Treponema denticola is an important member of a consortium of microorganisms that are etiologic in the initiation and progression of periodontitis. In diseased sites, the local periodontal environment has low levels of oxygen and often has high concentrations of H2S. This continuation application extends our studies on the role of H2S production in T. denticola virulence. Previously we had characterized two of the enzymes, gamma-glutamyltransferase and cystalysin, in the three step pathway (TSP) that catabolizes glutathione to H2S. More recently, we have purified and enzymatically characterized cysteinylglycinase (CGaseA), the third member of the pathway, and constructed and characterized a CGaseA mutant. Most interestingly, we have determined that T. denticola, an obligate anaerobe, can proliferate """"""""aerobically"""""""". Our novel results strongly suggest that the H2S generated by glutathione catabolism creates a low O2 microenvironment that allows the """"""""aerobic"""""""" growth of T. denticola. We have also discovered that the expression of a new protein, CGaseB, is induced under these """"""""aerobic"""""""" growth conditions. Based upon our latest results, our new hypothesis is that the production of H2S from the catabolism of glutathione by T. denticola may have two critical roles in periodontitis: (i) generating or helping to maintain the hypoxic microenvironment found in the periodontal pocket, and (ii) acting as a cytotoxin to produce some of the tissue damage seen in periodontal diseases. To begin to test these hypotheses, we propose (Aim 1) to complete the purification and enzymatic characterization CGaseB. We will construct mutants in each of the genes (ggt, cgaA/cgaB, hly) encoding the TSP catabolic proteins to prove that all of the enzymes in the pathway have been found and to provide valuable tools for the other Aims. In vitro approaches will be used (Aim 2) to prove that H2S production by the T. denticola TSP is responsible creating the low oxygen microenvironment that allow this anaerobe to grow """"""""aerobically"""""""". The pathogenic potential of H2S production by the TSP will then be tested (Aim 3) in vitro, looking at host cell apoptosis, and in vivo, in animal models of soft tissue destruction and aveolar bone resorption. Both wild type and mutant T. denticola cells will be used in these studies to assess the relative importance of the TSP in pathogenesis. Finally, we will show (Aim 4) that the hypoxic environment created by T. denticola's metabolism of glutathione allows other periodontal anaerobes, P. gingivalis and T. forsythia, to grow """"""""aerobically"""""""" and also test the possibility that this leads to an altered biofilm when T. denticola and P. gingivalis are co-cultured. The proposed experiments should uncover previously unrecognized contributions of T. denticola to pathogenesis. In the long term, the results derived from these studies could lead to novel ideas for the development of innovative strategies to diminish tissue pathology in periodontal disease.
Periodontal diseases are the most prevalent human bacterial infections resulting in pain, bone loss, and, ultimately, exfoliation of teeth. The inflammation found in periodontal diseases is clear due to a polymicrobial infection often including the treponeme Treponema denticola. Thus, it is important to unravel Treponema denticola's role in creating the low oxygen, high H2S microenvironment found in many diseased sites and, therefore, the results of the proposed studies may lead to the development of novel genetic and pharmacological strategies to diminish tissue pathology in periodontitis.
| Zhang, J-H; Dong, Z; Chu, L (2010) Hydrogen sulfide induces apoptosis in human periodontium cells. J Periodontal Res 45:71-8 |
| Chu, L; Xu, X; Su, J et al. (2009) Role of Aggregatibacter actinomycetemcomitans in glutathione catabolism. Oral Microbiol Immunol 24:236-42 |
