Wnt/β-Catenin Signaling Regulates the Proliferation and Differentiation of Mesenchymal Progenitor Cells through the p53 Pathway

OBJECTIVE: Mesenchymal progenitor cells (MPCs) are found in articular cartilage from normal controls and patients with osteoarthritis (OA). Nevertheless, the molecular mechanisms of the proliferation and differentiation of these cells remain unclear. In this study, we aimed to determine the involvement of Wnt/β-catenin signaling in regulating the proliferation and differentiation of MPCs. METHODS: MPCs were isolated from the articular cartilage of normal and OA patients. Cells were sorted by immunomagnetic cell separation. Cell proliferation capacity was evaluated using the MTT assay. Toluidine blue staining and immunostaining with anti-collagen II or anti-aggrecan antibodies were used to determine the chondrogenic differentiation capabilities of MPCs. The mRNA and protein expression of target genes were examined by quantitative real-time polymerase chain reaction and Western blotting, respectively. Knock-down of p53 expression was achieved with RNA interference. RESULTS: Most cells isolated from the normal and OA patients were CD105(+) and CD166(+) positive (Normal subjects: CD105(+)/CD166(+), 94.6%±1.1%; OA: CD105(+)/CD166(+), 93.5%±1.1%). MPCs derived from OA subjects exhibited decreased differentiation capabilities and enhanced Wnt/β-catenin activity. Inhibition of Wnt/β-catenin signaling promoted proliferation and differentiation, whereas activation of this pathway by treatment with rWnt3a protein decreased the proliferation and differentiation of normal MPCs. Additionally, Wnt/β-catenin signaling positively regulated p53 expression, and silencing of p53 increased proliferation and differentiation of MPCs. CONCLUSIONS: Wnt/β-catenin regulated the proliferation and differentiation of MPCs through the p53 pathway.