Oxygen tension regulates the osteogenic, chondrogenic and endochondral phenotype of bone marrow derived mesenchymal stem cells

The local oxygen tension is a key regulator of the fate of mesenchymal stem cells (MSCs). The objective of this study was to investigate the effect of a low oxygen tension during expansion and differentiation on the proliferation kinetics as well as the subsequent osteogenic and chondrogenic potential of MSCs. We first hypothesised that expansion in a low oxygen tension (5% pO2) would improve both the subsequent osteogenic and chondrogenic potential of MSCs compared to expansion in a normoxic environment (20% pO2). Furthermore, we hypothesised that chondrogenic differentiation in a low oxygen environment would suppress hypertrophy of MSCs cultured in both pellets and hydrogels used in tissue engineering strategies. MSCs expanded at 5% pO2 proliferated faster forming larger colonies, resulting in higher cell yields. Expansion at 5% pO2 also enhanced subsequent osteogenesis of MSCs, whereas differentiation at 5% pO2 was found to be a more potent promoter of chondrogenesis than expansion at 5% pO2. Greater collagen accumulation, and more intense staining for collagen types I and X, was observed in pellets maintained at 20% pO2 compared to 5% pO2. Both pellets and hydrogels stained more intensely for type II collagen when undergoing chondrogenesis in a low oxygen environment. Differentiation at 5% pO2 also appeared to inhibit hypertrophy in both pellets and hydrogels, as demonstrated by reduced collagen type X and Alizarin Red staining and alkaline phosphatase activity. This study demonstrates that the local oxygen environment can be manipulated in vitro to either stabilise a chondrogenic phenotype for use in cartilage repair therapies or to promote hypertrophy of cartilaginous grafts for endochondral bone repair strategies.

► Expansion in low oxygen enhances MSC proliferation and osteogenesis.
► Differentiation in low oxygen enhances chondrogenesis and suppresses hypertrophy.
► Oxygen can regulate the MSC phenotype for use in tissue engineering applications.