Mitochondria In Heart Failure Research Articles

The Identification of Prohibitin in the Rat Heart Mitochondria in Heart Failure.

Mitochondria are considered the main organelles in the cell. They play an important role in both normal and abnormal heart function. There is a supramolecular organization between the complexes of the respiratory chain (supercomplexes (SCs)), which are involved in mitochondrial respiration. Prohibitins (PHBs) participate in the regulation of oxidative phosphorylation (OXPHOS) activity and interact with some subunits of the OXPHOS complexes. In this study, we identified a protein whose level was decreased in the mitochondria of the heart in rats with heart failure. This protein was PHB. Isoproterenol (ISO) has been used as a compound to induce heart failure in rats. We observed that astaxanthin (AX) increased the content of PHB in rat heart mitochondria isolated from ISO-injected rats. Since it is known that PHB forms complexes with some mitochondrial proteins and proteins that are part of the complexes of the respiratory chain, the change in the levels of these proteins was investigated under our experimental conditions. We hypothesized that PHB may be a target for the protective action of AX.

A selective inhibitor of mitofusin 1-βIIPKC association improves heart failure outcome in rats

We previously demonstrated that beta II protein kinase C (βIIPKC) activity is elevated in failing hearts and contributes to this pathology. Here we report that βIIPKC accumulates on the mitochondrial outer membrane and phosphorylates mitofusin 1 (Mfn1) at serine 86. Mfn1 phosphorylation results in partial loss of its GTPase activity and in a buildup of fragmented and dysfunctional mitochondria in heart failure. βIIPKC siRNA or a βIIPKC inhibitor mitigates mitochondrial fragmentation and cell death. We confirm that Mfn1-βIIPKC interaction alone is critical in inhibiting mitochondrial function and cardiac myocyte viability using SAMβA, a rationally-designed peptide that selectively antagonizes Mfn1-βIIPKC association. SAMβA treatment protects cultured neonatal and adult cardiac myocytes, but not Mfn1 knockout cells, from stress-induced death. Importantly, SAMβA treatment re-establishes mitochondrial morphology and function and improves cardiac contractility in rats with heart failure, suggesting that SAMβA may be a potential treatment for patients with heart failure.

Mitochondrial dysfunction in pathophysiology of heart failure.

Mitochondrial dysfunction has been implicated in the development of heart failure. Oxidative metabolism in mitochondria is the main energy source of the heart, and the inability to generate and transfer energy has long been considered the primary mechanism linking mitochondrial dysfunction and contractile failure. However, the role of mitochondria in heart failure is now increasingly recognized to be beyond that of a failed power plant. In this Review, we summarize recent evidence demonstrating vicious cycles of pathophysiological mechanisms during the pathological remodeling of the heart that drive mitochondrial contributions from being compensatory to being a suicide mission. These mechanisms include bottlenecks of metabolic flux, redox imbalance, protein modification, ROS-induced ROS generation, impaired mitochondrial Ca2+ homeostasis, and inflammation. The interpretation of these findings will lead us to novel avenues for disease mechanisms and therapy.

Abstract 275: Quantification of the Mitochondrial Protein Interactome in Failing Hearts

Mitochondrial dysfunction is a maladaptive mechanism in the progression of heart failure. However, the cause of mitochondrial dysfunction during cardiac stress remains elusive. To understand the pathogenic role of mitochondria in heart failure, a systems biology approach was used to quantify the protein interaction network by comparing mitochondria isolated from healthy and failing mouse heart. This is achieved by Protein Interaction Reporter (PIR) technology consisting of a cleavable, MS-identifiable, isotope labelled cross-linker, which allows identification and quantification of interacting peptide pairs. Heart failure was induced in three month old, wild-type C57Bl6/NCrl mice using chronic pressure overload by transverse aortic constriction (TAC, n=8) surgery. Age-matched Sham-operated (Sham, n=8) mice were used as controls. Four weeks post-surgery, cardiac function was measured by echocardiography. TAC hearts showed significantly lower contractile function than Sham (fractional shortening 49±2.1% vs 13±4.0%), and were dilated (LVID 2.7±0.34mm vs 3.4±0.46mm). Cardiac hypertrophy of TAC hearts (HW/TL 5.0±0.35 vs 9.1±0.58) was associated with greater lung edema (LW wet/dry 3.9±0.49 vs 4.9±0.24). Freshly isolated mitochondria from TAC and Sham hearts were cross-linked with heavy- or light-isotope labelled crosslinkers, digested, enriched, and analyzed by LC/MS 3 . Released peptide spectra were identified and categorized by known molecular functions using a MitoCarta 2.0 constructed database. We identified 3502 non-redundant cross-linked peptide pairs from 297 proteins, involving 1758 lysine residues linked in 2571 lysine-lysine interactions. From 3502 total links, we detected 2304 intra- and 1016 inter-protein links. Inter-protein changes between TAC/Sham were most prevalent in the electron transport chain and ATP synthasome networks. Intra-protein changes were evident in TCA cycle, fatty acid oxidation, and nucleotide transport, suggesting conformational remodeling. Interactome changes in amino acid metabolism, mitochondrial transcription and translation pathways were undetected. A complete picture of mitochondrial protein landscape in the failing heart will lead us to novel mechanisms and therapy.

