1 School of Dentistry of Ribeirão Preto, Department of Pediatric, Preventive and Social Dentistry, University of São Paulo, Ribeirão Preto, Brazil.
2 School of Medicine of Ribeirão Preto, Department of Pharmacology, University of São Paulo, University of São Paulo, Ribeirão Preto, Brazil.
J Dent Res. 2019 Apr;98(4):476-484. doi: 10.1177/0022034518820289. Epub 2019 Jan 25.
Apical periodontitis is an inflammatory disorder that results from the host immune response to microbial infection through the dental pulp, leading to alveolar bone destruction. The nod-like receptor 12 (NLRP12) is an atypical intracellular sensor of the NLR family that is involved in the negative regulation of several inflammatory conditions and also osteoclastogenesis. However, the role of NLRP12 in the regulation of immune response and bone loss induced by bacterial infection remains unclear. Here we investigated the development of apical periodontitis in wild-type (WT) and NLRP12 knockout (NLRP12) mice by using micro-computed tomography together with histological, immunohistochemical, and molecular analyses. We found that NLRP12 mice are highly susceptible to apical periodontitis induced by bacterial infection, which is associated with an elevated infiltration of neutrophils and macrophages, periapical lesion extension, and alveolar bone destruction. Furthermore, NLRP12 mice showed a high expression of inflammatory cytokines ( Il1b, Il6, and Tnfa) and the osteoclastogenic markers ( Rankl and Acp5) in the periapical tissues. Consistent with this observation, NLRP12 mice showed an increased number of tartrate-resistant acid phosphatase-positive cells lining the apical periodontitis site, which was associated with augmented expression of the osteoclast effector genes, Ctsk and Mmp9. Mechanistically, NLRP12-deficient preosteoclasts showed elevated IκB-α degradation and p65 phosphorylation when stimulated with receptor activator of nuclear factor (NF)-κB ligand (RANKL). Similarly, increased IκB-α degradation was observed in the periapical tissue of NLRP12 mice. Furthermore, our in vitro study showed that preosteoclasts from NLRP12 mice exhibited higher RANKL-induced osteoclastogenesis, which was synergistically amplified by interleukin-1β and tumor necrosis factor α (mimicking an inflammatory periapical milieu). In conclusion, our data show that NLRP12 exhibits a protective role in the periapical bone destruction by attenuating inflammation and osteoclastogenesis through negative regulation of the NF-κB pathway.
根尖周炎是一种炎症性疾病，源于宿主对通过牙髓的微生物感染的免疫反应，导致牙槽骨破坏。核苷酸结合寡聚化结构域样受体 12（NLRP12）是 NLR 家族中的一种非典型细胞内传感器，参与几种炎症状态和破骨细胞形成的负调控。然而，NLRP12 在调节细菌感染诱导的免疫反应和骨丢失中的作用尚不清楚。在这里，我们通过使用微计算机断层扫描以及组织学、免疫组织化学和分子分析，研究了野生型（WT）和 NLRP12 敲除（NLRP12）小鼠根尖周炎的发展。我们发现，NLRP12 小鼠极易受到细菌感染引起的根尖周炎的影响，这与中性粒细胞和巨噬细胞浸润增加、根尖周病变扩展和牙槽骨破坏有关。此外，NLRP12 小鼠在根尖周组织中表现出炎症细胞因子（Il1b、Il6 和 Tnfa）和破骨细胞生成标记物（Rankl 和 Acp5）的高表达。与这一观察结果一致，NLRP12 小鼠在根尖周炎部位表现出更多的抗酒石酸酸性磷酸酶阳性细胞，这些细胞与破骨细胞效应基因 Ctsk 和 Mmp9 的表达增加有关。在机制上，当用核因子（NF）-κB 配体（RANKL）刺激时，NLRP12 缺陷的前破骨细胞表现出 IκB-α 降解和 p65 磷酸化的增加。同样，在 NLRP12 小鼠的根尖周组织中也观察到 IκB-α 降解增加。此外，我们的体外研究表明，NLRP12 小鼠的前破骨细胞表现出更高的 RANKL 诱导的破骨细胞生成，这在前破骨细胞中被白细胞介素 1β 和肿瘤坏死因子 α 协同放大（模拟炎症性根尖周环境）。总之，我们的数据表明，NLRP12 通过负调控 NF-κB 通路来减轻炎症和破骨细胞形成，从而在根尖周骨破坏中发挥保护作用。
