title: Distinct effects of loss of classical estrogen receptor signaling versus complete deletion of estrogen receptor alpha on bone.
abstract: Estrogen receptor (ER) α is a major regulator of bone metabolism which can modulate gene expression via a "classical" pathway involving direct DNA binding to estrogen-response elements (EREs) or via "non-classical" pathways involving protein-protein interactions. While the skeletal consequences of loss of ERE binding by ERα have been described, a significant unresolved question is how loss of ERE binding differs from complete loss of ERα. Thus, we compared the skeletal phenotype of wild-type (ERα(+/+)) and ERα knock out (ERα(-/-)) mice with that of mice in which the only ERα present had a knock-in mutation abolishing ERE binding (non-classical ERα knock-in [NERKI], ERα(-/NERKI)). All three groups were in the same genetic background (C57BL/6). As compared to both ERα(+/+) and ERα(-/-) mice, ERα(-/NERKI) mice had significantly reduced cortical volumetric bone mineral density and thickness at the tibial diaphysis; this was accompanied by significant decreases in periosteal and endocortical mineral apposition rates. Colony forming unit (CFU)-fibroblast, CFU-alkaline phosphatase, and CFU-osteoblast numbers were all increased in ERα(-/-) compared to ERα(+/+) mice, but reduced in ERα(-/NERKI) mice compared to the two other groups. Thus, using mice in identical genetic backgrounds, our data indicate that the presence of an ERα that cannot bind DNA but can function through protein-protein interactions may have more deleterious skeletal effects than complete loss of ERα. These findings suggest that shifting the balance of classical versus non-classical ERα signaling triggers pathways that impair bone formation. Further studies defining these pathways may lead to novel approaches to selectively modulate ER signaling for beneficial skeletal effects.
authors: Endocrine Research Unit, College of Medicine, Mayo Clinic, Rochester, MN 55905, USA. Farhan.Syed@abbott.com
authors: Farhan A
authors: FA
authors: Syed
authors: Daniel G
authors: DG
authors: Fraser
authors: David G
authors: DG
authors: Monroe
authors: Sundeep
authors: S
authors: Khosla
mesh_terms: D015502:Absorptiometry, Photon; D017667:Adipocytes / Q000166:cytology; D000818:Animals; D001823:Body Composition / Q000235:genetics / Q000502:physiology; D001835:Body Weight / Q000235:genetics / Q000502:physiology; D015519:Bone Density / Q000235:genetics; D001854:Bone Marrow Cells / Q000166:cytology; D001842:Bone and Bones / Q000166:cytology* / Q000378:metabolism*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D004958:Estradiol / Q000097:blood; D047628:Estrogen Receptor alpha / Q000172:deficiency* / Q000235:genetics; D005260:Female; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D010006:Osteoblasts / Q000166:cytology; D011863:Radioimmunoassay; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D055114:X-Ray Microtomography
chemical_list: D047628:Estrogen Receptor alpha; D011960:Receptors, Estrogen; D004958:Estradiol