Hypoxia-inducible factors 1α and 2α protein expression during redifferentiation of healthy and osteoarthritic chondrocytes. Representative images of banding patterns are shown. Normalization of nuclear protein loading was achieved by first running equal volumes of each sample and probing for histone H3. For hypoxia-inducible factor (HIF) blots, the volume loaded was adjusted to give equivalent nuclear loading based on each histone H3 band's signal relative to the signal from the lowest-intensity band. The location of the only oxygen-dependent band on HIF-2α blots is in the boxed area, and the blot is cropped to show only the bands in the molecular weight range where the HIF-2α product is predicted (115 kDa). Unmodified HIF-2α blots for healthy and OA chondrocytes are shown in Additional files 3 and 4, respectively. The consistency of the nonspecific band near 35 kDa (lowest band) was used as a loading control after histone H3 normalization.