PROTEIN METABOLISM IN CARDIAC HYPERTROPHY AND HEART FAILURE

Lipid in the midst of metabolic remodeling - Therapeutic implications for the failing heart

A healthy heart relies on an intact cardiac lipid metabolism. Fatty acids represent the major source for ATP production in the heart. Not less importantly, lipids are directly involved in critical processes such as cell growth, proliferation, and cell death by functioning as building blocks or signaling molecules. In the development of heart failure, perturbations in fatty acid utilization impair cardiac energetics. Furthermore, they may affect glucose and amino acid metabolism and induce the synthesis of several lipid intermediates, whose biological functions are still poorly understood. This work outlines the pivotal role of lipid metabolism in the heart and provides a lipocentric view of metabolic remodeling in heart failure. We will also critically revisit therapeutic attempts targeting cardiac lipid metabolism in heart failure and propose specific strategies for future investigations in this regard.

Genome-wide translational reprogramming of genes important for myocyte functions in overload-induced heart failure

Genome-wide changes in gene translational efficiency during the development of heart failure are poorly understood. We tested the hypothesis that aberrant changes in translational efficiency of cardiac genes are associated with the development of myocyte decompensation in response to persistent stress stimuli. We demonstrated that chronic pressure overload in mice resulted in a genome-wide reprogramming of translational efficiency, with >50% of the translatome exhibiting decreased translational efficiencies during the transition from myocardial compensation to decompensation. Importantly, these translationally repressed genes included those involved in angiogenesis and energy metabolism. Moreover, we showed that the stress-induced translational reprogramming was accompanied by persistent activation of the eukaryotic initiation factor 2α (eIF2α)-mediated stress response pathway. Counteracting the endogenous eIF2α functions by cardiac-specific overexpression of an eIF2α-S51A mutant ameliorated the development of myocyte decompensation, with concomitant improvements in translation of cardiac functional genes and increases in angiogenic responses. These data suggest that the mismatch between transcription and translation of the cardiac genes with essential functions may represent a novel molecular mechanism underlying the development of myocyte decompensation in response to chronic stress stimuli, and the eIF2α pathway may be a viable therapeutic target for recovering the optimal translation of the repressed cardiac genes.

Metabolomic analysis of pressure-overloaded and infarcted mouse hearts

BACKGROUND

Cardiac hypertrophy and heart failure are associated with metabolic dysregulation and a state of chronic energy deficiency. Although several disparate changes in individual metabolic pathways have been described, there has been no global assessment of metabolomic changes in hypertrophic and failing hearts in vivo. Hence, we investigated the impact of pressure overload and infarction on myocardial metabolism.

METHODS AND RESULTS

Male C57BL/6J mice were subjected to transverse aortic constriction or permanent coronary occlusion (myocardial infarction [MI]). A combination of LC/MS/MS and GC/MS techniques was used to measure 288 metabolites in these hearts. Both transverse aortic constriction and MI were associated with profound changes in myocardial metabolism affecting up to 40% of all metabolites measured. Prominent changes in branched-chain amino acids were observed after 1 week of transverse aortic constriction and 5 days after MI. Changes in branched-chain amino acids after MI were associated with myocardial insulin resistance. Longer duration of transverse aortic constriction and MI led to a decrease in purines, acylcarnitines, fatty acids, and several lysolipid and sphingolipid species but a marked increase in pyrimidines as well as ascorbate, heme, and other indices of oxidative stress. Cardiac remodeling and contractile dysfunction in hypertrophied hearts were associated with large increases in myocardial, but not plasma, levels of the polyamines putrescine and spermidine as well as the collagen breakdown product prolylhydroxyproline.

CONCLUSIONS

These findings reveal extensive metabolic remodeling common to both hypertrophic and failing hearts that are indicative of extracellular matrix remodeling, insulin resistance and perturbations in amino acid, and lipid and nucleotide metabolism.

Suppression of protein degradation in progressive cardiac hypertrophy of chronic aortic regurgitation

BACKGROUND

The heart adapts to the volume overload of aortic regurgitation with dilation and hypertrophy. The development of left ventricular hypertrophy at the protein level is a dynamic process resulting from an imbalance between cardiac protein synthesis and degradation. The objective of the present study was to determine in vivo the relative contributions of cardiac protein synthesis and degradation to the progressive hypertrophy that occurs in response to chronic aortic regurgitation and to compare these with responses earlier in the course of this stress.

