In the oral cavity, where multiple bacteria colonize, epithelial cells engage in innate defense mechanisms, which include building a physical barrier against infection and secreting innate immune antimicrobial peptides. ? ? Upon recognition of pathogenic bacteria via innate immune receptors, epithelial cells produce proinflammatory cytokines and antimicrobial peptides, such as defensins and LL-37. Some bacteria, however, in order to conquer such a host innate defense system, appear to produce factors that, in fact, disrupt the normal production of antimicrobial peptides. ? ? In contrast to multiple defensins, LL-37 is the only member of the cathelicidin family of peptides resident in the human body. For example, patients with a genetic disorder called Kostmann syndrome lack the production of antimicrobial peptide LL-37 in saliva. This can result in the onset of devastating periodontal disease, indicating that LL-37 is an indispensable, integral part of the oral innate immune defense system. LL-37 is characterized by extremely rapid gene and protein expression in epithelial cells (at 5 minutes after bacterial stimulus). Moreover, LL-37 can potentially stimulate additional innate immune defense through direct chemotactic activity for neutrophils or induction of IL-8 release from epithelial cells. ? ? In addition to previously identified virulent factors produced by Porphyromonas gingivalis (Pg), including gingipain, fimbriae and LPS, we recently discovered that Pg express unique lipids, also demonstrating a putatively virulent nature, including the change of morphological appearance of cultured gingival fibroblasts. This particular Pg lipid, phosphatidylethanolamine (PgPE), not only lacks LL-37 induction by gingival epithelial cells (GEC), but also disables GEC production of LL-37 in response to stimulus by Fusobacterium nucleatum or Actinobacillus actinomycetemcomitans. Furthermore, we have preliminarily demonstrated that PgPE interacts with a unique extracellular receptor, nucleolin, which is primary present in cytoplasm and nucleus. ? ? In the proposed project, then, we intend to perform the following aims: 1) characterize the basis of PgPE-mediated inhibition of LL-37 expression by GEC and possible influence of PgPE on the other innate immune molecules expressed by GEC and 2) determine the PgPE-binding receptor expressed on GEC, as well as define the enrollment of the PgPE-binding receptor in the Pg-mediated inhibition of LL-37 expression by GEC, using live Pg infection in primary 3D-GEC culture. In sum, the short-term goal of this project is to characterize the """"""""anti-innate immune"""""""" effects of PgPE by targeting GEC responses. The long-term goal is to explore the host receptor/signal system affected by anti-innate immune bacterial components and to catalog bacterial components with anti-innate immune effects. Finally, based on such accumulated knowledge, we will develop approaches that utilize antagonists to block the PgPE binding to its receptor, thus preventing periodontal disease caused by Pg infection. ? ? ?
