Control of oxygen free radical formation from mitochondrial complex I: roles for protein kinase A and pyruvate dehydrogenase kinase

Prenatal aripiprazole induces alterations of rat placenta: a histological, immunohistochemical and ultrastructural study

Antipsychotic drugs (APDs) are used to treat many psychiatric illnesses as schizophrenia. Typical antipsychotic drugs (TAPDs) are being used; however, they have many side effects. Atypical antipsychotic drugs (AAPDs) are newer medications with known fewer side effects. Aripiprazole (ARI) is an AAPD, recommended by healthcare providers, even during pregnancy. It can cross the placental barrier and enter fetal circulation, so it might be possible that ARI can adversely impair normal placental development and growth, if it is given prenatally. ARI was applied orally to pregnant female rats in two doses (3& 6 mg/kg body weight). On gestation day 20, the mothers were sacrificed, and the placentas were removed and processed for general histological and electron microscopic evaluations. Immunohistochemistry was done using anti-PCNA (proliferating cell nuclear antigen), anti-Bax (for apoptosis) and anti-vascular endothelial growth factor alpha (VEGFA). Morphological evaluation revealed degenerative changes in the placenta as dark nuclei, vacuolization, and cyst formation. Ultra-structurally, there was degeneration of cellular components including organelles and nuclei. These changes were found in different cells of the basal and labyrinth zones and were dose dependent. Immunohistochemistry revealed upregulation of Bax and VEGFA and downregulation of PCNA. Prenatal administration of the AAPD, ARI to pregnant female rats resulted in histological changes in the placenta. Additionally, there was a decrease in cellular proliferation and increase in apoptosis, and vascular impairment. This indicates placental atrophy and dysgenesis and might suggest possible teratogenic effects to ARI, which needs further evaluation.

Protection against Aβ-induced neuronal damage by KU-32: PDHK1 inhibition as important target

A feature of most neurodegenerative diseases is the presence of "mis-folded proteins" that form aggregates, suggesting suboptimal activity of neuronal molecular chaperones. Heat shock protein 90 (Hsp90) is the master regulator of cell responses to "proteotoxic" stresses. Some Hsp90 modulators activate cascades leading to upregulation of additional chaperones. Novobiocin is a modulator at the C-terminal ATP-binding site of Hsp90. Of several novobiocin analogs synthesized and tested for protection against amyloid beta (Aβ)-induced neuronal death, "KU-32" was the most potent in protecting primary neurons, but did not increase expression of other chaperones believed to help clear misfolded proteins. However, KU-32 reversed Aβ-induced superoxide formation, activated Complex I of the electron transfer chain in mitochondria, and blocked the Aβ-induced inhibition of Complex I in neuroblastoma cells. A mechanism for these effects of KU-32 on mitochondrial metabolism appeared to be the inhibition of pyruvate dehydrogenase kinase (PDHK), both in isolated brain mitochondria and in SH-SY5Y cells. PDHK inhibition by the classic enzyme inhibitor, dichloroacetate, led to neuroprotection from Aβ25-35-induced cell injury similarly to KU-32. Inhibition of PDHK in neurons would lead to activation of the PDH complex, increased acetyl-CoA generation, stimulation of the tricarboxylic acid cycle and Complex I in the electron transfer chain, and enhanced oxidative phosphorylation. A focus of future studies may be on the potential value of PDHK as a target in AD therapy.

Mitochondrial Complex I, a Possible Sensible Site of cAMP Pathway in Aging

In mammals during aging, reactive oxygen species (ROS), produced by the mitochondrial respiratory chain, cause oxidative damage of macromolecules leading to respiratory chain dysfunction, which in turn increases ROS mitochondrial production. Many efforts have been made to understand the role of oxidative stress in aging and age-related diseases. The complex I of the mitochondrial respiratory chain is the major source of ROS production and its dysfunctions have been associated with several forms of neurodegeneration, other common human diseases and aging. Complex I-ROS production and complex I content have been proposed as the major determinants for longevity. The cAMP signal has a role in the regulation of complex I activity and the decrease of ROS production. In the last years, an increasing number of studies have attempted to activate cAMP signaling to treat age-related diseases associated with mitochondrial dysfunctions and ROS production. This idea comes from a long-line of studies showing a main role of cAMP signal in the memory consolidation mechanism and in the regulation of mitochondrial functions. Here, we discuss several evidences on the possible connection between complex I and cAMP pathway in the aging process.

The mitochondrial multi-omic response to exercise training across tissues

Mitochondria are adaptable organelles with diverse cellular functions critical to whole-body metabolic homeostasis. While chronic endurance exercise training is known to alter mitochondrial activity, these adaptations have not yet been systematically characterized. Here, the Molecular Transducers of Physical Activity Consortium (MoTrPAC) mapped the longitudinal, multi-omic changes in mitochondrial analytes across 19 tissues in male and female rats endurance trained for 1, 2, 4 or 8 weeks. Training elicited substantial changes in the adrenal gland, brown adipose, colon, heart and skeletal muscle, while we detected mild responses in the brain, lung, small intestine and testes. The colon response was characterized by non-linear dynamics that resulted in upregulation of mitochondrial function that was more prominent in females. Brown adipose and adrenal tissues were characterized by substantial downregulation of mitochondrial pathways. Training induced a previously unrecognized robust upregulation of mitochondrial protein abundance and acetylation in the liver, and a concomitant shift in lipid metabolism. The striated muscles demonstrated a highly coordinated response to increase oxidative capacity, with the majority of changes occurring in protein abundance and post-translational modifications. We identified exercise upregulated networks that are downregulated in human type 2 diabetes and liver cirrhosis. In both cases HSD17B10, a central dehydrogenase in multiple metabolic pathways and mitochondrial tRNA maturation, was the main hub. In summary, we provide a multi-omic, cross-tissue atlas of the mitochondrial response to training and identify candidates for prevention of disease-associated mitochondrial dysfunction.

cAMP/PKA Signaling Modulates Mitochondrial Supercomplex Organization

The oxidative phosphorylation (OXPHOS) system couples the transfer of electrons to oxygen with pumping of protons across the inner mitochondrial membrane, ensuring the ATP production. Evidence suggests that respiratory chain complexes may also assemble into supramolecular structures, called supercomplexes (SCs). The SCs appear to increase the efficiency/capacity of OXPHOS and reduce the reactive oxygen species (ROS) production, especially that which is produced by complex I. Studies suggest a mutual regulation between complex I and SCs, while SCs organization is important for complex I assembly/stability, complex I is involved in the supercomplex formation. Complex I is a pacemaker of the OXPHOS system, and it has been shown that the PKA-dependent phosphorylation of some of its subunits increases the activity of the complex, reducing the ROS production. In this work, using in ex vivo and in vitro models, we show that the activation of cAMP/PKA cascade resulted in an increase in SCs formation associated with an enhanced capacity of electron flux and ATP production rate. This is also associated with the phosphorylation of the NDUFS4 subunit of complex I. This aspect highlights the key role of complex I in cellular energy production.

