Transcriptional Activity of Nuclei in Multinucleated Osteoclasts and Its Modulation by Calcitonin

• Published in: Endocrinology (Philadelphia) Vol. 143; no. 5; pp. 1913 - 1921
• Main Authors: Boissy, Patrice, Saltel, Frederic, Bouniol, Christine, Jurdic, Pierre, Machuca-Gayet, Irma
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01.05.2002; Oxford University Press
• Subjects: Animals; Bone Resorption; Calcitonin - pharmacology; Carrier Proteins - pharmacology; Cell Nucleus - drug effects; Cell Nucleus - genetics; Cells, Cultured; Chick Embryo; Cytological Techniques; Down-Regulation - genetics; Down-Regulation - physiology; Immunohistochemistry; Membrane Glycoproteins - pharmacology; Mice; Osteoclasts - drug effects; Osteoclasts - physiology; RANK Ligand; Receptor Activator of Nuclear Factor-kappa B; RNA, Messenger - biosynthesis; Spleen - cytology; Transcription, Genetic - drug effects; Transcription, Genetic - genetics; Transcription, Genetic - physiology
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endo.143.5.8813

The function of osteoclasts is to digest the calcified bone matrix. Osteoclasts, together with myotubes, are among the rare examples of multinucleated cells found in higher vertebrates, resulting from the fusion of mononucleated progenitors belonging to the monocyte/macrophage lineage. So far, no information is available about function and transcriptional activity of multiple nuclei in osteoclasts. We have used a run-on technique to visualize RNA synthesis in individual nucleus. We provide the first evidence that nuclei of resorbing osteoclasts, isolated from chick embryo long bones, or differentiated in vitro from murine spleen cells in presence of RANKL and macrophage-colony stimulating factor, are all transcriptionally active. Nevertheless, if transcriptional activity is the same for all the nuclei within a cell, its level varies between osteoclasts: osteoclasts with highly active nuclei are always associated with resorption pits. We found that global transcription activity of resorbing osteoclasts seeded on calcified matrix is down-regulated after 5-h treatment with calcitonin, which transiently blocks resorption. This effect is reversible because calcitonin removal led to nuclear transcription activation. These results indicate a strong correlation between transcription and resorption. Finally, our data indicate that the resorption pit surface is linearly related to the nuclei number per osteoclast, strongly suggesting that functional advantage of osteoclast multinucleation is to improve resorption efficiency.