Ciliary IFT88 inhibits intervertebral disc degeneration under excessive mechanical stress by regulating endplate cartilage calcification.

Abstract

INTRODUCTION: Endplate cartilage is crucial for nutrient transport to intervertebral disc (IVD), and its calcification due to abnormal mechanical stress significantly contributes to intervertebral disc degeneration (IDD). Primary cilia, which sense mechanical stimuli, are key to this process. Intraflagellar Transport 88 (IFT88) regulates endplate calcification under mechanical stress, but its specific mechanisms remain inadequately characterized. OBJECTIVES: We aimed to elucidate the role and regulatory mechanisms of IFT88 in primary cilia in endplate cartilage calcification and IVD. METHODS: Changes in IFT88 expression in endplate cartilage and its response to mechanical stress were assessed using histochemical staining, Western blotting, immunofluorescence, and transmission electron microscopy. The relationship between abnormal stress and calcium ions was explored through RNA sequencing, qPCR, and calcium staining. In vitro studies investigated the regulatory mechanisms of IFT88 in chondrocytes subjected to abnormal stress using molecular docking, co-immunoprecipitation, dual-luciferase assays, and flow cytometry. Rats tail crush model confirmed the role of IFT88 in chondral calcification and IDD as a potential therapeutic target. RESULTS: As intervertebral disc degeneration progresses, IFT88 expression in the primary cilia of cartilage endplate cells decreased. Under normal stress conditions, IFT88 levels increased with the intensity and duration of stress; however, excessively high stress triggered mechanisms that led to cilia depletion. Elevated intracellular calcium concentrations under tensile stress contributed to endplate calcification and IDD. Additionally, IFT88 negatively regulated its positive transcription factor C/EBPα under abnormal stress, potentially contributing to cilia depletion. IFT88 also inhibited the hyperactivation of transient receptor potential vanilloid 4 (TRPV4), reducing calcium influx and alleviating oxidative stress and Wnt pathway activation. In vivo studies showed that overexpressing IFT88 maintains disc height and structural integrity while reducing endplate ossification. CONCLUSION: Our study demonstrates that IFT88 inhibits TRPV4, thereby protecting endplate cartilage and positioning IFT88 as a promising therapeutic target for IDD and endplate calcification.