METHODS AND RESULTS

Continuous intravenous infusions of [3H]-leucine were administered 3 days and 1 month after surgical induction of aortic regurgitation and sham operation in rabbits. Total cardiac protein and myosin heavy chain fractional synthesis rates were obtained by analysis of plasma and protein hydrolysate data using [14C]-dansyl chloride assays. Left ventricular growth rates were determined from serial echocardiographic and postmortem left ventricular weight and protein concentration measurements; protein degradation rates were determined by subtraction of growth rates from synthesis rates.

CONCLUSIONS

In comparison with sham-operated control rabbits, protein fractional synthesis rates were increased at 3 days but not at 1 month after induction of aortic regurgitation Progressive cardiac hypertrophy occurring at 1 month was caused by a decrease in protein fractional degradation rates. An increase in protein synthesis contributes only to the early phase of hypertrophy caused by acute aortic regurgitation, whereas progressive eccentric hypertrophy in chronic volume overload is due to suppression of protein degradation.

Endocardium of the left ventricle in volume-loaded canine heart. A histological and ultrastructural study

To investigate the effects of volume loading of the heart, the endocardium was studied histologically and ultrastructurally. Thirteen adult female beagle dogs were used. An arterio-venous shunt was constructed between the right common carotid artery and the right external jugular vein in nine animals to induce a volume load. Four animals were used as controls. All were kept for 6-12 months. Heart weight, relative heart weight (heart weight/body weight), cardiac output index, stroke volume index and volumes of both ventricles in the experimental animals were significantly larger than in the controls. Shunted blood volume was significantly correlated with heart weight. The endocardium of the left ventricle in the experimental animals showed elastofibrosis and was significantly thicker than in the controls. In 5 hearts, it was more than 20 microns thick and its endothelial cells showed many long microvilli with a very thick basement membrane (1.5-2.0 microns). The thickness of the endocardium was significantly correlated with the heart weight, relative heart weight and cardiac output index, within 1%, 5% and 5% risk, respectively. These endocardial changes were thought to be induced by hemodynamic changes in the left ventricle of the volume-loaded heart, probably being correlated with changes in cardiac function and morphology.

Development and regression of right heart ventricular hypertrophy: biochemical and morphological aspects

Male Wistar rats were exposed, in a hypobaric chamber, to a simulated altitude of 6000 m for up to four weeks. The animals quickly developed pulmonary hypertension with an important media hypertrophy of the pulmonary arteries, followed by severe right heart hypertrophy (cor pulmonale). Right heart hypertrophy is evident in three morphologically and biochemically definable stages. In stage 1 (1st-2nd week) a manifest thickening of heart muscle cells develops due to increased protein synthesis. In stage 2 (2nd-3rd week) one can find, in the regular biochemical composition of heart muscle, an activation of mitochondrial ATPase, a multiplication of mitochondria, a proliferation of interstitial cells and an increase in interstitial volume. In stage 3 (3rd-4th week) the hypertrophied myocardium exhibits signs of biochemical and morphological decompensation. Besides a loss of myofibrils and a reduction in mitochondrial ATPase, DNA and protein concentrations sink to subnormal values. Only myocardium from stage 1 of hypertrophy shows complete reversibility after cessation of hypobaric conditions, but not so in stage 3. Parallel with the developing cor pulmonale, the animals also react with a small hypertrophy of the left heart ventricle. This concomitant growth persists under normobaric conditions, too. These investigations document that growth of myocardium under extreme conditions shows a phasic development. Severe forms of myocardial hypertrophy do not always seem to be reversible.

