Although potentially implicated in several physiological functions, few functional mutations have been identified in the human
5-hydroxytryptamine (HT) 2B receptor gene. A heterozygous mutation R393X ...in the 5-HT 2B receptor was recently identified in a patient diagnosed with pulmonary hypertension after intake of the anorexigenic dexfenfluramine.
Although reported to generate a lack of function, this C terminus-truncated 5-HT 2B receptor should somehow affect transduction pathways relevant to pulmonary hypertension. In our study, we investigated putative
modifications in transduction of the R393X-mutated 5-HT 2B receptor. In stably transfected cells, we confirmed the loss of inositol 1,4,5-trisphosphate stimulation caused by the G αq uncoupling, despite conserved ligand affinity between the normal and mutated receptors. We also observed a partial loss of
nitric-oxide synthase stimulation. However, the truncated R393X receptor presented 1) a strong gain of efficacy in cell proliferation
as assessed by mitogen-activated protein kinase activity and thymidine incorporation, 2) a preferential coupling to G α13 as shown by blocking antiserum, and 3) an apparent lack of internalization upon agonist stimulation as observed by confocal
microscopy. This work demonstrates that, in the 5-HT 2B receptor, the C terminus, including the palmitoylation and phosphorylation sites, is absolutely required for proper transduction
and internalization. For the first time, we show that the lack of C terminus can generate a switch of coupling to G α13 , a reduced NO synthase activation, and an increase in cell proliferation. All these modifications are relevant in pathophysiological
vasoconstriction.
The proper maturation of emotional and sensory circuits requires fine-tuning of serotonin (5-HT) level during early postnatal development. Consistently, dysfunctions of the serotonergic system have ...been associated with neurodevelopmental psychiatric diseases, including autism spectrum disorders (ASD). However, the mechanisms underlying the developmental effects of 5-HT remain partially unknown, one obstacle being the action of 5-HT on different cell types. Here, we focused on microglia, which play a role in brain wiring refinement, and we investigated whether the control of these cells by 5-HT is relevant for neurodevelopment and spontaneous behaviors in mice. Since the main 5-HT sensor in microglia is the 5-HT2B receptor subtype, we prevented 5-HT signaling specifically in microglia by conditional invalidation of the Htr2b gene in these cells. We observed that abrogating the serotonergic control of microglia during early postnatal development affects the phagolysosomal compartment of these cells and their proximity to dendritic spines and perturbs neuronal circuits maturation. Furthermore, this early ablation of microglial 5-HT2B receptors leads to adult hyperactivity in a novel environment and behavioral defects in sociability and flexibility. Importantly, we show that these behavioral alterations result from a developmental effect, since they are not observed when microglial Htr2b invalidation is induced later, at P30 onward. Thus, a primary alteration of 5-HT sensing in microglia, during a critical time window between birth and P30, is sufficient to impair social and flexibility skills. This link between 5-HT and microglia may explain the association between serotonergic dysfunctions and behavioral traits like impaired sociability and inadaptability to novelty, which are prominent in psychiatric disorders such as ASD.
Myocardial infarction (MI) induces an intense injury response that ultimately generates a collagen-dominated scar. Although required to prevent ventricular rupture, the fibrotic process is often ...sustained in a manner detrimental to optimal recovery. Cardiac myofibroblasts are the cells tasked with depositing and remodeling collagen and are a prime target to limit the fibrotic process after MI. Serotonin 2B receptor (5-HT2B) signaling has been shown to be harmful in a variety of cardiopulmonary pathologies and could play an important role in mediating scar formation after MI.BACKGROUNDMyocardial infarction (MI) induces an intense injury response that ultimately generates a collagen-dominated scar. Although required to prevent ventricular rupture, the fibrotic process is often sustained in a manner detrimental to optimal recovery. Cardiac myofibroblasts are the cells tasked with depositing and remodeling collagen and are a prime target to limit the fibrotic process after MI. Serotonin 2B receptor (5-HT2B) signaling has been shown to be harmful in a variety of cardiopulmonary pathologies and could play an important role in mediating scar formation after MI.We used 2 pharmacological antagonists to explore the effect of 5-HT2B inhibition on outcomes after MI and characterized the histological and microstructural changes involved in tissue remodeling. Inducible 5-HT2B ablation driven by Tcf21MCM and PostnMCM was used to evaluate resident cardiac fibroblast- and myofibroblast-specific contributions of 5-HT2B, respectively. RNA sequencing was used to motivate subsequent in vitro analyses to explore cardiac fibroblast phenotype.METHODSWe used 2 pharmacological antagonists to explore the effect of 5-HT2B inhibition on outcomes after MI and characterized the histological and microstructural