When the nose must remain responsive: glutathione conjugation of the mammary pheromone in the newborn rabbit

In insects, xenobiotic-metabolizing enzymes were demonstrated to regulate pheromones inactivation, clearing them from the olfactory periphery and keeping receptors ready for stimulation renewal. Here, we investigate whether similar processes could occur in mammals, focusing on the pheromonal communication between female rabbits and their newborns. Lactating rabbits emit in their milk a volatile aldehyde, 2-methylbut-2-enal, that elicits searching-grasping in neonates; called the mammary pheromone (MP), it is critical for pups which are constrained to find nipples within the 5 min of daily nursing. For newborns, it is thus essential to remain sensitive to this odorant during the whole nursing period to display several actions of sucking. Here, we show that the MP is enzymatically conjugated to glutathione in newborn olfactory epithelium (OE), in accordance with the high mRNA expression of glutathione transferases evidenced by quantitative reverse transcription-PCR. This activity in the nose is higher than in the liver and in OE of newborns compared with weanlings (no more responsive to the pheromone). Therefore, the results pinpoint the existence of a high level of MP-glutathione conjugation activity in the OE of young rabbits, especially in the developmental window where the perceptual sensitivity toward the MP is crucial for survival

Rôle des enzymes du métabolisme des xénobiotiques dans les processus chimiosensoriels. Contribution de deux modèles de perception phéromonale

Diplôme : Dr. d'UniversitéRésumé : Les individus peuvent détecter les stimuli présents dans l'environnement (nourriture, partenaire sexuel, ...) par l'intermédiaire de processus de chimioperception. Pour être efficace, ces processus doivent être très sensibles, discriminants et éviter la saturation des récepteurs. Dans l'espace périrécepteur, les enzymes du métabolisme des xénobiotiques (EMX), impliquées dans la détoxication en catalysant la biotransformation des xénobiotiques, pourraient avoir un rôle crucial dans la modification ou l'arrêt du signal sensoriel. Pour étudier l'implication des EMX dans les processus chimiosensoriels et particulièrement dans la perception phéromonale, deux approches complémentaires ont été utilisées. La première consistait à étudier le métabolisme olfactif de la phéromone mammaire chez le lapin et l'autre à étudier la fonction de différentes EMX chez un modèle génétique : la drosophile. Les résultats majeurs sont : (i) Chez le lapin, il existe in vitro un métabolisme de la phéromone mammaire dépendant du glutathion qui varie en fonction de l'âge et du tissu Ces variations sont aussi observées pour certains gènes d'EMX. Ex vivo, le métabolisme global de la muqueuse olfactive de lapereau vis- à-vis de la phéromone peut être modulé par un modulateur d'activité des glutathion-transférases ou par une pré-exposition à la phéromone. (ii) Chez la drosophile, à l'aide d'outils de transgénèse, nous avons mis en évidence un rôle fonctionnel de plusieurs types d'EMX dans la discrimination des phéromones sexuelles par les mâles. Les travaux de cette thèse ont permis de mettre en évidence de manière fonctionnelle une implication des EMX dans le métabolisme ou la perception phéromonale

Perineurial Barrier Glia Physically Respond to Alcohol in an Akap200-Dependent Manner to Promote Tolerance.

Ethanol is the most common drug of abuse. It exerts its behavioral effects by acting on widespread neural circuits; however, its impact on glial cells is less understood. We show that Drosophila perineurial glia are critical for ethanol tolerance, a simple form of behavioral plasticity. The perineurial glia form the continuous outer cellular layer of the blood-brain barrier and are the interface between the brain and the circulation. Ethanol tolerance development requires the A kinase anchoring protein Akap200 specifically in perineurial glia. Akap200 tightly coordinates protein kinase A, actin, and calcium signaling at the membrane to control tolerance. Furthermore, ethanol causes a structural remodeling of the actin cytoskeleton and perineurial membrane topology in an Akap200-dependent manner, without disrupting classical barrier functions. Our findings reveal an active molecular signaling process in the cells at the blood-brain interface that permits a form of behavioral plasticity induced by ethanol

Inhibition of the mammary pheromone catabolism by a second odorant present in the same mixture

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UDP-glucuronosyltransferases (UGTs) in neuro-olfactory tissues: expression, regulation, and function.

International audienceThis work aims to review uridine diphosphate (UDP)-glucuronosyltransferase (UGT) expression and activities along different neuronal structures involved in the common physiological process of olfaction: olfactory epithelium, olfactory bulb, and olfactory cortex. For the first time, using high-throughput in situ hybridization data generated by the Allen Brain Atlas (ABA), we present quantitative analysis of spatial distribution of UGT genes in the mouse brain. The olfactory area is a central nervous system site with the highest expression of UGTs, including UGT isoforms not previously identified in the brain. Since there is evidence of the transfer of xenobiotics to the brain through the nasal pathway, circumventing the blood-brain barrier, olfactory UGTs doubtlessly share the common function of detoxification, but they are also involved in the metabolism and turnover of exogenous or endogenous compounds critical for physiological olfactory processing in these tissues. The function of olfactory UGTs will be discussed with a special focus on their participation in the perireceptor events involved in the modulation of olfactory perception

