Engineering Ca2+/calmodulin-mediated modulation of protein translocation by overlapping binding and signaling peptide sequences

Protein translocation is used by cells to regulate protein activity in time and space. Synthetic systems have studied the effect of second messengers and exogenous chemicals on translocation, and have used translocation-based sensors to monitor unrelated pathways such as caspase activity. We have created a synthetic Ca2+-inducible protein using calmodulin binding peptides that selectively reveal nuclear localization and export signals in low Ca2+ (0 microM) and high Ca2+ (10 microM) environments, respectively. Experiments in live cells showed that our construct translocates between the nucleolus and plasma membrane with time constants of approximately 2 h. Further, a single amino acid mutation (Cys20Ala) in our construct prevented translocation to the plasma membrane and instead targeted it the mitochondria as predicted by bioinformatic analysis. Lastly, we studied the effect of cell line, Ca2+ concentration, chemical inhibitors, and cell morphology on translocation and found these conditions affected the rate, extent and direction of translocation. Our work demonstrates the feasibility of engineering Ca2+/calmodulin-mediated modulation of protein translocation and suggests that more natural analogs may exist.

Inotropic response of cardiac ventricular myocytes to beta-adrenergic stimulation with isoproterenol exhibits diurnal variation: involvement of nitric oxide

RATIONALE

Although >10% of cardiac gene expression displays diurnal variations, little is known of their impact on excitation-contraction coupling.

OBJECTIVE

To determine whether the time of day affects excitation-contraction coupling in rat ventricles.

METHODS AND RESULTS

Left ventricular myocytes were isolated from rat hearts at 2 opposing time points, corresponding to the animals resting or active periods. Basal contraction and [Ca(2+)](i) was significantly greater in myocytes isolated during the resting versus active periods (cell shortening 12.4+/-0.3 versus 11.0+/-0.2%; P<0.05 and systolic [Ca(2+)](i) 422+/-12 versus 341+/-9 nmol/L; P<0.01. This corresponded to a greater sarcoplasmic reticulum (SR) Ca(2+) load (672+/-20 versus 551+/-13 nmol/L P<0.001). The increase in systolic [Ca(2+)](i) in response to isoproterenol (>3 nmol/L) was also significantly greater in resting versus active period myocytes, reflecting a greater SR Ca(2+) load at this time. This diurnal variation in response of Ca(2+)-homeostasis to isoproterenol translated to a greater incidence of arrhythmic activity in resting period myocytes. Inhibition of neuronal NO synthase during stimulation with isoproterenol, further increased systolic [Ca(2+)](i) and the percentage of arrhythmic myocytes, but this effect was significantly greater in active period versus resting period myocytes. Quantitative RT-PCR analysis revealed a 2.65-fold increase in neuronal NO synthase mRNA levels in active over resting period myocytes (P<0.05).

CONCLUSIONS

The threshold for the development of arrhythmic activity in response to isoproterenol is higher during the active period of the rat. We suggest this reflects a reduction in SR Ca(2+) loading and a diurnal variation in neuronal NO synthase signaling.

Mineralocorticoid receptor inhibits CREB signaling by calcineurin activation

We investigated the interaction of MR with cAMP-response element binding protein (CREB) and provide a mechanistic explanation and insights into the cellular relevance. MR --> CREB crosstalk was assessed in vascular smooth muscle cells and heterologous expression systems. Experiments were designed in a way that only one variable changed at a time and the respective vehicles served as controls. MR, but not GR, activation (aldosterone or hydrocortisone, IC(50), approximately 0.3 nM) inhibits CREB transcriptional activity induced by stimulation of beta1/2-adrenoceptors and adenylyl cyclase or addition of membrane-permeable cAMP up to 70% within 2 h after addition. The MR DNA-binding domain is not required for this inhibition. cAMP formation is virtually unchanged, whereas MR exerts a robust inhibition of CREB(S133) phosphorylation via calcineurin/PP2B activation without changes in PP2B-Aalpha or beta expression. In parallel, the PP2B-sensitive NFaT-pathway is activated. The inhibitory crosstalk attenuates CREB-induced glucose-6-phosphate dehydrogenase expression. Overall, transcriptional relevant MR --> CREB crosstalk occurs at the level of CREB phosphorylation by enhanced calcineurin activity, enables GRE-independent genomic signaling of MR, and is of potential pathophysiological relevance.

The mAKAPbeta scaffold regulates cardiac myocyte hypertrophy via recruitment of activated calcineurin

mAKAPbeta is the scaffold for a multimolecular signaling complex in cardiac myocytes that is required for the induction of neonatal myocyte hypertrophy. We now show that the pro-hypertrophic phosphatase calcineurin binds directly to a single site on mAKAPbeta that does not conform to any of the previously reported consensus binding sites. Calcineurin-mAKAPbeta complex formation is increased in the presence of Ca(2+)/calmodulin and in norepinephrine-stimulated primary cardiac myocytes. This binding is of functional significance because myocytes exhibit diminished norepinephrine-stimulated hypertrophy when expressing a mAKAPbeta mutant incapable of binding calcineurin. In addition to calcineurin, the transcription factor NFATc3 also associates with the mAKAPbeta scaffold in myocytes. Calcineurin bound to mAKAPbeta can dephosphorylate NFATc3 in myocytes, and expression of mAKAPbeta is required for NFAT transcriptional activity. Taken together, our results reveal the importance of regulated calcineurin binding to mAKAPbeta for the induction of cardiac myocyte hypertrophy. Furthermore, these data illustrate how scaffold proteins organizing localized signaling complexes provide the molecular architecture for signal transduction networks regulating key cellular processes.

Neuronal nitric oxide synthase protects against myocardial infarction-induced ventricular arrhythmia and mortality in mice

BACKGROUND

Neuronal nitric oxide synthase (nNOS) is expressed in cardiomyocytes and plays a role in regulating cardiac function and Ca2+ homeostasis. However, the role of nNOS in cardiac electrophysiology after myocardial infarction (MI) is unclear. We hypothesized that nNOS deficiency increases ventricular arrhythmia and mortality after MI.

METHODS AND RESULTS

MI was induced in wild-type (WT) or nNOS(-/-) mice by ligation of the left coronary artery. Thirty-day mortality was significantly higher in nNOS(-/-) compared with WT mice. Additionally, nNOS(-/-) mice had impaired cardiac function 2 days after MI. Telemetric ECG monitoring showed that compared with WT, nNOS(-/-) mice had significantly more ventricular arrhythmias and were more likely to develop ventricular fibrillation after MI. Treatment with the L-type Ca2+ channel blocker verapamil reduced the incidence of arrhythmia and ventricular fibrillation in nNOS(-/-) mice after MI. To assess the role of nNOS in Ca2+ handling, patch-clamp and Ca2+ fluorescence techniques were used. Ca2+ transients and L-type Ca2+ currents were higher in nNOS(-/-) compared with WT cardiomyocytes. Additionally, nNOS(-/-) cardiomyocytes exhibited significantly higher systolic and diastolic Ca2+ over a range of pacing frequencies. Treatment with the NO donor S-nitroso N-acetyl-penicillamine decreased Ca2+ transients and L-type Ca2+ current in both nNOS(-/-) and WT cardiomyocytes. Furthermore, S-nitrosylation of Ca2+ handling proteins was significantly decreased in nNOS(-/-) myocardium after MI.

CONCLUSIONS

Deficiency in nNOS increases ventricular arrhythmia and mortality after MI in mice. The antiarrhythmic effect of nNOS involves inhibition of L-type Ca2+ channel activity and regulation of Ca2+ handling proteins via S-nitrosylation.

