Le clan « arrestine » est une superfamille de protéines adaptatrices regroupant les arrestines conventionnelles (β-arrestines et arrestines visuelles), bien décrites pour leur rôle dans la régulation des récepteurs membranaires couplés aux protéines G hétéro-trimériques et la signalisation associée et des protéines de type arrestin-like identifiées plus récemment, qui semblent partager des fonctions communes dans la régulation et le trafic de cargos membranaires. Ce travail de thèse a porté sur l'étude de la protéine arrestin-like AdcA de Dictyostelium discoideum dans l'objectif d'en définir le rôle fonctionnel. En plus de son module arrestine, caractéristique de cette famille de protéines, AdcA possède un domaine FYVE qui permet son association à la voie endocytaire, un domaine C-terminal riche en tyrosines et un domaine N-terminal riche en histidines impliqué dans son oligomérisation. Mes travaux ont permis d'établir que la protéine AdcA répond à des stress de natures diverses dont l'hyper-osmolarité, par une multi-phosphorylation massive, notamment au niveau du domaine N-terminal. La sensibilité d'AdcA à la dépolymérisation du réseau d'actine suggère un lien fonctionnel entre le cytosquelette d'actine et la cascade de signalisation menant à la phosphorylation de la protéine. En conditions de stress modéré, la phosphorylation d'AdcA est transitoire et sa déphosphorylation, en partie dépendante du facteur de transcription STATc, corrèle avec l'adaptation des cellules aux conditions de stress. Cette modification post-traductionnelle transitoire pourrait permettre de contrôler l'activité d'AdcA et d'optimiser la réponse des cellules au stress. Parallèlement, la caractérisation fonctionnelle d'un partenaire d'AdcA, la protéine FrmC, a été entreprise. FrmC est une nouvelle protéine, encore non caractérisée, présentant plusieurs domaines fonctionnels dont un domaine FERM capable de lier l'actine in vitro et un domaine à motifs LRR. Mes travaux ont notamment mis en évidence que FrmC est recrutée à la membrane plasmique et joue un rôle dans l'adhésion cellulaire. Par ailleurs, l'absence de FrmC affecte l'adaptation des cellules et la réponse d'AdcA en situation de stress hyper-osmotique. / The arrestin clan represents a large group of adaptor proteins which includes the canonical arrestins - β-arrestins and visual arrestins – well described for their role in the regulation of membrane receptors coupled to heterotrimeric G-proteins and associated signaling as well as arrestin-like proteins identified more recently that seem to share functions in the regulation and trafficking of membrane cargoes. This work focused on the study of the arrestin-like protein AdcA of Dictyostelium discoideum, to determine the functional role of this atypical member. In addition to the arrestin module common to all the members of the arrestin family, AdcA harbors a FYVE domain responsible for its association to the endocytic pathway, a C-terminal tyrosine-rich domain and an N-terminal extension rich in histidine residues mediating its oligomerization. I have established that AdcA responds to a variety of stresses such as hyperosmolarity by a massive multi-phosphorylation of the protein. Sensitivity of AdcA to changes in F-actin polymerization status suggests a link between the signaling cascade leading to AdcA phosphorylation and the actin cytoskeleton. In conditions of moderate stress, AdcA response is transient and its dephosphorylation depends on the transcription factor STATc and correlates with cell adaptation to the stress conditions. This post-translational modification of AdcA could modulate its activity and optimitize the cell response to stress. In parallel, the functional characterization of a partner of AdcA, the protein FrmC, has been undertaken. This so-far uncharacterized protein presents a multimodular structure with a FERM domain able to bind F-actin in vitro and several leucine-rich repeats (LRR). I have shown that FrmC is recruited to the plasma membrane and is involved in cell-substrate adhesion. In addition, disruption of FrmC affects cell adaptation and AdcA response in conditions of hyperosmotic stress.

