Induction of mitochondrial ROS production by electrophilic lipids: a new pathway of redox signaling?

Endothelial Progenitor Cells Dysfunctions and Cardiometabolic Disorders: From Mechanisms to Therapeutic Approaches

Metabolic syndrome (MetS) is a cluster of several disorders, such as hypertension, central obesity, dyslipidemia, hyperglycemia, insulin resistance and non-alcoholic fatty liver disease. Despite health policies based on the promotion of physical exercise, the reduction of calorie intake and the consumption of healthy food, there is still a global rise in the incidence and prevalence of MetS in the world. This phenomenon can partly be explained by the fact that adverse events in the perinatal period can increase the susceptibility to develop cardiometabolic diseases in adulthood. Individuals born after intrauterine growth restriction (IUGR) are particularly at risk of developing cardiovascular diseases (CVD) and metabolic disorders later in life. It has been shown that alterations in the structural and functional integrity of the endothelium can lead to the development of cardiometabolic diseases. The endothelial progenitor cells (EPCs) are circulating components of the endothelium playing a major role in vascular homeostasis. An association has been found between the maintenance of endothelial structure and function by EPCs and their ability to differentiate and repair damaged endothelial tissue. In this narrative review, we explore the alterations of EPCs observed in individuals with cardiometabolic disorders, describe some mechanisms related to such dysfunction and propose some therapeutical approaches to reverse the EPCs dysfunction.

Ginsenoside Rb3 exerts protective properties against cigarette smoke extract-induced cell injury by inhibiting the p38 MAPK/NF-κB and TGF-β1/VEGF pathways in fibroblasts and epithelial cells

Cigarette smoke causes many adverse effects such as inflammation, oxidative stress, and excessive accumulation of the extracellular matrix (ECM). Ginsenoside Rb3 has anti-inflammatory and anti-oxidative effects, which may contribute to delaying the injury caused by cigarette smoke. In this study, we used cigarette smoke extract (CSE) to establish cell injury models in WI-38 human fetal lung fibroblasts and 16HBE human bronchial epithelial cells. Our results showed that Rb3 protected against CSE-induced cytotoxicity in both cell lines. In addition, it significantly inhibited the secretion of inflammatory factors, such as interleukin-8 and tumor necrosis factor alpha, by inhibiting the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB). Moreover, Rb3 pre-treatment led to an increase in the levels of glutathione (GSH) and activities of superoxide dismutase, glutathione peroxidase (GSH-Px), and catalase to reduce the oxidative stress induced by CSE. Additionally, Rb3 decreased the levels of ECM proteins including collagen I (Col I), Col III, and elastin after CSE treatment by inhibiting the expression of transforming growth factor beta 1 (TGF-β1)-induced vascular endothelial growth factor (VEGF). Our findings suggest that Rb3 prevented CSE-induced inflammation and oxidative stress as well as the excessive accumulation of ECM in WI-38 and 16HBE cells to protect against cell injury by inhibiting the p38 MAPK/NF-κB and TGF-β1/VEGF pathways. The results of this study may be valuable for the development of Rb3 to combat the damage caused by cigarette smoke.

Advances in PCOS Pathogenesis and Progression-Mitochondrial Mutations and Dysfunction

Polycystic ovary syndrome (PCOS) is a common female endocrine disorder, which still remains largely unsolved in terms of etiology and pathogenesis despite important advances in our understanding of its genetic, epigenetic, or environmental factor implications. It is a heterogeneous disease, frequently associated with insulin resistance, chronic inflammation, and oxidative stress and probably accompanied with subclinical cardiovascular disease (CVD) and some malignant lesions as well, such as endometrial cancer. Discrepancies in the clinical phenotype and progression of PCOS exist between different population groups, which nuclear genetic studies have so far failed to explain. Over the last years, mitochondrial dysfunction has been increasingly recognized as an important contributor to an array of diseases. Because mitochondria are under the dual genetic control of both the mitochondrial and nuclear genomes, mutations within either DNA molecule may result in deficiency in respiratory chain function that leads to a reduced ability to produce cellular adenosine-5'-triphosphate and to an excessive production of reactive oxygen species. However, the association between variants in mitochondrial genome, mitochondrial dysfunction, and PCOS has been investigated to a lesser extent. May mutations in mitochondrial DNA (mtDNA) become an additional target of investigations on the missing PCOS heritability? Are mutations in mtDNA implicated in the initiation and progression of PCOS complications, e.g., CVDs, diabetes mellitus, cancers?

