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

Treatments for skeletal muscle abnormalities in heart failure: sodium-glucose transporter 2 and ketone bodies

Various skeletal muscle abnormalities are known to occur in heart failure (HF), and are closely associated with exercise intolerance. Particularly, abnormal energy metabolism caused by mitochondrial dysfunction in skeletal muscle is a cause of decreased endurance exercise capacity. However, to date, no specific drug treatment has been established for the skeletal muscle abnormalities and exercise intolerance occurring in HF patients. Sodium-glucose transporter 2 (SGLT2) inhibitors promote glucose excretion by suppressing glucose reabsorption in the renal tubules, which has a hypoglycemic effect independent of insulin secretion. Recently, large clinical trials have demonstrated that treatment with SGLT2 inhibitors suppresses cardiovascular events in patients who have HF with systolic dysfunction. Mechanisms of the therapeutic effects of SGLT2 inhibitors for HF have been suggested to be diuretic, suppression of neurohumoral factor activation, renal protection, and improvement of myocardial metabolism, but has not been clarified to date. SGLT2 inhibitors are known to increase blood ketone bodies. This suggests that they may improve the abnormal skeletal muscle metabolism in HF, i.e., improve fatty acid metabolism, suppress glycolysis, and utilize ketone bodies in mitochondrial energy production. Ultimately, they may improve aerobic metabolism in skeletal muscle, and suppress anaerobic metabolism and improve aerobic exercise capacity at the level of the anaerobic threshold. The potential actions of such SGLT2 inhibitors explain their effectiveness in HF, and may be candidates for new drug treatments aimed at improving exercise intolerance. In this review, we outlined the effects of SGLT2 inhibitors on skeletal muscle metabolism, with a particular focus on ketone metabolism.

Effects of high rosuvastatin doses on hepatocyte mitochondria of hypercholesterolemic mice

Statins are the cornerstone of therapy for individuals with hyperlipidemia. The aim of this study was to analyze the undesirable effects of mild, moderate and high doses of rosuvastatin in CD-1 male mice who received a cholesterol-rich diet, focusing on the morphological and functional changes on hepatocyte mitochondria. In a mouse model we studied the combined administration of a cholesterol-rich diet along with mild and moderate doses of rosuvastatin (1, 2.5 or 5 mg/kg/day) during several days. After the animals were sacrificed, liver mitochondria were isolated for microscopic studies and to analyze the respiratory function. The respiratory control (state-3/state-4) was evaluated in mice who received high doses of rosuvastatin. Rosuvastatin doses higher than 20 mg/kg/day induced premature death in mice with a hypercholesterolemic diet, but not in mice with a cholesterol-free diet. Doses from 2.5 to 5 mg/kg/day also induced morphological and functional alterations in mitochondria but these hypercholesterolemic animals survived longer. Giving 1 mg/kg/day, which is close to the maximal therapeutic dose for humans, did not affect mitochondrial architecture or respiratory function after two months of treatment. We analyzed the effect of rosuvastatin on hepatic tissue because it is where statins are mainly accumulated and it is the main site of endogenous cholesterol synthesis. Our results contribute to understand the side effects of rosuvastatin in hypercholesterolemic mice, effects that could also affect humans who are intolerant to statins.

High-fat diet affects skeletal muscle mitochondria comparable to pressure overload-induced heart failure

In heart failure, high-fat diet (HFD) may exert beneficial effects on cardiac mitochondria and contractility. Skeletal muscle mitochondrial dysfunction in heart failure is associated with myopathy. However, it is not clear if HFD affects skeletal muscle mitochondria in heart failure as well. To induce heart failure, we used pressure overload (PO) in rats fed normal chow or HFD. Interfibrillar mitochondria (IFM) and subsarcolemmal mitochondria (SSM) from gastrocnemius were isolated and functionally characterized. With PO heart failure, maximal respiratory capacity was impaired in IFM but increased in SSM of gastrocnemius. Unexpectedly, HFD affected mitochondria comparably to PO. In combination, PO and HFD showed additive effects on mitochondrial subpopulations which were reflected by isolated complex activities. While PO impaired diastolic as well as systolic cardiac function and increased glucose tolerance, HFD did not affect cardiac function but decreased glucose tolerance. We conclude that HFD and PO heart failure have comparable effects leading to more severe impairment of IFM. Glucose tolerance seems not causally related to skeletal muscle mitochondrial dysfunction. The additive effects of HFD and PO may suggest accelerated skeletal muscle mitochondrial dysfunction when heart failure is accompanied with a diet containing high fat.

