Periodontitis is an inflammatory response to the commensal oral bacterial flora and represents one of the most prevalent infections in humans. Approximately 90% of the population exhibits some form of early disease (gingivitis), with 48% of the US adult population having periodontitis and the severe form of the disease affecting 15-20%. Periodontal disease is a polygenic condition that is associated with an exaggerated inflammatory response to the commensal biofilm that drives chronic biofilm dysbiosis at the biofilm-gingival interface. An elevated level of gingival crevicular fluid (GCF) interleukin 1beta (IL-1?) has previously been established as a robust biomarker for a hyper- inflammatory phenotype and for mediating severe inflammation, bone loss and periodontal disease progression. We have recently completed a genome-wide association study (GWAS) of 4910 Caucasians with known levels of GCF-IL-1? to identify loci that are associated with high levels of GCF-IL-1?. We have identified two novel quantitative trait loci with missense polymorphisms within the coding region of the anti-inflammatory gene IL37 that are both statistically significanty associated with high GCF-IL-1? levels (defined as upper quartile or as a continuous variable), p=6.8 X10-21. These missense polymorphisms at two IL-37 loci, are present in 30% and 8.5% of the population. Not only are both loci strongly associated with high local IL-1? levels, but the are also associated with more severe periodontal disease. Under normal conditions IL-37 activates Smad3 and attenuates the innate immune response to TLR agonists to include suppression of IL-1?, IL-1?, TNF?, IL-6, MIP-2 (CXCL2) and GM-CSF. Thus, our central hypothesis is that these IL37 SNP variants cause a functional defect in IL-37 (either via altered mRNA splicing, protein synthesis, activation and/or bioactivity) that results in an excessive pro-inflammatory innate immune response to the commensal organisms of the oral cavity, thereby inducing greater clinical inflammation, bone loss and more severe clinical periodontal disease. Since mice do not express a murine homologue to hIL-37 we propose two aims in murine models to understand whether the two IL37 variants demonstrate impaired IL-37 function I.e. SMAD3 activation and suppression of the innate immune response. First we will transfect murine monocytic RAW cells with the human wild-type [IL37wt] or the two IL37 variants, IL37v1 or IL37v2, to assess the effects of these mutations on IL-37 function, stimulating cells with a range of TLR agonists. These experiments transfecting with IL37v1 or IL37v2 will be confirmed in the human monocytic line THP-1. We expect that the variants will have a hyper-inflammatory trait compared to hIL-37wt, measuring the levels of the mediators listed above, as the read-out. We will also create IL37 variant transgenic mice to measure the response to challenge with P gingivalis using a subcutaneous chamber model and an oral bone loss model. Finally, we will establish a new IL-37 genotyped cohort of subjects to study and confirm the role of these two IL37 variants on IL-37 function and response to TLR challenge using isolated human PBMC and hTERT immortalized cells. It is expected that understanding the role of this novel variant as a potential cause of the underlying hyper-inflammatory trait associated with severe periodontal disease, will ultimately improve diagnosis, prevention and treatment.
