MicroRNA-488 inhibits neural inflammation and apoptosis in spinal cord injury through restraint on the HMGB1/TLR4/NF-κB signaling pathway.

Abstract

Secondary spinal cord injury (SCI), a reversible pathological change, involves neural inflammation and apoptosis. This study explored how microRNA (miR)-488, an inflammatory regulator as reported affected secondary SCI. In vivo, Wistar rats were clipped on the spinal cord for SCI induction. In vitro, PC-12 cells were treated with lipopolysaccharide (LPS) to induce cell injuries to mimic the environment during the secondary SCI. Cell viability and apoptosis were measured by CCK-8 assay and flow cytometry. The levels of inflammation-related factors (interleukin (IL)-6, IL-1β and tumor necrosis factor (TNF)-α) in the serum and PC-12 cells were determined by ELISA. The expressions of miR-488, high mobility group box 1 (HMGB1), B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), cleaved caspase-3, toll-like receptor 4 (TLR4), phosphorylated (p)-p65 and total-p65 in rat spinal cord or PC-12 cells were analyzed by quantitative reverse transcription PCR or western blot. After SCI induction, rats exhibited low Basso-Beattie-Bresnahan scores, promoted the release of inflammation-related factors and downregulated miR-488. LPS treatment decreased cell viability, enhanced apoptosis and downregulated miR-488. Upregulating miR-488 neutralized LPS-induced releases of inflammation-related factors and expressions of Bax and cleaved caspase-3 and counteracted LPS-induced inhibition on Bcl-2 expression. MiR-488 directly targeted HMGB1 and miR-488 mimic decreased LPS-induced HMGB1 expression. Overexpressing HMGB1 counteracted miR-488 mimic-induced decreases in the expressions of TLR4 and p-p65 and the ratio of p-p65 to Total-p65 in LPS-treated PC-12 cells. MiR-488 inhibited neural inflammation and apoptosis in SCI via its binding with HMGB1-mediated restraint on the TLR4/NF-κB signaling pathway.