ABSTRACT
Recent genome-wide association studies have suggested novel risk loci associated with periodontitis, which is initiated by dysbiosis in subgingival plaque and leads to destruction of teeth-supporting structures. One such genetic locus was the tumor necrosis factor receptor-associated factor 3 interacting protein 2 (TRAF3IP2), a gene encoding the gate-keeping interleukin (IL)-17 receptor adaptor. In this study, we first determined that carriers of the lead exonic variant rs13190932 within the TRAF3IP2 locus combined with a high plaque microbial burden was associated with more severe periodontitis than noncarriers. We then demonstrated that TRAF3IP2 is essential in the IL-17-mediated CCL2 and IL-8 chemokine production in primary gingival epithelial cells. Further analysis suggested that rs13190932 may serve a surrogate variant for a genuine loss-of-function variant rs33980500 within the same gene. Traf3ip2 null mice (Traf3ip2-/-) were more susceptible than wild-type (WT) mice to the Porphyromonas gingivalis-induced periodontal alveolar bone loss. Such bone loss was associated with a delayed P. gingivalis clearance and an attenuated neutrophil recruitment in the gingiva of Traf3ip2-/- mice. Transcriptomic data showed decreased expression of antimicrobial genes, including Lcn2, S100a8, and Defb1, in the Traf3ip2-/- mouse gingiva in comparison to WT mice prior to or upon P. gingivalis oral challenge. Further 16S ribosomal RNA sequencing analysis identified a distinct microbial community in the Traf3ip2-/- mouse oral plaque, which was featured by a reduced microbial diversity and an overabundance of Streptococcus genus bacteria. More P. gingivalis was observed in the Traf3ip2-/- mouse gingiva than WT control animals in a ligature-promoted P. gingivalis invasion model. In agreement, neutrophil depletion resulted in more local gingival tissue invasion by P. gingivalis. Thus, we identified a homeostatic IL-17-TRAF3IP2-neutrophil axis underpinning host defense against a keystone periodontal pathogen.
Subject(s)
Alveolar Bone Loss , Periodontitis , Mice , Animals , Gingiva/metabolism , Interleukin-17/metabolism , Genome-Wide Association Study , Periodontitis/microbiology , Alveolar Bone Loss/metabolism , Porphyromonas gingivalis , Mice, Knockout , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/metabolismABSTRACT
GSTM has been used for long in the treatment of rheumatoid arthritis (RA). However, its mechanism of action is still poorly understood. In the last decade, tumor necrosis factor-alpha (TNF-alpha) has emerged as the major pro-inflammatory cytokine in the pathogenesis of RA. We studied the effect of GSTM on spontaneous and LPS-stimulated TNF-alpha production by human peripheral blood mononuclear cells (PBMCs) of normal volunteers. PBMCs were isolated from 20 normal volunteers and cultured in the presence of absence of lipopolysaccharide (LPS 10 ng/ml) and GSTM (1 microgram/ml). TNF-alpha level was measured using commercial enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). The TNF-alpha response to LPS was heterogeneous. PBMCs of 24 subjects showed high LPS-stimulated TNF-alpha production (LPS-responsive group), whereas that of six individuals had low LPS-stimulated TNF-alpha production (LPS-non-responsive group). GSTM-stimulated spontaneous TNF-alpha production and inhibited LPS-stimulated TNF-alpha production in 16 of 24 (75%) individuals of LPS-responsive group and one of six individuals (17%) of LPS-non-responsive group. The suppression of TNF-alpha by GSTM was also demonstrated at the mRNA level. We conclude that there is a heterogeneity among normal population for TNF-alpha production in response to LPS, and GSTM inhibits LPS-stimulated TNF-alpha production, primarily in LPS responders. Further study is needed to establish the relationship between LPS responsiveness and GSTM suppression.
