels of circulating CT-1. We therefore developed a competitive radioimmunoassay (RIA) for human CT-1 with rabbit antiserum recognizing the N-terminus region of human CT-1 and using recombinant human CT-1 as a calibrator. The assay displays no cross-reactivities with any of the IL-6 family of cytokines including IL-11, leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. The lower detection limit in buffer was found to be 43 fmol/ml, and the working range was 120-8300 fmol/ml (CV < 15%). This RIA directly recognizes CT-1-like immunoreactivity in human plasma with a mean value of 571 +/- 75 fmol/ml (mean +/- SD) in healthy volunteers. The RIA coupled with gel filtration chromatographic analyses showed that the major molecular form of circulating CT-1 corresponds to recombinant full-length human CT-1. Moreover, there is a significant increase in the plasma CT-1 concentration from the aorta and coronary sinus, which clearly indicates that the heart secretes CT-1 via the coronary sinus into the peripheral circulation. This RIA should serve as a powerful tool for investigating the clinical significance of CT-1.

The effect of valvular regurgitation on plasma Cardiotrophin-1 in patients with normal left ventricular systolic function

BACKGROUND

Cardiotrophin-1 (CT-1), a member of the interleukin-6 related cytokine family that act via the gp130 signalling pathway, has been shown to stimulate the assembly of sarcomeric units in series in cardiomyocytes resulting in eccentric hypertrophy, ventricular dilatation and finally loss of function. In situations of volume overload a similar form of eccentric hypertrophy occurs with time.

AIMS

We hypothesised that plasma CT-1 would be raised in patients with significant mitral, tricuspid and/or aortic regurgitation (MR/TR or AR, respectively) when compared to those with no (or mild) valvular regurgitant lesion.

METHODS

A novel competitive immunoluminometric assay using an in-house polyclonal antibody to amino acids 105-120 of the CT-1 sequence was developed. Seventy-eight patients (31 male, mean+/-S.D. age 63.5+/-17.9 years), all with normal left ventricular systolic function were studied. Results are expressed as mean+/-S.D. fmol/ml.

RESULTS

Sixty-three subjects had no significant valvular lesion, seven had moderate/severe MR, nine had moderate/severe TR and four had moderate/severe AR. These subjects had CT-1 concentrations of 53. 3+/-23.2, 90.5+/-44.4, 72.6+/-43.8 and 48.4+/-24.4, respectively (P=0.02, ANOVA). Mean log CT-1 was higher in those with moderate/severe MR when compared to those without a significant regurgitant valvular lesion (P<0.03). The only predictor of moderate/severe MR was log CT-1 (P=0.004).

CONCLUSION

These results suggest that plasma CT-1 is raised in those patients with moderate/severe MR in the presence of normal left ventricular systolic function. This secretion of CT-1 could potentially be the cause of ventricular dilatation and subsequent loss of contractile function in these patients. It also offers the intriguing possibility that plasma CT-1 could be used to monitor progression of mitral regurgitation biochemically.

beta-blocker therapy: a standard of care for heart failure

beta-Adrenergic-blocking agents underwent extensive research over the past 2 decades and emerged as a proven state-of-art therapy for the failing human heart. Through blockade of chronically elevated cardiac adrenergic stimulation, selective and nonselective agents with vasodilating properties prevent progression of myocardial dysfunction and cardiac remodeling. Most important, beta-adrenergic blockers added to conventional therapy of vasodilators and diuretics significantly increase survival to a 5-year rate similar to that of cardiac transplantation. The agents also significantly reduce hospitalizations, improve quality of life, and are well tolerated in clinical trials. The challenge in treating heart failure is to ensure that every eligible patient receives these life-saving drugs.

Augmented expression of cardiotrophin-1 and its receptor component, gp130, in both left and right ventricles after myocardial infarction in the rat

Cardiotrophin-1 (CT-1) is a potent cytokine that stimulates the assembly of sarcomeric units in series in cardiomyocytes through gp130 signaling, resulting in myocardial cell hypertrophy. To clarify the role of CT-1 and the gp130-signaling pathway during ventricular remodeling after myocardial infarction, we examined the expression of CT-1 and gp130 in a rat model of myocardial infarction. At 1, 3, 7, 14, 28 and 56 days (n=12 for each group) after ligation of a coronary artery, tissue samples were obtained from infarct tissue, the ventricular septum and the right ventricle. All animals developed large myocardial infarctions, with infarct sizes ranging from 39.8% to 50.3%. Progressive left ventricular dilatation and inadequate hypertrophy of the surviving myocardium were confirmed by echocardiography. CT-1 and gp130 mRNA levels were determined by semiquantitative reverse transcription-polymerase chain reaction using 1 or 5 microg of total RNA followed by Southern blotting. The densitometric analysis of the Southern blots revealed a significant increase in CT-1 and gp130 mRNA levels (P<0.01) compared with those of the sham-operated rats at 1, 3, 7, 14, 28 and 56 days post-infarct in the infarct area, the ventricular septum (non-infarcted area) and right ventricle. The protein levels of CT-1 and gp130, determined by Western blot analysis, were significantly increased (P<0.05) compared with those of sham-operated rats, peaked during the acute stage and declined thereafter in the three regions described above. Immunohistochemical staining showed that CT-1 and gp130-immunoreactivities were detected in cardiomyocytes and fibroblast-like cells and that the intensity of staining was increased at 7 days post-infarct compared with that in sham-operated rats. An augmented CT-1 and gp130 system thus appears to play an important role during ventricular remodeling after myocardial infarction.

Significance of ERK cascade compared with JAK/STAT and PI3-K pathway in gp130-mediated cardiac hypertrophy

We compared the role of the Raf-1/mitogen-activated protein kinase/extracellular signal-regulated protein kinase (MEK)/extracellular signal-regulated protein kinase (ERK)/p90(RSK) cascade in gp130-mediated cardiac hypertrophy with the contribution of the Janus kinase (JAK)/signal transduction and activation of transcription (STAT) and phosphatidylinositide 3-kinase (PI3-K) pathways. Primary cultured neonatal rat cardiomyocytes were stimulated with leukemia inhibitory factor (LIF). LIF sequentially activated Raf-1, MEK1/2, ERK1/2, and p90(RSK). We used PD-98059 (a specific MEK inhibitor), AG-490 (a JAK2 inhibitor), and wortmannin (a PI3-K inhibitor) to confirm that this cascade was independent of the JAK/STAT and PI3-K/p70 S6 kinase (S6K) pathways. PD-98059, AG-490, and wortmannin suppressed the LIF-induced increase in [(3)H]phenylalanine uptake by 54.7, 21.5, and 25.6%, respectively, and inhibited the increase in cell area by 61.2, 42.8, and 39.2%, respectively. Reorganization of myofilaments was predominantly suppressed by AG-490. LIF-induced expression of c-fos, brain natriuretic peptide, and skeletal alpha-actin mRNA was markedly suppressed by PD-98059 and moderately suppressed by wortmannin and AG-490. Atrial natriuretic peptide was significantly suppressed by AG-490. These findings indicate that this pathway is critically involved in protein synthesis, induction of c-fos, brain natriuretic peptide, and skeletal alpha-actin expression and is partially involved in myofilament reorganization and atrial natriuretic peptide induction in gp130-mediated cardiac hypertrophy.

