Cardiac mitochondrial damage and biogenesis in a chronic model of type 1 diabetes

Insulin stimulates Akt translocation to mitochondria: implications on dysregulation of mitochondrial oxidative phosphorylation in diabetic myocardium

Mitochondrial oxidative phosphorylation is the major source of energy in cardiac muscle. In the streptozotocin-induced diabetic (STZ-DM) mice, myocardial oxidative phosphorylation was perturbated and oxidative phosphorylation complex V (ATP synthase) activity was significantly reduced. To determine the independent effects of hyperglycemia and insulin deficiency on the changes of myocardial complex V, we used phlorizin (Ph) to normalize blood glucose in the diabetic mice. Ph treatment did not improve myocardial complex V activity in the STZ-DM mice, whereas insulin treatment normalized myocardial complex V activity in the diabetic mice. Therefore, the reduction of complex V activity was caused by insulin deficiency and not by hyperglycemia in STZ-DM myocardium. Acute insulin stimulation induced phosphorylation of Akt and translocation of Akt to mitochondria in myocardium. Translocation of phospho-Akt to mitochondria was enhanced in the STZ-DM mice and was blunted in the diet-induced diabetic mice. In parallel, insulin activation of complex V was enhanced in the STZ-DM myocardium and suppressed in the diet-induced diabetic myocardium. In vivo inhibition of Akt blocked insulin stimulation of phospho-Akt translocation and blunted activation of complex V. Insulin-activated Akt translocation to mitochondria in cardiac muscle is a novel paradigm that may have important implications on myocardial bioenergetics.

Contribution of impaired myocardial insulin signaling to mitochondrial dysfunction and oxidative stress in the heart

BACKGROUND

Diabetes-associated cardiac dysfunction is associated with mitochondrial dysfunction and oxidative stress, which may contribute to left ventricular dysfunction. The contribution of altered myocardial insulin action, independent of associated changes in systemic metabolism, is incompletely understood. The present study tested the hypothesis that perinatal loss of insulin signaling in the heart impairs mitochondrial function.

METHODS AND RESULTS

In 8-week-old mice with cardiomyocyte deletion of insulin receptors (CIRKO), inotropic reserves were reduced, and mitochondria manifested respiratory defects for pyruvate that was associated with proportionate reductions in catalytic subunits of pyruvate dehydrogenase. Progressive age-dependent defects in oxygen consumption and ATP synthesis with the substrate glutamate and the fatty acid derivative palmitoyl-carnitine were observed. Mitochondria also were uncoupled when exposed to palmitoyl-carnitine, in part as a result of increased reactive oxygen species production and oxidative stress. Although proteomic and genomic approaches revealed a reduction in subsets of genes and proteins related to oxidative phosphorylation, no reductions in maximal activities of mitochondrial electron transport chain complexes were found. However, a disproportionate reduction in tricarboxylic acid cycle and fatty acid oxidation proteins in mitochondria suggests that defects in fatty acid and pyruvate metabolism and tricarboxylic acid flux may explain the mitochondrial dysfunction observed.

CONCLUSIONS

Impaired myocardial insulin signaling promotes oxidative stress and mitochondrial uncoupling, which, together with reduced tricarboxylic acid and fatty acid oxidative capacity, impairs mitochondrial energetics. This study identifies specific contributions of impaired insulin action to mitochondrial dysfunction in the heart.

Effect of (+)-usnic acid on mitochondrial functions as measured by mitochondria-specific oligonucleotide microarray in liver of B6C3F1 mice

Usnic acid is a lichen metabolite used as a weight-loss dietary supplement due to its uncoupling action on mitochondria. However, its use has been associated with severe liver disorders in some individuals. Animal studies conducted thus far evaluated the effects of usnic acid on mitochondria primarily by measuring the rate of oxygen consumption and/or ATP generation. To obtain further insight into usnic acid-mediated effects on mitochondria, we examined the expression levels of 542 genes associated with mitochondrial structure and functions in liver of B6C3F(1) female mice using a mitochondria-specific microarray. Beginning at 8 weeks of age, mice received usnic acid at 0, 60, 180, and 600 ppm in ground, irradiated 5LG6 diet for 14 days. Microarray analysis showed a significant effect of usnic acid on the expression of several genes only at the highest dose of 600 ppm. A prominent finding of the study was a significant induction of genes associated with complexes I through IV of the electron transport chain. Moreover, several genes involved in fatty acid oxidation, the Krebs cycle, apoptosis, and membrane transporters were over-expressed. Usnic acid is a lipophilic weak acid that can diffuse through mitochondrial membranes and cause a proton leak (uncoupling). The up-regulation of complexes I-IV may be a compensatory mechanism to maintain the proton gradient across the mitochondrial inner membrane. In addition, induction of fatty acid oxidation and the Krebs cycle may be an adaptive response to uncoupling of mitochondria.

Diabetic cardiomyopathy-associated dysfunction in spatially distinct mitochondrial subpopulations

Diabetic cardiomyopathy is the leading cause of heart failure among diabetic patients, and mitochondrial dysfunction has been implicated as an underlying cause in the pathogenesis. Cardiac mitochondria consist of two spatially, functionally, and morphologically distinct subpopulations, termed subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). SSM are situated beneath the plasma membrane, whereas IFM are embedded between myofibrils. The goal of this study was to determine whether spatially distinct cardiac mitochondrial subpopulations respond differently to a diabetic phenotype. Swiss-Webster mice were subjected to intraperitoneal injections of streptozotocin or citrate saline vehicle. Five weeks after injections, diabetic hearts displayed decreased rates of contraction, relaxation, and left ventricular developed pressures (P < 0.05 for all three). Both mitochondrial size (forward scatter, P < 0.01) and complexity (side scatter, P < 0.01) were decreased in diabetic IFM but not diabetic SSM. Electron transport chain complex II respiration was decreased in diabetic SSM (P < 0.05) and diabetic IFM (P < 0.01), with the decrease being greater in IFM. Furthermore, IFM complex I respiration and complex III activity were decreased with diabetes (P < 0.01) but were unchanged in SSM. Superoxide production was increased only in diabetic IFM (P < 0.01). Oxidative damage to proteins and lipids, indexed through nitrotyrosine residues and lipid peroxidation, were higher in diabetic IFM (P < 0.05 and P < 0.01, respectively). The mitochondria-specific phospholipid cardiolipin was decreased in diabetic IFM (P < 0.01) but not SSM. These results indicate that diabetes mellitus imposes a greater stress on the IFM subpopulation, which is associated, in part, with increased superoxide generation and oxidative damage, resulting in morphological and functional abnormalities that may contribute to the pathogenesis of diabetic cardiomyopathy.

