Inactivation of mitochondrial aspartate aminotransferase contributes to the respiratory deficit of yeast frataxin-deficient cells

International audienceFriedreich's ataxia is a hereditary neurodegenerative disease caused by reduced expression of mitochondrial frataxin. Frataxin deficiency causes impairment in respiratory capacity, disruption of iron homoeostasis and hypersensitivity to oxidants. Although the redox properties of NAD (NAD + and NADH) are essential for energy metabolism, only few results are available concerning homoeostasis of these nucleotides in frataxin-deficient cells. In the present study, we show that the malate-aspartate NADH shuttle is impaired in Saccharomyces cerevisiae frataxin-deficient cells (yfh1) due to decreased activity of cytosolic and mitochondrial isoforms of malate dehydrogenase and to complete inactivation of the mitochondrial aspartate aminotransferase (Aat1). A considerable decrease in the amount of mitochondrial acetylated proteins was observed in the yfh1 mutant compared with wild-type. Aat1 is acetylated in wild-type mitochondria and deacetylated in yfh1 mitochondria suggesting that inactivation could be due to this post-translational modification. Mutants deficient in iron-sulfur cluster assembly or lacking mitochondrial DNA also showed decreased activity of Aat1, suggesting that Aat1 inactivation was a secondary phenotype in yfh1 cells. Interestingly, deletion of the AAT1 gene in a wild-type strain caused respiratory deficiency and disruption of iron homoeostasis without any sensitivity to oxidative stress. Our results show that secondary inactivation of Aat1 contributes to the amplification of the respiratory defect observed in yfh1 cells. Further implication of mitochondrial protein deacetylation in the physiology of frataxin-deficient cells is anticipated

Indoleamine 2 3-dioxygenase knockout limits angiotensin II-induced aneurysm in low density lipoprotein receptor-deficient mice fed with high fat diet.

AIMS: Abdominal aortic aneurysm (AAA) is an age-associated disease characterized by chronic inflammation, vascular cell apoptosis and metalloproteinase-mediated extracellular matrix degradation. Despite considerable progress in identifying targets involved in these processes, therapeutic approaches aiming to reduce aneurysm growth and rupture are still scarce. Indoleamine 2-3 dioxygenase 1 (IDO) is the first and rate-limiting enzyme involved in the conversion of tryptophan (Trp) into kynurenine (Kyn) pathway. In this study, we investigated the role of IDO in two different models of AAA in mice. METHODS AND RESULTS: Mice with deficiencies in both low density receptor-deficient (Ldlr-/-) and IDO (Ldlr-/-Ido1-/-) were generated by cross-breeding Ido1-/- mice with Ldlr-/-mice. To induce aneurysm, these mice were infused with angiotensin II (Ang II) (1000 ng/min/kg) and fed with high fat diet (HFD) during 28 days. AAAs were present in almost all Ldlr-/- infused with AngII, but only in 50% of Ldlr-/-Ido1-/- mice. Immunohistochemistry at an early time point (day 7) revealed no changes in macrophage and T lymphocyte infiltration within the vessel wall, but showed reduced apoptosis, as assessed by TUNEL assay, and increased α-actin staining within the media of Ldlr-/-Ido1-/- mice, suggesting enhanced survival of vascular smooth muscle cells (VSMCs) in the absence of IDO. In another model of elastase-induced AAA in C57Bl/6 mice, IDO deficiency had no effect on aneurysm formation. CONCLUSION: Our study showed that the knockout of IDO prevented VSMC apoptosis in AngII -treated Ldlr-/- mice fed with HFD, suggesting a detrimental role of IDO in AAA formation and thus would be an important target for the treatment of aneurysm

The Bacillus anthracis arylamine N-acetyltransferase ((BACAN)NAT1) that inactivates sulfamethoxazole, reveals unusual structural features compared with the other NAT isoenzymes

