LincRNA-SLC20A1 (SLC20A1) promotes extracellular matrix degradation in nucleus pulposus cells in human intervertebral disc degeneration by targeting the miR-31-5p/MMP3 axis.

Long non-coding RNAs (lncRNAs) are novel players in intervertebral disc degeneration (IDD) and show multiple functions. LncRNA lincRNA-SLC20A1 (SLC20A1) is aberrantly expressed in IDD. However, the role of SLC20A1 in degenerative nucleus pulposus (NP) cells and its underlying mechanism are unclear. The expressions of SLC20A1, miR-31-5p, and MMP3 were determined using RT-qPCR and western blotting. Extracellular matrix (ECM) degradation was evaluated by ECM-related genes collagen II, aggrecan, and ADAMTS4 using western blotting and an enzyme-linked immunosorbent assay (ELISA). The target binding between miR-31-5p and SLC20A1 or matrix metalloproteinase (MMP3) was predicted based on the miRcode or starBase websites and confirmed using a luciferase reporter assay and an RNA pull-down assay. SLC20A1 expression is upregulated in NP tissues from IDD patients, and this expression promotes ADAMTS5 expression and represses collagen II and aggrecan expression in degenerative NP cells derived from IDD patients. Mechanically, SLC20A1 acts as a competing endogenous RNA (ceRNA) to negatively regulate miRNA-31-5p (miR-31-5p) expression. Moreover, MMP3 is a downstream target for miR-31-5p and is positively modulated by SLC20A1 in degenerative NP cells. Similar to the SLC20A1 effect in human NP cells, the downregulation of miR-31-5p facilitates ECM degradation as well. On the contrary, miR-31-5p upregulation abolishes the promoting role of SLC20A1 in degenerative NP cells, the effect of which is then blocked by the ectopic expression of MMP3. The upregulation of SLC20A1 aggravates ECM degradation in degenerative human NP cells by targeting the miR-31-5p/MMP3 axis, suggesting that the SLC20A1/miR-31-5p/MMP3 pathway can contribute to IDD progression.