A randomized controlled trial of thymalfasin plus transarterial chemoembolization for unresectable hepatocellular carcinoma

PURPOSE

Patients with advanced hepatocellular carcinoma (HCC) have few treatment options. Thymalfasin (thymosin α-1) is an immunomodulator that may increase response to ablative therapy through direct anti-tumor action or enhanced protection against infections. We compared transarterial chemoembolization (TACE) plus thymalfasin with TACE alone for unresectable HCC.

METHODS

In this phase II, randomized trial, 25 patients received either TACE plus thymalfasin (1.6 mg SC, 5 times weekly; n = 14) or TACE alone (n = 11) for 24 weeks. Response was defined as transition to transplant eligibility or lack of disease progression through week 72. Survival was assessed through 24 months post-treatment.

RESULTS

Eight of fourteen (57.1%) patients in the TACE + thymalfasin group versus 5 of 11 (45.5%) patients in the TACE-only group became responders (P = 1.0). Four of fourteen TACE + thymalfasin patients versus none of 11 TACE-only patients became eligible for transplant. Median overall survival time was 110.3 weeks for the TACE + thymalfasin group versus 57.0 weeks for the TACE-only group (P = 0.45). Seven patients in each group experienced serious adverse events; there were no bacterial infections in the TACE + thymalfasin group versus 4 in the TACE-only group. There were 3 deaths in the TACE + thymalfasin group and 5 in the TACE-only group.

CONCLUSIONS

In patients with unresectable HCC, TACE + thymalfasin resulted in numerically higher rates of survival and tumor response, including transplant candidacy, with fewer bacterial infections, than TACE alone. Treatment regimens for HCC including thymalfasin as an immunomodulator should be evaluated in larger trials.

S-Nitrosylation of cardiac ion channels

Nitric oxide (NO) exerts ubiquitous signaling via posttranslational modification of cysteine residues, a reaction termed S-nitrosylation. Important substrates of S-nitrosylation that influence cardiac function include receptors, enzymes, ion channels, transcription factors, and structural proteins. Cardiac ion channels subserving excitation-contraction coupling are potentially regulated by S-nitrosylation. Specificity is achieved in part by spatial colocalization of ion channels with nitric oxide synthases (NOSs), enzymatic sources of NO in biologic systems, and by coupling of NOS activity to localized calcium/second messenger concentrations. Ion channels regulate cardiac excitability and contractility in millisecond timescales, raising the possibility that NO-related species modulate heart function on a beat-to-beat basis. This review focuses on recent advances in understanding of NO regulation of the cardiac action potential and of the calcium release channel ryanodine receptor, which is crucial for the generation of force. S-Nitrosylation signaling is disrupted in pathological states in which the redox state of the cell is dysregulated, including ischemia, heart failure, and atrial fibrillation.

The role of nitric oxide in myocardial repair and remodeling

Nitric oxide (NO) plays a crucial role in many aspects of the pathophysiology of heart failure. NO is a double-edged sword; NO inhibits ischemia/reperfusion (I/R) injury, represses inflammation, and prevents left ventricular (LV) remodeling, whereas excess NO and co-existence of reactive oxygen species (ROS) with NO are injurious. The failing heart is exposed to not only oxidative stress by a plethora of humoral factors and inflammatory cells but also nitrosative stress. Activation of nitric oxide synthase (NOS) of any isoforms, [i.e., endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS)], concomitant with oxidative stress results in NOS uncoupling, leading to further oxidative/nitrosative stress. Indiscriminate removal of oxidative stress is not an effective means to prevent this detrimental process, because oxidative stress is necessary for an adaptive mechanism for cell survival against noxious stimuli. Therefore, removal of ROS in a site-specific manner or inhibition of the source of injurious ROS without affecting redox-sensitive survival signal transduction pathways represents a promising approach to elicit the beneficial effect of NO. Recent emerging pharmacological tools and regular exercise inhibit ROS generation in the proximity of NOSs, thereby increasing bioavailable NO and exerting cardioprotection against I/R injury and LV remodeling.

Periostin mediates vascular smooth muscle cell migration through the integrins alphavbeta3 and alphavbeta5 and focal adhesion kinase (FAK) pathway

Smooth muscle cell (SMC) migration involves interactions of integrin receptors with extracellular matrix (ECM) and is an important process of neointimal formation in atherosclerosis and restenosis after vascular interventions. Previous studies have shown that periostin (PN), a novel ECM protein, is upregulated in rat carotid artery after balloon injury, and growth factor-stimulated expression of PN promotes SMC migration in vitro. Here, we address the mechanism by which PN-integrin interaction mediates SMC migration in vitro. Aortic SMCs isolated from PN null mice exhibited a significantly reduced ability to migrate and proliferate in vitro. Endogenous PN protein was absent and very low in the culture medium from the primary cultures of PN-/- and wildtype SMCs, respectively. In both types of SMCs, adenovirus-mediated overexpression of HA-tagged PN to a similar extent, which induced a robust cell migration concomitantly with an increase in beta3-integrin expression and phosphorylation of FAK (Tyr397). Furthermore, in cultured human SMCs, specific integrin blocking antibodies showed that interactions of PN-alphanubeta3 and PN-alphanubeta5, but not PN-beta1 integrins, are required for SMC migration. Inhibition of FAK signaling by overexpression of an endogenous FAK inhibitor termed FRNK (FAK-related nonkinase) significantly attenuated FAK (Tyr397) phosphorylation and the SMC migration induced by PN. These results reveal a mechanism whereby PN mediates vascular SMC migration through an interaction with alphaV-integrins (mainly alphanubeta3) and subsequent activation of FAK pathway.

Genetic variation in NOS1AP is associated with sudden cardiac death: evidence from the Rotterdam Study

Common variation within the nitric oxide-1 synthase activator protein (NOS1AP) locus is strongly related to QT interval, a sudden cardiac death (SCD) risk factor. A recent report describes common variation in NOS1AP associated with SCD in a US population of European ancestry. The objective of the current study was to obtain additional evidence by investigating the association between NOS1AP variants and SCD in the prospective population-based Rotterdam Study. The study population consisted of 5974 European ancestry subjects, aged 55 years and older, genotyped on Illumina arrays. SCD was defined according to European Society of Cardiology guidelines. Smoking, body mass index, diabetes mellitus, hypertension, heart failure and myocardial infarction were used as covariates in Cox proportional hazard models. Results were combined with reported evidence using inverse-variance weighted meta-analysis. Two hundred and eight (109 witnessed) cases of SCD occurred during a mean follow-up of 10.4 years. Within the Rotterdam Study alone, no significant associations were observed. Upon pooling of results with existing data, we observed strengthening of existing evidence for rs16847549 (US data HR = 1.31, P = 0.0024; Rotterdam Study HR = 1.18, P = 0.16; joint HR = 1.26, P = 0.0011). When the case definition in the Rotterdam Study was restricted to witnessed SCD, association of rs16847549 with SCD became stronger (joint P = 0.00019) and additionally the association between rs12567209 and SCD gained significance (US data HR = 0.57, P = 0.0035; Rotterdam Study HR = 0.69, P = 0.23; joint HR = 0.60, P = 0.0018). In conclusion, this study provided additional evidence for association between genetic variation within NOS1AP and SCD. The mechanism by which this effect is exerted remains to be elucidated.

