MicroRNA may regulate the content of the brain-derived neurotrophic factor in the frontal cortex of rats after spontaneous morphine withdrawal

Abstract

Brain-derived neurotrophic factor (BDNF) is involved in the formation of dependence on opiates. BDNF mRNA expression is altered during opiate dependence; however, the biological basis of this phenomenon has been insufficiently studied. At the posttranscriptional level, microRNAs may potentially regulate BDNF expression. Short non-coding microRNAs bind in a complementary manner, mostly to the 3'-noncoding area (3'-UTR) of mRNA and thus initiate degradation of a target by the RNA-induced silencing complex (RISC). In the present study, the potential contribution of microRNAs to the regulation of the BDNF mRNA expression was evaluated in the brain of rats with morphine dependence after spontaneous withdrawal. In order to form dependence in rats, morphine was injected twice a day in increasing doses of 10᾿00 mg/kg for 6 days. Expression of BDNF mRNA and microRNA, which may potentially regulate BDNF, was studied in brain regions 40 h after spontaneous morphine withdrawal using the real-time PCR method. Interaction of the Argonaute 2 protein (Ago-2), a component of RISC, with 3'-UTR BDNF mRNA was evaluated using RNA immunoprecipitation. We found that morphine withdrawal was followed by an increase in the BDNF exon I-containing mRNA in the frontal cortex and midbrain. In the frontal cortex, the increased BDNF mRNA level observed in abstinence was associated with a decrease in the miR-206 microRNA and Ago-2 bound to 3'-UTR BDNF mRNA contents. In the midbrain the abstinence condition was accompanied by a decrease in the miR-382 level, whereas Ago-2 binding to 3'-UTR BDNF mRNA remained unchanged. We believe that the weakening of miR-206-mediated degradation of BDNF mRNA may be responsible for the elevated BDNF expression in the frontal cortex in the conditions of morphine dependence.