Signal transduction to mitochondrial ATP synthase: evidence that PDGF-dependent phosphorylation of the delta-subunit occurs in several cell lines, involves tyrosine, and is modulated by lysophosphatidic acid

Mitochondrial dysfunction and endoplasmic reticulum stress in the promotion of fibrosis in obstructive nephropathy induced by unilateral ureteral obstruction

Obstructive nephropathy favors the progression to chronic kidney disease (CKD), a severe health problem worldwide. The unilateral ureteral obstruction (UUO) model is used to study the development of fibrosis. Impairment of renal mitochondria plays a crucial role in several types of CKD and has been strongly related to fibrosis onset. Nevertheless, in the UUO model, the impairment of mitochondria, their relationship with endoplasmic reticulum (ER) stress induction and the participation of both to induce the fibrotic process remain unclear. In this review, we summarize the current information about mitochondrial bioenergetics, redox dynamics, mitochondrial mass, and biogenesis alterations, as well as the relationship of these mitochondrial alterations with ER stress and their participation in fibrotic processes in UUO models. Early after obstruction, there is metabolic reprogramming related to mitochondrial fatty acid β-oxidation impairment, triggering lipid deposition, oxidative stress, (calcium) Ca²⁺ dysregulation, and a reduction in mitochondrial mass and biogenesis. Mitochondria and the ER establish a pathological feedback loop that promotes the impairment of both organelles by ER stress pathways and Ca²⁺ levels dysregulation. Preserving mitochondrial and ER function can prevent or at least delay the fibrotic process and loss of renal function. However, deeper understanding is still necessary for future clinically-useful therapies.

The Mitochondrial Permeability Transition Pore: Channel Formation by F-ATP Synthase, Integration in Signal Transduction, and Role in Pathophysiology

The mitochondrial permeability transition (PT) is a permeability increase of the inner mitochondrial membrane mediated by a channel, the permeability transition pore (PTP). After a brief historical introduction, we cover the key regulatory features of the PTP and provide a critical assessment of putative protein components that have been tested by genetic analysis. The discovery that under conditions of oxidative stress the F-ATP synthases of mammals, yeast, and Drosophila can be turned into Ca(2+)-dependent channels, whose electrophysiological properties match those of the corresponding PTPs, opens new perspectives to the field. We discuss structural and functional features of F-ATP synthases that may provide clues to its transition from an energy-conserving into an energy-dissipating device as well as recent advances on signal transduction to the PTP and on its role in cellular pathophysiology.

Differential hippocampal protein expression between normal aged rats and aged rats with postoperative cognitive dysfunction: A proteomic analysis

The aim of the present study was to investigate the differences in the expression of hippocampal proteins between normal control aged rats and aged rats with postoperative cognitive dysfunction (POCD). A total of 24 aged rats were randomly divided into a surgery group (n=12) and a control group (n=12). The rats in the surgery group were treated with 2 h isoflurane anesthesia and splenectomy, while the rats in the control group received 40% oxygen for 2 h without surgery. The cognitive functions of the two groups were examined using a Y-maze test. The protein expression profiles of the hippocampus of six aged rats (three rats with POCD and three from the normal control group) were assessed using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry. A total of three differential proteins were further confirmed between the POCD rats and normal rats using reverse transcription quantitative polymerase chain reaction (RT-qPCR). The expression levels of 21 proteins in the rats with POCD were significantly different compared with the normal control rats. These proteins were functionally clustered to synaptic plasticity (three proteins), oxidative stress (four proteins), energy production (six proteins), neuroinflammation (three proteins) and glutamate metabolism (two proteins). In addition, three proteins (fatty acid binding protein 7, brain, glutamate dehydrogenase 1 and glutamine synthetase), associated with astrocytic function, were significantly different in the rats with POCD compared with those in the normal control (P<0.05). Similar changes in the mRNA expression levels of the three proteins in the hippocampi of POCD rats were also detected using RT-qPCR. Neuroinflammation, glutamate toxicity and oxidative stress were possibly involved in the pathological mechanism underlying POCD in aged rats. In addition, astrocytes may also be important in POCD in aged rats.

Protein kinase C-α interaction with F0F1-ATPase promotes F0F1-ATPase activity and reduces energy deficits in injured renal cells

