bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2017‒02‒26
nine papers selected by
Gavin McStay
New York Institute of Technology

  1. Genetics. 2017 Feb 17. pii: genetics.116.199331. [Epub ahead of print]
      Respiration, the core of mitochondrial metabolism, depends on the function of five respiratory complexes. Many respiratory chain related proteins are encoded by the mitochondrial genome and their RNAs undergo post-transcriptional modifications by nuclear genome expressed factors, including pentatricopeptide repeat (PPR) proteins. Maize defective kernel 10 (dek10) is a classic mutant with small kernels and delayed development. Through positional cloning we found that Dek10 encodes an E-subgroup PPR protein localized in mitochondria. Sequencing analysis indicated that Dek10 is responsible for the C-to-U editing at nad3-61, nad3-62, and cox2-550 sites, those are specific editing sites in monocots. The defects of these editing sites result in significant reduction of Nad3 and the loss of Cox2. Interestingly, the assembly of Complex I was not reduced, but its NADH dehydrogenase activity was greatly decreased. The assembly of Complex IV was significantly reduced. Transcriptome and transmission electron microscopy (TEM) analysis revealed that proper editing of nad3 and cox2 is critical for mitochondrial functions, biogenesis and morphology. These results indicate that the E-subgroup PPR protein Dek10 is responsible for multiple editing sites in nad3 and cox2, that is essential for mitochondrial functions and plant development in maize.
    Keywords:  RNA-editing; Zea mays; dek10; mitochondrion; pentatricopeptide repeat protein
  2. Mech Ageing Dev. 2017 Feb 14. pii: S0047-6374(16)30226-3. [Epub ahead of print]162 9-17
      Calorie restriction (CR) has been amply demonstrated to modify mitochondrial function. However, little is known regarding the effects of this dietary regimen on mitochondrial membranes. We isolated phospholipids from rat liver mitochondria from animals on CR or ad libitum diets and found that mitochondria from ad libitum animals present an increased content of lipoperoxides and the content of cardiolipin. Cardiolipin is the main anionic phospholipid present in mitochondrial membranes, and plays a key role in mitochondrial function, signaling and stress response. Expression levels of the enzymes involved in cardiolipin biosynthesis and remodeling were quantified and found to be upregulated in CR animals. Interestingly, when mitochondrial membranes were fractionated, the outer membrane presented a higher content of cardiolipin, indicating a redistribution of this phospholipid mediated by a phospholipid scramblase in CR. This change is associated with Drp1-mediated mitochondrial fragmentation and autophagy. Overall, we find that CR promotes extensive mitochondrial membrane remodeling, decreasing oxidatively damaged lipids, and increasing cardiolipin levels and redistributing cardiolipin. These changes in membrane properties are consistent with and may be causative of changes in mitochondrial morphology, function and turnover previously found to occur in CR.
    Keywords:  Calorie restriction; Cardiolipin; Membrane; Mitochondria; Phospholipid
  3. Biochim Biophys Acta. 2017 Feb 14. pii: S0005-2728(17)30028-2. [Epub ahead of print]
      Energy homeostasis is pivotal for cell fate since metabolic regulation, cell proliferation and death are strongly dependent on the balance between catabolic and anabolic pathways. In particular, metabolic and energetic changes have been observed in cancer cells even before the discovery of oncogenes and tumor suppressors, but have been neglected for a long time. Instead, during the past 20years a renaissance of the study of tumor metabolism has led to a revised and more accurate sight of the metabolic landscape of cancer cells. In this scenario, genetic, biochemical and clinical evidences place mitochondria as key actors in cancer metabolic restructuring, not only because there are energy and biosynthetic intermediates manufacturers, but also because occurrence of mutations in metabolic enzymes encoded by both nuclear and mitochondrial DNA has been associated to different types of cancer. Here we provide an overview of the possible mechanisms modulating mitochondrial energy production and homeostasis in the intriguing scenario of neoplastic cells, focusing on the double-edged role of 5'-AMP activated protein kinase in cancer metabolism. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.
