Induction of Calcitonin Receptors by lα, 25- Dihydroxyvitamin D3in Osteoclast-Like Multinucleated Cells Formed from Mouse Bone Marrow Cells*

Abstract

We have developed a mouse marrow culture system, in which multinucleated cells (MNCs) are formed within 6-8 days. These MNCs showed several characteristics of osteoclasts, including tartrate-resistant acid phosphatase (TRACP) and the ability to resorb calcified dentine. lα,25-Dihydroxyvitamin D3 [lα,25(OH)₂D₃] stimulated the formation of TRACPpositive MNCs, and salmon calcitonin (CT) inhibited it. In this study, we examined whether the TRACP-positive MNCs formed from mouse marrow cells possess CT receptors, another typical characteristic of osteoclasts. Mouse marrow cells cultured for 8 days with 10 nM lα,25(OH)₂D₃ and freshly isolated authentic mouse osteoclasts were incubated with [¹²⁵I]-salmon CT in the presence or absence of excess amounts of unlabeled CT, stained for TRACP, and processed for autoradiography. The [¹²⁵I]-CT exclusively bound to TRACP-positive mononuclear cells and MNCs formed in the lα,25(OH)₂D₃-treated cultures and also to isolated mouse osteoclasts. Both [¹²⁵I]-CT binding and TRACP activity were induced simultaneously on mononuclear cells on day 3 in the cultures treated with lα,25(OH)₂D₃. CT markedly stimulated cAMP production in the lα,25(OH)₂D₃-treated cultures. The CT-dependent cAMP production increased in parallel with the increase in the number of TRACP-positive MNCs formed. Neither freshly isolated marrow cells nor cells cultured without lα,25(OH)₂D₃ showed CT-induced cAMP accumulation. Furthermore, CT induced cytoplasmic contraction of both marrow- derived MNCs and isolated osteoclasts. These results clearly indicate that lα,25(OH)₂D₃ induces TRACP activity and CT receptors almost simultaneously in mouse marrow cultures, and the MNCs formed in vitro respond to CT as authentic osteoclasts do. (Endocrinology123: 1504–1510,1988)