THESIS
2007
xiv, 101 leaves : ill. ; 30 cm
Abstract
Hydroxyapatite (HA) is a biomaterial widely used in both orthopedic and dental surgery because it exhibits the ability to promote bone growth. There were many evidences that hydroxyapatite alone is osteoinductive in vivo. However, the mechanism of such osteoinductive property of hydroxyapatite is not well characterized. The role of HA in regulating osteogenic cells has already been studied for its interaction with osteoblasts in vitro. However, the reported results of HA-osteoblasts interaction were somehow controversial....[
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Hydroxyapatite (HA) is a biomaterial widely used in both orthopedic and dental surgery because it exhibits the ability to promote bone growth. There were many evidences that hydroxyapatite alone is osteoinductive in vivo. However, the mechanism of such osteoinductive property of hydroxyapatite is not well characterized. The role of HA in regulating osteogenic cells has already been studied for its interaction with osteoblasts in vitro. However, the reported results of HA-osteoblasts interaction were somehow controversial.
In this present study, hydroxyapatite (HA) was investigated using uncommitted pluripotent mouse mesenchymal stem cells, C3H10T1/2, in an in vitro differentiation assay. For comparative analysis, the cells were cultured on the substrates made of HA, with biocompatible titanium and plastics as the negative control. HA exhibited impressive ability to induce in C3H10T1/2 expression of osteo-specific genes, including alkaline phosphatase (ALP), type I collagen (COLI) and osteocalcin (OCN), in contrast to its insignificant effect on the same genes in osteoblast-like cells, Saos-2. HA osteoinductivity monitored by up-regulation of osteo-specific genes in C3H10T1/2 was comparable to that of a bone morphogenetic protein (BMP). HA osteoinductivity was also demonstrated in the stem cells culture using conditioned medium derived from cells precultured on HA substrates. The results suggest that HA can interact with the cells and generate potent inductive substance released into the medium. Base on this medium assay, the interaction between different biomaterials and different cell lines was examined. Through this screening, hydroxyapatite showed the especially potent osteo-inductivity amount different biomaterials, and the developmental stage window that cells lines can interact with HA to generate secretory osteoinductive factor(s) into the conditioned media is between mesenchymal stem cells C3H10T1/2 and preosteoblasts MC3T3-E1.
In order to determine the potential signaling pathway triggered by hydroxyapatite, several pharmacological inhibitors were used to evaluate the requirement of different skeletogenic signaling pathways. The preliminary result showed that two of the inhibitors Rapamycin (a p70S6K inhibitor) and Gö6976 (a PKC inhibitor) had stronger suppressive effect on osteogenic differentiation and reduce the ALP activation upon HA co-culture. These assay results suggest that the osteoblast differentiation induced by HA may act through the p70S6 kinase and requires PKC signaling event as a mediating step.
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