Oral and maxillofacial surgery
Compressive mechanical stress promotes osteoclast formation through RANKL expression on synovial cells

https://doi.org/10.1016/j.tripleo.2006.05.026Get rights and content

Objectives

We investigated the effects of compressive mechanical stress on osteoclastogenesis of synovial cells to clarify the mechanism of osteoclast formation by those cells in temporomandibular joint (TMJ) disorders.

Study design

Synovial cells were isolated from rat knee joints and continuously compressed using a conventional method. The expression of receptor activator nuclear factor κB ligand (RANKL) mRNA and protein in synovial cells was analyzed by reverse transcriptase–polymerase chain reaction, immunoblotting, and immunofluorescence staining. Mouse bone marrow cells were cultured with synovial cells for 7 days to detect osteoclasts.

Results

The expressions of RANKL mRNA and protein in synovial cells were increased with compressive force. When mouse bone marrow cells were cultured with continuously compressed synovial cells, tartrate-resistant acid phosphatase–positive multinucleated cells were formed. Osteoprotegerin completely inhibited osteoclast formation induced by culturing with compressed synovial cells.

Conclusion

Our results indicated that the expression of RANKL in compressed synovial cells enhanced osteoclast formation, whereas continuous compressive force may induce osteoclastic bone destruction in the TMJ.

Section snippets

Primary rat synovial cells

Synovial tissues were obtained from the knee joints of male Sprague-Dawley rats (7 weeks old, 250∼350 g). All experiments followed the guidelines of the Intramural Animal Use and Care Committee of Kyushu Dental College. Synovial cells were isolated from the synovial tissues according to a method previously described.24 Briefly, the tissues were washed twice with α minimal essential medium (α-MEM) (Gibco-BRL, Gaithersburg, MD) and finely minced. The minced tissue samples were then mixed with 5

Expression of RANKL mRNA in synovial cells

After the synovial cells were cultured with or without PGE2 (10−6 mol/L) under the loading of compressive force (1.0 and 2.0 g/cm2) or application of uniaxial sinusoidal strain (10% or 20%), the changes in mRNA expression were examined by RT-PCR. As shown in Fig. 2, A, the expression of RANKL mRNA was detected under the condition of compressive force, with or without culturing with PGE2. In contrast, RANKL mRNA expression was not detected following the application of uniaxial sinusoidal strain,

Discussion

Bone and cartilage destruction in RA and TMJ disorders are partly mediated by proteinases, inflammatory cytokines, neuropeptides, and arachidonic acid catabolites.3, 12 Recently, the results of several studies have suggested that inflammatory osteoclastic bone resorption in the synovium plays an important role in bone destruction in RA.26, 27, 28 Several animal models of RA and TMJ disorders are currently available.29, 30 In the present study, we used the synovial cells from the knee joints to

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