Bacterial endotoxin LPS but not LTA can enhance osteogenic differentiation of human mesenchymal stem cells

Background & Objective: Dental implant requires osseointegration for anchoring and human’s oral cavity has plenty of bacterial oral flora. Whether these bacteria have any effects on the human mesenchymal Stem Cells (MSCs) that can differentiate into osteoblasts remains unknown. We therefore investigated the effect of bacterial endotoxins commonly found in the oral cavity and gastrointestinal tract, namely lipopolysaccharides (LPS, Escherichia coli) and lipoteichoic acid (LTA, Streptococcus pyogenes), on the proliferation and osteogenic differentiation of MSCs. Methods: Human MSCs are derived from bone marrow (BM) of normal healthy donors. The culture condition, immunophenotyping determination and tests of differentiating functions of the human MSCs were similar to what we reported previously (Li J, Br J Haematol 2004). The proliferation of MSCs under either a 3-day or a prolonged 7-day endotoxins challenge was evaluated by XTT assay. The extent of osteogenic differentiation was examined under microscopy and measured by the increase in alkaline phosphatase (ALP) activity at day 10 and the calcium mineralization/deposition per unit volume of protein at day 14. Results: There was no significant effect of LPS and LTA on the growth and proliferation of MSCs, even under a relatively high dose. However, continued LPS challenge on MSCs under osteogenic culture condition was shown to increase the ALP activity and calcium deposition in a dose-dependent manner (100ng/ml, 1 ug/ml, 10ug/ml). No such phenomenon can be identified when LTA challenge was used. Conclusions: LPS and LTA did not show any significant effect on the proliferation and growth of human MSCs. However, LPS enhanced the osteogenic differentiation of MSCs in a dose-dependent manner. Our finding suggests that the endotoxin from bacteria commonly found in the oral cavity and gut does not have any negative impact on MSCs induced osteogenesis