Physical and psychological stress can alter the immune system in both humans and animals. Stress is a known risk factor for numerous human diseases, such as infectious and autoimmune diseases, and cancer. Toll-like receptors (TLRs) play a pivotal role in the induction of innate and adaptive immune response. Our previous studies have shown that TLR4 deficiency prevents stress-induced splenocyte reduction. However, the role of TLR2 in stress-mediated lymphocyte reduction is unknown. In this study, we investigated the effects of TLR2 ligands on stress-induced lymphocyte reduction. We also defined whether the phosphoinositide 3-kinases (PI3Ks)/Akt pathway contributes to TLR2-mediated lymphocyte numbers altered by stress. Our data have shown that stimulation of TLR2 by TLR2 ligands peptidoglycan (PGN) or Pam3CSK4 (Pam3) attenuates stress-induced reduction in lymphocyte numbers. However, TLR2 ligand-induced protection from stress-induced lymphocyte reduction is lost in TLR2 deficiency in mice. Furthermore, stimulation of TLR2 by PGN induces protection from stress-induced reduction in the number of splenocytes through PI3K. Moreover, PGN dramatically increases the level of phosphorylation of Akt through a PI3K-dependent manner. Moreover, we found that stimulation of TLR2 by PGN induced protection from stress-induced reduction in splenocyte numbers is abolished in β-arrestin 2 deficient mice. In addition, PGN-induced immune protection in stress-induced changes of cytokine levels appears to require -arrestin 2, a multifunctional adaptor and signal transducer. Collectively, our study thus demonstrates that stimulation of TLR2-mediated PI3K signaling attenuates splenocyte reduction induced by stress, and that β-arrestin 2 modulates TLR2-mediated immune response following stress.

The CB1 cannabinoid receptor is a G-protein coupled receptor highly expressed throughout the central nervous system, that has been suggested as a target for the treatment of various disorders, including anxiety, pain and neurodegeneration. Despite the wide therapeutic potential of CB1, development of potential drug candidates has long been hindered by concerns about adverse effects, rapid tolerance development and abuse potential. Ligands that produce biased signaling have been proposed as a strategy to dissociate therapeutic and adverse effects for a variety of G-protein coupled receptors. Biased signaling involves selective activation of a signaling transducer in detriment of another, mainly involving selective activation of G-protein signaling or b-arrestin signaling. However, biased signaling at the CB1 receptor is poorly understood due to the lack of strongly biased agonists. The development of biased agonists would be aided by understanding the molecular mechanism that leads to biased signaling. Although the structure of CB1 has been resolved in the inactive state and in the canonical active state, which allows G-protein signaling, little is known about the alternative active state that allows b-arrestin biased signaling. Therefore, we set out to investigate molecular and pharmacological tools that could shed light on the mechanism of CB1 biased signaling and to characterize novel allosteric ligands with a biased signaling profile. Using molecular dynamics stimulation of CB1 bound to a ORG27569, an allosteric ligand that stimulates b-arrestin signaling and inhibits G-protein signaling, we proposed single amino acid mutations that were predicted to impact b-arrestin signaling, and expressed wild-type and mutated CB1 receptor in HEK293 cells to measure signaling through different signaling transducers. We found that N7.49 and Y7.53, two amino acids in the highly conserved NPXXY motif, were essential for b-arrestin recruitment and signaling, but mutating them to Ala and Phe, respectively, did not impact G-protein signaling. We also found that I2.43, a functionally conserved amino acid on transmembrane helix 2, negatively regulates a switch in the rotameric position of Y7.53, as mutating I2.43 to Ala reduced steric hindrance upon Y7.53 and enhanced b-arrestin1 recruitment and signaling, while mutating it to Thr, a polar residue that would further hinder Y7.53, partially inhibited b-arrestin recruitment. Therefore, we concluded that N7.49 and Y7.53 form a hydrogen bond network along with D2.50 that is essential for the alternative active state that stimulates b-arrestin biased signaling. N7.49 acts as a fulcrum on which transmembrane helix 7 can bend, and Y7.53 acts as a rotamer toggle switch, stabilizing conformational changes on the intracellular end of transmembrane helix 7. This is the first record of a molecular mechanism for CB1 b-arrestin biased signaling involving the NPXXY motif. Due to the highly conserved character of these residues, it is possible that this mechanism can also be applied to other class A G-protein coupled receptors. In addition, we characterized novel biased allosteric ligands that stimulate or inhibit b-arrestin1 signaling. Two ORG27569 analogs were found to enhance orthosteric agonist induced b-arrestin1 recruitment and extracellular-signal regulated kinase 1/2 phosphorylation (pERK), with no effect on G-protein signaling. Two pregnenolone analogs absent of the steroid scaffold were found to inhibit pERK signaling independent of Gprotein signaling, indicating that they hinder b-arrestin dependent signaling. Since these analogs are believed to mediate their effects via stimulation or inhibition of conformational changes on transmembrane helix 7, our findings support a role for this domain on the alternative active state of CB1. In contrast, a GAT211 analog, GAT1601, had no effect on recruitment of b-arrestin1, but stimulated G-protein signaling and slightly enhanced barrestin2 recruitment. This compound binds to an allosteric site, where it stimulates the canonical active state of CB1 by facilitating the outward movement of transmembrane helix 6. Altogether, the results presented in this dissertation suggest that CB1 b-arrestin biased signaling is regulated by the NPXXY motif, which stimulates conformational changes on the transmembrane helix 7/helix 8 elbow, and that stimulating or hindering these conformational changes can enhance or disrupt CB1 b-arrestin biased signaling. However, facilitating the movement of transmembrane helix 6 favors G-protein biased signaling. Our findings provide molecular and pharmacological tools that will be of great importance to structure guided drug design and to future studies on the functional consequences of biased signaling at the CB1 receptor.