As células endoteliais são capazes de converter o estímulo mecânico em sinais intracelulares e produzir fatores vasoativos como o óxido nítrico (oNO). Evidências recentes sugerem que as beta-arrestinas desempenham um papel importante não somente na dessensibilização e internalização de receptores acoplados à proteína G (GPCR) como também na mecanotransdução. Nós testamos a hipótese de que células endoteliais submetidas ao shear stress (SS) produzem oNO por meio da ativação da via de sinalização dependente de beta-arrestina. Para tal, células endoteliais de veia safena (hSVEC) foram transfectadas com siRNA contra as isoformas 1 e 2 da beta-arrestina e, posteriormente, submetidas ao SS (15 dinas/cm2) durante 10 min. Nós encontramos que as SVEC silenciadas para a beta-arrestina 1/2 (70%) exibiram uma menor produção de nitrito no meio de cultura em resposta ao SS (166±17 vs. 326±44% comparado com hSVEC transfectadas com siRNA controle). Além disso, o silenciamento da beta-arrestina 1 e 2 preveniu os níveis de fosforilação da Akt no resíduo de serina 473 e a fosforilação da eNOS no resíduo de serina 1177, enquanto que a fosforilação da ERK 1/2 manteve-se inalterada. Curiosamente, análises de imunoprecipitação mostraram que a beta-arrestina interage com caveolina-1, um mecanossensor do shear stress, mas não é influenciado pelo SS. Além disso, na situação estática, a beta-arrestina encontra-se em uma localização perinuclear e, após o SS, adquiriu um padrão mais difuso no citosol. Coletivamente, esses dados sugerem que a beta-arrestina e a sinalização downstream Akt/ eNOS são necessárias para a produção de oNO induzido por shear stress em células endoteliais vasculares humana / Endothelial cells are capable of converting mechanical stimuli into intracellular signals generating vasoactive factors such as nitric oxide (oNO). Recent evidence suggests that beta-arrestins play a role not only on G protein-coupled receptors (GPCR) desensibilization but also in mechanotransduction. We tested the hypothesis that beta-arrestin and its downstream signaling influence laminar shear stress (SS)-induced oNO production by endothelial cells. Towards this end, human saphenous vein endothelial cells (hSVEC) transfected with siRNA against beta-arrestins isoforms 1 and 2 were subjected to SS (15 dynes/cm2, 10 minutes). We found that the SS-induced production of nitrite in the cell culture medium from down-expressed beta-arrestin 1/ 2 (70%) SVEC decreased (166±17 vs. 326±44% compared to wild-type hSVEC; P < 0.001). The beta-arrestin 1 and 2 down-regulation in SVEC also inhibited the phosphorylation levels of Akt at the serine residue 473 and the phosphorylation levels of eNOS at the serine residue 1177, whereas ERK phosphorylation remained unchanged. Interestingly, immunoprecipitation analysis showed that beta-arrestin interacts with caveolin-1, a shear stress mechanosensor, which is not influenced by SS despite the fact that the static perinuclear localization of beta-arrestins changed to the cytosol upon SS. Collective these data suggest that beta-arrestin and Akt/eNOS downstream signaling are required for shear stress-induced nitric oxide production in human vascular endothelial cells

Les troubles cognitifs constituent des symptômes quasi constants parmi les patients souffrant de dépression caractérisée. De récentes études indiquent que ces troubles mentaux pourraient bénéficier de la modulation de la signalisation du récepteur sérotoninergique 5-HT4. Dans ce travail de thèse, nous avons dans un premier temps caractérisé les troubles cognitifs dans un modèle d’anxiété/dépression chez la Souris, le modèle CORT. Nous avons ensuite évalué l’efficacité d’un traitement chronique par un agoniste du récepteur 5-HT4, le RS 67333, en comparaison à la fluoxetine, un antidépresseur monoaminergique de référence sur les altérations émotionnelles et cognitives. D’autre part, des données de la littérature indiquent que la cascade de signalisation de la protéine β-arrestine 1 (impliquée dans la désensibilisation et l’internalisation du récepteur 5-HT4) serait un biomarqueur potentiel préclinique/clinique des états dépressifs et de la réponse au traitement antidépresseur. Nous avons donc cherché à définir le phénotype anxio/dépressif et cognitif chez des souris tissus-spécifiques conditionnelles, dont l’expression de la protéine β-arrestine 1 dans les cellules souches du gyrus dentelé a été supprimée. L’ensemble de ces travaux de thèse met en avant le rôle prépondérant de l’activation du récepteur 5-HT4 non seulement dans sa capacité à corriger