We showed previously that active PKC-α maintains F0F1-ATPase activity, whereas inactive PKC-α mutant (dnPKC-α) blocks recovery of F0F1-ATPase activity after injury in renal proximal tubules (RPTC). This study tested whether mitochondrial PKC-α interacts with and phosphorylates F0F1-ATPase. Wild-type PKC-α (wtPKC-α) and dnPKC-α were overexpressed in RPTC to increase their mitochondrial levels, and RPTC were exposed to oxidant or hypoxia. Mitochondrial levels of the γ-subunit, but not the α- and β-subunits, were decreased by injury, an event associated with 54% inhibition of F0F1-ATPase activity. Overexpressing wtPKC-α blocked decreases in γ-subunit levels, maintained F0F1-ATPase activity, and improved ATP levels after injury. Deletion of PKC-α decreased levels of α-, β-, and γ-subunits, decreased F0F1-ATPase activity, and hindered the recovery of ATP content after RPTC injury. Mitochondrial PKC-α co-immunoprecipitated with α-, β-, and γ-subunits of F0F1-ATPase. The association of PKC-α with these subunits decreased in injured RPTC overexpressing dnPKC-α. Immunocapture of F0F1-ATPase and immunoblotting with phospho(Ser) PKC substrate antibody identified phosphorylation of serine in the PKC consensus site on the α- or β- and γ-subunits. Overexpressing wtPKC-α increased phosphorylation and protein levels, whereas deletion of PKC-α decreased protein levels of α-, β-, and γ-subunits of F0F1-ATPase in RPTC. Phosphoproteomics revealed phosphorylation of Ser(146) on the γ subunit in response to wtPKC-α overexpression. We concluded that active PKC-α 1) prevents injury-induced decreases in levels of γ subunit of F0F1-ATPase, 2) interacts with α-, β-, and γ-subunits leading to increases in their phosphorylation, and 3) promotes the recovery of F0F1-ATPase activity and ATP content after injury in RPTC.

Mitochondrial dysfunction: a neglected component of skin diseases

Aberrant mitochondrial structure and function influence tissue homeostasis and thereby contribute to multiple human disorders and ageing. Ten per cent of patients with primary mitochondrial disorders present skin manifestations that can be categorized into hair abnormalities, rashes, pigmentation abnormalities and acrocyanosis. Less attention has been paid to the fact that several disorders of the skin are linked to alterations of mitochondrial energy metabolism. This review article summarizes the contribution of mitochondrial pathology to both common and rare skin diseases. We explore the intriguing observation that a wide array of skin disorders presents with primary or secondary mitochondrial pathology and that a variety of molecular defects can cause dysfunctional mitochondria. Among them are mutations in mitochondrial- and nuclear DNA-encoded subunits and assembly factors of oxidative phosphorylation (OXPHOS) complexes; mutations in intermediate filament proteins involved in linking, moving and shaping of mitochondria; and disorders of mitochondrial DNA metabolism, fatty acid metabolism and heme synthesis. Thus, we assume that mitochondrial involvement is the rule rather than the exception in skin diseases. We conclude the article by discussing how improving mitochondrial function can be beneficial for aged skin and can be used as an adjunct therapy for certain skin disorders. Consideration of mitochondrial energy metabolism in the skin creates a new perspective for both dermatologists and experts in metabolic disease.

Nitropropenyl benzodioxole, an anti-infective agent with action as a protein tyrosine phosphatase inhibitor

We report on the activities of a broad spectrum antimicrobial compound,nitropropenyl benzodioxole (NPBD) which are of relevance to its potential as an anti-infective drug. These investigations support the proposal that a major mechanism of NPBD is action as a tyrosine mimetic, competitively inhibiting bacterial and fungal protein tyrosine phosphatases (PTP). NPBD did not affect major anti-bacterial drug targets, namely, ATP production, cell wall or cell membrane integrity, or transcription and translation of RNA. NPBD inhibited bacterial YopH and human PTP1B and not human CD45 in enzyme assays. NPBD inhibited PTP-associated bacterial virulence factors, namely, endospore formation in Bacillus cereus, prodigiosin secretion in Serratia marcescens , motility in Proteus spp., and adherence and invasion of mammalian cells by Yersinia enterocolitica . NPBD acts intracellularly to inhibit the early development stages of the Chlamydia trachomatis infection cycle in mammalian cells known to involve sequestration of host cell PTPs. NPBD thus both kills pathogens and inhibits virulence factors relevant to early infection, making it a suitable candidate for development as an anti-infective agent, particularly for pathogens that enter through, or cause infections at, mucosal surfaces. Though much is yet to be understood about bacterial PTPs, they are proposed as suitable anti-infective targets and have been linked to agents similar to NPBD. The structural and functional diversity and heterogeneous distribution of PTPs across microbial species make them suitably selective targets for the development of both broadly active and pathogen-specific drugs.

The oligomycin-sensitivity conferring protein of mitochondrial ATP synthase: emerging new roles in mitochondrial pathophysiology

The oligomycin-sensitivity conferring protein (OSCP) of the mitochondrial F(O)F1 ATP synthase has long been recognized to be essential for the coupling of proton transport to ATP synthesis. Located on top of the catalytic F1 sector, it makes stable contacts with both F1 and the peripheral stalk, ensuring the structural and functional coupling between F(O) and F1, which is disrupted by the antibiotic, oligomycin. Recent data have established that OSCP is the binding target of cyclophilin (CyP) D, a well-characterized inducer of the mitochondrial permeability transition pore (PTP), whose opening can precipitate cell death. CyPD binding affects ATP synthase activity, and most importantly, it decreases the threshold matrix Ca²⁺ required for PTP opening, in striking analogy with benzodiazepine 423, an apoptosis-inducing agent that also binds OSCP. These findings are consistent with the demonstration that dimers of ATP synthase generate Ca²⁺-dependent currents with features indistinguishable from those of the PTP and suggest that ATP synthase is directly involved in PTP formation, although the underlying mechanism remains to be established. In this scenario, OSCP appears to play a fundamental role, sensing the signal(s) that switches the enzyme of life in a channel able to precipitate cell death.

