GPCR signaling: role in mediating the effects of early adversity in psychiatric disorders

Alterations in the brain serotonin system and serotonin-regulated behavior during aging in zebrafish males and females

The brain serotonin (5-HT) system performs a neurotrophic function and supports the plasticity of the nervous system, while its age-related changes can increase the risk of senile neurodegeneration. Zebrafish brain is highly resistant to damage and neurodegeneration due to its high regeneration potential and it is a promising model object in searching for molecular factors preventing age-related neurodegeneration. In the present study alterations in 5-HT-related behavior in the home tank and the novel tank diving test, as well as 5-HT, 5-HIAA levels, tryptophan hydroxylase (TPH), monoamine oxidase (MAO) activity and the expression of genes encoding TPH, MAO, 5-HT transporter and 5-HT receptors in the brain of 6, 12, 24 and 36 month old zebrafish males and females are investigated. Marked sexual dimorphism in the locomotor activity in the novel tank test is revealed: females of all ages move slower than males. No sexual dimorphism in 5-HT-related traits is observed. No changes in 5-HT and 5-HIAA levels in zebrafish brain during aging is observed. At the same time, the aging is accompanied by a decrease in the locomotor activity, TPH activity, tph2 and htr1aa genes expression as well as an increase in the MAO activity and slc6a4a gene expression in their brain. These results indicate that the brain 5-HT system in zebrafish is resistant to age-related alterations.

Effects of Maternal Separation and Subsequent Stress on Behaviors and Brain Monoamines in Rats

Childhood adversity can induce maladaptive behaviors and increase risk for affective disorders, post-traumatic stress disorder, personality disorders, and vulnerability to stress in adulthood. Deprivation of maternal care interrupts brain development through the disturbance of various neurotransmitters, however, the details remain unclear. The features of the symptoms of disorders are largely determined by early stress protocol, genetic characteristics (line), and the sex of the animals. The purpose of current study was (1) to assess behavioral changes in adult Wistar rats of both sexes after early life stress; (2) to determine the levels of monoamines in brain structures involved in the motor, emotional, and social reactions in rats aged 1 and 2 months; and (3) to determine the level of monoamines after physical or emotional stress in adult rats. The rat pups were separated from their dams and isolated from siblings in tight boxes at a temperature of 22-23 °C for 6 h during postnatal days 2-18. The data were processed predominantly using two-way analysis of variance and the Newman-Keys test as the post hoc analysis. The adult rats demonstrated an increase in motor activity and aggressiveness and a decrease in levels of anxiety and sociability. Behavioral disturbances were accompanied by region-, sex-, and age-dependent changes in the levels of monoamines and their metabolites. The dopaminergic and noradrenergic systems were found to be sensitive to psycho-emotional stress.

Methylome changes associated with functional movement/conversion disorder: Influence of biological sex and childhood abuse exposure

Epigenetic changes, such as DNA methylation (DNAm), may represent an important mechanism implicated in the etiopathogenesis of functional movement/conversion disorder (FMD). Here, we aimed to identify methylomic variations in a case-control cohort of FMD and to uncover specific epigenetic signatures associated with female sex and childhood abuse, two key risk factors for FMD and other functional neurological disorders. Genome-wide DNAm analysis was performed from peripheral blood in 57 patients with FMD and 47 healthy controls with and without childhood abuse. Using principal component analysis, we examined the association of principal components with FMD status in abused and non-abused individuals, in the entire study sample and in female subjects only. Next, we used enrichment pathway analysis to investigate the biological significance of DNAm changes and explored differences in methylation levels of genes annotated to the top enriched biological pathways shared across comparisons. We found that FMD was associated with DNAm variation across the genome and identified a common epigenetic 'signature' enriched for biological pathways implicated in chronic stress and chronic pain. However, methylation levels of genes included in the top two shared pathways hardly overlapped, suggesting that transcriptional profiles may differ as a function of childhood abuse exposure and sex among subjects with FMD. This study is unique in providing genome-wide evidence of DNAm changes in FMD and in indicating a potential mechanism linking childhood abuse exposure and female sex to differences in FMD pathophysiology. Future studies are needed to replicate our findings in independent cohorts.

