MMP13 and intervertebral disk degenerative disorder: In addition, M1-type Mφs could induce molecular changes associated with IDD in NP cells, including increased expression of pro-inflammation-related cytokines (IL-6, TNF-α, iNOS and COX-2), oxidative stress response (the levels of MDA and ROS) and matrix degradation markers (MMP-13, ADAMTS4 and ADAMTS5) and reduced matrix anabolic markers (COL2A1 and TIMP-1).