Emerging beneficial roles of sirtuins in heart failure

Microvascular Rarefaction and Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is characterized by diastolic dysfunction and is commonly seen in the elderly and diabetic and hypertensive patients. Despite its rising prevalence, the pathophysiology of HFpEF is poorly understood and its optimal treatment remains undefined. Recent clinical studies indicate that coronary microvascular rarefaction (reduced myocardial capillary density) with reduced coronary flow reserve (CFR) is a major contributor to diastolic dysfunction in HFpEF patients. On a molecular level, endothelial cells (EC) are dependent on glycolysis for supporting their functions and vascular homeostasis. Sirtuin 3 (SIRT3) has a critical role in the regulation of endothelial glycolytic metabolism and thus affects angiogenesis. Disruption of SIRT3-mediated EC metabolism and impairment of angiogenesis may promote cardiomyocyte hypoxia and myocardial fibrosis, leading to diastolic dysfunction and HFpEF. This review summarizes current knowledge of SIRT3 in EC metabolism, coronary microvascular rarefaction and HFpEF.

Current understanding and future perspectives of the roles of sirtuins in the reprogramming and differentiation of pluripotent stem cells

In mammalian cells, there are seven members of the sirtuin protein family (SIRT1-7). SIRT1, SIRT6, and SIRT7 catalyze posttranslational modification of proteins in the nucleus, SIRT3, SIRT4, and SIRT5 are in the mitochondria and SIRT2 is in the cytosol. SIRT1 can deacetylate the transcription factor SOX2 and regulate induced pluripotent stem cells (iPSCs) reprogramming through the miR-34a-SIRT1-p53 axis. SIRT2 can regulate the function of pluripotent stem cells through GSK3β. SIRT3 can positively regulate PPAR gamma coactivator 1-alpha (PGC-1α) expression during the differentiation of stem cells. SIRT4 has no direct role in regulating reprogramming but may have the potential to prevent senescence of somatic cells and to facilitate the reprogramming of iPSCs. SIRT5 can deacetylate STAT3, which is an important transcription factor in regulating pluripotency and differentiation of stem cells. SIRT6 can enhance the reprogramming efficiency of iPSCs from aged skin fibroblasts through miR-766 and increase the expression levels of the reprogramming genes including Sox2, Oct4, and Nanog through acetylation of histone H3 lysine 56. SIRT7 plays a regulatory role in the process of mesenchymal-to-epithelial transition (MET), which has been suggested to be a crucial process in the generation of iPSCs from fibroblasts. In this review, we summarize recent findings of the roles of sirtuins in the metabolic reprogramming and differentiation of stem cells and discuss the bidirectional changes in the gene expression and activities of sirtuins in the commitment of differentiation of mesenchymal stem cells (MSCs) and reprogramming of somatic cells to iPSCs, respectively. Thus, understanding the molecular basis of the interplay between different sirtuins and mitochondrial function will provide new insights into the regulation of differentiation of stem cells and iPSCs formation, respectively, and may help design effective stem cell therapies for regenerative medicine. Impact statement This is an extensive review of the recent advances in our understanding of the roles of some members of the sirtuins family, such as SIRT1, SIRT2, SIRT3, and SIRT6, in the regulation of intermediary metabolism during stem cell differentiation and in the reprogramming of somatic cells to form induced pluripotent stem cells (iPSCs). This article provides an updated integrated view on the mechanisms by which sirtuins-mediated posttranslational protein modifications regulate mitochondrial biogenesis, bioenergetics, and antioxidant defense in the maintenance and differentiation of stem cells and in iPSCs formation, respectively.

Cellular mechanisms promoting cachexia and how they are opposed by sirtuins 1

Many chronic diseases are associated with unintentional loss of body weight, which is termed "cachexia". Cachexia is a complex multifactorial syndrome associated with the underlying primary disease, and characterized by loss of skeletal muscle with or without loss of fat tissue. Patients with cachexia face dire symptoms like dyspnea, fatigue, edema, exercise intolerance, and low responsiveness to medical therapy, which worsen quality of life. Because cachexia is not a stand-alone disorder, treating primary disease - such as cancer - takes precedence for the physician, and it remains mostly a neglected illness. Existing clinical trials have demonstrated limited success mostly because of their monotherapeutic approach and late detection of the syndrome. To conquer cachexia, it is essential to identify as many molecular targets as possible using the latest technologies we have at our disposal. In this review, we have discussed different aspects of cachexia, which include various disease settings, active molecular pathways, and recent novel advances made in this field to understand consequences of this illness. We also discuss roles of the sirtuins, the NAD⁺-dependent lysine deacetylases, microRNAs, certain dietary options, and epigenetic drugs as potential approaches, which can be used to tackle cachexia as early as possible in its course.

MicroRNA 199a Is Downregulated in Patients After Coronary Artery Bypass Graft Surgery and Is Associated with Increased Levels of Sirtuin 1 (SIRT 1) Protein and Major Adverse Cardiovascular Events at 3-Year Follow-Up

Background

The cardioprotective protein SIRT1 is elevated in patients with coronary artery disease (CAD) to compensate for the disease-related adverse effects, but less is known about the prognostic role of SIRT 1 regulating microRNAs in patients after coronary artery bypass graft (CABG) surgery.

Material/Methods

The expression of the SIRT 1-specific microRNAs miR-199a and miR-195 was analyzed using real-time PCR in 68 patients referred for CABG surgery and 34 control patients undergoing heart valve surgery. In CABG patients, major adverse cardiac and cerebrovascular events (MACCEs), including all-cause death, myocardial infarction (MI), re-vascularization, heart failure symptoms ≥NYHA II, re-hospitalization for any cardiovascular reason, and stroke, were analyzed at a median follow-up (FU) of 3.2 years (range: 3.0–3.6).

Results

The level of miR-199a in patients with CAD was significantly reduced compared to the control group (relative expression: 0.89±0.49 vs. 1.90±0.90, p=0.001), while SIRT 1 protein was markedly enhanced (p<0.001). In patients undergoing CABG who had MACCEs, miR-199a was significantly lower compared to patients with an uneventful FU (0.71±0.25 vs. 0.98±0.53, p=0.007). Heart failure status, death, and total MACCEs rate were inversely correlated with the amount of miR-199a (p=0.039) at 3-year FU.

Conclusions

Altered expression of miR-199a in myocardial tissue was found to be associated with SIRT 1 upregulation in patients with CAD undergoing CABG and was associated with an increased MACCEs rate at mid-term follow-up.

Dihydromyricetin Attenuates Myocardial Hypertrophy Induced by Transverse Aortic Constriction via Oxidative Stress Inhibition and SIRT3 Pathway Enhancement

Dihydromyricetin (DMY), one of the flavonoids in vine tea, exerts several pharmacological actions. However, it is not clear whether DMY has a protective effect on pressure overload-induced myocardial hypertrophy. In the present study, male C57BL/6 mice aging 8⁻10 weeks were subjected to transverse aortic constriction (TAC) surgery after 2 weeks of DMY (250 mg/kg/day) intragastric administration. DMY was given for another 2 weeks after surgery. Blood pressure, myocardial structure, cardiomyocyte cross-sectional area, cardiac function, and cardiac index were observed. The level of oxidative stress in the myocardium was assessed with dihydroethidium staining. Our results showed that DMY had no significant effect on the blood pressure. DMY decreased inter ventricular septum and left ventricular posterior wall thickness, relative wall thickness, cardiomyocyte cross-sectional areas, as well as cardiac index after TAC. DMY pretreatment also significantly reduced arterial natriuretic peptide (ANP), brain natriuretic peptide (BNP) mRNA and protein expressions, decreased reactive oxygen species production and malondialdehyde (MDA) level, while increased total antioxidant capacity (T-AOC), activity of superoxide dismutase (SOD), expression of sirtuin 3 (SIRT3), forkhead-box-protein 3a (FOXO3a) and SOD2, and SIRT3 activity in the myocardium of mice after TAC. Taken together, DMY ameliorated TAC induced myocardial hypertrophy in mice related to oxidative stress inhibition and SIRT3 pathway enhancement.

