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Arginine-vasopressin (AVP) is a neurohypophysial peptide known as the antidiuretic hormone. It forms an active signalling complex with the V2 receptor (V2R) and the Gs protein, promoting a cAMP/PKA-dependent aquaporin insertion in apical membranes of principal cells of the renal collecting ducts and ultimately, water reabsorption. Molecular mechanisms underlying activation of this critical G protein-coupled receptor (GPCR) signalling system are still unknown. To fill this gap of knowledge, we report here the structure of the AVP-V2R-Gs complex using cryo-electron microscopy (cryo-EM). Single-particle analysis revealed the presence of three different states. The two best maps were combined with computational and NMR spectroscopy constraints to reconstruct two structures of the ternary complex. These structures differ in AVP and Gs binding modes and could thus represent distinct complex conformations along the signalling activation pathway. Importantly, as compared to those of other class A GPCR-Gs complexes, the structures revealed an original receptor-Gs interface in which the Gsα subunit penetrates deeper into the active V2R, notably forming an ionic bond between its free C-terminal carboxylic function and the side chain of R137 in the V2R. Interestingly, the structures help to explain how V2R R137H or R137L/C variants can lead to two severe genetic diseases with opposite clinical outcomes, cNDI or NSIAD respectively. Our study thus provides important structural insights into the function of this clinically relevant GPCR signalling complex.

International audience; The signaling pathway of G protein-coupled receptors is strongly linked to their trafficking profile. Little is known about the molecular mechanisms involved in the vasopressin receptor V1b subtype (V1b R) trafficking and its impact on receptor signaling and regulation. For this purpose, we investigated the role of β-arrestins in receptor desensitization, internalization and recycling and attempted to dissect the V1b R-mediated MAP kinase pathway. Using MEF cells Knocked-out for β-arrestins 1 and 2, we demonstrated that both β-arrestins 1 and 2 play a fundamental role in internalization and recycling of V1b R with a rapid and transient V1b R-β-arrestin interaction in contrast to a slow and long-lasting β-arrestin recruitment of the V2 vasopressin receptor subtype (V2 R). Using V1b R-V2 R chimeras and V1b R C-terminus truncations, we demonstrated the critical role of the V1b R C-terminus in its interaction with β-arrestins thereby regulating the receptor internalization and recycling kinetics in a phosphorylation-independent manner. In parallel, V1b R MAP kinase activation was dependent on arrestins and Src-kinase but independent on G proteins. Interestingly, Src interacted with hV1b R at basal state and dissociated when receptor internalization occurred. Altogether, our data describe for the first time the trafficking profile and MAP kinase pathway of V1b R involving both arrestins and Src kinase family.

International audience; Polycystic kidney diseases (PKDs) are genetic disorders that can cause renal failure and death in children and adults. Lowering cAMP in cystic tissues through the inhibition of the type-2 vasopressin receptor (V2R) constitutes a validated strategy to reduce disease progression. We identified a peptide from green mamba venom that exhibits nanomolar affinity for the V2R without any activity on 155 other G-protein-coupled receptors or on 15 ionic channels. Mambaquaretin-1 is a full antagonist of the V2R activation pathways studied: cAMP production, beta-arrestin interaction, and MAP kinase activity. This peptide adopts the Kunitz fold known to mostly act on potassium channels and serine proteases. Mambaquaretin-1 interacts selectively with the V2R through its first loop, in the same manner that aprotinin inhibits trypsin. Injected in mice, mambaquaretin-1 increases in a dose-dependent manner urine outflow with concomitant reduction of urine osmolality, indicating a purely aquaretic effect associated with the in vivo blockade of V2R. CD1-pcy/pcy mice, a juvenile model of PKD, daily treated with 13 [Formula: see text]g of mambaquaretin-1 for 99 d, developed less abundant (by 33%) and smaller (by 47%) cysts than control mice. Neither tachyphylaxis nor apparent toxicity has been noted. Mambaquaretin-1 represents a promising therapeutic agent against PKDs.

