Angiotensin II induced cardiac hypertrophy in vivo is inhibited by cyclosporin A in adult rats

Between Inflammation and Autophagy: The Role of Leptin-Adiponectin Axis in Cardiac Remodeling

Cardiac remodeling is the process by which the heart adapts to stressful stimuli, such as hypertension and ischemia/reperfusion; it ultimately leads to heart failure upon long-term exposure. Autophagy, a cellular catabolic process that was originally considered as a mechanism of cell death in response to detrimental stimuli, is thought to be one of the main mechanisms that controls cardiac remodeling and induces heart failure. Dysregulation of the adipokines leptin and adiponectin, which plays essential roles in lipid and glucose metabolism, and in the pathophysiology of the neuroendocrine and cardiovascular systems, has been shown to affect the autophagic response in the heart and to contribute to accelerate cardiac remodeling. The obesity-associated protein leptin is a pro-inflammatory, tumor-promoting adipocytokine whose elevated levels in obesity are associated with acute cardiovascular events, and obesity-related hypertension. Adiponectin exerts anti-inflammatory and anti-tumor effects, and its reduced levels in obesity correlate with the pathogenesis of obesity-associated cardiovascular diseases. Leptin- and adiponectin-induced changes in autophagic flux have been linked to cardiac remodeling and heart failure. In this review, we describe the different molecular mechanisms of hyperleptinemia- and hypoadiponectinemia-mediated pathogenesis of cardiac remodeling and the involvement of autophagy in this process. A better understanding of the roles of leptin, adiponectin, and autophagy in cardiac functions and remodeling, and the exact signal transduction pathways by which they contribute to cardiac diseases may well lead to discovery of new therapeutic agents for the treatment of cardiovascular remodeling.

Role of CyPA in cardiac hypertrophy and remodeling

Pathological cardiac hypertrophy is a complex process and eventually develops into heart failure, in which the heart responds to various intrinsic or external stress, involving increased interstitial fibrosis, cell death and cardiac dysfunction. Studies have shown that oxidative stress is an important mechanism for this maladaptation. Cyclophilin A (CyPA) is a member of the cyclophilin (CyPs) family. Many cells secrete CyPA to the outside of the cells in response to oxidative stress. CyPA from blood vessels and the heart itself participate in a variety of signaling pathways to regulate the production of reactive oxygen species (ROS) and mediate inflammation, promote cardiomyocyte hypertrophy and proliferation of cardiac fibroblasts, stimulate endothelial injury and vascular smooth muscle hyperplasia, and promote the dissolution of extracellular matrix (ECM) by activating matrix metalloproteinases (MMPs). The events triggered by CyPA cause a decline of diastolic and systolic function and finally lead to the occurrence of heart failure. This article aims to introduce the role and mechanism of CyPA in cardiac hypertrophy and remodeling, and highlights its potential role as a disease biomarker and therapeutic target.

Cardiomyocyte calcineurin is required for the onset and progression of cardiac hypertrophy and fibrosis in adult mice

Previous studies have demonstrated that activation of calcineurin induces pathological cardiac hypertrophy (CH). In these studies, loss-of-function was mostly achieved by systemic administration of the calcineurin inhibitor cyclosporin A. The lack of conditional knockout models for calcineurin function has impeded progress toward defining the role of this protein during the onset and the development of CH in adults. Here, we exploited a mouse model of CH based on the infusion of a hypertensive dose of angiotensin II (AngII) to model the role of calcineurin in CH in adulthood. AngII-induced CH in adult mice was reduced by treatment with cyclosporin A, without affecting the associated increase in blood pressure, and also by induction of calcineurin deletion in adult mouse cardiomyocytes, indicating that cardiomyocyte calcineurin is required for AngII-induced CH. Surprisingly, cardiac-specific deletion of calcineurin, but not treatment of mice with cyclosporin A, significantly reduced AngII-induced cardiac fibrosis and apoptosis. Analysis of profibrotic genes revealed that AngII-induced expression of Tgfβ family members and Lox was not inhibited by cyclosporin A but was markedly reduced by cardiac-specific calcineurin deletion. These results show that AngII induces a direct, calcineurin-dependent prohypertrophic effect in cardiomyocytes, as well as a systemic hypertensive effect that is independent of calcineurin activity.

