Cardiomegaly induced by pressure overload in newborn rats is accompanied by altered expression of the long isoform of G(s)alpha protein and deranged signaling of adenylyl cyclase

G proteins-coupled signaling pathways appear to play a role in the development of cardiac hypertrophy and its progression to heart failure. The present study aimed to investigate trimeric G proteins and adenylyl cyclase signaling in immature as well as in adult rat myocardium during this process caused by pressure overload. Pressure overload was induced in newborn (2-day-old) rats by abdominal aortic banding and myocardial preparations from left ventricular myocardium of immature (10-day-old) and adult (90-day-old) animals were analyzed for the relative content of different G protein subunits and adenylyl cyclase (AC) by immunoblotting with specific antibodies. A functional status of the AC signaling system was also evaluated. Normal maturation of rat heart was accompanied by increased expression of AC type V/VI and VII and of the long isoform (G(s)alphaL) of G(s)alpha protein. In parallel, the amounts of myocardial G(i)alpha/G(o)alpha proteins tended to decrease, and G(q)alpha/G(11)alpha and Gbeta did not change. Interestingly, whereas fluoride-stimulated AC activity increased in the course of maturation, activity of AC measured under other experimental conditions (stimulation by Mn2+, forskolin or isoproterenol) was lower in adult than in young rat myocardium. Pressure overload did not influence distribution of G proteins in immature myocardium, but considerably decreased the content of G(s)alphaL and increased G(o)alpha proteins in hearts of 90-day-old rats. These hearts exhibited worsened functional reserve as compared to age-matched controls and activity of AC was also markedly lower. A considerable reduction in Mn(2+)-stimulated AC activity together with similar decrease in AC activity determined under other stimulation conditions suggests that it is a function of AC catalytic subunit that is primarily impaired in this model of pressure overload.

Functional disorders of the oxidative phosphorylation system in the heart mitochondria of mice with juvenile visceral steatosis

Mice with juvenile visceral steatosis (JVS) develop remarkable cardiac hypertrophy and exhibit an increased number of mitochondria in their heart. However, the biochemical characteristics and physiological functions of these mitochondria cardiac are little known. Here we show that the respiratory activities at state 3 with glutamate plus malate or succinate in the heart mitochondria of JVS mice were greatly decreased to 47% or 77%, respectively, compared with those of control mice. The contents of cytochromes a+a(3), b, and c+c(1) in the heart mitochondria of these mice were also decreased, to 51%, 45%, and 79%, respectively, of those of the control mice. Oligomycin-sensitive ATPase activitiy in these mitochondria, however, was increased to about 2 times over that of the control mice. Surprisingly, the ATP-Pi exchange activity of the heart mitochondria of JVS mice was greatly decreased, to 35% of that of control mice. On the other hand, the expression levels of 2 subunits of H(+)-ATP synthase, i.e., coupling factor 6 and alpha subunit, in heart mitochondria from control and JVS mice were almost the same. These results indicate that the coordinate regulation of mitochondrial proliferation and gene expression for components of the oxidative phosphorylation system was markedly defective in the heart of JVS mice. Our current results also suggest the presence of a novel regulatory mechanisms of ATP synthase activities in the heart.

Roles of intercellular adhesion molecule-1 in hypertensive cardiac remodeling

Recently, we have shown that in rats with a suprarenal abdominal aortic constriction (AC), pressure overload induces early perivascular fibro-inflammatory changes (transforming growth factor [TGF]-beta induction and fibroblast proliferation) within the first week after AC and then causes the development of cardiac remodeling (myocyte hypertrophy and reactive myocardial fibrosis) associated with diastolic dysfunction. Intercellular adhesion molecule (ICAM)-1 is implicated in the recruitment of leukocytes, especially macrophages, in various inflammatory situations. Thus, we sought to investigate the causal relation of ICAM-1 to macrophage recruitment and cardiac remodeling in AC rats. In AC rats, immunoreactive ICAM-1 was observed transiently on endothelial cells of the intramyocardial coronary arterioles after day 1, with a peak at day 3, returning to baseline by day 7. Also, ED1+ macrophage accumulation was found in the area adjacent to the arteries expressing ICAM-1. Chronic treatment with an anti-ICAM-1 neutralizing antibody, but not with control IgG, remarkably reduced the accumulations of macrophages and proliferative fibroblasts and inhibited the upregulation of TGF-beta expression. Furthermore, the neutralizing antibody significantly prevented myocardial fibrosis without affecting arterial pressure and left ventricular and myocyte hypertrophy. In conclusion, ICAM-1 expression was induced by pressure overload in the intramyocardial arterioles, and triggered perivascular macrophage accumulation. In pressure-overloaded hearts, a crucial role in ICAM-1-mediated macrophage accumulation was suggested in the development of myocardial fibrosis, through TGF-beta induction and fibroblast activation.

