Upregulation of miR-26b alleviates morphine tolerance by inhibiting BDNF via Wnt/β-catenin pathway in rats

Background: Morphine is a commonly used analgesic drug. However, long-term use of morphine will cause tolerance which limits its clinical application in pain treatment. MicroRNAs (miRNAs) have been reported to be involved in the morphine tolerance, but the underlying mechanism is still poorly understood. Methods: Tail flick test was used to measure the maximum possible effect (MPE). Quantitative real-time PCR was employed to detect miR-26b, BDNF, and Wnt5a expression in rat dorsal root ganglia (DRG). Luciferase report assay was introduced to verify the binding relationship between miR-26b and Wnt5a. BDNF, Wnt5a and β-catenin protein level were tested by western blotting. Results: MiR-26b was down-regulated during the development of morphine tolerance while BDNF was upregulated. Overexpression of miR-26b or BDNF inhibition alleviated morphine tolerance. Wnt5a was directly targeted and inhibited by miR-26b via binding to the 3′-UTR of Wnt5a. The Wnt/β-catenin pathway was active in morphine tolerant rats. Moreover, overexpression of Wnt5a could partially enhance miR-26 mimic-mediated morphine tolerance, while a Wnt5a inhibitor could attenuate the tolerance. Conclusion: The present study demonstrated that miR-26b overexpression alleviated morphine tolerance by inhibiting BDNF via the Wnt/β-catenin pathway in rats, highlighting a promising target for the treatment of morphine tolerance.