Mechanical stress-mediated ferritinophagy aggravates cartilage endplate degeneration via a PIEZO1-NCOA4-ZBP1 axis

Abnormal mechanical stress is closely linked to intervertebral disc degeneration (IVDD). Iron homeostasis disorder occurs in various degenerative diseases, including IVDD. PIEZO1 serves as a mechanosensitive cation channel, involving in multiple physiological and pathological processes; however, its potential association with iron homeostasis and IVDD remain to be elucidated. Here, it is discovered that PIEZO1 accumulates in cartilage endplate (CEP) during IVDD, accompanied by intensive ferritinophagy. Specific activation of PIEZO1 or NCOA4 (nuclear receptor coactivator 4) aggravates CEP degeneration. Conversely, chondrocyte-specific knockout of Piezo1 mitigates CEP degeneration by restoring the labile iron pool and stabilizing the mitochondrial genome. Mechanistically, PIEZO1-mediated nuclear translocation of YAP1 (Yes1 associated transcriptional regulator) enhances NCOA4-dependent ferritinophagy by promoting extracellular CA²⁺ influx under oxidative stress. Moreover, ferritinophagy induces in the accumulation and release of Z-form mitochondrial DNA (Z-mtDNA), resulting in the activation of ZBP1 (Z-DNA binding protein 1), ultimately leading to NFKB-dependent inflammatory cascade. Therapeutically, blocking PIEZO1-mediated calcium influx or suppressing YAP1 activation alleviates ferritinophagy. Additionally, Ncoa4 silencing attenuates Z-mtDNA-ZBP1-NFKB axis-driven IVDD. Collectively, our findings suggest that mechanical overload induces ferritinophagy-dependent CEP degeneration via PIEZO1 activation and subsequent upregulation of the Z-mtDNA-ZBP1-NFKB axis, which might furnish a therapeutic target for IVDD.Abbreviation: AAV: adeno-associated virus; ALP: alkaline phosphatase; ARS: alizarin red S; BV:TV: bone volume:total volume; CAMK2/CaMKII: calcium/Calmodulin dependent protein kinase II; CEP: cartilage endplate; CEPCs: cartilage endplate chondrocytes; ChIP: chromatin immunoprecipitation; CKO: conditional knockout; CsA: cyclosporin A; Co-IP: co-immunoprecipitation; DHI: disc height index; ECM: extracellular matrix; EtBr: ethidium bromide; HIF: hypoxia inducible factor; IVDD: intervertebral disc degeneration; KD: knockdown; LAT: large tumor suppressor kinase; LSI: lumbar spine instability; MDA: malondialdehyde; Mito-ROS: mitochondrial reactive oxygen species; MRI: magnetic resonance imaging; mtDNA: mitochondrial DNA; NCOA4: nuclear receptor coactivator 4; PCBP: poly(rC) binding protein; ROS: reactive oxygen species; RT-qPCR: real-time quantitative reverse transcription; SOFG: safranin O and fast green; WWTR1/TAZ: WW domain containing transcription regulator 1; TEAD1: TEA domain transcription factor 1; TEM: transmission electron microscopy; YAP1: Yes1 associated transcriptional regulator; ZBP1: Z-DNA binding protein 1; Z-DNA: Z-form DNA; Z-mtDNA: Z-form mitochondrial DNA.