Heart failure-associated alterations in troponin I phosphorylation impair ventricular relaxation-afterload and force-frequency responses and systolic function

Recent studies have found that selective stimulation of troponin (Tn)I protein kinase A (PKA) phosphorylation enhances heart rate-dependent inotropy and blunts relaxation delay coupled to increased afterload. However, in failing hearts, TnI phosphorylation by PKA declines while protein kinase C (PKC) activity is enhanced, potentially augmenting TnI PKC phosphorylation. Accordingly, we hypothesized that these site-specific changes deleteriously affect both rate-responsive cardiac function and afterload dependence of relaxation, both prominent phenotypic features of the failing heart. A transgenic (TG) mouse model was generated in which PKA-TnI sites were mutated to mimic partial dephosphorylation (Ser22 to Ala; Ser23 to Asp) and dominant PKC sites were mutated to mimic constitutive phosphorylation (Ser42 and Ser44 to Asp). The two highest-expressing lines were further characterized. TG mice had reduced fractional shortening of 34.7 ± 1.4% vs. 41.3 ± 2.0% ( P = 0.018) and slight chamber dilation on echocardiography. In vivo cardiac pressure-volume studies revealed near doubling of isovolumic relaxation prolongation with increasing afterload in TG animals ( P < 0.001), and this remained elevated despite isoproterenol infusion (PKA stimulation). Increasing heart rate from 400 to 700 beats/min elevated contractility 13% in TG hearts, nearly half the response observed in nontransgenic animals ( P = 0.005). This blunted frequency response was normalized by isoproterenol infusion. Abnormal TnI phosphorylation observed in cardiac failure may explain exacerbated relaxation delay in response to increased afterload and contribute to blunted chronotropic reserve.

Activation of (Na++K+)-ATPase induces positive inotropy in intact mouse heart in vivo

OBJECTIVE

We have recently identified an activation site on (Na+ + K+)-ATPase and found that binding of antibody SSA412 to this specific site of the enzyme markedly augments (Na+ + K+)-ATPase catalytic activity. Demonstration of whether activation of (Na+ + K+)-ATPase affects heart function in animal in vivo was the object of this investigation.

METHODS

Male wild-type CD-1 mouse and specific antibody SSA412 were used for the study. A pressure-volume micromanometer-conductance catheter in anesthetized mouse assessed in vivo cardiac functions.

RESULTS

Specific antibody SSA412 infusion in mouse shifted pressure-volume loop leftward with increased stroke volume and enhanced end-systolic elastance. Global systolic parameters such as ejection fraction and cardiac output, and load independent contractile parameters including dP/dtmax/IP, PMX/EDV, Ees, and PRSW, were all increased without any effect on relaxation following administration of SSA412. Cardiac preload indexed by EDV and afterload by ESP did not alter, suggesting that SSA412-enhanced myocardial performance is a direct cardiac effect caused by the activation of (Na+ + K+)-ATPase.

CONCLUSION

Our study provides the first in vivo physiological evidence to demonstrate that activation of (Na+ + K+)-ATPase induces significant positive inotropic effect in intact animal heart. The finding may lead to new therapeutic strategies for the treatment of heart failure.

Oxidant stress from nitric oxide synthase-3 uncoupling stimulates cardiac pathologic remodeling from chronic pressure load

Cardiac pressure load stimulates hypertrophy, often leading to chamber dilation and dysfunction. ROS contribute to this process. Here we show that uncoupling of nitric oxide synthase-3 (NOS3) plays a major role in pressure load-induced myocardial ROS and consequent chamber remodeling/hypertrophy. Chronic transverse aortic constriction (TAC; for 3 and 9 weeks) in control mice induced marked cardiac hypertrophy, dilation, and dysfunction. Mice lacking NOS3 displayed modest and concentric hypertrophy to TAC with preserved function. NOS3(-/-) TAC hearts developed less fibrosis, myocyte hypertrophy, and fetal gene re-expression (B-natriuretic peptide and alpha-skeletal actin). ROS, nitrotyrosine, and gelatinase (MMP-2 and MMP-9) zymogen activity markedly increased in control TAC, but not in NOS3(-/-) TAC, hearts. TAC induced NOS3 uncoupling in the heart, reflected by reduced NOS3 dimer and tetrahydrobiopterin (BH4), increased NOS3-dependent generation of ROS, and lowered Ca(2+)-dependent NOS activity. Cotreatment with BH4 prevented NOS3 uncoupling and inhibited ROS, resulting in concentric nondilated hypertrophy. Mice given the antioxidant tetrahydroneopterin as a control did not display changes in TAC response. Thus, pressure overload triggers NOS3 uncoupling as a prominent source of myocardial ROS that contribute to dilatory remodeling and cardiac dysfunction. Reversal of this process by BH4 suggests a potential treatment to ameliorate the pathophysiology of chronic pressure-induced hypertrophy.

Phosphodiesterase-5A dysregulation in penile erectile tissue is a mechanism of priapism

The molecular mechanism for priapism is not well characterized. Although the nitric oxide (NO) pathway is known to mediate penile erection under normal conditions, we hypothesized that the mechanism of priapism rests in aberrant downstream signaling of this pathway based on our previous findings that mice lacking the gene for endothelial nitric oxide synthase (eNOS-/-) and mice lacking both neuronal NOS (nNOS) and eNOS (nNOS-/-, eNOS-/-) have a tendency for priapic activity. We investigated the role of downstream guanylate cyclase and phosphodiesterase type 5 (PDE5A) expression and function in mediating these responses in eNOS-/- and nNOS-/-, eNOS-/- mice. Erectile responses to both cavernous nerve stimulation and intracavernosal injection of the NO donor diethylamine-NONOate were augmented in eNOS-/- and nNOS-/-, eNOS-/- mice but not in WT or nNOS-/- mice. PDE5A protein expression and activity and cGMP levels were significantly lower in eNOS-/- and nNOS-/-, eNOS-/- mice, and this effect was reproduced in WT corpus cavernosum exposed to NOS inhibitors. Moreover, cavernous nerve stimulation was associated with a marked augmentation of cavernosal cGMP levels, suggesting that, although lower at baseline, the production of cGMP is unchecked in eNOS-/- and nNOS-/-, eNOS-/- mice upon neurostimulation. Transfection of eNOS-/- mice with an adenovirus encoding eNOS resulted in a normalization of PDE5A protein and activity as well as a correction of priapic activity. Coupled with the observation that sickle cell disease mice (which show a priapism phenotype) evince dysregulated PDE5A expression/activity, these data suggest that PDE5A dysregulation is a fundamental mechanism for priapism.

