RESUMO
Severe peripheral infections induce an adaptive sickness behavior and an innate immune reaction in various organs including the brain. On the long term, persistent alteration of microglia, the brain innate immune cells, is associated with an increased risk of psychiatric disorders. It is thus critical to identify genes and mechanisms controlling the intensity and duration of the neuroinflammation induced by peripheral immune challenges. We tested the hypothesis that the 5-HT2B receptor, the main serotonin receptor expressed by microglia, might represent a valuable candidate. First, we observed that Htr2b-/- mice, knock-out for the 5-HT2B receptor gene, developed, when exposed to a peripheral lipopolysaccharide (LPS) challenge, a stronger weight loss compared to wild-type mice; in addition, comparison of inflammatory markers in brain, 4 and 24 hr after LPS injection, showed that Htr2b deficiency leads to a prolonged neuroinflammation. Second, to assess the specific contribution of the microglial 5-HT2B receptor, we investigated the response to LPS of conditional knock-out mice invalidated for Htr2b in microglia only. We found that deletion of Htr2b in microglia since birth is sufficient to cause enhanced weight loss and increased neuroinflammatory response upon LPS injection at adult stage. In contrast, mice deleted for microglial Htr2b in adulthood responded normally to LPS, revealing a neonatal developmental effect. These results highlight the role of microglia in the response to a peripheral immune challenge and suggest the existence of a developmental, neonatal period, during which instruction of microglia through 5-HT2B receptors is necessary to prevent microglia overreactivity in adulthood.
Assuntos
Comportamento de Doença , Microglia , Animais , Lipopolissacarídeos/toxicidade , Camundongos , Camundongos Endogâmicos C57BL , Doenças Neuroinflamatórias , Receptor 5-HT2B de Serotonina/genética , Serotonina , Redução de PesoRESUMO
The putative role of the N-terminal region of rhodopsin-like 7 transmembrane biogenic amine receptors in agonist-induced signaling has not yet been clarified despite recent advances in 7 transmembrane receptor structural biology. Given the existence of N-terminal nonsynonymous polymorphisms (R6G;E42G) within the HTR2B gene in a drug-abusing population, we assessed whether these polymorphisms affect 5-hydroxytryptamine 2B (5-HT2B) receptor in vitro pharmacologic and coupling properties in transfected COS-7 cells. Modification of the 5-HT2B receptor N terminus by the R6G;E42G polymorphisms increases such agonist signaling pathways as inositol phosphate accumulation as assessed by either classic or operational models. The N-terminal R6G;E42G mutations of the 5-HT2B receptor also increase cell proliferation and slow its desensitization kinetics compared with the wild-type receptor, further supporting a role for the N terminus in transduction efficacy. Furthermore, by coexpressing a tethered wild-type 5-HT2B receptor N terminus with a 5-HT2B receptor bearing a N-terminal deletion, we were able to restore original coupling. This reversion to normal activity of a truncated 5-HT2B receptor by coexpression of the membrane-tethered wild-type 5-HT2B receptor N terminus was not observed using a membrane-tethered 5-HT2B receptor R6G;E42G N terminus. These data suggest that the N terminus exerts a negative control over basal as well as agonist-stimulated receptor activity that is lost in the R6G;E42G mutant. Our findings reveal a new and unanticipated role of the 5-HT2B receptor N terminus as a negative modulator, affecting both constitutive and agonist-stimulated activity. Moreover, our data caution against excluding the N terminus and extracellular loops in structural studies of this 7 transmembrane receptor family.
