Circuit-wide Transcriptional Profiling Reveals Brain Region-Specific Gene Networks Regulating Depression Susceptibility

Depression is a complex, heterogeneous disorder and a leading contributor to the global burden of disease. Most previous research has focused on individual brain regions and genes contributing to depression. However, emerging evidence in humans and animal models suggests that dysregulated circuit function and gene expression across multiple brain regions drive depressive phenotypes. Here we performed RNA-sequencing on 4 brain regions from control animals and those susceptible or resilient to chronic social defeat stress at multiple time points. We employed an integrative network biology approach to identify transcriptional networks and key driver genes that regulate susceptibility to depressive-like symptoms. Further, we validated in vivo several key drivers and their associated transcriptional networks that regulate depression susceptibility and confirmed their functional significance at the levels of gene transcription, synaptic regulation and behavior. Our study reveals novel transcriptional networks that control stress susceptibility and offers fundamentally new leads for antidepressant drug discovery

Transcriptional Networks of Resilience in a Mouse Model of Depression

Nearly all humans are exposed to stress. However, most individuals do not develop depression. This is modeled in animal stress paradigms such as chronic social defeat stress (CSDS) in which only a subset of exposed mice display depression-like behavior. RNA-seq studies in these animals report broad transcriptional adaptations in stress resilience. How these transcriptional changes are regulated, however, is not known. In this thesis, I utilize a combined bioinformatics and in vivo molecular approach to probe the mechanisms underlying transcriptional changes in resilience. I first performed upstream regulator analysis on differentially expressed genes following CSDS and identified estrogen receptor α (ERα) as the top upstream regulator of pro-resilient transcription in the nucleus accumbens (NAc), a brain region implicated in depression. Overexpression of ERα in the NAc promoted resilience to stress in both male and female mice. However, while ERα overexpression recapitulated the transcriptional signature of resilience in male mice, this was not the case for female mice, indicating a sex-specific transcriptional mechanism. I next evaluated a WGCNA dataset of resilient mice following CSDS, identifying a resilient-specific transcriptional network. Using key driver analysis, I found that Zfp189 was the top regulator and was upregulated in the prefrontal cortex (PFC) of resilient mice, another brain region implicated in depression. Overexpression of Zfp189 in the PFC was both pro-resilient and antidepressant, and significantly upregulated genes in the resilient-specific network where Zfp189 was the top regulator. Further interrogation of known binding motifs within this network identified CREB as a predicted upstream regulator and re-analysis of previously published ChIP- chip data defined a known molecular interaction between CREB and Zfp189. Consistent with these observations, knockout of CREB in the PFC increased susceptibility to stress, but the deleterious effects of CREB knockout were ablated by Zfp189 overexpression. In order to probe this connection directly, I utilized CRISPR to mimic endogenous CREB-Zfp189 interactions in vivo in the PFC. This was both sufficient to increase behavioral resilience and activate the resilient-specific network. As a whole, these findings provide novel mechanistic insight into the regulation of transcriptional changes in stress resilience

Social stress induces neurovascular pathology promoting depression

Studies suggest that heightened peripheral inflammation contributes to the pathogenesis of major depressive disorder. We investigated the effect of chronic social defeat stress, a mouse model of depression, on blood–brain barrier (BBB) permeability and infiltration of peripheral immune signals. We found reduced expression of the endothelial cell tight junction protein claudin-5 (Cldn5) and abnormal blood vessel morphology in nucleus accumbens (NAc) of stress-susceptible but not resilient mice. CLDN5 expression was also decreased in NAc of depressed patients. Cldn5 downregulation was sufficient to induce depression-like behaviors following subthreshold social stress whereas chronic antidepressant treatment rescued Cldn5 loss and promoted resilience. Reduced BBB integrity in NAc of stress-susceptible or mice injected with adeno-associated virus expressing shRNA against Cldn5 caused infiltration of the peripheral cytokine interleukin-6 (IL-6) into brain parenchyma and subsequent expression of depression-like behaviors. These findings suggest that chronic social stress alters BBB integrity through loss of tight junction protein Cldn5, promoting peripheral IL-6 passage across the BBB and depressio

