CircUSP36 knockdown alleviates oxidized low-density lipoprotein-induced cell injury and inflammatory responses in human umbilical vein endothelial cells via the miR-20a-5p/ROCK2 axis

The dysfunctions of human umbilical vein endothelial cells (HUVECs) are important features of atherosclerosis (AS). Circular RNAs (circRNAs) are regulators of a wide range of human diseases, including AS. The present study aimed to investigate the role of circUSP36 in the ectopic phenotype of HUVECs and to provide evidence of the involvement of circUSP36 in the pathogenesis of AS. AS cell models in vitro were established using HUVECs exposed to oxidized low-density lipoprotein (ox-LDL). Cell viability, cell cycle progression and apoptosis, and cell migration and invasion were assessed by cell counting kit-8 (CCK-8) assay, flow cytometric assay and Transwell assay, respectively. The expression levels or releases of pro-inflammatory factors were detected by western blot analysis or enzyme-linked immunosorbent assay (ELISA). The mRNA expression of circUSP36, miR-20a-5p and Rho-associated coiled-coil kinase 2 (ROCK2) was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and the protein level of ROCK2 was detected by western blot analysis. The targeted association between miR-20a-5p and circUSP36 or ROCK2 was verified by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. The results revealed that circUSP36 was highly expressed in ox-LDL-exposed HUVECs. CircUSP36 knockdown attenuated ox-LDL-induced cell cycle arrest, cell apoptosis and inflammatory responses, and promoted cell migration and invasion which had been blocked by ox-LDL. miR-20a-5p was found to be a target of circUSP36, and miR-20a-5p inhibition reversed the effects of circUSP36 knockdown. Moreover, miR-20a-5p directly bound to ROCK2, and miR-20a-5p inhibition aggravated ox-LDL-induced injury by increasing the ROCK2 level. More importantly, circUSP36 targeted miR-20a-5p to regulate the expression of ROCK2. On the whole, the present study demonstrates that, circUSP36 regulates ox-LDL-induced HUVEC injury and inflammation by modulating ROCK2 via competitively targeting miR-20a-5p.