Activation of 5-HT7 receptor stimulates neurite elongation through mTOR, Cdc42 and actin filaments dynamics

Modulation of neuronal morphology by antipsychotic drug: Involvement of serotonin receptor 7

Antipsychotic drugs (APDs) are the primary pharmacological treatment for schizophrenia, a complex disorder characterized by altered neuronal connectivity. Atypical or second-generation antipsychotics, such as Risperidone (RSP) and Clozapine (CZP) predominantly block dopaminergic D2 and serotonin receptor 2A (5-HT2A) neurotransmission. Both compounds also exhibit affinity for the 5-HT7R, with RSP acting as an antagonist and CZP as an inverse agonist. Our study aimed to determine whether RSP and CZP can influence neuronal morphology through a 5-HT7R-mediated mechanism. Here, we demonstrated that CZP promotes neurite outgrowth of early postnatal cortical neurons, and the 5-HT7R mediates its effect. Conversely, RSP leads to a reduction of neurite length of early postnatal cortical neurons, in a 5-HT7R-independent way. Furthermore, we found that the effects of CZP, mediated by 5-HT7R activation, require the participation of ERK and Cdk5 kinase pathways. At the same time, the modulation of neurite length by RSP does not involve these pathways. In conclusion, our findings provide valuable insights into the morphological changes induced by these two APDs in neurons and elucidate some of the associated molecular pathways. Investigating the 5-HT7R-dependent signaling pathways underlying the neuronal morphogenic effects of APDs may contribute to the identification of novel targets for the treatment of schizophrenia.

Dysregulation of mTOR signaling mediates common neurite and migration defects in both idiopathic and 16p11.2 deletion autism neural precursor cells

Autism spectrum disorder (ASD) is defined by common behavioral characteristics, raising the possibility of shared pathogenic mechanisms. Yet, vast clinical and etiological heterogeneity suggests personalized phenotypes. Surprisingly, our iPSC studies find that six individuals from two distinct ASD subtypes, idiopathic and 16p11.2 deletion, have common reductions in neural precursor cell (NPC) neurite outgrowth and migration even though whole genome sequencing demonstrates no genetic overlap between the datasets. To identify signaling differences that may contribute to these developmental defects, an unbiased phospho-(p)-proteome screen was performed. Surprisingly despite the genetic heterogeneity, hundreds of shared p-peptides were identified between autism subtypes including the mTOR pathway. mTOR signaling alterations were confirmed in all NPCs across both ASD subtypes, and mTOR modulation rescued ASD phenotypes and reproduced autism NPC-associated phenotypes in control NPCs. Thus, our studies demonstrate that genetically distinct ASD subtypes have common defects in neurite outgrowth and migration which are driven by the shared pathogenic mechanism of mTOR signaling dysregulation.

The Effects of Serotonin Receptor Type 7 Modulation on Bowel Sensitivity and Smooth Muscle Tone in Patients With Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a gut-brain disorder involving alterations in intestinal sensitivity and motility. Currently, IBS has no cure, and treatment focuses on the management of symptoms. The diverse, and sometimes contradictory, collections of symptoms reported across the different subtypes of IBS make treatment, as well as diagnosis, difficult for physicians. All subtypes of IBS have one symptom in common: abdominal pain caused by differences in the level of visceral sensitivity. Though current research on this topic is in its infancy, some researchers have proven, through experimental studies, that 5-hydroxytryptamine (serotonin) receptor type 7 (5-HT7) affects both visceral sensitivity and smooth muscle tone in the bowel. Therefore, this review will be discussing the future possibility of alleviating abdominal pain in patients with IBS and related disorders by modulating the 5-HT7 receptor.

Therapeutic Potential and Limitation of Serotonin Type 7 Receptor Modulation

Although a number of mood-stabilising atypical antipsychotics and antidepressants modulate serotonin type 7 receptor (5-HT7), the detailed contributions of 5-HT7 function to clinical efficacy and pathophysiology have not been fully understood. The mood-stabilising antipsychotic agent, lurasidone, and the serotonin partial agonist reuptake inhibitor, vortioxetine, exhibit higher binding affinity to 5-HT7 than other conventional antipsychotics and antidepressants. To date, the initially expected rapid onset of antidepressant effects-in comparison with conventional antidepressants or mood-stabilising antipsychotics-due to 5-HT7 inhibition has not been observed with lurasidone and vortioxetine; however, several clinical studies suggest that 5-HT7 inhibition likely contributes to quality of life of patients with schizophrenia and mood disorders via the improvement of cognition. Furthermore, recent preclinical studies reported that 5-HT7 inhibition might mitigate antipsychotic-induced weight gain and metabolic complication by blocking other monoamine receptors. Further preclinical studies for the development of 5-HT7 modulation against neurodevelopmental disorders and neurodegenerative diseases have been ongoing. To date, various findings from various preclinical studies indicate the possibility that 5-HT7 modifications can provide two independent strategies. The first is that 5-HT7 inhibition ameliorates the dysfunction of inter-neuronal transmission in mature networks. The other is that activation of 5-HT7 can improve transmission dysfunction due to microstructure abnormality in the neurotransmission network-which could be unaffected by conventional therapeutic agents-via modulating intracellular signalling during the neurodevelopmental stage or via loss of neural networks with aging. This review attempts to describe the current and novel clinical applications of 5-HT7 modulation based on preclinical findings.