Expression and genotype-dependent catalytic activity of N-acetyltransferase 2 (NAT2) in human peripheral blood mononuclear cells and its modulation by Sirtuin 1

N-acetyltransferase 2 (NAT2) catalyzes the biotransformation of numerous arylamine and hydrazine drugs and carcinogens. Genetic polymorphisms of NAT2 modify drug efficacy and toxicity and susceptibility to diseases such as cancer and type 2 diabetes. Expression of NAT2 has been documented in the liver and gastrointestinal tract but not in other tissues. Deacetylation of cytosolic proteins by sirtuins is a post-translational modification important in regulatory networks of diverse cellular processes. The aim of the present study was to investigate NAT2 expression in peripheral blood mononuclear cells (PBMC) and the effects of NAT2 genotype and Sirtuin 1 (SIRT1). Both NAT2 and SIRT1 proteins were expressed on PBMC. Their expression was more prevalent on CD3+ compared to CD19+ and CD56+ cell populations. N-acetylation capacity of PBMC exhibited a NAT2 gene-dose response toward the N-acetylation of isoniazid. Subjects with rapid NAT2 genotype showed an apparent V_max of 42.1 ± 2.4; intermediate NAT2 genotypes an apparent V_max of 22.6 ± 2.2; and slow acetylator NAT2 genotypes an apparent V_max of 19.9 ± 1.7 nM acetyl-isoniazid/24 h/million cells. The N-acetylation capacity of NAT2 in the presence of SIRT1 enhancer was significantly decreased (p < 0.001), conversely, the transient silencing of SIRT1 resulted in an increase of N-acetylation capacity (p < 0.001). These findings are the first report of NAT2 genotype-dependent expression on PBMC and post-translational modification by SIRT1. These findings constitute a substantial advance in our understanding of human N-acetyltransferase expression and a new much less invasive method for measurement of human NAT2 expression and phenotype.

Inhibition of prolyl hydroxylases alters cell metabolism and reverses pre-existing diastolic dysfunction in mice

BACKGROUND

Diastolic dysfunction is emerging as a leading cause of heart failure in aging population. Induction of hypoxia tolerance and reprogrammed cell metabolism have emerged as novel therapeutic strategies for the treatment of cardiovascular diseases.

METHODS AND RESULTS

In the present study, we showed that deletion of sirtuin 3 (SIRT3) resulted in a diastolic dysfunction together with a significant increase in the expression of prolyl hydroxylases (PHD) 1 and 2. We further investigated the involvement of PHD in the development of diastolic dysfunction by treating the 12-14 months old mice with a PHD inhibitor, dimethyloxalylglycine (DMOG) for 2 weeks. DMOG treatment increased the expression of hypoxia-inducible factor (HIF)-1α in the endothelium of coronary arteries. This was accompanied by a significant improvement of coronary flow reserve and diastolic function. Inhibition of PHD altered endothelial metabolism by increasing glycolysis and reducing oxygen consumption. Most importantly, treatment with DMOG completely reversed the pre-existing diastolic dysfunction in the endothelial-specific SIRT3 deficient mice.

CONCLUSIONS

Our findings demonstrate that inhibition of PHD and reprogrammed cell metabolism can reverse the pre-existed diastolic dysfunction in SIRT3 deficient mice. Our study provides a potential therapeutic strategy of induction of hypoxia tolerance for patients with diastolic dysfunction associated with coronary microvascular dysfunction, especially in the aging population with reduced SIRT3.

Emerging role of SIRT3 in endothelial metabolism, angiogenesis, and cardiovascular disease

Sirtuin 3 (SIRT3) a mitochondrial enzyme that plays an important role in energy homeostasis, cardiac remodeling, and heart failure (HF). The expression of SIRT3 declines with advanced age, cardiovascular, and metabolic diseases. Accumulating evidence suggests that SIRT3 plays a critical role in protecting the heart from cardiac hypertrophy, cardiac dysfunction associated with HF, and in the protection of cardiac cells from stress-mediated cell death. Clinical studies have demonstrated that HF with preserved ejection fraction (HFpEF) in patients present with abnormalities in coronary microcirculation related to endothelial dysfunction and coronary microvascular rarefaction. Although SIRT3-mediated regulation of mitochondrial homeostasis and heart function has been intensively investigated, the effect of SIRT3 on endothelial cell (EC) glycolytic metabolism and microvascular function has not been well studied. ECs utilize glycolysis for generating ATP rather than oxidative phosphorylation to maintain their normal functions and promote angiogenesis and EC-cardiomyocyte interactions. Emerging evidence indicates that SIRT3 is involved in the regulation of endothelial metabolism and angiogenesis and thus affects the development of cardiovascular diseases associated with aging. This review will discuss the current knowledge of SIRT3 and its functional role on endothelial metabolism, cardiac function, and cardiovascular diseases.

Cardiac and placental mitochondrial characterization in a rabbit model of intrauterine growth restriction

BACKGROUND

Intrauterine growth restriction (IUGR) is associated with cardiovascular remodeling persisting into adulthood. Mitochondrial bioenergetics, essential for embryonic development and cardiovascular function, are regulated by nuclear effectors as sirtuins. A rabbit model of IUGR and cardiovascular remodeling was generated, in which heart mitochondrial alterations were observed by microscopic and transcriptomic analysis. We aimed to evaluate if such alterations are translated at a functional mitochondrial level to establish the etiopathology and potential therapeutic targets for this obstetric complication.

METHODS

Hearts and placentas from 16 IUGR-offspring and 14 controls were included to characterize mitochondrial function.

RESULTS

Enzymatic activities of complexes II, IV and II + III in IUGR-hearts (-11.96 ± 3.16%; -15.58 ± 5.32%; -14.73 ± 4.37%; p < 0.05) and II and II + III in IUGR-placentas (-17.22 ± 3.46%; p < 0.005 and -29.64 ± 4.43%; p < 0.001) significantly decreased. This was accompanied by a not significant reduction in CI-stimulated oxygen consumption and significantly decreased complex II SDHB subunit expression in placenta (-44.12 ± 5.88%; p < 0.001). Levels of mitochondrial content, Coenzyme Q and cellular ATP were conserved. Lipid peroxidation significantly decreased in IUGR-hearts (-39.02 ± 4.35%; p < 0.001), but not significantly increased in IUGR-placentas. Sirtuin3 protein expression significantly increased in IUGR-hearts (84.21 ± 31.58%; p < 0.05) despite conserved anti-oxidant SOD2 protein expression and activity in both tissues.

CONCLUSIONS

IUGR is associated with cardiac and placental mitochondrial CII dysfunction. Up-regulated expression of Sirtuin3 may explain attenuation of cardiac oxidative damage and preserved ATP levels under CII deficiency.

GENERAL SIGNIFICANCE

These findings may allow the design of dietary interventions to modulate Sirtuin3 expression and consequent regulation of mitochondrial imbalance associated with IUGR and derived cardiovascular remodeling.

MicroRNA-34a regulates doxorubicin-induced cardiotoxicity in rat

New strategies to prevent and early detect the cardiotoxic effects of the anticancer drug doxorubicin (DOXO) are required. MicroRNAs emerged as potential diagnostic, therapeutic and prognostic approaches in cardiovascular diseases. MiR-34a has a role in cardiac dysfunction and ageing and is involved in several cellular processes associated with DOXO cardiotoxicity. Our in vitro and in vivo results indicated that after DOXO exposure the levels of miR-34a are enhanced in cardiac cells, including Cardiac Progenitor Cells (CPCs). Since one of the determining event responsible for the initiation and evolution of the DOXO toxicity arises at the level of the CPC compartment, we evaluated if miR-34a pharmacological inhibition in these cells ameliorates the detrimental aftermath of the drug. AntimiR-34a has beneficial consequences on vitality, proliferation, apoptosis and senescence of DOXO-treated rat CPC. These effects are mediated by an increase of prosurvival miR-34a targets Bcl-2 and SIRT1, accompanied by a decrease of acetylated-p53 and p16^INK4a. Importantly, miR-34a silencing also reduces the release of this miRNA from DOXO-exposed rCPCs, decreasing its negative paracrine effects on other rat cardiac cells. In conclusion, the silencing of miR-34a could represent a future therapeutic option for cardioprotection in DOXO toxicity and at the same time, it could be considered as a circulating biomarker for anthracycline-induced cardiac damage.

