Cardiac Mitochondrial Alterations Research Articles

Spermidine supplementation influences mitochondrial number and morphology in the heart of aged mice.

Aging is associated with cardiac hypertrophy and progressive decline in heart function. One of the hallmarks of cellular aging is the dysfunction of mitochondria. These organelles occupy around 1/4 to 1/3 of the cardiomyocyte volume. During cardiac aging, the removal of defective or dysfunctional mitochondria by mitophagy as well as the dynamic equilibrium between mitochondrial fusion and fission is distorted. Here, we hypothesized that these changes affect the number of mitochondria and alter their three-dimensional (3D) characteristics in aged mouse hearts. The polyamine spermidine stimulates both mitophagy and mitochondrial biogenesis, and these are associated with improved cardiac function and prolonged lifespan. Therefore, we speculated that oral spermidine administration normalizes the number of mitochondria and their 3D morphology in aged myocardium. Young (4-months old) and old (24-months old) mice, treated or not treated with spermidine, were used in this study (n=10 each). The number of mitochondria in the left ventricles was estimated by design-based stereology using the Euler-Poincaré characteristic based on a disector at the transmission electron microscopic level. The 3D morphology of mitochondria was investigated by 3D reconstruction (using manual contour drawing) from electron microscopic z-stacks obtained by focused ion beam scanning electron microscopy. The volume of the left ventricle and cardiomyocytes were significantly increased in aged mice with or without spermidine treatment. Although the number of mitochondria was similar in young and old control mice, it was significantly increased in aged mice treated with spermidine. The interfibrillar mitochondria from old mice exhibited a lower degree of organization and a greater variation in shape and size compared to young animals. The mitochondrial alignment along the myofibrils in the spermidine-treated mice appeared more regular than in control aged mice, however, old mitochondria from animals fed spermidine also showed a greater diversity of shape and size than young mitochondria. In conclusion, mitochondria of the aged mouse left ventricle exhibited changes in number and 3D ultrastructure that is likely the structural correlate of dysfunctional mitochondrial dynamics. Spermidine treatment reduced, at least in part, these morphological changes, indicating a beneficial effect on cardiac mitochondrial alterations associated with aging.

Mitochondrial dysfunction in fatal ventricular arrhythmias.

Ventricular fibrillation (VF) and sudden cardiac arrest (SCA) remain some of the most important public health concerns worldwide. For the past 50years, the recommendation in the Advanced Cardiac Life Support (ACLS) guidelines has been that defibrillation is the only option for shockable cardiac arrest. There is growing evidence to demonstrate that mitochondria play a vital role in the outcome of postresuscitation cardiac function. Although targeting mitochondria to improve resuscitation outcome following cardiac arrest has been proposed for many years, understanding concerning the changes in mitochondria during cardiac arrest, especially in the case of VF, is still limited. In addition, despite new research initiatives and improved medical technology, the overall survival rates of patients with SCA still remain the same. Understanding cardiac mitochondrial alterations during fatal arrhythmias may help to enable the formulation of strategies to improve the outcomes of resuscitation. The attenuation of cardiac mitochondrial dysfunction during VF through pharmacological intervention as well as ischaemic postconditioning could also be a promising target for intervention and inform a new paradigm of treatments. In this review, the existing evidence available from in vitro, ex vivo and in vivo studies regarding the roles of mitochondrial dysfunction during VF is comprehensively summarized and discussed. In addition, the effects of interventions targeting cardiac mitochondria during fatal ventricular arrhythmias are presented. Since there are no clinical reports from studies targeting mitochondria to improve resuscitation outcome available, this review will provide important information to encourage further investigations in a clinical setting.

Cardiac mitochondrial alterations in a mouse model of fabry disease

Cardiac mitochondrial alterations in a mouse model of fabry disease

PKD Translocation to the Outer Mitochondrial Membrane Induces Mitochondrial Fragmentation and Cell Death via DLP1 Phosphorylation in Cardiomyocytes

