Curculigoside upregulates BMAL1 to decrease nucleus pulposus cell apoptosis by inhibiting the JAK/STAT3 pathway

BACKGROUND: Intervertebral disc degeneration (IVDD) is a natural process that occurs with aging and is the main cause of low back pain. Basic helix-loop-helix ARNT-like 1 (BMAL1) plays key roles in the pathogenesis of many diseases. The present study investigates the role of curculigoside (CUR), which has been reported to be a potential anti-apoptotic compound in other diseases. METHODS: Dysregulated genes were identified by RNA sequencing (RNA-seq). Western blotting (WB), immunohistochemistry, immunofluorescence (IF) staining, and real-time fluorescent quantitative polymerase chain reaction were used to detect BMAL1 expression in 25 human intervertebral disc specimens (male: female =13:12), tissues from BMAL1-knockout mice and from an IVDD mouse model. The regulatory effects of CUR and BMAL1 in nucleus pulposus (NP) cells after Small Interfering RNA (siRNA) transfection were examined by flow cytometry, IF staining and WB. The therapeutic effect of intraperitoneal CUR injection was also evaluated in mice. RESULTS: BMAL1 expression was negatively correlated with IVDD severity and was significantly lower in degenerative NP cells. After BMAL1 knockdown using siRNA, the apoptosis rate of degenerative NP cells was significantly higher, while transfection with a lentivirus overexpressing BMAL1 exerted the opposite effect. Bioinformatics analysis revealed that BMAL1 is regulated by the JAK-STAT3 pathway, and CUR upregulated BMAL1 expression by inhibiting STAT3 phosphorylation, subsequently alleviating NP cell apoptosis and increasing extracellular matrix (ECM) components., thus alleviating IVDD. CONCLUSIONS: CUR can inhibit apoptosis and improve the ECM by upregulating BMAL1 expression, which is reduced in IVDD. This study provides a therapeutic strategy to alleviate apoptosis associated with inflammation-induced IVDD.