No description available.

No description available.

<p>The neuromodulator dopamine signals through the dopamine D2 receptor (D2R) to modulate central nervous system functions through diverse signal transduction pathways. D2R is a prominent target for drug treatments in disorders where dopamine function is aberrant, such as schizophrenia. D2R signals through distinct G protein and β-arrestin pathways and drugs that are functionally selective for these pathways could have improved therapeutic potential. How D2R signals through the two pathways is still not well defined, and efforts to elucidate these pathways have been hampered by the lack of adequate tools for assessing the contribution of each pathway independently. To address this, Evolutionary Trace was used to produce D2R mutants with strongly biased interactions for either G protein or β-arrestin. Additionally, various permutations of these mutants were used to identify critical determinants of D2R functional selectivity. D2R interactions with the two major downstream signal transducers were effectively dissociated and G protein signaling accounts for D2R canonical MAP kinase signaling cascade activation. Nevertheless, when expressed in mice, the β-arrestin biased D2R caused a significant potentiation of amphetamine-induced locomotion, while the G protein biased D2R had minimal effects. The mutant receptors generated here provide a new molecular tool set that enable a better definition of the individual roles of G protein and β-arrestin signaling in D2R pharmacology, neurobiology and associated pathologies.</p> / Dissertation

Les récepteurs couplés aux protéines G (RCPG) sont la famille de récepteurs membranaires la plus représentée chez les vertébrés, et la plus grande cible thérapeutique chez l'Homme. L'évolution du paradigme initial qui énonçait une stœchiométrie récepteur : protéine G : effecteur de 1 :1 :1 sera présentée sur le modèle des récepteurs aux chimiokines CXCR4 et CCR2. Grâce à la technique de transfert d'énergie par bioluminescence (BRET), les travaux réalisés durant cette thèse montrent (1) que c'est par un couplage alternatif de CXCR4 à Gα13 au lieu de la voie classique Gαi que les cellules de cancer du sein migrent pour former des métastases, (2) que la désensibilisation de CXCR4 implique le recrutement d'une combinaison définie de protéines (GRK et arrestines) permettant l'arrêt sélectif des multiples voies engagées en réponse à l'agoniste, et (3) que le protomère CXCR4 a un rôle déterminant dans l'engagement de la protéine Gαi et le recrutement de la β-arrestine par l'hétéro-oligomère CXCR4/CCR2 lorsque CCR2 est activé. Dans cette dernière et principale étude, les résultats montrent également que le dimère CCR2 peut s' assembler au dimère CXCR4 pour former un tétramère, et que l'activation de CCR2 influence la conformation du dimère CXCR4. Les phénomènes de coopérativité et d'activation asymétrique déjà rapportés pour cet hétérodimère pourraient donc impliquer l'interaction de quatre protomères. En conclusion les travaux effectués durant cette thèse démontrent une régulation supplémentaire de l'activité des récepteurs chimiokines au niveau de leur structure quaternaire, de leur signalisation, et de l'arrêt de cette signalisation. / G protein coupled receptors (GPCR) are the most represented cell surface receptors among vertebrates, and the major therapeutic target in humans. The initial paradigm stating a 1 :1 :1 stoichiometry for receptor :G protein :effector has evolved to a more complex model, as illustrated here with the example of the chemokine receptors CXCR4 and CCR2. Bioluminescence resonance energy transfer (BRET) was used to demonstrate that (1) CXCR4 is able to couple Gα13 instead of Gαi to promote breast cancer metastasis, (2) the multiple pathways engaged by stimulation of CXCR4 are selectively desensitized by the specific recruitment of a defined combination of proteins (GRKs and arrestins) and (3) the CXCR4 protomer plays a crucial role during Gαi engagement and β-arrestin recruitment by the CXCR4/CCR2 heterodimer upon CCR2 activation. In this last and main study, the results shown also demonstrate that CCR2 dimers could assemble with CX CR4 dimers into hetero-tetramers, and that CCR2 activation leads to a conformational change in the CXCR4 dimer. Former results showing cooperativity and asymmetric activation of a simple CXCR4/CCR2 heterodimer could then be applied to a tetramer. To conclude, the work done during this thesis demonstrates a more sophisticated regulation of chemokine receptors than previously suspected at 3 different levels: quaternary structure of the protomers, G protein signalling, and signalling termination

