Conditional expression of a Gi-coupled receptor in osteoblasts results in trabecular osteopenia
Conditional expression of a Gi-coupled receptor in osteoblasts results in trabecular osteopenia
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DOI：
10.1210/en.2007-0235
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发表时间：
2008-03-01
期刊：
影响因子：
4.8
通讯作者：
Nissenson, R. A.
中科院分区：
文献类型：
--
作者：
Peng, J.;Bencsik, M.;Nissenson, R. A.
G 蛋白偶联受体 (GPCR) 与 G 激活偶联，例如 PTH1 受体 (PTH1R)，长期以来一直被认为可以调节骨骼功能和体内平衡。然而，GPCR 与其他 G 蛋白（例如 Gi）偶联的作用尚未明确。我们使用 tet-off 系统来调节体内成骨细胞中激活的 Gi 偶联 GPCR (Ro1) 的表达。对表达 Ro1 的小鼠从受孕、胚胎发生后期和断奶后的骨骼表型进行了评估。通过组织学和微计算机断层扫描对长骨进行评估。受孕时 Ro1 的表达导致新生儿死亡，这与骨矿化减少有关。 Ro1 从胚胎发生晚期开始表达，导致 12 周龄时出现严重的骨小梁缺陷（与性别匹配的对照同窝仔鼠相比，近端胫骨的骨小梁体积分数减少了 51% 以上；n = 11；P < 0.01）。与性别匹配的对照同窝仔鼠相比，从 4 周龄开始持续 8 周的 Ro1 表达导致骨小梁体积分数减少 20% 以上（n = 16；P < 0.01）。骨组织形态计量学显示，Ro1 表达与骨形成和矿物质沉积率降低相关，而成骨细胞或破骨细胞表面没有显着变化。我们的结果表明，成骨细胞中 Gi 偶联 GPCR 的信号传导会导致骨小梁形成减少而导致骨质减少。表型的严重程度与生长发育过程中 Ro1 表达的时间和持续时间有关。 Ro1小鼠的骨骼表型与成骨细胞中Gs-α表达敲除产生的骨骼表型有一些相似之处，因此可能至少部分归因于Gi介导的腺苷酸环化酶抑制。
G protein-coupled receptors (GPCRs) coupled to activation of Gs, such as the PTH1 receptor (PTH1R), have longbeen known to regulate skeletal function and homeostasis. However, the role of GPCRs coupled to other G proteins such as Gi is not well established. We used the tet-off system to regulate the expression of an activated Gi-coupled GPCR (Ro1) in osteoblasts in vivo. Skeletal phenotypes were assessed in mice expressing Ro1 from conception, from late stages of embryogenesis, and after weaning. Long bones were assessed histologically and by microcomputed tomography. Expression of Ro1 from conception resulted in neonatal lethality that was associated with reduced bone mineralization. Expression of Ro1 starting at late embryogenesis resulted in a severe trabecular bone deficit at 12 wk of age (>51% reduction in trabecular bone volume fraction in the proximal tibia compared with sex-matched control littermates; n = 11; P < 0.01). Ro1 expression for 8 wk beginning at 4 wk of age resulted in a more than 20% reduction in trabecular bone volume fraction compared with sex-matched control littermates (n = 16; P < 0.01). Bone histomorphometry revealed that Ro1 expression is associated with reduced rates of bone formation and mineral apposition without a significant change in osteoblast or osteoclast surface. Our results indicate that signaling by a Gi-coupled GPCR in osteoblasts leads to osteopenia resulting from a reduction in trabecular bone formation. The severity of the phenotype is related to the timing and duration of Ro1 expression during growth and development. The skeletal phenotype in Ro1 mice bears some similarity to that produced by knockout of Gs-alpha expression in osteoblasts and thus may be due at least in part to Gi-mediated inhibition of adenylyl cyclase.