Mitochondrial Function in Non-ischemic Heart Failure.

Provision for the continuous demand for energy from the beating heart relies heavily on efficient mitochondrial activity. Non-ischemic cardiomyopathy in which oxygen supply is not limiting results from etiologies such as pressure overload. It is associated with progressive development of metabolic stress culminating in energy depletion and heart failure. The mitochondria from the ventricular walls undergoing non-ischemic cardiomyopathy are subjected to long periods of adaptation to support the changing metabolic milieu, which has been described as mal-adaptation since it ultimately results in loss of cardiac contractile function. While the chronicity of exposure to metabolic stressors, co-morbidities and thereby adaptive changes in mitochondria maybe different between ischemic and non-ischemic heart failure, the resulting pathology is very similar, especially in late stage heart failure. Understanding of the mitochondrial changes in early-stage heart failure may guide the development of mitochondrial-targeted therapeutic options to prevent progression of non-ischemic heart failure. This chapter reviews findings of mitochondrial functional changes in animal models and humans with non-ischemic heart failure. While most animal models of non-ischemic heart failure exhibit cardiac mitochondrial dysfunction, studies in humans have been inconsistent despite confirmed reduction in ATP production. This chapter also reviews the possibility of impairment of substrate supply processes upstream of the mitochondria in heart failure, and discusses potential metabolism-targeted therapeutic options.

Recombinant Atrial Natriuretic Peptide Prevents Aberrant Ca2+ Leakage through the Ryanodine Receptor by Suppressing Mitochondrial Reactive Oxygen Species Production Induced by Isoproterenol in Failing Cardiomyocytes.

Catecholamines induce intracellular reactive oxygen species (ROS), thus enhancing diastolic Ca2+ leakage through the ryanodine receptor during heart failure (HF). However, little is known regarding the effect of atrial natriuretic peptide (ANP) on ROS generation and Ca2+ handling in failing cardiomyocytes. The aim of the present study was to clarify the mechanism by which an exogenous ANP exerts cardioprotective effects during HF. Cardiomyocytes were isolated from the left ventricles of a canine tachycardia-induced HF model and sham-operated vehicle controls. The degree of mitochondrial oxidized DNA was evaluated by double immunohistochemical (IHC) staining using an anti-VDAC antibody for the mitochondria and an anti-8-hydroxy-2′-deoxyguanosine antibody for oxidized DNA. The effect of ANP on ROS was investigated using 2,7-dichlorofluorescin diacetate, diastolic Ca2+ sparks assessed by confocal microscopy using Fluo 4-AM, and the survival rate of myocytes after 48 h. The double IHC study revealed that isoproterenol (ISO) markedly increased oxidized DNA in the mitochondria in HF and that the ISO-induced DNA damage was markedly inhibited by the co-presence of ANP. ROS production and Ca2+ spark frequency (CaSF) were increased in HF compared to normal controls, and were further increased in the presence of ISO. Notably, ANP significantly suppressed both ISO-induced ROS and CaSF without changing sarcoplasmic reticulum Ca2+ content in HF (p<0.01, respectively). The survival rate after 48 h in HF was significantly decreased in the presence of ISO compared with baseline (p<0.01), whereas it was significantly improved by the co-presence of ANP (p<0.01). Together, our results suggest that ANP strongly suppresses ISO-induced mitochondrial ROS generation, which might correct aberrant diastolic Ca2+ sparks, eventually contributing to the improvement of cardiomyocyte survival in HF.

Renal Fanconi Syndrome Is Caused by a Mistargeting-Based Mitochondriopathy.

We recently reported an autosomal dominant form of renal Fanconi syndrome caused by a missense mutation in the third codon of the peroxisomal protein EHHADH. The mutation mistargets EHHADH to mitochondria, thereby impairing mitochondrial energy production and, consequently, reabsorption of electrolytes and low-molecular-weight nutrients in the proximal tubule. Here, we further elucidate the molecular mechanism underlying this pathology. We find that mutated EHHADH is incorporated into mitochondrial trifunctional protein (MTP), thereby disturbing β-oxidation of long-chain fatty acids. The resulting MTP deficiency leads to a characteristic accumulation of hydroxyacyl- and acylcarnitines. Mutated EHHADH also limits respiratory complex I and corresponding supercomplex formation, leading to decreases in oxidative phosphorylation capacity,mitochondrial membrane potential maintenance, and ATP generation. Activity of the Na(+)/K(+)-ATPase is thereby diminished, ultimately decreasing the transport activity of the proximal tubule cells.