Cellular localization of integrin isoforms in phenylephrine-induced hypertrophic cardiac myocytes

Cardiac hypertrophy is characterized by remodeling of the extracellular matrix (ECM). Integrins are cell-surface molecules that link the ECM to the cellular cytoskeleton where they play roles as signaling molecules and transducers of mechanical force. To clarify the possible roles of integrins in cardiac myocyte hypertrophy, we investigated the cellular localization and expression of ECM proteins and integrins in both normal cardiac myocytes and phenylephrine-induced hypertrophic myocytes. Addition of phenylephrine (PE) to cultured neonatal cardiac myocytes induced sarcomeric organization, increase in cell size, and synthesis of the hypertrophic marker, atrial natriuretic factor (ANF). In particular, fibronectin and collagen underwent dramatic localization changes during PE-induced cardiac hypertrophy. Significant changes were noted in the cellular localization of the respective collagen and fibronectin receptors, integrin alpha1 and alpha5, from diffuse to a sarcomeric banding pattern. Expression levels of integrins were also increased during hypertrophy. Treatment with okadaic acid (OA), an inhibitor of protein phosphatase 2A (PP2A), resulted in inhibition of hypertrophic response. These results suggest that dephosphorylation of integrin beta1 may be important in the induction of cardiac hypertrophy.

Altered calcium transient and development of hypertrophy in beta2-adrenoceptor overexpressing mice with and without pressure overload

Transgenic (TG) mice with cardiac specific 200-fold overexpression of beta(2)-adrenoceptors (beta(2)-AR) have a facilitated development of heart failure following thoracic aortic constriction (TAC). We have studied the alterations of intracellular Ca(2+) transients and myocyte size in wild-type (WT) and TG mice after TAC. Cardiomyocytes were isolated from mice 9 weeks after TAC or sham operation, and incubated with Fura 2/AM. The Ca(2+) transients were determined by Spex dual wavelength Spectrometer during electrical stimulation. The cell size was also determined planimetrically. Cells of sham operated TG mice displayed higher systolic Ca(2+) amplitude than respective WT group (DeltaF(340)/F(380) ratio: 1.05+/-0.08 vs. 0.63+/-0.05; P<0.01), a finding in keeping with enhanced ventricular contractility in the TG mice. However, hypertrophied and failing myocytes of TG animals showed a fall in Ca(2+) transients from sham-operated control levels and there was no difference between TG and WT groups following TAC. In sham-operated groups, the cell size of TG mice was significantly bigger than in WT animals (3212+/-139 vs. 2605+/-162 microm(2); P<0.05). The cell size increased to a similar extent in both groups after TAC (4715+/-216 vs. 5027+/-365 microm(2), P=n.s.). In summary, hypertrophy of cardiomyocytes was present in beta(2)-AR TG mice under baseline conditions. A further hypertrophy occurred during pressure overload to an extent similar to that in WT animals. However, the increased intracellular Ca(2+) transient, seen in sham-operated TG mice, was no longer detectable following development of severe hypertrophy and heart failure. These findings provide explanation on the lack of hemodynamic benefit in beta(2)-AR TG mice subjected to pressure overload.

Oxidative stress and heart failure

Despite advances in treatment, chronic congestive heart failure carries a poor prognosis and remains a leading cause of cardiovascular death. Accumulating evidence suggests that reactive oxygen species (ROS) play an important role in the development and progression of heart failure, regardless of the etiology. Under pathophysiological conditions, ROS have the potential to cause cellular damage and dysfunction. Whether the effects are beneficial or harmful will depend upon site, source and amount of ROS produced, and the overall redox status of the cell. All cardiovascular cell types are capable of producing ROS, and the major enzymatic sources in heart failure are mitochondria, xanthine oxidases and the nonphagocytic NADPH oxidases (Noxs). As well as direct effects on cellular enzymatic and protein function, ROS have been implicated in the development of agonist-induced cardiac hypertrophy, cardiomyocyte apoptosis and remodelling of the failing myocardium. These alterations in phenotype are driven by redox-sensitive gene expression, and in this way ROS may act a potent intracellular second messengers. Recent experimental studies have suggested a possible causal role for increased ROS in the development of contractile dysfunction following myocardial infarction and pressure overload, however the precise contribution of different cellular and enzymatic sources involved remain under investigation.