Insights for Oxidative Stress and mTOR Signaling in Myocardial Ischemia/Reperfusion Injury under Diabetes

Diabetes mellitus (DM) displays a high morbidity. The diabetic heart is susceptible to myocardial ischemia/reperfusion (MI/R) injury. Impaired activation of prosurvival pathways, endoplasmic reticulum (ER) stress, increased basal oxidative state, and decreased antioxidant defense and autophagy may render diabetic hearts more vulnerable to MI/R injury. Oxidative stress and mTOR signaling crucially regulate cardiometabolism, affecting MI/R injury under diabetes. Producing reactive oxygen species (ROS) and reactive nitrogen species (RNS), uncoupling nitric oxide synthase (NOS), and disturbing the mitochondrial quality control may be three major mechanisms of oxidative stress. mTOR signaling presents both cardioprotective and cardiotoxic effects on the diabetic heart, which interplays with oxidative stress directly or indirectly. Antihyperglycemic agent metformin and newly found free radicals scavengers, Sirt1 and CTRP9, may serve as promising pharmacological therapeutic targets. In this review, we will focus on the role of oxidative stress and mTOR signaling in the pathophysiology of MI/R injury in diabetes and discuss potential mechanisms and their interactions in an effort to provide some evidence for cardiometabolic targeted therapies for ischemic heart disease (IHD).

Fructose induces mitochondrial dysfunction and triggers apoptosis in skeletal muscle cells by provoking oxidative stress

Mitochondrial dysfunction in skeletal muscle has been implicated in the development of insulin resistance, a major characteristic of type 2 diabetes. There is evidence that oxidative stress results from the increased production of reactive oxygen species and reactive nitrogen species leads to mitochondrial dysfunction, tissue damage, insulin resistance, and other complications observed in type 2 diabetes. It has been suggested that intake of high fructose contributes to insulin resistance and other metabolic disturbances. However, there is limited information about the direct effect of fructose on the mitochondrial function of skeletal muscle, the major metabolic determinant of whole body insulin activity. Here, we assessed the effect of fructose exposure on mitochondria-mediated mechanisms in skeletal muscle cells. Exposure of L6 myotubes to high fructose stimulated the production of mitochondrial reactive oxygen species and nitric oxide (NO), and the expression of inducible NO synthase. Fructose-induced oxidative stress was associated with increased translocation of nuclear factor erythroid 2-related factor-2 to the nucleus, decreases in mitochondrial DNA content and mitochondrial dysfunctions, as evidenced by decreased activities of citrate synthase and mitochondrial dehydrogenases, loss of mitochondrial membrane potential, decreased activity of the mitochondrial respiratory complexes, and impaired mitochondrial energy metabolism. Furthermore, positive Annexin-propidium iodide staining and altered expression of Bcl-2 family members and caspases in L6 myotubes indicated that the cells progressively became apoptotic upon fructose exposure. Taken together, these findings suggest that exposure of skeletal muscle cells to fructose induced oxidative stress that decreased mitochondrial DNA content and triggered mitochondrial dysfunction, which caused apoptosis.