β2-adrenergic receptor drives the metastasis and invasion of pancreatic ductal adenocarcinoma through activating Cdc42 signaling pathway

Recent investigations indicate that β2-adrenergic receptor (β2-AR) signaling may facilitate the progression of various tumors, whose underlying mechanisms remain largely elusive. In the present study, we showed that β2-AR recruited Cdc42 in response to isoproterenol (ISO, a β-AR selective agonist) exposure in pancreatic ductal adenocarcinoma (PDAC) cells. The association of β2-AR and Cdc42 promoted the activation of Cdc42, as revealed by increased levels of Cdc42-GTP, and co-incubation with β2-AR antagonist abrogated ISO-induced activation of Cdc42. β2-AR-mediated Cdc42 activation further led to the phosphorylation of downstream PAK1, LIMK1 and Merlin. Furthermore, we showed that the activation of β2-AR/Cdc42 signaling facilitated the migration and invasion of PDAC cells. In addition, β2-AR and Cdc42 were overexpressed in PDAC specimens, compared with adjacent non-tumor tissues. High expression of β2-AR and Cdc42 were correlated with lymph node metastasis and TNM stage in PDAC patients. Finally, we showed that overexpression of β2-AR and Cdc42 were indicative of unfavorable prognosis in PDAC patients. Taken together, our findings suggested that β2-AR might facilitate Cdc42 signaling to drive the migration and invasion of PDAC cells, consequently resulting in the metastasis and dismal prognosis of PDAC. These studies highlight targeting β2-AR/Cdc42 signaling as a therapeutic strategy against PDAC.

Significance of mammalian N, N-dimethyltryptamine (DMT): A 60-year-old debate

N,N-dimethyltryptamine (DMT) is a potent psychedelic naturally produced by many plants and animals, including humans. Whether or not DMT is significant to mammalian physiology, especially within the central nervous system, is a debate that started in the early 1960s and continues to this day. This review integrates historical and recent literature to clarify this issue, giving special attention to the most controversial subjects of DMT's biosynthesis, its storage in synaptic vesicles and the activation receptors like sigma-1. Less discussed topics, like DMT's metabolic regulation or the biased activation of serotonin receptors, are highlighted. We conclude that most of the arguments dismissing endogenous DMT's relevance are based on obsolete data or misleading assumptions. Data strongly suggest that DMT can be relevant as a neurotransmitter, neuromodulator, hormone and immunomodulator, as well as being important to pregnancy and development. Key experiments are addressed to definitely prove what specific roles DMT plays in mammalian physiology.

Central nervous system effects of 5-HT7 receptors: a potential target for neurodegenerative diseases

5-HT₇ receptors (5-HT₇R) are the most recently identified among the family of serotonin receptors. Their role in health and disease, particularly as mediators of, and druggable targets for, neurodegenerative diseases, is incompletely understood. Unlike other serotonin receptors, for which abundant preclinical and clinical data evaluating their effect on neurodegenerative conditions exist, the available information on the role of the 5-HT₇R receptor is limited. In this review, we describe the signaling pathways and cellular mechanisms implicated in the activation of the 5-HT₇R; also, we analyze different mechanisms of neurodegeneration and the potential therapeutic implications of pharmacological interventions for 5-HT₇R signaling.

Rapamycin-filgrastim combination therapy ameliorates portal hypertension-induced splenomegaly: Role of β actin and S100A9 proteins modulation

Objectives

Thioacetamide (TAA) was administered to induce an animal model of liver disease with secondary splenomegaly to assess the mechanisms underlying the effects of rapamycin and filgrastim when taken separately or in combination on the biochemical and histopathological aspects of the liver and spleen.

Materials and Methods

Thirty adult male albino rats were divided into five groups (control, TAA-treated group, TAA+rapamycin, TAA+filgrastim, and TAA+rapamycin+filgrastim group). We measured relative liver and spleen weights, serum levels of alanine transaminase (ALT), aspartate transaminase (AST), and albumin. Molecular docking modeling and histopathological examination of liver and spleen sections with hematoxylin and eosin and Masson trichrome staining with immunohistochemical detection of splenic CD3 and CD20 lymphocytes, S100A9 and β actin antibodies were detected. Morphometric and statistical analyses of the results were performed.

Results

TAA administration altered the histological structure of the liver and spleen and impaired liver function. It increased the expression of splenic CD3, CD20 lymphocytes, and S100A9 while diminishing the expression of β actin. Each of rapamycin and filgrastim, when administered separately, improved liver and spleen indices and liver function, but rapamycin did not affect the albumin level. They lowered splenic B and T lymphocyte levels. Expression levels of S100A9 showed down-regulation while β actin levels were up-regulated when compared with TAA. Combination therapy improved liver and spleen tissue pathology and significantly ameliorated the expression of splenic lymphocytes through regulation of S100A9 and β actin expression.

Conclusion

The synergistic effect of combination therapy was dependent on the regulation of splenic S100A9 and β actin levels.

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.

Activation of the 5-HT7 receptor and MMP-9 signaling module in the hippocampal CA1 region is necessary for the development of depressive-like behavior

Major depressive disorder is a complex disease resulting from aberrant synaptic plasticity that may be caused by abnormal serotonergic signaling. Using a combination of behavioral, biochemical, and imaging methods, we analyze 5-HT7R/MMP-9 signaling and dendritic spine plasticity in the hippocampus in mice treated with the selective 5-HT7R agonist (LP-211) and in a model of chronic unpredictable stress (CUS)-induced depressive-like behavior. We show that acute 5-HT7R activation induces depressive-like behavior in mice in an MMP-9-dependent manner and that post mortem brain samples from human individuals with depression reveal increased MMP-9 enzymatic activity in the hippocampus. Both pharmacological activation of 5-HT7R and modulation of its downstream effectors as a result of CUS lead to dendritic spine elongation and decreased spine density in this region. Overall, the 5-HT7R/MMP-9 pathway is specifically activated in the CA1 subregion of the hippocampus during chronic stress and is crucial for inducing depressive-like behavior.