The transcriptional co-activators CREB-binding protein (CBP) and p300 play a critical role in cardiac hypertrophy that is dependent on their histone acetyltransferase activity

The CBP and p300 proteins are transcriptional co-activators that are involved in a variety of transcriptional pathways in development and in response to specific signaling pathways. We have previously demonstrated that the ability of both these factors to stimulate transcription is greatly enhanced by treatment of cardiac cells with the hypertrophic agent phenylephrine (PE). Here, we show that inhibition of either CBP or p300 with antisense or dominant negative mutant constructs inhibits PE-induced hypertrophy as assayed by atrial naturetic protein production, cardiac cell protein:DNA ratio and cell size. Furthermore, we show that overexpression of CBP or p300 can induce hypertrophy and that this effect requires their histone acetyltransferase (HAT) activity. Moreover, we show that PE can directly enhance CBP HAT activity and that artificial enhancement of HAT activity is sufficient to induce hypertrophy. Hence, CBP and p300 play an essential role in hypertrophy induced by PE, and this effect is mediated via PE-induced enhancement of their HAT activity. This is the first time a role for these factors, and their HAT activity, in hypertrophy has been directly demonstrated.

Insulin-like growth factor-II induces hypertrophy of adult cardiomyocytes via two alternative pathways

Insulin-like growth factor (IGF)-II is known to induce hypertrophy of isolated adult rat ventricular cardiomyocytes cultured in the absence of serum. However, it is not known how the growth factor exerts this hypertrophic effect. We show here that IGF-II induces hypertrophy of the cultured cardiomyocytes via two alternative pathways: (1) an IGF-I receptor-dependent pathway, or (2) a lysosome-dependent pathway when the IGF-I receptor-dependent pathway is blocked.

Calcineurin transgenic mice have mitochondrial dysfunction and elevated superoxide production

Introduction of the constitutively active calcineurin gene into neonatal rat cardiomyocytes by adenovirus resulted in decreased mitochondrial membrane potential (P < 0.05). Infection of H9c2 cells with calcineurin adenovirus resulted in increased superoxide production (P < 0.001). Transgenic mice with cardiac-specific expression of a constitutively active calcineurin cDNA (CalTG mice) exhibit a two- to threefold increase in heart size that progresses to heart failure. We prepared mitochondria enriched for the subsarcolemmal population from the hearts of CalTG mice and transgene negative littermates (control). Intact, well-coupled mitochondria prepared from one to two mouse hearts at a time yielded sufficient material for functional studies. Mitochondrial oxygen consumption was measured with a Clark-type oxygen electrode with substrates for mitochondrial complex II (succinate) and complex IV [tetramethylpentadecane (TMPD)/ascorbate]. CalTG mice exhibited a maximal rate of electron transfer in heart mitochondria that was reduced by approximately 50% (P < 0.002) without a loss of respiratory control. Mitochondrial respiration was unaffected in tropomodulin-overexpressing transgenic mice, another model of cardiomyopathy. Western blotting for mitochondrial electron transfer subunits from mitochondria of CalTG mice revealed a 20-30% reduction in subunit 3 of complex I (ND3) and subunits I and IV of cytochrome oxidase (CO-I, CO-IV) when normalized to total mitochondrial protein or to the adenine nucleotide transporter (ANT) and compared with littermate controls (P < 0.002). Impaired mitochondrial electron transport was associated with high levels of superoxide production in the CalTG mice. Taken together, these data indicate that calcineurin signaling affects mitochondrial energetics and superoxide production. The excessive production of superoxide may contribute to the development of cardiac failure.

Expression of smooth muscle MyHC B in blood vessels of hypertrophied heart in experimentally hypertensive rats

We demonstrated recently a significantly lower fraction of cardiac precapillary arterioles that expressed smooth muscle myosin heavy chain (MyHC) B (SMB) in spontaneously hypertensive rats. To clarify whether this reduction of SMB expression is of genetic origin, we investigated SMB expression in cardiac precapillary arterioles of normotensive and experimentally hypertensive rats (one clip, one kidney or ANG II minipump). We observed similar SMB expression patterns in precapillary arterioles of experimentally hypertensive rats compared with normotensive controls. These observations suggest that the downregulation of SMB in spontaneously hypertensive rats is of genetic origin rather than an adaptive response to chronically enhanced blood pressure and cardiac hypertrophy.

Down-regulation of acyl-CoA oxidase gene expression and increased NF-kappaB activity in etomoxir-induced cardiac hypertrophy

Activation of nuclear factor-kappaB (NF-kappaB) is required for hypertrophic growth of cardiomyocytes. Etomoxir is an irreversible inhibitor of carnitine palmitoyltransferase I (CPT-I) that activates peroxisome proliferator-activated receptor alpha (PPARalpha) and induces cardiac hypertrophy through an unknown mechanism. We studied the mRNA expression of genes involved in fatty acid oxidation in the heart of mice treated for 1 or 10 days with etomoxir (100 mg/kg/day). Etomoxir administration for 1 day significantly increased (4.4-fold induction) the mRNA expression of acyl-CoA oxidase (ACO), which catalyzes the rate-limiting step in peroxisomal beta-oxidation. In contrast, etomoxir treatment for 10 days dramatically decreased ACO mRNA levels by 96%. The reduction in ACO expression in the hearts of 10-day etomoxir-treated mice was accompanied by an increase in the mRNA expression of the antioxidant enzyme glutathione peroxidase and the cardiac marker of oxidative stress bax. Moreover, the activity of the redox-regulated transcription factor NF-kappaB was increased in heart after 10 days of etomoxir treatment. Overall, the findings here presented show that etomoxir treatment may induce cardiac hypertrophy via increased cellular oxidative stress and NF-kappaB activation.