Sex-Specific Role for the Long Non-coding RNA LINC00473 in Depression

Depression is a common disorder that affects women at twice the rate of men. Here we report that long non-coding RNAs (lncRNAs), a recently discovered class of regulatory transcripts, represent about one-third of the differentially expressed genes in the brains of depressed humans, and display complex region- and sex-specific patterns of regulation. We identified the primate-specific, neuronal-enriched gene, LINC00473, as downregulated in prefrontal cortex (PFC) of depressed females but not males. Using viral-mediated gene transfer to express LINC00473 in adult mouse PFC neurons, we mirrored the human sex-specific phenotype by inducing stress resilience solely in female mice. This sex-specific phenotype was accompanied by changes in synaptic function and gene expression selectively in female mice and, along with studies of human neuron-like cells in culture, implicates LINC00473 as a CREB effector. Together, our studies identify LINC00473 as a female-specific driver of stress resilience that is aberrant in female depression

Epigenetic basis of opiate suppression of Bdnf gene expression in the ventral tegmental area

International audienceBrain-derived neurotrophic factor (BDNF) has a crucial role in modulating neural and behavioral plasticity to drugs of abuse. We found a persistent downregulation of exon-specific Bdnf expression in the ventral tegmental area (VTA) in response to chronic opiate exposure, which was mediated by specific epigenetic modifications at the corresponding Bdnf gene promoters. Exposure to chronic morphine increased stalling of RNA polymerase II at these Bdnf promoters in VIA and altered permissive and repressive histone modifications and occupancy of their regulatory proteins at the specific promoters. Furthermore, we found that morphine suppressed binding of phospho-CREB (cAMP response element binding protein) to Bdnf promoters in VIA, which resulted from enrichment of trimethylated H3K27 at the promoters, and that decreased NURR1 (nuclear receptor related-1) expression also contributed to Bdnf repression and associated behavioral plasticity to morphine. Our findings suggest previously unknown epigenetic mechanisms of morphine-induced molecular and behavioral neuroadaptations

Circuit-wide Transcriptional Profiling Reveals Brain Region-Specific Gene Networks Regulating Depression Susceptibility

Depression is a complex, heterogeneous disorder and a leading contributor to the global burden of disease. Most previous research has focused on individual brain regions and genes contributing to depression. However, emerging evidence in humans and animal models suggests that dysregulated circuit function and gene expression across multiple brain regions drive depressive phenotypes. Here we performed RNA-sequencing on 4 brain regions from control animals and those susceptible or resilient to chronic social defeat stress at multiple time points. We employed an integrative network biology approach to identify transcriptional networks and key driver genes that regulate susceptibility to depressive-like symptoms. Further, we validated in vivo several key drivers and their associated transcriptional networks that regulate depression susceptibility and confirmed their functional significance at the levels of gene transcription, synaptic regulation and behavior. Our study reveals novel transcriptional networks that control stress susceptibility and offers fundamentally new leads for antidepressant drug discovery

Epigenetic basis of opiate suppression of Bdnf gene expression in the ventral tegmental area

International audienceBrain-derived neurotrophic factor (BDNF) has a crucial role in modulating neural and behavioral plasticity to drugs of abuse. We found a persistent downregulation of exon-specific Bdnf expression in the ventral tegmental area (VTA) in response to chronic opiate exposure, which was mediated by specific epigenetic modifications at the corresponding Bdnf gene promoters. Exposure to chronic morphine increased stalling of RNA polymerase II at these Bdnf promoters in VIA and altered permissive and repressive histone modifications and occupancy of their regulatory proteins at the specific promoters. Furthermore, we found that morphine suppressed binding of phospho-CREB (cAMP response element binding protein) to Bdnf promoters in VIA, which resulted from enrichment of trimethylated H3K27 at the promoters, and that decreased NURR1 (nuclear receptor related-1) expression also contributed to Bdnf repression and associated behavioral plasticity to morphine. Our findings suggest previously unknown epigenetic mechanisms of morphine-induced molecular and behavioral neuroadaptations