Background Postoperative cognitive dysfunction (POCD) is a common complication after surgery and its occurrence is associated with increased morbidity and mortality. However, the pathophysiology of this complication remains largely unknown. Efforts to identify causes of POCD have focused on the hippocampal neuroinflammation. Recently, accumulated evidence indicates that NeurimmiRs, a subset of microRNAs (miRNAs), which modulate both neuronal and immune processes, play an important role in neuroinflammation. However, the impact of NeurimmiRs on POCD has not been investigated. We hypothesized that NeurimmiRs is involved in surgery-induced cognitive impairment in adult mice via mediating hippocampal neuroinflammation. Methods MicroRNA(miR)-181b-5p was found to be downregulated in the hippocampi of mice with POCD using microRNA array, which was also verified in vivo in the mouse model of POCD by Quantitative real-time polymerase chain reaction (qPCR). Subsequently, the expression of miR-181b-5p was measured in lipopolysaccharide (LPS) stimulated BV-2 microglial cells and hippocampal tissues of the mice with POCD. Then, loss of function and overexpression studies were performed by transfection with miR-181b-5p mimic/ inhibitor in cultured BV-2 cell lines and intrahippocampal injection of miR-181b-5p agomir before Surgery/Anesthesia, to identify the role of miR-181b-5p in neuroinflammation and cognitive impairments. QPCR, western blot and ELISA were used to determine the expression of proinflammatory mediators. Immunofluorescence staining was applied to evaluate the activation of microglia. Furthermore, we used bioinformatics analysis and dual-luciferase assay to predict and verify the potential target of miR-181b-5p. Results The results indicated that miR-181b-5p mimic could repress the mRNA and protein expression of proinflammatory mediators, including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and monocyte chemoattractant protein (MCP)-1 in LPS-stimulated BV-2 microglial cells, while the miR-181b-5p inhibitor induced upregulation of the above-mentioned proinflammatory factors. Further bioinformatics analysis showed that miR-181b-5p was predicted to potentially target the 3′-untranslated region (UTR) of TNF-α, and binding sites of miR-181b-5p in the 3′-UTR of TNF-α were identified by dual-luciferase assay. Importantly, injecting miR-181b-5p agomir into the hippocampus of mice before surgery, ameliorated the hippocampus-dependent memory, and was accompanied by downregulation of proinflammatory factors expression and reduced microglial activation in the hippocampus of POCD mice. Conclusions Collectively, these findings suggest that miR-181b-5p attenuates early POCD by suppressing hippocampal neuroinflammation in mice. They also highlight the importance of studying miRNAs in the context of POCD and identify miR-181b-5p as a novel potential therapeutic target for improving POCD.