Beneficial effects of exercise on muscle mitochondrial function in diabetes mellitus

The physiopathology of diabetes mellitus has been closely associated with a variety of alterations in mitochondrial histology, biochemistry and function. Generally, the alterations comprise increased mitochondrial reactive oxygen and nitrogen species (RONS) generation, resulting in oxidative stress and damage; decreased capacity to metabolize lipids, leading to intramyocyte lipid accumulation; and diminished mitochondrial density and reduced levels of uncoupling proteins (UCPs), with consequent impairment in mitochondrial function. Chronic physical exercise is a physiological stimulus able to induce mitochondrial adaptations that can counteract the adverse effects of diabetes on muscle mitochondria. However, the mechanisms responsible for mitochondrial adaptations in the muscles of diabetic patients are still unclear. The main mechanisms by which exercise may be considered an important non-pharmacological strategy for preventing and/or attenuating diabetes-induced mitochondrial impairments may involve (i) increased mitochondrial biogenesis, which is dependent on the increased expression of some important proteins, such as the 'master switch' peroxisome proliferator-activated receptor (PPAR)-gamma-coactivator-1alpha (PGC-1alpha) and heat shock proteins (HSPs), both of which are severely downregulated in the muscles of diabetic patients; and (ii) the restoration or attenuation of the low UCP3 expression in skeletal muscle mitochondria of diabetic patients, which is suggested to play a pivotal role in mitochondrial dysfunction.There is evidence that chronic exercise and lifestyle interventions reverse impairments in mitochondrial density and size, in the activity of respiratory chain complexes and in cardiolipin content; however, the mechanisms by which chronic exercise alters mitochondrial respiratory parameters, mitochondrial antioxidant systems and other specific proteins involved in mitochondrial metabolism in the muscles of diabetic patients remain to be elucidated.

Peripheral blood mitochondrial DNA content and dysregulation of glucose metabolism

OBJECTIVE

The aim of this study was to examine the potential influence of insulin resistance (IR), hyperglycemia and oxidative stress on leucocytes mitochondrial DNA (mtDNA) content.

RESEARCH DESIGN AND METHOD

One hundred twenty-five T2DM, 101 IFG and 70 normal subjects were enrolled in this study. The quantity of relative mtDNA content was measured by a real-time PCR and corrected by simultaneous measurement of the nuclear DNA. Parameters of lipid peroxidation, thiobarbituric acid reactive substance (TBARS), and total free thiols as antioxidative status were measured from serum samples. IR was assessed by homeostasis model assessment in the non-diabetic groups. Relationships among different variables were analyzed by general linear model correlation.

RESULTS

In all subjects, after correcting for age, sex and BMI, there were progressive increases of leucocyte mtDNA copy number, TBARS, and total reduced thiols with progressive dysregulation of glucose metabolism (normal vs. IFG vs. T2DM). Furthermore, correlation between mtDNA content and glucose dysregulation persisted after sequential correction for age, sex, BMI and TBARS. The independent predictor of mtDNA content by regression analysis was hyperglycemia. In non-diabetic group, influence of family history of diabetes on mtDNA content turned to non-significant after correcting for fasting plasma glucose (FPG). Correlation study revealed that mtDNA content was correlated with FPG (P<0.001), but not IR.

CONCLUSION

Our results indicate that hyperglycemia, not IR, is associated with an increase of leucocyte mtDNA copy number in cases of glucose dysregulation.

KIF5B gene sequence variation and response of cardiac stroke volume to regular exercise

A genome-wide linkage scan for endurance training-induced changes in stroke volume detected a quantitative trait locus on chromosome 10p11 in white families of the HERITAGE Family Study. Dense microsatellite mapping narrowed down the linkage region to a 7 Mb area containing 16 known and 14 predicted genes. Association analyses with 90 single nucleotide polymorphisms (SNPs) provided suggestive evidence (P values from 0.03 to 0.06) for association in the kinesin heavy chain (KIF5B) gene locus in the whole cohort. The associations at the KIF5B locus were stronger (P values from 0.001 to 0.008) when the analyses were performed on linkage-informative families only (family-specific logarithm of the odds ratio scores >0.025 at peak linkage location). Resequencing the coding and regulatory regions of KIF5B revealed no new exonic SNPs. However, the putative promoter region was particularly polymorphic, containing eight SNPs with at least 5% minor allele frequency within 1850 bp upstream of the start codon. Functional analyses using promoter haplotype reporter constructs led to the identification of sequence variants that had significant effects on KIF5B promoter activity. Analogous inhibition and overexpression experiments showed that changes in KIF5B expression alter mitochondrial localization and biogenesis in a manner that could affect the ability of the heart to adjust to regular exercise. Our data suggest that KIF5B is a strong candidate gene for the response of stroke volume to regular exercise. Furthermore, training-induced changes in submaximal exercise stroke volume may be due to mitochondrial function and variation in KIF5B expression as determined by functional SNPs in its promoter.

Altering and analyzing glucose metabolism in perfused hearts of transgenic mice

Glucose metabolism plays an important role in cardiac bioenergetics that changes under various stress conditions including hypertrophy, diabetic cardiomyopathy, and ischemia-reperfusion injury. To understand the role of glycolysis under these conditions, we have altered several steps of the glycolytic pathway specifically in the heart. In this chapter, we describe methods used to produce cardiac-targeted transgenic mice and procedures for measuring various glucose metabolites including glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, and glycogen. Also, we describe methods for measuring glucose transport and glycolysis in perfused mouse hearts. Using these methods, we show that mice over-expressing cardiac-specific kinase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (Mykd-PFK-2) show reduced glucose transport and reduced glycolysis when compared with control. The metabolites glucose-6-phosphate, fructose-6-phosphate, and glycogen were elevated, whereas fructose-1,6-bisphosphate was reduced in the transgenic Mykd-PFK-2 mouse hearts.

Alterations in mitochondrial function and cytosolic calcium induced by hyperglycemia are restored by mitochondrial transcription factor A in cardiomyocytes

Mitochondrial transcription factor A (TFAM) is essential for mitochondrial DNA transcription and replication. TFAM transcriptional activity is decreased in diabetic cardiomyopathy; however, the functional implications are unknown. We hypothesized that a reduced TFAM activity may be responsible for some of the alterations caused by hyperglycemia. Therefore, we investigated the effect of TFAM overexpression on hyperglycemia-induced cytosolic calcium handling and mitochondrial abnormalities. Neonatal rat cardiomyocytes were exposed to high glucose (30 mM) for 48 h, and we examined whether TFAM overexpression, by protecting mitochondrial DNA, could reestablish calcium fluxes and mitochondrial alterations toward normal. Our results shown that TFAM overexpression increased to more than twofold mitochondria copy number in cells treated either with normal (5.5 mM) or high glucose. ATP content was reduced by 30% and mitochondrial calcium decreased by 40% after high glucose. TFAM overexpression returned these parameters to even higher than control values. Calcium transients were prolonged by 70% after high glucose, which was associated with diminished sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a and cytochrome-c oxidase subunit 1 expression. These parameters were returned to control values after TFAM overexpression. High glucose-induced protein oxidation was reduced by TFAM overexpression, indicating a reduction of the high glucose-induced oxidative stress. In addition, we found that TFAM activity can be modulated by O-linked beta-N-acetylglucosamine glycosylation. In conclusion, TFAM overexpression protected cell function against the damage induced by high glucose in cardiomyocytes.

