Effects of Porphyromonas gingivalis on cell cycle progression and apoptosis of primary human chondrocytes

Background: It has been suggested that bacterial infections have a role in the pathogenesis of rheumatoid arthritis (RA). P gingivalis , a Gram-negative, anaerobic rod, is one of the major pathogens associated with periodontal disease. Objective: To examine P gingivalis infection and its 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 analysed by scanning electron microscopy, double immunofluorescence and by antibiotic protection and invasion assay. Cell cycle progression of infected chondrocytes was evaluated by flow cytometry. Also, cell apoptosis was visualised by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) of DNA strand breaks and by western blot analysis. Results: Data showed that P gingivalis could adhere and infect primary human chondrocytes. After chondrocyte infection, intracellular localisation of P gingivalis was noted. Flow cytometry analyses demonstrated affected cell cycle progression, with an increase of the G 1 phase and a significant decrease of the G 2 phase after infection. In addition, increased apoptosis of P gingivalis -infected chondrocytes was visualised by TUNEL assay and by upregulation of caspase-3 protein expression. Conclusion: These 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 rheumatoid arthritis.