Chronic inhibition of cyclic GMP phosphodiesterase 5A prevents and reverses cardiac hypertrophy

Sustained cardiac pressure overload induces hypertrophy and pathological remodeling, frequently leading to heart failure. Genetically engineered hyperstimulation of guanosine 3',5'-cyclic monophosphate (cGMP) synthesis counters this response. Here, we show that blocking the intrinsic catabolism of cGMP with an oral phosphodiesterase-5A (PDE5A) inhibitor (sildenafil) suppresses chamber and myocyte hypertrophy, and improves in vivo heart function in mice exposed to chronic pressure overload induced by transverse aortic constriction. Sildenafil also reverses pre-established hypertrophy induced by pressure load while restoring chamber function to normal. cGMP catabolism by PDE5A increases in pressure-loaded hearts, leading to activation of cGMP-dependent protein kinase with inhibition of PDE5A. PDE5A inhibition deactivates multiple hypertrophy signaling pathways triggered by pressure load (the calcineurin/NFAT, phosphoinositide-3 kinase (PI3K)/Akt, and ERK1/2 signaling pathways). But it does not suppress hypertrophy induced by overexpression of calcineurin in vitro or Akt in vivo, suggesting upstream targeting of these pathways. PDE5A inhibition may provide a new treatment strategy for cardiac hypertrophy and remodeling.

Evidence that the H1‐H2 domain of α1 subunit of (Na++K+)‐ATPase participates in the regulation of cardiac contraction

(Na++K+)-ATPase (NKA) plays an important role in ion homeostasis and regulates cardiac contraction. To understand the molecular basis of its cardiac regulatory functions, we investigated whether the primary structure of the H1-H2 domain in alpha-1 (alpha1) subunit of the enzyme plays a role in myocardial contractile regulation. Here we show that site-specific binding to this 1 H1-H2 domain with a targeted antibody (SSA78) markedly augments intracellular Ca2+ transients and contraction of rat ventricular cardiomyocytes without inactivating NKA. In vivo SSA78 infusion in mice results in a positive inotropic effect with enhanced contractile function yet no change in relaxation, indicating a direct cardiac effect linked to the H1-H2 domain. Competitive immunofluorescent staining and flow cytometry reveal that SSA78 binding is antagonized by ouabain, supporting the interaction of SSA78 at one of the glycoside-effecter sites. These new findings suggest that the H1-H2 domain of 1 subunit of NKA is a critical determinant of enzyme biologic activity, which couples to enhanced myocyte calcium transient and inotropic action.

cGMP catabolism by phosphodiesterase 5A regulates cardiac adrenergic stimulation by NOS3-dependent mechanism

Beta-adrenergic agonists stimulate cardiac contractility and simultaneously blunt this response by coactivating NO synthase (NOS3) to enhance cGMP synthesis and activate protein kinase G (PKG-1). cGMP is also catabolically regulated by phosphodiesterase 5A (PDE5A). PDE5A inhibition by sildenafil (Viagra) increases cGMP and is used widely to treat erectile dysfunction; however, its role in the heart and its interaction with beta-adrenergic and NOS3/cGMP stimulation is largely unknown. In nontransgenic (control) murine in vivo hearts and isolated myocytes, PDE5A inhibition (sildenafil) minimally altered rest function. However, when the hearts or isolated myocytes were stimulated with isoproterenol, PDE5A inhibition was associated with a suppression of contractility that was coupled to elevated cGMP and increased PKG-1 activity. In contrast, NOS3-null hearts or controls with NOS inhibited by N(G)-nitro-L-arginine methyl ester, or soluble guanylate cyclase (sGC) inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one, showed no effect of PDE5A inhibition on beta-stimulated contractility or PKG-1 activation. This lack of response was not attributable to altered PDE5A gene or protein expression or in vitro PDE5A activity, but rather to an absence of sGC-generated cGMP specifically targeted to PDE5A catabolism and to a loss of PDE5A localization to z-bands. Re-expression of active NOS3 in NOS3-null hearts by adenoviral gene transfer restored PDE5A z-band localization and the antiadrenergic efficacy of PDE5A inhibition. These data support a novel regulatory role of PDE5A in hearts under adrenergic stimulation and highlight specific coupling of PDE5A catabolic regulation with NOS3-derived cGMP attributable to protein subcellular localization and targeted synthetic/catabolic coupling.

Frequency- and Afterload-Dependent Cardiac Modulation In Vivo by Troponin I With Constitutively Active Protein Kinase A Phosphorylation Sites

Acute beta-adrenergic stimulation enhances cardiac contractility, accelerates muscle relaxation, and amplifies the inotropic and lusitropic response to increased stimulation frequency. These effects are modulated by phosphorylation of calcium handling and myofilament proteins such as troponin I (TnI) by protein kinase A (PKA). To more directly delineate the role of TnI PKA phosphorylation, transgenic mice were generated that overexpress cardiac TnI in which the serine residues normally targeted by PKA are mutated to aspartic acid to mimic constitutive phosphorylation (TnIDD22,23). Native cardiac TnI was near completely replaced in one transgenic line as assessed by in vitro phosphorylation, and this led to reduced calcium sensitivity of myofibrillar MgATPase, as expected. TnIDD22,23 mice had mildly enhanced basal systolic and diastolic function, and displayed marked augmentation of frequency-dependent inotropy and relaxation, with a peak frequency response 2-fold greater in mutants than controls (P<0.005). Increasing afterload prolonged relaxation more in nontransgenic than TnIDD22,23 (P<0.02), whereas contractile responses to afterload were similar between these strains. Isoproterenol treatment eliminated the differential force-frequency and afterload response between TnIDD22,23 and controls. In contrast to in vivo studies, isolated isometric trabeculae from nontransgenic and TnIDD22,23 mice had similar basal, isoproterenol-, and frequency-stimulated function, suggesting that muscle shortening may be important to TnI PKA effects. These results support a novel role for cardiac TnI PKA phosphorylation in the rate-dependent enhancement of systolic and diastolic function in vivo and afterload sensitivity of relaxation. These results have implications for cardiac failure in which force-frequency modulation is blunted and afterload relaxation sensitivity increased in association with diminished PKA TnI phosphorylation.