Myocardial overexpression of adenine nucleotide translocase 1 ameliorates diabetic cardiomyopathy in mice

Mitochondrial dysfunction is implicated in the pathogenesis of diabetic cardiomyopathy, a common complication of diabetes. Adenosine nucleotide translocase (ANT) translocates ADP/ATP across the inner mitochondrial membrane. Our study aimed to test the hypothesis that overexpression of ANT1 in cardiomyocytes has cardioprotective effects in diabetic cardiomyopathy induced by streptozotocin (STZ). Mice specifically overexpressing murine ANT1 in the heart were generated using alpha-myosin heavy chain promoter. Expression of ANT1 mRNA and protein in hearts was characterized by real-time polymerase chain reaction and Western blot analysis. Five- to 6-month-old male transgenic mice and their age-matched wild-type littermates were subjected to type 1 diabetes induced by STZ. Six weeks later, haemodynamic measurement was performed to assess cardiac function. Ventricular mRNA expression of atrial natriuretic peptide, a molecular marker of heart failure, was characterized by RNase-protection assay. Both ANT1 mRNA and ANT1 protein were specifically overexpressed in the heart of transgenic mice. Heart weight was decreased and cardiac function was dramatically impaired in wild-type mice 6 weeks after induction of diabetes, but ANT1 overexpression prevented these significant changes. The mRNA expression level of atrial natriuretic peptide confirmed the haemodynamic findings, being upregulated in wild-type mice receiving STZ, but showing no statistical differences in ANT1 transgenic mice. Cardiomyocyte-restricted overexpression of ANT1 prevents the development of diabetic cardiomyopathy; therefore, accelerated ADP/ATP exchange could be a new promising target to treat diabetic cardiomyopathy.

Diet-induced metabolic disturbances as modulators of brain homeostasis

A number of metabolic disturbances occur in response to the consumption of a high fat western diet. Such metabolic disturbances can include the progressive development of hyperglycemia, hyperinsulemia, obesity, metabolic syndrome, and diabetes. Cumulatively, diet-induced disturbances in metabolism are known to promote increased morbidity and negatively impact life expectancy through a variety of mechanisms. While the impact of metabolic disturbances on the hepatic, endocrine, and cardiovascular systems is well established there remains a noticeable void in understanding the basis by which the central nervous system (CNS) becomes altered in response to diet-induced metabolic dysfunction. In particular, it remains to be fully elucidated which established features of diet-induced pathogenesis (observed in non-CNS tissues) are recapitulated in the brain, and identification as to whether the observed changes in the brain are a direct or indirect effect of peripheral metabolic disturbances. This review will focus on each of these key issues and identify some critical experimental questions which remain to be elucidated experimentally, as well as provide an outline of our current understanding for how diet-induced alterations in metabolism may impact the brain during aging and age-related diseases of the nervous system.

Is the failing heart out of fuel or a worn engine running rich? A study of mitochondria in old spontaneously hypertensive rats

Hypertension now affects about 600 million people worldwide and is a leading cause of death in the Western world. The spontaneously hypertensive rat (SHR), provides a useful model to investigate hypertensive heart failure (HF). The SHR model replicates the clinical progression of hypertension in humans, wherein early development of hypertension is followed by a long stable period of compensated cardiac hypertrophy that slowly progresses to HF. Although the hypertensive failing heart generally shows increased substrate preference towards glucose and impaired mitochondrial function, the cause-and-effect relationship between these characteristics is incompletely understood. To explore these pathogenic processes, we compared cardiac mitochondrial proteomes of 20-month-old SHR and Wistar-Kyoto controls by iTRAQ-labelling combined with multidimensional LC/MS/MS. Of 137 high-scoring proteins identified, 79 differed between groups. Changes were apparent in several metabolic pathways, chaperone and antioxidant systems, and multiple subunits of the oxidative phosphorylation complexes were increased (complexes I, III and IV) or decreased (complexes II and V) in SHR heart mitochondria. Respiration assays on skinned fibres and isolated mitochondria showed markedly lower respiratory capacity on succinate. Enzyme activity assays often also showed mismatches between increased protein expression and activities suggesting elevated protein expression may be compensatory in the face of pathological stress.

Cardiac remodeling in obesity

The dramatic increase in the prevalence of obesity and its strong association with cardiovascular disease have resulted in unprecedented interest in understanding the effects of obesity on the cardiovascular system. A consistent, but puzzling clinical observation is that obesity confers an increased susceptibility to the development of cardiac disease, while at the same time affording protection against subsequent mortality (termed the obesity paradox). In this review we focus on evidence available from human and animal model studies and summarize the ways in which obesity can influence structure and function of the heart. We also review current hypotheses regarding mechanisms linking obesity and various aspects of cardiac remodeling. There is currently great interest in the role of adipokines, factors secreted from adipose tissue, and their role in the numerous cardiovascular complications of obesity. Here we focus on the role of leptin and the emerging promise of adiponectin as a cardioprotective agent. The challenge of understanding the association between obesity and heart failure is complicated by the multifaceted interplay between various hemodynamic, metabolic, and other physiological factors that ultimately impact the myocardium. Furthermore, the end result of obesity-associated changes in the myocardial structure and function may vary at distinct stages in the progression of remodeling, may depend on the individual pathophysiology of heart failure, and may even remain undetected for decades before clinical manifestation. Here we summarize our current knowledge of this complex yet intriguing topic.

The PPAR trio: regulators of myocardial energy metabolism in health and disease

Common causes of heart failure are associated with derangements in myocardial fuel utilization. Evidence is emerging that metabolic abnormalities may contribute to the development and progression of myocardial disease. The peroxisome proliferator-activated receptor (PPAR) family of nuclear receptor transcription factors has been shown to regulate cardiac fuel metabolism at the gene expression level. The three PPAR family members (alpha, beta/delta and gamma) are uniquely suited to serve as transducers of developmental, physiological, and dietary cues that influence cardiac fatty acid and glucose metabolism. This review describes murine PPAR loss- and gain-of-function models that have shed light on the roles of these receptors in regulating myocardial metabolic pathways and have defined key links to disease states including the hypertensive and diabetic heart.

The complexities of diabetic cardiomyopathy: lessons from patients and animal models

Cardiovascular diseases are foreseeable complications of diabetes mellitus; heart failure is a prominent complication among these. Diabetic cardiomyopathy is a distinct entity independent of coronary artery disease and hypertension. Most of our knowledge on diabetic cardiomyopathy's pathogenesis comes from studies performed on various animal models. The recent advances in the domain confirm that the disease is above all a maladaptation of the heart mostly driven by the metabolic derangements that accompany diabetes mellitus.