International audience; We show here that the rat vasopressin V(1b) receptor simultaneously activates both the G(q/11)-inositol phosphate (IP) and G(s)-cAMP pathways when transiently expressed in Chinese hamster ovary, human embryonic kidney (HEK) 293, and COS-7 cells and stimulated with arginine-vasopressin. Higher concentrations of the hormone, however, were needed to trigger the cAMP pathway. The nonmammalian analog arginine-vasotocin and the selective V(1b) agonist d[Cha(4)]vasopressin also activated the cAMP and IP pathways, although d[Cha(4)]-vasopressin elicited the two responses with equivalent potencies. We determined that the V(1b) receptor is present as a homodimer at the plasma membrane. Treatment of V(1b)-transfected HEK-293 cells with methyl-beta-cyclodextrin, a drug known to dissociate cholesterol-rich domains of the plasma membrane, shifted the EC(50) of the vasopressin-induced cAMP accumulation to lower concentrations and, remarkably, increased the hormone efficacy related to the activation of this second messenger system. In parallel, the vasopressin-mediated activation of the IP pathway was slightly reduced without modification of its EC(50). These results suggest that, as with many other G protein-coupled receptors, when transfected in heterologous cell systems, the V(1b) receptor forms dimers that signal differentially through the G(q/11) and G(s) proteins depending on the nature of the ligand as well as on its localization within specialized compartments of the plasma membrane. The present study thus illustrates how signal transduction associated with the activation of a G protein-coupled receptor can be versatile and highly dependent on both the cell context and the chemical nature of the extracellular signaling messenger.

Activity of the magnocellular neurons that synthesize vasopressin in the supraoptic and paraventricular nuclei of the hypothalamus is modulated by local release of the neuropeptide within the nuclei. V1a and V1b vasopressin receptor genes are expressed in these cells. The present study reports the localization of V1a and V1b receptors using multiple labeling immunocytochemistry. Both receptors are mainly located in vasopressinergic magnocellular neurons and colocalized with vasopressin in cytoplasmic vesicles dispersed throughout the cell. Possible functional modifications of the mRNA and protein levels of the V1a receptor, the major isoform, were also investigated by semiquantitative in situ hybridization and immunocytochemistry in rats submitted to reduced or increased water intake. V1a mRNA and receptor levels varied with water balance. V1a mRNA level dropped in rats submitted to high water intake. Conversely, dehydration up-regulated the V1a receptor content. These observations suggest that the pathways that regulate the expression of the genes encoding vasopressin and the V1a receptor are linked, which fits the present findings that the two partners are colocalized in cytoplasmic vesicles. Colocalization might explain how V1 autoreceptors are controlled by cell activity and/or local concentration of vasopressin (released locally by the neurons themselves), allowing fine adjustment of magnocellular neuron activity.

To characterize the volume-sensitive, osmolyte permeable anion channels responsible for the osmodependent release of taurine from supraoptic nucleus (SON) astrocytes, we investigated the pharmacological properties of the [(3)H]-taurine efflux from acutely isolated SON. Taurine release induced by hypotonic stimulus (250 mosmol l(-1)) was not antagonized by the taurine transporter blocker guanidinoethyl sulphonate, confirming the lack of implication of the transporter. The osmodependent release of taurine was blocked by a variety of Cl(-) channel inhibitors with the order of potency: NPPB>niflumic acid>DPC>DIDS>ATP. On the other hand, release of taurine was only weakly affected by other compounds (dideoxyforskolin, 4-bromophenacyl bromide, mibefradil) known to block volume-activated anion channels in other cell preparations, and was completely insensitive to tamoxifen, a broad inhibitor of these channels. Although the molecular identity of volume-sensitive anion channels is not firmly established, a few genes have been postulated as potential candidates to encode such channels. We checked the expression in the SON of three of them, ClC(3), phospholemman and VDAC(1), and found that the transcripts of these genes are found in SON neurons, but not in astrocytes. Similar observation was previously reported for ClC(2). In conclusion, the osmodependent taurine permeable channels of SON astrocytes display a particular pharmacological profile, suggesting the expression of a particular type or subtype of volume-sensitive anion channel, which is likely to be formed by yet unidentified proteins.

Heterodimerization of G protein-coupled receptors has an impact on their signaling properties, but the molecular mechanisms underlying heteromer-directed selectivity remain elusive. Using purified monomers and dimers reconstituted into lipid discs, we explored how dimerization impacts the functional and structural behavior of the ghrelin receptor. In particular, we investigated how a naturally occurring truncated splice variant of the ghrelin receptor exerts a dominant negative effect on ghrelin signaling upon dimerization with the full-length receptor. We provide direct evidence that this dominant negative effect is due to the ability of the non-signaling truncated receptor to restrict the conformational landscape of the full-length protein. Indeed, associating both proteins within the same disc blocks all agonist- and signaling protein-induced changes in ghrelin receptor conformation, thus preventing it from activating its cognate G protein and triggering arrestin 2 recruitment. This is an unambiguous demonstration that allosteric conformational events within dimeric assemblies can be directly responsible for modulation of signaling mediated by G protein-coupled receptors.