changes involved in tissue remodeling. Inducible 5-HT2B ablation driven by Tcf21MCM and PostnMCM was used to evaluate resident cardiac fibroblast- and myofibroblast-specific contributions of 5-HT2B, respectively. RNA sequencing was used to motivate subsequent in vitro analyses to explore cardiac fibroblast phenotype.5-HT2B antagonism preserved cardiac structure and function by facilitating a less fibrotic scar, indicated by decreased scar thickness and decreased border zone area. 5-HT2B antagonism resulted in collagen fiber redistribution to thinner collagen fibers that were more anisotropic, enhancing left ventricular contractility, whereas fibrotic tissue stiffness was decreased, limiting the hypertrophic response of uninjured cardiomyocytes. Using a tamoxifen-inducible Cre, we ablated 5-HT2B from Tcf21-lineage resident cardiac fibroblasts and saw similar improvements to the pharmacological approach. Tamoxifen-inducible Cre-mediated ablation of 5-HT2B after onset of injury in Postn-lineage myofibroblasts also improved cardiac outcomes. RNA sequencing and subsequent in vitro analyses corroborate a decrease in fibroblast proliferation, migration, and remodeling capabilities through alterations in Dnajb4 expression and Src phosphorylation.RESULTS5-HT2B antagonism preserved cardiac structure and function by facilitating a less fibrotic scar, indicated by decreased scar thickness and decreased border zone area. 5-HT2B antagonism resulted in collagen fiber redistribution to thinner collagen fibers that were more anisotropic, enhancing left ventricular contractility, whereas fibrotic tissue stiffness was decreased, limiting the hypertrophic response of uninjured cardiomyocytes. Using a tamoxifen-inducible Cre, we ablated 5-HT2B from Tcf21-lineage resident cardiac fibroblasts and saw similar improvements to the pharmacological approach. Tamoxifen-inducible Cre-mediated ablation of 5-HT2B after onset of injury in Postn-lineage myofibroblasts also improved cardiac outcomes. RNA sequencing and subsequent in vitro analyses corroborate a decrease in fibroblast proliferation, migration, and remodeling capabilities through alterations in Dnajb4 expression and Src phosphorylation.Together, our findings illustrate that 5-HT2B expression in either cardiac fibroblasts or activated myofibroblasts directly contributes to excessive scar formation, resulting in adverse remodeling and impaired cardiac function after MI.CONCLUSIONSTogether, our findings illustrate that 5-HT2B expression in either cardiac fibroblasts or activated myofibroblasts directly contributes to excessive scar formation, resulting in adverse remodeling and impaired cardiac function after MI.
The proper maturation of emotional and sensory circuits requires fine-tuning of serotonin (5-HT) level during early postnatal development. Consistently, dysfunctions of the serotonergic system have ...been associated with neurodevelopmental psychiatric diseases, including autism spectrum disorders (ASD). However, the mechanisms underlying the developmental effects of 5-HT remain partially unknown, one obstacle being the action of 5-HT on different cell types. Here, we focused on microglia, which play a role in brain wiring refinement, and we investigated whether the control of these cells by 5-HT is relevant for neurodevelopment and spontaneous behaviors in mice. Since the main 5-HT sensor in microglia is the 5-HT
receptor subtype, we prevented 5-HT signaling specifically in microglia by conditional invalidation of the Htr2b gene in these cells. We observed that abrogating the serotonergic control of microglia during early postnatal development affects the phagolysosomal compartment of these cells and their proximity to dendritic spines and perturbs neuronal circuits maturation. Furthermore, this early ablation of microglial 5-HT
receptors leads to adult hyperactivity in a novel environment and behavioral defects in sociability and flexibility. Importantly, we show that these behavioral alterations result from a developmental effect, since they are not observed when microglial Htr2b invalidation is induced later, at P30 onward. Thus, a primary alteration of 5-HT sensing in microglia, during a critical time window between birth and P30, is sufficient to impair social and flexibility skills. This link between 5-HT and microglia may explain the association between serotonergic dysfunctions and behavioral traits like impaired sociability and inadaptability to novelty, which are prominent in psychiatric disorders such as ASD.
Cocaine dependence has a strong heritability component. The aim of this study was to investigate the putative association between the serotonin 2B receptor gene (
), crack use disorders and ...impulsivity.
A French Afro-Caribbean male population of patients with crack use disorders (
= 80) was compared to healthy Afro-Caribbean male controls (
= 60). Comorbid ADHD and impulsivity were assessed. Five single nucleotide polymorphisms (SNPs) in the
gene were selected: rs643700, rs6736017, rs1549339, rs17586428 and rs3806545. These SNPs were chosen to include most of the linkage disequilibrium blocks in the
gene. The French translation of the Barratt Impulsivity Scale BIS-11 was used to evaluate impulsivity. Comorbid ADHD was diagnosed using the Wender Utah Rating Scale-25 item for Attention Deficit-Hyperactivity Disorder.
