Mitochondrial energy metabolism is regulated via nuclear-coded subunits of cytochrome c oxidase

Fat accumulation in striped hamsters (Cricetulus barabensis) reflects the temperature of prior cold acclimation

BACKGROUND

Proper adjustments of metabolic thermogenesis play an important role in thermoregulation in endotherm to cope with cold and/or warm ambient temperatures, however its roles in energy balance and fat accumulation remain uncertain. Our study aimed to investigate the effect of previous cold exposure (10 and 0 °C) on the energy budgets and fat accumulation in the striped hamsters (Cricetulus barabensis) in response to warm acclimation. The body mass, energy intake, resting metabolic rate (RMR) and nonshivering thermogenesis (NST), serum thyroid hormone levels (THs: T3 and T4), and the activity of brown adipose tissue (BAT), indicated by cytochrome c oxidase (COX) activity and uncoupling protein 1 (ucp1) expression, were measured following exposure to the cold (10 °C and 0 °C) and transition to the warm temperature (30 °C).

RESULTS

The hamsters at 10 °C and 0 °C showed significant increases in energy intake, RMR and NST, and a considerable reduction in body fat than their counterparts kept at 21 °C. After being transferred from cold to warm temperature, the hamsters consumed less food, and decreased RMR and NST, but they significantly increased body fat content. Interestingly, the hamsters that were previously exposed to the colder temperature showed significantly more fat accumulation after transition to the warm. Serum T3 levels, BAT COX activity and ucp1 mRNA expression were significantly increased following cold exposure, and were considerably decreased after transition to the warm. Furthermore, body fat content was negatively correlated with serum T3 levels, BAT COX activity and UCP1 expression.

CONCLUSION

The data suggest that the positive energy balance resulting from the decreased RMR and NST in BAT under the transition from the cold to the warm plays important roles in inducing fat accumulation. The extent of fat accumulation in the warm appears to reflect the temperature of the previous cold acclimation.

Loss of Cardiac Splicing Regulator RBM20 Is Associated With Early-Onset Atrial Fibrillation

We showed an association between atrial fibrillation and rare loss-of-function (LOF) variants in the cardiac splicing regulator RBM20 in 2 independent cohorts. In a rat model with loss of RBM20, we demonstrated altered splicing of sarcomere genes (NEXN, TTN, TPM1, MYOM1, and LDB3), and differential expression in key cardiac genes. We identified altered sarcomere and mitochondrial structure on electron microscopy imaging and found compromised mitochondrial function. Finally, we demonstrated that 3 novel LOF variants in RBM20, identified in patients with atrial fibrillation, lead to significantly reduced splicing activity. Our results implicate alternative splicing as a novel proarrhythmic mechanism in the atria.

Calcium-Dependent Interaction of Nitric Oxide Synthase with Cytochrome c Oxidase: Implications for Brain Bioenergetics

Targeted nitric oxide production is relevant for maintaining cellular energy production, protecting against oxidative stress, regulating cell death, and promoting neuroprotection. This study aimed to characterize the putative interaction of nitric-oxide synthase with mitochondrial proteins. The primary finding of this study is that cytochrome c oxidase (CCO) subunit IV (CCOIV) is associated directly with NOS in brain mitochondria when calcium ions are present. The matrix side of CCOIV binds to the N-terminus of NOS, supported by the abrogation of the binding by antibodies towards the N-terminus of NOS. Evidence supporting the interaction between CCOIV and NOS was provided by the coimmunoprecipitation of NOS from detergent-solubilized whole rat brain mitochondria with antibodies to CCOIV and the coimmunoprecipitation of CCOIV from crude brain NOS preparations using antibodies to NOS. The CCOIV domain that interacts with NOS was identified using a series of overlapping peptides derived from the primary sequence of CCOIV. As calcium ions not only activate NOS, but also facilitate the docking of NOS to CCOIV, this study points to a dynamic mechanism of controlling the bioenergetics by calcium changes, thereby adapting bioenergetics to cellular demands.

Tetrazolium-based colorimetric assays underestimat the direct antitumor effects of anti-VEGF agent bevacizumab

The direct antitumor effect of bevacizumab (BEV) has long been debated. Assessment of the direct cytotoxic activities of drugs is usually conducted via in vitro experiments, of which tetrazolium-based colorimetric assays are widely employed to measure the direct antitumor activity of BEV. This study aimed to investigate whether tetrazolium-based colorimetric assays are applicable when evaluating the cytotoxicity of BEV against tumor cells. Our results showed that BEV significantly augmented tumor-cell mitochondrial metabolism. Enhanced mitochondrial metabolism caused changes in cellular oxidation-and-reduction environment and upregulated succinate dehydrogenase, which in turn promoted the reduction of tetrazolium to produce formazan. Increased formazan formation resulted in underestimation of the in vitro direct antitumor effect of BEV. Furthermore, inhibition of mitochondrial hypermetabolism partially corrected the underestimation of colorimetric assays in evaluating the direct antitumor activity of BEV. Our findings suggest that tetrazolium-based colorimetric assays are unsuitable for accurately assessing the in vitro cytotoxicity of anti-VEGF drugs and may be the methodological reason for the controversial direct antitumor effect of BEV.

The Acute Effect of Multi-Ingredient Antioxidant Supplementation following Ionizing Radiation

Radiation exposure is an undeniable health threat encountered in various occupations and procedures. High energy waves in ionizing radiation cause DNA damage and induce reactive oxygen species (ROS) production, which further exacerbate DNA, protein, and lipid damage, increasing risk of mutations. Although endogenous antioxidants such as superoxide dismutase have evolved to upregulate and neutralize ROS, exogenous dietary antioxidants also have the potential to combat ionizing radiation (IR)-induced ROS production. We evaluated a cocktail of ingredients (AOX) purported to have antioxidant and mitochondrial protective properties on the acute effects of IR. We show that IR stimulates DNA damage through phosphorylation of DNA repair proteins in the heart, brain, and liver of mice. AOX showed partial protection in brain and liver, through a lack of significant activation in given repair proteins. In addition, AOX attenuated the IR-induced increase in NF-kβ mRNA and protein expression in brain and liver. Lastly, cytochrome c oxidase complex transcripts were significantly higher in heart and brain following radiation, which was also diminished by prior ingestion of AOX. Together, our findings suggest that a multi-ingredient AOX supplement may attenuate the IR-induced cellular damage response and represents a feasible and cost-effective preventative supplement for at-risk populations of radiation exposure.

Peripheral Blood Mononuclear Cells Mitochondrial Respiration and Superoxide Anion after Heart Transplantation

INTRODUCTION

The mitochondrial function of circulating peripheral blood mononuclear cells (PBMCs) is an interesting new approach to cardiac diseases. Thus, PBMC's mitochondrial respiration decreases in relation to heart failure severity. However, no data are available on heart-transplanted patients (Htx).

POPULATION AND METHODS

We determined PBMCs mitochondrial respiration by high-resolution respirometry (Oroboros Instruments) and superoxide anion production using electron paramagnetic resonance (Bruker-Biospin) in 20 healthy subjects and 20 matched Htx and investigated clinical, biological, echocardiographic, coronarography and biopsy characteristics.

RESULTS

PBMCs mitochondrial respiratory chain complex II respiration was decreased in Htx (4.69 ± 0.84 vs. 7.69 ± 1.00 pmol/s/million cell in controls and Htx patients, respectively; p = 0.007) and complex IV respiration was increased (24.58 ± 2.57 vs. 15.68 ± 1.67 pmol/s/million cell; p = 0.0035). Superoxide anion production was also increased in Htx (1.47 ± 0.10 vs. 1.15 ± 0.10 µmol/min; p = 0.041). The leucocyte-to-lymphocyte ratio was increased in Htx, whom complex II correlated with leucocyte number (r = 0.51, p = 0.02) and with the left ventricular posterior wall peak early diastolic myocardial velocity (r = -0.62, p = 0.005). Complex IV was increased in the two patients with acute rejection and correlated negatively with Htx's isovolumetric relation time (r = -0.45, p = 0.045).

DISCUSSION

Although presenting with normal systolic function, Htx demonstrated abnormal PBMC's mitochondrial respiration. Unlike immunosuppressive therapies, subclinical diastolic dysfunction might be involved in these changes. Additionally, lymphopenia might reduce complex II, and acute rejection enhances complex IV respirations.

CONCLUSION

PBMC's mitochondrial respiration appears modified in Htx, potentially linked to cellular shift, mild diastolic dysfunction and/or acute rejection.

