Etude moléculaire et pharmacologique du récepteur H3 de l'histamine

PARIS5-BU Saints-Pères (751062109) / SudocSudocFranceF

Constitutive activity of the histamine H3 receptor

International audienceConstitutive activity has been mainly recorded for numerous overexpressed and/or mutated receptors. The histamine H 3 receptor (H 3R) is a target of choice to study the physiological relevance of this process. In rodent brain, postsynaptic H 3Rs show high constitutive activity, and presynaptic H 3 autoreceptors that show constitutive activity have a predominant role in inhibiting the activity of histamine neurons. H 3R inverse agonists abrogate this constitutive brake and enhance histamine release in vivo. Some of these inverse agonists have entered clinical trials for the treatment of cognitive and food intake disorders. Studies performed in vitro and in vivo with proxyfan show that this H 3R ligand is a ‘protean agonist’ – that is, a ligand with a spectrum of activity ranging from full agonism to full inverse agonism depending on the level of H 3R constitutive activity. Consistent with its physiological and therapeutic relevance, the constitutive activity of H 3R thus has a major function in the brain and regulates the activity of H 3R-targeted drugs

Oligomérisation des protéines humaines et virales à sept domaines transmembranaires

Les récepteurs couplés aux protéines G (RCPG), aussi appelés protéines à sept domaines transmembranaires (7TM), représentent la plus grande famille de protéines. Elle comprend, chez l’homme, environ 900 membres. Ces protéines se lient à une grande variété de ligands ce qui entraîne l’activation de voies de signalisation impliquées dans divers processus cellulaires. Certaines protéines à 7TM, communément appelés orphelines, n’ont pas de ligand identifié, mais semblent jouer un rôle important dans la modulation de la fonction cellulaire via leurs activités constitutives ou leurs interactions avec d’autres protéines à 7TM. Certains virus synthétisent des protéines orphelines à 7TM homologues aux récepteurs de chimiokines humains pour détourner les fonctions de la cellule hôte et promouvoir leur réplication et leur dissémination. En effet, les protéines virales à 7TM sont capables de former des homomères ou des hétéromères avec d’autres protéines virales à 7TM, voire avec des protéines à 7TM de la cellule hôte. L’hétéromérisation des protéines virales à 7TM constitue une stratégie pertinente pour contrôler les fonctions de la cellule hôte

Histamine H3 and dopamine D2 receptor-mediated [35S]GTPγ[S] binding in rat striatum: Evidence for additive effects but lack of interactions

International audienceThe interactions in the rat striatum between H3 receptors (H3Rs) and D2 receptors (D2Rs) were investigated with the [35S]GTPγ[S] binding assay. The H3R agonist (R)α-methylhistamine increased [35S]GTPγ[S] binding to striatal membranes with an EC50 = 14 ± 5 nM and a maximal effect of +19 ± 1%. This effect was inhibited by the H3R antagonist ciproxifan with a Ki = 1.0 ± 0.3 nM. The D2R agonist quinpirole increased [35S]GTPγ[S] binding to the same membranes with an EC50 = 1.5 ± 0.5 μM and a maximal effect of +28 ± 2%. Its effect was blocked by haloperidol with a Ki = 0.3 ± 0.1 nM. The maximal effects of the H3R and D2R agonists were additive (+46 ± 3%). However, D2R ligands did not modify the effects of H3R ligands and vice versa. Ciproxifan behaved as an H3R inverse agonist and decreased [35S]GTPγ[S] binding. Haloperidol had no effect and did not change the inverse agonist effect of ciproxifan. Administrations for 10 days of ciproxifan (1.5 mg/kg/day) or haloperidol (0.5 mg/kg/day) did not change the effects of quinpirole and (R)α-methylhistamine, respectively. These data suggest that striatal H3Rs and D2Rs do not interact through their coupling to G-proteins. However, a hyperactivity of histaminergic and dopaminergic neurons being observed in schizophrenia, the additive activations of H3Rs and D2Rs suggest that they cooperate to generate some schizophrenic symptoms. Such a postsynaptic mechanism may underlie the antipsychotic-like effects of H3R inverse agonists and supports their therapeutic interest, alone or as adjunctive treatment with neuroleptics