    Keywords:  AMPK; ATP; Cancer; Energy production; Mitochondria; OXPHOS
  4. Curr Opin Genet Dev. 2017 Feb 14. pii: S0959-437X(16)30215-5. [Epub ahead of print]44 47-53
      Mitochondria are essential organelles that provide cellular energy and buffer cytoplasmic calcium. At the same time they produce damaging reactive oxygen species and sequester pro-apoptotic factors. Hence, eukaryotes have evolved exquisite homeostatic processes that maintain mitochondrial integrity, or ultimately remove damaged organelles. This subject has garnered intense interest recently following the discovery that two Parkinson's disease genes, PINK1 and parkin, regulate mitochondrial degradation (mitophagy). The molecular details of PINK1/Parkin-induced mitophagy are emerging but much of our insight derives from work using cultured cells and potent mitochondrial toxins, raising questions about the physiological significance of these findings. Here we review the evidence supporting PINK1/Parkin mitophagy in vivo and its causative role in neurodegeneration, and outline outstanding questions for future investigations.
  5. Biochem Biophys Res Commun. 2017 Jan 15. pii: S0006-291X(16)31812-5. [Epub ahead of print]482(3): 388-398
      Sten Orrenius, M.D., Ph.D., pioneered many areas of cellular and molecular toxicology and made seminal contributions to our knowledge of oxidative stress and glutathione (GSH) metabolism, organellar functions and Ca+2-dependent mechanisms of cell death, and mechanisms of apoptosis. On the occasion of his 80th birthday, we summarize current knowledge on redox biology of manganese (Mn) and its role in mechanisms of cell death. Mn is found in all organisms and has critical roles in cell survival and death mechanisms by regulating Mn-containing enzymes such as manganese superoxide dismutase (SOD2) or affecting expression and activity of caspases. Occupational exposures to Mn cause "manganism", a Parkinson's disease-like condition of neurotoxicity, and experimental studies show that Mn exposure leads to accumulation of Mn in the brain, especially in mitochondria, and neuronal cell death occurs with features of an apoptotic mechanism. Interesting questions are why a ubiquitous metal that is essential for mitochondrial function would accumulate to excessive levels, cause increased H2O2 production and lead to cell death. Is this due to the interactions of Mn with other essential metals, such as iron, or with toxic metals, such as cadmium? Why is the Mn loading in the human brain so variable, and why is there such a narrow window between dietary adequacy and toxicity? Are non-neuronal tissues similarly vulnerable to insufficiency and excess, yet not characterized? We conclude that Mn is an important component of the redox interface between an organism and its environment and warrants detailed studies to understand the role of Mn as a mitochondrial life-death switch.
    Keywords:  Heavy metal; Hydrogen peroxide; MnSOD; Neurodegenerative disease; Nutritional metal; Redox state
  6. Biochem Biophys Res Commun. 2017 Jan 15. pii: S0006-291X(16)31951-9. [Epub ahead of print]482(3): 426-431
      Mitochondria are complex organelles that play a central role in energy metabolism, control of stress responses and are a hub for biosynthetic processes. Beyond its well-established role in cellular energetics, mitochondria are critical mediators of signals to propagate various cellular outcomes. In addition mitochondria are the primary source of intracellular reactive oxygen species (ROS) generation and are involved in cellular Ca2+ homeostasis, they contain a self-destructive arsenal of apoptogenic factors that can be unleashed to promote cell death, thus displaying a shared platform for metabolism and apoptosis. In the present review, we will give a brief account on the integration of mitochondrial metabolism and apoptotic cell death.