Elevated catalase and heme oxygenase-1 may contribute to improved postischaemic cardiac function in long-term type 1 diabetes

1. Although increased oxidative stress has been shown repeatedly to be implicated in diabetes, the cardiovascular anti-oxidant state and heart response to ischaemia in long-term Type 1 diabetes remain largely unknown. The present study was designed to observe heart tolerance to ischaemia-reperfusion and endogenous anti-oxidants in the cardiovascular system in long-term hyperglycaemic rats. 2. Hearts from Sprague-Dawley rats surviving up to 6 months with streptozocin-induced severe hyperglycaemia (blood glucose > 20 mmol/L) were isolated and subjected to global ischaemia and reperfusion. Cardiac function, electrocardiogram and anti-oxidants in the myocardium and aorta were examined. In addition, the morphology of the myocardial mitochondria and the in vitro function of aortic vessels were assessed. 3. Hearts from diabetic rats demonstrated lower baseline heart function but had higher postischaemic coronary flow and left ventricular developed pressure compared with their respective controls (P < 0.05). In addition, hearts from diabetic animals had fewer arrhythmias (P < 0.01) and lower left ventricular end-diastolic pressure during reperfusion (P < 0.05). Higher catalase and heme oxygenase-1 content was found in the aorta and myocardium from diabetic rats (P < 0.01). In aortas from diabetic animals, acetylcholine-induced vasodilatation was enhanced and was approximately 15% after inhibition of nitric oxide synthase, compared with 0% in controls. The 15% relaxation was abrogated by heme oxygenase blockade. Mitochondria from the myocardium of diabetic rats showed significant increases in both size and number (P < 0.05). 4. Hearts of long-term Type 1 diabetic rats demonstrated improved recovery of postischaemic cardiac function and reduced reperfusion arrhythmia. Hyperglycaemia may enhance cardiovascular anti-oxidant capacity and mitochondrial neogenesis, which renders the heart resistant to ischaemia and oxidative injury.

Proteomic studies in animal models of diabetes

The aim of this review is to provide an overview of proteomic studies in animal models of diabetes and to give some insight into the different methods available today in the rapidly developing field of proteomics. A summary of 31 papers published between 1997 and 2007 is presented. For instance, proteomics has been used to study the development of both type 1 and type 2 diabetes, diabetic complications in tissues like heart, kidney and retina and changes after treatment with anti-diabetic drugs like peroxisome proliferator-activated receptors agonists. Together, these studies give a good overview of a number of experimental approaches. Proteomics holds the promise of providing major contributions to the field of diabetes research. However, to achieve this, a number of issues need to be resolved. Appropriate data representation to facilitate data comparison, exchange, and verification is required, as well as improved statistical assessment of proteomic experiments. In addition, it is important to follow up the results with functional studies to be able to make biologically relevant conclusions. The potential of proteomics to dissect complex human disorders is now beginning to be realized. In the future, this will result in new important information concerning diabetes.

Gene expression profiles of mouse striatum in control and maneb + paraquat-induced Parkinson's disease phenotype: validation of differentially expressed energy metabolizing transcripts

The present study was undertaken to investigate the gene expression patterns of the striatum of control and maneb + paraquat-induced Parkinson's disease (PD) phenotype in mouse to identify the differentially expressed transcripts. The animals were treated with and without maneb (30 mg/kg, i.p.) + paraquat (10 mg/kg, i.p.), twice a week, for 3, 6, and 9 weeks. The RNA was isolated from control and treated mouse striatum and reverse transcribed, and equal quantities of labeled cDNA were mixed and hybridized with mouse 15 k arrays. Comparative transcription patterns showed the time of exposure dependent alteration in the expression of several transcripts associated with various pathways. RT-PCR reconfirmed the differential expression of some energy metabolizing transcripts. The study provides maneb + paraquat-induced differential expression of many transcripts using high-density microarray approach. Few transcripts, which were previously not reported to be associated with neuronal degeneration, were also identified. The results obtained thus suggest that maneb + paraquat induce neurotoxicity in the striatum in a time of exposure dependent manner via multiple pathways and defective energy metabolism could play a critical role.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

Nuclear receptors PPARbeta/delta and PPARalpha direct distinct metabolic regulatory programs in the mouse heart

In the diabetic heart, chronic activation of the PPARalpha pathway drives excessive fatty acid (FA) oxidation, lipid accumulation, reduced glucose utilization, and cardiomyopathy. The related nuclear receptor, PPARbeta/delta, is also highly expressed in the heart, yet its function has not been fully delineated. To address its role in myocardial metabolism, we generated transgenic mice with cardiac-specific expression of PPARbeta/delta, driven by the myosin heavy chain (MHC-PPARbeta/delta mice). In striking contrast to MHC-PPARalpha mice, MHC-PPARbeta/delta mice had increased myocardial glucose utilization, did not accumulate myocardial lipid, and had normal cardiac function. Consistent with these observed metabolic phenotypes, we found that expression of genes involved in cellular FA transport were activated by PPARalpha but not by PPARbeta/delta. Conversely, cardiac glucose transport and glycolytic genes were activated in MHC-PPARbeta/delta mice, but repressed in MHC-PPARalpha mice. In reporter assays, we showed that PPARbeta/delta and PPARalpha exerted differential transcriptional control of the GLUT4 promoter, which may explain the observed isotype-specific effects on glucose uptake. Furthermore, myocardial injury due to ischemia/reperfusion injury was significantly reduced in the MHC-PPARbeta/delta mice compared with control or MHC-PPARalpha mice, consistent with an increased capacity for myocardial glucose utilization. These results demonstrate that PPARalpha and PPARbeta/delta drive distinct cardiac metabolic regulatory programs and identify PPARbeta/delta as a potential target for metabolic modulation therapy aimed at cardiac dysfunction caused by diabetes and ischemia.

Molecular mechanisms for myocardial mitochondrial dysfunction in the metabolic syndrome

The metabolic syndrome represents a cluster of abnormalities, including obesity, insulin resistance, dyslipidaemia and Type 2 diabetes, that increases the risk of developing cardiovascular diseases, such as coronary artery disease and heart failure. The heart failure risk is increased even after adjusting for coronary artery disease and hypertension, and evidence is emerging that changes in cardiac energy metabolism might contribute to the development of contractile dysfunction. Recent findings suggest that myocardial mitochondrial dysfunction may play an important role in the pathogenesis of cardiac contractile dysfunction in obesity, insulin resistance and Type 2 diabetes. This review will discuss potential molecular mechanisms for these mitochondrial abnormalities.