Assuntos
Receptor 5-HT2B de Serotonina/genética , Sequência de Aminoácidos , Animais , Técnicas de Transferência de Energia por Ressonância de Bioluminescência , Células COS , Proliferação de Células , Chlorocebus aethiops , Subunidades alfa Gq-G11 de Proteínas de Ligação ao GTP/metabolismo , Humanos , Dados de Sequência Molecular , Mutação , Polimorfismo Genético , Ensaio Radioligante , Agonistas do Receptor 5-HT2 de Serotonina/farmacologia , Transdução de SinaisRESUMO
Early changes in neuroendocrine pathways are essential in the development of metabolic pathologies. Thus, it is important to have a better understanding of the signals involved in their initiation. Long-term consumption of high-fat diets induces insulin resistance, obesity, diabetes. Here, we have investigated early neural and endocrine events in the hypothalamus and hippocampus induced by a short-term high fat, low carbohydrate diet in adult male Wistar rats. The release of serotonin, which is closely associated with the actions of insulin and leptin, was measured, by electrochemical detection following reverse-phase liquid chromatography (HPLC), in the extracellular space of the medial hypothalamus and the dorsal hippocampus in samples obtained from non-anesthetized animals, by microdialysis. The high-fat diet had a specific effect on the hypothalamus. Serotonin release induced by food intake was reduced after 1 week, and effectively ceased after 6 weeks of the diet. After 1 week, there was an increased gene expression of the insulin receptor and the insulin receptor substrates IRS1 and IRS2, as measured by real-time PCR. After 6 weeks of diet, insulin gene expression increased. Leptinemia increased in all cases. This new data support the concept that high-fat diets, in addition to have peripheral effects, cause a rapid alteration in specific central mechanisms involved in energy and glucose homeostasis. The changes in the gene expression of insulin and signaling elements represent possible adaptations aimed at counterbalancing the reduced responsiveness of the serotonergic system to nutritional signals and maintaining homeostasis.
Assuntos
Encéfalo/metabolismo , Gorduras na Dieta/efeitos adversos , Insulina/metabolismo , Doenças Metabólicas/metabolismo , Sistemas Neurossecretores/metabolismo , Serotonina/metabolismo , Animais , Encéfalo/fisiopatologia , Modelos Animais de Doenças , Metabolismo Energético/fisiologia , Glucose/metabolismo , Hipocampo/metabolismo , Hipocampo/fisiopatologia , Homeostase/fisiologia , Hipotálamo/metabolismo , Hipotálamo/fisiopatologia , Proteínas Substratos do Receptor de Insulina/genética , Masculino , Doenças Metabólicas/fisiopatologia , Sistemas Neurossecretores/fisiopatologia , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Receptor de Insulina/genética , Transdução de Sinais/fisiologiaRESUMO
Serotonin is a neurotransmitter involved in many psychiatric diseases. In humans, a lack of 5-HT2B receptors is associated with serotonin-dependent phenotypes, including impulsivity and suicidality. A lack of 5-HT2B receptors in mice eliminates the effects of molecules that directly target serotonergic neurons including amphetamine derivative serotonin releasers, and selective serotonin reuptake inhibitor antidepressants. In this work, we tested the hypothesis that 5-HT2B receptors directly and positively regulate raphe serotonin neuron activity. By ex vivo electrophysiological recordings, we report that stimulation by the 5-HT2B receptor agonist, BW723C86, increased the firing frequency of serotonin Pet1-positive neurons. Viral overexpression of 5-HT2B receptors in these neurons increased their excitability. Furthermore, in vivo 5-HT2B-receptor stimulation by BW723C86 counteracted 5-HT1A autoreceptor-dependent reduction in firing rate and hypothermic response in wild-type mice. By a conditional genetic ablation that eliminates 5-HT2B receptor expression specifically and exclusively from Pet1-positive serotonin neurons (Htr2b 5-HTKO mice), we demonstrated that behavioral and sensitizing effects of MDMA (3,4-methylenedioxy-methamphetamine), as well as acute behavioral and chronic neurogenic effects of the antidepressant fluoxetine, require 5-HT2B receptor expression in serotonergic neurons. In Htr2b 5-HTKO mice, dorsal raphe serotonin neurons displayed a lower firing frequency compared to control Htr2b lox/lox mice as assessed by in vivo extracellular recordings and a stronger hypothermic effect of 5-HT1A-autoreceptor stimulation was observed. The increase in head-twitch response to DOI (2,5-dimethoxy-4-iodoamphetamine) further confirmed the lower serotonergic tone resulting from the absence of 5-HT2B receptors in serotonin neurons. Together, these observations indicate that the 5-HT2B receptor acts as a direct positive modulator of serotonin Pet1-positive neurons in an opposite way as the known 5-HT1A-negative autoreceptor.