Sepsis-induced Cardiac Mitochondrial Damage and Potential Therapeutic Interventions in the Elderly

The incidence of sepsis and its attendant mortality risk are significantly increased with aging. Thus, severe sepsis in the elderly is likely to become an emerging concern in critical care units. Cardiac dysfunction is an important component of multi-organ failure after sepsis. In our laboratory, utilizing a pneumonia-related sepsis animal model, our research has been focused on the mechanisms underlying sepsis-induced cardiac failure. In this review, based on findings from others and ours, we discussed age-dependent decay in mitochondria and the role of mitochondrial reactive oxygen species (mtROS) in sepsis-induced cardiac inflammation and autophagy. Our recent discovery of a potential signal transduction pathway that triggers myocardial mitochondrial damage is also discussed. Because of the significance of mitochondria damage in the aging process and in sepsis pathogenesis, we hypothesize that specific enhancing mitochondrial antioxidant defense by mitochondria-targeted antioxidants (MTAs) may provide important therapeutic potential in treating elder sepsis patients. In this review, we summarized the categories of currently published MTA molecules and the results of preclinical evaluation of MTAs in sepsis and aging models.

Screening of protein kinase inhibitors and knockdown experiments identified four kinases that affect mitochondrial ATP synthesis activity

Mitochondrial ATP synthase, a major ATP supplier in respiring cells, should be regulated in amount and in activity to respond to the varying demands of cells for ATP. We screened 80 protein kinase inhibitors and found that HeLa cells treated with four inhibitors exhibited reduced mitochondrial ATP synthesis activity. Consistently, knockdown of their target kinases (PKA, PKCδ, CaMKII and smMLCK) resulted in a decrease in mitochondrial ATP synthesis activity. Among them, mitochondria of smMLCK-knockdown cells contained only a small amount of ATP synthase, while the α- and β-subunits of ATP synthase were produced normally, suggesting that smMLCK affects assembly (or decay) of ATP synthase.

Proliferation-independent control of tumor glycolysis by PDGFR-mediated AKT activation

The differences in glucose metabolism that distinguish most malignant and normal tissues have called attention to the importance of understanding the molecular mechanisms by which tumor energy metabolism is regulated. Receptor tyrosine kinase (RTK) pathways that are implicated in proliferation and transformation have been linked to several aspects of tumor glucose metabolism. However, the regulation of glycolysis has invariably been examined under conditions in which proliferation is concomitantly altered. To determine whether RTKs directly regulate glycolysis without prerequisite growth modulation, we first identified a specific RTK signaling pathway, platelet-derived growth factor (PDGF)/PDGF receptor (PDGFR) that regulates glycolysis in glioma-derived tumor stem-like cells from a novel mouse model. We determined that PDGF-regulated glycolysis occurs independent of PDGF-regulated proliferation but requires the activation of AKT, a known metabolic regulator in tumor. Our findings identifying a key characteristic of brain tumors, aerobic glycolysis, mediated by a pathway with multiple therapeutic targets suggests the possibility of inhibiting tumor energy metabolism while also treating with agents that target other pathways of pathologic significance.

Phosphorylation of mammalian cytochrome c and cytochrome c oxidase in the regulation of cell destiny: respiration, apoptosis, and human disease

The mitochondrial oxidative phosphorylation (OxPhos) system not only generates the vast majority of cellular energy, but is also involved in the generation of reactive oxygen species (ROS), and apoptosis. Cytochrome c (Cytc) and cytochrome c oxidase (COX) represent the terminal step of the electron transport chain (ETC), the proposed rate-limiting reaction in mammals. Cytc and COX show unique regulatory features including allosteric regulation, isoform expression, and regulation through cell signaling pathways. This chapter focuses on the latter and discusses all mapped phosphorylation sites based on the crystal structures of COX and Cytc. Several signaling pathways have been identified that target COX including protein kinase A and C, receptor tyrosine kinase, and inflammatory signaling. In addition, four phosphorylation sites have been mapped on Cytc with potentially large implications due to its multiple functions including apoptosis, a pathway that is overactive in stressed cells but inactive in cancer. The role of COX and Cytc phosphorylation is reviewed in a human disease context, including cancer, inflammation, sepsis, asthma, and ischemia/reperfusion injury as seen in myocardial infarction and ischemic stroke.

