Association of the intronic rs2072621 polymorphism of the X-linked GPR50 gene with affective disorder with seasonal pattern

ERNEST COST action overview on the (patho)physiology of GPCRs and orphan GPCRs in the nervous system

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that play a critical role in nervous system function by transmitting signals between cells and their environment. They are involved in many, if not all, nervous system processes, and their dysfunction has been linked to various neurological disorders representing important drug targets. This overview emphasises the GPCRs of the nervous system, which are the research focus of the members of ERNEST COST action (CA18133) working group 'Biological roles of signal transduction'. First, the (patho)physiological role of the nervous system GPCRs in the modulation of synapse function is discussed. We then debate the (patho)physiology and pharmacology of opioid, acetylcholine, chemokine, melatonin and adhesion GPCRs in the nervous system. Finally, we address the orphan GPCRs, their implication in the nervous system function and disease, and the challenges that need to be addressed to deorphanize them.

High expression of GPR50 promotes the proliferation, migration and autophagy of hepatocellular carcinoma cells in vitro

G protein-coupled receptors (GPCRs) play important roles in tumorigenesis and the development of hepatocellular carcinoma (HCC). GPR50 is an orphan GPCR. Previous studies have indicated that GPR50 could protect against breast cancer development and decrease tumor growth in a xenograft mouse model. However, its role in HCC remains indistinct. To detect the role and the regulation mechanism of GPR50 in HCC, GPR50 expression was analyzed in HCC patients (gene expression omnibus database (GEO) (GSE45436)) and detected in HCC cell line CBRH-7919, and the results showed that GPR50 was significantly up-regulated in HCC patients and CBRH-7919 cell line compared to the corresponding normal control. Gpr50 cDNA was transfected into HCC cell line CBRH-7919, and we found that Gpr50 promoted the proliferation, migration, and autophagy of CBRH-7919. The regulation mechanism of GPR50 in HCC was detected by isobaric tags for relative and absolute quantification (iTRAQ) analysis, and we found that GPR50 promoted HCC was closely related to CCT6A and PGK1. Taken together, GPR50 may promote HCC progression via CCT6A-induced proliferation and PGK1-induced migration and autophagy, and GPR50 could be an important target for HCC.

The orphan GPR50 receptor interacting with TβRI induces G1/S-phase cell cycle arrest via Smad3-p27/p21 in BRL-3A cells

The liver has the powerful capacity to regenerate after injury or resection. In one of our previous studies, GPR50 was observed to be significantly upregulated at 6 h, following a partial hepatectomy (PH) in rat liver regeneration (LR) via gene expression profile. However, little research has been done on the regulation and mechanism of GPR50 in the liver. Herein, we observed that the overexpression of GPR50 inhibited the proliferation of BRL-3A cells. To further explore the molecular mechanisms of GPR50 in the regulation of BRL-3A cell proliferation, interaction between GPR50 and transforming growth factor-beta I (TβRI) and iTRAQ^TM differential proteomic analysis were elucidated, which suggested that GPR50 may interact with TβRI to activate the TGF-β signaling pathway and arrest BRL-3A cell cycle G1/S transition. Subsequently, the potential mechanism underlying the role of GPR50 in hepatocyte growth was also explored through the addition of a signaling pathway inhibitor. These data suggested that interaction between the orphan GPR50 receptor and TβRI induced the G1⁄S-phase cell cycle arrest of BRL-3A cells via the Smad3-p27/p21 pathway.

A new sex-specific underlying mechanism for female schizophrenia: accelerated skewed X chromosome inactivation

BACKGROUND

X chromosome inactivation (XCI) is the mechanism by which the X-linked gene dosage is adjusted between the sexes. Evidence shows that many sex-specific diseases have their basis in X chromosome biology. While female schizophrenia patients often have a delayed age of disease onset and clinical phenotypes that are different from those of males, it is unknown whether the sex differences in schizophrenia are associated with X-linked gene dosage and the choice of X chromosome silencing in female cells. Previous studies demonstrated that sex chromosome aneuploidies may be related to the pathogeneses of some psychiatric diseases. Here, we examined the changes in skewed XCI in patients with schizophrenia.

