Fusobacterium nucleatum Binding to Complement Regulatory Protein CD46 Modulates the Expression and Secretion of Cytokines and Matrix Metalloproteinases by Oral Epithelial Cells

Abstract

Periodontitis is a chronic inflammatory disease that results in the destruction of the supporting tissues of the teeth. Gingival epithelial cells are an important mechanical barrier and participate in the host inflammatory response to periodontopathogens. The aim of the present study is to investigate the capacity of Fusobacterium nucleatum to bind to the complement regulatory protein CD46 expressed by oral epithelial cells and to determine the impact of the binding on the gene expression and protein secretion of interleukin (IL)-6, IL-8, and matrix metalloproteinase (MMP)-9 by oral epithelial cells. Binding of recombinant human CD46 to the surface of F. nucleatum was demonstrated by immunologic assays. After stimulation of oral epithelial cells with F. nucleatum, gene expression was determined by real-time polymerase chain reaction analysis while protein secretion was monitored by enzyme-linked immunosorbent assays. Heat and protease treatments of bacterial cells reduced CD46 binding. F. nucleatum-bound CD46 mediated the cleavage of C3b in the presence of factor I. Stimulating oral epithelial cells with F. nucleatum at a multiplicity of infection of 50 resulted in a significant upregulation of the gene expression and protein secretion of IL-6, IL-8, and MMP-9 by oral epithelial cells. However, pretreating the epithelial cells with an anti-CD46 polyclonal antibody attenuated the production of IL-6, IL-8, and MMP-9 in response to F. nucleatum. Such an inhibitory effect was not observed with non-specific antibodies. The present study demonstrates that F. nucleatum can bind the complement regulatory protein CD46. The interaction of F. nucleatum with epithelial cell surface CD46 may contribute to increasing the levels of proinflammatory mediators and MMPs in periodontal sites and consequently modulate tissue destruction.