Src kinases are important regulators of mitochondrial functions

Mitochondria produce the most part of the energy used by the cells. This energetic production occurs through the oxidative phosphorylation (OXPHOS) process. Mitochondrial functions such as OXPHOS need to be tightly regulated to respect the needs of cells. Phosphorylation of mitochondrial proteins now appears as a major regulation pathway of mitochondrial functions. Several kinases and phosphatases are specifically targeted to mitochondria where they modulate mitochondrial functions. However, we still poorly understand the extent of tyrosine phosphorylation events on mitochondrial metabolism. Among the tyrosine-kinases observed in mitochondria, Src kinases emerge as key players. In the past years, several mitochondrial proteins were shown to be substrates of Src kinases. Notably, these kinases can impact greatly OXPHOS and apoptosis. Important regulators of Src kinases activity are also observed in mitochondria. The aim of this review is to summarize the recent findings on how overall mitochondrial tyrosine phosphorylation events and more specifically Src kinases can influence mitochondrial functions. The different mechanisms of Src kinases regulation and translocation into mitochondria will be also discussed. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Cardiac mitochondrial matrix and respiratory complex protein phosphorylation

It has become appreciated over the last several years that protein phosphorylation within the cardiac mitochondrial matrix and respiratory complexes is extensive. Given the importance of oxidative phosphorylation and the balance of energy metabolism in the heart, the potential regulatory effect of these classical signaling events on mitochondrial function is of interest. However, the functional impact of protein phosphorylation and the kinase/phosphatase system responsible for it are relatively unknown. Exceptions include the well-characterized pyruvate dehydrogenase and branched chain α-ketoacid dehydrogenase regulatory system. The first task of this review is to update the current status of protein phosphorylation detection primarily in the matrix and evaluate evidence linking these events with enzymatic function or protein processing. To manage the scope of this effort, we have focused on the pathways involved in energy metabolism. The high sensitivity of modern methods of detecting protein phosphorylation and the low specificity of many kinases suggests that detection of protein phosphorylation sites without information on the mole fraction of phosphorylation is difficult to interpret, especially in metabolic enzymes, and is likely irrelevant to function. However, several systems including protein translocation, adenine nucleotide translocase, cytochrome c, and complex IV protein phosphorylation have been well correlated with enzymatic function along with the classical dehydrogenase systems. The second task is to review the current understanding of the kinase/phosphatase system within the matrix. Though it is clear that protein phosphorylation occurs within the matrix, based on (32)P incorporation and quantitative mass spectrometry measures, the kinase/phosphatase system responsible for this process is ill-defined. An argument is presented that remnants of the much more labile bacterial protein phosphoryl transfer system may be present in the matrix and that the evaluation of this possibility will require the application of approaches developed for bacterial cell signaling to the mitochondria.

Mitochondrial protein phosphorylation as a regulatory modality: implications for mitochondrial dysfunction in heart failure

Phosphorylation of mitochondrial proteins has been recognized for decades, and the regulation of pyruvate- and branched-chain α-ketoacid dehydrogenases by an atypical kinase/phosphatase cascade is well established. More recently, the development of new mass spectrometry-based technologies has led to the discovery of many novel phosphorylation sites on a variety of mitochondrial targets. The evidence suggests that the major classes of kinase and several phosphatases may be present at the mitochondrial outer membrane, intermembrane space, inner membrane, and matrix, but many questions remain to be answered as to the location, timing, and reversibility of these phosphorylation events and whether they are functionally relevant. The authors review phosphorylation as a mitochondrial regulatory strategy and highlight its possible role in the pathophysiology of cardiac hypertrophy and failure.

Role of cellular bioenergetics in smooth muscle cell proliferation induced by platelet-derived growth factor

Abnormal smooth muscle cell proliferation is a hallmark of vascular disease. Although growth factors are known to contribute to cell hyperplasia, the changes in metabolism associated with this response, particularly mitochondrial respiration, remain unclear. Given the increased energy requirements for proliferation, we hypothesized that PDGF (platelet-derived growth factor) would stimulate glycolysis and mitochondrial respiration and that this elevated bioenergetic capacity is required for smooth muscle cell hyperplasia. To test this hypothesis, cell proliferation, glycolytic flux and mitochondrial oxygen consumption were measured after treatment of primary rat aortic VSMCs (vascular smooth muscle cells) with PDGF. PDGF increased basal and maximal rates of glycolytic flux and mitochondrial oxygen consumption; enhancement of these bioenergetic pathways led to a substantial increase in the mitochondrial reserve capacity. Interventions with the PI3K (phosphoinositide 3-kinase) inhibitor LY-294002 or the glycolysis inhibitor 2-deoxy-D-glucose abrogated PDGF-stimulated proliferation and prevented augmentation of glycolysis and mitochondrial reserve capacity. Similarly, when L-glucose was substituted for D-glucose, PDGF-dependent proliferation was abolished, as were changes in glycolysis and mitochondrial respiration. Interestingly, LDH (lactate dehydrogenase) protein levels and activity were significantly increased after PDGF treatment. Moreover, substitution of L-lactate for D-glucose was sufficient to increase mitochondrial reserve capacity and cell proliferation after treatment with PDGF; these effects were inhibited by the LDH inhibitor oxamate. These results suggest that glycolysis, by providing substrates that enhance the mitochondrial reserve capacity, plays an essential role in PDGF-induced cell proliferation, underscoring the integrated metabolic response required for proliferation of VSMCs in the diseased vasculature.