AbstractArylamine N-acetyltransferases (NATs) are xenobiotic-metabolizing enzymes that biotransform arylamine drugs. The Bacillus anthracis (BACAN)NAT1 enzyme affords increased resistance to the antibiotic sulfamethoxazole through its acetylation. We report the structure of (BACAN)NAT1. Unexpectedly, endogenous coenzymeA was present in the active site. The structure suggests that, contrary to the other prokaryotic NATs, (BACAN)NAT1 possesses a 14-residue insertion equivalent to the “mammalian insertion”, a structural feature considered unique to mammalian NATs. Moreover, (BACAN)NAT1 structure shows marked differences in the mode of binding and location of coenzymeA when compared to the other NATs. This suggests that the mechanisms of cofactor recognition by NATs is more diverse than expected and supports the cofactor-binding site as being a unique subsite to target in drug design against bacterial NATs

The xenobiotic-metabolizing enzymes arylamine N-acetyltransferases in human lens epithelial cells: inactivation by cellular oxidants and UVB-induced oxidative stress

The abbreviations used are: NAT, arylamine N-acetyltransferase; XME, xenobiotic-metabolizing enzymes; SIN1, 3-morpholinosydnonimine N-ethylcarbamide MOL 9738 3 ABSTRACT The human arylamine N-acetyltransferases NAT1 and NAT2 are important xenobioticmetabolizing enzymes involved in the detoxification and metabolic activation of numerous drugs and chemicals. NAT activity depends on genetic polymorphisms and on environmental factors. It has been shown that low NAT-acetylation activity could increase the risk of age-dependent cataract suggesting that NAT detoxification function may be important for lens cells homeostasis. We report here that the NAT acetylation pathway may occur in human lens epithelial (HLE) cells. Functional NAT1 enzyme was readily detected in HLE cells by RT-PCR, western-blotting and enzyme activity assays. NAT2 mRNA and enzymic activity was also detected. We investigated whether oxidants, known to be produced in HLE cells during oxidative stresses and involved in age-dependent cataract formation, decreased endogenous NAT1 and NAT2 activity. The exposure of HLE cells to peroxynitrite led to the dose-dependent irreversible inactivation of both NAT isoforms. Exposing HLE cells to continuously generated H 2 O 2 gave a dose-dependent inactivation of NAT1 and NAT2, reversible on addition of high concentrations of reducing agents. UVB irradiation also induced the reversible dose-dependent inactivation of endogenous NAT1 and NAT2, reversible on addition of reducing agents. Thus, our data suggest that functional NAT1 and NAT2 are present in HLE cells and may be impaired by oxidants produced during oxidative and photo-oxidative stresses. Oxidative-dependent inhibition of NATs in these cells may increase exposure of lens to the harmful effects of toxic chemicals which could contribute to cataractogenesis over time

The xenobiotic-metabolizing enzymes arylamine N-acetyltransferases in human lens epithelial cells: inactivation by cellular oxidants and UVB-induced oxidative stress

ABSTRACT The human arylamine N-acetyltransferases NAT1 and NAT2 are important xenobiotic-metabolizing enzymes involved in the detoxification and metabolic activation of numerous drugs and chemicals. NAT activity depends on genetic polymorphisms and on environmental factors. It has been shown that low NAT-acetylation activity could increase the risk of age-dependent cataract, suggesting that NAT detoxification function may be important for lens cells homeostasis. We report here that the NAT acetylation pathway may occur in human lens epithelial (HLE) cells. Functional NAT1 enzyme was readily detected in HLE cells by reverse transcription-polymerase chain reaction, Western blotting, and enzyme activity assays. NAT2 mRNA and enzymic activity were also detected. We investigated whether oxidants, known to be produced in HLE cells during oxidative stresses and involved in age-dependent cataract formation, decreased endogenous NAT1 and NAT2 activity. The exposure of HLE cells to peroxynitrite led to the dose-dependent irreversible inactivation of both NAT isoforms. Exposing HLE cells to continuously generated H 2 O 2 gave a dose-dependent inactivation of NAT1 and NAT2, reversible on addition of high concentrations of reducing agents. UVB irradiation also induced the reversible dose-dependent inactivation of endogenous NAT1 and NAT2, reversible on addition of reducing agents. Thus, our data suggest that functional NAT1 and NAT2 are present in HLE cells and may be impaired by oxidants produced during oxidative and photooxidative stresses. Oxidativedependent inhibition of NATs in these cells may increase exposure of lens to the harmful effects of toxic chemicals that could contribute to cataractogenesis over time

Genetic deficiency of indoleamine 2,3-dioxygenase promotes gut microbiota-mediated metabolic health.

