Horiki Mitsuru, Imamura Takeshi, Okamoto Mina, Hayashi Makoto, Murai Junko, Myoui Akira, Ochi Takahiro, Miyazono Kohei, Yoshikawa Hideki, Tsumaki Noriyuki
Department of Orthopaedics, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Cell Biol. 2004 May 10;165(3):433-45. doi: 10.1083/jcb.200311015. Epub 2004 May 3.
Biochemical experiments have shown that Smad6 and Smad ubiquitin regulatory factor 1 (Smurf1) block the signal transduction of bone morphogenetic proteins (BMPs). However, their in vivo functions are largely unknown. Here, we generated transgenic mice overexpressing Smad6 in chondrocytes. Smad6 transgenic mice showed postnatal dwarfism with osteopenia and inhibition of Smad1/5/8 phosphorylation in chondrocytes. Endochondral ossification during development in these mice was associated with almost normal chondrocyte proliferation, significantly delayed chondrocyte hypertrophy, and thin trabecular bone. The reduced population of hypertrophic chondrocytes after birth seemed to be related to impaired bone growth and formation. Organ culture of cartilage rudiments showed that chondrocyte hypertrophy induced by BMP2 was inhibited in cartilage prepared from Smad6 transgenic mice. We then generated transgenic mice overexpressing Smurf1 in chondrocytes. Abnormalities were undetectable in Smurf1 transgenic mice. Mating Smad6 and Smurf1 transgenic mice produced double-transgenic pups with more delayed endochondral ossification than Smad6 transgenic mice. These results provided evidence that Smurf1 supports Smad6 function in vivo.
生化实验表明，Smad6和Smad泛素调节因子1（Smurf1）可阻断骨形态发生蛋白（BMP）的信号转导。然而，它们在体内的功能在很大程度上尚不清楚。在此，我们构建了在软骨细胞中过表达Smad6的转基因小鼠。Smad6转基因小鼠表现出出生后侏儒症，伴有骨质减少以及软骨细胞中Smad1/5/8磷酸化受到抑制。这些小鼠在发育过程中的软骨内成骨与几乎正常的软骨细胞增殖、显著延迟的软骨细胞肥大以及纤细的骨小梁有关。出生后肥大软骨细胞数量的减少似乎与骨生长和形成受损有关。软骨原基的器官培养显示，在由Smad6转基因小鼠制备的软骨中，BMP2诱导的软骨细胞肥大受到抑制。然后，我们构建了在软骨细胞中过表达Smurf1的转基因小鼠。在Smurf1转基因小鼠中未检测到异常。将Smad6和Smurf1转基因小鼠交配产生的双转基因幼崽，其软骨内成骨的延迟程度比Smad6转基因小鼠更严重。这些结果证明Smurf1在体内支持Smad6的功能。