Anthracycline induced myocardial damage. An analysis of 16 autopsy cases

The hearts of 16 autopsy cases with a past history of administration of anthracycline antitumor drugs (DNR, ADR and ACM) and a sign of cardiac failure were investigated morphologically. In macroscopic observation, both ventricles were more or less dilated with thinning of the ventricular wall. Mural thrombi were recognized in the left ventricle of 2 cases. Histologically, the myocardial lesions could be roughly classified into two groups, a) myocardial changes in cases with rapidly developed cardiac failure (acute form), and b) myocardial changes in cases with relatively slowly developed cardiac failure. In acute form, myocardial cells showed marked swelling with dilatation of central sarcoplasmic core, marked reduction of myofibrils, vacuolization of cytoplasm and enlargement of nucleus accompanied by distinct large nucleolus. Necrotic myocardial cells were scattered among these degenerative cells. These degenerative and necrotic cells were distributed diffusely in both ventricular walls, but were more frequent in the left ventricular wall than in the right one. Inflammatory cell infiltration was also recognized not only in the myocardium, but also in the endocardium and epicardium. In chronic form, on the other hand, atrophy and attenuation of myocardial cells with a hypereosinophilic change of the cytoplasm and an increase in number of brown pigments, and marked reduction of myocardial cells were most common findings. These changes of chronic form, however, could not be identified as the specific changes of anthracycline cardiotoxicity. Fibrosis was hardly seen in the myocardium of both acute and chronic forms.

Aortic pressure as a determinant of cardiac protein degradation

Mechanical parameters and intracellular mediators that may control protein degradation were studied in isolated rat hearts subjected to increased aortic pressure. Elevation of aortic pressure from 60 to 120 mmHg in Langendorff preparations provided glucose or pyruvate as substrate decreased the rate of protein degradation during the second hour of perfusion. Intracellular contents of ATP or creatine phosphate or the creatine phosphate/creatine ratio did not indicate that energy depletion accounted for these effects. When ventricular pressure development was prevented by ventricular draining, and hearts were arrested with tetrodotoxin, protein degradation still decreased as aortic pressure was raised. The effect of elevated aortic pressure on proteolysis was unchanged when perfusate calcium concentrations were 0.6, 3.0, or 5.1 mM, or when indomethacin or meclofenamate was added to the perfusion buffer. These results provided no evidence to indicate that intraventricular pressure development or cardiac contraction was responsible for the inhibitory effect of increased aortic pressure on protein degradation. Instead, they suggested that stretch of the ventricular wall, as a consequence of increased aortic pressure, could be the mechanical parameter most closely related to the restraint on proteolysis. No evidence was obtained that the lower rate of degradation depended on energy or calcium availability or prostaglandin synthesis.

Metabolic aspects of the development of experimental cardiac hypertrophy

In three models of cardiac hypertrophy the significance of catecholamines and the adenylate cyclase-cyclic AMP-system was examined. Two approaches were utilized: 1. The time course of cyclic AMP alterations was correlated with the changes in adenine nucleotide and protein biosynthesis. 2. The effect of beta-receptor blockade on the obligatory increase in adenine nucleotide and protein synthesis was evaluated. In isoproterenol-elicited cardiac hypertrophy, the elevation of the cyclic AMP content was one of the earliest metabolic alterations preceding the enhancement of the biosynthesis of adenine nucleotides and proteins. beta-Receptor blockade with propranolol abolished the increase in adenine nucleotide synthesis. In pressure-induced cardiac hypertrophy due to constriction of the abdominal aorta, catecholamines and the adenylate cyclase-cyclic AMP-system were found not to play a significant role. In triiodothyronine-elicited hypertrophy, the cyclic AMP level was increased very early, but beta-receptor blockade did not prevent hypertrophy nor the enhancement of cardiac adenine nucleotide biosynthesis, although the positive chronotropic and inotropic effects of triiodothyronine were abolished. This result can best be interpreted to indicate a direct effect of triiodothyronine on myocardial carbohydrate metabolism including the pentose phosphate pathway.

Intracellular turnover and cardiac hypertrophy

Ultrastructural evidence is presented that intracellular autophagic degradation of cytoplasmic constituents is reduced during pressure induced hypertrophy of left ventricular myocardium after supravalvular aortic constriction in rats. This anti-catabolic reaction has to be considered as an important mechanism for shifting the balance between synthesis and degradation to the positive side. Short term studies after administration of isoproterenol suggest a close functional relationship between work load on the one hand and the anti-catabolic reaction on the other.