Genetic dissection of cardiac growth control pathways

Cardiac muscle cells exhibit two related but distinct modes of growth that are highly regulated during development and disease. Cardiac myocytes rapidly proliferate during fetal life but exit the cell cycle irreversibly soon after birth, following which the predominant form of growth shifts from hyperplastic to hypertrophic. Much research has focused on identifying the candidate mitogens, hypertrophic agonists, and signaling pathways that mediate these processes in isolated cells. What drives the proliferative growth of embryonic myocardium in vivo and the mechanisms by which adult cardiac myocytes hypertrophy in vivo are less clear. Efforts to answer these questions have benefited from rapid progress made in techniques to manipulate the murine genome. Complementary technologies for gain- and loss-of-function now permit a mutational analysis of these growth control pathways in vivo in the intact heart. These studies have confirmed the importance of suspected pathways, have implicated unexpected pathways as well, and have led to new paradigms for the control of cardiac growth.

Interleukin-6 family of cytokines mediate angiotensin II-induced cardiac hypertrophy in rodent cardiomyocytes

This study was designed to investigate whether angiotensin II induces the interleukin (IL)-6 family of cytokines in cardiac fibroblasts and, if so, whether these cytokines can augment cardiac hypertrophy. Angiotensin II increased IL-6, leukemia inhibitory factor (LIF) and cardiotrophin-1 mRNA by 6.5-, 10.2-, and 2.0-fold, respectively, but did not affect IL-11, ciliary neurotrophic factor, or oncostatin M in cardiac fibroblasts. Enzyme-linked immunosorbent assay revealed that angiotensin II-stimulated conditioned medium from cardiac fibroblasts contained 9.3 ng/ml IL-6 at 24 h, which was 24-fold higher than the control. It phosphorylated gp130 and STAT3 in cardiomyocytes, which was reduced with RX435 (anti-gp130 blocking antibody). It increased [(3)H]phenylalanine uptake and cell area by 44% and 86% in cardiomyocytes compared with mock medium. RX435 suppressed these increases by 26% and 38%, while TAK044 (endothelin-A/B-R blocker) suppressed them by 52% and 52%, respectively. Antisense oligonucleotides against LIF and cardiotrophin-1 blocked their up-regulation, and attenuated the conditioned medium-induced increase in [(3)H]phenylalanine uptake by 21% and 13%, respectively. The combination of antisense oligonucleotides to LIF and cardiotrophin-1 decreased their uptake by 33%. These results indicated that angiotensin II induced IL-6, LIF, and cardiotrophin-1 in cardiac fibroblasts, and that these cytokines, particularly LIF and cardiotrophin-1, activated gp130-linked signaling and contributed to angiotensin II-induced cardiomyocyte hypertrophy.

Effects of cardiotrophin-1 on hemodynamics and endocrine function of the heart

Cardiotrophin-1 (CT-1), a member of the interleukin-6 superfamily of cytokines, possesses hypertrophic actions and atrial natriuretic peptide (ANP)-producing activity in vitro. The goal of our study is to elucidate whether CT-1 affects the cardiovascular system in vivo. Intravenous injection of CT-1 (4-100 microg/kg) in conscious rats evoked significant declines in blood pressure and reflex increases in heart rate (HR) in a dose-dependent manner. CT-1 induced no significant change in cardiac output (from 260.7 +/- 11.0 to 264.7 +/- 26.6 ml. min(-1). kg(-1), P = not significant), which was compatible with the results from isolated perfused rat hearts; HR, change in pressure over time, left ventricular developed pressure, and perfusion pressure were unaffected. Northern blot and RT-PCR analyses revealed that CT-1 increased expression of inducible nitric oxide synthase (iNOS) in lung and aorta but not in heart or liver. Pretreatment with aminoguanidine, a specific iNOS inhibitor, inhibited both iNOS mRNA production and the depressor effect of CT-1. Interestingly, CT-1 increased ventricular expression of ANP and brain natriuretic peptide (BNP). The data demonstrate that CT-1 elicits its hypotensive effect via a nitric oxide-dependent mechanism and that CT-1 induces ANP and BNP mRNA expression in vivo.

Isolation and characterization of the murine cardiotrophin-1 gene: expression and norepinephrine-induced transcriptional activation

Cardiotrophin-1 (CT-1) is a novel cytokine capable of inducing hypertrophy in cardiac myocytes and belongs to the interleukin-6 family that exert their biological effects through gp130. To clarify the involvement and pathophysiological role of CT-1 in myocardial diseases, it is important to characterize the regulation of CT-1 gene expression. In this study, we isolated and characterized the mouse CT-1 gene and studied the expression of CT-1 mRNA under norepinephrine (NE) stimulation. The mouse CT-1 gene constitutes 5.4 kilobases (kb) in length and consists of three exons and two introns. When nucleotide sequences of the coding regions of exons were compared with those of human, exon 1, 2 and 3 share 96%, 84% and 81% homology, respectively. The 2.2 kb of 5; flanking lesion of the mouse CT-1 gene contains a variety of transcription factor binding motif (e.g. CREB, MyoD, NF-IL6, Nkx2.5, GATA). Fluorescent in situ hybridization (FISH) analysis demonstrated that the mouse CT-1 gene was located on chromosome 7F3. The expression of CT-1 mRNA in cardiac myocytes was markedly augmented by NE stimulation, both in vivo and in vitro. Promoter analysis using deletion constructs of the CT-1 gene indicated that the NE responsive element located between -2174/-1540 and this region contained the cAMP responsive element (CRE). Electrophoretic gel mobility shift assays showed enhanced binding activity to the CRE motif in the nuclear extracts from NE-stimulated cardiac myocytes. These studies indicate that CT-1 is abundantly expressed in the heart and that the CRE is a possible cis -acting element of the CT-1 gene under NE-stimulation. These data suggest that the CT-1 gene expression is regulated, at least partially, by transcriptional machinery.

Cardiotrophin-1 increases angiotensinogen mRNA in rat cardiac myocytes through STAT3 : an autocrine loop for hypertrophy

-Cardiotrophin-1, an interleukin-6-related cytokine, stimulates the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway and induces cardiac myocyte hypertrophy. In this study, we demonstrate that cardiotrophin-1 induces cardiac myocyte hypertrophy in part by upregulation of a local renin-angiotensin system through the JAK/STAT pathway. We found that cardiotrophin-1 increased angiotensinogen mRNA expression in cardiac myocytes via STAT3 activation. Tyrosine phosphorylation of STAT3 by cardiotrophin-1 treatment resulted in STAT3 homodimer binding to the St-domain in the angiotensinogen gene promoter, which lead to promoter activation in a transient transfection assay. Cardiotrophin-1-induced STAT3 tyrosine phosphorylation and binding to the St-domain were suppressed by AG490, a specific JAK2 inhibitor, which also attenuated cardiotrophin-1-stimulated angiotensinogen promoter activity. Cardiotrophin-1 did not activate the angiotensinogen gene promoter that contained a substitution mutation within the St-domain. Finally, losartan, an angiotensin II type 1 receptor antagonist, significantly attenuated cardiotrophin-1-induced hypertrophy of neonatal rat cardiac myocytes. Angiotensin II is known to induce cardiac myocyte hypertrophy by activating the G-protein-coupled angiotensin II type 1 receptor. Our results suggest that upregulation of angiotensinogen and angiotensin II production contribute to cardiotrophin-1-induced cardiac myocyte hypertrophy and emphasize an important interaction between G-protein-coupled and cytokine receptors.

Receptor recognition by gp130 cytokines

Cytokines of the gp130 family exert their diverse biological effects by formation of stable high affinity transmembrane receptor complexes that are characterized by the presence of the shared transmembrane signalling receptor gp130. Different gp130 ligands form signalling complexes that vary in both composition and stoichiometry. Analysis of the three-dimensional structure of selected ligands and receptor elements indicates that ligands display three topologically conserved receptor recognition epitopes that interact with complementary ligand recognition elements. The composition of the signalling complex and downstream biological responses is defined by the relative affinity of different receptor components for these epitopes. The detailed structure of receptor recognition epitopes indicates that the generation of small molecule cytokine mimetics may be a feasible objective.

