Diosgenin exerts dual impacts on Th17 cell differentiation in adjuvant-induced arthritis rats by impairing SIRT1-mediated deacetylation

Background: Dioscorea spongiosa is used in China as the herbal medicine Bixie.

Purpose: This study investigated how SIRT1-inhibitory effects affect its therapeutic outcomes in adjuvant-induced arthritis (AIA).

Methods: AIA rats were treated with the extract of D. spongiosa (BX), diosgenin, or together with an NF-κB Inhibitor. Therapeutic effects were assessed by ELISA, flow cytometry, and histology analyses. Affinities of compounds to SIRT1 were evaluated based on molecular simulation, immunoprecipitation, spectroscopy, protein stability, and isothermal titration calorimetry data. SIRT1 and NF-κB signals were regulated by siRNA, overexpression plasmids, and inhibitors. Pathway status was characterized by PCR, WB, immunohistochemistry, immunofluorescence, and reporter gene assays.

Results: BX ameliorated joint damage and inflammation in AIA rats. These effects weakened with increasing doses. This therapy upregulated acetylation in the spleen. Diosgenin, a major compound in BX bioactive fraction, exhibited distinct effects on IL-17A release at varied concentrations, which was identified as a SIRT1 Inhibitor subsequently. In Jurkat T cells, diosgenin impaired deacetylation, exerting different impacts on the transcriptional activities of p65 NF-κB and RORγt. The effects were antagonized by SIRT1 overexpression, and abolished when SIRT1 was silenced. In the presence of NF-κB inhibitors, diosgenin reduced IL-17A secretion of Jurkat cells in a concentration-dependent manner, and its therapeutic effects on AIA were further enhanced.

Conclusion: Diosgenin-mediated impairment of deacetylation benefited AIA rats by inhibiting RORγt activity. However, at high concentrations, this SIRT1-inhibitory effect promoted Th17 differentiation via NF-κB activation. These findings provide a theoretical basis for optimizing Bixie-relevant therapies, and highlight potential risks of SIRT1-targeted therapies.

Bixie; Inflammation; Rheumatoid arthritis; SIRT1 inhibitor; Th17 cell; p65.