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性破坏密切相关。然而，致病菌调节OC分化的确切机制仍然存在争议。NF-？B配体（RANKL）及其受体RANK是骨重建和OC活化的关键调节因子。牙龈卟啉单胞菌（Porphyromonas gingivalis，Pg）是引起牙周炎的主要病原菌。宿主免疫系统感知、识别和应答Pg的能力主要由先天免疫系统通过Toll样受体（TLR）2和4介导。我们的初步研究表明，在体外，Pg差异调节RANKL诱导的OC形成抑制OC分化从非定向前体和增强OC分化从RANKL定向细胞。此外，Pg利用TLR 2/MyD 88通过抑制RANKL诱导的c-Fos和NFATc 1活性来抑制破骨细胞生成。最重要的是，RANKL-定向OC前体对Pg/TLR/细胞因子信号传导变得难治。这些初步研究首次表征了Pg对RANKL诱导的破骨细胞生成的双相作用，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阐明TLR介导的调节破骨细胞生成的分子机制的背景下，Pg感染。基于我们的初步研究和已发表的工作，我们假设TLR和RANK信号传导之间的功能性相互作用，即Pg介导的TLR激活导致非定向前体细胞缺乏OC形成，以及RANKL定向细胞缺乏对TLR刺激的细胞因子反应，在体内Pg诱导的骨丢失中发挥重要作用。我们将通过追求两个具体目标来测试这个假设：1。阐明Pg体外刺激RANKL诱导破骨细胞生成过程中TLR和RANK信号之间功能性相互作用的分子机制; 2.确定TLR 2/MyD 88在体内小鼠模型中参与Pg诱导的骨丢失。细菌感染和OC分化之间的功能相互作用的鉴定和表征对于理解牙周病的发病机制至关重要。此外，对TLR信号调节破骨细胞生成的分子机制的深入了解有可能为预防和治疗该疾病定义新的治疗靶点。

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.