Adenine nucleotide translocator in heart

The UL16 protein of HSV-1 promotes the metabolism of cell mitochondria by binding to ANT2 protein

Long-term studies have shown that virus infection affects the energy metabolism of host cells, which mainly affects the function of mitochondria and leads to the hydrolysis of ATP in host cells, but it is not clear how virus infection participates in mitochondrial energy metabolism in host cells. In our study, HUVEC cells were infected with HSV-1, and the differentially expressed genes were obtained by microarray analysis and data analysis. The viral gene encoding protein UL16 was identified to interact with host protein ANT2 by immunoprecipitation and mass spectrometry. We also reported that UL16 transfection promoted oxidative phosphorylation of glucose and significantly increased intracellular ATP content. Furthermore, UL16 was transfected into the HUVEC cell model with mitochondrial dysfunction induced by d-Gal, and it was found that UL16 could restore the mitochondrial function of cells. It was first discovered that viral protein UL16 could enhance mitochondrial function in mammalian cells by promoting mitochondrial metabolism. This study provides a theoretical basis for the prevention and treatment of mitochondrial dysfunction or the pathological process related to mitochondrial dysfunction.

A Walk in the Memory, from the First Functional Approach up to Its Regulatory Role of Mitochondrial Bioenergetic Flow in Health and Disease: Focus on the Adenine Nucleotide Translocator

The mitochondrial adenine nucleotide translocator (ANT) plays the fundamental role of gatekeeper of cellular energy flow, carrying out the reversible exchange of ADP for ATP across the inner mitochondrial membrane. ADP enters the mitochondria where, through the oxidative phosphorylation process, it is the substrate of Fo-F1 ATP synthase, producing ATP that is dispatched from the mitochondrion to the cytoplasm of the host cell, where it can be used as energy currency for the metabolic needs of the cell that require energy. Long ago, we performed a method that allowed us to monitor the activity of ANT by continuously detecting the ATP gradually produced inside the mitochondria and exported in the extramitochondrial phase in exchange with externally added ADP, under conditions quite close to a physiological state, i.e., when oxidative phosphorylation takes place. More than 30 years after the development of the method, here we aim to put the spotlight on it and to emphasize its versatile applicability in the most varied pathophysiological conditions, reviewing all the studies, in which we were able to observe what really happened in the cell thanks to the use of the "ATP detecting system" allowing the functional activity of the ANT-mediated ADP/ATP exchange to be measured.

Downregulation of adenine nucleotide translocator 1 exacerbates tumor necrosis factor-α-mediated cardiac inflammatory responses

Inflammation contributes significantly to cardiac dysfunction. Although the initial phase of inflammation is essential for repair and healing, excessive proinflammatory cytokines are detrimental to the heart. We found that adenine nucleotide translocator isoform-1 (ANT1) protein levels were significantly decreased in the inflamed heart of C57BL/6 mice following cecal ligation and puncture. To understand the molecular mechanisms involved, we performed small-interfering RNA-mediated knockdown of ANT1 and studied tumor necrosis factor-α (TNFα)-induced inflammatory responses in myocardium-derived H9c2 cells and cardiomyocytes. ANT1 knockdown significantly increased swollen mitochondria and mitochondrial reactive oxygen species, concomitant with increased TNFα-induced NF-κB reporter gene activity and interleukin-6 and TNFα expression. A mitochondrial-targeted antioxidant mito-TEMPO attenuated TNFα-induced mitochondrial reactive oxygen species, NF-κB reporter gene activity, and cytokine expression in ANT1 knockdown cells. Interestingly, TNFα or lipopolysaccharide (LPS) treatment significantly decreased ANT1 protein levels, suggesting a feed-forward regulation of proinflammatory cytokine expression activated by ANT1 downregulation. These data suggest that ANT1 downregulation contributes to cardiac inflammation post-cecal ligation and puncture. Preventing ANT1 downregulation could provide a novel molecular target to temper cardiac inflammation.

Human myocardial protein pattern reveals cardiac diseases

Proteomic profiles of myocardial tissue in two different etiologies of heart failure were investigated using high performance liquid chromatography (HPLC)/Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Right atrial appendages from 10 patients with hemodynamically significant isolated aortic valve disease and from 10 patients with isolated symptomatic coronary heart disease were collected during elective cardiac surgery. As presented in an earlier study by our group (Baykut et al., 2006), both disease forms showed clearly different pattern distribution characteristics. Interesting enough, the classification patterns could be used for correctly sorting unknown test samples in their correct categories. However, in order to fully exploit and also validate these findings there is a definite need for unambiguous identification of the differences between different etiologies at molecular level. In this study, samples representative for the aortic valve disease and coronary heart disease were prepared, tryptically digested, and analyzed using an FT-ICR MS that allowed collision-induced dissociation (CID) of selected classifier masses. By using the fragment spectra, proteins were identified by database searches. For comparison and further validation, classifier masses were also fragmented and analyzed using HPLC-/Matrix-assisted laser desorption ionization (MALDI) time-of-flight/time-of-flight (TOF/TOF) mass spectrometry. Desmin and lumican precursor were examples of proteins found in aortic samples at higher abundances than in coronary samples. Similarly, adenylate kinase isoenzyme was found in coronary samples at a higher abundance. The described methodology could also be feasible in search for specific biomarkers in plasma or serum for diagnostic purposes.

