ß-arrestin biased signaling is not involved in the hypotensive actions of 5-HT7 receptor stimulation: use of Serodolin.

The 5-hydroxytryptamine 7 receptor (5-HT7) is necessary for 5-HT to cause a concentration-dependent vascular relaxation and hypotension. 5-HT7 is recognized as having biased signaling, transduced through either Gs or ß -arrestin. It is unknown whether 5-HT7 signals in a biased manner to cause vasorelaxation/hypotension. We used the recently described ß-arrestin selective 5-HT7 receptor agonist serodolin to test the hypothesis that 5-HT7 activation does not cause vascular relaxation or hypotension via the ß -arrestin pathway. Isolated abdominal aorta (no functional 5-HT7) and vena cava (functional 5-HT7) from male Sprague Dawley rats were used in isometric contractility studies. Serodolin (1 nM - 10 µM) did not change baseline tone of isolated tissues and did not relax the endothelin-1 (ET-1)-contracted vena cava or aorta. In the aorta, serodolin acted as a 5-HT2A receptor antagonist, evidenced by a rightward shift in 5-HT-induced concentration response curve [pEC50 5-HT [M]: Veh = 5.2 +/- 0.15; Ser (100 nM) = 4.49 +/- 0.08; p < 0.05]. In the vena cava, serodolin acted as a 5-HT7 receptor antagonist, shifting the concentration response curve to 5-HT left and upward (%10 µM NE contraction; Veh = 3.2 +/- 1.7; Ser (10 nM) = 58 +/- 11; p < 0.05) and blocking relaxation of pre-contracted tissue to the 5-HT1A/7 agonist 5-carboxamidotryptamine. In anesthetized rats, 5-HT or serodolin was infused at 5, 25 and 75 µg/kg/min, iv. Though 5-HT caused concentration-dependent depressor responses, serodolin caused an insignificant small depressor responses at all three infusion rates. With the final dose of serodolin on board, 5-HT was unable to reduce blood pressure. Collectively the data indicate that serodolin functions as a 5-HT7 antagonist with additional 5-HT2A blocking properties. 5-HT7 activation does not cause vascular relaxation or hypotension via the ß -arrestin pathway.

An adult Drosophila glioma model to highlight metabolic dysfunctions and evaluate the role of the serotonin 5-HT7 receptor as a potential therapeutic target.

Gliomas account for 50% of brain cancers and are therefore the most common brain tumors. Molecular alterations involved in adult gliomas have been identified and mainly affect tyrosine kinase receptors with amplification and/or mutation of the epidermal growth factor receptor (EGFR) and its associated signaling pathways. Several targeted therapies have been developed, but current treatments remain ineffective for glioblastomas, the most severe forms. Thus, it is a priority to identify new pharmacological targets. Drosophila glioma models established in larvae and adults are useful to identify new genes and signaling pathways involved in glioma progression. Here, we used a Drosophila glioma model in adults, to characterize metabolic disturbances associated with glioma and assess the consequences of 5-HT7 R expression on glioma development. First, by using in vivo magnetic resonance imaging, we have shown that expression of the constitutively active forms of EGFR and PI3K in adult glial cells induces brain enlargement. Then, we explored altered cellular metabolism by using high-resolution magic angle spinning NMR and 1 H-13 C heteronuclear single quantum coherence solution states. Discriminant metabolites identified highlight the rewiring of metabolic pathways in glioma and associated cachexia phenotypes. Finally, the expression of 5-HT7 R in this adult model attenuates phenotypes associated with glioma development. Collectively, this whole-animal approach in Drosophila allowed us to provide several rapid and robust phenotype readouts, such as enlarged brain volume and glioma-associated cachexia, as well as to determine the metabolic pathways involved in glioma genesis and finally to confirm the interest of the 5-HT7 R in the treatment of glioma.

An efficient site-selective, dual bioconjugation approach exploiting N-terminal cysteines as minimalistic handles to engineer tailored anti-HER2 affibody conjugates.