Antioxidant role of glutathione S-transferases: 4-Hydroxynonenal, a key molecule in stress-mediated signaling

4-Hydroxy-2-trans-nonenal (4HNE), one of the major end products of lipid peroxidation (LPO), has been shown to induce apoptosis in a variety of cell lines. It appears to modulate signaling processes in more than one way because it has been suggested to have a role in signaling for differentiation and proliferation. It has been known that glutathione S-transferases (GSTs) can reduce lipid hydroperoxides through their Se-independent glutathione-peroxidase activity and that these enzymes can also detoxify LPO end-products such as 4HNE. Available evidence from earlier studies together with results of recent studies in our laboratories strongly suggests that LPO products, particularly hydroperoxides and 4HNE, are involved in the mechanisms of stress-mediated signaling and that it can be modulated by the alpha-class GSTs through the regulation of the intracellular concentrations of 4HNE. We demonstrate that 4HNE induced apoptosis in various cell lines is accompanied with c-Jun-N-terminal kinase (JNK) and caspase-3 activation. Cells exposed to mild, transient heat or oxidative stress acquire the capacity to exclude intracellular 4HNE at a faster rate by inducing GSTA4-4 which conjugates 4HNE to glutathione (GSH), and RLIP76 which mediates the ATP-dependent transport of the GSH-conjugate of 4HNE (GS-HNE). The balance between formation and exclusion promotes different cellular processes - higher concentrations of 4HNE promote apoptosis; whereas, lower concentrations promote proliferation. In this article, we provide a brief summary of the cellular effects of 4HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTA4-4. Taken together, 4HNE is a key signaling molecule and that GSTs being determinants of its intracellular concentrations, can regulate stress-mediated signaling, are reviewed in this article.

Cytotoxicity and cellular mechanisms involved in the toxicity of CdS quantum dots in hemocytes and gill cells of the mussel Mytilus galloprovincialis

CdS quantum dots (QDs) show a great promise for treatment and diagnosis of cancer and for targeted drug delivery, due to their size-tunable fluorescence and ease of functionalization for tissue targeting. In spite of their advantages it is important to determine if CdS QDs can exert toxicity on biological systems. In the present work, cytotoxicity of CdS QDs (5 nm) at a wide range of concentrations (0.001-100 mg Cd/L) was screened using neutral red (NR) and thiazolyl blue tetrazolium bromide (MTT) assays in isolated hemocytes and gill cells of mussels (Mytilus galloprovincialis). The mechanisms of action of CdS QDs were assessed at sublethal concentrations (0.31-5 mg Cd/L) in the same cell types through a series of functional in vitro assays: production of reactive oxygen species (ROS), catalase (CAT) activity, DNA damage, lysosomal acid phosphatase (AcP) activity, multixenobiotic resistance (MXR) transport activity, Na-K-ATPase activity (only in gill cells) and phagocytic activity and damage to actin cytoskeleton (only in hemocytes). Exposures to CdS QDs lasted for 24h and were performed in parallel with exposures to bulk CdS and ionic Cd. Ionic Cd was the most toxic form to both cell types, followed by CdS QDs and bulk CdS. ROS production, DNA damage, AcP activity and MXR transport were significantly increased in both cell types exposed to the 3 forms of Cd. CAT activity increased in hemocytes exposed to the three forms of Cd while in gill cells only in those exposed to ionic Cd. No effects were found on hemocytes cytoskeleton integrity. Effects on phagocytosis were found in hemocytes exposed to bulk CdS and to CdS QDs at concentrations equal or higher than 1.25 mg Cd/L but not in those exposed to ionic Cd, indicating a particle-specific effect on phagocytosis. In conclusion, cell-mediated immunity and gill cell function represent significant targets for CdS QDs toxicity.

Metabolic syndrome in pediatric cancer survivors: a mechanistic review

Pediatric cancer survivors have increased risk of obesity, hypertension, dyslipidemia, and type 2 diabetes, leading to premature cardiovascular disease (CVD). Multiple tissues that are involved in glucose homeostasis and lipid metabolism are adversely affected by chemotherapy. This review highlights the relevant tissue and molecular end-organ effects of therapy exposures and synthesizes the current understanding of the mechanisms underlying CVD risk in this vulnerable population. The review also approaches the topic from a developmental perspective, with the goal of providing a translational approach to identifying the antecedents of overt CVD among survivors of pediatric cancer.

