Effects of mechanical force on RANKL expression and osteoclasts formation in PDL cells

我们在本研究中发现，施加于牙周韧带（PDL）细胞的压缩力而不是拉伸力诱导RANKL mRNA。这可能与正畸牙齿移动过程中压迫侧破骨细胞的发生有关。由于RANKL的表达通常很少，因此在任何实验中都很难清楚地检测到RANKL的表达。cox-2是PGE_2合成和破骨细胞生成的重要酶，在压力和拉力作用下，其表达显著受到刺激，且表达强度与供体年龄密切相关。这些数据可能与正畸治疗过程中成人患者的牙龈萎缩和牙槽嵴吸收比年轻患者更常见有关。即使PDL细胞响应机械力时cox-2表达较高，但RANKL表达不明确或很低。已知PGE_2可以刺激RANKL的表达，但RANKL不仅介导cox-2的表达，还介导其他因子的表达。另一实验表明，一定程度的成骨细胞压缩力（Saos-2）通过PGE_2合成刺激BSP的表达，cox-2可能在成骨过程中起重要作用。阐明低能量激光照射抗炎作用的实验表明，低能量激光照射可显著抑制PDL细胞对循环张力的cox-2表达。在正畸治疗中，低能量激光照射移动的牙齿很可能会减少牙槽嵴吸收。进一步研究不同激光剂量、频率和波长对PDL细胞骨吸收因子的影响可能是临床应用的必要条件。

We found in the present study that not tensile force but compressive force applied to the periodontal ligament (PDL) cells induces RANKL mRNA. It may be related to the osteoclasts genesis in the compression side during orthodontic tooth movement. As expression of RANKL is usually little, it is so difficult to detect RANKL expression clearly in any experiments. The expression of cox-2 in the PDL cells, the most important enzyme for PGE_2 synthesis and responsible for osteoclasts genesis, is significantly stimulated in response to both compressive and tensile forces, and the intensity of expression is much dependent on the donor age. These data may be involved in the fact that gingival recession and alveolar crest resorption during orthodontic treatment is more frequent in the adult patients than in the young patients. Even through the cox-2 expression of PDL cells in response to mechanical force is high, RANKL expression is unclear or very low. It is known that PGE_2 has been shown to stimulate RANKL expression, but RANKL is mediated not only expression of cox-2 but also other factors. Another experiments show that the certain magnitude of compressive force to the osteoblats (Saos-2) stimulates BSP expression via PGE_2 synthesis, and cox-2 may have important roles of bone formation. The experiments to clarify anti-inflammatory effects of low-energy laser irradiation show that low-energy laser irradiation dramatically inhibits cox-2 expression from PDL cells in response to cyclic tension force. There is high possibility that low-energy laser irradiation to the moved teeth may reduce alveolar crest resorption during orthodontic treatment. Further studies such as effects of different laser dose, frequency and wavelength to PDL cells on bone resorption factors may be necessary for clinical use.