METHODS

A total of 109 female schizophrenia (SCZ) patients and 80 age- and sex-matched healthy controls (CNTLs) were included in this study. We evaluated clinical features including disease onset age, disease duration, clinical symptoms by the Positive and Negative Syndrome Scale (PANSS) and antipsychotic treatment dosages. The XCI skewing patterns were analyzed by the methylation profile of the HUMARA gene found in DNA isolated from SCZ patient and CNTL leukocytes in the three age groups.

RESULTS

First, we found that the frequency of skewed XCI in SCZ patients was 4 times more than that in the age- and sex-matched CNTLs (p < 0.01). Second, we found an earlier onset of severe XCI skewing in the SCZ patients than in CNTLs. Third, we demonstrated a close relationship between the severity of skewed XCI and schizophrenic symptoms (PANSS score ≥ 90) as well as the age of disease onset. Fourth, we demonstrated that the skewed XCI in SCZ patients was not transmitted from the patients' mothers.

LIMITATIONS

The XCI skewing pattern might differ depending on tissues or organs. Although this is the first study to explore skewed XCI in SCZ, in the future, samples from different tissues or cells in SCZ patients might be important for understanding the impact of skewed XCI in this disease.

CONCLUSION

Our study, for the first time, investigated skewed XCI in female SCZ patients and presented a potential mechanism for the sex differences in SCZ. Our data also suggested that XCI might be a potential target for the development of female-specific interventions for SCZ.

Orphan G Protein Coupled Receptors in Affective Disorders

G protein coupled receptors (GPCRs) are the main mediators of signal transduction in the central nervous system. Therefore, it is not surprising that many GPCRs have long been investigated for their role in the development of anxiety and mood disorders, as well as in the mechanism of action of antidepressant therapies. Importantly, the endogenous ligands for a large group of GPCRs have not yet been identified and are therefore known as orphan GPCRs (oGPCRs). Nonetheless, growing evidence from animal studies, together with genome wide association studies (GWAS) and post-mortem transcriptomic analysis in patients, pointed at many oGPCRs as potential pharmacological targets. Among these discoveries, we summarize in this review how emotional behaviors are modulated by the following oGPCRs: ADGRB2 (BAI2), ADGRG1 (GPR56), GPR3, GPR26, GPR37, GPR50, GPR52, GPR61, GPR62, GPR88, GPR135, GPR158, and GPRC5B.

Sex chromosome abnormalities and psychiatric diseases

Excesses of sex chromosome abnormalities in patients with psychiatric diseases have recently been observed. It remains unclear whether sex chromosome abnormalities are related to sex differences in some psychiatric diseases. While studies showed evidence of susceptibility loci over many sex chromosomal regions related to various mental diseases, others demonstrated that the sex chromosome aneuploidies may be the key to exploring the pathogenesis of psychiatric disease. In this review, we will outline the current evidence on the interaction of sex chromosome abnormalities with schizophrenia, autism, ADHD and mood disorders.

Depressive disorders: Processes leading to neurogeneration and potential novel treatments

Mood disorders are wide spread with estimates that one in seven of the population are affected at some time in their life (Kessler et al., 2012). Many of those affected with severe depressive disorders have cognitive deficits which may progress to frank neurodegeneration. There are several peripheral markers shown by patients who have cognitive deficits that could represent causative factors and could potentially serve as guides to the prevention or even treatment of neurodegeneration. Circadian rhythm misalignment, immune dysfunction and oxidative stress are key pathologic processes implicated in neurodegeneration and cognitive dysfunction in depressive disorders. Novel treatments targeting these pathways may therefore potentially improve patient outcomes whereby the primary mechanism of action is outside of the monoaminergic system. Moreover, targeting immune dysfunction, oxidative stress and circadian rhythm misalignment (rather than primarily the monoaminergic system) may hold promise for truly disease modifying treatments that may prevent neurodegeneration rather than simply alleviating symptoms with no curative intent. Further research is required to more comprehensively understand the contributions of these pathways to the pathophysiology of depressive disorders to allow for disease modifying treatments to be discovered.

