Date of Award
5-26-2021
Document Type
Doctoral Dissertation - Restricted (NYMC/Touro only) Access
Degree Name
Doctor of Philosophy
Department
Basic Medical Sciences
First Advisor
Dr. Salomon Amar
Abstract
Periodontitis is a chronic inflammatory disease triggered by a dysbiosis of the oral microbiome that affects the gum and bone that supports and surrounds the teeth. The dysbiosis of the oral microbiome can be triggered by any range of factors which lead to an increase in the prevalence of the pathobionts Treptonema denticola, Tannerella forsythia, and Porphyromonas gingivalis (P. gingivalis). P. gingivalis has been strongly implicated as the orchestrator of periodontal inflammation driving alveolar bone loss and gingival tissue destruction. As a keystone pathogen, P. gingivalis drives oral microbiome dysbiosis through the subversion of the host immune response, promoting a hyper inflammatory environment (increased M1/M2 macrophage ratio) leading to bone resorption and epithelial barrier dysfunction. Akkermansia muciniphila (A. muciniphila) has become a bacterium of interest in probiotic research due to its association with the restoration of epithelial barrier integrity and reduced systemic inflammation. Furthermore, it has been demonstrated that the beneficial effects of A. muciniphila administration could be achieved with administration of the pasteurized form of the bacteria or even its pili-like protein Amuc_1100. We have tested the ability of A. muciniphila and its derivatives to mitigate inflammation in models of P. gingivalis-induced periodontal disease. We hypothesized that given A. muciniphila’s beneficial effects in the context of other inflammatory disease, that it would prevent the inflammatory tissue destruction and alveolar bone loss associated with P. gingivalis infection through the modulation of the innate immune response. To understand this, in vitro experiments were performed in telomerase immortalized gingival keratinocytes as a model of the gingival epithelium and bone marrow derived macrophages to represent the innate immune response. We found that in the model of the gingival epithelium only administration of viable A. muciniphila could maintain cell barrier integrity through expression of cell-cell adhesion molecules and prevent chemokine paralysis during P. gingivalis infection, suggesting an important bacteria-bacteria interaction. However, in bone marrow macrophage cultures administration of all three treatments: A. muciniphila, viable or pasteurized, and pili-like protein Amuc_1100 prevented the increase in inflammatory cytokine (TNFα), while increasing anti-inflammatory (IL-10) during P. gingivalis infection. The ability to modulate the host response was further tested in murine models of experimental periodontitis. In the calvaria model of acute infection A. muciniphila administration reduced lesion size and severity as well as osteoclast formation. Furthermore, when tested in the mouse ligature model of P. gingivalis-aggravated periodontitis, treatment with A. muciniphila reduced inflammatory infiltrate into the gingival tissues as well as osteoclast formation. Thus, A. muciniphila treatments inhibited the P. gingivalis-induced inflammatory bone loss. Mice that received A. muciniphila treatments, viable or pasteurized as well as pili-like protein Amuc_1100, in a 6-week gavage protocol demonstrated an increase in M2 macrophages found in the submandibular lymph nodes when compared to mice which received P. gingivalis alone. In addition to the increase in anti-inflammatory M2 macrophage in the draining lymph nodes, A. muciniphila treatments resulted in an increase in IL-10 at both the RNA and protein levels within the gingival tissue. The increased expression of IL-10 correlated with the reduced alveolar bone resorption observed in these groups. In these mice it was also found that there was a significant increase in the expression of the TLR3 associated cytokine CXCL10 in the gingival tissue of the A. muciniphila treated groups. The activation of TLR3 is required in normal inflammation after injury and CXCL10 is a chemoattractant for immune cells induced by interferons. Interestingly, this increased expression in CXCL10 correlated with the observed decrease in alveolar bone loss. We had additionally found that TLR3 was increased in bone marrow macrophage cultures treated with A. muciniphila, viable or pasteurized, or Amuc_1100. Furthermore, when TLR3 signaling was blocked with a specific inhibitor in bone marrow macrophages, CXCL10 production was decreased and there was an increased expression of osteoclast markers, indicating the important role of TLR3 in A. muciniphila’s beneficial effects in periodontitis. Taken together, this data indicates that treatment with A. muciniphila and its derivatives increase the production of IL-10 while also decreasing TNFα production preventing the hyperpolarization towards M1 macrophages caused by P. gingivalis infection. The polarization towards a M2 phenotype and manipulation of the immune response by A. muciniphila treatments prevents excessive bone loss associated with P. gingivalis infection. This work supports the use of either viable or pasteurized A. muciniphila or its pili-like protein Amuc_1100 as a promising adjuvant therapy to prevent the progression of periodontitis.
Recommended Citation
Mulhall, Hannah, "Akkermansia muciniphila ameliorates the host response to Porphyromonas gingivalis-induced experimental periodontitis" (2021). NYMC Student Theses and Dissertations. 21.
https://touroscholar.touro.edu/nymc_students_theses/21