Systematic integrated analyses of methylomic and transcriptomic impacts of early combined botanicals on estrogen receptor-negative mammary cancer

Dietary botanicals such as the cruciferous vegetable broccoli sprouts (BSp) as well as green tea polyphenols (GTPs) have shown exciting potential in preventing or delaying breast cancer (BC). However, little is known about their impact on epigenomic aberrations that are centrally involved in the initiation and progression of estrogen receptor-negative [ER(−)] BC. We have investigated the efficacy of combined BSp and GTPs diets on mammary tumor inhibition in transgenic Her2/neu mice that were administered the diets from prepubescence until adulthood. Herein, we present an integrated DNA methylome and transcriptome analyses for defining the early-life epigenetic impacts of combined BSp and GTPs on mammary tumors and our results indicate that a combinatorial administration of BSp and GTPs have a stronger impact at both transcriptome and methylome levels in comparison to BSp or GTPs administered alone. We also demonstrated a streamlined approach by performing an extensive preprocessing, quality assessment and downstream analyses on the genomic dataset. Our identification of differentially methylated regions in response to dietary botanicals administered during early-life will allow us to identify key genes and facilitate implementation of the subsequent downstream functional analyses on a genomic scale and various epigenetic modifications that are crucial in preventing ER(−) mammary cancer. Furthermore, our realtime PCR results were also found to be consistent with our genome-wide analysis results. These results could be exploited as a comprehensive resource for understanding understudied genes and their associated epigenetic modifications in response to these dietary botanicals.

Molecular and Supramolecular Structure of the Mitochondrial Oxidative Phosphorylation System: Implications for Pathology

Under aerobic conditions, mitochondrial oxidative phosphorylation (OXPHOS) converts the energy released by nutrient oxidation into ATP, the currency of living organisms. The whole biochemical machinery is hosted by the inner mitochondrial membrane (mtIM) where the protonmotive force built by respiratory complexes, dynamically assembled as super-complexes, allows the F1FO-ATP synthase to make ATP from ADP + Pi. Recently mitochondria emerged not only as cell powerhouses, but also as signaling hubs by way of reactive oxygen species (ROS) production. However, when ROS removal systems and/or OXPHOS constituents are defective, the physiological ROS generation can cause ROS imbalance and oxidative stress, which in turn damages cell components. Moreover, the morphology of mitochondria rules cell fate and the formation of the mitochondrial permeability transition pore in the mtIM, which, most likely with the F1FO-ATP synthase contribution, permeabilizes mitochondria and leads to cell death. As the multiple mitochondrial functions are mutually interconnected, changes in protein composition by mutations or in supercomplex assembly and/or in membrane structures often generate a dysfunctional cascade and lead to life-incompatible diseases or severe syndromes. The known structural/functional changes in mitochondrial proteins and structures, which impact mitochondrial bioenergetics because of an impaired or defective energy transduction system, here reviewed, constitute the main biochemical damage in a variety of genetic and age-related diseases.

Carotenoid metabolism in mitochondrial function

Mitochondria are highly dynamic organelles that are found in most eukaryotic organisms. It is broadly accepted that mitochondria originally evolved from prokaryotic bacteria, e.g. proteobacteria. The mitochondrion has its independent genome that encodes 37 genes, including 13 genes for oxidative phosphorylation. Accumulative evidence demonstrates that mitochondria are not only the powerhouse of the cells by supplying adenosine triphosphate, but also exert roles as signalling organelles in the cell fate and function. Numerous factors can affect mitochondria structurally and functionally. Carotenoids are a large group of fat-soluble pigments commonly found in our diets. Recently, much attention has been paid in carotenoids as dietary bioactives in mitochondrial structure and function in human health and disease, though the mechanistic research is limited. Here, we update the recent progress in mitochondrial functioning as signalling organelles in human health and disease, summarize the potential roles of carotenoids in regulation of mitochondrial redox homeostasis, biogenesis, and mitophagy, and discuss the possible approaches for future research in carotenoid regulation of mitochondrial function.

Successive contractile periods activate mitochondria at the onset of contractions in intact rat cardiac trabeculae

The rate of oxidative phosphorylation depends on the contractile activity of the heart. Cardiac mitochondrial oxidative phosphorylation is determined by free ADP concentration, mitochondrial Ca²⁺ accumulation, mitochondrial enzyme activities, and Krebs cycle intermediates. The purpose of the present study was to examine the factors that limit oxidative phosphorylation upon rapid changes in contractile activity in cardiac muscle. We tested the hypotheses that prior contractile performance enhances the changes in NAD(P)H and FAD concentration upon an increase in contractile activity and that this mitochondrial "priming" depends on pyruvate dehydrogenase activity. Intact rat cardiac trabeculae were electrically stimulated at 0.5 Hz for at least 30 min. Thereafter, two equal bouts at elevated stimulation frequency of 1, 2, or 3 Hz were applied for 3 min with 3 min of 0.5-Hz stimulation in between. No discernible time delay was observed in the changes in NAD(P)H and FAD fluorescence upon rapid changes in contractile activity. The amplitudes of the rapid changes in fluorescence upon an increase in stimulation frequency (the on-transients) were smaller than upon a decrease in stimulation frequency (the off-transients). A first bout in glucose-containing superfusion solution resulted, during the second bout, in an increase in the amplitudes of the on-transients, but the off-transients remained the same. No such priming effect was observed after addition of 10 mM pyruvate. These results indicate that mitochondrial priming can be observed in cardiac muscle in situ and that pyruvate dehydrogenase activity is critically involved in the mitochondrial adaptation to increases in contractile performance. NEW & NOTEWORTHY Mitochondrial respiration increases with increased cardiac contractile activity. Similar to mitochondrial "priming" in skeletal muscle, we hypothesized that cardiac mitochondrial activity is altered upon successive bouts of contractions and depends on pyruvate dehydrogenase activity. We found altered bioenergetics upon repeated contractile periods, indicative of mitochondrial priming in rat myocardium. No effect was seen when pyruvate was added to the perfusate. As such, pyruvate dehydrogenase activity is involved in the mitochondrial adaptation to increased contractile performance.

Adenosine A2 receptor activation ameliorates mitochondrial oxidative stress upon reperfusion through the posttranslational modification of NDUFV2 subunit of complex I in the heart

While it is well known that adenosine receptor activation protects the heart from ischemia/reperfusion injury, the precise mitochondrial mechanism responsible for the action remains unknown. This study probed the mitochondrial events associated with the cardioprotective effect of 5'-(N-ethylcarboxamido) adenosine (NECA), an adenosine A₂ receptor agonist. Isolated rat hearts were subjected to 30min ischemia followed by 10min of reperfusion, whereas H9c2 cells experienced 20min ischemia and 10min reperfusion. NECA prevented mitochondrial structural damage, decreases in respiratory control ratio (RCR), and collapse of mitochondrial membrane potential (ΔΨm). Both the adenosine A_2A receptor antagonist SCH58261 and A_2B receptor antagonist MRS1706 inhibited the action of NECA. NECA reduced mitochondrial proteins carbonylation, H₂O₂, and superoxide generation at reperfusion, but did not change superoxide dismutase (SOD) activity. In support, the protective effects of NECA and Peg-SOD on ΔΨm upon reperfusion were additive, implying that NECA's protection is attributable to the reduced superoxide generation but not to the enhancement of the superoxide-scavenging capacity. NECA increased the mitochondrial Src tyrosine kinase activity and suppressed complex I activity at reperfusion in a Src-dependent manner. NECA also reduced mitochondrial superoxide through Src tyrosine kinase. Studies with liquid chromatography-mass spectrometer (LC-MS) identified Tyr118 of the NDUFV2 subunit of complex 1 as a likely site of the tyrosine phosphorylation. Furthermore, the complex I activity of cells transfected with the Y118F mutant was increased, suggesting that this site might be a negative regulator of complex I activity. In support, NECA failed to suppress complex I activity at reperfusion in cells transfected with the Y118F mutant of NDUFV2. In conclusion, NECA prevents mitochondrial oxidative stress by decreasing mitochondrial superoxide generation through inhibition of complex I via the mitochondrial Src tyrosine kinase. Phosphorylation of Tyr¹¹⁸ residue in NDUFV2 subunit may account for the inhibitory effect of NECA on complex I.