Site-selective, dual-conjugation approaches for the incorporation of distinct payloads are key for the development of molecularly targeted biomolecules, such as antibody conjugates, endowed with better properties. Combinations of cytotoxic drugs, imaging probes, or pharmacokinetics modulators enabled for improved outcomes in both molecular imaging, and therapeutic settings. We have developed an efficacious dual-bioconjugation strategy to target the N-terminal cysteine of a chemically-synthesized, third-generation anti-HER2 affibody. Such two-step, one-purification approach can be carried out under mild conditions (without chaotropic agents, neutral pH) by means of a slight excess of commercially available N-hydroxysuccinimidyl esters and maleimido-functionalized payloads, to generate dual conjugates displaying drugs (DM1/MMAE) or probes (sulfo-Cy5/biotin) in high yields and purity. Remarkably, the double drug conjugate exhibited an exacerbated cytoxicity against HER2-expressing cell lines as compared to a combination of two monoconjugates, demonstrating a potent synergistic effect. Consistently, affibody-drug conjugates did not decrease the viability of HER2-negative cells, confirming their specificity for the target.

T Lymphocyte Serotonin 5-HT7 Receptor Is Dysregulated in Natalizumab-Treated Multiple Sclerosis Patients.

Serotonin (5-HT) is known as a potent immune cell modulator in autoimmune diseases and should be protective in the pathogenesis of multiple sclerosis (MS). Nevertheless, there is limited knowledge about receptors involved in 5-HT effects as well as induced mechanisms. Among 5-HT receptors, the 5-HT7 receptor is able to activate naïve T cells and influence the inflammatory response; however, its involvement in the disease has never been studied so far. In this study, we collected blood sample from three groups: acute relapsing MS patients (ARMS), natalizumab-treated MS patients (NTZ), and control subjects. We investigated the 5-HT7 expression on circulating lymphocytes and evaluated the effects of its activation on cytokine production with peripheral blood mononuclear cell (PBMC) cultures. We found a significant increase in the 5-HT7 surface expression on T lymphocytes and on the different CD4+ T cell subsets exclusively in NTZ-treated patients. We also showed that the selective agonist 5-carboxamidotryptamine (5-CT)-induced 5-HT7R activation significantly promotes the production of IL-10, a potent immunosuppressive cytokine in PBMCs. This study provides for the first time a dysregulation of 5-HT7 expression in NTZ-MS patients and its ability to promote IL-10 release, suggesting its protective role. These findings strengthen the evidence that 5-HT7 may play a role in the immuno-protective mechanisms of NTZ in MS disease and could be considered as an interesting therapeutic target in MS.

ß-N-Methyl-Amino-L-Alanine cyanotoxin promotes modification of undifferentiated cells population and disrupts the inflammatory status in primary cultures of neural stem cells.

ß-N-Methyl-Amino-L-Alanine (BMAA) produced by 95% of cyanobacteria is in constant augmentation with cyanobacteria worldwide proliferation due to global warming and eutrophication. Previously, it has been shown that this contaminant induced neurological disorders, notably by acting as a developmental toxin. However, very few studies focus on the impact of BMAA on neuroglial cells, like astrocytes and microglial cells, in a developmental context. In the present study, we investigated whether BMAA disturbs neurogenesis from mice subventricular zone (SVZ) cells and whether this neurotoxin induces neuroinflammation. We show that BMAA at 100 µM disturbs the population of undifferentiated cells (B1 and C cells) and promotes their proliferation. Further, BMAA affects the organization of neuroblasts, indicating that SVZ function could be impaired. BMAA affects neuroinflammatory processes by increasing the release of proinflammatory cytokines IL-1ß, IL-6 and TNFα. Our study adds to evidence that BMAA may disturb the central nervous system homeostasis by targeting glial cells. We highlighted that BMAA may impair SVZ niches and drives astrocytes and microglial cells into a proinflammatory status, with an ameboid shape for microglia.

Serodolin, a ß-arrestin-biased ligand of 5-HT7 receptor, attenuates pain-related behaviors.

