Osteoinductive pretreatment of human mesenchymal stromal cells (hMSCs) has been widely accepted in bone tissue engineering before the use of cell transplantation; however, the mechanisms by which osteoinductive medium (OIM) enhances osteoblastic differentiation are not well understood. Using periodontal ligament-derived hMSCs, we identified key signalling molecules for osteoblastogenesis. Alkaline phosphatase activity induced by OIM, which contains ascorbic acid, β-glycerophosphate, and dexamethasone, was decreased by XAV939, which is an inhibitor of canonical WNT signalling, in a dose-dependent manner. A quantitative RT-PCR array demonstrated the upregulation of secreted frizzled-related protein (SFRP) 3 and the downregulation of SFRP4 during osteoinduction. Functional studies showed that SFRP3 promoted and SFRP4 suppressed the osteoblastic differentiation of hMSCs. In addition, SFRP3 inhibited non-canonical WNT signalling by binding WNT5A, which is a representative non-canonical WNT protein. These results indicate the involvement of the WNT signalling pathway during the osteoblastic differentiation of hMSCs. SFRPs oppositely control osteoblastogenesis through canonical and non-canonical pathways and may be useful for directing the lineage of hMSCs in cytotherapeutic use.
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