The study of an effect of Porphyromonas gingivalis heat shock protein on bone resorption

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Porphyromonas gingivalis (P. gingivalis) is a Gram-negative bacterium implicated in the pathology of adult periodontitis, an involving destruction of alveolar bone. Chaperonins (cpns) are intracellular oligomeric protein complexes that fold and refold proteins in a catalytic manner. Cpns are also major immunogen in infectious diseases, because of some evidences that Escherichia coli GroEL and Mycobacterial cpn 60s can induce cytokine synthesis, and stimulate cytokine-dependent bone resorption. We have shown mechanisms of bone resorption by components of P. gingivalis such as lipopolysaccharide or fimbrillin by using 14-day-old mouse embryonic calvarial bone cell culture system. However, little is known concerning P. gingivalis chaperonin (Pcpn) 60 (GroEL) on bone resorption. In the present study, we show that P. gingivalis GroEL stimulates bone resorption in the presence of γδT cells was inhibited by osteoprotegerin (OPG). The osteoclast formation by stimulation of P. gingivalis GroEL was observed by coculture between precursor cells (Mac-1(+), c-Fms(+), RANK(+)) treated with both M-CSF (10ng/ml) and suboptimal dose of RANKL, and γδT cells, but not αβT cells. These data suggest that if GroEL was released from P. gingivalis and γδT cells was increased in alveolar bone or periodontal tissue, it could induce osteoclast formation.