Transcriptional Changes Associated with Long-Term Left Ventricle Volume Overload in Rats: Impact on Enzymes Related to Myocardial Energy Metabolism.

Patients with left ventricle (LV) volume overload (VO) remain in a compensated state for many years although severe dilation is present. The myocardial capacity to fulfill its energetic demand may delay decompensation. We performed a gene expression profile, a model of chronic VO in rat LV with severe aortic valve regurgitation (AR) for 9 months, and focused on the study of genes associated with myocardial energetics. Methods. LV gene expression profile was performed in rats after 9 months of AR and compared to sham-operated controls. LV glucose and fatty acid (FA) uptake was also evaluated in vivo by positron emission tomography in 8-week AR rats treated or not with fenofibrate, an activator of FA oxidation (FAO). Results. Many LV genes associated with mitochondrial function and metabolism were downregulated in AR rats. FA ß-oxidation capacity was significantly impaired as early as two weeks after AR. Treatment with fenofibrate, a PPARα agonist, normalized both FA and glucose uptake while reducing LV dilation caused by AR. Conclusion. Myocardial energy substrate preference is affected early in the evolution of LV-VO cardiomyopathy. Maintaining a relatively normal FA utilization in the myocardium could translate into less glucose uptake and possibly lesser LV remodeling.

Mitochondrial genetic background modulates bioenergetics and susceptibility to acute cardiac volume overload.

Dysfunctional bioenergetics has emerged as a key feature in many chronic pathologies such as diabetes and cardiovascular disease. This has led to the mitochondrial paradigm in which it has been proposed that mtDNA sequence variation contributes to disease susceptibility. In the present study we show a novel animal model of mtDNA polymorphisms, the MNX (mitochondrial-nuclear exchange) mouse, in which the mtDNA from the C3H/HeN mouse has been inserted on to the C57/BL6 nuclear background and vice versa to test this concept. Our data show a major contribution of the C57/BL6 mtDNA to the susceptibility to the pathological stress of cardiac volume overload which is independent of the nuclear background. Mitochondria harbouring the C57/BL6J mtDNA generate more ROS (reactive oxygen species) and have a higher mitochondrial membrane potential relative to those with C3H/HeN mtDNA, independent of nuclear background. We propose this is the primary mechanism associated with increased bioenergetic dysfunction in response to volume overload. In summary, these studies support the 'mitochondrial paradigm' for the development of disease susceptibility, and show that the mtDNA modulates cellular bioenergetics, mitochondrial ROS generation and susceptibility to cardiac stress.

miR-1 mediated suppression of Sorcin regulates myocardial contractility through modulation of Ca2+ signaling.

MicroRNAs are negative gene regulators and play important roles in cardiac development and disease. As evident by cardiomyopathy following cardiac-specific Dicer knockdown they also are required for maintaining normal cardiac contractile function but the specific role of miR-1 in the process is poorly understood. To characterize the role of miR-1 in particular and to identify its specific targets we created a tamoxifen-inducible, cardiac-specific Dicer knockdown mouse and demonstrated that Dicer downregulation results in a dramatic and rapid decline in cardiac function concurrent with significantly reduced levels of miR-1. The importance of miR-1 was established by miR-1 antagomir treatment of wild-type mice, which replicated the cardiac-specific Dicer knockdown phenotype. Down-regulation of miR-1 was associated with up-regulation of its predicted target Sorcin, an established modulator of calcium signaling and excitation-contraction coupling, subsequently verified as a miR-1 target with luciferase constructs. siRNA-mediated knockdown of Sorcin effectively rescued the cardiac phenotypes after Dicer or miR-1 knockdown affirming Sorcin as a critical mediator of the acute cardiomyopathy observed. The regulatory relationship between miR-1 and Sorcin was further confirmed in cultured mouse cardiomyocytes where modulation of miR-1 was associated with discordant Sorcin levels and dysregulation of calcium signaling. Pathological relevance of our findings included decreased miR-1 and increased Sorcin expression in end-stage cardiomyopathy. These findings demonstrate the importance of miR-1 in cardiac function and in the pathogenesis of heart failure via Sorcin-dependent calcium homeostasis.

Differential regulation of diacylglycerol kinase isoform in human failing hearts.

Evidence from several studies indicates the importance of Gαq protein-coupled receptor (GPCR) signaling pathway, which includes diacylglycerol (DAG), and protein kinase C, in the development of heart failure. DAG kinase (DGK) acts as an endogenous regulator of GPCR signaling pathway by catalyzing and regulating DAG. Expressions of DGK isoforms α, ε, and ζ in rodent hearts have been detected; however, the expression and alteration of DGK isoforms in a failing human heart has not yet been examined. In this study, we detected mRNA expressions of DGK isoforms γ, η, ε, and ζ in failing human heart samples obtained from patients undergoing cardiovascular surgery with cardiopulmonary bypass. Furthermore, we investigated modulation of DGK isoform expression in these hearts. We found that expressions of DGKη and DGKζ were increased and decreased, respectively, whereas those of DGKγ and DGKε remained unchanged. This is the first report that describes the differential regulation of DGK isoforms in normal and failing human hearts.

Overt expression of AP-1 reduces alpha myosin heavy chain expression and contributes to heart failure from chronic volume overload.

