Gαq Signal in Osteoblasts Is Inhibitory to the Osteoanabolic Action of Parathyroid Hormone

Naoshi Ogata,Yusuke Shinoda,Nina Wettschureck,Stefan Offermanns,Shu Takeda,Kozo Nakamura,Gino V Segre,Ung-Il Chung,Hiroshi Kawaguchi

doi:10.1074/jbc.m110.200196

Abstract

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 did not respond to the daily PTH treatment. We then established osteoblast-specific Gnα(q) and Gnα(11) double-knock-out (cDKO) mice by crossing the 2.3-kb Col1a1 promoter-Cre recombinase transgenic mice and those with Gnα(q) gene flanked with loxP and global ablation of Gnα(11) (Col1a1-Cre(+/-);Gna(q)(fl/fl);Gna(11)(-/-)) and found that the cDKO and single knock-out littermates of Gnα(q) or Gnα(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 Gα(q) signal deficiency in a cell-autonomous mechanism, in association with the membrane translocation of protein kinase Cδ. This enhancement was reproduced by overexpression of regulator of G protein signaling-2, a Gα(q) signal inhibitor, in osteoblastic MC3T3-E1 cells. Hence, the Gα(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.

Highlights

Bone anabolic action of parathyroid hormone (PTH)2 has attracted considerable clinical attention, and led to the Recently, we created transgenic mice with osteoblast-specific overexpression of the constitutively active Gn␣q gene under the control of the 2.3-kb type I collagen ␣1 chain (Col1a1) promoter (Col1a1-Gnaq-tg mice) and found that the mice exhibited osteopenia in trabecular and cortical bones, indicating an inhibitory function of the G␣q signal in bone formation under physiological conditions without PTH stimulation (13)
In transgenic mice, there were no significant differences between the vehicle and PTH treatment groups in bone volume or histomorphometric parameters, indicating that the gain-of-function of the G␣q signal in osteoblasts cancels the PTH osteoanabolic action
Effect of Osteoblast-specific Gn␣q and Gn␣11 Double-knockout on Osteoanabolic Action of PTH—To explore further the role of endogenous G␣q signal in bone, we established conditional Gn␣q and Gn␣11 double-knock-out mice with osteoblast-specific ablation of Gn␣q and global ablation of Gn␣11 to avoid the compensation by the redundant functionality of G␣q and G␣11

Summary

Introduction

Bone anabolic action of parathyroid hormone (PTH)2 has attracted considerable clinical attention, and led to the Recently, we created transgenic mice with osteoblast-specific overexpression of the constitutively active Gn␣q gene under the control of the 2.3-kb type I collagen ␣1 chain (Col1a1) promoter (Col1a1-Gnaq-tg mice) and found that the mice exhibited osteopenia in trabecular and cortical bones, indicating an inhibitory function of the G␣q signal in bone formation under physiological conditions without PTH stimulation (13). 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.

Results

Conclusion