MEF2C transcription factor is associated with the genetic and epigenetic risk architecture of schizophrenia and improves cognition in mice

Cell-Type-Specific Epigenetic Editing at the Fosb Gene Controls Susceptibility to Social Defeat Stress

Chronic social defeat stress regulates the expression of Fosb in the nucleus accumbens (NAc) to promote the cell-type-specific accumulation of ΔFosB in the two medium spiny neuron (MSN) subtypes in this region. ΔFosB is selectively induced in D1-MSNs in the NAc of resilient mice, and in D2-MSNs of susceptible mice. However, little is known about the consequences of such selective induction, particularly in D2-MSNs. This study examined how cell-type-specific control of the endogenous Fosb gene in NAc regulates susceptibility to social defeat stress. Histone post-translational modifications (HPTMs) were targeted specifically to Fosb using engineered zinc-finger proteins (ZFPs). Fosb-ZFPs were fused to either the transcriptional repressor, G9a, which promotes histone methylation or the transcriptional activator, p65, which promotes histone acetylation. These ZFPs were expressed in D1- vs D2-MSNs using Cre-dependent viral expression in the NAc of mice transgenic for Cre recombinase in these MSN subtypes. We found that stress susceptibility is oppositely regulated by the specific cell type and HPTM targeted. We report that Fosb-targeted histone acetylation in D2-MSNs or histone methylation in D1-MSNs promotes a stress-susceptible, depressive-like phenotype, while histone methylation in D2-MSNs or histone acetylation in D1-MSNs increases resilience to social stress as quantified by social interaction behavior and sucrose preference. This work presents the first demonstration of cell- and gene-specific targeting of histone modifications, which model naturally occurring transcriptional phenomena that control social defeat stress behavior. This epigenetic-editing approach, which recapitulates physiological changes in gene expression, reveals clear differences in the social defeat phenotype induced by Fosb gene manipulation in MSN subtypes.

Neuroepigenetic Editing

Studies of the mammalian nervous system have revealed widespread epigenetic regulation underlying gene expression intrinsic to basic neurobiological function as well as neurological disease. Over the past decade, a critical role has emerged for the neural regulation of chromatin-modifying enzymes during both development and adulthood, and in response to external stimuli. These biochemical data are complemented by numerous next generation sequencing (NGS) studies that quantify the extent of chromatin and DNA modifications in neurons. Neuroepigenetic editing tools can be applied to distinguish between the mere presence and functional relevance of such modifications to neural transcription and animal behavior. This review discusses current advances in neuroepigenetic editing, highlighting methodological considerations pertinent to neuroscience, such as delivery methods and the spatiotemporal specificity of editing. Although neuroepigenetic editing is a nascent field, the studies presented in this review demonstrate the enormous potential of this approach for basic neurobiological research and therapeutic application.

A Genome-Wide Association Study and Complex Network Identify Four Core Hub Genes in Bipolar Disorder

Bipolar disorder is a common and severe mental illness with unsolved pathophysiology. A genome-wide association study (GWAS) has been used to find a number of risk genes, but it is difficult for a GWAS to find genes indirectly associated with a disease. To find core hub genes, we introduce a network analysis after the GWAS was conducted. Six thousand four hundred fifty eight single nucleotide polymorphisms (SNPs) with p < 0.01 were sifted out from Wellcome Trust Case Control Consortium (WTCCC) dataset and mapped to 2045 genes, which are then compared with the protein–protein network. One hundred twelve genes with a degree >17 were chosen as hub genes from which five significant modules and four core hub genes (FBXL13, WDFY2, bFGF, and MTHFD1L) were found. These core hub genes have not been reported to be directly associated with BD but may function by interacting with genes directly related to BD. Our method engenders new thoughts on finding genes indirectly associated with, but important for, complex diseases.

Role of 108 schizophrenia-associated loci in modulating psychopathological dimensions in schizophrenia and bipolar disorder

The Schizophrenia Working Group of the Psychiatric Genomics Consortium (PGC) identified 108 loci associated with schizophrenia, but their role in modulating specific psychopathological dimensions of the disease is unknown. This study investigated which symptom dimensions may be affected by these loci in schizophrenia, and bipolar disorder. Positive, negative and depressive symptoms, suicidal ideation, cognition, violent behaviors, quality of life, and early onset were investigated in schizophrenia and bipolar disorder using the clinical antipsychotic trials of intervention effectiveness (CATIE) and systematic treatment enhancement program for bipolar disorder (STEP-BD) studies. Individual loci were investigated, then genes within 50 Kbp from polymorphisms with p < 0.10 were included in an enrichment analysis (Cytoscape GeneMania plugin) and used to estimate polygenic risk scores (PRS). Covariates were center, age, gender, ancestry-informative population, principal components, and for cognition, also years of education were considered. Eighty-nine polymorphisms were available, 479 and 810 white subjects were included from CATIE and STEP-BD, respectively. rs75059851 (IGSF9B gene) was associated with negative symptoms in CATIE (p = 0.00048). Genes within 50 Kbp from variants contributing to negative symptoms and suicide were enriched with GO terms involved in acetylcholine neurotransmission, cognition showed enrichment with GO terms involved in vitamin B6 and fucose metabolism while early onset with GO terms related to extracellular matrix structure. PRS showed nominal associations with violent behaviors and depressive symptoms. This study provided preliminary evidence that a schizophrenia-associated variant (rs75059851) may modulate negative symptoms. Multi-locus models may provide interesting insights about the biological mechanisms that mediate psychopathological dimensions.

The epigenomics of schizophrenia, in the mouse

Large-scale consortia including the Psychiatric Genomics Consortium, the Common Minds Consortium, BrainSeq and PsychENCODE, and many other studies taken together provide increasingly detailed insights into the genetic and epigenetic risk architectures of schizophrenia (SCZ) and offer vast amounts of molecular information, but with largely unexplored therapeutic potential. Here we discuss how epigenomic studies in human brain could guide animal work to test the impact of disease-associated alterations in chromatin structure and function on cognition and behavior. For example, transcription factors such as MYOCYTE-SPECIFIC ENHANCER FACTOR 2C (MEF2C), or multiple regulators of the open chromatin mark, methyl-histone H3-lysine 4, are associated with the genetic risk architectures of common psychiatric disease and alterations in chromatin structure and function in diseased brain tissue. Importantly, these molecules also affect cognition and behavior in genetically engineered mice, including virus-mediated expression changes in prefrontal cortex (PFC) and other key nodes in the circuitry underlying psychosis. Therefore, preclinical and small laboratory animal work could target genomic sequences affected by chromatin alterations in SCZ. To this end, in vivo editing of enhancer and other regulatory non-coding DNA by RNA-guided nucleases including CRISPR-Cas, and designer transcription factors, could be expected to deliver pipelines for novel therapeutic approaches aimed at improving cognitive dysfunction and other core symptoms of SCZ.