Site-Specific Bone Characteristics in MYO9B Deficient Mice

Objectives: Single nucleotide polymorphisms in Myosin IXB (MYO9B) are linked to variations in height and inflammatory bowel diseases, often associated with compromised growth and bone quality in humans. However, a lack of knowledge exists its effect on oral bone. The objective of this study was to investigate whether MYO9B deficiency on bone traits in mice alters bone characteristics differently between jaw and limb bones.
Methods: Following IACUC protocol, 12 weeks old wild-type (WT) (8 males, 8 females) and global MYO9B knockout (KO) (7 females, 8 males) were obtained. Hemi-mandibles and femurs were dissected to scan using micro-computed tomography (micro-CT) with 10 mm and 20 mm voxel size, respectively. After segmentation between bone and non-bone voxels, a frequency plot of tissue mineral density (TMD) was obtained to compute mean and 5th percentile of low and high (Low₅ and High₅) TMD values. Trabecular morphological parameters of femur were also measured. Following the non-destructive micro-CT analysis, the mandible and femur were subject to non-destructive dynamic mechanical analysis (DMA) at 1, 2, and 3 Hz for assessing dynamic stiffness and energy dissipation (tan d). Finally, mechanical strength of femurs were measured by static loading to fracture. Analysis of variance was performed to compare the values measured for each parameter between the WT and KO groups. Statistical significance was set at p<0.05.
Results: The KO group of femurs had significantly lower values of volume, mineral density, and strength than the WT group (p<0.05) except a higher value of tan d (p=0.03). All parameters of mandible were not significantly different between WT and KO groups (p>0.09).
Conclusions: The current findings indicate that MYO9B deficiency has the site-specific effects on bone properties without significant changes in jawbone.