    Keywords:  Cell death; Metabolism; Mitochondria
  7. Biochem Biophys Res Commun. 2017 Jan 15. pii: S0006-291X(16)31773-9. [Epub ahead of print]482(3): 432-439
      Mitophagy, the selective degradation of mitochondria via the autophagic pathway, is a vital mechanism of mitochondrial quality control in cells. Mitophagy is responsible for the removal of malfunctioning or damaged mitochondria, which is essential for normal cellular physiology and tissue development. Pathways involved in the regulation of mitophagy, tumorigenesis, and cell death are overlapping in many cases and may be triggered by common upstream signals, which converge at the mitochondria. The failure to properly modulate mitochondrial turnover in response to oncogenic stresses can either stimulate or suppress tumorigenesis. Thus, the analysis of crosstalk among the processes of mitophagy, cell death and tumorigenesis is important for the identification of targets responsible for the stimulation of cell death and selective elimination of cancer cells. In the present review, we analyze the mechanisms of mitophagy regulation, the pathways underlying the utilization of damaged mitochondria, and how intervention with mitophagy can affect tumor cell resistance to treatment.
    Keywords:  Autophagy; Cancer; Cell death; Mitochondria; Mitophagy; Therapy
  8. Redox Biol. 2017 Feb 12. pii: S2213-2317(17)30014-9. [Epub ahead of print]12 50-57
      Energy metabolism and redox state are intrinsically linked. In order to mount an adequate immune response, cells must have an adequate and rapidly available energy resource to migrate to the inflammatory site, to generate reactive oxygen species using NADPH as a cofactor and to engulf bacteria or damaged tissue. The first responder cells of the innate immune response, neutrophils, are largely dependent on glycolysis. Neutrophils are relatively short-lived, dying via apoptosis in the process of bacterial killing through production of hypochlorous acid and release of extracellular NETs. Later on, the most prevalent recruited innate immune cells are monocytes. Their role is to complete a damage limitation exercise initiated by neutrophils and then, as re-programmed M2 macrophages, to resolve the inflammatory event. Almost twenty five years ago, it was noted that macrophages lose their glycolytic capacity and become anti-inflammatory after treatment with corticosteroids. In support of this we now understand that, in contrast to early responders, M2 macrophages are predominantly dependent on oxidative phosphorylation for energy. During early inflammation, polarisation towards M1 macrophages is dependent on NOX2 activation which, via protein tyrosine phosphatase oxidation and AKT activation, increases trafficking of glucose transporters to the membrane and consequently increases glucose uptake for glycolysis. In parallel, mitochondrial efficiency is likely to be compromised via nitrosylation of the electron transport chain. Resolution of inflammation is triggered by encounter with apoptotic membranes exposing oxidised phosphatidylserine that interact with the scavenger receptor, CD36. Downstream of CD36, activation of AMPK and PPARγ elicits mitochondrial biogenesis, arginase expression and a switch towards oxidative phosphorylation in the M2 macrophage. Proinflammatory cytokine production by M2 cells decreases, but anti-inflammatory and wound healing growth factor production is maintained to support restoration of normal function.
  9. PLoS One. 2017 ;12(2): e0172344
      Temperature is a fundamental physical parameter that plays an important role in biological reactions and events. Although thermometers developed previously have been used to investigate several important phenomena, such as heterogeneous temperature distribution in a single living cell and heat generation in mitochondria, the development of a thermometer with a sensitivity over a wide temperature range and rapid response is still desired to quantify temperature change in not only homeotherms but also poikilotherms from the cellular level to in vivo. To overcome the weaknesses of the conventional thermometers, such as a limitation of applicable species and a low temporal resolution, owing to the narrow temperature range of sensitivity and the thermometry method, respectively, we developed a genetically encoded ratiometric fluorescent temperature indicator, gTEMP, by using two fluorescent proteins with different temperature sensitivities. Our thermometric method enabled a fast tracking of the temperature change with a time resolution of 50 ms. We used this method to observe the spatiotemporal temperature change between the cytoplasm and nucleus in cells, and quantified thermogenesis from the mitochondria matrix in a single living cell after stimulation with carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, which was an uncoupler of oxidative phosphorylation. Moreover, exploiting the wide temperature range of sensitivity from 5°C to 50°C of gTEMP, we monitored the temperature in a living medaka embryo for 15 hours and showed the feasibility of in vivo thermometry in various living species.