Modulation of in vivo cardiac function by myocyte-specific nitric oxide synthase-3

Nitric oxide (NO) functions principally as a diffusible paracrine effector. The exception is in cardiomyocytes where both NO synthases (NOS) and target proteins coexist, allowing NO to work in an autocrine/intracrine fashion. However, the most abundant myocyte isoform (NOS3) is far more expressed in vascular endothelium; thus, the in vivo contribution of myocyte-NOS3 remains less clear. The present study tested this role by transfecting whole hearts of NOS3-null (NOS3(-/-)) mice with adenovirus-expressing NOS3 coupled to a alpha-MHC promoter (AdV(NOS3)), comparing results to hearts transfected with marker-gene beta-galactosidase (AdVbeta(gal)). Total myocardial NOS3 protein and activity were restored to near wild-type (WT) levels in NOS3(-/-)+AdV(NOS3) hearts, and NOS3 relocalized normally with caveolin-3. Ejection function by pressure-volume analysis was enhanced in NOS3(-/-)+AdVbeta(gal) over WT or NOS3(-/-)+AdV(NOS3). More prominently, isoproterenol (ISO)-stimulated systolic and diastolic function in WT was amplified in NOS3(-/-)+AdVbeta(gal), whereas NOS3(-/-)+AdV(NOS3) returned the response to control. ISO-activated systolic function was inhibited 85% by concomitant muscarinic stimulation (carbachol) in NOS3(-/-)+AdV(NOS3) but not NOS3(-/-)+AdVbeta(gal) hearts. Lastly, NOS3(-/-)+AdVbeta(gal) mice displayed enhanced inotropy and lusitropy over WT at slower heart rates but a blunted rate augmentation versus controls. A more positive rate response was restored in NOS3(-/-)+AdV(NOS3) (P<0.001). Thus, myocyte autocrine/intracrine NOS3 regulation in vivo can underlie key roles in beta-adrenergic, muscarinic, and frequency-dependent cardiac regulation.

The Polycomb-group gene Rae28 sustains Nkx2.5/Csx expression and is essential for cardiac morphogenesis

The Polycomb-group (PcG) gene Rae28 is a mammalian homologue of the Drosophila gene polyhomeotic. PcG genes are known to maintain transcription states, once initiated, probably by regulating chromatin structure. Since homozygous Rae28-deficient (Rae28(-/-)) mice displayed cardiac anomalies similar to congenital heart diseases in humans, we examined the role of Rae28 in cardiac morphogenesis at the molecular level. In Rae28(-/-) embryos, expression of the cardiac selector gene Nkx2.5/Csx (Nkx2.5) was initiated properly but was not sufficiently sustained later in development. This impaired expression of Nkx2.5 in the maintenance phase proved to have a crucial effect on cardiac morphogenesis, as demonstrated by the results of a genetic complementation experiment in which the cardiac anomalies were suppressed by overexpression of human NKX2.5/CSX1 in Rae28(-/-) embryos. Ubiquitous expression of exogenous Rae28 likewise restored the impaired Nkx2.5 expression in Rae28(-/-) embryos, further supporting the notion that Rae28 sustains Nkx2.5 expression in cardiomyocytes. Thus, our data show that a mammalian PcG gene can play a key role in organogenesis by helping to maintain the expression of a selector gene.

Csx/Nkx2-5 is required for homeostasis and survival of cardiac myocytes in the adult heart

Csx/Nkx2-5, which is essential for cardiac development of the embryo, is abundantly expressed in the adult heart. We here examined the role of Csx/Nkx2-5 in the adult heart using two kinds of transgenic mice. Transgenic mice that overexpress a dominant negative mutant of Csx/Nkx2-5 (DN-TG mice) showed degeneration of cardiac myocytes and impairment of cardiac function. Doxorubicin induced more marked cardiac dysfunction in DN-TG mice and less in transgenic mice that overexpress wild type Csx/Nkx2-5 (WT-TG mice) compared with non-transgenic mice. Doxorubicin induced cardiomyocyte apoptosis, and the number of apoptotic cardiomyocytes was high in the order of DN-TG mice, non-transgenic mice, and WT-TG mice. Overexpression of the dominant negative mutant of Csx/Nkx2-5 induced apoptosis in cultured cardiomyocytes, while expression of wild type Csx/Nkx2-5 protected cardiomyocytes from doxorubicin-induced apoptotic death. These results suggest that Csx/Nkx2-5 plays a critical role in maintaining highly differentiated cardiac phenotype and in protecting the heart from stresses including doxorubicin.

Sodium calcium exchanger plays a key role in alteration of cardiac function in response to pressure overload

The Na+-Ca2+ exchanger (NCX) on the plasma membrane is thought to be the main calcium extrusion system from the cytosol to the extracellular space in many mammalian excitable cells, including cardiac myocytes. However, the pathophysiological role of NCX in the heart is still unclear because of the lack of known specific inhibitors of NCX. To determine the role of NCX in cardiac contraction and the development of cardiac hypertrophy, we imposed pressure overload on the heart of heterozygous NCX knockout (KO) mice by constricting transverse aorta, and examined cardiac function and morphology 3 wk after operation. Although there was no difference in cardiac function between sham-operated KO mice and sham-operated wild-type (WT) mice, KO mice showed higher left ventricular pressure and better systolic function than WT mice in response to pressure overload. Northern blot analysis revealed that mRNA levels of sarcoplasmic reticulum Ca2+-ATPase were reduced by pressure overload in left ventricles of WT but not of KO mice. However, hypertrophic changes with interstitial fibrosis were more prominent in KO mice than WT mice. These results suggest that reduction of NCX results in supernormalized cardiac function and causes marked cardiac hypertrophy in response to pressure overload.

