Epigenetic mechanisms of sustained transcription across cocaine abstinence

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PROJECT SUMMARY Cocaine addiction is characterized by compulsive drug seeking and high vulnerability to relapse even after prolonged abstinence. A major focus of the field of addiction research has therefore been to identify stable, cocaine-induced neuroadaptations occurring in brain reward circuits. Transcriptional changes are known to persist throughout abstinence, yet the underlying molecular mechanisms of such persistence remain elusive. We recently discovered that the transcription factor, Nr4a1 (nuclear receptor subfamily 4) represses cocaine reward and seeking behavior. Our preliminary data show that Nr4a1 is a central regulator of cocaine-induced transcription, including target gene expression in late abstinence. The significance of this study is strengthened by the utility of therapeutic agents that regulate Nr4a1 and block mouse cocaine self-administration, underscoring the enormous potential of this basic research program in combating drug addiction. Given that histone posttranslational modifications (hPTMs) confer long-lasting changes in gene expression necessary for stable cellular phenotypes, histone modifications acquired during abstinence may explain how individual genes “remember” prior drug exposure. We have previously found that Nr4a1 regulates hPTMs at individual target genes at late abstinence. This proposal aims to define the mechanism(s) of persistent gene expression in the nucleus accumbens (NAc) of male and female mice following volitional cocaine self-administration. We apply novel methods for cell-type specific quantification of both chromatin and gene expression in a single sample. We then validate the causal mechanism of Nr4a1 action using epigenetic editing in vivo. At the conclusion of this study we will have defined the cell-type specific mechanism by which Nr4a1 regulates stable gene expression across cocaine abstinence. Beyond this, we will apply machine learning to identify novel regulators of persistent gene expression relevant to cocaine addiction.