Stable silencing of matrix metalloproteinase 2 (MMP-2) by using shRNA-mediated RNAi. Silencing of MMP2 in primary rat caudal annulus fibrosus (AF) cells at 4 and 10 days after lentivirus infection, with and without treatment with blasticidin to select for pure populations of transduced cells. (a) Relative expression of treatment groups compared with noninfected controls, as quantified with real-time RT-PCR. At 4 and 10 days, MMP2 transcript levels were significantly decreased by 70% and 88%, respectively, in blasticidin-treated cultures (*P < 0.03). (b) Total protein levels for MMP-2 in cell lysates and (c) in conditioned media. At 10 days, total MMP-2 is 95% and 90% lower (*P < 0.05) in blasticidin-treated cell lysates and culture media, respectively, compared with that in noninfected controls (Cells).