Decoding the glycome of oral Treponema denticola

PROJECT SUMMARY The bacterium Treponema denticola (Td) is an important and yet understudied oral pathobiont that is highly associated with periodontitis, necrotic root canals, and endodontic infections. Growing evidence also shows that Td is implicated in several systemic illnesses such as Alzheimer’s disease and oral squamous cell carcinoma. As a keystone pathogen, Td shows various pathogenic traits, e.g., cell adherence and invasion, stimulation of proinflammation, modulation of host immune responses, and inducing osteoclastogenesis (OCG) and alveolar bone loss. However, bacterial virulence determinants associated with these pathogenic traits remain largely unknown. For instance, there is a longstanding conundrum as to whether or not Td produces lipopolysaccharides (LPS), an endotoxin that is of paramount importance to most Gram-negative bacterial pathogens. Early studies indicate that Td produces LPS; however, later reports from different groups uncover that Td produces lipooligosaccharide (LOS), lipoteichoic acids or membrane associated lipids. These inconsistent reports have been a longstanding obstacle to understanding the role of Td in the pathogenesis of periodontitis and other diseases. During the past five years, we have been striving to address this longstanding conundrum by using a multidisciplinary approach combining bioinformatics, genetics, glycomics, immunology, and structural biology along with several cutting-edge techniques and have made significant progress to understanding the chemical structure, biosynthesis, regulation, and pathogenic role of LPS-like fractions purified from Td. Based on these preliminary studies, we hypothesize that, instead of LPS/LOS, Td produces a new class of sulfated glycolipids (SGLs) with a distinct chemical composition and structure, its biosynthesis is regulated in response to biofilm formation, and that this new type of glycolipids plays a critical role in the pathophysiology of Td. To test this hypothesis, the following three aims are proposed: (1) Delineating the chemical composition, glycosidic linkage, and key genetic determinants required for the biosynthesis of SGLs; (2) Elucidating the regulatory mechanism of SGLs and their role in Td cell structure, motility, and biofilm formation; and (3) Investigating the role of SGLs in Td-induced OCS and alveolar bone loss. To the best of our knowledge, this is the first project to mechanistically investigate the chemical composition, glycosidic linkages, biosynthesis, regulation, and roles of SGLs in the pathophysiology of Td. Completion of this project will provide new insights into understanding the glycome of Td and its role in the pathogenesis of oral infections and systemic diseases. In addition, this application will open new avenues to investigate SGLs in other oral pathogens.