E4BP4 inhibits AngII-induced apoptosis in H9c2 cardiomyoblasts by activating the PI3K-Akt pathway and promoting calcium uptake

The bZIP transcription factor E4BP4 is a survival factor that is known to be elevated in diseased heart and promote cell survival. In this study the role of E4BP4 on angiotensin-II (AngII)-induced apoptosis has been examined in in vitro cell model. H9c2 cardiomyoblast cells that overexpressed E4BP4 were exposed to AngII to observe the cardio-protective effects of E4BP4 on hypertension related apoptosis. The results from TUNEL assays revealed that E4BP4 significantly attenuated AngII-induced apoptosis. Further analysis by Western blot and RT-PCR showed that E4BP4 inhibited AngII-induced IGF-II mRNA expression and cleavage of caspase-3 through the PI3K-Akt pathway. In addition, E4BP4 enhanced calcium reuptake into the sacroplasmic reticulum by down-regulating PP2A and by up-regulating the phosphorylation of PKA and PLB proteins. Our findings indicate that E4BP4 functions as a survival factor in cardiomyoblasts by inhibiting IGF-II transcription and by regulating calcium cycling.

Calcium Signaling and Transcriptional Regulation in Cardiomyocytes

Calcium (Ca 2+ ) is a universal regulator of various cellular functions. In cardiomyocytes, Ca 2+ is the central element of excitation–contraction coupling, but also impacts diverse signaling cascades and influences the regulation of gene expression, referred to as excitation–transcription coupling. Disturbances in cellular Ca 2+ -handling and alterations in Ca 2+ -dependent gene expression patterns are pivotal characteristics of failing cardiomyocytes, with several excitation–transcription coupling pathways shown to be critically involved in structural and functional remodeling processes. Thus, targeting Ca 2+ -dependent transcriptional pathways might offer broad therapeutic potential. In this article, we (1) review cytosolic and nuclear Ca 2+ dynamics in cardiomyocytes with respect to their impact on Ca 2+ -dependent signaling, (2) give an overview on Ca 2+ -dependent transcriptional pathways in cardiomyocytes, and (3) discuss implications of excitation–transcription coupling in the diseased heart.

E2/ER β inhibit ISO-induced cardiac cellular hypertrophy by suppressing Ca2+-calcineurin signaling

Cardiovascular incidences are markedly higher in men than in pre-menstrual women. However, this advantage in women declines with aging and therefore can be correlated with the sex hormone 17β-Estradiol (E2) which is reported to protect heart cells by acting though estrogen receptors (ERs). In this study we have determined the effect of E2/ERβ against ISO induced cellular hypertrophy in H9c2 cardiomyoblast cells. The results confirm that ISO induced cardiac-hypertrophy by elevating the levels of hypertrophy associated proteins, ANP and BNP and further by upregulating p-CaMKII, calcineurin, p-GATA4 and NFATc3 which was correlated with a significant enlargement of the H9c2 cardiomyoblast. However, overexpression of ERβ and/or administration of E2 inhibited ISO-induced hypertrophy in H9c2 cells. In addition, E2/ERβ also inhibited ISO-induced NFATc3 translocation, and reduced the protein level of downstream marker, BNP. Furthermore, by testing with the calcineurin inhibitor (CsA), it was confirmed that calcineurin acted as a key mediator for the anti-hypertrophic effect of E2/ERβ. In cells treated with calcium blocker (BATPA), the inhibitory effect of E2/ERβ on ISO-induced Ca²⁺ influx and hypertrophic effects were totally blocked suggesting that E2/ERβ inhibited calcineurin activity to activate I-1 protein and suppress PP1, then induce PLB protein phosphorylation and activation, resulting in Ca²⁺ reuptake into sarcoplasmic reticulum through SR Ca²⁺ cycling modification. In conclusion, E2/ERβ suppresses the Ca²⁺ influx and calcineurin activity induced by ISO to enhance the PLB protein activity and SR Ca²⁺ cycling.

Compensatory renal hypertrophy following uninephrectomy is calcineurin-independent

Calcineurin is a calcium-dependent phosphatase that is involved in many cellular processes including hypertrophy. Inhibition or genetic loss of calcineurin blocks pathological cardiac hypertrophy and diabetic renal hypertrophy. However, calcineurin does not appear to be involved in physiological cardiac hypertrophy induced by exercise. The role of calcineurin in a compensatory, non-pathological model of renal hypertrophy has not been tested. Therefore, in this study, we examined activation of calcineurin and the effect of calcineurin inhibition or knockout on compensatory hypertrophy following uninephrectomy (UNX). UNX induces ∼15% increase in the size of the remaining kidney; the data show no change in the generation of reactive oxygen species (ROS), Nox4 or transforming growth factor-β expression confirming the model as one of compensatory hypertrophy. Next, analyses of the remaining kidney reveal that total calcineurin activity is increased, and, to a lesser extent, transcriptional activity of the calcineurin substrate nuclear factor of activated T cell is up-regulated following UNX. However, inhibition of calcineurin with cyclosporine failed to prevent compensatory renal hypertrophy. Likewise, hypertrophy was comparable to WT in mice lacking either isoform of the catalytic subunit of calcineurin (CnAα−/− or CnAβ−/−). In conclusion, similar to its role in the heart, calcineurin is required for pathological but not compensatory renal hypertrophy. This separation of signalling pathways could therefore help further define key factors necessary for pathological hypertrophy including diabetic nephropathy.

