Interleukin‐37 ameliorates periodontitis development by inhibiting NLRP3 inflammasome activation and modulating M1/M2 macrophage polarization

Abstract Objective Our study was designed to explore the role of IL‐37 in M1/M2 macrophage polarization imbalance in the pathogenesis of periodontitis. Background Periodontitis is a chronic progressive inflammatory disease featured by gingival inflammation and alveolar bone resorption. Recent research has revealed that regulating macrophage polarization is a viable method to ameliorate periodontal inflammation. IL‐37 is an anti‐inflammatory cytokine, which has been reported to inhibit innate and adaptive immunity. Methods For in vitro experiment, mouse macrophage RAW264.7 cells were pretreated with 0.1 ng/mL recombinant human IL‐37. M1 and M2 polarizations of RAW264.7 cells were induced by 100 ng/mL LPS and 20 ng/mL IL‐4, respectively. The expression of M1 (iNOS, TNF‐α, and IL‐6) and M2 (CD206, Arg1, and IL‐10) phenotype markers in RAW264.7 cells was detected by RT‐qPCR, western blotting, and immunofluorescence staining. For in vivo experiment, experimental periodontitis mouse models were established by sterile silk ligation (5–0) around the bilateral maxillary second molar of mice for 1 week. H&E staining of the maxillary alveolar bone was used to show the resorption of root cementum and dentin. Alveolar bone loss in mouse models was evaluated through micro‐CT analysis. The expression of iNOS and CD206 in gingival tissues was assessed by immunohistochemistry staining. NLRP3 inflammasome activation was confirmed by western blotting. Results IL‐37 pretreatment reduced iNOS, TNF‐α, and IL‐6 expression in LPS‐treated RAW264.7 cells but increased CD206, Arg1, and IL‐10 in IL‐4‐treated RAW264.7 cells. LPS‐induced upregulation in NLRP3, GSDMD, cleaved‐IL‐1β, and cleaved‐caspase‐1 expression was antagonized by IL‐37 treatment. In addition, IL‐37 administration ameliorated the resorption of root cementum and dentin in periodontitis mouse models. IL‐37 prominently decreased iNOS+ cell population but increased CD206+ cell population in gingival tissues of periodontitis mice. The enhancement in NLRP3, GSDMD, cleaved‐IL‐1β, and cleaved‐caspase‐1 expression in the gingival tissues of periodontitis mice was offset by IL‐37 administration. Conclusion IL‐37 prevents the progression of periodontitis by suppressing NLRP3 inflammasome activation and mediating M1/M2 macrophage polarization.