G protein­coupled receptors (GPCRs) are involved in regulation of manifold physiological processes through coupling to heterotrimeric G proteins upon ligand stimulation. Classical therapeutically active drugs simultaneously initiate several downstream signaling pathways, whereas biased ligands, which stabilize subsets of receptor conformations, elicit more selective signaling. This concept of functional selectivity of a ligand has emerged as an interesting property for the development of new therapeutic molecules. Biased ligands are expected to have superior efficacy and/or reduced side effects by regulating biological functions of GPCRs in a more precise way. In the last decade, 5-HT7 receptor (5-HT7R) has become a promising target for the treatment of neuropsychiatric disorders, sleep and circadian rhythm disorders, and pathological pain. In this study, we showed that Serodolin is unique among a number of agonists and antagonists tested: it behaves as an antagonist/inverse agonist on Gs signaling while inducing ERK activation through a ß-arrestin­dependent signaling mechanism that requires c-SRC activation. Moreover, we showed that Serodolin clearly decreases hyperalgesia and pain sensation in response to inflammatory, thermal, and mechanical stimulation. This antinociceptive effect could not be observed in 5-HT7R knockout (KO) mice and was fully blocked by administration of SB269-970, a specific 5-HT7R antagonist, demonstrating the specificity of action of Serodolin. Physiological effects of 5-HT7R stimulation have been classically shown to result from Gs-dependent adenylyl cyclase activation. In this study, using a ß-arrestin­biased agonist, we provided insight into the molecular mechanism triggered by 5-HT7R and revealed its therapeutic potential in the modulation of pain response.

Expression of the Human Serotonin 5-HT7 Receptor Rescues Phenotype Profile and Restores Dysregulated Biomarkers in a Drosophila melanogaster Glioma Model.

Gliomas are the most common primary brain tumors in adults. Significant progress has been made in recent years in identifying the molecular alterations involved in gliomas. Among them, an amplification/overexpression of the EGFR (Epidermal Growth Factor Receptor) proto-oncogene and its associated signaling pathways have been widely described. However, current treatments remain ineffective for glioblastomas, the most severe forms. Thus, the identification of other pharmacological targets could open new therapeutic avenues. We used a glioma model in Drosophila melanogaster that results from the overexpression of constitutively active forms of EGFR and PI3K specifically in glial cells. We observed hyperproliferation of glial cells that leads to an increase in brain size and lethality at the third instar larval stage. After expression of the human serotonin 5-HT7 receptor in this glioma model, we observed a decrease in larval lethality associated with the presence of surviving adults and a return to a normal morphology of brain for some Drosophila. Those phenotypic changes are accompanied by the normalization of certain metabolic biomarkers measured by High-Resolution Magic Angle Spinning NMR (HR-MAS NMR). The 5-HT7R expression in glioma also restores some epigenetic modifications and characteristic markers of the signaling pathways associated with tumor growth. This study demonstrates the role of the serotonin 5-HT7 receptor as a tumor suppressor gene which is in agreement with transcriptomic analysis obtained on human glioblastomas.

BRET Analysis of GPCR Dimers in Neurons and Non-Neuronal Cells: Evidence for Inactive, Agonist, and Constitutive Conformations.

G-protein-coupled receptors (GPCRs) are dimeric proteins, but the functional consequences of the process are still debated. Active GPCR conformations are promoted either by agonists or constitutive activity. Inverse agonists decrease constitutive activity by promoting inactive conformations. The histamine H3 receptor (H3R) is the target of choice for the study of GPCRs because it displays high constitutive activity. Here, we study the dimerization of recombinant and brain H3R and explore the effects of H3R ligands of different intrinsic efficacy on dimerization. Co-immunoprecipitations and Western blots showed that H3R dimers co-exist with monomers in transfected HEK 293 cells and in rodent brains. Bioluminescence energy transfer (BRET) analysis confirmed the existence of spontaneous H3R dimers, not only in living HEK 293 cells but also in transfected cortical neurons. In both cells, agonists and constitutive activity of the H3R decreased BRET signals, whereas inverse agonists and GTPγS, which promote inactive conformations, increased BRET signals. These findings show the existence of spontaneous H3R dimers not only in heterologous systems but also in native tissues, which are able to adopt a number of allosteric conformations, from more inactive to more active states.

Complementary Nuclear Magnetic Resonance-Based Metabolomics Approaches for Glioma Biomarker Identification in a Drosophila melanogaster Model.

