Association study of a functional promoter polymorphism of the X-box binding protein 1 gene in Japanese patients with schizophrenia

CARD8 and IL1B Polymorphisms Influence MRI Brain Patterns in Newborns with Hypoxic-Ischemic Encephalopathy Treated with Hypothermia

Inflammation and oxidative stress are recognized as important contributors of brain injury in newborns due to a perinatal hypoxic-ischemic (HI) insult. Genetic variability in these pathways could influence the response to HI and the outcome of brain injury. The aim of our study was to evaluate the impact of common single-nucleotide polymorphisms in the genes involved in inflammation and response to oxidative stress on brain injury in newborns after perinatal HI insult based on the severity and pattern of magnetic resonance imaging (MRI) findings. The DNA of 44 subjects was isolated from buccal swabs. Genotyping was performed for NLRP3 rs35829419, CARD8 rs2043211, IL1B rs16944, IL1B rs1143623, IL1B rs1071676, TNF rs1800629, CAT rs1001179, SOD2 rs4880, and GPX1 rs1050450. Polymorphism in CARD8 was found to be protective against HI brain injury detected by MRI overall findings. Polymorphisms in IL1B were associated with posterior limb of internal capsule, basal ganglia, and white matter brain patterns determined by MRI. Our results suggest a possible association between genetic variability in inflammation- and antioxidant-related pathways and the severity of brain injury after HI insult in newborns.

The Unfolded Protein Response and Autophagy as Drug Targets in Neuropsychiatric Disorders

Neurons are polarized in structure with a cytoplasmic compartment extending into dendrites and a long axon that terminates at the synapse. The high level of compartmentalization imposes specific challenges for protein quality control in neurons making them vulnerable to disturbances that may lead to neurological dysfunctions including neuropsychiatric diseases. Synapse and dendrites undergo structural modulations regulated by neuronal activity involve key proteins requiring strict control of their turnover rates and degradation pathways. Recent advances in the study of the unfolded protein response (UPR) and autophagy processes have brought novel insights into the specific roles of these processes in neuronal physiology and synaptic signaling. In this review, we highlight recent data and concepts about UPR and autophagy in neuropsychiatric disorders and synaptic plasticity including a brief outline of possible therapeutic approaches to influence UPR and autophagy signaling in these diseases.

Whole-exome sequencing in a family with a monozygotic twin pair concordant for schizophrenia and a follow-up case-control study of identified de-novo variants

Whole-exome sequencing (WES) studies have shown that de-novo variants contribute to the genetic etiology of schizophrenia. WES studies of families with a monozygotic twin pair concordant or discordant for a disease may be fruitful for identifying de-novo pathogenic variants. Here, we performed WES in six individuals from one family (affected monozygotic twins, their unaffected parents, and two siblings) and identified three de-novo missense variants (CPT2 Ala283Thr, CPSF3 Val584Ile, and RNF148 Val210Ile) in the monozygotic twin pair concordant for schizophrenia. These three missense variants were not found in 1760 patients with schizophrenia or schizoaffective disorder or 1508 healthy controls. Our data do not support the role of the three missense variants in conferring risk for schizophrenia.

Transcriptome sequencing study implicates immune-related genes differentially expressed in schizophrenia: new data and a meta-analysis

We undertook an RNA sequencing (RNAseq)-based transcriptomic profiling study on lymphoblastoid cell lines of a European ancestry sample of 529 schizophrenia cases and 660 controls, and found 1058 genes to be differentially expressed by affection status. These differentially expressed genes were enriched for involvement in immunity, especially the 697 genes with higher expression in cases. Comparing the current RNAseq transcriptomic profiling to our previous findings in an array-based study of 268 schizophrenia cases and 446 controls showed a highly significant positive correlation over all genes. Fifteen (18%) of the 84 genes with significant (false discovery rate<0.05) expression differences between cases and controls in the previous study and analyzed here again were differentially expressed by affection status here at a genome-wide significance level (Bonferroni P<0.05 adjusted for 8141 analyzed genes in total, or P<~6.1 × 10^-6), all with the same direction of effect, thus providing corroborative evidence despite each sample of fully independent subjects being studied by different technological approaches. Meta-analysis of the RNAseq and array data sets (797 cases and 1106 controls) showed 169 additional genes (besides those found in the primary RNAseq-based analysis) to be differentially expressed, and provided further evidence of immune gene enrichment. In addition to strengthening our previous array-based gene expression differences in schizophrenia cases versus controls and providing transcriptomic support for some genes implicated by other approaches for schizophrenia, our study detected new genes differentially expressed in schizophrenia. We highlight RNAseq-based differential expression of various genes involved in neurodevelopment and/or neuronal function, and discuss caveats of the approach.

