MMP9 and intervertebral disk degenerative disorder: It is well documented that MMPs, including MMP-2, MMP-9 and MMP-13, playimportant roles in the regulation of extracellular matrix degradation, a major cause inthe pathology of IDD, mainly through regulating cell inflammation, extracellular matrixdeposition and tissue rearrangement (38).Therefore, based on our results, it is reasonable to suggest that miR-21 may regulatethe expression of MMP-2 and MMP-9 via PDCD4 targeting.