TNF and intervertebral disk degenerative disorder: Moreover, TNF-α has been considered to play a critical role in NPC apoptosis and can enhance the expression levels of multiple proinflammatory cytokines, such as cytochrome C oxidase subunit 2 (COX-2), and inducible nitric oxide synthase (iNOS), which amplify the inflammatory response and aggravate the IDD [20–22].