Figure 4

Oxygen-dependent expression of matrix metalloproteinases in healthy and osteoarthritic chondrocytes. (A) through (D) The relative gene expression levels of MMP1, MMP3, MMP13 and MMP2 in pellet cultures following 2 wk of redifferentiation in either 20% oxygen (gray bars) or 2% oxygen (white bars) were analyzed by real-time quantitative polymerase chain reaction. (E) Gelatin zymography of supernatants pooled from days 9 to 14 of pellet cultures indicates levels of secreted pro-MMP2 and active MMP2 in healthy and osteoarthritic (OA) cells at 20% and 2% oxygen. (F) and (G) The relative gene expression levels of TIMP2 and MMP14 in pellet cultures following 2 wk of redifferentiation in either 20% oxygen (gray bars) or 2% oxygen (white bars) were analyzed by real-time quantitative polymerase chain reaction. All expression values are the mean mRNA levels normalized to 18S ribosomal RNA for chondrocyte pellets from n = 5 donors. Error bars represent 1 SD. Statistical significance was determined by performing independent t-tests (between disease conditions) and paired t-tests (between oxygen levels). *P < 0.05.