Mitochondrial gene expression and respiratory enzyme activities in cardiac diseases

Human cardiac metabolism

The heart is the most metabolically active organ in the human body, and cardiac metabolism has been studied for decades. However, the bulk of studies have focused on animal models. The objective of this review is to summarize specifically what is known about cardiac metabolism in humans. Techniques available to study human cardiac metabolism are first discussed, followed by a review of human cardiac metabolism in health and in heart failure. Mechanistic insights, where available, are reviewed, and the evidence for the contribution of metabolic insufficiency to heart failure, as well as past and current attempts at metabolism-based therapies, is also discussed.

Correlation of Sperm Mitochondrial DNA 7345 bp and 7599 bp Deletions with Asthenozoospermia in Jordanian Population

Background:

Alterations in sperm mitochondrial DNA (mtDNA) affect the functions of some OXPHOS proteins which will affect sperm motility and may be associated with asthenozoospermia. The purpose of this study was to investigate the correlation between 7599-bp and 7345-bp sperm mtDNA deletions and asthenozoospermia in Jordan.

Methods:

Semen specimens from 200 men including 121 infertile and 79 healthy individuals were collected at the Royal Jordanian Medical Services In-vitro fertilization (IVF) units. The mtDNA was extracted followed by mtDNA amplification. Polymerase chain reaction (PCR) was conducted for the target sequences, then DNA sequencing was performed for the PCR products. Chi-square, Fisher’s and Spearman’s tests were used to calculate the correlation.

Results:

The results showed a significant correlation between the presence of 7599-bp mtDNA deletion and infertility where the frequency of the 7599-bp deletion was 63.6% in the infertile group compared to the fertile 34.2% (p<0.001, (OR=3.37, 95% CI=1.860 to 6.108)). Additionally, the sperm motility showed a significant association with the frequency of the 7599-bp deletion (p=0.001, r=−0.887). The 7345-bp mtDNA deletion showed no assoctiation with the infertility (p=0.65, (OR=0.837, 95% CI= 0.464–1.51)) or asthenozoospermia (p=0.98, r=0.008).

Conclusion:

We demonstrated a significant correlation between asthenozoospermia and the 7599-bp mtDNA deletion but not the 7345-bp mtDNA deletion in the infertile men in Jordan. Screening for deletions in sperm mtDNA can be used as a pre-diagnostic molecular marker for male infertility.

Distinct Myocardial Transcriptomic Profiles of Cardiomyopathies Stratified by the Mutant Genes

Cardiovascular diseases are the number one cause of morbidity and mortality worldwide, but the underlying molecular mechanisms remain not well understood. Cardiomyopathies are primary diseases of the heart muscle and contribute to high rates of heart failure and sudden cardiac deaths. Here, we distinguished four different genetic cardiomyopathies based on gene expression signatures. In this study, RNA-Sequencing was used to identify gene expression signatures in myocardial tissue of cardiomyopathy patients in comparison to non-failing human hearts. Therefore, expression differences between patients with specific affected genes, namely LMNA (lamin A/C), RBM20 (RNA binding motif protein 20), TTN (titin) and PKP2 (plakophilin 2) were investigated. We identified genotype-specific differences in regulated pathways, Gene Ontology (GO) terms as well as gene groups like secreted or regulatory proteins and potential candidate drug targets revealing specific molecular pathomechanisms for the four subtypes of genetic cardiomyopathies. Some regulated pathways are common between patients with mutations in RBM20 and TTN as the splice factor RBM20 targets amongst other genes TTN, leading to a similar response on pathway level, even though many differentially expressed genes (DEGs) still differ between both sample types. The myocardium of patients with mutations in LMNA is widely associated with upregulated genes/pathways involved in immune response, whereas mutations in PKP2 lead to a downregulation of genes of the extracellular matrix. Our results contribute to further understanding of the underlying molecular pathomechanisms aiming for novel and better treatment of genetic cardiomyopathies.

Association between mitochondrial DNA copy number and cardiovascular disease: Current evidence based on a systematic review and meta-analysis

Background

Mitochondria are energy-producing structure of the cell and help to maintain redox environment. In cardiovascular disease, the number of mitochondrial DNA (mtDNA) will changes accordingly compare to normal condition. Some investigators ask whether it has a clear association between mtDNA and cardiovascular disease with its adverse events. Thus, we conduct the meta-analysis to assess the role of circulating mtDNA in evaluating cardiovascular disease.