Heart failure (HF) occurs in response to various types of stimulus including Gq‐protein coupled receptor (GqPCR) stimulation. GqPCR‐mediated mitochondrial dysfunction is frequently observed in HF animal models, but the molecular mechanism remains unclear. Recently, Protein kinase D (PKD) located at GqPCR downstream has been recognized as a key signaling nodal point affecting various cardiac functions. Therefore, we hypothesize that PKD acts as a mitochondrial signaling component and induces mitochondrial dysfunctions under GqPCR‐mediated HF. Using the outer mitochondrial membrane (OMM)‐targeted CFP (mt‐CFP), we found that the value of the Förster resonance energy transfer (FRET) between mt‐CFP and YFP‐tagged PKD significantly increases upon GqPCR stimulation, indicating PKD translocation from cytosol to the OMM. Next, using the FRET‐based OMM‐targeted PKD‐activity sensor, we observed that PKD is activated at the OMM after GqPCR stimulation. Furthermore, we found that GqPCR‐mediated PKD activation at the OMM induced mitochondrial fragmentation, increased reactive oxygen species generation and mitochondrial permeability transition pore opening, followed by caspase‐3 activation in cardiomyocytes. These morphological and functional alterations in cardiac mitochondria were mediated via PKD‐dependent phosphorylation of Dynamin‐Like Protein 1 (DLP1) at S637. Importantly, PKD‐dependent DLP1 phosphorylation concurrent with abnormal mitochondrial morphology and apoptotic signaling were also observed in ventricular tissue from transgenic mice with cardiac‐specific overexpression of constitutively active Gaq. In summary, we conclude that GqPCR stimulation induces PKD translocation to the OMM and induces mitochondrial fragmentation and dysfunction, which likely contributes to cardiomyocyte dysfunction during HF.Support or Funding InformationThis work was partly supported by American Heart Association (AHA) grant (14BGIA18830032 to J.O.‐U.), Medical Research Grant from W.W. Smith Charitable Trust (H1403 to J.O.‐U.) and NIH grants (2R01HL093671 and 1R01HL122124 to SSS).

Ionising radiation induces persistent alterations in the cardiac mitochondrial function of C57BL/6 mice 40 weeks after local heart exposure

Background and purposeRadiotherapy of thoracic and chest-wall tumours increases the long-term risk of radiation-induced heart disease. The aim of this study was to investigate the long-term effect of local heart irradiation on cardiac mitochondria. MethodsC57BL/6 and atherosclerosis-prone ApoE−/− mice received local heart irradiation with a single X-ray dose of 2Gy. To investigate the low-dose effect, C57BL/6 mice also received a single heart dose of 0.2Gy. Functional and proteomic alterations of cardiac mitochondria were evaluated after 40weeks, compared to age-matched controls. ResultsThe respiratory capacity of irradiated C57BL/6 cardiac mitochondria was significantly reduced at 40weeks. In parallel, protein carbonylation was increased, suggesting enhanced oxidative stress. Considerable alterations were found in the levels of proteins of mitochondria-associated cytoskeleton, respiratory chain, ion transport and lipid metabolism. Radiation induced similar but less pronounced effects in the mitochondrial proteome of ApoE−/− mice. In ApoE−/−, no significant change was observed in mitochondrial respiration or protein carbonylation. The dose of 0.2Gy had no significant effects on cardiac mitochondria. ConclusionThis study suggests that ionising radiation causes non-transient alterations in cardiac mitochondria, resulting in oxidative stress that may ultimately lead to malfunctioning of the heart muscle.

Mitochondrial involvement in chronic chagasic cardiomyopathy

The pathogenesis of chronic chagasic cardiopathy is still under discussion; there is considerable evidence that inflammatory infiltrates and their mediators have a direct effect on cardiac cells. Here we studied the structure and function of cardiac mitochondria in chronic chagasic myocardiopathy. Cardiac mitochondrial structure and enzyme activity of citrate synthase and complexes I to IV of the respiratory chain were studied in albino Swiss mice infected with Trypanosoma cruzi (Tulahuen strain or SGO Z12 isolate) on 365 days post-infection (dpi). The presence of parasites in cardiac and skeletal muscle was also investigated. The activity of complexes I to IV was altered in different ways, according to the strain employed (P<0.0001), in relation to the cristae disorganisation and the parasite persistence found in the Tulahuen group, and the chronic inflammatory process described in both groups; citrate synthase activity also increased in both infected groups. Changes in mitochondrial structure were detected in 89% of Tulahuen- and 58% of SGO Z12-infected mice. In this paper we demonstrate that parasite persistence and inflammation are likely to be involved in the structural and functional alterations in cardiac mitochondria from chronically T. cruzi-infected mice, demonstrating that the parasite strain determines different mitochondrial changes in chagasic cardiopathy.

