SHORT TREATMENT OF OSTEOCLASTS IN BONE-MARROW CULTURE WITH CALCITONINCAUSES PROLONGED SUPPRESSION OF CALCITONIN RECEPTOR MESSENGER-RNA

Cells exhibiting osteoclast characteristics of calcitonin receptors (C TRs) and tartrate-resistant acid phosphatase (TRAP) histochemistry are formed in murine bone marrow cultures treated with 1 alpha,25-dihydro xyvitamin D-3[1,25-(OH)(2)D-3]. We have previously demonstrated that C TR mRNA is highly expressed in these cultures, The aim of this study w as to investigate homologous regulation of the CTR, and regulation of TRAP expression in osteoclast-like cells after brief treatment with sa lmon CT (sCT). Murine bone marrow cells were cultured in 9 cm dishes i n the presence of 10 nmol/L 1,25-(OH)(2)D-3. On day 6 of culture, when multinucleated cells were abundant, the cells were treated with 1 nmo l/l sCT for 1 h, Both control and treated cells were then harvested at intervals up to 72 h postreatment, and both CTR and TRAP mRNA levels assessed by reverse-transcription PCR (RT-PCR). In parallel cultures, cells with CTR expression detectable by autoradiography, and TRAP posi tivity by histochemistry, were counted, The effects of brief sCT treat ment could be seen 6 h after treatment when the CTR RT-PCR product was markedly reduced, Total recovery of CTR mRNA levels had not occurred even after 72 h, Calcitonin treatment had little effect on TRAP mRNA l evels, There was no difference in the numbers of multinucleated TRAP() osteoclast-like cells between treated and control cells, These resul ts indicate that brief sCT treatment, while not influencing multinucle ated osteoclast-like cell number, causes specific, acute reduction of CTR mRNA in bone marrow culture-derived osteoclasts, The prolonged dec rease in CTR mRNA levels suggests that recovery may require new osteoc last formation, and indicates that regulation of the CTR in cells of t he osteoclast lineage is different from that in nonosteoclastic cells and tissues.