Chromosomal mapping and organization of the human histamine H3 receptor gene

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Le système histaminergique : une cible pour de nouveaux traitements des deficits cognitifs

International audienceThe central effects of histamine are mediated by H1,H2 and H3 receptors. The H3 receptor inhibits histamine release in brain. Therefore, H3 receptor inverse agonists, by suppressing this brake, enhance histamine neuron activity.The histaminergic system plays a major role in cognition and H3 receptor inverse agonists are expected to be a potential therapeutics for cognitive deficits of Alzheimer’s disease (AD). They are eagerly awaited inasmuch as other treatments of the disease, such as tacrine or memantine, also enhance, through different mechanisms, histaminergic neurotransmission.An important loss of histaminergic neurons has been observed in AD. In contrast, levels of the histamine metabolite in the CSF of AD patients show that their global activity is decreased by only 25%. This indicates that activating histamine neurons in AD can be envisaged.L’histamine exerce ses effets centraux en activant des récepteurs H1,H2 et H3. Le récepteur H3 inhibe la liberation de l’histamine cérébrale. Ainsi, les agonistes inverses H3, en levant ce frein, augmentent l’activité des neurones à histamine.Le système histaminergique est un système majeur de la cognition et les agonistes inverses H3 sont pressentis comme thérapeutique potentielle des déficits cognitifs de la maladie d’Alzheimer (AD). Ils sont d’autant plus attendus que d’autres traitements de la maladie, tels que la tacrine ou la mémantine, augmentent aussi, mais par d’autres mécanismes, la neurotransmission histaminergique.Il existe une perte importante de neurones histaminergiques dans l’AD, mais la mesure des taux du métabolite de l’histamine dans le LCR de patients atteints d’AD montre que leur activité globale n’est diminuée que de 25 %. Ces données montrent qu’il devrait bien être possible d’activer les neurones histaminergiques dans l’AD

Luminogenic HiBiT peptide-based NanoBRET ligand binding assays for melatonin receptors

The two human melatonin receptors MT and MT , which belong to the G protein-coupled receptor (GPCR) family, are important drug targets with approved indications for circadian rhythm- and sleep-related disorders and major depression. Currently, most of the pharmacological studies were performed using [ H]melatonin and 2-[ I]iodomelatonin (2-[ I]-MLT) radioligands. Recently, NanoLuc-based bioluminescence resonance energy transfer (NanoBRET) monitoring competitive binding between fluorescent tracers and unmodified test compounds has emerged as a sensitive, nonradioactive alternative for quantifying GPCR ligand engagement on the surface of living cells in equilibrium and real time. However, developing such assays for the two melatonin receptors depends on the availability of fluorescent tracers, which has been challenging predominantly owing to their narrow ligand entry channel and small ligand binding pocket. Here, we generated a set of melatonergic fluorescent tracers and used NanoBRET to evaluate their engagement with MT and MT receptors that are genetically fused to an N-terminal luminogenic HiBiT-peptide. We identified several nonselective and subtype-selective tracers. Among the selective tracers, PBI-8238 exhibited high nanomolar affinity to MT , and PBI-8192 exhibited low nanomolar affinity to MT . The pharmacological profiles of both tracers were in good agreement with those obtained with the current standard 2-[ I]-MLT radioligand. Molecular docking and mutagenesis studies suggested the binding mode of PBI-8192 in MT and its selectivity over MT . In conclusion, we describe the development of the first nonradioactive, real-time binding assays for melatonin receptors expressed at the cell surface of living cells that are likely to accelerate drug discovery for melatonin receptors. [Abstract copyright: © 2022 American Chemical Society.

The Rat H3 Receptor: Gene Organization and Multiple Isoforms

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