骨细胞的募集随着骨单位的填充而减少:骨细胞硬化素和既往髋部骨折对股骨颈皮质管大小的相互作用影响。

Osteocyte recruitment declines as the osteon fills in: interacting effects of osteocytic sclerostin and previous hip fracture on the size of cortical canals in the femoral neck.

机构信息

University Department of Medicine, Bone Division, Box 157, Addenbrooke's Hospital, Cambridge CB2 0QQ, UK.

出版信息

Bone. 2012 May;50(5):1107-14. doi: 10.1016/j.bone.2012.01.016. Epub 2012 Jan 28.

Abstract

There is little information on the distribution of osteocytes within the individual cortical osteon, but using direct 3-D imaging in a single subject, Hannah et al. found a gradient with a two-fold higher density of cells adjacent to the cement line compared to near the canal. Since a limiting factor for bone formation might be the availability of osteoblasts due to their recruitment as osteocytes, we studied distributions of osteonal osteocytes in frozen sections of the femoral neck cortex. Osteocytes were stained with an anti-sclerostin antibody and counter-stained with toluidine blue. Adjacent sections were stained for alkaline phosphatase (ALP). Each osteonal osteocyte was categorised as being sclerostin-positive (scl+) or negative (scl-). ImageJ was used to measure the perimeter and area of each osteon and canal, while special purpose routines were used to measure the minimum distances of each osteocyte from the cement line and the canal. Canal area was strongly correlated with osteon area. Osteocytes were most dense close to the cement line; and their areal density within the matrix declined up to three-fold between the cement line and the canal, depending on osteon diameter. Large and small osteons had similar densities of osteocytes close to the cement line, but fractured neck of femur cases had significantly lower densities of osteocytes close to the canal. Higher osteocyte density close to the canal was associated with ALP expression. It is concluded that entombment of osteocytes newly drawn from the osteoblast pool into the mineralising matrix is independent of preceding bone resorption depth. As osteonal infilling proceeds, osteocyte formation declines more rapidly than matrix formation, leading to a progressive reduction in osteocyte density. A shrinking supply of precursor osteoblasts due to previous osteocyte recruitment, apoptosis, or both could produce this effect. In a statistically significant contrast, sclerostin negative osteocytes adjacent to the canal had the expected effect of reducing canal size in controls but this was not seen in hip fracture. This demonstrated the failure of osteonal osteoblasts to sustain bone formation through a complete remodelling cycle in osteoporosis, perhaps due to insufficient osteoblasts remaining capable of mineralized matrix formation. The failure of osteocytic sclerostin suppression to associate with bone formation in these osteons might alternatively be explained by downstream interference with sclerostin's effect on wnt signalling.

摘要

关于单个皮质骨单位内骨细胞的分布信息很少,但 Hannah 等人在一个单独的个体中使用直接 3-D 成像,发现细胞密度与靠近黏合线相比在靠近管腔处有两倍的梯度。由于由于其募集为成骨细胞,因此骨形成的限制因素可能是成骨细胞的可用性,我们研究了股骨颈皮质骨冷冻切片中骨单位的骨细胞分布。用抗硬化蛋白抗体对骨细胞进行染色,并使用甲苯胺蓝进行复染。相邻切片用碱性磷酸酶 (ALP) 染色。每个骨单位的骨细胞被归类为硬化蛋白阳性 (scl+) 或阴性 (scl-)。ImageJ 用于测量每个骨单位和管腔的周长和面积,而特殊目的例程用于测量每个骨细胞距黏合线和管腔的最小距离。管腔面积与骨单位面积强烈相关。骨细胞在靠近黏合线的地方最密集;并且它们在基质中的面积密度在黏合线和管腔之间下降了三倍,具体取决于骨单位直径。大骨单位和小骨单位靠近黏合线的骨细胞密度相似,但股骨颈骨折病例靠近管腔的骨细胞密度明显较低。靠近管腔的骨细胞密度较高与 ALP 表达相关。结论是,从成骨细胞池中提取的新骨细胞被埋葬在矿化基质中与先前的骨吸收深度无关。随着骨单位的填充进行,骨细胞的形成比基质的形成更快地下降,导致骨细胞密度的逐渐降低。由于先前的骨细胞募集、细胞凋亡或两者的原因,前体细胞成骨细胞的供应减少可能会产生这种效果。在统计学上有显著差异的是,靠近管腔的硬化蛋白阴性骨细胞在对照组中具有减小管腔大小的预期作用,但在髋部骨折中未见这种作用。这表明在骨质疏松症中,骨单位的成骨细胞不能通过完整的重塑周期维持骨形成,这可能是由于剩余的成骨细胞不足以进行矿化基质形成。这些骨单位中骨细胞的硬化蛋白抑制作用与骨形成的失败可能通过下游干扰硬化蛋白对 wnt 信号的作用来解释。

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