Osteoprotegerin induces osteopontin via syndecan-1 and phosphoinositol 3-kinase/Akt in human periodontal ligament cells.
OBJECTIVE
Our previous study found that thrombin induced osteoprotegerin synthesis in human periodontal ligament cells. As elevated levels of osteoprotegerin can exert biological effects on various cell types, in the present study we investigated the effect of osteoprotegerin on the expression of osteopontin in human periodontal ligament cells.


METHODS
Cultured human periodontal ligament cells were treated with recombinant human osteoprotegerin (0-100 ng/mL) for 24-48 h. The expression of osteopontin mRNA and protein was analyzed using reverse transcription-polymerase chain reaction and western blot analyses, respectively. Phosphoinositol 3-kinase inhibitor, Akt inhibitor, heparinase, neutralizing antibody against receptor activator of nuclear factor-kappaB ligand (RANKL) and syndecan-1, and small interfering RNA against syndecan-1, were used to determine the mechanism involved.


RESULTS
Osteoprotegerin up-regulated the mRNA and protein expression of osteopontin in human periodontal ligament cells in a dose-dependent manner. Addition of neutralizing antibody against RANKL attenuated the inductive effect of osteoprotegerin on osteopontin expression. In addition, the inductive effect of osteoprotegerin was abolished by phosphoinositol 3-kinase and Akt inhibitors, as well as by syndecan-1 antibody or syndecan-1 small interfering RNA. None of the inhibitors had any effect on the background level of osteopontin expression.


CONCLUSIONS
An increased level of osteoprotegerin can generate signals via a RANKL/syndecan-1/phosphoinositol 3-kinase/Akt pathway. The results also suggest that osteopontin is one of the downstream targets of the pathway mediated by osteoprotegerin in human periodontal ligament cells. Thus, in addition to counteracting RANKL in the RANKL-osteoprotegerin system, osteoprotegerin may play a role in periodontal tissue remodeling through modulation of the extracellular matrix.
Yongchaitrakul
T
T
Department of Anatomy, Faculty of Dentistry, Chulalongkorn University, Patumwan, Bangkok, Thailand.
Manokawinchoke
J
J
Pavasant
P
P
D057134:Antibodies, Neutralizing / Q000494:pharmacology; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D053495:Osteopontin / Q000187:drug effects*; D053244:Osteoprotegerin / Q000008:administration & dosage / Q000494:pharmacology*; D010513:Periodontal Ligament / Q000166:cytology / Q000187:drug effects*; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011133:Polysaccharide-Lyases / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000187:drug effects*; D053245:RANK Ligand / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000187:drug effects; D034741:RNA, Small Interfering / Q000494:pharmacology; D011994:Recombinant Proteins; D053668:Syndecan-1 / Q000032:analysis* / Q000037:antagonists & inhibitors; D013997:Time Factors; D015854:Up-Regulation
D057134:Antibodies, Neutralizing; D002867:Chromones; D004791:Enzyme Inhibitors; D007074:Immunoglobulin G; D009025:Morpholines; D053495:Osteopontin; D053244:Osteoprotegerin; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011133:Polysaccharide-Lyases; D051057:Proto-Oncogene Proteins c-akt; D053245:RANK Ligand; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D053668:Syndecan-1; C508241:SDC1 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C021349:heparitinsulfate lyase