Introduction:
MiR-202-3p is involved in the pathogenesis of intervertebral disc degeneration (IDD) via regulating MMP-1 expression in neuronal precursor cells (NPCs). As an activator of miR-202-3p and KDM6A expression, metformin (MET) may regulate the expression of SOX9 via regulating the methylation status of the SOX9 promoter. However, the role of MET in the treatment of IDD remains to be explored.

Material and methods:
Quantitative real-time PCR was performed to analyze the expression of KDM66, SOX9, MMP-1 and miR-202-3p in NPCs and IDD rabbits. Western blot was carried out to evaluate the expression of KDM6A, SOX9 and MMP-1 protein under different conditions. Bisulfite sequencing PCR was used to analyze the DNA methylation of the SOX9 promoter. Luciferase assay was carried out to explore the inhibitory effect of miR-202-3p upon MMP-1.

Results:
The expression of KDM6A, SOX9 and MMP-1 was abnormal in IDD cells and rabbits, while the MET treatment restored the normal expression of KDM6A, SOX9 and MMP-1 and miR-202-3p. Mechanistically, MET treatment reduced the level of hypermethylation of the SOX9 promoter, thus restoring the expression of SOX9 in IDD cells and rabbits. The elevation in SOX9 expression promoted the expression of miR-202-3p, therefore inhibiting the expression of MMP-1, a downstream target of miR-202-3p.

Conclusions:
In this study, we set up cellular and animal models of IDD and treated them with MET to probe the effect of MET on IDD and the signaling pathway of KDM6A/SOX9/miR-202-3p/MMP-1. Our work provided deep insight into the molecular mechanism underlying the therapeutic role of MET in the treatment of IDD.