Social interaction following prepubertal stress alters prefrontal gene expression associated with cell signalling and oligodendrocytes

Early-life adversity is associated with an increased risk of psychopathology, including mood disorders, later in life. Early-life stress affects several physiological systems, however, the exact mechanisms underlying pathological risk are not fully understood. This knowledge is crucial in developing appropriate therapeutic interventions. The prepubertal period is documented as a key developmental period for the maturation of the prefrontal cortex (PFC), a brain region involved in higher cognitive functions, including social function. In this study, we performed RNA sequencing on the PFC of adult rats who had experienced prepubertal stress (PPS) and controls to investigate the genome-wide consequences of this stress. PPS alters social behaviour in adulthood, therefore we also performed RNA sequencing on PPS and control rats following a social interaction test to determine social activity-dependent gene changes. At a baseline state (1 week following a social interaction test), no genes were differentially expressed in the PPS group. However, 1603 genes were differentially expressed in PPS rats compared to controls following a social interaction. These genes were enriched in biological pathways associated with cell signalling and axon myelination dynamics. Cell enrichment analysis showed these genes were associated with oligodendrocytes, and a comparison with an existing early-life stress sequencing dataset showed that pathways linked to oligodendrocyte morphology are impacted in a range of models of early-life stress in rodents. In conclusion, we identify pathways, including those involved in axon myelination, that are differentially activated in the adult in response to social stimulation following PPS. These differential responses may contribute to vulnerability to psychiatric pathology.

Network pharmacological investigation into the mechanism of Kaixinsan powder for the treatment of depression

Kaixinsan powder (KXS), a classic prescription of traditional Chinese Medicine (TCM), is widely used in the treatment of depression, but its mechanism remains unclear. The network pharmacology method was used to constructe the "herb-component-target" network, and elucidated KXS potential mechanisms of action in the treatment of depression. Moreover, molecular docking was applied to valid the important interactions between the ingredients and the target protein. The "herb-component-target" network indicated that the ingredients of Girinimbin, Gomisin B and Asarone, and the protein targets of ESR, AR and NR3C1 mostly contribute to the antidepressant effect of KXS. KEGG pathway analysis highlighted the most significant pathways associated with depression treatment, including neuroactive ligand-receptor interaction pathway, serotonergic synapse pathway, PI3K-Akt signaling pathway and MAPK signaling pathway. Go enrichment analysis indicated that the mechanism of KXS in treating depression was involved in the biological process of GPCR signal transduction, hormone metabolism and nerve cell apoptosis. Moreover, molecular docking results showed that Polygalaxanthone III, Girinimbine and Pachymic acid performed greater binding ability with key antidepressant target 5-HTR. In conclusion, this study preliminarily revealed key active components in KXS, including Gomisin B, Asarone, Ginsenoside Rg1, Polygalaxanthone III and Pachymic acid, could interact with multiple targets (5-HTR, DR, ADRA, AR, ESR, NR3C1) and modulate the activation of multiple pathways (Neuroactive ligand -receptor interaction pathway, serotonergic synapse pathway, PI3K-Akt signaling pathway and MAPK signaling pathway).

Chronic hM4Di-DREADD-Mediated Chemogenetic Inhibition of Forebrain Excitatory Neurons in Postnatal or Juvenile Life Does Not Alter Adult Mood-Related Behavior

G-protein-coupled receptors (GPCRs) coupled to G_i signaling, in particular downstream of monoaminergic neurotransmission, are posited to play a key role during developmental epochs (postnatal and juvenile) in shaping the emergence of adult anxiodepressive behaviors and sensorimotor gating. To address the role of G_i signaling in these developmental windows, we used a CaMKIIα-tTA::TRE hM4Di bigenic mouse line to express the hM4Di-DREADD (designer receptor exclusively activated by designer drugs) in forebrain excitatory neurons and enhanced G_i signaling via chronic administration of the DREADD agonist, clozapine-N-oxide (CNO) in the postnatal window (postnatal days 2–14) or the juvenile window (postnatal days 28–40). We confirmed that the expression of the HA-tagged hM4Di-DREADD was restricted to CaMKIIα-positive neurons in the forebrain, and that the administration of CNO in postnatal or juvenile windows evoked inhibition in forebrain circuits of the hippocampus and cortex, as indicated by a decline in expression of the neuronal activity marker c-Fos. hM4Di-DREADD-mediated inhibition of CaMKIIα-positive forebrain excitatory neurons in postnatal or juvenile life did not impact the weight profile of mouse pups, and also did not influence the normal ontogeny of sensory reflexes. Further, postnatal or juvenile hM4Di-DREADD-mediated inhibition of CaMKIIα-positive forebrain excitatory neurons did not alter anxiety- or despair-like behaviors in adulthood and did not impact sensorimotor gating. Collectively, these results indicate that chemogenetic induction of G_i signaling in CaMKIIα-positive forebrain excitatory neurons in postnatal and juvenile temporal windows does not appear to impinge on the programming of anxiodepressive behaviors in adulthood.