Assuntos
Sensibilização do Sistema Nervoso Central/fisiologia , Indóis/farmacologia , Núcleos da Rafe/fisiologia , Receptor 5-HT2B de Serotonina/fisiologia , Neurônios Serotoninérgicos/fisiologia , Tiofenos/farmacologia , 3,4-Metilenodioxianfetamina/farmacologia , 8-Hidroxi-2-(di-n-propilamino)tetralina/farmacologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Anfetaminas/farmacologia , Animais , Temperatura Corporal/efeitos dos fármacos , Feminino , Fluoxetina/farmacologia , Masculino , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Neurogênese/fisiologia , Inibição Pré-Pulso/efeitos dos fármacos , Inibição Pré-Pulso/fisiologia , Receptor 5-HT2B de Serotonina/genética , Agonistas do Receptor 5-HT2 de Serotonina/farmacologia , Fatores de Transcrição/genéticaRESUMO
Serotonergic dysfunction is mainly associated with neuropsychiatric and cardiovascular disorders but has also been linked with many other pathological conditions. Serotonin (5-hydroxytryptamine, 5-HT) mediates numerous physiological functions in the brain and the periphery by activating a variety of receptors. 5-HT receptors are divided into four classes, three of which belong to the G protein-coupled receptor family. This review provides an overview of the recent pharmacological developments involving the Gq-coupled 5-HT2 receptor subfamily as well as the pathological implications of this receptor subfamily with regard to fibrosis, the central nervous system, cardiovascular disorders, and cancer. The final section highlights new therapeutic opportunities and emerging research revealing unexplored medical opportunities for this class of 5-HT receptors. The development of biased 5-HT2 receptor ligands appears to be an interesting topic in various areas. In light of recent discoveries, the need for the development of new and safer drugs should take into account the risk of cardiovascular side effects such as pulmonary hypertension and heart valve disease.
Assuntos
Desenho de Fármacos , Receptores 5-HT2 de Serotonina/efeitos dos fármacos , Serotonina/metabolismo , Animais , Doenças Cardiovasculares/tratamento farmacológico , Doenças Cardiovasculares/fisiopatologia , Doenças do Sistema Nervoso Central/tratamento farmacológico , Doenças do Sistema Nervoso Central/fisiopatologia , Humanos , Ligantes , Neoplasias/tratamento farmacológico , Neoplasias/patologia , Receptores 5-HT2 de Serotonina/metabolismoRESUMO
BACKGROUND AND PURPOSE: Valvular heart disease (VHD) is highly prevalent in industrialized countries. Chronic use of anorexigens, amphetamine or ergot derivatives targeting the 5-HT system is associated with VHD. Here, we investigated the contribution of 5-HT receptors in a model of valve degeneration induced by nordexfenfluramine, the main metabolite of the anorexigens, dexfenfluramine and benfluorex. EXPERIMENTAL APPROACH: Nordexfenfluramine was infused chronically (28 days) in mice ((WT and transgenic Htr2B -/- , Htr2A -/- , and Htr2B/2A -/- ) to induce mitral valve lesions. Bone marrow transplantation was also carried out. Haemodynamics were measured with echocardiography; tissues and cells were analysed by histology, immunocytochemistry, flow cytometry and RT -qPCR. Samples of human prolapsed mitral valves were also analysed. KEY RESULTS: Chronic treatment of mice with nordexfenfluramine activated 5-HT2B receptors and increased valve thickness and cell density in a thick extracellular matrix, mimicking early steps of mitral valve remodelling. Lesions were prevented by 5-HT2A or 5-HT2B receptor antagonists and in transgenic Htr2B -/- or Htr2A/2B -/- mice. Surprisingly, valve lesions were mainly formed by numerous non-proliferative CD34+ endothelial progenitors. These progenitors originated from bone marrow (BM) as revealed by BM transplantation. The initial steps of mitral valve remodelling involved mobilization of BM-derived CD34+ CD31+ cells by 5-HT2B receptor stimulation. Analysis of human prolapsed mitral valves showing spontaneous degenerative lesions, demonstrated the presence of non-proliferating CD34+ /CD309+ /NOS3+ endothelial progenitors expressing 5-HT2B receptors. CONCLUSIONS AND IMPLICATIONS: BM-derived endothelial progenitor cells make a crucial contribution to the remodelling of mitral valve tissue. Our data describe a new and important mechanism underlying human VHD.