Role of TRIB3 in regulation of insulin sensitivity and nutrient metabolism during short-term fasting and nutrient excess

We have suggested previously that Tribbles homolog 3 (TRIB3), a negative regulator of Akt activity in insulin-sensitive tissues, could mediate glucose-induced insulin resistance in muscle under conditions of chronic hyperglycemia (Liu J, Wu X, Franklin JL, Messina JL, Hill HS, Moellering DR, Walton RG, Martin M, Garvey WT. Am J Physiol Endocrinol Metab 298: E565-E576, 2010). In the current study, we have assessed short-term physiological regulation of TRIB3 in skeletal muscle and adipose tissues by nutrient excess and fasting as well as TRIB3's ability to modulate glucose transport and mitochondrial oxidation. In Sprague-Dawley rats, we found that short-term fasting enhanced insulin sensitivity concomitantly with decrements in TRIB3 mRNA (66%, P < 0.05) and protein (81%, P < 0.05) in muscle and increments in TRIB3 mRNA (96%, P < 0.05) and protein (~10-fold, P < 0.05) in adipose tissue compared with nonfasted controls. On the other hand, rats fed a Western diet for 7 days became insulin resistant concomitantly with increments in TRIB3 mRNA (155%, P < 0.05) and protein (69%, P = 0.0567) in muscle and a decrease in the mRNA (76%, P < 0.05) and protein (70%, P < 0.05) in adipose. In glucose transport and mitochondria oxidation studies using skeletal muscle cells, we found that stable TRIB3 overexpression impaired insulin-stimulated glucose uptake without affecting basal glucose transport and increased both basal glucose oxidation and the maximal uncoupled oxygen consumption rate. With stable knockdown of TRIB3, basal and insulin-stimulated glucose transport rates were increased, whereas basal glucose oxidation and the maximal uncoupled oxygen consumption rate were decreased. In conclusion, TRIB3 impacts glucose uptake and oxidation oppositely in muscle and fat according to levels of nutrient availability. The above data for the first time implicate TRIB3 as a potent physiological regulator of insulin sensitivity and mitochondrial glucose oxidation under conditions of nutrient deprivation and excess.

Mitochondria as a source and target of lipid peroxidation products in healthy and diseased heart

The heart is a highly oxidative organ in which cardiomyocyte turnover is virtually absent, making it particularly vulnerable to accumulation of lipid peroxidation products (LPP) formed as a result of oxidative damage. Reactive oxygen and nitrogen species are the most common electrophiles formed during lipid peroxidation and lead to the formation of both stable and unstable LPP. Of the LPP formed, highly reactive aldehydes are a well-recognized causative factor in ageing and age-associated diseases, including cardiovascular disease and diabetes. Recent studies have identified that the mitochondria are both a primary source and target of LPP, with specific emphasis on aldehydes in cardiomyocytes and how these affect the electron transport system and Ca(2+) balance. Numerous studies have found that there are functional consequences in the heart following exposure to specific aldehydes (acrolein, trans-2-hexanal, 4-hydroxynonenal and acetaldehyde). Because these LPP are known to form in heart failure, cardiac ischaemia-reperfusion injury and diabetes, they may have an underappreciated role in the pathophysiology of these disease processes. Lipid peroxidation products are involved in the transcriptional regulation of endogenous anti-oxidant systems. Recent evidence demonstrates that transient increases in LPP may be beneficial in cardioprotection by contributing to mitohormesis (i.e. induction of anti-oxidant systems) in cardiomyocytes. Thus, exploitation of the cardioprotective actions of the LPP may represent a novel therapeutic strategy for future treatment of heart disease.

