Maintaining barrier function of infected gingival epithelial cells by inhibition of DNA methylation

Infection and inflammation induce epigenetic changes that alter gene expression. In periodontal disease, inflammation, and microbial dysbiosis occur, which can lead to compromised barrier function of the gingival epithelia. Here, we tested the hypotheses that infection of cultured human gingival epithelial (HGEp) cells with Porphyromonas gingivalis disrupts barrier function by inducing epigenetic alterations and that these effects can be blocked by inhibitors of DNA methylation.

Primary HGEp cells were infected with P. gingivalis either in the presence or absence of the non-nucleoside DNA methyltransferase (DNMT) inhibitors RG108, (-) epigallocatechin-3-gallate (EGCG), or curcumin. Barrier function was assessed as transepithelial electrical resistance (TEER). DNA methylation and mRNA abundance were quantified for genes encoding components of three cell-cell junction complexes, CDH1, PKP2, and TJP1. Cell morphology and the abundance of cell-cell junction proteins were evaluated by confocal microscopy.

Compared to non-infected cells, P. gingivalis infection decreased TEER (P < 0.0001) of HGEp cells; increased methylation of the CDH1, PKP2, and TJP1 (P < 0.0001); and reduced their expression (mRNA abundance) (P < 0.005). Pretreatment with DNMT inhibitors prevented these infection-induced changes in HGEp cells, as well as the altered morphology associated with infection.

Pathogenic infection induced changes in DNA methylation and impaired the barrier function of cultured primary gingival epithelial cells, which suggests a mechanism for systemic consequences of periodontal disease. Inhibition of these events by non-nucleoside DNMT inhibitors represents a potential strategy to treat periodontal disease.