Spatial proteomics reveals layer-specific molecular landscapes and keratin 17-mediated inflammatory crosstalk in oral lichen planus of the tongue

BACKGROUND: Oral lichen planus (OLP) is a chronic immune-mediated inflammatory disease that affects the oral mucosa, with tongue lesions being clinically significant due to their association with oral cancer risk and taste dysfunction. However, the layer-specific molecular heterogeneity of the basal layer (BL), spinous layer (SL) and lamina propria (LP) in tongue OLP remains poorly characterized, limiting mechanistic understanding and therapeutic development. METHODS: We used spatial proteomics combined with laser capture microdissection to analyse layer-specific protein expression in tongue OLP lesions (with lymphocyte infiltration) and adjacent nonlesional tissues from three patients. Histopathological validation via immunohistochemistry was performed on samples from an expanded cohort of 10 patients with OLP and 10 healthy tongue dorsum tissue samples. Multiplex fluorescent staining was used to analyse the spatial associations between keratin 17 (KRT17) and relevant immune cells and cytokines. In vitro functional assays, including tumour necrosis factor/interferon (IFN)-γ or lipopolysaccharide (LPS)-induced inflammation models, scratch wound healing, apoptosis detection and KRT17 knockdown, were done in human oral keratinocytes (HOKs) to explore the mechanistic roles of key proteins. RESULTS: A total of 4434 proteins were identified, revealing distinct layer-specific dysregulation: 183 upregulated and 98 downregulated proteins in the BL; 262 upregulated and 330 downregulated in the LP; and 91 upregulated and 112 downregulated in the SL. In the BL, immune activation markers (lymphocyte cytosolic protein 1, RAC2, KRT17) were enriched, while metabolic enzymes (argininosuccinate synthetase 1, phosphoglycerate dehydrogenase) were suppressed. The LP showed upregulated proinflammatory mediators [coronin-1A, interleukin (IL)-16] and downregulated extracellular matrix proteins (tenascin X, keratin 9). The SL exhibited disrupted differentiation markers (transglutaminase 3, keratin 13) and innate immune molecules (IFN-induced GTP-binding protein, IFN-stimulated gene 15). Functional enrichment analyses confirmed layer-specific pathogenic axes: immune-metabolic crosstalk in the BL, inflammatory-stromal loops in the LP and differentiation defects in the SL. Multiplex staining revealed spatial correlation between KRT17, T-cell infiltration and IL-1β. In vitro, KRT17 knockdown attenuated LPS-induced inflammation (IL-6, IL-1β), was accompanied by restored HOK migration and reduced apoptosis. CONCLUSIONS: Our study uncovers layer-specific molecular landscapes in tongue OLP and identifies KRT17 as a candidate implicated in immune-epithelial crosstalk, providing novel insights into pathogenesis and a potential direction for future therapeutic exploration.