Diabetic Cardiomyopathy in OVE26 Mice Shows Mitochondrial ROS Production and Divergence Between In Vivo and In Vitro Contractility

Many diabetic patients suffer from a cardiomyopathy that cannot be explained solely by poor coronary perfusion. This cardiomyopathy may be due to either organ-based damage like fibrosis, or to direct damage to cardiomyocytes. Mitochondrial-derived reactive oxygen species (ROS) have been proposed to contribute to this cardiomyopathy. To address these questions, we used the OVE26 mouse model of severe type 1 diabetes to measure contractility in isolated cardiomyocytes by edge detection and in vivo with echocardiography. We also assessed the source of ROS generation using both a general and a mitochondrial specific indicator. When contractility was assayed in freshly isolated myocytes, contraction was much stronger in control myocytes. However, contractility of normal myocytes became weaker during 24 hours of in vitro culture. In contrast, contractility of diabetic OVE26 myocytes remains stable during culture. Echocardiography revealed normal or hyperdynamic function in OVE26 hearts under basal conditions but with a sharply reduced response to isoproterenol, a beta-adrenergic agonist. For ROS generation, we found that ROS production in diabetic myocytes was elevated after exposure to either high glucose or angiotensin II (AngII). Superoxide detection with the mitochondrial sensor MitoSOX Red confirmed that mitochondria are a major source of ROS generation in diabetic myocytes. These results show that contractile deficits in OVE26 diabetic hearts are due primarily to cardiomyocyte impairment and that ROS from mitochondria are a cause of that impairment.

Mitochondrial energetics in the heart in obesity-related diabetes: direct evidence for increased uncoupled respiration and activation of uncoupling proteins

OBJECTIVE

In obesity and diabetes, myocardial fatty acid utilization and myocardial oxygen consumption (MVo(2)) are increased, and cardiac efficiency is reduced. Mitochondrial uncoupling has been proposed to contribute to these metabolic abnormalities but has not been directly demonstrated.

RESEARCH DESIGN AND METHODS

Oxygen consumption and cardiac function were determined in db/db hearts perfused with glucose or glucose and palmitate. Mitochondrial function was determined in saponin-permeabilized fibers and proton leak kinetics and H(2)O(2) generation determined in isolated mitochondria.

RESULTS

db/db hearts exhibited reduced cardiac function and increased MVo(2). Mitochondrial reactive oxygen species (ROS) generation and lipid and protein peroxidation products were increased. Mitochondrial proliferation was increased in db/db hearts, oxidative phosphorylation capacity was impaired, but H(2)O(2) production was increased. Mitochondria from db/db mice exhibited fatty acid-induced mitochondrial uncoupling that is inhibitable by GDP, suggesting that these changes are mediated by uncoupling proteins (UCPs). Mitochondrial uncoupling was not associated with an increase in UCP content, but fatty acid oxidation genes and expression of electron transfer flavoproteins were increased, whereas the content of the F1 alpha-subunit of ATP synthase was reduced.

CONCLUSIONS

These data demonstrate that mitochondrial uncoupling in the heart in obesity and diabetes is mediated by activation of UCPs independently of changes in expression levels. This likely occurs on the basis of increased delivery of reducing equivalents from beta-oxidation to the electron transport chain, which coupled with decreased oxidative phosphorylation capacity increases ROS production and lipid peroxidation.

Responses of mitochondrial biogenesis and function to maternal diabetes in rat embryo during the placentation period

Mitochondria are cellular organelles that have been reported to be altered in diabetes, being closely related to its associated complications. Moreover, mitochondrial biogenesis and function are essential for proper embryo development throughout the placentation period, occurring during organogenesis, when a great rate of congenital malformations have been associated with diabetic pregnancy. Thus, the aim of the current work was to investigate the effect of the diabetic environment on mitochondrial function and biogenesis during the placentation period. For this purpose, we studied the oxidative phosphorylation system (OXPHOS) enzymatic activities as well as the expression of genes involved in the coordinated regulation of both mitochondrial and nuclear genome (PGC-1alpha, NRF-1, NRF-2alpha, mtSSB, and TFAM) and mitochondrial function (COX-IV, COX-I, and beta-ATPase) in rat embryos from control and streptozotocin-induced diabetic mothers. Our results reflected that diabetic pregnancy retarded and altered embryo growth. The embryos from diabetic mothers showing normal morphology presented a reduced content of proteins regulated through the PGC-1alpha mitochondriogenic pathway on gestational day 12. This fact was accompanied by several responses that entailed the activation of OXPHOS activities on the same day and the recovery of the content of the studied proteins to control levels on day 13. As a result, the mitochondria of these embryos would reach a situation close to control on day 13 that could allow them to follow the normal mitochondriogenic schedule throughout a gestational period in which the mitochondrial differentiation process is critical. Nevertheless, malformed embryos from diabetic mothers seemed to show a lower adaptation capability, which could exacerbate their maldevelopment.

Diabetic cardiomyopathy revisited

Diabetes mellitus increases the risk of heart failure independently of underlying coronary artery disease, and many believe that diabetes leads to cardiomyopathy. The underlying pathogenesis is partially understood. Several factors may contribute to the development of cardiac dysfunction in the absence of coronary artery disease in diabetes mellitus. This review discusses the latest findings in diabetic humans and in animal models and reviews emerging new mechanisms that may be involved in the development and progression of cardiac dysfunction in diabetes.

Cardiovascular proteomics: past, present, and future

With cardiovascular (CV)-related disorders accounting for the highest mortality rates in the world, affecting the quantity and quality of life of patients and creating an economic burden of prolonged therapeutic intervention, there is great significance in understanding the cellular and molecular alterations that influence the progression of these pathologies. The cellular genotype is regulated by the DNA component, whilst the cellular phenotype is influenced by the protein complement. By improving the understanding of the molecular mechanisms that influence the protein profile, the pathologies that influence the intrinsic functions of the CV system may be detected earlier or managed more efficiently. This is achievable with technologies encompassed by 'proteomics.' Proteomic investigations of CV diseases, including dilated cardiomyopathy (DCM), atherosclerosis, and ischemia/reperfusion (I/R) injury, have identified candidate proteins altered with the pathologic states, complementing past biochemical and physiologic observations. Whilst proteomics is still a relatively new discipline to be applied to the basic scientific investigation of CV diseases, it is emerging as a technique to screen for potential biomarkers in both tissues/cells and biologic fluids (biofluids), as well as to identify the targets of existing therapeutics. By enabling the separation of complex mixtures over numerous dimensions, exploiting the intrinsic properties of proteins, including charge state, molecular mass, and hydrophobicity, in addition to cellular location, the discrete alterations within the cell may be resolved. Proteomics has shown alterations to myofilament proteins including troponin I and myosin light chain, correlating with the reduction in contractility in the myocardium from DCM and I/R. The diverse cell types that coalesce to induce atherosclerotic plaque formation have been investigated both collectively and individually to elucidate the influence of the modifications to single cell types on the developing plaque as a whole. Proteomics has also been used to observe changes to biofluids occurring with these pathologies, a new potential link between basic science and clinical applications. The development of CV proteomics has helped to identify a number of possible protein candidates, and offers the potential to treat and diagnose CV disease more effectively in the future.

Recipes for creating animal models of diabetic cardiovascular disease

For more than 50 years, investigators have unsuccessfully tried to recreate in experimental animals the cardiovascular complications of diabetes seen in humans. In particular, accelerated atherosclerosis and dilated cardiomyopathy, the major causes of mortality in patients with diabetes, have been conspicuously absent in many mouse models of the disease. Under the auspices of the NIH, the Animal Models of Diabetic Complications Consortium has worked to address this issue. This effort has focused on the development of mouse models because of the high level of genomic information available and the many well-developed genetic manipulations that may be performed in mice. Importantly, the consortium has also worked to standardize many methods to assess metabolic and cardiovascular end points for measurement of the diabetic state and its macrovascular complications. Finally, for maximum benefits from these animal models in the study of atherosclerosis and of other diabetic complications, the consortium has created a system for sharing both the animal models and the accumulated phenotypic data with the greater scientific community.

