Department of Biophysics, Gesellschaft für Schwerionenforschung (GSI) Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany.
Department of Macromolecular and Paper Chemistry and Membrane Dynamics, Technical University Darmstadt, Darmstadt, Germany.
Front Immunol. 2022 May 4;13:817281. doi: 10.3389/fimmu.2022.817281. eCollection 2022.
Low-dose radiotherapy (LD-RT) is a local treatment option for patients with chronic degenerative and inflammatory diseases, in particular musculoskeletal diseases. Despite reported analgesic and anti-inflammatory effects, cellular and molecular mechanisms related to osteoimmunological effects are still elusive. Here we test the hypothesis that X-irradiation inhibits the differentiation of precursor osteoclasts into mature osteoclasts (mOC) and their bone resorbing activity. Circulating monocytes from healthy donors were isolated and irradiated after attachment with single or fractionated X-ray doses, comparable to an LD-RT treatment scheme. Then monocytes underwent differentiation into OC during cultivation up to 21 days, under conditions mimicking the physiological microenvironment of OC on bone. After irradiation, apoptotic frequencies were low, but the total number of OC precursors and mOC decreased up to the end of the cultivation period. On top, we observed an impairment of terminal differentiation, i.e. a smaller fraction of mOC, reduced resorbing activity on bone, and release of collagen fragments. We further analyzed the effect of X-irradiation on multinucleation, resulting from the fusion of precursor OC, which occurs late during OC differentiation. At 21 days after exposure, the observation of smaller cellular areas and a reduced number of nuclei per mOC suggest an impaired fusion of OC precursors to form mOC. Before, at 14 days, the nuclear translocation of Nuclear Factor Of Activated T Cells 1 (NFATc1), a master regulator of osteoclast differentiation and fusion, was decreased. In first results, obtained in the frame of a longitudinal LD-RT study, we previously reported a pain-relieving effect in patients. However, in a subgroup of patients suffering from Calcaneodynia or Achillodynia, we did not observe a consistent decrease of established blood markers for resorption and formation of bone, or modified T cell subtypes involved in regulating these processes. To assess the relevance of changes in bone metabolism for other diseases treated with LD-RT will be subject of further studies. Taken together, we observed that X-irradiation of monocytes results in an inhibition of the differentiation into bone-resorbing OC and a concomitant reduction of resorbing activity. The detected reduced NFATc1 signaling could be one underlying mechanism.
低剂量放射疗法（LD-RT）是一种治疗慢性退行性和炎症性疾病，特别是肌肉骨骼疾病的局部治疗选择。尽管有报道称其具有镇痛和抗炎作用，但与骨免疫学相关的细胞和分子机制仍不清楚。在这里，我们验证了这样一个假设，即 X 射线照射会抑制前体破骨细胞向成熟破骨细胞（mOC）分化及其骨吸收活性。我们从健康供体中分离循环单核细胞，在附着后用单次或分次 X 射线剂量照射，类似于 LD-RT 治疗方案。然后，在培养过程中，单核细胞在模拟 OC 在骨上的生理微环境的条件下分化为 OC，培养时间长达 21 天。照射后，细胞凋亡频率较低，但 OC 前体和 mOC 的总数减少，直至培养结束。此外，我们观察到终末分化受损，即 mOC 的比例较小，在骨上的吸收活性降低，以及胶原片段的释放。我们进一步分析了 X 射线照射对多核化的影响，多核化是 OC 分化过程中晚期前体 OC 融合的结果。照射后 21 天，观察到 mOC 的细胞面积较小和每个 mOC 的核数减少，提示 OC 前体融合形成 mOC 受损。在此之前，在 14 天时，破骨细胞分化和融合的主调控因子核因子活化 T 细胞 1（NFATc1）的核易位减少。在一项纵向 LD-RT 研究的初步结果中，我们之前报道了患者的止痛效果。然而，在患有跟痛症或跟腱痛的患者亚组中，我们没有观察到骨吸收和形成的既定血液标志物的一致下降，或调节这些过程的 T 细胞亚型的改变。进一步研究将评估 LD-RT 治疗的其他疾病中骨代谢变化的相关性。总之，我们观察到单核细胞的 X 射线照射会导致向骨吸收 OC 的分化受到抑制，同时骨吸收活性降低。检测到的 NFATc1 信号转导减少可能是一个潜在的机制。