The rate of ATP export in the extramitochondrial phase via the adenine nucleotide translocator changes in aging in mitochondria isolated from heart left ventricle of either normotensive or spontaneously hypertensive rats

To find out whether and how deficit of cellular energy supply from mitochondria to cytosol occurs in aging and hypertension, we used mitochondria isolated from 5 to 72 week-old heart left ventricle of either normotensive (WKY) or spontaneous hypertensive (SH) rats as a model system. Measurements were made of the rate of ATP appearance outside mitochondria, due to externally added ADP, as an increase of NADPH absorbance which occurs when ATP is produced in the presence of glucose, hexokinase and glucose-6-phosphate dehydrogenase. Such a rate proved to mirror the function of the adenine nucleotide translocator (ANT) rather than other processes linked to the both oxidative and substrate level phosphorylation. The changes in both Ki for atractyloside and Km for ADP suggest the occurrence of modification of the ANT conformation during aging in which the ANT Vmax was found to decrease in normotensive but to increase under spontaneously hypertension in 24 week-old rats with a subsequent decrease in both cases. ANT function, as investigated in the ADP physiological range (20-60μM), is expected to decrease in normotensive, but to increase in hypertensive rats up to 48 weeks. Later a decrease in the ATP rate of export outside mitochondria should occur in both cases.

Accelerated mitochondrial adenosine diphosphate/adenosine triphosphate transport improves hypertension-induced heart disease

BACKGROUND

Strong evidence suggests that mitochondrial malfunction, which leads to disturbed energy metabolism and stimulated apoptosis, is a linchpin in the induction and manifestation of cardiac failure. An adequate exchange of ATP and ADP over the inner mitochondrial membrane by the adenine nucleotide translocase (ANT) is thereby essential to guarantee the cellular energy supply.

METHODS AND RESULTS

To explore the effect of an ameliorated mitochondrial ATP/ADP transportation on cardiac dysfunction, we generated transgenic rats overexpressing ANT1 in the heart (ANT rats) and crossed them with renin-overexpressing rats (REN rats) suffering from hypertension-induced cardiac insufficiency. Cardiac-specific ANT1 overexpression resulted in a higher ATP/ADP transportation and elevated activities of respiratory chain complexes. Increased ANT activity in double-transgenic (ANT/REN) animals did not influence excessive hypertension seen in REN rats. Hypertension-induced cardiac hypertrophy in the REN rats was prevented by parallel ANT1 overexpression, however, and left ventricular function remarkably improved. The ANT1 overexpression led to a reduction in fibrosis and an improvement in cardiac tissue architecture. Consequently, the survival rate of ANT/REN rats was enhanced. Further investigations into the cardioprotective mechanism of ANT1 overexpression revealed improved mitochondrial structure and function and significantly reduced apoptosis in ANT/REN rats, shown by lowered cytosolic/mitochondrial cytochrome c ratio, reduced caspase 3 level, and prevented DNA degradation.

CONCLUSIONS

Myocardial ANT1 overexpression protects against hypertension-induced cardiac pathology. Thus, the improvement in mitochondrial function may be a basic principle for new strategies in treating heart disease.

Depletion of adenine nucleotide translocator protein in heart mitochondria from doxorubicin-treated rats—Relevance for mitochondrial dysfunction

Doxorubicin (DOX) is a highly effective treatment for several forms of cancer. However, DOX induces a cumulative and dose-dependent cardiomyopathy that has been ascribed to redox-cycling of the molecule on the mitochondrial complex I generating in the process increased oxidative stress. Mitochondrial dysfunction, including induction of the mitochondrial permeability transition (MPT) and inhibition of mitochondrial respiration have been implicated as major determinants in the pathogenesis of DOX cardiotoxicity. The adenine nucleotide translocator (ANT) has been suggested to be a principal component of the MPT pore and a possible target for DOX-induced cardiotoxicity. Nonetheless, no definitive evidence has been presented showing that altered ANT activity is due to decreased amount of the protein. By using carboxyatractyloside as a specific modulator of ANT activity and Western blotting, we observed that following DOX treatment in rats: (1) the amount of "functional ANT" that contributes to cardiac mitochondrial respiration with different substrates is reduced, (2) titrations with carboxyatracyloside revealed a lower threshold for MPT induction and most importantly, (3) a specific decrease in the amount of the ANT protein. This study identifies the ANT as one important target for DOX-induced cardiac toxicity and correlates the decrease in ANT protein concentration with inhibition of mitochondrial respiration and increased ability to form or at least regulate MPT pores.

