Background/aims: Interleukin 33 (IL-33) plays a significant role in immunity but its role in bone physiology and periodontitis needs to be further investigated. The aim of this study was to decipher the contribution of IL-33 to bone homeostasis under physiological conditions, and to alveolar bone loss associated with experimental periodontitis (EP) in IL-33 knockout (KO) mice and their wildtype (WT) littermates.
Methods: The bone phenotype of IL-33 KO mice was studied in the maxilla, femur, and fifth lumbar vertebra by micro-computed tomography (micro-CT). EP was induced by a ligature soaked with the periopathogen Porphyromonas gingivalis (Pg) around a maxillary molar. Alveolar bone loss was quantified by micro-CT. The resorption parameters were assessed via toluidine blue staining on maxillary sections. In vitro osteoclastic differentiation assays using bone marrow cells were performed with or without lipopolysaccharide from Pg (LPS-Pg).
Results: First, we showed that under physiological conditions, IL-33 deficiency increased the trabecular bone volume/total volume ratio (BV/TV) of the maxillary bone in male and female mice, but not in the femur and fifth lumbar vertebra, suggesting an osteoprotective role for IL-33 in a site-dependent manner. The severity of EP induced by Pg-soaked ligature was increased in IL-33 KO mice but in female mice only, through an increase in the number of osteoclasts. Moreover, osteoclastic differentiation from bone marrow osteoclast progenitors in IL-33-deficient female mice is enhanced in the presence of LPS-Pg.
Conclusion: Taken together, our data demonstrate that IL-33 plays a sex-dependent osteoprotective role both under physiological conditions and in EP with Pg.
Keywords: Interleukin-33; Inflammation; Periodontitis; Porphyromonas gingivalis; Osteoclasts.
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