The mitochondria in heart failure: a target for coenzyme Q10 therapy?

Clinical Pharmacology & TherapeuticsVolume 96, Issue 6 p. 645-647 Point-Counterpoint The Mitochondria in Heart Failure: A Target for Coenzyme Q10 Therapy? S A Mortensen, Corresponding Author S A Mortensen sam@rh.dk Heart Center, Department of Cardiology, Copenhagen University Hospital, Copenhagen, DenmarkSearch for more papers by this authorA L Mortensen, A L Mortensen Pcovery ApS, Copenhagen, DenmarkSearch for more papers by this author S A Mortensen, Corresponding Author S A Mortensen sam@rh.dk Heart Center, Department of Cardiology, Copenhagen University Hospital, Copenhagen, DenmarkSearch for more papers by this authorA L Mortensen, A L Mortensen Pcovery ApS, Copenhagen, DenmarkSearch for more papers by this author First published: 13 August 2014 https://doi.org/10.1038/clpt.2014.175Citations: 2Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume96, Issue6Mitochondrial PharmacologyDecember 2014Pages 645-647 RelatedInformation

Cardiac mitochondria in heart failure: Normal cardiolipin profile and increased threonine phosphorylation of complex IV

Mitochondrial dysfunction is a major contributor in heart failure (HF). We investigated whether the decrease in respirasome organization reported by us previously in cardiac mitochondria in HF is due to changes in the phospholipids of the mitochondrial inner membrane or modifications of the subunits of the electron transport chain (ETC) complexes. The contents of the main phospholipid species, including cardiolipin, as well as the molecular species of cardiolipin were unchanged in cardiac mitochondria in HF. Oxidized cardiolipin molecular species were not observed. In heart mitochondria isolated from HF, complex IV not incorporated into respirasomes exhibits increased threonine phosphorylation. Since HF is associated with increased adrenergic drive to cardiomyocytes, this increased protein phosphorylation might be explained by the involvement of cAMP-activated protein kinase. Does the preservation of cAMP-induced phosphorylation changes of mitochondrial proteins or the addition of exogenous cAMP have similar effects on oxidative phosphorylation? The usage of phosphatase inhibitors revealed a specific decrease in complex I-supported respiration with glutamate. In saponin-permeabilized cardiac fibers, pre-incubation with cAMP decreases oxidative phosphorylation due to a defect localized at complex IV of the ETC inter alia. We propose that phosphorylation of specific complex IV subunits decreases oxidative phosphorylation either by limiting the incorporation of complex IV in supercomplexes or by decreasing supercomplex stability.

Proteomic analysis of mitochondria reveals a metabolic switch from fatty acid oxidation to glycolysis in the failing heart

This work characterizes the mitochondrial proteomic profile in the failing heart and elucidates the molecular basis of mitochondria in heart failure. Heart failure was induced in rats by myocardial infarction, and mitochondria were isolated from hearts by differential centrifugation. Using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry, a system biology approach was employed to investigate differences in mitochondrial proteins between normal and failing hearts. Mass spectrometry identified 27 proteins differentially expressed that involved in energy metabolism. Among those, the up-regulated proteins included tricarboxylic acid cycle enzymes and pyruvate dehydrogenase complex subunits while the down-regulated proteins were involved in fatty acid oxidation and the OXPHOS complex. These results suggest a substantial metabolic switch from free fatty acid oxidation to glycolysis in heart failure and provide molecular evidence for alterations in the structural and functional parameters of mitochondria that may contribute to cardiac dysfunction during ischemic injury.

Mitochondrial OPA1, apoptosis, and heart failure

Mitochondrial fusion and fission are essential processes for preservation of normal mitochondrial function. We hypothesized that fusion proteins would be decreased in heart failure (HF), as the mitochondria in HF have been reported to be small and dysfunctional. Expression of optic atrophy 1 (OPA1), a mitochondrial fusion protein, was decreased in both human and rat HF, as observed by western blotting. OPA1 is important for maintaining normal cristae structure and function, for preserving the inner membrane structure and for protecting cells from apoptosis. Confocal and electron microscopy studies demonstrated that the mitochondria in the failing hearts were small and fragmented, consistent with decreased fusion. OPA1 mRNA levels did not differ between failing and normal hearts, suggesting post-transcriptional control. Simulated ischaemia in the cardiac myogenic cell line H9c2 cells reduced OPA protein levels. Reduction of OPA1 expression with shRNA resulted in increased apoptosis and fragmentation of the mitochondria. Overexpression of OPA1 increased mitochondrial tubularity, but did not protect against simulated ischaemia-induced apoptosis. Cytochrome c release from the mitochondria was increased both with reduction in OPA1 and with overexpression of OPA1. This is the first report, to our knowledge, of changes in mitochondrial fusion/fission proteins in cardiovascular disease. These changes have implications for mitochondrial function and apoptosis, contributing to the cell loss which is part of the downward progression of the failing heart.

