The role of DNA breaks and repairs in opioid addiction

Abstract Opioid use disorder is a debilitating disease with a high rate of relapse despite current treatment efforts. Clinical and preclinical studies have found that opioid-induced chronic changes in gene expression underlie neuroplastic alterations within the brain reward circuitry, including in the prefrontal cortex (PFC), which lead to the life-long propensity for relapse. Recent studies highlighted that epigenetic changes orchestrate the opioid abuse-induced transcriptional plasticity. However, the causes for the epigenome changes and consequent transcriptome alterations remain unclear. DNA damage and repair processes play important roles in chromatin integrity relating to proper epigenetic signature and gene expression in cells. Postmitotic neurons are particularly susceptible to DNA damage because of their high metabolic and transcriptional output. DNA breaks trigger the DNA damage repair response, which involves extensive chromatin remodeling to incorporate DNA repair machinery. Therefore, DNA breaks and repairs can progressively alter chromatin structure to alter gene expression patterns in neurons and, ultimately, affect behaviors. Consistent with studies linking DNA damage and opioid addiction, our preliminary data suggest that DNA breaks are increased in the postmortem PFC tissues from individuals with opioid use disorder and from mice that self-administered heroin (a valid animal model for opioid addiction). Additionally, the increase in DNA breaks was accompanied by altered expression of genes that are involved in DNA damage repair. More importantly, experimentally introducing DNA breaks in the PFC potentiated heroin-seeking behavior in mice. Taken together, these preliminary data provide evidence that DNA break and repair processes are linked to opioid addiction. Our goal in this proposal is to identify and characterize the precise role of DNA breaks and repairs in opioid addiction. Using a unique combination of genomic, epigenomic, and translatomic approaches coupled with affinity purification, we will fully characterize heroin-induced neuron-specific (PFC parvalbumin interneurons and pyramidal neurons) alterations in DNA break and repair sites (i.e., the breakome) and the associated changes in chromatin accessibility (i.e., the epigenome) and gene expression (i.e., the translatome). Additionally, using CRISPR/Cas9 genome editing approaches, we will identify whether heroin-induced changes in DNA break and repair sites are directly and causally linked to heroin-induced behavioral plasticity. This proposal will provide a solid foundation for a wide range of future research endeavors addressing the genetic and epigenetic mechanisms that underlie opioid-induced long-term transcriptional maladaptation and ultimately contribute to opioid addiction.