Metformin disrupts Danio rerio metabolism at environmentally relevant concentrations: A full life-cycle study

Metformin (MET), an anti-diabetic pharmaceutical of large-scale consumption, is increasingly detected in surface waters. However, current knowledge on the long-term effects of MET on non-target organisms is limited. The present study aimed to investigate the effects of MET in the model freshwater teleost Danio rerio, following a full life-cycle exposure to environmentally relevant concentrations (390 to 14 423 ng/L). Considering that the mode of action (MoA) of MET on non-target organisms remains underexplored and that MET may act through similar human pathways, i.e., lipid and energy metabolisms, biochemical markers were used to determine cholesterol and triglycerides levels, as well as mitochondrial complex I activity in zebrafish liver. Also, the hepatosomatic index as an indication of metabolic disruption, and the expression levels of genes involved in MET's putative MoA, i.e. acaca, acadm, cox5aa, idh3a, hmgcra, prkaa1, were determined, the last by qRT-PCR. A screening of mRNA transcripts, associated with lipid and energy metabolisms, and other signaling pathways potentially involved in MET-induced toxicity were also assessed using an exploratory RNA-seq analysis. The findings here reported indicate that MET significantly disrupted critical biochemical and molecular processes involved in zebrafish metabolism, such as cholesterol and fatty acid biosynthesis, mitochondrial electron transport chain and tricarboxylic acid cycle, concomitantly to changes on the hepatosomatic index. Likewise, MET impacted other relevant pathways mainly associated with cell cycle, DNA repair and steroid hormone biosynthesis, here reported for the first time in a non-target aquatic organism. Non-monotonic dose response curves were frequently detected in biochemical and qRT-PCR data, with higher effects observed at 390 and 2 929 ng/L MET treatments. Collectively, the results suggest that environmentally relevant concentrations of MET severely disrupt D. rerio metabolism and other important biological processes, supporting the need to revise the proposed environmental quality standard (EQS) and predicted no-effect concentration (PNEC) for MET.

Metabolic rate increases with acclimation temperature and is associated with mitochondrial function in some tissues of threespine stickleback

The metabolic rate (ṀO2) of eurythermal fishes changes in response to temperature, yet it is unclear how changes in mitochondrial function contribute to changes in ṀO2. We hypothesized that ṀO2 would increase with acclimation temperature in the threespine stickleback (Gasterosteus aculeatus) in parallel with metabolic remodeling at the cellular level but that changes in metabolism in some tissues, such as liver, would contribute more to changes in ṀO2 than others. Threespine stickleback were acclimated to 5, 12 and 20°C for 7 to 21 weeks. At each temperature, standard and maximum metabolic rate (SMR and MMR, respectively), and absolute aerobic scope (AAS) were quantified, along with mitochondrial respiration rates in liver, oxidative skeletal and cardiac muscles, and the maximal activity of citrate synthase (CS) and lactate dehydrogenase (LDH) in liver, and oxidative and glycolytic skeletal muscles. SMR, MMR and AAS increased with acclimation temperature, along with rates of mitochondrial phosphorylating respiration in all tissues. Low SMR and MMR at 5°C were associated with low or undetectable rates of mitochondrial complex II activity and a greater reliance on complex I activity in liver, oxidative skeletal muscle and heart. SMR was positively correlated with cytochrome c oxidase (CCO) activity in liver and oxidative muscle, but not mitochondrial proton leak, whereas MMR was positively correlated with CCO activity in liver. Overall, the results suggest that changes in ṀO2 in response to temperature are driven by changes in some aspects of mitochondrial function in some, but not all, tissues of threespine stickleback.

Energy status-promoted growth and development of Arabidopsis require copper deficiency response transcriptional regulator SPL7

Copper (Cu) is a cofactor of around 300 Arabidopsis proteins, including photosynthetic and mitochondrial electron transfer chain enzymes critical for adenosine triphosphate (ATP) production and carbon fixation. Plant acclimation to Cu deficiency requires the transcription factor SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE7 (SPL7). We report that in the wild type (WT) and in the spl7-1 mutant, respiratory electron flux via Cu-dependent cytochrome c oxidase is unaffected under both normal and low-Cu cultivation conditions. Supplementing Cu-deficient medium with exogenous sugar stimulated growth of the WT, but not of spl7 mutants. Instead, these mutants accumulated carbohydrates, including the signaling sugar trehalose 6-phosphate, as well as ATP and NADH, even under normal Cu supply and without sugar supplementation. Delayed spl7-1 development was in agreement with its attenuated sugar responsiveness. Functional TARGET OF RAPAMYCIN and SNF1-RELATED KINASE1 signaling in spl7-1 argued against fundamental defects in these energy-signaling hubs. Sequencing of chromatin immunoprecipitates combined with transcriptome profiling identified direct targets of SPL7-mediated positive regulation, including Fe SUPEROXIDE DISMUTASE1 (FSD1), COPPER-DEFICIENCY-INDUCED TRANSCRIPTION FACTOR1 (CITF1), and the uncharacterized bHLH23 (CITF2), as well as an enriched upstream GTACTRC motif. In summary, transducing energy availability into growth and reproductive development requires the function of SPL7. Our results could help increase crop yields, especially on Cu-deficient soils.

Yeast Protein Kinase A Isoforms: A Means of Encoding Specificity in the Response to Diverse Stress Conditions?

Eukaryotic cells have developed a complex circuitry of signalling molecules which monitor changes in their intra- and extracellular environments. One of the most widely studied signalling pathways is the highly conserved cyclic AMP (cAMP)/protein kinase A (PKA) pathway, which is a major glucose sensing circuit in the yeast Saccharomyces cerevisiae. PKA activity regulates diverse targets in yeast, positively activating the processes that are associated with rapid cell growth (e.g., fermentative metabolism, ribosome biogenesis and cell division) and negatively regulating the processes that are associated with slow growth, such as respiratory growth, carbohydrate storage and entry into stationary phase. As in higher eukaryotes, yeast has evolved complexity at the level of the PKA catalytic subunit, and Saccharomyces cerevisiae expresses three isoforms, denoted Tpk1-3. Despite evidence for isoform differences in multiple biological processes, the molecular basis of PKA signalling specificity remains poorly defined, and many studies continue to assume redundancy with regards to PKA-mediated regulation. PKA has canonically been shown to play a key role in fine-tuning the cellular response to diverse stressors; however, recent studies have now begun to interrogate the requirement for individual PKA catalytic isoforms in coordinating distinct steps in stress response pathways. In this review, we discuss the known non-redundant functions of the Tpk catalytic subunits and the evolving picture of how these isoforms establish specificity in the response to different stress conditions.

Bioenergetic Aspects of Mitochondrial Actions of Thyroid Hormones

Much is known, but there is also much more to discover, about the actions that thyroid hormones (TH) exert on metabolism. Indeed, despite the fact that thyroid hormones are recognized as one of the most important regulators of metabolic rate, much remains to be clarified on which mechanisms control/regulate these actions. Given their actions on energy metabolism and that mitochondria are the main cellular site where metabolic transformations take place, these organelles have been the subject of extensive investigations. In relatively recent times, new knowledge concerning both thyroid hormones (such as the mechanisms of action, the existence of metabolically active TH derivatives) and the mechanisms of energy transduction such as (among others) dynamics, respiratory chain organization in supercomplexes and cristes organization, have opened new pathways of investigation in the field of the control of energy metabolism and of the mechanisms of action of TH at cellular level. In this review, we highlight the knowledge and approaches about the complex relationship between TH, including some of their derivatives, and the mitochondrial respiratory chain.

COX4-like, a Nuclear-Encoded Mitochondrial Gene Duplicate, Is Essential for Male Fertility in Drosophila melanogaster

Recent studies on nuclear-encoded mitochondrial genes (N-mt genes) in Drosophila melanogaster have shown a unique pattern of expression for newly duplicated N-mt genes, with many duplicates having a testis-biased expression and playing an essential role in spermatogenesis. In this study, we investigated a newly duplicated N-mt gene—i.e., Cytochrome c oxidase 4-like (COX4L)—in order to understand its function and, consequently, the reason behind its retention in the D. melanogaster genome. The COX4L gene is a duplicate of the Cytochrome c oxidase 4 (COX4) gene of OXPHOS complex IV. While the parental COX4 gene has been found in all eukaryotes, including single-cell eukaryotes such as yeast, we show that COX4L is only present in the Brachycera suborder of Diptera; thus, both genes are present in all Drosophila species, but have significantly different patterns of expression: COX4 is highly expressed in all tissues, while COX4L has a testis-specific expression. To understand the function of this new gene, we first knocked down its expression in the D. melanogaster germline using two different RNAi lines driven by the bam-Gal4 driver; second, we created a knockout strain for this gene using CRISPR-Cas9 technology. Our results showed that knockdown and knockout lines of COX4L produce partial sterility and complete sterility in males, respectively, where a lack of sperm individualization was observed in both cases. Male infertility was prevented by driving COX4L-HA in the germline, but not when driving COX4-HA. In addition, ectopic expression of COX4L in the soma caused embryonic lethality, while overexpression in the germline led to a reduction in male fertility. COX4L-KO mitochondria show reduced membrane potential, providing a plausible explanation for the male sterility observed in these flies. This prominent loss-of-function phenotype, along with its testis-biased expression and its presence in the Drosophila sperm proteome, suggests that COX4L is a paralogous, specialized gene that is assembled in OXPHOS complex IV of male germline cells and/or sperm mitochondria.