Alterations of skeletal muscle bioenergetics in a mouse with F508del mutation leading to a cystic fibrosis-like condition

High energy expenditure is reported in cystic fibrosis (CF) animal models and patients. Alterations in skeletal muscle oxidative capacity, fuel utilization, and the creatine kinase-phosphocreatine system suggest mitochondrial dysfunction. Studies were performed on congenic C57BL/6J and F508del (Cftr^tm1kth) mice. Indirect calorimetry was used to measure gas exchange to evaluate aerobic capacity during treadmill exercise. The bioenergetic function of skeletal muscle subsarcolemmal (SSM) and interfibrillar mitochondria (IFM) was evaluated using an integrated approach combining measurement of the rate of oxidative phosphorylation by polarography and of electron transport chain activities by spectrophotometry. CF mice have reduced maximal aerobic capacity. In SSM of these mice, oxidative phosphorylation was impaired in the presence of complex I, II, III, and IV substrates except when glutamate was used as substrate. This impairment appeared to be caused by a defect in complex V activity, whereas the oxidative system of the electron transport chain was unchanged. In IFM, oxidative phosphorylation and electron transport chain activities were preserved, whereas complex V activity was reduced, in CF. Furthermore, creatine kinase activity was reduced in both SSM and IFM of CF skeletal muscle. The decreased complex V activity in SSM resulted in reduced oxidative phosphorylation, which could explain the reduced skeletal muscle response to exercise in CF mice. The decrease in mitochondrial creatine kinase activity also contributed to this poor exercise response.

Kummitha C, Rosca MG, Fujioka H, Tandler B, Hoppel CL. Isolation of mitochondrial subpopulations from skeletal muscle: Optimizing recovery and preserving integrity

AIM

The subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria in skeletal muscle appear to have distinct biochemical properties affecting metabolism in health and disease. The isolation of mitochondrial subpopulations has been a long-time challenge while the presence of a continuous mitochondrial reticulum challenges the view of distinctive SSM and IFM bioenergetics. Here, a comprehensive approach is developed to identify the best conditions to separate mitochondrial fractions.

METHODS

The main modifications to the protocol to isolate SSM and IFM from rat skeletal muscle were: (a) decreased dispase content and homogenization speed; (b) trypsin treatment of SSM fractions; (c) recentrifugation of mitochondrial fractions at low speed to remove subcellular components. To identify the conditions preserving mitochondrial function, integrity, and maximizing their recovery, microscopy (light and electron) were used to monitor effectiveness and efficiency in separating mitochondrial subpopulations while respiratory and enzyme activities were employed to evaluate function, recovery, and integrity.

RESULTS

With the modifications described, the total mitochondrial yield increased with a recovery of 80% of mitochondria contained in the original skeletal muscle sample. The difference between SSM and IFM oxidative capacity (10%) with complex-I substrate was significant only with a saturated ADP concentration. The inner and outer membrane damage for both subpopulations was <1% and 8%, respectively, while the respiratory control ratio was 16.

CONCLUSION

Using a multidisciplinary approach, conditions were identified to maximize SSM and IFM recovery while preserving mitochondrial integrity, biochemistry, and morphology. High quality and recovery of mitochondrial subpopulations allow to study the relationship between these organelles and disease.

Defects in skeletal muscle subsarcolemmal mitochondria in a non-obese model of type 2 diabetes mellitus

Skeletal muscle resistance to insulin is related to accumulation of lipid-derived products, but it is not clear whether this accumulation is caused by skeletal muscle mitochondrial dysfunction. Diabetes and obesity are reported to have a selective effect on the function of subsarcolemmal and interfibrillar mitochondria in insulin-resistant skeletal muscle. The current study investigated the role of the subpopulations of mitochondria in the pathogenesis of insulin resistance in the absence of obesity. A non-obese spontaneous rat model of type 2 diabetes mellitus, (Goto-Kakizaki), was used to evaluate function and biochemical properties in both populations of skeletal muscle mitochondria. In subsarcolemmal mitochondria, minor defects are observed whereas in interfibrillar mitochondria function is preserved. Subsarcolemmal mitochondria defects characterized by a mild decline of oxidative phosphorylation efficiency are related to ATP synthase and structural alterations of inner mitochondria membrane but are considered unimportant because of the absence of defects upstream as shown with polarographic and spectrophometric assays. Fatty acid transport and oxidation is preserved in both population of mitochondria, whereas palmitoyl-CoA increased 25% in interfibrillar mitochondria of diabetic rats. Contrary to popular belief, these data provide compelling evidence that mitochondrial function is unaffected in insulin-resistant skeletal muscle from T2DM non-obese rats.

Respiratory Muscle Training Improves Diaphragm Citrate Synthase Activity and Hemodynamic Function in Rats with Heart Failure

Introduction

Enhanced respiratory muscle strength in patients with heart failure positively alters the clinical trajectory of heart failure. In an experimental model, respiratory muscle training in rats with heart failure has been shown to improve cardiopulmonary function through mechanisms yet to be entirely elucidated.

