Potential role of periodontal pathogens in compromising epithelial barrier function by inducing epithelial-mesenchymal transition.

Abstract

Epithelial-mesenchymal transition (EMT) is a process by which epithelial cells acquire a mesenchymal-like phenotype and this may be induced by exposure to gram-negative bacteria. It has been proposed that EMT is responsible for compromising epithelial barrier function in the pathogenesis of several diseases. However, the possible role of EMT in the pathogenesis of periodontitis has not previously been investigated. The aim of this study therefore was to investigate whether gram-negative, anaerobic periodontal pathogens could trigger EMT in primary oral keratinocytes in vitro. Primary oral keratinocytes were harvested from labial mandibular mucosa of Wistar Han rats. Cells were exposed to heat-killed Fusobacterium nucleatum and Porphyromonas gingivalis (100 bacteria/epithelial cell) and to 20μg/mL of Escherichia coli lipopolysaccharide over an 8-day period. Exposure to bacteria did not significantly change epithelial cell number or vitality in comparison with unstimulated controls at the majority of time-points examined. Expression of EMT marker genes was determined by semiquantitative RT-PCR at 1, 5, and 8days following stimulation. The expression of EMT markers was also assessed by immunofluorescence (E-cadherin and vimentin) and using immunocytochemistry to determine Snail activation. The loss of epithelial monolayer coherence, in response to bacterial challenge, was determined by measuring trans-epithelial electrical resistance. The induction of a migratory phenotype was investigated using scratch-wound and transwell migration assays. Exposure of primary epithelial cell cultures to periodontal pathogens was associated with a significant decrease in transcription (~3-fold) of E-cadherin and the upregulation of N-cadherin, vimentin, Snail, matrix metalloproteinase-2 (~3-5 fold) and toll-like receptor 4. Bacterial stimulation (for 8 days) also resulted in an increased percentage of vimentin-positive cells (an increase of 20% after stimulation with P.gingivalis and an increase of 30% after stimulation with F.nucleatum, compared with controls). Furthermore, periodontal pathogens significantly increased the activation of Snail (60%) and cultures exhibited a decrease in electrical impedance (P<.001) in comparison with unexposed controls. The migratory ability of the cells increased significantly in response to bacterial stimulation, as shown by both the number of migrated cells and scratch-wound closure rates. Prolonged exposure of primary rat oral keratinocyte cultures to periodontal pathogens generated EMT-like features, which introduces the possibility that this process may be involved in loss of epithelial integrity during periodontitis.