Title Caries Induced Cytokine Network in the Odontoblast Layer of Human Teeth Permalink

Background: Immunologic responses of the tooth to caries begin with odontoblasts recognizing carious bacteria. Inflammatory propagation eventually leads to tooth pulp necrosis and danger to health. The present study aims to determine cytokine gene expression profiles generated within human teeth in response to dental caries in vivo and to build a mechanistic model of these responses and the downstream signaling network. Results: We demonstrate profound differential up-regulation of inflammatory genes in the odontoblast layer (ODL) in human teeth with caries in vivo, while the pulp remains largely unchanged. Interleukins, chemokines, and all tested receptors thereof were differentially up-regulated in ODL of carious teeth, well over one hundred-fold for 35 of 84 genes. By interrogating reconstructed protein interaction networks corresponding to the differentially upregulated genes, we develop the hypothesis that pro-inflammatory cytokines highly expressed in ODL of carious teeth, IL-1b, IL-1a, and TNF-a, carry the converged inflammatory signal. We show that IL1b amplifies antimicrobial peptide production in odontoblasts in vitro 100-fold more than lipopolysaccharide, in a manner matching subsequent in vivo measurements. Conclusions: Our data suggest that ODL amplifies bacterial signals dramatically by self-feedback cytokinechemokine signal-receptor cycling, and signal convergence through IL1R1 and possibly others, to increase defensive capacity including antimicrobial peptide production to protect the tooth and contain the battle against carious bacteria within the dentin. Background Cytokines generate and maintain host responses to microbial infection. Living cells of the host secrete these molecules as paracrine or autocrine signals to recruit cells of the immune system (chemokines), produce inflammation (proinflammatory cytokines), or control the inflammatory responses (anti-inflammatory cytokines). The fine-tuned cytokine networks facilitate the eradication of invading microbes but maintain a balance between proand anti-inflammation thereby creating a favorable environment for tissue repair [1]. Dental caries and subsequent tooth pulp inflammation are major oral health problems caused by bacterial infection. Previous studies have reported increased expression of various cytokines in caries-affected dental pulp and/or odontoblasts including transforming growth factor-b1 (TGFb1), vascular endothelial cell growth factor (VEGF), C-C chemokine ligand 2 (CCL2/MCP1), CCL20/MIP3a, interleukin 8 (IL8/CXCL8), CXC chemokine ligand 10 (CXCL10), epithelial cell-derived neutrophil attractant 78 (ENA78), IL-1b, IL2, IL4, IL6, IL10, IL11, interferon-g (IFN-g) and tumor necrotic factor-a (TNF-a) [2-13]. The induction of these cytokines was also shown in cultured pulp-derived fibroblasts and odontoblast-like cells exposed to bacteria or their products in vitro [9,10,14-20]. However, these molecular events induced in odontoblast layer (ODL) have not been characterized or distinguished from those of the underlying pulp during the carious process in vivo. Like osteoblasts and other blast cells, the primary function of odontoblasts is generally understood as producing the extracellular structure of dentin. The functional response of odontoblasts to caries is recognized as extending a barrier to the spread of infection by forming reparative dentin. Recently our group and * Correspondence: Orapin.Horst@ucsf.edu Department of Orofacial Sciences, School of Dentistry, University of California, San Francisco, 513 Parnassus Street, San Francisco, CA, 94143, Box 0422, USA Full list of author information is available at the end of the article Horst et al. BMC Immunology 2011, 12:9 http://www.biomedcentral. com/1471-2172/12/9 © 2011 Horst et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. others showed that odontoblasts can also mediate host inflammatory responses to caries directly through production of antimicrobial peptides and cytokines, and indirectly through activation of migratory immune cells using in vitro and ex vivo models [10,13-15,18-20]. In this study we aim to characterize cytokine expression profiles generated within human teeth in response to dental caries in vivo, and to build a mechanistic model of these responses by mapping the in vivo differential gene expression of ODL and pulp in healthy (intact) and diseased (carious) teeth across known protein interactions. We assessed the tooth inflammatory regulatory network as the combined response of cells in ODL and pulp to dental caries in vivo. First we described gene expression profiling of cytokines and related immune components in ODL and pulp of normal teeth. Second we analyzed expression changes in carious teeth using cDNA microarrays and verified with quantitative realtime PCR. Additional gene transcripts with significant changes in carious teeth were identified by real-time PCR arrays. We mapped the connectivity between differentially expressed gene transcripts onto a network of experimentally demonstrated protein interactions. The reconstructed interaction network between differentially expressed gene products suggested that ODL amplifies responses through self-feedback cycling of signal-receptor events, building the capacity to dramatically increase cytokine and antimicrobial peptide production to protect the tooth and contain the battle against oral pathogens within the dentin.