Gene expression profiling of alpha(1b)-adrenergic receptor-induced cardiac hypertrophy by oligonucleotide arrays

OBJECTIVE

Cardiac hypertrophy is closely associated with the development of cardiomyopathies that lead to heart failure. The alpha(1B) adrenergic receptor (alpha(1)-AR) is an important regulator of the hypertrophic process. Cardiac hypertrophy induced by systemic overexpression of the alpha(1b)-AR in a mouse model does not progress to heart failure. We wanted to explore potential gene expression differences that characterize this type of hypertrophy that may identify genes that prevent progression to heart failure.

METHODS

Transgenic and normal mice (B6CBA) representing two time points were compared; one at 2-3 months of age before disease manifests and the other at 12 months when the hypertrophy is significant. Age-matched hearts were removed, cRNA prepared and biotinylated. Aliquots of the cRNA was subjected to hybridization with Affymetrix chips representing 12,656 murine genes. Gene expression profiles were compared with normal age-matched controls as the baseline and confirmed by Northern and Western analysis.

RESULTS

The non-EST genes could be grouped into five functional classifications: embryonic, proliferative, inflammatory, cardiac-related, and apoptotic. Growth response genes involved primarily Src-related receptors and signaling pathways. Transgenic hearts also had a 60% higher Src protein content. There was an inflammatory response that was verified by an increase in IgG and kappa-chained immunoglobulins by western analysis. Apoptosis may be regulated by cell cycle arrest through a p53-dependent mechanism. Cardiac gene expression was decreased for common hypertrophy-inducing proteins such as actin, collagen and GP130 pathways.

CONCLUSIONS

Our results suggest a profile of gene expression in a case of atypical cardiac hypertrophy that does not progress to heart failure. Since many of these altered gene expressions have not been linked to heart failure models, our findings may provide a novel insight into the particular role that the alpha(1B)AR plays in its overall progression or regression.

Coordinated down-regulation of KCNQ1 and KCNE1 expression contributes to reduction of I(Ks) in canine hypertrophied hearts

OBJECTIVE

In animal models of hypertrophy, electrical remodeling giving rise to QT prolongation occurs rapidly and is associated with the development of torsade de pointes (TdP) arrhythmias and sudden death. Chronic AV block (CAVB)-induced hypertrophy in dogs has been associated with a reduction in the slow component (I(Ks)) of the delayed rectifier potassium current (I(K)), which contributes to a prolongation of ventricular repolarization, the development of an acquired form of long QT, and the substrate for triggered activity and TdP. The present study was designed to probe the molecular basis for the decrease in I(Ks) by studying the characteristics of KCNE1 and KCNQ1, the putative genes responsible for formation of the channel.

METHODS AND RESULTS

Using a combination of Northern blot, competitive multiplex PCR and immunoblot assays, we found that CAVB reduces KCNE1 and KCNQ1 RNA in the canine ventricles by 70 and 80%, respectively. Protein levels of KCNE1 and KCNQ1 were reduced by 60 and 50%, respectively. We also demonstrate at the molecular level the basis for inter-ventricular difference in I(Ks) density previously reported in hearts of normal dogs and show the basis for reduction of this difference in the CAVB dog.

CONCLUSIONS

Our results indicate that the CAVB-induced reduction in I(Ks) is due to a down-regulation of KCNE1 and KCNQ1 transcription. The data suggest that electrical remodeling of the cardiac ventricle during hypertrophy involves regulation of the gene expression through modulation of transcriptional and translational regulatory pathways. The reduction in KCNE1 and KCNQ1 expression increases the dependence of ventricular repolarization on the rapid component of I(K) and may potentiate the action of Class III antiarrhythmic agents.