Nitric oxide and nitric oxide synthase isoforms in the normal, hypertrophic, and failing heart

Nitric oxide (NO) produced in the heart by nitric oxide synthase (NOS) is a highly reactive signaling molecule and an important modulator of myocardial function. NOS catalyzes the conversion of L: -arginine to L: -citrulline and NO but under particular circumstances reactive oxygen species (ROS) can be formed instead of NO (uncoupling). In the heart, three NOS isoforms are present: neuronal NOS (nNOS, NOS1) and endothelial NOS (eNOS, NOS3) are constitutively present enzymes in distinct subcellular locations within cardiomyocytes, whereas inducible NOS (iNOS, NOS2) is absent in the healthy heart, but its expression is induced by pro-inflammatory mediators. In the tissue, NO has two main effects: (i) NO stimulates the activity of guanylate cyclase, leading to cGMP generation and activation of protein kinase G, and (ii) NO nitrosylates tyrosine and thiol-groups of cysteine in proteins. Upon nitrosylation, proteins may change their properties. Changes in (i) NOS expression and activity, (ii) subcellular compartmentation of NOS activity, and (iii) the occurrence of uncoupling may lead to multiple NO-induced effects, some of which being particularly evident during myocardial overload as occurs during aortic constriction and myocardial infarction. Many of these NO-induced effects are considered to be cardioprotective but particularly if NOS becomes uncoupled, formation of ROS in combination with a low NO bioavailability predisposes for cardiac damage.

An update on nuclear calcium signalling

Over the past 15 years or so, numerous studies have sought to characterise how nuclear calcium (Ca2+) signals are generated and reversed, and to understand how events that occur in the nucleoplasm influence cellular Ca2+ activity, and vice versa. In this Commentary, we describe mechanisms of nuclear Ca2+ signalling and discuss what is known about the origin and physiological significance of nuclear Ca2+ transients. In particular, we focus on the idea that the nucleus has an autonomous Ca2+ signalling system that can generate its own Ca2+ transients that modulate processes such as gene transcription. We also discuss the role of nuclear pores and the nuclear envelope in controlling ion flux into the nucleoplasm.

Cardiac extracellular matrix remodeling: fibrillar collagens and Secreted Protein Acidic and Rich in Cysteine (SPARC)

The cardiac interstitium is a unique and adaptable extracellular matrix (ECM) that provides a milieu in which myocytes, fibroblasts, and endothelial cells communicate and function. The composition of the ECM in the heart includes structural proteins such as fibrillar collagens and matricellular proteins that modulate cell:ECM interaction. Secreted Protein Acidic and Rich in Cysteine (SPARC), a collagen-binding matricellular protein, serves a key role in collagen assembly into the ECM. Recent results demonstrated increased cardiac rupture, dysfunction and mortality in SPARC-null mice in response to myocardial infarction that was associated with a decreased capacity to generate organized, mature collagen fibers. In response to pressure overload induced-hypertrophy, the decrease in insoluble collagen incorporation in the left ventricle of SPARC-null hearts was coincident with diminished ventricular stiffness in comparison to WT mice with pressure overload. This review will focus on the role of SPARC in the regulation of interstitial collagen during cardiac remodeling following myocardial infarction and pressure overload with a discussion of potential cellular mechanisms that control SPARC-dependent collagen assembly in the heart.

[Treatment of hepatitis B: new perspectives]

Despite the development of new anitiviral agents, the treatment of chronic hepatitis B remains a major clinical challenge. Major achievements have been made with the rationale use of antivirals exhibiting a complementary cross resistance profile to prevent antiviral drug resistance. The current concept of modern antiviral therapy of chronic hepatitis B relies on a precise virologic monitoring and early treatment adaptation to prevent drug resistance. The difficulty of achieving viral clearance and the risk of drug resistance development are major arguments to continue research in the field of antivirals and to identify new targets for therapy. The development of true combination therapy is highly desirable to fulfil the objective of long-term viral suppression, clearance of viral cccDNA and infected cells and ultimately cure of the disease.

Nitric oxide synthases and cardiovascular diseases: insights from genetically modified mice

Nitric oxide (NO) is produced in almost all tissues and organs, exerting a variety of biological actions under both physiological and pathological conditions. NO is synthesized by 3 distinct NO synthase (NOS) isoforms (neuronal, inducible, and endothelial NOS), all of which are expressed in the human cardiovascular system. The regulatory roles of NOSs in cardiovascular diseases have been described in pharmacological studies with selective and non-selective NOS inhibitors. However, the specificity of the NOS inhibitors continues to be an issue of debate. To overcome this issue, genetically engineered animals have been used. All types of NOS gene-deficient (knockout: KO) animals, including singly, doubly, and triply NOS-KO mice, and various types of NOS gene-transgenic (TG) animals, including conditional and non-conditional TG mice bearing endothelium-specific or cardiomyocyte-specific overexpression of each NOS gene, have thus far been developed. The roles of individual NOS isoforms, as well as the entire NOS system, in the cardiovascular system have been extensively investigated in those mice, and the results provide pivotal insights into the pathophysiology of NOSs in human cardiovascular diseases. Based on studies with murine NOS genetic models, this review summarizes the latest knowledge of NOSs and cardiovascular diseases.

The heart is an early target of anthrax lethal toxin in mice: a protective role for neuronal nitric oxide synthase (nNOS)

Anthrax lethal toxin (LT) induces vascular insufficiency in experimental animals through unknown mechanisms. In this study, we show that neuronal nitric oxide synthase (nNOS) deficiency in mice causes strikingly increased sensitivity to LT, while deficiencies in the two other NOS enzymes (iNOS and eNOS) have no effect on LT-mediated mortality. The increased sensitivity of nNOS-/- mice was independent of macrophage sensitivity to toxin, or cytokine responses, and could be replicated in nNOS-sufficient wild-type (WT) mice through pharmacological inhibition of the enzyme with 7-nitroindazole. Histopathological analyses showed that LT induced architectural changes in heart morphology of nNOS-/- mice, with rapid appearance of novel inter-fiber spaces but no associated apoptosis of cardiomyocytes. LT-treated WT mice had no histopathology observed at the light microscopy level. Electron microscopic analyses of LT-treated mice, however, revealed striking pathological changes in the hearts of both nNOS-/- and WT mice, varying only in severity and timing. Endothelial/capillary necrosis and degeneration, inter-myocyte edema, myofilament and mitochondrial degeneration, and altered sarcoplasmic reticulum cisternae were observed in both LT-treated WT and nNOS-/- mice. Furthermore, multiple biomarkers of cardiac injury (myoglobin, cardiac troponin-I, and heart fatty acid binding protein) were elevated in LT-treated mice very rapidly (by 6 h after LT injection) and reached concentrations rarely reported in mice. Cardiac protective nitrite therapy and allopurinol therapy did not have beneficial effects in LT-treated mice. Surprisingly, the potent nitric oxide scavenger, carboxy-PTIO, showed some protective effect against LT. Echocardiography on LT-treated mice indicated an average reduction in ejection fraction following LT treatment in both nNOS-/- and WT mice, indicative of decreased contractile function in the heart. We report the heart as an early target of LT in mice and discuss a protective role for nNOS against LT-mediated cardiac damage.

Myocyte remodeling in response to hypertrophic stimuli requires nucleocytoplasmic shuttling of muscle LIM protein

CSRP3 or muscle LIM protein (MLP) is a nucleocytoplasmic shuttling protein and a mechanosensor in cardiac myocytes. MLP regulation and function was studied in cultured neonatal rat myocytes treated with pharmacological or mechanical stimuli. Either verapamil or BDM decreased nuclear MLP while phenylephrine and cyclic strain increased it. These results suggest that myocyte contractility regulates MLP subcellular localization. When RNA polymerase II was inhibited with alpha-amanitin, nuclear MLP was reduced by 30%. However, when both RNA polymerase I and II were inhibited with actinomycin D, there was a 90% decrease in nuclear MLP suggesting that its nuclear translocation is regulated by both nuclear and nucleolar transcriptional activity. Using cell permeable synthetic peptides containing the putative nuclear localization signal (NLS) of MLP, nuclear import of the protein in cultured rat neonatal myocytes was inhibited. The NLS of MLP also localizes to the nucleolus. Inhibition of nuclear translocation prevented the increased protein accumulation in response to phenylephrine. Furthermore, cyclic strain of myocytes after prior NLS treatment to remove nuclear MLP resulted in disarrayed sarcomeres. Increased protein synthesis and brain natriuretic peptide expression were also prevented suggesting that MLP is required for remodeling of the myofilaments and gene expression. These findings suggest that nucleocytoplasmic shuttling MLP plays an important role in the regulation of the myocyte remodeling and hypertrophy and is required for adaptation to hypertrophic stimuli.

