Circulating microRNAs predict future fatal myocardial infarction in healthy individuals - The HUNT study.

Coronary heart disease is the most common cause of death, and the number of individuals at risk is increasing. To better manage this pandemic, improved tool for risk prediction, including more accurate biomarkers are needed. The objective of this study was to assess the utility of circulating microRNAs (miRs) to predict future fatal acute myocardial infarction (AMI) in healthy participants. We performed a prospective nested case-control study with 10-year observation period and fatal AMI as endpoint. In total, 179 miRs were quantified by real-time polymerase chain reaction in serum of 112 healthy participants (40-70years) that either (1) suffered from fatal AMI within 10years [n=56], or (2) remained healthy [n=56, risk factor-matched controls]. Candidate miRs were validated in a separate cohort of healthy individuals (n=100). Twelve miRs were differently expressed in cases and controls in the derivation cohort (p<0.05). Among these, 10 miRs differed significantly between cases and controls in the validation cohort (p<0.05). We identified gender dimorphisms, as miR-424-5p and miR-26a-5p were associated exclusively with risk in men and women, respectively. The best model for predicting future AMI consisted of miR-106a-5p, miR-424-5p, let-7g-5p, miR-144-3p and miR-660-5p, providing 77.6% correct classification for both genders, and 74.1% and 81.8% for men and women, respectively. Adding these 5 miRs to the Framingham Risk Score, increased the AUC from 0.72 to 0.91 (p<0.001). In conclusion, we identified several miRs associated with future AMI, revealed gender-specific associations, and proposed a panel of 5 miRs to enhance AMI risk prediction in healthy individuals.

Lack of UCP3 does not affect skeletal muscle mitochondrial function under lipid-challenged conditions, but leads to sudden cardiac death.

UCP3's exact physiological function in lipid handling in skeletal and cardiac muscle remains unknown. Interestingly, etomoxir, a fat oxidation inhibitor and strong inducer of UCP3, is proposed for treating both diabetes and heart failure. We hypothesize that the upregulation of UCP3 upon etomoxir serves to protect mitochondria against lipotoxicity. To evaluate UCP3's role in skeletal muscle (skm) and heart under lipid-challenged conditions, the effect of UCP3 ablation was examined in a state of dysbalance between fat availability and oxidative capacity. Wild type (WT) and UCP3(-/-) mice were subjected to high-fat feeding for 14 days. From day 6 onwards, they were given either saline or etomoxir. Etomoxir treatment induced an increase in markers of lipotoxicity in skm compared to saline. This increase upon etomoxir was similar for both, WT and UCP3(-/-) mice, suggesting that UCP3 does not play a role in protection against lipotoxicity. Interestingly, we observed 25 % mortality in UCP3(-/-)s upon etomoxir administration vs. 11 % in WTs. This increased mortality in UCP3(-/-) compared to WT mice could not be explained by differences in cardiac lipotoxicity, apoptosis, fibrosis (histology, immunohistochemistry), oxidative capacity (respirometry) or function (echocardiography). Electrophysiology demonstrated, however, prolonged QRS and QTc intervals and greater susceptibility to ventricular tachycardia upon programmed electrical stimulation in etomoxir-treated UCP3(-/-)s versus WTs. Isoproterenol administration after pacing resulted in 75 % mortality in UCP3(-/-)s vs. 14 % in WTs. Our results argue against a protective role for UCP3 on skm metabolism under lipid overload, but suggest UCP3 to be crucial in prevention of arrhythmias upon lipid-challenged conditions.

Diagnostic performance of microRNAs in the detection of heart failure with reduced or preserved ejection fraction: a systematic review and meta-analysis.

