Wnt receptor gene FZD1 was associated with schizophrenia in genome-wide SNP analysis of the Australian Schizophrenia Research Bank cohort

Identification of a Novel Functional Non-synonymous Single Nucleotide Polymorphism in Frizzled Class Receptor 6 Gene for Involvement in Depressive Symptoms

Although numerous susceptibility loci for depression have been identified in recent years, their biological function and molecular mechanism remain largely unknown. By using an exome-wide association study for depressive symptoms assessed by the Center for Epidemiological Studies Depression (CES-D) score, we discovered a novel missense single nucleotide polymorphism (SNP), rs61753730 (Q152E), located in the fourth exon of the frizzled class receptor 6 gene (FZD6), which is a potential causal variant and is significantly associated with the CES-D score. Computer-based in silico analysis revealed that the protein configuration and stability, as well as the secondary structure of FZD6 differed greatly between the wild-type (WT) and Q152E mutant. We further found that rs61753730 significantly affected the luciferase activity and expression of FZD6 in an allele-specific way. Finally, we generated Fzd6-knockin (Fzd6-KI) mice with rs61753730 mutation using the CRISPR/Cas9 genome editing system and found that these mice presented greater immobility in the forced swimming test, less preference for sucrose in the sucrose preference test, as well as decreased center entries, center time, and distance traveled in the open filed test compared with WT mice after exposed to chronic social defeat stress. These results indicate the involvement of rs61753730 in depression. Taken together, our findings demonstrate that SNP rs61753730 is a novel functional variant and plays an important role in depressive symptoms.

Brain vasculature disturbance in schizophrenia

PURPOSE OF REVIEW

The vascular hypothesis of schizophrenia (SZ) postulates that brain endothelial dysfunction contributes to brain pathophysiology. This review discusses recent evidence for and against this hypothesis, including data related to blood-brain barrier (BBB), brain endothelium, and brain blood supply, to provide a critical weighed update.

RECENT FINDINGS

Different studies report a consistent proportion of SZ patients showing increased BBB permeability, reflected by higher levels of albumin in the cerebral spinal fluid. Of note, this was not a result of antipsychotic medication. The high inflammatory profile observed in some SZ patients is strongly associated with increased BBB permeability to circulating immune cells, and with more severe cognitive deficiencies. Also, sex was found to interact with BBB integrity and permeability in SZ. The strongest independent genetic association with SZ has been identified in FZD1, a hypoxia-response gene that is 600-fold higher expressed in early development endothelium as compared to adult brain endothelium. Regarding brain blood supply, there is evidence to suggest alterations in proper brain perfusion in SZ. Nonetheless, ex-vivo experiments suggested that widely used antipsychotics favor vasoconstriction; thus, alterations in cerebral perfusion might be related to the patients' medication.

SUMMARY

In some patients with SZ, a vulnerable brain endothelium may be interacting with environmental stressors, such as inflammation or hypoxia, converging into a more severe SZ symptomatology. Gene expression and performance of human brain endothelium could vary along with development and the establishment of the BBB; therefore, we encourage to investigate its possible contribution to SZ considering this dynamic context.

Neuroinflammation in Schizophrenia: The Key Role of the WNT/β-Catenin Pathway

Schizophrenia is a very complex syndrome involving widespread brain multi-dysconnectivity. Schizophrenia is marked by cognitive, behavioral, and emotional dysregulations. Recent studies suggest that inflammation in the central nervous system (CNS) and immune dysfunction could have a role in the pathogenesis of schizophrenia. This hypothesis is supported by immunogenetic evidence, and a higher incidence rate of autoimmune diseases in patients with schizophrenia. The dysregulation of the WNT/β-catenin pathway is associated with the involvement of neuroinflammation in schizophrenia. Several studies have shown that there is a vicious and positive interplay operating between neuroinflammation and oxidative stress. This interplay is modulated by WNT/β-catenin, which interacts with the NF-kB pathway; inflammatory factors (including IL-6, IL-8, TNF-α); factors of oxidative stress such as glutamate; and dopamine. Neuroinflammation is associated with increased levels of PPARγ. In schizophrenia, the expression of PPAR-γ is increased, whereas the WNT/β-catenin pathway and PPARα are downregulated. This suggests that a metabolic-inflammatory imbalance occurs in this disorder. Thus, this research’s triptych could be a novel therapeutic approach to counteract both neuroinflammation and oxidative stress in schizophrenia.