Erythropoietin protects the heart from ventricular arrhythmia during ischemia and reperfusion via neuronal nitric-oxide synthase

Erythropoietin (EPO) is a potent cardioprotective agent in models of myocardial ischemia and reperfusion (I/R). It has been suggested recently that EPO may also reduce ventricular arrhythmia after I/R. The present study investigated the role of neuronal nitric oxide synthase (nNOS) on the antiarrhythmic effects of EPO. EPO treatment increased nNOS expression in isolated neonatal mouse ventricular myocytes. Cotreatment with the phosphatidylinositol 3 (PI3)-kinase inhibitor, LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride], or treatment of cardiomyocytes infected with a dominant negative adenovirus targeted to Akt1 (ADV-dnAkt1) blocked the effects of EPO on nNOS expression, suggesting that EPO regulates nNOS expression via PI3-kinase and Akt. To examine the in vivo antiarrhythmic effects of EPO, wild-type (WT) and nNOS(-/-) mice were anesthetized and, after a baseline measurement, subjected to myocardial I/R to provoke ventricular arrhythmias. Pretreatment with EPO 24 h before ischemia increased nNOS expression and significantly reduced the number of premature ventricular contractions (PVCs) and the incidence of ventricular tachycardia (VT) in WT mice. In contrast, treatment with EPO had no effect on PVCs or the incidence of VT in nNOS(-/-) mice. Furthermore, EPO treatment after ischemia significantly reduced the threshold dose of cesium chloride (CsCl) to induce VT. We conclude that EPO via nNOS protects the heart from spontaneous and CsCl-induced ventricular arrhythmia during myocardial I/R.

Specific role of neuronal nitric-oxide synthase when tethered to the plasma membrane calcium pump in regulating the beta-adrenergic signal in the myocardium

The cardiac neuronal nitric-oxide synthase (nNOS) has been described as a modulator of cardiac contractility. We have demonstrated previously that isoform 4b of the sarcolemmal calcium pump (PMCA4b) binds to nNOS in the heart and that this complex regulates beta-adrenergic signal transmission in vivo. Here, we investigated whether the nNOS-PMCA4b complex serves as a specific signaling modulator in the heart. PMCA4b transgenic mice (PMCA4b-TG) showed a significant reduction in nNOS and total NOS activities as well as in cGMP levels in the heart compared with their wild type (WT) littermates. In contrast, PMCA4b-TG hearts showed an elevation in cAMP levels compared with the WT. Adult cardiomyocytes isolated from PMCA4b-TG mice demonstrated a 3-fold increase in Ser(16) phospholamban (PLB) phosphorylation as well as Ser(22) and Ser(23) cardiac troponin I (cTnI) phosphorylation at base line compared with the WT. In addition, the relative induction of PLB phosphorylation and cTnI phosphorylation following isoproterenol treatment was severely reduced in PMCA4b-TG myocytes, explaining the blunted physiological response to the beta-adrenergic stimulation. In keeping with the data from the transgenic animals, neonatal rat cardiomyocytes overexpressing PMCA4b showed a significant reduction in nitric oxide and cGMP levels. This was accompanied by an increase in cAMP levels, which led to an increase in both PLB and cTnI phosphorylation at base line. Elevated cAMP levels were likely due to the modulation of cardiac phosphodiesterase, which determined the balance between cGMP and cAMP following PMCA4b overexpression. In conclusion, these results showed that the nNOS-PMCA4b complex regulates contractility via cAMP and phosphorylation of both PLB and cTnI.

Common variation in NOS1AP and KCNH2 genes and QT interval duration in young adults. The Cardiovascular Risk in Young Finns Study

BACKGROUND

Common genetic variants in the nitric oxide synthase 1 adaptor protein gene (NOS1AP) and in the HERG potassium channel gene (KCNH2) have been associated with cardiac repolarization in middle-aged and elderly subjects.

AIM

We examined the relation between these variants and QT interval duration in a population of healthy young adults.

METHODS

We measured QT interval duration and genotyped rs10494366 T>G (NOS1AP gene, n=1,842) and rs1805123 A>C (KCNH2 gene, n=1,894) in subjects aged 24-39 years.

RESULTS

The NOS1AP variant was significantly related with heart rate-corrected QT interval duration (QTc). Additive regression model adjusting for age, sex, systolic blood pressure, body mass index, alcohol use, and smoking indicated that the G allele was associated with a 3.2 ms (95% confidence interval (CI) 1.7-4.6 ms, P<0.0001) increase in QTc interval duration for each additional copy. The KCNH2 variant was not significantly related with QTc interval duration in the study sample.

CONCLUSION

These findings provide evidence from a population of healthy young adults that a common variation in the NOS1AP gene influences cardiac repolarization within the normal physiological range. Further studies are warranted to investigate the effects of this variant on sudden cardiac death and ventricular arrhythmias.

A common NOS1AP genetic polymorphism is associated with increased cardiovascular mortality in users of dihydropyridine calcium channel blockers

AIM

Recently, a polymorphism in the NOS1AP gene (rs10494366), a regulator of neuronal nitric oxide synthase (nNOS), was associated with QTc prolongation. Both nNOS and calcium channel blockers (CCBs) regulate intracellular calcium levels and have an important role in cardiovascular homeostasis. The aim was to investigate whether this polymorphism is associated with cardiovascular mortality in users of CCBs.

METHODS

The data from the Rotterdam study, a population-based closed cohort study of Caucasian individuals of > or =55 years of age, were used. We identified 1113 participants in the Rotterdam Study who were prescribed CCBs for the first time between 1991 and 2005. All-cause and cardiovascular mortality was assessed in participants who were prescribed CCBs with different NOS1AP rs10494366 genotypes using Cox proportional hazard models.

RESULTS

In participants starting on dihydropyridine CCBs (amlodipine, nifedipine and others) all-cause mortality (n = 79) risks were higher in participants with the TG [hazard ratio (HR) 2.57, 95% confidence interval (CI) 1.24, 5.34] or the GG genotype (HR 3.18, 95% CI 1.18, 8.58) than in participants with the referent TT genotype. Cardiovascular mortality (n = 54) risks were 3.51 (95% CI 1.41, 8.78) for the TG genotype and 6.00 (95% CI 1.80, 20.0) for the GG genotype. No differences in all-cause mortality or cardiovascular mortality were seen in participants starting with the nondihydropyridine CCBs verapamil or diltiazem.

CONCLUSION

The minor G allele of rs10494366 in the NOS1AP gene is associated with increased all-cause and cardiovascular mortality in Caucasian users of dihydropyridine CCBs. The mechanism underlying the observed association is unknown.

Role of healing-specific-matricellular proteins and matrix metalloproteinases in age-related enhanced early remodeling after reperfused STEMI in dogs

We assessed whether aging augments left ventricular (LV) damage, remodeling, and dysfunction and alters expression of healing-specific-matricellular proteins (HSMPs), matrix metalloproteinases (MMPs) and other pertinent proteins after acute reperfused-ST-segment-elevation myocardial infarction (RSTEMI) in the dog model. The findings suggest a novel role for HSMPs, MMPs, and the other proteins in the age-related increase in LV damage, remodeling, and dysfunction. Potentially detrimental effects of the altered proteins appear to outweigh beneficial effects and contribute to adverse outcome. Deleterious changes include the increase in matrix-degrading MMPs, inducible nitric oxide synthase (iNOS) and pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha, HSMPs such as secreted-protein-acidic-and-rich-in-cysteine (SPARC) and osteopontin (OPN), the blunted increase in endothelial-NOS (eNOS), and the decrease in IL-10 and neuronal NOS (nNOS). Potentially beneficial changes include increases in the HSMP secretory-leucocyte-protease-inhibitor (SLPI) and cytokine transforming growth factor (TGF)-beta(1). Targeting these proteins may mitigate enhanced LV remodeling and dysfunction with aging.