Effect of in utero exposure to the atypical anti-psychotic risperidone on histopathological features of the rat placenta

For clinical management of different forms of psychosis, both classical and atypical anti-psychotic drugs (APDs) are available. These drugs are widely prescribed, even during pregnancy considering their minimal extra-pyramidal side effects and teratogenic potential compared to classical APDs. Among AAPDs, risperidone (RIS) is a first-line drug of choice by physicians. The molecular weight of RIS is 410.49 g/mol; hence, it can easily cross the placental barrier and enter the foetal bloodstream. It is not known whether or not AAPDs like RIS may affect the developing placenta and foetus adversely. Reports on this issue are limited and sketchy. Therefore, this study has evaluated the effects of maternal exposure to equivalent therapeutic doses of RIS on placental growth, histopathological and cytoarchitectural changes, and to establish a relationship between placental dysfunction and foetal outcomes. Pregnant rats (n = 24) were exposed to selected doses (0.8, 1.0 and 2.0 mg/kg) of RIS from gestation days 6-21. These dams were sacrificed; their placentas and foetuses were collected, morphometrically examined and further processed for histopathological examination. This study revealed that in utero exposure to equivalent therapeutic doses of RIS during organogenesis-induced placental dystrophy (size and weight), disturbed cytoarchitectural organization (thickness of different placental layers), histopathological lesions (necrosis in trophoblast with disruption of trophoblastic septa and rupturing of maternal-foetal interface) and intrauterine growth restriction of the foetuses. It may be concluded that multifactorial mechanisms might be involved in the dysregulation of structure and function of the placenta and of poor foetal growth and development.

Post-Translational Modifications of Cardiac Mitochondrial Proteins in Cardiovascular Disease: Not Lost in Translation

Protein post-translational modifications (PTMs) are crucial in regulating cellular biology by playing key roles in processes such as the rapid on and off switching of signaling network and the regulation of enzymatic activities without affecting gene expressions. PTMs lead to conformational changes in the tertiary structure of protein and resultant regulation of protein function such as activation, inhibition, or signaling roles. PTMs such as phosphorylation, acetylation, and S-nitrosylation of specific sites in proteins have key roles in regulation of mitochondrial functions, thereby contributing to the progression to heart failure. Despite the extensive study of PTMs in mitochondrial proteins much remains unclear. Further research is yet to be undertaken to elucidate how changes in the proteins may lead to cardiovascular and metabolic disease progression in particular. We aimed to summarize the various types of PTMs that occur in mitochondrial proteins, which might be associated with heart failure. This study will increase the understanding of cardiovascular diseases through PTM.

Protein Kinase A Governs Oxidative Phosphorylation Kinetics and Oxidant Emitting Potential at Complex I

The mitochondrial electron transport system (ETS) is responsible for setting and maintaining both the energy and redox charges throughout the cell. Reversible phosphorylation of mitochondrial proteins, particularly via the soluble adenylyl cyclase (sAC)/cyclic AMP (cAMP)/Protein kinase A (PKA) axis, has recently been revealed as a potential mechanism regulating the ETS. However, the governance of cAMP/PKA signaling and its implications on ETS function are incompletely understood. In contrast to prior reports using exogenous bicarbonate, we provide evidence that endogenous CO₂ produced by increased tricarboxylic acid (TCA) cycle flux is insufficient to increase mitochondrial cAMP levels, and that exogenous addition of membrane permeant 8Br-cAMP does not enhance mitochondrial respiratory capacity. We also report important non-specific effects of commonly used inhibitors of sAC which preclude their use in studies of mitochondrial function. In isolated liver mitochondria, inhibition of PKA reduced complex I-, but not complex II-supported respiratory capacity. In permeabilized myofibers, inhibition of PKA lowered both the K_m and V_max for complex I-supported respiration as well as succinate-supported H₂O₂ emitting potential. In summary, the data provided here improve our understanding of how mitochondrial cAMP production is regulated, illustrate a need for better tools to examine the impact of sAC activity on mitochondrial biology, and suggest that cAMP/PKA signaling contributes to the governance of electron flow through complex I of the ETS.

The Interplay Between Respiratory Supercomplexes and ROS in Aging

SIGNIFICANCE

The molecular mechanism of aging is still vigorously debated, although a general consensus exists that mitochondria are significantly involved in this process. However, the previously postulated role of mitochondrial-derived reactive oxygen species (ROS) as the damaging agents inducing functional loss in aging has fallen out of favor in the recent past. In this review, we critically examine the role of ROS in aging in the light of recent advances on the relationship between mitochondrial structure and function.

RECENT ADVANCES

The functional mitochondrial respiratory chain is now recognized as a reflection of the dynamic association of respiratory complexes in the form of supercomplexes (SCs). Besides providing kinetic advantage (channeling), SCs control ROS generation by the respiratory chain, thus providing a means to regulate ROS levels in the cell. Depending on their concentration, these ROS are either physiological signals essential for the life of the cell or toxic species that damage cell structure and functions.

CRITICAL ISSUES

We propose that under physiological conditions the dynamic nature of SCs reversibly controls the generation of ROS as signals involved in mitochondrial-nuclear communication. During aging, there is a progressive loss of control of ROS generation so that their production is irreversibly enhanced, inducing a vicious circle in which signaling is altered and structural damage takes place.

FUTURE DIRECTIONS

A better understanding on the forces affecting SC association would allow the manipulation of ROS generation, directing these species to their physiological signaling role.

Respiratory supercomplexes: plasticity and implications

The plasticity model of the electron transport chain has slowly begun to replace both the liquid model of free complexes and the solid model of supercomplexes. The plasticity model predicts that respiratory complexes exist and function both as single complexes and as supercomplexes. The advantages of this system is an electron transport train which is able to adapt to changes in its environment. This review will investigate the current body of work on supercomplexes including their assembly, regulation, and plasticity, and particularly their role in the generation of reactive oxygen species and aging.

Coenzyme q and the respiratory chain: coenzyme q pool and mitochondrial supercomplexes

Two alternative models of organization of the mitochondrial electron transport chain (mETC) have been alternatively favored or questioned by the accumulation evidences of different sources, the solid model or the random collision model. Both agree in the number of respiratory complexes (I-IV) that participate in the mETC, but while the random collision model proposes that Complexes I-IV do not interact physically and that electrons are transferred between them by coenzyme Q and cytochrome c, the solid model proposes that all complexes super-assemble in the so-called respirasome. Recently, the plasticity model has been developed to incorporate the solid and the random collision model as extreme situations of a dynamic organization, allowing super-assembly free movement of the respiratory complexes. In this review, we evaluate the supporting evidences of each model and the implications of the super-assembly in the physiological role of coenzyme Q.

