MMP2 and intervertebral disk degenerative disorder: Our research also found that miR-21 could promote the proliferation of NP cells bytargeting PDCD4 and its downstream signaling molecules including c-Jun and MMPs.Numerous studies demonstrated that MMPs, including MMP-2 and MMP-9, were positivelyassociated with IDD grades (28, –30).Furthermore, c-Jun was reported to be activated in disc cells and cell clusters inherniated disc tissues (31).