Melatonin Modulation of Sirtuin-1 Attenuates Liver Injury in a Hypercholesterolemic Mouse Model

Hypercholesterolemia increases and exacerbates stress signals leading also to liver damage (LD) and failure. Sirtuin1 (SIRT1) is involved in lifespan extension and it plays an essential role in hepatic lipid metabolism. However, its involvement in liver hypercholesterolemic damage is not yet completely defined. This in vivo study evaluated the role of SIRT1 in the hypercholesterolemic-related LD and, then, investigated how oral supplementation of melatonin, pleiotropic indoleamine, may be protective. Control mice and apolipoprotein E-deficient mice (ApoE^−/−) of 6 and 15 weeks of age were treated or not treated with melatonin at the dose of 10 mg/kg/day for 9 weeks. In this study, we evaluated serum biochemical markers, liver SIRT1 expression, and oxidative stress markers. We observed that hypercholesterolemia increased significantly serum cholesterol and triglycerides, reduced significantly liver SIRT1, and, in turn, induced hepatic oxidative stress in untreated ApoE^−/− mice with respect to control mice. Interestingly, melatonin treatment improved serum biochemical markers and hepatic morphological impairment and inhibited oxidative stress through its antioxidant properties and also by SIRT1 upregulation. In summary, melatonin oral supplementation may represent a new protective approach to block hypercholesterolemic liver alterations involving also a SIRT1-dependent mechanism.

MicroRNA-195 Regulates Metabolism in Failing Myocardium Via Alterations in Sirtuin 3 Expression and Mitochondrial Protein Acetylation

BACKGROUND

Heart failure leads to mitochondrial dysfunction and metabolic abnormalities of the failing myocardium coupled with an energy-depleted state and cardiac remodeling. The mitochondrial deacetylase sirtuin 3 (SIRT3) plays a pivotal role in the maintenance of mitochondrial function through regulating the mitochondrial acetylome. It is interesting to note that unique cardiac and systemic microRNAs have been shown to play an important role in cardiac remodeling by modulating key signaling elements in the myocardium.

METHODS

Cellular signaling was analyzed in human cardiomyocyte-like AC16 cells, and acetylation levels in rodent models of SIRT3^-/-and transgenic microRNA-195 (miR-195) overexpression were compared with wild type. Luciferase assays, Western blotting, immunoprecipitation assays, and echocardiographic analysis were performed. Enzymatic activities of pyruvate dehydrogenase (PDH) and ATP synthase were measured.

RESULTS

In failing human myocardium, we observed induction of miR-195 along with decreased expression of the mitochondrial deacetylase SIRT3 that was associated with increased global protein acetylation. We further investigated the role of miR-195 in SIRT3-mediated metabolic processes and its impact on regulating enzymes involved in deacetylation. Proteomic analysis of the total acetylome showed increased overall acetylation, and specific lysine acetylation of 2 central mitochondrial metabolic enzymes, PDH and ATP synthase, as well. miR-195 downregulates SIRT3 expression through direct 3'-untranslated region targeting. Treatments with either sirtuin inhibitor nicotinamide, small interfering RNA-mediated SIRT3 knockdown or miR-195 overexpression enhanced acetylation of PDH complex and ATP synthase. This effect diminished PDH and ATP synthase activity and impaired mitochondrial respiration.SIRT3^-/- and miR-195 transgenic mice consistently showed enhanced global protein acetylation, including PDH complex and ATP synthase, associated with decreased enzymatic activity.

CONCLUSIONS

Altogether, these data suggest that increased levels of miR-195 in failing myocardium regulate a novel pathway that involves direct SIRT3 suppression and enzymatic inhibition via increased acetylation of PDH and ATP synthase that are essential for cardiac energy metabolism.

Curcumin elevates sirtuin level but does not postpone in vitro senescence of human cells building the vasculature

It is believed that curcumin, a component of the turmeric that belongs to hormetins, possesses anti-aging propensity. This property of curcumin can be partially explained by its influence on the level of sirtuins. Previously, we have shown that relatively high (2.5-10 µM) doses of curcumin induce senescence of cancer cells and cells building the vasculature. In the present study we examined whether curcumin at low doses (0.1 and 1 µM) is able to delay cell senescence and upregulate the level of sirtuins in human cells building the vasculature, namely vascular smooth muscle (VSMC) and endothelial (EC) cells. To this end we used cells senescing in a replicative and premature manner. We showed that low doses of curcumin in case of VSMC neither postponed the replicative senescence nor protected from premature senescence induced by doxorubicin. Moreover, curcumin slightly accelerated replicative senescence of EC. Despite some fluctuations, a clear increasing tendency in the level of sirtuins was observed in curcumin-treated young, senescing or already senescent cells. Sirtuin activation could be caused by the activation of AMPK resulting from superoxide elevation and ATP reduction. Our results show that curcumin at low doses can increase the level of sirtuins without delaying senescence of VSMC.

Histone deacetylase adaptation in single ventricle heart disease and a young animal model of right ventricular hypertrophy

BackgroundHistone deacetylase (HDAC) inhibitors are promising therapeutics for various forms of cardiac diseases. The purpose of this study was to assess cardiac HDAC catalytic activity and expression in children with single ventricle (SV) heart disease of right ventricular morphology, as well as in a rodent model of right ventricular hypertrophy (RVH).MethodsHomogenates of right ventricle (RV) explants from non-failing controls and children born with a SV were assayed for HDAC catalytic activity and HDAC isoform expression. Postnatal 1-day-old rat pups were placed in hypoxic conditions, and echocardiographic analysis, gene expression, HDAC catalytic activity, and isoform expression studies of the RV were performed.ResultsClass I, IIa, and IIb HDAC catalytic activity and protein expression were elevated in the hearts of children born with a SV. Hypoxic neonatal rats demonstrated RVH, abnormal gene expression, elevated class I and class IIb HDAC catalytic activity, and protein expression in the RV compared with those in the control.ConclusionsThese data suggest that myocardial HDAC adaptations occur in the SV heart and could represent a novel therapeutic target. Although further characterization of the hypoxic neonatal rat is needed, this animal model may be suitable for preclinical investigations of pediatric RV disease and could serve as a useful model for future mechanistic studies.

Endothelial specific SIRT3 deletion impairs glycolysis and angiogenesis and causes diastolic dysfunction

Endothelial glycolysis plays a critical role in the regulation of angiogenesis. We investigated the role of Sirtuin 3 (SIRT3) on endothelial cell (EC) glycolytic metabolism, angiogenesis, and diastolic function. Our aim was to test the hypothesis that loss of SIRT3 in ECs impairs endothelial glycolytic metabolism and angiogenesis and contributes to myocardial capillary rarefaction and the development of diastolic dysfunction. Using SIRT3 deficient ECs, SIRT3 was found to regulate a metabolic switch between mitochondrial respiration and glycolysis. SIRT3 knockout (KO)-ECs exhibited higher mitochondrial respiration and reactive oxygen species (ROS) formation. SIRT3 knockout (KO)-ECs exhibited a reduction in the expression of glycolytic enzyme, PFKFB3, and a fall in glycolysis and angiogenesis. Blockade of PFKFB3 reduced glycolysis and downregulated expression of VEGF and Angiopoietin-1 (Ang-1) in ECs. Deletion of SIRT3 in ECs also impaired hypoxia-induced expression of HIF-2α, VEGF, and Ang-1, as well as reduced angiogenesis. In vivo, endothelial-specific SIRT3 KO (ECKO) mice exhibited a myocardial capillary rarefaction together with a reduced coronary flow reserve (CFR) and diastolic dysfunction. Histologic study further demonstrated that knockout of SIRT3 in ECs significantly increased perivascular fibrosis in the coronary artery. These results implicate a role of SIRT3 in modulating endothelial function and cardiac function. Ablation of SIRT3 leads to impairment of EC glycolytic metabolism and angiogenic signaling, which may contribute to coronary microvascular rarefaction and diastolic dysfunction in SIRT3 ECKO mice.

