Evaluation of RGS4 as a candidate gene for schizophrenia

Glial changes in schizophrenia: Genetic and epigenetic approach

BACKGROUND

Schizophrenia (SCZ) is a severe mental illness that affects one percent of the population, affecting how people think, feel, and behave. Evidence suggests glial cell alteration and some researchers have found genetic risk loci and epigenetic marks that may regulate glia-related genes implicated in SCZ.

AIM

The aim of this study is to identify genetic and epigenetic changes that have been reported in glial cells or glial-associated genes in SCZ.

MATERIALS AND METHODS

We searched the articles from PubMed, PubMed Central, Medline, Medscape, and Embase databases up to December 2020 to identify relevant peer-reviewed articles in English. The titles and abstracts were screened to eliminate irrelevant citations.

RESULTS

Twenty-four original articles were included in the review. Studies were categorized into the following four thematic via: (1) oligodendrocytes, (2) microglia, (3) astrocytes, and (4) perspectives.

CONCLUSION

This study is the first of its kind to review research on genetic variants and epigenetic modifications associated with glia-related genes implicated in SCZ. Epigenetic evidence is considerably less than genetic evidence in this field. Understanding the pathways of some risk genes and their genetic and epigenetic regulation allows us to understand and find potential targets for future interventions in this mental illness.

A gene-based review of RGS4 as a putative risk gene for psychiatric illness

Considerable efforts have been made to characterize RGS4 as a potential candidate gene for schizophrenia. Investigations span across numerous modalities and include explorations of genetic risk associations, mRNA and protein levels in the brain, and functionally relevant interactions with other candidate genes as well as links to schizophrenia relevant neural phenotypes. While these lines of investigations have yielded partially inconsistent findings, they provide a perspective on RGS4 as an important part of a larger biological system contributing to schizophrenia risk. This gene-based review aims to provide a comprehensive overview of published data from different experimental modalities and discusses the current knowledge of RGS4's systems-biological impact on the schizophrenia pathology.

Taiwan Schizophrenia Linkage Study: lessons learned from endophenotype-based genome-wide linkage scans and perspective

Taiwan Schizophrenia Linkage Study (TSLS) was initiated with a linkage strategy for locating multiple genes, each of small to moderate effect, and aimed to recruit a large enough sample of pairs of affected siblings and their families ascertained from a multisite study. With a sample of 607 families successfully recruited, a total of 2,242 individuals (1,207 affected and 1,035 unaffected) from 557 families were genotyped using 386 microsatellite markers spaced at an average of 9-cM intervals. Here the author reviews the establishment of TSLS and initial signal derived from linkage scan using the diagnosis of schizophrenia. Based on the limited success of the initial linkage analysis, a sufficient-component causal model is proposed to incorporate endophenotypes and genes for schizophrenia. Four types of candidate endophenotype measured in TSLS, including schizotypal personality, Continuous Performance Test, Wisconsin Card Sorting Test, and niacin skin flush test, are briefly described. The author discusses different strategies of linkage analysis incorporating these endophenotypes, including quantitative trait loci (QTL) linkage analysis, clustering-derived subgroups, ordered subset analysis (OSA), and latent classes for linkage scan. Then the author summarizes the linkage signals generated from seven studies of endophenotype-based linkage analysis using TSLS, including QTL scan of neurocognitive performance, QTL scan of niacin skin flush, the family cluster of attention deficit and execution deficit, OSA by schizophrenia-schizotypy factors, nested OSA by age at onset and neurocognitive performance, and the latent class of deficit schizophrenia for linkage analysis. The perspective of combining next-generation sequencing with linkage analysis of families is also discussed.

Brain RGS4 and RGS10 protein expression in schizophrenia and depression. Effect of drug treatment

RATIONALE

Regulator of G-protein signaling (RGS) proteins, RGS4 and RGS10, may be involved in the pathophysiology of schizophrenia. RGS4 has attracted special interest since the reports of genetic association between SNPs in RGS4 and schizophrenia. However, there is no information about the subcellular distribution of RGS4 and RGS10 proteins in psychiatric disorders.

OBJECTIVES

Plasma membrane RGS4 and cytosolic RGS10 protein immunoreactivity in prefrontal cortex from schizophrenic subjects (n = 25), non-diagnosed suicides (n = 13), and control subjects (n = 35), matched by age, gender, and postmortem delay, was analyzed by western blot. A second group of depressed subjects (n = 25) and control subjects (n = 25) was evaluated. The effect of the antipsychotic or antidepressant treatments was also assessed.