Assuntos
Células Progenitoras Endoteliais , Doenças das Valvas Cardíacas/metabolismo , Valva Mitral/metabolismo , Receptor 5-HT2B de Serotonina/metabolismo , Animais , Transplante de Medula Óssea , Células Progenitoras Endoteliais/metabolismo , Doenças das Valvas Cardíacas/patologia , Masculino , Camundongos Transgênicos , Valva Mitral/efeitos dos fármacos , Valva Mitral/patologia , Norfenfluramina/farmacologia , Receptor 5-HT2A de Serotonina/genética , Receptor 5-HT2B de Serotonina/genética , Antagonistas do Receptor 5-HT2 de Serotonina/farmacologiaRESUMO
Serotonin and bone-marrow-derived stem cells participate together in triggering pulmonary hypertension. Our work has shown that the absence of 5-HT2B receptors generates permanent changes in the composition of the blood and bone-marrow in the myeloid lineages, particularly in endothelial cell progenitors. The initial functions of 5-HT2B receptors in pulmonary arterial hypertension (PAH) are restricted to bone-marrow cells. They contribute to the differentiation/proliferation/mobilization of endothelial progenitor cells from the bone-marrow. Those bone-marrow-derived cells have a critical role in the development of pulmonary hypertension and pulmonary vascular remodeling. These data indicate that bone-marrow derived endothelial progenitors play a key role in the pathogenesis of PAH and suggest that interactions involving serotonin and bone morphogenic protein type 2 receptor (BMPR2) could take place at the level of the bone-marrow.
Assuntos
Medula Óssea/fisiologia , Células Endoteliais/fisiologia , Hipertensão Pulmonar/etiologia , Serotonina/fisiologia , Células-Tronco/fisiologia , Animais , Células da Medula Óssea/fisiologia , Receptores de Proteínas Morfogenéticas Ósseas Tipo II/fisiologia , Humanos , CamundongosRESUMO
Maturation of functional neuronal circuits during central nervous system development relies on sophisticated mechanisms. First, axonal and dendritic growth should reach appropriate targets for correct synapse elaboration. Second, pruning and neuronal death are required to eliminate redundant or inappropriate neuronal connections. Serotonin, in addition to its role as a neurotransmitter, actively participates in postnatal establishment and refinement of brain wiring in mammals. Brain resident macrophages, that is, microglia, also play an important role in developmentally regulated neuronal death as well as in synaptic maturation and elimination. Here, we tested the hypothesis of cross-regulation between microglia and serotonin during postnatal brain development in a mouse model of synaptic refinement. We found expression of the serotonin 5-HT2B receptor on postnatal microglia, suggesting that serotonin could participate in temporal and spatial synchronization of microglial functions. Using two-photon microscopy, acute brain slices, and local delivery of serotonin, we observed that microglial processes moved rapidly toward the source of serotonin in Htr2B(+/+) mice, but not in Htr2B(-/-) mice lacking the 5-HT2B receptor. We then investigated whether some developmental steps known to be controlled by serotonin could potentially result from microglia sensitivity to serotonin. Using an in vivo model of synaptic refinement during early brain development, we investigated the maturation of the retinal projections to the thalamus and observed that Htr2B(-/-) mice present anatomical alterations of the ipsilateral projecting area of retinal axons into the thalamus. In addition, activation markers were upregulated in microglia from Htr2B(-/-) compared to control neonates, in the absence of apparent morphological modifications. These results support the hypothesis that serotonin interacts with microglial cells and these interactions participate in brain maturation.