Liganded vitamin D receptor displays anti-hypertrophic activity in the murine heart

Vitamin D and its analogs have been suggested to have palliative effects in the cardiovascular system. We have examined the effects of co-administration of the vitamin D receptor agonist, paricalcitol, on the hypertension, cardiac hypertrophy and interstitial fibrosis produced by chronic angiotensin II (AII) infusion. Administration of AII (800ng/kg/min) over a 14-day period resulted in increased blood pressure, myocyte hypertrophy, activation of the hypertrophic fetal gene program (atrial natriuretic peptide, B-type natriuretic peptide and alpha skeletal actin gene expression), increased expression of the pro-hypertrophic modulatory calcineurin inhibitor protein 1 (MCIP 1), and increased fibrosis with augmented procollagen 1 and 3 gene expression. In each case co-administration of paricalcitol (300ng/kg intraperitoneally every 48h) at least partially reversed the AII-dependent effect. These studies demonstrate that the liganded vitamin D receptor possesses potent anti-hypertrophic activity in this non-renin-dependent model of cardiac hypertrophy. The anti-hypertrophic activity appears to be at least partially intrinsic to the cardiac myocyte and may involve suppression of the MCIP 1 protein. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Calcineurin regulation of cytoskeleton organization: a new paradigm to analyse the effects of calcineurin inhibitors on the kidney

Calcineurin is a serine/threonine phosphatase originally involved in the immune response but is also known for its role as a central mediator in various non-immunological intracellular signals. The nuclear factor of activated T cell (NFAT) proteins are the most widely described substrates of calcineurin, but ongoing work has uncovered other substrates among which are the cytoskeleton organizing proteins (i.e. cofilin, synaptopodin, WAVE-1). Control over cytoskeletal proteins is of outmost interest because the phenotypic properties of cells are dependent on cytoskeleton architecture integrity, while rearrangements of the cytoskeleton are implicated in both physiological and pathological processes. Previous works investigating the role of calcineurin on the cytoskeleton have focused on neurite elongation, myocyte hypertrophic response and recently in kidney cells structure. Nuclear factor of activated T cell activation is expectedly identified in the signalling pathways for calcineurin-induced cytoskeleton organization, however new NFAT-independent pathways have also been uncovered. The aim of this review is to summarize the current knowledge on the effects of calcineurin on cytoskeletal proteins and related intracellular pathways. These newly described properties of calcineurin on cytoskeletal proteins may explain some of the beneficial or deleterious effects observed in kidney cells associated with the use of the calcineurin inhibitors, cyclosporine and tacrolimus.

Calcineurin A-β is required for hypertrophy but not matrix expansion in the diabetic kidney

Calcineurin is an important signalling protein that regulates a number of molecular and cellular processes. Previously, we found that inhibition of calcineurin with cyclosporine reduced renal hypertrophy and blocked glomerular matrix expansion in the diabetic kidney. Isoforms of the catalytic subunit of calcineurin are reported to have tissue specific expression and functions. In particular, the β isoform has been implicated in cardiac and skeletal muscle hypertrophy. Therefore, we examined the role of calcineurin β in diabetic renal hypertrophy and glomerular matrix expansion. Type I diabetes was induced in wild-type and β^−/− mice and then renal function, extracellular matrix expansion and hypertrophy were evaluated. The absence of β produced a significant decrease in total calcineurin activity in the inner medulla (IM) and reduced nuclear factor of activated T-cells (NFATc) activity. Loss of β did not alter diabetic renal dysfunction assessed by glomerular filtration rate, urine albumin excretion and blood urea nitrogen. Similarly, matrix expansion in the whole kidney and glomerulus was not different between diabetic wild-type and β^−/− mice. In contrast, whole kidney and glomerular hypertrophy were significantly reduced in diabetic β^−/− mice. Moreover, β^−/− renal fibroblasts demonstrated impaired phosphorylation of Erk1/Erk2, c-Jun N-terminal kinases (JNK) and mammalian target of rapamycin (mTOR) following stimulation with transforming growth factor-β and did not undergo hypertrophy with 48 hrs culture in high glucose. In conclusion, loss of the β isoform of calcineurin is sufficient to reproduce beneficial aspects of cyclosporine on diabetic renal hypertrophy but not matrix expansion. Therefore, while multiple signals appear to regulate matrix, calcineurin β appears to be a central mechanism involved in organ hypertrophy.