In Vitro and In Silico Analysis of the Residence Time of Serotonin 5-HT7 Receptor Ligands with Arylpiperazine Structure: A Structure-Kinetics Relationship Study

During the last decade, the kinetics of drug-target interaction has received increasing attention as an important pharmacological parameter in the drug development process. Several studies have suggested that the lipophilicity of a molecule can play an important role. To date, this aspect has been studied for several G protein-coupled receptors (GPCRs) ligands but not for the 5-HT₇ receptor (5-HT₇R), a GPCR proposed as a valid therapeutic target in neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. In this study, we report on structure-kinetics relationships of a set of arylpiperazine-based 5-HT₇R ligands. We found that it is not the overall lipophilicity of the molecule that influences drug-target interaction kinetics but rather the position of polar groups within the molecule. Next, we performed a combination of molecular docking studies and molecular dynamics simulations to gain insights into structure-kinetics relationships. These studies did not suggest specific contact patterns between the ligands and the receptor-binding site as determinants for compounds kinetics. Finally, we compared the abilities of two 5-HT₇R agonists with similar receptor-binding affinities and different residence times to stimulate the 5-HT₇R-mediated neurite outgrowth in mouse neuronal primary cultures and found that the compounds induced the effect with different timing. This study provides the first insights into the binding kinetics of arylpiperazine-based 5-HT₇R ligands that can be helpful to design new 5-HT₇R ligands with fine-tuning of the kinetic profile.

Behavioral, Anti-Inflammatory, and Neuroprotective Effects of a Novel FPR2 Agonist in Two Mouse Models of Autism

Autism spectrum disorders (ASD) are a group of heterogeneous neurodevelopmental conditions characterized by social deficits, repetitive stereotyped behaviors, and altered inflammatory responses. Accordingly, children with ASD show decreased plasma levels of lipoxin A4 (LXA4), a mediator involved in the resolution of inflammation, which is the endogenous ligand of the formyl peptide receptor 2 (FPR2). To investigate the role of FPR2 in ASDs, we have used a new ureidopropanamide derivative able to activate the receptor, named MR-39. The effects of MR-39 (10 mg/kg, for 8 days) on hippocampal pro-inflammatory profile, neuronal plasticity, and social behavior were evaluated in two validated animal models of ASD: BTBR mouse strain and mice prenatally exposed to valproic acid (VPA). Primary cultures of hippocampal neurons from BTBR mice were also used to evaluate the effect of MR-39 on neurite elongation. Our results show that MR-39 treatment reduced several inflammatory markers, restored the low expression of LXA4, and modulated FPR2 expression in hippocampal tissues of both ASD animal models. These findings were accompanied by a significant positive effect of MR-39 on social behavioral tests of ASD mice. Finally, MR-39 stimulates neurite elongation in isolated hippocampal neurons of BTBR mice. In conclusion, these data indicate FPR2 as a potential target for an innovative therapeutical approach for the cure of ASD.

Modulation of Serotonin Receptors in Neurodevelopmental Disorders: Focus on 5-HT7 Receptor

Since neurodevelopmental disorders (NDDs) influence more than 3% of children worldwide, there has been intense investigation to understand the etiology of disorders and develop treatments. Although there are drugs such as aripiprazole, risperidone, and lurasidone, these medications are not cures for the disorders and can only help people feel better or alleviate their symptoms. Thus, it is required to discover therapeutic targets in order to find the ultimate treatments of neurodevelopmental disorders. It is suggested that abnormal neuronal morphology in the neurodevelopment process is a main cause of NDDs, in which the serotonergic system is emerging as playing a crucial role. From this point of view, we noticed the correlation between serotonin receptor subtype 7 (5-HT₇R) and NDDs including autism spectrum disorder (ASD), fragile X syndrome (FXS), and Rett syndrome (RTT). 5-HT₇R modulators improved altered behaviors in animal models and also affected neuronal morphology via the 5-HT₇R/G₁₂ signaling pathway. Through the investigation of recent studies, it is suggested that 5-HT₇R could be a potential therapeutic target for the treatment of NDDs.

Serotonin 5-HT7 receptors require cyclin-dependent kinase 5 to rescue hippocampal synaptic plasticity in a mouse model of Fragile X Syndrome

Fragile X Syndrome is a genetic form of intellectual disability associated with autism, epilepsy and mood disorders. Electrophysiology studies in Fmr1 knockout (KO) mice, a murine model of Fragile X Syndrome, have demonstrated alterations of synaptic plasticity, with exaggerated long-term depression induced by activation of metabotropic glutamate receptors (mGluR-LTD) in Fmr1 KO hippocampus. We have previously demonstrated that activation of serotonin 5-HT7 receptors reverses mGluR-LTD in the hippocampus of wild-type and Fmr1 KO mice, thus correcting a synaptic dysfunction typically observed in this disease model. Here we show that pharmacological inhibition of cyclin-dependent kinase 5 (Cdk5, a signaling molecule recently shown to be a modulator of brain synaptic plasticity) enhanced mGluR-LTD in wild-type hippocampal neurons, which became comparable to exaggerated mGluR-LTD observed in Fmr1 KO neurons. Furthermore, Cdk5 inhibition prevented 5-HT7 receptor-mediated reversal of mGluR-LTD both in wild-type and in Fmr1 KO neurons. Our results show that Cdk5 modulates hippocampal synaptic plasticity. 5-HT7 receptors require Cdk5 to modulate synaptic plasticity in wild-type and rescue abnormal plasticity in Fmr1 KO neurons, pointing out Cdk5 as a possible novel target in Fragile X Syndrome.

Rewiring of the Serotonin System in Major Depression

Serotonin is a key neurotransmitter that is implicated in a wide variety of behavioral and cognitive phenotypes. Originating in the raphe nuclei, 5-HT neurons project widely to innervate many brain regions implicated in the functions. During the development of the brain, as serotonin axons project and innervate brain regions, there is evidence that 5-HT plays key roles in wiring the developing brain, both by modulating 5-HT innervation and by influencing synaptic organization within corticolimbic structures. These actions are mediated by 14 different 5-HT receptors, with region- and cell-specific patterns of expression. More recently, the role of the 5-HT system in synaptic re-organization during adulthood has been suggested. The 5-HT neurons have the unusual capacity to regrow and reinnervate brain regions following insults such as brain injury, chronic stress, or altered development that result in disconnection of the 5-HT system and often cause depression, anxiety, and cognitive impairment. Chronic treatment with antidepressants that amplify 5-HT action, such as selective serotonin reuptake inhibitors (SSRIs), appears to accelerate the rewiring of the 5-HT system by mechanisms that may be critical to the behavioral and cognitive improvements induced in these models. In this review, we survey the possible 5-HT receptor mechanisms that could mediate 5-HT rewiring and assess the evidence that 5-HT-mediated brain rewiring is impacting recovery from mental illness. By amplifying 5-HT-induced rewiring processes using SSRIs and selective 5-HT agonists, more rapid and effective treatments for injury-induced mental illness or cognitive impairment may be achieved.

