Cells in regenerating deer antler cartilage provide a microenvironmentthat supports osteoclast differentiation

摘要

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 nonmineralised 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 kappaB 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 nonmineralised 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.