A novel myocyte-specific gene Midori promotes the differentiation of P19CL6 cells into cardiomyocytes

Although several cardiac-specific transcription factors have been shown to play vital roles in various steps during the heart formation, the precise mechanism of the early stage of cardiogenesis has yet to be elucidated. By differential display technique, we tried to identify molecules that are expressed earlier than cardiac transcription factors such as CSX/NKX2-5 and GATA-4 and are involved in cardiomyocyte differentiation using the P19CL6 cell line, which efficiently differentiates into cardiomyocytes when treated with dimethyl sulfoxide. We isolated a novel gene designated Midori. Its deduced amino acid sequence contained an ATP/GTP-binding site, Ig-like domain, and Kringle-like domain. Northern blot analysis revealed that expression of Midori was restricted to the fetal and adult heart and adult skeletal muscle in mice. In whole mount in situ hybridization, Midori was expressed in cardiac crescent and developing heart but not in somites. The MIDORI protein was localized in the nucleus and overexpression of Midori induced expression of endogenous Midori itself, suggesting that MIDORI may act as a transcriptional regulator. Permanent P19CL6 cell lines overexpressing Midori more efficiently differentiated into cardiomyocytes than did parental cells, whereas those overexpressing the antisense Midori less efficiently differentiated. These results suggest that Midori may promote the differentiation of P19CL6 into cardiomyocytes.

Calcineurin plays a critical role in the development of pressure overload-induced cardiac hypertrophy

BACKGROUND

Although activation of the Ca(2+)-dependent phosphatase calcineurin has been reported to induce cardiomyocyte hypertrophy, whether calcineurin is involved in pressure overload-induced cardiac hypertrophy remains controversial.

METHODS AND RESULTS

We examined in the present study the role of calcineurin in pressure overload-induced cardiac hypertrophy using transgenic mice that overexpress the dominant negative mutant of calcineurin specifically in the heart. There were no significant differences in body weight, blood pressure, heart rate, heart weight, and the cardiac calcineurin activity between the transgenic mice and their littermate wild-type mice at basal state. The activity of calcineurin was markedly increased by pressure overload produced by constriction of the abdominal aorta in the heart of wild-type mice but less increased in the heart of the transgenic mice. Pressure overload induced increases in heart weight, wall thickness of the left ventricle, and diameter of cardiomyocytes; reprogramming of expressions of immediate early response genes and fetal-type genes; activation of extracellular signal-regulated protein kinases; and fibrosis. All these hypertrophic responses were more prominent in the wild-type mice than in the transgenic mice.

CONCLUSIONS

These results suggest that calcineurin plays a critical role in the development of pressure overload-induced cardiac hypertrophy.

gp130 plays a critical role in pressure overload-induced cardiac hypertrophy

gp130, a common receptor for the interleukin 6 family, plays pivotal roles in growth and survival of cardiac myocytes. In the present study, we examined the role of gp130 in pressure overload-induced cardiac hypertrophy using transgenic (TG) mice, which express a dominant negative mutant of gp130 in the heart under the control of alpha myosin heavy chain promoter. TG mice were apparently healthy and fertile. There were no differences in body weight and heart weight between TG mice and littermate wild type (WT) mice. Pressure overload-induced increases in the heart weight/body weight ratio, ventricular wall thickness, and cross-sectional areas of cardiac myocytes were significantly smaller in TG mice than in WT mice. Northern blot analysis revealed that pressure overload-induced up-regulation of brain natriuretic factor gene and down-regulation of sarcoplasmic reticulum Ca(2+) ATPase 2 gene were attenuated in TG mice. Pressure overload activated ERKs and STAT3 in the heart of WT mice, whereas pressure overload-induced activation of STAT3, but not of ERKs, was suppressed in TG mice. These results suggest that gp130 plays a critical role in pressure overload-induced cardiac hypertrophy possibly through the STAT3 pathway.

Smads, TAK1, and their common target ATF-2 play a critical role in cardiomyocyte differentiation

We previously demonstrated that bone morphogenetic proteins (BMPs) induce cardiomyocyte differentiation through the mitogen-activated protein kinase kinase kinase TAK1. Transcription factors Smads mediate transforming growth factor-β signaling and the ATF/CREB family transcription factor ATF-2 has recently been shown to act as a common target of the Smad and the TAK1 pathways. We here examined the role of Smads and ATF-2 in cardiomyocyte differentiation of P19CL6, a clonal derivative of murine P19 cells. Although P19CL6 efficiently differentiates into cardiomyocytes when treated with dimethyl sulfoxide, P19CL6noggin, a P19CL6 cell line constitutively overexpressing the BMP antagonist noggin, did not differentiate into cardiomyocytes. Cooverexpression of Smad1, a ligand-specific Smad, and Smad4, a common Smad, restored the ability of P19CL6noggin to differentiate into cardiomyocytes, whereas stable overexpression of Smad6, an inhibitory Smad, completely blocked differentiation of P19CL6, suggesting that the Smad pathway is necessary for cardiomyocyte differentiation. ATF-2 stimulated the βMHC promoter activity by the synergistic manner with Smad1/4 and TAK1 and promoted terminal cardiomyocyte differentiation of P19CL6noggin, whereas overexpression of the dominant negative form of ATF-2 reduced the promoter activities of several cardiac-specific genes and inhibited differentiation of P19CL6. These results suggest that Smads, TAK1, and their common target ATF-2 cooperatively play a critical role in cardiomyocyte differentiation.

[Analysis of Na+/Ca2+ exchanger knockout mice]

The Na(+)/Ca(2+) exchanger (NCX) on the plasma membrane is thought to be the main calcium extrusion system from the cytosol to the extracellular space in many mammalian excitable cells including cardiac myocytes. However, the precise roles of NCX are still unclear because of lack of its specific inhibitors. We generated NCX1-deficient mice by gene targeting to determine the in vivo function of the exchanger. Homozygous mutant died at 9.5 days post coitum. Embryonic hearts did not beat and cardiac myocytes showed apoptosis. These results suggest that NCX1 is required for heart beats and survival of cardiac myocytes in embryos. Heterozygous mutant mice were viable and indistinguishable from wild type mice. mRNA and protein levels in the heart of heterozygous mutant were half as much as wild type mice. In response to pressure overload, mutant mice showed better systolic and diastolic relaxation functions than wild type mice. Intracellular Ca(2+) measurement revealed an increase in calcium content of cytoplasm and sarcoplasmic reticulum (SR) and RNA analysis revealed preserved SR Ca(2+) ATPase expression in the ventricle of mutant mice. These results suggest that NCX plays an important role in cardiac performance in these pathological situations.