Trypanosoma cruzi: Cardiac mitochondrial alterations produced by different strains in the acute phase of the infection

The parasite Trypanosoma cruzi is the causative agent of Chagas disease. T. cruzi invasion and replication in cardiomyocytes induce cellular injuries and cytotoxic reactions, with the production of inflammatory cytokines and nitric oxide, both source of reactive oxygen species. The myocyte response to oxidative stress involves the progression of cellular changes primarily targeting mitochondria. We studied the cardiac mitochondrial structure and the enzymatic activity of citrate synthase and respiratory chain CI–CIV complexes, in Albino Swiss mice infected with T. cruzi, Tulahuen strain and SGO Z12 isolate, in two periods of the acute infection. Changes in the mitochondrial structure were detected in both infected groups, reaching values of 71% for Tulahuen and 88% for SGO Z12 infected mice, 30 days post infection. The citrate synthase activity was different according to the evolution of the infection and the parasite strain, but the respiratory chain alterations were similar with either strain.

Cardiac mitochondrial alterations induced by insulin deficiency and hyperinsulinaemia in rats: Targeting membrane homeostasis with trimetazidine

The present study investigated the ability of trimetazidine (TMZ) to maintain cardiac mitochondrial function during the development of insulin deficiency and hyperinsulinaemia. The anti-ischaemic drug TMZ is known to increase phospholipid synthesis in cardiac membranes and to have a cardioprotective effect. Insulin deficiency was obtained by streptozotocin injection and hyperinsulinaemia was achieved via a fructose diet. Trimetazidine was incorporated into the diet (7.8 mg/day) and mitochondrial function was evaluated in skinned cardiac fibres. Insulin deficiency decreased mitochondrial affinity for ADP and the index of creatine kinase functional activity. This last alteration was partially prevented by TMZ treatment. Insulin deficiency strongly decreased n-3 polyunsaturated fatty acids, especially the docosahexaenoic acid (DHA) content, in cardiac and mitochondrial membranes, inducing a strong increase in the n-6/n-3 ratio. Trimetazidine treatment limited the increase in the n-6/n-3 ratio and prevented the decrease in DHA content in mitochondrial membranes. Insulin deficiency decreased glutamate- and palmitoylcarnitine-supported respiration. Hyperinsulinaemia affected neither mitochondrial affinity for ADP nor the index of creatine kinase functional activity. Hyperinsulinaemia slightly and significantly affected mitochondrial fatty acid composition, by a small increase the n-6/n-3 ratio. Trimetazidine did not modify membrane-bound mitochondrial function but increased the n-6/n-3 ratio. Moreover, hyperinsulinaemia decreased glutamate-supported respiration. In conclusion, modification of membrane homeostasis with TMZ partially prevented the alterations in fatty acid composition and function in cardiac mitochondria induced by insulin deficiency. Three months of hyperinsulinaemia did not modify membrane-bound mitochondrial function and had only slight effects on fatty acid composition.

Cardiac Mitochondrial Alterations Observed in Hyperglycaemic Rats - What Can We Learn From Cell Biology?

Diabetes mellitus is one of the most common metabolic diseases in the world. The complications associated with this disease are often responsible for a decreased quality of life in many patients. For example, the diabetic population has a greater probability to suffer from cardiovascular problems and heart failure than the general population. Due to the importance heart mitochondria have in the context of the bioenergetics of the myocardium, it appears logical to explore mitochondrial dysfunction as an important link between hyperglycaemia and heart alterations observed during diabetes. One important factor that can lead to mitochondrial dysfunction is the mitochondrial permeability transition (MPT), caused by the formation of poly-protein pores (MPT pores), occurring with mitochondrial calcium overload and increased oxidative stress, conditions already described to exist in myocytes exposed to hyperglycaemia. The MPT has been involved as determinant in the survival of myocytes after anoxia and reoxigenation, as well as in triggering cell death. The present review deals with cardiac mitochondrial alterations observed in drug-induced hyperglycaemic animals or in the GK rat, a hereditary model of hyperglycaemia. Respiration rates, susceptibility to oxidative stress, protein expression and MPT induction are altered in hyperglycaemic animals, which in extreme conditions can alter the bioenergetics of the diabetic myocardium and even cause myocardial cell death. The study of the cardiac mitochondrial function of hyperglycaemic animals offer an important insight, not only to explain cardiac alterations found in diabetic patients, but also in the design of new therapeutic approaches to reduce mitochondrial dysfunction and cell death typically associated with diabetes.

