The administration of exogenous HSP47 as a collagen specific therapeutic approach.

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The proof-of-principle of the therapeutic potential of heat shock protein 47 (HSP47) for diseases characterized by defects in the collagen I synthesis is here proved in osteogenesis imperfecta (OI), a prototype of collagen disorders. Most of the OI mutations delay collagen I chains folding, increasing their exposure to post translational modifications that affect collagen secretion and impact extracellular matrix fibrils assembly. As model, we used primary fibroblasts from OI individuals with defect in the collagen prolyl-3-hydroxylation complex, since are characterized by the synthesis of homogeneously overmodified collagen molecules. We demonstrated that the exogenous recombinant HSP47 (rHSP47) is uptaken by the cells and localizes at the ER exit sites and ER Golgi intermediate compartment. rHSP47 treatment increased collagen secretion, reduced collagen post translational modifications and intracellular collagen retention and ameliorated the 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 three probands with collagen I mutations, for which rHSP47 was effective only in cells with the most N-term defect. A beneficial effect on bone mineralization was proved in vivo in the zebrafish p3h1-/- OI model.