Current Limitations and Candidate Potential of 5-HT7 Receptor Antagonism in Psychiatric Pharmacotherapy

Several mood-stabilizing atypical antipsychotics and antidepressants weakly block serotonin (5-HT) receptor type-7 (5-HT7R); however, the contributions of 5-HT7R antagonism to clinical efficacy and pathophysiology are yet to be clarified. A novel mood-stabilizing antipsychotic agent, lurasidone exhibits predominant binding affinity to 5-HT7R when compared with other monoamine receptors. To date, we have failed to discover the superior clinical efficacy of lurasidone on schizophrenia, mood, or anxiety disorders when compared with conventional mood-stabilizing atypical antipsychotics; however, numerous preclinical findings have indicated the possible potential of 5-HT7R antagonism against several neuropsychiatric disorders, as well as the generation of novel therapeutic options that could not be expected with conventional atypical antipsychotics. Traditional experimental techniques, electrophysiology, and microdialysis have demonstrated that the effects of 5-HT receptor type-1A (5-HT1AR) and 5-HT7R on neurotransmission are in contrast, but the effect of 5-HT1AR is more predominant than that of 5-HT7R, resulting in an insufficient understanding of the 5-HT7R function in the field of psychopharmacology. Accumulating knowledge regarding the pharmacodynamic profiles of 5-HT7R suggests that 5-HT7R is one of the key players in the establishment and remodeling of neural development and cytoarchitecture during the early developmental stage to the mature brain, and dysfunction or modulation of 5-HT7R is linked to the pathogenesis/pathophysiology of neuropsychiatric and neurodevelopmental disorders. In this review, to explore candidate novel applications for the treatment of several neuropsychiatric disorders, including mood disorders, schizophrenia, and other cognitive disturbance disorders, we discuss perspectives of psychopharmacology regarding the effects of 5-HT7R antagonism on transmission and intracellular signaling systems, based on preclinical findings.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Cross Talk at the Cytoskeleton-Plasma Membrane Interface: Impact on Neuronal Morphology and Functions

The cytoskeleton and its associated proteins present at the plasma membrane not only determine the cell shape but also modulate important aspects of cell physiology such as intracellular transport including secretory and endocytic pathways. Continuous remodeling of the cell structure and intense communication with extracellular environment heavily depend on interactions between cytoskeletal elements and plasma membrane. This review focuses on the plasma membrane-cytoskeleton interface in neurons, with a special emphasis on the axon and nerve endings. We discuss the interaction between the cytoskeleton and membrane mainly in two emerging topics of neurobiology: (i) production and release of extracellular vesicles and (ii) local synthesis of new proteins at the synapses upon signaling cues. Both of these events contribute to synaptic plasticity. Our review provides new insights into the physiological and pathological significance of the cytoskeleton-membrane interface in the nervous system.

Neurodevelopmental Disorders: Effect of High-Fat Diet on Synaptic Plasticity and Mitochondrial Functions

Neurodevelopmental disorders (NDDs) include diverse neuropathologies characterized by abnormal brain development leading to impaired cognition, communication and social skills. A common feature of NDDs is defective synaptic plasticity, but the underlying molecular mechanisms are only partially known. Several studies have indicated that people’s lifestyles such as diet pattern and physical exercise have significant influence on synaptic plasticity of the brain. Indeed, it has been reported that a high-fat diet (HFD, with 30–50% fat content), which leads to systemic low-grade inflammation, has also a detrimental effect on synaptic efficiency. Interestingly, metabolic alterations associated with obesity in pregnant woman may represent a risk factor for NDDs in the offspring. In this review, we have discussed the potential molecular mechanisms linking the HFD-induced metabolic dysfunctions to altered synaptic plasticity underlying NDDs, with a special emphasis on the roles played by synaptic protein synthesis and mitochondrial functions.

Neurotrophic Factor BDNF, Physiological Functions and Therapeutic Potential in Depression, Neurodegeneration and Brain Cancer

Brain-derived neurotrophic factor (BDNF) is one of the most distributed and extensively studied neurotrophins in the mammalian brain. BDNF signals through the tropomycin receptor kinase B (TrkB) and the low affinity p75 neurotrophin receptor (p75NTR). BDNF plays an important role in proper growth, development, and plasticity of glutamatergic and GABAergic synapses and through modulation of neuronal differentiation, it influences serotonergic and dopaminergic neurotransmission. BDNF acts as paracrine and autocrine factor, on both pre-synaptic and post-synaptic target sites. It is crucial in the transformation of synaptic activity into long-term synaptic memories. BDNF is considered an instructive mediator of functional and structural plasticity in the central nervous system (CNS), influencing dendritic spines and, at least in the hippocampus, the adult neurogenesis. Changes in the rate of adult neurogenesis and in spine density can influence several forms of learning and memory and can contribute to depression-like behaviors. The possible roles of BDNF in neuronal plasticity highlighted in this review focus on the effect of antidepressant therapies on BDNF-mediated plasticity. Moreover, we will review data that illustrate the role of BDNF as a potent protective factor that is able to confer protection against neurodegeneration, in particular in Alzheimer’s disease. Finally, we will give evidence of how the involvement of BDNF in the pathogenesis of brain glioblastoma has emerged, thus opening new avenues for the treatment of this deadly cancer.