Methods

The meta-analysis was conducted in accordance with a predetermined protocol following the recommendations of Cochrane Handbook of Systematic Reviews. We searched the Pubmed, Embase, the Cochrane Central Register of Controlled Trials and World Health Organization clinical trials registry center to identify relevant studies up to the end of October 2017. Data were analyzed using STATA. Besides, publication bias and meta-regression analysis were also conducted.

Results

We collected results from 5 articles for further analyses with 8,252 cases and 20,904 control. The normalized mtDNA copy number level is lower in cardiovascular disease (CVD) than the control groups with a pooled standard mean difference (SMD) of -0.36(95%CI,-0.65 to -0.08); The pooled odds ratio (OR) for CVD proportion associated with a 1-SD (standard deviation) decrease in mtDNA copy number level is 1.23 (95% CI,1.06–1.42); The OR for CVD patients with mtDNA copy number lower than median level is 1.88(95% CI,1.65–2.13); The OR for CVD patients with mtDNA copy number located in the lowest quartile part is 2.15(95% CI, 1.46–3.18); the OR between mtDNA copy number and the risk of sudden cardiac death (SCD) is 1.83(95% CI, 1.22–2.74).

Conclusion

Although inter-study variability, the overall performance test of mtDNA for evaluating CVD and SCD revealed that the mtDNA copy number presented the potential to be a biomarker for CVD and SCD prediction. Given that, the fewer copies of mtDNA, the higher the risk of CVD.

Metabolic remodeling in hypertrophied and failing myocardium: a review

The energy starvation hypothesis proposes that maladaptive metabolic remodeling antedates, initiates, and maintains adverse contractile dysfunction in heart failure (HF). Better understanding of the cardiac metabolic phenotype and metabolic signaling could help identify the role metabolic remodeling plays within HF and the conditions known to transition toward HF, including "pathological" hypertrophy. In this review, we discuss metabolic phenotype and metabolic signaling in the contexts of pathological hypertrophy and HF. We discuss the significance of alterations in energy supply (substrate utilization, oxidative capacity, and phosphotransfer) and energy sensing using observations from human and animal disease models and models of manipulated energy supply/sensing. We aim to provide ways of thinking about metabolic remodeling that center around metabolic flexibility, capacity (reserve), and efficiency rather than around particular substrate preferences or transcriptomic profiles. We show that maladaptive metabolic remodeling takes multiple forms across multiple energy-handling domains. We suggest that lack of metabolic flexibility and reserve (substrate, oxidative, and phosphotransfer) represents a final common denominator ultimately compromising efficiency and contractile reserve in stressful contexts.

Posttranslational modifications and dysfunction of mitochondrial enzymes in human heart failure

Deficiency of energy supply is a major complication contributing to the syndrome of heart failure (HF). Because the concurrent activity profile of mitochondrial bioenergetic enzymes has not been studied collectively in human HF, our aim was to examine the mitochondrial enzyme defects in left ventricular myocardium obtained from explanted end-stage failing hearts. Compared with nonfailing donor hearts, activity rates of complexes I and IV and the Krebs cycle enzymes isocitrate dehydrogenase, malate dehydrogenase, and aconitase were lower in HF, as determined spectrophotometrically. However, activity rates of complexes II and III and citrate synthase did not differ significantly between the two groups. Protein expression, determined by Western blotting, did not differ between the groups, implying posttranslational perturbation. In the face of diminished total glutathione and coenzyme Q10 levels, oxidative modification was explored as an underlying cause of enzyme dysfunction. Of the three oxidative modifications measured, protein carbonylation was increased significantly by 31% in HF (P < 0.01; n = 18), whereas levels of 4-hydroxynonenal and protein nitration, although elevated, did not differ. Isolation of complexes I and IV and F1FoATP synthase by immunocapture revealed that proteins containing iron-sulphur or heme redox centers were targets of oxidative modification. Energy deficiency in end-stage failing human left ventricle involves impaired activity of key electron transport chain and Krebs cycle enzymes without altered expression of protein levels. Augmented oxidative modification of crucial enzyme subunit structures implicates dysfunction due to diminished capacity for management of mitochondrial reactive oxygen species, thus contributing further to reduced bioenergetics in human HF.