NLRP3-inflammasome inhibition prevents high fat and high sugar diets-induced heart damage through autophagy induction

The NLRP3-inflammasome complex has emerged as an important component of inflammatory processes in metabolic dysfunction induced by high-caloric diets. In this study, we investigate the molecular mechanisms by which NLRP3 inhibition may attenuate diet-induced cardiac injury. Here we show the cardiac damage induced by high sugar diet (HSD), high fat diet (HFD) or high sugar/fat diet (HSFD) over 15 weeks. Genetic ablation of NLRP3 protected against this damage by autophagy induction and apoptotic control. Furthermore, NLRP3 inhibition by the selective small molecule MCC950 resulted in similar autophagy induction and apoptotic control in hearts after diets. These data were reproduced in THP-1 cells treated with MCC950 and cultured in media supplemented with serum from mice dosed with MCC950 and fed with diets. NLRP3 inhibition exerted beneficial metabolic, and autophagic adaptations in hearts from obesogenic diets. The inhibition of NLRP3 activation may hold promise in the treatment of metabolic and cardiovascular diseases.

Altered glycometabolism in zebrafish exposed to thifluzamide

Thifluzamide exerts toxic effects to zebrafish and causes liver mitochondrial damage. To better understand the further mechanism, adult zebrafish were exposed to a range of thifluzamide concentrations (0, 0.019, 0.19, and 1.90 mg/L) for 28 days. In response to 1.90 mg/L exposure, liver glycogen significantly increased and blood glucose decreased. The expression of genes related to glycometabolism showed corresponding changes. Genes related to mtDNA replication and transcription and genes participating in mitochondrial complexes showed altered expression, which might lead to the inhibition of the tricarboxylic acid cycle (TCA). Additionally, the activity of glucose-6-phosphate dehydrogenase (G6PDH) was markedly increased at 1.90 mg/L, which might result in the activation of the pentose phosphate pathway. Moreover, the activity of lactate dehydrogenase (LDH) was significantly reduced at 1.90 mg/L, which might indicate that anaerobic glycolysis was inhibited. This study suggests that the altered gene expression and enzyme activities might be responsible for changes in glycometabolism, as evidenced by the altered expression of glycometabolism-related genes, the increased amount of glycogen in the liver and the decreased blood glucose levels. Overall, thifluzamide caused dysfunctional glycometabolism and led to events that might contribute to various thifluzamide-induced abnormalities in zebrafish.

Berberine-induced cardioprotection and Sirt3 modulation in doxorubicin-treated H9c2 cardiomyoblasts

Doxorubicin (DOX) is one of the most widely used anti-neoplastic agents. However, treatment with DOX is associated with cumulative cardiotoxicity inducing progressive cardiomyocyte death. Sirtuin 3 (Sirt3), a mitochondrial deacetylase, regulates the activity of proteins involved in apoptosis, autophagy and metabolism. Our hypothesis is that pharmacological modulation by berberine (BER) pre-conditioning of Sirt3 protein levels decreases DOX-induced cardiotoxicity. Our results showed that DOX induces cell death in all experimental groups. Increase in Sirt3 content by transfection-mediated overexpression decreased DOX cytotoxicity, mostly by maintaining mitochondrial network integrity and reducing oxidative stress. p53 was upregulated by DOX, and appeared to be a direct target of Sirt3, suggesting that Sirt3-mediated protection against cell death could be related to this protein. BER pre-treatment increased Sirt3 and Sirt1 protein levels in the presence of DOX and inhibited DOX-induced caspase 9 and 3-like activation. Moreover, BER modulated autophagy in DOX-treated H9c2 cardiomyoblasts. Interestingly, mitochondrial biogenesis markers were upregulated in in BER/DOX-treated cells. Sirt3 over-expression contributes to decrease DOX cytotoxicity on H9c2 cardiomyoblasts, while BER can be used as a modulator of Sirtuin function and cell quality control pathways to decrease DOX toxicity.

Suppression of miR-34a Expression in the Myocardium Protects Against Ischemia-Reperfusion Injury Through SIRT1 Protective Pathway

MicroRNA-34a (miR-34a) is expressed in the myocardium and expression is altered after myocardial injury. We investigated the effects of miR-34a on heart function after ischemia-reperfusion (IR) injury. Cardiomyocytes were isolated from neonatal rat hearts and simulated IR injury was induced in vitro. Following IR injury in rats, infarct size was measured and left ventricular (LV) function was evaluated using echocardiography. Protein expression of silent information regulator 1 (SIRT1), acetylated p53 (ac-p53), Bcl-2 and Bax, and miR-34a and SIRT1 gene levels were analyzed. miR-34a overexpression exacerbated myocardial injury by increasing apoptosis and infarct size and decreasing LV function. Suppression of miR-34a attenuated myocardial IR injury. SIRT1 was negatively regulated by miR-34a and the expression of downstream genes, such as ac-p53, Bcl-2, and Bax were altered correspondingly. Increased expression of miR-34a aggravates injury after IR; miR-34a suppression therapy may represent a new line of treatment for myocardial IR injury.

Hydrogen sulfide pretreatment improves mitochondrial function in myocardial hypertrophy via a SIRT3-dependent manner

BACKGROUND AND PURPOSE

Hydrogen sulfide (H₂ S) is a gaseous signal molecule with antioxidative properties. Sirtuin 3 (SIRT3) is closely associated with mitochondrial function and oxidative stress. The study was to investigate whether and how H₂ S improved myocardial hypertrophy via a SIRT3-dependent manner.

EXPERIMENTAL APPROACH

Neonatal rat cardiomyocytes were pretreated with NaHS (50 μM) for 4 h followed by angiotensin II (Ang II, 100 nM) for 24 h. SIRT3 was silenced with siRNA technology. SIRT3 promoter activity and expression, cell surface, hypertrophic gene mRNA expression, mitochondrial oxygen consumption rate and membrane potential were measured. Male 129S1/SvImJ [wild-type (WT)] and SIRT3 knockout (KO) mice were injected with NaHS (50 μmol·kg^-1 ·day^-1 ; i.p.) followed by transverse aortic constriction (TAC). Echocardiography, heart mass, mitochondrial ultrastructure, volume and number, oxidative stress, mitochondria fusion and fission-related protein expression were measured.

KEY RESULTS

In vitro, NaHS increased SIRT3 promoter activity and SIRT3 expression in Ang II-induced cardiomyocyte hypertrophy. SIRT3 silencing abolished the ability of NaHS to reverse the Ang II-induced cardiomyocyte hypertrophy, mitochondrial function impairment and permeability potential dysfunction, along with the decline in FOXO3a and SOD2 expression. In vivo, after TAC. NaHS attenuated myocardial hypertrophy, inhibited oxidative stress, improved mitochondrial ultrastructure, suppressed mitochondrial volume but increased mitochondrial numbers, enhanced OPA1, MFN1 and MFN2 expression but suppressed DRP1 and FIS1 expression in WT mice but not in SIRT3 KO mice CONCLUSION AND IMPLICATIONS: NaHS improved mitochondrial function and inhibited oxidative stress in myocardial hypertrophy in a SIRT3-dependent manner.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Cardioprotective Effects of SIRT6 in a Mouse Model of Transverse Aortic Constriction-Induced Heart Failure

SIRT6, a member of the NAD (+)-dependent class III deacetylase sirtuin family, plays important roles in the maintenance of cardiovascular homeostasis. Telomere shortening is a risk factor for age-associated diseases, including heart disease. In the present study, we investigated the role of SIRT6 and telomerase in a mouse model of transverse aortic constriction (TAC)-induced heart failure. SIRT6, telomerase reverse transcriptase (TERT), and telomere repeat binding factor (TRF)-1 were significantly downregulated in TAC mice compared with their expression in sham-operated mice. Lentiviral vector-mediated overexpression of SIRT6 upregulated TERT and TRF1 and increased the survival of mice after TAC. Echocardiography and hemodynamic measurements as well as histological analyses indicated that SIRT6 overexpression attenuated TAC-induced heart dysfunction and decreased TAC-induced cardiac inflammatory responses, reducing cardiac fibrosis and decreasing infarct size. Taken together, our findings indicate that SIRT6 protects the myocardium against damage and this effect may be mediated by the modulation of telomeres. Our findings linking SIRT6 and telomere integrity in the heart warrant further investigation into the underlying mechanisms and support SIRT6 as a promising therapeutic target for the treatment of cardiovascular diseases.