Autophagy, mitochondria and oxidative stress: cross-talk and redox signalling

Reactive oxygen and nitrogen species change cellular responses through diverse mechanisms that are now being defined. At low levels, they are signalling molecules, and at high levels, they damage organelles, particularly the mitochondria. Oxidative damage and the associated mitochondrial dysfunction may result in energy depletion, accumulation of cytotoxic mediators and cell death. Understanding the interface between stress adaptation and cell death then is important for understanding redox biology and disease pathogenesis. Recent studies have found that one major sensor of redox signalling at this switch in cellular responses is autophagy. Autophagic activities are mediated by a complex molecular machinery including more than 30 Atg (AuTophaGy-related) proteins and 50 lysosomal hydrolases. Autophagosomes form membrane structures, sequester damaged, oxidized or dysfunctional intracellular components and organelles, and direct them to the lysosomes for degradation. This autophagic process is the sole known mechanism for mitochondrial turnover. It has been speculated that dysfunction of autophagy may result in abnormal mitochondrial function and oxidative or nitrative stress. Emerging investigations have provided new understanding of how autophagy of mitochondria (also known as mitophagy) is controlled, and the impact of autophagic dysfunction on cellular oxidative stress. The present review highlights recent studies on redox signalling in the regulation of autophagy, in the context of the basic mechanisms of mitophagy. Furthermore, we discuss the impact of autophagy on mitochondrial function and accumulation of reactive species. This is particularly relevant to degenerative diseases in which oxidative stress occurs over time, and dysfunction in both the mitochondrial and autophagic pathways play a role.

Chronic and acute exposure of mouse hearts to fatty acids increases oxygen cost of excitation-contraction coupling

The aim of the present study was to evaluate the underlying processes involved in the oxygen wasting induced by inotropic drugs and acute and chronic elevation of fatty acid (FA) supply, using unloaded perfused mouse hearts from normal and type 2 diabetic ( db/db) mice. We found that an acute elevation of the FA supply in normal hearts, as well as a chronic (in vivo) exposure to elevated FA as in db/db hearts, increased myocardial oxygen consumption (MV̇o2unloaded) due to increased oxygen cost for basal metabolism and for excitation-contraction (EC) coupling. Isoproterenol stimulation, on top of a high FA supply, led to an additive increase in MV̇o2unloaded, because of a further increase in oxygen cost for EC coupling. In db/db hearts, the acute elevation of FA did not further increase MV̇o2. Since the elevation in the FA supply is accompanied by increased rates of myocardial FA oxidation, the present study compared MV̇o2 following increased FA load versus FA oxidation rate by exposing normal hearts to normal and high FA concentration (NF and HF, respectively) and to compounds that either stimulate (GW-610742) or inhibit [dichloroacetate (DCA)] FA oxidation. While HF and NF + GW-610742 increased FA oxidation to the same extent, only HF increased MV̇o2unloaded. Although DCA counteracted the HF-induced increase in FA oxidation, DCA did not reduce MV̇o2unloaded. Thus, in normal hearts, acute FA-induced oxygen waste is 1) due to an increase in the oxygen cost for both basal metabolism and EC coupling and 2) not dependent on the myocardial FA oxidation rate per se, but on processes initiated by the presence of FAs. In diabetic hearts, chronic exposure to elevated circulating FAs leads to adaptations that afford protection against the detrimental effect of an acute FA load, suggesting different underlying mechanisms behind the increased MV̇o2 following acute and chronic FA load.

Lipid binding to cytoglobin leads to a change in haem co-ordination: a role for cytoglobin in lipid signalling of oxidative stress