COX5B-Mediated Bioenergetic Alterations Modulate Cell Growth and Anticancer Drug Susceptibility by Orchestrating Claudin-2 Expression in Colorectal Cancers

Oxidative phosphorylation (OXPHOS) consists of four enzyme complexes and ATP synthase, and is crucial for maintaining physiological tissue and cell growth by supporting the main bioenergy pool. Cytochrome c oxidase (COX) has been implicated as a primary regulatory site of OXPHOS. Recently, COX subunit 5B (COX5B) emerged as a potential biomarker associated with unfavorable prognosis by modulating cell behaviors in specific cancer types. However, its molecular mechanism remains unclear, particularly in colorectal cancers (CRCs). To understand the role of COX5B in CRCs, the expression and postoperative outcome associations using independent in-house patient cohorts were evaluated. A higher COX5B tumor/nontumor expression ratio was associated with unfavorable clinical outcomes (p = 0.001 and 0.011 for overall and disease-free survival, respectively. In cell-based experiments, the silencing of COX5B repressed cell growth and enhanced the susceptibility of CRCs cells to anticancer drugs. Finally, downstream effectors identified by RNA sequencing followed by RT-qPCR and functional compensation experiments revealed that the tight junction protein Claudin-2 (CLDN2) acts downstream of COX5B-mediated bioenergetic alterations in controlling cell growth and the sensitivity to anticancer drugs in CRCs cells. In conclusion, it was found that COX5B promoted cell growth and attenuated anticancer drugs susceptibility in CRCs cells by orchestrating CLDN2 expression, which may contribute to unfavorable postoperative outcomes of patients with CRCs.

The role of the electron transport chain in immunity

The electron transport chain (ETC) couples oxidative phosphorylation (OXPHOS) with ATP synthase to drive the generation of ATP. In immune cells, research surrounding the ETC has drifted away from bioenergetics since the discovery of cytochrome c (Cyt c) release as a signal for programmed cell death. Complex I has been shown to generate reactive oxygen species (ROS), with key roles identified in inflammatory macrophages and T helper 17 cells (T_H 17) cells. Complex II is the site of reverse electron transport (RET) in inflammatory macrophages and is also responsible for regulating fumarate levels linking to epigenetic changes. Complex III also produces ROS which activate hypoxia-inducible factor 1-alpha (HIF-1α) and can participate in regulatory T cell (T_reg ) function. Complex IV is required for T cell activation and differentiation and the proper development of T_reg subsets. Complex V is required for T_H 17 differentiation and can be expressed on the surface of tumor cells where it is recognized by anti-tumor T and NK cells. In this review, we summarize these findings and speculate on the therapeutic potential of targeting the ETC as an anti-inflammatory strategy.

Colorectal Cancer Progression Is Potently Reduced by a Glucose-Free, High-Protein Diet: Comparison to Anti-EGFR Therapy

Simple Summary

To study the interplay between nutrition and intestinal metabolism in the context of colitis-driven colorectal carcinoma (CRC), we here investigated a nutritional therapy strategy in the presence or absence of EGFR-directed antibody therapy in mice to treat established colitis-driven CRCs in vivo. After CRC development, mice were fed a control diet or an isoenergetic glucose-free high-protein (GFHP) diet in the presence or absence of EGFR-directed antibody therapy. The GFHP diet was accompanied by a metabolic shift of the mice towards lower glycolysis activity. Both, GFHP diet or anti-EGFR antibody treatment, improved tumor differentiation and anti-tumor immune response, resulting in an efficient reduction of colonic tumor burden.

Abstract

To enable rapid proliferation, colorectal tumor cells up-regulate epidermal growth factor receptor (EGFR) signaling and aerobic glycolysis, resulting in substantial lactate release into the tumor microenvironment and impaired anti-tumor immune responses. We hypothesized that a nutritional intervention designed to reduce aerobic glycolysis may boost the EGFR-directed antibody (Ab)-based therapy of pre-existing colitis-driven colorectal carcinoma (CRC). CRC development was induced by azoxymethane (AOM) and dextran sodium sulfate (DSS) administration to C57BL/6 mice. AOM/DSS-treated mice were fed a glucose-free, high-protein diet (GFHPD) or an isoenergetic control diet (CD) in the presence or absence of an i.p. injection of an anti-EGFR mIgG2a or respective controls. AOM/DSS-treated mice on a GFHPD displayed a reduced systemic glucose metabolism associated with reduced oxidative phosphorylation (OXPHOS) complex IV expression and diminished tumor loads. Comparable but not additive to an anti-EGFR-Ab therapy, the GFHPD was accompanied by enhanced tumoral goblet cell differentiation and decreased colonic PD-L1 and splenic CD3ε, as well as PD-1 immune checkpoint expression. In vitro, glucose-free, high-amino acid culture conditions reduced proliferation but improved goblet cell differentiation of murine and human CRC cell lines MC-38 and HT29-MTX in combination with down-regulation of PD-L1 expression. We here found GFHPD to systemically dampen glycolysis activity, thereby reducing CRC progression with a similar efficacy to EGFR-directed antibody therapy.

Evaluation of the Molecular Mechanisms of Sepsis Using Proteomics

Sepsis is a complex syndrome promoted by pathogenic and host factors; it is characterized by dysregulated host responses and multiple organ dysfunction, which can lead to death. However, its underlying molecular mechanisms remain unknown. Proteomics, as a biotechnology research area in the post-genomic era, paves the way for large-scale protein characterization. With the rapid development of proteomics technology, various approaches can be used to monitor proteome changes and identify differentially expressed proteins in sepsis, which may help to understand the pathophysiological process of sepsis. Although previous reports have summarized proteomics-related data on the diagnosis of sepsis and sepsis-related biomarkers, the present review aims to comprehensively summarize the available literature concerning “sepsis”, “proteomics”, “cecal ligation and puncture”, “lipopolysaccharide”, and “post-translational modifications” in relation to proteomics research to provide novel insights into the molecular mechanisms of sepsis.

Acute high-intensity exercise and skeletal muscle mitochondrial respiratory function: role of metabolic perturbation

Recently it was documented that fatiguing, high-intensity exercise resulted in a significant attenuation in maximal skeletal muscle mitochondrial respiratory capacity, potentially due to the intramuscular metabolic perturbation elicited by such intense exercise. With the utilization of intrathecal fentanyl to attenuate afferent feedback from group III/IV muscle afferents, permitting increased muscle activation and greater intramuscular metabolic disturbance, this study aimed to better elucidate the role of metabolic perturbation on mitochondrial respiratory function. Eight young, healthy males performed high-intensity cycle exercise in control (CTRL) and fentanyl-treated (FENT) conditions. Liquid chromatography-mass spectrometry and high-resolution respirometry were used to assess metabolites and mitochondrial respiratory function, respectively, pre- and postexercise in muscle biopsies from the vastus lateralis. Compared with CTRL, FENT yielded a significantly greater exercise-induced metabolic perturbation (PCr: -67% vs. -82%, Pi: 353% vs. 534%, pH: -0.22 vs. -0.31, lactate: 820% vs. 1,160%). Somewhat surprisingly, despite this greater metabolic perturbation in FENT compared with CTRL, with the only exception of respiratory control ratio (RCR) (-3% and -36%) for which the impact of FENT was significantly greater, the degree of attenuated mitochondrial respiratory capacity postexercise was not different between CTRL and FENT, respectively, as assessed by maximal respiratory flux through complex I (-15% and -33%), complex II (-36% and -23%), complex I + II (-31% and -20%), and state 3_CI+CII control ratio (-24% and -39%). Although a basement effect cannot be ruled out, this failure of an augmented metabolic perturbation to extensively further attenuate mitochondrial function questions the direct role of high-intensity exercise-induced metabolite accumulation in this postexercise response.

