TLR9 is a critical nucleic acid sensing receptor in mediating periodontitis and periodontitis-associated comorbidities. Emerging evidence implicates TLR9 as a key sensor during aging, although its participation in periodontal aging is unexplored. Here, we investigated whether TLR9-mediated host responses can promote key hallmarks of aging, inflammaging, and senescence, in the course of periodontitis using a multipronged approach comprising clinical and preclinical studies. In a case-control model, we found increased TLR9 gene expression in gingival tissues of older (≥55 y) subjects with periodontitis compared to older healthy subjects as well as those who are younger (<55 y old) with and without the disease. Mechanistically, this finding was supported by an in vivo model in which wild-type (WT) and TLR9^–/– mice were followed for 8 to 10 wk (young) and 18 to 22 mo (aged). In this longitudinal model, aged WT mice developed severe alveolar bone resorption when compared to their younger counterpart, whereas aged TLR9^–/– animals presented insignificant bone loss when compared to the younger groups. In parallel, a boosted inflammaging milieu exhibiting higher expression of inflammatory/osteoclast mediators (Il-6, Rankl, Cxcl8) and danger signals (S100A8, S100A9) was noted in gingival tissues of aged WT mice compared to the those of aged TLR9^–/– mice. Consistently, WT aged mice displayed an increase in prosenescence balance as measured by p16^INK4a/p19^ARF ratio compared to the younger groups and aged TLR9^–/– animals. Ex vivo experiments with bone marrow–derived macrophages primed by TLR9 ligand (ODN 1668) further corroborated in vivo and clinical data and showed enhanced inflammatory-senescence circuit followed by increased osteoclast differentiation. Together, these findings reveal first systematic evidence implicating TLR9 as one of the drivers of periodontitis during aging and functioning by boosting a deleterious inflammaging/senescence environment. This finding calls for further investigations to determine whether targeting TLR9 will improve periodontal health in an aging population.

TLR9 是介导牙周炎和牙周炎相关合并症的关键核酸传感受体。新的证据表明 TLR9 是衰老过程中的关键传感器，尽管它在牙周衰老中的作用尚未被探索。在这里，我们采用包括临床和临床前研究在内的多管齐下的方法，研究了 TLR9 介导的宿主反应是否可以在牙周炎过程中促进衰老、炎症和衰老的关键标志。在病例对照模型中，我们发现，与老年健康受试者以及年轻受试者（<55 id=2>-/- 小鼠）相比，患有牙周炎的老年受试者（≥55 岁）的牙龈组织中 TLR9 基因表达增加随访8至10周（年轻）和18至22个月（老年）。在这个纵向模型中，与年轻小鼠相比，老年WT小鼠出现严重的牙槽骨吸收，而老年TLR9 ^-/-小鼠则表现出不显着的骨质流失。与此同时，与年轻组相比，老年WT小鼠的牙龈组织中炎症/破骨细胞介质（ Il-6 、 Rankl 、 Cxcl8 ）和危险信号（ S100A8 、 S100A9 ）的表达更高。与年轻组和老年 TLR9 ^–/–小鼠相比，通过 p16 ^INK4a /p19 ^ARF比率测量，老年 TLR9 ^–/–小鼠的衰老平衡有所增加。 使用由 TLR9 配体 (ODN 1668) 引发的骨髓源性巨噬细胞进行的离体实验进一步证实了体内和临床数据，并显示炎症-衰老回路增强，随后破骨细胞分化增加。总之，这些发现揭示了第一个系统证据，表明 TLR9 通过促进有害的炎症/衰老环境，成为衰老和功能过程中牙周炎的驱动因素之一。这一发现需要进一步研究，以确定靶向 TLR9 是否会改善老龄化人口的牙周健康。