title: Loss of fibulin-4 results in abnormal collagen fibril assembly in bone, caused by impaired lysyl oxidase processing and collagen cross-linking.
abstract: The extracellular matrix protein fibulin-4 has been shown to be indispensable for elastic fiber assembly, but there is also evidence from human mutations that it is involved in controlling skeletal development and bone stability. Fibulin-4 mutations were identified in patients suffering from vascular abnormality and/or cutis laxa, and some of these patients exhibited bone fragility, arachnodactyly and joint laxity. In order to elucidate the role of fibulin-4 in bone structure and skeletal development, we analyzed structural changes in skeletal tissues of Fbln4(-/-) mice. Immunostaining confirmed that fibulin-4 is highly expressed in cartilage, bone, ligaments and tendons. No morphological abnormalities were found in the skeleton of Fbln4(-/-) mice as compared to wild type littermates except forelimb contractures as well as unusually thick collagen fibrils. Furthermore, fibulin-4 deficiency caused enhanced susceptibility of bone collagen for acid extraction, consistent with significantly reduced lysylpyridinoline and hydroxylysylpyridinoline cross-links in bone. In accordance with that, the amount of lysyl oxidase in long bones and calvaria was strongly decreased and proteolytic activation of lysyl oxidase was reduced in fibulin-4 deficient osteoblasts, while addition of recombinant fibulin-4 rescued the activation. The finding suggested that fibulin-4 is important for the proteolytic activation of lysyl oxidase which has a pivotal role in cross-linking of collagen and elastin.
authors.affiliation: Department of Experimental Medicine I, Nikolaus-Fiebiger Center of Molecular Medicine, University of Erlangen-Nürnberg, 91054 Erlangen, Germany; Department of Biochemistry II, Faculty of Medicine, Oita University, Oita 879-5593, Japan. Electronic address: tsasaki@oita-u.ac.jp.
authors.forename: Takako
authors.initials: T
authors.lastname: Sasaki
authors.affiliation: Metabolic Health Research, TNO, NL-2333CK Leiden, The Netherlands.
authors.forename: Reinout
authors.initials: R
authors.lastname: Stoop
authors.affiliation: Department of Molecular and Clinical Pharmacology, Institute of Translational Medicine, The University of Liverpool, Liverpool, England.
authors.forename: Takao
authors.initials: T
authors.lastname: Sakai
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nürnberg, 91054 Erlangen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hess
authors.affiliation: Institute of Biochemistry, Microbiology and Genetics, University of Regensburg, 93053 Regensburg, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Deutzmann
authors.affiliation: Department of Ophthalmology, University of Erlangen-Nürnberg, 91054 Erlangen, Germany.
authors.forename: Ursula
authors.initials: U
authors.lastname: Schlötzer-Schrehardt
authors.affiliation: Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Mon-Li
authors.initials: ML
authors.lastname: Chu
authors.affiliation: Department of Experimental Medicine I, Nikolaus-Fiebiger Center of Molecular Medicine, University of Erlangen-Nürnberg, 91054 Erlangen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: von der Mark
mesh_terms: D000818:Animals; D001846:Bone Development; D001842:Bone and Bones / Q000166:cytology* / Q000378:metabolism; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D004549:Elastin / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D051379:Mice; D009154:Mutation; D008249:Protein-Lysine 6-Oxidase / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: C403672:EFEMP2 protein, human; D016326:Extracellular Matrix Proteins; D003094:Collagen; D004549:Elastin; D008249:Protein-Lysine 6-Oxidase
keywords: Collagen cross-linking; Elastic fiber; Fibulin-4; Lysyl oxidase