Actions of calcitonin, parathyroid hormone, and prostaglandin E₂ on cyclic AMP formation in chicken and rat osteoclasts

Abstract

The effects of calcitonin, parathyroid hormone, and prostaglandin E2 on cyclic AMP production were studied in osteoclast-rich cultures derived from medullary bone of laying hens and from the long bones of newborn rats. Cyclic AMP was assayed biochemically in replicate cultures, and furthermore, changes in cytoplasmic fluorescence were sought by indirect immunofluorescence with rabbit anti-cyclic AMP and FITC-labelled goat anti-rabbit IgG. Treatment of rat osteoclasts with calcitonin increased cyclic AMP formation as measured biochemically, and this was confirmed by the immunofluorescence method. No such increase took place in chick osteoclasts. Prostaglandin E2 increased cyclic AMP production in both rat and chick osteoclasts as determined by both methods. Since the immunofluorescence method failed to detect a response to parathyroid hormone either in chick or rat osteoclasts, its variable biochemical effects were concluded to be due to actions on contaminating osteoblasts in the cultures. Thus it has been possible with a combined biochemical and immunocytochemical approach to define the cyclic AMP responses to the calcium-regulating hormones in rat and chick osteoclasts. The failure of calcitonin to increase cyclic AMP in chick osteoclasts identifies a need to investigate the nature of calcitonin action on avian osteoclasts, which may contribute to understanding of its actions on mammalian cells.

Cytoskeletal changes in osteoclasts during the resorption cycle

“…The effect of calcitonin is dose-dependent and specific for osteoclasts. Raising the cytoplasmic level of cAMP by dibutyryl cAMP causes similar effects on microfilaments in resorbing osteoclasts as seen with calcitonin , supporting other findings that the effect of calcitonin is mediated by cAMP (Nicholson et al, 1986(Nicholson et al, , 1987Ransjo et al, 1988). This also suggests that the effect of calcitonin on microfilaments is mediated by a rise an CAMP, although the other signaling pathways may also be involved.…”

“…Calcitonin is a peptide hormone, which inhibits bone resorption by exerting a direct effect on the osteoclasts. It is now well documented that calcitonin causes a rapid cessation of the motility and cytoplasmic spread of osteoclasts in vitro (Chambers and Magnus, 1982;Chambers et al, 1984a) by increasing the intracellular level of cAMP (Chambers and Dunn, 1983;Nicholson et al, 1986;Ransjo et al, 1988). Evidence has also been presented that the inhibition of motility and cytoplasmic retraction caused by calcitonin is associated with the rearrangement of cytoskeleton (Hunter et al, 1989;Warshafsky et al, 1985).…”

Calcitonin induces expression of the inducible cAMP early repressor in osteoclasts

“…In addition to cAMP-PKA pathway [27,36], both activation of protein kinase C (PKC) [28] and increased calcium levels [25,30,[37][38][39] have been reported to be involved in the inhibition of osteoclastic bone resorption by calcitonin. Therefore, at least three signaling pathways (PKA, PKC and intracellular calcium) are involved in mediating the actions of calcitonin on osteoclasts.…”

Detection of estrogen receptor alpha, carbonic anhydrase II and tartrate-resistant acid phosphatase mRNAs in putative mononuclear osteoclast precursor cells of neonatal rats by fluorescence in situ hybridization

“…MOPC have abundant free ribosomes, mitochondria and extensive Golgi apparatus associated with dense specific granules (Scott 1967, Baron et al 1986, Nicholson et al 1986, Akisaka et al 1989, Simpson & Horton 1989, James et al 1996. Under the light microscope these cells have been identified as oval-shaped mononuclear cells with strong basophilic cytoplasm (Ries 1984).…”