Structure and Mechanism of Respiratory III-IV Supercomplexes in Bioenergetic Membranes

In the final steps of energy conservation in aerobic organisms, free energy from electron transfer through the respiratory chain is transduced into a proton electrochemical gradient across a membrane. In mitochondria and many bacteria, reduction of the dioxygen electron acceptor is catalyzed by cytochrome c oxidase (complex IV), which receives electrons from cytochrome bc1 (complex III), via membrane-bound or water-soluble cytochrome c. These complexes function independently, but in many organisms they associate to form supercomplexes. Here, we review the structural features and the functional significance of the nonobligate III2IV1/2 Saccharomyces cerevisiae mitochondrial supercomplex as well as the obligate III2IV2 supercomplex from actinobacteria. The analysis is centered around the Q-cycle of complex III, proton uptake by CytcO, as well as mechanistic and structural solutions to the electronic link between complexes III and IV.

Responses of microRNA and predicted mRNA and enzymatic targets in liver of two salmonids (Oncorhynchus mykiss and Salvelinus fontinalis) following air exposure

The acute stress response is well-characterized, with rainbow trout as a teleost model for physiological and molecular responses. Air exposure, which stimulates an acute stress response, modulates liver microRNAs in rainbow trout; however, these highly conserved non-coding RNAs that bind to mRNA and repress translation, have never been measured in brook trout and it is unknown how miRNA expression responds following air exposure in this less studied salmonid. Our objective was to characterize the effects of air exposure on rainbow and brook trout liver miRNA expression, as well as the mRNA expression and enzyme activity that the miRNAs are predicted to target. Brook and rainbow trout were sampled pre- and 1-, 3-, and 24-h post- a three-minute air exposure. Plasma cortisol, glucose, and lactate were measured. Relative expression of miR-21a-5p, miR-143-3p, let-7a-5p and relative expression and enzyme activities of five predicted targets (pyruvate kinase, glucokinase, citrate synthase, cytochrome c oxidase, and catalase) were measured in liver. Rainbow and brook trout both had increases in plasma cortisol and lactate, while only rainbow trout had significant post-stress increases in plasma glucose. Furthermore, both trout species had increased miR-143-3p and miR-21a-5p relative expression 24-h post-stress. Four of the five enzymes measured had altered activity following stress. Brook trout miRNAs had inverse relative expression with relative catalase mRNA expression and cytochrome c oxidase enzyme activity, but no relationship was found in rainbow trout. Therefore, we have further characterized the transcriptional and enzymatic response to air exposure in two salmonids.

Evaluation of dietary selenium, vitamin C and E as the multi-antioxidants on the methylmercury intoxicated mice based on mercury bioaccumulation, antioxidant enzyme activity, lipid peroxidation and mitochondrial oxidative stress

Mercury (Hg) in high exposures can be a potent life threatening heavy metal that bioaccumulate in aquatic food-chain mainly as organic methylmercury (MeHg). In this regard, fish and seafood consumptions could be the primary sources of MeHg exposure for human and fish-eating animals. The objective of the present study was to elucidate the effects of dietary supplementation of some antioxidants on induced mercury toxicity in mice model. In this study, a 30-day long investigation has been conducted to evaluate the dietary effect of selenium (Se) in combination with vitamin C and vitamin E on methylmercury induced toxicity in mice. Total 54 mice fed the diets with three levels of Hg (0, 50 or 500 μg kg^-1) and two levels of Se in combination with vitamin C and E (Se: 0, 2 mg kg^-1; vitamin C: 0, 400 mg kg^-1; vitamin E: 0, 200 mg kg^-1) in triplicates. The results show that Hg accumulated in blood and different tissues such as muscle, liver and kidney tissues of mice on dose dependent manner. The bioaccumulation pattern of dietary Hg, in decreasing order, kidney > liver > muscle > blood. Superoxide dismutase levels in blood serum showed no significant differences in mice fed the diets. However, dietary antioxidants significantly reduced the levels of thiobarbituric acid reactive substances in mice fed the mercury containing diets. Cytochrome c oxidase enzyme activities showed no significant differences as the mercury level increases in liver and kidney tissues of mice. Kaplan-Meier curve showed a dose- and time-dependent survivability of mice. Cumulative survival rate of Hg intoxicated mice fed the antioxidant supplemented diets were increased during the experimental period. Overall, the results showed that dietary Se, vitamin C and vitamin E had no effect on reducing the mercury bioaccumulation in tissues but reduced the serum lipid peroxidation as well as prolonged the cumulative survival rate in terms of high Hg exposures in mice.

Outer and inner mitochondrial membrane proteins TOMM40 and TIMM50 are intensively concentrated and localized at Purkinje and pyramidal neurons in the New Zealand white rabbit brain

Mitochondria are involved in a variety of developmental processes and neurodegenerative diseases. The translocase complexes of the outer and inner mitochondrial membranes (TOM and TIM) are protein complexes involved in transporting protein precursors across mitochondrial membranes. Although rabbits are important animal models for neurodegenerative diseases, the expression of TOM and TIM complexes has yet to be examined in the rabbit brain. In the present study, we quantitatively evaluated the protein expression of the translocase of outer mitochondrial membrane 40 (TOMM40) and inner mitochondrial membrane 50 (TIMM50) complexes, two of the TOM/TIM complexes, in the cerebral, cerebellar, and hippocampal cortices of the New Zealand white rabbit brain, using immunohistochemistry. Sections from brain specimens were initially stained for cytochrome c oxidase (COX), a well-known mitochondrial marker, which was found to be homogeneously expressed in the cerebrum, but localized to the Purkinje and pyramidal neurons of the cerebellum and hippocampus, respectively. TOMM40 and TIMM50 proteins consistently revealed a similar expression pattern, although at different ratios. In the cerebrum, TOMM40 and TIMM50 immunoreactions were homogeneously distributed within the cytoplasm of various neurons. Meanwhile, Purkinje cells in the cerebellum and pyramidal neurons in the hippocampus displayed higher intensities in their cytoplasm. The specific cellular localization of TOMM40 and TIMM50 proteins in various regions of the rabbit brain suggests a distinct function of each protein in these regions. Further analysis will be required to evaluate the molecular functions of these proteins.

Possible Effects of Beetroot Supplementation on Physical Performance Through Metabolic, Neuroendocrine, and Antioxidant Mechanisms: A Narrative Review of the Literature

Athletes often seek to use dietary supplements to increase performance during exercise. Among various supplements, much attention has been paid to beetroot in recent years. Beetroot is a source of carbohydrates, fiber, protein, minerals, and vitamins; also, it is a natural source of nitrate and associated with improved sports performance. Nitrates can the modification of skeletal muscle contractile proteins or calcium handling after translation. The time to reach the peak plasma nitrate is between 1 and 3 h after consumption of a single dose of nitrate. Nitrate is metabolized by conversion to nitrite and subsequently nitric oxide. Beetroot can have various effects on athletic performance through nitric oxide. Nitric oxide is an intracellular and extracellular messenger for regulating certain cellular functions and causes vasodilation of blood vessels and increases blood flow. Nitric oxide seems to be effective in improving athletic performance by increasing oxygen, glucose, and other nutrients for better muscle fueling. Nitric oxide plays the main role in anabolic hormones, modulates the release of several neurotransmitters and the major mediators of stress involved in the acute hypothalamic-pituitary-adrenal response to exercise. Beetroot is an important source of compounds such as ascorbic acid, carotenoids, phenolic acids, flavonoids, betaline, and highly active phenolics and has high antioxidant properties. Beetroot supplement provides an important source of dietary polyphenols and due to the many health benefits. Phytochemicals of Beetroot through signaling pathways inhibit inflammatory diseases. In this study, the mechanisms responsible for these effects were examined and the research in this regard was reviewed.

S100B/RAGE/Ceramide signaling pathway is involved in sepsis-associated encephalopathy

AIMS

Sepsis-associated encephalopathy (SAE) is one of the most common complications of sepsis, and it might lead to long-term cognitive dysfunction and disability. This study aimed to explore the role of S100 calcium binding protein B (S100B)/RAGE/ceramide signaling pathway in SAE.

MAIN METHODS

FPS-ZM1 (an inhibitor of RAGE), myriocin and GW4869 (an inhibitor of ceramide) were used to explore the role of S100B/RAGE/ceramide in acute brain injury and long-term cognitive impairment in sepsis. In addition, Mdivi-1 (inhibitor of Drp1) and Drp1 siRNA were utilized to assess the effects of C2-ceramide on neuronal mitochondria, and to explore the specific underlying mechanism in C2 ceramide-induced death of HT22 mouse hippocampal neuronal cells.