CB1 receptors (CB1R) mediate the psychoactive and therapeutic effects of cannabinoids including ∆9-tetrahydrocannabinol (THC), the main psychoactive constituent in marijuana. However, therapeutic use is limited by side effects and tolerance and dependence with chronic administration. Tolerance to cannabinoid-mediated effects is associated with CB1R adaptations, including desensitization (receptor-G-protein uncoupling) and downregulation (receptor degradation). The objectives of this thesis are to investigate the regional-specificity in CB1R function and regulation. Previous studies have investigated CB1Rs in a subset of regions involved in cannabinoid effects, but an inclusive regional comparison of the relative efficacies of different classes of cannabinoids to activate G-proteins has not been conducted. A novel unbiased whole-brain analysis was developed based on Statistical Parametric Mapping (SPM) for 3D-reconstructed mouse brain images derived from agonist-stimulated [35S]GTPgS autoradiography, which has not been described before. SPM demonstrated regional differences in the relative efficacies of cannabinoid agonists methanandamide (M-AEA), CP55,940 (CP), and WIN55,212-2 (WIN) in mouse brains. To assess potential contribution of novel sites, CB1R knockout (KO) mice were used. SPM analysis revealed that WIN, but not CP or M-AEA, stimulated [35S]GTPgS binding in regions that partially overlapped with the expression of CB1Rs. We then examined the role of the regulatory protein Beta-arrestin-2 (βarr2) in CB1R adaptations to chronic THC treatment. Deletion of βarr2 reduced CB1R desensitization/downregulation in the cerebellum, caudal periaqueductal gray (PAG), and spinal cord. However in hippocampus, amygdala and rostral PAG, similar desensitization was present in both genotypes. Interestingly, enhanced desensitization was found in the hypothalamus and cortex in βarr2 KO animals. Intra-regional differences in the magnitude of desensitization were noted in the caudal hippocampus, where βarr2 KO animals exhibited greater desensitization compared to WT. Regional differences in βarr2-mediated CB1R adaptation were associated with differential effects on tolerance, where THC-mediated antinociception, but not catalepsy or hypothermia, was attenuated in βarr2 KO mice. Overall, studies using SPM revealed intra- and inter-regional specificity in the function and regulation of CB1Rs and underscores an advantage of using a whole-brain unbiased approach. Understanding the regulation of CB1R signaling within different anatomical contexts represents an important fundamental prerequisite in the therapeutic exploitation of the cannabinoid system.

