miR-424 inhibits apoptosis and inflammatory responses induced by sevoflurane through TLR4/MyD88/NF-κB pathway

Side effects of sevoflurane in anterograde and retrograde memory have been widely reported. However, there is no convincing evidence that sevoflurane directly causes the development of neurotoxicity. miR-424 has the potential to regulate the neurotoxicity caused by isoflurane anesthesia, and it has a complementary sequence with the 3'UTR region of TLR4. Thus, our study aims to explore whether sevoflurane directly causes neurotoxicity, the effects of miR-424 on sevoflurane induced apoptosis and inflammation, and the underlying mechanism.

Sevoflurane effects were identified both in mouse and in PC12 cells. Western blots and ELISA were used for protein detection, while micro (mi) RNA expression was measured with RT-qPCR. Dual luciferase reporter assays were employed to study the interaction between miR-424 and Toll-like receptor 4 (TLR4) using miR-424 mimics and TLR4 over-expression.

Sevoflurane stimulated expression of Bax2 and Caspase-3, and increased apoptosis ratio both in vivo and vitro (P < 0.05). Inflammatory cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6, were up-regulated by sevoflurane, while IL-10 was downregulated (P < 0.05). Sevoflurane treatment enhanced the phosphorylation of NF-κB, and up-regulated the expressions of TLR4 and MyD88 (P < 0.05), which demonstrated that sevoflurane inhibited proliferation and differentiation of neuronal cells by activating TLR4/MyD88/NF-κB signaling both in vitro and vivo. However, up-regulation of miR-424 attenuated the negative effects of sevoflurane by targeting the 3'-untranslated region (UTR) of TLR4 and inducing the degradation of mRNA (P < 0.05).

In vitro, sevoflurane induces activation of the endogenous TLR4 signaling pathway, thereby promoting apoptosis and inflammatory cytokine expression. Exogenous TLR4 acts as an agonist to stimulate TLR4 signaling, whereas miR-424 inhibits both endogenous and exogenous TLR4 signaling, thereby preserving proliferation and differentiation of neuronal cells.