KEY FINDINGS

Western blot analysis showed that sepsis significantly up-regulated S100B and RAGE. Nissl staining and Morris water maze (MWM) test revealed that inhibition of RAGE with FPS-ZM1 markedly attenuated cecal ligation and puncture (CLP)-induced brain damage and cognitive dysfunction. Furthermore, FPS-ZM1 relieved sepsis-induced C2-ceramide accumulation and abnormal mitochondrial dynamics. Moreover, inhibition of ceramide also showed similar protective effects both in vivo and in vitro. Furthermore, Mdivi-1 and Drp1 siRNA significantly reduced C2-ceramide-induced neuronal mitochondrial fragmentation and cell apoptosis in vitro.

SIGNIFICANCE

This study confirmed that S100B regulates mitochondrial dynamics through RAGE/ceramide pathway, in addition to the role of this pathway in acute brain injury and long-term cognitive impairment during sepsis.

Multiple Mechanisms Regulate Eukaryotic Cytochrome C Oxidase

Cytochrome c oxidase (COX), the rate-limiting enzyme of mitochondrial respiration, is regulated by various mechanisms. Its regulation by ATP (adenosine triphosphate) appears of particular importance, since it evolved early during evolution and is still found in cyanobacteria, but not in other bacteria. Therefore the "allosteric ATP inhibition of COX" is described here in more detail. Most regulatory properties of COX are related to "supernumerary" subunits, which are largely absent in bacterial COX. The "allosteric ATP inhibition of COX" was also recently described in intact isolated rat heart mitochondria.

Similarities and differences in metabolites of tongue cancer cells among two- and three-dimensional cultures and xenografts

Metabolic programming of cancer cells is an essential step in transformation and tumor growth. We established two-dimensional (2D) monolayer and three-dimensional (3D) cultures, the latter called a "tissueoid cell culture system", using four types of tongue cancer cell lines. We also undertook a comprehensive metabolome analysis of three groups that included xenografts created by transplanting the cell lines into nude mice. In addition, we undertook a functional analysis of the mitochondria, which plays a key role in cancer metabolism. Principal component analysis revealed the plots of the four cell lines to be much narrower in 2D culture than in 3D culture and xenograft groups. Moreover, compared to xenografts, the 2D culture had significantly lower levels of most metabolites. These results suggest that the unique characteristics of each cell disappeared in 2D culture, and a type of metabolism unique to monolayer culture took over. Conversely, ATP production, biomass synthesis, and maintenance of redox balance were shown in 3D culture using sufficient nutrients, which closely resembled the metabolic activity in the xenografts. However, there were several differences between the metabolic activity in the 3D culture and xenografts. In vivo, the cancer tissue had blood flow with stromal cells present around the cancer cells. In the xenografts, we detected metabolized and degraded products in the liver and other organs of the host mice. Furthermore, the 3D system did not show impairment of mitochondrial function in the cancer cells, suggesting that cancer cells produce energy simultaneously through mitochondria, as well as aerobic glycolysis.

Cytochrome C Oxidase Subunit 4 (COX4): A Potential Therapeutic Target for the Treatment of Medullary Thyroid Cancer

The nuclear-encoded subunit 4 of cytochrome c oxidase (COX4) plays a role in regulation of oxidative phosphorylation and contributes to cancer progression. We sought to determine the role of COX4 in differentiated (DTC) and medullary (MTC) thyroid cancers. We examined the expression of COX4 in human thyroid tumors by immunostaining and used shRNA-mediated knockdown of COX4 to evaluate its functional contributions in thyroid cancer cell lines. In human thyroid tissue, the expression of COX4 was higher in cancers than in either normal thyroid (p = 0.0001) or adenomas (p = 0.001). The level of COX4 expression correlated with tumor size (p = 0.04) and lymph-node metastases (p = 0.024) in patients with MTCs. COX4 silencing had no effects on cell signaling activation and mitochondrial respiration in DTC cell lines (FTC133 and BCPAP). In MTC-derived TT cells, COX4 silencing inhibited p70S6K/pS6 and p-ERK signaling, and was associated with decreased oxygen consumption and ATP production. Treatment with potassium cyanide had minimal effects on FTC133 and BCPAP, but inhibited mitochondrial respiration and induced apoptosis in MTC-derived TT cells. Our data demonstrated that metastatic MTCs are characterized by increased expression of COX4, and MTC-derived TT cells are vulnerable to COX4 silencing. These data suggest that COX4 can be considered as a novel molecular target for the treatment of MTC.

COX5B-Mediated Bioenergetic Alteration Regulates Tumor Growth and Migration by Modulating AMPK-UHMK1-ERK Cascade in Hepatoma

The oxidative phosphorylation machinery in mitochondria, which generates the main bioenergy pool in cells, includes four enzyme complexes for electron transport and ATP synthase. Among them, the cytochrome c oxidase (COX), which constitutes the fourth complex, has been suggested as the major regulatory site. Recently, abnormalities in COX were linked to tumor progression in several cancers. However, it remains unclear whether COX and its subunits play a role in tumor progression of hepatoma. To search for the key regulatory factor(s) in COX for hepatoma development, in silico analysis using public transcriptomic database followed by validation for postoperative outcome associations using independent in-house patient cohorts was performed. In which, COX5B was highly expressed in hepatoma and associated with unfavorable postoperative prognosis. In addressing the role of COX5B in hepatoma, the loss- and gain-of-function experiments for COX5B were conducted. Consequently, COX5B expression was associated with increased hepatoma cell proliferation, migration and xenograft growth. Downstream effectors searched by cDNA microarray analysis identified UHMK1, an oncogenic protein, which manifested a positively correlated expression level of COX5B. The COX5B-mediated regulatory event on UHMK1 expression was subsequently demonstrated as bioenergetic alteration-dependent activation of AMPK in hepatoma cells. Phosphoproteomic analysis uncovered activation of ERK- and stathmin-mediated pathways downstream of UHMK1. Finally, comprehensive phenotypic assays supported the impacts of COX5B-UHMK1-ERK axis on hepatoma cell growth and migration.

Stress-mediated generation of deleterious ROS in healthy individuals - role of cytochrome c oxidase

Psychosocial stress is known to cause an increased incidence of coronary heart disease. In addition, multiple other diseases like cancer and diabetes mellitus have been related to stress and are mainly based on excessive formation of reactive oxygen species (ROS) in mitochondria. The molecular interactions between stress and ROS, however, are still unknown. Here we describe the missing molecular link between stress and an increased cellular ROS, based on the regulation of cytochrome c oxidase (COX). In normal healthy cells, the "allosteric ATP inhibition of COX" decreases the oxygen uptake of mitochondria at high ATP/ADP ratios and keeps the mitochondrial membrane potential (ΔΨm) low. Above ΔΨm values of 140 mV, the production of ROS in mitochondria increases exponentially. Stress signals like hypoxia, stress hormones, and high glutamate or glucose in neurons increase the cytosolic Ca2+ concentration which activates a mitochondrial phosphatase that dephosphorylates COX. This dephosphorylated COX exhibits no allosteric ATP inhibition; consequently, an increase of ΔΨm and ROS formation takes place. The excess production of mitochondrial ROS causes apoptosis or multiple diseases.

Mitochondrial Dysfunction and Parkinson's Disease-Near-Infrared Photobiomodulation as a Potential Therapeutic Strategy

As the main driver of energy production in eukaryotes, mitochondria are invariably implicated in disorders of cellular bioenergetics. Given that dopaminergic neurons affected in Parkinson's disease (PD) are particularly susceptible to energy fluctuations by their high basal energy demand, it is not surprising to note that mitochondrial dysfunction has emerged as a compelling candidate underlying PD. A recent approach towards forestalling dopaminergic neurodegeneration in PD involves near-infrared (NIR) photobiomodulation (PBM), which is thought to enhance mitochondrial function of stimulated cells through augmenting the activity of cytochrome C oxidase. Notwithstanding this, our understanding of the neuroprotective mechanism of PBM remains far from complete. For example, studies focusing on the effects of PBM on gene transcription are limited, and the mechanism through which PBM exerts its effects on distant sites (i.e., its "abscopal effect") remains unclear. Also, the clinical application of NIR in PD proves to be challenging. Efficacious delivery of NIR light to the substantia nigra pars compacta (SNpc), the primary site of disease pathology in PD, is fraught with technical challenges. Concerted efforts focused on understanding the biological effects of PBM and improving the efficiency of intracranial NIR delivery are therefore essential for its successful clinical translation. Nonetheless, PBM represents a potential novel therapy for PD. In this review, we provide an update on the role of mitochondrial dysfunction in PD and how PBM may help mitigate the neurodegenerative process. We also discussed clinical translation aspects of this treatment modality using intracranially implanted NIR delivery devices.