Fluvastatin reduces pulmonary vein spontaneous activity through nitric oxide pathway

INTRODUCTION

Pulmonary veins (PVs) are the most important focus for the generation of atrial fibrillation. The HMG-CoA reductase inhibitors (statins) can reduce the occurrence of atrial fibrillation. The purposes of this study were to evaluate whether statins may inhibit the PV arrhythmogenic activity to prevent atrial arrhythmias from PVs and to investigate the link between fluvastatin, nitric oxide synthase (NOS) activity, mechanical activity, and electrical activity.

METHODS

Conventional microelectrodes and Western blot were used to record the electrical activity, diastolic tension, contractility and expression of Akt, endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and phosphorylated Akt and eNOS before and after the administration of fluvastatin in rabbit PVs or atria.

RESULTS

Fluvastatin decreased the PV spontaneous activity, diastolic tension, and contractility, but did not change the action potential duration or resting membrane potential. The effects of fluvastatin on the PV firing rate and diastolic tension were attenuated in the presence of L-NAME (100 microM), wortmannin (100 nM), and ODQ (3 microM). Fluvastatin (1 muM) increased the phosphorylated Akt and eNOS, but did not change the total Akt or eNOS in the PVs and atria. In contrast, fluvastatin (1 microM) decreased the total nNOS in the PVs and atria.

CONCLUSIONS AND IMPLICATIONS

Fluvastatin produced nitric oxide through the PI3kinase/Akt pathway, thus reducing the PV vascular diastolic tension and PV spontaneous activity. These results may contribute to the beneficial effects of statins.

Nuclear co-translocation of myotrophin and p65 stimulates myocyte growth. Regulation by myotrophin hairpin loops

Myotrophin, a 12-kDa ankyrin repeat protein, stimulates protein synthesis and cardiomyocyte growth to initiate cardiac hypertrophy by activating the NF-kappaB signaling cascade. We found that, after internalization into myocytes, myotrophin cotranslocates into the nucleus with p65 to stimulate myocyte growth. We used structure-based mutations on the hairpin loops of myotrophin to determine the effect of the loops on myotrophin and p65 localization, induction of protein synthesis, and cardiac hypertrophy. Loop mutants, most prominently glutamic acid 33-->alanine (E33A), stimulated protein synthesis much less than wild type. Myotrophin-E33A internalized into myocytes but did not translocate into the nucleus and failed to promote nuclear translocation of p65. In addition, two cardiac hypertrophy marker genes, atrial natriuretic factor and beta-myosin heavy chain, were not up-regulated in E33A-treated cells. Myotrophin-induced myocyte growth and initiation of hypertrophy thus require nuclear co-translocation of myotrophin and p65, in a manner that depends crucially on the myotrophin hairpin loops.

Nitric oxide signaling and the regulation of myocardial function

Nitric oxide, which is produced endogenously within cardiac myocytes by three distinct isoforms of nitric oxide synthase, is a key regulator of myocardial function. This review will focus on the regulation of myocardial function by each nitric oxide synthase isoform during health and disease, with a specific emphasis on the proposed end-targets and signaling pathways.

Activation of peroxisome proliferator-activated receptor gamma inhibits endothelin-1-induced cardiac hypertrophy via the calcineurin/NFAT signaling pathway

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) has been described as a negative regulator of cardiac hypertrophy. A better understanding of PPAR-gamma and cardiac hypertrophy may facilitate the development of novel therapeutic strategies to treat heart diseases related to cardiac hypertrophy by mimicking the naturally preferred mechanisms. In the present study, we investigated the interaction between PPAR-gamma and calcineurin/nuclear factor of activated T-cells (NFAT) in endothelin-1 (ET-1)-induced hypertrophy of neonatal rat cardiac myocytes. The results suggest that the treatment of cultured cardiac myocytes with a PPAR-gamma ligand, rosiglitazone, inhibited the ET-1-induced increase in protein synthesis, surface area, calcineurin enzymatic activity, and protein expression. Both the application of rosiglitazone and overexpression of the PPAR-gamma inhibited the nuclear translocation of NFATc4. Moreover, co-immunoprecipitation studies showed that rosiglitazone enhanced the association between PPAR-gamma and calcineurin/NFAT. These results suggest that ET-1-induced cardiac hypertrophy is inhibited by activation of PPAR-gamma, which is at least partly due to cross-talk between PPAR-gamma and calcineurin/NFAT.

IFATS collection: Combinatorial peptides identify alpha5beta1 integrin as a receptor for the matricellular protein SPARC on adipose stromal cells

The biological features of adipose stromal (stem) cells (ASC), which serve as progenitors for differentiated cells of white adipose tissue (WAT), are still largely undefined. In an initiative to identify functional ASC surface receptors, we screened a combinatorial library for peptide ligands binding to patient-derived ASC. We demonstrate that both primary and cultured human and mouse stromal cells express a conserved receptor targeted by peptides found to mimic SPARC, a matricellular protein that is required for normal WAT development. A signaling receptor for SPARC has not as yet been determined. By using the SPARC-mimicking peptides CMLAGWIPC (termed hPep) and CWLGEWLGC (termed mPep), isolated by panning on human and mouse cells, respectively, we identified the alpha5beta1 integrin complex as a candidate receptor for SPARC. On the basis of these results, we evaluated ASC responses to SPARC or SPARC-mimicking peptide exposure. Our results suggest that extracellular SPARC binds to alpha5beta1 integrin at sites of focal adhesions, an interaction disrupting firm attachment of ASC to extracellular matrix. We propose that SPARC-mediated mobilization of ASC through its effect on alpha5beta1 integrin complex provides a functional basis for the regulation of WAT body composition by SPARC. We also show that alpha5beta1 integrin is a potential target for ASC-selective intracellular delivery of bioactive peptides and gene therapy vectors directed by the SPARC-mimicking peptides. Disclosure of potential conflicts of interest is found at the end of this article.

Cardiomyocyte Overexpression of Neuronal Nitric Oxide Synthase Delays Transition Toward Heart Failure in Response to Pressure Overload by Preserving Calcium Cycling

Background— Defects in cardiomyocyte Ca 2+ cycling are a signature feature of heart failure (HF) that occurs in response to sustained hemodynamic overload, and they largely account for contractile dysfunction. Neuronal nitric oxide synthase (NOS1) influences myocyte excitation-contraction coupling through modulation of Ca 2+ cycling, but the potential relevance of this in HF is unknown.

Methods and Results— We generated a transgenic mouse with conditional, cardiomyocyte-specific NOS1 overexpression (double-transgenic [DT]) and studied cardiac remodeling, myocardial Ca 2+ handling, and contractility in DT and control mice subjected to transverse aortic constriction (TAC). After TAC, control mice developed eccentric hypertrophy with evolution toward HF as revealed by a significantly reduced fractional shortening. In contrast, DT mice developed a greater increase in wall thickness ( P <0.0001 versus control+TAC) and less left ventricular dilatation than control+TAC mice ( P <0.0001 for both end-systolic and end-diastolic dimensions). Thus, DT mice displayed concentric hypertrophy with fully preserved fractional shortening (43.7±0.6% versus 30.3±2.6% in control+TAC mice, P <0.05). Isolated cardiomyocytes from DT+TAC mice had greater shortening, intracellular Ca 2+ transients, and sarcoplasmic reticulum Ca 2+ load ( P <0.05 versus control+TAC for all parameters). These effects could be explained, at least in part, through modulation of phospholamban phosphorylation status.

