Region-specific regulation of the serotonin 2A receptor expression in development and ageing inpost mortemhuman brain

Association of serotonin receptor gene polymorphisms with anorexia nervosa: a systematic review and meta-analysis

PURPOSE

Several studies have investigated the association between anorexia nervosa and polymorphisms of genes regulating serotonin neurotransmission, with a focus on the rs6311 polymorphism of 5-HTR2A. However, inconsistent results of these studies and conflicting conclusions of existing meta-analyses complicate the understanding of a possible association. We have updated these results and evaluated the involvement of other serotonin receptor gene polymorphisms in anorexia nervosa.

METHODS

Adhering to PRISMA guidelines, we have searched studies on anorexia nervosa and serotonin-regulating genes published from 1997 to 2022, selected those concerning receptor genes and meta-analyzed the results from twenty candidate gene studies on the 5-HTR2A rs6311 polymorphism and the 5-HTR2C rs6318 polymorphism.

RESULTS

Present analyses reveal an association for the 5-HTR2A rs6311 polymorphism, with G and A alleles, across eighteen studies (2049 patients, 2877 controls; A vs. G allele, Odds Ratio = 1.24; 95% Confidence Interval = 1.06-1.47; p = 0.009). However, after geographic subgrouping, an association emerged only in a Southern European area, involving five studies (722 patients, 773 controls; A vs. G allele, Odds Ratio = 1.82; 95% Confidence Interval = 1.41-2.37; p < 0.00001). No association was observed for the 5-HTR2C rs6318 polymorphism across three studies.

CONCLUSIONS

To date, the involvement in the pathophysiology of anorexia nervosa of the 5-HTR2A rs6311 polymorphism appears limited to a specific genetic and/or environmental context, while that of the 5-HTR2C rs6318 polymorphism seems excluded. Genome-wide association studies and epigenetic studies will likely offer deeper insights of genetic and environmental factors possibly contributing to the disorder.

LEVEL OF EVIDENCE

III Evidence obtained from well-designed cohort or case-control analytic studies. Clinical trial registration PROSPERO registration number: CRD42021246122.

Examining Whether Genetic Variants Moderate the Skeletal Effects of Selective Serotonin Reuptake Inhibitors in Older Adolescents and Young Adults

Objective: To examine whether serotonin (5-HT) related genetic variants moderate the effects of selective serotonin reuptake inhibitors (SSRIs) on skeletal outcomes. Methods: Trabecular bone mineral density (BMD) at the radius, lumbar spine (LS) BMD, total body less head (TBLH) bone mineral content (BMC) and markers of bone metabolism (osteocalcin, C-terminal telopeptide of type I collagen [CTX-1], and bone specific alkaline phosphatase to CTX-1 ratio) were examined in an observational study, enrolling 15- to 20-year-old participants, unmedicated or within a month of SSRI initiation. Variants in HTR1A (rs6295), HTR1B (rs6296), HTR1D (rs6300), HTR2A (rs6311 and rs6314), HTR2B (rs6736017), and the serotonin transporter intron 2 variable number tandem repeat (STin2 VNTR) were genotyped. Linear mixed-effects regression analysis examined associations between SSRI use, genetic variants, and skeletal outcomes. Results: After adjusting for relevant covariates, rs6295 CC and GC genotypes in 262 participants (60% female, mean ± SD age = 18.9 ± 1.6 years) were significantly associated with higher LS BMD compared to the GG genotype. Rs6311 GG SSRI users had greater LS BMD compared to nonusers (β = 0.18, p = <0.0001). Female SSRI users with the combination of rs6295 CC+GC and rs6311 GG genotypes had greater LS BMD than female SSRI nonusers (β = 0.29, p < 0.0001). SSRI users with the rs6295 GG genotype had higher trabecular BMD compared to nonusers (β = 3.60, p = 0.05). No significant interactions were found for TBLH BMC or bone turnover markers. After correcting for multiple comparisons, none of the results retained significance. Conclusions: In older adolescents and young adults, HTR1A (rs6295) and HTR2A (rs6311) variants may moderate the effect of SSRIs on BMD. Sex differences may exist and require further examination. Further research with larger sample sizes is needed to confirm our preliminary findings. Clinical Trial Registration: clinicaltrials.gov NCT02147184.

