Purpose: The osteocyte is considered the major mechanosensor in bone, capable of detecting forces at a cellular level to coordinate bone formation and resorption. The pathology of age-related bone loss, a hallmark of osteoporosis, is attributed in part to impaired osteocyte mechanosensing. However, real-time evidence of the effect of aging on osteocyte responses to mechanical load is lacking. Intracellular calcium (Ca²⁺) oscillations have been characterized as an early mechanosensitive response in osteocytes in systems of multiple scales and thus can serve as a real-time measure of osteocyte mechanosensitivity. Our objective was to utilize an ex vivo model to investigate potentially altered mechanosensing in the osteocyte network with aging.

Methods: Tibiae were explanted from young-adult (5 mo) and aged (22 mo) female mice and incubated with Fluo-8 AM to visualize osteocyte intracellular Ca²⁺. Whole tibiae were cyclically loaded while in situ osteocyte Ca²⁺ dynamics were simultaneously imaged with confocal microscopy. Responsive osteocyte percentage and Ca²⁺ peak characteristics were quantified, as well as signaling synchrony between paired cells in the field of view.

Results: Fewer osteocytes responded to mechanical loading in aged mice compared to young-adult and did so in a delayed manner. Osteocytes from aged mice also lacked the well-correlated relationship between Ca²⁺ signaling synchrony and cell-cell distance exhibited by young-adult osteocytes.

Conclusions: We have demonstrated, for the first time, real-time evidence of the diminished mechanosensing and lack of signaling coordination in aged osteocyte networks in tibial explants, which may contribute to pathology of age-induced bone loss.

目的：骨细胞被认为是骨中的主要机械传感器，能够检测细胞水平的力以协调骨形成和骨吸收。与年龄相关的骨质流失是骨质疏松症的标志，其病理学部分归因于骨细胞机械传感受损。然而，缺乏关于老化对骨细胞对机械负荷反应的影响的实时证据。细胞内钙 (Ca ²⁺ ) 振荡已被表征为多尺度系统中骨细胞中的早期机械敏感性反应，因此可以作为骨细胞机械敏感性的实时测量。我们的目标是利用离体模型来研究骨细胞网络中随着年龄的增长而可能改变的机械传感。

方法：从年轻成年（5 个月）和老年（22 个月）雌性小鼠中取出胫骨，并用 Fluo-8 AM 孵育以观察骨细胞细胞内 Ca ²⁺。整个胫骨循环加载，同时用共聚焦显微镜对原位骨细胞 Ca ^{2+动力学进行成像。}对反应性骨细胞百分比和 Ca ²⁺峰特征以及视野中成对细胞之间的信号同步进行量化。

结果：与年轻成年小鼠相比，老年小鼠的骨细胞对机械负荷的反应较少，而且反应迟缓。来自老年小鼠的骨细胞也缺乏年轻成年骨细胞表现出的 Ca ²⁺信号同步与细胞间距离之间的良好相关关系。

结论：我们首次证明了胫骨外植体中老化骨细胞网络中机械传感减弱和信号协调缺乏的实时证据，这可能导致年龄引起的骨质流失的病理学。