What can modern bacteria and endosymbionts teach us about eukaryote mitochondria? O que as bactérias modernas e os endosimbiontes podem nos ensinar sobre as mitocôndrias em eucariontes?

In animals, plants and unicellular eukaryotes, mitochondria perform many tasks such as the Krebs cycle, β-oxidation, and oxidative phosphorylation. The “endosymbiotic hypothesis” proposed by Lynn Margulis suggests that this organelle originated from the relationship of an endosymbiotic bacterium and a host-cell. As their relationship evolved, these organisms faced adverse environmental conditions together, each profiting from the other. During coevolution, the endosymbiont transferred genes to the host thus progressing to obligate intracellular and eventually lost all independence, to become a mitochondrion. This organelle shares diverse traits with modern bacteria proving its origin. In addition, modern endosymbiotic bacteria such as Wolbachia sp. and their hosts are coevolving, becoming more interdependent and expressing different metabolic routes in a process that illustrates the pathway that ancient mitochondrial ancestors may have followed

Oxygen: From Toxic Waste to Optimal (Toxic) Fuel of Life

Some 2.5 billion years ago, the great oxygenation event (GOE) led to a 105‐fold rise in atmospheric oxygen [O2], killing most species on Earth. In spite of the tendency to produce toxic reactive oxygen species (ROS), the highly exergonic reduction of O2 made it the ideal biological electron acceptor. During aerobic metabolism, O2 is reduced to water liberating energy, which is coupled to adenosine triphosphate (ATP) synthesis. Today, all organisms either aerobic or not need to deal with O2 toxicity. O2‐permeant organisms need to seek adequate [O2], for example, aquatic crustaceans bury themselves in the sea bottom where O2 is scarce. Also, the intestinal lumen and cytoplasm of eukaryotes is a microaerobic environment where many facultative bacteria or intracellular symbionts hide from oxygen. Organisms such as plants, fish, reptiles and mammals developed O2‐impermeable epithelia, plus specialized external respiratory systems in combination with O2‐binding proteins such as hemoglobin or leg‐hemoglobin control [O2] in tissues. Inside the cell, ROS production is prevented by rapid O2 consumption during the oxidative phosphorylation (OxPhos) of ATP. When ATP is in excess, OxPhos becomes uncoupled in an effort to continue eliminating O2. Branched respiratory chains, unspecific pores and uncoupling proteins (UCPs) uncouple OxPhos. One last line of resistance against ROS is deactivation by enzymes such as super oxide dismutase and catalase. Aerobic organisms profit from the high energy released by the reduction of O2, while at the same time they need to avoid the toxicity of ROS

Effect of Cross-Sex Hormonal Replacement on Antioxidant Enzymes in Rat Retroperitoneal Fat Adipocytes

We report the effect of cross-sex hormonal replacement on antioxidant enzymes from rat retroperitoneal fat adipocytes. Eight rats of each gender were assigned to each of the following groups: control groups were intact female or male (F and M, resp.). Experimental groups were ovariectomized F (OvxF), castrated M (CasM), OvxF plus testosterone (OvxF + T), and CasM plus estradiol (CasM + E2) groups. After sacrifice, retroperitoneal fat was dissected and processed for histology. Adipocytes were isolated and the following enzymatic activities were determined: Cu-Zn superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST), and glutathione reductase (GR). Also, glutathione (GSH) and lipid peroxidation (LPO) were measured. In OvxF, retroperitoneal fat increased and adipocytes were enlarged, while in CasM rats a decrease in retroperitoneal fat and small adipocytes are observed. The cross-sex hormonal replacement in F rats was associated with larger adipocytes and a further decreased activity of Cu-Zn SOD, CAT, GPx, GST, GR, and GSH, in addition to an increase in LPO. CasM + E2 exhibited the opposite effects showing further activation antioxidant enzymes and decreases in LPO. In conclusion, E2 deficiency favors an increase in retroperitoneal fat and large adipocytes. Cross-sex hormonal replacement in F rats aggravates the condition by inhibiting antioxidant enzymes

Hepatocyte Growth Factor Reduces Free Cholesterol-Mediated Lipotoxicity in Primary Hepatocytes by Countering Oxidative Stress

Cholesterol overload in the liver has shown toxic effects by inducing the aggravation of nonalcoholic fatty liver disease to steatohepatitis and sensitizing to damage. Although the mechanism of damage is complex, it has been demonstrated that oxidative stress plays a prominent role in the process. In addition, we have proved that hepatocyte growth factor induces an antioxidant response in hepatic cells; in the present work we aimed to figure out the protective effect of this growth factor in hepatocytes overloaded with free cholesterol. Hepatocytes from mice fed with a high-cholesterol diet were treated or not with HGF, reactive oxygen species present in cholesterol overloaded hepatocytes significantly decreased, and this effect was particularly associated with the increase in glutathione and related enzymes, such as γ-gamma glutamyl cysteine synthetase, GSH peroxidase, and GSH-S-transferase. Our data clearly indicate that HGF displays an antioxidant response by inducing the glutathione-related protection system

Inhibitory to non-inhibitory evolution of the ζ subunit of the F1FO-ATPase of Paracoccus denitrificans and α-proteobacteria as related to mitochondrial endosymbiosis