Signaling properties and functions of two distinct cardiomyocyte protease-activated receptors

Previous studies have established that cardiomyocytes express protease-activated receptor (PAR)-1, a high-affinity receptor for thrombin, which is also activated by the tethered-ligand domain sequence (SFLLRN) and which promotes inositol trisphosphate accumulation, stimulates extracellular signal-regulated protein kinase, and modulates contractile function. A single previous report identified PAR-1 as a hypertrophic stimulus, but there have been no subsequent investigations of the mechanism. This study reveals the coexpression of PAR-1 and PAR-2 (a second PAR, which is activated by trypsin/tryptase but not thrombin) by Northern blot analysis and compares their signaling properties in neonatal rat ventricular cardiomyocytes. SFLLRN and SLIGRL (an agonist peptide for PAR-2) promote inositol trisphosphate accumulation, stimulate mitogen-activated protein kinases (extracellular signal-regulated protein kinase and p38-mitogen-activated protein kinase), elevate calcium concentration, and increase spontaneous automaticity. SFLLRN (but not SLIGRL) also activates c-Jun NH(2)-terminal kinase and AKT. In keeping with their linkage to pathways that have been associated with growth and/or survival, SFLLRN and SLIGRL both induce hypertrophy. However, PAR agonists promote cell elongation, a morphology that is distinct from the uniform increase in cell dimension induced by alpha(1)-adrenergic receptor activation. These studies provide novel evidence that cardiomyocytes coexpress 2 functional PARs, which link to a common set of signals that culminate in changes in contractile function and hypertrophic growth. PAR actions may assume clinical importance in the border zone surrounding an infarction, where local proteolysis of PARs by serine proteases generated during inflammatory or thrombogenic pathways would elevate calcium concentration (setting the stage for arrhythmias), promote hypertrophic growth, and/or influence cardiomyocyte survival.

Chronic stretch of engineered heart tissue induces hypertrophy and functional improvement

To examine the influence of chronic mechanical stretch on functional behavior of cardiac myocytes, we reconstituted embryonic chick or neonatal rat cardiac myocytes to a 3-dimensional engineered heart tissue (EHT) by mixing freshly isolated cells with neutralized collagen I and culturing them between two Velcro-coated silicone tubes, held at a fixed distance with a metal spacer. After 4 days, EHTs were subjected to a phasic unidirectional stretch for 6 days in serum-containing medium. Compared to unstretched controls, RNA/DNA and protein/cell ratios increased by 100% and 50%, respectively. ANF mRNA and alpha-sarcomeric actin increased by 98% and 40%, respectively. Morphologically, stretched EHTs exhibited improved organization of cardiac myocytes into parallel arrays of rod-shaped cells, increased cell length and width, longer myofilaments, and increased mitochondrial density. Thus, stretch induced phenotypic changes, generally referred to as hypertrophy. Concomitantly, force of contraction was two- to fourfold higher both under basal conditions and after stimulation with calcium or the beta-adrenergic agonist isoprenaline. Contraction kinetics were accelerated with a 14-44% decrease in twitch duration under all those conditions. In summary, we have developed a new in vitro model that allows morphological, molecular, and functional consequences of stretch to be studied under defined conditions. The main finding was that stretch of EHTs induced cardiac myocyte hypertrophy, which was accompanied by marked improvement of contractile function.

The cardiac Fas (APO-1/CD95) Receptor/Fas ligand system : relation to diastolic wall stress in volume-overload hypertrophy in vivo and activation of the transcription factor AP-1 in cardiac myocytes

BACKGROUND

Fas (APO-1/CD95) is a transmembrane receptor belonging to the tumor necrosis factor receptor superfamily. Cross-linking of Fas by Fas ligand (FasL), a tumor necrosis factor-alpha-related cytokine, promotes apoptosis and/or transcription factor activation in a highly cell-type-specific manner. The biological consequences of Fas activation in cardiomyocytes and the regulation of Fas and FasL abundance in the myocardium in vivo remain largely unknown.

METHODS AND RESULTS

As shown by immunohistochemistry, Fas was expressed on the sarcolemma of cardiomyocytes in left ventricular tissue sections. Moreover, FasL was constitutively expressed in the myocardium and in isolated cardiomyocytes, as revealed by reverse transcription polymerase chain reaction and Western blotting. Left ventricular abundance of Fas but not FasL was upregulated in a rat model of compensated volume-overload hypertrophy and was closely related to diastolic but not systolic wall stress as determined by MRI. Cardiomyocyte apoptosis was not enhanced in volume-overload hypertrophy despite the increased expression of Fas and the presence of FasL in the myocardium. Moreover, injection of mice with an agonistic anti-Fas antibody promoted hepatocyte but not cardiomyocyte apoptosis in vivo. Stimulation of isolated cardiomyocytes with recombinant FasL promoted an activation of the transcription factor AP-1 as shown by electrophoretic mobility shift assays but did not induce cell death.

CONCLUSIONS

Fas and FasL are constitutively expressed in the myocardium and in cardiomyocytes. Myocardial expression of Fas is closely related to diastolic loading conditions in vivo. Signaling pathways emanating from Fas are coupled to an activation of the transcription factor AP-1 in cardiomyocytes.

Expressional patterns of cytokines in a murine model of acute myocarditis: early expression of cardiotrophin-1

To determine the role of cytokines in acute myocarditis, we examined expressional patterns of cardiotrophin-1 (CT-1), TNF-alpha, and IL-1alpha in a murine model of acute myocarditis. Ten-day-old Institute of Cancer Research mice were injected with Coxsackievirus B3 and killed on Days 1, 2, 3, 4, 5, 7, 10, 14, and 28 of injection. TNF-alpha and IL-1alpha expressions were investigated on histological sections from each heart, and mRNA expression of TNF-alpha, IL-1alpha, and CT-1 in the heart was examined by reverse transcription-polymerase chain reaction and RNase protection assay. To determine myocardial regeneration, cardiomyocytic DNA synthesis was investigated using bromodeoxyuridine on Days 3, 5, 7, and 10, and the labeling index was calculated in each heart. Age-matched uninfected mice were used as controls. TNFalpha and IL-1alpha expression was first detected in the cardiomyocytes on Day 3 and reached the maximum level on Day 7, when inflammatory changes were most prominent. Although an increased expression of TNFalpha and IL-1alpha mRNA was also detected on Day 3, CT-1 mRNA expression was distinctly augmented on Day 2. The labeling indices in the hearts with myocarditis were significantly higher than in those of the controls in all of the time points examined. CT-1 expression preceded TNF-alpha and IL-1alpha expressions and active DNA synthesis in a murine model of acute myocarditis. All CVB3-infected mice with anti-glycoprotein-130 antibody treatment died within 6 days. CT-1 may exert a protective role by modulating cytokine production and by inducing cardiomyocytic proliferation in CVB3-infected murine hearts.

Linkage between alpha(1) adrenergic receptor and the Jak/STAT signaling pathway in vascular smooth muscle cells

The Jak/STAT pathway is activated following stimulation of the type I angiotensin II receptor. To examine whether this pathway is shared among other G-protein-coupled receptors, we studied the linkage between the alpha(1) adrenergic receptor and this pathway. The alpha(1) agonist phenylephrine induced tyrosine phosphorylation of Jak2, Tyk2, and STAT1 in vascular smooth muscle cells. The phosphorylation of Jak2 was prevented by the alpha(1) receptor antagonists prazosin and chloroethylclonidine, but not by WB4101, and that of STAT1 was inhibited by prazosin and the Jak2 inhibitor AG490. After stimulation with phenylephrine, Jak2 and STAT1 were found to associate with alpha(1B) receptor. Phenylephrine stimulated the DNA binding activity of STAT1. Protein synthesis promoted by phenylephrine was inhibited by prazosin, AG490, and the introduction of a decoy oligonucleotide for STAT1. These results suggested that alpha(1) receptor is linked to the Jak/STAT pathway and that this pathway mediates alpha(1) agonist-induced smooth muscle hypertrophy.

