A Study On The Effect Of Calcium Phosphate Bioceramics On Bone-related Gene Expression In Osteoblasts In Vitro

The clinical cases of bone repairing are just second to those of blood transferring in human tissue transplantation. For a very long time, materials resources for bone substitute are auotgraft and allograft. They are natural materials. The main disadvantages of autograft are the limited resource and the undesired injury to the donor site. In the same time, allograft encounters the serious problems of immuno-rejection and the possibility of infecting serious diseases from the donor.Calcium phosphate ceramics (including hydroxyapatite ceramics, tricalcium phosphate ceramics and biphasic calcium phosphate ceramics) are a series of typical bioactive ceramics. Except for their excellent biocompatibility, calcium phosphate ceramics are osteoconductive and osteoinductive.However, the mechanism of the bioactivity of calcium phosphate ceramics has not fully elucidated. How material factors (chemical composition, porosity, surface microstructure and crystal defects) affect osteoblast behavior, especially bone-related gene expression has not been reported before. Therefore, this study has quantitatively detected osteoblast proliferation and bone-related gene expression in mRNA and protein production level in order to study the effect of different calcium phosphate ceramics on osteoblast behavior and the mechanism of the bioactivity and biocompatibility of calcium phosphate ceramics.Some genes' expression has proved to play a significant role in osteogenesis. They are alkaline phosphatase, type I collagen, osteocalcin, bone sialoprotein, osteopontin and osteonectin, which are collectively called bone-related genes.The discovery of OPG/RANKL/RANK pathway in the end of the 1990s is a milestone of bone biology research. OPG belongs to the TNF superfamily and its ligand, RANKL, is a member of TNF ligand family.Their expression of the above-mentioned genes is very important in the process of osteogenesis, bone growth, bone fracture healing and bone remodeling and are markers of the natural bone-formation. Except for alkaline phosphatase, which is a cell membrane-bound protein, all the other genes are bone matrix proteins. In theprocess of osteogenesis, their expression is strictly regulated. Alkaline phosphatase and collagen I usually expressed in the early stage of bone development while osteocalcin and bone sialoprotein in the late stage. Uncontrolled expression of these genes may result in abnormality of bone development.Tissue non-specific alkaline phosphatase is highly expressed in liver, bone and kidney. This enzyme can reduce phosphate-containing substances to produce free phosphate for the requirement of bone mineralization. It can also modulate phosphate metabolism, transmembrane-phosphate transportation, controlling transportation of calcium, fat, protein and carbonate and the Na/K pump.Type I collagen, the main organic component of the extracellular matrix of bone, serves as the template of bone matrix and controls the nucleation site and growth space of hydroxyapatite.Osteocalcin, distributed mainly in bone and teeth, can inhibit the formation of hydroxyapatite crystal and thus, negatively modulate the mineralization of bone tissue. Osteocalcin can also combine with another non-collagen metrical protein-osteopontin to form osteocalcin-osteopontin complex, which can enhance bone resorption.Osteonectin plays an important role in the interaction of extracellular metrical proteins. There are Ca++ binding sites in its structure, which closely relates to the formation, differentiation and remodeling of bone tissue. Osteonectin can bind with metal ions, several kinds of collagen and hydroxyapatite.Bone sialoprotein has high affinity to calcium ions and hydroxyapatite and also bind to collagen protein. It can also induce calcium ion response in osteoclast and enhance bone resorption activity of osteoclast.OPG/RANK/RANKL pathway functions to modulate osteoclast differentiation, the activity of osteclast and inhibit osteoclast necrosis and thus, to modulate bone-remodelling.Bioceramics can affect osteoblast behavior at different le...