HIF-2α induces aggravated intervertebral disc degeneration by activating the IL-6/hepcidin-FPN1 axis and promoting ferroptosis in nucleus pulposus cells

Intervertebral disc degeneration (IVDD) is one of the main causes of spinal diseases and chronic low back pain. Nucleus pulposus (NP) cells are in a hypoxic environment, and their functions may be regulated by the hypoxia-inducible factor (HIF) family. In recent years, ferroptosis has been confirmed to be closely related to IVDD. HIF-2α plays a key role in hypoxic response, but its mechanism of regulating ferroptosis in IVDD remains unclear. This study aims to explore whether HIF-2α promotes ferroptosis of NP cells by activating the IL-6/hepcidin pathway and inhibiting the expression of iron transporter FPN1. Primary nucleus pulposus cells from rats were cultured under normoxic and hypoxic conditions, with RSL3 and TBHP used as ferroptosis inducers. Cell viability was detected by CCK-8 assay. The expressions of HIF-2α, IL-6 and hepcidin were regulated by siRNA and overexpression plasmids. Gene and protein expressions and their interaction were analyzed by RT-qPCR, Western blot, Co-IP and immunofluorescence. A rat tail vertebra needling-induced IVDD model was established, and MRI assessment, histological staining and biochemical index detection were performed. Hypoxia significantly increased the sensitivity of NP cells to RSL3 and TBHP at 6, 12, and 24 h, and upregulated HIF-2α expression at both mRNA and protein levels. HIF-2α overexpression promoted IL-6 transcription and hepcidin expression, while HIF-2α knockdown blocked hypoxia-induced upregulation of IL-6 and hepcidin. Dual-luciferase reporter assay confirmed that HIF-2α directly activated the IL-6 promoter. Co-IP demonstrated direct binding between hepcidin-25 and FPN1. HIF-2α overexpression increased cell death, lipid ROS, Fe²⁺, MDA and 4-HNE levels, and induced mitochondrial shrinkage characteristic of ferroptosis; these effects were reversed by knockdown of IL-6 or hepcidin. In the rat IVDD model, MRI showed that the Sham group had Grade I-II degeneration, while the IVDD group and IVDD+adenovirus vector group exhibited severe degeneration (Grade III-IV). HIF-2α knockdown significantly alleviated degeneration to Grade II-III. HE staining revealed that HIF-2α knockdown reduced NP tissue damage. HIF-2α knockdown also decreased lipid ROS levels, restored FPN1 and GPX4 protein expression, and reduced hepcidin-25, HIF-2α and IL-6 expression in NP tissues. Immunohistochemistry confirmed that HIF-2α knockdown partially restored FPN1 positive expression and reduced HIF-2α, IL-6 and hepcidin signals. HIF-2α in IVDD promotes ferroptosis by activating the IL-6/hepcidin signaling pathway, inhibiting FPN1 expression, and thereby exacerbating intervertebral disc degeneration. Targeting this pathway may offer a new therapeutic strategy for IVDD.