Sen S, Diercke K, Zingler S, Lux C J, Erber R
Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Heidelberg, Germany.
Department of Orthodontics and Dentofacial Orthopaedics, Dental School, University of Heidelberg, Heidelberg, Germany
J Dent Res. 2015 Mar;94(3):464-72. doi: 10.1177/0022034514567197. Epub 2015 Jan 20.
Ephrin-A2-EphA2 and ephrin-B2-EphB4 interactions have been implicated in the regulation of bone remodeling. We previously demonstrated a potential role for members of the Eph-ephrin family of receptor tyrosine kinases for bone remodeling during orthodontic tooth movement: compression-dependent upregulation of ephrin-A2 in fibroblasts of the periodontal ligament (PDL) attenuated osteogenesis in osteoblasts of the alveolar bone. However, factors affecting the regulation of ephrin-A2 expression upon the application of compressive forces remained unclear. Here, we report a mechano-dependent pathway of ephrin-A2 induction in PDL fibroblasts (PDLFs) involving extracellular signal-regulated kinases (ERK) 1/2 and c-fos. PDLF subjected to compressive forces (30.3 g/cm(2)) upregulated c-fos and ephrin-A2 mRNA and protein expression and displayed increased ERK1/2 phosphorylation. Inhibition of the MAP kinase kinase (MEK)/ERK1/2 pathway using the specific MEK inhibitor U0126 significantly reduced ephrin-A2 messenger RNA upregulation upon compression. Silencing of c-fos using a small interfering RNA approach led to a significant inhibition of ephrin-A2 induction upon the application of compressive forces. Interestingly, ephrin-A2 stimulation of PDLF induced c-fos expression and led also to the induction of ephrin-A2 expression. Using a reporter gene construct in murine 3T3 cells, we found that ephrin-A2 was able to stimulate serum response element (SRE)-dependent luciferase activity. As the regulation of c-fos is SRE dependent, ephrin-A2 might induce c-fos via SRE activation. Taken together, we provide evidence for an ERK1/2- and c-fos-dependent regulation of ephrin-A2 in compressed PDLF and suggest a novel pathway for ephrin-A2 induction emanating from ephrin-A2 itself. We showed previously that ephrin-A2 at compression sites might contribute to tooth movement by inhibiting osteogenic differentiation. The regulatory pathway of ephrin-A2 induction during tooth movement identified in this study might be accessible for pharmacological interventions.
Ephrin-A2-EphA2和ephrin-B2-EphB4相互作用与骨重塑的调节有关。我们之前证明了受体酪氨酸激酶Eph-ephrin家族成员在正畸牙齿移动过程中对骨重塑的潜在作用：牙周膜（PDL）成纤维细胞中ephrin-A2的压缩依赖性上调减弱了牙槽骨成骨细胞的成骨作用。然而，施加压缩力后影响ephrin-A2表达调控的因素仍不清楚。在此，我们报告了一条在PDL成纤维细胞（PDLFs）中ephrin-A2诱导的机械依赖性途径，该途径涉及细胞外信号调节激酶（ERK）1/2和c-fos。受到压缩力（30.3 g/cm²）的PDLF上调了c-fos和ephrin-A2的mRNA及蛋白表达，并表现出ERK1/2磷酸化增加。使用特异性MEK抑制剂U0126抑制丝裂原活化蛋白激酶激酶（MEK）/ERK1/2途径可显著降低压缩后ephrin-A2信使RNA的上调。使用小干扰RNA方法沉默c-fos导致施加压缩力后ephrin-A2诱导受到显著抑制。有趣的是，ephrin-A2刺激PDLF可诱导c-fos表达，也可导致ephrin-A2表达的诱导。在小鼠3T3细胞中使用报告基因构建体，我们发现ephrin-A2能够刺激血清反应元件（SRE）依赖性荧光素酶活性。由于c-fos的调节是SRE依赖性的，ephrin-A2可能通过SRE激活诱导c-fos。综上所述，我们提供了证据表明在压缩的PDLF中ephrin-A2受ERK1/2和c-fos依赖性调节，并提出了一条由ephrin-A2自身引发的ephrin-A2诱导新途径。我们之前表明压缩部位的ephrin-A2可能通过抑制成骨分化促进牙齿移动。本研究中确定的牙齿移动过程中ephrin-A2诱导的调节途径可能适用于药物干预。