Development of a Novel Senolysis Approach Targeting the Senescent Fibroblast Marker HTR2A via Antibody-Dependent Cellular Cytotoxicity

Abnormal remodeling of collagen and extracellular matrix caused by the accumulation of senescent fibroblasts in the dermis is the most likely cause of skin aging. Therefore, the application of "senolysis," in which only senescent cells are cleared from the body, has a potential in the development of antiaging treatments for skin. However, markers that label senescent fibroblasts only reflect the state of senescence, and it is important to develop markers as therapeutic targets to aid senolysis application. We investigated the potential of serotonin 2A receptor (HTR2A), which is involved in melanin production in response to ultraviolet light, as a senescent cell marker. The results showed that HTR2A is upregulated in aging dermal fibroblasts but is expressed at low levels in proliferating young cells. Flow cytometry demonstrated the presence of many HTR2A-positive cells in the aging cell population and few in the young cells. Furthermore, antibody-dependent cytotoxicity assays revealed that HTR2A preferentially sensitizes senescent fibroblasts and specifically damages only senescent cells by natural killer cells that recognize it. In conclusion, selective labeling of the novel senescent cell marker, HTR2A, could preferentially eliminate senescent cells and may contribute to the future development of novel skin senolysis approaches.

Proteomics analysis of the gut-brain axis in a gut microbiota-dysbiosis model of depression

Major depressive disorder (MDD) is a serious mental illness. Increasing evidence from both animal and human studies suggested that the gut microbiota might be involved in the onset of depression via the gut-brain axis. However, the mechanism in depression remains unclear. To explore the protein changes of the gut-brain axis modulated by gut microbiota, germ-free mice were transplanted with gut microbiota from MDD patients to induce depression-like behaviors. Behavioral tests were performed following fecal microbiota transplantation. A quantitative proteomics approach was used to examine changes in protein expression in the prefrontal cortex (PFC), liver, cecum, and serum. Then differential protein analysis and weighted gene coexpression network analysis were used to identify microbiota-related protein modules. Our results suggested that gut microbiota induced the alteration of protein expression levels in multiple tissues of the gut-brain axis in mice with depression-like phenotype, and these changes of the PFC and liver were model specific compared to chronic stress models. Gene ontology enrichment analysis revealed that the protein changes of the gut-brain axis were involved in a variety of biological functions, including metabolic process and inflammatory response, in which energy metabolism is the core change of the protein network. Our data provide clues for future studies in the gut-brain axis on protein level and deepen the understanding of how gut microbiota cause depression-like behaviors.

The Cerebellar Dopaminergic System

In the central nervous system (CNS), dopamine (DA) is involved in motor and cognitive functions. Although the cerebellum is not been considered an elective dopaminergic region, studies attributed to it a critical role in dopamine deficit-related neurological and psychiatric disorders [e.g., Parkinson's disease (PD) and schizophrenia (SCZ)]. Data on the cerebellar dopaminergic neuronal system are still lacking. Nevertheless, biochemical studies detected in the mammalians cerebellum high dopamine levels, while chemical neuroanatomy studies revealed the presence of midbrain dopaminergic afferents to the cerebellum as well as wide distribution of the dopaminergic receptor subtypes (DRD1-DRD5). The present review summarizes the data on the cerebellar dopaminergic system including its involvement in associative and projective circuits. Furthermore, this study also briefly discusses the role of the cerebellar dopaminergic system in some neurologic and psychiatric disorders and suggests its potential involvement as a target in pharmacologic and non-pharmacologic treatments.

The rs6311 of serotonin receptor 2A (5-HT2A) gene is associated with alexithymia and mental health

BACKGROUNDS

Alexithymia, difficulties in identifying and describing one's own feelings, is related to substantial clinical practice. Inspired by the links between serotonin functions and affective disorders, this study investigated associations of the serotonin receptor 2A (5-HT2A) gene with alexithymia and mental health.

METHODS

We differentiated subjects according to two functional polymorphisms (i.e., rs6311 and rs6313) of 5-HT2A gene and scored alexithymia and mental health of college students with the Toronto Alexithymia Scale (TAS-20) and the Symptom Check List-90 (SCL-90), respectively.

RESULTS

The analyses basing on sample 1 (N = 566) and sample 2 (N = 602) indicated that the G allele of rs6311 was related to higher score on the TAS-20 as compared to the AA genotype. The analysis with 467 individuals from sample 2 indicated that the rs6311 was associated with mental health, and this association was mediated by alexithymia.

LIMITATIONS

The potential confounding variables such as depression and anxiety were neglected in the analyses.

CONCLUSIONS

These findings demonstrate the contribution of the 5-HT2A to alexithymia, and highlight the link between alexithymia and mental health at genetic level.

