title: Cells in regenerating deer antler cartilage provide a microenvironment that supports osteoclast differentiation.
abstract: Deer antlers are a rare example of mammalian epimorphic regeneration. Each year, the antlers re-grow by a modified endochondral ossification process that involves extensive remodelling of cartilage by osteoclasts. This study identified regenerating antler cartilage as a site of osteoclastogenesis in vivo. An in vitro model was then developed to study antler osteoclast differentiation. Cultured as a high-density micromass, cells from non-mineralised cartilage supported the differentiation of large numbers of osteoclast-like multinucleated cells (MNCs) in the absence of factors normally required for osteoclastogenesis. After 48 h of culture, tartrate-resistant acid phosphatase (TRAP)-positive mononuclear cells (osteoclast precursors) were visible, and by day 14 a large number of TRAP-positive MNCs had formed (783+/-200 per well, mean +/- s.e.m., N=4). Reverse transcriptase/polymerase chain reaction (RT-PCR) showed that receptor activator of NF &kgr; B ligand (RANKL) and macrophage colony stimulating factor (M-CSF) mRNAs were expressed in micromass cultures. Antler MNCs have the phenotype of osteoclasts from mammalian bone; they expressed TRAP, vitronectin and calcitonin receptors and, when cultured on dentine, formed F-actin rings and large resorption pits. When cultured on glass, antler MNCs appeared to digest the matrix of the micromass and endocytose type I collagen. Matrix metalloproteinase-9 (MMP-9) may play a role in the resorption of this non-mineralised matrix since it is highly expressed in 100 % of MNCs. In contrast, cathepsin K, another enzyme expressed in osteoclasts from bone, is only highly expressed in resorbing MNCs cultured on dentine. This study identifies the deer antler as a valuable model that can be used to study the differentiation and function of osteoclasts in adult regenerating mineralised tissues.
authors.affiliation: The Bone and Mineral Centre, Department of Medicine, University College London, The Rayne Institute, London WC1E 6JJ, UK. c.faucheux@ucl.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Faucheux
authors.forename: S A
authors.initials: SA
authors.lastname: Nesbitt
authors.forename: M A
authors.initials: MA
authors.lastname: Horton
authors.forename: J S
authors.initials: JS
authors.lastname: Price
mesh_terms: D000135:Acid Phosphatase / Q000502:physiology; D000818:Animals; D000999:Antlers / Q000166:cytology* / Q000502:physiology; D002356:Cartilage / Q000166:cytology*; D002454:Cell Differentiation / Q000502:physiology; D003670:Deer; D007527:Isoenzymes / Q000502:physiology; D020780:Matrix Metalloproteinase 9 / Q000502:physiology; D016328:NF-kappa B / Q000502:physiology; D010010:Osteoclasts / Q000166:cytology* / Q000502:physiology; D012038:Regeneration; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D007527:Isoenzymes; D016328:NF-kappa B; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D020780:Matrix Metalloproteinase 9