Peri-Lacunar and Peri-Canalicular Tissue Mass Densities and Gradients are Determined by Tissue Age and Remodeling Rate
Résumé
Osteocytes are believed not only to orchestrate osteoclast and osteoblast activity in bone remodeling, but also to actively participate in the homeostasis of mineral through osteolysis. In this study we hypothesized that this process is achieved through diffusion of mineral from the lacuno-canalicular network to the bone matrix and vice versa, resulting in a gradual change of tissue mineralization with respect to the distance from the pore-matrix interface. We expected to observe the same phenomena in newly formed osteonal tissue versus aged interstitial tissue and even more emphasized in highly dosed bisphosphonate treatment. The aim of this study was therefore to investigate the spatial distribution of mass density in the peri-lacunar and peri-canalicular bone tissue using phase-contrast synchrotron nanoCT with 50nm voxel size and to evaluate if density gradients exist in human jaw bone specimens originating from four healthy and four high-dosed bisphosphonate treated donors. Our results show first experimental evidence that mass density in the direct vicinity of both lacunae (p<0.001) and canaliculi (p=0.004) are different from the mean matrix density, resulting in gradients with respect to the distance from both pore-matrix interfaces. We found that mass densities (R=0.77, p=0.006) and gradients (R=0.73, p=0.010) between peri-lacunar and peri-canalicular tissues were correlated. Moreover, we observed that both peri-lacunar (p=0.039) and peri-canalicular (p<0.001) mass densities were significantly affected by the tissue age and drug treatment (osteonal-tissue < interstitial-tissue & bisphosphonate-treated). The density gradient was more pronounced around the lacunae than around the canaliculi and was the highest in interstitial tissue. On average, 50% of the mineralized tissue was found to be within less than 1.5µm distance from the canaliculi, which is approximately ten times smaller compared to the distance from the lacunae. These findings support the important role of the entire lacunar-canalicular network in the remodeling process and the mineral homeostasis.