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This dissertation, Effects of Bacterial Toxins on the Proliferation, Osteogenic Differentiation and Toll-like Receptor Expressions of Human Mesenchymal Stromal Cells by Fung-ying, Irene, Mo, 毛鳳英, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Effects of bacterial toxins on the proliferation, osteogenic differentiation and Toll-like receptor expressions of human Mesenchymal Stromal Cells Submitted by Mo Fung Ying, Irene for the degree of Master of Philosophy at The University of Hong Kong in December 2006 Human mesenchymal stromal cells (MSCs, also known as mesenchymal stem cells) are multipotent cells with potential therapeutic value. Owing to their osteogenic capability, MSCs may be clinically applied for facilitating osseointegration in dental implants or orthopedic repair of bony defect. However, whether wound infection or oral microflora may interfere with the growth and osteogenic differentiation of human MSCs remains unknown. This study investigated whether proliferation and osteogenic differentiation of MSCs would be affected by potent gram-positive and gram-negative derived bacterial toxins commonly found in human settings. We selected lipoteichoic acid (LTA) from Streptococcus pyogenes and lipopolysaccharide (LPS) from Escherichia coli as our toxins of choice. Our findings showed neither LPS nor LTA affected MSC proliferation, but prolonged LPS challenge upregulated the osteogenic differentiation of MSCs, as assessed by alkaline phosphatase activity and calcium deposition. Because Toll-like receptors (TLRs), in particularly TLR4 and TLR2, are important for the cellular responsiveness to LPS and LTA respectively, we evaluated their expression profiles serially from MSCs to various stages of osteoprogenitors by quantitative PCR. We found that during osteogenic differentiation, MSC-derived osteoprogenitors gradually expressed TLR4 and TLR2 by Day 12. But under prolonged incubation with LPS, MSC-derived osteoprogenitors had reduced TLR4 and TLR2 gene expression. This peculiar response to LPS suggests a possible adaptive mechanism when MSCs are subjected to continuous exposure with bacteria. In conclusion, our findings support the potential of using human MSCs as a biological graft, even under a bacterial toxin-rich environment. DOI: 10.5353/th_b3860765 Subjects: Bacterial toxinsStem cellsCell proliferationCell differentiationGene expression

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