There is virtually no information on the role of NLRC4 inflammasome on bone resorption and inflammation associated with periodontitis. Bacterial-associated experimental periodontitis was induced in wild-type (WT) and Nlrc4-KO C57BL/6 mice. 3 μL of a 1 × 109 UFC/mL PBS suspension of heat-killed Gram-negative bacteria were injected (3x/week for 4 weeks) directly into the gingival tissues of WT and Nlrc4-KO mice (n = 6/genotype). Control animals were injected bilaterally (3x/week for 4 weeks) in the same sites with the same volume of the PBS vehicle. Alveolar bone resorption was quantified by μCT. Inflammatory infiltrate in the gingival tissues was assessed qualitatively in H&E-stained slides and by the detection of a pan-leukocyte marker (CD45) and a neutrophil marker (Ly6G) using immunofluorescence. Modulation of Rankl, Mmp-13, Tnf-a, Il-6 and Il-10 expression in the gingival tissues was determined by RT-qPCR. Osteoclastogenesis was assessed in vivo by biochemical staining for TRAP. The relevance of NLRC4 for RANKL-induced osteoclastic differentiation and activity was investigated in vitro using bone marrow-derived macrophages from WT and Nlrc4-KO mice. Bone resorption was significantly greater in Nlrc4-KO mice; however there were no differences between WT and Nlrc4-KO mice on osteoclast numbers and on the inflammatory infiltrate. In vitro, osteoclast activity was significantly enhanced in Nlrc4-deficient macrophages; whereas RANKL-induced differentiation was not affected. Expression of the selected candidate genes was also similarly increased by the induction of experimental periodontal disease, except for the expression of Tnf-alpha and Il-10, which was already significantly higher in the gingival tissues of Nlrc4-KO mice. We conclude that NLRC4 inflammasome has a protective role on inflammatory bone resorption in this experimental model. Furthermore, the bone-sparing effect may be related with the modulation of osteoclast activity.

中文翻译：

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NLRC4炎性小体在牙周疾病的小鼠模型中对炎性骨吸收具有保护作用。

几乎没有关于NLRC4炎性体在与牙周炎有关的骨吸收和炎症中的作用的信息。在野生型（WT）和Nlrc4-KO C57BL / 6小鼠中诱导细菌相关的实验性牙周炎。将3μL热灭活的革兰氏阴性细菌的1×109 UFC / mL PBS悬浮液（3次/周，共4周）直接注射到WT和Nlrc4-KO小鼠的牙龈组织中（n = 6 /基因型）。对照动物在相同部位以相同体积的PBS媒介物双侧注射（3次/周，共4周）。肺泡骨吸收通过μCT定量。定性评估H＆E染色玻片中牙龈组织中的炎性浸润，并通过免疫荧光检测泛白细胞标志物（CD45）和嗜中性白细胞标志物（Ly6G）进行定性评估。调制Rankl，Mmp-13，Tnf-a，通过RT-qPCR确定牙龈组织中的Il-6和Il-10表达。通过生化染色对TRAP进行体内评估破骨细胞生成。使用WT和Nlrc4-KO小鼠的骨髓巨噬细胞体外研究了NLRC4与RANKL诱导的破骨细胞分化和活性的相关性。Nlrc4-KO小鼠的骨吸收明显更高；但是，WT和Nlrc4-KO小鼠的破骨细胞数量和炎性浸润率没有差异。在体外，破骨细胞活性在Nlrc4缺陷型巨噬细胞中显着增强；而RANKL诱导的分化不受影响。通过诱导实验性牙周疾病，所选候选基因的表达也类似地增加，除了Tnf-alpha和Il-10的表达，在Nlrc4-KO小鼠的牙龈组织中已经明显更高。我们得出的结论是，NLRC4炎性小体在该实验模型中对炎症性骨吸收具有保护作用。此外，保骨作用可能与破骨细胞活性的调节有关。