Modification of mitochondrial function, cytoplasmic lipid content and cryosensitivity of bovine embryos by resveratrol

Resveratrol is a potent activator of NAD-dependent deacetyltransferase sirtuin-1 (SIRT1) and affects lipid metabolism and ATP generation in somatic cells. In the present study, the effects of supplementing culture medium with resveratrol on lipid metabolism, ATP generation, and cryosensitivity of bovine in vitro produced embryos were investigated. Bovine early cleaved-stage embryos were cultured in medium containing 0 or 0.5 µM resveratrol for 1 or 5 days. Resveratrol treatment for both 1 day and 5 days increased the expression levels of SIRT1 and phosphorylated AMP-activated protein kinase (pAMPK) in the embryos. Furthermore, resveratrol treatment was effective to increase ATP generation and reduce lipid content of the embryos. The effects of resveratrol treatment were diminished by the SIRT1 inhibitor “EX527”, and the reduced lipid content was reversed by treatment with etomoxir (a potent inhibitor of beta-oxidation). Blastocysts developed after resveratrol treatment showed low levels reactive oxygen species and increased cryotolerance. These results demonstrate that resveratrol improves in vitro development of bovine embryos, while reducing cytoplasmic lipid content through activation of beta-oxidation, thereby effective for production of bovine blastocysts with enhanced cryotolerance.

Platycodon grandiflorum (PG) reverses angiotensin II-induced apoptosis by repressing IGF-IIR expression

ETHNOPHARMACOLOGICAL RELEVANCE

Platycodon grandiflorum (PG) is a Chinese medical plant used for decades as a traditional prescription to eliminate phlegm, relieve cough, reduce inflammation and lower blood pressure. PG also has a significant effect on the cardiovascular systems.

MATERIALS AND METHODS

The aqueous extract of Platycodon grandiflorum (JACQ.) A. DC. root was screened for inhibiting Ang II-induced IGF-IIR activation and apoptosis pathway in H9c2 cardiomyocytes. The effects were also studied in spontaneously hypertensive rats (five groups, n=5) using low and high doses of PG for 50 days. The Ang II-induced IGF-IIR activation was analyzed by luciferase reporter, RT-PCR, western blot and surface IGF-IIR expression assay. Furthermore, the major active constituent of PG was carried out by high performance liquid chromatography-mass spectrometry (HPLC-MS).

RESULTS

Our results indicate that a crude extract of PG significantly suppresses the Ang II-induced IGF-IIR signaling pathway to prevent cardiomyocyte apoptosis. PG extract inhibits Ang II-mediated JNK activation and SIRT1 degradation to reduce IGF-IIR activity. Moreover, PG maintains SIRT1 stability to enhance HSF1-mediated IGF-IIR suppression, which prevents cardiomyocyte apoptosis. In animal models, the administration of PG markedly reduced this apoptotic pathway in the heart of SHRs.

CONCLUSION

Taken together, PG may be considered as an effective treatment for cardiac diseases in hypertensive patients.

Mitochondrial dysfunction and oxidative stress in metabolic disorders - A step towards mitochondria based therapeutic strategies

Mitochondria are the powerhouses of the cell and are involved in essential functions of the cell, including ATP production, intracellular Ca2+ regulation, reactive oxygen species production & scavenging, regulation of apoptotic cell death and activation of the caspase family of proteases. Mitochondrial dysfunction and oxidative stress are largely involved in aging, cancer, age-related neurodegenerative and metabolic syndrome. In the last decade, tremendous progress has been made in understanding mitochondrial structure, function and their physiology in metabolic syndromes such as diabetes, obesity, stroke and hypertension, and heart disease. Further, progress has also been made in developing therapeutic strategies, including lifestyle interventions (healthy diet and regular exercise), pharmacological strategies and mitochondria-targeted approaches. These strategies were mainly focused to reduce mitochondrial dysfunction and oxidative stress and to maintain mitochondrial quality in metabolic syndromes. The purpose of our article is to highlight the recent progress on the mitochondrial role in metabolic syndromes and also summarize the progress of mitochondria-targeted molecules as therapeutic targets to treat metabolic syndromes. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

The anti-ageing molecule sirt1 mediates beneficial effects of cardiac rehabilitation

Background

An exercise-based Cardiac Rehabilitation Programme (CRP) is established as adjuvant therapy in heart failure (HF), nevertheless it is underutilized, especially in the elderly. While the functional and hemodynamic effects of CRP are well known, its underlying molecular mechanisms have not been fully clarified. The present study aims to evaluate the effects of a well-structured 4-week CRP in patients with stable HF from a molecular point of view.

Results

A prospective longitudinal observational study was conducted on patients consecutively admitted to cardiac rehabilitation. In fifty elderly HF patients with preserved ejection fraction (HFpEF), levels of sirtuin 1 (Sirt1) in peripheral blood mononuclear cells (PBMCs) and of its targets, the antioxidants catalase (Cat) and superoxide dismutase (SOD) in serum were measured before (Patients, P) and at the end of the CRP (Rehabilitated Patients, RP), showing a rise of their activities after rehabilitation.

Endothelial cells (ECs) were conditioned with serum from P and RP, and oxidative stress was induced using hydrogen peroxide. An increase of Sirt1 and Cat activity was detected in RP-conditioned ECs in both the absence and presence of oxidative stress, together with a decrease of senescence, an effect not observed during Sirt1 and Cat inhibition.

Conclusions

In addition to the improvement in functional and hemodynamic parameters, a supervised exercise-based CRP increases Sirt1 activity and stimulates a systemic antioxidant defence in elderly HFpEF patients. Moreover, CRP produces antioxidant and anti-senescent effects in human endothelial cells mediated, at least in part, by Sirt1 and its target Cat.

Sirtuin1 protects endothelial Caveolin-1 expression and preserves endothelial function via suppressing miR-204 and endoplasmic reticulum stress

Sirtuin1 (Sirt1) is a class III histone deacetylase that regulates a variety of physiological processes, including endothelial function. Caveolin1 (Cav1) is also an important determinant of endothelial function. We asked if Sirt1 governs endothelial Cav1 and endothelial function by regulating miR-204 expression and endoplasmic reticulum (ER) stress. Knockdown of Sirt1 in endothelial cells, and in vivo deletion of endothelial Sirt1, induced endothelial ER stress and miR-204 expression, reduced Cav1, and impaired endothelium-dependent vasorelaxation. All of these effects were reversed by a miR-204 inhibitor (miR-204 I) or with overexpression of Cav1. A miR-204 mimic (miR-204 M) decreased Cav1 in endothelial cells. In addition, high-fat diet (HFD) feeding induced vascular miR-204 and reduced endothelial Cav1. MiR-204-I protected against HFD-induced downregulation of endothelial Cav1. Moreover, pharmacologic induction of ER stress with tunicamycin downregulated endothelial Cav1 and impaired endothelium-dependent vasorelaxation that was rescued by overexpressing Cav1. In conclusion, Sirt1 preserves Cav1-dependent endothelial function by mitigating miR-204-mediated vascular ER stress.

Therapeutic Strategies for Mitochondrial Dysfunction and Oxidative Stress in Age-Related Metabolic Disorders

Mitochondria are complex, intercellular organelles present in the cells and are involved in multiple roles including ATP formation, free radicals generation and scavenging, calcium homeostasis, cellular differentiation, and cell death. Many studies depicted the involvement of mitochondrial dysfunction and oxidative damage in aging and pathogenesis of age-related metabolic disorders and neurodegenerative diseases. Remarkable advancements have been made in understanding the structure, function, and physiology of mitochondria in metabolic disorders such as diabetes, obesity, cardiovascular diseases, and stroke. Further, much progress has been done in the improvement of therapeutic strategies, including lifestyle interventions, pharmacological, and mitochondria-targeted therapeutic approaches. These strategies were mainly focused to reduce the mitochondrial dysfunction caused by oxidative stress and to retain the mitochondrial health in various diseases. In this chapter, we have highlighted the involvement of mitochondrial dysfunction in the pathophysiology of various disorders and recent progress in the development of mitochondria-targeted molecules as therapeutic measures for metabolic disorders.

