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Activation of dimeric glucocorticoid receptors in osteoclast progenitors potentiates RANKL induced mature osteoclast bone resorbing activity

Journal article
Authors H. H. Conaway
Petra Henning
A. Lie
J. Tuckermann
Ulf H Lerner
Published in Bone
Volume 93
Pages 43-54
ISSN 8756-3282
Publication year 2016
Published at Centre for Bone and Arthritis Research
Institute of Medicine, Department of Internal Medicine and Clinical Nutrition
Pages 43-54
Language en
Links dx.doi.org/10.1016/j.bone.2016.08.0...
Keywords Bone resorption, Glucocorticoid, Glucocorticoid receptor, Osteoclast, Osteoporosis
Subject categories Pharmacology and Toxicology, Cell Biology, Cell and Molecular Biology

Abstract

Glucocorticoid (GC) therapy is the greatest risk factor for secondary osteoporosis. Pathogenic mechanisms involve an initial increase in bone resorption followed by decreased bone formation. To gain a better understanding of the resorptive activity of GCs, we have used mouse bone marrow macrophages (BMM) to determine if GCs can directly modulate RANKL stimulated osteoclast formation and/or activity. In agreement with previous studies, experiments performed in plastic wells showed that GCs (dexamethasone, hydrocortisone, and prednisolone) inhibited osteoclast number and size during the initial phases of RANKL stimulated osteoclastogenesis; however, in prolonged cultures, decreased apoptosis was observed and escape from GC induced inhibition occurred with an enhanced number of osteoclasts formed, many with an increased area. When BMM cells were seeded on bone slices, GCs robustly enhanced RANKL stimulated formation of resorption pits and release of CTX without affecting the number or size of osteoclasts formed and with no effect on apoptosis. Stimulation of pit formation was not associated with increased life span of osteoclasts or an effect on mRNA expression of several osteoclastic or osteoclastogenic genes. The potentiation of RANKL induced CTX release by dexamethasone was significantly less in BMM cells from mice with conditional knockout of the osteoclastic glucocorticoid receptor and completely absent in cells from GRdim mice, which carry a point mutation in one dimerizing interface of the GC receptor. These data suggest that: 1. Plastic is a poor medium to use for studying direct effects of GCs on osteoclasts 2. GCs can enhance bone resorption without decreasing apoptosis, and 3. A direct enhancement of RANKL mediated resorption is stimulated by the dimeric GC-receptor. © 2016 Elsevier Inc.

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