title: Mineral composition is altered by osteoblast expression of an engineered G(s)-coupled receptor.
abstract: Activation of the G(s) G protein-coupled receptor Rs1 in osteoblasts increases bone mineral density by 5- to 15-fold in mice and recapitulates histologic aspects of fibrous dysplasia of the bone. However, the effects of constitutive G(s) signaling on bone tissue quality are not known. The goal of this study was to determine bone tissue quality in mice resulting from osteoblast-specific constitutive G(s) activation, by the complementary techniques of FTIR spectroscopy and synchrotron radiation micro-computed tomography (SRμCT). Col1(2.3)-tTA/TetO-Rs1 double transgenic (DT) mice, which showed osteoblast-specific constitutive G(s) signaling activity by the Rs1 receptor, were created. Femora and calvariae of DT and wild-type (WT) mice (6 and 15 weeks old) were analyzed by FTIR spectroscopy. WT and DT femora (3 and 9 weeks old) were imaged by SRμCT. Mineral-to-matrix ratio was 25% lower (P = 0.010), carbonate-to-phosphate ratio was 20% higher (P = 0.025), crystallinity was 4% lower (P = 0.004), and cross-link ratio was 11% lower (P = 0.025) in 6-week DT bone. Differences persisted in 15-week animals. Quantitative SRμCT analysis revealed substantial differences in mean values and heterogeneity of tissue mineral density (TMD). TMD values were 1,156 ± 100 and 711 ± 251 mg/cm(3) (mean ± SD) in WT and DT femoral diaphyses, respectively, at 3 weeks. Similar differences were found in 9-week animals. These results demonstrate that continuous G(s) activation in murine osteoblasts leads to deposition of immature bone tissue with reduced mineralization. Our findings suggest that bone tissue quality may be an important contributor to increased fracture risk in fibrous dysplasia patients.
authors.affiliation: Musculoskeletal Quantitative Imaging Research Group, Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA 94107, USA. galateia.kazakia@ucsf.edu
authors.forename: G J
authors.initials: GJ
authors.lastname: Kazakia
authors.forename: D
authors.initials: D
authors.lastname: Speer
authors.forename: S
authors.initials: S
authors.lastname: Shanbhag
authors.forename: S
authors.initials: S
authors.lastname: Majumdar
authors.forename: B R
authors.initials: BR
authors.lastname: Conklin
authors.forename: R A
authors.initials: RA
authors.lastname: Nissenson
authors.forename: E C
authors.initials: EC
authors.lastname: Hsiao
mesh_terms: D000818:Animals; D015519:Bone Density; D001842:Bone and Bones / Q000737:chemistry* / Q000378:metabolism; D005269:Femur / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D015398:Signal Transduction; D017550:Spectroscopy, Fourier Transform Infrared; D017356:Synchrotrons; D014057:Tomography, X-Ray Computed
chemical_list: D043562:Receptors, G-Protein-Coupled; D019205:GTP-Binding Protein alpha Subunits, Gs