Transcriptome study of differential expression in schizophrenia

Schizophrenia genome-wide association studies (GWAS) have identified common SNPs, rare copy number variants (CNVs) and a large polygenic contribution to illness risk, but biological mechanisms remain unclear. Bioinformatic analyses of significantly associated genetic variants point to a large role for regulatory variants. To identify gene expression abnormalities in schizophrenia, we generated whole-genome gene expression profiles using microarrays on lymphoblastoid cell lines (LCLs) from 413 cases and 446 controls. Regression analysis identified 95 transcripts differentially expressed by affection status at a genome-wide false discovery rate (FDR) of 0.05, while simultaneously controlling for confounding effects. These transcripts represented 89 genes with functions such as neurotransmission, gene regulation, cell cycle progression, differentiation, apoptosis, microRNA (miRNA) processing and immunity. This functional diversity is consistent with schizophrenia's likely significant pathophysiological heterogeneity. The overall enrichment of immune-related genes among those differentially expressed by affection status is consistent with hypothesized immune contributions to schizophrenia risk. The observed differential expression of extended major histocompatibility complex (xMHC) region histones (HIST1H2BD, HIST1H2BC, HIST1H2BH, HIST1H2BG and HIST1H4K) converges with the genetic evidence from GWAS, which find the xMHC to be the most significant susceptibility locus. Among the differentially expressed immune-related genes, B3GNT2 is implicated in autoimmune disorders previously tied to schizophrenia risk (rheumatoid arthritis and Graves' disease), and DICER1 is pivotal in miRNA processing potentially linking to miRNA alterations in schizophrenia (e.g. MIR137, the second strongest GWAS finding). Our analysis provides novel candidate genes for further study to assess their potential contribution to schizophrenia.

Polymorphism -116C/G of human X-box-binding protein 1 promoter is associated with risk of Alzheimer's disease

AIM

Alzheimer's disease (AD) is a multifactor disease that has been reported to have a close association with endoplasmic reticulum (ER) stress response. In the response, the regulator factor human X-box-binding protein 1 (XBP1) has been shown to facilitate the refolding and degradation of misfolded proteins, prevent neurotoxicity of amyloid-beta (Aβ) and tau, and play an important role in the survival of neurons. The aim in the study was to analyze the potential association between the -116C/G polymorphism of XBP1 and the risk of AD.

METHODS

The association between -116C/G polymorphism of XBP1 promoter and possible risk of AD was assessed among 276 patients with AD and 254 matched healthy individuals in a case-control study.

RESULTS

Overall, there was a significantly statistical difference in genotype (P = 0.0354) and allele frequencies (P = 0.0150, OR = 1.3642, 95% CI = 1.0618-1.7528) between the AD subjects and control subjects, showing that the -116C/G polymorphism of XBP1 might lead to increased susceptibility for AD in a Chinese Han population. In addition, the -116CG and -116GG genotypes were significantly associated with increased AD risk in female (P = 0.0217) and in subjects with APOE є4 (-) (P = 0.0070) in stratified analyses, and the -116CC genotype was significantly associated with fast cognitive deterioration in the AD patients (P = 0.0270).

CONCLUSION

The study supports a role for the -116C/G polymorphism of XBP1 gene in the pathogenesis of AD, and further studies with a larger sample size and detailed data should be performed in other populations.

Genetic variation of promoter sequence modulates XBP1 expression and genetic risk for vitiligo

Our previous genome-wide linkage analysis identified a susceptibility locus for generalized vitiligo on 22q12. To search for susceptibility genes within the locus, we investigated a biological candidate gene, X-box binding protein 1(XBP1). First, we sequenced all the exons, exon-intron boundaries as well as some 5′ and 3′ flanking sequences of XBP1 in 319 cases and 294 controls of Chinese Hans. Of the 8 common variants identified, the significant association was observed at rs2269577 (p__trend = 0.007, OR = 1.36, 95% CI = 1.09–1.71), a putative regulatory polymorphism within the promoter region of XBP1. We then sequenced the variant in an additional 365 cases and 404 controls and found supporting evidence for the association (p__trend = 0.008, OR = 1.31, 95% CI = 1.07–1.59). To further validate the association, we genotyped the variant in another independent sample of 1,402 cases and 1,288 controls, including 94 parent-child trios, and confirmed the association by both case-control analysis (p__trend = 0.003, OR = 1.18, 95% CI = 1.06–1.32) and the family-based transmission disequilibrium test (TDT, p = 0.005, OR = 1.93, 95% CI = 1.21–3.07). The analysis of the combined 2,086 cases and 1,986 controls provided highly significant evidence for the association (p__trend = 2.94×10⁻⁶, OR = 1.23, 95% CI = 1.13–1.35). Furthermore, we also found suggestive epistatic effect between rs2269577 and HLA-DRB1*07 allele on the development of vitiligo (p = 0.033). Our subsequent functional study showed that the risk-associated C allele of rs2269577 had a stronger promoter activity than the non-risk G allele, and there was an elevated expression of XBP1 in the lesional skins of patients carrying the risk-associated C allele. Therefore, our study has demonstrated that the transcriptional modulation of XBP1 expression by a germ-line regulatory polymorphism has an impact on the development of vitiligo.

