Department of Orthopedics, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany; Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Lottestr. 59, 22529 Hamburg, Germany.
Bone. 2020 Jun;135:115324. doi: 10.1016/j.bone.2020.115324. Epub 2020 Mar 19.
The enlargement of osteocyte lacunae via osteocytic osteolysis was previously detected in situations of increased calcium demand (e.g., lactation, vitamin D deficiency). However, it is unclear whether similar processes occur also in the growing infantile skeleton and how this is linked to the mineral distribution within the bone matrix. Human iliac crest biopsies of 30 subjects (0-6 months, n = 14; 2-8 years, n = 6 and 18-25 years, n = 10) were acquired. Bone microarchitecture was assessed by micro-CT, while cellular bone histomorphometry was performed on undecalcified histological sections. Quantitative backscattered electron imaging (qBEI) was conducted to determine the bone mineral density distribution (BMDD) as well as osteocyte lacunar size and density. We additionally evaluated cathepsin K positive osteocytes using immunohistochemistry. Infantile bone was characterized by various signs of ongoing bone development such as higher bone (re)modeling, lower cortical and trabecular thickness compared to young adults. Importantly, a significantly higher osteocyte lacunar density and increased lacunar area were detected. Large osteocyte lacunae were associated with a more heterogeneous bone mineral density distribution of the trabecular bone matrix due to the presence of hypermineralized cartilage remnants, whereas the mean mineralization (i.e., CaMean) was not different in infantile bone. Absence of cathepsin K expression in osteocyte lacunae indicated nonexistent osteocytic osteolysis. Taken together, we demonstrated that the overall mineralization distribution in infantile bone is not altered compared to young adults besides high trabecular mineralization heterogeneity. Our study also provides important reference values for bone microstructure, BMDD and osteocyte characteristics in infants, children and young adults. Infantile bone displays large osteocyte lacunae indicating a developmental phenomenon rather than osteocytic osteolysis. Larger osteocytes may have superior mechanosensory abilities to enable bone adaption during growth.
破骨细胞性骨吸收导致的骨细胞陷窝扩大以前仅在钙需求增加的情况下（例如哺乳期、维生素 D 缺乏）被检测到。然而，目前尚不清楚在生长中的婴儿骨骼中是否也会发生类似的过程，以及这与骨基质内的矿物质分布有何关联。采集了 30 名受试者（0-6 个月，n=14；2-8 岁，n=6；18-25 岁，n=10）的髂嵴活检样本。通过微 CT 评估骨微结构，在未脱钙组织切片上进行细胞性骨组织形态计量学分析。进行定量背散射电子成像（qBEI）以确定骨矿物质密度分布（BMDD）以及骨细胞陷窝的大小和密度。我们还使用免疫组织化学评估了组织蛋白酶 K 阳性的骨细胞。与年轻成年人相比，婴儿骨骼具有各种正在进行的骨发育迹象，例如更高的骨（再）塑造率、更低的皮质骨和小梁厚度。重要的是，检测到骨细胞陷窝密度显著增加和陷窝面积增大。由于存在矿化软骨残余物，大的骨细胞陷窝与小梁骨基质的矿物质密度分布更加不均匀相关，而婴儿骨骼的平均矿化（即 CaMean）并无差异。骨细胞陷窝中不存在组织蛋白酶 K 的表达表明不存在破骨细胞性骨溶解。总之，我们的研究表明，与年轻成年人相比，婴儿骨骼的整体矿物质分布除了小梁矿化不均匀性较高外并无改变。我们的研究还为婴儿、儿童和年轻成年人的骨微观结构、BMDD 和骨细胞特征提供了重要的参考值。婴儿骨骼中存在较大的骨细胞陷窝，这表明这是一种发育现象，而不是破骨细胞性骨溶解。较大的骨细胞可能具有更好的机械感觉能力，以在生长过程中实现骨骼适应。
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