les symptômes d’anxiété/dépression mais aussi les troubles cognitifs associés à la dépression dans un modèle d’anxiété/dépression chez la Souris. D’un point de vue mécanistique, ces données confirment l’implication de la protéine β-arrestine 1 dans la réponse à la fluoxetine au niveau comportemental et directement au sein du processus de neurogenèse hippocampique chez la souris adulte. Enfin, l’expression de la protéine β-arrestine 1 dans les jeunes neurones de l’hippocampe se révèle aussi être un acteur déterminant dans les processus cognitifs et la réponse à la fluoxetine et au RS 67333. / Cognitive disturbances are often reported as serious incapacitating symptoms by patients suffering from major depressive disorders. Recent studies showed that these mood disorders could benefit from the modulation of 5-HT4 receptor pathway. Here, we performed a complete characterization of cognitive functions in a neuroendocrine mouse model of depression, the CORT model. We then evaluated emotional and cognitive effects of either a chronic 5-HT4 receptor agonist treatment, RS 67333 or fluoxetine, a classical monoaminergic antidepressant. Recent data indicate that β-arrestins proteins could be an important molecular determinant in depressive states and in the effects of antidepressants. We determined emotional and cognitive phenotypes in conditional tissue-specific mice in which expression of β-arrestin 1 in adult hippocampal stem cells was deleted. This work suggests that the 5-HT4 receptor plays a major role to correct not only anxiety/depression-related symptoms but also cognitive alterations in a mouse model of anxiety/depression model. Moreover, these data confirm the involvement of β-arrestin 1 protein in behavioral and neurogenic responses to fluoxetine treatment in adult mice. Finally, β-arrestin 1 protein expression in adult born neuron is critical for cognition and also to fluoxetine and RS 67333 response.

G protein-coupled receptors (GPCRs) are the largest group of membrane-bound receptors. Transmission of signals into the cell interior is mediated through the interactions of these receptors with other signaling molecules. Nowadays, a great attention is devoted to biased ligands which are able to alter the conformation of the receptor in a specific way and thus distinctly affect its function. This diploma thesis was focused on a study of µ-opioid receptor (MOR), which is important in nociception. The aim of this study was to find out, how the activation of MOR by specific biased ligands (morphine, endomorphin-2 and DAMGO) affects the function and the interactions of MOR with potential molecular partners (for example G proteins or β-arrestin) A method of siRNA interference was used to knock down the following selected signaling molecules: Gαi1, Gαi2, Gαi3, Gαz and β-arrestin2. The effect of biased ligands on lateral mobility of MOR in the plasma membrane and on activity of adenylyl cyclase (AC) was examined under these conditions. We observed a possible involvement of Gαz subunit in the lateral mobility of MOR after the effect of morphine and endomorphin-2. The lateral mobility of MOR was significantly increased in cells lacking Gαi2 or Gαi3 or β-arrestin2. In this case the MOR was in inactive state....

Toll-like receptor 4 (TLR4), a key member of the TLR family, has been well characterized by its function in the induction of inflammatory products of innate immunity. However, the involvement of TLR4 in a variety of apoptotic events by an unknown mechanism has been the focus of great interest. Our investigation found that TLR4 promoted apoptotic signalling by affecting the glycogen synthase kinase-3β (GSK-3β) pathway in a serum-deprivation- induced apoptotic paradigm. Serum deprivation induces GSK-3β activation in a pathway that leads to subsequent cell apoptosis. Intriguingly, this apoptotic cascade is amplified in presence of TLR4 but greatly attenuated by β-arrestin 2, another critical molecule implicated in TLR4-mediated immune responses. Our data suggest that the association of β-arrestin 2 with GSK-3β contributes to the stabilization of phospho-GSK-3β, an inactive form of GSK-3β. It becomes a critical determinant for the attenuation of TLR4-initiated apoptosis by β-arrestin 2. Taken together, we demonstrate that the TLR4 possesses the capability of accelerating GSK-3β activation thereby deteriorating serum-deprivation-induced apoptosis; β-arrestin 2 represents an inhibitory effect on the TLR4-mediated apoptotic cascade, through controlling the homeostasis of activation and inactivation of GSK-3β.