Human malignant gliomas are the most common type of primary brain tumor. Composed of glial cells and their precursors, they are aggressive and highly invasive, leading to a poor prognosis. Due to the difficulty of surgically removing tumors and their resistance to treatments, novel therapeutic approaches are needed to improve patient life expectancy and comfort. Drosophila melanogaster is a compelling genetic model to better understanding human neurological diseases owing to its high conservation in signaling pathways and cellular content of the brain. Here, glioma has been induced in Drosophila by co-activating the epidermal growth factor receptor and the phosphatidyl-inositol-3 kinase signaling pathways. Complementary nuclear magnetic resonance (NMR) techniques were used to obtain metabolic profiles in the third instar larvae brains. Fresh organs were directly studied by 1H high resolution-magic angle spinning (HR-MAS) NMR, and brain extracts were analyzed by solution-state 1H-NMR. Statistical analyses revealed differential metabolic signatures, impacted metabolic pathways, and glioma biomarkers. Each method was efficient to determine biomarkers. The highlighted metabolites including glucose, myo-inositol, sarcosine, glycine, alanine, and pyruvate for solution-state NMR and proline, myo-inositol, acetate, and glucose for HR-MAS show very good performances in discriminating samples according to their nature with data mining based on receiver operating characteristic curves. Combining results allows for a more complete view of induced disturbances and opens the possibility of deciphering the biochemical mechanisms of these tumors. The identified biomarkers provide a means to rebalance specific pathways through targeted metabolic therapy and to study the effects of pharmacological treatments using Drosophila as a model organism.

Chemical Synthesis of TFF3 Reveals Novel Mechanistic Insights and a Gut-Stable Metabolite.

TFF3 regulates essential gastro- and neuroprotective functions, but its molecular mode of action remains poorly understood. Synthetic intractability and lack of reliable bioassays and validated receptors are bottlenecks for mechanistic and structure-activity relationship studies. Here, we report the chemical synthesis of TFF3 and its homodimer via native chemical ligation followed by oxidative folding. Correct folding was confirmed by NMR and circular dichroism, and TFF3 and its homodimer were not cytotoxic or hemolytic. TFF3, its homodimer, and the trefoil domain (TFF310-50) were susceptible to gastrointestinal degradation, revealing a gut-stable metabolite (TFF37-54; t1/2 > 24 h) that retained its trefoil structure and antiapoptotic bioactivity. We tried to validate the putative TFF3 receptors CXCR4 and LINGO2, but neither TFF3 nor its homodimer displayed any activity up to 10 µM. The discovery of a gut-stable bioactive metabolite and reliable synthetic accessibility to TFF3 and its analogues are cornerstones for future molecular probe development and structure-activity relationship studies.

Defective Oligodendroglial Lineage and Demyelination in Amyotrophic Lateral Sclerosis.

Motor neurons and their axons reaching the skeletal muscle have long been considered as the best characterized targets of the degenerative process observed in amyotrophic lateral sclerosis (ALS). However, the involvement of glial cells was also more recently reported. Although oligodendrocytes have been underestimated for a longer time than other cells, they are presently considered as critically involved in axonal injury and also conversely constitute a target for the toxic effects of the degenerative neurons. In the present review, we highlight the recent advances regarding oligodendroglial cell involvement in the pathogenesis of ALS. First, we present the oligodendroglial cells, the process of myelination, and the tight relationship between axons and myelin. The histological abnormalities observed in ALS and animal models of the disease are described, including myelin defects and oligodendroglial accumulation of pathological protein aggregates. Then, we present data that establish the existence of dysfunctional and degenerating oligodendroglial cells, the chain of events resulting in oligodendrocyte degeneration, and the most recent molecular mechanisms supporting oligodendrocyte death and dysfunction. Finally, we review the arguments in support of the primary versus secondary involvement of oligodendrocytes in the disease and discuss the therapeutic perspectives related to oligodendrocyte implication in ALS pathogenesis.

The GTPase-activating protein-related domain of neurofibromin interacts with MC1R and regulates pigmentation-mediated signaling in human melanocytes.

The melanocortin 1 receptor (MC1R) is a G-protein coupled receptor (GPCR) which plays a major role in controlling melanogenesis. A large body of evidence indicates that GPCRs are part of large protein complexes that are critical for their signal transduction properties. Among proteins which may affect MC1R signaling, neurofibromin (Nf1), a GTPase activating protein (GAP) for Ras, is of special interest as it regulates adenylyl cyclase activity and ERK signaling, two pathways involved in MC1R signaling. Moreover, mutations in this gene encoding Nf1 are responsible for neurofibromatosis type I, a disease inducing hyperpigmented flat skin lesions. Using co-immunoprecipitation and Bioluminescence Resonance Energy Transfer experiments we demonstrated a physical interaction of Nf1 with MC1R. In particular, the GAP domain of Nf1 directly and constitutively interacts with MC1R in melanocytes. Pharmacologic and genetic approaches revealed that the GAP activity of Nf1 is important to regulate intracellular signaling pathways involved in melanogenesis and, consequently, melanogenic enzyme expression and melanin production. These finding shed new light on the understanding and cure of skin pigmentation disorders.

