Transcriptomic Profiling Reveals Mesolimbic Gene Targets Associated with Oxycodone‐Seeking During Abstinence
Authors: Silva Jacqueline , Stocheff Stephanea , Merritt Christina , Routh Andrew , Anastasio Noelle , Cunningham Kathryn 
Published: May 2022

Aims

Over three million Americans suffer from opioid use disorder (OUD), a debilitating neurobiological disease characterized by dysfunctional physical and cognitive states. Despite success for medication‐assisted treatment, 50% of OUD patients exhibit recurring relapse episodes, emphasizing the need to identify novel drug targets to reduce recidivism rates. Individuals seeking to maintain abstinence from opioids are challenged by environmental context(s) and stimuli associated with previous drug use (e.g., paraphernalia). Cellular adaptations within the mesolimbic dopaminergic pathway from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) are important in driving sensitivity to drug‐associated cues and relapse to drug consumption. The present study was designed to identify distinctions within the VTA and NAc transcriptomic landscape that associate with cue‐evoked oxycodone‐seeking during abstinence to identify novel gene targets for future OUD medications development.

Methods

Male, Sprague‐Dawley rats were trained to stably self‐administer oxycodone (0.1 mg/kg/infusion) or saline (n=12/group) and underwent 10 days of abstinence prior to quantification of lever presses for cues previously associated with either oxycodone or saline self‐administration. Immediately following the test session, the VTA and NAc were isolated, and mRNA was processed for poly‐A tail transcriptomic profiling. We employed Poly(A)‐ClickSeq for generating RNAseq libraries adapted to direct the cDNA synthesis specifically toward the 3΄UTR/poly(A) tail junction of cellular RNA. This assay allows sensitive and specific enrichment for poly(A) site junctions without the need for complex sample preparation, fragmentation, or purification. The simple, scalable procedure generates high‐quality RNA‐Seq poly(A) libraries to identify and characterize the frequency and positions of poly(A) sites within the transcriptome. Genes that exhibited a false discovery rate (FDR)‐adjusted p< 0.1 and a fold change ≥ ±1.5 were considered differentially expressed. Ingenuity Pathway Analysis (IPA) was used to identify neurobiological signatures within the VTA and NAc that associate with drug‐seeking during abstinence from oxycodone vs. self‐administration.

Results

Abstinence from oxycodone vs. saline self‐administration associated with a registry of 9,561 candidate gene targets in the VTA, but only 96 candidates in the NAc. IPA analysis identified differentially expressed genes in several biological pathways. Axonal guidance signaling was highly represented in the VTA, and synapse formation pathways were highly represented in the NAc. Excitingly, of the 261 genes represented in the opioid signaling pathway, 29 were differentially expressed in the VTA and eight were differentially expressed in the NAc following abstinence from oxycodone relative to saline self‐administration.

Conclusion

The results of the present study identified unique differences in the transcriptomic landscape of key nodes in the mesolimbic circuitry following abstinence from saline or oxycodone self‐administration. In addition, the shared differentially expressed genes within the opioid signaling pathway (i.e., GNAS) provide prioritized candidates for future pharmacotherapeutics aimed to help maintain abstinence from oxycodone and prevent relapse in OUD.