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 four 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.
•A large-scale multi-brain region transcriptomic cohort to probe stress susceptibility•Reveals susceptible and resilient transcriptional networks across brain regions•Identifies many novel hub genes that emerge in susceptible mice•In vivo validation of key regulators at molecular, synaptic, and behavioral levels
Molecular mechanisms of dysregulated circuit function in depression are poorly understood. Employing integrative network analysis of large-scale RNA sequencing data, Bagot et al. identify distinct inter-regional transcriptional networks regulating depression susceptibility versus resilience. In vivo validation of networks suggests novel antidepressant targets.
Early life stress increases risk for depression. Here we establish a “two-hit” stress model in mice wherein stress at a specific postnatal period increases susceptibility to adult social defeat ...stress and causes long-lasting transcriptional alterations that prime the ventral tegmental area (VTA)—a brain reward region—to be in a depression-like state. We identify a role for the developmental transcription factor orthodenticle homeobox 2 (Otx2) as an upstream mediator of these enduring effects. Transient juvenile—but not adult—knockdown of Otx2 in VTA mimics early life stress by increasing stress susceptibility, whereas its overexpression reverses the effects of early life stress. This work establishes a mechanism by which early life stress encodes lifelong susceptibility to stress via long-lasting transcriptional programming in VTA mediated by Otx2.
Abuse, neglect, and other forms of early life stress (ELS) significantly increase risk for psychiatric disorders including depression. In this study, we show that ELS in a postnatal sensitive period ...increases sensitivity to adult stress in female mice, consistent with our earlier findings in male mice. We used RNA-sequencing in the ventral tegmental area, nucleus accumbens, and prefrontal cortex of male and female mice to show that adult stress is distinctly represented in the brain's transcriptome depending on ELS history. We identify: 1) biological pathways disrupted after ELS and associated with increased behavioral stress sensitivity, 2) putative transcriptional regulators of the effect of ELS on adult stress response, and 3) subsets of primed genes specifically associated with latent behavioral changes. We also provide transcriptomic evidence that ELS increases sensitivity to future stress through enhancement of known programs of cortical plasticity.
Dendritic spines are the sites of most excitatory synapses in the CNS, and opposing alterations in the synaptic structure of medium spiny neurons (MSNs) of the nucleus accumbens (NAc), a primary ...brain reward region, are seen at early versus late time points after cocaine administration. Here we investigate the time-dependent molecular and biochemical processes that regulate this bidirectional synaptic structural plasticity of NAc MSNs and associated changes in cocaine reward in response to chronic cocaine exposure. Our findings reveal key roles for the bidirectional synaptic expression of the Rap1b small GTPase and an associated local synaptic protein translation network in this process. The transcriptional mechanisms and pathway-specific inputs to NAc that regulate Rap1b expression are also characterized. Collectively, these findings provide a precise mechanism by which nuclear to synaptic interactions induce “metaplasticity” in NAc MSNs, and we reveal the specific effects of this plasticity on reward behavior in a brain circuit-specific manner.
•Cocaine bidirectionally alters a synaptic Rap1b signaling pathway•Altered Rap1b signaling controls the rewarding effects of cocaine•Bidirectional alterations in Rap1b regulate dendritic spine metaplasticity•A specific neural circuit controls synaptic Rap1b signaling and reward
Nucleus accumbens neurons undergo synaptic structural changes at early versus longer times after chronic cocaine exposure. Cahill et al. reveal a mechanism by which cocaine induces this form of “metaplasticity” and delineate the effects of this plasticity on reward behavior in a circuit-specific manner.
Cocaine-associated memories are persistent, but, on retrieval, become temporarily destabilized and vulnerable to disruptions, followed by reconsolidation. To explore the synaptic underpinnings for ...these memory dynamics, we studied AMPA receptor (AMPAR)-silent excitatory synapses, which are generated in the nucleus accumbens by cocaine self-administration, and subsequently mature after prolonged withdrawal by recruiting AMPARs, echoing acquisition and consolidation of cocaine memories. We show that, on memory retrieval after prolonged withdrawal, the matured silent synapses become AMPAR-silent again, followed by re-maturation ~6 h later, defining the onset and termination of a destabilization window of cocaine memories. These synaptic dynamics are timed by Rac1, with decreased and increased Rac1 activities opening and closing, respectively, the silent synapse-mediated destabilization window. Preventing silent synapse re-maturation within the destabilization window decreases cue-induced cocaine seeking. Thus, cocaine-generated silent synapses constitute a discrete synaptic ensemble dictating the dynamics of cocaine-associated memories and can be targeted for memory disruption.
Global changes in gene expression underlying circuit and behavioral dysregulation associated with cocaine addiction remain incompletely understood. Here, we show how a history of cocaine ...self-administration (SA) reprograms transcriptome-wide responses throughout the brain’s reward circuitry at baseline and in response to context and/or cocaine re-exposure after prolonged withdrawal (WD).
We assigned male mice to one of six groups: saline/cocaine SA + 24-hour WD or saline/cocaine SA + 30-day WD + an acute saline/cocaine challenge within the previous drug-paired context. RNA sequencing was conducted on six interconnected brain reward regions. Using pattern analysis of gene expression and factor analysis of behavior, we identified genes that are strongly associated with addiction-related behaviors and uniquely altered by a history of cocaine SA. We then identified potential upstream regulators of these genes.