Defective mitochondrial biogenesis: a hallmark of the high cardiovascular risk in the metabolic syndrome?

The metabolic syndrome is a group of risk factors of metabolic origin that are accompanied by increased risk for type 2 diabetes mellitus and cardiovascular disease. These risk factors include atherogenic dyslipidemia, elevated blood pressure and plasma glucose, and a prothrombotic and proinflammatory state. The condition is progressive and is exacerbated by physical inactivity, advancing age, hormonal imbalance, and genetic predisposition. The metabolic syndrome is a particularly challenging clinical condition because its complex molecular basis is still largely undefined. Impaired cell metabolism has, however, been suggested as a relevant pathophysiological process underlying several clinical features of the syndrome. In particular, defective oxidative metabolism seems to be involved in visceral fat gain and in the development of insulin resistance in skeletal muscle. This suggests that mitochondrial function may be impaired in the metabolic syndrome and, thus, in the consequent cardiovascular disease. We have recently found that mitochondrial biogenesis and function are enhanced by nitric oxide in various cell types and tissues, including cardiac muscle. Increasing evidence suggests that this mediator acts as a metabolic sensor in cardiomyocytes. This implies that a defective production of nitric oxide might be linked to dysfunction of the cardiomyocyte metabolism. Here we summarize some recent findings and propose a hypothesis for the high cardiovascular risk linked to the metabolic syndrome.

Alterations in the diabetic myocardial proteome coupled with increased myocardial oxidative stress underlies diabetic cardiomyopathy

Diabetic cardiomyopathy has been documented as an underlying etiology of heart failure (HF) among diabetics. Although oxidative stress has been proposed to contribute to diabetic cardiomyopathy, much of the evidence lacks specificity. Furthermore, whether alterations occur at the cardiac proteome level in diabetic cardiac complications with attendant oxidative stress remains unknown. Therefore, we sought to identify cardiac protein changes in relation to myocardial oxidative stress that are specific to diabetic cardiomyopathy. Diabetes was induced in rats by a single injection of streptozotocin (STZ). STZ-treated rats were examined for diabetic cardiomyopathy at 8 weeks post-STZ by left ventricular (LV) hemodynamic analysis. LV systolic pressure (LVSP), rate of pressure rise (+dP/dt), and rate of pressure decay (-dP/dt) were depressed while LV end-diastolic pressure (LVEDP) was increased. Myocardial oxidative stress was increased in STZ-diabetic rats, as indexed by significant increases in myocardial formation of 8-iso PGF(2alpha) and oxidized glutathione (GSSG). In-depth mining of the diabetic myocardial proteome by proteomic analysis utilizing two-dimensional difference gel electrophoresis and mass spectrometry (DIGE/MS) techniques revealed that a high proportion (12 of 24) of the altered proteins that could be identified by mass spectrometry were localized to the mitochondria. Down-regulation of antioxidant and anti-apoptotic proteins was also observed in STZ-diabetic hearts. These results characterize a specific 'type I diabetic' pattern of cardiac proteome changes indicative of diabetic cardiomyopathy presenting with higher oxidative stress, supporting the idea that analysis of isoprostane biosynthesis and protein expression profiles may be useful diagnostically to assess the efficacy of antioxidant therapies as prophylactic treatments against type I diabetes mellitus complications involving the heart.

Insulin-resistant heart exhibits a mitochondrial biogenic response driven by the peroxisome proliferator-activated receptor-alpha/PGC-1alpha gene regulatory pathway

BACKGROUND

Obesity and diabetes mellitus are complex metabolic problems of pandemic proportion, contributing to significant cardiovascular mortality. Recent studies have shown altered mitochondrial function in the hearts of diabetic animals. We hypothesized that regulatory events involved in the control of mitochondrial function are activated in the prediabetic, insulin-resistant stage.

METHODS AND RESULTS

Morphometric analyses demonstrated that cardiac myocyte mitochondrial volume density was increased in insulin-resistant uncoupling protein-diphtheria toxin A (UCP-DTA) transgenic mice, a murine model of metabolic syndrome, compared with littermate controls. Mitochondrial DNA content and expression of genes involved in multiple mitochondrial pathways were also increased in insulin-resistant UCP-DTA hearts. The nuclear receptor, peroxisome proliferator-activated receptor-alpha (PPARalpha), is known to activate metabolic genes in the diabetic heart. Therefore, we evaluated the role of PPARalpha in the observed mitochondrial biogenesis response in the insulin-resistant heart. Insulin-resistant UCP-DTA mice crossed into a PPARalpha-null background did not exhibit evidence of mitochondrial biogenesis or induction of mitochondrial gene expression. Conversely, transgenic mice with cardiac-specific overexpression of PPARalpha exhibited signatures of cardiac mitochondrial biogenesis. A screen for candidate mediators of the PPARalpha-driven mitochondrial biogenic response revealed that expression of PPARgamma coactivator-1alpha (PGC-1alpha), a known regulator of mitochondrial biogenesis, was activated in wild-type UCP-DTA mice but not in PPARalpha-deficient UCP-DTA mice.

CONCLUSIONS

These results demonstrate that mitochondrial biogenesis occurs early in the development of diabetic cardiac dysfunction through a transcriptional regulatory circuit that involves activation of PGC-1alpha gene expression by the fatty acid-activated nuclear receptor PPARalpha.

Early myocardial dysfunction in streptozotocin-induced diabetic mice: a study using in vivo magnetic resonance imaging (MRI)

Background

Diabetes is associated with a cardiomyopathy that is independent of coronary artery disease or hypertension. In the present study we used in vivo magnetic resonance imaging (MRI) and echocardiographic techniques to examine and characterize early changes in myocardial function in a mouse model of type 1 diabetes.

Methods

Diabetes was induced in 8-week old C57BL/6 mice with two intraperitoneal injections of streptozotocin. The blood glucose levels were maintained at 19–25 mmol/l using intermittent low dosages of long acting insulin glargine. MRI and echocardiography were performed at 4 weeks of diabetes (age of 12 weeks) in diabetic mice and age-matched controls.

Results

After 4 weeks of hyperglycemia one marker of mitochondrial function, NADH oxidase activity, was decreased to 50% of control animals. MRI studies of diabetic mice at 4 weeks demonstrated significant deficits in myocardial morphology and functionality including: a decreased left ventricular (LV) wall thickness, an increased LV end-systolic diameter and volume, a diminished LV ejection fraction and cardiac output, a decreased LV circumferential shortening, and decreased LV peak ejection and filling rates. M-mode echocardiographic and Doppler flow studies of diabetic mice at 4 weeks showed a decreased wall thickening and increased E/A ratio, supporting both systolic and diastolic dysfunction.

