TNF and intervertebral disk degenerative disorder: Although the pathogenesis of IDD is complicated and not fully understood, recent studies suggest that abnormal microenvironment of NP cells, especially the overactive inflammatory response and overproduced inflammatory cytokines [such as interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α)], disturbs the homeostasis of ECM and aggravates degenerative changes in IVD [6–8].