CircSmox knockdown alleviates PC12 cell apoptosis and inflammation in spinal cord injury by miR‐340‐5p/Smurf1 axis

BACKGROUND: Spinal cord injury (SCI) is a traumatic central nervous system disorder that leads to irreversible neurological dysfunction. Emerging evidence has shown that differentially expressed circular RNAs (circRNAs) after SCI is closely associated with the pathophysiological process. Herein, the potential function of circRNA spermine oxidase (circSmox) in functional recovery after SCI was investigated. METHODS: Differentiated PC12 cells stimulated with lipopolysaccharide (LPS) were employed as an in vitro model for neurotoxicity research. Levels of genes and proteins were detected by quantitative real‐time PCR and Western blot analysis. Cell viability and apoptosis were determined by CCK‐8 assay and flow cytometry. Western blot analysis was used to detect the protein level of apoptosis‐related markers. The levels of interleukin (IL)‐1β, IL‐6, IL‐8, and tumor necrosis factor (TNF)‐α. Dual‐luciferase reporter, RIP, and pull‐down assays were used to confirm the target relationship between miR‐340‐5p and circSmox or Smurf1 (SMAD Specific E3 Ubiquitin Protein Ligase 1). RESULTS: LPS elevated the levels of circSmox and Smurf1, but decreased the levels of miR‐340‐5p in PC12 cells in a dose‐dependent manner. Functionally, circSmox silencing alleviated LPS‐induced apoptosis and inflammation in PC12 cells in vitro. Mechanistically, circSmox directly sponged miR‐340‐5p, which targeted Smurf1. Rescue experiments showed that miR‐340‐5p inhibition attenuated the neuroprotective effect of circSmox siRNA in PC12 cells. Moreover, miR‐340‐5p suppressed LPS‐triggered neurotoxicity in PC12 cells, which was reversed by Smurf1 overexpression. CONCLUSION: CircSmox enhances LPS‐induced apoptosis and inflammation via miR‐340‐5p/Smurf1 axis, providing an exciting view of the potential involvement of circSmox in SCI pathogenesis.