MicroRNA-494 inhibition protects nucleus pulposus cells from TNF-α-induced apoptosis by targeting JunD

• TNF-α successfully induced HNPCs apoptosis, established cell apoptosis model.
• miR-494 was strongly upregulated in NP cells after TNF-α treatment.
• Inhibition of miR-494 reversed TNF-α induced apoptosis.
• JunD may be targeted and regulated by miRNA-494.
• The use of miRNAs or inhibitors as therapeutic strategy is showing great promise.

BackgroundHuman nucleus pulposus cell (HNPC) apoptosis plays an important role in the development of intervertebral disc degeneration (IVDD). Our previous research revealed that among all of the dysregulated microRNAs in the degenerated nucleus pulposus tissues of patient with IVDD, miRNA-494 (miR-494) is the most significantly increased. However, the influence of miR-494 HNPC apoptosis has not been confirmed.ObjectiveThis study was designed to evaluate the effect of miR-494 on the HNPC apoptosis induced by TNF-α and to explore the possible mechanism of this process.MethodsFirst, HNPCs were stimulated with TNF-α at different concentrations (0 ng/ml, 10 ng/ml, 50 ng/ml, or 100 ng/ml) for 0 h, 8 h, 16 h, or 24 h. Annexin V-PE/7-AAD assays and real-time quantitative PCR were used to detect the cell apoptosis rates and miR-494 expression. Second, we successfully knocked down endogenous miR-494 in HNPCs via lentiviral antigomiR-494 vector infection and then stimulated with TNF-α (100 ng/ml, 16 h). The rates of apoptosis and miR-494 expression were then detected again. Additionally, a dual-luciferase reporter assay and western blotting were used to determine whether JunD is a target of miR-494. Finally, western blotting was used to analyze the expression of cytochrome C.ResultsWe found that the rate of apoptosis increased with concentration, time (p < 0.05) and miR-494 expression (p < 0.05). The rate of apoptosis in the 100 ng/ml, 16 h group appeared to be suitable. After transfection, the apoptosis rate and miR-494 expression were significantly decreased in the antigomiR-494+TNF-α group compared to the controls (p < 0.05). We also revealed that JunD is a target of miR-494. Western blotting analysis demonstrated that treatment with the lentiviral antigomiR-494 vector resulted in increased expression of JunD (p < 0.05) and decreased expression of cytochrome C (p < 0.05).ConclusionThese results indicated that miR-494 is a novel regulator of HNPC apoptosis induced by TNF-α. The knock-out of miR-494 expression protected the HNPCs from apoptosis via the up-regulation of JunD, which was possibly mediated via cytochrome C apoptotic signaling. These findings suggest that the miR-494/JunD signaling pathway might represent a novel therapeutic target for the prevention of IVDD.