Cytokines and their receptors in cardiovascular diseases--role of gp130 signalling pathway in cardiac myocyte growth and maintenance

Interleukin (IL)-6-related cytokines share gp130 as the signal-transducing protein. Cardiac myocytes produce various kinds of cytokines including IL-6 and cardiotrophin-1. Activation of gp130 transduces hypertrophic and cytoprotective signals in cardiac myocytes via JAK/STAT, MAP kinase and PI-3 kinase pathways. Besides various well-established mechanisms by which cardiac growth and myocardial remodeling are regulated, gp130 signalling may be a newly discovered mechanism that regulates these events in association with cytoprotective effect in myocardial diseases.

Cytokine-induced nuclear factor kappa B activation promotes the survival of developing neurons

Ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), and interleukin 6 (IL-6) comprise a group of structurally related cytokines that promote the survival of subsets of neurons in the developing peripheral nervous system, but the signaling pathways activated by these cytokines that prevent neuronal apoptosis are unclear. Here, we show that these cytokines activate NF-kappaB in cytokine-dependent developing sensory neurons. Preventing NF-kappaB activation with a super-repressor IkappaB-alpha protein markedly reduces the number of neurons that survive in the presence of cytokines, but has no effect on the survival response of the same neurons to brain-derived neurotrophic factors (BDNF), an unrelated neurotrophic factor that binds to a different class of receptors. Cytokine-dependent sensory neurons cultured from embryos that lack p65, a transcriptionally active subunit of NF-kappaB, have a markedly impaired ability to survive in response to cytokines, but respond normally to BDNF. There is increased apoptosis of cytokine- dependent neurons in p65(-/)- embryos in vivo, resulting in a reduction in the total number of these neurons compared with their numbers in wild-type embryos. These results demonstrate that NF-kappaB plays a key role in mediating the survival response of developing neurons to cytokines.

Augmented cardiac cardiotrophin-1 in experimental congestive heart failure

BACKGROUND

Cardiotrophin-1 (CT-1) is a potent hypertrophic factor discovered by coupling expression cloning in a mouse embryonic stem cell-based model of cardiogenesis.

METHODS AND RESULTS

The present study was designed to investigate the potential activation of atrial and ventricular CT-1 expression in pacing-induced experimental congestive heart failure (CHF) and its relationship to left ventricular hypertrophy by the method of Northern blot analysis and immunohistochemistry. We used a canine model of pacing-induced experimental CHF based on hemodynamic and neurohumoral characteristics that closely mimic human dilated cardiomyopathy. Northern blot analysis demonstrated that CT-1 gene expression was present in normal atrium and ventricle and was increased in CHF hearts. There was a positive correlation between ventricular CT-1 mRNA and left ventricular mass index. Immunohistochemistry revealed positive immunostaining in the atrial and ventricular cardiomyocytes from both normal and CHF hearts. CT-1 immunoreactivity was more intense in the atrium and ventricle from CHF hearts than in normal hearts.

CONCLUSIONS

The present study demonstrates that both atrium and ventricle synthesize CT-1 and that cardiac production of CT-1 is augmented in a canine model of experimental CHF. This study also demonstrates that ventricular CT-1 mRNA correlates with left ventricular hypertrophy, suggesting that CT-1 plays an important role in the structural remodeling that characterizes CHF.

Cardiotrophin-1: a novel cytokine and its effects in the heart and other tissues

Cardiotrophin-1 (CT-1) originally was discovered as a factor that can induce hypertrophy of cardiac myocytes, both in vitro and in vivo. Subsequently, CT-1 has been shown to have a wide variety of different effects on cardiac and noncardiac, cells including the ability to stimulate the survival of both cardiac and neuronal cells. Like other members of the interleukin-6 family of cytokines, CT-1 stimulates both the p42/p44 mitogen-activated protein kinase pathway and the Janus-activated kinase/signal transducers and activators of transcription pathway. Interestingly, whilst activation of the p42/p44 mitogen-activated protein kinase pathway is necessary for the survival-promoting effects of CT-1 in cardiac cells, it is not required for its hypertrophic effect, which is likely to involve activation of the Janus-activated kinase/signal transducer and activator of transcription-3 pathway. CT-1, therefore, may be of use as a novel cardioprotective agent, particularly if its hypertrophic effect can be specifically inhibited.

Angiotensin blockade inhibits SIF DNA binding activities via STAT3 after myocardial infarction

The in vivo activation of transcription factors, which is important for cell regulation by gene expression, has not been well examined in myocardial infarcted heart. The purpose of this study was to determine whether myocardial signal transducer and activator of transcription (STAT) pathway is activated as sis-inducing factor (SIF) in infarcted heart, and to assess the angiotensin blockade on SIF activity in ischemic and non-ischemic myocardium of rat. Myocardial infarction was made by ligation of the coronary artery in Wistar rats. In electrophoretic mobility shift assay, myocardial SIF DNA binding activities gradually increased and reached to peak at 1 week in infarcted and non-infarcted regions after myocardial infarction. Imidapril and candesartan cilexitil significantly prevented the increase in SIF DNA binding activity in infarcted and non-infarcted regions. This increased SIF DNA complex was supershifted by specific anti-STAT3 antibody, indicating that increased SIF complex at least contained activated STAT3 proteins in myocardial infarcted heart. Furthermore, immunoprecipitation-Western blot analysis revealed that STAT3 of infarcted and non-infarcted regions were tyrosine-phosphorylated at 1 week after myocardial infarction. Imidapril and candesartan cilexitil prevented the increase in phosphorylated STAT3. Thus, the transcriptional activation of STAT3 through AT1 receptor may be partially involved in cardiac remodeling after myocardial infarction.

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.

Adenoviral cardiotrophin-1 gene transfer protects pmn mice from progressive motor neuronopathy

Cardiotrophin-1 (CT-1), an IL-6-related cytokine, causes hypertrophy of cardiac myocytes and has pleiotropic effects on various other cell types, including motoneurons. Here, we analyzed systemic CT-1 effects in progressive motor neuronopathy (pmn) mice that suffer from progressive motoneuronal degeneration, muscle paralysis, and premature death. Administration of an adenoviral CT-1 vector to newborn pmn mice leads to sustained CT-1 expression in the injected muscles and bloodstream, prolonged survival of animals, and improved motor functions. CT-1-treated pmn mice showed a significantly reduced degeneration of facial motoneuron cytons and phrenic nerve myelinated axons. The terminal innervation of skeletal muscle, grossly disturbed in untreated pmn mice, was almost completely preserved in CT-1-treated pmn mice. The remarkable neuroprotection conferred by CT-1 might become clinically relevant if CT-1 side effects, including cardiotoxicity, could be circumvented by a more targeted delivery of this cytokine to the nervous system.