RESULTS

No significant differences in plasma membrane RGS4 and cytosolic RGS10 protein expression were observed between schizophrenic subjects, non-diagnosed suicides, and control subjects. However, RGS4 immunoreactivity was significantly higher (Δ = 33 ± 10 %, p < 0.05) in the antipsychotic-treated subgroup (n = 12) than in the antipsychotic-free subgroup (n = 13). Immunodensities of plasma membrane RGS4 and cytosolic RGS10 proteins did not differ between depressed and matched control subjects.

CONCLUSIONS

Expression of RGS4 and RGS10 proteins at their predominant subcellular location was studied in the postmortem brain of subjects with psychiatric disorders. The results suggest unaltered membrane RGS4 and cytosolic RGS10 proteins levels in schizophrenia and major depression. Antipsychotic treatment seems to increase membrane RGS4 immunoreactivity. Further studies are needed to elucidate RGS4 and RGS10 functional status.

Regulators of G protein signaling in neuropsychiatric disorders

Regulators of G protein signaling (RGS) comprise a diverse group of about 40 proteins which determine signaling amplitude and duration via modulation of receptor/G protein or receptor/effector coupling. Several members of the RGS family are expressed in the brain, where they have precise roles in regulation of important physiological processes. The unique functions of each RGS can be attributed to its structure, distinct pattern of expression, and regulation, and its preferential interactions with receptors, Galpha subunits and other signaling proteins. Evidence suggests dysfunction of RGS proteins is related to several neuropathological conditions. Moreover, clinical and preclinical work reveals that the efficacy and/or side effects of treatments are highly influenced by RGS activity. This article summarizes findings on RGS proteins in vulnerability to several neuropsychiatric disorders, the mechanism via which RGS proteins control neuronal responses and their potential use as drug targets.

Abnormal expression of glutamate transporter and transporter interacting molecules in prefrontal cortex in elderly patients with schizophrenia

Glutamate cycling is critically important for neurotransmission, and may be altered in schizophrenia. The excitatory amino acid transporters (EAATs) facilitate the reuptake of glutamate from the synaptic cleft and have a key role in glutamate cycling. We hypothesized that expression of the EAATs and the EAAT regulating proteins ARHGEF11, JWA, G-protein suppressor pathway 1 (GPS1), and KIAA0302 are altered in the brain in schizophrenia. To test this, we measured expression of EAAT1, EAAT2, EAAT3, and EAAT interacting proteins in postmortem tissue from the dorsolateral prefrontal and anterior cingulate cortex of patients with schizophrenia and a comparison group using in situ hybridization and Western blot analysis. We found increased EAAT1 transcripts and decreased protein expression, increased EAAT3 transcripts and protein, and elevated protein expression of both GPS1 and KIAA0302 protein. We did not find any changes in expression of EAAT2. These data indicate that proteins involved in glutamate reuptake and cycling are altered in the cortex in schizophrenia, and may provide potential targets for future treatment strategies.

Association of RGS2 and RGS5 variants with schizophrenia symptom severity

BACKGROUND

Several lines of evidence indicate that Regulator of G Protein Signaling 4 (RGS4) contributes to schizophrenia vulnerability. RGS4 is one of a family of molecules that modulate signaling via G-protein coupled receptors. Five genes encoding members of this family (RGS2, RGS4, RGS5, RGS8 and RGS16) map to chromosome 1q23.3-1q31. Due to overlapping cellular functions and chromosomal proximity, we hypothesized that multiple RGS genes may contribute to schizophrenia severity and treatment responsiveness.

METHODS

Subjects were 750 individuals with schizophrenia who participated in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Inferred ancestries were: 221 (30%) 'Africa only', 422 (56%) 'Europe only' and 107 (14%) 'Other'. Fifty-nine single nucleotide polymorphisms (SNPs) in or near the RGS5, RGS16, RGS8 and RGS2 genes were genotyped. Multiple linear regression was used to analyze association of markers with Positive and Negative Symptoms Scale (PANSS) total scores at baseline and throughout antipsychotic treatment.

RESULTS

RGS5 marker rs10799902 was associated with altered baseline PANSS total score in both the Africa only (P=0.0440) and Europe only (P=0.0143) strata, although neither association survived multiple comparisons correction. A common five-marker haplotype of the RGS2 gene was associated with more severe baseline PANSS total score in the Europe only strata (global P=0.0254; haplotype-specific P=0.0196). In contrast to RGS4, none of the markers showed association with antipsychotic treatment response.

CONCLUSIONS

RGS2 and RGS5 genotypes predicted severity of baseline symptoms in schizophrenia. Although these analyses are exploratory and replication is required, these data suggest a possible role for multiple RGS proteins in schizophrenia.

