Objectives: Root resorptions are common undesirable side effects of orthodontic treatment. In most patients, these defects are repaired by cementoblasts. However, in 1-5 % of patients, the repair fails. The repair mechanism is not well understood. Apoptosis of cementoblasts might contribute to an impaired repair of root resorptions induced by orthodontic forces.
Materials and methods: To gain insight into putative molecular pathways leading to compression-induced apoptosis of human primary cementoblasts (HPCBs), three independent cell populations were subjected to compressive loading at 5, 20, and 30 g/cm2 for 1, 6, and 10 h. The mRNA expression of AXUD1, a novel pro-apoptotic gene, was monitored by quantitative reverse transcription PCR (qRT-PCR). To identify a possible function in compression-dependent apoptosis, AXUD1 was silenced in cementoblasts using an siRNA approach. Apoptosis of cementoblasts was measured by annexin V staining and flow cytometry. The phosphorylation of c-Jun-N-terminal kinases (JNKs) was investigated by Western blotting.
Results: AXUD1 was significantly induced in a time- and force-dependent manner. The rate of apoptotic HPCBs increased by 20-40 % after 10 h of compression (30 g/cm2). Phosphorylation of JNKs was detected after 10 h at 30 g/cm2. SiRNA-mediated knockdown of AXUD1 led to decreased phosphorylation of JNKs and reduced apoptosis rates in compressed HPCBs.
Conclusions: Compression-induced apoptosis of HPCBs is mediated by AXUD1 via a JNK-dependent pathway.
Clinical relevance: AXUD1-dependent apoptosis of human cementoblasts might contribute to an impaired repair of root resorptions during orthodontic tooth movement. Further studies are needed to develop treatment strategies aiming to minimize root resorption during orthodontic tooth movement.
Keywords: Mechanical stress; Orthodontics; Periodontal ligament; Programmed cell death; Root resorption; Tooth movement.