TNF and intervertebral disk degenerative disorder: Another FDA-approved chemical chaperone, 4-phenylbutyricacid (4-PBA), has also been verified to alleviate IDD by inhibiting ER stress in different experiment condition, such as the application of cyclic tension on AF cells and the treatment of AGEs, H2O2, or TNF-α on NP cells (Chen et al., 2018; Chen J. et al., 2019; Luo et al., 2019a; Luo et al., 2019b).