Phosphorylation of the F(1)F(o) ATP synthase beta subunit: functional and structural consequences assessed in a model system

RATIONALE

We previously discovered several phosphorylations to the beta subunit of the mitochondrial F(1)F(o) ATP synthase complex in isolated rabbit myocytes on adenosine treatment, an agent that induces cardioprotection. The role of these phosphorylations is unknown.

OBJECTIVE

The present study focuses on the functional consequences of phosphorylation of the ATP synthase complex beta subunit by generating nonphosphorylatable and phosphomimetic analogs in a model system, Saccharomyces cerevisiae.

METHODS AND RESULTS

The 4 amino acid residues with homology in yeast (T58, S213, T262, and T318) were studied with respect to growth, complex and supercomplex formation, and enzymatic activity (ATPase rate). The most striking mutant was the T262 site, for which the phosphomimetic (T262E) abolished activity, whereas the nonphosphorylatable strain (T262A) had an ATPase rate equivalent to wild type. Although T262E, like all of the beta subunit mutants, was able to form the intact complex (F(1)F(o)), this strain lacked a free F(1) component found in wild-type and had a corresponding increase of lower-molecular-weight forms of the protein, indicating an assembly/stability defect. In addition, the ATPase activity was reduced but not abolished with the phosphomimetic mutation at T58, a site that altered the formation/maintenance of dimers of the F(1)F(o) ATP synthase complex.

CONCLUSIONS

Taken together, these data show that pseudophosphorylation of specific amino acid residues can have separate and distinctive effects on the F(1)F(o) ATP synthase complex, suggesting the possibility that several of the phosphorylations observed in the rabbit heart can have structural and functional consequences to the F(1)F(o) ATP synthase complex.

A suggested role for mitochondria in Noonan syndrome

Noonan syndrome (NS) is an autosomal dominant disorder, and a main feature is congenital heart malformation. About 50% of cases are caused by gain-of-function mutations in the tyrosine phosphatase SHP2/PTPN11, a downstream regulator of ERK/MAPK. Recently it was reported that SHP2 also localizes to the mitochondrial intercristae/intermembrane space (IMS), but the role of SHP2 in mitochondria is unclear. The mitochondrial oxidative phosphorylation (OxPhos) system provides the vast majority of cellular energy and produces reactive oxygen species (ROS). Changes in ROS may interfere with organ development such as that observed in NS patients. Several phosphorylation sites have been found in OxPhos components including cytochrome c oxidase (CcO) and cytochrome c (Cytc), and we hypothesized that OxPhos complexes may be direct or indirect targets of SHP2. We analyzed mitochondrial function using mouse fibroblasts from wild-types, SHP2 knockdowns, and D61G SHP2 mutants leading to constitutively active SHP2, as found in NS patients. Levels of OxPhos complexes were similar except for CcO and Cytc, which were 37% and 28% reduced in the D61G cells. However, CcO activity was significantly increased, as we also found for two lymphoblast cell lines from NS patients with two independent mutations in PTPN11. D61G cells showed lower mitochondrial membrane potential and 30% lower ATP content compared to controls. ROS were significantly increased; aconitase activity, a marker for ROS-induced damage, was decreased; and catalase activity was increased in D61G cells. We propose that decreased energy levels and/or increased ROS may explain, at least in part, some of the clinical features in NS that overlap with children with mitochondrial disorders.

Mitochondrial and cell-surface F0F1ATPsynthase in innate and acquired cardioprotection

Mitochondria are central to heart function and dysfunction, and the pathways activated by different cardioprotective interventions mostly converge on mitochondria. In a context of perspectives in innate and acquired cardioprotection, we review some recent advances in F(0)F(1)ATPsynthase structure/function and regulation in cardiac cells. We focus on three topics regarding the mitochondrial F(0)F(1)ATPsynthase and the plasma membrane enzyme, i.e.: i) the crucial role of cardiac mitochondrial F(0)F(1)ATPsynthase regulation by the inhibitory protein IF(1) in heart preconditioning strategies; ii) the structure and function of mitochondrial F(0)F(1)ATPsynthase oligomers in mammalian myocardium as possible endogenous factors of mitochondria resistance to ischemic insult; iii) the external location and characterization of plasma membrane F(0)F(1) ATP synthase in search for possible actors of its regulation, such as IF(1) and calmodulin, at cell surface.

