Molecular mechanisms of the innate regulation of osteoclastogenesis.

描述（由申请人提供）：牙周病细菌感染通过直接和间接影响破骨细胞（OC）分化与牙周炎中牙槽骨的炎症性破坏密切相关。然而，病原菌调控OC分化的确切机制仍然存在争议。NF-?受体激活剂B配体（RANKL）及其受体RANK是骨重塑和OC活化的关键调节因子。牙龈卟啉单胞菌（Pg）被认为是牙周炎的主要病因。宿主免疫系统对Pg的感知、识别和应答能力主要是由先天免疫系统通过toll样受体（TLR） 2和4介导的。我们在体外的初步研究表明，Pg通过抑制OC从非承诺前体分化和增强OC从rankl承诺细胞分化来差异性调节rankl诱导的OC形成。此外，Pg利用TLR2/MyD88通过抑制rankl诱导的c-Fos和NFATc1活性来抑制破骨细胞的发生。最重要的是，含有rankl的OC前体对Pg/TLR/细胞因子信号变得难治性。这些初步研究首次描述了Pg在rankl诱导的破骨细胞发生中的双相作用，并确定了TLR和RANK信号通路之间的串扰。本研究的总体目标是进一步描述Pg感染背景下tlr介导的破骨细胞发生调节的分子机制。基于我们的初步研究和已发表的工作，我们假设TLR和RANK信号之间的功能相互作用，即通过pg介导的TLR激活缺乏非承诺前体细胞形成OC，以及缺乏细胞因子对rankl承诺细胞刺激TLR的反应，在体内pg诱导的骨质流失中起重要作用。我们将通过追求两个具体目标来检验这一假设：描述Pg刺激下rankl诱导的体外破骨细胞形成过程中TLR和RANK信号相互作用的分子机制；2. 在体内小鼠模型中确定TLR2/MyD88参与pg诱导的骨丢失。鉴定和表征细菌感染与OC分化之间的功能相互作用对于了解牙周病的发病机制至关重要。此外，深入了解TLR信号调节破骨细胞发生的分子机制有可能为预防和治疗该疾病确定新的治疗靶点。

DESCRIPTION (provided by applicant): Periodontopathic bacterial infection is closely associated with the inflammatory destruction of alveolar bone in periodontitis by both direct and indirect effects on osteoclast (OC) differentiation. However, the precise mechanisms by which pathogenic bacteria regulate OC differentiation still remain controversial. The receptor activator of NF-?B ligand (RANKL) and its receptor RANK are the key regulators for bone remodeling and for the activation of OC. Porphyromonas gingivalis (Pg) is considered a major etiologic agent of periodontitis. The ability of the host's immune system to sense, recognize and respond to Pg is largely mediated by the innate immune system via Toll-like receptors (TLR) 2 and 4. Our preliminary studies have demonstrated in vitro that Pg differentially modulates RANKL-induced OC formation by inhibiting OC differentiation from non-committed precursors and by potentiating OC differentiation from RANKL-committed cells. Furthermore, Pg utilizes TLR2/MyD88 to inhibit osteoclastogenesis by suppressing RANKL-induced c-Fos and NFATc1 activity. Most importantly, RANKL-committed OC precursors become refractory to Pg/TLR/cytokine signaling. These preliminary studies are the first to characterize a biphasic role of Pg on RANKL-induced osteoclastogenesis, and have identified a crosstalk between TLR and RANK signaling pathways. The overall goal of this study is to further delineate the molecular mechanisms of TLR-mediated regulation of osteoclastogenesis in the context of Pg infection. Based on our preliminary studies and published work, we hypothesize that the functional interaction between TLR and RANK signaling, namely a lack of OC formation from non-committed precursor cells by Pg-mediated TLR activation and a lack of cytokine response to TLR stimulation by RANKL-committed cells, plays an essential role in Pg-induced bone loss in vivo. We will test this hypothesis by pursuing two specific aims: 1. Delineate the molecular mechanisms underlying the functional interaction between TLR and RANK signaling during RANKL-induced osteoclastogenesis upon Pg stimulation in vitro; 2. Determine the involvement of TLR2/MyD88 in Pg-induced bone loss in an in vivo mouse model. The identification and characterization of the functional interaction between bacterial infection and OC differentiation i critical for an understanding of periodontal disease pathogenesis. Furthermore, insight into the molecular mechanisms by which TLR signaling regulates osteoclastogenesis has potential to define novel therapeutic targets for prevention and treatment of the disease.