Catalases Are NAD(P)H-Dependent Tellurite Reductases

Reactive oxygen species damage intracellular targets and are implicated in cancer, genetic disease, mutagenesis, and aging. Catalases are among the key enzymatic defenses against one of the most physiologically abundant reactive oxygen species, hydrogen peroxide. The well-studied, heme-dependent catalases accelerate the rate of the dismutation of peroxide to molecular oxygen and water with near kinetic perfection. Many catalases also bind the cofactors NADPH and NADH tenaciously, but, surprisingly, NAD(P)H is not required for their dismutase activity. Although NAD(P)H protects bovine catalase against oxidative damage by its peroxide substrate, the catalytic role of the nicotinamide cofactor in the function of this enzyme has remained a biochemical mystery to date. Anions formed by heavy metal oxides are among the most highly reactive, natural oxidizing agents. Here, we show that a natural isolate of Staphylococcus epidermidis resistant to tellurite detoxifies this anion thanks to a novel activity of its catalase, and that a subset of both bacterial and mammalian catalases carry out the NAD(P)H-dependent reduction of soluble tellurite ion (TeO(3) (2−)) to the less toxic, insoluble metal, tellurium (Te°), in vitro. An Escherichia coli mutant defective in the KatG catalase/peroxidase is sensitive to tellurite, and expression of the S. epidermidis catalase gene in a heterologous E. coli host confers increased resistance to tellurite as well as to hydrogen peroxide in vivo, arguing that S. epidermidis catalase provides a physiological line of defense against both of these strong oxidizing agents. Kinetic studies reveal that bovine catalase reduces tellurite with a low Michaelis-Menten constant, a result suggesting that tellurite is among the natural substrates of this enzyme. The reduction of tellurite by bovine catalase occurs at the expense of producing the highly reactive superoxide radical

Uranium exposure of human dopaminergic cells results in low cytotoxicity, accumulation within sub-cytoplasmic regions, and down regulation of MAO-B

Natural uranium is an ubiquitous element present in the environment and human exposure to low levels of uranium is unavoidable. Although the main target of acute uranium toxicity is the kidney, some concerns have been recently raised about neurological effects of chronic exposure to low levels of uranium. Only very few studies have addressed the molecular mechanisms of uranium neurotoxicity, indicating that the cholinergic and dopaminergic systems could be altered. The main objective of this study was to investigate the mechanisms of natural uranium toxicity, after 7-day continuous exposure, on terminally differentiated human SH-SY5Y cells exhibiting a dopaminergic phenotype. Cell viability was first assessed showing that uranium cytotoxicity only occurred at high exposure concentrations (> 125 $\mu$M), far from the expected values for uranium in the blood even after occupational exposure. SH-SY5Y differentiated cells were then continuously exposed to 1, 10, 125 or 250 $\mu$M of natural uranium for 7 days and uranium quantitative subcellular distribution was investigated by means of micro-PIXE (Particle Induced X-ray Emission). The subcellular element imaging revealed that uranium was located in defined perinuclear regions of the cytoplasm, suggesting its accumulation in organelles. Uranium was not detected in the nucleus of the differentiated cells. Quantitative analysis evidenced a very low intracellular uranium content at non-cytotoxic levels of exposure (1 and 10 $\mu$M). At higher levels of exposure (125 and 250 $\mu$M), when cytotoxic effects begin, a larger and disproportional intracellular accumulation of uranium was observed. Finally the expression of dopamine-related genes was quantified using real time qRT-PCR. The expression of monoamine oxidase B (MAO-B) gene was statistically significantly decreased after exposure to uranium while other dopamine-related genes were not modified. The down regulation of MAO-B was confirmed at the protein level. This original result suggests that the inhibition of dopamine catabolism, but also of other MAO-B substrates, could constitute selective effects of uranium neurotoxicity

High precision isotopic analysis of U, Cu and Zn in a human neuronal cell model

International audienc

Comment le dialogue moléculaire entre bactéries et neurones change le comportement de l’hôte infecté

National audienceLes eucaryotes vivent dans un environnement contaminé par des microorganismes. Il n'est donc pas surprenant qu'ils aient forgé, au fil du temps, des relations extrêmement complexes et intimes entre eux. Les eucaryotes sont capables de percevoir la présence de bactéries et d’adapter leur réponse immunitaire, leur état physiologique ou même leur comportement en conséquence. Nombreuses sont les études qui ont démontré que les bactéries peuvent interagir avec le système nerveux eucaryote, soit au bénéfice du microbe qui modifie le comportement de l'hôte, soit au bénéfice de l'hôte qui adapte son comportement à l'infection. Dans la plupart des cas, cependant, les molécules et les mécanismes qui sous- tendent le dialogue entre les bactéries et leur système nerveux hôte n'ont pas été identifiés et leur mode d'action mal compris. Je présenterai les données obtenues avec le modèle Drosophile, sur la dissection des mécanismes cellulaires et moléculaires par lesquels un seul composé dérivé de microbiote, appelé peptidoglycane, influence le comportement des hôtes infectés en agissant directement sur certains neurones du cerveau

Peptidoglycan-dependent NF-κB activation in a small subset of brain octopaminergic neurons controls female oviposition

Indexation en cours. PMCID: PMC6819134International audienceWhen facing microbes, animals engage in behaviors that lower the impact of the infection. We previously demonstrated that internal sensing of bacterial peptidoglycan reduces Drosophila female oviposition via NF-kB pathway activation in some neurons (Kurz et al., 2017). Although we showed that the neuromodulator octopamine is implicated, the identity of the involved neurons, as well as the physiological mechanism blocking egg-laying, remained unknown. In this study, we identified few ventral nerve cord and brain octopaminergic neurons expressing an NF-kB pathway component. We functionally demonstrated that NF-kB pathway activation in the brain, but not in the ventral nerve cord octopaminergic neurons, triggers an egg-laying drop in response to infection. Furthermore, we demonstrated via calcium imaging that the activity of these neurons can be directly modulated by peptidoglycan and that these cells do not control other octopamine-dependent behaviors such as female receptivity. This study shows that by sensing peptidoglycan and hence activating NF-kB cascade, a couple of brain neurons modulate a specific octopamine-dependent behavior to adapt female physiology status to their infectious state

Phospholipase C-β1 Signaling Affects Reproductive Behavior, Ovulation, and Implantation

Infertility can result from a wide range of defects, from behavioral, through germ cell development and maturation, to fertilization or embryo development. Many of the hormones regulating these processes signal via G protein-coupled receptors, which in turn activate a range of plasma membrane enzymes including phospholipase C (PLC)-β isoforms. Transgenic mice lacking functional Plc-β1 (Plc-β1 KO mice) have been noted to have severely impaired fertility, but there has been little study of the reproductive processes affected by lack of this enzyme. This study examined reproductive behavior, gonadal development, fertilization, and implantation in Plc-β1 KO mice. Male and female Plc-β1 KO mice exhibited impaired reproductive behavior. No other defect in reproduction was noted in males, raising the possibility that the reduced fertility of Plc-β1 KO males could be due solely to impaired behavior. In contrast, female Plc-β1 KO mice exhibited both behavioral and nonbehavioral defects. Plc-β1 KO females ovulated only in response to exogenous hormones, with a large proportion of in vivo embryos recovered on embryonic d 4.5 exhibiting abnormal morphology. In addition, uteri of pregnant Plc-β1 KO females exhibited an implantation defect, with poor embryo attachment and a failure to up-regulate cyclooxygenase-2 mRNA

A genetic analysis of in vivo selenate reduction by Salmonella enterica serovar Typhimurium LT2 and Escherichia coli K12

The twin-arginine transport (Tat) system is dedicated to the translocation of folded proteins across the bacterial cytoplasmic membrane. Proteins are targeted to the Tat system by signal peptides containing a twin-arginine motif. In Salmonella enterica serovar Typhimurium and Escherichia coli many Tat substrates are known or predicted to bind a molybdenum cofactor in the cytoplasm prior to export. In the case of N- and S-oxide reductases, co-ordination of molybdenum cofactor insertion with protein export involves a 'Tat proofreading' process where chaperones of the TorD family bind the signal peptides, thus preventing premature export. Here, a genetic approach was taken to determine factors required for selenate reductase activity in Salmonella and E. coli. It is reported for both biological systems that an active Tat translocase and a TorD-like chaperone (DmsD) are required for complete in vivo reduction of selenate to elemental red selenium. Further mutagenesis and in vitro biophysical experiments implicate the Salmonella ynfE gene product, and the E. coli YnfE and YnfF proteins, as putative Tat-targeted selenate reductases