"Cherubism" is a human autosomal dominant disorder characterized by excessive bone resorption and the accumulation of inflammatory fibrous tissue in the jaws. We identified the gene responsible for this human disease, a signaling adaptor protein called "SH3 domain binding protein 2 (SH3BP2)", and pinpointed the mutations responsible for this condition. To further investigate the pathogenesis of Cherubism, we have generated a knock-in mouse model carrying this mutation (P416R in mice). Similar to the human disease, the cherubism mice exhibit systemic macrophage-driven inflammation with increased tumor necrosis factor-alpha (TNF-1) production as well as enhanced osteoclast differentiation, resulting in severe systemic inflammatory bone loss. Therefore these mice are useful, not only as a model of cherubism, but also potentially as a model for other inflammatory bone diseases. The overall hypothesis for the proposed studies is that the misexpression and disregulation of TNF-1 in Cherubism-associated inflammatory bone disease is mediated through SH3BP2 signaling in myeloid lineage cells. We propose SH3BP2 mutations result in abnormal signaling in macrophages and osteoclast precursors in response to macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor-KB (NF-KB) ligand (RANKL), respectively. We also propose that the hyperactive macrophages are responsible for elevated TNF-1 which can feed back to further activate the osteoclasts, already made hyperactive through mutant SH3BP2. Our preliminary data suggest that ERK and MyD88 are involved in TNF- 1 production by hyperactive macrophages, while Syk and NFATc1 are involved in osteoclast hyperactivation. To test these hypotheses, the following specific aims are proposed: 1) Determine the mechanisms by which SH3BP2 regulates TNF-1 production in macrophages, 2) Determine the role of SH3BP2 in NFATc1-mediated osteoclast differentiation, and 3) Determine the role of the MyD88-mediated signaling pathway in the pathogenesis of inflammation in cherubism. The cherubism mouse model will be crossed with other mouse models such as the SHP-1 and MyD88 null mice in conjunction with relevant in vitro assays to test these hypotheses. Detailed analyses of the SH3BP2- and MyD88-mediated signaling pathway, the production of TNF-1 and their roles in inflammation and osteoclast activation will greatly contribute to better understanding of inflammatory bone disease in cherubism. Identifying the molecular components of these pathways and how they function will also aid in developing new targets for therapeutic intervention for other inflammatory diseases, such as rheumatoid arthritis and periodontal disease.
The goal of this project is to identify the novel molecular pathways involved in the inflammatory bone disease associated with Cherubism. Successful identification of these pathways will facilitate the design of more effective drugs for the treatment of patients suffering from Cherubism as well as other inflammatory diseases such as rheumatoid arthritis and periodontal disease.
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