Objective

The present report aimed to evaluate the respiratory muscle training effects in diaphragm citrate synthase activity and hemodynamic function in rats with heart failure.

Methods

Wistar rats were divided into four experimental groups: sedentary sham (Sed-Sham, n=8), trained sham (RMT-Sham, n=8), sedentary heart failure (Sed-HF, n=7) and trained heart failure (RMT-HF, n=7). The animals were submitted to a RMT protocol performed 30 minutes a day, 5 days/week, for 6 weeks.

Results

In rats with heart failure, respiratory muscle training decreased pulmonary congestion and right ventricular hypertrophy. Deleterious alterations in left ventricular pressures, as well as left ventricular contractility and relaxation, were assuaged by respiratory muscle training in heart failure rats. Citrate synthase activity, which was significantly reduced in heart failure rats, was preserved by respiratory muscle training. Additionally, a negative correlation was found between citrate synthase and left ventricular end diastolic pressure and positive correlation was found between citrate synthase and left ventricular systolic pressure.

Conclusion

Respiratory muscle training produces beneficial adaptations in the diaphragmatic musculature, which is linked to improvements in left ventricular hemodynamics and blood pressure in heart failure rats. The RMT-induced improvements in cardiac architecture and the oxidative capacity of the diaphragm may improve the clinical trajectory of patients with heart failure.

Skeletal Muscle Abnormalities in Heart Failure

Exercise capacity is lowered in patients with heart failure, which limits their daily activities and also reduces their quality of life. Furthermore, lowered exercise capacity has been well demonstrated to be closely related to the severity and prognosis of heart failure. Skeletal muscle abnormalities including abnormal energy metabolism, transition of myofibers from type I to type II, mitochondrial dysfunction, reduction in muscular strength, and muscle atrophy have been shown to play a central role in lowered exercise capacity. The skeletal muscle abnormalities can be classified into the following main types: 1) low endurance due to mitochondrial dysfunction; and 2) low muscle mass and muscle strength due to imbalance of protein synthesis and degradation. The molecular mechanisms of these skeletal muscle abnormalities have been studied mainly using animal models. The current review including our recent study will focus upon the skeletal muscle abnormalities in heart failure.

Skeletal muscle mitochondria exhibit decreased pyruvate oxidation capacity and increased ROS emission during surgery-induced acute insulin resistance

Development of acute insulin resistance represents a negative factor after surgery, but the underlying mechanisms are not fully understood. We investigated the postoperative changes in insulin sensitivity, mitochondrial function, enzyme activities, and release of reactive oxygen species (ROS) in skeletal muscle and liver in pigs on the 2nd postoperative day after major abdominal surgery. Peripheral and hepatic insulin sensitivity were assessed by D-[6,6-²H₂]glucose infusion and hyperinsulinemic euglycemic step clamping. Surgical trauma elicited a decline in peripheral insulin sensitivity (∼34%, P<0.01), whereas hepatic insulin sensitivity remained unchanged. Intramyofibrillar (IFM) and subsarcolemma mitochondria (SSM) isolated from skeletal muscle showed a postoperative decline in ADP-stimulated respiration (V(ADP)) for pyruvate (∼61%, P<0.05, and ∼40%, P<0.001, respectively), whereas V(ADP) for glutamate and palmitoyl-L-carnitine (PC) was unchanged. Mitochondrial leak respiration with PC was increased in SSM (1.9-fold, P<0.05) and IFM (2.5-fold, P<0.05), indicating FFA-induced uncoupling. The activity of the pyruvate dehydrogenase complex (PDC) was reduced (∼32%, P<0.01) and positively correlated to the decline in peripheral insulin sensitivity (r=0.748, P<0.05). All other mitochondrial enzyme activities were unchanged. No changes in mitochondrial function in liver were observed. Mitochondrial H₂O₂ and O₂·⁻ emission was measured spectrofluorometrically, and H₂O₂ was increased in SSM, IFM, and liver mitochondria (∼2.3-, ∼2.5-, and ∼2.3-fold, respectively, all P<0.05). We conclude that an impairment in skeletal muscle mitochondrial PDC activity and pyruvate oxidation capacity arises in the postoperative phase along with increased ROS emission, suggesting a link between mitochondrial function and development of acute postoperative insulin resistance.