Function of the SIRT3 mitochondrial deacetylase in cellular physiology, cancer, and neurodegenerative disease

In mammals, seven members of the sirtuin protein family known as class III histone deacetylase have been identified for their characteristic features. These distinguished characteristics include the tissues where they are distributed or located, enzymatic activities, molecular functions, and involvement in diseases. Among the sirtuin members, SIRT3 has received much attention for its role in cancer genetics, aging, neurodegenerative disease, and stress resistance. SIRT3 controls energy demand during stress conditions such as fasting and exercise as well as metabolism through the deacetylation and acetylation of mitochondrial enzymes. SIRT3 is well known for its ability to eliminate reactive oxygen species and to prevent the development of cancerous cells or apoptosis. This review article provides a comprehensive review on numerous (noteworthy) molecular functions of SIRT3 and its effect on cancer cells and various diseases including Huntington's disease, amyotrophic lateral sclerosis, and Alzheimer's disease.

Resveratrol

Cardiovascular disease (CVD) is the leading cause of death in both men and women and has largely been attributed to genetic makeup and lifestyle factors. However, genetic regulation does not fully explain the pathophysiology. Recently, epigenetic regulation, the regulation of the genetic code by modifications that affect the transcription and translation of target genes, has been shown to be important. Silent information regulator-2 proteins or sirtuins are an epigenetic regulator family of class III histone deacetylases (HDACs), unique in their dependency on coenzyme NAD+, that are postulated to mediate the beneficial effects of calorie restriction, thus promoting longevity by reducing the incidence of chronic diseases such as cancer, diabetes, and CVD. Emerging evidence shows that SIRT1 is ubiquitously expressed throughout the body. Resveratrol, a plant polyphenol, has cardioprotective effects and its mechanism of action is attributed to regulation of SIRT1. Incoproation of resveratrol into the diet may be a powerful therapeutic option for the prevention and treatment of CVD.

Sirtuins in metabolism, DNA repair and cancer

The mammalian sirtuin family has attracted tremendous attention over the past few years as stress adaptors and post-translational modifier. They have involved in diverse cellular processes including DNA repair, energy metabolism, and tumorigenesis. Notably, genomic instability and metabolic reprogramming are two of characteristic hallmarks in cancer. In this review, we summarize current knowledge on the functions of sirtuins mainly regarding DNA repair and energy metabolism, and further discuss the implication of sirtuins in cancer specifically by regulating genome integrity and cancer-related metabolism.

The role of mitochondrial sirtuins in health and disease

Mitochondria play a critical role in energy production, cell signalling and cell survival. Defects in mitochondrial function contribute to the ageing process and ageing-related disorders such as metabolic disease, cancer, and neurodegeneration. The sirtuin family of deacylase enzymes have a variety of subcellular localisations and have been found to remove a growing list of post-translational acyl modifications from target proteins. SIRT3, SIRT4, and SIRT5 are found primarily located in the mitochondria, and are involved in many of the key processes of this organelle. SIRT3 has been the subject of intense research and is primarily a deacetylase thought to function as a mitochondrial fidelity protein, with roles in mitochondrial substrate metabolism, protection against oxidative stress, and cell survival pathways. Less is known about the functional targets of SIRT4, which has deacetylase, ADP-ribosylase, and a newly-described lipoamidase function, although key roles in lipid and glutamine metabolism have been reported. SIRT5 modulates a host of newly-discovered acyl modifications including succinylation, malonylation, and glutarylation in both mitochondrial and extra-mitochondrial compartments, however the functional significance of SIRT5 in the regulation of many of its proposed target proteins remains to be discovered. Because of their influence on a broad range of pathways, SIRT3, SIRT4, and SIRT5 are implicated in a range of disease-states including metabolic disease such as diabetes, neurodegenerative diseases, cancer, and ageing-related disorders such as hearing-loss and cardiac dysfunction. We review the current knowledge on the function of the three mitochondrial sirtuins, their role in disease, and the current outstanding questions in the field.

Anthocyanin Attenuates Doxorubicin-Induced Cardiomyotoxicity via Estrogen Receptor-α/β and Stabilizes HSF1 to Inhibit the IGF-IIR Apoptotic Pathway

Doxorubicin (Dox) is extensively used for chemotherapy in different types of cancer, but its use is limited to because of its cardiotoxicity. Our previous studies found that doxorubicin-induced insulin-like growth factor II receptor (IGF-IIR) accumulation causes cardiomyocytes apoptosis via down-regulation of HSF1 pathway. In these studies, we demonstrated a new mechanism through which anthocyanin protects cardiomyoblast cells against doxorubicin-induced injury. We found that anthocyanin decreased IGF-IIR expression via estrogen receptors and stabilized heat shock factor 1 (HSF1) to inhibit caspase 3 activation and apoptosis of cardiomyocytes. Therefore, the phytoestrogen from plants has been considered as another potential treatment for heart failure. It has been reported that the natural compound anthocyanin (ACN) has the ability to reduce the risk of cardiovascular disease (CVD). Here, we demonstrated that anthocyanin acts as a cardioprotective drug against doxorubicin-induced heart failure by attenuating cardiac apoptosis via estrogen receptors to stabilize HSF1 expression and down-regulated IGF-IIR-induced cardiomyocyte apoptosis.

MicroRNAs in heart failure: Non-coding regulators of metabolic function

Heart failure (HF) is the inability of the heart to provide sufficient cardiac output for the energy demands of the body. Over the last decades, our understanding of the role of microRNAs (miRNAs), a class of small non-coding RNA regulators of gene expression at the post-transcriptional level, in cardiovascular diseases has expanded at a rapid rate. Importantly, multiple miRNAs have been specifically implicated in the progression of HF. Growing evidence suggests that miRNAs regulate central metabolic pathways and thus are highly implicated in the maintenance of energy homeostasis. In this review, we highlight recent discoveries of the mechanistic role of miRNAs in regulating metabolic functions in HF, with specific focus on the implication of miRNAs in metabolic rearrangements, discuss the potential value of miRNA profiles as novel HF biomarkers, and summarize the recent investigations on therapeutic approaches using miRNAs in heart disease. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Epigenetic regulation in heart failure: part II DNA and chromatin

Epigenetic regulatory mechanisms play key roles in cardiac development, differentiation, homeostasis, response to stress and injury, and disease. Human heart failure (HF) epigenetic regulatory mechanisms have not been deciphered to date. This 2-part review distills the rapidly evolving research focused on human HF epigenetic regulatory mechanisms. Part I, which was published in the September/October issue, focused on epigenetic regulatory mechanisms involving RNA, specifically the role of short, intermediate, and long noncoding RNAs (lncRNAs) and endogenous competing RNA regulatory networks. Part II, now in the November/December issue, focuses on the epigenetic regulatory mechanisms involving DNA, including DNA methylation, histone modifications, and chromatin conformational changes. Part II concludes with 2 examples of well-studied integrated epigenetic regulatory mechanisms: the structural and functional roles of the Mediator complex in regulating transcription and the epigenetic networked "cross-talk" regulating atrial natriuretic peptide and brain natriuretic peptide promoter activation.

Ablation of SIRT3 causes coronary microvascular dysfunction and impairs cardiac recovery post myocardial ischemia

RATIONALE

Sirtuin (SIRT3), a major nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase in mitochondria, declines with aging and its ablation is associated with accelerated development of cardiovascular diseases. However, the role of SIRT3 in coronary microvascular function and post-MI recovery has not been completely understood.

OBJECTIVE

The goal was to investigate whether ablation of SIRT3 causes coronary microvascular dysfunction, exacerbates post-myocardial ischemia (MI) cardiac dysfunction and impairs cardiac recovery.

