Expression of 11?-hydroxysteroid dehydrogenase in rat osteoblastic cells: Pre-receptor regulation of glucocorticoid responses in bone

Abstract

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) acts as a pre-receptor signaling mechanism for corticosteroids by regulating the access of active glucocorticoids to both glucocorticoid (GR) and mineralocorticoid receptors (MR). To examine the relationship between endogenous glucocorticoid metabolism and osteoblast function, we have characterized the expression of 11 beta-HSD isozymes in rat osteosarcoma cells. Analysis of mRNA from ROS 25/1, UMR 106 and ROS 17/2.8 cells revealed transcripts for both 11 beta-HSD type 1 (11 beta-HSD1) and type 2 (11 beta-HSD2) in all three cell lines. However, enzyme activity studies showed only high affinity dehydrogenase activity (inactivation of corticosterone (B) to 11-dehydrocorticosterone (A)), characteristic of 11 beta-HSD2; conversion of B to A was higher in ROS 25/1> UMR 106 cells>ROS 17/2.8. Although all three cell lines had similar numbers of GR (50,000/cell), glucocorticoid modulation of alkaline phosphatase activity and cell proliferation was only detectable in ROS 17/2.8 cells. Further studies showed that 11 beta-HSD2 activity in each of the cells was potently stimulated by both A and B, but not by synthetic dexamethasone. This effect was blocked by the 11 beta-HSD inhibitor, 18 beta-glycyrrhetinic acid (but not by GR or MR antagonists) suggesting direct, allosteric regulation of 11 beta-HSD2 activity. These data indicate that in osteosarcoma cells 11 beta-HSD2 plays a key role in controlling GR-mediated responses; cells with relatively high levels of 11 beta-HSD2 activity were insensitive to glucocorticoids, whilst cells with low levels showed functional responses to both dexamethasone and B. In addition to the established effects of 11 beta-HSD2 in protecting MR in the kidney and colon, our data suggest that 11 beta-HSD2 in bone represents an important pre-receptor mechanism in determining ligand availability to GR.

Expression of 11β-hydroxysteroid dehydrogenase enzymes in human osteosarcoma: potential role in pathogenesis and as targets for treatments

“…The 11b-HSD1 enzyme metabolises endogenous glucocorticoids, cortisone and cortisol, in a bidirectional manner, whereas 11b-HSD2 is a unidirectional inactivator of endogenous glucocorticoids. We have previously demonstrated that OS cell lines express the 11b-HSD2 enzyme (Bland et al 1999, Eyre et al 2001. This is in contrast to normal osteoblasts that express the 11b-HSD1 enzyme (Cooper et al 2000.…”

Mice Deficient in 11β-Hydroxysteroid Dehydrogenase Type 1 Lack Bone Marrow Adipocytes, but Maintain Normal Bone Formation

“…However, our results did not reveal any clear skeletal phenotype of HSD1 Ϫ/Ϫ mice. Previous in vitro data have demonstrated that osteoblastic overexpression of 11␤HSD1 led to decreased cell proliferation and in- creased cell differentiation (20). However, in our experiments 11␤HSD1 Ϫ/Ϫ bone cells did not reveal any change in their proliferation or expression of osteoblastic markers.…”

Differential expression of 11β-hydroxysteroid dehydrogenase types 1 and 2 mRNA and glucocorticoid receptor protein during mouse embryonic development

“…Furthermore, mice with targeted GR gene disruption exhibit bone marrow disfunctions [33], suggesting that glucocorticoids play a vital role in both fetal bone and thymus development. Although 11␤-HSD1 activity has been reported in both adult and fetal human bone [38] and 11␤-HSD2 mRNA has been detected in rat osteoblastic cells [39], neither isoform was expressed in the skeleton of the embryonic mice utilized in the current study. It is likely therefore that GR as well as 11␤-HSD1 and/or 11␤-HSD2 may be switched on in the mouse bone and thymus postnatally.…”