Quantitative trait loci that modulate trabecular bone's risk of failure during unloading and reloading

Area of Science:

• Genetics
• Biomechanics
• Skeletal Biology

Background:

• Bone's mechanical properties are influenced by an individual's genetic makeup.
• Understanding genetic contributions to bone adaptation under mechanical stress is crucial for skeletal health.

Purpose of the Study:

• To identify quantitative trait loci (QTLs) associated with changes in trabecular bone mechanical properties during simulated unloading and reambulation.
• To investigate the genetic basis of bone's response to altered mechanical loading conditions.

Main Methods:

• 352 female BALB/cByJ mice underwent 3 weeks of hindlimb unloading followed by 3 weeks of reambulation.
• Longitudinal in vivo microcomputed tomography (μCT) tracked trabecular bone changes in the distal femur.
• Finite element (FE) models derived from μCT scans were subjected to mechanical testing to compute stiffness and stress distributions, which were then associated with QTLs.

Main Results:

• At baseline, five QTLs explained 20% of peak stress variation. During unloading, three QTLs accounted for 14% of peak stress variability.
• During reambulation, one QTL explained 5% of peak stress variability.
• Distinct QTLs were identified for baseline mechanical properties, unloading-induced changes, and reambulation-induced changes, with little overlap.

Conclusions:

• Distinct genetic factors influence baseline trabecular bone mechanics versus its response to unloading and reambulation.
• These findings may reveal novel gene targets for mitigating fracture risk during unloading and enhancing bone recovery.
• Genetic regulation of trabecular bone's response to mechanical demand differs from that of its morphology.