Colocalization of Glucocorticoid and Mineralocorticoid Receptors in Human Bone

• Published in: Journal of bone and mineral research 2001-08, Vol.16 (8), p.1496-1504
• Main Authors: Beavan, Siân, Horner, Alan, Bord, Sharyn, Ireland, Deborah, Compston, Juliet
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Bone and Bones - chemistry; Cells, Cultured; Female; Fundamental and applied biological sciences. Psychology; Gene Expression; glucocorticoid receptor; Humans; immunolocalization; Male; Middle Aged; mineralocorticoid receptor; osteoblasts; Osteoblasts - cytology; Osteoblasts - metabolism; osteoclasts; Receptors, Glucocorticoid - analysis; Receptors, Glucocorticoid - genetics; Receptors, Mineralocorticoid - analysis; Receptors, Mineralocorticoid - genetics; Ribs - chemistry; RNA, Messenger; Skeleton and joints; Vertebrates: osteoarticular system, musculoskeletal system
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.2001.16.8.1496

Osteoporosis is a poorly understood but common complication of glucocorticoid therapy. The actions of glucocorticoids are mediated via glucocorticoid receptors (GRs), but in vitro, glucocorticoids also can bind to mineralocorticoid receptors (MRs). It is not known if MR protein is present in human bone and little is known of GR isoform expression (GRα and GRβ). GR and MR protein expression and possible sites of action were investigated in neonatal rib and adult iliac crest biopsy specimens using antibodies specific for MR, GRα, and GRαβ. Colocalization [MR GRα] [MR GRαβ] was performed using fluorescent‐conjugated secondary antibodies. GRα, GRβ, and MR show distinct but overlapping patterns of expression, suggesting important functions for each receptor type. Osteoclasts showed no staining for GRα but strong staining for GRαβ, indicating expression of GRβ and a specific role in addition to antagonizing the transcriptional activity of GRα. MR also was observed in osteoclasts and colocalized with GRαβ. Coexpression of MR, GRα, and GRαβ was seen in osteoblasts. Reverse‐transcription‐polymerase chain reaction (RT‐PCR) of cultured osteoblast RNA confirmed expression of both GRα and GRβ. Osteocytes stained with MR, GRα, and GRαβ antibodies but to a lesser degree than osteoblasts. In the neonatal rib cartilage, staining for GRα, GRαβ, and MR was present in approximately one‐half of the resting and hypertrophic chondrocytes and in most of proliferating chondrocytes and chondrocytes within the mineralizing matrix. Identification of MR raises the possibility that the physiological and pharmacologic effects of glucocorticoids on bone may be mediated via MR as well as GR and that GRα, GRβ, and MR synergize to influence corticosteroid metabolism in human bone.