Role of Gadd45b in Cocaine-driven Epigenetic and Behavioral Dynamics

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Psychostimulant abuse is a public health crisis that affects millions of individuals in the United States and results in profound economic, social, and individual harm. However, despite rapid increases in overdose deaths linked to stimulant drugs like cocaine, there are still no approved therapeutic options for stimulant abuse disorders. Psychostimulant drugs act through well-defined signaling mechanisms to elevate dopaminergic neurotransmission in the nucleus accumbens (NAc), a key reward-linked brain structure that integrates information from diverse brain regions to directly influence motivated behavior. Further, cocaine causes epigenetic and transcriptional reorganization in medium spiny neurons (MSNs) in the NAc, promoting maladaptive shifts in cell signaling and synaptic function. Our preliminary data indicates that expression of Gadd45b (Growth, arrest, and DNA-damage inducible protein 45b) mRNA is upregulated in the MSNs after both cocaine and dopamine receptor stimulation, and that Gadd45b is required for cocaine-related memory formation. However, although Gadd45b plays a critical role in epigenetic reprogramming and memory formation in other brain regions, the role of Gadd45b in cocaine-related epigenetic, molecular, and behavioral adaptations is not clear. In this proposal, we will test the overarching hypothesis that Gadd45b regulates drug- induced behavioral plasticity by control of activity-dependent DNA demethylation in the NAc. Specific Aim 1 of this proposal will combine bidirectional CRISPR-based manipulations and single-nucleus RNA sequencing to determine how Gadd45b signaling impacts transcriptional responses to cocaine. Specific Aim 2 will use novel Gadd45b tools and genome-wide DNA methylation profiling to identify the molecular interactions that regulate Gadd45b-dependent epigenetic programming in the NAc. Finally, Specific Aim 3 will use cell-specific in vivo Gadd45b manipulations in combination with behavioral assays of cocaine and natural reward to test the hypothesis that Gadd45b enhances the behavioral effects of cocaine. Together, these experiments will identify Gadd45b target genes in the NAc, dissect epigenetic mechanisms by which Gadd45b contributes to cocaine’s epigenetic effects, and define a role for Gadd45b in cocaine-related behavioral plasticity. These studies will reveal fundamental mechanisms by which Gadd45b contributes to psychostimulant response, and will pave the way for future experiments to explore how drugs of abuse engage the epigenome to alter motivated behavior.