Conditioned medium from cultured normal human foreskin keratinocytes enhanced the release of calcium from neonatal mouse calvaria in organ culture. Unfractionated keratinocyte-conditioned medium (KCM) stimulated bone resorption in a dose-dependent manner, but it did not increase the concentration of prostaglandin E2 (PGE2) in the bone culture medium until a maximal dose of KCM for resorption was used. Furthermore, inhibitors of PGE2 synthesis, indomethacin, ibuprofen, and piroxicam, did not inhibit KCM-induced calcium release. High concentrations of KCM increased cAMP production by calvaria in the presence of isobutylmethylxanthine, but the increase was small compared with that produced by a dose of bovine PTH that caused a similar level of bone resorption. The bone resorption-stimulating activity of KCM was not lost after incubation at 56 C for 60 min, but it was lost after heating at 100 C for 10 min. Fractionation of KCM by gel filtration chromatography revealed two distinct peaks of bone resorption-stimulating activity. One peak, KCM(I), caused a significant increase in bone resorption at 2 μg protein/ml. KCM(I) did not increase medium PGE2, and inhibition of PGE2 synthesis in bone had no effect on KCM(I)-induced bone resorption. KCM(I) failed to increase cAMP production by human osteosarcoma SaOS-2 cells. Another peak, KCM(II), caused a dose-dependent increase in bone resorption, and a significant increase in medium calcium was noted at a 20-fold lower concentration (0.1 μg protein/ml) than with KCM(I). In contrast to KCM(I), the increase in bone resorption stimulated by KCM(II) was accompanied by a parallel increase in the production of PGE2, and inhibition of PGE2 synthesis completely inhibited the bone resorption-stimulating activity of KCM(II). KCM(II) also caused an increase in cAMP production by SaOS-2 cells. We conclude that KCM contains at least two distinct bone resorption-stimulating factors, one of which acts via a PG-mediated mechanism and the other by a PG-independent pathway.
|Original language||English (US)|
|Number of pages||9|
|State||Published - 1988|
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism