16 research outputs found
Enzymes involved in the repair of hydrated forms of NADH and NADPH : identification, characterization and subcellular distribution
No full textNADH and NADPH may undergo a hydration reaction that converts them to damaged forms, named NADHX and NADPHX and existing as two different, (S) and (R) epimers. This hydration reaction is spontaneous or enzyme-catalysed, being then due to the side-activity of glyceraldehyde-3-phosphate dehydrogenase. NADHX and NADPHX do not function anymore as coenzymes, but rather as inhibitors of several dehydrogenases. This work shows the existence of an extremely conserved enzymatic system that catalyses the repair of the two NAD(P)HX epimers. It consists of an ATP- or ADP-dependent dehydratase, which specifically acts on the (S) epimer, and an epimerase, which catalyses the interconversion of the (R) and (S) epimers. In addition, we show that, in mammals, the two enzymes are ubiquitous and present in the major NAD(P)H-containing subcellular compartments, and that their endogenous activity is sufficient to cope with NAD(P)HX formation in cells.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 201
Climate change risks illustrated by the Intergovernmental Panel on Climate Change (IPCC) “burning embers”
No full textThe completion of the Sixth Assessment Cycle of the Intergovernmental Panel on Climate Change (IPCC) provides a unique opportunity to understand where the world stands on climate-change-related risks to natural and human systems at the global level, as well as for specific regions and sectors. Since its Third Assessment Report (AR3), released 2 decades ago, the IPCC has developed a synthetic representation of how risks increase with global warming, with risk levels reflected by the colours used, including shades of yellow and red, which led to the nickname “burning embers”. While initially designed to illustrate five overarching Reasons for Concern, these diagrams have been progressively applied to risks in specific systems and regions over the last 10 years. However, the information gathered through expert elicitation and the resulting quantitative risk assessments have hitherto remained scattered within and across reports and specific data files. This paper overcomes this limitation by developing a database containing all embers from AR3 to AR6 and an associated online “Climate Risks Embers Explorer” (CREE) to facilitate the exploration of the assessed risks. The data are also available in an archive file in a widely accessible format (https://doi.org/10.5281/zenodo.12626976, Marbaix et al., 2024). Important aspects of data homogenization are discussed, and an approach to structuring information on assessed risk increases is presented. Potential uses of the data are explored through aggregated analyses of risks and adaptation benefits, which show that, excluding high-adaptation cases, half of the assessed risk levels increase from a moderate risk to a high risk between 1.5 and 2 to 2.3 °C of global warming, a result which is consistent with the separate assessment of the Reasons for Concern by the IPCC. The database lays the groundwork for future risk assessments and the development of burning embers by providing a standardized baseline of risk data. It also highlights important areas for improvement in the forthcoming Seventh Assessment Cycle of the IPCC, particularly towards the systematic, homogeneous, and structured collection of information on illustrated risk increases; comprehensive coverage of impacted regions; a systematic consideration of adaptation and/or vulnerability levels; and, possibly, the coverage of risks from response measures. In the context of an ever-growing body of literature and knowledge, the facility described herein has the potential to help in synthesizing and illustrating risks across scales and systems in a more consistent and comprehensive way
Extremely conserved ATP- or ADP-dependent enzymatic system for nicotinamide nucleotide repair
No full textpeer reviewedThe reduced forms of NAD and NADP, two major nucleotides playing a central role in metabolism, are continuously damaged by enzymatic or heat-dependent hydration. We report the molecular identification of the eukaryotic dehydratase that repairs these nucleotides and show that this enzyme (Carkd in mammals, YKL151C in yeast) catalyzes the dehydration of the S form of NADHX and NADPHX, at the expense of ATP, which is converted to ADP. Surprisingly, the Escherichia coli homolog, YjeF, a bidomain protein, catalyzes a similar reaction, but using ADP instead of ATP. The latter reaction is ascribable to the C-terminal domain of YjeF. This represents an unprecedented example of orthologous enzymes using either ADP or ATP as phosphoryl donor. We also show that eukaryotic proteins homologous to the N-terminal domain of YjeF (apolipoprotein A-1-binding protein (AIBP) in mammals, YNL200C in yeast) catalyze the epimerization of the S and R forms of NAD(P)HX, thereby allowing, in conjunction with the energy-dependent dehydratase, the repair of both epimers of NAD(P)HX. Both enzymes are very widespread in eukaryotes, prokaryotes, and archaea, which together with the ADP dependence of the dehydratase in some species indicates the ancient origin of this repair system
Occurrence and subcellular distribution of the NAD(P)HX repair system in mammals.
