[Effects of Fusobacterium nucleus derived outer membrane vesicles on claudin-4 expression in oral epithelial cells]

To investigate the effect of outer membrane vesicles (OMVs) secreted by Fusobacterium nucleatum (F.n) on Claudin-4 of human oral keratinocytes (HOK) and oral epithelial barrier function.

Fusobacterium nucleatum was cultured under anaerobic conditions. The OMVs were extracted by dialysis and characterized by nanosight and transmission electron microscopy (TEM). HOK were stimulated with OMVs at different mass concentrations(0-100 μg/mL) for 12 h, and stimulated with 100 μg/mL OMVs for 6 h and 12 h respectively. The expression of Claudin-4 at gene and protein level was analyzed by RT-qPCR and Western blotting. Inverted fluorescence microscope was used to observe co-localization of HOK and OMVs and localization and distribution of Claudin-4 protein. Human oral epithelial barrier was constructed by Transwell apical chamber. Transepithelial electrical resistance(TER) of barrier was measured with a transmembrane resistance measuring instrument(EVOM2), and the permeability of the barrier was evaluated by transmittance of fluorescein isothiocyanate-dextran(FD-4). Statistical analysis was performed with GraphPad Prism 8.0 software package.

Compared with the control group, the expression of Claudin-4 at protein and gene level in the HOK of OMVs stimulated group was significantly reduced (P＜0.05), and immunofluorescence showed that the continuity of Claudin-4 fluorescence among cells was destroyed. OMVs stimulation decreased TER value of oral epithelial barrier(P＜0.05) and increased the transmittance of FD-4(P＜0.05).

OMVs derived from Fusobacterium nucleatum may damage oral mucosal epithelial barrier function through inhibiting the expression of Claudin-4.