HBM Mice Have Altered Bone Matrix Composition and Improved Material Toughness.

Area of Science:

• Biomaterials science
• Skeletal biology
• Genetics

Background:

• The G171V mutation in low-density lipoprotein receptor-related protein 5 (LRP5) causes a high bone mass (HBM) phenotype.
• Previous research on HBM mouse models shows increased bone mass and strength, but bone matrix composition remains understudied.

Purpose of the Study:

• To investigate differences in cortical bone matrix composition between HBM and wild-type mice.
• To quantify the contribution of matrix composition to bone material properties in HBM mice.

Main Methods:

• Fourier transform infrared microspectroscopy (FTIR) to analyze mineral-to-matrix ratios, crystallinity, and substitutions.
• X-ray scattering to assess crystal size, spacing, and intra-fibular strains.
• Step-wise regression analysis to correlate matrix composition with material properties.

Main Results:

• HBM mice exhibited greater cortical area, moment of inertia, ultimate force, stiffness, and energy to failure.
• Significant differences in matrix composition were observed, including increased mineral-to-matrix and collagen cross-link ratios, and decreased crystallinity and carbonate substitution.
• HBM mice showed a twofold increase in the modulus of toughness, driven by enhanced post-yield behavior.

Conclusions:

• The LRP5 mutation alters cortical bone matrix composition, contributing to improved material properties and toughness.
• Matrix compositional parameters associated with material properties differ between HBM and wild-type genotypes.
• LRP5 is a potential target for enhancing both bone mass and quality.