LINGO family receptors are differentially expressed in the mouse brain and form native multimeric complexes.

Leucine-rich repeat and immunoglobin-domain containing (LRRIG) proteins that are commonly involved in protein-protein interactions play important roles in nervous system development and maintenance. LINGO-1, one of this family members, is characterized as a negative regulator of neuronal survival, axonal regeneration, and oligodendrocyte precursor cell (OPC) differentiation into mature myelinating oligodendrocytes. Three LINGO-1 homologs named LINGO-2, LINGO-3, and LINGO-4 have been described. However, their relative expression and functions remain unexplored. Here, we show by in situ hybridization and quantitative polymerase chain reaction that the transcripts of LINGO homologs are differentially expressed in the central nervous system. The immunostaining of brain slices confirmed this observation and showed the co-expression of LINGO-1 with its homologs. Using BRET (bioluminescence resonance energy transfer) analysis, we demonstrate that LINGO proteins can physically interact with each of the other ones with comparable affinities and thus form the oligomeric states. Furthermore, co-immunoprecipitation experiments indicate that LINGO proteins form heterocomplexes in both heterologous systems and cortical neurons. Since LINGO-1 is a promising target for the treatment of demyelinating diseases, its ability to form heteromeric complexes reveals a new level of complexity in its functioning and opens the way for new strategies to achieve diverse and nuanced LINGO-1 regulation.

Bioluminescence Resonance Energy Transfer as a Method to Study Protein-Protein Interactions: Application to G Protein Coupled Receptor Biology.

The bioluminescence resonance energy transfer (BRET) approach involves resonance energy transfer between a light-emitting enzyme and fluorescent acceptors. The major advantage of this technique over biochemical methods is that protein-protein interactions (PPI) can be monitored without disrupting the natural environment, frequently altered by detergents and membrane preparations. Thus, it is considered as one of the most versatile technique for studying molecular interactions in living cells at "physiological" expression levels. BRET analysis has been applied to study many transmembrane receptor classes including G-protein coupled receptors (GPCR). It is well established that these receptors may function as dimeric/oligomeric forms and interact with multiple effectors to transduce the signal. Therefore, they are considered as attractive targets to identify PPI modulators. In this review, we present an overview of the different BRET systems developed up to now and their relevance to identify inhibitors/modulators of protein⁻protein interaction. Then, we introduce the different classes of agents that have been recently developed to target PPI, and provide some examples illustrating the use of BRET-based assays to identify and characterize innovative PPI modulators in the field of GPCRs biology. Finally, we discuss the main advantages and the limits of BRET approach to characterize PPI modulators.

Pharmacomodulation of microRNA Expression in Neurocognitive Diseases: Obstacles and Future Opportunities.

Given the importance of microRNAs (miRNAs) in modulating brain functions and their implications in neurocognitive disorders there are currently significant efforts devoted in the field of miRNA-based therapeutics to correct and/or to treat these brain diseases. The observation that miRNA 29a/b-1 cluster, miRNA 10b and miRNA 7, for instance, are frequently deregulated in the brains of patients with neurocognitive diseases and in animal models of Alzheimer, Huntington's and Parkinson's diseases, suggest that correction of miRNA expression using agonist or antagonist miRNA oligonucleotides might be a promising approach to correct or even to cure such diseases. The encouraging results from recent clinical trials allow envisioning that pharmacological approaches based on miRNAs might, in a near future, reach the requirements for successful therapeutic outcomes and will improve the healthcare of patients with brain injuries or disorders. This review will focus on the current strategies used to modulate pharmacological function of miRNA using chemically modified oligonucleotides. We will then review the recent literature on strategies to improve nucleic acid delivery across the blood-brain barrier which remains a severe obstacle to the widespread application of miRNA therapeutics to treat brain diseases. Finally, we provide a state-of-art of current preclinical research performed in animal models for the treatment of neurocognitive disorders using miRNA as therapeutic agents and discuss future developments of miRNA therapeutics.