This study analyzed whether the positive allosteric modulator of metabotropic glutamate receptor type 5 (mGlu5) 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB) would alleviate deficits in prepulse inhibition (PPI) and affect dopamine (DA) D2 signaling in the dorsal striatum and prefrontal cortex (PFC) in the neonatal quinpirole (NQ) model of schizophrenia (SZ). Male and female Sprague-Dawley rats were neonatally treated with either saline (NS) or quinpirole HCL (1 mg/kg; NQ), a DAD2 receptor agonist, from postnatal days (P) 1–21. Rats were raised to P44 and behaviorally tested on PPI from P44-P48. Before each trial, rats were subcutaneous (sc) administered saline or CDPPB (10 mg/kg or 30 mg/kg). On P50, rats were given a spontaneous locomotor activity test after CDPPB or saline administration. On P51, the dorsal striatum and PFC were evaluated for both arrestin-2 (βA-2) and phospho-AKT protein levels. NQ-treated rats demonstrated a significant deficit in PPI, which was alleviated to control levels by the 30 mg/kg dose of CDPPB. There were no significant effects of CDPPB on locomotor activity. NQ treatment increased βA-2 and decreased phospho-AKT in both the dorsal striatum and PFC, consistent with an increase DAD2 signaling. The 30 mg/kg dose of CDPPB significantly reversed changes in βA-2 in the dorsal striatum and PFC and phospho-AKT in the PFC equivalent to controls. Both doses of CDPPB produced a decrease of phospho-AKT in the PFC compared to controls. This study revealed that a mGlu5 positive allosteric modulator was effective to alleviate PPI deficits and striatal DAD2 signaling in the NQ model of SZ.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第24525号 / 医博第4967号 / 新制||医||1065(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 渡邊 直樹, 教授 中川 一路, 教授 秋山 芳展 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Résumé : La contraction cellulaire est une activité centrale dans plusieurs processus physiologiques. Entre autre, elle joue un rôle dans la régulation de la perméabilité vasculaire et de la pression artérielle. Il est également établi qu’une contraction anormale des cellules du muscle lisse vasculaire (VSMC) est souvent associée à l’hypertension et ses complications. Il est donc suggéré que l’étude des mécanismes impliqués dans la transduction de signaux menant à la contraction cellulaire et les mécanismes impliqués dans la régulation de celle-ci pourrait permettre d’identifier de nouvelles cibles potentielles afin d’envisager de nouveaux traitements pour cette maladie. Étant donné le rôle connu du système angiotensinergique dans l’activité contractile des VSMC et les nombreux indices suggérant une dérégulation de ce système dans de développement de l’hypertension; la présente thèse a été consacrée, dans un premier temps, à identifier de nouveaux mécanismes de signalisation impliqués dans la contraction cellulaire induite par l’angiotensine II. Ainsi, il est montré, pour la première fois, que les β-arrestines; des protéines adaptatrices impliquées dans la désensibilisation et la signalisation des récepteurs couplés aux protéines G, participent à la contraction cellulaire associée à l’activation du récepteur de l’angiotensine de type 1, et ce, en exerçant des effets opposés sur la phosphorylation de la chaîne légère de la myosine. Dans un second temps, étant donné qu’en condition diabétique une dysfonction vasculaire est observée et que cette dernière serait reliée à des changements dans le phénotype fonctionnel des VSMC; la deuxième partie de cette thèse traite des effets de l’exposition aux produits de glycation avancée (AGE) sur le phénotype et l’activité contractile des VSMC. Effet, les AGE, issus de la réaction entre les protéines et le glucose et dont la formation est particulièrement favorisée en contexte diabétique, pourraient être impliqués dans la dysfonction vasculaire observée. Ainsi, il est montré, pour la première fois, que l’exposition des VSMC aux AGE inhibe l’expression de leur phénotype contractile en affectant leurs propriétés mécaniques et diverses fonctions cellulaires telles que la signalisation, la contraction et l’organisation du cytosquelette. Dans un contexte plus large, cette thèse confirme également l’importance d’intégrer les approches biophysiques à la biologie cellulaire. En effet, les résultats obtenus par microscopie à force atomique sont uniques puisqu’ils offrent une nouvelle perspective concernant l’activité