Objective: A role of bacterial infections in the pathogenesis of rheumatoid arthritis (RA) has been suggested. P. gingivalis, a Gram-negative, anaerobic rod, is one of the major pathogens associated with periodontal disease (PD). The present study examines P. gingivalis infection and effects on cell cycle progression and apoptosis of human articular chondrocytes.
Methods: Primary human chondrocytes cultured in monolayers were challenged with P. gingivalis. Infection and invasion of P. gingivalis into chondrocytes was analyzed by scanning electron microscopy (SEM), double immunofluorescence and by antibiotic protection and invasion assay. Cell cycle progression of infected chondrocytes was evaluated by flow cytometry. Also, cell apoptosis was visualized by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) of DNA strand breaks and by Western blot analysis.
Results: Data revealed that P. gingivalis was able to adhere and infect primary human chondrocytes. Following chondrocyte infection intracellular localization of P. gingivalis was noted. Flow cytometry analyses demonstrated affected cell cycle progression, with an increase of G1 phase and significant decrease of G2 phase post-infection. In addition, increased apoptosis of P. gingivalis infected chondrocytes was visualized by TUNEL assay as well as by an up-regulation of caspase-3 protein expression.
Conclusion: The present data demonstrate that P. gingivalis infects primary human chondrocytes and affects cellular responses, which might contribute to the tissue damage seen in the pathogenesis of RA.