Inactivation of Epidermal Growth Factor by Porphyromonas gingivalis as a Potential Mechanism for Periodontal Tissue Damage

Abstract

f Porphyromonas gingivalis is a Gram-negative bacterium associated with the development of periodontitis. The evolutionary success of this pathogen results directly from the presence of numerous virulence factors, including peptidylarginine deiminase (PPAD), an enzyme that converts arginine to citrulline in proteins and peptides. Such posttranslational modification is thought to affect the function of many different signaling molecules. Taking into account the importance of tissue remodeling and repair mechanisms for periodontal homeostasis, which are orchestrated by ligands of the epidermal growth factor receptor (EGFR), we investigated the ability of PPAD to distort cross talk between the epithelium and the epidermal growth factor (EGF) signaling pathway. We found that EGF preincubation with purified recombinant PPAD, or a wild-type strain of P. gingivalis, but not with a PPAD-deficient isogenic mutant, efficiently hindered the ability of the growth factor to stimulate epidermal cell proliferation and migration. In addition, PPAD abrogated EGFR-EGF interaction-dependent stimulation of expression of suppressor of cytokine signaling 3 and interferon regulatory factor 1. Biochemical analysis clearly showed that the PPAD-exerted effects on EGF activities were solely due to deimination of the C-terminal arginine. Interestingly, citrullination of two internal Arg residues with human endogenous peptidylarginine deiminases did not alter EFG function, arguing that the C-terminal arginine is essential for EGF biological activity. Cumulatively, these data suggest that the PPAD-activity-abrogating EGF function in gingival pockets may at least partially contribute to tissue damage and delayed healing within P. gingivalis-infected periodontia.

Citrullination as a plausible link to periodontitis, rheumatoid arthritis, atherosclerosis and Alzheimer’s disease

“…The virulence factor under focus here is the enzyme P. gingivalis peptidyl-arginine deiminase (PPAD). This enzyme modifies both bacterial and host proteins by deimination of arginine residues in proteins and peptides, converting them to citrulline [11–13] (Figure 2). Protein citrullination causes deregulation of the host’s inflammatory signalling network by altering the spatial arrangement of the original 3D-structure and function of the protein [3,6].…”

“…The secreted PPAD may spread deeply within the connective tissue by shedding P. gingivalis outer membrane vesicles, or through tissue diffusion of the soluble enzyme [13]. The soluble enzyme modifies the epidermal growth factor (EGF) located in the inflamed periodontium which subsequently interferes with EGF function by blocking the recognition between the epithelium and the EGF signalling pathway molecules [13]. This is a mechanism for breaking local protective epithelial cell–periodontal tissue barriers and delaying the healing process [13].…”

“…The soluble enzyme modifies the epidermal growth factor (EGF) located in the inflamed periodontium which subsequently interferes with EGF function by blocking the recognition between the epithelium and the EGF signalling pathway molecules [13]. This is a mechanism for breaking local protective epithelial cell–periodontal tissue barriers and delaying the healing process [13]. In addition, PPAD inhibits the ability of EGF to stimulate epidermal cell proliferation and migration and prevents epidermal growth factor receptor (EGFR)–EGF interaction-dependent stimulation by suppressing cytokine signalling 3 and interferon regulatory factor 1 signalling [13].…”

“…This is a mechanism for breaking local protective epithelial cell–periodontal tissue barriers and delaying the healing process [13]. In addition, PPAD inhibits the ability of EGF to stimulate epidermal cell proliferation and migration and prevents epidermal growth factor receptor (EGFR)–EGF interaction-dependent stimulation by suppressing cytokine signalling 3 and interferon regulatory factor 1 signalling [13]. Ammonia produced as a byproduct during deimination can promote the survival of P. gingivalis in the periodontal pocket [12] and potentially optimize the pH-dependent function of Rgp and PPAD.…”

“…Ammonia produced as a byproduct during deimination can promote the survival of P. gingivalis in the periodontal pocket [12] and potentially optimize the pH-dependent function of Rgp and PPAD. In this way, Rgps and PPAD may inactivate hemagglutinins, promote ATP production, and exert negative effects on neutrophil functions [11,13,27,31]. …”