Acetyl-L-carnitine increases mitochondrial protein acetylation in the aged rat heart

Previously we showed that in vivo treatment of elderly Fisher 344 rats with acetylcarnitine abolished the age-associated defect in respiratory chain complex III in interfibrillar mitochondria and improved the functional recovery of the ischemic/reperfused heart. Herein, we explored mitochondrial protein acetylation as a possible mechanism for acetylcarnitine's effect. In vivo treatment of elderly rats with acetylcarnitine restored cardiac acetylcarnitine content and increased mitochondrial protein lysine acetylation and increased the number of lysine-acetylated proteins in cardiac subsarcolemmal and interfibrillar mitochondria. Enzymes of the tricarboxylic acid cycle, mitochondrial β-oxidation, and ATP synthase of the respiratory chain showed the greatest acetylation. Acetylation of isocitrate dehydrogenase, long-chain acyl-CoA dehydrogenase, complex V, and aspartate aminotransferase was accompanied by decreased catalytic activity. Several proteins were found to be acetylated only after treatment with acetylcarnitine, suggesting that exogenous acetylcarnitine served as the acetyl-donor. Two-dimensional fluorescence difference gel electrophoresis analysis revealed that acetylcarnitine treatment also induced changes in mitochondrial protein amount; a two-fold or greater increase/decrease in abundance was observed for thirty one proteins. Collectively, our data provide evidence for the first time that in the aged rat heart in vivo administration of acetylcarnitine provides acetyl groups for protein acetylation and affects the amount of mitochondrial proteins.

Transgenic overexpression of mitofilin attenuates diabetes mellitus-associated cardiac and mitochondria dysfunction

Mitofilin, also known as heart muscle protein, is an inner mitochondrial membrane structural protein that plays a central role in maintaining cristae morphology and structure. It is a critical component of the mitochondrial contact site and cristae organizing system (MICOS) complex which is important for mitochondrial architecture and cristae morphology. Our laboratory has previously reported alterations in mitochondrial morphology and proteomic make-up during type 1 diabetes mellitus, with mitofilin being significantly down-regulated in interfibrillar mitochondria (IFM). The goal of this study was to investigate whether overexpression of mitofilin can limit mitochondrial disruption associated with the diabetic heart through restoration of mitochondrial morphology and function. A transgenic mouse line overexpressing mitofilin was generated and mice injected intraperitoneally with streptozotocin using a multi low-dose approach. Five weeks following diabetes mellitus onset, cardiac contractile function was assessed. Restoration of ejection fraction and fractional shortening was observed in mitofilin diabetic mice as compared to wild-type controls (P<0.05 for both). Decrements observed in electron transport chain (ETC) complex I, III, IV and V activities, state 3 respiration, lipid peroxidation as well as mitochondria membrane potential in type 1 diabetic IFM were restored in mitofilin diabetic mice (P<0.05 for all). Qualitative analyses of electron micrographs revealed restoration of mitochondrial cristae structure in mitofilin diabetic mice as compared to wild-type controls. Furthermore, measurement of mitochondrial internal complexity using flow cytometry displayed significant reduction in internal complexity in diabetic IFM which was restored in mitofilin diabetic IFM (P<0.05). Taken together these results suggest that transgenic overexpression of mitofilin preserves mitochondrial structure, leading to restoration of mitochondrial function and attenuation of cardiac contractile dysfunction in the diabetic heart.

Heart mitochondrial proteome study elucidates changes in cardiac energy metabolism and antioxidant PRDX3 in human dilated cardiomyopathy

Background

Dilated cardiomyopathy (DCM) is a public health problem with no available curative treatment, and mitochondrial dysfunction plays a critical role in its development. The present study is the first to analyze the mitochondrial proteome in cardiac tissue of patients with DCM to identify potential molecular targets for its therapeutic intervention.

Methods and Results

16 left ventricular (LV) samples obtained from explanted human hearts with DCM (n = 8) and control donors (n = 8) were extracted to perform a proteomic approach to investigate the variations in mitochondrial protein expression. The proteome of the samples was analyzed by quantitative differential electrophoresis and Mass Spectrometry. These changes were validated by classical techniques and by novel and precise selected reaction monitoring analysis and RNA sequencing approach increasing the total heart samples up to 25. We found significant alterations in energy metabolism, especially in molecules involved in substrate utilization (ODPA, ETFD, DLDH), energy production (ATPA), other metabolic pathways (AL4A1) and protein synthesis (EFTU), obtaining considerable and specific relationships between the alterations detected in these processes. Importantly, we observed that the antioxidant PRDX3 overexpression is associated with impaired ventricular function. PRDX3 is significantly related to LV end systolic and diastolic diameter (r = 0.73, p value<0.01; r = 0.71, p value<0.01), fractional shortening, and ejection fraction (r = −0.61, p value<0.05; and r = −0.62, p value<0.05, respectively).

Conclusion

This work could be a pivotal study to gain more knowledge on the cellular mechanisms related to the pathophysiology of this disease and may lead to the development of etiology-specific heart failure therapies. We suggest new molecular targets for therapeutic interventions, something that up to now has been lacking.