CaMKII in the cardiovascular system: sensing redox states

The multifunctional Ca(2+)- and calmodulin-dependent protein kinase II (CaMKII) is now recognized to play a central role in pathological events in the cardiovascular system. CaMKII has diverse downstream targets that promote vascular disease, heart failure, and arrhythmias, so improved understanding of CaMKII signaling has the potential to lead to new therapies for cardiovascular disease. CaMKII is a multimeric serine-threonine kinase that is initially activated by binding calcified calmodulin (Ca(2+)/CaM). Under conditions of sustained exposure to elevated Ca(2+)/CaM, CaMKII transitions into a Ca(2+)/CaM-autonomous enzyme by two distinct but parallel processes. Autophosphorylation of threonine-287 in the CaMKII regulatory domain "traps" CaMKII into an open configuration even after Ca(2+)/CaM unbinding. More recently, our group identified a pair of methionines (281/282) in the CaMKII regulatory domain that undergo a partially reversible oxidation which, like autophosphorylation, prevents CaMKII from inactivating after Ca(2+)/CaM unbinding. Here we review roles of CaMKII in cardiovascular disease with an eye to understanding how CaMKII may act as a transduction signal to connect pro-oxidant conditions into specific downstream pathological effects that are relevant to rare and common forms of cardiovascular disease.

Activated NHE1 is required to induce early cardiac hypertrophy in mice

The Na+/H+ exchanger isoform 1 (NHE1) has been implicated as being causal in cardiac hypertrophy and the protein level and activity are elevated in the diseased myocardium. However, it is unclear whether mere elevation of the protein is sufficient for cardiac pathology, or whether activation of the protein is required. In this study, we examined the comparative effects of elevation of wild type and activated NHE1. Two mouse transgenic models that expressed either a wild type NHE1 protein or an activated NHE1 protein were characterized. Expression of activated NHE1 caused significant increases in heart weight to body weight, apoptosis, cross-sectional area, interstitial fibrosis and decreased cardiac performance. Expression of wild type NHE1 caused a much milder pathology. When we examined 2 or 10-week-old mouse hearts, there was neither elevation of calcineurin levels nor increased phosphorylation of ERK or p38 in either NHE1 transgenic mouse line. Expression of activated NHE1 in intact mice caused an increased sensitivity to phenylephrine-induced hypertrophy. Our results show that expression of activated NHE1 promotes cardiac hypertrophy to a much greater degree than elevated levels of wild type NHE1 alone. In addition, expression of activated NHE1 promotes greater sensitivity to neurohormonal stimulation. The results suggest that activation of NHE1 is a key component that accentuates NHE1-induced myocardial pathology.

What causes a broken heart--molecular insights into heart failure

Our understanding of the molecular processes which regulate cardiac function has grown immeasurably in recent years. Even with the advent of β-blockers, angiotensin inhibitors and calcium modulating agents, heart failure (HF) still remains a seriously debilitating and life-threatening condition. Here, we review the molecular changes which occur in the heart in response to increased load and the pathways which control cardiac hypertrophy, calcium homeostasis, and immune activation during HF. These can occur as a result of genetic mutation in the case of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) or as a result of ischemic or hypertensive heart disease. In the majority of cases, calcineurin and CaMK respond to dysregulated calcium signaling and adrenergic drive is increased, each of which has a role to play in controlling blood pressure, heart rate, and left ventricular function. Many major pathways for pathological remodeling converge on a set of transcriptional regulators such as myocyte enhancer factor 2 (MEF2), nuclear factors of activated T cells (NFAT), and GATA4 and these are opposed by the action of the natriuretic peptides ANP and BNP. Epigenetic modification has emerged in recent years as a major influence cardiac physiology and histone acetyl transferases (HATs) and histone deacetylases (HDACs) are now known to both induce and antagonize hypertrophic growth. The newly emerging roles of microRNAs in regulating left ventricular dysfunction and fibrosis also has great potential for novel therapeutic intervention. Finally, we discuss the role of the immune system in mediating left ventricular dysfunction and fibrosis and ways this can be targeted in the setting of viral myocarditis.

