Spatially resolved single cell atlas deciphers SAA1 inflammatory epithelial cells.

Disruption of epithelial integrity is a pivotal event in inflammation, disease pathogenesis, and tissue homeostasis. To investigate these processes in chronic inflammatory disease, we performed spatial transcriptomics integrated with single-cell RNA sequencing (scRNA-seq) on human gingival tissue, coupled with metagenomic analysis of matched subgingival plaque. This approach allowed in situ characterization of epithelial heterogeneity and microbiome-epithelium-connective tissue crosstalk. We identified a distinct inflammatory epithelial subpopulation (SAA1+Epi), situated within the junctional epithelium, that becomes activated through the TLR2-PITX2 axis by Porphyromonas gingivalis lipopolysaccharide. These SAA1+Epi cells secrete TGFβ, which induces an inflammatory program in the connective tissue by driving the differentiation of inflammation-associated fibroblasts (C3+FB) via the PI3K/Akt pathway. Concurrently, SAA1+Epi cells express chemotactic factors such as CXCL6 to recruit NK cells, thereby sustaining the inflammatory niche. The transcription factor PITX2 emerged as a critical regulator of SAA1+Epi differentiation; targeting PITX2 suppressed  C3+FB induction and natural killer (NK) cells recruitment, ultimately attenuating periodontitis progression. Our findings position SAA1+Epi as a frontline responder to dysbiotic bacteria at the inflammatory interface and underscore its essential role in regulating epithelial-connective tissue homeostasis during inflammation.