Identification and characterization of N6-methyladenosine circular RNAs in the spinal cord of morphine-tolerant rats.

Morphine tolerance (MT) is a tricky problem, the mechanism of it is currently unknown. Circular RNAs (circRNAs) serve significant functions in the biological processes (BPs) of the central nervous system. N6-methyladenosine (mA), as a key post-transcriptional modification of RNA, can regulate the metabolism and functions of circRNAs. Here we explore the patterns of mA-methylation of circRNAs in the spinal cord of morphine-tolerant rats. In brief, we constructed a morphine-tolerant rat model, performed mA epitranscriptomic microarray using RNA samples collected from the spinal cords of morphine-tolerant rats and normal saline rats, and implemented the bioinformatics analysis. In the spinal cord of morphine-tolerant rats, 120 circRNAs with different mA modifications were identified, 54 of which were hypermethylated and 66 of which were hypomethylated. Functional analysis of these mA circRNAs found some important pathways involved in the pathogenesis of MT, such as the calcium signaling pathway. In the mA circRNA-miRNA networks, several critical miRNAs that participated in the occurrence and development of MT were discovered to bind to these mA circRNAs, such as miR-873a-5p, miR-103-1-5p, miR-107-5p. MA modification of circRNAs may be involved in the pathogenesis of MT. These findings may lead to new insights into the epigenetic etiology and pathology of MT.