Periodontitis is a destructive inflammatory disease instigated by a number of microbial pathogens which have evolved mechanisms to manipulate the innate immune response for their own benefit. Among those microbes, Porphyromonas gingivalis stands as a primary contributor to pathology, significantly via its ability to interact with and manipulate Toll-like receptors (TLRs) and other pattern-recognition receptors (PRRs) that trigger innate immune responses. P. gingivalis is predominantly recognized by TLR2 and this interaction leads to two independent downstream pathways: the TLR2 antimicrobial pathway and the TLR2 proadhesive pathway, which transactivates complement receptor 3 (CR3) and allows P. gingivalis to hijack CR3 for safe entry into macrophages. This proposal hypothesizes that P. gingivalis exploits the chemokine receptor CXCR4, not only to suppress the TLR2 antimicrobial pathway (as recently shown), but also to upregulate the TLR2 proadhesive pathway, the focus of Aim 1. Both of these activities have the potential to increase the survival capacity of the pathogen, thereby prolonging P. gingivalis infection and potentiating its impact on periodontal disease. This notion will be tested in vivo using a mouse model of periodontitis (Aim 2). Regarding Aim 1, in vitro immunological approaches using transfected cell lines or primary cells will elucidate the mechanistic basis of P. gingivalis-induced CXCR4/TLR2 crosstalk which transactivates CR3. It is hypothesized that the CXCR4 and TLR2 signaling pathways crosstalk via cAMP-dependent protein kinase A and the small GTPase Rac1, respectively.
Aim 2 is designed to show that P. gingivalis exploits CXCR4 leading to increased pathogen persistence and periodontal disease activity in vivo. Treatment with AMD3100, a mouse/human CXCR4 antagonist which has a proven safety record in HIV clinical trials, will be assessed for its potential to prevent the progression of periodontal disease in an established preclinical mouse periodontitis model. Also, transgenic CXCR4 conditional knockout mice will be used to substantiate our AMD3100 studies as well as provide mechanistic insight into the role CXCR4 plays in P. gingivalis-mediated periodontal disease. This investigation will involve evaluation of the host response and persistence of the infection, as well as induction of periodontal bone loss.
Aim 2 is expected to provide proof-of-principle evidence that by antagonizing CXCR4 with AMD3100 or ablating CXCR4 in mice, therefore preventing P. gingivalis from exploiting it, protection against the destructive periodontal inflammation can be provided. The long-term objective is to identify effective small- molecule antagonists like AMD3100 which can counteract microbial immune evasion mechanistically and thus redirect the immune response to benefit the host.
Periodontitis is perhaps the most common chronic disease of infectious origin in humans, and is moreover associated with systemic inflammatory diseases such as atherosclerosis. This research proposal is based on evidence that periodontal bacteria exploit a host receptor, namely CXCR4, for undermining host immunity and promoting their virulence. Using a preclinical periodontitis model, this application proposes to test AMD3100 (a potent antagonist of mouse/human CXCR4 shown to be safe in clinical trials for HIV treatment) as an intervention treatment in periodontitis. This work is expected to help propel development of prophylactic and post-infection treatments which could drastically improve the quality of life of periodontal patients.
|Hajishengallis, G; McIntosh, M L; Nishiyama, S-I et al. (2013) Mechanism and implications of CXCR4-mediated integrin activation by Porphyromonas gingivalis. Mol Oral Microbiol 28:239-49|