title: Collagens VI and XII form complexes mediating osteoblast interactions during osteogenesis.
abstract: Bone formation is precisely regulated by cell-cell communication in osteoblasts. We have previously demonstrated that genetic deletion of Col6a1 or Col12a1 impairs osteoblast connections and/or communication in mice, resulting in bone mass reduction and bone fragility. Mutations of the genes encoding collagen VI cause Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM), which have overlapping phenotypes involving connective tissue and muscle. Recent studies have identified COL12A1 gene mutations in patients with UCMD- and BM-like disorders harboring no COL6 mutations, indicating the shared functions of these collagens in connective tissue homeostasis. The purpose of this investigation has been to test the hypothesis that collagens VI and XII have coordinate regulatory role(s) during bone formation. We analyzed the localization of collagens VI and XII relative to primary osteoblasts during osteogenesis. Immunofluorescence analysis demonstrated that collagens VI and XII colocalized in matrix bridges between adjacent cells during periods when osteoblasts were establishing cell-cell connections. Quantification of cells harboring collagen bridges demonstrated that matrix bridges were composed of collagens VI and XII but not collagen I. Interestingly, matrix bridge formation was impaired in osteoblasts deficient in either Col6a1 or Col12a1, suggesting that both collagens were indispensable for matrix bridge formation. These data demonstrate, for the first time, a functional relationship between collagens VI and XII during osteogenesis and indicate that a complex containing collagens VI and XII is essential for the formation of a communicating cellular network during bone formation.
authors.affiliation: Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, M&D Tower 24th, 5-45 1-Chome Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan. izu.mph@mri.tmd.ac.jp.
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Izu
authors.affiliation: Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, M&D Tower 24th, 5-45 1-Chome Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ezura
authors.affiliation: Institute for Dental Research and Musculoskeletal Biology, Center for Biochemistry, University of Cologne, Cologne, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Koch
authors.affiliation: Department of Molecular Pharmacology & Physiology, University of South Florida, Morsani College of Medicine, Tampa, Florida, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Birk
authors.affiliation: Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, M&D Tower 24th, 5-45 1-Chome Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Noda
mesh_terms: D000818:Animals; D002450:Cell Communication; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D024142:Collagen Type VI / Q000378:metabolism*; D024082:Collagen Type XII / Q000378:metabolism*; D003470:Culture Media / Q000494:pharmacology; D005109:Extracellular Matrix / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism*; D010012:Osteogenesis; D011485:Protein Binding
chemical_list: D024042:Collagen Type I; D024142:Collagen Type VI; D024082:Collagen Type XII; D003470:Culture Media
keywords: Collagen VI; Collagen XII; Communicating cell network; Osteogenesis; Primary osteoblasts