Conclusions— Cardiomyocyte NOS1 may be a useful target against cardiac deterioration during chronic pressure-overload–induced HF through modulation of calcium cycling.

Secreted protein acidic, rich in cysteine induces pulp cell migration via alphavbeta3 integrin and extracellular signal-regulated kinase

AIM

The aim of this study was to investigate the influence of secreted protein acidic, rich in cysteine (SPARC) on the migration of human dental pulp (HDP) cells.

METHODS

Secreted protein acidic, rich in cysteine was applied in the lower chamber of the chemotaxis apparatus and migration was determined by counting the cells that migrated through the membrane. To determine the signaling pathway involved, cells were incubated with inhibitors for 30 min prior to the migration assay.

RESULTS

The results indicated that SPARC induced HDP cell migration in a dose-dependent manner via extracellular signal-regulated kinase (ERK). The migration could be inhibited both by the anti-alphavbeta3 integrin antibody and by suramin, a non-selective growth factor receptor and G-protein coupled receptor antagonists. The anti-alphavbeta3 integrin antibody could also inhibit ERK activation, suggesting the possible role of alphavbeta3 integrin on the regulation of ERK and cell migration. Interestingly, both suramin and SB225002, another G-protein coupled receptor antagonist, suppressed ERK activation.

CONCLUSIONS

Secreted protein acidic, rich in cysteine could act as a chemotactic factor and facilitate migration, possibly through the G-protein coupled receptor, alphavbeta3 integrin and ERK. The data support that SPARC could play a crucial role in dental pulp tissue repair by inducing dental pulp cell migration.

Angiotensin II: a hormone involved in and contributing to pro-hypertrophic cardiac networks and target of anti-hypertrophic cross-talks

Angiotensin II (Ang II) plays a major role in the progression of myocardial hypertrophy to heart failure. Inhibiting the angiotensin converting enzyme (ACE) or blockade of the corresponding Ang II receptors is used extensively in clinical practice, but there is scope for refinement of this mode of therapy. This review summarizes the current understanding of the direct effects of Ang II on cardiomyocytes and then focus particularly on interaction of components of the renin-angiotensin system with other hormones and cytokines. New findings described in approximately 400 papers identified in the PubMed database and published during the 2.5 years are discussed in the context of previous relevant literature. The cardiac action of Ang II is influenced by the activity of different isoforms of ACE leading to different amounts of Ang II by comparison with other angiotensinogen-derived peptides. The effect of Ang II is mediated by at least two different AT receptors that are differentially expressed in cardiomyocytes from neonatal, adult and failing hearts. The intracellular effects of Ang II are influenced by nitric oxide (NO)/cGMP-dependent cross talk and are mediated by the release of autocrine factors, such as transforming growth factor (TGF)-beta1 and interleukin (IL)-6. Besides interactions with cytokines, Ang II is involved in systemic networks including aldosterone, parathyroid hormone and adrenomedullin, which have their own effects on cardiomyocytes that modify, amplify or antagonize the primary effect of Ang II. Finally, hyperinsulemia and hyperglycaemia influence Ang II-dependent processes in diabetes and its cardiac sequelae.

Constitutive nitric oxide synthases in the heart from hypertrophy to failure

1. Endogenous myocardial nitric oxide (NO) may modulate the transition from adaptive to maladaptive hypertrophy leading to heart failure. This review summarizes the information on the interrelations between the precise localization of NO synthases (NOS) and their regulatory functions within different compartments of the heart. 2. In rodent models of pressure overload or myocardial infarction, the three NOS isoforms (NOS1, NOS2, NOS3) were shown to play a neutral, protective, or even adverse role in myocardial remodelling, depending on the NOS activity, the location of each NOS and their regulators. 3. The analysis of conditions that modulate the expression of NOS1 and NOS3 in the heart according to physiopathological situations, indicated that, beside the level of total NOS activity, unique changes in NO compartmentation secondary to NOS1 or NOS3 subcellular location might be involved in the development of cardiac hypertrophy and failure. 4. Thus, different circuits in NO-signalling pathways in myocardium might be activated and this principle is a key to understand contradictions existing in NO biology in the heart. Unravelling the mechanisms behind the NO, NOS and cardiac function is still an ongoing challenge.

Asian-Pacific consensus statement on the management of chronic hepatitis B: a 2008 update

Large amounts of new data on the natural history and treatment of chronic hepatitis B virus (HBV) infection have become available since 2005. These include long-term follow-up studies in large community-based cohorts or asymptomatic subjects with chronic HBV infection, further studies on the role of HBV genotype/naturally occurring HBV mutations, treatment of drug resistance and new therapies. In addition, Pegylated interferon alpha2a, entecavir and telbivudine have been approved globally. To update HBV management guidelines, relevant new data were reviewed and assessed by experts from the region, and the significance of the reported findings were discussed and debated. The earlier "Asian-Pacific consensus statement on the management of chronic hepatitis B" was revised accordingly. The key terms used in the statement were also defined. The new guidelines include general management, special indications for liver biopsy in patients with persistently normal alanine aminotransferase, time to start or stop drug therapy, choice of drug to initiate therapy, when and how to monitor the patients during and after stopping drug therapy. Recommendations on the therapy of patients in special circumstances, including women in childbearing age, patients with antiviral drug resistance, concurrent viral infection, hepatic decompensation, patients receiving immune-suppressive medications or chemotherapy and patients in the setting of liver transplantation, are also included.

Asian-Pacific consensus statement on the management of chronic hepatitis B: a 2008 update

Large amounts of new data on the natural history and treatment of chronic hepatitis B virus (HBV) infection have become available since 2005. These include long-term follow-up studies in large community-based cohorts or asymptomatic subjects with chronic HBV infection, further studies on the role of HBV genotype/naturally occurring HBV mutations, treatment of drug resistance and new therapies. In addition, Pegylated interferon alpha2a, entecavir and telbivudine have been approved globally. To update HBV management guidelines, relevant new data were reviewed and assessed by experts from the region, and the significance of the reported findings were discussed and debated. The earlier "Asian-Pacific consensus statement on the management of chronic hepatitis B" was revised accordingly. The key terms used in the statement were also defined. The new guidelines include general management, special indications for liver biopsy in patients with persistently normal alanine aminotransferase, time to start or stop drug therapy, choice of drug to initiate therapy, when and how to monitor the patients during and after stopping drug therapy. Recommendations on the therapy of patients in special circumstances, including women in childbearing age, patients with antiviral drug resistance, concurrent viral infection, hepatic decompensation, patients receiving immune-suppressive medications or chemotherapy and patients in the setting of liver transplantation, are also included.

Matricellular proteins at the crossroad of inflammation and cancer

Some proteins of the extracellular matrix known as matricellular proteins have regulatory function in all aspects of physiological and pathological stroma rearrangement. Many aspects of their activity are related to inflammation and immune response suggesting their role in bridging inflammation and cancer.

CAPON modulates cardiac repolarization via neuronal nitric oxide synthase signaling in the heart

Congenital long- or short-QT syndrome may lead to life-threatening ventricular tachycardia and sudden cardiac death. Apart from the rare disease-causing mutations, common genetic variants in CAPON, a neuronal nitric oxide synthase (NOS1) regulator, have recently been associated with QT interval variations in a human whole-genome association study. CAPON had been unsuspected of playing a role in cardiac repolarization; indeed, its physiological role in the heart (if any) is unknown. To define the biological effects of CAPON in the heart, we investigated endogenous CAPON protein expression and protein-protein interactions in the heart and performed electrophysiological studies in isolated ventricular myocytes with and without CAPON overexpression. We find that CAPON protein is expressed in the heart and interacts with NOS1 to accelerate cardiac repolarization by inhibition of L-type calcium channel. Our findings provide a rationale for the association of CAPON gene variants with extremes of the QT interval in human populations.

