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.

Due to ageing of the population, bone frailty is dramatically increasing worldwide. Although some therapeutic options exist, they do not fully protect or prevent against the occurrence of new fractures. All current drugs approved for the treatment of bone fragility target bone mass. However, bone resistance to fracture is not solely due to bone mass but relies also on bone ECM material properties, i.e. the quality of the bone matrix component. Here, we introduce the first-in-class unimolecular dual GIP/GLP-2 analogues, GL-0001, that activate simultaneously the glucose-dependent insulinotropic polypeptide receptor (GIPr) and the glucagonlike peptide-2 receptor (GLP-2r). GL-0001 acts synergistically through a cAMP-LOX pathway to enhance collagen maturity. Furthermore, in mice with ovariectomy-induced bone fragility, GL-0001 prevented excess trabecular bone degradation at the appendicular skeleton and also enhanced bone ECM material properties through reduction of the degree of mineralization and augmentation in enzymatic collagen crosslinking. These results demonstrate that targeting bone ECM material properties is a viable option to enhance bone strength and opens an innovative pathway for the treatment of patients suffering of bone fragility.