We have observed a positive association between the rs6736017 polymorphism and crack use disorders in a French Afro-Caribbean male population.
In our population, the risk effect of
rs6736017 appeared to be specific to individuals with crack use disorders rather than being driven by impulsivity or ADHD alone.
Summary Plasma 5-hydroxytryptamine (5-HT; serotonin), released from blood platelets, plays a major role in the human cardiovascular system. Besides the effect of endogenous serotonin, many drugs ...targeting serotonergic receptors are widely used in the general population (antiobesity agents, antidepressants, antipsychotics, antimigraine agents), and may enhance the cardiovascular risk. Depending on the type of serotonin receptor activated and its location, the use of these compounds triggers acute and chronic effects. The acute cardiovascular response to 5-HT, named the Bezold-Jarish reflex, leads to intense bradycardia associated with atrioventricular block, and involves 5-HT3 , 5-HT1B/1D , 5-HT7 and 5-HT2A/2B receptors. The chronic contribution of 5-HT and its receptors (5-HT4 and 5-HT2A/2B ) in cardiovascular tissue remodeling, with a particular emphasis on cardiac hypertrophy, fibrosis and valve degeneration, will be explored in this review. Finally, through the analysis of the effects of sarpogrelate, some new aspects of 5-HT2A receptor pharmacology in vasomotor tone regulation and the interaction between endothelial and smooth muscle cells will also be discussed. The aim of this review is to emphasize the cardiac side effects caused by serotonin receptor activation, and to highlight their possible prevention by the development of new drugs targeting this system.
Major depression is a psychiatric disorder with complex etiology. About 30% of depressive patients are resistant to antidepressants that are currently available, likely because they only target the ...monoaminergic systems. Thus, identification of novel antidepressants with a larger action spectrum is urgently required. Epidemiological data indicate high comorbidity between metabolic and psychiatric disorders, particularly obesity and depression. We used a well-characterized anxiety/depressive-like mouse model consisting of continuous input of corticosterone for seven consecutive weeks. A panel of reliable behavioral tests were conducted to assessing numerous facets of the depression-like state, including anxiety, resignation, reduced motivation, loss of pleasure, and social withdrawal. Furthermore, metabolic features including weight, adiposity, and plasma biological parameters (lipids, adipokines, and cytokines) were investigated in corticosterone-treated mice. Our data show that chronic administration of corticosterone induced the parallel onset of metabolic and behavioral dysfunctions in mice. AdipoRon, a potent adiponectin receptor agonist, prevented the corticosterone-induced early onset of moderate obesity and metabolic syndromes. Moreover, in all the behavioral tests, daily treatment with AdipoRon successfully reversed the corticosterone-induced depression-like state in mice. AdipoRon exerted its pleiotropic actions on various systems including hippocampal neurogenesis, serotonergic neurotransmission, neuroinflammation, and the tryptophan metabolic pathway, which can explain its antidepressant properties. Our study highlights the pivotal role of the adiponergic system in the development of both metabolic and psychiatric disorders. AdipoRon may constitute a promising novel antidepressant.
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.
Main Points
Lack of 5‐HT2B receptor in microglia since birth sensitizes to the neuroinflammation induced by a peripheral LPS injection in adulthood.
This effect is not observed if the gene is invalidated in adulthood, suggesting a neonatal critical period for instruction of microglia by 5‐HT.
Abstract Depressive disorders are among the most prevalent neuropsychiatric dysfunctions worldwide, with high rates of resistance to antidepressant treatment. Genetic factors clearly contribute to ...the manifestation of depression as well as to the response to antidepressants. Transgenic mouse models appear as seminal tools to disentangle this complex disorder. Here, we analyzed new key aspects of the phenotype of knock-out mice for the gene encoding the serotonin 2B receptor ( Htr 2B−/− ), including basal phenotype, ability to develop a depressive-like phenotype upon chronic isolation, and effect of chronic exposure to fluoxetine on chronically stressed Htr 2B−/− mice. We find, here, that Htr 2B−/− mice display an antidepressant-like phenotype, which includes reduced latency to feed in the novelty suppressed feeding test, basal increase in hippocampal BDNF levels, no change in TrkB and p75 protein levels, and an increased preference for sucrose consumption compared to wild type ( Htr 2B+/+ ) mice. Nevertheless, we show that these mice can develop depressive-like behaviors when socially isolated during four weeks. Selective serotonin reuptake inhibitors (SSRI) have been previously shown to be ineffective in non-stressed Htr 2B−/− mice. We evaluated, here, the effects of the SSRI fluoxetine in chronically stressed Htr 2B−/− mice and similarly no behavioral or plastic effect was induced by this antidepressant. All together, these results highlight the suitability to study resistance to SSRI antidepressants of this mouse model displaying panoply of conditions among which behavioral, neurotrophic and plastic causative factors can be analyzed.
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