We focused on three patterns of gene expression that reflect responses to 1) acute cocaine, 2) context re-exposure, and 3) drug + context re-exposure. These patterns revealed region-specific regulation of gene expression. Further analysis revealed that each of these gene expression patterns correlated with an addiction index—a composite score of several addiction-like behaviors during cocaine SA—in a region-specific manner. Cyclic adenosine monophosphate response element binding protein and nuclear receptor families were identified as key upstream regulators of genes associated with such behaviors.
This comprehensive picture of transcriptome-wide regulation in the brain’s reward circuitry by cocaine SA and prolonged WD provides new insight into the molecular basis of cocaine addiction, which will guide future studies of the key molecular pathways involved.
Abstract Background Examining transcriptional regulation by antidepressants in key neural circuits implicated in depression, and understanding the relationship to transcriptional mechanisms of ...susceptibility and natural resilience, may help in the search for new therapeutics. Given the heterogeneity of treatment response in human populations, examining both treatment response and non-response is critical. Methods We compared the effects of a conventional monoamine-based tricyclic antidepressant, imipramine, and a rapidly acting, non-monoamine-based antidepressant, ketamine, in mice subjected to chronic social defeat stress, a validated depression model, and used RNA-sequencing to analyze transcriptional profiles associated with susceptibility, resilience and antidepressant response and non-response in prefrontal cortex (PFC), nucleus accumbens, hippocampus, and amygdala. Results We identified similar numbers of responders and non-responders following ketamine or imipramine treatment. Ketamine induced more expression changes in hippocampus; imipramine induced more expression changes in nucleus accumbens and amygdala. Transcriptional profiles in treatment responders were most similar in PFC. Non-response reflected both the lack of response-associated gene expression changes and unique gene regulation. In responders, both drugs reversed susceptibility-associated transcriptional changes as well as induced resilience-associated transcription in PFC. Conclusions We generated a uniquely large resource of gene expression data in four inter-connected limbic brain regions implicated in depression and its treatment with imipramine or ketamine. Our analyses highlight the PFC as a key site of common transcriptional regulation by both antidepressant drugs and in both reversing susceptibility- and inducing resilience-associated molecular adaptations. In addition, we found region-specific effects of each drug suggesting both common and unique effects of imipramine versus ketamine.
Highlights • We highlight evidence that histone modifications play a key role in drug addiction. • Drugs of abuse increase active histone marks and decrease repressive histone marks. • Drugs of abuse ...alter expression of ‘writers’ and ‘erasers’ of histone modifications. • Manipulating ‘writers’ and ‘erasers’ alters drug-induced behaviors. • Future studies must focus on other histone modifications and their interactions.
Sex differences in addiction have been described in humans and animal models. A key factor that influences addiction in both males and females is adolescent experience. Adolescence is associated with ...higher vulnerability to substance use disorders, and male rodents subjected to adolescent social isolation (SI) stress form stronger preferences for drugs of abuse in adulthood. However, little is known about how females respond to SI, and few studies have investigated the transcriptional changes induced by SI in the brain’s reward circuitry.
We tested the hypothesis that SI alters the transcriptome in a persistent and sex-specific manner in prefrontal cortex, nucleus accumbens, and ventral tegmental area. Mice were isolated or group housed from postnatal day P22 to P42, then group housed until ∼P90. Transcriptome-wide changes were investigated by RNA sequencing after acute or chronic cocaine or saline administration.
We found that SI disrupts sex-specific transcriptional responses to cocaine and reduces sex differences in gene expression across all three brain regions. Furthermore, SI induces gene expression profiles in males that more closely resemble group-housed females, suggesting that SI “feminizes” the male transcriptome. Coexpression analysis reveals that such disruption of sex differences in gene expression alters sex-specific gene networks and identifies potential sex-specific key drivers of these transcriptional changes.
Together, these data show that SI has region-specific effects on sex-specific transcriptional responses to cocaine and provide a better understanding of reward-associated transcription that differs in males and females.
Major depressive disorder (MDD) is the leading cause of disability worldwide. There is an urgent need for objective biomarkers to diagnose this highly heterogeneous syndrome, assign treatment, and ...evaluate treatment response and prognosis. MicroRNAs (miRNAs) are short non-coding RNAs, which are detected in body fluids that have emerged as potential biomarkers of many disease conditions. The present study explored the potential use of miRNAs as biomarkers for MDD and its treatment. We profiled the expression levels of circulating blood miRNAs from mice that were collected before and after exposure to chronic social defeat stress (CSDS), an extensively validated mouse model used to study depression, as well as after either repeated imipramine or single-dose ketamine treatment. We observed robust differences in blood miRNA signatures between stress-resilient and stress-susceptible mice after an incubation period, but not immediately after exposure to the stress. Furthermore, ketamine treatment was more effective than imipramine at re-establishing baseline miRNA expression levels, but only in mice that responded behaviorally to the drug. We identified the red blood cell-specific miR-144-3p as a candidate biomarker to aid depression diagnosis and predict ketamine treatment response in stress-susceptible mice and MDD patients. Lastly, we demonstrate that systemic knockdown of miR-144-3p, via subcutaneous administration of a specific antagomir, is sufficient to reduce the depression-related phenotype in stress-susceptible mice. RNA-sequencing analysis of blood after such miR-144-3p knockdown revealed a blunted transcriptional stress signature as well. These findings identify miR-144-3p as a novel target for diagnosis of MDD as well as for antidepressant treatment, and enhance our understanding of epigenetic processes associated with depression.
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