International audience; G protein-coupled receptors (GPCRs) are seven-transmembrane proteins that mediate most cellular responses to hormones and neurotransmitters, representing the largest group of therapeutic targets. Recent studies show that some GPCRs signal through both G protein and arrestin pathways in a ligand-specific manner. Ligands that direct signaling through a specific pathway are known as biased ligands. The arginine-vasopressin type 2 receptor (V2R), a prototypical peptide-activated GPCR, is an ideal model system to investigate the structural basis of biased signaling. Although the native hormone arginine-vasopressin leads to activation of both the stimulatory G protein (Gs) for the adenylyl cyclase and arrestin pathways, synthetic ligands exhibit highly biased signaling through either Gs alone or arrestin alone. We used purified V2R stabilized in neutral amphipols and developed fluorescence-based assays to investigate the structural basis of biased signaling for the V2R. Our studies demonstrate that the Gs-biased agonist stabilizes a conformation that is distinct from that stabilized by the arrestin-biased agonists. This study provides unique insights into the structural mechanisms of GPCR activation by biased ligands that may be relevant to the design of pathway-biased drugs.

International audience; Accumulating evidence indicates that G protein-coupled receptors can assemble as dimers/oligomers but the role of this phenomenon in G protein coupling and signaling is not yet clear. We have used the purified leukotriene B(4) receptor BLT2 as a model to investigate the capacity of receptor monomers and dimers to activate the adenylyl cyclase inhibitory G(i2) protein. For this, we overexpressed the recombinant receptor as inclusion bodies in the Escherichia coli prokaryotic system, using a human alpha(5) integrin as a fusion partner. This strategy allowed the BLT2 as well as several other G protein-coupled receptors from different families to be produced and purified in large amounts. The BLT2 receptor was then successfully refolded to its native state, as measured by high-affinity LTB(4) binding in the presence of the purified G protein G alpha(i2). The receptor dimer, in which the two protomers displayed a well defined parallel orientation as assessed by fluorescence resonance energy transfer, was then separated from the monomer. Using two methods of receptor-catalyzed guanosine 5'-3-O-(thio)triphosphate binding assay, we clearly demonstrated that monomeric BLT2 stimulates the purified G alpha(i2) beta(1) gamma(2) protein more efficiently than the dimer. These data suggest that assembly of two BLT2 protomers into a dimer results in the reduced ability to signal.

International audience; The G protein-coupled receptors (GPCRs) play a major role in the regulation of physiological function. The emergence of the concept of GPCR oligomerization deeply modifies our understanding of their functioning. Much more than a simple association leading to an independent functioning, the GPCR oligomerization affects various steps such as membrane targeting of the receptors, binding of ligands, coupling to the intracellular pathways and internalization. Although significant advances have been performed in proving the existence of GPCR oligomers, its physiological impact remains to be established. Vasopressin and oxytocin receptors have constituted interesting experimental models in oligomer analysis. Because of the pharmacological tools available regarding these receptors and their expression at a high level in various tissues they can constitute very promising models to study the consequences of oligomerization in physiology.

The increase of plasma arginin-vasopressin (AVP) release, which translates hypothalamic AVP neuron activation in response to immune challenge, appears to occur independently of plasma osmolality or blood pressure changes. Many studies have shown that major inflammatory mediators produced in response to peripheral inflammation, such as prostaglandin (PG)-E2 and interleukin (IL)-1β, excite AVP neurons. However, in vivo electrical activation of AVP neurons was still not assessed in relation to plasma AVP release, osmolality, or blood pressure or to the expression and role of inflammatory molecules like PG-E2, IL-1β, IL-6, and tumor necrosis factor-α (TNFα). This study aims at elucidating those factors that underlie the activation of AVP neurons in response to immune stimulation mimicked by an intraperitoneal injection of lipopolysaccharide (LPS) in male Wistar rats. LPS treatment concomittanlty decreased diuresis and increased plasma AVP as well as AVP neuron activity in vivo, and these effects occurred as early as 30 min. Activation was sustained for more than 6 h. Plasma osmolality did not change, whereas blood pressure only transiently increased during the first hour post-LPS. PG-E2, IL-1β, and TNFα mRNA expression were raised 3 h after LPS, whereas IL-6 mRNA level increased 30 min post-LPS. In vivo electrophysiological recordings showed that brain IL-6 injection increased AVP neuron activity similarly to peripheral LPS treatment. In contrast, brain injection of anti-IL-6 antibodies prevented the LPS induced-activation of AVP neurons. Taken together, these results suggest that the early activation of AVP neurons in response to LPS injection is induced by brain IL-6.

