Gene expression profiling of glucocorticoid-inhibited osteoblasts

Abstract

Glucocorticoid (GC) treatment for the management of autoimmune and inflammatory diseases is associated with decreased bone formation and increased risk for fracture. In MC3T3-E1 cell cultures, 0·1 -1 µM dexamethasone (DEX) arrests development of the osteoblast phenotype when administration commences at a commitment stage around the time of confluency. To gain new insights into GC-induced osteoporosis, we performed microarray-based gene expression analysis of GC-arrested MC3T3-E1 cultures, 2·5 days after the administration of DEX. Of the .12 000 transcripts interrogated, 74 were up-regulated and 17 were down-regulated by at least 2·5-fold (P¯0·05). Some of these genes, such as Mmp13, Serum/GC-regulated kinase and Tieg, have previously been reported as GC-responsive. Others are shown here for the first time to respond to GCs. DEX strongly repressed Krox20/Egr2 at both the mRNA and the protein level. This is especially significant because mice lacking this transcription factor develop osteoporosis. The data also suggest that the bone morphogenetic protein (BMP) pathway, which is involved in regulating bone mass, and other pathways that influence BMP signaling, are abrogated by GCs: (i) DEX increased the mRNA levels of the BMP antagonists Follistatin and Dan; (ii) DEX increased the levels of p21 Rasgap3 and Ptpn16/MKP-1 mRNAs, negative regulators of the MAP kinase pathway; and (iii) DEX decreased Cox mRNA levels. DEX also increased thrombospondin mRNA levels, which negatively regulate bone mass in vivo, as well as the adipocytic marker Fkbp51. These and other observations disclose novel gene targets, whose regulation by GCs in osteoblasts may shed light on and provide new therapeutic approaches to osteoporosis.

Thrombospondin-1 is a glucocorticoid responsive protein in humans

“…consistent with previous in vitro assessments of the effects of dexamethasone on TSP1 in a number of different human cell types including PBMCs (20), endometrial cells (22) and osteoblasts (21). However, the current study is the first to demonstrate that administering dexamethasone to humans in vivo increases PBMC TSP1 mRNA levels and circulating plasma TSP1 concentrations.…”

Novel arylpyrazole compounds selectively modulate glucocorticoid receptor regulatory activity

“…1C; Luppen et al 2003;Leclerc et al 2004). Strikingly, none of the compounds inhibited MC3T3-E1 preosteoblast differentiation as measured by alizarin red staining (Fig.…”

Anti-inflammatory functions of glucocorticoid-induced genes

“…It is expressed in response to GCs A Clark Anti-inflammatory functions of glucocorticoid-induced genes Page 18 of 53 in a wide variety of cell types including mast cells (Kassel et al, 2001), monocytes or macrophages (Abraham et al, 2006;Aeberli et al, 2006;Bhattacharyya et al, 2007;Chen et al, 2002;Zhao et al, 2005), microglia (Zhou et al, 2007), T lymphocytes , dermal, lung and synovial fibroblasts (Phillips et al, 2006;Toh et al, 2004;Yang et al, 2006), endothelial cells (Furst et al, 2007), osteoblasts (Engelbrecht et al, 2003;Leclerc et al, 2004), keratinocytes (Onda et al, 2006;Stojadinovic et al, 2006), adipocytes (Bazuine et al, 2004), lung epithelial cells (Chivers et al, 2006;Hermoso et al, 2004), airway smooth muscle cells (Issa et al, 2007) and HeLa cells (Imasato et al, 2002;Lasa et al, 2002). Typically expression is quite rapid (within one hour), sustained (up to 24 hours), requires relatively low concentrations of GC, and is blocked by the GR antagonist RU486.…”