Circular RNA circ_0003420 mediates inflammation in sepsis-induced liver damage by downregulating neuronal PAS domain protein 4.

ABSTRACT

OBJECTIVE: Our aim was to investigate whether circular RNA (circRNA) circ_0003420 mediates inflammation in sepsis-induced liver damage and to determine the mechanism involved. MATERIALS AND METHODS: Liver tissue samples from patients with sepsis and healthy subjects were used to identify differentially expressed circRNAs. Additionally, Kupffer cells were treated with lipopolysaccharide (LPS) to establish an in vitro model of sepsis-induced liver damage. Cell viability and proliferation were measured with a cell counting kit-8 and 5-ethynyl-2'-deoxyuridine (EdU) labeling, respectively. Relative mRNA and protein levels of IL-6, IL-1ß, tumor necrosis factor (TNF)-α, and neuronal PAS domain protein 4 (NPAS4) were determined via reverse-transcription quantitative PCR and western blotting, respectively. RESULTS: We observed circ_0003420 upregulation accompanied by NPAS4 downregulation in liver samples from patients with sepsis-associated damage and in Kupffer cells treated with LPS. Results of in vitro experiments indicated that LPS treatment reduced cell viability and induced well-pronounced apoptosis and inflammatory signs. Circ_0003420 silencing counteracted LPS's influence on cell proliferation, apoptosis, and inflammation signs. Bioinformatics and a dual-luciferase reporter assay revealed that circ_0003420 targets NPAS4 mRNA and negatively correlates with NPAS4 expression. Moreover, NPAS4 knockdown recovered the apoptosis rate and expression levels of inflammatory cytokines in the LPS-treated circ_0003420 knockdown cells, whereas NPAS4 overexpression had similar effects on Kupffer cell properties as circ_0003420 silencing. CONCLUSION: We demonstrate that circ_0003420 targets NPAS4 mRNA thereby mediating the cell damage and inflammation caused by LPS. This study provides a possible target for treatment of liver damage induced by sepsis.