MiR-499a-5p suppresses apoptosis of human nucleus pulposus cells and degradation of their extracellular matrix by targeting SOX4

Emerging evidence suggests that microRNAs (miRNAs, miRs) play important roles in the development of intervertebral disc degeneration (IVDD). Nonetheless, the expression level and biological function of miR-499a-5p in IVDD are still unclear. In this study, we found that miR-499a-5p was significantly downregulated in degenerative tissues of the human nucleus pulposus (NP) compared with healthy tissues. Knockdown of miR-499a-5p promoted NP cell (NPC) apoptosis, stimulated caspase activation, enhanced MMP3 and MMP13 expression, and downregulated aggrecan and type II collagen. Furthermore, TNF-alpha-treated NPCs showed increased apoptosis and induced an imbalance between anabolism and catabolism of the extracellular matrix (ECM); these changes were attenuated by miR-499a-5p overexpression. Research into possible mechanisms revealed that miR-499a-5p suppressed the expression of SOX4 both at mRNA and protein levels and directly bound to the 3' untranslated region of SOX4 mRNA. Ectopic expression of SOX4 attenuated the negative effect of miR-499a-5p on NPC apoptosis and the positive effect on ECM synthesis. Taken together, these results indicate that miR-499a-5p may attenuate TNF-alpha-induced NPC apoptosis and an imbalance between anabolism and catabolism of the ECM by downregulating SOX4.