Cytoglobin is a recently discovered hexa-co-ordinate haemoglobin that does not appear to function as a classical oxygen-binding protein. Its function is unknown and studies on the effects of changes in its expression have not decisively determined its role within the cell. In the present paper, we report that the protein is transformed from hexa-co-ordinate to penta-co-ordinate on binding a lipid molecule. This transformation occurs with the ferric oxidation state of the protein, but not the ferrous state, indicating that this process only occurs under an oxidative environment and may thus be related to redox-linked cell signalling mechanisms. Oleate binds to the protein in a 1:1 stoichiometry and with high affinity (K(d)=0.7 μM); however, stopped-flow kinetic measurements yield a K(d) value of 110 μM. The discrepancy between these K(d) values may be rationalized by recognizing that cytoglobin is a disulfide-linked dimer and invoking co-operativity in oleate binding. The lipid-induced transformation of cytoglobin from hexa-co-ordinate to penta-co-ordinate does not occur with similar hexa-co-ordinate haemoglobins such as neuroglobin, and therefore appears to be a unique property of cytoglobin among the haemoglobin superfamily. The lipid-derived transformation may explain why cytoglobin has enhanced peroxidatic activity, converting lipids into various oxidized products, a property virtually absent from neuroglobin and much decreased in myoglobin. We propose that the binding of ferric cytoglobin to lipids and their subsequent transformation may be integral to the physiological function of cytoglobin, generating cell signalling lipid molecules under an oxidative environment.

Impaired redox signaling and antioxidant gene expression in endothelial cells in diabetes: a role for mitochondria and the nuclear factor-E2-related factor 2-Kelch-like ECH-associated protein 1 defense pathway

Type 2 diabetes is an age-related disease associated with vascular pathologies, including severe blindness, renal failure, atherosclerosis, and stroke. Reactive oxygen species (ROS), especially mitochondrial ROS, play a key role in regulating the cellular redox status, and an overproduction of ROS may in part underlie the pathogenesis of diabetes and other age-related diseases. Cells have evolved endogenous defense mechanisms against sustained oxidative stress such as the redox-sensitive transcription factor nuclear factor E2-related factor 2 (Nrf2), which regulates antioxidant response element (ARE/electrophile response element)-mediated expression of detoxifying and antioxidant enzymes and the cystine/glutamate transporter involved in glutathione biosynthesis. We hypothesize that diminished Nrf2/ARE activity contributes to increased oxidative stress and mitochondrial dysfunction in the vasculature leading to endothelial dysfunction, insulin resistance, and abnormal angiogenesis observed in diabetes. Sustained hyperglycemia further exacerbates redox dysregulation, thereby providing a positive feedback loop for severe diabetic complications. This review focuses on the role that Nrf2/ARE-linked gene expression plays in regulating endothelial redox homeostasis in health and type 2 diabetes, highlighting recent evidence that Nrf2 may provide a therapeutic target for countering oxidative stress associated with vascular disease and aging.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Regulated production of reactive oxygen species (ROS)/reactive nitrogen species (RNS) adequately balanced by antioxidant systems is a prerequisite for the participation of these active substances in physiological processes, including insulin action. Yet, increasing evidence implicates ROS and RNS as negative regulators of insulin signaling, rendering them putative mediators in the development of insulin resistance, a common endocrine abnormality that accompanies obesity and is a risk factor of type 2 diabetes. This review deals with this dual, seemingly contradictory, function of ROS and RNS in regulating insulin action: the major processes for ROS and RNS generation and detoxification are presented, and a critical review of the evidence that they participate in the positive and negative regulation of insulin action is provided. The cellular and molecular mechanisms by which ROS and RNS are thought to participate in normal insulin action and in the induction of insulin resistance are then described. Finally, we explore the potential usefulness and the challenges in modulating the oxidant-antioxidant balance as a potentially promising, but currently disappointing, means of improving insulin action in insulin resistance-associated conditions, leading causes of human morbidity and mortality of our era.