Post-translational modifications of ATP synthase in the heart: biology and function

The ATP synthase complex is a critical enzyme in the energetic pathways of cells because it is the enzyme complex that produces the majority of cellular ATP. It has been shown to be involved in several cardiac phenotypes including heart failure and preconditioning, a cellular protective mechanism. Understanding the regulation of this enzyme is important in understanding the mechanisms behind these important phenomena. Recently there have been several post-translational modifications (PTM) reported for various subunits of this enzyme complex, opening up the possibility of differential regulation by these PTMs. Here we discuss the known PTMs in the heart and other mammalian tissues and their implication to function and regulation of the ATP synthase.

Regulation of oxidative phosphorylation, the mitochondrial membrane potential, and their role in human disease

Thirty years after Peter Mitchell was awarded the Nobel Prize for the chemiosmotic hypothesis, which links the mitochondrial membrane potential generated by the proton pumps of the electron transport chain to ATP production by ATP synthase, the molecular players involved once again attract attention. This is so because medical research increasingly recognizes mitochondrial dysfunction as a major factor in the pathology of numerous human diseases, including diabetes, cancer, neurodegenerative diseases, and ischemia reperfusion injury. We propose a model linking mitochondrial oxidative phosphorylation (OxPhos) to human disease, through a lack of energy, excessive free radical production, or a combination of both. We discuss the regulation of OxPhos by cell signaling pathways as a main regulatory mechanism in higher organisms, which in turn determines the magnitude of the mitochondrial membrane potential: if too low, ATP production cannot meet demand, and if too high, free radicals are produced. This model is presented in light of the recently emerging understanding of mechanisms that regulate mammalian cytochrome c oxidase and its substrate cytochrome c as representative enzymes for the entire OxPhos system.

Mammalian liver cytochrome c is tyrosine-48 phosphorylated in vivo, inhibiting mitochondrial respiration

Cytochrome c (Cyt c) is part of the mitochondrial electron transport chain (ETC), accepting electrons from bc(1) complex and transferring them to cytochrome c oxidase (CcO). The ETC generates the mitochondrial membrane potential, which is used by ATP synthase to produce ATP. In addition, the release of Cyt c from the mitochondria often commits a cell to undergo apoptosis. Considering its central role in life (respiration) and death (apoptosis) decisions one would expect tight regulation of Cyt c function. Reversible phosphorylation is a main cellular regulatory mechanism, but the effect of cell signaling targeting the mitochondrial oxidative phosphorylation system is not well understood, and only a small number of proteins that can be phosphorylated have been identified to date. We have recently shown that Cyt c isolated from cow heart tissue is phosphorylated on tyrosine 97 in vivo, which leads to inhibition of respiration in the reaction with CcO. In this study we isolated Cyt c from a different organ, cow liver, under conditions preserving the physiological phosphorylation state. Western analysis with a phosphotyrosine specific antibody suggested that liver Cyt c is phosphorylated. Surprisingly, the phosphorylation site was unambiguously assigned to Tyr-48 by immobilized metal affinity chromatography/nano-liquid chromatography/electrospray ionization mass spectrometry (IMAC/nano-LC/ESI-MS), and not to the previously identified phospho-Tyr-97 in cow heart. As is true of Tyr-97, Tyr-48 is conserved in eukaryotes. As one possible consequence of Tyr-48 phosphorylation we analyzed the in vitro reaction kinetics with isolated cow liver CcO revealing striking differences. Maximal turnover of Tyr-48 phosphorylated Cyt c was 3.7 s(-1) whereas dephosphorylation resulted in a 2.2 fold increase in activity to 8.2 s(-1). Effects of Tyr-48 phosphorylation based on the Cyt c crystal structure are discussed.

Valsartan reverses post-translational modifications of the δ-subunit of ATP synthase duringin vivo canine reperfused myocardial infarction

To determine whether reperfused myocardial infarction (RMI) induces PTM of the delta-subunit of the mitochondrial metabolic enzyme ATP synthase (ATP/delta) in the ischemic zone (IZ) and whether this can be reversed by the angiotensin II type 1 receptor (AT(1)R) blocker valsartan, we applied a pharmaco-proteomics approach in canine RMI hearts with or without valsartan pretreatment. Using the 2-DE technique, we identified differential regional expression of ATP/delta in the IZ compared to the non-ischemic zone (NIZ), with an approximately 2-fold increase in the IZ that was normalized by valsartan. Furthermore in the IZ, RMI triggered S-nitrosylation of cysteine-100, nitration of the two tyrosines 88 and 225, and hydroxylation of lysine-182 in ATP/delta followed by its myristoylation. Importantly, valsartan abolished these modifications of ATP/delta in the IZ, triggered phosphorylation of serine-76 in both the IZ and NIZ, and decreased necrosis, apoptosis, left ventricular dysfunction and remodeling. Thus, AT(1)R-blocker-induced cardioprotection during RMI is associated with phosphorylation of ATP/delta and inhibition of nitric oxide-related chemical modifications such as S-nitrosylation, nitration and hydroxylation. Targeting specific PTMs during RMI, such as those of ATP/delta with AT(1)R blockade, might be a potentially powerful novel therapeutic approach. However, the identification of S-nitrosylation was putative and requires MS/MS verification.

