Subversion of Lipopolysaccharide Signaling in Gingival Keratinocytes via MCPIP-1 Degradation as a Novel Pathogenic Strategy of Inflammophilic Pathobionts.

Periodontal disease (PD) is an inflammatory disease of the supporting tissues of the teeth that develops in response to formation of a dysbiotic biofilm on the subgingival tooth surface. Although exacerbated inflammation leads to alveolar bone destruction and may cause tooth loss, the molecular basis of PD initiation and progression remains elusive. Control over the inflammatory reaction and return to homeostasis can be efficiently restored by negative regulators of Toll-like receptor (TLR) signaling pathways such as monocyte chemoattractant protein-induced protein 1 (MCPIP-1), which is constitutively expressed in gingival keratinocytes and prevents hyperresponsiveness in the gingiva. Here, we found that inflammophilic periodontal species influence the stability of MCPIP-1, leading to an aggravated response of the epithelium to proinflammatory stimulation. Among enzymes secreted by periodontal species, gingipains-cysteine proteases from Porphyromonas gingivalis-are considered major contributors to the pathogenic potential of bacteria, strongly influencing the components of the innate and adaptive immune system. Gingipain proteolytic activity leads to a rapid degradation of MCPIP-1, exacerbating the inflammatory response induced by endotoxin. Collectively, these results establish a novel mechanism of corruption of inflammatory signaling by periodontal pathogens, indicating new possibilities for treatment of this chronic disease. IMPORTANCE Periodontitis is a highly prevalent disease caused by accumulation of a bacterial biofilm. Periodontal pathogens use a number of virulence strategies that are under intensive study to find optimal therapeutic approaches against bone loss. In our work, we present a novel mechanism utilized by the key periodontal pathogen Porphyromonas gingivalis, based on the selective degradation of the negative regulator of inflammation, MCPIP-1. We found that the diminished levels of MCPIP-1 in gingival keratinocytes-cells at the forefront of the fight against bacteria-cause sensitization to endotoxins produced by other oral species. This results in an enhanced inflammatory response, which promotes the growth of inflammophilic pathobionts and damage of tooth-supporting tissues. Our observation is relevant to understanding the molecular basis of periodontitis and the development of new methods for treatment.