Docosahexaenoic acid affects insulin deficiency- and insulin resistance-induced alterations in cardiac mitochondria

The effect of docosahexaenoic acid (DHA) intake on cardiac mitochondrial function was evaluated in permeabilized fibers in insulin deficiency and insulin resistance in rats. The insulin-deficient state was obtained by streptozotocin injection 2 mo before investigations. Insulin resistance was obtained by feeding a 62% fructose diet for 3 mo. DHA was incorporated in the diet to modify the fatty acid composition of cardiac membranes, including mitochondria. Insulin deficiency decreased mitochondrial creatine kinase (mi-CK) activity and mitochondrial sensitivity to ADP. DHA intake prevented these alterations. Moreover, the insulin-deficient state significantly decreased n-3 polyunsaturated fatty acids (PUFA) and slightly increased n-6 PUFA in both cardiac and mitochondrial membranes, inducing a significant increase in the n-6-to-n-3 ratio. DHA intake maintained high myocardial and mitochondrial DHA content. Insulin deficiency also decreased glutamate- and palmitoylcarnitine-supported mitochondrial respiration, but DHA intake did not prevent these effects. In contrast, insulin resistance did not affect mi-CK activity or sensitivity to ADP. However, insulin resistance influenced the myocardial fatty acid composition with decreased n-6 and n-3 PUFA contents and increased monounsaturated fatty acid content. Only slight alterations were observed in mitochondrial fatty acid composition, and they were corrected by DHA intake. Moreover, insulin resistance decreased the glutamate-supported respiration, and DHA intake did not influence this effect. In conclusion, the impairment of cardiac mitochondrial function was more pronounced in the insulin-deficient state than in insulin resistance. The modification of fatty acid composition of cardiac and mitochondrial membranes by DHA partially prevented the mitochondrial alterations induced in the two models.

Functional consequences of thyroid hormone-induced changes in the mitochondrial protein import pathway.

Thyroid hormone [3,5,3'-triiodo-l-thyronine (T(3))] induces phenotypic alterations in cardiac mitochondria, in part by influencing protein import and the expression of the import motor mitochondrial heat shock protein (mtHsp70). Here we examined the adaptability of translocases of the inner membrane (Tim) proteins, as well as the outer membrane receptor Tom34, to T(3). Administration of T(3) to rats for 5 days increased cardiac Tim23 and Tim44 mRNA levels by 55 and 50%, respectively, but had no effect on Tim17. T(3) treatment also induced a 45% increase in Tom34 mRNA, with no accompanying changes at the protein level, suggesting regulation at the posttranscriptional level. In H9c2 cardiac cells, Tim17 mRNA was elevated by 114% by 9 days of differentiation, whereas Tim23 and Tim44 declined by 25 and 29%, respectively. To determine the functional consequences of these T(3)-induced changes, malate dehydrogenase (MDH) import rates were measured in H9c2 cells stably overexpressing Tim44 and mtHsp70, either alone or in combination. MDH import remained unaltered in cells overexpressing Tim44 or in cells overexpressing both Tim44 and mtHsp70. However, when mtHsp70 was overexpressed alone, a 13% (P < 0.05) increase in MDH import rate was observed. These findings indicate that import machinery components are differentially regulated in response to stimuli that induce mitochondrial biogenesis, like T(3) and differentiation. In addition, the induction of an import machinery component in response to T(3) may not necessarily result in functional changes in protein import during mitochondrial biogenesis. Finally, mtHsp70 may play a regulatory role in the import process that is independent of its interaction with Tim44.

Effects of newly-developed benzodiazepine ligands on noise-induced mitochondrial damage in the rat

In this study we measured the ability of three newly-synthesized N-arylalkylindol-3-ylglyoxylylamide derivatives, which have recently been characterized as partial agonists at central benzodiazepine binding sites, to prevent the rat cardiac mitochondrial alterations resulting from acute loud noise exposure. In particular, we evaluated the effects of these new compounds on the ultrastructural damage induced by noise stress on the right atrium and ventricle after 6 and 12 hr of loud noise exposure. In parallel experiments, we measured the affinity of these compounds for peripheral benzodiazepine binding sites. Following a single injection of the test products, we observed a cardioprotective effect which was more marked after 6 hr compared with 12 hr of noise exposure. Confirming our recent data showing that full agonists at benzodiazepine receptors produce cardioprotection, we demonstrate in this study that partial agonists, like indolylglyoxylylamides, can also produce a cardioprotective effect. Based on their greater affinity in binding studies, the protective activity seems to be related more to their action at central than at peripheral benzodiazepine receptors.