Osteocyte-directed bone demineralization along canaliculi.

Area of Science:

• Bone Biology
• Skeletal Physiology
• Mineral Metabolism

Background:

• The mammalian skeleton stores calcium and phosphate, with osteocytes residing in lacunae and extending dendrites through canaliculi.
• Osteoclasts are known bone resorbers, but osteocytes' role in dissolving hydroxyapatite at the peri-lacunar matrix is debated.
• Robust 3D evidence for peri-canalicular bone mineral dissolution has been lacking.

Purpose of the Study:

• To investigate and provide robust 3D evidence for peri-canalicular bone mineral dissolution.
• To determine if osteocytes directly contribute to bone demineralization within the lacuno-canalicular network.
• To explore the role of osteocytes in bone remodeling independent of osteoclasts.

Main Methods:

• Talbot-defocus multiscan tomography using synchrotron X-ray microscopy to analyze bone mineralization.
• Examination of mouse cortical bone, focusing on the lacuno-canalicular network.
• Transmission electron microscopy to visualize bone matrix integrity around canaliculi.

Main Results:

• Detected cylindrical regions of low mineral density surrounding canaliculi, originating from a subset of osteocytes.
• Transmission electron microscopy confirmed both intact and demineralized bone matrix adjacent to canaliculi.
• Peri-canalicular demineralization was observed even in osteopetrotic mice lacking osteoclasts.

Conclusions:

• Osteocytes can induce localized bone demineralization through the canalicular system, suggesting an 'inside-out' mechanism.
• Peri-canalicular demineralization is directed by individual osteocytes, not uniformly distributed.
• Targeting and blocking peri-canalicular demineralization by osteocytes may represent a novel therapeutic strategy for enhancing bone mass and quality.