Intracellular Na+ and altered Na+ transport mechanisms in cardiac hypertrophy and failure

Altered intracellular Na(+) ([Na(+)](i)) is a potentially important factor in the functional adaptation of the hypertrophied and failing heart. We review the currently reported changes in [Na(+)](i) and Na(+) transport in different models of cardiac hypertrophy and heart failure. Direct measurements are limited, but most of these indicate that there is a rise in [Na(+)](i), in particular in hypertrophy. In addition to these direct measurements, several studies report a rise in Na(+) influx or an upregulation of Na(+) influx transporters. The most extensive literature on Na(+) regulating pathways concerns the Na/K-ATPase. Total Na/K-ATPase activity decreases in most models of cardiac hypertrophy and failure, though few measurements were actually performed in intact cells. This decrease can been related to a selective reduction of high-affinity (for cardiac glycosides) Na/K pump alpha-isoforms, across many species and models, including human heart failure. We have used these data to predict changes of [Na(+)](i) in a simulation model, varying the contribution of total Na/K pump capacity and expression of isoforms with different Na(+)(i) affinities, and varying Na(+) influx. A rise in Na(+) in cardiac hypertrophy and failure may improve systolic contractile function, though at the cost of worsening of diastolic function and increased risk of ventricular arrhythmias. The benefit of further increasing [Na(+)](i,) e.g. with cardiac glycosides, is thus compromised. Future therapies may include selective isoform blockers, which could raise [Na(+)](i) in restricted subcellular compartments, drug associations that reduce the arrhythmic risk, or even drugs that lower [Na(+)](i) and thus interfere with the remodelling pathways.

A novel pleiotropic effect of statins: prevention of cardiac hypertrophy by cholesterol-independent mechanisms

Cardiac hypertrophy is an initial physiological adaptive response by the heart to pressure overload. However, if pressure overload persists, frequently, the heart decompensates and develops 'pathophysiological' hypertrophy. This leads to increased mortality and morbidity and is an independent risk factor for heart failure. Because cardiac myocytes convert this pressure overload into intracellular biochemical signals, blocking this critical signaling pathway may be an important therapeutic target to prevent cardiac hypertrophy. Small GTP-binding proteins, in particular Rac1, have been suggested to play a key role in the development of cardiac hypertrophy. Recently, 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, also called statins, have been shown to inhibit cardiac hypertrophy independent of their cholesterol lowering property. Statins block the isoprenylation and activation of members of the Rho family, such as RhoA and Rac1. Rac1 also regulates NADPH oxidase, which is a major source of reactive oxygen species (ROS) in cardiovascular cells. Growing evidence suggests that ROS may be involved in the process of cardiac hypertrophy and recent research has shown that statins attenuate oxidative stress through inhibition of Rac1. Overall, these pleiotropic effects of statins will give new insights into the process of cardiac hypertrophy.

Time course of right ventricular remodeling in rats with experimental myocardial infarction

Right ventricular (RV) weight increases dependent on time after myocardial infarction (MI) and on MI size. The sequential changes in RV volume and hemodynamics and their relations to left ventricular (LV) remodeling after MI are unknown. We therefore examined the time course of RV remodeling in rats with LV MI. MI was produced by left coronary artery ligation. Four, eight, and sixteen weeks later, LV and RV hemodynamic measurements were performed and pressure-volume curves were obtained. For serial measurement of RV volumes and performance, cine-MRI was performed 2 and 8 wk after MI. The ratios of beta-myosin heavy chain (MHC) to alpha-MHC and skeletal to cardiac alpha-actin were determined for the RV and LV after large MI or sham operation. RV weight increased in rats with MI, as did RV volume. RV pressure-volume curves were shifted toward larger volumes 16 wk after large MI. RV systolic pressure increased gradually over time; however, the gain in RV weight was always in excess of RV systolic pressure. The ratios of skeletal to cardiac alpha-actin and beta-MHC to alpha-MHC were increased after MI in both ventricles in a similar fashion. Because RV wall stress was not increased after infarction, mechanical factors may not conclusively explain hypertrophy, which maintained balanced loading conditions for the RV even after large LV infarction.

Biological activities of fibroblast growth factor-2 in the adult myocardium

Fibroblast growth factor-2 (FGF-2) is a potent regulator of many cellular functions and phenomena, including cell proliferation, differentiation, survival, adhesion, migration, motility and apoptosis, and processes such as limb formation, wound healing, tumorigenesis, angiogenesis, vasculogenesis and blood vessel remodeling. In the adult myocardium, FGF-2 is expressed by various cell types, including cardiomyocytes, fibroblasts and smooth muscle cells. The biological effects of FGF-2 in the myocardium are mediated by the high-affinity tyrosine kinase receptor FGFR-1, the major FGF receptor in the heart. Here, we give an overview of current insights into the multiple roles of FGF-2 in the myocardium, as they pertain to two basic phenomena: ischemia-reperfusion injury and cardiac hypertrophy. The first category includes roles for FGF-2 in cardioprotection, the inflammatory response, angiogenesis and vascular remodeling, while the second includes myocyte hypertrophy, fibrosis, and gap junction functioning (conduction). Given the strong evidence for FGF-2 as both a cardioprotective and angiogenic agent, the therapeutic potential of FGF-2 in the ischemic myocardium is discussed.

