Fig. 1

Schematic diagram of healthy IVD, degenerated IVD, and inflammatory pathological microenvironment. a Overview of the IVD. The IVD consists of three parts: the NP, the AF, and the CEP. b Cells and ECM in healthy IVD. In healthy IVD, the NP mainly consists of notochordal cells and nucleus pulposus cells. The AF primarily consists of annulus fibrosus cells. The CEP mainly consists of chondrocytes. c Mechanical function of the IVD. The primary function of the IVD is to provide mechanical support for the vertebrae and allow movement of the spine (flexion, extension, and rotation). d IVDD and IVD herniation. Severe IVDD leads to NP degeneration, AF rupture, and endplate calcification, resulting in IVD herniation that compresses the spinal cord and nerve roots. e Change of cells and ECM in degenerated IVD. In degenerated IVD, notochordal cells disappear, and due to cell senescence and PCD, the number of IVD cells significantly decreases, and their function markedly declines. f Macrophage infiltration and polarization. Under the induction of chemokines, macrophages infiltrate the IVD via neovascularization. Macrophages can polarize into M1 and M2 subtypes under different stimuli