Knockdown of circ-UQCRC2 ameliorated lipopolysaccharide-induced injury in MRC-5 cells by the miR-326/PDCD4/NF-κB pathway

Circular RNAs (circRNAs) have been shown as important modulators in the pathogenesis of pediatric pneumonia. In this paper, we focused on the molecular basis of circRNA ubiquinol-cytochrome c reductase core protein 2 (circ-UQCRC2, circ_0038467) in lipopolysaccharide (LPS)-induced cell injury.Quantitative real-time polymerase chain reaction (qRT-PCR) was used to gauge the levels of circ-UQCRC2, microRNA (miR)-326 and programmed cell death 4 (PDCD4) mRNA. PDCD4 protein expression and the activation of the NF-κB signaling pathway were evaluated by western blot. Ribonuclease R (RNase R) assay was performed to assess the stability of circ-UQCRC2. Cell viability and apoptosis were detected by the Cell Counting Kit-8 (CCK-8) and flow cytometry assays, respectively. The levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6 were measured by the enzyme-linked immunosorbent assay (ELISA). Targeted relationship between miR-326 and circ-UQCRC2 or PDCD4 was confirmed by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays.Our data showed the up-regulation of circ-UQCRC2 level in pneumonia serum and LPS-treated MRC-5 cells. The silencing of circ-UQCRC2 attenuated LPS-induced MRC-5 cell injury. Mechanistically, circ-UQCRC2 directly targeted miR-326, and circ-UQCRC2 regulated PDCD4 expression through miR-326. MiR-326 was a downstream effector of circ-UQCRC2 function, and PDCD4 was a functional target of miR-326 in regulating LPS-induced MRC-5 cell injury. Additionally, circ-UQCRC2 knockdown inactivated the NF-κB signaling pathway by regulating the miR-326/PDCD4 axis.Our findings demonstrated a novel regulatory network, the miR-326/PDCD4/NF-κB pathway, for the function of circ-UQCRC2 in LPS-induced cell injury in MRC-5 cells.