AIM: Chronic heart failure (CHF) can be classified as heart failure with preserved ejection fraction (HFpEF) or with reduced ejection fraction (HFrEF). Currently, there is an unmet need for a minimally invasive diagnostic tool for different forms of CHF. We aimed to investigate the diagnostic potential of circulating microRNAs (miRNAs) for the detection of different CHF forms via a systematic review and meta-analysis approach. METHODS AND RESULTS: Comprehensive search on Medline, Web of Science, Scopus, and EMBASE identified 45 relevant studies which were used for qualitative assessment. Out of these, 29 studies were used for qualitative and quantitative assessment and allowed to identify a miRNA panel able to detect HFrEF and HFpEF with areas under the curve (AUC) of 0.86 and 0.79, respectively. A panel of eight miRNAs (hsa-miR-18b-3p, hsa-miR-21-5p, hsa-miR-22-3p, hsa-miR-92b-3p, hsa-miR-129-5p, hsa-miR-320a-5p, hsa-miR-423-5p, and hsa-miR-675-5p) detected HFrEF cases with a sensitivity of 0.85, specificity of 0.88 and AUC of 0.91. A panel of seven miRNAs (hsa-miR-19b-3p, hsa-miR-30c-5p, hsa-miR-206, hsa-miR-221-3p, hsa-miR-328-5p, hsa-miR-375-3p, and hsa-miR-424-5p) identified HFpEF cases with a sensitivity of 0.82 and a specificity of 0.61. CONCLUSIONS: Although conventional biomarkers (N-terminal pro-B-type natriuretic peptide and B-type natriuretic peptide) presented a better performance in detecting CHF patients, the results presented here pointed towards specific miRNA panels with potential additive values to circulating natriuretic peptides in the diagnosis of different classes of CHF. Equally important, miRNAs alone showed a reasonable capacity for 'ruling out' patients with HFrEF or HFpEF. Additional studies with large populations are required to confirm the diagnostic potential of miRNAs for sub-classes of CHF.

Early cardiac-chamber-specific fingerprints in heart failure with preserved ejection fraction detected by FTIR and Raman spectroscopic techniques.

The pathophysiology of heart failure with preserved ejection fraction (HFpEF) is a matter of investigation and its diagnosis remains challenging. Although the mechanisms that are responsible for the development of HFpEF are not fully understood, it is well known that nearly 80% of patients with HFpEF have concomitant hypertension. We investigated whether early biochemical alterations were detectable during HFpEF progression in salt-induced hypertensive rats, using Fourier-transformed infrared (FTIR) and Raman spectroscopic techniques as a new diagnostic approach. Greater protein content and, specifically, greater collagen deposition were observed in the left atrium and right ventricle of hypertensive rats, together with altered metabolism of myocytes. Additionally, Raman spectra indicated a conformational change, or different degree of phosphorylation/methylation, in tyrosine-rich proteins. A correlation was found between tyrosine content and cardiac fibrosis of both right and left ventricles. Microcalcifications were detected in the left and right atria of control animals, with a progressive augmentation from six to 22 weeks. A further increase occurred in the left ventricle and right atrium of 22-week salt-fed animals, and a positive correlation was shown between the mineral deposits and the cardiac size of the left ventricle. Overall, FTIR and Raman techniques proved to be sensitive to early biochemical changes in HFpEF and preceded clinical humoral and imaging markers.

Etiology-Dependent Impairment of Diastolic Cardiomyocyte Calcium Homeostasis in Heart Failure With Preserved Ejection Fraction.