Glutathione conjugation of the rabbit mammary pheromone 2-methylbut-2-enal

International audienceIn the process of smell, the olfactory signal is initiated by the binding of odorous molecules to olfactory receptors. In the receptor environment,associated events are supposed to modulate this signal.Thus, the xenobiotic metabolizing enzymes, potentially involved in the clearance of the odorous molecules, could modulate the availability of these molecules for the olfactory receptors, and consequently could participate indirectly in the olfactory signal termination. A mammary pheromone, which is an odorous aldehyde (2-methylbut-2-enal or 2MB2) has been recently characterized in the rabbit by our group. The aim of this work was to elucidate the metabolism of 2MB2 in the rabbit olfactory mucosa (OM). Results of in vitro studies demonstrate that 2MB2 is conjugated to glutathione in OM, and that this metabolism is much stronger than in the liver. Besides, 2MB2 is less conjugated to glutathione in newborn rabbit OM than in weanling or adult animal mucosa. This last result is correlated with age-related variations in the expression of different olfactory glutathione transferase isoforms. In addition to in vitro studies, we developed an ex-vivo method in order to evaluate the metabolism of 2MB2 in a whole-tissue sample. This approach allows the nasal cavity to keep its complex structure, which is necessary for the olfactory physiological process. The disappearance of the volatile aldehyde is measured in the headspace around the isolated nasal cavity put in a closed vial, enabling a global measurement of the pheromone metabolism. These results demonstrate that 2MB2 is metabolized by the rabbit olfactory mucosa especially as glutathione conjugates, and suggest the use of this pheromone as an interesting tool for further investigations on the possible involvement of the xenobiotic metabolizing enzymes in the process of smell

Odorant Metabolism Analysis by an Automated Ex Vivo Headspace Gas-Chromatography Method

International audienceIn the olfactory epithelium (OE), odorant metabolizing enzymes have the dual function of volatile component detoxification and active clearance of odorants from the perireceptor environment to respectively maintain the integrity of the tissues and the sensitivity of the detection. Although emphasized by recent studies, this enzymatic mechanism is poorly documented in mammals. Thus, olfactory metabolism has been characterized mainly in vitro and for a limited number of odorants. The automated ex vivo headspace gas-chromatography method that was developed here was validated to account for odorant olfactory metabolism. This method easily permits the measurement of the fate of an odorant in the OE environment, taking into account the odorant gaseous state and the cellular structure of the tissue, under experimental conditions close to physiological conditions and with a high reproducibility. We confirmed here our previous results showing that a high olfactory metabolizing activity of the mammary pheromone may be necessary to maintain a high level of sensitivity toward this molecule, which is critical for newborn rabbit survival. More generally, the method that is presented here may permit the screening of odorants metabolism alone or in mixture or studying the impact of aging, pathology, polymorphism or inhibitors on odorant metabolism., (C) Copyright Oxford University Press 2016

Modulation of sex pheromone discrimination by a UDP-glycosyltransferase in Drosophila melanogaster

WOS:000529189000001This article belongs to the Special Issue Olfaction: From Genes to Behavior.International audienceThe detection and processing of chemical stimuli involve coordinated neuronal networks that process sensory information. This allows animals, such as the model species Drosophila melanogaster, to detect food sources and to choose a potential mate. In peripheral olfactory tissues, several classes of proteins are acting to modulate the detection of chemosensory signals. This includes odorant-binding proteins together with odorant-degrading enzymes (ODEs). These enzymes, which primarily act to eliminate toxic compounds from the whole organism also modulate chemodetection. ODEs are thought to neutralize the stimulus molecule concurrently to its detection, avoiding receptor saturation thus allowing chemosensory neurons to respond to the next stimulus. Here, we show that one UDP-glycosyltransferase (UGT36E1) expressed in D. melanogaster antennal olfactory sensory neurons (OSNs) is involved in sex pheromone discrimination. UGT36E1 overexpression caused by an insertion mutation affected male behavioral ability to discriminate sex pheromones while it increased OSN electrophysiological activity to male pheromones. Reciprocally, the decreased expression of UGT36E1, controlled by an RNAi transgene, improved male ability to discriminate sex pheromones whereas it decreased electrophysiological activity in the relevant OSNs. When we combined the two genotypes (mutation and RNAi), we restored wild-type-like levels both for the behavioral discrimination and UGT36E1 expression. Taken together, our results strongly suggest that this UGT plays a pivotal role in Drosophila pheromonal detection

Odorant-binding proteins and xenobiotic metabolizing enzymes: implications in olfactory perireceptor events.

http://onlinelibrary.wiley.com/doi/10.1002/ar.22735/abstractInternational audienceAt the periphery of the olfactory system, the binding of odorants on olfactory receptors (ORs) is usually thought to be the first level of the perception of smell. However, at this stage, there is evidence that other molecular mechanisms also interfere with this chemoreception by ORs. These perireceptor events are mainly supported by two groups of proteins present in the olfactory nasal mucus or in the nasal epithelium. Odorant-binding proteins (OBPs), the first group of proteins have been investigated for many years. OBPs are small carrier proteins capable of binding odorants with affinities in the micromolar range. Although there is no absolute evidence to support their functional roles in vertebrates, OBPs are good candidates for the transport of inhaled odorants towards the ORs via the nasal mucus. The second group of proteins involves xenobiotic metabolizing enzymes, which are strongly expressed in the olfactory epithelium and supposed to be involved in odorant transformation, degradation, and/or olfactory signal termination. Following an overview of these proteins, this review explores their roles, which are still a matter of debate. Anat Rec, 296:1333-1345, 2013. © 2013 Wiley Periodicals, Inc