Fibroblasts
Fibroblast, which is also called periodontal ligament cells, is the most common cells in periodontal ligament. Its main function is collagen synthesis, at the same time swallowing and degrading the old collagen fibers[1]. The function of periodontal ligament cells decides its importance in the regeneration of periodontal tissue.
In our experiment, we obtained periodontal ligament cells from premolar periodontal membrane of healthy adolescents by orthodontic extraction, which was easy to get and fresh periodontal tissues. Although the number of periodontal ligament cells in pericementum is not large, it has many advantages for scientific research, such as easy for primary culture and amplification in vitro, no pollution of other cell lines, stable biological characters, mature culture technology and so on. Therefore, it is a good way for studying the role of bFGF on periodontal ligament cells through culturing them in vitro.
The role of bFGF on periodontal ligament cells
Immunohistochemical staining showed that bFGF exists in the periodontal ligament fibroblasts, endothelial cells and some fibroblasts, which can synthesize and secrete bFGF by themselves, and begin to store bFGF from the stage of fibroblast cells. The bFGF distributes in the cytoplasm and nucleus of periodontal ligament cells. As bFGF growth factor can promote the proliferation of periodontal ligament cells, it can induce the growth of periodontal tissue[5]. What’s more, bFGF promotes the proliferation of human gingival fibroblasts, human periodontal ligament fibroblasts and human alveolar bone cells, just having different concentrations for the best effect[6].
For many substances related to the regeneration of periodontal tissues, such as alkaline phosphatase and hyaluronic acid, bFGF plays a role of either promoting or inhibiting them. This study shows that the numbers of hyaluronic acid molecules in periodontal ligament cells cultured with the conditioned medium adding bFGF were much larger than that cultured in the medium without bFGF. The mRNA expression level of hyaluronan synthase 1 and 2, both of which are involved in the synthesis of hyaluronic acid, had been enhanced as detected by RT-PCR. These results indicate that bFGF is involved in the regulation of hyaluronic acid’s synthesis, the maintenance of homoeostasis and the regeneration of periodontal tissues.
As for the gene expression of type Ⅰ collagen and metalloprotease-1, bFGF has the reverse time and dose dependence, it can reduce the gene expression of typeⅠ collagen as well as increase the metalloproteinase-1 gene expression at the same time, but no such affection on collagen Ⅲ. The influence of bFGF on these three gene expressions can be regulated by the culture time in the bFGF-contained medium. These results show that bFGF is one of the important regulators for the effective reconstruction of collagen I in pericementum. The bFGF may also have the same function to other connective tissue.
Influence of bFGF on decorin
As a major proteoglycan in periodontal tissue, decorin distributes in collagen fiber bundles at the basement membrane zone of gingival epithelial as well as the gingival and periodontal connective tissue. Stronger immune expression was observed in the subepithelial gingival than in the deep periodontal region. Decorin can bind different types of collagen fibers, such as collagen Ⅰ and collagen Ⅵ, owing to its horseshoe-shaped core protein[7]. Therefore, it was considered to be impacting the collagen synthesis and its final diameter.
Our experiment shows that the mRNA expression level of decorin in periodontal ligament cells was obviously reduced with the presence of bFGF. Moreover, the inhibitory effect gradually weakened with the increased concentration of bFGF, the strongest inhibitory effect appeared in the 0.1 µg/L, while the weakest in the 10 µg/L. The following points discussed are its significance: ① The inhibition effect of bFGF on decorin has changed the homeostasis of the extracellular matrix, decreasing the synthesis of collagen I. Decorin is an important factor regulating collagen degradation, and bFGF may also regulate collagen synthesis through this way. ② In the teeth and periodontal tissues, the small interstitial proteoglycan expresses in dentin and the non-mineralized areas of cementum. Especially the collagen fibers from the cementum and alveolar bone inserting at the junction of soft and hard tissue, and the osteoblasts in the inner alveolar bone showed strong positive immunohistochemical characteristics, indicating that small interstitial proteoglycan may affect the mineralization of dentin, cementum and alveolar bone. ③ Decorin can mediate cell proliferation, its expression increases in the dormancy stage, while is very low in the active proliferation of cells. ④ Decorin plays an important role in the process of growth, development and damage repairs, and also participates in the tissue stability and damage repairs. The inhibition effect of bFGF on the decorin indicates that it may be involved in the inflammatory process of periodontal disease and bFGF plays a great role on the decorin gene expression in periodontal ligament cells, providing a theoretical basis for promoting the pluripotent cells functions of periodontal ligament cells in regeneration of periodontal tissues.
In short, the periodontal tissue regeneration is a very complex process. However, the inhibition of bFGF on the decorin synthesis is one of the important regulators of promoting periodontal ligament cells proliferation. Application of bFGF can effectively induce regeneration of periodontal tissues, not only inducing the connective tissue regeneration, but also inducing the bone regeneration and alveolar bone regeneration, having a broad application prospect.
