Many psychiatric diseases have been associated with serotonin (5-HT) neuron dysfunction. The firing of 5-HT neurons is known to be under 5-HT
receptor-mediated autoinhibition, but functional ...consequences of coexpressed receptors are unknown. Using co-immunoprecipitation, BRET, confocal, and super-resolution microscopy in hippocampal and 5-HT neurons, we present evidence that 5-HT
and 5-HT
receptors can form heterodimers and co-cluster at the plasma membrane of dendrites. Selective agonist stimulation of coexpressed 5-HT
and 5-HT
receptors prevents 5-HT
receptor internalization and increases 5-HT
receptor membrane clustering. Current clamp recordings of 5-HT neurons revealed that 5-HT
receptor stimulation of acute slices from mice lacking 5-HT
receptors in 5-HT neurons increased their firing activity trough Ca
-activated potassium channel inhibition compared to 5-HT neurons from control mice. This work supports the hypothesis that the relative expression of 5-HT
and 5-HT
receptors tunes the neuronal excitability of serotonergic neurons through potassium channel regulation.
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-HT
) 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-HT
inhibition on outcomes after MI and characterized the histological and microstructural changes involved in tissue remodeling. Inducible 5-HT
ablation driven by
and
was used to evaluate resident cardiac fibroblast- and myofibroblast-specific contributions of 5-HT
, respectively. RNA sequencing was used to motivate subsequent in vitro analyses to explore cardiac fibroblast phenotype.
5-HT
antagonism preserved cardiac structure and function by facilitating a less fibrotic scar, indicated by decreased scar thickness and decreased border zone area. 5-HT
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-HT
from
-lineage resident cardiac fibroblasts and saw similar improvements to the pharmacological approach. Tamoxifen-inducible Cre-mediated ablation of 5-HT
after onset of injury in
-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
expression and Src phosphorylation.
Together, our findings illustrate that 5-HT
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 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.
The monoamine serotonin (5-HT), a well-known neurotransmitter, is also important in peripheral tissues. Several studies have suggested that 5-HT is involved in bone metabolism. Starting from our ...original observation of increased 5-HT₂B receptor (5-HT₂BR) expression during in vitro osteoblast differentiation, we investigated a putative bone phenotype in vivo in 5-HT₂BR knockout mice. Of interest, 5-HT₂BR mutant female mice displayed reduced bone density that was significant from age 4 months and had intensified by 12 and 18 months. This histomorphometrically confirmed osteopenia seems to be due to reduced bone formation because 1) the alkaline phosphatase-positive colony-forming unit capacity of bone marrow precursors was markedly reduced in the 5-HT₂BR mutant mice from 4 to 12 months of age, 2) ex vivo primary osteoblasts from mutant mice exhibited reduced proliferation and delayed differentiation, and 3) calcium incorporation was markedly reduced in osteoblasts after 5-HT₂BR depletion (produced genetically or by pharmacological inactivation). These findings support the hypothesis that the 5-HT₂BR receptor facilitates osteoblast recruitment and proliferation and that its absence leads to osteopenia that worsens with age. We show here, for the first time, that the 5-HT₂BR receptor is a physiological mediator of 5-HT in bone formation and, potentially, in the onset of osteoporosis in aging women.--Collet, C., Schiltz, C., Geoffroy, V., Maroteaux, L., Launay, J.-M., de Vernejoul, M.-C. The serotonin 5-HT₂B receptor controls bone mass via osteoblast recruitment and proliferation.
Impulsivity and hyperactivity share common ground with numerous mental disorders, including schizophrenia. Recently, a population-specific serotonin 2B (5-HT sub(2B)) receptor stop codon (ie, HTR2B ...Q20*) was reported to segregate with severely impulsive individuals, whereas 5-HT sub(2B) mutant (Htr sub(2B) super(-/-)) mice also showed high impulsivity. Interestingly, in the same cohort, early-onset schizophrenia was more prevalent in HTR2B Q*20 carriers. However, the putative role of 5-HT sub(2B) receptor in the neurobiology of schizophrenia has never been investigated. We assessed the effects of the genetic and the pharmacological ablation of 5-HT sub(2B) receptors in mice subjected to a comprehensive series of behavioral test screenings for schizophrenic-like symptoms and investigated relevant dopaminergic and glutamatergic neurochemical alterations in the cortex and the striatum. Domains related to the positive, negative, and cognitive symptom clusters of schizophrenia were affected in Htr sub(2B) super(-/-) mice, as shown by deficits in sensorimotor gating, in selective attention, in social interactions, and in learning and memory processes. In addition, Htr sub(2B) super(-/-) mice presented with enhanced locomotor response to the psychostimulants dizocilpine and amphetamine, and with robust alterations in sleep architecture. Moreover, ablation of 5-HT sub(2B) receptors induced a region-selective decrease of dopamine and glutamate concentrations in the dorsal striatum. Importantly, selected schizophrenic-like phenotypes and endophenotypes were rescued by chronic haloperidol treatment. We report herein that 5-HT sub(2B) receptor deficiency confers a wide spectrum of antipsychotic-sensitive schizophrenic-like behavioral and psychopharmacological phenotypes in mice and provide first evidence for a role of 5-HT sub(2B) receptors in the neurobiology of psychotic disorders.
Impulsivity and hyperactivity share common ground with numerous mental disorders, including schizophrenia. Recently, a population-specific serotonin 2B (5-HT2B) receptor stop codon (ie, HTR2B Q20*) ...was reported to segregate with severely impulsive individuals, whereas 5-HT2B mutant (Htr2B(-/-)) mice also showed high impulsivity. Interestingly, in the same cohort, early-onset schizophrenia was more prevalent in HTR2B Q*20 carriers. However, the putative role of 5-HT2B receptor in the neurobiology of schizophrenia has never been investigated. We assessed the effects of the genetic and the pharmacological ablation of 5-HT2B receptors in mice subjected to a comprehensive series of behavioral test screenings for schizophrenic-like symptoms and investigated relevant dopaminergic and glutamatergic neurochemical alterations in the cortex and the striatum. Domains related to the positive, negative, and cognitive symptom clusters of schizophrenia were affected in Htr2B(-/-) mice, as shown by deficits in sensorimotor gating, in selective attention, in social interactions, and in learning and memory processes. In addition, Htr2B(-/-) mice presented with enhanced locomotor response to the psychostimulants dizocilpine and amphetamine, and with robust alterations in sleep architecture. Moreover, ablation of 5-HT2B receptors induced a region-selective decrease of dopamine and glutamate concentrations in the dorsal striatum. Importantly, selected schizophrenic-like phenotypes and endophenotypes were rescued by chronic haloperidol treatment. We report herein that 5-HT2B receptor deficiency confers a wide spectrum of antipsychotic-sensitive schizophrenic-like behavioral and psychopharmacological phenotypes in mice and provide first evidence for a role of 5-HT2B receptors in the neurobiology of psychotic disorders.
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 Htr 2B +/+ mice, but not in Htr 2B –/– 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 Htr 2B –/– mice present anatomical alterations of the ipsilateral projecting area of retinal axons into the thalamus. In addition, activation markers were upregulated in microglia from Htr 2B –/– 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.
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