The role of circTMOD3 in regulating LPS-induced acute inflammation and injury in human lung fibroblast WI-38 cells.

Background: Circular RNAs (circRNAs) have been implicated in the molecular etiology of pediatric pneumonia. Here, we investigated the precise action of circRNA tropomodulin 3 (circTMOD3, hsa_circ_0035292) in cell injury and inflammation induced by lipopolysaccharide (LPS). Methods: Cell viability was gauged by Cell Counting Kit-8 (CCK-8) assay. Cell apoptosis and cycle distribution were assessed by flow cytometry. Enzyme-linked immunosorbent assay (ELISA) was used to measure interleukin-6 (IL-6), IL-1β and tumor necrosis factor alpha (TNF-α) production. The levels of circTMOD3, microRNA (miR)-146b-3p, and C-X-C motif chemokine receptor 1 (CXCR1) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. Ribonuclease (RNase) R, Actinomycin D and subcellular localization assays were done to characterize circTMOD3. The direct relationship between miR-146b-3p and circTMOD3 or CXCR1 was confirmed by dual-luciferase reporter assays. Results: Our data showed that LPS induced the expression of circTMOD3 in WI-38 cells. CircTMOD3 was resistant to RNase R and was mainly present in the cytoplasm. Silencing endogenous circTMOD3 alleviated WI-38 cell injury and inflammation triggered by LPS. Mechanistically, circTMOD3 directly targeted miR-146b-3p, and CXCR1 was a direct and functional target of miR-146b-3p. CircTMOD3 regulated LPS-induced cell inflammation and injury by targeting miR-146b-3p, and miR-146b-3p-mediated suppression of CXCR1 impacted LPS-evoked cytotoxicity and inflammation. Furthermore, circTMOD3 functioned as a competing endogenous RNA (ceRNA) for miR-146b-3p to induce CXCR1 expression. Conclusion: Our findings demonstrated the regulation of circTMOD3 in LPS-induced cell injury and inflammation at least partially via miR-146b-3p-independent modulation of CXCR1.