Morphological and mechanical characterization of bone phenotypes in the Amish G610C murine model of osteogenesis imperfecta

Abstract

Osteogenesis imperfecta (OI) is a hereditary bone disease where gene mutations affect Type I collagen formation resulting in osteopenia and increased fracture risk. There are several established mouse models of OI, but some are severe and result in spontaneous fractures or early animal death. The Amish Col1a2G610C/+ (G610C) mouse model is a newer, moderate OI model that is currently being used in a variety of intervention studies, with differing background strains, sexes, ages, and bone endpoints. This study is a comprehensive mechanical and architectural characterization of bone in G610C mice bred on a C57BL/6 inbred strain and will provide a baseline for future treatment studies. Male and female wild-type (WT) and G610C mice were euthanized at 10 and 16 weeks (n = 13–16). Harvested tibiae, femora, and L4 vertebrae were scanned via micro-computed tomography and analyzed for cortical and trabecular architectural properties. Femora and tibiae were then mechanically tested to failure. G610C mice had less bone but more highly mineralized cortical and trabecular tissue than their sex- and age-matched WT counterparts, with cortical cross-sectional area, thickness, and mineral density, and trabecular bone volume, mineral density, spacing, and number all differing significantly as a function of genotype (2 Way ANOVA with main effects of sex and genotype at each age). In addition, mechanical yield force, ultimate force, displacement, strain, and toughness were all significantly lower in G610C vs. WT, highlighting a brittle phenotype. This characterization demonstrates that despite being a moderate OI model, the Amish G610C mouse model maintains a distinctly brittle phenotype and is well-suited for use in future intervention studies.

The effect of carbamazepine on bone structure and strength in control and Osteogenesis Imperfecta (Col1a2+/p.G610C) mice

“…Six week old Col1a2 +/p.G610C mice have defective bone structure that is not modified by CBZ treatment from 3 weeks of age Previous studies have shown that from 8 weeks of age (but not at 10 days of age), Col1a2 +/p.G610C mice have less cortical and trabecular bone and lower bone strength than controls 5,7,9,18 . We showed that the phenotype can also be detected at 6 weeks of age.…”

“…density bone). Since cortical diaphyseal bone of Col1a2 +/p.G610C mice has greater average tissue mineral density 18 , we used multi-level thresholding to assess whether high density material accrued more rapidly in less mature regions of the femoral metaphysis of Col1a2 +/p.G610C mice.…”

“…This transition can be measured along the length of the growing bone from the growth plate (more low density bone) to the diaphysis (more high density bone). Since cortical diaphyseal bone of Col1a2 +/p.G610C mice has greater average tissue mineral density 18 , we used multi-level thresholding to assess whether high density material accrued more rapidly in less mature regions of the femoral metaphysis of Col1a2 +/p.G610C mice.…”

The effect of carbamazepine on bone structure and strength in control and osteogenesis imperfecta (Col1a2+/p.G610C) mice

“…3.1 | Six-week-old Col1a2 +/p.G610C mice have defective bone structure that is not modified by CBZ treatment from 3 weeks of age Previous studies have shown that from 8 weeks of age (but not at 10 days of age), Col1a2 +/p.G610C mice have less cortical and trabecular bone and lower bone strength than controls. 5,7,9,18 We showed that the phenotype can also be detected at 6 weeks of age. Femora from 6-week-old vehicle-treated Col1a2 +/p.G610C mice were narrower with significantly lower cortical area, periosteal and endocortical perimeters compared to controls (Figure 1A-D).…”

“…A limitation of our study was that it was conducted only on male mice. A recent detailed study of the morphological and mechanical phenotypes of the bone in Col1a2 +/p.G610C mice showed that the OI defects were similar in mice of both sexes 18 . It is a reasonable expectation that a therapeutic targeting a fundamental process, such as CBZ‐induction of autophagy, would work in both male and female mice, albeit possibly to different extents because of sex‐dependent skeletal variation.…”