Involvement of cardiotrophin-1 in cardiac myocyte-nonmyocyte interactions during hypertrophy of rat cardiac myocytes in vitro

BACKGROUND

The mechanism responsible for cardiac hypertrophy is currently conceptualized as having 2 components, mediated by cardiac myocytes and nonmyocytes, respectively. The interaction between myocytes and nonmyocytes via growth factors and/or cytokines plays an important role in the development of cardiac hypertrophy. We found that cardiac myocytes showed hypertrophic changes when cocultured with cardiac nonmyocytes. Cardiotrophin-1 (CT-1), a new member of the interleukin-6 family of cytokines, was identified by its ability to induce hypertrophic response in cardiac myocytes. In this study, we used the in vitro coculture system to examine how CT-1 is involved in the interaction between cardiac myocytes and nonmyocytes during the hypertrophy process.

METHODS AND RESULTS

RNase protection assay revealed that CT-1 mRNA levels were 3. 5 times higher in cultured cardiac nonmyocytes than in cultured cardiac myocytes. We developed anti-CT-1 antibodies and found that they significantly inhibited the increased atrial and brain natriuretic peptide secretion and protein synthesis characteristic of hypertrophic changes of myocytes in the coculture. In addition, non-myocyte-conditioned medium rapidly elicited tyrosine phosphorylation of STAT3 and induced an increase in natriuretic peptide secretion and protein synthesis in cultured cardiac myocytes; these effects were partially suppressed by anti-CT-1 antibodies. Finally, the hypertrophic effects of CT-1 and endothelin-1, which we had previously implicated in the hypertrophic activity in the coculture, were additive in cardiac myocytes.

CONCLUSIONS

These results show that CT-1 secreted from cardiac nonmyocytes is significantly involved in the hypertrophic changes of cardiac myocytes in the coculture and suggest that CT-1 is an important local regulator in the process of cardiac hypertrophy.

Involvement of gp130-mediated signaling in pressure overload-induced activation of the JAK/STAT pathway in rodent heart

Previously, we showed that the JAK/STAT pathway was activated in pressure-overloaded rat heart, and that angiotensin II was partially involved in this activation. The present study was designed to investigate whether gp130-mediated signaling is involved in this activation, and if so, which interleukin (IL)-6 family cytokine is involved. Pressure overload was produced by ligation of the abdominal aorta of Wistar rats or ICR mice. IP-Western blot was performed to detect tyrosine phosphorylation of STATs, gp130, and the association of gp130 with JAK kinases. The serum concentration of IL-6 was measured by enzyme-linked immunosorbent assay. Expression of IL-6, IL-11, leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), oncostatin M (OSM), and cardiotrophin-1 (CT-1) mRNA was quantitated. After pressure overload, rapid phosphorylation of STAT1 and STAT3 was observed at 5 min, STAT1 was rephosphorylated at 60 min, and intense phosphorylation of STAT3 was observed at 60 min. Both the phosphorylation of gp130 and the association of gp130 with JAK1 and JAK2 were increased after pressure overload. IL-6 was significantly increased by two-fold in the pressure-overloaded rats. Only CT-1 mRNA expression could be detected by Northern blot, and it increased after pressure overload. Reverse transcription-polymerase chain reaction revealed that IL-6 mRNA expression was increased 9.5-fold. IL-11, LIF, CNTF, and OSM expression were unaffected by pressure overload. These results suggested that gp130-mediated signaling was involved in the pressure overload-induced activation of the JAK/STAT pathway, and that IL-6 and CT-1 might be involved in this activation.

An immunoluminometric assay for cardiotrophin-1: a newly identified cytokine is present in normal human plasma and is increased in heart failure

Cardiotrophin-1, a member of the interleukin-6 related cytokine family which acts via the glycoprotein 130 signalling pathway, may be involved in the process of ventricular remodelling. Its presence in human plasma has never been reported. We have devised a non-radioactive immunoluminometric sensitive and specific assay for CT-1 based on a competitive ligand binding principle. The chemiluminescent label 4-(2-succinimidyl-oxycarbonylethyl)phenyl-10-methylacridinium 9-carboxylate fluorosulfonate was used to label a peptide representing a domain in the middle section of CT-1. Assay of this domain of CT-1 (amino acids 105-120) in patients with heart failure revealed elevated CT-1 values median 87 [range 74.3-182.8] fmol/ml) compared to normal controls (CT-1 median 29.55 [range 6.9-48.3] fmol/ml, P<0.0005). The molecular weight of human CT-1 was estimated to be 26.7 kD from sodium dodecyl sulphate polyacrylamide gel electrophoresis. This is the first quantitative assessment of CT-1 in humans. Furthermore, this is the first demonstration of significant elevation of plasma CT-1 in patients with heart failure.

Cardiotrophin-1 (CT-1): a novel hypertrophic and cardioprotective agent

Cardiotrophin-1 (CT-1) is a member of the IL-6 family of cytokines which was originally discovered as a factor which can induce hypertrophy of cardiac myocytes both in vitro and in vivo. Subsequently, CT-1 has been shown to have a wide variety of different effects on cardiac and non cardiac cells including the ability to stimulate the survival of both cardiac and neuronal cells. Interestingly, whilst activation of the p42/p44 MAP kinase pathway is necessary for the survival promoting effects of CT-1 in cardiac cells, it is not required for its hypertrophic effect which is likely to involve activation of the Jak/STAT-3 pathway. CT-1 may therefore be of use as a novel cardio-protective agent, particularly if its hypertrophic effect can be specifically inhibited.

2-Tetradecylglycidic acid, an inhibitor of carnitine palmitoyltransferase-1, induces myocardial hypertrophy via the AT1 receptor

Activation of the antiogensin II, type 1 (AT1) receptor mediates the myocardial response to numerous hypertrophic stimuli. This study tested the hypothesis that 2-tetradecylglycidic acid (TDGA), an oxirane carboxylate inhibitor of mitochondrial carnitine plamitoyltransferase-1, induces myocardial hypertrophy via the AT1 receptor system. Male Sprague-Dawley rats treated with 10 mg TDGA/kg/day for 7 days had a heart wet weight:body weight ratio of 3. 58+/-0.16 mg/g compared with a ratio of 2.79+/-0.07 for rats treated with vehicle (P<0.05). The plasma level of antiogensin II was 117. 75+/-17.39 pg/ml in rats treated with 10 mg TDGA/kg/day compared with 54.0+/-11.38 pg/ml for rats treated with vehicle (P<0.05). The plasma level of angiotensin I in these two groups of rats was not different statistically. Rats treated with TDGA and given drinking water containing 1 mg losartan/ml had a heart wet weight:body weight ratio of 2.84+/-0.05 mg/g. This value was not statistically different from the value measured in rats given drinking water containing 1 mg losartan/ml and treated with vehicle alone. No significant difference in the heart wet weight:dry weight ratio occurred among these groups of rats. Finally, treating rats with TDGA or giving rats drinking water that contained 1 mg losartan/ml altered neither their heart rate nor their mean arterial blood pressure when compared with untreated rats. This data, therefore, suggests that oxirane carboxylates induce myocardial hypertrophy by activating the AT1 receptor independent of changes in systemic hemodynamics.

Endothelin-1 induces expression of fetal genes through the interleukin-6 family of cytokines in cardiac myocytes

We here examined the role of the interleukin-6 (IL-6) family of cytokines in endothelin-1 (ET-1)-induced hypertrophic responses using cultured cardiac myocytes of neonatal rats. ET-1 induced expression of IL-6 and leukemia inhibitory factor (LIF) genes. ET-1-induced LIF gene expression was abolished by inhibition of protein kinase C activity. ET-1 activated the promoter of atrial natriuretic peptide and beta-type myosin heavy chain genes through the tyrosine kinase pathway and IL-6 receptor gp130. These results suggest that the IL-6 family of cytokines mediates ET-1-induced expression of some fetal genes in cardiac myocytes.

