The proof of principle of the therapeutic potential of heat shock protein 47 (HSP47) for diseases characterized by defects in collagen I synthesis is here demonstrated in osteogenesis imperfecta (OI), a prototype of collagen disorders. Most of the OI mutations delay collagen I chain folding, increasing their exposure to posttranslational modifications that affect collagen secretion and impact extracellular matrix fibril assembly. As a model, we used primary fibroblasts from OI individuals with a defect in the collagen prolyl 3-hydroxylation complex, since they are characterized by the synthesis of homogeneously overmodified collagen molecules. We demonstrated that exogenous recombinant HSP47 (rHSP47) is taken up by the cells and localizes at the ER exit sites and ER-Golgi intermediate compartment. rHSP47 treatment increased collagen secretion, reduced collagen posttranslational modifications and intracellular collagen retention, and ameliorated general ER proteostasis, leading to improved cellular homeostasis and vitality. These positive changes were also mirrored by an increased collagen content in the OI matrix. A mutation-dependent effect was found in fibroblasts from 3 probands with collagen I mutations, for which rHSP47 was effective only in cells with the most N-terminal defect. A beneficial effect on bone mineralization was demonstrated in vivo in the zebrafish p3h1 ^–/– OI model.

Factor VIII (FVIII) is involved in several molecular pathways and biological processes; indeed, it has a role in the coagulative cascade, cardiovascular disease, hypertension, brain and renal function, cancer incidence and spread, macrophage polarization, and angiogenesis. Hemophilic patients usually present an increase in fracture risk, bone resorption, and an excess of osteoporosis as compared to healthy individuals. Several studies have tried to clarify their etiology but unfortunately it is still unclear. This review focuses on the role of FVIII in bone biology by summarizing all the knowledge present in the literature. We carried out a systematic review of the available literature following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Several studies demonstrated that FVIII is involved in different molecular pathways interfering with bone physiology; it exerts interesting effects on OPG/RANK/RANKL pathways and thrombin/PAR1 pathways. These data confirm a relationship between FVIII and bone metabolism; however, there are still many aspects to be clarified. This review highlights the role of the coagulation factor FVIII in bone metabolism, suggesting new hypotheses for future studies both in vitro and in vivo to better understand the important pleiotropic role of FVIII and hopefully to develop new therapeutic agents for skeletal diseases.