[Calcineurin inhibitor attenuates the development and induces the regression of cardiac hypertrophy in rats with salt-sensitive hypertension]

BACKGROUND

It remains unclear how hemodynamic overload induces cardiac hypertrophy. Recently, activation of calcium-dependent phosphatase, calcineurin, has been elucidated to induce cardiac hypertrophy. In the present study, we examined the role of calcineurin in load-induced cardiac hypertrophy by using Dahl salt-sensitive (DS) rats, which develop both pressure and volume overload when fed a high salt diet.

METHODS AND RESULTS

In the DS rat heart, the activity of calcineurin was increased and cardiac hypertrophy was induced by high salt diet. Treatment of DS rats with the calcineurin inhibitor FK506 (0.1 or 0.01 mg/kg every second day) from the age of 6 weeks to 12 weeks inhibited the activation of calcineurin in the heart in a dose-dependent manner and attenuated the development of load-induced cardiac hypertrophy and fibrosis without change of hemodynamic parameters. Additionally, treatment with 0.1 mg/kg every second day but not with 0.01 mg/kg every second day of FK506 from the age of 12 weeks to 16 weeks induced regression of cardiac hypertrophy in DS rats. Load-induced reprogramming of gene expression was also suppressed by the FK506 treatment.

CONCLUSIONS

These results suggest that calcineurin is involved in the development of cardiac hypertrophy in rats with salt-sensitive hypertension and that inhibition of calcineurin could induce regression of cardiac hypertrophy.

Calcineurin inhibitor attenuates the development and induces the regression of cardiac hypertrophy in rats with salt-sensitive hypertension

BACKGROUND

It remains unclear how hemodynamic overload induces cardiac hypertrophy. Recently, activation of calcium-dependent phosphatase, calcineurin, has been elucidated to induce cardiac hypertrophy. In the present study, we examined the role of calcineurin in load-induced cardiac hypertrophy by using Dahl salt-sensitive (DS) rats, which develop both pressure and volume overload when fed a high salt diet.

METHODS AND RESULTS

In the DS rat heart, the activity of calcineurin was increased and cardiac hypertrophy was induced by high salt diet. Treatment of DS rats with the calcineurin inhibitor FK506 (0.1 or 0.01 mg/kg twice daily) from the age of 6 weeks to 12 weeks inhibited the activation of calcineurin in the heart in a dose-dependent manner and attenuated the development of load-induced cardiac hypertrophy and fibrosis without change of hemodynamic parameters. Additionally, treatment with 0.1 mg/kg twice daily but not with 0.01 mg/kg twice daily of FK506 from the age of 12 weeks to 16 weeks induced regression of cardiac hypertrophy in DS rats. Load-induced reprogramming of gene expression was also suppressed by the FK506 treatment.

CONCLUSIONS

These results suggest that calcineurin is involved in the development of cardiac hypertrophy in rats with salt-sensitive hypertension and that inhibition of calcineurin could induce regression of cardiac hypertrophy.

Up-regulation of natriuretic peptides in the ventricle of Csx/Nkx2-5 transgenic mice

A cardiac homeobox-containing gene Csx/Nkx2-5, which is essential for cardiac development, is abundantly expressed in the adult heart as well as in the heart primordia. Targeted disruption of this gene results in embryonic lethality due to abnormal heart morphogenesis. To elucidate the role of Csx/Nkx2-5 in the adult heart, we generated transgenic mice which overexpress human Csx/Nkx2-5. The transgene was expressed abundantly in the heart and the skeletal muscle. mRNA levels of several cardiac genes including natriuretic peptides, CARP, MLC2v, and endogenous Csx/Nkx2-5 were increased in the ventricle of the transgenic mice. Electron microscopic analysis revealed that the ventricular myocardium of the transgenic mice had many secretory granules, which disappeared after administration of vasopressin. These results suggest that Csx/Nkx2-5 regulates many cardiac genes and induces formation of secretory granules in the adult ventricle.

Calcineurin plays a critical role in pressure overload-induced cardiac hypertrophy

BACKGROUND

Cardiac hypertrophy is a fundamental adaptive response to hemodynamic overload; how mechanical load induces cardiac hypertrophy, however, remains elusive. It was recently reported that activation of a calcium-dependent phosphatase, calcineurin, induces cardiac hypertrophy. In the present study, we examined whether calcineurin plays a critical role in pressure overload-induced cardiac hypertrophy.

METHODS AND RESULTS

Pressure overload produced by constriction of the abdominal aorta increased the activity of calcineurin in the rat heart and induced cardiac hypertrophy, including reprogramming of gene expression. Treatment of rats with a calcineurin inhibitor, FK506, inhibited the activation of calcineurin and prevented the pressure overload-induced cardiac hypertrophy and fibrosis without change of hemodynamic parameters. Load-induced expression of immediate-early-response genes and fetal genes was also suppressed by the FK506 treatment.

CONCLUSIONS

The present results suggest that the calcineurin signaling pathway plays a pivotal role in load-induced cardiac hypertrophy and may pave the way for a novel pharmacological approach to prevent cardiac hypertrophy.

Bone morphogenetic proteins induce cardiomyocyte differentiation through the mitogen-activated protein kinase kinase kinase TAK1 and cardiac transcription factors Csx/Nkx-2.5 and GATA-4

Bone morphogenetic proteins (BMPs) have been shown to induce ectopic expression of cardiac transcription factors and beating cardiomyocytes in nonprecardiac mesodermal cells in chicks, suggesting that BMPs are inductive signaling molecules that participate in the development of the heart. However, the precise molecular mechanisms by which BMPs regulate cardiac development are largely unknown. In the present study, we examined the molecular mechanisms by which BMPs induce cardiac differentiation by using the P19CL6 in vitro cardiomyocyte differentiation system, a clonal derivative of P19 embryonic teratocarcinoma cells. We established a permanent P19CL6 cell line, P19CL6noggin, which constitutively overexpresses the BMP antagonist noggin. Although almost all parental P19CL6 cells differentiate into beating cardiomyocytes when treated with 1% dimethyl sulfoxide, P19CL6noggin cells did not differentiate into beating cardiomyocytes nor did they express cardiac transcription factors or contractile protein genes. The failure of differentiation was rescued by overexpression of BMP-2 or addition of BMP protein to the culture media, indicating that BMPs were indispensable for cardiomyocyte differentiation in this system. Overexpression of TAK1, a member of the mitogen-activated protein kinase kinase kinase superfamily which transduces BMP signaling, restored the ability of P19CL6noggin cells to differentiate into cardiomyocytes and concomitantly express cardiac genes, whereas overexpression of the dominant negative form of TAK1 in parental P19CL6 cells inhibited cardiomyocyte differentiation. Overexpression of both cardiac transcription factors Csx/Nkx-2.5 and GATA-4 but not of Csx/Nkx-2.5 or GATA-4 alone also induced differentiation of P19CL6noggin cells into cardiomyocytes. These results suggest that TAK1, Csx/Nkx-2.5, and GATA-4 play a pivotal role in the cardiogenic BMP signaling pathway.

