Indole-3-aldehyde Preserves Gingival Epithelial Barrier Structure and Function Via AhR/Nrf2 Signaling Pathway

Indole-3-aldehyde (IAld), an indole derivative of tryptophan metabolized by microorganisms, has been observed to improve epithelial barriers in multiple chronic inflammatory diseases through the aryl hydrocarbon receptor (AhR). This study aimed to elucidate the role and underlying mechanism of IAld in preserving the gingival epithelium via AhR activation in periodontitis. An experimental mouse model of periodontitis was established to assess the anti-periodontitis effect of IAld by using micro-computed tomography (Micro-CT), hematoxylin-eosin staining, immunohistochemical staining and 16S rRNA amplicon sequencing. Subsequently, CCK-8 assays, FITC-FD4 flux measurements, western blotting, and immunofluorescence staining were performed to confirm the protective effect of IAld on P. gingivalis-treated human gingival epithelial cells (hGECs) in vitro. Finally, RNA sequencing, immunofluorescence and immunohistochemical staining were used to thoroughly explore the underlying mechanism. We observed that in periodontitis mice, IAld treatment inhibited alveolar bone loss and periodontal tissue inflammation; activated the AhR pathway; increased the expression levels of E-cadherin, Claudin1, Occludin and ZO-1; and reshaped the oral microbial composition. In vitro, P. gingivalis-stimulated hGECs treated with IAld exhibited decreased FITC-FD4 permeability and upregulated expression of CYP1A1, E-cadherin and Claudin1 compared to the P. gingivalis group. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses revealed downregulation of oxidative stress pathways and overexpression of the antioxidants NrF2 and Hmox1. In vitro, IAld treatment reduced reactive oxygen species (ROS) production and upregulated the expression of Nrf2 and HO-1. Overall, our study demonstrated that IAld improved the function and integrity of the gingival epithelial barrier via the AhR/Nrf2 signaling pathway, thus providing a potential strategy for periodontitis treatment.