Les pertes de la fonction et de la masse des cellules beta pancréatiques jouent un rôle central dans le diabète de type 2 (DT2). Les beta-arrestines 1 et 2 (ARRB1 et ARRB2), sont impliquées dans la sécrétion et/ou la survie des cellules beta pancréatiques.Dans une première étude, afin de caractériser précisément la fonction d’ARRB1 dans les cellules beta pancréatiques, nous avons eu pour objectif de générer des souris invalidées spécifiquement dans ces cellules en utilisant le système Cre/lox sous le contrôle du promoteur Ins1. Des études avaient été publiées à partir des deux lignées Ins1Cre-/+ et Arrb1f/f. Nous avons généré et travaillé sur les souris Arrb1f/f :Ins1Cre-/+. Le phénotype des souris Arrb1f/f :Ins1Cre-/+ était faible et surtout non reproductible comparé aux souris Arrb1f/f :Ins1Cre-/- utilisées comme témoins. Le faible niveau d’expression d'Arrb1 dans les cellules beta et le manque d'anticorps spécifique pour l'immunocytochimie ont rendu difficile la vérification de l'absence d'expression de ARRB1 dans ces cellules. Après séquençage du gène modifié Arrb1 des souris “floxées“, nous avons pu montrer que l'insertion du premier site loxP avait induit un décalage du cadre de lecture introduisant un codon stop et, par conséquent, la non-expression du gène Arrb1. Étant donné que les souris Arrb1 “floxées“ utilisées comme témoins étaient déjà knockout (KO), le projet utilisant ces souris a dû être arrêté.Notre équipe a rapporté l'implication d'ARRB2 dans la régulation de la masse des cellules bêta pancréatique, mais son rôle dans la signalisation du récepteur du Glucagon-Like Peptide-1 (GLP-1R), une cible thérapeutique majeure du DT2, n'avait pas encore été exploré.Nous avons montré, dans une deuxième étude, une meilleure tolérance orale au glucose ainsi qu’une augmentation de la sécrétion d’insuline chez les souris Arrb2 KO par rapport aux souris témoins sur les îlots en présence des concentrations physiologiques circulantes de GLP-1. Ceci est corrélé à une production d’AMPc et un recrutement de la PKA plus élevés dans les cellules beta Arrb2 KO. A l’inverse, l’activation des kinases ERK1/2 est diminuée indiquant un recrutement majeur des ERK1/2 par ARRB2 au GLP-1R. En parallèle, j’ai montré que les taux de ARRB1 et ARRB2 des îlots pancréatiques sont altérés par des conditions diabétogènes et diabétiques. Mes résultats démontrent clairement un rôle critique de ARRB2 dans la signalisation du GLP-1R. Un défaut d’expression de la protéine pourrait participer au déficit des mécanismes de compensation de la masse fonctionnelle des cellules beta conduisant au DT2. / The loss of function and mass of pancreatic beta-cells play a central role in type 2 diabetes (T2D). Beta-arrestin 1 and 2 (ARRB1 and ARRB2) are involved in insulin secretion and/or beta-cell survival. In a first study, in order to characterize the role of ARRB1 in beta-cells, we aimed to invalidate the Arrb1 gene specifically in these cells using the Cre/lox system under the control of the Ins1 promoter. Studies had been published with both Ins1Cre-/+ and Arrb1f/f lines. We generated Arrb1f/f:Ins1Cre-/+ mice. The phenotype of Arrb1f/f :Ins1Cre-/+ mice was weak with a lack of reproducibility compared to Arrb1f/f :Ins1Cre-/- mice used as controls. The low expression level of Arrb1 in beta-cells and the lack of specific antibody for immunocytochemistry made it difficult to verify the absence of expression of ARRB1 in these cells. After sequencing the modified Arrb1 gene of the “floxed” mice, we observed that the insertion of the first loxP site induced a shift in the reading frame introducing a stop codon and, consequently, the non-expression of the Arrb1 gene. Since the “floxed“ Arrb1 mice used as controls were already knockout (KO), the project using these mice was stopped.Our team has reported the involvement of ARRB2 in the regulation of beta-cell mass, but its role in Glucagon-Like Peptide-1 (GLP-1) receptor signaling, a major therapeutic target for T2D, remained to be explored. In a second study, we showed a better glucose tolerance and an increase in insulin secretion from isolated islets in Arrb2KO compared to control mice in the presence of physiological circulating concentrations of GLP-1. This was correlated with higher cAMP production and PKA activation in Arrb2KO beta-cells. By contrast, the activation of ERK1/2 kinases was decreased indicating a major recruitment of ERK1/2 by ARRB2 to GLP-1R. In parallel, we showed that the expression levels of ARRB1 and ARRB2 in pancreatic islets were altered in diabetogenic and diabetic conditions. My results clearly demonstrate a critical role of ARRB2 in GLP-1R singaling which could impact the function, maintenance and plasticity of beta-cell mass in response to GLP-1. A lack of expression of ARRB2 could participate in the deficit of compensatory mechanisms of the functional beta-cell mass leading to T2D.

