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G alpha(q) signal in osteoblasts is inhibitory to the osteoanabolic action of parathyroid hormone.

ABSTRACT: This study examined the role of the G?(q) signal constituted by G?(q) and G?(11) (encoded by Gn?(q) and Gn?(11), respectively), a major intracellular pathway of parathyroid hormone (PTH), in the PTH osteoanabolic action by the gain- and loss-of-function analyses. Transgenic mice with osteoblast-specific overexpression of the constitutively active Gn?(q) gene under the control of 2.3-kb type I collagen ?1 chain (Col1a1) promoter exhibited osteopenia with decreased bone formation parameters and did not respond to the daily PTH treatment. We then established osteoblast-specific Gn?(q) and Gn?(11) double-knock-out (cDKO) mice by crossing the 2.3-kb Col1a1 promoter-Cre recombinase transgenic mice and those with Gn?(q) gene flanked with loxP and global ablation of Gn?(11) (Col1a1-Cre(+/-);Gna(q)(fl/fl);Gna(11)(-/-)) and found that the cDKO and single knock-out littermates of Gn?(q) or Gn?(11) exhibited normal bone volume and turnover under physiological conditions. With a daily injection of PTH, however, the cDKO mice, but not the single knock-out mice, showed higher bone volume and turnover than the wild-type littermates. Cultures of primary osteoblasts derived from cDKO and wild-type littermates confirmed enhancement of the PTH osteoanabolic action by the G?(q) signal deficiency in a cell-autonomous mechanism, in association with the membrane translocation of protein kinase C?. This enhancement was reproduced by overexpression of regulator of G protein signaling-2, a G?(q) signal inhibitor, in osteoblastic MC3T3-E1 cells. Hence, the G?(q) signal plays an inhibitory role in the PTH osteoanabolic action, suggesting that its suppression may lead to a novel treatment in combination with PTH against osteoporosis.

SUBMITTER: Ogata N

PROVIDER: S-EPMC3075717 | biostudies-literature | 2011 Apr

REPOSITORIES: biostudies-literature

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G alpha(q) signal in osteoblasts is inhibitory to the osteoanabolic action of parathyroid hormone.

Ogata Naoshi N Shinoda Yusuke Y Wettschureck Nina N Offermanns Stefan S Takeda Shu S Nakamura Kozo K Segre Gino V GV Chung Ung-il UI Kawaguchi Hiroshi H

The Journal of biological chemistry 20110223 15

This study examined the role of the Gα(q) signal constituted by Gα(q) and Gα(11) (encoded by Gnα(q) and Gnα(11), respectively), a major intracellular pathway of parathyroid hormone (PTH), in the PTH osteoanabolic action by the gain- and loss-of-function analyses. Transgenic mice with osteoblast-specific overexpression of the constitutively active Gnα(q) gene under the control of 2.3-kb type I collagen α1 chain (Col1a1) promoter exhibited osteopenia with decreased bone formation parameters and di ...[more]

PMID: 21345793

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Project description:Parathyroid hormone (PTH) exerts dual effects, anabolic or catabolic, on bone when administrated intermittently or continuously, via mechanisms that remain largely unknown. PTH binding to cells induces PTH-responsive genes including primary response genes (PRGs). PRGs are rapidly induced without the need for de novo protein synthesis, thereby playing pivotal roles in directing subsequent molecular responses. In this study, to understand the role of PRGs in mediating osteoblastic cellular responses to PTH, we investigated whether various durations of PTH differentially induce PRGs in primary osteoblasts and MC3T3-E1. Nurr1 and RANKL, PRGs known for their anabolic and catabolic roles in bone metabolism respectively, presented distinctive transient vs. sustained induction kinetics. Corroborating their roles, maximum induction of Nurr1 was sufficiently achieved by brief PTH in as little as 30 minutes and continued beyond that, while maximum induction of RANKL was achieved only by prolonged PTH over 4 hours. Our data suggested distinctive regulatory mechanisms for Nurr1 and RANKL: PKA-mediated chromatin rearrangement for transcriptional regulation of both PRGs and ERK-mediated transcriptional regulation for RANKL but not Nurr1. Lastly, we classified PRGs into two groups based on the induction kinetics: The group that required brief PTH for maximum induction included Nur77, cox-2, and Nurr1, all of which are reported to play roles in bone formation. The other group that required prolonged PTH for maximum induction included IL-6 and RANKL, which play roles in bone resorption. Together, our data suggested the crucial role of PRG groups in mediating differential osteoblastic cellular responses to intermittent vs. continuous PTH. Continued research into the regulatory mechanisms of PKA and ERK for PRGs will help us better understand the molecular mechanisms underlying the dual effects of PTH, thereby optimizing the current therapeutic use of PTH for osteoporosis.

Project description:AimTo investigate the mechanism of the bone-forming effects of intermittent parathyroid hormone (PTH) administration and to search for novel molecules of bone anabolism via the PTH signaling pathway.MethodsPrimary cultures of rat osteoblasts (ROBs) were divided into an intermittent PTH-treated group (Itm) and a control group (Ctr). Imitating the pharmacokinetics of intermittent PTH administration in vivo, the ROBs in the Itm group were exposed to PTH for 6 h in a 24-h incubation cycle, and the ROBs in the Ctr group were exposed to vehicle for the entire incubation cycle. The cells were collected at 6 h and 24 h of the final cycle, and the proteins in the Itm and Ctr groups were analyzed by two-dimensional electrophoresis (2-DE) coupled with peptide mass fingerprinting and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to detect proteins that were differentially expressed. The proteins with the most significant changes in vitro were validated by immunohistochemistry (IHC) in a rat model.ResultsThe proteomics analysis indicated that a total of 26 proteins were up- or down-regulated in the Itm group compared with the Ctr group at 6 h and 24 h; among these, 15 proteins were successfully identified. These proteins mainly belong to the cytoskeleton and molecular chaperone protein families, and most of these have anti-apoptotic effects in various cells. Rho GDP-dissociation inhibitor alpha (RhoGDIalpha) and vimentin were the most significantly changed proteins. Further studies by IHC showed that the expression of RhoGDIalpha in ROBs was significantly higher in PTH-treated sham-operated rats than in vehicle-treated sham-operated rats, but the difference was not significant between PTH-treated and vehicle-treated OVX rats. Vimentin expression was not changed in either PTH-treated sham-operated rats or PTH-treated OVX rats.ConclusionOur research suggests that intermittent PTH treatment induces changes in expression of many proteins in ROBs in vitro, and it results in RhoGDIalpha up-regulation in ROBs both in vitro and in vivo when estrogen is present. This up-regulation of RhoGDIalpha may be one of the mechanisms underlying the synergistic bone-forming effect of PTH and estrogen.Acta Pharmacologica Sinica (2009) 30: 1001-1007; doi: 10.1038/aps.2009.60.

Dataset Information

G alpha(q) signal in osteoblasts is inhibitory to the osteoanabolic action of parathyroid hormone.

Publications

G alpha(q) signal in osteoblasts is inhibitory to the osteoanabolic action of parathyroid hormone.

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