title: Molecular Consequences of the SERPINH1/HSP47 Mutation in the Dachshund Natural Model of Osteogenesis Imperfecta.
abstract: Osteogenesis imperfecta (OI) is a heritable connective tissue disease characterized by bone fragility and increased risk of fractures. Up to now, mutations in at least 18 genes have been associated with dominant and recessive forms of OI that affect the production or post-translational processing of procollagen or alter bone homeostasis. Among those, SERPINH1 encoding heat shock protein 47 (HSP47), a chaperone exclusive for collagen folding in the ER, was identified to cause a severe form of OI in dachshunds (L326P) as well as in humans (one single case with a L78P mutation). To elucidate the disease mechanism underlying OI in the dog model, we applied a range of biochemical assays to mutant and control skin fibroblasts as well as on bone samples. These experiments revealed that type I collagen synthesized by mutant cells had decreased electrophoretic mobility. Procollagen was retained intracellularly with concomitant dilation of ER cisternae and activation of the ER stress response markers GRP78 and phospho-eIF2α, thus suggesting a defect in procollagen processing. In line with the migration shift detected on SDS-PAGE of cell culture collagen, extracts of bone collagen from the OI dog showed a similar mobility shift, and on tandem mass spectrometry, the chains were post-translationally overmodified. The bone collagen had a higher content of pyridinoline than control dog bone. We conclude that the SERPINH1 mutation in this naturally occurring model of OI impairs how HSP47 acts as a chaperone in the ER. This results in abnormal post-translational modification and cross-linking of the bone collagen.
authors.affiliation: Division of Metabolism, Connective Tissue Unit, University Children's Hospital Zurich, Children's Research Center, 8032 Zurich, Switzerland.
authors.forename: Uschi
authors.initials: U
authors.lastname: Lindert
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington 98195.
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Weis
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington 98195.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Rai
authors.affiliation: AstraZeneca, Drug Safety and Metabolism, 431 83 Mölndal, Sweden.
authors.forename: Frank
authors.initials: F
authors.lastname: Seeliger
authors.affiliation: Institute of Pathology, University Hospital Heidelberg and Electron Microscopy Core Facility, Heidelberg University, 69120 Heidelberg, Germany.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Hausser
authors.affiliation: Institute of Genetics, Vetsuisse Faculty, University of Bern, CH-3001 Bern, Switzerland.
authors.forename: Tosso
authors.initials: T
authors.lastname: Leeb
authors.affiliation: Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington 98195.
authors.forename: David
authors.initials: D
authors.lastname: Eyre
authors.affiliation: Division of Metabolism, Connective Tissue Unit, University Children's Hospital Zurich, Children's Research Center, 8032 Zurich, Switzerland.
authors.forename: Marianne
authors.initials: M
authors.lastname: Rohrbach
authors.affiliation: Division of Metabolism, Connective Tissue Unit, University Children's Hospital Zurich, Children's Research Center, 8032 Zurich, Switzerland. Electronic address: Cecilia.Giunta@kispi.uzh.ch.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Giunta
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000737:chemistry / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D024042:Collagen Type I / Q000032:analysis / Q000378:metabolism*; D004195:Disease Models, Animal; D004285:Dogs; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D050958:HSP47 Heat-Shock Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D010013:Osteogenesis Imperfecta / Q000235:genetics* / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D017354:Point Mutation; D011499:Protein Processing, Post-Translational; D055550:Protein Stability
chemical_list: D024042:Collagen Type I; D000091342:Endoplasmic Reticulum Chaperone BiP; D050958:HSP47 Heat-Shock Proteins; C000717247:HSPA5 protein, human
keywords: SERPINH1; bone; collagen; connective tissue; cross-links; endoplasmic reticulum stress (ER stress); extracellular matrix; heat shock protein 47; osteogenesis