UCSF

Bone marrow-derived mesenchymal stem cells are a promising source of cells for cartilage regeneration therapies due to their ease of isolation and capacity to differentiate into cells resembling articular chondrocytes. However, the current differentiation protocols result in the development of additional phenotypic features, common to hypertrophic and osteoarthritic chondrocytes, which are undesirable in the context of articular cartilage repair. In this work we investigated the roles of cyclic hydrostatic pressure and canonical Wnt/β-catenin signaling in regulating the phenotype of chondrogenic MSCs. We used a standard chemically defined medium containing TGF-β to induce chondrogenic differentiation in pellets of human MSCs. Hydrostatic pressure was applied using a custom-built loading chamber. β-catenin signaling was modified using small molecules; XAV939 for inhibition and CHIR99021 for stimulation. The chondrogenic MSCs in this culture system resembled osteoarthritic chondrocytes, co-expressing features of both articular and hypertrophic chondrocytes. Cyclic hydrostatic pressure favored a modest shift in the phenotypic balance away from hypertrophy and toward chondrogenesis. In addition, cyclic hydrostatic pressure inhibited intracellular signaling via the ERK1/2 and canonical Wnt/β-catenin pathways. Inhibition of β-catenin signaling with XAV939 significantly augmented chondrogenesis and inhibited hypertrophy, suggesting that this may be a potential mechanism by which hydrostatic pressure is transduced in MSCs. Stimulation of β-catenin with CHIR99021, inhibited both types of chondrogenic differentiation. Our results indicate that β-catenin is an attractive target for phenotypic modulation of chondrogenic MSCs, and has potential applications in cartilage regeneration therapies from tissue engineering to targeted drug delivery to gene therapy.