title: The metalloproteinase MT1-MMP is required for normal development and maintenance of osteocyte processes in bone.
abstract: The osteocyte is the terminally differentiated state of the osteogenic mesenchymal progenitor immobilized in the bone matrix. Despite their numerical prominence, little is known about osteocytes and their formation. Osteocytes are physically separated in the bone matrix but seemingly compensate for their seclusion from other cells by maintaining an elaborate network of cell processes through which they interact with other osteocytes and bone-lining cells at the periosteal and endosteal surfaces of the bone. This highly organized architecture suggests that osteocytes make an active contribution to the structure and maintenance of their environment rather than passively submitting to random embedding during bone growth or repair. The most abundant matrix protein in the osteocyte environment is type-I collagen and we demonstrate here that, in the mouse, osteocyte phenotype and the formation of osteocyte processes is highly dependent on continuous cleavage of type-I collagen. This collagenolytic activity and formation of osteocyte processes is dependent on matrix metalloproteinase activity. Specifically, a deficiency of membrane type-1 matrix metalloproteinase leads to disruption of collagen cleavage in osteocytes and ultimately to the loss of formation of osteocyte processes. Osteocytogenesis is thus an active invasive process requiring cleavage of collagen for maintenance of the osteocyte phenotype.
authors.affiliation: Matrix Metalloproteinase Unit, National Institute of Dental and Craniofacial Research, Bethesda, MD 20892, USA.
authors.forename: Kenn
authors.initials: K
authors.lastname: Holmbeck
authors.forename: Paolo
authors.initials: P
authors.lastname: Bianco
authors.forename: Isabelle
authors.initials: I
authors.lastname: Pidoux
authors.forename: S
authors.initials: S
authors.lastname: Inoue
authors.forename: R C
authors.initials: RC
authors.lastname: Billinghurst
authors.forename: W
authors.initials: W
authors.lastname: Wu
authors.forename: Kali
authors.initials: K
authors.lastname: Chrysovergis
authors.forename: Susan
authors.initials: S
authors.lastname: Yamada
authors.forename: Henning
authors.initials: H
authors.lastname: Birkedal-Hansen
authors.forename: A Robin
authors.initials: AR
authors.lastname: Poole
mesh_terms: D000818:Animals; D001399:Azure Stains; D001842:Bone and Bones / Q000502:physiology*; D024042:Collagen Type I / Q000378:metabolism; D017403:In Situ Hybridization; D053511:Matrix Metalloproteinase 14; D053504:Matrix Metalloproteinases, Membrane-Associated; D008666:Metalloendopeptidases / Q000172:deficiency* / Q000502:physiology* / Q000648:ultrastructure; D051379:Mice; D046529:Microscopy, Electron, Transmission; D010011:Osteocytes / Q000201:enzymology* / Q000502:physiology* / Q000648:ultrastructure; D016622:Silver Staining; D013997:Time Factors
chemical_list: D001399:Azure Stains; D024042:Collagen Type I; C507096:Mmp14 protein, mouse; D053504:Matrix Metalloproteinases, Membrane-Associated; D008666:Metalloendopeptidases; D053511:Matrix Metalloproteinase 14