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Open Access Research article

Porphyromonas gingivalis infection increases osteoclastic bone resorption and osteoblastic bone formation in a periodontitis mouse model

Wenjian Zhang1*, Jun Ju1, Todd Rigney2 and Gena Tribble2

Author Affiliations

1 Department of Diagnostic and Biomedical Sciences, 7500 Cambridge Street, Suite 5366, Houston 77054, TX, USA

2 Department of Periodontics and Dental Hygiene, University of Texas School of Dentistry at Houston, 7500 Cambridge Street, Houston 77054, TX, USA

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BMC Oral Health 2014, 14:89  doi:10.1186/1472-6831-14-89

Published: 15 July 2014

Abstract

Background

Porphyromonas gingivalis has been shown to invade osteoblasts and inhibit their differentiation and mineralization in vitro. However, it is unclear if P. gingivalis can invade osteoblasts in vivo and how this would affect alveolar osteoblast/osteoclast dynamics. This study aims to answer these questions using a periodontitis mouse model under repetitive P. gingivalis inoculations.

Methods

For 3-month-old BALB/cByJ female mice, 109 CFU of P. gingivalis were inoculated onto the gingival margin of maxillary molars 4 times at 2-day intervals. After 2 weeks, another 4 inoculations at 2-day intervals were applied. Calcein was injected 7 and 2 days before sacrificing animals to label the newly formed bone. Four weeks after final inoculation, mice were sacrificed and maxilla collected. Immunohistochemistry, micro-CT, and bone histomorphometry were performed on the specimens. Sham infection with only vehicle was the control.

Results

P. gingivalis was found to invade gingival epithelia, periodontal ligament fibroblasts, and alveolar osteoblasts. Micro-CT showed alveolar bone resorption and significant reduction of bone mineral density and content in the infected mice compared to the controls. Bone histomorphometry showed a decrease in osteoblasts, an increase in osteoclasts and bone resorption, and a surprisingly increased osteoblastic bone formation in the infected mice compared to the controls.

Conclusions

P. gingivalis invades alveolar osteoblasts in the periodontitis mouse model and cause alveolar bone loss. Although P. gingivalis appears to suppress osteoblast pool and enhance osteoclastic bone resorption, the bone formation capacity is temporarily elevated in the infected mice, possibly via some anti-microbial compensational mechanisms.

Keywords:
Osteoblasts; P. gingivalis; Invasion; Micro-CT; Bone histomorphometry