A new open-source tool for measuring 3D osteocyte lacunar geometries from confocal laser scanning microscopy reveals age-related changes to lacunar size and shape in cortical mouse bone
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Abstract
<p class="first" id="P1">Osteocytes can participate in systemic mineral homeostasis
through perilacunar maintenance
and remodeling, where changes to osteocyte lacunar morphology may affect bone structural
integrity, tissue strains, and osteocyte mechanosensitivity. Though aging is associated
with both decreased bone quality and altered mineral metabolism, it is not known if
osteocyte lacunae undergo age-related changes in geometry. In order to survey lacunar
changes with age, we developed an open-source program whereby 3D osteocyte lacunae
are automatically segmented and then subsequently reconstructed from confocal laser
scanning microscopy (CLSM) depth stacks for quantitative analysis of geometry and
orientation. This approach takes advantage of the availability and speed of CLSM while
avoiding time-consuming and bias-prone manual segmentation. Unlike conventional approaches
used to quantify osteocyte lacunar morphology, CLSM enables facile analysis in three-dimensions
with clear identification of osteocyte lacunae. We report that 3D osteocyte lacunae
measured by CLSM become smaller, more spherical, more oblate, more spatially disorganized,
and more sparsely populated with increased age in C57Bl/6 mouse cortical bone in groups
spanning 6 – 24 months old. Critically, these age-related changes are in large part
not observed in 2D analyses from the same samples. These results (1) demonstrate proof-of-concept
of an efficient method to quantitatively assess osteocyte lacunae in 3D for application
to a wide range of studies and (2) motivate further inquiry into how changes to osteocyte
lacunar geometries and perilacunar material contribute to diminished bone quality
in aging.
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