METHODS AND RESULTS

Using endothelial cells (ECs) isolated from SIRT3 knockout (KO) mice, we revealed that the angiogenic capabilities were significantly reduced in SIRT3 deficient ECs. SIRT3 KO mice presented a pre-existing coronary microvascular dysfunction and microvascular rarefaction, as evidenced by a reduction in hyperemic peak diastolic blood flow velocity and coronary flow reserve (CFR), accompanied by loss of capillary-pericytes in the heart. Furthermore, SIRT3 KO mice subjected to myocardial ischemia by the ligation of left anterior descending coronary artery (LAD) exhibited more severe cardiac dysfunction together with decreased pericyte/EC coverage than that of wild type (WT) mice. In contrast, overexpression of SIRT3 preserved cardiac function in post-MI mice. Immunoblot analysis further showed that the expression of angiopoietin-1 (Ang-1), vascular endothelial growth factor (VEGF) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) were significantly decreased in the SIRT3-deficient ischemic hearts than those of WT ischemic hearts. This was accompanied by higher levels of cleaved caspase-3 and apoptosis.

CONCLUSION

Our results reveal a potential mechanism by which SIRT3 deletion exacerbates post-MI cardiac dysfunction and impairment of cardiac recovery involving microvascular rarefaction and pre-existing coronary microvascular dysfunction.

Epigenetic regulation in heart failure

PURPOSE OF REVIEW

This article provides an overview, highlighting recent findings, of a major mechanism of gene regulation and its relevance to the pathophysiology of heart failure.

RECENT FINDINGS

The syndrome of heart failure is a complex and highly prevalent condition, one in which the heart undergoes substantial structural remodeling. Triggered by a wide range of disease-related cues, heart failure pathophysiology is governed by both genetic and epigenetic events. Epigenetic mechanisms, such as chromatin/DNA modifications and noncoding RNAs, have emerged as molecular transducers of environmental stimuli to control gene expression. Here, we emphasize metabolic milieu, aging, and hemodynamic stress as they impact the epigenetic landscape of the myocardium.

SUMMARY

Recent studies in multiple fields, including cancer, stem cells, development, and cardiovascular biology, have uncovered biochemical ties linking epigenetic machinery and cellular energetics and mitochondrial function. Elucidation of these connections will afford molecular insights into long-established epidemiological observations. With time, exploitation of the epigenetic machinery therapeutically may emerge with clinical relevance.

Caffeic acid ethanolamide prevents cardiac dysfunction through sirtuin dependent cardiac bioenergetics preservation

BACKGROUND

Cardiac oxidative stress, bioenergetics and catecholamine play major roles in heart failure progression. However, the relationships between these three dominant heart failure factors are not fully elucidated. Caffeic acid ethanolamide (CAEA), a synthesized derivative from caffeic acid that exerted antioxidative properties, was thus applied in this study to explore its effects on the pathogenesis of heart failure.

RESULTS

In vitro studies in HL-1 cells exposed to isoproterenol showed an increase in cellular and mitochondria oxidative stress. Two-week isoproterenol injections into mice resulted in ventricular hypertrophy, myocardial fibrosis, elevated lipid peroxidation, cardiac adenosine triphosphate and left ventricular ejection fraction decline, suggesting oxidative stress and bioenergetics changes in catecholamine-induced heart failure. CAEA restored oxygen consumption rates and adenosine triphosphate contents. In addition, CAEA alleviated isoproterenol-induced cardiac remodeling, cardiac oxidative stress, cardiac bioenergetics and function insufficiency in mice. CAEA treatment recovered sirtuin 1 and sirtuin 3 activity, and attenuated the changes of proteins, including manganese superoxide dismutase and hypoxia-inducible factor 1-α, which are the most likely mechanisms responsible for the alleviation of isoproterenol-caused cardiac injury

CONCLUSION

CAEA prevents catecholamine-induced cardiac damage and is therefore a possible new therapeutic approach for preventing heart failure progression.

Association of Nicotinamide Phosphoribosyltransferase (NAMPT) Gene Polymorphisms and of Serum NAMPT Levels with Dilated Cardiomyopathy in a Chinese Population

Nicotinamide phosphoribosyltransferase (NAMPT) has crucial roles for myocardial development, cardiomyocyte energy metabolism and cell death/survival by regulating NAD⁺-dependent sirtuin-1 (SIRT1) deacetylase. This study aimed to determine if the single nucleotide polymorphisms (SNPs) of the NAMPT gene may affect the susceptibility and prognosis for patients with dilated cardiomyopathy (DCM) and to describe the association of serum NAMPT levels with clinical features of DCM. Three SNPs (rs61330082, rs2505568, and rs9034) were analyzed by the polymerase chain reaction-restriction fragment length polymorphism method in a case-control study of 394 DCM patients and 395 controls from China. Serum NAMPT levels were measured by enzyme-linked immunosorbent assay kits. The homozygote for the minor allele at rs2505568 and rs9034 could not be detected in this study. Rs9034 T allele and CT genotype were associated with increased DCM risk (OR: 1.63, 95% CI = 1.16–2.27, p = 0.005 and OR: 1.72, 95% CI = 1.20–2.50, p = 0.0027, respectively). Nominally significant decreased DCM risk was found to be associated with the A allele and AT genotype of rs2505568 (OR: 0.48, 95% CI = 0.35–0.67, p < 0.0001 and OR: 0.44, 95% CI = 0.31–0.62, p < 0.0001, respectively), but it should be interpreted with caution because of Hardy-Weinberg disequilibrium in the control group. Of five haplotypes constructed, TAC (rs61330082-rs2505568-rs9034) was a protective haplotype to DCM (OR: 0.22, 95% CI = 0.13–0.39, p = 1.84 × 10⁻⁸). The Cox multivariate survival analysis indicated that the rs9034 CT genotype (hazard ratio (HR): 0.59, 95% CI = 0.37–0.96, p = 0.03) was an independently multivariate predictor for longer overall survival in DCM patients. Serum NAMPT levels were significantly higher in the DCM group than controls (p < 0.0001) and gradually increased with the increase of New York Heart Association grade in DCM patients. However, there was a lack of association of the three SNPs with serum NAMPT levels. Spearman correlation test revealed that the NAMPT level was positively associated with brain natriuretic peptide (r = 0.56, p = 0.001), left ventricular end-diastolic diameter (r = 0.293, p = 0.011) and left ventricular end-diastolic volume (r = 0.294, p = 0.011). Our study suggested that NAMPT may play an important role in the development of DCM.

The role of sirtuins in cardiac disease

Modification of histones is one of the important mechanisms of epigenetics, in which genetic control is determined by factors other than an individual's DNA sequence. Sirtuin family proteins, which are class III histone deacetylases, were originally identified as gene silencers that affect the mating type of yeast, leading to the name "silent mating-type information regulation 2" (SIR2). They are characterized by their requirement of nicotinamide adenine dinucleotide for their enzyme activity, unlike other classes of histone deacetylases. Sirtuins have been traditionally linked to longevity and the beneficial effects of calorie restriction and DNA damage repair. Recently, sirtuins have been shown to be involved in a wide range of physiological and pathological processes, including aging, energy responses to low calorie availability, and stress resistance, as well as apoptosis and inflammation. Sirtuins can also regulate mitochondrial biogenesis and circadian clocks. Seven sirtuin family proteins (Sirt1-7) have been identified as mammalian SIR2 orthologs, localized in different subcellular compartments, namely, the cytoplasm (Sirt1, 2), the mitochondria (Sirt3, 4, 5), and the nucleus (Sirt1, 2, 6, 7). Sirt1 is evolutionarily close to yeast SIR2 and has been the most intensively investigated in the cardiovascular system. Endogenous Sirt1 plays a pivotal role in mediating the cell death/survival process and has been implicated in the pathogenesis of cardiovascular disease. Downregulation of Sirt2 is protective against ischemic-reperfusion injury. Increased Sirt3 expression has been shown to correlate with longevity in humans. In addition, Sirt3 protects cardiomyocytes from aging and oxidative stress and suppresses cardiac hypertrophy. Sirt6 has also recently been demonstrated to attenuate cardiac hypertrophy, and Sirt7 is known to regulate apoptosis and stress responses in the heart. On the other hand, the roles of Sirt4 and Sirt5 in the heart remain largely uncharacterized.