BACKGROUND: Whereas heart failure with reduced ejection fraction (HFrEF) is associated with ventricular dilation and markedly reduced systolic function, heart failure with preserved ejection fraction (HFpEF) patients exhibit concentric hypertrophy and diastolic dysfunction. Impaired cardiomyocyte Ca2+ homeostasis in HFrEF has been linked to disruption of membrane invaginations called t-tubules, but it is unknown if such changes occur in HFpEF. OBJECTIVES: This study examined whether distinct cardiomyocyte phenotypes underlie the heart failure entities of HFrEF and HFpEF. METHODS: T-tubule structure was investigated in left ventricular biopsies obtained from HFrEF and HFpEF patients, whereas cardiomyocyte Ca2+ homeostasis was studied in rat models of these conditions. RESULTS: HFpEF patients exhibited increased t-tubule density in comparison with control subjects. Super-resolution imaging revealed that higher t-tubule density resulted from both tubule dilation and proliferation. In contrast, t-tubule density was reduced in patients with HFrEF. Augmented collagen deposition within t-tubules was observed in HFrEF but not HFpEF hearts. A causative link between mechanical stress and t-tubule disruption was supported by markedly elevated ventricular wall stress in HFrEF patients. In HFrEF rats, t-tubule loss was linked to impaired systolic Ca2+ homeostasis, although diastolic Ca2+ removal was also reduced. In contrast, Ca2+ transient magnitude and release kinetics were largely maintained in HFpEF rats. However, diastolic Ca2+ impairments, including reduced sarco/endoplasmic reticulum Ca2+-ATPase activity, were specifically observed in diabetic HFpEF but not in ischemic or hypertensive models. CONCLUSIONS: Although t-tubule disruption and impaired cardiomyocyte Ca2+ release are hallmarks of HFrEF, such changes are not prominent in HFpEF. Impaired diastolic Ca2+ homeostasis occurs in both conditions, but in HFpEF, this mechanism for diastolic dysfunction is etiology-dependent.

Ace gene dosage influences the development of renovascular hypertension.

1. Clinical and experimental evidence highlights the importance of the renin-angiotensin system in renovascular hypertension. Furthermore, genetic factors affecting angiotensin-converting enzyme (ACE) could influence the development of renovascular hypertension. 2. To test the effect of small gene perturbations on the development of renovascular hypertension, mice harbouring two or three copies of the Ace gene were submitted to 4 weeks of two-kidney, one-clip (2K1C) hypertension. Blood pressure (BP), cardiac hypertrophy, baroreflex sensitivity and blood pressure and heart rate variability were assessed and compared between the different groups. 3. The increase in BP induced by 2K1C was higher in mice with three copies of the Ace gene compared with mice with only two copies (46 vs 23 mmHg, respectively). Moreover, there was a 3.8-fold increase in the slope of the left ventricle mass/BP relationship in mice with three copies of the Ace gene. Micewith three copies of the Ace gene exhibited greater increases in cardiac and serum ACE activity than mice with only two copies of the gene. Both baroreflex bradycardia and tachycardia were significantly depressed in mice with three copies of the Ace gene after induction of 2K1C hypertension. The variance in basal systolic BP was greater in mice with three copies of the Ace gene after 2K1C hypertension compared with those with only two copies of the gene (106 vs 54%, respectively). In addition, the low-frequency component of the pulse interval was higher mice with three copies of the Ace gene after 2K1C hypertension compared with those with only two (168 vs 86%, respectively). Finally, in mice with three copies of the Ace gene, renovascular hypertension induced a 6.1-fold increase in the sympathovagal balance compared with a 3.2-fold increase in mice with only two copies of the gene. 4. Collectively, these data provide direct evidence that small genetic disturbances in ACE levels per se have an influence on haemodynamic, cardiac mass and autonomic nervous system responses in mice under pathological perturbation.

Cardioprotective Effects of the Novel Compound Vastiras in a Preclinical Model of End-Organ Damage.