cellulaire via la caractérisation du phénotype mécanique de la cellule et la mesure de la contraction au niveau d’une seule cellule. || Abstract : Cell contraction plays a key role in a variety of physiological processes, among those; it regulates vascular permeability and blood pressure. It is known that abnormal contraction of vascular smooth muscle cells (VSMC) is often associated with hypertension and its complications. Therefore, it is suggested that studying mechanisms involved in signal transduction leading to cell contraction and mechanisms regulating the cell ability to contract may allow identifying new therapeutic targets in order to suggest new treatments for hypertension. Knowing the role of the angiotensin system in VSMC contractility and the numerous evidences suggesting a dysregulation of this system in the development of hypertension; this thesis first sought to identify new signaling mechanisms involved in cell contraction induced by angiotensin II. Therefore, it is shown here, for the first time, that β- arrestins; which are scaffolding proteins involved in the desensitisation and the signalling of protein G-coupled receptors, participate in cell contractile activity induced by angiotensin receptor type 1 activation by reciprocally regulating myosin activity through its light chain phosphorylation. Secondly, knowing that a vascular dysfunction is observed in diabetes which could be attributed to changes in VSCM functional phenotype; this thesis also investigated the effect of advanced glycation end-products (AGE) exposure on the contractile phenotype and function of VSMC. Indeed, AGE, which are the product of a reaction between proteins and glucose, are increased significantly in diabetes and are suspected to be involved in the vascular dysfunction observed in this metabolic disease. Therefore, it shown, for the first time, that AGE stimulation of the VSMC A7r5 interfere with the expression of their contractile phenotype by changing their mechanical properties and various cellular functions such as signal transduction, contraction and cytoskeletal organisation. Finally, this thesis also underlines the utility of integrating biophysical tools into studying cellular biology. Indeed, the various results obtained using atomic force microscopy are unique in a way that they provide new insights into studying cellular activity trough the measurement of single cell contraction and characterisation its mechanical phenotype

Os receptores medeiam a maioria das respostas fisiológicas em resposta a diversidade de estímulos. A ativação da sinalização mediada pelo receptor de angiotensina II tipo 1 é o principal responsável pelos efeitos do hormônio angiotensina II (Ang II) nos tecidos alvo. No rim concentrações fisiológicas de Ang II aumentam a atividade no túbulo proximal da isoforma 3 do trocador de Na+/H+ (NHE3). Este efeito é crucial para a manutenção do volume extracelular e pressão arterial. Evidências recentes mostraram que a ativação seletiva da sinalização enviesada da beta-arrestina/ receptor AT1 induz diurese e natriurese independentemente da sinalização via proteína G. Neste estudo testamos a hipótese de que a sinalização enviesada do receptor AT1/ beta-arrestina inibe a atividade do NHE3 no túbulo proximal, bem como investigar os possíveis mecanismos moleculares que medeio este efeito. Para tal, nós determinamos os efeitos do composto TRV120023, que se liga ao receptor AT1, bloqueando o acoplamento da proteína G e estimulando a sinalização da beta-arrestina, na função do NHE3 in vivo e in vitro. A atividade do NHE3 foi medida quer em túbulo proximal nativo, por meio de microperfusão estacionária, bem como em uma linha celular de túbulo proximal de gamba (OKP), por meio de recuperação de pH intracelular dependente de Na+. Os nossos resultados mostram que o TRV120023 na concentração de 10-7 M inibe marcadamente a atividade do NHE3 em túbulo proximal quer in vivo quer in vitro, sendo que este efeito é completamente abolido nas células silenciadas para a beta-arrestina 1 e 2 através de RNA de interferência. Adicionalmente, a estimulação do NHE3 pela Ang II é completamente suprimida pelo TRV120023 quer in vivo quer in vitro. A inibição do NHE3 pelo TRV120023 foi associada com a diminuição do NHE3 expresso na superfície da membrana plasmática em células OKP e com a redistribuição entre o corpo e a base das microvilosidades em túbulo proximal de