Reviews for APASL guidelines: immunomodulator therapy of chronic hepatitis B

The primary aim of immunomodulator therapy is to help the natural human immune system to mount a defense against hepatitis B virus. IFN-alpha has been used for the treatment of HBeAg-positive and HBeAg-negative chronic hepatitis B for over two decades and has been shown to be effective in suppressing HBV replication and in inducing serological response leading to long-term clinical benefits. IFN-alpha has been used in patients with well-compensated cirrhosis with comparable or better response to that in non-cirrhotic patients. IFN-alpha therapy in patients with cirrhosis has a similar side effect profile as in those without cirrhosis. However, IFN-alpha is contraindicated in patients with overt or decompensated cirrhosis. Pegylated IFN-alpha has been shown to be effective in treatment of chronic hepatitis B with sustained response rate in about one-third of the treated patients. Peg IFN-alpha treatment in non-responders to lamivudine or adefovir dipivoxil showed similar response rate to that seen in naïve patients. Thymosin alpha(1) is effective in treatment of HBeAg-positive and HBeAg-negative chronic hepatitis B with a significantly increasing virological response over time after therapy.

Differential effects of calcineurin inhibitors, tacrolimus and cyclosporin a, on interferon-induced antiviral protein in human hepatocyte cells

The premise of our study is that selective inhibition of interferon (IFN) by calcineurin inhibitors contribute to the increased severity of hepatitis C virus (HCV) posttransplantation. Therefore, we examined the influence of calcineurin inhibitors in the human hepatocyte cell line on IFN-alpha-induced phosphorylation of Janus kinase (Jak) and signal transducers and activators of transcription (STAT), nuclear translocation of IFN-stimulated gene factor 3 (ISGF-3), IFN-stimulated regulatory element (ISRE)-contained promoter activity, and the expressions of antiviral proteins. Tacrolimus (Tac), but not cyclosporin A (CyA), had an inhibitory effect on IFN-alpha-induced double-stranded ribonucleic acid (RNA)-dependent protein kinase (PKR) in a dose-dependent manner. STAT-1 also acted in a similar fashion to PKR. IFN-alpha combined with Tac attenuated the ISRE-containing promoter gene activity as compared with IFN-alpha alone. In contrast, its expression in pretreated CyA was slightly attenuated. In pretreated Tac, but not CyA, the levels of IFN-alpha-induced tyrosine phosphorylated STAT-1 and -2 were clearly lower than those induced by IFN-alpha alone. Tac and CyA did not decrease the IFN-alpha-induced JAK-1 phosphorylation. The nuclear translocation rate of tyrosine phosphorylated STAT-1 was inhibited by pretreatment of both Tac and CyA by western blotting and immunohistochemistry. In an HCV replicon system, pretreated Tac diminished the replication inhibitory effect of IFN-alpha. In this study, we show that calcineurin inhibitors, especially Tac, are the negative regulators of IFN signaling in the hepatocyte; the greatest cause of such inhibition is the phosphorylation disturbance of STAT-1, next to inhibition of the nuclear translocation of STAT-1. In conclusion, disturbance of tyrosine phosphorylation of STAT-1 resulted in diminished ISRE-containing promoter activity and a decline in antiviral protein expression. Moreover, the replication of HCV was activated. This phenomenon is detrimental to IFN therapy after liver transplantation, and the selection of calcineurin inhibitors may warrant further discussion depending on the transplant situation.

PICOT attenuates cardiac hypertrophy by disrupting calcineurin-NFAT signaling

PICOT (protein kinase C-interacting cousin of thioredoxin) was previously shown to inhibit pressure overload-induced cardiac hypertrophy, concomitant with an increase in ventricular function and cardiomyocyte contractility. The combined analyses of glutathione S-transferase pull-down experiments and mass spectrometry enabled us to determine that PICOT directly interacts with muscle LIM protein (MLP) via its carboxyl-terminal half (PICOT-C). It was also shown that PICOT colocalizes with MLP in the Z-disc. MLP is known to play a role in anchoring calcineurin to the Z-disc in the sarcomere, which is critical for calcineurin-NFAT (nuclear factor of activated T cells) signaling. We, therefore, suggested that PICOT may affect calcineurin-NFAT signaling through its interaction with MLP. Consistent with this hypothesis, PICOT, or more specifically PICOT-C, abrogated phenylephrine-induced increases in calcineurin phosphatase activity, NFAT dephosphorylation/nuclear translocation, and NFAT-dependent transcriptional activation in neonatal cardiomyocytes. In addition, pressure overload-induced upregulation of NFAT target genes was significantly diminished in the hearts of PICOT-overexpressing transgenic mice. PICOT interfered with MLP-calcineurin interactions in a dose-dependent manner. Moreover, calcineurin was displaced from the Z-disc, concomitant with an abrogated interaction between calcineurin and MLP, in the hearts of PICOT transgenic mice. Replenishment of MLP restored the hypertrophic responses and the increase in calcineurin phosphatase activity that was inhibited by PICOT in phenylephrine-treated cardiomyocytes. Finally, PICOT-C inhibited cardiac hypertrophy to an extent that was comparable to that of full-length PICOT. Taken together, these data suggest that PICOT inhibits cardiac hypertrophy largely by negatively regulating calcineurin-NFAT signaling via disruption of the MLP-calcineurin interaction.

Nuclear Ca2+ regulates cardiomyocyte function

In the heart, cytosolic Ca(2+) signals are well-characterized events that participate in the activation of cell contraction. In contrast, nuclear Ca(2+) contribution to cardiomyocyte function remains elusive. Here, we examined functional consequences of buffering nuclear Ca(2+) in neonatal cardiomyocytes. We report that cardiomyocytes contain a nucleoplasmic reticulum, which expresses both ryanodine receptor (RyR) and inositol 1,4,5-trisphosphate receptor (InsP(3)R), providing a possible way for active regulation of nuclear Ca(2+). Adenovirus constructs encoding the Ca(2+) buffer protein parvalbumin were targeted to the nucleus with a nuclear localization signal (Ad-PV-NLS) or to the cytoplasm with a nuclear exclusion signal (Ad-PV-NES). A decrease in the amplitude of global Ca(2+) transients and RyR-II expression, as well as an increase in cell beating rate were observed in Ad-PV-NES and Ad-PV-NLS cells. When nuclear Ca(2+) buffering was imposed nuclear enlargement, increased calcineurin expression, NFAT translocation to the nucleus and subcellular redistribution of atrial natriuretic peptide were observed. Furthermore, prolongation of action potential duration occurred in adult ventricular myocytes. These results suggest that nuclear Ca(2+) levels underlie the regulation of specific protein targets and thereby modulate cardiomyocyte function. The local nuclear Ca(2+) signaling and the structures that control it constitute a novel regulatory motif in the heart.

