title: Osteoblastic γ-aminobutyric acid, type B receptors negatively regulate osteoblastogenesis toward disturbance of osteoclastogenesis mediated by receptor activator of nuclear factor κB ligand in mouse bone.
abstract: The prevailing view is that signaling machineries for the neurotransmitter GABA are also expressed by cells outside the CNS. In cultured murine calvarial osteoblasts, mRNA was constitutively expressed for both subunits 1 and 2 of metabotropic GABA(B) receptor (GABA(B)R), along with inhibition by the GABA(B)R agonist baclofen of cAMP formation, alkaline phosphatase (ALP) activity, and Ca(2+) accumulation. Moreover, baclofen significantly inhibited the transactivation of receptor activator of nuclear factor-κB ligand (RANKL) gene in a manner sensitive to a GABA(B)R antagonist, in addition to decreasing mRNA expression of bone morphogenetic protein-2 (BMP2), osteocalcin, and osterix. In osteoblastic MC3T3-E1 cells stably transfected with GABA(B)R1 subunit, significant reductions were seen in ALP activity and Ca(2+) accumulation, as well as mRNA expression of osteocalcin, osteopontin, and osterix. In cultured calvarial osteoblasts from GABA(B)R1-null mice exhibiting low bone mineral density in tibia and femur, by contrast, both ALP activity and Ca(2+) accumulation were significantly increased together with promoted expression of both mRNA and proteins for BMP2 and osterix. No significant change was seen in the number of multinucleated cells stained for tartrate-resistant acid phosphatase during the culture of osteoclasts prepared from GABA(B)R1-null mice, whereas a significant increase was seen in the number of tartrate-resistant acid phosphatase-positive multinucleated cells in co-culture of osteoclasts with osteoblasts isolated from GABA(B)R1-null mice. These results suggest that GABA(B)R is predominantly expressed by osteoblasts to negatively regulate osteoblastogenesis through down-regulation of BMP2 expression toward disturbance of osteoclastogenesis after down-regulation of RANKL expression in mouse bone.
authors.affiliation: Laboratory of Molecular Pharmacology, Division of Pharmaceutical Sciences, Kanazawa University Graduate School of Natural Science and Technology, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Takahata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Takarada
authors.forename: Eiichi
authors.initials: E
authors.lastname: Hinoi
authors.forename: Yukari
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Fujita
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yoneda
mesh_terms: D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D001842:Bone and Bones / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D017930:Genes, Reporter / Q000235:genetics; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects / Q000235:genetics; D010641:Phenotype; D053245:RANK Ligand / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000172:deficiency / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D015533:Transcriptional Activation / Q000187:drug effects / Q000235:genetics; D014162:Transfection
chemical_list: D015415:Biomarkers; C485504:Gabbr2 protein, mouse; D053245:RANK Ligand; D018080:Receptors, GABA-B; D008156:Luciferases; D001418:Baclofen