Privileged scaffold-based design to identify a novel drug-like 5-HT7 receptor-preferring agonist to target Fragile X syndrome

Recent preclinical studies have shown that activation of the serotonin 5-HT₇ receptor has the potential to treat neurodevelopmental disorders such as Fragile X syndrome, a rare disease characterized by autistic features. With the aim to provide the scientific community with diversified drug-like 5-HT₇ receptor-preferring agonists, we designed a set of new long-chain arylpiperazines by exploiting structural fragments present in clinically approved drugs or in preclinical candidates (privileged scaffolds). The new compounds were synthesized, tested for their affinity at 5-HT₇ and 5-HT_1A receptors, and screened for their in vitro stability to microsomal degradation and toxicity. Selected compounds were characterized as 5-HT₇ receptor-preferring ligands, endowed with high metabolic stability and low toxicity. Compound 7g emerged as a drug-like 5-HT₇ receptor-preferring agonist capable to rescue synaptic plasticity and attenuate stereotyped behavior in a mouse model of Fragile X syndrome.

5-HT7 Receptor Contributes to Proliferation, Migration and Invasion in NSCLC Cells

Introduction

Because only a small portion of NSCLC (non-small-cell lung cancer) patients benefit from molecular targeted therapy or immunotherapy and do not develop therapeutic resistance, continued research on new targets is warranted. Serotonin has recently emerged as a growth factor for tumor cells, and its receptors may be potential therapeutic targets. The mechanism related to the behavior of the 5-HT₇ receptor in NSCLC remains unknown.

Methods

Both gene expression analysis and immunohistochemical analysis were conducted to evaluate 5-HT₇ receptor expression in NSCLC tissues. The correlation between 5-HT₇ receptor expression and clinicopathological features was also examined. Cell proliferation was measured using a CCK8 (Cell Counting Kit-8) assay and colony formation, migration and invasion were evaluated by the Transwell assay. siRNA transfection and stimulation with the selective agonist LP211 were used to identify the involvement of molecules in proliferation, migration and invasion. Quantitative real-time chain reaction (qRT-PCR) and Western blotting were used to quantifiy mRNA and protein levels, respectively. Pathway inhibitors facilitated the exploration of possible signaling pathways regulated by the 5-HT₇ receptor in migration and invasion.

Results

The 5-HT₇ receptor was overexpressed in NSCLC tumor tissues compared with adjacent normal lung tissues. High 5-HT₇ receptor expression levels were correlated with lymph node metastasis (P=0.007) and advanced TNM stage (P=0.000) in NSCLC patients. The 5-HT₇ receptor positively regulated cell proliferation, migration and invasion in NSCLC cells. The stimulatory effect of the 5-HT₇ receptor on A549 cell migration and invasion may occur through the P38 pathway. In H1299 cells, the 5-HT₇ receptor might positively regulate Src to promote cell migration and invasion.

Conclusion

Our findings suggest that the 5-HT₇ receptor, which mediates NSCLC progression, may be a potential therapeutic target.

Role of the Serotonin Receptor 7 in Brain Plasticity: From Development to Disease

Our knowledge on the plastic functions of the serotonin (5-HT) receptor subtype 7 (5-HT7R) in the brain physiology and pathology have advanced considerably in recent years. A wealth of data show that 5-HT7R is a key player in the establishment and remodeling of neuronal cytoarchitecture during development and in the mature brain, and its dysfunction is linked to neuropsychiatric and neurodevelopmental diseases. The involvement of this receptor in synaptic plasticity is further demonstrated by data showing that its activation allows the rescue of long-term potentiation (LTP) and long-term depression (LTD) deficits in various animal models of neurodevelopmental diseases. In addition, it is becoming clear that the 5-HT7R is involved in inflammatory intestinal diseases, modulates the function of immune cells, and is likely to play a role in the gut-brain axis. In this review, we will mainly focus on recent findings on this receptor’s role in the structural and synaptic plasticity of the mammalian brain, although we will also illustrate novel aspects highlighted in gastrointestinal (GI) tract and immune system.

Serotonin Type 6 and 7 Receptors as a Novel Therapeutic Target for the Treatment of Schizophrenia

Schizophrenia is a serious disease of the central nervous system that affects a person's ability to think, feel and behave clearly. Even though the pathophysiological hypothesis of the disease is not clearly understood, dysfunction of dopamine, glutamate, serotonin and other neurotransmitters is widely believed to be involved. Serotonin within the synaptic vesicles functions as neurotransmitter and neurohormone in regulation of emotion, learning, memory, hormone release, cognition and motor function. Dysfunction of normal brain activity of serotonin is associated with schizophrenia. The role of serotonin 6 and 7 receptors in schizophrenia, interaction with neurotransmitters and the effect of drugs on those receptors in schizophrenia are the goal of this review. The aim of this review was to provide information for researchers and other scholars to identify the possible intervention points in the management of schizophrenia. The serotonin 6 and 7 receptors are associated with schizophrenia via modulating cyclic adenosine monophosphate, regulation of Fyn kinase and induction of structural plasticity. The above modulatory effects affect cholinergic, dopaminergic, glutamatergic, adrenergic and GABAergic systems. Recently, diverse numbers of selective agonist and antagonist ligands were developed for both receptors. SGS-518, ABT-354, Lu AE58054, SB-742,457, S-518, AVN-211, AVN-322, SYN-114 and SYN-120 are serotonin 6 receptor antagonists and aripiprazole-controlled release serotonin 7 receptor agonists under clinical trial for schizophrenia. Thus, research on novel drugs that act on serotonin 6 and 7 receptors likely facilitates the intervention into schizophrenia patients seeking better quality of life in the future.

Nonylphenol acts on prostate adenocarcinoma cells via estrogen molecular pathways

Estrogens play a role in the patho-physiology of the prostate. In the present work we studied the effects of nonylphenol (NP), a xenoestrogen, on human adenocarcinoma prostate cells (LNCaP). In order to understand molecular and cellular involvement, we observed the effects on cell cycle and we investigated the expression and the cellular localization of estrogen receptors and gene expression of cyclin D1, ki-67, c-myc, IL-8, IL-1β. We performed the same experiments with 17β-estradiol (E2), the most abundant estrogen circulating in nonpregnant humans in order to compare these two different substances. We demonstrated the ability of 1 × 10^-10 M NP to induce proliferation of LNCaP, S-phase progression, increase of ERα expression and its translocation from the cytoplasm to the nucleus. Moreover, we observed an up-regulation of key target genes involved in cell cycle and inflammation process. Particularly, after NP treatment, IL-8 and IL-1β mRNA levels are increased more than 50% indicating a major NP involvement in inflammation processes than E2. These data suggest the proliferative effects of NP on prostate adenocarcinoma cells and highlight some aspects of molecular pathways involved in prostate responses to NP.

The microRNA-29a Modulates Serotonin 5-HT7 Receptor Expression and Its Effects on Hippocampal Neuronal Morphology

miRNAs are master regulators of gene expression in diverse biological processes, including the modulation of neuronal cytoarchitecture. The identification of their physiological target genes remains one of the outstanding challenges. Recently, it has been demonstrated that the activation of serotonin receptor 7 (5-HT7R) plays a key role in regulating the neuronal structure, synaptogenesis, and synaptic plasticity during embryonic and early postnatal development of the central nervous system (CNS). In order to identify putative miRNAs targeting the 3'UTR of 5-HT7R mouse transcript, we used a computational prediction tool and detected the miR-29 family members as the only candidates. Thus, since miR-29a is more expressed than other members in the brain, we investigated its possible involvement in the regulation of neuronal morphology mediated by 5-HT7R. By luciferase assay, we show that miR-29a can act as a post-transcriptional regulator of 5-HT7R mRNA. Indeed, it downregulates 5-HT7R gene expression in cultured hippocampal neurons, while the expression of other serotonin receptors is not affected. From a functional point of view, miR-29a overexpression in hippocampal primary cultures impairs the 5HT7R-dependent neurite elongation and remodeling through the inhibition of the ERK intracellular signaling pathway. In vivo, the upregulation of miR-29a in the developing hippocampus parallels with the downregulation of 5-HT7R expression, supporting the hypothesis that this miRNA is a physiological modulator of 5-HT7R expression in the CNS.

Visualizing DC morphology and T cell motility to characterize DC-T cell encounters in mouse lymph nodes under mTOR inhibition

Mammalian target of rapamycin (mTOR), a serine/threonine kinase orchestrating cellular metabolism, is a crucial immune system regulator. However, it remains unclear how mTOR regulates dendritic cell (DC) function in vivo, especially DC-T cell encounters, a critical step for initiating adaptive immune responses. We dynamically visualized DC-T contacts in mouse lymph node using confocal microscopy and established an encounter model to characterize the effect of mTOR inhibition on DC-T cell encounters using DC morphology. Quantitative data showed mTOR inhibition via rapamycin altered DC shape, with an increased form factor (30.17%) and decreased cellular surface area (20.36%) and perimeter (22.43%), which were associated with Cdc42 protein downregulation (52.71%). Additionally, DCs adopted a similar morphological change with Cdc42 inhibition via ZCL278 as that observed with mTOR inhibition. These morphologically altered DCs displayed low encounter rates with T cells. Time-lapse imaging data of T cell motility supported the simulated result of the encounter model, where antigen-specific T cells appeared to reduce arrest in the lymph nodes of rapamycin-pretreated mice relative to the untreated group. Therefore, mTOR inhibition altered DC morphology in vivo and decreased the DC-T cell encounter rate, as well as Cdc42 inhibition. By establishing an encounter model, our study provides an intuitive approach for the early prediction of DC function through morphological quantification of form factor and area.

Structure-Activity Relationships and Therapeutic Potentials of 5-HT7 Receptor Ligands: An Update

Serotonin 5-HT₇ receptor (5-HT₇R) has been the subject of intense research efforts because of its presence in brain areas such as the hippocampus, hypothalamus, and cortex. Preclinical data link the 5-HT₇R to a variety of central nervous system processes including the regulation of circadian rhythms, mood, cognition, pain processing, and mechanisms of addiction. 5-HT₇R blockade has antidepressant effects and may ameliorate cognitive deficits associated with schizophrenia. 5-HT₇R has been recently shown to modulate neuronal morphology, excitability, and plasticity, thus contributing to shape brain networks during development and to remodel neuronal wiring in the mature brain. Therefore, the activation of 5-HT₇R has been proposed as a therapeutic approach for neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. This Perspective celebrates the silver jubilee of the discovery of 5-HT₇R by providing a survey of recent studies on the medicinal chemistry of 5-HT₇R ligands and on the neuropharmacology of 5-HT₇R.

The effect of chronic stimulation of serotonin receptor type 7 on recognition, passive avoidance memory, hippocampal long-term potentiation, and neuronal apoptosis in the amyloid β protein treated rat

RATIONALE

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory impairment, neuronal death, and synaptic loss in the hippocampus. Long-term potentiation (LTP), a type of synaptic plasticity, occurs during learning and memory. Serotonin receptor type 7 (5-HTR7) activation is suggested as a possible therapeutic target for AD.

OBJECTIVE

The aim of the present study was to examine the effects of chronic treatment with the 5-HTR7 agonist, AS19, on cognitive function, memory, hippocampal plasticity, amyloid beta (Aβ) plaque accumulation, and apoptosis in an adult rat model of AD.

METHODS

AD was induced in rats using Aβ (single 1 μg/μL intracerebroventricular (icv) injection during surgery). The following experimental groups were included: control, sham-operated, Aβ + saline (1 μL icv for 30 days), and Aβ + AS19 (1 μg/μL icv for 30 days) groups. The animals were tested for cognition and memory performance using the novel object recognition and passive avoidance tests, respectively. Next, anesthetized rats were placed in a stereotaxic apparatus for electrode implantation, and field potentials were recorded in the hippocampal dentate gyrus. Lastly, brains were removed and Aβ plaques and neuronal apoptosis were evaluated using Congo red staining and TUNEL assay, respectively.

RESULTS

Administration of AS19 in the Aβ rats increased the discrimination index of the novel object recognition test. Furthermore, AS19 treatment decreased time spent in the dark compartment during the passive avoidance test. AS19 also enhanced both the population spike (PS) amplitude and the field excitatory postsynaptic potential (fEPSP) slope evoked potentials of the LTP components. Aβ plaques and neuronal apoptosis were decreased in the AS19-treated Aβ rats.

CONCLUSIONS

These results indicate that chronic treatment with a 5-HTR7 agonist can prevent Aβ-related impairments in cognition and memory performance by alleviating Aβ plaque accumulation and neuronal apoptosis, hence improving neuronal plasticity. AS19 may be useful as a therapeutic agent for AD.

mTOR-Dependent Cell Proliferation in the Brain

The mammalian Target of Rapamycin (mTOR) is a molecular complex equipped with kinase activity which controls cell viability being key in the PI3K/PTEN/Akt pathway. mTOR acts by integrating a number of environmental stimuli to regulate cell growth, proliferation, autophagy, and protein synthesis. These effects are based on the modulation of different metabolic pathways. Upregulation of mTOR associates with various pathological conditions, such as obesity, neurodegeneration, and brain tumors. This is the case of high-grade gliomas with a high propensity to proliferation and tissue invasion. Glioblastoma Multiforme (GBM) is a WHO grade IV malignant, aggressive, and lethal glioma. To date, a few treatments are available although the outcome of GBM patients remains poor. Experimental and pathological findings suggest that mTOR upregulation plays a major role in determining an aggressive phenotype, thus determining relapse and chemoresistance. Among several activities, mTOR-induced autophagy suppression is key in GBM malignancy. In this article, we discuss recent evidence about mTOR signaling and its role in normal brain development and pathological conditions, with a special emphasis on its role in GBM.

Targets for Drug Therapy for Autism Spectrum Disorder: Challenges and Future Directions

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by persistent deficits in social communication and interaction and restricted, repetitive patterns of behavior, interests, and activities. Various factors are involved in the etiopathogenesis of ASD, including genetic factors, environmental toxins and stressors, impaired immune responses, mitochondrial dysfunction, and neuroinflammation. The heterogeneity in the phenotype among ASD patients and the complex etiology of the condition have long impeded the advancement of the development of pharmacological therapies. In the recent years, the integration of findings from mouse models to human genetics resulted in considerable progress toward the understanding of ASD pathophysiology. Currently, strategies to treat core symptoms of ASD are directed to correct synaptic dysfunctions, abnormalities in central oxytocin, vasopressin, and serotonin neurotransmission, and neuroinflammation. Here, we present a survey of the studies that have suggested molecular targets for drug development for ASD and the state-of-the-art of medicinal chemistry efforts in related areas.

5-Hydroxytryptamine 6 Receptor (5-HT6R)-Mediated Morphological Changes via RhoA-Dependent Pathways

The 5-HT6R has been considered as an attractive therapeutic target in the brain due to its exclusive expression in the brain. However, the mechanistic linkage between 5-HT6Rs and brain functions remains poorly understood. Here, we examined the effects of 5-HT6R-mediated cell morphological changes using immunocytochemistry, Western blot, and live-cell imaging assays. Our results showed that the activation of 5-HT6Rs caused morphological changes and increased cell surface area in HEK293 cells expressing 5-HT6Rs. Treatment with 5-HT specifically increased RhoA-GTP activity without affecting other Rho family proteins, such as Rac1 and Cdc42. Furthermore, live-cell imaging in hippocampal neurons revealed that activation of 5-HT6Rs using a selective agonist, ST1936, increased the density and size of dendritic protrusions along with the activation of RhoA-GTP activity and that both effects were blocked by pretreatment with a selective 5-HT6R antagonist, SB258585. Taken together, our results show that 5-HT6R plays an important role in the regulation of cell morphology via a RhoA-dependent pathway in mammalian cell lines and primary neurons.

Serotonin and neuroplasticity - Links between molecular, functional and structural pathophysiology in depression

Serotonin modulates neuroplasticity, especially during early life, and dysfunctions in both systems likewise contribute to pathophysiology of depression. Recent findings demonstrate that serotonin reuptake inhibitors trigger reactivation of juvenile-like neuroplasticity. How these findings translate to clinical antidepressant treatment in major depressive disorder remains unclear. With this review, we link preclinical with clinical work on serotonin and neuroplasticity to bring two pathophysiologic models in clinical depression closer together. Dysfunctional developmental plasticity impacts on later-life cognitive and emotional functions, changes of synaptic serotonin levels and receptor levels are coupled with altered synaptic plasticity and neurogenesis. Structural magnetic resonance imaging in patients reveals disease-state-specific reductions of gray matter, a marker of neuroplasticity, and reversibility upon selective serotonin reuptake inhibitor treatment. Translational evidence from magnetic resonance imaging in animals support that reduced densities and sizes of neurons and reduced hippocampal volumes in depressive patients could be attributable to changes of serotonergic neuroplasticity. Since ketamine, physical exercise or learning enhance neuroplasticity, combinatory paradigms with selective serotonin reuptake inhibitors could enhance clinical treatment of depression.

Alix is required during development for normal growth of the mouse brain

Alix (ALG-2 interacting protein X) drives deformation and fission of endosomal and cell surface membranes and thereby intervenes in diverse biological processes including cell proliferation and apoptosis. Using embryonic fibroblasts of Alix knock-out mice, we recently demonstrated that Alix is required for clathrin-independent endocytosis. Here we show that mice lacking Alix suffer from severe reduction in the volume of the brain which affects equally all regions examined. The cerebral cortex of adult animals shows normal layering but is reduced in both medio-lateral length and thickness. Alix controls brain size by regulating its expansion during two distinct developmental stages. Indeed, embryonic surface expansion of the Alix ko cortex is reduced because of the loss of neural progenitors during a transient phase of apoptosis occurring between E11.5 and E12.5. Subsequent development of the Alix ko cortex occurs normally until birth, when Alix is again required for the post-natal radial expansion of the cortex through its capacity to allow proper neurite outgrowth. The need of Alix for both survival of neural progenitor cells and neurite outgrowth is correlated with its role in clathrin-independent endocytosis in neural progenitors and at growth cones. Thus Alix-dependent, clathrin independent endocytosis is essential for controlling brain size.

Mammalian Target of Rapamycin: Its Role in Early Neural Development and in Adult and Aged Brain Function

The kinase mammalian target of rapamycin (mTOR) integrates signals triggered by energy, stress, oxygen levels, and growth factors. It regulates ribosome biogenesis, mRNA translation, nutrient metabolism, and autophagy. mTOR participates in various functions of the brain, such as synaptic plasticity, adult neurogenesis, memory, and learning. mTOR is present during early neural development and participates in axon and dendrite development, neuron differentiation, and gliogenesis, among other processes. Furthermore, mTOR has been shown to modulate lifespan in multiple organisms. This protein is an important energy sensor that is present throughout our lifetime its role must be precisely described in order to develop therapeutic strategies and prevent diseases of the central nervous system. The aim of this review is to present our current understanding of the functions of mTOR in neural development, the adult brain and aging.

Structural modifications of the serotonin 5-HT7 receptor agonist N-(4-cyanophenylmethyl)-4-(2-biphenyl)-1-piperazinehexanamide (LP-211) to improve in vitro microsomal stability: A case study

The 5-HT7 serotonin receptor is revealing a promising target for innovative therapeutic strategies of neurodevelopmental and neuropsychiatric disorders. Here, we report the synthesis of thirty long-chain arylpiperazine analogs of the selective and brain penetrant 5-HT7 receptor agonist LP-211 (1) designed to enhance stability towards microsomal oxidative metabolism. Commonly used medicinal chemistry strategies were used (i.e., reduction of overall lipophilicity, introduction of electron-withdrawing groups, blocking of potential vulnerable sites of metabolism), and in vitro microsomal stability was tested. The data showed that the adopted design strategy does not directly translate into improvements in stability. Instead, the metabolic stability of the compounds was related to the presence of specific substituents in well-defined regions of the molecule. The collected data allowed for the construction of a machine learning model that, in a given chemical space, is able to describe and quantitatively predict the metabolic stability of the compounds. The majority of the synthesized compounds maintained high affinity for 5-HT7 receptors and showed selectivity towards 5-HT6 and dopamine D2 receptors and different selectivity for 5-HT1A and α1 adrenergic receptors. Compound 50 showed 3-fold higher in vitro stability towards oxidative metabolism than 1 and was able to stimulate neurite outgrowth in neuronal primary cultures through the 5-HT7 receptor in a shorter time and at a lower concentration than the agonist 1. A preliminary disposition study in mice revealed that compound 50 was metabolically stable and was able to pass the blood-brain barrier, thus representing a new tool for studying the pharmacotherapeutic potential of 5-HT7 receptor in vivo.

Impairments in dendrite morphogenesis as etiology for neurodevelopmental disorders and implications for therapeutic treatments

Dendrite morphology is pivotal for neural circuitry functioning. While the causative relationship between small-scale dendrite morphological abnormalities (shape, density of dendritic spines) and neurodevelopmental disorders is well established, such relationship remains elusive for larger-scale dendrite morphological impairments (size, shape, branching pattern of dendritic trees). Here, we summarize published data on dendrite morphological irregularities in human patients and animal models for neurodevelopmental disorders, with focus on autism and schizophrenia. We next discuss high-risk genes for these disorders and their role in dendrite morphogenesis. We finally overview recent developments in therapeutic attempts and we discuss how they relate to dendrite morphology. We find that both autism and schizophrenia are accompanied by dendritic arbor morphological irregularities, and that majority of their high-risk genes regulate dendrite morphogenesis. Thus, we present a compelling argument that, along with smaller-scale morphological impairments in dendrites (spines and synapse), irregularities in larger-scale dendrite morphology (arbor shape, size) may be an important part of neurodevelopmental disorders' etiology. We suggest that this should not be ignored when developing future therapeutic treatments.

The 5-HT7 receptor triggers cerebellar long-term synaptic depression via PKC-MAPK

The 5-HT7 receptor (5-HT7R) mediates important physiological effects of serotonin, such as memory and emotion, and is emerging as a therapeutic target for the treatment of cognitive disorders and depression. Although previous studies have revealed an expression of 5-HT7R in cerebellum, particularly at Purkinje cells, its functional role and signaling mechanisms have never been described. Using patch-clamp recordings in cerebellar slices of adult mice, we investigated the effects of a selective 5-HT7R agonist, LP-211, on the main plastic site of the cerebellar cortex, the parallel fiber-Purkinje cell synapse. Here we show that 5-HT7R activation induces long-term depression of parallel fiber-Purkinje cell synapse via a postsynaptic mechanism that involves the PKC-MAPK signaling pathway. Moreover, a 5-HT7R antagonist abolished the expression of PF-LTD, produced by pairing parallel fiber stimulation with Purkinje cell depolarization; whereas, application of a 5-HT7R agonist impaired LTP induced by 1 Hz parallel fiber stimulation. Our results indicate for the first time that 5-HT7R exerts a fine regulation of cerebellar bidirectional synaptic plasticity that might be involved in cognitive processes and neuropsychiatric disorders involving the cerebellum.