Mitochondrial respiratory supercomplex association limits production of reactive oxygen species from complex I

AIMS

The mitochondrial respiratory chain is recognized today to be arranged in supramolecular assemblies (supercomplexes). Besides conferring a kinetic advantage (substrate channeling) and being required for the assembly and stability of Complex I, indirect considerations support the view that supercomplexes may also prevent excessive formation of reactive oxygen species (ROS) from the respiratory chain. In the present study, we have directly addressed this issue by testing the ROS generation by Complex I in two experimental systems in which the supramolecular organization of the respiratory assemblies is impaired by: (i) treatment either of bovine heart mitochondria or liposome-reconstituted supercomplex I-III with dodecyl maltoside; (ii) reconstitution of Complexes I and III at high phospholipids to protein ratio.

RESULTS

The results of our investigation provide experimental evidence that the production of ROS is strongly increased in either model, supporting the view that disruption or prevention of the association between Complex I and Complex III by different means enhances the generation of superoxide from Complex I.

INNOVATION

Dissociation of supercomplexes may link oxidative stress and energy failure in a vicious circle.

CONCLUSION

Our findings support a central role of mitochondrial supramolecular structure in the development of the aging process and in the etiology and pathogenesis of most major chronic diseases.

Viruses as modulators of mitochondrial functions

Mitochondria are multifunctional organelles with diverse roles including energy production and distribution, apoptosis, eliciting host immune response, and causing diseases and aging. Mitochondria-mediated immune responses might be an evolutionary adaptation by which mitochondria might have prevented the entry of invading microorganisms thus establishing them as an integral part of the cell. This makes them a target for all the invading pathogens including viruses. Viruses either induce or inhibit various mitochondrial processes in a highly specific manner so that they can replicate and produce progeny. Some viruses encode the Bcl2 homologues to counter the proapoptotic functions of the cellular and mitochondrial proteins. Others modulate the permeability transition pore and either prevent or induce the release of the apoptotic proteins from the mitochondria. Viruses like Herpes simplex virus 1 deplete the host mitochondrial DNA and some, like human immunodeficiency virus, hijack the host mitochondrial proteins to function fully inside the host cell. All these processes involve the participation of cellular proteins, mitochondrial proteins, and virus specific proteins. This review will summarize the strategies employed by viruses to utilize cellular mitochondria for successful multiplication and production of progeny virus.

Susceptibility of mitochondrial electron-transport complexes to oxidative damage. Focus on cytochrome c oxidase

Reactive oxygen species (ROS) are associated with a number of mitochondrial disorders. These include: ischemia/reperfusion injury, Parkinson's disease, Alzheimer's disease, neurodegenerative diseases, and other age-related degenerative changes. ROS can be generated at numerous sites within the cell, but the mitochondrial electron transport chain is recognized as the major source of intracellular ROS. Two mitochondrial electron-transfer complexes are major sources of ROS: complex I and complex III. Oxidative damage to either of these complexes, or to electron transport complexes that are in close proximity to these ROS sources, e.g., cytochrome c oxidase, would be expected to inhibit electron transport. Such inhibition would lead to increased electron leakage and more ROS production, much like the well-known effect of adding electron transport inhibitors. Recent studies reveal that ROS and lipid peroxidation products are effective inhibitors of the electron-transport complexes. In some cases, inactivation of enzymes correlates with chemical modification of only a small number of unusually reactive amino acids. In this article, we review current knowledge of ROS-induced alterations within three complexes: (1) complex IV; (2) complex III; and (3) complex I. Our goal is to identify "hot spots" within each complex that are easily chemically modified and could be responsible for ROS-induced inhibition of the individual complexes. Special attention has been placed on ROS-induced damage to cardiolipin that is tightly bound to each of the inner membrane protein complexes. Peroxidation of the bound cardiolipin is thought to be particularly important since its close proximity and long residence time on the protein make it an especially effective reagent for subsequent ROS-induced damage to these proteins.

Effect of atypical antipsychotics on fetal growth: is the placenta involved?

There is currently considerable uncertainty regarding prescribing practices for pregnant women with severe and persistent psychiatric disorders. The physician and the mother have to balance the risks of untreated psychiatric illness against the potential fetal toxicity associated with pharmacological exposure. This is especially true for women taking atypical antipsychotics. Although these drugs have limited evidence for teratological risk, there are reports of altered fetal growth, both increased and decreased, with maternal atypical antipsychotic use. These effects may be mediated through changes in the maternal metabolism which in turn impacts placental function. However, the presence of receptors targeted by atypical antipsychotics in cell lineages present in the placenta suggests that these drugs can also have direct effects on placental function and development. The signaling pathways involved in linking the effects of atypical antipsychotics to placental dysfunction, ultimately resulting in altered fetal growth, remain elusive. This paper focuses on some possible pathways which may link atypical antipsychotics to placental dysfunction.

Adverse fetal and neonatal outcomes associated with a life-long high fat diet: role of altered development of the placental vasculature

Maternal obesity results in a number of obstetrical and fetal complications with both immediate and long-term consequences. The increased prevalence of obesity has resulted in increasing numbers of women of reproductive age in this high-risk group. Since many of these obese women have been subjected to hypercaloric diets from early childhood we have developed a rodent model of life-long maternal obesity to more clearly understand the mechanisms that contribute to adverse pregnancy outcomes in obese women. Female Sprague Dawley rats were fed a control diet (CON--16% of calories from fat) or high fat diet (HF--45% of calories from fat) from 3 to 19 weeks of age. Prior to pregnancy HF-fed dams exhibited significant increases in body fat, serum leptin and triglycerides. A subset of dams was sacrificed at gestational day 15 to evaluate fetal and placental development. The remaining animals were allowed to deliver normally. HF-fed dams exhibited a more than 3-fold increase in fetal death and decreased neonatal survival. These outcomes were associated with altered vascular development in the placenta, as well as increased hypoxia in the labyrinth. We propose that the altered placental vasculature may result in reduced oxygenation of the fetal tissues contributing to premature demise and poor neonatal survival.

Mitochondria and reactive oxygen species. Which role in physiology and pathology?

Oxidative stress is among the major causes of toxicity due to interaction of Reactive Oxygen Species (ROS) with cellular macromolecules and structures and interference with signal transduction pathways. The mitochondrial respiratory chain, specially from Complexes I and III, is considered the main origin of ROS particularly under conditions of high membrane potential, but several other sources may be important for ROS generation, such as mitochondrial p66(Shc), monoamine oxidase, α-ketoglutarate dehydogenase, besides redox cycling of redox-active molecules. ROS are able to oxidatively modify lipids, proteins, carbohydrates and nucleic acids in mitochondria and to activate/inactivate signalling pathways by oxidative modification of redox-active factors. Cells are endowed with several defence mechanisms including repair or removal of damaged molecules, and antioxidant systems, either enzymatic or non-enzymatic. Oxidative stress is at the basis of ageing and many pathological disorders, such as ischemic diseases, neurodegenerative diseases, diabetes, and cancer, although the underlying mechanisms are not always completely understood.

Mitochondria, PPARs, and Cancer: Is Receptor-Independent Action of PPAR Agonists a Key?