Context-dependent transcriptional cooperation mediated by cardiac transcription factors Csx/Nkx-2.5 and GATA-4

Although the cardiac homeobox gene Csx/Nkx-2.5 is essential for normal heart development, little is known about its regulatory mechanisms. In a search for the downstream target genes of Csx/Nkx-2. 5, we found that the atrial natriuretic peptide (ANP) gene promoter was strongly transactivated by Csx/Nkx-2.5. Deletion and mutational analyses of the ANP promoter revealed that the Csx/Nkx-2.5-binding element (NKE2) located at -240 was required for high level transactivation by Csx/Nkx-2.5. We also found that Csx/Nkx-2.5 and GATA-4 displayed synergistic transcriptional activation of the ANP promoter, and in contrast to previous reports (Durocher, D., Charron, F., Warren, R., Schwartz, R. J., and Nemer, M. (1997) EMBO J. 16, 5687-5696; Lee, Y., Shioi, T., Kasahara, H., Jobe, S. M., Wiese, R. J., Markham, B., and Izumo, S (1998) Mol. Cell. Biol. 18, 3120-3129), this synergism was dependent on binding of Csx/Nkx-2.5 to NKE2, but not on GATA-4-DNA interactions. Although GATA-4 also potentiated the Csx/Nkx-2.5-induced transactivation of the artificial promoter that contains multimerized Csx/Nkx-2.5-binding sites, Csx/Nkx-2.5 reduced the GATA-4-induced transactivation of the GATA-4-dependent promoters. These findings indicate that the cooperative transcriptional regulation mediated by Csx/Nkx-2.5 and GATA-4 is promoter context-dependent and suggest that the complex cis-trans interactions may fine-tune gene expression in cardiac myocytes.

Rescue of angiotensinogen-knockout mice

Angiotensinogen, the precursor of angiotensins I and II, is a critical component of the renin-angiotensin system that plays an important role in regulating blood pressure and electrolyte homeostasis. Genetically altered mice lacking angiotensinogen (Agt-KO) showed an expected phenotype, such as marked hypotension, but unexpected ones including abnormal kidney morphology, reduced survival rates of newborns, and impaired blood-brain barrier function after cold injury. To examine whether disruption of the angiotensinogen gene is responsible for the observed phenotypes, we generated a line of mice heterozygous for the mouse angiotensinogen gene under the control of a mouse metallothionein-I promoter (MT-Agt) and crossmated transgenic mice with Agt-KO mice. The resulting mice (MT-Agt(+/-)/Agt(-/-):MT-Agt/KO) produced the plasma level of angiotensin I comparable to that of wild-type mice, and the mutant phenotypes were rescued. These results indicated that the resultant phenotypes due to the genetic deficiency of mouse angiotensinogen can be corrected by restoring angiotensinogen and angiotensin I in the circulation.

[A case of pheochromocytoma incorrectly diagnosed before and during surgery]

In a patient with an adrenal tumor, although norepinephrine levels in the blood and urine were abnormally high, findings in CT and 131 I-MIBG scintigraphy denied pheochromocytoma. The preoperative diagnosis was metastatic adrenal tumor. The surgical manipulation of the tumor increased the blood pressure from 110/60 to 210/110 mmHg. However, intraoperative microscopic examination in frozen section excluded again possibility of pheochromocytoma. Later, findings in the permanent specimen confirmed that the tumor was pheochromocytoma. The problem of this case was that each specialist made judgment only on the subject of his own interest without considering of the patient's status as a whole. Anesthesiologist should have the ability to make preoperative assessment of a patient by using all available information with his unbiased mind.

Greater incidence of delirium during recovery from sevoflurane anesthesia in preschool boys

BACKGROUND

In the authors' clinical experience, preschool children are more likely to show delirium after sevoflurane than are older children.

METHODS

Sixty-three preschool boys aged 3-5 yr (classified as American Society of Anesthesiologists [ASA] physical status I), and 53 school-age boys aged 6-10 yr (ASA physical status I) who underwent minor urologic surgery were randomly assigned to receive either halothane or sevoflurane, thus creating four groups: preschool-halothane (n = 32), preschool-sevoflurane (n = 31), school-halothane (n = 27), and school-sevoflurane (n = 26). Anesthesia was induced by inhalation of halothane or sevoflurane in oxygen and was maintained at 1 minimum alveolar concentration of each agent throughout surgery. For intra- and postoperative analgesia, caudal block with 0.5-1.0 ml/kg 0.25% plain bupivacaine and topical infiltration with 3-5 ml 1% lidocaine were provided for all patients. Recovery characteristics and incidence of delirium on emergence were compared among the four groups.

RESULTS

Two patients in the preschool-halothane group, one in the preschool-sevoflurane group, and one in the school-halothane group were excluded from the comparison because of insufficient analgesia or agitation before induction. In both age groups, the time to emergence from sevoflurane was significantly faster (about 3 min) than from halothane. The incidence of delirium during recovery in the preschool-sevoflurane group (40%) was significantly greater than that in the other groups (preschool-halothane, 10%; school-halothane, 15.4%; school-sevoflurane, 11.5%).

CONCLUSION

Sevoflurane provided quicker emergence and early recovery compared with halothane, but the incidence of delirium was greater in preschool boys after sevoflurane.

