Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit, Amsterdam, Netherlands.
Amsterdam University College, Amsterdam, Netherlands.
Front Immunol. 2020 Jul 23;11:1693. doi: 10.3389/fimmu.2020.01693. eCollection 2020.
Chronic exposure to periodontopathogenic bacteria such as and the products of these bacteria that interact with the cells of the tooth surrounding tissues can ultimately result in periodontitis. This is a disease that is characterized by inflammation-related alveolar bone degradation by the bone-resorbing cells, the osteoclasts. Interactions of bacterial products with Toll-like receptors (TLRs), in particular TLR2 and TLR4, play a significant role in this chronic inflammatory reaction, which possibly affects osteoclastic activity and osteogenic capacity. Little is known about how chronic exposure to specific TLR activators affects these two antagonistic activities. Here, we studied the effect of TLR activation on gingival fibroblasts (GF), cells that are anatomically close to infiltrating bacterial products in the mouth. These were co-cultured with naive osteoclast precursor cells (i.e., monocytes), as part of the peripheral blood mononuclear cells (PBMCs). Activation of GF co-cultures (GF + PBMCs) with TLR2 or TLR4 agonists resulted in a weak reduction of the osteoclastogenic potential of these cultures, predominantly due to TLR2. Interestingly, chronic exposure, especially to TLR2 agonist, resulted in increased release of TNF-α at early time points. This effect, was reversed at later time points, thus suggesting an adaptation to chronic exposure. Monocyte cultures primed with M-CSF + RANKL, led to the formation of bone-resorbing osteoclasts, irrespective of being activated with TLR agonists. Late activation of these co-cultures with TLR2 and with TLR4 agonists led to a slight decrease in bone resorption. Activation of GF with TLR2 and TLR4 agonists did not affect the osteogenic capacity of the GF cells. In conclusion, chronic exposure leads to diverse reactions; inhibitory with naive osteoclast precursors, not effecting already formed (pre-)osteoclasts. We suggest that early encounter of naive monocytes with TLR agonists may result in differentiation toward the macrophage lineage, desirable for clearing bacterial products. Once (pre-)osteoclasts are formed, these cells may be relatively insensitive for direct TLR stimulation. Possibly, TLR activation of periodontal cells indirectly stimulates osteoclasts, by secreting osteoclastogenesis stimulating inflammatory cytokines.
慢性暴露于牙周病病原体，如 和这些细菌的产物与牙齿周围组织的细胞相互作用，最终可能导致牙周炎。这种疾病的特征是炎症相关的牙槽骨降解由破骨细胞，即破骨细胞。细菌产物与 Toll 样受体 (TLR) 的相互作用，特别是 TLR2 和 TLR4，在这种慢性炎症反应中起着重要作用，这可能影响破骨细胞的活性和成骨能力。关于慢性暴露于特定 TLR 激活剂如何影响这两种拮抗活性知之甚少。在这里，我们研究了 TLR 激活对牙龈成纤维细胞 (GF) 的影响，这些细胞在解剖上与口腔中浸润的细菌产物接近。将这些细胞与幼稚的破骨细胞前体细胞（即单核细胞）共培养，作为外周血单核细胞 (PBMC) 的一部分。TLR2 或 TLR4 激动剂激活 GF 共培养物 (GF + PBMCs) 导致这些培养物的破骨细胞生成潜力减弱，主要是由于 TLR2。有趣的是，慢性暴露，尤其是 TLR2 激动剂，导致早期 TNF-α 的释放增加。这种作用在稍后的时间点逆转，因此表明对慢性暴露的适应。用 M-CSF + RANKL 预先刺激单核细胞培养物，导致形成骨吸收破骨细胞，而与用 TLR 激动剂激活无关。这些共培养物晚期用 TLR2 和 TLR4 激动剂激活导致骨吸收略有减少。用 TLR2 和 TLR4 激动剂激活 GF 不影响 GF 细胞的成骨能力。总之，慢性暴露会导致多种反应；对幼稚的破骨细胞前体具有抑制作用，对已经形成的（前）破骨细胞没有影响。我们认为，幼稚单核细胞早期与 TLR 激动剂接触可能导致向清除细菌产物的巨噬细胞谱系分化。一旦形成（前）破骨细胞，这些细胞可能对直接 TLR 刺激相对不敏感。可能，牙周细胞的 TLR 激活通过分泌刺激破骨细胞生成的炎症细胞因子间接刺激破骨细胞。
