title: Effects of continuous calcitonin treatment on osteoclast-like cell development and calcitonin receptor expression in mouse bone marrow cultures.
abstract: Continuous treatment with calcitonin (CT) to inhibit osteoclastic bone resorption results in acquired resistance. The mechanisms of this "escape" phenomenon are not yet established. The aim of this study was to examine the effects of continuous treatment with CT on the generation of osteoclasts and calcitonin receptor (CTR) expression in mouse bone marrow cultures. This was done by daily CT treatment of mouse bone marrow cultures from day 0, when only undifferentiated mononuclear precursors of osteoclast-like cells were present, or commencing from day 6, when differentiated osteoclast-like cells were abundant. The response to CT treatment was determined by quantitation of cells positive for tartrate-resistant acid phosphatase (TRAP) and binding of 125I-salmon CT. Calcitonin receptor and TRAP mRNA levels were determined using semi-quantitative reverse transcription/polymerase chain reaction. When cultures were treated with CT from day 0, TRAP-positive multinucleated cells appeared. These cells expressed only very low levels of CTR or CTR mRNA and were morphologically indistinguishable from osteoclast-like cells formed in control cultures. They also displayed the ability to resorb bone. Continuous CT treatment of cultures from day 6 rapidly reduced the CTR mRNA levels, with a t1/2 of 6 to 12 h, and these levels remained low thereafter. 125I-salmon CT binding capacity, as determined by autoradiography, was lost in parallel. These effects were specific for the CTR since there was no consistent effect on TRAP mRNA levels. Based on these data, we suggest that the "escape" phenomenon may result from a prolonged CT-induced loss of CT responsiveness due, at least in part, both to reduced synthesis of CTR, and to the appearance in bone of CTR-deficient osteoclasts.
authors.affiliation: St. Vincent's Institute of Medical Research, Melbourne, Victoria, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Ikegame
authors.forename: M
authors.initials: M
authors.lastname: Rakopoulos
authors.forename: T J
authors.initials: TJ
authors.lastname: Martin
authors.forename: J M
authors.initials: JM
authors.lastname: Moseley
authors.forename: D M
authors.initials: DM
authors.lastname: Findlay
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D001853:Bone Marrow / Q000187:drug effects* / Q000378:metabolism; D001854:Bone Marrow Cells; D001862:Bone Resorption / Q000139:chemically induced; D002116:Calcitonin / Q000378:metabolism / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D005269:Femur / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D015726:Giant Cells / Q000166:cytology / Q000187:drug effects; D006811:Humerus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D007457:Iodine Radioisotopes; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D018003:Receptors, Calcitonin / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000071681:Tartrate-Resistant Acid Phosphatase; D013977:Tibia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D017931:DNA Primers; D007457:Iodine Radioisotopes; D007527:Isoenzymes; D012333:RNA, Messenger; D018003:Receptors, Calcitonin; C028815:salmon calcitonin; D002116:Calcitonin; D000135:Acid Phosphatase; C000605511:Acp5 protein, mouse; D000071681:Tartrate-Resistant Acid Phosphatase