rato. A diminuição do NHE3 na superfície da membrana plasmática em células OKP estava associado com um aumento na internalização do NHE via endocitose mediada por clatrina. A inibição do NHE3 mediada pela beta-arrestina não envolve a sinalização do receptor AT2, cAMP/ PKA, Akt e ERK1/2. Estes achados indicam que a sinalização enviesada do receptor AT1/beta-arretina inibe a atividade do NHE3 em túbulo proximal, pelo menos em parte, devido a alterações na localização subcelular do NHE3 / Cell surface receptors mediate most of our physiological responses to an array of stimulus. The triggering of the angiotensin II type I (AT1) receptor signaling is the major control point in the regulation of the ultimate effects of the peptide hormone angiotensin II (Ang II) on its target tissue. In the kidney physiological concentrations of Ang II upregulate the activity of proximal tubule Na+/H+ exchanger isoform 3 (NHE3). This effect is crucial for maintenance of extracellular fluid volume homeostasis and blood pressure. Recent findings have shown that selective activation of the betaarrestin-biased AT1 receptor signalingpathway induces diuresis and natriuresis independent of G-protein mediated signaling. This study tested the hypothesis that activation of this AT1 receptor/beta-arrestin signaling inhibits NHE3 activity in proximal tubule as well as investigate the underlying molecular mechanisms mediating this effect. To this end, we determined the effects of the compound TRV120023, which binds to the AT1R, blocks G protein coupling, and stimulates beta-arrestin signaling, on NHE3 function in vivo and in vitro. NHE3 activity was measured in both native proximal tubules, by stationary microperfusion, and in opossum proximal tubule (OKP) cells, by Na+-dependent intracellular pH recovery. Our results showed that 10-7 MTRV120023 remarkably inhibited proximal tubule NHE3 activity both in vivo and in vitro, and the effect was completely abolished in OKP cells silenced for beta-arrestin 1 and 2 by small interference RNA. Additionally, stimulation of NHE3 by Ang II was completely suppressed by TRV120023 both in vivo as well as in vitro. Inhibition of NHE3 activity by TRV120023 was associated with a decrease in NHE3 surface expression in OKP cells and with a redistribution from the body to the base of the microvilli in the rat proximal tubule. The decreased surface NHE3 in OKP cells was associated with an increase in NHE3 internalization via clathrin mediated endocytic. Beta-arrestin mediated NHE3 inhibition did not involve AT2 receptor, cAMP/ PKA, Akt and ERK1/2 signaling. These findings indicate that biased signaling of the AT1 receptor/beta-arrestin pathway inhibits NHE3 activity in the proximal tubule at least in part due to changes in NHE3 subcellular localization

Les inhibiteurs sélectifs de recapture de la sérotonine (ISRS), agonistes indirects des récepteurs de la sérotonine (5-HT), ont un début d'effet antidépresseur retardé de plusieurs semaines. Des travaux antérieurs suggèrent que le récepteur 5-HT4 de la sérotonine serait une cible directe pour traiter la dépression et un nouvel espoir pour traiter plus rapidement ces pathologies anxio-dépressives. Toutefois, l'hypothèse « 5-HT4 » doit encore être validée dans des modèles animaux d'anxiété/dépression. Les questions posées étaient : la stimulation des récepteurs 5-HT4 centraux est-elle nécessaire aux effets comportementaux des ISRS ? la neurogenèse hippocampique adulte contribue-t-elle à ces effets ? En utilisant le modèle de stress chronique à la corticostérone (CORT) chez la souris, nous avons évalué les effets sur ces paramètres d’un traitement chronique avec un agoniste du récepteur 5-HT4 (RS67333, 1,5 mg/kg/jour pendant 4 semaines) comparé à un traitement à la fluoxétine (18 mg/kg/jour). Nous avons ensuite utilisé ce modèle murin combiné à l’ablation de la neurogenèse hippocampique par rayons-X afin d’examiner si la neurogenèse est nécessaire aux effets comportementaux d’un traitement subchronique (7 jours) ou chronique (28 jours) avec le RS67333. Nous avons également évalué le blocage des effets de la fluoxétine par un antagoniste du récepteur 5-HT4 (GR125487, 1 mg/kg/jour). Le traitement chronique avec RS67333, comme celui de la fluoxétine, induit une activité anxiolytique/antidépressive et stimule la neurogenèse hippocampique adulte. Cependant, contrairement à la fluoxétine , les effets anxiolytiques du RS67333 sont déjà