Proteomic technologies in the study of kinases: novel tools for the investigation of PKC in the heart

Recent developments in the field of protein separation allows for the analysis of qualitative and quantitative global protein changes in a particular state of a biological system. Due to the enormous number of proteins potentially present in a cell, sub-fractionation and the enrichment of specific organelles are emerging as a necessary step to allow a more comprehensive representation of the protein content. The proteomic studies demonstrate that a key to understand the mechanisms underlying physiological or pathological phenotypes lies, at least in part, in post-translational modifications (PTMs), including phosphorylation of proteins. Rapid improvements in proteomic characterization of amino acid modifications are further expanding our comprehension of the importance of these mechanisms. The present review will provide an overview of technologies available for the study of a proteome, including tools to assess changes in protein quantity (abundance) as well as in quality (PTM forms). Examples of the recent application of these technologies and strategies in the field of kinase signalling will be provided with particular attention on the role of PKC in the heart. Studies of PKC-mediated phosphorylation of cytoskeletal, myofilament and mitochondrial proteins in the heart have provided great insight into the phenotypes of heart failure, hypertrophy and cardioprotection. Proteomics studies of the mitochondria have provided novel evidences for kinase signalling cascades localized to the mitochondria, some of which are known to involve various isoforms of PKC. Proteomics technologies allow for the identification of the different PTM forms of specific proteins and this information is likely to provide insight into the determinants of morphological as well as metabolic mal-adaptations, both in the heart and other tissues.

Proteomics and electron microscopic characterization of the unusual mitochondrial ribosome-related 45S complex in Leishmania tarentolae

A novel type of ribonucleoprotein (RNP) complex has been described from the kinetoplast-mitochondria of Leishmania tarentolae. The complex, termed the 45S SSU*, contains the 9S small subunit rRNA but does not contain the 12S large subunit rRNA. This complex is the most stable and abundant mitochondrial RNP complex present in Leishmania. As shown by tandem mass spectrometry, the complex contains at least 39 polypeptides with a combined molecular mass of almost 2.1 MDa. These components include several homologs of small subunit ribosomal proteins (S5, S6, S8, S9, S11, S15, S16, S17, S18, MRPS29); however, most of the polypeptides present are unique. Only a few of them show recognizable motifs, such as protein-protein (coiled-coil, Rhodanese) or protein-RNA (pentatricopeptide repeat) interaction domains. A cryo-electron microscopy examination of the 45S SSU* fraction reveals that 27% of particles represent SSU homodimers arranged in a head-to-tail orientation, while the majority of particles are clearly different and show an asymmetric bilobed morphology. Multiple classes of two-dimensional averages were derived for the asymmetrical particles, probably reflecting random orientations of the particles and difficulties in correlating these views with the known projections of ribosomal complexes. One class of the two-dimensional averages shows a SSU moiety attached to a protein mass or masses in a monosome-like appearance. The combined mass spectrometry and electron microscopy data thus indicate that the majority 45S SSU* particles represents a heterodimeric complex in which the SSU of the Leishmania mitochondrial ribosome is associated with an additional protein mass. The biological role of these particles is not known.

Differential steady-state tyrosine phosphorylation of two oligomeric forms of mitochondrial F0F1ATPsynthase: a structural proteomic analysis

We investigated tyrosine phosphorylation of F(0)F(1)ATPsynthase using 3-D blue native (BN)-SDS-PAGE, a refinement of the electrophoretic analysis of mitochondrial complexes. Bovine heart mitochondria were detergent-solubilized and subjected to BN-PAGE. Bands of ATPsynthase monomer (Vmon) and dimer (Vdim) were excised and submitted to SDS-PAGE and immunoblotting. One protein corresponding to F(1)gamma subunit was detected by anti-phosphotyrosine antibody in monomer but not in dimer. This was confirmed by MS peptide mapping. LC-ESI/MS analysis after 3-D SDS-PAGE demonstrated phosphotyrosine in fragment 43-54. NetPhos scores predicted the phosphorylated residue to be Tyr52, in a solvent-accessible loop at the foot of the F(1) central stalk.

Mitochondrial AKAP121 links cAMP and src signaling to oxidative metabolism

AKAP121 focuses distinct signaling events from membrane to mitochondria by binding and targeting cAMP-dependent protein kinase (PKA), protein tyrosine phosphatase (PTPD1), and mRNA. We find that AKAP121 also targets src tyrosine kinase to mitochondria via PTPD1. AKAP121 increased src-dependent phosphorylation of mitochondrial substrates and enhanced the activity of cytochrome c oxidase, a component of the mitochondrial respiratory chain. Mitochondrial membrane potential and ATP oxidative synthesis were enhanced by AKAP121 in an src- and PKA-dependent manner. Finally, siRNA-mediated silencing of endogenous AKAP121 drastically impaired synthesis and accumulation of mitochondrial ATP. These findings indicate that AKAP121, through its role in enhancing cAMP and tyrosine kinase signaling to distal organelles, is an important regulator in mitochondrial metabolism.

