The role and mechanism of NORAD in proliferation and apoptosis of mouse mesangial cells induced by high glucose

Abstract

Objective: To uncover the role and mechanism of non-coding RNA-activated by DNA damage (NORAD) in proliferation and apoptosis of mouse mesangial cells induced by high glucose. Methods: SV40-MES-13 cells were divided into high glucose group and low glucose group according to the concentration of glucose in the culture medium. After 24 hours of treatment, SV40-MES-13 cells were transfected with si-NORAD and si-Toll-like receptor (TLR4), and real-time fluorescence quantitative PCR (qRT-PCR) was used to detect the expression of NORAD and TLR4. NORAD, TLR4 overexpression plasmids and small interfering RNA were transfected into SV40-MES-13 cells respectively. Cell counting kit (CCK-8) assay, 5-ethynyl-2'-deoxyuridine (EdU) assay and flow cytometry were performed to determine the results of cell proliferation and apoptosis. Luciferase activity and their mRNA levels were detected after cotransfection of pGL3-NORAD WT and miR-520h mimics or pGL3-TLR4 WT and miR-520h mimics. After cotransfection of si-NORAD and miR-520h inhibitors, TLR4 overexpression plasmids and miR-520h mimics, and cotransfection of si-TLR4 and miR-520h inhibitors, the levels of NORAD, miR-520h and TLR4, as well as cell proliferation were detected to verify the regulatory relationship among them. Results: NORAD and TLR4 were upregulated in SV40-MES-13 cells in high glucose group (1.65±0.08 vs 1.00±0.06, P=0.003; 1.96±0.09 vs 1.01±0.07, P=0.001). Overexpression of NORAD and TLR4 promoted the proliferative ability (1.34±0.04 vs 0.85±0.04, P=0.001; 1.33±0.02 vs 0.82±0.03, P<0.001) and inhibited the apoptosis in SV40-MES-13 cells (0.45±0.03 vs 0.94±0.06, P=0.001; 0.51±0.05 vs 0.99±0.03, P=0.001). The dual-luciferase reporter gene assay showed that miR-520h was confirmed to bind to NORAD and TLR4. The expression of NORAD and miR-520h affected each other, and miR-520h mimics reduced the expression of TLR4. The expression of TLR4 in cotransfected NORAD small interference RNA and miR-520h inhibitor was higher than that in NORAD small interference RNA alone (0.74±0.03 vs 0.55±0.03, P=0.014). Cotransfection of miR-520h mimics and TLR4 overexpression plasmids increased cell proliferation compared with miR-520h mimics alone (0.73±0.01 vs 0.61±0.02, P=0.007). Cotransfection of miR-520h inhibitors and TLR4 small interference RNA reduced cell proliferation compared with miR-520h inhibitors alone (1.31±0.04 vs 1.55±0.04, P=0.013). Conclusions: The regulatory loop NORAD/miR-520h/TLR4 promotes the proliferative ability and inhibits apoptosis in glomerular mesangial cells induced by high glucose.