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Psychiatric disorders such as schizophrenia and bipolar disorder are caused by complex gene–environment interactions. While recent advances in genomic technologies have enabled the identification of several risk variants for psychiatric conditions, including single-nucleotide variants and copy-number variations, these factors can explain only a portion of the liability to these disorders. Although non-inherited factors had previously been attributed to environmental causes, recent genomic analyses have demonstrated that de novo mutations are among the main non-inherited risk factors for several psychiatric conditions. Somatic mutations in the brain may also explain how stochastic developmental events and environmental insults confer risk for a psychiatric disorder following fertilization. Here, we review evidence regarding somatic mutations in the brains of individuals with and without neuropsychiatric diseases. We further discuss the potential biological mechanisms underlying somatic mutations in the brain as well as the technical issues associated with the detection of somatic mutations in psychiatric research.

Bipolar disorder (BD) is a severe mental disorder characterized by repeated mood swings. Although genetic factors are collectively associated with the etiology of BD, the underlying molecular mechanisms, particularly how environmental factors affect the brain, remain largely unknown. We performed promoter-wide DNA methylation analysis of neuronal and nonneuronal nuclei in the prefrontal cortex of patients with BD (N = 34) and controls (N = 35). We found decreased DNA methylation at promoters in both cell types in the BD patients. Gene Ontology (GO) analysis of differentially methylated region (DMR)-associated genes revealed enrichment of molecular motor-related genes in neurons, chemokines in both cell types, and ion channel- and transporter-related genes in nonneurons. Detailed GO analysis further revealed that growth cone- and dendrite-related genes, including NTRK2 and GRIN1, were hypermethylated in neurons of BD patients. To assess the effect of medication, neuroblastoma cells were cultured under therapeutic concentrations of three mood stabilizers. We observed that up to 37.9% of DMRs detected in BD overlapped with mood stabilizer-induced DMRs. Interestingly, mood stabilizer-induced DMRs showed the opposite direction of changes in DMRs, suggesting the therapeutic effects of mood stabilizers. Among the DMRs, 12 overlapped with loci identified in a genome-wide association study (GWAS) of BD. We also found significant enrichment of neuronal DMRs in the loci reported in another GWAS of BD. Finally, we performed qPCR of DNA methylation-related genes and found that DNMT3B was overexpressed in BD. The cell-type-specific DMRs identified in this study will be useful for understanding the pathophysiology of BD.

The long interspersed nuclear element‐1 (LINE‐1) retrotransposons are a major family of mobile genetic elements, comprising approximately 17% of the human genome. The methylation state of LINE‐1 is often used as an indicator of global DNA methylation levels and it regulates the retrotransposition and somatic insertion of the genetic element. We have previously reported the significant relationship between LINE‐1 hypomethylation and poor prognosis in upper gastrointestinal (GI) cancers. However, the causal relationships between LINE‐1 hypomethylation, retrotransposition, and tumor‐specific insertion in upper GI cancers remain unknown. We used bisulfite‐pyrosequencing and quantitative real‐time PCR to verify LINE‐1 methylation and copy number in tissue samples of 101 patients with esophageal and 103 patients with gastric cancer. Furthermore, we analyzed the LINE‐1 retrotransposition profile with an originally developed L1Hs‐seq. In tumor samples, LINE‐1 methylation levels were significantly lower than non‐tumor controls, while LINE‐1 copy numbers were markedly increased. As such, there was a significant inverse correlation between the LINE‐1 methylation level and copy number in tumor tissues, with lower LINE‐1 methylation levels corresponding to higher LINE‐1 copy numbers. Of particular importance is that somatic LINE‐1 insertions were more numerous in tumor than normal tissues. Furthermore, we observed that LINE‐1 was inserted evenly across all chromosomes, and most often within genomic regions associated with tumor‐suppressive genes. LINE‐1 hypomethylation in upper GI cancers is related to increased LINE‐1 retrotransposition and tumor‐specific insertion events, which may collectively contribute to the acquisition of aggressive tumor features through the inactivation of tumor‐suppressive genes. Methylation of long interspersed nuclear element‐1 (LINE‐1) is indicative of global DNA methylation level and regulates LINE‐1 retrotransposition and somatic insertion. We have previously reported the significant relationship between LINE‐1 hypomethylation and poor prognosis in upper gastrointestinal (GI) cancers. LINE‐1 hypomethylation in upper GI cancers was related to increased LINE‐1 retrotransposition and tumor‐specific insertion events, which might collectively contribute to the acquisition of aggressive tumor features through the inactivation of tumor‐suppressive genes.

