Dimethyl fumarate inhibits noncanonical pyroptosis in dental fibroblasts

Backgound: Pyroptosis is a type of inflammatory cell death and is related to some oral inflammatory diseases. However, how dental fibroblasts, the major cell type in inflamed pulp and periodontium, respond to pyroptotic stimuli is not fully understood. Dimethyl fumarate (DMF), a derivative of fumarate, has immunomodulatory effects and is used as an anti-inflammatory drug. However, the effects of DMF on dental fibroblasts under exposure to pyroptotic stimuli are unclear. Methods We used three methods (stimulation with lipopolysaccharide (LPS) plus nigericin, poly(dA:dT) transfection and LPS transfection) to induce pyroptosis in periodontal ligament fibroblasts (PDLFs) and dental pulp cells (DPCs), two types of dental fibroblasts. THP-1 cell was used as a positive control. After that, PDLFs and DPCs were treated with or without DMF before inducing pyroptosis to examine the inhibitory effect of DMF. Pyroptotic cell death was measured by lactic dehydrogenase (LDH) release assays, cell viability assays, propidium iodide (PI) staining and flow cytometry. The expression levels of cleaved gasdermin D N-terminal (GSDMD NT), caspase-1 p20, caspase-4 p31 and cleaved PARP were examined by immunoblotting. Immunofluorescence analysis was used to detect the cellular distribution of GSDMD NT. Results We showed that PDLFs and DPCs were more sensitive to cytoplasmic LPS-induced noncanonical pyroptosis than to canonical pyroptosis induced by stimulation with LPS priming plus nigericin or by poly(dA:dT) transfection. In addition, treatment with DMF attenuated cytoplasmic LPS-induced pyroptotic cell death in PDLFs and DPCs. Mechanistically, we demonstrated that the expression and plasma membrane translocation of GSDMD NT were inhibited in DMF-treated PDLFs and DPCs. Conclusions The current study indicates that dental fibroblasts are more sensitive to cytoplasmic LPS-induced noncanonical pyroptosis and that DMF treatment blocks pyroptosis in LPS-transfected dental fibroblasts by targeting GSDMD, suggesting DMF might be a promising drug for oral inflammatory diseases.