No full textpeer reviewedHydration of NAD(P)H to NAD(P)HX, which inhibits several dehydrogenases, is corrected by an ATP-dependent dehydratase and an epimerase recently identified as the products of the vertebrate Carkd (carbohydrate kinase domain) and Aibp (apolipoprotein AI-binding protein) genes respectively. The purpose of the present study was to assess the presence of these enzymes in mammalian tissues and determine their subcellular localization. The Carkd gene encodes proteins with a predicted mitochondrial propeptide (mCARKD), a signal peptide (spCARKD) or neither of them (cCARKD). Confocal microscopy analysis of transfected CHO (Chinese-hamster ovary) cells indicated that cCARKD remains in the cytosol, whereas mCARKD and spCARKD are targeted to the mitochondria and the endoplasmic reticulum respectively. Unlike the other two forms, spCARKD is N-glycosylated, supporting its targeting to the endoplasmic reticulum. The Aibp gene encodes two different proteins, which we show to be targeted to the mitochondria (mAIBP) and the cytosol (cAIBP). Quantification of the NAD(P)HX dehydratase and epimerase activities in rat tissues, performed after partial purification, indicated that both enzymes are widely distributed, with total activities of approximately 3-10 nmol/min per g of tissue. Liver fractionation by differential centrifugation confirmed the presence of the dehydratase and the epimerase in the cytosol and in mitochondria. These data support the notion that NAD(P)HX repair is extremely widespread
Pyridoxamine-phosphate oxidases and pyridoxamine-phosphate oxidase-related proteins catalyze the oxidation of 6-NAD(P)H to NAD(P).
No full text6-NADH and 6-NADPH are strong inhibitors of several dehydrogenases that may form spontaneously from NAD(P)H. They are known to be oxidized to NAD(P)+ by mammalian renalase, an FAD-linked enzyme mainly present in heart and kidney, and by related bacterial enzymes. We partially purified an enzyme oxidizing 6-NADPH from rat liver, and, surprisingly, identified it as pyridoxamine-phosphate oxidase (PNPO). This was confirmed by the finding that recombinant mouse PNPO oxidized 6-NADH and 6-NADPH with catalytic efficiencies comparable to those observed with pyridoxine- and pyridoxamine-5'-phosphate. PNPOs from Escherichia coli, Saccharomyces cerevisiae and Arabidopsis thaliana also displayed 6-NAD(P)H oxidase activity, indicating that this 'side-activity' is conserved. Remarkably, 'pyridoxamine-phosphate oxidase-related proteins' (PNPO-RP) from Nostoc punctiforme, A. thaliana and the yeast S. cerevisiae (Ygr017w) were not detectably active on pyridox(am)ine-5'-P, but oxidized 6-NADH, 6-NADPH and 2-NADH suggesting that this may be their main catalytic function. Their specificity profiles were therefore similar to that of renalase. Inactivation of renalase and of PNPO in mammalian cells and of Ygr017w in yeasts led to the accumulation of a reduced form of 6-NADH, tentatively identified as 4,5,6-NADH3, which can also be produced in vitro by reduction of 6-NADH by glyceraldehyde-3-phosphate dehydrogenase or glucose-6-phosphate dehydrogenase. As 4,5,6-NADH3 is not a substrate for renalase, PNPO or PNPO-RP, its accumulation presumably reflects the block in the oxidation of 6-NADH. These findings indicate that two different classes of enzymes using either FAD (renalase) or FMN (PNPOs and PNPO-RPs) as a cofactor play an as yet unsuspected role in removing damaged forms of NAD(P)
Recurrence of Focal Glomerulosclerosis Despite Cyclosporine Treatment After Renal-transplantation
No full textRecurrence of focal glomerulosclerosis despite cyclosporin treatment after renal transplantation.
No full textOptimalisation du traitement de la néphrite lupique
No full textLes travaux de recherche décrits dans cette thèse concernent l’optimalisation du traitement de la néphrite lupique (NL), avec un intérêt particulier pour la recherche de marqueurs prédictifs précoces de l’évolution rénale au long cours. Dans un premier travail, nous démontrons, par des dosages sériques du taux d’hormone anti-Müllérienne, que de petites doses intraveineuses de cyclophosphamide, administrées selon le schéma d’induction Euro-Lupus (3g cumulés), n’affectent pas la réserve ovarienne, une conclusion importante puisque la NL survient essentiellement chez des jeunes femmes. Un second volet concerne le traitement immunosuppresseur d’entretien de la NL. Plus spécifiquement, il décrit les résultats à 10 ans d’un essai clinique (MAINTAIN) comparant l’azathioprine et le mycophénolate mofetil. Les deux molécules sont comparables en termes de risque de rechutes rénales, d’insuffisance rénale terminale et de toxicité. Cette analyse a par ailleurs permis de confirmer qu’une chute rapide de la protéinurie pendant la première année de traitement prédisait remarquablement la conservation de la fonction rénale à 10 ans. Logiquement, l’étape suivante a consisté à déterminer la valeur seuil de protéinurie qui, si elle était atteinte, prédisait une évolution rénale ultérieure favorable. La valeur prédictive positive d’une protéinurie inférieure à <0,7g/j après un an de traitement est excellente (94%). Par contre, la non-atteinte de cette cible n’est pas discriminante puisque la valeur prédictive négative n’est que de 31%. Nous discutons dans cette thèse d’autres marqueurs pronostiques, à la lumière de nouvelles technologies. Un dernier volet discute de la sévérité de la NL dans la population d’origine maghrébine vivant en Europe. Pour la première fois, nous démontrons une fréquence accrue de récidives rénales et d’insuffisance rénale terminale en comparaison aux populations autochtones.(MED - Sciences médicales) -- UCL, 201
