MiR-140-5p inhibits morphine tolerance in rats by targeting TLR4

Purpose: To determine the influence of miR-140-5p on morphine tolerance in rats. Methods: Sprague-Dawley (SD) rats were randomly divided into morphine tolerance (MT) and saline control (NS) groups, respectively. Rats in MT group were injected with 10 mu L (10 mu g) morphine twice daily for seven consecutive days while those in NS group were administered the equivalent volume of normal saline. The maximum effect of morphine (MPE) was computed from tail-flick test results. MiR140-5p mimics and toll-like receptor 4 (TLR4) lentivirus were transfected separately or co-transfected into model rats. MiR-140-5p and TLR4 expression were determined by quantitative real-time polymerase chain reaction (RT-qPCR) or western blotting. Dual-luciferase reporter assay was used to verify the target relationship between miR-140-5p and TLR4. Results: The expression of miR-140-5p was decreased, while the expression of TLR4 increased in morphine-tolerant rats (p < 0.05). TLR4 was a target of miR-140-5p. At 24 and 48 h after injection, MPE clearly increased and TLR4 expression was reduced under miR-140-5p overexpression or TLR4 knockdown (p < 0.05). Moreover, there were no significant changes in MPE or levels of TLR4 when miR-140-5p and TLR4 were co-transfected into morphine-tolerant rats. Conclusion: MiR-140-5p inhibits morphine resistance in rats via targeted regulation of TLR4 expression. These provide a theoretical basis for the clinical management of morphine tolerance.