Loss of fibulin-4 results in abnormal collagen fibril assembly in bone, caused by impaired lysyl oxidase processing and collagen cross-linking

• Published in: Matrix biology 2016-03, Vol.50, p.53-66
• Main Authors: Sasaki, Takako, Stoop, Reinout, Sakai, Takao, Hess, Andreas, Deutzmann, Rainer, Schlötzer-Schrehardt, Ursula, Chu, Mon-Li, von der Mark, Klaus
• Format: Article
• Language: English
• Subjects: Animals; Bone and Bones - cytology; Bone and Bones - metabolism; Bone Development; Cells, Cultured; Collagen - metabolism; Collagen cross-linking; Elastic fiber; Elastin - metabolism; Extracellular Matrix Proteins - genetics; Extracellular Matrix Proteins - metabolism; Fibulin-4; Humans; Lysyl oxidase; Mice; Mutation; Protein-Lysine 6-Oxidase - metabolism; Tissue Distribution
• ISSN: 0945-053X; 1569-1802
• DOI: 10.1016/j.matbio.2015.12.002

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. •Fibulin-4 deficiency results in abnormal collagen fibrillogenesis in bone.•Collagen cross-links in bone are reduced in fibulin-4 deficient mice.•Fibulin-4 plays a role in proteolytic activation of lysyl oxidase.