ATP synthase subunit alpha and LV mass in ischaemic human hearts

Mitochondrial dysfunction plays a critical role in the development of ischaemic cardiomyopathy (ICM). In this study, the mitochondrial proteome in the cardiac tissue of ICM patients was analysed by quantitative differential electrophoresis (2D-DIGE) and mass spectrometry (MS) for the first time to provide new insights into cardiac dysfunction in this cardiomyopathy. We isolated mitochondria from LV samples of explanted hearts of ICM patients (n = 8) and control donors (n = 8) and used a proteomic approach to investigate the variations in mitochondrial protein expression. We found that most of the altered proteins were involved in cardiac energy metabolism (82%). We focused on ATPA, which is involved in energy production, and dihydrolipoyl dehydrogenase, implicated in substrate utilization, and observed that these molecules were overexpressed and that the changes detected in the processes mediated by these proteins were closely related. Notably, we found that ATPA overexpression was associated with reduction in LV mass (r = −0.74, P < 0.01). We also found a substantial increase in the expression of elongation factor Tu, a molecule implicated in protein synthesis, and PRDX3, involved in the stress response. All of these changes were validated using classical techniques and by using novel and precise selected reaction monitoring analysis and an RNA sequencing approach, with the total heart samples being increased to 24. This study provides key insights that enhance our understanding of the cellular mechanisms related to the pathophysiology of ICM and could lead to the development of aetiology-specific heart failure therapies. ATPA could serve as a molecular target suitable for new therapeutic interventions.

Mitochondrial dysfunction in heart failure

Heart failure (HF) is a complex chronic clinical syndrome. Energy deficit is considered to be a key contributor to the development of both cardiac and skeletal myopathy. In HF, several components of cardiac and skeletal muscle bioenergetics are altered, such as oxygen availability, substrate oxidation, mitochondrial ATP production, and ATP transfer to the contractile apparatus via the creatine kinase shuttle. This review focuses on alterations in mitochondrial biogenesis and respirasome organization, substrate oxidation coupled with ATP synthesis in the context of their contribution to the chronic energy deficit, and mechanical dysfunction of the cardiac and skeletal muscle in HF. We conclude that HF is associated with decreased mitochondrial biogenesis and function in both heart and skeletal muscle, supporting the concept of a systemic mitochondrial cytopathy. The sites of mitochondrial defects are located within the electron transport and phosphorylation apparatus and differ with the etiology and progression of HF in the two mitochondrial populations (subsarcolemmal and interfibrillar) of cardiac and skeletal muscle. The roles of adrenergic stimulation, the renin-angiotensin system, and cytokines are evaluated as factors responsible for the systemic energy deficit. We propose a cyclic AMP-mediated mechanism by which increased adrenergic stimulation contributes to the mitochondrial dysfunction.

MITOCHONDRIA: investigation of in vivo muscle mitochondrial function by 31P magnetic resonance spectroscopy

The most important function of mitochondria is the production of energy in the form of ATP. The socio-economic impact of human diseases that affect skeletal muscle mitochondrial function is growing, and improving their clinical management critically depends on the development of non-invasive assays to assess mitochondrial function and monitor the effects of interventions. 31P magnetic resonance spectroscopy provides two approaches that have been used to assess in vivo ATP synthesis in skeletal muscle: measuring Pi→ATP exchange flux using saturation transfer in resting muscle, and measuring phosphocreatine recovery kinetics after exercise. However, Pi→ATP exchange does not represent net mitochondrial ATP synthesis flux and has no simple relationship with mitochondrial function. Post-exercise phosphocreatine recovery kinetics, on the other hand, yield reliable measures of muscle mitochondrial capacity in vivo, whose ability to define the site of functional defects is enhanced by combination with other non-invasive techniques.

The mitochondrial ADP/ATP carrier (SLC25 family): pathological implications of its dysfunction

In aerobic eukaryotic cells, the high energy metabolite ATP is generated mainly within the mitochondria following the process of oxidative phosphorylation. The mitochondrial ATP is exported to the cytoplasm using a specialized transport protein, the ADP/ATP carrier, to provide energy to the cell. Any deficiency or dysfunction of this membrane protein leads to serious consequences on cell metabolism and can cause various diseases such as muscular dystrophy. Described as a decisive player in the programmed cell death, it was recently shown to play a role in cancer. The objective of this review is to summarize the current knowledge of the involvement of the ADP/ATP carrier, encoded by the SLC25A4, SLC25A5, SLC25A6 and SLC25A31 genes, in human diseases and of the efforts made at designing different model systems to study this carrier and the associated pathologies through biochemical, genetic, and structural approaches.

