Perilacunar bone tissue exhibits sub-micrometer modulus gradation which depends on the recency of osteocyte bone formation in both young adult and early-old-age female C57Bl/6 mice.

Abstract

Osteocytes resorb and replace bone local to the lacunar-canalicular system (LCS). However, whether osteocyte remodeling impacts bone quality adjacent to the LCS is not understood. Further, while aging is well-established to decrease osteocyte viability and truncate LCS geometry, it is unclear if aging also decreases perilacunar bone quality. To address these questions, we employed atomic force microscopy (AFM) to generate nanoscale-resolution modulus maps for cortical femur osteocyte lacunae from young (5-month) and early-old-age (22-month) female C57Bl/6 mice. AFM-mapped lacunae were also imaged with confocal laser scanning microscopy to determine which osteocytes recently deposited bone as determined by the presence of fluorochrome labels administered 2d and 8d before euthanasia. Modulus gradation with distance from the lacunar wall was compared for labeled (i.e., bone forming) and non-labeled lacunae in both young and aged mice. All mapped lacunae showed sub-microscale modulus gradation, with peak modulus values 200-400nm from the lacunar wall. Perilacunar modulus gradations depended on the recency of osteocyte bone formation (i.e., the presence of labels). For both ages, 2d-labeled perilacunar bone had lower peak and bulk modulus compared to non-labeled perilacunar bone. Lacunar length reduced with age, but lacunar shape and size were not strong predictors of modulus gradation. Our findings demonstrate for the first time that osteocyte perilacunar remodeling impacts bone tissue modulus, one contributor to bone quality. Given the immense scale of the LCS, differences in perilacunar modulus resulting from osteocyte remodeling activity may affect the quality of a substantial amount of bone tissue.