TNF and intervertebral disk degenerative disorder: GDF-5 gene polymorphism is associated with IDD susceptibility.150 GDF-5 deficiency in mice resulted in decreased proteoglycan and collagen II levels and abnormal histology in the IVD.151 In rat NP cells,152 GDF‐5 overexpression inhibited the secretion of TNF‐α, IL‐1β, PGE2, and NO in culture medium induced by LPS, inhibited the decrease in matrix production, including collagen II and aggrecan, and prevented NF‐κB activation induced by LPS.