Effects inhibition of HIF-1α on anabolic and catabolic gene regulation at low oxygen percentage. (A) Experimental design: human articular chondrocytes from three donors were cultured as pellets in chondrogenic medium (ChM) at 19% O2 (Phase I) and subsequently maintained at the same oxygen percentage or exposed to 5% O2 in the absence or presence of 5 μM CdCl2 for six hours or three days (Phase II). Real time reverse transcription-polymerase chain reaction analysis of type II collagen mRNA expression after six hours (B) and of MMP-1 mRNA expression after three days (C). Levels are expressed as fold of difference from ribosomal 18S. Values for each donor are mean ± SD of measurements obtained from three independent pellets.