Glycosaminoglycan remodeling during chondrogenic differentiation of human bone marrow-/synovial-derived mesenchymal stem/stromal cells under normoxia and hypoxia.

Glycosaminoglycans (GAGs) are major components of cartilage extracellular matrix (ECM), which play an important role in tissue homeostasis not only by providing mechanical load resistance, but also as signaling mediators of key cellular processes such as adhesion, migration, proliferation and differentiation. Specific GAG types as well as their disaccharide sulfation patterns can be predictive of the tissue maturation level but also of disease states such as osteoarthritis. In this work, we used a highly sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to perform a comparative study in terms of temporal changes in GAG and disaccharide composition between tissues generated from human bone marrow- and synovial-derived mesenchymal stem/stromal cells (hBMSC/hSMSC) after chondrogenic differentiation under normoxic (21% O₂) and hypoxic (5% O₂) micromass cultures. The chondrogenic differentiation of hBMSC/hSMSC cultured under different oxygen tensions was assessed through aggregate size measurement, chondrogenic gene expression analysis and histological/immunofluorescence staining in comparison to human chondrocytes. For all the studied conditions, the compositional analysis demonstrated a notable increase in the average relative percentage of chondroitin sulfate (CS), the main GAG in cartilage composition, throughout MSC chondrogenic differentiation. Additionally, hypoxic culture conditions resulted in significantly different average GAG and CS disaccharide percentage compositions compared to the normoxic ones. However, such effect was considerably more evident for hBMSC-derived chondrogenic aggregates. In summary, the GAG profiles described here may provide new insights for the prediction of cartilage tissue differentiation/disease states and to characterize the quality of MSC-generated chondrocytes obtained under different oxygen tension culture conditions.