Cardiac Hypertrophy by Hypertension and Exercise Training Exhibits Different Gene Expression of Enzymes in Energy Metabolism

Hypertension-induced pathological cardiac hypertrophy (hypertensive heart) and exercise training-induced physiological cardiac hypertrophy (athletic heart) have differences in cardiac properties. We hypothesized that gene expression of energy metabolic enzymes differs between these two types of cardiac hypertrophy. To investigate whether mRNA expression of key enzymes in the long-chain fatty acid (FA), glucose, and lactic acid metabolic pathways differs between these two types of cardiac hypertrophy, we used the hearts of spontaneously hypertensive rats (SHR; 19 weeks old) as a model of the hypertensive heart, swim-trained rats (Trained; 19 weeks old, swimming training for 15 weeks) as a model of the athletic heart, and sedentary Wistar-Kyoto rats (Control; 19 weeks old). SHR developed hypertensive cardiac hypertrophy, of which cardiac function was deteriorated, whereas Trained rats developed an athletic heart, of which cardiac function was enhanced. The mRNA expression of CD36, which involved in uptake of long-chain FA, in the heart was almost never detected in the SHR group. Furthermore, the mRNA expression of key enzymes in the long-chain FA metabolic pathway (acyl CoA synthase [ACoAS], carnitine palmitoyl transferase [CPT]-I, CPT-II, and isocitrate dehydrogenase [ISCD]) in the heart was significantly higher in the SHR group compared with the Control group. The mRNA expression of ACoAS, CPT-I, ISCD, and CD36 in the heart did not differ between Trained group and Control group, whereas that of CPT-II in the Trained group was significantly higher compared with the Control group. The mRNA expression of key enzymes (phosphofructokinase and lactate dehydrogenase) in glycolytic metabolic pathway in the heart was markedly higher in the SHR group compared with the Control group, whereas these mRNA expressions did not differ between Trained group and Control group. These findings suggest that the molecular phenotypes in the energy metabolic system differ in hypertension-induced pathological and exercise training-induced physiological cardiac hypertrophy, and these differences may participate in the differences in cardiac function.

Changes in distinct species of 1,2-diacylglycerol in cardiac hypertrophy due to energy metabolic disorder

OBJECTIVE

The juvenile visceral steatosis (JVS) mouse, a genetic model of systemic carnitine deficiency resulting from carnitine transport mutation, develops cardiac hypertrophy. We determined two putative lipid messengers, 1,2-diacylglycerol (DAG) and ceramide, in JVS and carnitine palmitoyltransferase-I (CPT-I) inhibitor etomoxir-treated mice because these lipids function as co-messengers in the myocardium via modification of protein kinase C activity.

METHODS

JVS mice were evaluated at 4 and 8 weeks of age. The effect of long-term etomoxir treatment (45 mg/day) (ET) on mice was investigated in control mice from 4 to 8 weeks of age. As a model of inhibited cardiac hypertrophy, carnitine-treated JVS (CT) mice were produced. Myocardial DAG and ceramide levels and their fatty acid composition were measured.

RESULTS

The heart/body weight ratio increased by 100% in JVS mice compared with that in controls, while that of CT mice was normalized in comparison with controls at 8 weeks of age. DAG markedly increased in both JVS and ET mice compared with that in controls (1,677+/-84, 1,258+/-49, and 585+/-58 ng/dry wt, respectively; P<0.01 for controls versus JVS or ET mice), whereas it was decreased significantly in CT mice compared with that in JVS mice (1,066+/-54 ng/dry wt, P<0.01). Furthermore, the fatty acid composition of DAG was similar in JVS and ET mice; in particular, 18:1 and 18:2 were significantly elevated in the myocardium (P<0.01 versus controls). On the other hand, that of DAG in CT mice was similar to that of the control group. In contrast, no difference was observed in myocardial ceramide levels among the groups.

CONCLUSIONS

Pharmacological intervention with etomoxir mimics changes in the lipid second messenger characteristic of genetic JVS mice. The results suggest that the increases in distinct DAG species might be involved in the pathogenesis of cardiac hypertrophy as a result of disorder of fatty acid transport.

Effects of temocapril and olmesartan on myocardial sympathetic nervous activity and fatty acid metabolism in rats with chronic beta-adrenergic stimulation

