Periodontitis, an inflammatory disease initiated by Gram-negative bacteria such as Porphyromonas gingivalis ( Pg), is considered as a risk factor for rheumatoid arthritis (RA). Our study aimed to determine the effect of Pg and its LPS on the expression of peptidyl arginine deiminase isotypes (PADs) in human primary chondrocytes (HC). HCs were infected with Pg and activated by its LPS (LPS- Pg). The mRNA expression levels of human PADs (1, 2, 3, 4 and 6) and bacterial enzyme (PADPg) were quantified by RT-qPCR. Cellular extracts served to measure the enzymatic activities of PADs and PADPg and to visualize the profiles of citrullinated proteins/peptides by Western blotting. Our data showed significant inhibitions of mRNA expressions of human PAD-2, PAD-3 and PAD-4 during infection of HC with live Pg. Activation of HC by LPS- Pg increased mRNA expressions of human PAD-2 and PAD-3. The PADPg enzymatic activity was significantly increased in only infected HC. Analysis of citrullinated proteins/peptides profiles revealed the occurrence of low molecular bands only in cellular extracts from HC infected with Pg. Our data showed that Pg and its LPS differentially regulate the expression of PADs in human chondrocytes and that Pg favors the apparition of new citrullinated proteins/peptides.
Keywords: Periodontitis; arthritis; gene expression; innate immunity; microbiology.