Locally overexpressing hepatocyte growth factor prevents post-ischemic heart failure by inhibition of apoptosis via calcineurin-mediated pathway and angiogenesis

BACKGROUND

Myocardial infarction is a significant cause of heart failure. Currently, therapies are limited and novel revascularization methods may play a role. We investigated the effects of hepatocyte growth factor (HGF) expressed by bone marrow-derived mesenchymal stem cells (MSCs) on post-ischemic heart failure.

METHODS

Four weeks after myocardial infarction (MI), Sprague Dawley rats were randomly divided into saline control group, MSC-GFP group, MSC-HGF group, and MSC-HGF+CsA group. After another 4 weeks, hearts were analyzed for ventricular geometry, myocardial function, angiogenesis and endothelial cell density, apoptosis and the expression of calcineurin, Akt, and Bcl-2 protein.

RESULTS

In MSC-HGF group, rats exhibited better LV systolic and diastolic function compared with other groups after 8 weeks of MI. Angiogenesis was significantly enhanced by HGF through inducing proliferation of endothelial cells. The effects of HGF on apoptosis were associated with the expression level of calcineurin protein.

CONCLUSIONS

Our findings suggest that overexpression of HGF improved ischemic cardiac function through angiogenesis and reduction of apoptosis partly mediated by upregulation of calcineurin.

Imbalance between CaM kinase II and calcineurin activities impairs caffeine-induced calcium release in hypertrophic cardiomyocytes

Cardiac hypertrophy impairs Ca(2+) handling in the sarcoplasmic reticulum, thereby impairing cardiac contraction. To identify the mechanisms underlying impaired Ca(2+) release from the sarcoplasmic reticulum in hypertrophic cardiomyocytes, we assessed Ca(2+)-dependent signaling and the phosphorylation of phospholamban, which regulates Ca(2+) uptake during myocardial relaxation and is in turn regulated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and calcineurin. In cultured rat cardiomyocytes, treatment with endothelin-1, angiotensin II, and phenylephrine-induced hypertrophy and increased CaMKII autophosphorylation and calcineurin expression. The calcineurin level reached its maximum at 72h and remained elevated for at least 96h after endothelin-1 or angiotensin II treatment. By contrast, CaMKII autophosphorylation, phospholamban phosphorylation, and caffeine-induced Ca(2+) mobilization all peaked 48h after these treatments. By 96h after treatment, CaMKII autophosphorylation and phospholamban phosphorylation had returned to baseline, and caffeine-induced Ca(2+) mobilization was impaired relative to baseline. A similar biphasic change was observed in dystrophin levels in endothelin-1-induced hypertrophic cardiomyocytes, and treatment with the novel CaM antagonists DY-9760e and DY-9836 significantly inhibited the hypertrophy-induced dystrophin breakdown. Taken together, the abnormal Ca(2+) regulation in cardiomyocytes following hypertrophy is in part mediated by an imbalance in calcineurin and CaMKII activities, which leads to abnormal phospholamban activity.

Cyclosporin A inhibits hypoxia-induced pulmonary hypertension and right ventricle hypertrophy

RATIONALE

Hypoxia-induced pulmonary hypertension involves hypoxia-inducible factor-1alpha (HIF-1alpha) activation as well as elevated resting calcium levels. Cyclosporin A (CsA) inhibits calcium-induced calcineurin activation and blocks the stabilization of HIF-1alpha in cultured cells.

OBJECTIVES

We hypothesized that treatment of rats with CsA would prevent HIF-1-dependent gene transcription, lower specific responses to acute hypoxia, and prevent pulmonary hypertension and right ventricle hypertrophy resulting from prolonged exposure to hypoxia.

METHODS

Acute and chronic responses to hypoxia were studied in rats treated or not treated with CsA (25 mg x kg(-1) x d(-1)).

MEASUREMENTS

Transcript levels of genes encoding the serotonin transporter or four HIF-1 target genes, in rats exposed for 6 h to ambient hypoxia, treated or not by CsA, were measured. In vivo hemodynamics, hematocrit, and heart morphologic characteristics were assessed in rats subjected to hypoxia for 3 wk, treated or not treated with CsA. Changes in mRNA levels of the modulatory calcineurin-interacting protein-1 (MCIP-1) were used as a sensitive indicator of calcineurin activity in lung and heart.

MAIN RESULTS

Acute exposure to hypoxia led to a marked increase in mRNA levels of serotonin transporter, modulatory calcineurin-interacting protein-1, and HIF-1 target genes, which was blunted by CsA treatment. Prolonged exposure to hypoxia raised right ventricle pressure, induced right ventricle hypertrophy, and activated cardiac calcineurin, effects that were fully prevented by CsA treatment.