We investigated the effects of an angiotensin-converting enzyme inhibitor (temocapril) and an angiotensin II type 1 receptor blocker (olmesartan) on changes in myocardial sympathetic nervous activity, fatty acid metabolism and myocardial blood flow using 131I-meta-iodobenzylguanidine, 125I-beta-methyl-iodophenyl pentadecanoic acid and 99mTc-tetrofosmin, respectively, in rats with isoproterenol-induced cardiac hypertrophy. Male Sprague-Dawley rats underwent isoproterenol administration (3 mg/kg per day) for 1 week by osmotic mini-pump. The hearts were excised and analyzed for the uptake of meta-iodobenzylguanidine. Beta-methyl-iodophenyl pentadecanoic acid and tetrofosmin in 11 segments in four groups; sham group (saline), isoproterenol group (isoproterenol alone), angiotensin-converting enzyme inhibitor group (isoproterenol and temocapril), and angiotensin II type 1 receptor blocker group (isoproterenol and olmesartan). Isoproterenol significantly increased the heart weight compared with the sham group, whereas it was significantly blunted in the angiotensin-converting enzyme inhibitor and angiotensin II type 1 receptor blocker groups. The ratio of the percent kilogram dose per gram of meta-iodobenzylguanidine to tetrofosmin, an index of myocardial sympathetic nervous activity, was significantly decreased in the isoproterenol group (0.18 +/- 0.01) compared with the sham group (0.41 +/- 0.03). Importantly, these changes were significantly improved in the angiotensin-converting enzyme inhibitor (0.28 +/- 0.01) and the angiotensin II type 1 receptor blocker groups (0.32 +/- 0.01). The ratio of the percent kilogram dose per gram of beta-methyl-iodophenyl pentadecanoic acid to tetrofosmin, an index of myocardial fatty acid metabolism, was significantly decreased in the isoproterenol group (1.30 +/- 0.03) compared with the sham group (1.60 +/- 0.10). In contrast, there were no significant differences in beta-methyl-iodophenyl pentadecanoic acid to tetrofosmin ratios between the sham and angiotensin-converting enzyme inhibitor groups, or the angiotensin II type 1 receptor blocker group. Cardiac hypertrophy induced by chronic beta-adrenergic stimulation is accompanied by impairment of sympathetic nervous activity and fatty acid metabolism. These abnormalities are effectively prevented by the angiotensin-converting enzyme inhibitor and the angiotensin II type 1 receptor blocker.

[Increased generation of hydroxyl radicals in the rat hypertrophied myocardium: in vivo study by microdialysis]

A comparative study of the generation of hydroxyl radicals (OH*) in the hypertrophic myocardium of SHR-SP rats (n = 8) and in the myocardium of WKY (n = 5) and Wistar (n = 12) rats was performed using the microdialysis technique. The experiments were carried out on anesthetized open-chest male rats (ketamine intraperitoneally, 10 mg/kg) with artificial ventilation. The amount of OH* produced was estimated by high-performance liquid chromatography with electrochemical detection using as a marker 2,3-dihydroxybenzoic acid (2,3-DHBA), a product of the reaction of the hydroxyl radical with salicylic acid added to the perfusate. The quantity of 2,3-DHBA in the dialysate was estimated by the external standard method and expressed in percent of the 2,3-DHBA concentration in the perfusion fluid. The mean baseline value of 2,3-DHBA in dialysate samples in SHR-SP rats (157 +/- 22%, n = 8) was significantly higher than in Wistar (90 +/- 15%, n = 12, p = 0.0001) and Wistar-Kyoto rats (106 +/- 12%, n = 5, p = 0.005). The basal 2,3-DHBA level in SHR-SP rats was positively correlated (r = 0.831, n = 7, p < 0.05) with the degree of hypertrophy of the left ventricle expressed as the ratio of the left ventricle weight to the body weight. The data presented demonstrate that the hypertrophy of the left ventricle in SHR-SP rats is accompanied by the elevation of the level of free oxygen radicals.

Cardiac energetics correlates to myocardial hypertrophy in Friedreich's ataxia

Friedreich's ataxia is a neurodegenerative disease frequently associated with hypertrophic cardiomyopathy. We have determined mitochondrial ATP, phosphocreatine, and intracellular inorganic phosphate levels by 31P nuclear magnetic resonance spectroscopy in the heart of 11 Friedreich's ataxia patients and 11 healthy controls. For the first time, to our knowledge, we showed a significant correlation between the extent of myocardial energy deficiency and the degree of myocardial hypertrophy. When combining our results with previous works on Friedreich's ataxia, these novel findings suggest that energy metabolism is most likely the cause and hypertrophy the effect in Friedreich's ataxia.