A heart-specific increase in cardiotrophin-1 gene expression precedes the establishment of ventricular hypertrophy in genetically hypertensive rats

OBJECTIVE

Cardiotrophin-1 is a cytokine, a novel member of the interleukin-6 superfamily, which is isolated from mouse embryoid bodies. It is known to bind a gp130/ leukemia inhibitory factor (LIF) receptor heterodimer and to induce myocyte hypertrophy. Accumulating evidence indicates that a gp130 signaling pathway is involved in cardiac development and ventricular hypertrophy.

METHODS

In order to elucidate the pathophysiologic significance of cardiotrophin-1 in ventricular hypertrophy associated with hypertension, we examined the level of cardiotrophin-1 mRNA in the ventricle of spontaneously hypertensive rats/Izm stroke-prone (SHRSP/Izm) in neonates, and at 4-, 12- and 20-weeks of age by Northern blot analysis. We also examined the gene expression of LIF by Northern blot and reverse transcription-polymerase chain reaction analyses.

RESULTS

No significant difference was observed in the level of cardiotrophin-1 mRNA in the ventricle between SHRSP/ Izm and Wistar-Kyoto/Izm (WKY/Izm) neonates. However, the level of cardiotrophin-1 mRNA in the ventricle was significantly augmented in 4-week-old SHRSP/Izm, which did not yet show overt ventricular hypertrophy, and its augmented expression lasted for the duration of the experimental period. The difference in the level of cardiotrophin-1 mRNA between the two strains was most prominent at the age of 4 weeks. This augmented expression of the cardiotrophin-1 gene was not related to the severity of left ventricular hypertrophy. The level of cardiotrophin-1 mRNA in other organs, including the kidney and lung, showed no significant change with aging and was not different between the two strains. After long-term treatment with lisinopril, levels of cardiotrophin-1 mRNA were not changed, although it morphologically prevented the development of left ventricular hypertrophy. LIF mRNA was not detected in any ventricles examined by Northern blot analysis.

CONCLUSIONS

The present study demonstrates that the expression of cardiotrophin-1 mRNA is increased in the early stage of ventricular hypertrophy in SHRSP/Izm and it remains elevated after hypertrophy has been established. However, it is unlikely that cardiotrophin-1 plays a mechanistic role in the development and maintenance of left ventricular hypertrophy in SHRSP/Izm. The present study also suggests that cardiotrophin-1, but not LIF, is a possible candidate for natural ligand of a gp130 signaling pathway in the heart.

Development and validation of real-time quantitative reverse transcriptase-polymerase chain reaction for monitoring gene expression in cardiac myocytes in vitro

In this article we present validation of a real-time RT-PCR method to quantitate mRNA expression levels of atrial natriuretic peptide and c-fos in an in vitro model of cardiac hypertrophy. This method requires minimal sample and no postreaction manipulation. In real-time RT-PCR a dual-labeled fluorescent probe is degraded concomitant with PCR amplification. Input target mRNA levels are correlated with the time (measured in PCR cycles) at which the reporter fluorescent emission increases beyond a threshold level. The use of an oligo(dt) magnetic bead protocol to harvest poly(A) mRNA from cultured cells in 96-well plates minimized DNA contamination. We show that the GAPDH gene chosen for normalization of the RNA load is truly invariant throughout the biological treatments examined. We discuss two methods of calculating fold increase: a standard curve method and the DeltaDelta Ct method. Real-time quantitative RT-PCR was used to determine the time course of c-fos induction and the effect of varying doses of four known hypertrophy agents on atrial naturitic factor messenger RNA expression in cultured cardiac muscle cells. Our results agree with published data obtained from Northern blot analysis.

GATA-5 is involved in leukemia inhibitory factor-responsive transcription of the beta-myosin heavy chain gene in cardiac myocytes

Leukemia inhibitory factor is a member of a family of structurally related cytokines sharing the receptor component gp130. Activation of gp130 by leukemia inhibitory factor is sufficient to induce myocardial cell hypertrophy accompanied by specific changes in the pattern of gene expression. However, the molecular mechanisms that link gp130 activation to these changes have not been clarified. The present study investigated the transcriptional pathways by which leukemia inhibitory factor activates beta-myosin heavy chain expression during myocardial cell hypertrophy. Mutation of the GATA motif in the beta-myosin heavy chain promoter totally abolished leukemia inhibitory factor-responsive transcription without changing basal transcriptional activity. In contrast, endothelin-1 responsiveness was unaffected by the GATA mutation. Among members of the cardiac GATA transcription factor subfamily (GATA-4, -5, and -6), GATA-5 was the sole and potent transactivator for the beta-myosin heavy chain promoter. This transactivation was dependent on sequence-specific binding of GATA-5 to the beta-myosin heavy chain GATA element. Cardiac nuclear factors that bind to to the beta-myosin heavy chain GATA element were induced by leukemia inhibitory factor stimulation. Last, leukemia inhibitory factor stimulation markedly increased transcripts of cardiac GATA-5, the expression of which is normally restricted to the early embryo. Thus, GATA-5 may be involved in gp130 signaling in cardiac myocytes.

Loss of a gp130 cardiac muscle cell survival pathway is a critical event in the onset of heart failure during biomechanical stress

Biomechanical stress is a major stimulus for cardiac hypertrophy and the transition to heart failure. By generating mice that harbor a ventricular restricted knockout of the gp130 cytokine receptor via Cre-IoxP-mediated recombination, we demonstrate a critical role for a gp130-dependent myocyte survival pathway in the transition to heart failure. Such conditional mutant mice have normal cardiac structure and function, but during aortic pressure overload, these mice display rapid onset of dilated cardiomyopathy and massive induction of myocyte apoptosis versus the control mice that exhibit compensatory hypertrophy. Thus, cardiac myocyte apoptosis is a critical point in the transition between compensatory cardiac hypertrophy and heart failure. gp130-dependent cytokines may represent a novel therapeutic strategy for preventing in vivo heart failure.

Right ventricular phenotypic characteristics in subjects with primary pulmonary hypertension or idiopathic dilated cardiomyopathy

BACKGROUND

Studies of animal models and human subjects with cardiomyopathies suggest that cardiac myocyte and ventricular chamber remodeling show distinct phenotypic characteristics that may be dependent on specific signaling pathways.

METHODS AND RESULTS

In this study, we characterize right ventricular (RV) chamber size, end-diastolic thickness, myocardial mass, and ejection fraction (EF) in human subjects with chronic heart failure from primary pulmonary hypertension (PPH; n = 10) and idiopathic dilated cardiomyopathy (IDC; n = 10). Subjects underwent gated cardiac magnetic resonance imaging (MRI), and the RVs were phenotypically classified based on the presence or absence of hypertrophy (increased mass), systolic dysfunction (reduced EF), and degree of wall thickness (concentric v eccentric pattern of hypertrophy). Within this schema, five abnormal phenotypes could be identified. In PPH subjects, in whom the RV is subjected to the uniform insult of chronic pressure overload, four different abnormal phenotypes were identified.

CONCLUSIONS

These data indicate that distinct structural/functional ventricular chamber phenotypes may be classified by MRI, and that a uniform insult can result in multiple RV phenotypes.

Cardiotrophin-1 requires LIFRbeta to promote survival of mouse motoneurons purified by a novel technique

The cytokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) signal through a receptor complex formed between two transmembrane proteins, gp130 and LIFRbeta. In addition, CNTF also uses a ligand-binding component which is anchored to the cell membrane. In the case of cardiotrophin-1 (CT-1), LIFRbeta is also required in cardiomyocytes, but this has not been proven in neurons, and published data suggest that motoneurons may use a different receptor complex. We used Lifrbeta knockout mice to assess the requirement for this receptor component in the signal transduction of CT-1 in motoneurons. To study purified motoneurons from such mutants, we have developed a method allowing for isolation of highly purified mouse motoneurons. This protocol is based on the immunoaffinity purification of motoneurons using antibodies against the extracellular domain of the neurotrophin receptor, p75, followed by cell sorting using magnetic microbeads. We show that CNTF, LIF, and CT-1 are unable to promote the survival of motoneurons derived from homozygous Lifrbeta-/- mutant embryos. Thus, LIFRbeta is absolutely required to transduce the CT-1 survival signal in motoneurons.