Cytochrome c Oxidase Subunit 4 Isoform Exchange Results in Modulation of Oxygen Affinity

Cytochrome c oxidase (COX) is regulated through tissue-, development- or environment-controlled expression of subunit isoforms. The COX4 subunit is thought to optimize respiratory chain function according to oxygen-controlled expression of its isoforms COX4i1 and COX4i2. However, biochemical mechanisms of regulation by the two variants are only partly understood. We created an HEK293-based knock-out cellular model devoid of both isoforms (COX4i1/2 KO). Subsequent knock-in of COX4i1 or COX4i2 generated cells with exclusive expression of respective isoform. Both isoforms complemented the respiratory defect of COX4i1/2 KO. The content, composition, and incorporation of COX into supercomplexes were comparable in COX4i1- and COX4i2-expressing cells. Also, COX activity, cytochrome c affinity, and respiratory rates were undistinguishable in cells expressing either isoform. Analysis of energy metabolism and the redox state in intact cells uncovered modestly increased preference for mitochondrial ATP production, consistent with the increased NADH pool oxidation and lower ROS in COX4i2-expressing cells in normoxia. Most remarkable changes were uncovered in COX oxygen kinetics. The p₅₀ (partial pressure of oxygen at half-maximal respiration) was increased twofold in COX4i2 versus COX4i1 cells, indicating decreased oxygen affinity of the COX4i2-containing enzyme. Our finding supports the key role of the COX4i2-containing enzyme in hypoxia-sensing pathways of energy metabolism.

Transcriptome profiling of differentially expressed genes in cytoplasmic male-sterile line and its fertility restorer line in pigeon pea (Cajanus cajan L.)

BACKGROUND

Pigeon pea (Cajanus cajan L.) is the sixth major legume crop widely cultivated in the Indian sub-continent, Africa, and South-east Asia. Cytoplasmic male-sterility (CMS) is the incompetence of flowering plants to produce viable pollens during anther development. CMS has been extensively utilized for commercial hybrid seeds production in pigeon pea. However, the molecular basis governing CMS in pigeon pea remains unclear and undetermined. In this study transcriptome analysis for exploring differentially expressed genes (DEGs) between cytoplasmic male-sterile line (AKCMS11) and its fertility restorer line (AKPR303) was performed using Illumina paired-end sequencing.

RESULTS

A total of 3167 DEGs were identified, of which 1432 were up-regulated and 1390 were down-regulated in AKCMS11 in comparison to AKPR303. By querying, all the 3167 DEGs against TAIR database, 34 pigeon pea homologous genes were identified, few involved in pollen development (EMS1, MS1, ARF17) and encoding MYB and bHLH transcription factors with lower expression in the sterile buds, implying their possible role in pollen sterility. Many of these DEGs implicated in carbon metabolism, tricarboxylic acid cycle (TCA), oxidative phosphorylation and elimination of reactive oxygen species (ROS) showed reduced expression in the AKCMS11 (sterile) buds.

CONCLUSION

The comparative transcriptome findings suggest the potential role of these DEGs in pollen development or abortion, pointing towards their involvement in cytoplasmic male-sterility in pigeon pea. The candidate DEGs identified in this investigation will be highly significant for further research, as they could lend a comprehensive basis in unravelling the molecular mechanism governing CMS in pigeon pea.

Chronic exposure to environmentally relevant levels of simvastatin disrupts zebrafish brain gene signaling involved in energy metabolism

Simvastatin (SIM), a hypocholesterolaemic drug belonging to the statins group, is a widely prescribed pharmaceutical for prevention of cardiovascular diseases. Several studies showed that lipophilic statins, as SIM, cross the blood-brain barrier and interfere with the energy metabolism of the central nervous system in humans and mammalian models. In fish and other aquatic organisms, the effects of SIM on the brain energy metabolism are unknown, particularly following exposure to low environmentally relevant concentrations. Therefore, the present study aimed at investigating the influence of SIM on gene signaling pathways involved in brain energy metabolism of adult zebrafish (Danio rerio) following chronic exposure (90 days) to environmentally relevant SIM concentrations ranging from 8 ng/L to 1000 ng/L. Real-time PCR was used to determine the transcript levels of several genes involved in different pathways of the brain energy metabolism (glut1b, gapdh, acadm, accα, fasn, idh3a, cox4i1, and cox5aa). The findings here reported integrated well with ecological and biochemical responses obtained in a parallel study. Data demonstrated that SIM modulates transcription of key genes involved in the mitochondrial electron transport chain, in glucose transport and metabolism, in fatty acid synthesis and β-oxidation. Further, SIM exposure led to a sex-dependent transcription profile for some of the studied genes. Overall, the present study demonstrated, for the first time, that SIM modulates gene regulation of key pathways involved in the energy metabolism in fish brain at environmentally relevant concentrations.

Adaptation of aerobic training essentially involved autophagy, mitochondrial marker and muscle fibre genetic modulation in rat cardiac muscles

Information about the role of moderate acute treadmill training in modulating autophagy and mitochondrial markers that might be correlated with alteration of muscle fibre gene expression in rat cardiac muscles is very limited. In this present study, the researchers divided twenty male Wistar rats into four groups: sedentary control, 3, 6 and 15 days and subjected them to treadmill training with moderate intensity (20 m/min), 30 min each day. RNA was extracted from cardiac muscles and stored in temperature of -80°C. Specific primers were utilized for semi-quantitative PCR. Treadmill training decreased autophagy-related gene expression (LC3, p62) and upper stream signalling of autophagy (PIK3CA, Akt and mTOR) in 3 and 6 d, but stimulated gene expression of mitochondrial markers (PGC1α, Cox1, Cox2 and Cox4) in 15 days. αMHC gene expression increased while βMHC gene expression decreased in 15 days. In line with this, autophagy-related genes increased in 3 and 6 days and returned to baseline in 15 days. The increment in mitochondrial gene expression might be correlated with shifting gene expression of αMHC and βMHC in 15 days. Taken together, acute adaptation in cardiac muscles is stimulated by genetic modulation of autophagy, mitochondrial marker and muscle fibre that may explain physiological cardiac adaptation after training. This study can be used as a reference for optimizing performance in period of cardiac muscle adaptation stimulated by treadmill training.

Explaining leak states in the proton pump of heme-copper oxidases observed in single-molecule experiments

Heme-copper oxidases couple the exergonic oxygen reduction with the endergonic proton translocation. Redox-linked structural changes have been localized in deeply buried regions of the protein, near the low-potential heme. How these movements can modulate distant gating events along the intramolecular proton path, where the entry (exit) of pumped proton occurs, is a major concern for the proton pump models. Generally, these models associate, more or less directly, all translocation events with redox transitions. Although they can account for many phenomenological aspects of the pump, evidences from single-molecules experiments about leak states of the pump represent a formidable challenge. Disconnecting the redox-linked pK_a shifts of the proton loading site from the external barriers, we obtain a simple stochastic mechanism which behaves similarly to the real enzyme, able to reverse the flow of the proton transfer.

Acute High-Intensity Exercise Impairs Skeletal Muscle Respiratory Capacity

PURPOSE

The effect of an acute bout of exercise, especially high-intensity exercise, on the function of mitochondrial respiratory complexes is not well understood, with potential implications for both the healthy population and patients undergoing exercise-based rehabilitation. Therefore, this study sought to comprehensively examine respiratory flux through the different complexes of the electron transport chain in skeletal muscle mitochondria before and immediately after high-intensity aerobic exercise.

METHODS

Muscle biopsies of the vastus lateralis were obtained at baseline and immediately after a 5-km time trial performed on a cycle ergometer. Mitochondrial respiratory flux through the complexes of the electron transport chain was measured in permeabilized skeletal muscle fibers by high-resolution respirometry.

RESULTS

Complex I + II state 3 (state 3CI + CII) respiration, a measure of oxidative phosphorylation capacity, was diminished immediately after the exercise (pre, 27 ± 3 ρm·mg·s; post, 17 ± 2 ρm·mg·s; P < 0.05). This decreased oxidative phosphorylation capacity was predominantly the consequence of attenuated complex II-driven state 3 (state 3CII) respiration (pre, 17 ± 1 ρm·mg·s; post, 9 ± 2 ρm·mg·s; P < 0.05). Although complex I-driven state 3 (3CI) respiration was also lower (pre, 20 ± 2 ρm·mg·s; post, 14 ± 4 ρm·mg·s), this did not reach statistical significance (P = 0.27). In contrast, citrate synthase activity, proton leak (state 2 respiration), and complex IV capacity were not significantly altered immediately after the exercise.

