Altered post-fracture systemic bone loss in a mouse model of osteocyte dysfunction

Area of Science:

• Bone Biology and Skeletal Remodeling
• Cellular Mechanisms of Bone Homeostasis
• Trauma and Fracture Repair

Background:

• Femur fracture causes systemic bone loss, increasing subsequent fracture risk.
• Osteocytes' role in systemic bone loss post-fracture is poorly understood.
• Osteocytes regulate bone resorption and influence osteoblast/osteoclast activity.

Purpose of the Study:

• To investigate the role of osteocytes in systemic bone loss after femur fracture.
• To determine if reduced viable osteocyte density impacts bone loss, remodeling, and callus formation.
• To utilize a transgenic mouse model with altered osteocyte viability.

Main Methods:

• Transgenic (TG+) mice overexpressing BCL-2 in osteoblasts/osteocytes were used.
• Micro-computed tomography, high-resolution x-ray microscopy, mechanical testing, and Raman spectroscopy were employed.
• Serum biomarkers assessed bone formation and resorption at 5 days post-fracture; structural/compositional analysis at 2 weeks.

Main Results:

• Transgenic mice (TG+) showed higher bone mass and cortical elastic modulus.
• Fracture led to reduced trabecular bone loss in TG+ mice compared to non-transgenic (TG-) mice.
• While TG+ mice had greater lacunar density, fracture did not alter lacunar volume in either group.

Conclusions:

• Osteocytes play a significant role in the systemic response to femur fracture.
• Reduced osteocyte density may decrease systemic trabecular bone loss post-fracture.
• The impact of osteocytes on bone loss differs between trabecular and cortical bone compartments.