Genetic Factors Affecting Seasonality, Mood, and the Circadian Clock

In healthy humans, seasonality has been documented in psychological variables, chronotype, sleep, feeding, metabolic and autonomic function, thermoregulation, neurotransmission, and hormonal response to stimulation, thus representing a relevant factor to account for, especially when considering the individual susceptibility to disease. Mood is largely recognized as one of the central aspects of human behavior influenced by seasonal variations. This historical notion, already mentioned in ancient medical reports, has been recently confirmed by fMRI findings, which showed that seasonality in human cognitive brain functions may influence affective control with annual variations. Thus, seasonality plays a major role in mood disorders, affecting psychopathology, and representing the behavioral correlate of a heightened sensitivity to factors influencing circannual rhythms in patients. Although the genetic basis of seasonality and seasonal affective disorder (SAD) has not been established so far, there is growing evidence that factors affecting the biological clock, such as gene polymorphisms of the core clock machinery and seasonal changes of the light-dark cycle, exert a marked influence on the behavior of patients affected by mood disorders. Here we review recent findings about the effects of individual gene variants on seasonality, mood, and psychopathological characteristics.

Lifetime Characteristics of Evening-Preference and Irregular Bed-Rise Time Are Associated With Lifetime Seasonal Variation of Mood and Behavior: Comparison Between Individuals With Bipolar Disorder and Healthy Controls

Sleep-wake cycle disruption and seasonal variation in mood and behavior have been associated with mood disorders. This study aimed to investigate the lifetime characteristics of the sleep-wake cycle and its association with the lifetime characteristics of seasonality in individuals with bipolar disorder. Circadian preference, regularity of bed-rise time, and seasonality were evaluated on a lifetime basis using the Composite Scale of Morningness, the Sleep Timing Questionnaire, and the Seasonal Pattern Assessment Questionnaire in clinically stable individuals with bipolar I/II disorders (n = 103/97) and healthy controls (n = 270). Bipolar groups were more likely to have evening preference and irregular bed-rise time. These characteristics were interrelated and, particularly, more prevalent in bipolar II disorder. Seasonality, which was also more prevalent in the bipolar groups, was associated with evening preference and irregularity of the weekday bed-rise time.

The emerging role of GPR50 receptor in brain

GPR50 receptor one of the member of G protein-coupled receptors (GPCRs) is extensively expressed in the pituitary, hypothalamus,cortex, midbrain, pons, amygdala, and in several brainstem nuclei. The exact function of this receptor in brain is remains unclear. This review presents current knowledge regarding the function of GPR50 receptor in brain, with a focus on role of this receptor in the hypothalamus-pituitary-adrenal (HPA) axis and the glucocorticoid receptor (GR) signaling, leptin signaling, adaptive thermogenesis, torpor, neurite outgrowth, and self-renewal and neuronal differentiation of neural progenitor cells NPCs. Although the results are encouraging, further research is needed to clarify GPR50 role in neurobiology of mood disorders, adaptive thermogenesis, torpor, and in the pathophysiology of neurological disorders.

Genetic association study of circadian genes with seasonal pattern in bipolar disorders

About one fourth of patients with bipolar disorders (BD) have depressive episodes with a seasonal pattern (SP) coupled to a more severe disease. However, the underlying genetic influence on a SP in BD remains to be identified. We studied 269 BD Caucasian patients, with and without SP, recruited from university-affiliated psychiatric departments in France and performed a genetic single-marker analysis followed by a gene-based analysis on 349 single nucleotide polymorphisms (SNPs) spanning 21 circadian genes and 3 melatonin pathway genes. A SP in BD was nominally associated with 14 SNPs identified in 6 circadian genes: NPAS2, CRY2, ARNTL, ARNTL2, RORA and RORB. After correcting for multiple testing, using a false discovery rate approach, the associations remained significant for 5 SNPs in NPAS2 (chromosome 2:100793045–100989719): rs6738097 (p_c = 0.006), rs12622050 (p_c = 0.006), rs2305159 (p_c = 0.01), rs1542179 (p_c = 0.01), and rs1562313 (p_c = 0.02). The gene-based analysis of the 349 SNPs showed that rs6738097 (NPAS2) and rs1554338 (CRY2) were significantly associated with the SP phenotype (respective Empirical p-values of 0.0003 and 0.005). The associations remained significant for rs6738097 (NPAS2) after Bonferroni correction. The epistasis analysis between rs6738097 (NPAS2) and rs1554338 (CRY2) suggested an additive effect. Genetic variations in NPAS2 might be a biomarker for a seasonal pattern in BD.