Reduced expression of alpha-MHC plays a significant role in cardiac contractile dysfunction from hemodynamic overload. Previously, Pur proteins and YY1 have been shown to play a role in alpha-MHC repression during heart failure induced by pressure overload and by spontaneous hypertension, respectively. This was not observed in volume-overload-induced heart failure, suggesting additional regulatory mechanisms for alpha-MHC repression. The present study was performed to identify volume overload responsive transcription factors involved in alpha-MHC gene regulation. DNA binding activity of several transcription factors was evaluated in a functionally characterized rat model of heart failure induced by aorto-caval shunt. After 10 weeks of shunt, severe LV dilatation and reduced LV function were accompanied by increased expression of ANF and beta-MHC, and decreased expression of alpha-MHC. This was associated with dramatic (10-fold) activation of AP-1 together with increased expression of c-fos and c-jun. AP-1 activation was not observed following 4 weeks of shunt when cardiac function was preserved. In cultured cardiomyocytes, induction of AP-1 by PMA attenuated alpha-MHC mRNA by 60%. Transient transfection assays mapped PMA responsive sequence to -582 to -588 bp of alpha-MHC promoter. Deletion or mutation of these nucleotides had minimal effect on basal promoter activity but played a dominant role in PMA-mediated repression of alpha-MHC promoter activity. Over-expression of c-fos and c-jun in cardiomyocytes inhibited alpha-MHC promoter activity in a concentration dependent manner. Data suggest a repressive role of AP-1 in alpha-MHC expression and its possible involvement in the transition from compensatory hypertrophy to heart failure in chronic volume overload.

The effect of mannan-binding lectin variant alleles on coronary artery reactivity in healthy young men.

Mannan-binding lectin (MBL) is a serum acute-phase protein and a complement component secreted by the liver. Its deficiency caused by point mutations in the MBL gene has recently been associated with severe atherosclerosis. In this study, we investigated the effect of MBL variant alleles on coronary artery reactivity, which is an early marker of coronary dysfunction and predicts the development of atherosclerosis and coronary artery disease. The study population consisted of 51 apparently healthy, normo- or mildly hypercholesterolemic young men. Myocardial blood flow was measured at baseline and during adenosine-induced hyperemia with positron emission tomography (PET), and MBL genotyping was performed using restriction fragment-length polymorphism. As a result, MBL variant alleles had no effect on coronary artery reactivity. This finding suggests that MBL deficiency is not an independent risk factor for coronary dysfunction and early atherogenic changes but rather a co-factor in the development of atherosclerosis. Thus, the connection of MBL variant alleles with environmental risk factors in atherosclerosis should further be assessed.

Familial predisposition of left ventricular hypertrophy.

OBJECTIVES: The study evaluated the contribution of familial predisposition to the risk of left ventricular hypertrophy (LVH). BACKGROUND: Left ventricular hypertrophy is a multifactorial condition that serves as an important predictor of cardiovascular mortality. At present it is unclear whether familial predisposition contributes to the manifestation of LVH. Thus, we determined whether siblings of subjects with LVH are at increased risk to present with an elevation of LV mass or an abnormal LV geometry. METHODS: Echocardiographic and anthropometric measurements were performed in 2,293 individuals who participated in the echocardiographic substudies of population-based MONICA Augsburg surveys. In addition, a total of 319 siblings of survey participants with echocardiographic evidence of LVH were evaluated. The risk of these siblings to present with LVH or abnormal LV geometry was estimated by comparison with 636 subjects matched for gender and age that were selected from the entire echocardiography study base. RESULTS: Blood pressure, body mass index, age, and gender (i.e., known determinants of LV mass) were comparable in LVH-siblings and the matched comparison group. However, septal and posterior wall thicknesses, relative wall thickness as well as LV mass index were significantly elevated in LVH-siblings (p < 0.001, each) whereas LV dimensions did not differ. Likewise, the prevalence of LVH was raised in LVH-siblings, as was the relative risk of LVH after adjustment for confounders (p < 0.05). More specifically, LVH-siblings displayed increased prevalences of concentric remodeling and concentric LVH (p < 0.05) but not of eccentric LVH. CONCLUSIONS: Familial predisposition appears to contribute to increased LV wall thickness, to the development of LV hypertrophy and abnormal LV geometry.

Variants of renin-angiotensin system genes and echocardiographic left ventricular mass.

AIMS: Variants of renin-angiotensin system genes are shown to be associated with cardiovascular pathology. The association between renin-angiotensin system genes and left ventricular mass was investigated in a population-based case-control study. METHODS AND RESULTS: The association between echocardiographic left ventricular mass and both insertion/deletion polymorphism of the angiotensin-converting enzyme gene and the methionine-threonine variant at position 235 of the angiotensinogen gene was studied in a random cohort of 430 hypertensive and 426 control subjects. No differences in the adjusted left ventricular mass values between the different genotypes were seen among either the hypertensive or the control subjects, whether men or women, or in the subgroups of normotensive or physically active subjects. Gene variation had no statistically significant synergistic effect on left ventricular mass values. In control women, the deletion allele of the angiotensin-converting enzyme gene was associated with an increased risk of left ventricular hypertrophy. However, this finding was based on a small number of women with left ventricular hypertrophy and should be interpreted with caution. CONCLUSION: Variations in renin-angiotensin system genes had no major effect on left ventricular mass in this middle-aged population-based cohort of hypertensives and control subjects.