Cardiac hypertrophy and renal damage associated with hypertension are independent predictors of morbidity and mortality. In a model of hypertensive heart disease and renal damage, we tested the actions of continuous administration of Vastiras, a novel compound derived from the linear fragment of ANP (atrial natriuretic peptide), namely pro-ANP31-67, on blood pressure and associated renal and cardiac function and remodeling. Of note, this peptide, unlike the ring structured forms, does not bind to the classic natriuretic peptide receptors. Dahl/Salt-Sensitive rats fed a 4% NaCl diet for 6 weeks developed hypertension, cardiac hypertrophy, and renal damage. Four weeks of treatment with 50 to 100 ng/kg per day of Vastiras exhibited positive effects on renal function, independent of blood pressure regulation. Treated rats had increased urine excretion, natriuresis, and enhanced glomerular filtration rate. Importantly, these favorable renal effects were accompanied by improved cardiac structure and function, including attenuated cardiac hypertrophy, as indicated by decreased heart weight to body weight ratio, relative wall thickness, and left atrial diameter, as well as reduced fibrosis and normalized ratio of the diastolic mitral inflow E wave to A wave. A renal subtherapeutic dose of Vastiras (25 ng/kg per day) induced similar protective effects on the heart. At the cellular level, cardiomyocyte size and t-tubule density were preserved in Vastiras-treated compared with untreated animals. In conclusion, these data demonstrate the cardiorenal protective actions of chronic supplementation of a first-in-class compound, Vastiras, in a preclinical model of maladaptive cardiac hypertrophy and renal damage induced by hypertension.

Cuff-induced vascular intima thickening is influenced by titration of the Ace gene in mice.

We tested the hypothesis that small changes in angiotensin I-converting enzyme (ACE) expression can alter the vascular response to injury. Male mice containing one, two, three, and four copies of the Ace gene with no detectable vascular abnormality or changes in blood pressure were submitted to cuff-induced femoral artery injury. Femoral thickening was higher in 3- and 4-copy mice (42.4 +/- 4.3% and 45.7 +/- 6.5%, respectively) compared with 1- and 2-copy mice (8.3 +/- 1.3% and 8.5 +/- 0.9%, respectively). Femoral ACE levels from control and injured vessels were assessed in 1- and 3-copy Ace mice, which represent the extremes of the observed response. ACE vascular activity was higher in 3- vs. 1-copy Ace mice (2.4-fold, P < 0.05) in the control uninjured vessel. Upon injury, ACE activity significantly increased in both groups [2.41-fold and 2.14-fold (P < 0.05) for 1- and 3-copy groups, respectively] but reached higher levels in 3- vs. 1-copy Ace mice (P < 0.05). Pharmacological interventions were then used as a counterproof and to indirectly assess the role of angiotensin II (ANG II) on this response. Interestingly, ACE inhibition (enalapril) and ANG II AT(1) receptor blocker (losartan) reduced intima thickening in 3-copy mice to 1-copy mouse values (P < 0.05) while ANG II treatment significantly increased intima thickening in 1-copy mice to 3-copy mouse levels (P < 0.05). Together, these data indicate that small physiologically relevant changes in ACE, not associated with basal vascular abnormalities or blood pressure levels, do influence the magnitude of cuff-induced neointima thickening in mice.

Congenic strains provide evidence that four mapped loci in chromosomes 2, 4, and 16 influence hypertension in the SHR.

To dissect the genetic architecture controlling blood pressure (BP) regulation in the spontaneously hypertensive rat (SHR) we derived congenic rat strains for four previously mapped BP quantitative trait loci (QTLs) in chromosomes 2, 4, and 16. Target chromosomal regions from the Brown Norway rat (BN) averaging 13-29 cM were introgressed by marker-assisted breeding onto the SHR genome in 12 or 13 generations. Under normal salt intake, QTLs on chromosomes 2a, 2c, and 4 were associated with significant changes in systolic BP (13, 20, and 15 mmHg, respectively), whereas the QTL on chromosome 16 had no measurable effect. On high salt intake (1% NaCl in drinking water for 2 wk), the chromosome 16 QTL had a marked impact on SBP, as did the QTLs on chromosome 2a and 2c (18, 17, and 19 mmHg, respectively), but not the QTL on chromosome 4. Thus these four QTLs affected BP phenotypes differently: 1) in the presence of high salt intake (chromosome 16), 2) only associated with normal salt intake (chromosome 4), and 3) regardless of salt intake (chromosome 2c and 2a). Moreover, salt sensitivity was abrogated in congenics SHR.BN2a and SHR.BN16. Finally, we provide evidence for the influence of genetic background on the expression of the mapped QTLs individually or as a group. Collectively, these data reveal previously unsuspected nuances of the physiological roles of each of the four mapped BP QTLs in the SHR under basal and/or salt loading conditions unforeseen by the analysis of the F2 cross.

