title: Stimulation of osteoprotegerin ligand and inhibition of osteoprotegerin production by glucocorticoids in human osteoblastic lineage cells: potential paracrine mechanisms of glucocorticoid-induced osteoporosis.
abstract: Osteoporosis is a serious complication of systemic glucocorticoid use. However, while glucocorticoids increase bone resorption in vitro and in vivo, the mechanism(s) of this effect are at present unclear. Recent studies have identified the osteoprotegerin (OPG) ligand (OPG-L) as the final effector of osteoclastogenesis, an action that is opposed by the soluble neutralizing receptor, OPG. Thus, we assessed glucocorticoid regulation of OPG and OPG-L in various human osteoblastic lineage cells using Northern analysis, RT-PCR, and ELISA. Dexamethasone inhibited constitutive OPG messenger RNA (mRNA) steady-state levels by 70-90% in primary (MS) and immortalized stromal cells (hMS), primary trabecular osteoblasts (hOB), immortalized fetal osteoblasts (hFOB), and osteosarcoma cells (MG-63). In hFOB cells, dexamethasone inhibited constitutive OPG mRNA steady-state levels in a dose- and time-dependent fashion by 90%, and also suppressed cytokine-stimulated OPG mRNA steady-state levels. Dexamethasone-induced inhibition of OPG mRNA levels was not affected by the protein synthesis inhibitor, cycloheximide, and was shown to be due to inhibition of OPG gene transcription using a nuclear run-on assay. Moreover, dexamethasone also dose dependently (10(-10) M-10(-7) M) inhibited constitutive OPG protein concentrations in the conditioned medium of hFOB cells from 2.59 +/- 0.02 ng/ml (control) to 0.30 +/- 0.01 ng/ml (88% inhibition; P < 0.001 by ANOVA). Concurrently, dexamethasone stimulated OPG-L mRNA steady-state levels in MS and hFOB cells by 2- and 4-fold, respectively. Treatment of murine marrow cultures with conditioned medium harvested from dexamethasone-treated MG-63 cells increased tartrate-resistant acid phosphatase (TRAP) activity by 54% (P < 0.005) compared with medium harvested from control-treated cells (in the presence of OPG-L and macrophage colony-stimulating factor). Moreover, dexamethasone (10(-8) M) promoted osteoclast formation in vitro, as assessed by a 2.5-fold increase of TRAP activity in cell lysates (P < 0.001) and the appearance of TRAP-positive multinucleated cells. Our data are thus consistent with the hypothesis that glucocorticoids promote osteoclastogenesis by inhibiting OPG and concurrently stimulating OPG-L production by osteoblastic lineage cells, thereby enhancing bone resorption.
authors.affiliation: Endocrine Research Unit, Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
authors.forename: L C
authors.initials: LC
authors.lastname: Hofbauer
authors.forename: F
authors.initials: F
authors.lastname: Gori
authors.forename: B L
authors.initials: BL
authors.lastname: Riggs
authors.forename: D L
authors.initials: DL
authors.lastname: Lacey
authors.forename: C R
authors.initials: CR
authors.lastname: Dunstan
authors.forename: T C
authors.initials: TC
authors.lastname: Spelsberg
authors.forename: S
authors.initials: S
authors.lastname: Khosla
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D005938:Glucocorticoids / Q000009:adverse effects / Q000494:pharmacology*; D006023:Glycoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology; D010024:Osteoporosis / Q000139:chemically induced; D053244:Osteoprotegerin; D019899:Paracrine Communication / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D053245:RANK Ligand; D012333:RNA, Messenger / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor
chemical_list: D002352:Carrier Proteins; D005938:Glucocorticoids; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D011500:Protein Synthesis Inhibitors; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505686:TNFRSF11A protein, human; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; D003907:Dexamethasone; D003513:Cycloheximide