Serotonin Regulation of the Prefrontal Cortex: Cognitive Relevance and the Impact of Developmental Perturbation

The prefrontal cortex is essential for both executive function and emotional regulation. The interrelationships among these behavioral domains are increasingly recognized, as well as their sensitivity to serotonin (5-hydroxytryptamine, 5-HT). Prefrontal cortex receives serotonergic inputs from the dorsal and median raphe nuclei and is modulated by multiple subtypes of 5-HT receptor across its layers and cell types. Extremes of serotonergic modulation alter mood regulation in vulnerable individuals, yet the impact of serotonin under more typical physiological parameters remains unclear. In this regard, new tools are permitting a closer examination of the behavioral impact of the serotonin system. Optogenetic and chemogenetic manipulations of dorsal raphe 5-HT neurons reveal that serotonin has a greater impact on executive function than previously appreciated. Domains that appear sensitive to fluctuations in 5-HT neuronal excitability include patience and cognitive flexibility. This work is broadly consistent with ex vivo research investigating how 5-HT regulates prefrontal cortex and its output projections. A growing literature suggests 5-HT modulation of these prefrontal circuits is unexpectedly flexible to alteration during development by genetic, behavioral, environmental or pharmacological manipulations, with lasting repercussions for cognition and emotional regulation. Here, we review the cellular and circuit mechanisms of prefrontal serotonergic modulation, investigate recent research into the cognitive consequences of the serotonergic system, and probe the lasting consequences of developmental perturbations. Understanding both the complexity of the prefrontal serotonin system and its sensitivity during development are essential to learn more about the vulnerabilities of this system in mood and anxiety disorders and the underappreciated cognitive consequences of these disorders and their treatment.

Cyto- and receptor architectonic mapping of the human brain

Mapping of the human brain is more than the generation of an atlas-based parcellation of brain regions using histologic or histochemical criteria. It is the attempt to provide a topographically informed model of the structural and functional organization of the brain. To achieve this goal a multimodal atlas of the detailed microscopic and neurochemical structure of the brain must be registered to a stereotaxic reference space or brain, which also serves as reference for topographic assignment of functional data, e.g., functional magnet resonance imaging, electroencephalography, or magnetoencephalography, as well as metabolic imaging, e.g., positron emission tomography. Although classic maps remain pioneering steps, they do not match recent concepts of the functional organization in many regions, and suffer from methodic drawbacks. This chapter provides a summary of the recent status of human brain mapping, which is based on multimodal approaches integrating results of quantitative cyto- and receptor architectonic studies with focus on the cerebral cortex in a widely used reference brain. Descriptions of the methods for observer-independent and statistically testable cytoarchitectonic parcellations, quantitative multireceptor mapping, and registration to the reference brain, including the concept of probability maps and a toolbox for using the maps in functional neuroimaging studies, are provided.

Novel miR-b2122 regulates several ALS-related RNA-binding proteins

Common pathological features of amyotrophic lateral sclerosis (ALS) include cytoplasmic aggregation of several RNA-binding proteins. Out of these RNA-binding proteins, TDP-43, FUS/TLS and RGNEF have been shown to co-aggregate with one another within motor neurons of sporadic ALS (sALS) patients, suggesting that there may be a common regulatory network disrupted. MiRNAs have been a recent focus in ALS research as they have been identified to be globally down-regulated in the spinal cord of ALS patients. The objective of this study was to identify if there are miRNA(s) dysregulated in sALS that are responsible for regulating the TDP-43, FUS/TLS and RGNEF network. In this study, we identify miR-194 and miR-b2122 to be significantly down-regulated in sALS patients, and were predicted to regulate TARDBP, FUS/TLS and RGNEF expression. Reporter gene assays and RT-qPCR revealed that miR-b2122 down-regulates the reporter gene through direct interactions with either the TARDBP, FUS/TLS, or RGNEF 3’UTR, while miR-194 down-regulates firefly expression when it contained either the TARDBP or FUS/TLS 3’UTR. Further, we showed that miR-b2122 regulates endogenous expression of all three of these genes in a neuronal-derived cell line. Also, an ALS-associated mutation in the FUS/TLS 3’UTR ablates the ability of miR-b2122 to regulate reporter gene linked to FUS/TLS 3’UTR, and sALS samples which showed a down-regulation in miR-b2122 also showed an increase in FUS/TLS protein expression. Overall, we have identified a novel miRNA that is down-regulated in sALS that appears to be a central regulator of disease-related RNA-binding proteins, and thus its dysregulation likely contributes to TDP-43, FUS/TLS and RGNEF pathogenesis in sALS.