Ketamine-induced ulcerative cystitis and bladder apoptosis involve oxidative stress mediated by mitochondria and the endoplasmic reticulum

Ketamine abusers develop severe lower urinary tract symptoms. The major aims of the present study were to elucidate ketamine-induced ulcerative cystitis and bladder apoptosis in association with oxidative stress mediated by mitochondria and the endoplasmic reticulum (ER). Sprague-Dawley rats were distributed into three different groups, which received normal saline or ketamine for a period of 14 or 28 days, respectively. Double-labeled immunofluorescence experiments were performed to investigate tight junction proteins for urothelial barrier functions. A TUNEL assay was performed to evaluate the distribution of apoptotic cells. Western blot analysis was carried out to examine the expressions of urothelial tight junction proteins, ER stress markers, and apoptosis-associated proteins. Antioxidant enzymes, including SOD and catalase, were investigated by real-time PCR and immunofluorescence experiments. Ketamine-treated rats were found to display bladder hyperactivity. This bladder dysfunction was accompanied by disruptions of epithelial cadherin- and tight junction-associated proteins as well as increases in the expressions of apoptosis-associated proteins, which displayed features of mitochondria-dependent apoptotic signals and ER stress markers. Meanwhile, expressions of mitochondria respiratory subunit enzymes were significantly increased in ketamine-treated bladders. Conversely, mRNA expressions of the antioxidant enzymes Mn-SOD (SOD2), Cu/Zn-SOD (SOD1), and catalase were decreased after 28 days of ketamine treatment. These results demonstrate that ketamine enhanced the generation of oxidative stress mediated by mitochondria- and ER-dependent pathways and consequently contributed to bladder apoptosis and urothelial lining defects. Such oxidative stress-enhanced bladder cell apoptosis and urothelial barrier defects are potential factors that may play a crucial role in bladder overactivity and ulceration.

Mitochondrial respiratory control and early defects of oxidative phosphorylation in the failing human heart

Heart failure is a consequence of progressive deterioration of cardiac performance. Little is known about the role of impaired oxidative phosphorylation in the progression of the disease, since previous studies of mitochondrial injuries are restricted to end-stage chronic heart failure. The present study aimed at evaluating the involvement of mitochondrial dysfunction in the development of human heart failure. We measured the control of oxidative phosphorylation with high-resolution respirometry in permeabilized myocardial fibres from donor hearts (controls), and patients with no or mild heart failure but presenting with heart disease, or chronic heart failure due to dilated or ischemic cardiomyopathy. The capacity of the phosphorylation system exerted a strong limitation on oxidative phosphorylation in the human heart, estimated at 121 pmol O(2)s(-1)mg(-1) in the healthy left ventricle. In heart disease, a specific defect of the phosphorylation system, Complex I-linked respiration, and mass-specific fatty acid oxidation were identified. These early defects were also significant in chronic heart failure, where the capacities of the oxidative phosphorylation and electron transfer systems per cardiac tissue mass were decreased with all tested substrate combinations, suggesting a decline of mitochondrial density. Oxidative phosphorylation and electron transfer system capacities were higher in ventricles compared to atria, but the impaired mitochondrial quality was identical in the four cardiac chambers of chronic heart failure patients. Coupling was preserved in heart disease and chronic heart failure, in contrast to the mitochondrial dysfunction observed after prolonged cold storage of cardiac tissue. Mitochondrial defects in the phosphorylation system, Complex I respiration and mass-specific fatty acid oxidation occurred early in the development of heart failure. Targeting these mitochondrial injuries with metabolic therapy may offer a promising approach to delay the progression of heart disease.

Ubiquinol–cytochrome-c reductase 7.2 kDa protein of mitochondrial complex III is steroid-responsive and increases in cardiac hypertrophy and hypertension

Women and men do not respond identically to cardiac insults; premenopausal women are somewhat protected from cardiovascular disease. Our objective was to isolate and characterize hormone-responsive genes in the heart. Differential display identified an estrogen-inducible fragment that was found to encode the ubiquinol–cytochrome-c reductase (UCCR) 7.2 kDa protein of the mitochondrial respiratory complex III. We found UCCR7.2 mRNA to be highly expressed in the heart, and this expression increased in hearts of 4-, 10-, and 28-week-old spontaneously hypertensive rats (SHR) compared with normotensive Wistar–Kyoto rats. Oral hydralazine treatment to reduce hypertension reduced SHR UCCR7.2 expression. Cardiac UCCR7.2 mRNA expression was also increased significantly after a 5/6 nephrectomy compared with mock surgery. Cardiac expression after ovariectomy was 50% that of intact rats. Supplementation of ovariectomized rats with estrogen had no effect, whereas progesterone increased cardiac expression, although not to intact levels. No change in cardiac UCCR7.2 expression was found when intact rats were treated with either tamoxifen or ICI 182780. Thus, UCCR7.2 expression is reduced in the absence of ovarian hormones, but is not directly regulated by estrogen in the heart. We conclude that UCCR7.2 is a steroid hormone-responsive gene in the heart, with expression increased in cardiac hypertrophy and in response to hypertension.