Before the discovery of peroxisome proliferator activated receptors (PPARs), it was well known that certain drugs considered as classical PPAR-alpha agonists induced hepatocarcinoma or peroxisome proliferation in rodents. These drugs were derivatives of fibric acid, and they included clofibrate, bezafibrate, and fenofibrate. However, such toxicity has never been observed in human patients treated with these hypolipidemic drugs. Thiazolidinediones are a new class of PPAR activators showing greater specificity for the γ isoform of PPARs. These drugs are used as insulin sensitizers in the treatment of type II diabetes. In addition, they have been shown to induce cell differentiation or apoptosis in various experimental models of cancer. PPAR-α ligands have also been shown to induce cancer cell differentiation and, paradoxically, PPAR-γ drug activators have been reported to act as carcinogens. The confusing picture that emerges from these data is further complicated by the series of intriguing side effects observed following administration of pharmacological PPAR ligands (rhabdomyolysis, liver and heart toxicity, anemia, leucopenia). These side effects cannot be easily explained by simple interactions between the drug and nuclear receptors. Rather, these side effects seem to indicate that the ligands have biological activity independent of the nuclear receptors. Considering the emerging role of mitochondria in cancer and the potential metabolic connections between this organelle and PPAR physiology, characterization of the reciprocal influences is fundamental not only for a better understanding of cancer biology, but also for more defined pharmacotoxicological profiles of drugs that modulate PPARs.

Cardiac mitochondria in heart failure: normal cardiolipin profile and increased threonine phosphorylation of complex IV

Mitochondrial dysfunction is a major contributor in heart failure (HF). We investigated whether the decrease in respirasome organization reported by us previously in cardiac mitochondria in HF is due to changes in the phospholipids of the mitochondrial inner membrane or modifications of the subunits of the electron transport chain (ETC) complexes. The contents of the main phospholipid species, including cardiolipin, as well as the molecular species of cardiolipin were unchanged in cardiac mitochondria in HF. Oxidized cardiolipin molecular species were not observed. In heart mitochondria isolated from HF, complex IV not incorporated into respirasomes exhibits increased threonine phosphorylation. Since HF is associated with increased adrenergic drive to cardiomyocytes, this increased protein phosphorylation might be explained by the involvement of cAMP-activated protein kinase. Does the preservation of cAMP-induced phosphorylation changes of mitochondrial proteins or the addition of exogenous cAMP have similar effects on oxidative phosphorylation? The usage of phosphatase inhibitors revealed a specific decrease in complex I-supported respiration with glutamate. In saponin-permeabilized cardiac fibers, pre-incubation with cAMP decreases oxidative phosphorylation due to a defect localized at complex IV of the ETC inter alia. We propose that phosphorylation of specific complex IV subunits decreases oxidative phosphorylation either by limiting the incorporation of complex IV in supercomplexes or by decreasing supercomplex stability.

Redox control of protein kinase C: cell- and disease-specific aspects

Hormones, growth factors, electrical stimulation, and cell-cell interactions regulate numerous cellular processes by altering the levels of second messengers, thus influencing biochemical reactions inside the cells. The Protein Kinase C family (PKCs) is a group of serine/threonine kinases that are dependent on calcium (Ca(2+)), diacylglycerol, and phospholipids. Signaling pathways that induce variations on the levels of PKC activators have been implicated in the regulation of diverse cellular functions and, in turn, PKCs are key regulators of a plethora of cellular processes, including proliferation, differentiation, and tumorigenesis. Importantly, PKCs contain regions, both in the N-terminal regulatory domain and in the C-terminal catalytic domain, that are susceptible to redox modifications. In several pathophysiological conditions when the balance between oxidants, antioxidants, and alkylants is compromised, cells undergo redox stress. PKCs are cell-signaling proteins that are particularly sensitive to redox stress because modification of their redox-sensitive regions interferes with their activity and, thus, with their biological effects. In this review, we summarize the involvement of PKCs in health and disease and the importance of redox signaling in the regulation of this family of kinases.

Mitochondria in heart failure

This review focuses on the evidence accumulated in humans and animal models to the effect that mitochondria are key players in the progression of heart failure (HF). Mitochondria are the primary source of energy in the form of adenosine triphosphate that fuels the contractile apparatus, and are thus essential for the pumping activity of the heart. We evaluate changes in mitochondrial morphology and alterations in the main components of mitochondrial energetics, such as substrate utilization and oxidative phosphorylation coupled with the level of respirasomes, in the context of their contribution to the chronic energy deficit and mechanical dysfunction in HF.

ROS accumulation and IGF-IR inhibition contribute to fenofibrate/PPARalpha -mediated inhibition of glioma cell motility in vitro

BACKGROUND

Glioblastomas are characterized by rapid cell growth, aggressive CNS infiltration, and are resistant to all known anticancer regimens. Recent studies indicate that fibrates and statins possess anticancer potential. Fenofibrate is a potent agonist of peroxisome proliferator activated receptor alpha (PPARalpha) that can switch energy metabolism from glycolysis to fatty acid beta-oxidation, and has low systemic toxicity. Fenofibrate also attenuates IGF-I-mediated cellular responses, which could be relevant in the process of glioblastoma cell dispersal.

METHODS

The effects of fenofibrate on Glioma cell motility, IGF-I receptor (IGF-IR) signaling, PPARalpha activity, reactive oxygen species (ROS) metabolism, mitochondrial potential, and ATP production were analyzed in human glioma cell lines.

RESULTS

Fenofibrate treatment attenuated IGF-I signaling responses and repressed cell motility of LN-229 and T98G Glioma cell lines. In the absence of fenofibrate, specific inhibition of the IGF-IR had only modest effects on Glioma cell motility. Further experiments revealed that PPARalpha-dependent accumulation of ROS is a strong contributing factor in Glioma cell lines responses to fenofibrate. The ROS scavenger, N-acetyl-cysteine (NAC), restored cell motility, improved mitochondrial potential, and increased ATP levels in fenofibrate treated Glioma cell lines.

CONCLUSIONS

Our results indicate that although fenofibrate-mediated inhibition of the IGF-IR may not be sufficient in counteracting Glioma cell dispersal, PPARalpha-dependent metabolic switch and the resulting ROS accumulation strongly contribute to the inhibition of these devastating brain tumor cells.

Structure and organization of mitochondrial respiratory complexes: a new understanding of an old subject

The enzymatic complexes of the mitochondrial respiratory chain have been extensively investigated in their structural and functional properties. A clear distinction is possible today between three complexes in which the difference in redox potential allows proton translocation (complexes I, III, and IV) and those having the mere function to convey electrons to the respiratory chain. We also have a clearer understanding of the structure and function of most respiratory complexes, of their biogenesis and regulation, and of their capacity to generate reactive oxygen species. Past investigations led to the conclusion that the complexes are randomly dispersed and functionally connected by diffusion of smaller redox components, coenzyme Q and cytochrome c. More-recent investigations by native gel electrophoresis and single-particle image processing showed the existence of supramolecular associations. Flux-control analysis demonstrated that complexes I and III in mammals and I, III, and IV in plants kinetically behave as single units, suggesting the existence of substrate channeling. This review discusses conditions affecting the formation of supercomplexes that, besides kinetic advantage, have a role in the stability and assembly of the individual complexes and in preventing excess oxygen radical formation. Disruption of supercomplex organization may lead to functional derangements responsible for pathologic changes.