CONCLUSIONS

These findings reveal that acute high-intensity aerobic exercise significantly inhibits skeletal muscle state 3CII and oxidative phosphorylation capacity. This, likely transient, mitochondrial defect might amplify the exercise-induced development of fatigue and play an important role in initiating exercise-induced mitochondrial adaptations.

Neuroprotective Role of Hypothermia in Hypoxic-ischemic Brain Injury: Combined Therapies using Estrogen

Hypoxic-ischemic brain injury is a complex network of factors, which is mainly characterized by a decrease in levels of oxygen concentration and blood flow, which lead to an inefficient supply of nutrients to the brain. Hypoxic-ischemic brain injury can be found in perinatal asphyxia and ischemic-stroke, which represent one of the main causes of mortality and morbidity in children and adults worldwide. Therefore, knowledge of underlying mechanisms triggering these insults may help establish neuroprotective treatments. Selective Estrogen Receptor Modulators and Selective Tissue Estrogenic Activity Regulators exert several neuroprotective effects, including a decrease of reactive oxygen species, maintenance of cell viability, mitochondrial survival, among others. However, these strategies represent a traditional approach of targeting a single factor of pathology without satisfactory results. Hence, combined therapies, such as the administration of therapeutic hypothermia with a complementary neuroprotective agent, constitute a promising alternative. In this sense, the present review summarizes the underlying mechanisms of hypoxic-ischemic brain injury and compiles several neuroprotective strategies, including Selective Estrogen Receptor Modulators and Selective Tissue Estrogenic Activity Regulators, which represent putative agents for combined therapies with therapeutic hypothermia.

Essential roles of mitochondrial and heme function in lung cancer bioenergetics and tumorigenesis

Contrary to Warburg’s hypothesis, mitochondrial oxidative phosphorylation (OXPHOS) contributes significantly to fueling cancer cells. Several recent studies have demonstrated that radiotherapy-resistant and chemotherapy-resistant cancer cells depend on OXPHOS for survival and progression. Several cancers exhibit an increased risk in association with heme intake. Mitochondria are widely known to carry out oxidative phosphorylation. In addition, mitochondria are also involved in heme synthesis. Heme serves as a prosthetic group for several proteins that constitute the complexes of mitochondrial electron transport chain. Therefore, heme plays a pivotal role in OXPHOS and oxygen consumption. Further, lung cancer cells exhibit heme accumulation and require heme for proliferation and invasion in vitro. Abnormalities in mitochondrial biogenesis and mutations are implicated in cancer. This review delves into mitochondrial OXPHOS and lesser explored area of heme metabolism in lung cancer.

Myocardial insufficiency is related to reduced subunit 4 content of cytochrome c oxidase

BACKGROUND

Treatment of heart failure remains one of the most challenging task for intensive care medicine, cardiology and cardiac surgery. New options and better indicators are always required. Understanding the basic mechanisms underlying heart failure promote the development of adjusted therapy e.g. assist devices and monitoring of recovery. If cardiac failure is related to compromised cellular respiration of the heart, remains unclear. Myocardial respiration depends on Cytochrome c- Oxidase (CytOx) activity representing the rate limiting step for the mitochondrial respiratory chain. The enzymatic activity as well as mRNA expression of enzyme's mitochondrial encoded catalytic subunit 2, nuclear encoded regulatory subunit 4 and protein contents were studied in biopsies of cardiac patients suffering from myocardial insufficiency and dilated cardiomyopathy (DCM).

METHODS

Fifty-four patients were enrolled in the study and underwent coronary angiography. Thirty male patients (mean age: 45 +/- 15 yrs.) had a reduced ejection fraction (EF) 35 ± 12% below 45% and a left ventricular end diastolic diameter (LVEDD) of 71 ± 10 mm bigger than 56 mm. They were diagnosed as having idiopathic dilated cardiomyopathy (DCM) without coronary heart disease and NYHA-class 3 and 4. Additionally, 24 male patients (mean age: 52 +/- 11 yrs.) after exclusion of secondary cardiomyopathies, coronary artery or valve disease, served as control (EF: 68 ± 7, LVEDD: 51 ± 7 mm). Total RNA was extracted from two biopsies of each person. Real-time PCR analysis was performed with specific primers followed by a melt curve analysis. Corresponding protein expression in the tissue was studied with immune-histochemistry while enzymatic activity was evaluated by spectroscopy.

RESULTS

Gene and protein expression analysis of patients showed a significant decrease of subunit 4 (1.1 vs. 0.6, p < 0.001; 7.7 ± 3.1% vs. 2.8 ± 1.4%, p < 0.0001) but no differences in subunit 2. Correlations were found between reduced subunit 2 expression, low EF (r = 0.766, p < 0.00045) and increased LVEDD (r = 0.492, p < 0.0068). In case of DCM less subunit 4 expression and reduced shortening fraction (r = 0.524, p < 0.017) was found, but enzymatic activity was higher (0.08 ± 0.06 vs. 0.26 ± 0.08 U/mg, p < 0.001) although myocardial oxygen consumption continued to the same extent.

CONCLUSION

In case of myocardial insufficiency and DCM, decreased expression of COX 4 results in an impaired CytOx activity. Higher enzymatic activity but equal oxygen consumption contribute to the pathophysiology of the myocardial insufficiency and appears as an indicator of oxidative stress. This kind of dysregulation should be in the focus for the development of diagnostic and therapy procedures.

Comparison of Pre- and Post-translational Expressions of COXIV-1 and MT-ATPase 6 Genes in Colorectal Adenoma-Carcinoma Tissues

OBJECTIVE

Colorectal cancer (CRC) develops from precancerous adenomatous polyps to malignant lesions of adenocarcinoma. Elucidating inhibition mechanisms for this route in patients with a risk of developing CRC is highly important for a potential diagnostic or prognostic marker. Differential expression of nuclear-encoded cytochrome c oxidase subunit 4 (COXIV) seems to contribute to a more unregulated respiration due to loss of ATP inhibition. Majority of energy for tumor transformations are mitochondrial origin. Differences in mitochondrial efficiency may be reflected in the progression of colorectal adenomatous polyps to adenocarcinomas. Here, we evaluate expression levels of COXIV isoform 1 (COXIV-1) and Mitochondrial (MT)-ATP synthase Subunit 6 (ATPase6) in adenomas of tubular, tubulovillous and villous tissues as compared to adenocarcinoma tissues.

METHOD

Both RT-qPCR and western blot techniques were used to assess COXIV-1 and ATPase6 expression levels in 42 pairs of patients' tissue samples. Protein carbonyl assay was performed to determine levels of oxidized proteins, as a measurement of ROS productions, in the tissue samples.

RESULTS

Differential RNA expression levels of COXIV-1 and ATPase6 from whole tissues were observed. Interestingly, RNA expression levels obtained from mitochondrial for COXIV-1 were significantly decreased in tubulovillous, villous adenomas and adenocarcinoma, but not in the tubular-polyps. Moreover, mitochondrial ATPase6 RNA expression levels decreased progressively from adenopolyps to adenocarcinoma. In mitochondrial protein, expression levels of both genes progressively decreased with a three folds from adenomatous polyps to adenocarcinoma. Whilst the ATPase6 protein expression significantly decreased in adenocarcinoma compared to villous, conversely, the levels of oxidized carbonyl proteins were considerably increased from adenomatous polyps to adenocarcinoma.

CONCLUSION

Our findings provide evidence that decreased mitochondrial protein expression of COXIV-1 and ATPase6 correlates with increased ROS production during colorectal adenomatous polyps' progression, suggesting the pivotal role of COXIV-1 in energy metabolism of colorectal cells as they progress from polyps to carcinoma.

Oxidative stress and mitochondrial adaptive shift during pituitary tumoral growth

The cellular transformation of normal functional cells to neoplastic ones implies alterations in the cellular metabolism and mitochondrial function in order to provide the bioenergetics and growth requirements for tumour growth progression. Currently, the mitochondrial physiology and dynamic shift during pituitary tumour development are not well understood. Pituitary tumours present endocrine neoplastic benign growth which, in previous reports, we had shown that in addition to increased proliferation, these tumours were also characterized by cellular senescence signs with no indication of apoptosis. Here, we show clear evidence of oxidative stress in pituitary cells, accompanied by bigger and round mitochondria during tumour development, associated with augmented biogenesis and an increased fusion process. An activation of the Nrf2 stress response pathway together with the attenuation of the oxidative damage signs occurring during tumour development were also observed which will probably provide survival advantages to the pituitary cells. These neoplasms also presented a progressive increase in lactate production, suggesting a metabolic shift towards glycolysis metabolism. These findings might imply an oxidative stress state that could impact on the pathogenesis of pituitary tumours. These data may also reflect that pituitary cells can modulate their metabolism to adapt to different energy requirements and signalling events in a pathophysiological situation to obtain protection from damage and enhance their survival chances. Thus, we suggest that mitochondria function, oxidative stress or damage might play a critical role in pituitary tumour progression.