Paracrine induction of stem cell renewal by LIF-deficient cells: a new ES cell regulatory pathway

The propagation of pluripotential mouse embryonic stem (ES) cells is sustained by leukemia inhibitory factor (LIF) or related cytokines that act through a common receptor complex comprising the LIF receptor subunit (LIF-R) and the signal transducer gp130. However, the findings that embryos lacking LIF-R or gp130 can develop beyond gastrulation argue for the existence of an alternative pathway(s) governing the maintenance of pluripotency in vivo. In order to define those factors that contribute to self-renewal in ES cell cultures, we have generated ES cells in which both copies of the lif gene are deleted. These cells showed a significantly reduced capacity for regeneration of stem cell colonies when induced to differentiate, confirming that LIF is the major endogenous regulatory cytokine in ES cell cultures. However, self-renewal was not abolished and undifferentiated ES cell colonies were still obtained in the complete absence of LIF. A differentiated, LIF-deficient, parietal endoderm-like cell line was derived and shown to support ES cell propagation via production of a soluble, macromolecular, trypsin-sensitive activity. This activity, which we name ES cell renewal factor (ESRF), is distinct from members of the IL-6/LIF family because (i) it is effective on ES cells lacking LIF-R; (ii) it is not blocked by anti-gp130 neutralizing antibodies; and (iii) it acts without activation of STAT3. ES cells propagated clonally using ESRF alone can contribute fully to chimaeras and engender germline transmission. These findings establish that ES cell pluripotency can be sustained via a LIF-R/gp130-independent, STAT-3 independent, signaling pathway. Operation of this pathway in vivo could play an important role in the regulation of pluripotency in the epiblast and account for the viability of lifr -/- and gp130 -/- embryos.

Medical therapy of chronic heart failure. Role of ACE inhibitors and beta-blockers

Heart failure has long been considered to have a progressive downhill course leading inexorably to an early demise. This course often occurs silently, in the absence of any obvious cardiac insults. The reason for this is a combination of cell loss, myocyte dysfunction, impaired energetics, and pathologic remodeling of the chamber. Improved clinical outcome should result from strategies that reduce the biologic signals responsible for myocyte growth, dysfunction, and loss and chamber remodeling. Clinicians should no longer attempt to treat chronic heart failure with pharmacologic growth and remodeling process. In time, it may be possible for the clinician to view the treatment of heart failure largely as a matter of improving the biologic function of the myocardium.

Reciprocal regulation of ciliary neurotrophic factor receptors and acetylcholine receptors during synaptogenesis in embryonic chick atria

Ciliary neurotrophic factor (CNTF) has been implicated in the development, survival, and maintenance of a broad range of neurons and glia in the peripheral nervous system and the CNS. Evidence also suggests that CNTF may affect development of cells outside the nervous system. We have found that functional CNTF and its receptor are expressed in developing embryonic chick heart and may be involved in parasympathetic synapse formation. CNTF and CNTF receptor mRNA levels were highest at embryonic day 11 (E11)-E13, the period of parasympathetic innervation in chick atria. Levels of atrial CNTF receptor mRNA were fourfold greater at E13 than at E6 and at E13 were 2.5-fold higher in atria than in ventricle, corresponding to the higher degree of parasympathetic innervation occurring in atria. Treatment of isolated atria or cultured atrial myocytes with recombinant human or avian CNTF resulted in the tyrosine phosphorylation and nuclear translocation of the signal transducer and activator of transcription STAT3. The developmental increase in atrial CNTF receptor mRNA was enhanced by stimulating muscarinic receptors with carbachol in ovo and was inhibited by blocking muscarinic cholinergic receptors with atropine. Treatment of cultured atrial myocytes with CNTF resulted in a twofold increase in the levels of muscarinic receptors. Thus, CNTF was able to regulate a key component of parasympathetic synapses on atrial myocytes. These results suggest a postsynaptic role for CNTF in the onset of parasympathetic function in the developing heart and provide new clues to molecular mechanisms directing synapse formation at targets of the autonomic nervous system.

Maladaptive remodeling of cardiac myocyte shape begins long before failure in hypertension

Progression to failure in hypertension is associated with ventricular dilation, excessive myocyte lengthening, and an increase in myocyte length/width ratio. The temporal development of these changes in relation to impaired pump performance is unknown. We examined isolated myocytes from 1- to 12-month-old spontaneously hypertensive heart failure (SHHF) rats who develop heart failure at approximately 24 months of age. Left ventricular myocyte cross-sectional area reached a maximum of approximately 350 to 400 microm2 at 3 months of age and did not change significantly thereafter. Nonetheless, LV systolic wall stress, a known stimulus for myocyte transverse growth, increased progressively between 3 and 12 months of age. Unlike the situation in normally aging rats with stable body mass, myocyte length in SHHF rats continued to increase with aging (P<0.05 from 9 to 12 months of age). In summary, (1) left ventricular myocyte transverse growth reaches an upper limit by 3 months of age although systolic wall stress continues to rise; and (2) cell length is significantly increased by 12 months of age. This study suggests that maladaptive remodeling of cardiac myocyte shape begins long before pump failure in hypertension. Additionally, it appears that the left ventricle may be robbed of an important adaptive mechanism to normalize wall stress (eg, myocyte transverse growth) early in the progression to failure.

Neurohumoral activation and progression of heart failure: hypothetical and clinical considerations

The model for heart failure has changed radically over the past 20 years. No longer a simple hemodynamic paradigm of pump dysfunction, heart failure is now characterized as a complex clinical syndrome with release of many neurohormones and cytokines, which are believed to be most responsible for progression of disease. This change in our understanding of the pathophysiology of heart failure has important therapeutic implications. Drugs designed to influence the myocardial contractile state have been found over the past few decades to have either a neutral or an adverse effect on long-term survival, whereas agents designed to block the renin-angiotensin-aldosterone and other neurohormonal systems have proved to be remarkably effective treatment. Recently, drugs designed to block excessive sympathetic nervous system activity have been demonstrated in well-controlled studies to be safe and effective forms of therapy for heart failure. Carvedilol, a nonselective beta-adrenergic blocker with alpha1-blocking and antioxidant properties, is associated with prevention of progression of heart failure as manifested by improvement in left ventricular (LV) function, reduction in heart size, and improved survival in patients with New York Heart Association functional Class II and III symptoms. This improvement is observed equally in patients with ischemic and non-ischemic heart failure. It is tempting to speculate that beta-adrenergic blockers prevent the progression of heart failure by reducing LV mass and LV chamber size. In essence, carvedilol, and perhaps other beta-adrenergic blockers, appear to abrogate relentless LV remodeling which is typically associated with progression of heart failure. The combination of angiotensin-converting enzyme inhibitors and beta-adrenergic blockers may be particularly effective in this regard, although more data on beta-adrenergic blockers in patients with advanced heart failure are needed. Data from experimental heart failure animal models also suggest that endothelin (ET) subtype A (ET(A)) receptor blockers have the potential to lessen the pace of progressive LV remodeling. As our understanding of the neuroendocrine response to diminished cardiac performance improves, novel and even more imaginative neurohormonal and cytokine antagonists are likely to emerge as important new treatments for both hypertension and heart failure.