Conclusion

Our study demonstrates that MRI interrogation can identify the onset of diabetic cardiomyopathy in mice with its impaired functional capacity and altered morphology. The MRI technique will lend itself to repetitive study of early changes in cardiac function in small animal models of diabetic cardiomyopathy.

Mitochondria and ageing: winning and losing in the numbers game

Mitochondrial dysfunction has long been considered a key mechanism in the ageing process but surprisingly little attention has been paid to the impact of mitochondrial number or density within cells. Recent reports suggest a positive association between mitochondrial density, energy homeostasis and longevity. However, mitochondrial number also determines the number of sites generating reactive oxygen species (ROS) and we suggest that the links between mitochondrial density and ageing are more complex, potentially acting in both directions. The idea that increased density, especially when combined with mitochondrial dysfunction, might accelerate ageing is supported by a negative correlation between mitochondrial density and maximum longevity in an interspecies comparison in mammals, and by evidence for an intimate interconnection between cellular ROS levels, mitochondrial density and cellular ageing. Recent data suggest that retrograde response, which activates mitochondrial biogenesis, accompanies cellular ageing processes. We hypothesise that increased mitochondrial biogenesis, and possibly also impaired degradation and segregation of mitochondria, if occurring as adaptation to pre-existing mitochondrial dysfunction, might aggravate ROS production and thus actively contribute to ageing.

Regulation of IGF-I receptor signaling in diabetic cardiac muscle: dysregulation of cytosolic and mitochondria HSP60

Insulin deficiency downregulates HSP60 and IGF-I receptor signaling and disrupts intracellular signaling homeostasis in diabetic cardiac muscle. Our previous studies had shown that IGF-I receptor signaling can be modulated by the abundance of HSP60. Since HSP60 localizes to the cytoplasmic compartment and mitochondria, this study was carried out to determine the distribution of cytosolic and mitochondria HSP60 in diabetic myocardium and to explore whether cytosolic HSP60 can modulate IGF-I receptor signaling in cardiac muscle cells. In streptozotocin-induced diabetes, both the cytosolic and mitochondrial fractions of HSP60 were decreased in the myocardium. Incubating primary cardiomyocytes with insulin leads to increased abundance of HSP60 in the cytosolic and mitochondria compartments. To determine whether cytosolic HSP60 can modulate IGF-I receptor signaling, we used rhodamine 6G to deplete functional mitochondria in cardiomyocytes. In the mitochondria-depleted cells, overexpression of HSP60 with adenoviral vector increased the abundance of IGF-I receptor, enhanced IGF-I-activated receptor phosphorylation, and augmented IGF-I activation of Akt and ERK. Thus overexpressing HSP60 in the cytosolic compartment enhanced IGF-I receptor signaling through upregulation of IGF-I receptor protein. However, IGF-I receptor signaling was significantly reduced in the mitochondria-depleted cells, which suggested that maintaining normal IGF-I receptor signaling in cardiomyocytes required functioning mitochondria. The effect of cytosolic HSP60 involved suppression of ubiquitin conjugation to IGF-I receptor in cardiomyocytes. These data suggest two different mechanisms that can regulate IGF-I signaling, one via cytosolic HSP60 suppression of IGF-I receptor ubiquitination and the other via mitochondria modulation. These findings provide new insight into the regulation of IGF-I signaling in diabetic cardiomyopathy.

Causes and characteristics of diabetic cardiomyopathy

Type 1 and type 2 diabetic patients are at increased risk of cardiomyopathy and heart failure is a major cause of death for these patients. Cardiomyopathy in diabetes is associated with a cluster of features including decreased diastolic compliance, interstitial fibrosis and myocyte hypertrophy. The mechanisms leading to diabetic cardiomyopathy remain uncertain. Diabetes is associated with most known risk factors for cardiac failure seen in the overall population, including obesity, dyslipidemia, thrombosis, infarction, hypertension, activation of multiple hormone and cytokine systems, autonomic neuropathy, endothelial dysfunction and coronary artery disease. In light of these common contributing pathologies it remains uncertain whether diabetic cardiomyopathy is a distinct disease. It is also uncertain which factors are most important to the overall incidence of heart failure in diabetic patients. This review focuses on factors that can have direct effects on diabetic cardiomyocytes: hyperglycemia, altered fuel use, and changes in the activity of insulin and angiotensin. Particular attention is given to the changes these factors can have on cardiac mitochondria and the role of reactive oxygen species in mediating injury to cardiomyocytes.

Mitochondrial uncoupling: a key contributor to reduced cardiac efficiency in diabetes

Cardiovascular disease is the primary cause of death in individuals with obesity and diabetes. However, the underlying mechanisms for cardiac dysfunction are partially understood. Studies have suggested that altered cardiac metabolism may play a role. The diabetic heart is characterized by increased fatty acid oxidation, increased myocardial oxygen consumption, and reduced cardiac efficiency. Here, we review possible mechanisms for reduced cardiac efficiency in obesity and diabetes by focusing on the potential role of mitochondrial uncoupling.

Proteomics for diabetes research: an update and future perspectives

Diabetes is a common disease worldwide and can cause several complications, leading to systemic derangements and end-organ damage. Despite blood sugar control and adequate therapy with currently available drugs, diabetic complications remain a serious issue in clinical practice, indicating that our knowledge of diabetes and its complications is only at the tip of the iceberg. Better understanding of its pathogenesis and pathophysiology is crucial to achieve better therapeutic outcomes and to prevent its complications. This review provides an overview of proteomics and introduces proteomic technologies commonly used for diabetes research. Recent proteomic studies for the investigation of diabetes and its complications are summarized. Finally, the future perspectives for the field of proteomics in diabetes research are discussed.

Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

In patients with diabetes, an increased risk of symptomatic heart failure usually develops in the presence of hypertension or ischemic heart disease. However, a predisposition to heart failure might also reflect the effects of underlying abnormalities in diastolic function that can occur in asymptomatic patients with diabetes alone (termed diabetic cardiomyopathy). Evidence of cardiomyopathy has also been demonstrated in animal models of both Type 1 (streptozotocin-induced diabetes) and Type 2 diabetes (Zucker diabetic fatty rats and ob/ob or db/db mice). During insulin resistance or diabetes, the heart rapidly modifies its energy metabolism, resulting in augmented fatty acid and decreased glucose consumption. Accumulating evidence suggests that this alteration of cardiac metabolism plays an important role in the development of cardiomyopathy. Hence, a better understanding of this dysregulation in cardiac substrate utilization during insulin resistance and diabetes could provide information as to potential targets for the treatment of cardiomyopathy. This review is focused on evaluating the acute and chronic regulation and dysregulation of cardiac metabolism in normal and insulin-resistant/diabetic hearts and how these changes could contribute toward the development of cardiomyopathy.