CONCLUSIONS

These results suggest that CsA prevents hypoxia-induced pulmonary hypertension and right ventricle hypertrophy, either by inhibiting HIF-1 transcriptional activity in lung, by decreasing calcineurin activity in lung and heart, by direct effects of CsA, or by a combination of these factors.

Activation of ERK and suppression of calcineurin are interacting mechanisms of cardioprotection afforded by δ-opioid receptor activation

The aim of this study was to examine possible interactions of ERK and calcineurin in cardioprotection afforded by delta-opioid receptor stimulation. Infarction was induced in rat hearts by 20-min coronary occlusion and reperfusion. Tissue ERK level and calcienurin activity were determined by immunoblotting and an assay using a phosphopeptide substrate, respectively. Administration of a delta-opioid receptor agonist, D-Ala2-D-Leu5-enkephalin (DADLE, 1 mg/kg), before ischemia increased the phospho-ERK levels during ischemia and reduced infarct size (as percentage of risk area, %IS/AR) from 47.7 +/- 2.3% to 23.2 +/- 2.5%. This protection was abolished by 10 mg/kg of natrindole hydrochloride (NTI), a delta-opioid receptor antagonist. PD98059, a MEK1/2 inhibitor, abolished both ERK1/2 activation and infarct size limitation by DADLE. Calcineurin inhibitors, cyclosporine-A (5 mg/kg) and FK506 (3.5 mg/kg), reduced %IS/AR (27.4 +/- 4.4% and 29.9 +/- 3.4%, respectively). The protective effects of these calcineurin inhibitors were inhibited by PD98059, and the combination of DADLE with cyclosporine-A or FK506 did not afford further cardioprotection. DADLE significantly suppressed myocardial calcineurin activity, and this effect was inhibited by NTI. Suppression of calcineurin activity by FK506 was associated with modest activation of ERK1/2. These results suggest that suppression of calcineurin and activation of ERK1/2 are interacting mechanisms involved in cardioprotection by delta-opioid receptor activation.

Sex dimorphism in cardiac pathophysiology: experimental findings, hormonal mechanisms, and molecular mechanisms

The higher cardiovascular risk in men and post-menopausal women implies a protective action of estrogen. A large number of experimental studies have provided strong support to this concept. However, the recent clinical trials with negative outcomes regarding hormone replacement therapy call for "post hoc" reassessment of existing information, models, and research strategies as well as a summary of recent findings. Sex steroid hormones, in particular estrogen, regulate numerous processes that are related to the development and progression of cardiovascular disease through a variety of signaling pathways. Use of genetically modified models has resulted in interesting information on diverse actions mediated by steroid receptors. By focusing on experimental findings, we have reviewed hormonal, cellular, and signaling mechanisms responsible for sex dimorphism and actions of hormone replacement therapy and addressed current limitations and future directions of experimental research.

Vascular but not cardiac remodeling is associated with superoxide production in angiotensin II hypertension

OBJECTIVE

Angiotensin (Ang) II increases reactive oxygen species (ROS), decreases nitric oxide (NO) bioavailability and promotes cardiovascular remodeling. ROS have been identified as critical second messengers of the trophic responses by Ang II. In rats with Ang II-induced hypertension, we investigated the role of ROS in cardiac hypertrophy as well as the remodeling of aortas and mesenteric (resistance) arteries.

METHODS

Sprague-Dawley rats received Ang II (0.7 mg/kg per day by mini-pump, n = 7) or vehicle (n = 7) for 5 days. Endothelium-dependent relaxation to acetylcholine (EDR) in aortas was determined in organ baths and in mesenteric resistance vessels in a pressurized myograph. Superoxide (O2) production was measured by lucigenin chemiluminescence, laser-confocal fluorescence microscopy (LCM) and NADPH oxidase assay.

RESULTS

Ang II-treated rats developed hypertension (183 +/- 3 versus 138 +/- 4 mmHg, P < 0.05), increased aortic O2 (50%), aortic hypertrophy (12%) and impaired EDR. Mesenteric arteries manifested impaired EDR, increased NADPH oxidase activity (356%) and eutrophic inward remodeling (decreased lumen diameter and increased wall/lumen ratio). However, although Ang II-treated rats developed cardiac hypertrophy (13%), this was not accompanied by an increase in cardiac O2, as measured by lucigenin, LCM or NADPH oxidase assay. On the other hand, cardiac calcineurin, a molecule that promotes cardiac hypertrophy linked to Ang II, was increased by 40% (52 +/- 8 versus 33 +/- 5 pmol/min per mg protein, P < 0.05).

