TNF and intervertebral disk degenerative disorder: The abnormal increase in the degradation of NPC extracellular matrix (ECM) components, such as aggrecan and collagen II (Roughley, 2004; Fontana et al., 2015; Oichi et al., 2020); NPC apoptosis (Ding et al., 2013; Fontana et al., 2015; Oichi et al., 2020); and levels of proinflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) secreted by NPCs (Risbud and Shapiro, 2014; Fontana et al., 2015; Oichi et al., 2020; Wang et al., 2020), are the most important pathological characteristics during IDD.