Hyperactivation of Mincle in exacerbated apical periodontitis in an autoinflammatory mouse model for cherubism

Aims: To examine the role of Mincle, a C-type lectin (Clec) pathogen recognition receptor (PRR), in exacerbated apical periodontitis (AP) in an autoinflammatory mouse model for cherubism (CBM). Methodology: Patients with immune system dysfunction have higher prevalence of AP but the mechanism remains largely unknown. We studied a knock-in (KI) mouse model carrying a Sh3bp2 mutation for CBM. We performed pulp exposure in one lower 1st molar of 5- to 6-week-old mice to introduce pathogen-associated molecular patterns (PAMP)-induced endodontic infection. We determined the expression levels of Clec subfamily genes by qPCR. To suppress Mincle, we generated Sh3bp2+/+Mincle+/+, Sh3bp2+/KIMincle+/+, and Sh3bp2+/KIMincleKO/KO mice or injected Sh3bp2+/KI mice with a Mincle-binding DNA aptamer (AptMincle). Mice were analyzed 42 days after pulp exposure by micro-CT (mCT), qPCR and immunoblotting. Statistical analysis was performed by one-way ANOVA followed by post-hoc analysis with Tukeys test or two-way ANOVA followed by Sidak correction. p < 0.05 was considered statistically significant. Results: Expression of Clec4e (Mincle) was significantly increased in Sh3bp2 mutant mice after pulp exposure compared to WT littermates (p<0.0001). Sh3bp2+/KIMincle+/+ and Sh3bp2+/KIMincleKO/KO mice had a comparable response to pulp exposure, including the degree of bone loss and induction of inducible NOS (iNOS), IL-1b, and TNF-a. Sh3bp2+/KI mice injected with AptMincle after pulp exposure for 21 days showed significant amelioration of bone loss compared to mice with vehicle injection (p<0.0001). Conclusions: These seemingly conflicting data of suppressing Mincle by crossing with Mincle KO mice and AptMincle injection suggest that Mincle has dual functions upon PAMPs stimulation, consistent with a previous study showing that Mincle enhances tissue destruction during the inflammatory stage and is subsequently needed for inflammation resolution. Fine-tuned suppression of Mincle significantly reduces the severity of AP in Sh3bp2+/KI mice. This study suggests that patients with CBM may benefit from more frequent dental examinations and early intervention to reduce or prevent severe progressive bone loss in periapical tissues.