Deficient ryanodine receptor S-nitrosylation increases sarcoplasmic reticulum calcium leak and arrhythmogenesis in cardiomyocytes

Altered Ca(2+) homeostasis is a salient feature of heart disease, where the calcium release channel ryanodine receptor (RyR) plays a major role. Accumulating data support the notion that neuronal nitric oxide synthase (NOS1) regulates the cardiac RyR via S-nitrosylation. We tested the hypothesis that NOS1 deficiency impairs RyR S-nitrosylation, leading to altered Ca(2+) homeostasis. Diastolic Ca(2+) levels are elevated in NOS1(-/-) and NOS1/NOS3(-/-) but not NOS3(-/-) myocytes compared with wild-type (WT), suggesting diastolic Ca(2+) leakage. Measured leak was increased in NOS1(-/-) and NOS1/NOS3(-/-) but not in NOS3(-/-) myocytes compared with WT. Importantly, NOS1(-/-) and NOS1/NOS3(-/-) myocytes also exhibited spontaneous calcium waves. Whereas the stoichiometry and binding of FK-binding protein 12.6 to RyR and the degree of RyR phosphorylation were not altered in NOS1(-/-) hearts, RyR2 S-nitrosylation was substantially decreased, and the level of thiol oxidation increased. Together, these findings demonstrate that NOS1 deficiency causes RyR2 hyponitrosylation, leading to diastolic Ca(2+) leak and a proarrhythmic phenotype. NOS1 dysregulation may be a proximate cause of key phenotypes associated with heart disease.

Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis

Chronic hepatitis B virus (HBV) infection is a serious problem because of its worldwide distribution and possible adverse sequelae, such as cirrhosis and hepatocellular carcinoma. Thymosin alpha-1 (Talpha1) is an immune modifier that has been shown to be effective for chronic hepatitis B (CHB) in some trials. But the trials comparing Talpha1 vs. interferon alpha (IFNalpha) treatment in CHB have been small and the results have been inconsistent. So we conducted a meta-analysis to compare the efficacy of Talpha1 and IFNalpha in the treatment of CHB. Generally, four randomized controlled trials including 199 CHB patients who received Talpha1 or IFNalpha treatment were identified through MEDLINE and EMBASE online search. Virological (for hepatitis B e antigen (HBeAg) positive patients, loss of HBV DNA and HBeAg; for HBeAg negative patients, loss of HBV DNA), biochemical (normalization of transaminases) and complete responses (fulfill criteria of biochemical and virological response simultaneously) were analyzed using the intention-to-treat method. The odds ratio (OR) was used to measure the magnitude of the efficacy. The ORs (95% confidence interval) of the virological response, biochemical response and complete response of Talpha1 over IFNalpha at the end of 6 months treatment were 0.62 (0.35, 1.10), 0.60 (0.34, 1.05) and 0.54 (0.30, 0.97), respectively. The ORs (95% confidence interval) of the virological response, biochemical response and complete response of Talpha1 over IFNalpha at the end of follow-up (6 months post-treatment) were 3.71 (2.05, 6.71), 3.12 (1.74, 5.62) and 2.69 (1.47, 4.91), respectively. These data showed that compared with IFNalpha, the benefit of Talpha1 was not immediately significant at the end of therapy, but virological, biochemical and complete response had a tendency to increase or accumulate gradually after the therapy. For three of the four trials that studied HBeAg-negative patients, the results are mostly applicable to HBeAg-negative CHB.

Effects of sex differences on constitutive nitric oxide synthase expression and activity in response to pressure overload in rats

Clinical studies have documented sex differences in left ventricular (LV) hypertrophy patterns, but the mechanisms are so far poorly defined. This study aimed to determine whether 1) severe pressure overload altered expression and/or activity of cardiac constitutive nitric oxide synthase (NOS1 and NOS3) and 2) these changes were modulated according to sex. Analyses were performed 0.4–20 wk after thoracic aortic constriction (TAC) in male and female Wistar rats. Male rats with TAC exhibited early signs of cardiac dysfunction, as shown by echocardiographic and LV end-diastolic pressure measurements, whereas females with TAC exhibited higher LV hypertrophy (+96% vs. males at 20 wk; P < 0.05). After TAC, cardiac NOS1 expression was rapidly induced (0.4 wk) and stable afterward in males ( P < 0.05 vs. sham groups), whereas it was delayed in females. Accordingly, specific NOS1 activity was increased by 2 wk in male rats with TAC (+122%; P < 0.001 vs. sham groups) and only by 20 wk in females (+220%; P < 0.001 vs. sham groups). NOS1 activity was correlated with NOS1 level. Regarding cardiac NOS3, expression was unaffected by TAC, and the decrease in activity observed at early and late times in male and female rats with TAC, respectively, is shown to be related to NOS3 allosteric regulator caveolin-1 level. The data demonstrated a unique sex-dependent regulation of the constitutive NOSs in response to TAC in rats; such a difference might play a role in the sex-dependent adaptability of the heart in response to pressure overload.

Sympathetic control of heart rate in nNOS knockout mice

Inhibition of neuronal nitric oxide synthase (nNOS) in cardiac postganglionic sympathetic neurons leads to enhanced cardiac sympathetic responsiveness in normal animals, as well as in animal models of cardiovascular diseases. We used isolated atria from mice with selective genetic disruption of nNOS (nNOS(-/-)) and their wild-type littermates (WT) to investigate whether sympathetic heart rate (HR) responses were dependent on nNOS. Immunohistochemistry was initially used to determine the presence of nNOS in sympathetic [tyrosine hydroxylase (TH) immunoreactive] nerve terminals in the mouse sinoatrial node (SAN). After this, the effects of postganglionic sympathetic nerve stimulation (1-10 Hz) and bath-applied norepinephrine (NE; 10(-8)-10(-4) mol/l) on HR were examined in atria from nNOS(-/-) and WT mice. In the SAN region of WT mice, TH and nNOS immunoreactivity was virtually never colocalized in nerve fibers. nNOS(-/-) atria showed significantly reduced HR responses to sympathetic nerve activation and NE (P < 0.05). Similarly, the positive chronotropic response to the adenylate cyclase activator forskolin (10(-7)-10(-5) mol/l) was attenuated in nNOS(-/-) atria (P < 0.05). Constitutive NOS inhibition with L-nitroarginine (0.1 mmol/l) did not affect the sympathetic HR responses in nNOS(-/-) and WT atria. The paucity of nNOS in the sympathetic innervation of the mouse SAN, in addition to the attenuated HR responses to neuronal and applied NE, indicates that presynaptic sympathetic neuronal NO does not modulate neuronal NE release and SAN pacemaking in this species. It appears that genetic deletion of nNOS results in the inhibition of adrenergic-adenylate cyclase signaling within SAN myocytes.

Differential role of S-nitrosylation and the NO-cGMP-PKG pathway in cardiac contractility

The role of nitric oxide (NO) in cardiac contractility is complex and controversial. Several NO donors have been reported to cause positive or negative inotropism. NO can bind to guanylate cyclase, increasing cGMP production and activating PKG. NO may also directly S-nitrosylate cysteine residues of specific proteins. We used the isolated rat heart preparation to test the hypothesis that the differential inotropic effects depend on the degree of NO production and the signaling recruited. SNAP (S-nitroso-N-acetylpenicillamine), a NO donor, increased contractility at 0.1, 1 and 10 microM. This effect was independent of phospholamban phosphorylation, was not affected by PKA inhibition with H-89 (N-[2((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide), but it was abolished by the radical scavenger Tempol (4-hydroxy-[2,2,4,4]-tetramethyl-piperidine-1-oxyl). However, at 100 microM SNAP reduced contractility, effect reversed to positive inotropism by guanylyl cyclase blockade with ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), and abolished by PKG inhibition with KT5823, but not affected by Tempol. SNAP increased tissue cGMP at 100 microM, but not at lower concentrations. Consistently, a cGMP analog also reduced cardiac contractility. Finally, SNAP at 1 microM increased the level of S-nitrosylation of various cardiac proteins, including the ryanodine receptor. This study demonstrates the biphasic role for NO in cardiac contractility in a given preparation; furthermore, the differential effect is clearly ascribed to the signaling pathways involved. We conclude that although NO is highly diffusible, its output determines the fate of the messenger: low NO concentrations activate redox processes (S-nitrosylation), increasing contractility; while the cGMP-PKG pathway is activated at high NO concentrations, reducing contractility.