Transcriptome Profiling of Dysregulated GPCRs Reveals Overlapping Patterns across Psychiatric Disorders and Age-Disease Interactions

G-protein-coupled receptors (GPCRs) play an integral role in the neurobiology of psychiatric disorders. Almost all neurotransmitters involved in psychiatric disorders act through GPCRs, and GPCRs are the most common targets of therapeutic drugs currently used in the treatment of psychiatric disorders. However, the roles of GPCRs in the etiology and pathophysiology of psychiatric disorders are not fully understood. Using publically available datasets, we performed a comprehensive analysis of the transcriptomic signatures of G-protein-linked signaling across the major psychiatric disorders: autism spectrum disorder (ASD), schizophrenia (SCZ), bipolar disorder (BP), and major depressive disorder (MDD). We also used the BrainSpan transcriptomic dataset of the developing human brain to examine whether GPCRs that exhibit chronological age-associated expressions have a higher tendency to be dysregulated in psychiatric disorders than age-independent GPCRs. We found that most GPCR genes were differentially expressed in the four disorders and that the GPCR superfamily as a gene cluster was overrepresented in the four disorders. We also identified a greater amplitude of gene expression changes in GPCRs than other gene families in the four psychiatric disorders. Further, dysregulated GPCRs overlapped across the four psychiatric disorders, with SCZ exhibiting the highest overlap with the three other disorders. Finally, the results revealed a greater tendency of age-associated GPCRs to be dysregulated in ASD than random GPCRs. Our results substantiate the central role of GPCR signaling pathways in the etiology and pathophysiology of psychiatric disorders. Furthermore, our study suggests that common GPCRs’ signaling may mediate distinct phenotypic presentations across psychiatric disorders. Consequently, targeting these GPCRs could serve as a common therapeutic strategy to treat specific clinical symptoms across psychiatric disorders.

Fast-Trk(B)ing the mechanism of antidepressants

The mechanism by which antidepressants elicit clinical improvements has proven elusive. In a recent publication in Cell, Casarotto et al. (2021) reveal a surprising direct interaction between antidepressants and TrkB. This link provides an important mechanistic insight into synaptic remodeling that may assist in the design of improved antidepressant therapeutics.

Serotonin-related rodent models of early-life exposure relevant for neurodevelopmental vulnerability to psychiatric disorders

Mental disorders including depression and anxiety are continuously rising their prevalence across the globe. Early-life experience of individuals emerges as a main risk factor contributing to the developmental vulnerability to psychiatric disorders. That is, perturbing environmental conditions during neurodevelopmental stages can have detrimental effects on adult mood and emotional responses. However, the possible maladaptive neural mechanisms contributing to such psychopathological phenomenon still remain poorly understood. In this review, we explore preclinical rodent models of developmental vulnerability to psychiatric disorders, focusing on the impact of early-life environmental perturbations on behavioral aspects relevant to stress-related and psychiatric disorders. We limit our analysis to well-established models in which alterations in the serotonin (5-HT) system appear to have a crucial role in the pathophysiological mechanisms. We analyze long-term behavioral outcomes produced by early-life exposures to stress and psychotropic drugs such as the selective 5-HT reuptake inhibitor (SSRI) antidepressants or the anticonvulsant valproic acid (VPA). We perform a comparative analysis, identifying differences and commonalities in the behavioral effects produced in these models. Furthermore, this review discusses recent advances on neurodevelopmental substrates engaged in these behavioral effects, emphasizing the possible existence of maladaptive mechanisms that could be shared by the different models.

Emerging paradigms in activation, signaling, and regulation of G protein-coupled receptors

This Special Issue of The FEBS Journal brings together a set of review articles focused on recent developments in the field of GPCR biology, with particular emphasis on novel paradigms of their activation, signaling, and regulation. These articles cover a broad repertoire of cellular, physiological, and structural aspects ranging from the interaction of GPCRs with their signal transducers, allosteric modulation of these receptors with therapeutic implications, and emerging technologies aimed to probe critical aspects of receptor signaling and regulation.