Effects of sinoaortic denervation on hemodynamic parameters during natural sleep in rats.

STUDY OBJECTIVES: To analyze the role of arterial baroreflex on hemodynamic changes during synchronized and desynchronized sleep phases of natural sleep in rats. DESIGN: Experimental study. SETTING: Laboratory. PARTICIPANTS: Seventeen male Wistar rats. INTERVENTIONS: No intervention (control, n = 8) or sinoaortic denervation (SAD, n = 9). MEASUREMENTS AND RESULTS: Sleep phases were monitored by electrocorticogram, and blood pressure was measured directly by a catheter in the carotid artery. Cardiac output, as well as total and regional vascular resistances, were determined by measuring the subdiaphragmatic aorta and iliac artery flows with Doppler flow probes, respectively. In contrast to the control group, the SAD group had a strong reduction in blood pressure (-19.9% +/- 2.6% vs -0.7% +/- 2.1%) during desynchronized sleep, and cardiac output showed an exacerbated reduction (-10.4% +/- 3.5% vs 1.1% +/- 1.7%). In SAD rats, total vascular resistance decreased during desynchronized sleep (-10.1% +/- 3.5% vs -1.0% +/- 1.7%), and the increase in regional vascular resistance observed in the control group was abolished (27.5% +/- 8.3% vs -0.8% +/- 9.4%). CONCLUSIONS: SAD caused profound changes in blood pressure, cardiac output, and total vascular resistance, with a significant increase in muscle vascular resistance during synchronized sleep. Our results suggest that baroreflex plays an important role in maintaining the normal balance of cardiac output and total vascular resistance during sleep.

Differential regulation of cysteine oxidative post-translational modifications in high and low aerobic capacity.

Given the association between high aerobic capacity and the prevention of metabolic diseases, elucidating the mechanisms by which high aerobic capacity regulates whole-body metabolic homeostasis is a major research challenge. Oxidative post-translational modifications (Ox-PTMs) of proteins can regulate cellular homeostasis in skeletal and cardiac muscles, but the relationship between Ox-PTMs and intrinsic components of oxidative energy metabolism is still unclear. Here, we evaluated the Ox-PTM profile in cardiac and skeletal muscles of rats bred for low (LCR) and high (HCR) intrinsic aerobic capacity. Redox proteomics screening revealed different cysteine (Cys) Ox-PTM profile between HCR and LCR rats. HCR showed a higher number of oxidized Cys residues in skeletal muscle compared to LCR, while the opposite was observed in the heart. Most proteins with differentially oxidized Cys residues in the skeletal muscle are important regulators of oxidative metabolism. The most oxidized protein in the skeletal muscle of HCR rats was malate dehydrogenase (MDH1). HCR showed higher MDH1 activity compared to LCR in skeletal, but not cardiac muscle. These novel findings indicate a clear association between Cys Ox-PTMs and aerobic capacity, leading to novel insights into the role of Ox-PTMs as an essential signal to maintain metabolic homeostasis.

Genetic mapping of a new heart rate QTL on chromosome 8 of spontaneously hypertensive rats.