Atrial fibrillation is associated with accumulation of aging-related common type mitochondrial DNA deletion mutation in human atrial tissue

STUDY OBJECTIVE

Accumulation of somatic mutations of mitochondrial DNA (mtDNA) contributes to the aging process and progressive organ dysfunction. We investigated the mitochondrial DNA with 4977-base-pair mtDNA deletion mutation (mtDNA(4977)) in human atrial tissue and correlated the amount of mtDNA(4977) to clinical atrial fibrillation (AF).

METHODS AND RESULTS

Atrial tissue from the right atrial appendage was obtained in 88 patients during open-heart surgery (22 children/adolescents and 66 adults). The amount of mtDNA(4977) was measured using a nested polymerase chain reaction protocol and normalized to wild-type mtDNA. We found that the mtDNA(4977) was absent in all 22 pediatric/adolescent patients. In the adult group, the relative amount of mtDNA(4977) was significantly higher in patients with AF than in patients without AF (0.55 +/- 0.26 vs 0.35 +/- 0.29, p < 0.007) [mean +/- SD]. The amount of mtDNA(4977) was also positively associated with age (r = 0.29, p < 0.01). Left and right atrial pressures, left atrial dimension, hypertension, and cardiac diagnosis did not influence the amount of mtDNA(4977) significantly. Further multivariate analysis showed that both aging and AF contributed independently to the accumulation of mtDNA(4977).

CONCLUSION

AF is associated with an increase of mtDNA(4977). This change is similar to the aging process of atrial tissue and might contribute to atrial dysfunction in AF.

Electron transport chain defects in heart failure

In recent years, the possibility that disorders of cardiac metabolism play a role in the mechanisms that lead to ventricular dilatation and dysfunction in heart failure has attracted much attention. Electron transport chain is constituted by a series of multimeric protein complexes, located in the inner mitochondrial membranes, whose genes are distributed over both nuclear and mitochondrial DNA. Its normal function is essential to provide the energy for cardiac function. Many studies have described abnormalities in mitochondrial DNA genes encoding for electron transport chain (ETC) in dilated cardiomyopathies. In some cases, heart failure is one more or less relevant symptom among other multisystem manifestations characteristic of mitochondrial encephalomyopathies, being heart failure imputable to a primary mitochondrial disease. In the case of idiopathic dilated cardiomyopathies (IDC), many mitochondrial abnormalities have also been described using hystological, biochemical or molecular studies. The importance of such findings is under debate. The great variability in the mitochondrial abnormalities described has prompted the proposal that mitochondrial dysfunction could be a secondary phenomenon in IDC, and not a primary one. Among other possible explanations for such findings, the presence of an increased oxidative damage due to a free radical excess has been postulated. In this setting, the dysfunction of ETC could be a consequence, but also a cause of the presence of an increased free radical damage. Independently of its origin, ETC dysfunction may contribute to the persistence and worsening of heart failure. If this hypothesis, still to be proven, was certain, the modulation of cardiac metabolism could be an interesting approach to treat IDC. The precise mechanisms that lead to ventricular dilatation and dysfunction in heart failure are still nowadays poorly understood. Circumstances such as cytotoxic insults, viral infections, immune abnormalities, contractile protein defects, ischemic factors and familial conditions have been thoroughly investigated [1]. It is possible that several mechanisms combine to produce the clinical syndrome of heart failure. In recent years the possibility that disorders of energy metabolism, either isolated or in combination with the other aforementioned factors, may play a role in the development of heart failure in susceptible patients has attracted much attention. The present paper reviews the current knowledge on mitochondrial function in the failing myocardium. We restrain our discussion to heart failure where an impaired inotropic state leads to a weakened systolic contraction (i.e. the so-called systolic heart failure). Idiopathic dilated cardiomyopathy (IDC) is the prototype of the conditions under discussion. Other circumstances where a defect in myocardial contraction is due to a chronic excessive work load (i.e., hypertension, valvular or congenital heart diseases), and states in which the principal abnormality involves impaired relaxation of the ventricle (i.e. diastolic heart failure), as well as mitochondrial defects outside the electron transport chain (i.e., defects in Krebs cycle or beta-oxidation of fatty acids) are only approached circumstantially.

