A preliminary study exploring the mechanical properties of normal and Mgp-deficient mouse femurs during early growth

Matrix Gla protein (MGP) is mostly known to be a calcification inhibitor, as its absence leads to ectopic calcification of different tissues such as cartilage or arteries. MGP deficiency also leads to low bone mass and delayed bone growth. In the present contribution, we investigate the effect of MGP deficiency on the structural and material mechanical bone properties by focusing on the elastic response of femurs undergoing three-points bending. To this aim, biomechanical tests are performed on femurs issued from Mgp-deficient mice at 14, 21, 28, and 35 days of postnatal life and compared to healthy control femurs. µCT acquisitions enable to reconstruct bone geometries and are used to construct subject-specific finite element models avoiding some of the reported limitations concerning the use of beam-like assumptions for small bone samples. Our results indicate that MGP deficiency may be associated to differences in both structural and material properties of femurs during early stages of development. MGP deficiency appears to be related to a decrease in bone dimensions, compensated by higher material properties resulting in similar structural bone properties at P35. The search for a unique density-elasticity relationship based on calibrated bone mineral density (BMD) indicates that MGP deficiency may affect bone tissue in several ways, that may not be represented uniquely from the quantification of BMD. Despite of its limitation to elastic response, the present preliminary study reports for the very first time the mechanical skeletal properties of Mgp-deficient mice at early stages of development.

T-2 toxin-induced femur lesion is accompanied by autophagy and apoptosis associated with Wnt/β-catenin signaling in mice

T-2 toxin is one of the most common mycotoxins found in grain foods, animal feed, and other agricultural by-products causing food contamination and health threat. The skeletal system is the main target tissue for T-2 toxin. T-2 toxin exposure is also recognized as a potential contributor to multiple types of bone diseases, including Kashin-Beck disease. However, the mechanisms of T-2 toxin-induced bone toxicity remain unclear. In this study, 60 male C57BL/6 mice were exposed T-2 toxin with 0, 0.5, 1 or 2 mg/kg body weight by intragastric administration for 28 days, respectively. Femora were collected for the detections of femur lesion, bone formation factors, oxidative stress, autophagy, apoptosis, and Wnt/β-catenin signaling. Our research showed that T-2 toxin caused bone formation disorders, presenting as the reduction of the BMD and femur length, bone structure changes and abnormal bone formation proteins expressions, along with enhanced oxidative stress. Meanwhile, T-2 toxin increased expressions of autophagy-related proteins (Beclin 1, ATG5, p62, and LC3), and promoted apoptosis in mouse femur. Moreover, T-2 toxin suppressed the Wnt/β-catenin signaling and expressions of downstream target genes. Taken together, our data indicated T-2 toxin-induced femur lesion was accompanied by autophagy and apoptosis, which was associated with Wnt/β-catenin signaling.

CRTAP deficiency leads to abnormally high bone matrix mineralization in a murine model and in children with osteogenesis imperfecta type VII

Cartilage-associated protein (CRTAP) is an essential cofactor for the proper post-translational chain modification and collagen folding. CRTAP mutations lead mice (Crtap-/- mice) and humans (OI type VII) to a severe/lethal osteochondrodystrophy; patients have fractures at birth, deformities of the lower extremities and impaired growth. The consequences of CRTAP deficiency on intrinsic bone material properties are still unknown. In the present study we evaluated bone quality based on quantitative backscattered electron imaging (qBEI) to assess bone mineralization density distribution (BMDD) in femurs from 12 weeks old Crtap-/- mice and transiliac bone biopsies from 4 children with hypomorphic mutations and having residual CRTAP expression. The analyses revealed in the bone matrix of Crtap-/- animals and OI type VII patients a significant increase in mean (CaMean) and most frequent mineral concentration (CaPeak) compared to wild-type littermates and control children, respectively. The heterogeneity of mineralization (CaWidth) was reduced in Crtap-/- mice but normal in OI type VII patients. The fraction of highly mineralized bone matrix (CaHigh) was remarkably increased in the patients: cancellous bone from 2.1 to 3.7 times and cortical bone from 7.6 to 25.5 times, associated with an increased persistence of primary bone. In conclusion, the BMDD data show that CRTAP deficiency results in a shift towards higher mineral content of the bone matrix similar to classical OI with collagen gene mutations. Our data further suggest altered mineralization kinetics resulting ultimately in an overall elevated tissue mineralization density. Finally, in OI type VII patients the increased portion of primary bone is most likely reflecting a disturbed bone development.