Heme oxygenase-1 enhances renal mitochondrial transport carriers and cytochrome C oxidase activity in experimental diabetes

Up-regulation of heme oxygenase (HO-1) by either cobalt protoporphyrin (CoPP) or human gene transfer improves vascular and renal function by several mechanisms, including increases in antioxidant levels and decreases in reactive oxygen species (ROS) in vascular and renal tissue. The purpose of the present study was to determine the effect of HO-1 overexpression on mitochondrial transporters, cytochrome c oxidase, and anti-apoptotic proteins in diabetic rats (streptozotocin, (STZ)-induced type 1 diabetes). Renal mitochondrial carnitine, deoxynucleotide, and ADP/ATP carriers were significantly reduced in diabetic compared with nondiabetic rats (p < 0.05). The citrate carrier was not significantly decreased in diabetic tissue. CoPP administration produced a robust increase in carnitine, citrate, deoxynucleotide, dicarboxylate, and ADP/ATP carriers and no significant change in oxoglutarate and aspartate/glutamate carriers. The increase in mitochondrial carriers (MCs) was associated with a significant increase in cytochrome c oxidase activity. The administration of tin mesoporphyrin (SnMP), an inhibitor of HO-1 activity, prevented the restoration of MCs in diabetic rats. Human HO-1 cDNA transfer into diabetic rats increased both HO-1 protein and activity, and restored mitochondrial ADP/ATP and deoxynucleotide carriers. The increase in HO-1 by CoPP administration was associated with a significant increase in the phosphorylation of AKT and levels of BcL-XL proteins. These observations in experimental diabetes suggest that the cytoprotective mechanism of HO-1 against oxidative stress involves an increase in the levels of MCs and anti-apoptotic proteins as well as in cytochrome c oxidase activity.

Protection of cardiac mitochondria by overexpression of MnSOD reduces diabetic cardiomyopathy

We previously reported damage and elevated biogenesis in cardiac mitochondria of a type 1 diabetic mouse model and proposed that mitochondria are one of the major targets of oxidative stress. In this study, we targeted overexpression of the mitochondrial antioxidant protein manganese superoxide dismutase (MnSOD) to the heart to protect cardiac mitochondria from oxidative damage. Transgenic hearts had a 10- to 20-fold increase in superoxide dismutase (SOD) activity, and the transgenic SOD was located in mitochondria. The transgene caused a twofold increase in cardiac catalase activity. MnSOD transgenic mice demonstrated normal cardiac morphology, contractility, and mitochondria, and their cardiomyocytes were protected from exogenous oxidants. Crossing MnSOD transgenic mice with our type 1 model tested the benefit of eliminating mitochondrial reactive oxygen species. Overexpression of MnSOD improved respiration and normalized mass in diabetic mitochondria. MnSOD also protected the morphology of diabetic hearts and completely normalized contractility in diabetic cardiomyocytes. These results showed that elevating MnSOD provided extensive protection to diabetic mitochondria and provided overall protection to the diabetic heart.

Cardiomyocyte apoptosis induced by short-term diabetes requires mitochondrial GSH depletion

Oxidative stress due to excessive reactive oxygen species (ROS) and depleted antioxidants such as glutathione (GSH) can give rise to apoptotic cell death in acutely diabetic hearts and lead to heart disease. At present, the source of these cardiac ROS or the subcellular site of cardiac GSH loss [i.e., cytosolic (cGSH) or mitochondrial (mGSH) GSH] has not been completely elucidated. With the use of rotenone (an inhibitor of the electron transport chain) to decrease the excessive ROS in acute streptozotocin (STZ)-induced diabetic rat heart, the mitochondrial origin of ROS was established. Furthermore, mitochondrial damage, as evidenced by loss of membrane potential, increases in oxidative stress, and reduction in mGSH was associated with increased apoptosis via increases in caspase-9 and -3 activities in acutely diabetic hearts. To validate the role of mGSH in regulating cardiac apoptosis, l-buthionine-sulfoximine (BSO; 10 mmol/kg ip), which blocks GSH synthesis, or diethyl maleate (DEM; 4 mmol/kg ip), which inactivates preformed GSH, was administered in diabetic rats for 4 days after STZ administration. Although both BSO and DEM lowered cGSH, they were ineffective in reducing mGSH or augmenting cardiomyocyte apoptosis. To circumvent the lack of mGSH depletion, BSO and DEM were coadministered in diabetic rats. In this setting, mGSH was undetectable and cardiac apoptosis was further aggravated compared with the untreated diabetic group. In a separate group, GSH supplementation induced a robust amplification of mGSH in diabetic rat hearts and prevented apoptosis. Our data suggest for the first time that mGSH is crucial for modulating the cell suicide program in short-term diabetic rat hearts.

Differential effects of diabetes on the expression of the gp91phox homologues nox1 and nox4

The nox2-dependent NADPH oxidase was shown to be a major superoxide source in vascular disease, including diabetes. Smooth muscle cells of large arteries lack the phagocytic gp91phox subunit of the enzyme; however, two homologues have been identified in these cells, nox1 and nox4. It remained to be established whether also increases in protein levels of the nonphagocytic NADPH oxidase contribute to increased superoxide formation in diabetic vessels. To investigate changes in the expression of these homologues, we measured their expression in aortic vessels of type I diabetic rats. Eight weeks after streptozotocin treatment, we found a doubling in nox1 protein expression, while the expression of nox4 remained unchanged. This was associated with a significant increase in the NADPH oxidase activity in membrane fractions of diabetic heart and aortic tissue. Furthermore, we observed a decreased sensitivity of diabetic vessels to acetylcholine and nitroglycerin and a decrease in both acetylcholine-stimulated NO production and phosphorylation of VASP, despite an increase in endothelial NO synthase (NOSIII) expression. In addition, xanthine oxidase activity was markedly increased in plasma and 100,000 g supernatant of cardiac tissue of diabetic rats, while myocardial mitochondrial superoxide formation was only weakly enhanced. We conclude that in addition to phagocytic NADPH oxidase, also nonphagocytic, vascular NADPH oxidase subunit nox1, uncoupled NOSIII, and plasma xanthine oxidase contribute to endothelial dysfunction in the setting of diabetes mellitus.

Mitochondrial energy metabolism in heart failure: a question of balance

The mitochondrion serves a critical role as a platform for energy transduction, signaling, and cell death pathways relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events and downstream effector pathways involved in mitochondrial energy metabolic derangements known to occur during the development of heart failure.

Mitochondrial energy metabolism in heart failure: a question of balance

The mitochondrion serves a critical role as a platform for energy transduction, signaling, and cell death pathways relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events and downstream effector pathways involved in mitochondrial energy metabolic derangements known to occur during the development of heart failure.

The application of proteomics to diabetes

Poteomics is the investigation of all the proteins and their various modifications making up a system, be that a cell, tissue or organism. The techniques involved in proteomics allow the global screening of complex samples of proteins and provide qualitative and quantitative evidence of altered protein expression. This lends itself to the investigation of the molecular mechanisms underpinning disease processes and the effects of treatment. This review describes the main techniques of proteomics and how they have begun to be applied to diabetes research.