International audience; Adaptive metabolic changes associated with bacterial infections are likely to cause dehydration. Activation of hypothalamic neurons in the supraoptic nucleus that release anti-diuretic arginine-vasopressin in plasma provides water retention. Aging is characterized by arginine-vasopressin neuron hyper-activity and over-expression of pro-inflammatory cytokines like interleukin (IL)-6. Conversely, insulin-like growth factor (IGF)-I, known to exhibit anti-inflammatory properties, decreases with age. We compared activation of arginine-vasopressin neurons in adult (3 months) and aged (22 months) Wistar rats by measuring not only c-fos expression, plasma arginine-vasopressin and diuresis but also the expression of IL-6 and IGF-I in the supraoptic nuclei after intraperitoneal lipopolysaccharide injection. Aged rats displayed a heightened, shorter lasting activation of arginine-vasopressin neurons following lipopolysaccharide as compared to adults. IL-6 mRNA was 3-fold higher while IGF-I mRNA was 10-fold lower in aged than in adult rats. Brain pre-treatment with neutralizing anti-IL-6 antibodies or recombinant IGF-I in aged rats reversed lipopolysaccharide-induced anti-diuresis. These data extend the concept of neuroendocrine-immune interactions to the arginine-vasopressin neuronal system by establishing a relationship between brain IL-6/IGF-I balance and age-associated arginine-vasopressin neuronal dysfunction.

Glycine receptors are ionotropic receptors formed by either the homomeric assembly of ligand-binding alpha subunits or the heteromeric combination of an alpha subunit and the auxiliary beta subunit. Glycine receptors in the brain are found at either pre- or post-synaptic sites. Rat supraoptic nucleus neurons express glycine receptors on the membrane of both their soma and dendrites within the supraoptic nucleus, and their axon terminals in the neurohypophysis. Taking advantage of the well-separated cellular compartments of this system, we correlated the structural properties of the receptors to their subcellular localization. Immunohistochemical study using the generic mAb4a antibody revealed that somatodendritic receptors were clustered, whereas axonal glycine receptors showed a more diffuse distribution. This was paralleled by the presence of clusters of the glycine receptor aggregating protein gephyrin in the supraoptic nucleus and its complete absence in the neurohypophysis. Moreover, another antibody recognizing the alpha1/alpha2 subunits similarly labeled the axonal glycine receptors, but did not recognize the somatodendritic receptor clusters of supraoptic nucleus neurons, indicative of structural differences between somatic and axonal glycine receptors. Furthermore, the subunits composing the somatic and axonal receptors have different molecular weight. Functional study further differentiated the two types of glycine receptors on the basis of their sensitivity to picrotoxin, identifying somatic receptors as alpha/beta heteromers, and axonal receptors as alpha homomers. These results indicate that targeting of glycine receptors to axonal or somatodendritic compartment is directly related to their subunit composition, and set the hypothalamo-neurohypophysial system as an excellent model to study the mechanisms of targeting of proteins to various neuronal cellular compartments.

International audience; We have identified and visualized the vasopressin (VP) receptors expressed by hypothalamic magnocellular neurons in supraop-tic and paraventricular nuclei. To do this, we used RT-PCR on total RNA extracts from supraoptic nuclei or on single freshly dissociated supraoptic neurons, and in situ hybridization on frontal sections of hypothalamus of Wistar rats. The RT-PCR on supraoptic RNA extracts revealed that mainly V 1a , but also V 1b , subtypes of VP receptors are expressed from birth to adult-hood. No V 2 receptor messenger RNA (mRNA) was detected. Furthermore , the single-cell RT-nested PCR indicated that the V 1a receptor mRNA is present in vasopressinergic magnocellular neurons. In light of these results, in situ hybridization was performed to visualize the V 1a and V 1b receptor mRNAs in supraoptic and para-ventricular nuclei. Simultaneously, we coupled this approach to: 1) in situ hybridization detection of oxytocin or VP mRNAs; or 2) immu-nocytochemistry to detect the neuropeptides. This provided a way of identifying the neurons expressing perceptible amounts of V 1a or V 1b receptor mRNAs as vasopressinergic neurons. Here, we suggest that the autocontrol exerted specifically by VP on vasopressinergic neurons is mediated through, at least, V 1a and V 1b subtype receptors.