Circ-HACE1 Aggravates Cigarette Smoke Extract-Induced Injury in Human Bronchial Epithelial Cells via Regulating Toll-Like Receptor 4 by Sponging miR-485-3p.

Background: Smoking is the most common cause of chronic obstructive pulmonary disease (COPD), and the early diagnosis for COPD remains poor. Exploring the molecular mechanism and finding feasible biomarkers will be beneficial for clinical management of COPD. Circular RNAs (circRNAs) are noncoding RNAs that act as miRNA sponges to regulate the expression levels of genes, leading to the changes of cellular phenotypes and disease progression. CircRNA HECT domain and ankyrin repeat containing E3 ubiquitin protein ligase 1 (circ-HACE1) was abnormally expressed after the induction of cigarette smoke extract (CSE) in cell model. This study was performed to explore its function and mechanism in COPD.

Methods: Circ-HACE1, microRNA-485-3p (miR-485-3p) and toll-like receptor 4 (TLR4) detection was performed by quantitative real-time polymerase chain reaction (qRT-PCR). Cell viability and apoptosis/cell cycle were respectively examined using cell counting kit-8 (CCK-8) and flow cytometry. Inflammatory cytokines were determined by enzyme-linked immunosorbent assay (ELISA). Oxidative stress was evaluated through the measurement of malondialdehyde (MDA) and superoxide dismutase (SOD). The target binding analysis was conducted via dual-luciferase reporter assay. Western blot was employed for protein expression detection of TLR4.

Results: Circ-HACE1 was overexpressed in smokers or smokers with COPD and CSE upregulated circ-HACE1 expression in 16HBE cells. Knockdown of circ-HACE1 attenuated CSE-stimulated cell viability and cell cycle repression, as well as the enhancement of cell apoptosis, inflammatory response and oxidative stress. MiR-485-3p was a target of circ-HACE1. Circ-HACE1 regulated CSE-induced cell injury via targeting miR-485-3p. TLR4 was a downstream target of miR-485-3p, and miR-485-3p inhibited the CSE-induced cell damages by directly downregulating the level of TLR4. Circ-HACE1/miR-485-3p regulated TLR4 expression in CSE-treated 16HBE cells, and TLR4 overexpression also reversed all effects of si-circ-HACE1 on CSE-treated 16HBE cells.

Conclusion: These findings elucidated that circ-HACE1 contributed to the CSE-induced cell damages in COPD cell models via regulating TLR4 by acting as the sponge of miR-485-3p.