Subculture affects the phenotypic expression of human periodontal ligament cells and their response to fibroblast growth factor-2 and bone morphogenetic protein-7 in vitro.
OBJECTIVE
Although periodontal ligament cells display several osteoblastic traits, their phenotypic expression is still not well established. It remains a matter of debate whether they resemble a terminally differentiated cell type or an intermediate maturation state that potentially can be directed towards a fibroblastic or an osteoblastic phenotype.


METHODS
To explore the characteristics of periodontal ligament cells in greater detail, fourth-passage, sixth-passage and eighth-passage human periodontal ligament cells were cultured for up to 3 wk. Ki-67, alkaline phosphatase, osteocalcin, osteoprotegerin and receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA expression was quantified by real-time polymerase chain reaction. Furthermore, the cellular response to fibroblast growth factor-2 and bone morphogenetic protein-7 was examined in first-passage and fourth-passage cells. Dermal fibroblasts (1BR.3.G) and osteoblast-like cells (MG63) served as reference cell lines.


RESULTS
Proliferation decreased over time and was highest in fourth-passage cells. The expression of differentiation parameters, osteoprotegerin and RANKL increased with culture time and was higher in fourth-passage cells than in cells of later passages. The RANKL/osteoprotegerin ratio increased steadily until day 21. Administration of fibroblast growth factor-2 enhanced cell numbers in both passages, whereas alkaline phosphatase and osteocalcin production remained unchanged. By contrast, exposure of periodontal ligament cells to bone morphogenetic protein-7 resulted in a reduction of cell number in the first and fourth passages, whereas the production of alkaline phosphatase and osteocalcin was enhanced. In dermal fibroblasts, differentiation parameters did not respond to both stimuli. MG63 cells behaved similarly to periodontal ligament cells.


CONCLUSIONS
These results indicate that subculture affects the phenotypic expression of human periodontal ligament cells with respect to the characteristics that these cells share with osteoblasts. Furthermore, the periodontal ligament cell phenotype can be altered by fibroblastic and osteoblastic growth factors.
Lossdörfer
S
S
Department of Orthodontics, Dental Clinic, University of Bonn, Bonn, Germany. s.lossdoerfer@gmx.de
Fiekens
D
D
Salik
M I
MI
Götz
W
W
Jäger
A
A
D000293:Adolescent; D000469:Alkaline Phosphatase / Q000096:biosynthesis; D055419:Bone Morphogenetic Protein 7 / Q000494:pharmacology*; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D002478:Cells, Cultured; D002648:Child; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D005347:Fibroblasts; D006801:Humans; D019394:Ki-67 Antigen / Q000096:biosynthesis; D010006:Osteoblasts / Q000378:metabolism; D015675:Osteocalcin / Q000096:biosynthesis; D053244:Osteoprotegerin / Q000096:biosynthesis; D010513:Periodontal Ligament / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D010641:Phenotype; D016133:Polymerase Chain Reaction; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000096:biosynthesis
D055419:Bone Morphogenetic Protein 7; D019394:Ki-67 Antigen; D053244:Osteoprotegerin; D053246:Receptor Activator of Nuclear Factor-kappa B; D016222:Fibroblast Growth Factor 2; D015675:Osteocalcin; D000469:Alkaline Phosphatase