Lymphocytes T CD4+ régulateurs et polarisation immunitaire : étude appliquée à la dermatomyosite et au contexte des syndromes myélodysplasiques et la leucémie aiguë myéloïde en rechute après allogreffe
No full textRegulatory CD4 + T cells (Treg) are essential for maintaining peripheral tolerance, preventing autoimmune diseases like dermatomyositis, and play a role in the anti-tumor response and prevention of graft versus host disease (graft versus host disease - GVHD) after allogeneic bone marrow transplantation. Using two markers associated with ATP metabolism, CD26 and CD39, and the CD45RA maturation marker, we separated the Treg into 5 distinct subpopulations, each representing a different stage of maturation. Micro-environmental factors dictate this maturation as well as the functions of these different sub-populations. Dermatomyositis is an autoimmune disease primarily affecting the skin and muscle. During this pathology, we observed a phenotypic modification of Treg with a decrease in CD25 expression and an accumulation of CD39+ populations. The study of immune polarization revealed the disappearance of circulating MAIT (mucosal-associated invariant T cells) cells, the existence of a similar lymphocyte profile between the classic form and the amyopathic form and a skin "type I interferon” polarization during anti-MDA5 associated with the presence of interferon kappa. Finally, we were interested in patients presenting with relapsing MDS or AML after allogeneic transplantation treated with azacytidine (AZA), a hypomethylating agent. We were able to show that the Treg phenotype was modified compared to ungrafted individuals, but that it did not differ between relapse and non-relapse. Treatment with AZA appears to have a different dose-dependent effect on Tregs, both in vivo and in vitro, resulting in particular in the acquisition of FOXP3 and CD39.Les cellules T CD4+ régulatrices (Treg) sont essentielles au maintien de la tolérance périphérique, la prévention des maladies auto-immunes comme la DM et jouent un rôle dans la réponse anti-tumorale et la prévention de la maladie du greffon contre l’hôte (graft versus host disease – GVHD), après allogreffe de moelle. Grâce à deux marqueurs associés au métabolisme de l’ATP, le CD26 et le CD39, et au marqueur de maturation CD45RA, nous avons séparé les Treg en 5 sous-populations distinctes, chacune représentant un stade de maturation différent. Les facteurs micro-environnementaux dictent cette maturation ainsi que les fonctions de ces différentes sous-populations. La DM est une maladie auto-immune affectant principalement la peau et le muscle. Au cours de cette pathologie, nous avons observé une modification phénotypique des Treg avec une diminution d’expression du CD25 et une accumulation de populations CD39+. L’étude de la polarisation immunitaire a révélé la disparition des cellules MAIT (mucosal-associated invariant T cells) circulantes, l’existence d’un profil lymphocytaire similaire entre la forme classique et la forme amyopathique et une polarisation cutanée « interféron de type I » importante au cours de la forme avec anticorps anti-MDA5 en lien avec la présence d’interféron kappa. Enfin, nous nous sommes intéressés à des patients présentant un SMD ou une LAM en rechute après allogreffe traités par azacytidine (AZA), un agent hypométhylant. Nous avons pu montrer que le phénotype des Treg était modifié par rapport à des individus non greffés mais qu’il ne différait pas entre rechuteurs et non rechuteurs. Le traitement par AZA semble exercer un effet sur les Treg différent en fonction de la dose, à la fois in vivo et in vitro, aboutissant notamment à l’acquisition du FOXP3 et du CD39.(MED - Sciences médicales) -- UCL, 202
Metabolite proofreading, a neglected aspect of intermediary metabolism
No full textpeer reviewedEnzymes of intermediary metabolism are less specific than what is usually assumed: they often act on metabolites that are not their 'true' substrate, making abnormal metabolites that may be deleterious if they accumulate. Some of these abnormal metabolites are reconverted to normal metabolites by repair enzymes, which play therefore a role akin to the proofreading activities of DNA polymerases and aminoacyl-tRNA synthetases. An illustrative example of such repair enzymes is L-2-hydroxyglutarate dehydrogenase, which eliminates a metabolite abnormally made by a Krebs cycle enzyme. Mutations in L-2-hydroxyglutarate dehydrogenase lead to L-2-hydroxyglutaric aciduria, a leukoencephalopathy. Other examples are the epimerase and the ATP-dependent dehydratase that repair hydrated forms of NADH and NADPH; ethylmalonyl-CoA decarboxylase, which eliminates an abnormal metabolite formed by acetyl-CoA carboxylase, an enzyme of fatty acid synthesis; L-pipecolate oxidase, which repairs a metabolite formed by a side activity of an enzyme of L-proline biosynthesis. Metabolite proofreading enzymes are likely quite common, but most of them are still unidentified. A defect in these enzymes may account for new metabolic disorders
