Inhibitory effect of the TSG-6 on the BMP-4/Smad signaling pathway and odonto/osteogenic differentiation of dental pulp stem cells

This study aimed to observe the molecular mechanism underlying the effect of tumor necrosis factor-inducible protein 6 (TSG-6) on the bone morphogenetic protein-4 (BMP-4)/drosophila mothers against decapentaplegic protein(Smad) signaling pathway and mineralization of dental pulp stem cells (DPSCs) in inflammatory environment. Normal and TSG-6 gene-modified DPSCs were cultured in a mineralization-inducing fluid containing 0 and 50 ng/mL TNF- separately. The real-time polymerase chain reaction was used to measure the expression of TSG-6 and odonto/osteogenic differentiation makers at the mRNA level. Western blot analysis and cellular immunofluorescence were used to observe the odonto/osteogenic differentiation of DPSCs and the variation of BMP-4/Smad signaling pathway at the protein level. Moreover, normal and modified DPSCs combined with hydrogel were used for subcutaneous implantation in nude mice. The expression of odonto/osteogenic markers and BMP-4/Smad-related proteins was lower in Ad-TSG-6 DPSCs than in normal DPSCs after mineralization induction, and was higher in TSG-6-RNAi DPSCs than in normal DPSCs after culturing with mineralization-inducing fluid containing 50 ng/mL TNF-. The subcutaneous transplantation of normal and modified DPSCs combined with hydrogel in nude mice demonstrated that normal DPSCs were formed in the tissue containing collagen. The tissue formed by Ad-TSG-6 DPSCs was highly variable, and the cells were very dense. The expression of odonto/osteogenic markers of Ad-TSG-6 DPSCs were lower in Ad-TSG-6 DPSCs than in normal DPSCs. We can know that TNF- regulates the expression of TSG-6, thereby inhibiting the BMP-4/Smad signaling pathway and the odonto/osteogenic differentiation ability of DPSCs.