Once disseminated tumor cells (DTCs) arrive at a metastatic organ, they remain there, latent, and become seeds of metastasis. However, the clonal composition of DTCs in a latent state remains unclear. Here, we applied high-resolution DNA barcode tracking to a mouse model that recapitulated the metastatic dormancy of head and neck squamous cell carcinoma (HNSCC). We found that clones abundantly circulated peripheral blood dominated DTCs. Through analyses of multiple barcoded clonal lines, we identified specific subclonal population that preferentially generated homotypic circulating tumor cell (CTC) clusters and dominated DTCs. Despite no notable features under static conditions, this population significantly generated stable cell aggregates that were resistant to anoikis under fluid shear stress (FSS) conditions in an E-cadherin-dependent manner. Our data from various cancer cell lines indicated that the ability of aggregate-constituting cells to regulate cortical actin-myosin dynamics governed the aggregates’ stability in FSS. The CTC cluster-originating cells were characterized by the expression of a subset of E-cadherin binding factors enriched with actin cytoskeleton regulators. Furthermore, this expression signature was associated with locoregional and metastatic recurrence in HNSCC patients. These results reveal a biological selection of tumor cells capable of generating FSS-adaptive CTC clusters, which leads to distant colonization.

The authors analyze gene coexpression relationships in microarray data generated from specific human regions. They identify modules of coexpressed genes that correspond to neurons, oligodendrocytes, astrocytes and microglia, demonstrating that cell type-specific information can be obtained from whole brain tissue without isolating homogenous populations of cells. The enormous complexity of the human brain ultimately derives from a finite set of molecular instructions encoded in the human genome. These instructions can be directly studied by exploring the organization of the brain's transcriptome through systematic analysis of gene coexpression relationships. We analyzed gene coexpression relationships in microarray data generated from specific human brain regions and identified modules of coexpressed genes that correspond to neurons, oligodendrocytes, astrocytes and microglia. These modules provide an initial description of the transcriptional programs that distinguish the major cell classes of the human brain and indicate that cell type–specific information can be obtained from whole brain tissue without isolating homogeneous populations of cells. Other modules corresponded to additional cell types, organelles, synaptic function, gender differences and the subventricular neurogenic niche. We found that subventricular zone astrocytes, which are thought to function as neural stem cells in adults, have a distinct gene expression pattern relative to protoplasmic astrocytes. Our findings provide a new foundation for neurogenetic inquiries by revealing a robust and previously unrecognized organization to the human brain transcriptome.

Mice with the C3H background show greater behavioral propensity for schizophrenia, including lower prepulse inhibition (PPI), than C57BL/6 (B6) mice. To characterize as‐yet‐unknown pathophysiologies of schizophrenia, we undertook proteomics analysis of the brain in these strains, and detected elevated levels of Mpst, a hydrogen sulfide (H 2 S)/polysulfide‐producing enzyme, and greater sulfide deposition in C3H than B6 mice. Mpst ‐deficient mice exhibited improved PPI with reduced storage sulfide levels, while Mpst ‐transgenic (Tg) mice showed deteriorated PPI, suggesting that “sulfide stress” may be linked to PPI impairment. Analysis of human samples demonstrated that the H 2 S/polysulfides production system is upregulated in schizophrenia. Mechanistically, the Mpst‐ Tg brain revealed dampened energy metabolism, while maternal immune activation model mice showed upregulation of genes for H 2 S/polysulfides production along with typical antioxidative genes, partly via epigenetic modifications. These results suggest that inflammatory/oxidative insults in early brain development result in upregulated H 2 S/polysulfides production as an antioxidative response, which in turn cause deficits in bioenergetic processes. Collectively, this study presents a novel aspect of the neurodevelopmental theory for schizophrenia, unraveling a role of excess H 2 S/polysulfides production. Synopsis This study proposes a novel concept that excess hydrogen sulfide production (sulfide stress) underlies a schizophrenia pathophysiology in the realm of neurodevelopmental hypothesis of the disease. Targeting the metabolic pathway of hydrogen sulfide provides a novel therapeutic approach. Mpst‐deficient mice exhibited improved prepulse inhibition (PPI), a typical schizophrenia‐relevant endophenotype, with reduced sulfide levels, while Mpst‐transgenic mice showed deteriorated PPI. Postmortem brains and iPS‐derived cells from a subset of schizophrenia patients displayed evidence for sulfide stress. Sulfide stress condition stemmed from insults in developing brain in mouse models and elicited dampened energy metabolism. MPST expression level in hair follicles has a potential to stratify schizophrenia patients with sulfide stress. Graphical Abstract This study proposes a novel concept that excess hydrogen sulfide production (sulfide stress) underlies a schizophrenia pathophysiology in the realm of neurodevelopmental hypothesis of the disease. Targeting the metabolic pathway of hydrogen sulfide provides a novel therapeutic approach.

Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor, which is important for neuronal survival, development and synaptic plasticity. Accumulating evidence suggests that epigenetic modifications of BDNF are associated with the pathophysiology of psychiatric disorders, such as schizophrenia and mood disorders. Patients with psychiatric disorders generally show decreased neural BDNF levels, which are often associated with increased DNA methylation at the specific BDNF promoters. Importantly, observed DNA methylation changes are consistent across tissues including brain and peripheral blood, which suggests potential usefulness of these findings as a biomarker of psychiatric disorders. Here we review DNA methylation characteristics of BDNF promoters of cellular, animal and clinical samples and discuss future perspectives.

Background The protein syntenin-1 is expressed by a variety of cell types, and is upregulated in various malignancies, including melanoma, breast cancer and glioma. Although the mechanism by which elevated syntenin-1 expression contributes to cancer has been described, the exact pathway has not been elucidated. Methods To investigate the involvement of syntenin-1 in colorectal cancer (CRC), we performed immunohistochemical analysis of 139 CRC surgical specimens. We also examined syntenin-1 knockdown in CRC cell lines. Results High syntenin-1 expression was associated with less differentiated histologic grade and poor prognosis, and was an independent prognostic indicator in CRC. Syntenin-1 knockdown in CRC cells reduced the presence of cancer stem cells (CSCs), oxaliplatin chemoresistance and migration. DNA microarray analysis and quantitative real-time polymerase chain reaction showed decreased prostaglandin E2 receptor 2 (PTGER2) expression in syntenin-1-knockdown cells. PTGER2 knockdown in CRC cells yielded the same phenotype as syntenin-1 knockdown. Celecoxib, which has anti-inflammatory effects by targeting cyclooxygenase-2, reduced CSCs and decreased chemoresistance, while prostaglandin E2 (PGE2) had the opposite effect. Conclusions Our findings suggested that syntenin-1 enhanced CSC expansion, oxaliplatin chemoresistance and migration capability through regulation of PTGER2 expression. Syntenin-1 may be a promising new prognostic factor and target for anti-cancer therapies.

Serotonin-transporter-linked polymorphic region (5-HTTLPR), a variable number of tandem repeats in the promoter region of serotonin transporter gene, is classified into short (S) and long (L) alleles. Initial case-control association studies claiming the risks of the S allele in depression and anxiety were not completely supported by recent studies. However, most studies, especially those on East Asian populations, have overlooked the complexity of 5-HTTLPR, which involves multiple different alleles with distinct functional properties. To address this issue, distinguishing multiple 5-HTTLPR alleles is essential. Here, using the 5-HTTLPR genotypes previously determined by exhaustive Sanger sequencing of approximately 1,500 Japanese subjects and their comprehensive SNP data, we constructed a method for 5-HTTLPR genotype imputation. We identified 28 tag SNPs for the imputation of four major 5-HTTLPR alleles, which collectively account for 97.6% of 5-HTTLPR alleles in the Japanese population. Our imputation method, achieved an accuracy of 0.872 in cross-validation, will contribute to association analysis of 5-HTTLPR in the Japanese subjects.

Prototypic antidepressants, such as tricyclic/tetracyclic antidepressants (TCAs), have multiple pharmacological properties and have been considered to be more effective than newer antidepressants, such as selective serotonin reuptake inhibitors, in treating severe depression. However, the clinical contribution of non-monoaminergic effects of TCAs remains elusive. In this study, we discovered that amitriptyline, a typical TCA, directly binds to the lysophosphatidic acid receptor 1 (LPAR1), a G protein-coupled receptor, and activates downstream G protein signaling, while exerting a little effect on β-arrestin recruitment. This suggests that amitriptyline acts as a G protein-biased agonist of LPAR1. This biased agonism was specific to TCAs and was not observed with other antidepressants. LPAR1 was found to be involved in the behavioral effects of amitriptyline. Notably, long-term infusion of mouse hippocampus with the potent G protein-biased LPAR agonist OMPT, but not the non-biased agonist LPA, induced antidepressant-like behavior, indicating that G protein-biased agonism might be necessary for the antidepressant-like effects. Furthermore, RNA-seq analysis revealed that LPA and OMPT have opposite patterns of gene expression changes in the hippocampus. Pathway analysis indicated that long-term treatment with OMPT activated LPAR1 downstream signaling (Rho and MAPK), whereas LPA suppressed LPAR1 signaling. Our findings provide insights into the mechanisms underlying the non-monoaminergic antidepressant effects of TCAs and identify the G protein-biased agonism of LPAR1 as a promising target for the development of novel antidepressants.