Differential protein expression in human articular chondrocytes expanded in serum-free media of different medium osmolalities by DIGE.

Expansion of human articular chondrocytes (HACs) in serum-free medium (SFM) has been shown to be enhanced by the control of medium osmolality. HACs attained better growth when cultured at osmolalities lower than the average osmolality found in articular cartilage in vivo, although the specific causes for this improved expansion were not speculated. The aim of this study was to perform monolayer cultures of HACs in SFM at two different medium osmolalities, 320 and 400 mOsm/kg, and observe changes in protein content. A proteomics approach using differential in gel electrophoresis (DIGE) revealed differences in 20 spots. MALDI-TOF/TOF mass spectrometry identified 18 of the 20 spots. Proteins affected by higher osmolality in SFM were identified and found to function, traditionally, in the cytoskeleton, protection against reactive oxygen species, mRNA biogenesis, and the heat shock response. All of these proteins were correlated with the cell cycle and proliferation, emphasizing the importance of medium osmolality control in the expansion of HACs in SFM. In addition, no protein expression changes were observed regarding chondrogenic markers, which supports our previous result that adjusting medium osmolality in SFM, while enhancing growth, does not deter the tissue-forming capability of HACs.