New aspects of impaired mitochondrial function in heart failure

This minireview focuses on the impairment of function in cardiac mitochondria in heart failure (HF). It is generally accepted that chronic energy starvation leads to cardiac mechanical dysfunction in HF. Mitochondria are the primary ATP generator for the heart. Current evidence suggests that the assembly of the electron transport chain (ETC) into respirasomes provides structural support for mitochondrial oxidative phosphorylation by facilitating electron channeling and perhaps by preventing electron leak and superoxide production. Defects have been purported to occur in the individual ETC complexes or components of the phosphorylation apparatus in HF, but these defects have not been linked to impaired mitochondrial function. Moreover, studies that reported decreased mitochondrial oxidative phosphorylation in HF did not identify the site of the defect. We propose a sequential mechanistic pathway in which the decrease in functional respirasomes in HF is the primary event causing decreased oxidative phosphorylation and increased reactive oxygen species production, leading to a progressive decrease in cardiac performance.

Altered expression of the adenine nucleotide translocase isoforms and decreased ATP synthase activity in skeletal muscle mitochondria in heart failure

Exercise intolerance is a component of heart failure (HF) syndrome. We aimed to identify the defects in skeletal muscle mitochondria which may contribute to the development of peripheral myopathy. Subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria were isolated from gastrocnemius muscle of control dogs ( N = 5) and dogs with pacing-induced HF ( N = 5). The measurement of integrated mitochondrial function (oxidative phosphorylation) and of individual activities of mitochondrial electron transport chain (ETC) complexes was complemented with the assessment of the amount and activity of the components of the phosphorylation apparatus. Both populations of skeletal muscle mitochondria isolated from HF have significantly decreased ADP-stimulated (state 3) respiratory rates with complex I, II and III substrates. The decrease in respiratory rates of skeletal muscle SSM are neither relieved upon collapsing the mitochondrial potential with an uncoupler nor increased in the presence of maximal ADP concentrations showing a defect in the ETC, which needs further investigation. In contrast, respiratory rates of skeletal muscle IFM from HF were relieved with the uncoupler and partially improved in the presence of maximal ADP concentrations. In these IFM, alterations in the phosphorylation apparatus were detected with a decreased amount of ANT isoform 2 and increased amount of isoform 1. The IFM dysfunction may be explained by this shift in ANT isoforms. In conclusion, pacing-induced HF causes a decrease in the oxidative phosphorylation of skeletal muscle mitochondria due to defects in the ETC and phosphorylation apparatus.

Mitochondrial Function in Heart Failure

Experimental and clinical studies have detected an impaired respiratory function of cardiomyocyte mitochondria in heart failure. Since the reasons for heart failure are manifold, so is mitochondrial involvement. Characteristics of mitochondrial participation in heart failure are as follows: (1) Inherited or acquired mutations of the mitochondrial or nuclear genome cause defects in different mitochondrial components, eventually resulting in cardiomyopathy. (2a) Oxidative stress depresses mitochondrial function. This occurs slowly and inevitably in the 'physiological' process of ageing, but rapidly in “pathophysiologic” conditions such as post-ischemic reperfusion. (2b) Free radicals damage mitochondrial DNA, proteins, and membrane lipids. Interactions between altered membrane lipids, respiratory chain components, and carrier proteins further enhance mitochondrial dysfunction. (3) Mitochondrial energy transfer via the adenine nucleotide translocator (ANT) and the mitochondrial creatine kinase is disturbed in heart failure. Especially an altered expression and a functional impairment of the ANT seems to be involved in the disturbed energy metabolism of dilated and inflammatory cardiomyopathy. (4) Mitochondria are mainly involved in the initiation and modulation of the process of programmed cell death (apoptosis). (5) Triggered by a variety of conditions during cellular dysfunction mitochondrial membrane permeability suddenly increases, followed by the collapse of the membrane potential, thus abolishing energy production and further aggravating cellular damage. (6a) Increased levels of cytokines, in particular TNF-α, in heart failure and cardiomyopathy modulate mitochondrial function. (6b) Cytokines activate the generation of nitric oxide and heat shock proteins, thus further depressing or preserving mitochondrial activity.