The association between altered gut microbiota, intestinal permeability, inflammation and cardiometabolic diseases is becoming increasingly clear but remains poorly understood1,2. Indoleamine 2,3-dioxygenase is an enzyme induced in many types of immune cells, including macrophages in response to inflammatory stimuli, and catalyzes the degradation of tryptophan along the kynurenine pathway. Indoleamine 2,3-dioxygenase activity is better known for its suppression of effector T cell immunity and its activation of regulatory T cells3,4. However, high indoleamine 2,3-dioxygenase activity predicts worse cardiovascular outcome5-9 and may promote atherosclerosis and vascular inflammation6, suggesting a more complex role in chronic inflammatory settings. Indoleamine 2,3-dioxygenase activity is also increased in obesity10-13, yet its role in metabolic disease is still unexplored. Here, we show that obesity is associated with an increase of intestinal indoleamine 2,3-dioxygenase activity, which shifts tryptophan metabolism from indole derivative and interleukin-22 production toward kynurenine production. Indoleamine 2,3-dioxygenase deletion or inhibition improves insulin sensitivity, preserves the gut mucosal barrier, decreases endotoxemia and chronic inflammation, and regulates lipid metabolism in liver and adipose tissues. These beneficial effects are due to rewiring of tryptophan metabolism toward a microbiota-dependent production of interleukin-22 and are abrogated after treatment with a neutralizing anti-interleukin-22 antibody. In summary, we identify an unexpected function of indoleamine 2,3-dioxygenase in the fine tuning of intestinal tryptophan metabolism with major consequences on microbiota-dependent control of metabolic disease, which suggests indoleamine 2,3-dioxygenase as a potential therapeutic target

Safety and preliminary efficacy on cognitive performance and adaptive functionality of epigallocatechin gallate (EGCG) in children with Down syndrome. A randomized phase Ib clinical trial (PERSEUS study)

Purpose: Although some caregivers are using epigallocatechin gallate (EGCG) off label in hopes of improving cognition in young adults with Down syndrome (DS), nothing is known about its safety, tolerability, and efficacy in the DS pediatric population. We aimed to evaluate safety and tolerability of a dietary supplement containing EGCG and if EGCG improves cognitive and functional performance. Methods: A total of 73 children with DS (aged 6-12 years) were randomized. Participants received 0.5% EGCG (10 mg/kg daily dose) or placebo for 6 months with 3 months follow up after treatment discontinuation. Results: In total, 72 children were treated and 66 completed the study. A total of 38 participants were included in the EGCG group and 35 in the placebo group. Of 72 treated participants, 62 (86%) had 229 treatment-emergent adverse events (AEs). Of 37 participants in the EGCG group, 13 (35%) had 18 drug-related treatment-emergent AEs and 12 of 35 (34%) from the placebo group had 22 events. In the EGCG group, neither severe AEs nor increase in the incidence of AEs related to safety biomarkers were observed. Cognition and functionality were not improved compared with placebo. Secondary efficacy outcomes in girls point to a need for future work. Conclusion: The use of EGCG is safe and well-tolerated in children with DS, but efficacy results do not support its use in this population. (C) 2022 The Authors. Published by Elsevier Inc. on behalf of American College of Medical Genetics and Genomics

Hypothalamic AgRP-neurons control peripheral substrate utilization and nutrient partitioning

Obesity-related diseases such as diabetes and dyslipidemia result from metabolic alterations including the defective conversion, storage and utilization of nutrients, but the central mechanisms that regulate this process of nutrient partitioning remain elusive. As positive regulators of feeding behaviour, agouti-related protein (AgRP) producing neurons are indispensible for the hypothalamic integration of energy balance. Here, we demonstrate a role for AgRP-neurons in the control of nutrient partitioning. We report that ablation of AgRP-neurons leads to a change in autonomic output onto liver, muscle and pancreas affecting the relative balance between lipids and carbohydrates metabolism. As a consequence, mice lacking AgRP-neurons become obese and hyperinsulinemic on regular chow but display reduced body weight gain and paradoxical improvement in glucose tolerance on high-fat diet. These results provide a direct demonstration of a role for AgRP-neurons in the coordination of efferent organ activity and nutrient partitioning, providing a mechanistic link between obesity and obesity-related disorders