CONCLUSION

These studies demonstrate that the role of ROS in Ang II-induced vascular remodeling differ across vascular territories. Although in conduit and resistance vessels, vascular hypertrophy and endothelial dysfunction are linked to increased ROS production, cardiac hypertrophy is not. Instead, cardiac hypertrophy is associated, at least in part, with an increase in calcineurin. These studies unveil novel mechanisms that may play an important role in the pathogenesis of cardiac and vascular injury in hypertension.

Activation of calcineurin in human failing heart ventricle by endothelin-1, angiotensin II and urotensin II

1 The calcineurin (CaN) enzyme-transcriptional pathway is critically involved in hypertrophy of heart muscle in some animal models. Currently there is no information concerning the regulation of CaN activation by endogenous agonists in human heart. 2 Human right ventricular trabeculae from explanted human (14 male/2 female) failing hearts were set up in a tissue bath and electrically paced at 1 Hz and incubated with or without 100 nM endothelin-1 (ET-1), 10 M, angiotensin-II (Ang II) or 20 nM human urotensin-II (hUII) for 30 min. Tissues from four patients were incubated with 200 nM tacrolimus (FK506) for 30 min and then incubated in the presence or absence of ET-1 for a further 30 min. 3 ET-1 increased contractile force in all 13 patients (P<0.001). Ang II and hUII increased contractile force in three out of eight and four out of 10 patients but overall nonsignificantly (P>0.1). FK506 had no effect on contractile force (P=0.12). 4 ET-1, Ang II and hUII increased calcineurin activity by 32, 71 and 15%, respectively, while FK506 reduced activity by 34%. ET-1 in the presence of FK506 did not restore calcineurin activity (P=0.1). 5 There was no relationship between basal CaN activity and expression levels in the right ventricle. Increased levels of free phosphate were detected in ventricular homogenates that were incubated with PKC(epsilon) compared to samples incubated without PKC(epsilon). 6 Endogenous cardiostimulants which activate G(alpha)q-coupled receptors increase the activity of calcineurin in human heart following acute (30 min) exposure. PKC may contribute to this effect by increasing levels of phosphorylated calcineurin substrate.

Calcium-calcineurin signaling in the regulation of cardiac hypertrophy

Cardiac hypertrophy is a leading predicator of progressive heart disease that often leads to heart failure and a loss of cardiac contractile performance associated with profound alterations in intracellular calcium handling. Recent investigation has centered on identifying the molecular signaling pathways that regulate cardiac myocyte hypertrophy, as well as the mechanisms whereby alterations in calcium handling are associated with progressive heart failure. One potential focal regulator of cardiomyocyte hypertrophy that also responds to altered calcium handling is the calmodulin-activated serine/threonine protein phosphatase calcineurin (PP2B). Once activated by increases in calcium, calcineurin mediates the hypertrophic response through its downstream transcriptional effector nuclear factor of activated T cells (NFAT), which is directly dephosphorylated by calcineurin resulting in nuclear translocation. While previous studies have convincingly demonstrated the sufficiency of calcineurin to mediate cardiac hypertrophy and progressive heart failure, its necessity remains an area of ongoing investigation. Here we weigh an increasing body of literature that suggests a causal link between calcineurin signaling and the cardiac hypertrophic response and heart failure through the use of pharmacologic inhibitors (cyclosporine A and FK506) and genetic approaches. We will also discuss the manner in which calcineurin-NFAT signaling is negatively regulated in the heart through a diverse array of kinases and inhibitory proteins. Finally, we will discuss emerging theories as to the mechanisms whereby alterations in intracellular calcium handling might stimulate calcineurin within the context of a contractile cell continually experiencing calcium flux.

Calcineurin independent development of myocardial hypertrophy in transgenic rats overexpressing the mouse renin gene, TGR(mREN2)27

