title: Regulation of collagen deposition and lysyl oxidase by tumor necrosis factor-alpha in osteoblasts.
abstract: Tumor necrosis factor-alpha (TNF-alpha) inhibits osteoblast function in vitro by inhibiting collagen deposition. Studies generally support that TNF-alpha does not inhibit collagen biosynthesis by osteoblasts but that collagen deposition is in some way diminished. The study investigated TNF-alpha regulation of biosynthetic enzymes and proteins crucial for posttranslational extracellular collagen maturation in osteoblasts including procollagen C-proteinases, procollagen C-proteinase enhancer, and lysyl oxidase. The working hypothesis is that such regulation could inhibit collagen deposition by osteoblasts. We report that in phenotypically normal MC3T3-E1 osteoblasts, TNF-alpha decreases collagen deposition without decreasing collagen mRNA levels or procollagen protein synthesis. Analyses of the cell layers revealed that TNF-alpha diminished the levels of mature collagen cross-links, pyridinoline and deoxypyridinoline. Further analyses revealed that the mRNA expression for lysyl oxidase, the determining enzyme required for collagen cross-linking, is down-regulated by TNF-alpha in a concentration- and time-dependent manner by up to 50%. The decrease was accompanied by a significant reduction of lysyl oxidase protein levels and enzyme activity. By contrast, Northern and Western blotting studies revealed that procollagen C-proteinases bone morphogenic protein-1 and mammalians Tolloid and procollagen C-proteinase enhancer were expressed in MC3T3-E1 cells and not down-regulated. The data together demonstrate that TNF-alpha does not inhibit collagen synthesis but does inhibit the expression and activity of lysyl oxidase in osteoblasts, thereby contributing to perturbed collagen cross-linking and accumulation. These studies identify a novel mechanism in which proinflammatory cytokine modulation of an extracellular biosynthetic enzyme plays a determining role in the control of collagen accumulation by osteoblasts.
authors.affiliation: Department of Oral Biology, Goldman School of Dental Medicine, Boston University, Boston, Massachussetts 02118, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Pischon
authors.forename: Laurent M
authors.initials: LM
authors.lastname: Darbois
authors.forename: Amitha H
authors.initials: AH
authors.lastname: Palamakumbura
authors.forename: Efrat
authors.initials: E
authors.lastname: Kessler
authors.forename: Philip C
authors.initials: PC
authors.lastname: Trackman
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D003094:Collagen / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D007249:Inflammation; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D008249:Protein-Lysine 6-Oxidase / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D003432:Cross-Linking Reagents; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; C015484:pyridinoline; C036020:deoxypyridinoline; D003094:Collagen; D008249:Protein-Lysine 6-Oxidase