MicroRNA-421 protects against chronic intermittent hypoxia-induced vascular endothelial cell injury by targeting TLR4

Abstract

Purpose: To investigate the role of miR-421 in endothelial cell injury caused by chronic intermittent hypoxia (CIH), and to unravel the mechanism of action.
 Methods: A rat aortic endothelial cell model of CIH was established by 18-h exposure to hypoxic treatment. Cell viability was evaluated by MTT while cell apoptosis was determined by flow cytometry. Cellular reactive oxygen species (ROS) levels were assessed by cellular reactive oxygen species (ROS) assay kit. The mRNA and protein levels were also determined. Sprague Dawley rats were used to establish a rat CIH model over a 6-week hypoxic exposure. The degree of lung and renal injuries in the rats were observed by HE staining.
 Results: MiR-421 was downregulated and toll-like receptor 4 (TLR4) upregulated in CIH cells compared to control cells. Treatment of CIH cells decreased their viability, increased cellular ROS levels, promoted cell apoptosis, and caused changes in protein levels of apoptosis- and inflammation-related genes. However, miR-421 mimics reversed these results caused by CIH treatment. Dual luciferase reporter assay verified that TLR4 was targeted by miR-421. Moreover, TLR4 overexpression suppressed the protective effect of miR-421 on CIH cells. Finally, miR-421 agomiR inhibited CIH-induced TLR4 upregulation in rats. Histopathological examinations confirmed that miR-421 agomiR inhibited CIHinduced injury and collagen deposition in rat lungs and kidneys.
 Conclusion: MiR-421 protects vascular endothelial cells against CIH-induced injury in rats by targeting TLR4, which may provide a biomarker for the diagnosis and treatment of CIH-induced injury.
 Keywords: Obstructive sleep apnea syndrome, MiR-421, TLR4, Chronic intermittent hypoxia, Vascular endothelial cells