Regulated production of free radicals by the mitochondrial electron transport chain: Cardiac ischemic preconditioning

Excessive production of free radicals by mitochondria is associated with, and likely contributes to, the progression of numerous pathological conditions. Nevertheless, the production of free radicals by the mitochondria may have important biological functions under normal or stressed conditions by activating or modulating redox-sensitive cellular signaling pathways. This raises the intriguing possibility that regulated mitochondrial free radical production occurs via mechanisms that are distinct from pathologies associated with oxidative damage. Indeed, the capacity of mitochondria to produce free radicals in a limited manner may play a role in ischemic preconditioning, the phenomenon whereby short bouts of ischemia protect from subsequent prolonged ischemia and reperfusion. Ischemic preconditioning can thus serve as an important model system for defining regulatory mechanisms that allow for transient, signal-inducing, production of free radicals by mitochondria. Defining how these mechanism(s) occur will provide insight into therapeutic approaches that minimize oxidative damage without altering normal cellular redox biology. The aim of this review is to present and discuss evidence for the regulated production of superoxide by the electron transport chain within the ischemic preconditioning paradigm of redox regulation.

Structural and functional organization of the mitochondrial respiratory chain: a dynamic super-assembly

The structural organization of the mitochondrial oxidative phosphorylation (OXPHOS) system has received large attention in the past and most investigations led to the conclusion that the respiratory enzymatic complexes are randomly dispersed in the lipid bilayer of the inner membrane and functionally connected by fast diffusion of smaller redox components, Coenzyme Q and cytochrome c. More recent investigations by native gel electrophoresis, however, have shown the existence of supramolecular associations of the respiratory complexes, confirmed by electron microscopy analysis and single particle image processing. Flux control analysis has demonstrated that Complexes I and III in mammalian mitochondria and Complexes I, III, and IV in plant mitochondria kinetically behave as single units with control coefficients approaching unity for each single component, suggesting the existence of substrate channelling within the supercomplexes. The reasons why the presence of substrate channelling for Coenzyme Q and cytochrome c was overlooked in the past are analytically discussed. The review also discusses the forces and the conditions responsible for the formation of the supramolecular units. The function of the supercomplexes appears not to be restricted to kinetic advantages in electron transfer: we discuss evidence on their role in the stability and assembly of the individual complexes and in preventing excess oxygen radical formation. Finally, there is increasing evidence that disruption of the supercomplex organization leads to functional derangements responsible for pathological changes.

Data recovery and integration from public databases uncovers transformation-specific transcriptional downregulation of cAMP-PKA pathway-encoding genes

BACKGROUND

The integration of data from multiple genome-wide assays is essential for understanding dynamic spatio-temporal interactions within cells. Such integration, which leads to a more complete view of cellular processes, offers the opportunity to rationalize better the high amount of "omics" data freely available in several public databases.In particular, integration of microarray-derived transcriptome data with other high-throughput analyses (genomic and mutational analysis, promoter analysis) may allow us to unravel transcriptional regulatory networks under a variety of physio-pathological situations, such as the alteration in the cross-talk between signal transduction pathways in transformed cells.

RESULTS

Here we sequentially apply web-based and statistical tools to a case study: the role of oncogenic activation of different signal transduction pathways in the transcriptional regulation of genes encoding proteins involved in the cAMP-PKA pathway. To this end, we first re-analyzed available genome-wide expression data for genes encoding proteins of the downstream branch of the PKA pathway in normal tissues and human tumor cell lines. Then, in order to identify mutation-dependent transcriptional signatures, we classified cancer cells as a function of their mutational state. The results of such procedure were used as a starting point to analyze the structure of PKA pathway-encoding genes promoters, leading to identification of specific combinations of transcription factor binding sites, which are neatly consistent with available experimental data and help to clarify the relation between gene expression, transcriptional factors and oncogenes in our case study.

CONCLUSIONS

Genome-wide, large-scale "omics" experimental technologies give different, complementary perspectives on the structure and regulatory properties of complex systems. Even the relatively simple, integrated workflow presented here offers opportunities not only for filtering data noise intrinsic in high throughput data, but also to progressively extract novel information that would have remained hidden otherwise. In fact we have been able to detect a strong transcriptional repression of genes encoding proteins of cAMP/PKA pathway in cancer cells of different genetic origins. The basic workflow presented herein may be easily extended by incorporating other tools and can be applied even by researchers with poor bioinformatics skills.

Redox regulation of tumor necrosis factor signaling

Tumor necrosis factor-alpha (TNF) is a key cytokine that has been shown to play important physiologic (e.g., inflammation) and pathophysiologic (e.g., various liver pathologies) roles. In liver and other tissues, TNF treatment results in the simultaneous activation of an apoptotic pathway (i.e., TRADD, RIP, JNK) and a survival pathway mediated by NF-kappaB transcription of survival genes (i.e., GADD45beta, Mn-SOD, cFLIP). The cellular response (e.g., proliferation versus apoptosis) to TNF is determined by the balance between the apoptotic signaling pathway and the NF-kappaB survival pathway stimulated by TNF. Reactive oxygen species (ROS) are important modulators of signaling pathways and can regulate both apoptotic signaling and NF-kappaB transcription triggered by TNF. ROS are important in mediating the sustained activation of JNK, to help mediate apoptosis after TNF treatment. In some cells, ROS are second messengers that mediate apoptosis after TNF stimulation. Conversely, ROS can cause redox modifications that inhibit NF-kappaB activation, which can lead to cell death triggered by TNF. Consequently, the redox status of cells can determine the biologic response that TNF will induce in cells. In many liver pathologies, ROS generated extrinsically (e.g., inflammation) or intrinsically (i.e., drugs, toxins) may act in concert with TNF to promote hepatocyte death and liver injury through redox inhibition of NF-kappaB.

Dual mitochondrial localization and different roles of the reversible reaction of mammalian ferrochelatase

Ferrochelatase catalyzes the insertion of ferrous ions into protoporphyrin IX to produce heme. Previously, it was found that this enzyme also participates in the reverse reaction of iron removal from heme. To clarify the role of the reverse reaction of ferrochelatase in cells, mouse liver mitochondria were fractionated to examine the localization of ferrochelatase, and it was found that the enzyme localizes not only to the inner membrane, but also to the outer membrane. Observations by immunoelectron microscopy confirmed the dual localization of ferrochelatase in ferrochelatase-expressing human embryonic kidney cells and mouse liver mitochondria. The conventional (zinc-insertion) activities of the enzyme in the inner and outer membranes were similar, whereas the iron-removal activity was high in the outer membrane. 2D gel analysis revealed that two types of the enzyme with different isoelectric points were present in mitochondria, and the acidic form, which was enriched in the outer membrane, was found to be phosphorylated. Mutation of human ferrochelatase showed that serine residues at positions 130 and 303 were phosphorylated, and serine at position 130 may be involved in the balance of the reversible catalytic reaction. When mouse erythroleukemia cells were treated with 12-O-tetradecanoyl-phorbol 13-acetate, an activator of protein kinase C, or hemin, phospho-ferrochelatase levels increased, with a concomitant decrease in zinc-insertion activity and a slight increase in iron-removal activity. These results suggest that ferrochelatase localizes to both the mitochondrial outer and inner membranes and that the change in the equilibrium position of the forward and reverse activities may be regulated by the phosphorylation of ferrochelatase.

