Effect of Porphyromonas gingivalis on citrullination of proteins by macrophages in vitro

Abstract

Background & Objectives: Citrullination of proteins within inflamed periodontal tissues may provide an important link between periodontitis and rheumatoid arthritis. The aim of this study was to determine whether the presence of Porphyromonas gingivalis peptidylarginine deiminase (PPAD) can influence citrullination of proteins either by increasing the amount of local citrullinated protein or by influencing the peptidylarginine deiminase (PAD) enzymes found in the monocyte/macrophage population. Materials and Methods: Human peripheral blood monocytes and macrophages were incubated in the presence of live or heat-killed Porphyromonas gingivalis. Expression of peptidyl arginine deiminase 2 and 4, P. gingivalis peptidyl arginine deiminase and citrullinated proteins were assessed by either or a combination of real time polymerase chain reaction (PCR), western blotting or a colorimetric assay. Results: P. gingivalis peptidyl arginine deiminase was detected only in mononuclear cells incubated in the presence of live P gingivalis and resulted in increased extracellular citrullination. Endogenous peptidyl arginine deiminase (mRNA and protein) expression was detected in monocytes and macrophages but was not affected by P. gingivalis. Conclusion: Although P. gingivalis produces a peptidylarginine deiminase which can citrullinate extracellular proteins and may contribute to the citrullinated protein load in gingival tissues, it does not appear to affect PAD expression or citrullination by host monocytes or macrophages.