Myocardial hypertrophy is an independent risk factor for development of heart failure. The intracellular calcium homeostasis is altered in myocardial hypertrophy, and recent studies in animal models have confirmed an interaction between the Ca2+/calmodulin-dependent calcineurin signaling cascade and development of cardiac hypertrophy. There is evidence for the involvement of various pathways in development of hypertrophy. A transgenic rat model overexpressing the mouse renin gene, TGR(mREN2)27 has been shown to progress profound cardiac hypertrophy, possibly due to a monogenetic disorder. However, the exact mode of action is not known. To study a possible involvement of calcineurin and its downstream pathway in development of cardiac hypertrophy in this transgenic rat model we measured the protein expression of marker proteins of the calcineurin cascade (calcineurin, NFAT-3, GATA-4) and calcineurin phosphatase activity and GATA-4 DNA binding in TGR ( n=10) compared to age-matched Sprague-Dawley rats ( n=10). In our study there was no significant difference in calcineurin activity between the transgenic hearts and the hearts of Sprague-Dawley rats. Furthermore, we found neither an increase in protein expression of calcineurin B nor a rise in nuclear translocated NFAT-3 DU. Interestingly, the protein expression of GATA-4 and its DNA binding activity were significantly higher in hypertrophied myocardium than in control hearts. In transgenic rats overexpressing the mouse renin gene and thereby developing pronounced cardiac hypertrophy [TGR(mREN2)27] we thus found no activation of calcineurin or its downstream pathway. However, the expression of the transcriptional factor GATA-4 and its DNA binding activity were significantly increased in hearts of transgenic rats. Thus GATA-4 seems to be a marker of hypertrophy independently of calcineurin activation, possibly activated by various pathways.

Calcineurin-mediated pathway involved in the differentiated phenotype of smooth muscle cells

The calcineurin-mediated pathway is involved in skeletal and cardiac hypertrophy and vascular development in vivo, but the relationship between this pathway and the phenotype of smooth muscle cells (SMCs) remains unknown. Using visceral SMCs in culture as a model system of differentiated SMCs, we investigated the role of the calcineurin-mediated pathway in maintaining the differentiated phenotype of SMCs, which depends on the insulin-like growth factor (IGF-I)-triggered activation of the phosphatidylinositol 3-kinase (PI3-K)/protein kinase B (PKB(Akt)) pathway. Treatment with calcineurin inhibitors, cyclosporin A or FK506, or the forced expression of the natural calcineurin inhibitor, CAIN, induced SMC dedifferentiation. Notably, suppression of the promoter activities of the SMC molecular markers caldesmon and alpha1 integrin by blocking the PI3-K/PKB(Akt) pathway was rescued by the forced expression of constitutively active calcineurin Aalpha, suggesting that the calcineurin-mediated pathway is critical for maintaining the differentiated phenotype of SMCs and works downstream of the PI3-K/PKB(Akt) pathway.

Targeted disruption of NFATc3, but not NFATc4, reveals an intrinsic defect in calcineurin-mediated cardiac hypertrophic growth

A calcineurin-nuclear factor of activated T cells (NFAT) regulatory pathway has been implicated in the control of cardiac hypertrophy, suggesting one mechanism whereby alterations in intracellular calcium handling are linked to the expression of hypertrophy-associated genes. Although recent studies have demonstrated a necessary role for calcineurin as a mediator of cardiac hypertrophy, the potential involvement of NFAT transcription factors as downstream effectors of calcineurin signaling has not been evaluated. Accordingly, mice with targeted disruptions in NFATc3 and NFATc4 genes were characterized. Whereas the loss of NFATc4 did not compromise the ability of the myocardium to undergo hypertrophic growth, NFATc3-null mice demonstrated a significant reduction in calcineurin transgene-induced cardiac hypertrophy at 19 days, 26 days, 6 weeks, 8 weeks, and 10 weeks of age. NFATc3-null mice also demonstrated attenuated pressure overload- and angiotensin II-induced cardiac hypertrophy. These results provide genetic evidence that calcineurin-regulated responses require NFAT effectors in vivo.

Calcineurin and cardiac hypertrophy: where have we been? Where are we going?

The heart is a dynamic organ capable of adapting its size and architecture in response to alterations in workload associated with developmental maturation, physiological stimulation and pathological diseases. Such alterations in heart size typically result from the hypertrophic growth of individual myocytes, but not myocyte cellular proliferation. In recent years, a great deal of investigation has gone toward elucidating the molecular signalling machinery that underlies the hypertrophic response and manner in which increased cardiac load promotes alterations in gene expression. To this end, the Ca(2+)-calmodulin-activated phosphatase calcineurin has been proposed as a necessary component of the multi-pathway hypertrophy program in the heart. Despite initial controversy over this hypothesis due to disparate results from pharmacological inhibitory studies in animal models of hypertrophy, compelling data from genetic models with calcineurin inhibition now exist. This review will summarize many of these studies and will attempt to address a number of unanswered issues. In particular, specific downstream mediators of calcineurin signalling will be discussed, as well as the need to identify calcineurin's temporal activation profile, transcriptional targets and cross-communication with other reactive signalling pathways in the heart. Finally, we will present evidence suggesting that calcineurin, as a Ca(2+)-responsive enzyme, may function as an internal load sensor in cardiac myocytes, matching output demands to hypertrophic growth.