Oxygen-dependent expression of hyaluronic acid synthase 2 ( HAS2 ) in healthy and osteoarthritic chondrocytes and correlation with sulfated glycosaminoglycan retention. (A) The relative gene expression levels of HAS2 in pellet cultures following 2 wk of redifferentiation in either 20% oxygen (gray bars) or 2% oxygen (white bars) was analyzed by real-time quantitative polymerase chain reaction. All 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. (B) and (C) The oxygen-dependent change in sulfated glycosaminoglycan (sGAG) matrix retention (percentage retained at 2% oxygen/percentage retained at 20% oxygen) was plotted against the oxygen-dependent changes in HAS2 expression (HAS2 at 2% oxygen/HAS2 at 20% oxygen) for healthy (B) and osteoarthritic (OA) pellets (C). Linear regression fit and coefficient of determination (R2) are shown. Bivariate analysis revealed a strong and statistically significant correlation between the oxygen-dependent difference in HAS2 and that of sGAG retention in both OA cells (P = 0.032) and healthy cells (P = 0.023).