The contribution of the pericanalicular matrix to mineral content in human osteonal bone

Abstract

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 3). 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.

Network architecture strongly influences the fluid flow pattern through the lacunocanalicular network in human osteons

“…For an idealized canalicular network, where the canaliculi just run straight from the cement line to the Haversian canal, the fluid velocity would be constant in all canaliculi. Realistic osteon networks show a slight tree-like network topology, where the number of parallel canaliculi increases with distance from the center of the osteon (Repp et al 2017b;Roschger et al 2019). Consequently, the resistance of the network is higher close to the Haversian canal resulting in a larger than average drop in pressure (Fig.…”

“…The large surface area of the LCN (Buenzli and Sims 2015) is used to provide access to the mineral reservoir of bone. Osteocytic osteolysis and perilacunar/pericanalicular remodeling refer to processes in which the osteocytes actively change the surrounding bone matrix (Roschger et al 2019;Teti and Zallone 2009;Tsourdi et al 2018). Furthermore, osteocyte death can cause local hypermineralization and intra-lacunocanalicular calcification (micropetrosis) (Busse et al 2010;Frost 1960;Milovanovic et al 2017;Repp et al 2017b).…”

An Early Myeloma Bone Disease Model in Skeletally Mature Mice as a Platform for Biomaterial Characterization of the Extracellular Matrix

“…For the network characterization, we used an established protocol based on previously published work [ 17 , 18 ]. In short, raw CLSM data were segmented to automatically differentiate between canaliculi and lacunae based on their bulkiness.…”

The mechanoresponse of bone is closely related to the osteocyte lacunocanalicular network architecture

“…Confocal laser-scanning microscopy (CLSM) was used after rhodamine staining to image the LCN in whole cross-sections of the mouse tibiae. Tibia samples with only their knee and ankle joints removed were immersed in an ethanol solution with rhodamine 6G for 24 h. This was repeated three times with a fresh rhodamine 6G solution and then embedded in poly(methyl methacrylate) (PMMA) using our previously established protocol (76). The bone was kept wet with ethanol until the PMMA embedding process was finished to prevent crack formation.…”