Hypertension induced in pregnant mice by placental renin and maternal angiotensinogen

Maternal hypertension is a common complication of pregnancy and its pathophysiology is poorly understood. This phenomenon was studied in an animal model by mating transgenic mice expressing components of the human renin-angiotensin system. When transgenic females expressing angiotensinogen were mated with transgenic males expressing renin, the pregnant females displayed a transient elevation of blood pressure in late pregnancy, due to secretion of placental human renin into the maternal circulation. Blood pressure returned to normal levels after delivery of the pups. Histopathologic examination revealed uniform enlargement of glomeruli associated with an increase in urinary protein excretion, myocardial hypertrophy, and necrosis and edema in the placenta. These mice may provide molecular insights into pregnancy-associated hypertension in humans.

[Successful coronary angioplasty in a patient with acute myocardial infarction caused by prosthetic valve endocarditis]

A 65-year-old man was hospitalized with persistent fever (up to 39 degrees C) of 3 weeks' duration 9 years after aortic valve replacement with a Hall-Kaster prosthesis. Multiple blood cultures demonstrated beta-Streptococcus. Transesophageal echocardiography disclosed mobile vegetations at the prosthetic valve with normal valve function. A diagnosis of late prosthetic valve endocarditis was made. Therapy was begun with penicillin G, cefazolin, and gentamycin. On the 20th hospital day, he suddenly developed severe chest pain. Electrocardiography was consistent with acute extensive anterior myocardial infarction. Coronary angiography revealed that the left anterior descending coronary artery was occluded in its proximal portion with an intraluminal filling defect, which was morphologically the same as the vegetation that had been demonstrated previously. Percutaneous transluminal coronary angioplasty was performed, and coronary artery perfusion was restored 4.5 hours after the onset of chest pain. Transesophageal echocardiography performed 2 days later revealed that the vegetation at the prosthetic valve level had nearly disappeared. This is the first reported case of coronary angioplasty in a patient with acute myocardial infarction caused by prosthetic valve endocarditis in Japan.

Ephedrine-induced increases in arterial blood pressure accelerate regression of epidural block

We investigated the hypothesis that ephedrine-induced increases in blood pressure accelerate the regression of epidural block. In patients undergoing minor gynecologic surgery, we performed lumbar epidural blockade using 2% lidocaine containing 1:200,000 epinephrine to which was added 0.1 mg of fentanyl. Eighty minutes after the epidural injection, we started an ephedrine infusion to increase the systolic blood pressure by 20% in 10 min and maintained the value for the following 20 min. Then we compared the proximal extent of sensory analgesia at 80 min with that at 140 min. Ephedrine significantly (P = 0.001) hastened the regression of sensory analgesia. We conclude that an ephedrine-induced blood pressure increase accelerates regression of epidural blockade.

Angiotensin II type 1a receptor-deficient mice with hypotension and hyperreninemia

Angiotensin (AT) II, the bioactive octapeptide in the renin-angiotensin system that plays a key role in cardiovascular homeostasis, exerts its multiple effects through the different types of AT receptors, AT1a, AT1b, and AT2. Previously, we showed chronic hypotension in angiotensinogen (the precursor of AT)-deficient mice and a dramatic increase in renin mRNA levels in its kidney, but it remains unclear which types of AT receptors regulate the blood pressure and renin gene expression. In order to elucidate the physiological roles of AT1a receptor, we generated mutant mice with a targeted replacement of the AT1a receptor loci by the lacZ gene. In the heterozygous mutant mice, the strong lacZ staining was found in the glomerulus and juxtaglomerular apparatus of the renal cortex, which coincided with that of the signals detected by in situ hybridization. Chronic hypotension was observed in the heterozygous and homozygous mutant mice, with 10 and 22 mm Hg lower systolic blood pressure, respectively, than that of wild-type littermates. Both levels of renin mRNA in the kidney and plasma renin activity were markedly increased only in the homozygous mutant mice. These results demonstrated that an AT1a-mediated signal transduction pathway is, at least in part, involved in the regulation of blood pressure and renin gene expression.

Alterations of angiotensin II receptor contents in hypertrophied hearts

Tsukuba hypertensive mice, which carry the human genes for renin and angiotensinogen, show cardiac hypertrophy as well as hypertension due to activation of the renin-angiotensin system (RAS). Here, we compared the cardiac angiotensin II (Ang II) receptor contents in these and normotensive control mice by means of ligand binding studies and competitive reverse transcription-polymerase chain reaction analyses. The content of the Ang II receptor type 1 (AT1) was significantly higher at both the protein (2.5-fold; p < 0.01) and mRNA (1.4-fold; p < 0.05) levels in the hypertensive mice than that in control mice. Almost identical levels of the Ang II receptor type 2 (AT2) expression were identified at the mRNA levels in the two types of mice, although the levels were less than 20% of those of AT1 mRNA in control mice. These results suggest that AT1 in the heart is upregulated in response to Ang II-induced hypertrophic change and that, in particular, the upregulation of AT1 in particular contributes to the development and/or maintenance of cardiac hypertrophy in conjunction with the increase in Ang II production, because AT1 is responsible for cardiac hypertrophy related to the RAS.

Angiotensinogen-deficient mice with hypotension

The renin-angiotensin system is an enzymatic cascade that produces a potent vasoconstrictor octapeptide angiotensin II, through its physiologically inactive intermediate decapeptide angiotensin I, from their precursor angiotensinogen. In the present study, we generated angiotensinogen-deficient mice by homologous recombination in mouse embryonic stem cells. These mice do not produce angiotensinogen in the liver, resulting in the complete loss of plasma immunoreactive angiotensin I. The systolic blood pressure of the homozygous mutant mice was 66.9 +/- 4.1 mm Hg, significantly lower than that of wild-type mice (100.4 +/- 4.4 mm Hg). This profound hypotension in angiotensinogen-deficient mice demonstrates an indispensable role for the renin-angiotensin system in maintaining blood pressure.

Comparative studies on species-specific reactivity between renin and angiotensinogen

The renin-angiotensin system (RAS) is the most important regulator of electrolyte homeostasis and blood pressure. Our recently generated transgenic mice carrying either the human renin (hREN) or human angiotensinogen (hANG) genes did not develop hypertension but dual gene strains obtained by cross-mating separate lines of mice exhibited a chronically sustained increase in blood pressure, suggesting the presence of species-specific reactivity between renin and angiotensinogen. In order to examine this specificity, the present study was designed to perform a strictly comparative study on hydrolysis of hANG by hREN and mouse submandibular renin (mREN) in vitro by using pure proteins. The recombinant hANG (rhANG) and the synthetic human-type tridecapeptide (hTDP), Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His, corresponding to the N-terminal sequences of hANG, were used to determine the species specificity of recombinant hREN (rhREN) and mREN. While hTDP was cleaved by both rhREN and mREN with similar Km and with the same order of kcat, rhANG was cleaved by mREN with 16.7-fold higher Km and with 28.2-fold lower kcat than by rhREN. These results showed that kcat/Km value of mREN for rhANG was 468-fold lower than that for rhREN acting on rhANG.

