Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, 14476 Potsdam, Germany; Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Centre Meidling, 1st Medical Department, Hanusch Hospital, Heinrich Collin Str. 30, A-1140 Vienna, Austria.
Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Centre Meidling, 1st Medical Department, Hanusch Hospital, Heinrich Collin Str. 30, A-1140 Vienna, Austria.
Bone. 2019 Jun;123:76-85. doi: 10.1016/j.bone.2019.03.018. Epub 2019 Mar 18.
The osteocyte lacunar-canalicular network (LCN) penetrates bone and houses the osteocytes and their processes. Despite its rather low volume fraction, the LCN represents an outstanding large surface that is possibly used by the osteocytes to interact with the surrounding mineralized bone matrix thereby contributing to mineral homeostasis. The aim of this study was to quantitatively describe such contributions by spatially correlating the local density of the LCN with the mineral content at the same location in micrometer-sized volume elements in human osteons. For this purpose, 65 osteons from the femur midshaft from healthy adults (n = 4) and children (n = 2) were structurally characterized with two different techniques. The 3D structure of the LCN in the osteons was imaged with confocal laser scanning microscopy after staining the bone samples with rhodamine. Subsequent image analysis provided the canalicular length density, i.e. the total length of the canaliculi per unit volume (μm/μm). Quantitative information on the mineral content (wt%Ca) from the identical regions was obtained using quantitative backscattered electron imaging. As the LCN-porosity lowers the mineral content, a negative correlation between Ca content and network density was expected. Calculations predict a reduction of around -0.97 fmol Ca per μm of network. However, the experiment revealed for 62 out of 65 osteons a positive correlation resulting in an average additional Ca loading of +1.15 fmol per μm of canalicular network, i.e. an accumulation of mineral has occurred at dense network regions. We hypothesize that this accumulation happens in the close vicinity of canaliculi forming mineral reservoirs that can be utilized by osteocytes. Significant differences found between individuals indicate that the extent of mineral loading of the reservoir zone reflects an important parameter for mineral homeostasis.
骨陷窝-骨小管网络 (LCN) 贯穿骨骼，容纳骨细胞及其突起。尽管 LCN 的体积分数相当低，但它代表了一个可能很大的表面积，骨细胞可能会利用这个表面积与周围矿化的骨基质相互作用，从而有助于维持矿物质平衡。本研究的目的是通过在微米级体积元中，将 LCN 的局部密度与同一位置的矿物质含量进行空间相关，定量描述这种相互作用。为此，从健康成年人（n=4）和儿童（n=2）的股骨中段采集了 65 个骨单位，分别使用两种不同的技术对其进行结构特征描述。用罗丹明对骨样本进行染色后，用共聚焦激光扫描显微镜对骨单位中 LCN 的 3D 结构进行成像。随后的图像分析提供了管腔长度密度，即单位体积内的小管总长度（μm/μm）。使用定量背散射电子成像获得相同区域的矿物质含量（wt%Ca）的定量信息。由于 LCN 孔隙降低了矿物质含量，因此预计 Ca 含量与网络密度之间存在负相关。计算预测网络每增加 1μm 会减少约 -0.97 fmol Ca。然而，实验显示在 65 个骨单位中的 62 个骨单位中存在正相关，导致每个管腔网络的平均额外 Ca 加载为 +1.15 fmol/μm，即矿物质在密集网络区域发生了聚集。我们假设这种聚集发生在形成矿物质储库的小管附近，骨细胞可以利用这些储库。个体之间存在显著差异表明，储库区域的矿物质加载程度反映了矿物质平衡的一个重要参数。
