RESEARCH ARTICLE Deletion of RBPJK in Mesenchymal Stem Cells Enhances Osteogenic Activity by Up- Regulation of BMP Signaling

Recently we have demonstrated the importance of RBPjk-dependent Notch signaling in the regulation of mesenchymal stem cell (MSC) differentiation during skeletogenesis both in vivo and in vitro. Here we further performed RBPJK loss-of-function experiments to demon-strate for the first time that RBPJK deficient MSC shows enhanced differentiation and osteo-genesis acts via up-regulation of the BMP signaling. In the present study, we first compared the spontaneous and osteogenic differentiation in normal and recombination signal binding protein for immunoglobulin kappa J region (RBPJK) deficient human bone marrow-derived mesenchymal stem cells (MSCs). It was found that RBPJK highly expressed in fresh iso-lated MSCs and its expression was progressing down-regulated during spontaneous differ-entiation and even greater in osteogenic media inducted differentiation. Deletion of RBPJK in MSCs not only enhances cell spontaneous differentiation, but also significantly acceler-ates condition media inducted osteogenic differentiation by showing enhanced alkaline phosphatase (ALP) activity, Alizarin red staining, gene expression of Runx2, Osteopontin (OPN), Type I collagen (COL1a1) in culture. Additionally, BMP signaling responsive reporter activity and phosphor-smad1/5/8 expression were also significantly increased upon removal of RBPJK in MSCs. These data proved that inhibition of Notch signaling in MSCs promotes cell osteogenic differentiation by up-regulation of BMP signaling, and RBPJK deficient MSCmaybe a better cell population for cell-based bone tissue engineering