Tannic acid inhibits TNF-α signaling by targeting the protein disulfide isomerase and alleviates symptoms in an imiquimod-induced psoriasis mouse model.

BACKGROUND: Inhibiting TNF-α signaling is an effective approach to prevent inflammation, which can mitigate the symptoms of autoimmune diseases. Activation of the ADAM17-TNFR1 signaling module using small-molecule protein disulfide isomerase (PDI) inhibitors effectively induces TNFR1 shedding and TNF-α signaling inhibition. However, it is not known whether tannic acid (TA), a verified PDI inhibitor with outstanding anti-inflammatory effects, could alleviate autoimmune diseases. OBJECTIVE: We set out to explore the anti-inflammatory mechanism of TA and whether it could be used to treat the classical autoimmune disease, psoriasis. METHODS: Molecular interactions were assessed using insulin reduction assays with full-length PDI and its domain fragments to identify TA binding sites. Non-covalent binding and conformational changes were evaluated using AMS-modified SDS-PAGE and ANS fluorescence. Molecular chaperone activity was measured using rhodanese refolding. Cellular assays included cytotoxicity, apoptosis, and NF-κB activation in L929 cells using CCK-8, flow cytometry, western blot, and RT-qPCR. PDI dependency was confirmed using CRISPR-Cas9 knockout. TNFR1 shedding was quantified using flow cytometry and ELISA. In vivo efficacy was tested in an imiquimod (IMQ)-induced psoriasis mouse model treated with TA ointment (5% and 10%), and the outcomes were evaluated using the psoriasis area and severity index (PASI), histopathology, blood routines, and blood biochemical examinations. RESULTS: TA selectively inhibited the reductase activity of the b’ domain of PDI and induced non-covalent conformational changes, reducing hydrophobicity and chaperone function. TA effectively suppressed TNF-α-induced apoptosis in cells, NF-κB activation, and inflammatory gene expression. PDI knockout abolished TA-induced TNFR1 shedding, confirming PDI dependence. In IMQ-induced psoriatic mice, 10% TA ointment significantly reduced the PASI scores and the incidence of histopathological features. TA also normalized blood inflammation and restored physical functions. CONCLUSIONS: In summary, our study showed that TA blocks TNF-α signaling by inhibiting PDI, and exhibits potential application value in combating autoimmune diseases, especially psoriasis.