MicroRNAs in Neurocognitive Dysfunctions: New Molecular Targets for Pharmacological Treatments?

BACKGROUND: Neurodegenerative and cognitive disorders are multifactorial diseases (i.e., involving neurodevelopmental, genetic, age or environmental factors) characterized by an abnormal development that affects neuronal function and integrity. Recently, an increasing number of studies revealed that the dysregulation of microRNAs (miRNAs) may be involved in the etiology of cognitive disorders as Alzheimer, Parkinson, and Huntington's diseases, Schizophrenia and Autism spectrum disorders. METHODS: From an extensive search in bibliographic databases of peer-reviewed research literature, we identified relevant published studies related to specific key words such as memory, cognition, neurodegenerative disorders, neurogenesis and miRNA. We then analysed, evaluated and summerized scientific evidences derived from these studies. RESULTS: We first briefly summarize the basic molecular events involved in memory, a process inherent to cognitive disease, and then describe the role of miRNAs in neurodevelopment, synaptic plasticity and memory. Secondly, we provide an overview of the impact of miRNA dysregulation in the pathogenesis of different neurocognitive disorders, and lastly discuss the feasibility of miRNA-based therapeutics in the treatment of these disorders. CONCLUSION: This review highlights the molecular basis of neurodegenerative and cognitive disorders by focusing on the impact of miRNAs dysregulation in these pathological phenotypes. Altogether, the published reports suggest that miRNAs-based therapy could be a viable therapeutic alternative to current treatment options in the future.

Physical interaction between neurofibromin and serotonin 5-HT6 receptor promotes receptor constitutive activity.

Active G protein-coupled receptor (GPCR) conformations not only are promoted by agonists but also occur in their absence, leading to constitutive activity. Association of GPCRs with intracellular protein partners might be one of the mechanisms underlying GPCR constitutive activity. Here, we show that serotonin 5 hydroxytryptamine 6 (5-HT6) receptor constitutively activates the Gs/adenylyl cyclase pathway in various cell types, including neurons. Constitutive activity is strongly reduced by silencing expression of the Ras-GTPase activating protein (Ras-GAP) neurofibromin, a 5-HT6 receptor partner. Neurofibromin is a multidomain protein encoded by the NF1 gene, the mutation of which causes Neurofibromatosis type 1 (NF1), a genetic disorder characterized by multiple benign and malignant nervous system tumors and cognitive deficits. Disrupting association of 5-HT6 receptor with neurofibromin Pleckstrin Homology (PH) domain also inhibits receptor constitutive activity, and PH domain expression rescues 5-HT6 receptor-operated cAMP signaling in neurofibromin-deficient cells. Furthermore, PH domains carrying mutations identified in NF1 patients that prevent interaction with the 5-HT6 receptor fail to rescue receptor constitutive activity in neurofibromin-depleted cells. Further supporting a role of neurofibromin in agonist-independent Gs signaling elicited by native receptors, the phosphorylation of cAMP-responsive element-binding protein (CREB) is strongly decreased in prefrontal cortex of Nf1+/- mice compared with WT mice. Moreover, systemic administration of a 5-HT6 receptor inverse agonist reduces CREB phosphorylation in prefrontal cortex of WT mice but not Nf1+/- mice. Collectively, these findings suggest that disrupting 5-HT6 receptor-neurofibromin interaction prevents agonist-independent 5-HT6 receptor-operated cAMP signaling in prefrontal cortex, an effect that might underlie neuronal abnormalities in NF1 patients.

Enhanced responsiveness of Ghsr Q343X rats to ghrelin results in enhanced adiposity without increased appetite.

