Role of Exosomes from Nucleus Pulposus Cells in Attenuating Intervertebral Disc Degeneration by Inhibiting Nucleus Pulposus Cell Apoptosis via the miR-8485/GSK-3β/Wnt/β-catenin Signaling Axis.

Abstract

Background: Studies have shown that abnormal stress is a significant inducer of Intervertebral Disc Degeneration (IVDD). Although traction force is commonly used to delay IVDD, its effects on Nucleus Pulposus Cells (NPCs) and their secreted exosomes remain unclear. In addition, this study systematically revealed the relationship between miR-8485 and IVDD for the first time.

Methods: Cellular experiments were performed using a Flexcell cell stretching platform to apply traction force to NPCs. After optimizing loading parameters, NPCderived exosomes (NPCs-exo) were isolated and subjected to miRNA high-throughput sequencing. Differentially expressed miRNAs were identified, and their regulatory effects on the Wnt/β-catenin pathway were investigated. Ex vivo rabbit spinal samples were used to validate the cellular experimental results under traction force loading.

Results: NPCs-exo were found to be internalized by NPCs, and traction force promoted NPCs-exo secretion. High-throughput sequencing and differential expression analysis identified miR-8485 as a differentially expressed miRNA in NPCsexo secreted under Cyclic Mechanical Tension (CMT) conditions. Dual-luciferase reporter assays confirmed the targeted regulatory relationship between miR-8485 and GSK-3β, as well as its involvement in the Wnt/β-catenin pathway-mediated regulation of NPCs degeneration. Ex vivo experiments, including morphological and immunofluorescence analyses, revealed that the traction group exhibited better morphology than the pressure group, with a more organized AF, NP, and higher NPCs content, though some loss persisted. Both groups showed significant differences in ECM markers (Collagen II, Aggrecan, MMP3) compared to the control (p < 0.05). Additionally, the traction group had significantly higher Collagen II and Aggrecan levels than the pressure group (p < 0.05).

Conclusion: CMT can promote the secretion of NPCs-exo, which are internalized by the NPCs. Through the delivery of miR-8485, NPCs-exo target and regulate GSK-3β, thereby enhancing Wnt/β-catenin pathway activity. This mechanism increases NPCs viability and extracellular matrix synthesis while suppressing apoptosis, ultimately delaying IVDD progression. Immunofluorescence staining in animal experiments confirmed that traction force effectively improves extracellular matrix expression in the IVD and mitigates stress-induced morphological alterations of the IVD.