Myocardial carnitine and carnitine palmitoyltransferase deficiencies in patients with severe heart failure

We studied myocardial tissue from 25 cardiac transplant recipients, who had end-stage congestive heart failure (CHF), and from 21 control donor hearts. Concentrations of total carnitine (TC), free carnitine (FC), short-chain acylcarnitines, long-chain acylcarnitines (LCAC) as well as carnitine palmitoyltransferase (CPT) activities were measured in myocardial tissue homogenates and referred to the concentration of non-collagen protein. Compared to controls, the concentrations of TC and FC as well as total CPT activities were significantly lower in patients. LCAC levels and the LCAC to FC ratio values were significantly greater in patients than in controls. While the malonyl-CoA sensitive fraction of CPT, which represents CPT I activity, was similar in patients and controls, the residual CPT activity after inhibition by malonyl-CoA, representing CPT II activity, was significantly reduced in patients compared to controls. Moreover, the activity of CPT in the presence of Triton X-100, which also represents the activity of CPT II, was significantly lower in patients than in controls. Malonyl-CoA concentrations required for half-maximal inhibition of CPT activity were significantly greater in patients than in controls. There was a linear relationship between ejection fraction (EF) values and concentrations of TC, FC, or total CPT activities. Values for LCAC and the LCAC to FC ratio were inversely related to EF values. We conclude that failing heart shows decreased total CPT and CPT II activities and carnitine deficiency that may be related to ventricle function.

Exercise modulates antioxidant enzyme gene expression in rat myocardium and liver

Our previous studies have shown that exercise caused changes in the tissue activities of the antioxidant enzymes glutathione peroxidase, superoxide dismutase, and catalase in spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats. To determine whether the changes observed were due to changes in mRNA levels of the enzymes, levels of tissue mRNA were determined by quantitative RNase protection assay. Comparisons of tissue enzyme activities and mRNA levels in sedentary and exercised animals showed that, in some cases (e.g., glutathione peroxidase in SH and WKY myocardium), parallel changes in enzyme activity and mRNA levels occurred, whereas in other cases (e.g., catalase in SH and WKY liver), nonparallel changes were found. Exercise of hypertensive rats altered antioxidant enzyme mRNA levels to those seen in normotensive animals in some, but not all, cases. The results suggest that transcriptional control over changes in exercise-related antioxidant enzyme activities is operative in some cases, although in other cases posttranscriptional regulatory mechanisms may exist.

Is age a contributory factor of mitochondrial bioenergetic decline and DNA defects in idiopathic dilated cardiomyopathy?

While mitochondrial abnormalities are increasingly recognized in cardiac diseases including hypertrophic cardiomyopathy, their presence in idiopathic dilated cardiomyopathy and the role that age plays in their incidence and severity have yet not been assessed. Levels of cardiac respiratory enzyme activities and mitochondrial DNA (mtDNA) were examined in 55 subjects with idiopathic dilated cardiomyopathy divided into 3 age groups. Respiratory enzyme activity levels were significantly lower in 37 patients (67%) compared to age-matched controls and increased activity levels were noted in 9 (16%). Decreased activities were found in complex I (n = 11), III (n = 16), IV (n = 12) and V (n = 13), but not in II, the only respiratory complex entirely nuclear-encoded. No age-specific differences were found in the overall frequency of enzymatic abnormalities. However, older patients had significantly increased multiple enzyme activity defects as well as increases in abundance and frequency of the 7.4 kb deletion. In addition, 3 patients were noted with marked reduction in mtDNA levels. None of the pathogenic mtDNA mutations previously associated with hypertrophic cardiomyopathy were found, nor was there any relationship that could be established between levels of specific mtDNA deletions and enzyme activities. In summary, specific mitochondrial abnormalities are heterogenous and frequent in both adults and children with idiopathic dilated cardiomyopathy. Older patients are more likely to have mtDNA deletions and multiple enzyme activity defects. The molecular basis for these abnormalities remains undefined.