Dental plaque metabolites induce polymorphonuclear leukocyte death accompanying peptidyl arginine deiminase 4 and citrullinated protein release: Potential contribution to rheumatoid arthritis pathogenesis.

OBJECTIVES: Neutrophils form the front line of defense in the periodontal pocket. They release the web-like DNA structures, known as neutrophil extracellular traps (NETs). NETosis, a form of programmed cell death, is characterized by the release of NETs, peptidyl arginine deiminase (PAD), and citrullinated proteins. Plaque bacteria produce a variety of metabolites that can interact with neutrophils and potentially modulate its function. In this study, how these bacterial metabolites influence NETosis-like cell death in polymorphonuclear leukocytes (PMNL) was investigated.

METHODS: SYTOX Green dye, which strongly fluoresces on binding to double-stranded DNA, was used to quantify and visualize NETosis-like cell death. The release of neutrophil elastase, PAD4, and citrullinated histone H3 were evaluated using western blotting.

RESULTS: Culture supernatants of various oral pathogens induced NETosis-like cell death. As these supernatants were rich in short-chain fatty acids (SCFAs), each SCFA was tested individually, and they all induced cell death. Similarly, SCFA mixtures replicating the composition of the bacterial supernatant induced PMNL death. Interestingly, SCFA treatment enhanced the release of extracellular neutrophil elastase, PAD4, and citrullinated histone H3. These effects were significantly attenuated by ROS scavenging and PAD4 inhibition.

CONCLUSIONS: SCFAs produced by plaque bacteria trigger ROS- and PAD4-dependent NETosis-like cell death, leading to the release of PAD4 and citrullinated proteins. Given that protein citrullination plays a pivotal role in the generation of autoantibodies during the onset and progression of rheumatoid arthritis (RA), these findings indicate that bacterial SCFAs may substantially contribute to the initiation and exacerbation of RA.