Myocardial metabolism in diabetic cardiomyopathy: potential therapeutic targets

SIGNIFICANCE

Cardiovascular complications in diabetes are particularly serious and represent the primary cause of morbidity and mortality in diabetic patients. Despite early observations of cardiac dysfunction in diabetic humans, cardiomyopathy unique to diabetes has only recently been recognized.

RECENT ADVANCES

Research has focused on understanding the pathogenic mechanisms underlying the initiation and development of diabetic cardiomyopathy. Emerging data highlight the importance of altered mitochondrial function as a major contributor to cardiac dysfunction in diabetes. Mitochondrial dysfunction occurs by several mechanisms involving altered cardiac substrate metabolism, lipotoxicity, impaired cardiac insulin and glucose homeostasis, impaired cellular and mitochondrial calcium handling, oxidative stress, and mitochondrial uncoupling.

CRITICAL ISSUES

Currently, treatment is not specifically tailored for diabetic patients with cardiac dysfunction. Given the multifactorial development and progression of diabetic cardiomyopathy, traditional treatments such as anti-diabetic agents, as well as cellular and mitochondrial fatty acid uptake inhibitors aimed at shifting the balance of cardiac metabolism from utilizing fat to glucose may not adequately target all aspects of this condition. Thus, an alternative treatment such as resveratrol, which targets multiple facets of diabetes, may represent a safe and promising supplement to currently recommended clinical therapy and lifestyle changes.

FUTURE DIRECTIONS

Elucidation of the mechanisms underlying the initiation and progression of diabetic cardiomyopathy is essential for development of effective and targeted treatment strategies. Of particular interest is the investigation of alternative therapies such as resveratrol, which can function as both preventative and mitigating agents in the management of diabetic cardiomyopathy.

SIRT3 deficiency impairs mitochondrial and contractile function in the heart

Sirtuin 3 (SIRT3) is a mitochondrial NAD(+)-dependent deacetylase that regulates energy metabolic enzymes by reversible protein lysine acetylation in various extracardiac tissues. The role of SIRT3 in myocardial energetics and in the development of mitochondrial dysfunction in cardiac pathologies, such as the failing heart, remains to be elucidated. To investigate the role of SIRT3 in the regulation of myocardial energetics and function SIRT3(-/-) mice developed progressive age-related deterioration of cardiac function, as evidenced by a decrease in ejection fraction and an increase in enddiastolic volume at 24 but not 8 weeks of age using echocardiography. Four weeks following transverse aortic constriction, ejection fraction was further decreased in SIRT3(-/-) mice compared to WT mice, accompanied by a greater degree of cardiac hypertrophy and fibrosis. In isolated working hearts, a decrease in cardiac function in SIRT3(-/-) mice was accompanied by a decrease in palmitate oxidation, glucose oxidation, and oxygen consumption, whereas rates of glycolysis were increased. Respiratory capacity and ATP synthesis were decreased in cardiac mitochondria of SIRT3(-/-) mice. HPLC measurements revealed a decrease of the myocardial ATP/AMP ratio and of myocardial energy charge. Using LC-MS/MS, we identified increased acetylation of 84 mitochondrial proteins, including 6 enzymes of fatty acid import and oxidation, 50 subunits of the electron transport chain, and 3 enzymes of the tricarboxylic acid cycle. Lack of SIRT3 impairs mitochondrial and contractile function in the heart, likely due to increased acetylation of various energy metabolic proteins and subsequent myocardial energy depletion.

Role of mitochondrial dysfunction in hyperglycaemia-induced coronary microvascular dysfunction: Protective role of resveratrol

Microvascular complications are now recognized to play a major role in diabetic complications, and understanding the mechanisms is critical. Endothelial dysfunction occurs early in the course of the development of complications; the precise mechanisms remain poorly understood. Mitochondrial dysfunction may occur in a diabetic rat heart and may act as a source of the oxidative stress. However, the role of endothelial cell-specific mitochondrial dysfunction in diabetic vascular complications is poorly studied. Here, we studied the role of diabetes-induced abnormal endothelial mitochondrial function and the resultant endothelial dysfunction. Understanding the role of endothelial mitochondrial dysfunction in diabetic vasculature is critical in order to develop new therapies. We demonstrate that hyperglycaemia leads to mitochondrial dysfunction in microvascular endothelial cells, and that mitochondrial inhibition induces endothelial dysfunction. Additionally, we show that resveratrol acts as a protective agent; resveratrol-mediated mitochondrial protection may be used to prevent long-term diabetic cardiovascular complications.

SIRT1 activation rescues doxorubicin-induced loss of functional competence of human cardiac progenitor cells

BACKGROUND

The search for compounds able to counteract chemotherapy-induced heart failure is extremely important at the age of global cancer epidemic. The role of SIRT1 in the maintenance of progenitor cell homeostasis may contribute to its cardioprotective effects. SIRT1 activators, by preserving progenitor cells, could have a clinical relevance for the prevention of doxorubicin (DOXO)-cardiotoxicity.

METHODS

To determine whether SIRT1 activator, resveratrol (RES), interferes with adverse effects of DOXO on cardiac progenitor cells (CPCs): 1) human CPCs (hCPCs) were exposed in vitro to DOXO or DOXO+RES and their regenerative potential was tested in vivo in an animal model of DOXO-induced heart failure; 2) the in vivo effects of DOXO+RES co-treatment on CPCs were studied in a rat model.

RESULTS

In contrast to healthy cells, DOXO-exposed hCPCs were ineffective in a model of anthracycline cardiomyopathy. The in vitro activation of SIRT1 decreased p53 acetylation, overcame suppression of the IGF-1/Akt pro-survival and anti-apoptotic signaling, enhanced oxidative stress defense and prevented senescence and growth arrest of hCPCs. Priming with RES counterbalanced the onset of dysfunctional phenotype in DOXO-exposed hCPCs, partly restoring their ability to repair the damage with improvement in cardiac function and animal survival. The in vivo co-treatment DOXO+RES prevented the anthracycline-induced alterations in CPCs, partly preserving cardiac function.

CONCLUSION

SIRT1 activation protects DOXO-exposed CPCs and re-establishes their proper function. Pharmacological intervention at the level of tissue-specific progenitor cells may provide cardiac benefits for the growing population of long-term cancer survivors that are at risk of chemotherapy-induced cardiovascular toxicity.

Effect of 5-aminoimidazole-4-carboxamide ribonucleoside on the mitochondrial function and developmental ability of bovine oocytes

Oocyte nuclear maturation depends on sufficient energy supply through oxidative phosphorylation and β-oxidation. AMP-activated protein kinase (AMPK) is an energy sensor controlling the oocyte energy metabolism. The main aim of this study was to examine the effect of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a potent activator of AMPK, on the ATP content and mitochondrial DNA copy number (Mt-number) of bovine oocytes and on their developmental ability. Oocytes were collected from slaughterhouse-derived bovine ovaries. When these oocytes were cultured in a maturation medium containing 0-, 50-, 250-, and 500-μM AICAR, higher AICAR concentrations reduced the rate of meiotic maturation and the ATP content in oocytes, whereas lower AICAR increased the ATP content in oocytes without affecting the maturation rate. Supplementation of the maturation medium with a low concentration of AICAR (50 and 250 μM) increased phospho-AMPK expression level, as determined by immunostaining. In addition, AICAR treatment increased the ATP content in oocytes, which remained elevated for as long as 2 days after fertilization. On culturing the oocytes with AICAR (250 μM), the fertilization outcome, rate of blastulation, and total cell number of the blastocysts significantly improved. When the proteosomal mitochondrial degradation was inhibited by supplementing the maturation medium with MG132, the Mt-number, as determined by real-time polymerase chain reaction, significantly increased. However, the treatment of oocytes with AICAR did not affect the Mt-number in the presence or absence of MG132. From these data, we conclude that low concentrations of AICAR improved the embryonic developmental ability, presumably via the upregulation of the ATP content in oocytes, but the increase in the ATP content was not due to the upregulation of mitochondrial biogeneration.