title: Porphyromonas gingivalis infection increases osteoclastic bone resorption and osteoblastic bone formation in a periodontitis mouse model.
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, 10(9) 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.
authors.affiliation: Department of Diagnostic and Biomedical Sciences, 7500 Cambridge Street, Suite 5366, Houston 77054, TX, USA. Wenjian.Zhang@uth.tmc.edu.
authors.forename: Wenjian
authors.initials: W
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Ju
authors.forename: Todd
authors.initials: T
authors.lastname: Rigney
authors.forename: Gena
authors.initials: G
authors.lastname: Tribble
mesh_terms: D016301:Alveolar Bone Loss / Q000382:microbiology* / Q000473:pathology; D000539:Alveolar Process / Q000382:microbiology / Q000473:pathology; D000818:Animals; D016866:Bacteroidaceae Infections / Q000503:physiopathology*; D015519:Bone Density / Q000502:physiology; D002452:Cell Count; D004195:Disease Models, Animal; D004848:Epithelium / Q000382:microbiology; D005260:Female; D005347:Fibroblasts / Q000382:microbiology; D005452:Fluoresceins; D005456:Fluorescent Dyes; D005881:Gingiva / Q000382:microbiology; D008437:Maxilla / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008815:Mice, Inbred Strains; D010006:Osteoblasts / Q000382:microbiology*; D010010:Osteoclasts / Q000382:microbiology*; D010012:Osteogenesis / Q000502:physiology*; D010513:Periodontal Ligament / Q000382:microbiology / Q000473:pathology; D010518:Periodontitis / Q000382:microbiology*; D016966:Porphyromonas gingivalis / Q000502:physiology*; D055114:X-Ray Microtomography / Q000379:methods
chemical_list: D005452:Fluoresceins; D005456:Fluorescent Dyes; C007740:fluorexon