Washio-Oikawa Kaoru, Nakamura Takahisa, Usui Michihiko, Yoneda Mitsuhiro, Ezura Youichi, Ishikawa Isao, Nakashima Kazuhisa, Noda Tetsuo, Yamamoto Tadashi, Noda Masaki
Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.
J Bone Miner Res. 2007 Aug;22(8):1217-23. doi: 10.1359/jbmr.070411.
Cnot7 is a recently identified regulator of spermatogenesis in adult mice. Because Cnot7 binds to Tob, a BMP inhibitor shown to be involved in bone metabolism, we examined whether Cnot7 is involved in bone mass regulation by using adult Cnot7 deficient mice. Cnot7-/- mice exhibited a high bone mass phenotype. This was associated with an increase in bone formation rate but not with any alteration in bone resorption parameters. On BMP treatment, Cnot7-/- cells expressed higher levels of alkaline phosphatase compared with control cells. Direct BMP2 injection induced larger bone mass in Cnot7-/- calvaria than control in vivo. These observations revealed that Cnot7 is an endogenous suppressor of bone mass and inhibits BMP actions in osteoblasts.
The molecular mechanisms involved in the determination of bone mass have been gradually understood based on recent analyses. Cnot7 (Ccr4-Not complex 7) is a component of transcriptional Ccr4-Not complex, is conserved from yeast to human, and binds to Tob, but its function in bone is not understood.
To elucidate the role of involvement of Cnot7 in bone mass determination, we examined the bone of adult male Cnot7-null and heterozygous mice based on microCT analyses, histomorphometry, cell cultures, and in vivo BMP assays.
Cnot7-/- mice showed an increase in bone mass levels by >50% compared with controls. Analyses of the histomorphometric parameters indicated that bone formation activity in Cnot7-/- mice was enhanced, whereas bone resorption activity was not altered. These effects on osteoblasts were cell autonomous because mineralized nodule formation was enhanced in the cultures of bone marrow cells prepared from Cnot7-/- mice. In vitro analyses to elucidate Cnot7 effects revealed that BMP-induced expression of alkaline phosphatase in Cnot7-/- calvaria-derived osteoblastic cells was enhanced compared with controls. Moreover, BMP injection-induced new bone formation in vivo was enhanced in Cnot7-/- mice.
These observations indicated that Cnot7 is an endogenous suppressor of bone mass in adult mice and inhibits BMP actions.
Cnot7是最近在成年小鼠中发现的精子发生调节因子。由于Cnot7与Tob结合，Tob是一种参与骨代谢的骨形态发生蛋白（BMP）抑制剂，我们使用成年Cnot7基因缺失小鼠研究了Cnot7是否参与骨量调节。Cnot7基因敲除（Cnot7-/-）小鼠表现出高骨量表型。这与骨形成率增加有关，但与骨吸收参数的任何改变无关。在BMP处理下，与对照细胞相比，Cnot7-/-细胞中碱性磷酸酶表达水平更高。直接注射BMP2在体内诱导Cnot7-/-颅骨形成的骨量比对照更大。这些观察结果表明，Cnot7是骨量的内源性抑制因子，并抑制成骨细胞中的BMP作用。
基于最近的分析，参与骨量测定的分子机制已逐渐被了解。Cnot7（Ccr4-Not复合物7）是转录Ccr4-Not复合物的一个组成部分，从酵母到人类都保守，并且与Tob结合，但其在骨骼中的功能尚不清楚。
为了阐明Cnot7在骨量测定中的作用，我们基于显微计算机断层扫描（microCT）分析、组织形态计量学、细胞培养和体内BMP测定，研究了成年雄性Cnot7基因敲除小鼠和杂合小鼠的骨骼。
与对照相比，Cnot7-/-小鼠的骨量水平增加了50%以上。组织形态计量学参数分析表明，Cnot7-/-小鼠的骨形成活性增强，而骨吸收活性未改变。这些对成骨细胞的影响是细胞自主性的，因为从Cnot7-/-小鼠制备的骨髓细胞培养物中矿化结节形成增强。为阐明Cnot7作用的体外分析表明，与对照相比，BMP诱导的Cnot7-/-颅骨来源的成骨细胞中碱性磷酸酶表达增强。此外，BMP注射诱导的体内新骨形成在Cnot7-/-小鼠中增强。
这些观察结果表明，Cnot7是成年小鼠骨量的内源性抑制因子，并抑制BMP作用。
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