Targeting Endogenous Homeostatic Mechanisms For The Treatment Of Cocaine Use Disorder: Contribution Of Nr4a1 And Target Gene Expression
Cocaine use disorder continues to be a worldwide public health problem and currently there are no approved medications for its treatment. Decades of research have identified a number of targets that have largely been ineffective in reducing relapse. Drug- and cue-associated memories are important components of relapse that remain relatively unexplored. Given that chromatin modifications confer long-lasting changes in gene expression necessary for stable cellular phenotypes, histone modifications acquired during abstinence may cause individual genes to “remember” prior drug exposure. Additional research on the homeostatic mechanisms active during prolonged abstinence is required to develop novel pharmacotherapies that reduce context-dependent drug memories. In this dissertation, we address this gap in knowledge using our established cocaine self-administration model which induces long-lasting changes in gene expression and chromatin. First, we profiled gene expression at early and late abstinence across several different brain reward regions, including the nucleus accumbens (NAc), ventral tegmental area (VTA), and prefrontal cortex (PFC). We found that the transcription factor, nuclear receptor subfamily 4 group A member 1 (Nr4a1), is activated during early abstinence but declines at late abstinence. Nr4a1 target genes were differentially expressed at both early and late abstinence. Therefore, we asked if Nr4a1 mediates transient and sustained changes in gene transcription via the enrichment of permissive and repressive histone modifications associated with Nr4a1 binding at target genes. Using clustered regularly interspaced short palindromic repeats (CRISPR) activation and inactivation (CRISPRa/i), we demonstrated that activation of Nr4a1 suppresses cocaine mediated behavior via epigenetic regulation of target genes. Next, we established the utility of Cytosporone B, a pharmacological activator of Nr4a1, in regulating Nr4a1 activation and reducing context-dependent cocaine memories. Finally, to identify the source of Nr4a1 expression, we isolated specific neuronal cell types in the NAc and analyzed gene expression and histone modification enrichment. Then, using cell-type specific CRISPRa we show that Nr4a1 activation in adenosine A2a receptor neurons suppresses context dependent cocaine memories. Together, research from this dissertation describes the role of cell-type specific Nr4a1 in persistent gene activation during abstinence and cocaine reward.