Biomechanical, Microstructural and Material Properties of Tendon and Bone in the Young Oim Mice Model of Osteogenesis Imperfecta

Abstract

Osteogenesis imperfecta (OI) is a genetic disorder of connective tissue characterized by low bone mass and spontaneous fractures, as well as extra-skeletal manifestations, such as dental abnormalities, blue sclera, hearing loss and joint hypermobility. Tendon ruptures have been reported in OI patients. Here, we characterized the biomechanical, structural and tissue material properties of bone and tendon in 5-week-old female osteogenesis imperfecta mice (oim), a validated model of severe type III OI, and compared these data with age- and sex-matched WT littermates. Oim tendons were less rigid and less resistant than those of WT mice. They also presented a significantly higher rate of pentosidine, without significant modification of enzymatic crosslinking. The oim bones were less resistant and avulsion fractures were evident at high tendinous stress areas. Alterations of trabecular and cortical bone microarchitectures were noticed in young female oim. Bone tissue material properties were also modified, with a less mature and more mineralized matrix in association with lower collagen maturity. Our data suggest that the tendon-to-bone unit is affected in young oim mice, which could explain tendon ruptures and bone fragility observed in OI patients.

Keywords: Raman; biomechanics; bone; oim; osteogenesis imperfecta; tendon.

Figure 1

(A) Lower limb imaging with in vivo CT of WT and oim mice. Both oim calcanei show avulsion fractures (arrow). (B) pQCT total bone mineral density (BMD, mg/cm³) in ulna epiphysis. (C) Sagittal section through ulna epiphysis with insertion of triceps brachii tendon on the olecranon of the ulna in WT and oim mice; Sirius Red staining, T = tendon and E = epiphysis of olecranon (ulna). (D) Tendon thickness (mm) of triceps brachii tendon. (E) Bone volume/total volume (BV/TV, %) ratio in ulna epiphysis, *** p < 0.001.

Figure 2

Biomechanical parameters of flexor digitorum longus (FDL) tendons in 5-week-old WT and oim mice. (A) Stress–strain curve of one WT mouse (green line) and one oim (red line). (B) Evolution of stress through time during a cycle of deformation in the same tendons as in A. (C–F) Ultimate stress (N/mm²), ultimate strain (%), toughness (N/mm²) and elastic modulus (N/mm²) of FDL tendons. n = 7 for oim and 9 for WT mice. * p < 0.05, ** p < 0.01.

Figure 3

Biomechanical parameters of bone in 5-week-old WT and oim mice. (A) Example of load–deformation curves obtained in WT mice (green line) and oim (red line). (B) Ultimate load (N), (C) stiffness (N/mm), (D) yield load (N), (E) post-yield displacement (P.Y.D, mm) and (F) work to fracture (N.mm) computed from load–displacement curves. n = 10 and n = 8 for WT mice and oim, respectively. ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 4

Three-dimensional (3D) models and micro-architecture analysis of trabecular and cortical bone in oim and WT femurs. (A) Three-dimensional models of bone metaphysis and diaphysis. (B–D) Trabecular and (E–I) cortical microarchitectural parameters. BV/TV = bone volume/total volume, Tb.N = trabecular number, Tb.Th = trabecular thickness, Ct.Th = cortical thickness, CSMI = cross-sectional moment of inertia, Tt.Ar = total area, Ma.Ar = marrow area. n = 10 and n = 5 for WT mice and oim, respectively. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 5

Western blot in tail tendon; the expressions of tenomodulin, decorin and collagen type III are normalized to beta-actin; n = 6 for both groups; * p < 0.05.

Figure 6

Bone tissue material properties at the femur. (A) Mean spectrum in WT mice (green line) and oim (red line). (B) Inset of the spectrum in the v1, v3 PO4 band with position, width and intensity of subpeaks determined by second-derivative and curve-fitting spectroscopy. (C) Inset of the spectrum in the amide I band with position, width and intensity of subpeaks determined by second-derivative and curve-fitting spectroscopy. (D) Mineral and (E) organic bone tissue material properties. n = 10 and n = 6 for WT mice and oim, respectively *: p < 0.05; **: p < 0.01.