Characterization of Porphyromonas gingivalis -Induced Degradation of Epithelial Cell Junctional Complexes

Abstract

Porphyromonas gingivalis is considered among the etiological agents of human adult periodontitis. Although in vitro studies have shown that P. gingivalis has the ability to invade epithelial cell lines, its effect on the epithelial barrier junctions is not known. Immunofluorescence analysis of human gingival epithelial cells confirmed the presence of tight-junction (occludin), adherens junction (E-cadherin), and cell-extracellular matrix junction (␤1-integrin) transmembrane proteins. These transmembrane proteins are expressed in Madin-Darby canine kidney (MDCK) cells. In addition, MDCK cells polarize and therefore serve as a useful in vitro model for studies on the epithelial cell barrier. Using the MDCK cell system, we examined the effect of P. gingivalis on epithelial barrier function. Exposure of the basolateral surfaces of MDCK cells to P. gingivalis (>10 9 bacteria/ml) resulted in a decrease in transepithelial resistance. Immunofluorescence microscopy demonstrated decreases in the amounts of immunoreactive occludin, E-cadherin, and ␤1-integrin at specific times which were related to a disruption of cell-cell junctions in MDCK cells exposed to basolateral P. gingivalis. Disruption of cell-cell junctions was also observed upon apical exposure to bacteria; however, the effects took longer than those seen upon basolateral exposure. Cell viability was not affected by either basolateral or apical exposure to P. gingivalis. Western blot analysis demonstrated hydrolysis of occludin, E-cadherin, and ␤1-integrin in lysates derived from MDCK cells exposed to P. gingivalis. Immunoprecipitated occludin and E-cadherin molecules from MDCK cell lysates were also degraded by P. gingivalis, suggesting a bacterial protease(s) capable of cleaving these epithelial junction transmembrane proteins. Collectively, these data suggest that P. gingivalis is able to invade the deeper structures of connective tissues via a paracellular pathway by degrading epithelial cell-cell junction complexes, thus allowing the spread of the bacterium. These results also indicate the importance of a critical threshold concentration of P. gingivalis to initiate epithelial barrier destruction.

Cerebral Oxidative Stress and Microvasculature Defects in TNF-α Expressing Transgenic and Porphyromonas gingivalis-Infected ApoE–/– Mice

“…Therefore, the detection of increased protein carbonyl levels in these mice is expected, as these mice appear to be less efficient in counteracting the elevated levels of oxidative stress induced by TNF-α and the cerebellar BBB defect. In addition, live P. gingivalis infection is likely to exert its effect on the host through other virulence factors, such as its proteolytic activity mediated by gingipains [13][14][15]. Concerning the microvascular structure of the brain, it is plausible to extrapolate relevant information from cell-cell junctional protein (catenins, occludin, E-cadherin and β1-integrin) disruption from in vitro infection data already documented [13][14][15].…”

“…In response to chronic bacterial infection, TNF-α release represents a proinflammatory cytokine at the apex of the inflammatory cascade that mediates local inflammatory damage including the production of locallized oxidative stress and has been shown to be upregulated in response to P. gingivalis LPS in vivo [13][14][15]. In the TNF-α trangenic mouse, TNF-α mRNA is stabilized and its expression appears to be increased within all tissues, including the brain.…”

“…Furthermore, live P. gingivalis infection is likely to exert its effect on the host through a diverse range of virulence factors. Apart from its lipopolysaccharide (LPS), which can cause the host to respond through oxidative burst and other mechanisms, proteolytic activity mediated by P. ginivalis gingipains are capable of targetting cell-cell adhesion molecules [13,14,15]. It is, therefore, likely that gingipains also contribute to the degradation of endothelial cell tight junction proteins and the subsequent loss of blood-brain barrier (BBB) functional integrity.…”

Salivary antioxidants and periodontal disease status

“…Once in the cytoplasm, P. gingivalis replicates in relative safety from the host immune cells due to its location within the cell. Ingression deeper into connective tissue structures occurs via degradation of the network of cell junctions, leading to a proliferation into the host tissues (Katz et al 2000). P. gingivalis possesses an array of agents that can damage host tissue, modulate host cells and evade detection.…”

Computer-assisted identification of the gingival sulcus and periodontal epithelial junction on high-frequency ultrasound images

“…The first effects of an infection with Porphyromonas gingivalis occur at the level of the epithelial junction, through al-terations in keratinization, the degree of desquamation, and mitotic activity [5]. The concentration of P. gingivalis is directly related to the onset of the destruction of the epithelial barrier [6]. In response to the increased forces (such as orthodontic forces) on the teeth, the epithelial insertion becomes modified, setting off an immunological response in addition to inflammation [7].…”