Role of mitochondrial dysfunction in insulin resistance

Insulin resistance is characteristic of obesity, type 2 diabetes, and components of the cardiometabolic syndrome, including hypertension and dyslipidemia, that collectively contribute to a substantial risk for cardiovascular disease. Metabolic actions of insulin in classic insulin target tissues (eg, skeletal muscle, fat, and liver), as well as actions in nonclassic targets (eg, cardiovascular tissue), help to explain why insulin resistance and metabolic dysregulation are central in the pathogenesis of the cardiometabolic syndrome and cardiovascular disease. Glucose and lipid metabolism are largely dependent on mitochondria to generate energy in cells. Thereby, when nutrient oxidation is inefficient, the ratio of ATP production/oxygen consumption is low, leading to an increased production of superoxide anions. Reactive oxygen species formation may have maladaptive consequences that increase the rate of mutagenesis and stimulate proinflammatory processes. In addition to reactive oxygen species formation, genetic factors, aging, and reduced mitochondrial biogenesis all contribute to mitochondrial dysfunction. These factors also contribute to insulin resistance in classic and nonclassic insulin target tissues. Insulin resistance emanating from mitochondrial dysfunction may contribute to metabolic and cardiovascular abnormalities and subsequent increases in cardiovascular disease. Furthermore, interventions that improve mitochondrial function also improve insulin resistance. Collectively, these observations suggest that mitochondrial dysfunction may be a central cause of insulin resistance and associated complications. In this review, we discuss mechanisms of mitochondrial dysfunction related to the pathophysiology of insulin resistance in classic insulin-responsive tissue, as well as cardiovascular tissue.

4-Hydroxy-2-nonenal increases superoxide anion radical in endothelial cells via stimulated GTP cyclohydrolase proteasomal degradation

OBJECTIVE

4-Hydroxy-2-nonenal (4-HNE) is an abundant electrophilic lipid that mediates oxidative stress in endothelium by mechanisms that remain controversial. This study examines the effects of 4-HNE on nitric oxide (NO) and superoxide levels in bovine aorta endothelial cells (BAECs).

METHODS AND RESULTS

Exposure of BAECs to 4-HNE caused a dose-dependent inhibition of NO that correlated with losses of hsp90 and phosphorylated eNOS-serine1179 but not eNOS protein levels. 4-HNE failed to inhibit NO production in sepiapterin and ascorbate supplemented cells suggesting that tetrahydrobiopterin (BH4) is a limiting factor in non supplemented cells. This was verified by quantification of BH4 by high-performance liquid chromatography analysis with electrochemical detection and by examining GTP cyclohydrolase I (GTPCH) protein levels and activity all of which were diminished by 4-HNE treatment. Analysis of 2-hydroxyethidium indicated that 4-HNE increased superoxide release in BAECs. The effects of 4-HNE on GTPCH and hsp90 were efficiently counteracted by proteasomal inhibition, indicating that depletion of BH4 by 4-HNE is attributable to specific mechanisms involving protein degradation.

CONCLUSIONS

4-HNE by altering BH4 homeostasis mediates eNOS-uncoupling and superoxide generation in BAECs. By also decreasing phosphorylation of eNOS-serine 1179 4-HNE may specifically regulate NO/reactive oxygen species fluxes in the endothelium with important consequences to redox signaling.

Mitochondrial reactive oxygen species-mediated signaling in endothelial cells

Once thought of as toxic by-products of cellular metabolism, reactive oxygen species (ROS) have been implicated in a large variety of cell-signaling processes. Several enzymatic systems contribute to ROS production in vascular endothelial cells, including NA(D)PH oxidase, xanthine oxidase, uncoupled endothelial nitric oxide synthase, and the mitochondrial electron transport chain. The respiratory chain is the major source of ROS in most mammalian cells, but the role of mitochondria-derived ROS in vascular cell signaling has received little attention. A new paradigm has evolved in recent years postulating that, in addition to producing ATP, mitochondria also play a key role in cell signaling and regulate a variety of cellular functions. This review focuses on the emerging role of mitochondrial ROS as signaling molecules in vascular endothelial cells. Specifically, we discuss some recent findings that indicate that mitochondrial ROS regulate vascular endothelial function, focusing on major sites of ROS production in endothelial mitochondria, factors modulating mitochondrial ROS production, the physiological and clinical implications of endothelial mitochondrial ROS, and methodological considerations in the study of mitochondrial contribution to vascular ROS generation.