BACKGROUND: Tachycardia is commonly observed in hypertensive patients, predominantly mediated by regulatory mechanisms integrated within the autonomic nervous system. The genetic loci and genes associated with increased heart rate in hypertension, however, have not yet been identified. METHODS: An F2 intercross of Spontaneously Hypertensive Rats (SHR) x Brown Norway (BN) linkage analysis of quantitative trait loci mapping was utilized to identify candidate genes associated with an increased heart rate in arterial hypertension. RESULTS: Basal heart rate in SHR was higher compared to that of normotensive BN rats (365 +/- 3 vs. 314 +/- 6 bpm, p < 0.05 for SHR and BN, respectively). A total genome scan identified one quantitative trait locus in a 6.78 cM interval on rat chromosome 8 (8q22-q24) that was responsible for elevated heart rate. This interval contained 241 genes, of which 65 are known genes. CONCLUSION: Our data suggest that an influential genetic region located on the rat chromosome 8 contributes to the regulation of heart rate. Candidate genes that have previously been associated with tachycardia and/or hypertension were found within this QTL, strengthening our hypothesis that these genes are, potentially, associated with the increase in heart rate in a hypertension rat model.

MicroRNAs as Important Regulators of Exercise Adaptation.

A significant body of evidence supports the protective role of exercise training (ET) in cardiovascular diseases, skeletal muscle dystrophies, several types of cancer, Alzheimer disease or even in the recovery of spinal cord injury. In spite of this, the molecular mechanisms underlying the beneficial effects of exercise training are not well understood and remain elusive. Several mechanisms have been proposed in the past, but more recently microRNAs (miRNAs), small non-coding RNA molecules involved in a variety of basic biological processes that negatively modulate gene expression, recognized as important regulatory molecules. In this review, we highlight recent advances on the miRNA involvement in the benefits of ET. Here, we assess the role of microRNAs expressed in the heart, in the skeletal muscle, detected in the circulation (serum and plasma), and in other conditions (e.g., spinal cord injury). Additionally, the long-term effects of diverse ET modalities (e.g., running, cycling, resistance training) in the cardiac miRNA profile are properly addressed.

ACE gene dosage modulates pressure-induced cardiac hypertrophy in mice and men.

The influence of genetic factors on complex phenotypes is context dependent, posing a challenge to quantify the role of single gene variants on this process. Moreover, redundancy and reserve capacity among control systems prevent most physiological stimuli to destabilize these processes. To test whether small gene perturbation can disrupt this equilibrium under pathological conditions, mice harboring one, two, or three copies of the angiotensin converting enzyme (Ace) gene were submitted to 3 and 6 wk of pressure overload (PO). Direct systolic blood pressure (SBP), as an index of cardiac afterload, and left ventricle mass index (LVMI) were measured. LVMI under normotension was the same regardless of the Ace genotype, but the slopes of the LVMI/SBP curves increased in the three- vs. one-copy group by approximately 50% upon 3- or 6-wk PO. Angiotensin II AT1 receptor blocker treatment produced a significant pressure independent decrease in the LVMI/SBP ratio. Unlike the one-copy group, PO resulted in a significant reduction in angiotensinogen and an increase in Ace mRNA expression accompanied by an increase in cardiac angiotensin II levels in the three-copy group. Similarly, the human ACE D gene variant influenced cardiac mass, estimated by Sokolov-Lyon index, in a sample of 1,507 individuals from an urban population only in individuals in the 4th quartile of the blood pressure distribution. Collectively, these data provide direct evidence that ACE gene dosage per se does not influence cardiac mass but upon a pathological stimulus, such as elevation in blood pressure, it modulates cardiac mass in both mice and humans.

Preservation of cardiac function in left ventricle cardiac hypertrophy using an AAV vector which provides VEGF-A expression in response to p53.

Here we present the application of our adeno-associated virus (AAV2) vector where transgene expression is driven by a synthetic, p53-responsive promoter, termed PG, used to supply human vascular endothelial growth factor-A165 (VEGF-A). Thus, p53 is harnessed to promote the beneficial expression of VEGF-A encoded by the AAVPG vector, bypassing the negative effect of p53 on HIF-1α which occurs during cardiac hypertrophy. Wistar rats were submitted to pressure overload induced by thoracic aorta coarctation (TAC) with or without concomitant gene therapy (intramuscular delivery in the left ventricle). After 12 weeks, rats receiving AAVPG-VEGF gene therapy were compared to those that did not, revealing significantly improved cardiac function under hemodynamic stress, lack of fibrosis and reversal of capillary rarefaction. With these functional assays, we have demonstrated that application of the AAVPG-VEGF vector under physiologic conditions known to stimulate p53 resulted in the preservation of cardiac performance.