Introduction: The ζ subunit is a potent inhibitor of the F1FO-ATPase of Paracoccus denitrificans (PdF1FO-ATPase) and related α-proteobacteria different from the other two canonical inhibitors of bacterial (ε) and mitochondrial (IF1) F1FO-ATPases. ζ mimics mitochondrial IF1 in its inhibitory N-terminus, blocking the PdF1FO-ATPase activity as a unidirectional pawl-ratchet and allowing the PdF1FO-ATP synthase turnover. ζ is essential for the respiratory growth of P. denitrificans, as we showed by a Δζ knockout. Given the vital role of ζ in the physiology of P. denitrificans, here, we assessed the evolution of ζ across the α-proteobacteria class.Methods: Through bioinformatic, biochemical, molecular biology, functional, and structural analyses of several ζ subunits, we confirmed the conservation of the inhibitory N-terminus of ζ and its divergence toward its C-terminus. We reconstituted homologously or heterologously the recombinant ζ subunits from several α-proteobacteria into the respective F-ATPases, including free-living photosynthetic, facultative symbiont, and intracellular facultative or obligate parasitic α-proteobacteria.Results and discussion: The results show that ζ evolved, preserving its inhibitory function in free-living α-proteobacteria exposed to broad environmental changes that could compromise the cellular ATP pools. However, the ζ inhibitory function was diminished or lost in some symbiotic α-proteobacteria where ζ is non-essential given the possible exchange of nutrients and ATP from hosts. Accordingly, the ζ gene is absent in some strictly parasitic pathogenic Rickettsiales, which may obtain ATP from the parasitized hosts. We also resolved the NMR structure of the ζ subunit of Sinorhizobium meliloti (Sm-ζ) and compared it with its structure modeled in AlphaFold. We found a transition from a compact ordered non-inhibitory conformation into an extended α-helical inhibitory N-terminus conformation, thus explaining why the Sm-ζ cannot exert homologous inhibition. However, it is still able to inhibit the PdF1FO-ATPase heterologously. Together with the loss of the inhibitory function of α-proteobacterial ε, the data confirm that the primary inhibitory function of the α-proteobacterial F1FO-ATPase was transferred from ε to ζ and that ζ, ε, and IF1 evolved by convergent evolution. Some key evolutionary implications on the endosymbiotic origin of mitochondria, as most likely derived from α-proteobacteria, are also discussed

Participation du fructose 1,6-biphosphate dans l'induction de l'effet Crabtree chez la levure Saccharomyces cerevisiae

Lorsque la levure Saccharomyces cerevisiae pousse en aérobiose, la respiration est immédiatement réprimée après l addition de glucose au milieu de culture. Ce phénomène est appellé l effet Crabtree . Il a été rapporté que l inhibition du flux respiratoire est concomitant avec l accumulation cytoplasmique des hexoses phosphates provenant de la glycolyse. Dans ce travail, la levure Saccharomyces cerevisiae a été utilisée pour chercher à identifier les événements regulatoires à court terme qui sont associés à l effet Crabtree ainsi que le possible rôle des hexoses phosphates dans l inhibition de la respiration. En utilisant des mitochondries isolées il a été trouvé que le glucose 6-phosphate et le fructose 6-phosphate stimulent le flux respiratoire. Cet effet est compensé par des niveaux physiologiques de fructose 1,6-biphosphate, lequel inhibe la respiration en absence des autres hexoses phosphates. Cet effet est aussi observé in situ puisqu il est obtenu en utiisant des sphéroplastes perméabilisés de levure. La répression du flux respiratoire induite par le fructose 1,6-biphosphate est due à une inhibition de l activité des complexes respiratoires III et IV. Les résultats suggérent que le fructose 1,6-biphosphate pourrait être un des inducteurs de l effet Crabtree chez la levure. Il est également possible que aussi chez les cellules mammifières cet hexose phosphate puisse réguler le metabolisme des tumeurs, où l effet Crabtree a aussi été observé.When the yeast Saccharomyces cerevisiae grows aerobically, its respiration is immediately repressed when adding glucose to the culture media. This phenomenon has been termed the Crabtree effect . It has been reported that the respiratory flux inhibition is concomitant with the cytoplasmic accumulation of the glycolysis-derived hexoses phosphates. In this work, S. cerevisiae was used to investigate the short-term regulatory events associated to the Crabtree effect and the role of the hexoses phosphates during the respiratory inhibition. Using yeast isolated mitochondria it was found that glucose 6-phosphate and fructose 6-phosphate stimulate the respiratory flux. This was counteracted by physiological concentrations of fructose 1,6-biphosphate, which also inhibits respiration in the absence of the other two hexoses phosphate. This occurs in situ, as the effect mediated by the fructose biphosphate was also observed in yeast permeabilized spheroplasts. The respiratory flux repression mediated by fructose 1,6-biphosphate is due to an inhibition of the activity of respiratory complexes III and IV. The results suggest that fructose 1,6-biphosphate could be one of the Crabtree effect inducers in yeast. In mammals, this hexose phosphate might regulate as well tumour cell metabolism, where the Crabtree effect has also been observed.BORDEAUX2-Bib. électronique (335229905) / SudocSudocFranceF