<p>Chemokine receptors are members of the seven transmembrane receptor (7TMR) superfamily and are regulated by the G-protein coupled Receptor Kinase (GRK)/ b-arrestin system. CCL19 and CCL21 are endogenous agonists for the chemokine receptor CCR7. They are known to be equipotent in promoting Gi/o mediated calcium mobilization, chemotaxis and inhibition of adenylyl cyclase activity. Here we test the hypothesis that these ligands are biased agonists that differentially activate the G-protein coupled Receptor Kinase (GRK)/ b-arrestin system.</p><p>In order to test whether these ligands have distinct activity, murine T lymphocytes were used to compare the effects of CCL19 and CCL21 activation of CCR7 at endogenous expression levels. While each ligand stimulates similar chemotactic responses, we also find that CCR7 ligands lead to differential signaling. For instance, CCL19 is markedly more efficacious than CCL21 for the activation of ERK and JNK, but not AKT in these cells. Furthermore, ERK activation and chemotaxis are maintained as separate pathways, also distinguishable by their dependency upon PKC and PI3 kinase, respectively. Thus, CCL19 and CCL21 stimulate equal activation of PI3 kinase, AKT, and chemotaxis, but are in fact biased agonists leading to differential activation of MAP kinase in murine T lymphocytes. </p><p>To determine the mechanism of CCR7 ligand bias, we used HEK-293 cells expressing CCR7 to compare the proximate signaling events following CCL19 and CCL21 activation. We found striking differences in the activation of the GRK/ b-arrestin system. CCL19 leads to robust CCR7 phosphorylation and b-arrestin2 recruitment catalyzed by both GRK3 and GRK6 while CCL21 activates GRK6 alone. This differential GRK activation leads to distinct functional consequences. Only CCL19 leads to the recruitment of b-arrestin2-GFP into endocytic vesicles and classical receptor desensitization. In contrast, each agonist is fully capable of signaling to MAP kinase through b-arrestin2 in a GRK6 dependent fashion. </p><p>Therefore, CCR7 and its ligands represent a natural example of ligand bias whose mechanism involves differential GRK isoform utilization by CCL19 and CCL21 despite similar G-protein signaling. This study suggests that the GRK signatures of 7TMRs can determine the function of discrete pools of b-arrestin and thus guide its cellular effects.</p> / Dissertation

The following thesis research was undertaken to gain a better understanding of the mechanisms that regulate the cellular trafficking and signaling of the endothelial differentiation gene (EDG) family of G-protein coupled receptors, LPA1, LPA2, and LPA3. This thesis will specifically focus on the regulation of the trafficking of the LPA1 Lysophosphatidic acid receptor, which is the most widely expressed and has been shown to be a major regulator of migration of cells expressing it. The initial studies undertaken in this project were aimed at understanding the endocytic pathway followed by the LPA1 receptor. Lysophosphatidic acid (LPA), an abundant serum phospholipid, stimulates heterotrimeric G protein signaling by activating three closely related receptors, termed LPA1, LPA2 and LPA3. In the first part of the project we show that in addition to promoting LPA1 signaling, membrane cholesterol is essential for the association of LPA1 with β-arrestin, which leads to signal attenuation and clathrin dependent endocytosis of LPA1. The second phase of the project was aimed at elucidating the different structural motifs required for the trafficking and signaling of the LPA1 receptor and helping us gain a more mechanistic view of the processes involved in its regulation. In the second part of the project we show that agonist-independent internalization of the LPA1 receptor is clathrin adaptor, AP-2 dependent and PKC-dependent and that it requires a distal dileucine motif, whereas agonist-dependent internalization of the LPA1 receptor is β-arrestin and clathrin-dependent and requires a cluster of serine residues in the tail region, which is upstream of the dileucine motif. These studies collectively vastly enhance our understanding of mechanisms that regulate LPA1 trafficking and signaling. These studies can also be applied to other G-protein coupled receptors making the task easier for other scientists to understand this vast family of receptors.