Cardiac hypertrophy in rats after supravalvular aortic constriction. II. Inhibition of cellular autophagy in hypertrophying cardiomyocytes

Adult male Sprague-Dawley rats were killed by retrograde perfusion fixation 3, 7, 14, 21 and 35 days after supravalvular aortic constriction (n = 33) or sham-operation (n = 25). Subepicardial specimens of the left ventricular myocardium were evaluated by conventional electron microscopic morphometry, and in addition were examined for the occurrence of autophagic vacuoles (AVs) using large test areas (3.9 X 10(4) micron 2 per animal). The quotient of mitochondrial to myofibrillar volume fraction was largely unchanged during hypertrophy but was reduced by 25% compared with controls after termination of growth at 35 days. During the process of hypertrophy which eventually led to an increase in average single cell volume of the cardiomyocytes by 78%, the volume fraction and the numerical density of AVs was significantly lower than in sham-operated rats. The most striking difference was observed 7 days after the operations, the stage at which the growth rate of the cardiomyocytes relative to controls was at its maximum of 4.5% per day. At this point the volume fraction as well as the numerical density of AVs were reduced by about 50% compared with controls. At 14 and 21 days after operation, when the relative growth rate of the hypertrophying cardiomyocytes was still 2% and 1% per day, the AV volume fraction was reduced to a lesser extent (by 47% and 28%, respectively). After termination of adaptive growth at 35 days significant differences in fractional volume and numerical density of AVs were no longer detectable. These results suggest that degradation of cytoplasmic components is inhibited in cardiomyocytes undergoing hypertrophy. Such an anticatabolic reaction seems to play an important role in establishing the positive balance of cellular metabolism generally required for growth processes.

Relative synthesis of cardiac contractile proteins. Evidence for synthesis from the same precursor pool

The relative molar synthesis of cardiac contractile proteins has been measured in the perfused heart under control haemodynamic conditions. This synthesis, of myosin heavy chains, individual light chains (1 and 2), actin and tropomyosin, was determined from isolated guinea-pig hearts perfused for 3h simultaneously with constant specific radioactivities and concentrations of [3H]lysine and [3H]phenylalanine. The data strongly suggest that all of the proteins studied were synthesized from the same precursor pools of lysine and phenylalanine, since the ratio of the specific activities of the two labels was the same in all of the proteins. Measurement of molar synthesis of each contractile protein was the same with either labelled amino acid. Under control haemodynamic-perfusion conditions, the relative molar synthesis of the contractile proteins was actin greater than heavy chains greater than light chain 2 greater than light chain 1 greater than tropomyosin.

Development of cardiac hypertrophy in rats exposed to acute hypobaric hypoxia. - Studies with protein synthesis inhibitors

The study is based on the experimental model of myocardial hypertrophy in rats. Male Sprague-Dawley adult rats were exposed to acute hypoxia in a hypobaric chamber (0.40 atmospheres of air for 24 hours). Myocardial hypertrophy was detected by wet and dry heart weight values when calculated on the basis of total body weight; i.e., ratio heart weight in mg to body weight in 100 g. The behaviour of myocardial hypertrophy was assessed after treatment of intact animals with Puromycin (10 mg/rat i.p.) or Actinomycin-D (100 micrograms/rat i.p.). The experimental results showed the following dry heart weight values (mean +/- SEM): room pressure 60.5 +/- 1.5; hypoxia 69.2 +/- 0.9; Actinomycin-D + hypoxia 63.5 +/- 0.6; Puromycin + hypoxia 62.4 +/- 1.5, (P less than 0.001). From the comparison of data reveals that inhibitors of protein synthesis completely inhibit the myocardial hypertrophy due to hypoxia. Thus it is documented that acute hypobaric hypoxia is able to induce in the rat an actual myocardial hypertrophy condition as expressed of the enhanced protein synthesis.

Dietary protein intake and 3-methylhistidine excretion in the rat

1. Rats were fed for 14 d on diets containing 50, 150 or 250 g/kg casein as the protein source. The daily excretion of Nt-methylhistidine (His(tau Me)), a non-re-utilized amino acid, was determined. 2. His(tau Me) excretion/100 g body-weight appeared to be unaffected by increasing the concentration of dietary protein from 150 to 250 g/kg. Assuming no change in the proportion of muscle in the animals these results are indicative of no change in myofibrillar protein catabolic rate. The excretion rate/100 g body-weight of the animal given 50 g/kg casein was lower than the other two treatments, especially towards the end of the 14 d treatment period. Thus at this time the myofibrillar protein catabolic rate was lower than in the animals fed on the higher protein diet. 3. In the animals fed on the high protein diet there was a tendency for this (tau Me) excretion rate/100 g body-weight to increase with age. 4. Nitrogen balance and creatinine excretion results are also presented.