Involvement of GPR50 polymorphisms in depression: independent replication in a prospective elderly cohort

INTRODUCTION

Despite the explosion in genetic association studies over the last decade, clearly identified genetic risk factors for depression remain scarce and replication studies are becoming increasingly important. G-protein-coupled receptor 50 (GPR50) has been implicated in psychiatric disorders in a small number of studies, although not consistently.

METHODS

Data were obtained from 1010 elderly men and women from the prospective population-based ESPRIT study. Logistic regression and survival models were used to determine whether three common GPR50 polymorphisms were associated with depression prevalence or the incidence of depression over 12-years. The analyses were adjusted for a range of covariates such as comorbidity and cholesterol levels, to determine independent associations.

RESULTS

All three variants showed some evidence of an association with late-life depression in women, although these were not consistent across outcomes, the overall effect sizes were relatively small, and most would not remain significant after correction for multiple testing. Women heterozygous for rs13440581, had a 1.6-fold increased risk of baseline depression, while the odds of depression comorbid with anxiety were increased fourfold for women homozygous for the minor allele of rs2072621. When depressed women at baseline were excluded from the analysis, however, neither variant was associated with the 12-year incidence of depression. In contrast, rs561077 was associated with a 1.8-fold increased risk of incident depression specifically. No significant associations were observed in men.

DISCUSSION

Our results thus provide only weak support for the involvement of GPR50 variants in late-life depression, which appear specific to certain subgroups of depressed individuals (i.e., women and those with more severe forms of depression).

Induction of the metabolic regulator Txnip in fasting-induced and natural torpor

Torpor is a physiological state characterized by controlled lowering of metabolic rate and core body temperature, allowing substantial energy savings during periods of reduced food availability or harsh environmental conditions. The hypothalamus coordinates energy homeostasis and thermoregulation and plays a key role in directing torpor. We recently showed that mice lacking the orphan G protein-coupled receptor Gpr50 readily enter torpor in response to fasting and have now used these mice to conduct a microarray analysis of hypothalamic gene expression changes related to the torpor state. This revealed a strong induction of thioredoxin-interacting protein (Txnip) in the hypothalamus of torpid mice, which was confirmed by quantitative RT-PCR and Western blot analyses. In situ hybridization identified the ependyma lining the third ventricle as the principal site of torpor-related expression of Txnip. To characterize further the relationship between Txnip and torpor, we profiled Txnip expression in mice during prolonged fasting, cold exposure, and 2-deoxyglucose-induced hypometabolism, as well as in naturally occurring torpor bouts in the Siberian hamster. Strikingly, pronounced up-regulation of Txnip expression was only observed in wild-type mice when driven into torpor and during torpor in the Siberian hamster. Increase of Txnip was not limited to the hypothalamus, with exaggerated expression in white adipose tissue, brown adipose tissue, and liver also demonstrated in torpid mice. Given the recent identification of Txnip as a molecular nutrient sensor important in the regulation of energy metabolism, our data suggest that elevated Txnip expression is critical to regulating energy expenditure and fuel use during the extreme hypometabolic state of torpor.

Melatonin receptor genes in vertebrates

Melatonin receptors are members of the G protein-coupled receptor (GPCR) family. Three genes for melatonin receptors have been cloned. The MT1 (or Mel1a or MTNR1A) and MT2 (or Mel1b or MTNR1B) receptor subtypes are present in humans and other mammals, while an additional melatonin receptor subtype, Mel1c (or MTNR1C), has been identified in fish, amphibians and birds. Another melatonin related orphan receptor, GPR50, which does not bind melatonin, is found exclusively in mammals. The hormone melatonin is secreted primarily by the pineal gland, with highest levels occurring during the dark period of a circadian cycle. This hormone acts systemically in numerous organs. In the brain, it is involved in the regulation of various neural and endocrine processes, and it readjusts the circadian pacemaker, the suprachiasmatic nucleus. This article reviews recent studies of gene organization, expression, evolution and mutations of melatonin receptor genes of vertebrates. Gene polymorphisms reveal that numerous mutations are associated with diseases and disorders. The phylogenetic analysis of receptor genes indicates that GPR50 is an outgroup to all other melatonin receptor sequences. GPR50 may have separated from a melatonin receptor ancestor before the split between MTNR1C and the MTNR1A/B ancestor.