Arachidonic acid induces specific membrane permeability increase in heart mitochondria

Micromolar concentrations of arachidonic acid cause in Ca2+ loaded heart mitochondria matrix swelling and Ca2+ release. These effects appear to be unrelated to the classical membrane permeability transition (MPT), as they are CsA insensitive, membrane potential independent and can also be activated by Sr2+. Atractyloside potentiated and ATP inhibited the arachidonic acid induced swelling. These observations suggest that the ATP/ADP translocator (ANT) may be involved in the AA induced, CsA insensitive membrane permeability increase. Under the same experimental conditions used for heart mitochondria, arachidonic acid induced the classical CsA sensitive, ADP inhibitable MPT in liver mitochondria.

Serotonin is a novel survival factor of cardiomyocytes: mitochondria as a target of 5-HT2B receptor signaling

Identification of factors regulating cardiomyocyte survival and growth is important to understand the pathogenesis of congenital heart diseases. Little is known about the molecular mechanism of cardiac functions triggered by serotonin. The link between signaling circuitry of external stimuli and the mitochondrial apoptotic machinery is of wide interest in cardiac diseases. Using cultured cardiomyocytes and 5-hydroxytryptamine (5-HT)2B-receptor knockout mice as an animal model of dilated cardiomyopathy, for the first time we show that serotonin via the Gq-coupled 5-HT2B-receptor protect cardiomyocytes against serum deprivation-induced apoptosis as manifested by DNA fragmentation, nuclear chromatin condensation, and TUNEL labeling. Serotonin prevents cytochrome c release and caspase-9 and -3 activation after serum deprivation via cross-talks between phosphatidylinositol-3 kinase/Akt and extracellular signal-regulated kinase (ERK) 1/2 signaling pathways. Serotonin binding to 5-HT2B-receptor activates ERK kinases to inhibit Bax expression induced by serum deprivation. Serotonin via phosphatidylinositol-3 kinase/Akt can activate NF-kappaB that is required for the regulation of the mitochondrial adenine nucleotide translocator (ANT-1). Parallel to these observations, ultrastructural analysis in the 5-HT2B-receptor knockout mice heart revealed pronounced mitochondrial defects in addition to altered mitochondrial enzyme activities (cytochrome oxidase and succinate dehydrogenase) and ANT-1 and Bax expressions. These findings identify 5-HT as a novel survival factor targeting mitochondria in cardiomyocytes.

Overexpression of the serotonin 5-HT2B receptor in heart leads to abnormal mitochondrial function and cardiac hypertrophy

BACKGROUND

Identification of factors regulating myocardial structure and function is important to understand the pathogenesis of heart disease. We previously reported that 5-HT2B receptor ablation in mice leads to dilated cardiomyopathy. In this study, we investigated the pathological consequence of overexpressing 5-HT2B receptors in heart in vivo.

METHODS AND RESULTS

We have generated transgenic mice overexpressing the Gq-coupled 5-HT2B receptor specifically in heart. We found that overexpression of 5-HT2B receptor in heart leads to ventricular hypertrophy as the result of increased cell number and size. Increased atrial natriuretic peptide and myosin heavy chain expression demonstrated activation of the molecular program for cardiac hypertrophy. Echocardiographic analysis indicated the presence of thickened ventricular free wall without alteration of the systolic function, showing that transgenic mice have compensated hypertrophy. Electron microscopic analysis revealed structural abnormalities including mitochondrial proliferation, as also manifested by histological staining. Transgenic mouse heart displayed a specific reduction in the expression levels of the adenine nucleotide translocator associated to increase in the succinate dehydrogenase and cytochrome C oxidase mitochondrial activities.

CONCLUSIONS

Our results constitute the first genetic evidence that overexpression of the 5-HT2B receptor in the heart leads to compensated hypertrophic cardiomyopathy associated with proliferation of the mitochondria. This observation suggests a role for mitochondria in the hypertrophic signaling that is regulated by serotonin. These transgenic mice provide a new genetic model for hypertrophic heart disease.

The role of mitochondrial transport in energy metabolism

Since mitochondria are closed spaces in the cell, metabolite traffic across the mitochondrial membrane is needed to accomplish energy metabolism. The mitochondrial carriers play this function by uniport, symport and antiport processes. We give here a survey of about 50 transport processes catalysed by more than 30 carriers with a survey of the methods used to investigate metabolite transport in isolated mammalian mitochondria. The role of mitochondria in metabolic pathways including ammoniogenesis, amino acid metabolism, mitochondrial shuttles etc. is also reported in more detail, mainly in the light of the existence of new transport processes.