The ability of the gut hormone ghrelin to promote positive energy balance is mediated by the growth hormone secretagogue receptor (GHSR). GHSR is a G protein-coupled receptor (GPCR) that is found centrally and peripherally and that can signal in a ligand-independent manner basally or when heterodimerized with other GPCRs. However, current Ghsr knockout models cannot dissect ghrelin-dependent and ghrelin-independent signaling, precluding assessment of the physiological importance of these signaling pathways. An animal model carrying a Ghsr mutation that preserves GHSR cell surface abundance, but selectively alters GHSR signaling, would be a useful tool to decipher GHSR signaling in vivo. We used rats with the Ghsr(Q343X) mutation (Ghsr(M/M)), which is predicted to delete the distal part of the GHSR carboxyl-terminal tail, a domain critical for the signal termination processes of receptor internalization and ß-arrestin recruitment. In cells, the GHSR-Q343X mutant showed enhanced ligand-induced G protein-dependent signaling and blunted activity of processes involved in GPCR signal termination. Ghsr(M/M)rats displayed enhanced responses to submaximal doses of ghrelin or GHSR agonist. Moreover, Ghsr(M/M)rats had a more stable body weight under caloric restriction, a condition that increases endogenous ghrelin tone, whereas under standard housing conditions,Ghsr(M/M)rats showed increased body weight and adiposity and reduced glucose tolerance. Overall, our data stress the physiological role of the distal domain of GHSR carboxyl terminus as a suppressor of ghrelin sensitivity, and we propose using the Ghsr(M/M)rat as a physiological model of gain of function in Ghsr to identify treatments for obesity-related conditions.

Rational Design, Pharmacomodulation, and Synthesis of Dual 5-Hydroxytryptamine 7 (5-HT7)/5-Hydroxytryptamine 2A (5-HT2A) Receptor Antagonists and Evaluation by [(18)F]-PET Imaging in a Primate Brain.

We report the synthesis of 46 tertiary amine-bearing N-alkylated benzo[d]imidazol-2(3H)-ones, imidazo[4,5-b]pyridin-2(3H)-ones, imidazo[4,5-c]pyridin-2(3H)-ones, benzo[d]oxazol-2(3H)-ones, oxazolo[4,5-b]pyridin-2(3H)-ones and N,N'-dialkylated benzo[d]imidazol-2(3H)-ones. These compounds were evaluated against 5-HT7R, 5-HT2AR, 5-HT1AR, and 5-HT6R as potent dual 5-HT7/5-HT2A serotonin receptors ligands. A thorough study of the structure-activity relationship of the aromatic rings and their substituents, the alkyl chain length and the tertiary amine was conducted. 1-(4-(4-(4-Fluorobenzoyl)piperidin-1-yl)butyl)-1H-benzo[d]imidazol-2(3H)-one (79) and 1-(6-(4-(4-fluorobenzoyl)piperidin-1-yl)hexyl)-1H-benzo[d]imidazol-2(3H)-one (81) were identified as full antagonist ligands on cyclic adenosine monophosphate (cAMP, KB = 4.9 and 5.9 nM, respectively) and inositol monophosphate (IP1, KB = 0.6 and 16 nM, respectively) signaling pathways of 5-HT7R and 5-HT2AR. Both antagonists crossed the blood-brain barrier as evaluated with [(18)F] radiolabeled compounds [(18)F]79 and [(18)F]81 in a primate's central nervous system using positron emission tomography. Both radioligands showed standard uptake values ranging from 0.8 to 1.1, a good plasmatic stability, and a distribution consistent with 5-HT7R and 5-HT2AR in the CNS.

Cdk5 induces constitutive activation of 5-HT6 receptors to promote neurite growth.

The serotonin6 receptor (5-HT6R) is a promising target for treating cognitive deficits of schizophrenia often linked to alterations of neuronal development. This receptor controls neurodevelopmental processes, but the signaling mechanisms involved remain poorly understood. Using a proteomic strategy, we show that 5-HT6Rs constitutively interact with cyclin-dependent kinase 5 (Cdk5). Expression of 5-HT6Rs in NG108-15 cells induced neurite growth and expression of voltage-gated Ca(2+) channels, two hallmarks of neuronal differentiation. 5-HT6R-elicited neurite growth was agonist independent and prevented by the 5-HT6R antagonist SB258585, which behaved as an inverse agonist. Moreover, it required receptor phosphorylation at Ser350 by Cdk5 and Cdc42 activity. Supporting a role of native 5-HT6Rs in neuronal differentiation, neurite growth of primary neurons was reduced by SB258585, by silencing 5-HT6R expression or by mutating Ser350 into alanine. These results reveal a functional interplay between Cdk5 and a G protein-coupled receptor to control neuronal differentiation.