PDCD4 and intervertebral disk degenerative disorder: NP cells from IDD patients were collected and divided into blank controlgroup, negative control group (transfected with miR-21 negative sequences), miR-21inhibitor group (transfected with miR-21 inhibitors), miR-21 mimics group(transfected with miR-21 mimics) and PDCD4 siRNA group (transfected with PDCD4siRNAs).