présents après 7 jours de traitement, sans nécessité l’activation de la neurogenèse. Le traitement chronique avec le GR125487 empêche les deux effets anxiolytique/antidépresseur et neurogènique de la fluoxétine, indiquant que l'activation du récepteur 5-HT4 est nécessaire à ces effets de l’ISRS. Nous avons ensuite cherché à savoir si le court délai d’action antidépresseur du RS67333 peut être prédit par l'expression d'un biomarqueur périphérique. Des données de la littérature indiquent que la cascade de signalisation de β-arrestine 1 (impliquée dans la désensibilisation et l’internalisation du récepteur 5-HT4) serait un biomarqueur potentiel pré-clinique/clinique des états dépressifs et des effets d’un traitement antidépresseur. À cette fin, nous avons développé une nouvelle méthode d’évaluation des taux de protéines circulantes grâce à une analyse par immunoblot des leucocytes (PBMC) isolés à partir du sang total de souris. Les taux de β-arrestine 1 sont diminués dans les leucocytes des souris pré-traitées à la CORT. Il faut 7 jours de traitement avec le RS67333, mais 28 jours avec la fluoxétine chez ces animaux pour restaurer un taux de β-arrestine 1 comparable à celui des animaux contrôles. Ces résultats suggèrent que le taux sanguin de β-arrestine 1 est un biomarqueur de la rapidité de la réponse antidépressive. Enfin, l'activation du récepteur 5-HT4 dans le cerveau peut représenter une approche thérapeutique innovante d’apparition pour traiter plus rapidement des symptômes dépressifs associés à l’anxiété. / Selective serotonin reuptake inhibitors (SSRIs) display a delayed onset of action of several weeks. Past work demonstrated evidence that the 5-HT4 receptor may be a direct target for treating depression and a new hope for fast acting antidepressant treatment. However, the 5-HT4 hypothesis still needs to be validated in models of anxiety/depression.We decided to investigate whether 5-HT4 receptor stimulation was necessary for the effects of SSRIs in a mouse model of anxiety/depression and whether hippocampal neurogenesis contributed to these effects. Using the mouse corticosterone model of anxiety/depression, we assessed whether chronic treatment with a 5-HT4 receptor agonist (RS67333, 1.5 mg/kg/day) had effects on anxiety and depression-related behaviors as well as on hippocampal neurogenesis in comparison to chronic fluoxetine treatment (18 mg/kg/day). Then, using our model combined with ablation of hippocampal neurogenesis, we investigated whether neurogenesis was necessary for the behavioral effects of subchronic (7-days) or chronic (28-days) RS67333 treatment. We also assessed whether a 5-HT4 receptor antagonist, (GR125487, 1 mg/kg/day) could prevent the behavioral and neurogenic effects of fluoxetine. Chronic treatment with RS67333, similar to fluoxetine, induced anxiolytic/antidepressant-like activity and stimulated adult hippocampal neurogenesis. However, unlike fluoxetine, the anxiolytic effects of RS67333 were already present after 7 days and did not require hippocampal neurogenesis. Chronic treatment with GR125487 prevented both anxiolytic/antidepressant-like and neurogenic effects of fluoxetine, indicating that 5-HT4 receptor activation is necessary for these effects of SSRIs. We then explored whether the fast onset of action of the 5-HT4 receptor agonist RS67333 could be predicted by expression of a peripheral biomarker. The β-arrestin-signaling cascade which is involved in 5-HT4 receptor desensitization and internalization, has recently gained attention as a potential pre-clinical/clinical bridging biomarker for depressive states and treatment effects. To this end, we developed a new method to assess levels of circulating proteins through immunoblot analyses of mouse PBMCs isolated from whole blood of anesthetized animals. While we did not detect any change in β-arrestin 1 in mouse leukocytes after 7 days of fluoxetine in corticosterone-treated animals, a short term treatment with RS67333, restored the level of this protein to control levels. In fluoxetine-treated animals, a restoration was only observed in the corticosterone model after a longer exposure. These results suggest that blood levels of β-arrestin 1 may be a useful biomarker to predict antidepressant/anxiolytic activities. Finally, the activation of 5-HT4 receptors in the brain may represent an innovative and rapid onset therapeutic approach to treat depression with comorbid anxiety.