UCLA

Background: Periodontitis is an infectious, inflammatory disease resulting in destruction of the supporting tissues of the teeth. While bacterial biofilm is central to disease pathogenesis, the host response plays an important role in the severity and progression of periodontitis. Studies have shown a strong genetic influence, accounting for as much as 50% of disease presentation. Previous work in our laboratory utilized a Genome-wide Association Study (GWAS) with a Lipopolysaccharide (LPS)-induced periodontitis murine model to identify candidate genes associated with periodontitis. Using GWAS, mRNA, and protein expression data, chemokines Cxcl9 and Cxcl10 were found to be associated and significantly upregulated in a high bone loss strain C57BL/6J compared to bone loss resistant strain A/J. Cxcl9 and Cxcl10 both exert their function through the receptor CXCR3.

Objective: The purpose of this study was to investigate the influence of Cxcl9 and Cxcl10 on LPS-induced periodontal bone loss by blocking their action utilizing a CXCR3 knockout mouse.

Materials and Methods: 12 wild-type (WT) and 12 CXCR3 knockout (KO) C57BL/6J mice were included in this study. Periodontitis was induced using P.gingivalis-LPS injections between the maxillary first and second molars 2x/week for 6 weeks. Following sacrifice, maxillae were scanned (microCT) and bone loss quantified. Histologic analysis of osteoclasts and pro-inflammatory mediators was performed.

Results: Deleting CXCR3 demonstrated ~50% reduction in bone loss after LPS- injections compared to WT mice. 3D volumetric analysis showed no significant differences in initial bone volume/tissue volume (BV/TV) between CXCR3 KO and WT animals, indicating the changes observed were due to LPS treatment and not inherent differences in bone quality. Histologically, an increase in cellular infiltrates was seen in WT LPS treated mice compared to CXCR3 KO LPS treated mice, visualized through H&E and COX-2 immunostaining. Quantification of osteoclasts through TRAP staining revealed significantly more TRAP+ cells in WT LPS treated compared to CXCR3 KO LPS treated mice, correlating with the increased bone loss seen in the WT LPS treated animals.

Conclusion: CXCR3 and binding chemokines Cxcl9 and Cxcl10 are likely key players in the maintenance and amplification of inflammatory pathways. CXCR3 may be a possible target for modulating the host response in periodontitis by dampening the inflammatory cascade following LPS-stimulation. Further work is needed to characterize the CXCR3 pathway and validate other candidate genes associated with LPS-induced bone loss. The ultimate goal is to identify patients at high risk for periodontal disease and manage them with individualized treatment.