Cytokine-Like Factor-1, a Novel Soluble Protein, Shares Homology with Members of the Cytokine Type I Receptor Family

In this report we describe the identification, cloning, and expression pattern of human cytokine-like factor 1 (hCLF-1) and the identification and cloning of its murine homologue. They were identified from expressed sequence tags using amino acid sequences from conserved regions of the cytokine type I receptor family. Human CLF-1 and murine CLF-1 shared 96% amino acid identity and significant homology with many cytokine type I receptors. CLF-1 is a secreted protein, suggesting that it is either a soluble subunit within a cytokine receptor complex, like the soluble form of the IL-6R α-chain, or a subunit of a multimeric cytokine, e.g., IL-12 p40. The highest levels of hCLF-1 mRNA were observed in lymph node, spleen, thymus, appendix, placenta, stomach, bone marrow, and fetal lung, with constitutive expression of CLF-1 mRNA detected in a human kidney fibroblastic cell line. In fibroblast primary cell cultures, CLF-1 mRNA was up-regulated by TNF-α, IL-6, and IFN-γ. Western blot analysis of recombinant forms of hCLF-1 showed that the protein has the tendency to form covalently linked di- and tetramers. These results suggest that CLF-1 is a novel soluble cytokine receptor subunit or part of a novel cytokine complex, possibly playing a regulatory role in the immune system and during fetal development.

Activation of gp130 transduces hypertrophic signals via STAT3 in cardiac myocytes

BACKGROUND

gp130, a signal transducer of the IL-6-related cytokines, is expressed ubiquitously, including in the heart. The activation of gp130 in cardiac myocytes was reported to induce myocardial hypertrophy. The downstream side of gp130 consists of two distinct pathways in cardiac myocytes, one a Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, the other a mitogen-activated protein kinase (MAPK) pathway. In the present study, we examined whether the JAK/STAT pathway, especially the STAT3-mediated pathway, plays a critical role in gp130-dependent myocardial hypertrophy by transfecting wild-type and mutated-type STAT3 cDNA to cardiac myocytes.

METHODS AND RESULTS

We constructed three kinds of replication-defective adenovirus vectors carrying wild-type (AD/WT) or mutated-type (AD/DN) STAT3 cDNA or adenovirus vector itself (AD). Cultured murine cardiac myocytes infected with adenovirus were stimulated with leukemia inhibitory factor (LIF), and the expression of c-fos and atrial natriuretic factor (ANF) mRNAs and [3H]leucine incorporation were examined. There were no significant differences in MAPK activity among the three groups. Compared with AD-transfected cardiac myocytes, induction of c-fos and ANF mRNAs and protein synthesis after LIF stimulation were significantly augmented in AD/WT-transfected cells. In contrast, induction of c-fos and ANF mRNA expression and protein synthesis were attenuated after LIF stimulation in cardiac myocytes transfected with AD/DN.

CONCLUSIONS

These results suggest that the STAT3-dependent signaling pathway downstream of gp 130 promotes cardiac myocyte hypertrophy under stimulation with LIF.

Multiple signal transduction pathways link Na+/K+-ATPase to growth-related genes in cardiac myocytes. The roles of Ras and mitogen-activated protein kinases

We showed before that in neonatal rat cardiac myocytes partial inhibition of Na+/K+-ATPase by nontoxic concentrations of ouabain causes hypertrophic growth and transcriptional regulations of genes that are markers of cardiac hypertrophy. In view of the suggested roles of Ras and p42/44 mitogen-activated protein kinases (MAPKs) as key mediators of cardiac hypertrophy, the aim of this work was to explore their roles in ouabain-initiated signal pathways regulating four growth-related genes of these myocytes, i.e. those for c-Fos, skeletal alpha-actin, atrial natriuretic factor, and the alpha3-subunit of Na+/K+-ATPase. Ouabain caused rapid activations of Ras and p42/44 MAPKs; the latter was sustained longer than 90 min. Using high efficiency adenoviral-mediated expression of a dominant-negative Ras mutant, and a specific inhibitor of MAPK kinase (MEK), activation of Ras-Raf-MEK-p42/44 MAPK cascade by ouabain was shown. The effects of the mutant Ras, an inhibitor of Ras farnesylation, and the MEK inhibitor on ouabain-induced changes in mRNAs of the four genes indicated that (a) skeletal alpha-actin induction was dependent on Ras but not on p42/44 MAPKs, (b) alpha3 repression was dependent on the Ras-p42/44 MAPK cascade, and (c) induction of c-fos or atrial natriuretic factor gene occurred partly through the Ras-p42/44 MAPK cascade, and partly through pathways independent of Ras and p42/44 MAPKs. All ouabain effects required extracellular Ca2+, and were attenuated by a Ca2+/calmodulin antagonist or a protein kinase C inhibitor. The findings show that (a) signal pathways linked to sarcolemmal Na+/K+-ATPase share early segments involving Ca2+ and protein kinase C, but diverge into multiple branches only some of which involve Ras, or p42/44 MAPKs, or both; and (b) there are significant differences between this network and the related gene regulatory pathways activated by other hypertrophic stimuli, including those whose responses involve increases in intracellular free Ca2+ through different mechanisms.

Autocrine/paracrine determinants of strain-activated brain natriuretic peptide gene expression in cultured cardiac myocytes

The application of mechanical strain leads to activation of human brain natriuretic peptide gene promoter activity, a marker of hypertrophy, in cultured neonatal rat ventricular myocytes. We have used a combination of transient transfection analysis and reverse transcriptase-polymerase chain reaction to examine the role of locally produced factors in contributing to this activation. Conditioned media from strained, but not static, cultures led to a dose-dependent increase in human brain natriuretic peptide gene promoter activity. This increase was completely blocked by losartan or BQ-123, implying a role for angiotensin and endothelin as autocrine/paracrine mediators of the response to strain. Inclusion of the same antagonists in the cultures themselves led to only partial inhibition (approximately 60%), whereas inclusion of exogenous endothelin or angiotensin II resulted in amplification of the strain response. Angiotensin II and endothelin appear to be arrayed in series in the regulatory circuitry; the angiotensin response was blocked by BQ-123, whereas the endothelin response was unaffected by losartan. Mechanical strain was also shown to stimulate expression of the endogenous angiotensinogen, angiotensin-converting enzyme, and endothelin genes in this system. Collectively, these data indicate that locally generated angiotensin II and endothelin, acting in series, play an important autocrine/paracrine role in mediating strain-dependent activation of cardiac-specific gene expression.

Endothelin-1 and cardiotrophin-1 induce brain natriuretic peptide gene expression by distinct transcriptional mechanisms

Cardiotrophin-1 (CT-1) a novel IL-6-related cytokine, induces distinct hypertrophic responses to endothelin-1 (ET-1) on cultured neonatal rat cardiac myocytes. We found that ET-1 and CT-1 show a distinct pattern of gene induction of natriuretic peptides. Elucidation of the transcriptional mechanisms of brain natriuretic peptide (BNP) gene induction by. ET-1 or CT-1 will provide better information for our understanding of the molecular mechanisms of cardiac hypertrophy. In this study, reporter constructs containing the human BNP 5' flanking sequence were transfected into neonatal rat cardiac myocytes and the cells were stimulated with ET-1 or CT-1. A total of 1813 bp of the human BNP 5' flanking sequence conferred an ET-1 inducibility on the reporter gene. However, it did not confer CT-1 inducibility. These results show that distinct mechanisms are involved in BNP gene induction by ET-1 or CT-1, and (in this study) that the CT-1 responsive element is not located in the region examined.