Vitiligo is a genetically complex skin disorder that afflicts 0.1%–2% of the population throughout the world. Linkage and association studies in different populations have implicated several genomic regions and candidate genes that are linked to the development of vitiligo. Our previous genome-wide linkage analysis identified a genetic susceptibility locus for vitiligo on 22q12 in a Chinese population. In this study, we conducted a genetic and molecular study of a biologically plausible candidate gene, XBP1, within the region. We first performed a progressive association analysis in three independent samples of vitiligo, which revealed significant association between a putative promoter polymorphism, rs2269577, and vitiligo. Then, our functional analysis also demonstrated that the risk-associated allele of this variant has a stronger promoter activity and was associated with a significantly elevated expression of XBP1 in lesional skins in patients carrying the risk-associated allele. Our findings have provided the first evidence for XBP1 to play an important role in the development of vitiligo.

Relationship Between Functional Promoter Polymorphism in the XBP1 Gene (-116C/G) and Obesity

Endoplasmic reticulum stress is a central feature of obesity, insulin resistance, and type 2 diabetes. A polymorphism of the XBP1 gene (-116C/G), a transcription factor that modulates the endoplasmic reticulum stress response, causes an impairment of its positive feedback system. The authors examined a role of the polymorphism in the development of obesity. The polymorphism was investigated in clinically obese children and compared with controls. Significant difference of genotype distribution was observed, which suggested that the -116C/G genotype may be a risk factor for at least pediatric obesity.

Unconventional splicing of XBP-1 mRNA in the unfolded protein response

Cytoplasmic splicing is one of the major regulatory mechanisms of the unfolded protein response (UPR). The molecular mechanism of cytoplasmic splicing is unique and completely different from that of conventional nuclear splicing. The mammalian substrate of cytoplasmic splicing is XBP1 pre-mRNA, which is converted to spliced mRNA in response to UPR, leading to the production of an active transcription factor [pXBP1(S)] responsible for UPR. Interestingly, XBP1 pre-mRNA is also translated into a functional protein [pXBP1(U)] that negatively regulates the UPR. Thus, mammalian cells can quickly adapt to a change in conditions in the endoplasmic reticulum by switching proteins encoded in the mRNA from a negative regulator to an activator. This elaborate system contributes to various cellular functions, including plasma cell differentiation, viral infections, and carcinogenesis. In this short review, I briefly summarize research on cytoplasmic splicing and focus on current hot topics.

Lack of association between the interleukin-1 gene complex and schizophrenia in a Japanese population

Interleukin-1 (IL1) is an inflammatory cytokine and exerts neurodegenerative effects in the brain. Several studies have indicated that IL1 is likely to be involved in the pathogenesis of schizophrenia. Recent genetic studies have revealed that the IL1 gene complex (IL,1 alpha, IL1, beta and IL1 receptor antagonist) was associated with schizophrenia, although contradictory findings have also been reported. To assess whether the IL1 gene complex was implicated in vulnerability to schizophrenia, the authors conducted a case-control association study (416 patients with schizophrenia and 440 control subjects) for nine polymorphisms in Japanese subjects. The authors found no association between the IL1 gene complex polymorphisms and schizophrenia using either single-marker or haplotype analyses. The results of the present study suggest that the IL1 gene complex does not play a major role in conferring susceptibility to schizophrenia in the Japanese population.

No associations exist between five functional polymorphisms in the catechol-O-methyltransferase gene and schizophrenia in a Japanese population

Catechol-O-methyltransferase (COMT) is one of the enzymes that degrade catecholamine neurotransmitters including dopamine. The COMT gene is located on 22q11.2, a common susceptibility locus for schizophrenia. Therefore, COMT is a strong functional and positional candidate gene for schizophrenia. A common functional polymorphism (rs4680, Val158Met) has been extensively tested for an association with schizophrenia, but with conflicting results. Recent studies indicate that if COMT is implicated in susceptibility to schizophrenia, this cannot be wholly accounted for by the Val158Met polymorphism. To assess this view, the authors conducted a case-control association study (399 patients with schizophrenia and 440 control subjects) for five functional polymorphisms (rs2075507, rs737865, rs6267, rs4680 and rs165599) in Japanese subjects. There were no significant associations found between the polymorphisms or haplotypes of COMT and schizophrenia. The present study shows that these five functional COMT polymorphisms do not play a major role in conferring susceptibility to schizophrenia in Japanese.

No association between the ERBB3 gene and schizophrenia in a Japanese population

There is cumulative evidence that neuregulin 1 (NRG1) is a susceptibility gene for schizophrenia. Postmortem studies on brains from schizophrenia patients have revealed changes in the mRNA expression levels of v-erb-b2 erythroblastic leukemia viral oncogene homolog 3 (ERBB3), one of the NRG1 receptor genes. These observations suggest that NRG1-ERBB signaling is involved in the pathogenesis of schizophrenia. To assess whether the ERBB3 gene could be implicated in vulnerability to schizophrenia, we conducted a case-control (399 patients and 438 controls) association study in Japanese subjects. There were no significant association between the polymorphisms or haplotypes of ERBB3 and schizophrenia. The present study shows that ERBB3 does not play a major role in conferring susceptibility to schizophrenia in the Japanese population.