Cardiac protein changes in ischaemic and dilated cardiomyopathy: a proteomic study of human left ventricular tissue

The development of heart failure (HF) is characterized by progressive alteration of left ventricle structure and function. Previous works on proteomic analysis in cardiac tissue from patients with HF remain scant. The purpose of our study was to use a proteomic approach to investigate variations in protein expression of left ventricle tissue from patients with ischaemic (ICM) and dilated cardiomyopathy (DCM). Twenty-four explanted human hearts, 12 from patients with ICM and 12 with DCM undergoing cardiac transplantation and six non-diseased donor hearts (CNT) were analysed by 2DE. Proteins of interest were identified by mass spectrometry and validated by Western blotting and immunofluorescence. We encountered 35 differentially regulated spots in the comparison CNT versus ICM, 33 in CNT versus DCM, and 34 in ICM versus DCM. We identified glyceraldehyde 3-phophate dehydrogenase up-regulation in both ICM and DCM, and alpha-crystallin B down-regulation in both ICM and DCM. Heat shock 70 protein 1 was up-regulated only in ICM. Ten of the eleven differentially regulated proteins common to both aetiologies are interconnected as a part of a same network. In summary, we have shown by proteomics analysis that HF is associated with changes in proteins involved in the cellular stress response, respiratory chain and cardiac metabolism. Although we found altered expression of eleven proteins common to both ischaemic and dilated aetiology, we also observed different proteins altered in both groups. Furthermore, we obtained that seven of these eleven proteins are involved in cell death and apoptosis processes, and therefore in HF progression.

Reversal of mitochondrial proteomic loss in Type 1 diabetic heart with overexpression of phospholipid hydroperoxide glutathione peroxidase

Mitochondrial dysfunction is a contributor to diabetic cardiomyopathy. Previously, we observed proteomic decrements within the inner mitochondrial membrane (IMM) and matrix of diabetic cardiac interfibrillar mitochondria (IFM) correlating with dysfunctional mitochondrial protein import. The goal of this study was to determine whether overexpression of mitochondria phospholipid hydroperoxide glutathione peroxidase 4 (mPHGPx), an antioxidant enzyme capable of scavenging membrane-associated lipid peroxides in the IMM, could reverse proteomic alterations, dysfunctional protein import, and ultimately, mitochondrial dysfunction associated with the diabetic heart. MPHGPx transgenic mice and controls were made diabetic by multiple low-dose streptozotocin injections and examined after 5 wk of hyperglycemia. Five weeks after hyperglycemia onset, in vivo analysis of cardiac contractile function revealed decreased ejection fraction and fractional shortening in diabetic hearts that was reversed with mPHGPx overexpression. MPHGPx overexpression increased electron transport chain function while attenuating hydrogen peroxide production and lipid peroxidation in diabetic mPHGPx IFM. MPHGPx overexpression lessened proteomic loss observed in diabetic IFM. Posttranslational modifications, including oxidations and deamidations, were attenuated in diabetic IFM with mPHGPx overexpression. Mitochondrial protein import dysfunction in diabetic IFM was reversed with mPHGPx overexpression correlating with protein import constituent preservation. Ingenuity Pathway Analyses indicated that oxidative phosphorylation, tricarboxylic acid cycle, and fatty acid oxidation processes most influenced in diabetic IFM were preserved by mPHGPx overexpression. Specific mitochondrial networks preserved included complex I and II, mitochondrial ultrastructure, and mitochondrial protein import. These results indicate that mPHGPx overexpression can preserve the mitochondrial proteome and provide cardioprotective benefits to the diabetic heart.

miR-141 as a regulator of the mitochondrial phosphate carrier (Slc25a3) in the type 1 diabetic heart

Dysfunctional mitochondria are central in the pathogenesis of diabetic cardiomyopathy. Mitochondrial proteomic alterations resulting from diabetes mellitus have been reported although the mechanisms driving changes in proteomic signatures are unknown. microRNAs (miRNAs) have been considered as potential regulators of proteins. The goal of this study was to determine whether miRNAs play a role in diabetes-induced mitochondrial proteomic alterations. Quanitative RT-PCR miRNA screening in diabetic mice, 5 wk following multiple low-dose streptozotocin treatment was associated with alteration in the expression of 29 miRNAs in the diabetic heart compared with control. Among those miRNAs upregulated in the diabetic heart was miR-141 (P < 0.002). miRNA target prediction analyses identified miR-141 as a potential regulator of the inner mitochondrial membrane phosphate transporter, solute carrier family 25 member 3 (Slc25a3), which provides inorganic phosphate to the mitochondrial matrix and is essential for ATP production. With the use of a luciferase reporter construct with a Slc25a3 3'-untranslated region (UTR) target sequence, overexpression of miR-141 downregulated luciferase activity levels confirming miR-141/Slc25a3 3'-UTR binding. miR-141 overexpression in HL-1 cells elicited a decrease in Slc25a3 protein content, ATP production and a decrease in ATP synthase activity, similar to the diabetic phenotype (P < 0.05, for both). Diabetic interfibrillar mitochondria (IFM) displayed decreased Slc25a3 protein content, which was inversely correlated with increased miR-141 expression. Further, diabetic IFM ATP synthase activity was also decreased (P < 0.05). Together these results indicate that miR-141 can regulate Slc25a3 protein expression in the diabetic heart. Further, diabetes-induced miRNA changes may influence mitochondrial proteomes and functional processes such as mitochondrial ATP production.