Hypertrophic phenotype of cardiac calcium/calmodulin-dependent protein kinase II is reversed by angiotensin converting enzyme inhibition

Calcium-dependent mechanisms and the renin angiotensin system (RAS) are critically involved in the hypertrophic growth of the myocardium. The calcium/calmodulin-dependent protein kinase II (CaMKII) is a ubiquitous mediator in calcium signaling and modulates calcium handling and growth mechanisms in cardiomyocytes. Here we present data on expression of cardiac isoforms of CaMKIIdelta, the dominant form in the myocardium, in compensatory hypertrophy of stroke-prone spontaneously hypertensive rats (SHRSP) compared to the normotensive Wistar-Kyoto (WKY) control strain. Cardiac hypertrophy in SHRSP was documented by an increased heart weight/body weight ratio (HW/BW) of 31% (p < 0.05) and a more than six-fold elevated atrial natriuretic factor (ANF) transcript level (p < 0.05). Compensatory hypertrophic growth in SHRSP produced a specific phenotype of CaMKIIdelta isoforms characterized by increased transcript levels of the embryonic/neonatal isoform delta4 (48%, p < 0.05) and the isoform delta9 (31%, p < 0.05) with no changes in delta2 and delta3. Inhibition of angiotensin converting enzyme (ACE) by cilazapril completely regressed myocardial hypertrophy, normalized ANF transcript levels, and restored the normal phenotype of CaMKIIdelta by reducing transcripts for delta4 and delta9 to levels present in WKY controls. Our data suggest the importance of specific changes in the CaMKII isoform composition for growth processes in the myocardium.

Increased Ca2+-sensitivity of myofibrillar tension in heart failure and its functional implication

In human failing myocardium, an increased Ca2+-sensitivity of myofilament tension development has been described in Triton X skinned cardiac myocytes compared to cardiomyocytes obtained from non-failing human donor hearts. The present study aimed to investigate whether there are functional implications of the increased Ca2+-sensitivity in heart failure and whether alterations of myofilament function are already obvious at earlier stages of heart failure, such as in cardiac hypertrophy or whether alterations of the intracellular Ca2+-homeostasis are able to induce alterations in myofilament function. Ca2+-activated tension development was measured in Triton X-skinned fibers from human failing and non-failing myocardium. Ca2+-sensitivity of myofilament tension development was significantly shifted to the left in human failing myocardium. Plots of diastolic free Ca2+ versus diastolic tension development showed that in a range of similar diastolic Ca2+-concentrations, diastolic tension was significantly enhanced in the failing hearts. The Ca2+/tension relationship was shifted to the right in Triton X-skinned fiber preparations from transgenic renin overexpressing rats (TG(mREN2)27), shown to have concentric hypertrophy. In addition, the Ca2+/tension relationship was unchanged in phospholamban knock-out mice with an increased systolic Ca2+ (and enhanced diastolic Ca2+-load). It is concluded that the increased Ca2+-sensitivity of myofilament tension observed in single cardiomyocytes from failing human myocardium may be a phenomenon also present in multicellular preparations and may contribute to the diastolic dysfunction observed in human heart failure. Alterations of myofilament function occur at very early stages of heart failure and may be species dependent, or dependent on intracellular free Ca2+-levels.

Effects of tanshinone VI on the hypertrophy of cardiac myocytes and fibrosis of cardiac fibroblasts of neonatal rats

The possible effects of tanshinone VI (tsh), a diterpene from the root of Tan-Shen (Salvia miltiorrhiza, Bunge (Labiatae)) on hypertrophy and fibrosis in cultured neonatal rat cardiac myocytes and fibroblasts were examined. Tsh had no significant effect on protein synthesis, which was evaluated by [3H]-leucine incorporation into the acid insoluble fraction in the cells, in the absence of stimulatory factors in cardiac myocytes. The amount of protein produced in cardiac myocytes was increased by 10(-8) M endothelin-1 (ET-1), 10(-6) M phenylephrine (PE), or 10(-8) M insulin-like growth factor-1 (IGF-1), suggesting that hypertrophy of cardiac myocytes in vitro was induced by these factors. The ET-1-, PE-, or IGF-1-induced increase in protein synthesis was attenuated by treatment with 10(-5) M tsh. Treatment with 10(-5) M tsh significantly decreased the synthesis of collagen by cardiac fibroblasts, which was evaluated by [3H]-proline incorpolation into acid-insoluble fraction of the fiblobrasts, in the absence of stimulatory factors for the production. Fetal bovine serum (FBS) or IGF-1 increased collagen synthesis in a concentration-dependent manner. The increase at 5% FBS or 10(-8) M IGF-1 was inhibited by 10(-5) M tsh. Fibroblast-conditioned medium (FB-CM) increased protein synthesis in cardiac myocytes in a concentration-dependent manner (10; - 100 %). Tsh attenuated the FB-CM-induced increase in protein synthesis by cardiac myocytes. These results show that tsh may attenuate the humoral factor-induced hypertrophy of cardiac myocytes and fibrosis of cardiac fibroblasts. The findings suggest that tsh may improve the development of cardiac remodeling under pathophysiological conditions. Abbreviations. ANP:atrial natriuretic peptide DMEM:Dulbecco-modified Eagle's medium ET-1:endothelin-1 FB-CM:fibroblast-conditioned medium FBS:fetal bovine serum IGF-1:insulin-like growth factor-1 PE:phenylephrine tsh:tanshinone VI