Regulation of protein synthesis and degradation during in vitro cardiac work

Cardiac work increased protein synthesis in hearts supplied glucose (mixture 1), glucose-insulin-glucagon-lactate-beta-hydroxybutyrate (mixture 2) or palmitate-beta-hydroxybutyrate-glucose (mixture 3). In hearts provided mixture 1, acceleration of synthesis involved increased rates of peptide chain initiation. In these hearts intracellular concentrations of 5 amino acids decreased and 13 others were unchanged, indicating that faster protein synthesis did not depend on increased amino acid availability. In hearts supplied mixtures 2, 3, or 4 (lactate-glucose-insulin), intracellular concentrations of branched-chain amino acids were decreased by work, whereas intracellular levels of some acidic and neutral amino acids increased. Protein degradation was decreased by work in hearts supplied mixtures 1 and 2, but not mixtures 3 and 4. In hearts provided mixture 1, nitrogen balance was negative, but less so in working preparations. Nitrogen balance was zero or positive in working hearts provided mixtures 2 and 4. These studies indicated that in hearts supplied some, but not all, of the substrate mixtures, cardiac work maintained efficiently of protein synthesis and inhibited protein degradation. An improved method for perfusion of working hearts with albumin-containing buffer is described.

[The regulation of protein synthesis in heart muscle. Biochemical data, stimulative and inhibitory factors and their clinical significance (author's transl)]

The regulation of protein synthesis in heart muscle has been investigated by many authors under both normal and pathological conditions. This review summarizes the evidence for the dependence of normal heart protein synthesis from normal serum levels of insulin, amino acids, fatty acids and glucose. A decreased serum concentration of these substances causes an inhibition of heart muscle protein synthesis by 30--60%. Various drugs and other chemical lead to similar impairments of heat muscle protein synthesis. The resulting imbalance between synthesis and degradation of myocardial proteins with their half-times of 5--12 days gradually leads to a decrease in their myocellular concentration with a consequent impairment of myocardial function. Finally, the biochemial sequences are described which represent the important pathogenetic mechanisms in the development of heart muscle hypertrophy and in the adriamycin-induced cardiomyopathy.

Comparative effects of chronic ethanol and acetaldehyde exposure on myocardial function in rats

This study was conducted to compare separately the chronic effects of high blood levels of ethanol and acetaldehyde on the metabolism of the heart. Levels of ethanol and acetaldehyde were altered by administration of either 4-methylpyrazole (4-MP), a potent alcohol dehydrogenase inhibitor, or pargyline (PAR), a monoamine oxidase inhibitor that markedly increases acetaldehyde levels in the blood following ethanol administration. Measurements were made in rats consuming ethanol for three to four weeks. Mitochondrial respiration, in vitro contractility of glycerinated heart muscle fibers, and myocardial protein synthesis were determined. As compared to animals receiving only ethanol, administration of either-4-methyl-pyrazole or pargyline plus ethanol resulted in more severe damage to mitochondrial respiration and myocardial protein synthesis. The data illustrate that both acetaldehyde and ethanol in high concentrations can cause severe damage to myocardial metabolism.

Changes of myocardial adenine nucleotide and protein synthesis during development of cardiac hypertrophy

1. Studies on three models of cardiac hypertrophy (aortic constriction, application of isoproterenol, daily administrations of 3,3'5-triiodo-L-thyronine, respectively) reveal that the enhancement of de novo synthesis of adenine nucleotides occurs very early during the development of cardiac hypertorphy and always precedes the increase of protein synthesis. Therefore, it seems likely that the accelerated synthesis of adenine nucleotides is an important factor among those metabolic processes involved in the stimulation of protein synthesis in the hypertrophying heart. 2. As far as the mechanism for the observed enhancement of adenine nucleotide synthesis is concerned, it has been demonstrated that the available pool of 5-phosphoribosyl-l-pyrophosphate, an essential precursor substance of de novo synthesis, is increased in the hypertrophying heart due to isoproterenol and 3,3'5-triiodo-L-thyronine, respectively.