Metabolic adaptation to chronic hypoxia in cardiac mitochondria

Chronic hypoxia decreases cardiomyocyte respiration, yet the mitochondrial mechanisms remain largely unknown. We investigated the mitochondrial metabolic pathways and enzymes that were decreased following in vivo hypoxia, and questioned whether hypoxic adaptation was protective for the mitochondria. Wistar rats were housed in hypoxia (7 days acclimatisation and 14 days at 11% oxygen), while control rats were housed in normoxia. Chronic exposure to physiological hypoxia increased haematocrit and cardiac vascular endothelial growth factor, in the absence of weight loss and changes in cardiac mass. In both subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria isolated from hypoxic hearts, state 3 respiration rates with fatty acid were decreased by 17-18%, and with pyruvate were decreased by 29-15%, respectively. State 3 respiration rates with electron transport chain (ETC) substrates were decreased only in hypoxic SSM, not in hypoxic IFM. SSM from hypoxic hearts had decreased activities of ETC complexes I, II and IV, which were associated with decreased reactive oxygen species generation and protection against mitochondrial permeability transition pore (MPTP) opening. In contrast, IFM from hypoxic hearts had decreased activity of the Krebs cycle enzyme, aconitase, which did not modify ROS production or MPTP opening. In conclusion, cardiac mitochondrial respiration was decreased following chronic hypoxia, associated with downregulation of different pathways in the two mitochondrial populations, determined by their subcellular location. Hypoxic adaptation was not deleterious for the mitochondria, in fact, SSM acquired increased protection against oxidative damage under the oxygen-limited conditions.

Biphasic response of skeletal muscle mitochondria to chronic cardiac pressure overload - role of respiratory chain complex activity

Pressure overload induced heart failure affects cardiac mitochondrial function and leads to decreased respiratory capacity during contractile dysfunction. A similar cardiac mitochondrial dysfunction has been demonstrated by studies which induce heart failure through myocardial infarction or pacing. These heart failure models differ in their loading conditions to the heart and show nevertheless the same cardiac mitochondrial changes. Based on these observations we speculated that a workload independent mechanism may be responsible for the impairment in mitochondrial function after pressure overload, which may then also affect the skeletal muscle. We aimed to characterize changes in mitochondrial function of skeletal muscle during the transition from pressure overload (PO) induced cardiac hypertrophy to chronic heart failure. PO by transverse aortic constriction caused compensated hypertrophy at 2 weeks, HF with normal ejection fraction (EF) at 6 and 10 weeks, and hypertrophy with reduced EF at 20 weeks. Cardiac output was normal at all investigated time points. PO did not cause skeletal muscle atrophy. Mitochondrial respiratory capacity in soleus and gastrocnemius muscles showed an early increase (up to 6 weeks) and a later decline (significant at 20 weeks). Respiratory chain complex activities responded to PO in a biphasic manner. At 2 weeks, activity of complexes I and II was increased. These changes pseudo-normalized within the 6-10 week interval. At 20 weeks, all complexes showed reduced activities which coincided with clinical heart failure symptoms. However, both protein expression and supercomplex assembly (Blue-Native gel) remained normal. There were also no relevant changes in mRNA expression of genes involved in mitochondrial biogenesis. This temporal analysis reveals that mitochondrial function of skeletal muscle is changed early in the development of pressure overload induced heart failure without being directly influenced by an increased loading condition. The observed early increase and the later decline in respiratory capacity can be explained by concomitant activity changes of complex I and complex II and is not due to differences in gene expression or supercomplex assembly.

Improvement of left ventricular diastolic function induced by β-blockade: a comparison between nebivolol and metoprolol

OBJECTIVES

Enhanced adrenergic drive is involved in the development of left ventricular (LV) diastolic dysfunction observed in metabolic syndrome (MS). Thus, β-blockers might improve LV dysfunction observed in MS, but whether this occurs is unknown.

METHODS

We assessed in Zucker fa/fa rats the effects of short- (5 days) and long-term (90 days) metoprolol ('pure' β-blockade; 80 mg/kg/day) or nebivolol (β-blocker with vasodilating properties; 5mg/kg/day) treatment on LV hemodynamics and remodeling, as well as the long-term effects on coronary and peripheral endothelial dysfunction.