Cholesterol transport in steroid biosynthesis: role of protein-protein interactions and implications in disease states

The transfer of cholesterol from the outer to the inner mitochondrial membrane is the rate-limiting step in hormone-induced steroid formation. To ensure that this step is achieved efficiently, free cholesterol must accumulate in excess at the outer mitochondrial membrane and then be transferred to the inner membrane. This is accomplished through a series of steps that involve various intracellular organelles, including lysosomes and lipid droplets, and proteins such as the translocator protein (18 kDa, TSPO) and steroidogenic acute regulatory (StAR) proteins. TSPO, previously known as the peripheral-type benzodiazepine receptor, is a high-affinity drug- and cholesterol-binding mitochondrial protein. StAR is a hormone-induced mitochondria-targeted protein that has been shown to initiate cholesterol transfer into mitochondria. Through the assistance of proteins such as the cAMP-dependent protein kinase regulatory subunit Ialpha (PKA-RIalpha) and the PKA-RIalpha- and TSPO-associated acyl-coenzyme A binding domain containing 3 (ACBD3) protein, PAP7, cholesterol is transferred to and docked at the outer mitochondrial membrane. The TSPO-dependent import of StAR into mitochondria, and the association of TSPO with the outer/inner mitochondrial membrane contact sites, drives the intramitochondrial cholesterol transfer and subsequent steroid formation. The focus of this review is on (i) the intracellular pathways and protein-protein interactions involved in cholesterol transport and steroid biosynthesis and (ii) the roles and interactions of these proteins in endocrine pathologies and neurological diseases where steroid synthesis plays a critical role.

Ischemic preconditioning targets the respiration of synaptic mitochondria via protein kinase C epsilon

In the brain, ischemic preconditioning (IPC) diminishes mitochondrial dysfunction after ischemia and confers neuroprotection. Activation of epsilon protein kinase C (epsilonPKC) has been proposed to be a key neuroprotective pathway during IPC. We tested the hypothesis that IPC increases the levels of epsilonPKC in synaptosomes from rat hippocampus, resulting in improved synaptic mitochondrial respiration. Preconditioning significantly increased the level of hippocampal synaptosomal epsilonPKC to 152% of sham-operated animals at 2 d of reperfusion, the time of peak neuroprotection. We tested the effect of epsilonPKC activation on hippocampal synaptic mitochondrial respiration 2 d after preconditioning. Treatment with the specific epsilonPKC activating peptide, tat-psiepsilonRACK (tat-psiepsilon-receptor for activated C kinase), increased the rate of oxygen consumption in the presence of substrates for complexes I, II, and IV to 157, 153, and 131% of control (tat peptide alone). In parallel, we found that epsilonPKC activation in synaptosomes from preconditioned animals resulted in altered levels of phosphorylated mitochondrial respiratory chain proteins: increased serine and tyrosine phosphorylation of 18 kDa subunit of complex I, decreased serine phosphorylation of FeS protein in complex III, increased threonine phosphorylation of COX IV (cytochrome oxidase IV), increased mitochondrial membrane potential, and decreased H2O2 production. In brief, ischemic preconditioning promoted significant increases in the level of synaptosomal epsilonPKC. Activation of epsilonPKC increased synaptosomal mitochondrial respiration and phosphorylation of mitochondrial respiratory chain proteins. We propose that, at 48 h of reperfusion after ischemic preconditioning, epsilonPKC is poised at synaptic mitochondria to respond to ischemia either by direct phosphorylation or activation of the epsilonPKC signaling pathway.

Human mitochondrial complex I assembly: A dynamic and versatile process

One can but admire the intricate way in which biomolecular structures are formed and cooperate to allow proper cellular function. A prominent example of such intricacy is the assembly of the five inner membrane embedded enzymatic complexes of the mitochondrial oxidative phosphorylation (OXPHOS) system, which involves the stepwise combination of >80 subunits and prosthetic groups encoded by both the mitochondrial and nuclear genomes. This review will focus on the assembly of the most complicated OXPHOS structure: complex I (NADH:ubiquinone oxidoreductase, EC 1.6.5.3). Recent studies into complex I assembly in human cells have resulted in several models elucidating a thus far enigmatic process. In this review, special attention will be given to the overlap between the various assembly models proposed in different organisms. Complex I being a complicated structure, its assembly must be prone to some form of coordination. This is where chaperone proteins come into play, some of which may relate complex I assembly to processes such as apoptosis and even immunity.

Sphingolipid metabolite ceramide causes metabolic perturbation contributing to HERG K+ channel dysfunction

Ceramide, a sphingolipid metabolite, has emerged as a key second messenger molecule that mediates multiple cellular functions. Its de nova synthesis and accumulation in ischemic myocardium, congestive heart failure and diabetic cardiomyopathy is associated with the abnormalities such as abnormal QT prolongation and increased risk of arrhythmias. To investigate how ceramide is involved in modulating cardiac repolarization, we performed whole-cell patch-clamp studies on HERG current (I(HERG)), a critical determinant of cardiac repolarization, expressed in HEK293 cells. Acute application (superfusion for 25 min) of membrane permeable ceramide (C2, 5 microM) did not alter I(HERG). Prolonged incubation with C2 for 10 hrs caused pronounced I(HERG) inhibition in a concentration-dependent and voltage-independent fashion and positive shift of voltage-dependent HERG activation. The IC(50) for I(HERG) suppression was 19.5 microM. C2 did not affect the inactivation property and time-dependent kinetics of I(HERG). Similar effects were observed with production of endogenous ceramide catalyzed by sphingomyelinase. Tyrosine kinase inhibitors failed to reverse C2-induced suppression of HERG function, and PKA and PKC inhibitors only slightly reversed the I(HERG) depression. Western blotting and immunocytochemical analyses indicate that C2 does not alter HERG protein expression on the cytoplasmic membrane. The inhibitory effect of C2 on I(HERG) was reversed by antioxidants vitamin E or MnTBAP. C2 caused considerable production of intracellular reactive oxygen species (ROS), which was prevented by vitamin E or MnTBAP. We conclude that ceramide depresses I(HERG) mainly via ROS overproduction and ceramide-induced I(HERG) impairment may contribute to QT prolongation in prolonged myocardial ischemia, heart failure and diabetic cardiomyopathy.

Investigations of the potential effects of phosphorylation of the MWFE and ESSS subunits on complex I activity and assembly

There have been several reports on the phosphorylation of various subunits of NADH-ubiquinone oxidoreductase (complex I) in mammalian mitochondria. The effects of phosphorylation on assembly or activity of these subunits have not been investigated directly. The cAMP-dependent phosphorylation of the MWFE and ESSS subunits in isolated bovine heart mitochondria has been recently reported. We have investigated the significance of potential phosphorylation of these two subunits in complex I assembly and function by mutational analysis of the phosphorylation sites. Chinese hamster mutant cell lines missing either the MWFE or the ESSS subunits were transfected and complemented with the corresponding wild type and mutant cDNAs made by site-directed mutagenesis. In MWFE the serine 55 was substituted by alanine, glutamate, glutamine, and aspartate (S55A, S55E, S55Q, and S55D, respectively). The glutamate substitutions might be expected to mimic the phosphorylated state of the protein. With the exception of the MWFE(S55A) mutant protein the assembly of complex I was completely blocked, and no activity could be detected. Various substitutions in the ESSS protein (S2A, S2E, S8A, S8E, T21A, T21E, S30A, S30E) appeared to cause lower levels of mature protein and a significantly reduced complex I activity measured polarographically. The ESSS (S2/8A) double mutant protein caused a complete failure to assemble. These mutational analyses suggest that if phosphorylation occurs in vivo, the effects on complex I activity are significant.

Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent phosphoregulation of mitochondrial complex I is inhibited by nucleoside reverse transcriptase inhibitors

Nucleoside analog reverse transcriptase inhibitors (NRTIs) are known to directly inhibit mitochondrial complex I activity as well as various mitochondrial kinases. Recent observations that complex I activity and superoxide production are modulated through cAMP-dependent phosphorylation suggests a mechanism through which NRTIs may affect mitochondrial respiration via kinase-dependent protein phosphorylation. In the current study, we examine the potential for NRTIs to inhibit the cAMP-dependent phosphorylation of complex I and the associated NADH:CoQ oxidoreductase activities and rates of superoxide production using HepG2 cells. Phosphoprotein staining of immunocaptured complex I revealed that 3'-azido-3'-deoxythymidine (AZT; 10 and 50 microM), AZT monophosphate (150 microM), and 2',3'-dideoxycytidine (ddC; 1 microM) prevented the phosphorylation of the NDUFB11 subunit of complex I. This was associated with a decrease in complex I activity with AZT and AZT monophosphate only. In the presence of succinate, superoxide production was increased with 2',3'-dideoxyinosine (ddI; 10 microM) and ddC (1 microM). In the presence of succinate+cAMP, AZT showed an inverse dose-dependent effect on superoxide production. None of the NRTIs examined inhibit PKA activity suggesting that the observed effects are due to a direct interaction with complex I. These data demonstrate a direct effect of NRTIs on cAMP-dependent regulation of mitochondrial bioenergetics independent of DNA polymerase-gamma activity; in the case of AZT, these observations may provide a mechanism for the observed long-term toxicity with this drug.

Protein kinase A catalytic subunit alters cardiac mitochondrial redox state and membrane potential via the formation of reactive oxygen species

BACKGROUND

The identification of protein kinase A (PKA) anchoring proteins on mitochondria implies a direct effect of PKA on mitochondrial function. However, little is known about the relationship between PKA and mitochondrial metabolism.

METHODS AND RESULTS

The effects of PKA on the mitochondrial redox state (flavin adenine dinucleotide (FAD)), mitochondrial membrane potential (DeltaPsi(m)) and reactive oxygen species (ROS) production were investigated in saponin-permeabilized rat cardiomyocytes. The PKA catalytic subunit (PKAcat; 50 unit/ml) increased FAD intensities by 56.6+/-7.9% (p<0.01), 2'7'-dichlorofluorescin diacetate (DCF) intensities by 10.5+/-3.3 fold (p<0.01) and depolarized DeltaPsi(m) to 48.1+/-9.5% of the control (p<0.01). Trolox (a ROS scavenger; 100 micromol/L) inhibited PKAcat-induced DeltaPsi(m), FAD and DCF alteration. PKAcat-induced DeltaPsi(m) depolarization was inhibited by an inhibitor of the inner membrane anion channel (IMAC), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS: 1 micromol/L) but not by an inhibitor of mitochondrial permeability transition pore (mPTP), cyclosporine A (100 nmol/L).

CONCLUSIONS

PKAcat alters FAD and DeltaPsi(m) via mitochodrial ROS generation, and PKAcat-induced DeltaPsi(m) depolarization was not caused by mPTP but rather by DIDS-sensitive mechanisms, which could be caused by opening of the IMAC. The effects of PKA on mitochondrial function could be related to myocardial function under the condition of extensive beta-adrenergic stimulation.

Increased mitochondrial H2O2 production promotes endothelial NF-kappaB activation in aged rat arteries

Previous studies have shown that the aging vascular system undergoes pro-atherogenic phenotypic changes, including increased oxidative stress and a pro-inflammatory shift in endothelial gene expression profile. To elucidate the link between increased oxidative stress and vascular inflammation in aging, we compared the carotid arteries and aortas of young and aged (24 mo old) Fisher 344 rats. In aged vessels there was an increased NF-kappaB activity (assessed by luciferase reporter gene assay and NF-kappaB binding assay), which was attenuated by scavenging H(2)O(2). Aging did not alter the vascular mRNA and protein expression of p65 and p50 subunits of NF-kappaB. In endothelial cells of aged vessels there was an increased production of H(2)O(2) (assessed by 5,6-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate-acetyl ester fluorescence), which was attenuated by the mitochondrial uncoupler FCCP. In young arteries and cultured endothelial cells, antimycin A plus succinate significantly increased FCCP-sensitive mitochondrial H(2)O(2) generation, which was associated with activation of NF-kappaB. In aged vessels inhibition of NF-kappaB (by pyrrolidenedithiocarbamate, resveratrol) significantly attenuated inflammatory gene expression and inhibited monocyte adhesiveness. Thus increased mitochondrial oxidative stress contributes to endothelial NF-kappaB activation, which contributes to the pro-inflammatory phenotypic alterations in the aged vaculature. Our model predicts that by reducing mitochondrial H(2)O(2) production and/or directly inhibiting NF-kappaB novel anti-aging pharmacological treatments (e.g., calorie restriction mimetics) will exert significant anti-inflammatory and vasoprotective effects.

Is there a mitochondrial signaling complex facilitating cholesterol import?

Cholesterol transport into mitochondria is the rate-determining and hormone-sensitive step in steroid biosynthesis. During the last few years two proteins were shown to be critical for this process: the mitochondrial translocator protein, previously known as peripheral-type benzodiazepine receptor, and the steroidogenic acute regulatory protein. In this manuscript we review evidence suggesting that these two proteins functionally interact to facilitate cholesterol transport and may be part of a larger multimeric mitochondrial complex of proteins assembled to facilitate the hormone-induced cholesterol transfer into mitochondria. This complex might include proteins such as the mitochondrial voltage-dependent anion channel, the translocator protein-associated protein PAP7 which also functions as an A kinase anchor protein that binds and brings into the complex the regulatory subunit Ialpha of the cAMP-dependent protein kinase.

Nuclear and Mitochondrial Interaction Involving mt-Nd2 Leads to Increased Mitochondrial Reactive Oxygen Species Production

NADH dehydrogenase subunit 2, encoded by the mtDNA, has been associated with resistance to autoimmune type I diabetes (T1D) in a case control study. Recently, we confirmed a role for the mouse ortholog of the protective allele (mt-Nd2(a)) in resistance to T1D using genetic analysis of outcrosses between T1D-resistant ALR and T1D-susceptible NOD mice. We sought to determine the mechanism of disease protection by elucidating whether mt-Nd2(a) affects basal mitochondrial function or mitochondrial function in the presence of oxidative stress. Two lines of reciprocal conplastic mouse strains were generated: one with ALR nuclear DNA and NOD mtDNA (ALR.mt(NOD)) and the reciprocal with NOD nuclear DNA and ALR mtDNA (NOD.mt(ALR)). Basal mitochondrial respiration, transmembrane potential, and electron transport system enzymatic activities showed no difference among the strains. However, ALR.mt(NOD) mitochondria supported by either complex I or complex II substrates produced significantly more reactive oxygen species when compared with both parental strains, NOD.mt(ALR) or C57BL/6 controls. Nitric oxide inhibited respiration to a similar extent for mitochondria from the five strains due to competitive antagonism with molecular oxygen at complex IV. Superoxide and hydrogen peroxide generated by xanthine oxidase did not significantly decrease complex I function. The protein nitrating agents peroxynitrite or nitrogen dioxide radicals significantly decreased complex I function but with no significant difference among the five strains. In summary, mt-Nd2(a) does not confer elevated resistance to oxidative stress; however, it plays a critical role in the control of the mitochondrial reactive oxygen species production.