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.

Misregulation of Wnt Signaling Pathways at the Plasma Membrane in Brain and Metabolic Diseases

Wnt signaling pathways constitute a group of signal transduction pathways that direct many physiological processes, such as development, growth, and differentiation. Dysregulation of these pathways is thus associated with many pathological processes, including neurodegenerative diseases, metabolic disorders, and cancer. At the same time, alterations are observed in plasma membrane compositions, lipid organizations, and ordered membrane domains in brain and metabolic diseases that are associated with Wnt signaling pathway activation. Here, we discuss the relationships between plasma membrane components-specifically ligands, (co) receptors, and extracellular or membrane-associated modulators-to activate Wnt pathways in several brain and metabolic diseases. Thus, the Wnt-receptor complex can be targeted based on the composition and organization of the plasma membrane, in order to develop effective targeted therapy drugs.

Genome-wide DNA methylation patterns associated with general psychopathology in children

Psychiatric symptoms are interrelated and found to be largely captured by a general psychopathology factor (GPF). Although epigenetic mechanisms, such as DNA methylation (DNAm), have been linked to individual psychiatric outcomes, associations with GPF remain unclear. Using data from 440 children aged 10 years participating in the Generation R Study, we examined the associations of DNAm with both general and specific (internalizing, externalizing) factors of psychopathology. Genome-wide DNAm levels, measured in peripheral blood using the Illumina 450K array, were clustered into wider co-methylation networks ('modules') using a weighted gene co-expression network analysis. One co-methylated module associated with GPF after multiple testing correction, while none associated with the specific factors. This module comprised of 218 CpG probes, of which 198 mapped onto different genes. The CpG most strongly driving the association with GPF was annotated to FZD1, a gene that has been implicated in schizophrenia and wider neurological processes. Associations between the probes contained in the co-methylated module and GPF were supported in an independent sample of children from the Avon Longitudinal Study of Parents and Children (ALSPAC), as evidenced by significant correlations in effect sizes. These findings might contribute to improving our understanding of dynamic molecular processes underlying complex psychiatric phenotypes.

Individual deviations from normative models of brain structure in a large cross-sectional schizophrenia cohort

The heterogeneity of schizophrenia has defied efforts to derive reproducible and definitive anatomical maps of structural brain changes associated with the disorder. We aimed to map deviations from normative ranges of brain structure for individual patients and evaluate whether the loci of individual deviations recapitulated group-average brain maps of schizophrenia pathology. For each of 48 white matter tracts and 68 cortical regions, normative percentiles of variation in fractional anisotropy (FA) and cortical thickness (CT) were established using diffusion-weighted and structural MRI from healthy adults (n = 195). Individuals with schizophrenia (n = 322) were classified as either within the normative range for healthy individuals of the same age and sex (5-95% percentiles), infra-normal (<5% percentile) or supra-normal (>95% percentile). Repeating this classification for each tract and region yielded a deviation map for each individual. Compared to the healthy comparison group, the schizophrenia group showed widespread reductions in FA and CT, involving virtually all white matter tracts and cortical regions. Paradoxically, however, no more than 15-20% of patients deviated from the normative range for any single tract or region. Furthermore, 79% of patients showed infra-normal deviations for at least one locus (healthy individuals: 59 ± 2%, p < 0.001). Thus, while infra-normal deviations were common among patients, their anatomical loci were highly inconsistent between individuals. Higher polygenic risk for schizophrenia associated with a greater number of regions with infra-normal deviations in CT (r = -0.17, p = 0.006). We conclude that anatomical loci of schizophrenia-related changes are highly heterogeneous across individuals to the extent that group-consensus pathological maps are not representative of most individual patients. Normative modeling can aid in parsing schizophrenia heterogeneity and guiding personalized interventions.