Kinetic properties of F1-ATPase influence the ability of yeasts to grow in anoxia or absence of mtDNA

A mechanism for hypoxia survival by eukaryotic cells is suggested from studies on the petite mutation of yeasts. Previous work has shown that mutations in the alpha, beta and gamma subunit genes of F1-ATPase can suppress lethality due to loss of the mitochondrial genome from the petite-negative yeast Kluyveromyceslactis. Here it is reported that suppressor mutations appear to increase the affinity of F1-ATPase for ATP. Extension of this study to other yeasts shows that petite-positive species have a higher affinity for ATP in the hydrolysis reaction than petite-negative species. Possession of a F1-ATPase with a low K(m) for ATP is considered to be an adaptation for hypoxic growth, enabling maintenance of the mitochondrial inner membrane potential, deltapsi, by enhanced export of protons through F1F0-ATP synthase connected to increased ATP hydrolysis at low substrate concentration.

A historical review of cellular calcium handling, with emphasis on mitochondria

Calcium ions are of central importance in cellular physiology, as they carry the signal activating cells to perform their programmed function. Ca(2+) is particularly suitable for this role because of its chemical properties and because its free concentration gradient between the extra-cellular and the cytosolic concentrations is very high, about four orders of magnitude. The cytosolic concentration of Ca(2+) is regulated by binding and chelation by various substances and by transport across plasma and intracellular membranes. Various channels, transport ATPases, uniporters, and antiporters in the plasma membrane, endoplasmic and sarcoplasmic reticulum, and mitochondria are responsible for the transport of Ca(2+). The regulation of these transport systems is the subject of an increasing number of studies. In this short review, we focus on the mitochondrial transporters, i.e. the calcium uniporter used for Ca(2+) uptake, and the antiporters used for the efflux, i.e. the Ca(2+)/Na(+) antiporter in mitochondria and the plasma membrane of excitable cells, and the Ca(2+)/nH(+) antiporter in liver and some other mitochondrial types. Mitochondria are of special interest in that Ca(2+) stimulates respiration and oxidative phosphorylation to meet the energy needs of activated cells. The studies on Ca(2+) and mitochondria began in the fifties, but interest in mitochondrial Ca(2+) handling faded in the late seventies since it had become apparent that mitochondria in resting cells contain very low Ca(2+). Interest increased again in the nineties also because it was discovered that mitochondria and Ca(2+) had a central role in apoptosis and necrosis. This is of special interest in calcium overload and oxidative stress conditions, when the opening of the mitochondrial permeability transition pore is stimulated.

A functionally active human F1F0 ATPase can be purified by immunocapture from heart tissue and fibroblast cell lines. Subunit structure and activity studies

Human mitochondrial F(1)F(0) ATP synthase was isolated with a one-step immunological approach, using a monoclonal antibody against F(1) in a 96-well microplate activity assay system, to establish a method for fast high throughput screening of inhibitors, toxins, and drugs with very small amounts of enzyme. For preparative purification, mitochondria from human heart tissue as well as cultured fibroblasts were solubilized with dodecyl-beta-d-maltoside, and the F(1)F(0) was isolated with anti-F(1) monoclonal antibody coupled to protein G-agarose beads. The immunoprecipitated F(1)F(0) contained a full complement of subunits that were identified with specific antibodies against five of the subunits (alpha, beta, OSCP, d, and IF(1)) and by MALDI-TOF and/or LC/MS/MS for all subunits except subunit c, which could not be resolved by these methods because of the limits of detection. Microscale immunocapture of F(1)F(0) from detergent-solubilized mitochondria or whole cell fibroblast extracts was performed using anti-F(1) monoclonal antibody immobilized on 96-well microplates. The captured complex V displayed ATP hydrolysis activity that was fully oligomycin and inhibitor protein IF(1)-sensitive. Moreover, IF(1) could be co-isolated with F(1)F(0) when the immunocapture procedure was carried out at pH 6.5 but was absent when the ATP synthase was isolated at pH 8.0. Immunocaptured F(1)F(0) lacking IF(1) could be inhibited by more than 90% by addition of recombinant inhibitor protein, and conversely, F(1)F(0) containing IF(1) could be activated more than 10-fold by brief exposure to pH 8.0, inducing the release of inhibitor protein. With this microplate system an ATP hydrolysis assay of complex V could be carried out with as little as 10 ng of heart mitochondria/well and as few as 3 x 10(4) cells/well from fibroblast cultures. The system is therefore suitable to screen patient-derived samples for alterations in amount or functionality of both the F(1)F(0) ATPase and IF(1).