Chimeric renin-angiotensin system demonstrates sustained increase in blood pressure of transgenic mice carrying both human renin and human angiotensinogen genes

A reaction between enzyme renin and its only natural substrate angiotensinogen is the initial and rate-limiting step for producing a potent vasoconstrictor angiotensin II as the final product of the renin-angiotensin system, a contributory factor in the pathogenesis of hypertension. In order to assess the role of the interaction of human renin with human angiotensinogen in the development of high blood pressure, we have constructed the chimeric renin-angiotensin cascade in mice comprising both human renin and human angiotensinogen as well as the endogenous angiotensin-converting enzyme and angiotensin II receptor by cross-mating separate lines of transgenic mice carrying either the human renin or human angiotensinogen genes. Although each single gene carrier did not develop hypertension despite the observed normal tissue-specific expression of the transgenes, dual gene strains exhibited a chronically sustained increase in blood pressure. Administration of a human renin-specific inhibitor (ES-8891) was effective in reducing the elevated blood pressure only against the cross-mated hybrid mice, but treatment of an angiotensin-converting enzyme inhibitor (captopril) and a selective antagonist (DuP 753) directed at the angiotensin II receptor decreased the basal level of blood pressure even in single gene carriers as well as in dual gene mice. These results clearly demonstrated that the sustained increase in blood pressure of the hybrid mice was initiated by the interaction between the products of the two human genes.

[Effect of deliberate hypotension with PGE1 on PaO2 in pediatric patients]

We compared the effect of deliberate hypotension with PGE1 on PaO2 between pediatric and adult patients. Seven children, aged 3-9 yrs and 10 adults, aged 35-65 yrs who were scheduled for elective head and neck surgeries were studied. Anesthesia was maintained with enflurane, 50% N2O in oxygen and supplemental infusion of fentanyl. Ventilation was controlled to maintain PaCO2 at 35-40 mmHg. Hypotension was induced with continuous infusion of PGE1 and the systolic blood pressure was maintained at 70% of the presurgical value. Blood gases were measured three times, i.e. before, during, and after hypotension. The hypotension in adults caused a significant reduction in PaO2. In children, on the contrary, PaO2 was not affected by the hypotension. The results suggest that intrapulmonary shunting is smaller in children than in adults during PGE1-induced hypotension.

Dependence of angiotensin production in transgenic mice carrying either the human renin or human angiotensinogen genes on species-specific kinetics of the renin-angiotensin system

In order to study the functional role of the renin-angiotensin system in the control of blood pressure, projects were initiated using transgenic mice carrying either the human renin gene or the human angiotensinogen gene. To extend the usefulness of the transgenic model system of hypertension research, a two-tiered strategy for generation of transgenic mice with high blood pressure has been developed. This unique system allows the establishment of transgenic lines with a strict species specificity of the renin-angiotensinogen reaction exhibited by transgene products that are regulated in a tissue specific manner. In this report, the strategy concerning the "two-tiered method" is presented and evidence is provided the overproduction of angiotensin occurs only in the combined reaction with human renin and human angiotensinogen expressed in transgenic mice.

Expression and purification of human angiotensinogen in Chinese hamster ovary cells

We have produced human angiotensinogen in Chinese hamster ovary (CHO) cells. The expression products were purified to homogeneity by a single column chromatography and its 17 amino-terminal sequences were identical to those of the native protein. We demonstrated the recombinant human angiotensinogen to be a substrate for human renin.

[Liquid crystal thermography; a reliable method for detecting soda lime exhaustion]

The dynamic and functional state of soda lime can be more precisely assessed by measuring changes in wall temperatures of the absorption chambers rather than observing color change of the soda lime granules. We demonstrated in this report that the liquid crystal thermometer is an inexpensive and reliable measuring device for this purpose.

[Anesthetic care of a patient intoxicated with thinner]

This is a report of a 28 year old male who underwent emergency laparotomy. He had a history of asthma and chronic abuse of thinner (toluene), and he stabbed himself after acute intoxication by the drug. Anesthesia was induced and maintained by halothane and oxygen. Vecuronium was used for muscle relaxation. Abnormal EKG was seen during perioperative period: A-V dissociation and incomplete RBBB. After emergence from anesthesia, so called "flash back" phenomenon was observed but this was controlled by diazepam. Since the chronic abuse of toluene causes organic changes in many vital organs, we must take special precautions when we anesthetize a patient with thinner intoxication: (1) toluene has a negative inotropic effect and also delays the S-A and A-V conduction rate, which may potentiate the cardiac effect of inhalation anesthetics; (2) toluene causes liver damages; and (3) the patient may experience "flash back" phenomenon.

The binding of a thyroid hormone metabolite, 3-monoiodo-L-thyronine, to bovine serum albumin as measured by circular dichroism

The interaction between a thyroid hormone metabolite, 3-monoiodo-L-thyronine (3-T1) and bovine serum albumin (BSA) was investigated by using the CD method. An enhanced CD band was observed at the absorption wavelength region of 3-T1 around 293 nm suggesting the binding of 3-T1 to the BSA molecule. The ellipticity at 293 nm was measured at various molar ratios of 3-T1 to BSA, and the apparent binding constant and the maximum number of binding sites could be estimated as Kapp = 8.85 +/- 1.07 X 10(4) M-1 and n = 23.8 +/- 0.9 respectively. The CD of a mixture of BSA, 3-T1 and thyroxine (T4) was also studied at various pH's. The pH profile of the two characteristic CD bands at 293 nm and 320 nm, attributed to bound 3-T1 and T4, suggested that the optimum binding condition of 3-T1 was attained at alkaline pH of around 9, while that of T4 was attained over a wide pH range between 5-10. A significant role of the ionized 4'-hydroxyl group of 3-T1 in the binding reaction with BSA is also suggested.