Oral epithelia serve as a first line of defense for oral and periodontal health via innate host defense mechanisms. Human gingival epithelial cells (HGECs) express two antimicrobial peptides of the beta-defensin family, human beta-defensin-1 (hBD-1) and -2 (hBD-2) that contribute to innate immune responses. The potential importance of these peptides in oral health and disease susceptibility is only recently beginning to be appreciated. Production of hBD-1 and hBD-2 is stimulated when HGECs are exposed to an oral commensal bacterium, Fusobacterium nucleatum. HBD-1 mRNA is also up regulated by exposure to TNFalpha, an inflammatory mediator, while hBD-1 mRNA is constitutively expressed. These preliminary studies suggest that commensal organisms may be important in maintaining the normal protective barrier function of the oral mucosa in vivo by partial activation of the innate immune system. Several findings or hypotheses are the focus of this project: 1) that expression of beta-defensins is associated with differentiation in oral mucosa; 2) that beta-defensins are regulated by known or novel cell surface receptors, possibly including CD14 and TLRs, 3) that signal transduction via the transcription factor NF kB is critical for hBD-2 mRNA expression, 4) that the pathway for stimulation may differ from that of other host innate immune responses, such as the chemokine IL-8, 5) that new gene expression may be required. The present proposal uses cell and molecular studies to investigate the regulation of expression of beta-defensins in relation to epithelial differentiation, and to identify cell surface receptors and signaling pathways responsible for their expression in response to the oral commensal organism, F. nucleatum. Understanding the signaling pathways and means to enhance peptide expression will have future potential for enhancing antimicrobial peptide expression for prevention and treatment of oral microbial disorders, including periodontal disease, caries, recurrent candidal infections, and oral mucositis.
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