Integrative bulk and single-cell transcriptomic analyses reveal nucleus pulposus cell fibrosis as a therapeutic target in intervertebral disc degeneration and identify quercetin as a potential antifibrotic agent.

Intervertebral disc degeneration (IVDD) is a leading cause of chronic low back pain, in which fibrotic transformation of nucleus pulposus cells (NPCs) plays a critical pathological role. However, the regulatory mechanisms underlying NP cell fibrosis remain poorly understood. This study aimed to explore the role of NP cell fibrosis in IVDD and identify natural compounds capable of targeting this process. Bulk and single-cell transcriptomic data were integrated to explore the role of NP cell fibrosis in IVDD and to identify natural compounds capable of targeting this pathological process. Cellular and animal experiments were conducted for validation. Transcriptomic analysis revealed that the intersection of differentially expressed genes (DEGs), WGCNA-identified module genes, and fibrosis-related genes-termed fibrosis-related differentially expressed genes (FRDEGs)-was significantly enriched in the TGF-β signaling pathway. Based on FRDEGs, quercetin (QUE), a natural flavonoid, was identified as a candidate compound. TGF-β and TGF-βR2 were identified as hub genes. Single-cell analysis confirmed high expression of these genes in NP cells, especially within fibrotic subpopulations (Fibro-NPCs), where TGF-β pathway activity was notably elevated. Molecular docking indicated strong binding affinity between QUE and TGF-β. In vitro, QUE treatment suppressed IL-1β-induced expression of TGF-β/TGF-βR2 in degenerative NP cells. In vivo, QUE administration attenuated NP fibrosis and mitigated IVDD progression in a rat puncture model. This study uncovers the critical role of NP cell fibrosis in IVDD and demonstrates that QUE mitigates disc degeneration by targeting the TGF-β signaling pathway. These findings suggest a novel anti-fibrotic therapeutic strategy for IVDD based on natural compound intervention.