Abstract: Several lines of evidence indicate that microRNAs (miRNAs) modulate tolerance to the analgesic effects of morphine via regulation of pain-related genes, making dysregulation of miRNA levels a clinical target for controlling opioid tolerance. However, the precise mechanisms by which miRNAs regulate opioid tolerance are unclear. In the present study, we noted that the miR-375 level was downregulated but the expression of Janus kinase 2 (JAK2) was upregulated in mouse dorsal root ganglia (DRG) following chronic morphine treatment. The miR-375 levels and JAK2 expression were correlated with the progression of morphine tolerance, and upregulation of miR-375 level could significantly hinder morphine tolerance. This was ameliorated by JAK2 knockdown. Prolonged morphine exposure induced the expression of brain-derived neurotrophic factor (BDNF) in a time-dependent manner in the DRG. This was regulated by the miR-375 and JAK2–signal transducer and activator of transcription 3 (STAT3) pathway, and inhibition of this pathway decreased BDNF production, and thus, attenuated morphine tolerance. More importantly, we found that miR-375 could target JAK2 and increase BDNF expression in a JAK2/STAT3 pathway-dependent manner.
Keywords: morphine tolerance, miR-375, JAK2, BDNF