Heart failure with preserved ejection fraction induces molecular, mitochondrial, histological, and functional alterations in rat respiratory and limb skeletal muscle.

AIMS: Peripheral muscle dysfunction is a key mechanism contributing to exercise intolerance (i.e. breathlessness and fatigue) in heart failure patients with preserved ejection fraction (HFpEF); however, the underlying molecular and cellular mechanisms remain unknown. We therefore used an animal model to elucidate potential molecular, mitochondrial, histological, and functional alterations induced by HFpEF in the diaphragm and soleus, while also determining the possible benefits associated with exercise training. METHODS AND RESULTS: Female Dahl salt-sensitive rats were fed a low (CON; n = 10) or high salt (HFpEF; n = 11) diet of 0.3% or 8% NaCl, respectively, or a high salt diet in combination with treadmill exercise training (n = 11). Compared with low-salt rats, high-salt rats developed (P < 0.05) HFpEF. Compared with CON, the diaphragm of HFpEF rats demonstrated (P < 0.05): a fibre type shift from fast-to-slow twitch; fibre atrophy; a decreased pro-oxidative but increased anti-oxidant capacity; reduced proteasome activation; impaired in situ mitochondrial respiration; and in vitro muscle weakness and increased fatigability. The soleus also demonstrated numerous alterations (P < 0.05), including fibre atrophy, decreased anti-oxidant capacity, reduced mitochondrial density, and increased fatigability. Exercise training, however, prevented mitochondrial and functional impairments in both the diaphragm and soleus (P < 0.05). CONCLUSION: Our findings are the first to demonstrate that HFpEF induces significant molecular, mitochondrial, histological, and functional alterations in the diaphragm and soleus, which were attenuated by exercise training. These data therefore reveal novel mechanisms and potential therapeutic treatments of exercise intolerance in HFpEF.

Cardiac LXRα protects against pathological cardiac hypertrophy and dysfunction by enhancing glucose uptake and utilization.

Pathological cardiac hypertrophy is characterized by a shift in metabolic substrate utilization from fatty acids to glucose, but the molecular events underlying the metabolic remodeling remain poorly understood. Here, we investigated the role of liver X receptors (LXRs), which are key regulators of glucose and lipid metabolism, in cardiac hypertrophic pathogenesis. Using a transgenic approach in mice, we show that overexpression of LXRα acts to protect the heart against hypertrophy, fibrosis, and dysfunction. Gene expression profiling studies revealed that genes regulating metabolic pathways were differentially expressed in hearts with elevated LXRα. Functionally, LXRα overexpression in isolated cardiomyocytes and murine hearts markedly enhanced the capacity for myocardial glucose uptake following hypertrophic stress. Conversely, this adaptive response was diminished in LXRα-deficient mice. Transcriptional changes induced by LXRα overexpression promoted energy-independent utilization of glucose via the hexosamine biosynthesis pathway, resulting in O-GlcNAc modification of GATA4 and Mef2c and the induction of cytoprotective natriuretic peptide expression. Our results identify LXRα as a key cardiac transcriptional regulator that helps orchestrate an adaptive metabolic response to chronic cardiac stress, and suggest that modulating LXRα may provide a unique opportunity for intervening in myocyte metabolism.

Reversible pulmonary trunk banding VIII: Intermittent overload causes harmless hypertrophy in adult goat.