Assuntos
Corpos Geniculados/crescimento & desenvolvimento , Microglia/fisiologia , Receptor 5-HT2A de Serotonina/metabolismo , Retina/crescimento & desenvolvimento , Serotonina/metabolismo , Sinapses/fisiologia , Animais , Receptor 1 de Quimiocina CX3C , Células Cultivadas , Córtex Cerebral/crescimento & desenvolvimento , Córtex Cerebral/fisiologia , Corpos Geniculados/fisiologia , Hipocampo/crescimento & desenvolvimento , Hipocampo/fisiologia , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Receptor 5-HT2A de Serotonina/genética , Receptores de Quimiocinas/genética , Receptores de Quimiocinas/metabolismo , Retina/fisiologia , Técnicas de Cultura de Tecidos , Vias Visuais/crescimento & desenvolvimento , Vias Visuais/fisiologiaRESUMO
The now-banned anorectic molecule, dexfenfluramine, promotes serotonin release through a serotonin transporter-dependent mechanism, and it has been widely prescribed for the treatment of obesity. Previous studies have identified that 5-HT(2B) receptors have important roles in dexfenfluramine side effects, that is, pulmonary hypertension, plasma serotonin level regulation, and valvulopathy. We thus investigated a putative contribution of 5-HT(2B) receptors in dexfenfluramine-dependent feeding behavior in mice. Interestingly, the hypophagic response to dexfenfluramine (3-10 mg/kg) observed in wild-type mice (1-4 h) was eliminated in mice lacking 5-HT(2B) receptors (5-HT(2B)(-/-)). These findings were further validated by the lack of hypophagic response to dexfenfluramine in wild-type mice treated with RS127445, a highly selective and potent antagonist (pKi=8.22 ± 0.24). Using microdialysis, we observed that in 5-HT(2B)(-/-) awake mice, the dexfenfluramine-induced hypothalamic peak of serotonin release (1 h) was strongly reduced (fourfold) compared with wild type. Moreover, using hypothalamic synaptosomes, we established the serotonergic neuron autonomous properties of this effect: a strong serotonin release was observed upon dexfenfluramine stimulation of synaptosome preparation from wild type but not from mice lacking active 5-HT(2B) receptors. These findings strongly suggest that activation of presynaptic 5-HT(2B) receptors is a limiting step in the serotonin transporter dependent-releasing effect of dexfenfluramine, whereas other serotonin receptors act downstream with respect to feeding behavior.
Assuntos
Depressores do Apetite/farmacologia , Regulação do Apetite/efeitos dos fármacos , Dexfenfluramina/farmacologia , Obesidade/tratamento farmacológico , Receptor 5-HT2B de Serotonina/fisiologia , Agonistas do Receptor de Serotonina/farmacologia , Animais , Depressores do Apetite/uso terapêutico , Regulação do Apetite/fisiologia , Dexfenfluramina/uso terapêutico , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Masculino , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Knockout , Obesidade/genética , Obesidade/metabolismo , Pirimidinas/farmacologia , Pirimidinas/uso terapêutico , Receptor 5-HT2B de Serotonina/deficiência , Receptor 5-HT2B de Serotonina/genética , Serotonina/metabolismo , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismoRESUMO
The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) reverses dopamine and serotonin transporters to produce efflux of dopamine and serotonin, respectively, in regions of the brain that have been implicated in reward. However, the role of serotonin/dopamine interactions in the behavioral effects of MDMA remains unclear. We previously showed that MDMA-induced locomotion, serotonin and dopamine release are 5-HT(2B) receptor-dependent. The aim of the present study was to determine the contribution of serotonin and 5-HT(2B) receptors to the reinforcing properties of MDMA.We show here that 5-HT(2B) (-/-) mice do not exhibit behavioral sensitization or conditioned place preference following MDMA (10 mg/kg) injections. In addition, MDMA-induced reinstatement of conditioned place preference after extinction and locomotor sensitization development are each abolished by a 5-HT(2B) receptor antagonist (RS127445) in wild type mice. Accordingly, MDMA-induced dopamine D1 receptor-dependent phosphorylation of extracellular regulated kinase in nucleus accumbens is abolished in mice lacking functional 5-HT(2B) receptors. Nevertheless, high doses (30 mg/kg) of MDMA induce dopamine-dependent but serotonin and 5-HT(2B) receptor-independent behavioral effects.These results underpin the importance of 5-HT(2B) receptors in the reinforcing properties of MDMA and illustrate the importance of dose-dependent effects of MDMA on serotonin/dopamine interactions.