RESULTS

At identical degree of β(1)-receptor blockade, metoprolol and nebivolol decreased heart rate to the same extent and preserved cardiac output via increased stroke volume. None of the β-blockers, either after long- or short-term administration, modified LV end-systolic pressure-volume relation. Both β-blockers reduced, after long-term administration, LV end-diastolic pressure, Tau and end-diastolic pressure-volume relation, and this was associated with reduced LV collagen density, but not heart weight. Similar hemodynamic effects were also observed after short-term nebivolol, but not short-term metoprolol. These short-term effects of nebivolol were abolished by NO synthase inhibition. At the vascular level, nebivolol, and to a lesser extend metoprolol, improved NO dependent coronary vasorelaxation, which was abolished by NO synthase inhibition.

CONCLUSIONS

In a model of MS, the β-blockers metoprolol and nebivolol improve to the same extent LV hemodynamics, remodeling and diastolic function, but nebivolol prevent more markedly endothelium dependent vasorelaxation involving a more marked enhancement of NO bio-availability.

Mitochondrial dysfunction in the type 2 diabetic heart is associated with alterations in spatially distinct mitochondrial proteomes

Cardiac complications and heart failure are the leading cause of death in type 2 diabetic patients. Mitochondrial dysfunction is central in the pathogenesis of the type 2 diabetic heart. However, it is unclear whether this dysfunction is specific for a particular subcellular region. The purpose of this study was to determine whether mitochondrial dysfunction in the type 2 diabetic heart is specific to a spatially distinct subset of mitochondria. We investigated mitochondrial morphology, function, and proteomic composition of subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM) in 18-wk-old db/db mice. Oxidative damage was assessed in subpopulations through the measurement of lipid peroxidation byproducts and nitrotyrosine residues. Proteomic profiles and posttranslational modifications were assessed in mitochondrial subpopulations using iTRAQ and multi-dimensional protein identification technologies, respectively. SSM from db/db hearts had altered morphology, including a decrease in size and internal complexity, whereas db/db IFM were increased in internal complexity. Db/db SSM displayed decreased state 3 respiration rates, electron transport chain activities, ATP synthase activities, and mitochondrial membrane potential and increased oxidative damage, with no change in IFM. Proteomic assessment revealed a greater impact on db/db SSM compared with db/db IFM. Inner mitochondrial membrane proteins, including electron transport chain, ATP synthesis, and mitochondrial protein import machinery, were predominantly decreased. We provide evidence that mitochondrial dysfunction in the type 2 diabetic heart is associated with a specific subcellular locale. Furthermore, mitochondrial morphological and functional indexes are impacted differently during type 2 diabetic insult and may result from the modulation of spatially distinct mitochondrial proteomes.

Transient upregulation of PGC-1alpha diminishes cardiac ischemia tolerance via upregulation of ANT1

Prolonged cardiac overexpression of the mitochondrial biogenesis regulatory transcriptional coactivator PGC-1alpha disrupts cardiac contractile function and its genetic ablation limits cardiac capacity to enhance workload. In contrast, transient induction of PGC-1alpha alleviates neuronal cell oxidative stress and enhances skeletal myotube anti-oxidant defenses. We explored whether transient upregulation of PGC-1alpha in the heart protects against ischemia-reperfusion injury. The transient induction of PGC-1alpha in the cardiac-restricted inducible PGC-1alpha transgenic mouse, increased PGC-1alpha protein levels 5-fold. Following 25 min of ischemia and 2h of reperfusion on a Langendorff perfusion apparatus, contractile recovery and the rate pressure product was significantly blunted in mice overexpressing PGC-1alpha vs. controls. Affymetrix gene array analysis showed a 3-fold PGC-1alpha-mediated upregulation of adenine nucleotide translocase 1 (ANT1). As ANT1 upregulation induces cardiomyocyte cell death we investigated whether the induction of ANT1 by PGC-1alpha contributes to this enhanced ischemia-stress susceptibility. Infection with adenovirus harboring PGC-1alpha into cardiac-derived H9c2 cells significantly upregulates ANT1 without changing basal cell viability. In response to anoxia-reoxygenation injury cell death is significantly increased following PGC-1alpha overexpression. This detrimental effect is abolished following siRNA knockdown of ANT1. Similarly, the attenuation of ANT-1 in the presence of PGC-1alpha overexpression preserves the mitochondrial membrane potential in response to hydrogen-peroxide stress. Interestingly, the isolated knockdown of ANT1 also protects H9c2 cells from anoxia-reoxygenation injury. Taken together these data suggest that transient induction of PGC-1alpha in the murine heart decreases ischemia-reperfusion contractile recovery and diminishes anoxia-reoxygenation tolerance in H9c2 cells. These adverse phenotypes appear to be mediated, in part, by PGC-1alpha induced upregulation of ANT1.