Vitamin D deficiency promotes intervertebral disc degeneration via p38/NCoR2-mediated extracellular matrix degradation.

PURPOSE: Vitamin D (VD) deficiency significantly contributes to intervertebral disc degeneration (IDD), a common cause of low back pain, yet the underlying mechanisms remain unclear. This study investigates how VD deficiency exacerbates IDD and identifies potential therapeutic targets.

METHODS

We used real-time quantitative PCR, immunoblots, immunoprecipitation, liquid chromatography with tandem mass spectrometry analysis, co-immunoprecipitation, and chromatin immunoprecipitation to study gene and protein expressions, protein complex assembly, and transcriptional complex binding. Degeneration of IVDs was assessed via hematoxylin and eosin staining.

RESULTS

Eight members of ADAMTSs (A disintegrin and metalloproteinase with thrombospondin motifs) are enriched in lumbar discs of both VD-deficient and VD receptor (VDR)-knockout (VDR-/-) mice. Sufficient VD suppresses ADAMTS genes through a complex formed by nuclear receptor corepressor 2 (NCoR2) and signal transducer and activator of transcription 6 (STAT6). VD deficiency activates p38 kinase, leading to NCoR2 phosphorylation and subsequent degradation by a Cullin 4-RING (CRL4) E3 ligase, impairing NCoR2's transrepression function and upregulating ADAMTS genes, accelerating extracellular matrix (ECM) degradation in discs. This mechanism is replicated in VDR-deficient cells. In vitro treatments with p38 inhibitor (BIRB-796) and CRL4 inhibitor (KH-4-43) reduce ADAMTS expression, and in vivo application of these inhibitors improves disc integrity in VD-deficient mice.

CONCLUSION

Our findings highlight NCoR2 degradation, mediated by p38 kinase and CRL4 E3 ligase, as crucial in VD deficiency-induced IDD. Targeting this pathway offers promising therapeutic potential to mitigate IDD progression in individuals with VD deficiency or VDR abnormalities.