Characterization of the circular RNA landscape of human dorsal root ganglia reveals a neurotrophin-related circRNA is modulated by opioid exposure.

Abstract

Opioids are among the most widely prescribed treatments for pain; however, prolonged use leads to adverse effects, including tolerance and opioid-induced hyperalgesia. Neurons that detect noxious stimuli (nociceptors) within the dorsal root ganglion (DRG) are critical for both the analgesic and adverse effects of opioids. Although post-transcriptional RNA control 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. Furthermore, the effect of opioids on the circRNA landscape of human DRG (hDRG) is unknown. To address these gaps, we performed high-coverage total RNA sequencing on hDRG tissue obtained from opioid-exposed donors and compared circRNA and linear transcriptomic profiles to age- and sex-matched controls. Opioid exposure was associated with a global reduction in circRNA abundance, as well as specific alterations in 43 differentially expressed circRNAs. Parallel analysis of linear transcripts (mRNAs) revealed 349 differentially expressed transcripts, including genes involved in neuronal signaling and immune responses. Integrative circRNA-mRNA network analyses suggest that opioid-responsive circRNAs may modulate nociceptor gene expression through miRNA- and RNA-binding protein-binding mechanisms. Among opioid-associated circRNAs, circNTRK2, derived from NTRK2, the tyrosine kinase B receptor gene, was downregulated in both opioid-exposed hDRG tissue and a repeat morphine exposure paradigm in nociceptor-like cell line. Collectively, these findings establish the landscape of circRNAs in hDRG, reveal opioid-associated circRNA dysregulation, and highlight circRNAs as potential modulators of post-transcriptional gene expression in nociceptors.