BACKGROUND: Traditional pulmonary artery banding (PAB) is not always suitable for mature subpulmonary ventricle retraining. We sought to assess in detail the myocardial morphologic adaptations of two different protocols for inducing right ventricular (RV) hypertrophy in an adult animal model. METHODS: Eighteen adult goats were distributed into three groups: sham (no systolic overload), traditional (continuous systolic overload), and intermittent (daily 12-hour systolic overload). Systolic overload was adjusted to achieve a 0.7 RV-to-aortic pressure ratio. All animals underwent weekly echocardiographic studies, and hemodynamic evaluations were performed 3 times a week. After 4 weeks, the animals were humanely killed for morphologic assessment. RESULTS: A 37.2% increase was observed in the RV wall thickness of the intermittent group (p<0.05), but no significant echocardiographic changes were observed in the other two groups. The intermittent and traditional groups had a 55.7% and 36.7% increase in RV mass, respectively, compared with the sham group (p<0.05). No differences were observed in myocardial water content of the three groups (p=0.27). RV myocardial fiber and nuclei diameters were increased in the intermittent group compared with the sham group (p<0.05). The area of collagen deposition in the RV interstitium was increased 98% in traditional group compared with the sham group (p<0.05). No significant cellular proliferation occurred in any group. CONCLUSIONS: This study suggests that a more effective and harmless hypertrophy can be achieved in adult animals using intermittent PAB compared with the traditional approach.

Reversible pulmonary trunk banding: VII. Stress echocardiographic assessment of rapid ventricular hypertrophy in young goats.

BACKGROUND: Ventricle retraining with abrupt systolic overload can cause myocardial edema and necrosis, followed by late ventricular failure. Intermittent systolic overload could minimize the inadequacy of conventional pulmonary artery banding. The present study compared ventricle function under dobutamine stress in 2 protocols of systolic overload in young goats. METHODS: Nineteen young goats were divided into 3 groups: sham (n = 7; no systolic pressure overload), continuous (n = 6; systolic overload maintained for 96 hours), and intermittent (n = 6; 4 periods of 12-hour systolic overload, paired with a 12-hour resting period). Echocardiographic and hemodynamic evaluations were performed daily. The myocardial performance index and ejection fraction were evaluated at rest and during dobutamine stress. The goats were then killed for morphologic evaluation. RESULTS: The intermittent group underwent less systolic overload than the continuous group (P < .05). Nevertheless, both groups had increased right ventricular and septal masses compared with the sham group (P < .0002). Echocardiography revealed a major increase in right ventricular wall thickness in the intermittent group (+64.8% ± 23.37%) compared with the continuous group (+43.9% ± 19.26%; P = .015). Only the continuous group remained with significant right ventricular dilation throughout the protocol (P < .001). The intermittent group had a significantly better myocardial performance index at the end of the protocol, under resting and dobutamine infusion, compared with the continuous group (P < .012). CONCLUSIONS: Both systolic overload protocols have induced rapid right ventricular hypertrophy. However, only the intermittent group had better preservation of right ventricular function at the end of the protocol, both at rest and during dobutamine infusion.

Nfat and miR-25 cooperate to reactivate the transcription factor Hand2 in heart failure.

Although aberrant reactivation of embryonic gene programs is intricately linked to pathological heart disease, the transcription factors driving these gene programs remain ill-defined. Here we report that increased calcineurin/Nfat signalling and decreased miR-25 expression integrate to re-express the basic helix-loop-helix (bHLH) transcription factor dHAND (also known as Hand2) in the diseased human and mouse myocardium. In line, mutant mice overexpressing Hand2 in otherwise healthy heart muscle cells developed a phenotype of pathological hypertrophy. Conversely, conditional gene-targeted Hand2 mice demonstrated a marked resistance to pressure-overload-induced hypertrophy, fibrosis, ventricular dysfunction and induction of a fetal gene program. Furthermore, in vivo inhibition of miR-25 by a specific antagomir evoked spontaneous cardiac dysfunction and sensitized the murine myocardium to heart failure in a Hand2-dependent manner. Our results reveal that signalling cascades integrate with microRNAs to induce the expression of the bHLH transcription factor Hand2 in the postnatal mammalian myocardium with impact on embryonic gene programs in heart failure.