An assay of optimal cytochrome c oxidase activity in fish gills

Cytochrome c oxidase (COX) catalyzes the terminal oxidation reaction in the electron transport chain (ETC) of aerobic respiratory systems. COX activity is an important indicator for the evaluation of energy production by aerobic respiration in various tissues. On the basis of the respiratory characteristics of muscle, we established an optimal method for the measurement of maximal COX activity. To validate the measurement of cytochrome c absorbance, different ionic buffer concentrations and tissue homogenate protein concentrations were used to investigate COX activity. The results showed that optimal COX activity is achieved when using 50-100 μg fish gill homogenate in conjunction with 75-100 mM potassium phosphate buffer. Furthermore, we compared branchial COX activities among three species of euryhaline teleost (Chanos chanos, Oreochromis mossambicus, and Oryzias dancena) to investigate differences in aerobic respiration of osmoregulatory organs. COX activities in the gills of these three euryhaline species were compared with COX subunit 4 (COX4) protein levels. COX4 protein abundance and COX activity patterns in the three species occurring in environments with various salinities increased when fish encountered salinity challenges. This COX activity assay therefore provides an effective and accurate means of assessing aerobic metabolism in fish.

Role of the Bone Microenvironment in the Development of Painful Complications of Skeletal Metastases

Cancer-induced bone pain (CIBP) is the most common and painful complication in patients with bone metastases. It causes a significant reduction in patient quality of life. Available analgesic treatments for CIBP, such as opioids that target the central nervous system, come with severe side effects as well as the risk of abuse and addiction. Therefore, alternative treatments for CIBP are desperately needed. Although the exact mechanisms of CIBP have not been fully elucidated, recent studies using preclinical models have demonstrated the role of the bone marrow microenvironment (e.g., osteoclasts, osteoblasts, macrophages, mast cells, mesenchymal stem cells, and fibroblasts) in CIBP development. Several clinical trials have been performed based on these findings. CIBP is a complex and challenging condition that currently has no standard effective treatments other than opioids. Further studies are clearly warranted to better understand this painful condition and develop more effective and safer targeted therapies.

Repositioning chlorpromazine for treating chemoresistant glioma through the inhibition of cytochrome c oxidase bearing the COX4-1 regulatory subunit

Patients with glioblastoma have one of the lowest overall survival rates among patients with cancer. Standard of care for patients with glioblastoma includes temozolomide and radiation therapy, yet 30% of patients do not respond to these treatments and nearly all glioblastoma tumors become resistant. Chlorpromazine is a United States Food and Drug Administration-approved phenothiazine widely used as a psychotropic in clinical practice. Recently, experimental evidence revealed the anti-proliferative activity of chlorpromazine against colon and brain tumors. Here, we used chemoresistant patient-derived glioma stem cells and chemoresistant human glioma cell lines to investigate the effects of chlorpromazine against chemoresistant glioma. Chlorpromazine selectively and significantly inhibited proliferation in chemoresistant glioma cells and glioma stem cells. Mechanistically, chlorpromazine inhibited cytochrome c oxidase (CcO, complex IV) activity from chemoresistant but not chemosensitive cells, without affecting other mitochondrial complexes. Notably, our previous studies revealed that the switch to chemoresistance in glioma cells is accompanied by a switch from the expression of CcO subunit 4 isoform 2 (COX4-2) to COX4-1. In this study, chlorpromazine induced cell cycle arrest selectively in glioma cells expressing COX4-1, and computer-simulated docking studies indicated that chlorpromazine binds more tightly to CcO expressing COX4-1 than to CcO expressing COX4-2. In orthotopic mouse brain tumor models, chlorpromazine treatment significantly increased the median overall survival of mice harboring chemoresistant tumors. These data indicate that chlorpromazine selectively inhibits the growth and proliferation of chemoresistant glioma cells expressing COX4-1. The feasibility of repositioning chlorpromazine for selectively treating chemoresistant glioma tumors should be further explored.

3,5-Diiodothyronine: A Novel Thyroid Hormone Metabolite and Potent Modulator of Energy Metabolism

Over 30 years of research has demonstrated that 3,5-diiodo-L-thyronine (3,5-T2), an endogenous metabolite of thyroid hormones, exhibits interesting metabolic activities. In rodent models, exogenously administered 3,5-T2 rapidly increases resting metabolic rate and elicits short-term beneficial hypolipidemic effects; however, very few studies have evaluated the effects of endogenous and exogenous T2 in humans. Further analyses on larger cohorts are needed to determine whether 3,5-T2 is a potent additional modulator of energy metabolism. In addition, while several lines of evidence suggest that 3,5-T2 mainly acts through Thyroid hormone receptors (THRs)- independent ways, with mitochondria as a likely cellular target, THRs-mediated actions have also been described. The detailed cellular and molecular mechanisms through which 3,5-T2 elicits a multiplicity of actions remains unknown. Here, we provide an overview of the most recent literature on 3,5-T2 bioactivity with a particular focus on short-term and long-term effects, describing data obtained through in vivo and in vitro approaches in both mammalian and non-mammalian species.

Direct and rapid effects of 3,5-diiodo-L-thyronine (T2)

A growing number of researchers are focusing their attention on the possibility that thyroid hormone metabolites, particularly 3,5-diiodothyronine (T2), may actively regulate energy metabolism at the cellular, rather than the nuclear, level. Due to their biochemical features, mitochondria have been the focus of research on the thermogenic effects of thyroid hormones. Indeed, mitochondrial activities have been shown to be regulated both directly and indirectly by T2-specific pathways. Herein, we describe the effects of T2 on energy metabolism.

Acquired resistance to PI3K/mTOR inhibition is associated with mitochondrial DNA mutation and glycolysis

Acquired resistance (AQR) to drug treatment occurs frequently in cancer patients and remains an impediment to successful therapy. The aim of this study was to gain insight into how AQR arises following the application of PI3K/mTOR inhibitors. H1975 lung cancer cells with EGFR T790M mutations that confer resistance to EGFR inhibitors underwent prolonged treatment with the PI3K/mTOR inhibitor, BEZ235. Monoclonal cells with stable and increased resistance to BEZ235 were obtained after 8 months treatment. These AQR clones showed class-specific resistance to PI3K/mTOR inhibitors, reduced G1 cell cycle arrest and impedance of migration following PI3K/mTOR inhibition, reduced PTEN expression and increased Akt and S6RP phosphorylation. Transcriptome analysis revealed the AQR clones had increased expression of the metabolite transporters SLC16A9 and SLC16A7, suggestive of altered cell metabolism. Subsequent experiments revealed that AQR clones possess features consistent with elevated glycolysis, including increased levels of glucose, lactate, glutamine, glucose dependence, GLUT1 expression, and rates of post-glucose extracellular acidification, and decreased levels of reactive oxygen species and rates of oxygen consumption. Combination treatment of BEZ235 with the glycolysis inhibitor 3-bromopyruvate was synergistic in AQR clones, but only additive in parental cells. DNA sequencing revealed the presence of a mitochondrial DNA (mtDNA) MT-C01 variant in AQR but not parental cells. Depletion of mitochondrial DNA in parental cells induced resistance to BEZ235 and other PI3K/mTOR inhibitors, and was accompanied by increased glycolysis. The results of this study provide the first evidence that a metabolic switch associated with mtDNA mutation can be an underlying mechanism for AQR.

Comparative biochemistry of cytochrome c oxidase in animals

Cytochrome c oxidase (COX), the terminal enzyme of the electron transport system, is central to aerobic metabolism of animals. Many aspects of its structure and function are highly conserved, yet, paradoxically, it is also an important model for studying the evolution of the metabolic phenotype. In this review, part of a special issue honouring Peter Hochachka, we consider the biology of COX from the perspective of comparative and evolutionary biochemistry. The approach is to consider what is known about the enzyme in the context of conventional biochemistry, but focus on how evolutionary researchers have used this background to explore the role of the enzyme in biochemical adaptation of animals. In synthesizing the conventional and evolutionary biochemistry, we hope to identify synergies and future research opportunities. COX represents a rare opportunity for researchers to design studies that span the breadth of biology: molecular genetics, protein biochemistry, enzymology, metabolic physiology, organismal performance, evolutionary biology, and phylogeography.