CCL4 and intervertebral disk degenerative disorder: Relevant studies have shown that the number of senescent nucleus pulposus cells increases significantly during IDD, and senescent cells can produce a large amount of cytokines, including pro-inflammatory cytokines (IL-1, IL-6, IL-8, and TNF-α), matrix-degrading proteases (MMPs and ADAMTS), growth factors (VEGF and TGFβ), and chemokines (CCL2 and CCL4), causing changes in ECM metabolism [32–35].