Circ_0026218 ameliorates oxidized low-density lipoprotein-induced vascular endothelial cell dysfunction by regulating miR-188-3p/TLR4/NF-κB pathway

Background: Circular RNAs (circRNAs) have shown important regulatory roles in cardiovascular diseases, including atherosclerosis (AS). However, the role and mechanism of circ_0026218 in AS remain unclear.

Methods: The cell model of AS in vitro was established by stimulating human umbilical vein endothelial cells (HUVECs) with oxidized low-density lipoprotein (ox-LDL). In addition, circ_0026218, microRNA-188-3p (miR-188-3p), and toll-like receptor 4 (TLR4) expression was determined via real-time quantitative polymerase chain reaction (RT-qPCR) in serum samples from AS patients and healthy volunteers. Cell proliferation was assessed using Cell Counting Kit-8 (CCK-8) assay and 5-ethynyl-2'-deoxyuridine (EdU) assay. Cell apoptosis was measured using flow cytometry. The inflammatory response was assessed using enzyme-linked immunosorbent assay (ELISA). Oxidative stress level was assessed using corresponding kits. Nitric oxide (NO) level was examined using NO detection assay. The interaction between miR-188-3p and circ_0026218 or TLR4 was determined via dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pull-down assays. Exosomes were observed using transmission electron microscopy (TEM). The size distribution of exosomes was analyzed using nanoparticle tracking analysis (NTA).

Results: Ox-LDL treatment caused HUVEC dysfunction by inhibiting cell proliferation and promoting apoptosis, inflammation, and oxidative stress. Circ_0026218 was upregulated in AS serum samples and ox-LDL-treated HUVECs. Knockdown of circ_0026218 attenuated ox-LDL-induced dysfunction in HUVECs. MiR-188-3p acted as a target of circ_0026218, and miR-188-3p downregulation reversed the suppression role of circ_0026218 knockdown on ox-LDL-induced HUVEC disorder. TLR4 was a target of miR-188-3p, and miR-188-3p overexpression alleviated ox-LDL-induced dysfunction in HUVECs by targeting TLR4. Circ_0026218 could deregulate the TLR4/NF-κB pathway by sponging the miR-188-3p. Importantly, circ_0026218 was overexpressed in exosomes from ox-LDL-treated HUVECs and could be delivered via exosomes.

Conclusion: Circ_0026218 knockdown attenuated ox-LDL-induced dysfunction in HUVECs via regulating miR-188-3p/TLR4/NF-κB pathway.