Influence of Inflammation on Bone Regeneration of Dental Stem Cells: Role of TGF-β2/BMP-2

Abstract

and the anti-inflammatory cytokine TSG-6 in MSCs. IL-1β expression was downregulated by TSG-6 treatment of THP-1 cells. TSG-6 secreted by MSCs suppressed inflammatory reactions through p38 and ERK in the mitogen-activated protein kinase (MAPK) pathway. [Part 2] In inflamed DFSCs, ALP activity and alizarin red S staining were decreased in the presence of osteogenic differentiation. Also, in vivo transplantation showed severe impairment of osteogenesis in inflamed DFSCs. Protein profile analysis showed that TGF-β1 and TGF-β2 have different expressions in inflamed DFSCs. Osteogenic differentiation was suppressed in LPS-treated DFSCs due to a low level of TGF-β1 and high level of TGF-β2. TGF-β2 inhibitors increased osteogenesis in DFSCs. Moreover, TGF-β1 expression was also increased with inhibition of TGF-β2.

4. Conclusions In conclusion, an inflammatory environment affects the osteogenic differentiation on MSCs. MSCs in inflammatory conditions have the low osteogenic differentiation potentials, caused by TGF-β2. Also, MSCs triggered by inflammatory conditions secreted the anti-inflammatory cytokine, TSG-6, to inhibit inflammatory reactions and increase osteogenic differentiation. Understanding the relationship between inflammation and bone formation in MSCs is important in regenerative medicine and for the future clinical use of dental stem cells.

1. Purpose Bone formation is important for reconstructing the bone-related structure in areas damaged by inflammation. Inflammatory conditions inhibits osteoblastic differentiation, as shown in rheumatoid arthritis, cystic fibrosis, and periodontitis. In this study, periodontal ligament stem cells (PDLSCs), bone marrow stem cells from the maxilla (BMSCs), and dental follicle stem cells (DFSCs), as known for mesenchymal stem cells (MSCs), were used to demonstrate the relationship between inflammation and osteogenesis.

2. Materials and methods Human PDLSCs and BMSCs are MSCs obtained from the periodontal ligament of extracted third molars and from bone marrow of the maxilla, respectively. Osteogenic differentiation was measured by ALP activity and alizarin red S staining. Proteins were assessed by flow cytometry, ELISA, western blotting, and immunocytochemistry. Changes of gene expression were measured by RT-PCR and real-time PCR. DFSCs, founded in developing tooth germ, were tested in conjunction with the role of TGF-β2 in the relationship between an inflammatory environment and bone formation. Protein analysis was performed by liquid chromatography coupled with tandem mass spectrometry to analyze the difference between inflamed and normal tissue.

3. Results [Part 1] A high BMP-2 concentration inhibited the early stages of osteogenesis in MSCs. Also, co-culturing THP-1 with MSCs suppressed the late stages of osteogenesis. In addition, high-dose BMP-2 induced inflammatory cytokines in THP-1 cells