NLRC4 Inflammasome has a Relevant Role in Experimental Periodontal Disease

Objectives: Periodontal disease is initiated and maintained by microorganisms in the dental biofilm, but most of tissue damage is mediated by immune response to microorganisms. Inflammasomes are multi-protein complexes that include a nucleotide-oligomerization domain leucine-rich repeat containing receptor (NLR), caspase-1 and an adaptor protein. These complexes participate in the sensing of microbial (MAMPs) and tissue damage (DAMPs)-derived molecular patterns by the innate immunity. The purpose was to assess the role of NLRC4 inflammasome in the immune response and bone resorption in experimentally-induced periodontal disease in mice.
Methods: Heat-killed Aggregatibacter actinomycetemcomitans (Aa) suspended in PBS was injected into the palatal gingival tissues adjacent to the upper first molar in mice, three times in a week (1x10⁶ CFU/injection) for four weeks. The same volume of PBS was injected on the contralateral side as control. Wild-type (WT), NLRC4 knockout (NLRC4-KO) and Caspase-1 knockout (Casp1-KO) mice of C57BL/6 background were used (n=6 / genotype). Gene expression of TNFa, IL-6, IL-10, RANKL and MMP-13 in the gingival palatal tissues was determined by RT-qPCR. Stereometric analysis (H/E) was be used to quantitate inflammatory cells in periodontal microenviroment. Extent of bone resorption was assessed by uCT.
Results: Gene expression was similarly modulated by induction of periodontal disease in all genotypes, except for MMP-13, which was significantly increased only in Casp1-KO mice. Casp1-KO presented higher number of mononuclear cells (p<0.05), whereas NLRC4-KO mice had a significantly (p<0.05) higher number of polymorphonuclear neutrophils. uCT analysis showed that bone loss was more severe (p<0.05) in NLRC-4 KO and less severe (p<0.05) Casp1-KO.
Conclusions: The results suggest that the NLRC4 inflammasome has a relevant role in inflammatory-induced bone resorption.