The circular RNA landscape of human dorsal root ganglia and its association with opioid exposure

Opioids are among the most widely prescribed treatments for pain; however, prolonged use leads to adverse effects, including reduced analgesic efficacy (tolerance) and paradoxically heightened pain sensitivity (opioid-induced hyperalgesia, OIH). Neurons that detect noxious stimuli within the dorsal root ganglion (DRG), referred to as nociceptors, mediate both the beneficial and maladaptive effects of opioids. Although post-transcriptional regulation is critical for DRG function, the role of circular RNAs (circRNAs)--an evolutionarily conserved and highly stable class of RNA--in nociceptive processes remains largely unexplored in humans. Further, how opioids might alter the circRNA landscape of human DRG (hDRG) is unknown. To address this gap, we performed high-coverage RNA sequencing on hDRG tissue obtained from opioid-positive organ donors and compared these profiles with those from age- and sex-matched opioid-negative controls. The circRNA expression profiles were analyzed using the CIRI2/CIRIquant pipeline, and parallel measurements were made for the linear transcriptome (e.g. mRNA). Our data revealed a significant overall decrease in circRNA abundance in the opioid-exposed group. Among the top differentially expressed circRNAs (FDR [≤] 0.05) were circSH3D19, circSMARCA5, circHLA-A, and circAMY2B, with an additional 39 circRNAs (p [≤] 0.005) altered in opioid-exposed tissue. To explore potential interactions with the linear transcriptome, we constructed a competing endogenous RNA (ceRNA) network using established pipelines and databases (circAtlas, miRanda, TargetScan, PITA, and miRDB). Gene Ontology enrichment analysis of predicted mRNA targets of these circRNAs identified overrepresented pathways related to neuronal development, synaptic signaling, inflammatory processes, and pain perception. These findings suggest that circRNAs may play a key regulatory role in the DRGs response to opioid exposure and modulation of pain. Future studies will investigate the spatial and temporal dynamics and functional and behavioral effects of these circRNA.