Effect of triiodothyronine on the biosynthesis of adenine nucleotides and proteins in the rat heart

1) During the development of myocardial hypertrophy induced by 3,3',5-triiodo-L-thyronine the enhancement of de novo synthesis of adenine nucleotides occurs very early and precedes the increase of protein synthesis. In this respect there is a striking parallelism with other types of cardiac hypertrophy. 2) The acceleration of adenine nucleotide synthesis under these experimental conditions seems to be due to a greater availability of cardiac 5-phosphoribosyl-1-pyrophosphate. 3) The triiodothyronine-induced enhancement of adenine nucleotide synthesis can be attenuated by beta-receptor-blocking agents.

Heart contractile proteins

That several proteins of the sarcomere differ from one muscle to the next is well documented, and it is becoming evident that homogeneous muscles, like the heart, are also species specific. 1) Clear-cut evidence is available concerning myosin, and, to date, several types of molecules have been described. a) The myosins of white skeletal, heart, and smooth muscle differ in the activity of their Ca2+ and K+ATPases, as also in the structure of their light subunits. b) The Ca2+ATPases of the various cardiac myosins have been shown to exhibit species differences and correlate with the speed of shortening of the muscle. 2) The structures of tropomyosin, some troponin components, and alpha actinin (but not actin) appear to be unlike in the different types of muscle. 3) These phylogenic modifications may be related to the changes characteristic of the particular muscles under pathological conditions, which are accompanied by substantial increase in protein synthesis.

Protocollagen proline hydroxylase activity in rat heart during experimental cardiac hypertrophy

Cardiac hypertrophy was produced in rats by constricting the abdominal aorta subdiaphragmatically. The weight of the left ventricle was significantly elevated 2 days after aortic constriction and was 19% higher than in shamoperated animals at 11 days. The activity of protocollagen proline hydroxylase (PPH), an enzyme participating in collagen biosynthesis, and the hydroxyproline content of the heart muscle were determined. PPH activity was increased at 2 days after aortic constriction and declined thereafter, being still above the control level at 11 days. The hydroxyproline content of the left ventricle was significantly increased at 11 days in hypertrophied heart muscle compared to controls. The present results suggest that in cardiac hypertrophy an early connective tissue activation occurs. Later, this leads to connective tissue accumulation. The increased collagen content may give support to the cardiac muscle contracting against systolic overload.

Hypertrophied non-failing rat heart; partial biochemical characterization

Cardiac hypertrophy was induced in rats by constructing an arteriovenous fistula. Heart weights approximately doubled in 7.5 weeks. The levels of activity, expressed per gram of heart, of a variety of enzymes of the mitochondrial respiratory chain and of the citric acid cycle, as well as the concentrations of cytochrome c and of mitochondrial protein, were the same in the hypertrophied and control hearts. Similarly, the capacity of whole heart homogenate to oxidize pyruvate was unaltered in hypertrophy.

There was also no change in the levels of activity of cytochrome oxidase and malate dehydrogenase, or in the concentration of cytochrome c in early hypertrophy (3 to 10 days after construction of an A-V fistula). These results suggest that cardiac mitochondria increase in parallel with the other components of the myocardial cell.

The levels of activity, per gram of heart, of creatine phosphokinase and adenylate kinase, and of the rate-limiting enzymes of glycolysis and glycogenolysis, were the same in the hypertrophied and the control hearts.

The above findings suggest that the capacity, per gram of heart, for regenerating ATP, both aerobically and anaerobically, is unchanged in the non-failing, hypertrophied heart.

Relationship between cortisone and muscle work in determining muscle size

1. Large doses of cortisone caused marked atrophy of the plantaris muscle and other pale muscles of hind limbs of hypophysectomized rats, but hormone treatment had little effect on the size of the red soleus muscle.2. Denervation increased the sensitivity of the soleus and plantaris to the catabolic effects of cortisone.3. Increased work induced by tenotomy of the synergistic gastrocnemius made the plantaris muscle less sensitive to cortisone-induced atrophy.4. Since the catabolic effects of cortisone are more pronounced in the less active muscles, it is suggested that in mobilizing body protein for gluconeogenesis the hormone spares those muscles physiologically most active.5. The rapidity with which muscles lose weight in response to cortisone indicates that the hormone must decrease protein half-lives as well as decrease protein synthesis.