An association study of RGS4 polymorphisms with clinical phenotypes of schizophrenia in a Chinese population

The regulator of G-protein signaling 4 (RGS4) has been suggested as a candidate gene for schizophrenia. However, following an initial positive report, subsequent association studies between RGS4 and schizophrenia have yielded inconclusive results. Also, few studies have investigated the association of RGS4 polymorphisms with the phenotypic subgroups of schizophrenia. To further clarify the role of RGS4 in this disease, we performed a case-control study (504 cases and 531 controls of Han Chinese descent) to examine the association of RGS4 with schizophrenia and with clinical and neurocognitive profiles. The four markers (SNPs 1, 4, 7, and 18) implicated in the original association study were genotyped. We detected significant association of four-marker haplotypes with schizophrenia (UNPHASED: global P = 0.037; PHASE: global P = 0.048). The haplotype G-G-G-G, which was implicated in at least three previous studies, was the major risk haplotype (UNPHASED: P = 0.019; PHASE: P = 0.010). Regarding the clinical phenotypes, the Wechsler Adult Intelligence Test (WAIS) information subtest score was associated with SNP4 genotypes (P = 0.001). PANSS total and global psychopathology scores were also associated with SNP4, but may not reliably reflect the general severity of disease as the scores may be affected by confounders like medication response. Our study provides further support for a role of RGS4 in the pathogenesis of schizophrenia. We identified G-G-G-G as the risk haplotype in our Chinese sample. The association with information subtest score suggests an effect of RGS4 on premorbid functioning, which may be related to neurodevelopmental processes. Further independent studies are required to verify our findings.

Linkage disequilibrium patterns and functional analysis of RGS4 polymorphisms in relation to schizophrenia

The regulator of G-protein signaling 4 (RGS4, chromosome 1q23.3) plays a critical role in G-protein function. Four common single-nucleotide polymorphisms (SNPs) localized between the 5' upstream sequence and the first intron, as well as 2 haplotypes derived from these SNPs may confer liability to schizophrenia (SZ). However, the pattern of associations varies among samples. To help clarify the putative associations, we report the following analyses: (1) a comprehensive catalog of common polymorphisms, (2) linkage disequilibrium (LD) and association analyses using these SNPs, and (3) functional analysis based on dual-luciferase promoter assays. We identified 62 SNPs from a 20-kb genomic region spanning RGS4, of which 26 are common polymorphisms with a minor allele frequency (MAF) of >5%. LD analysis suggested 5 clusters of SNPs (r(2) > .8). Association analyses using the novel SNPs were consistent with the prior reports, but further localization was constrained by significant LD across the region. The 2 haplotypes reported to confer liability to SZ had significant promoter activity compared with promoterless constructs, suggesting a functional role for both haplotypes. Further analyses of promoter sequences are warranted to understand transcriptional regulation at RGS4. This information will be useful for further analysis of samples in which genetic association of RGS4 polymorphisms with SZ has been reported.

Ethnic stratification of the association of RGS4 variants with antipsychotic treatment response in schizophrenia

BACKGROUND

Genetic association studies, including a large meta-analysis, report association of regulator of G protein signaling 4 (RGS4) with schizophrenia in the context of heterogeneity. The central role of RGS4 in regulating signaling via Gi/o coupled neurotransmitter receptors led us to hypothesize that there may be RGS4 genotypes predictive of specific disease phenotypes and antipsychotic treatment responses.

METHODS

Subjects were 678 individuals with schizophrenia who participated in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE). Among the 678 subjects, the inferred ancestries were 198 (29%) "Africa only," 397 (59%) "Europe only," and 83 (12%) "Other." Eight single nucleotide polymorphisms (SNPs) spanning RGS4 were genotyped. Multiple linear regression was used to analyze association of RGS4 markers with Positive and Negative Symptoms Scale (PANSS) scores at baseline and throughout antipsychotic treatment.

RESULTS

Two consecutive markers within RGS4, rs2661319 and rs2842030, were associated with more severe baseline PANSS total score. Treatment with perphenazine was more effective than treatment with quetiapine (p = .010) or ziprasidone (p = .002) in individuals of inferred African ancestry and homozygous for the rs951439 C allele.

CONCLUSIONS

RGS4 genotypes predicted both the severity of baseline symptoms and relative responsiveness to antipsychotic treatment. Although these analyses are exploratory and replication is required, these data provide support for RGS4 in schizophrenia pathogenesis and suggest a functional role for RGS4 in differential antipsychotic treatment efficacy of schizophrenia.