Smad7 inhibits chondrocyte differentiation at multiple steps during endochondral bone formation and down-regulates p38 MAPK pathways
Smad7 inhibits chondrocyte differentiation at multiple steps during endochondral bone formation and down-regulates p38 MAPK pathways
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DOI：
10.1074/jbc.m801175200
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发表时间：
2008-10-03
影响因子：
4.8
通讯作者：
Tsumaki, Noriyuki
中科院分区：
文献类型：
--
作者：
Iwai, Takao;Murai, Junko;Tsumaki, Noriyuki
骨形态发生蛋白（BMPs）在软骨内成骨的各个阶段起着关键作用。体外研究表明，Smad 7通过抑制软骨细胞中的Smad通路来调节转化生长因子β和BMP信号。然而，Smad 7在软骨发育过程中的体内作用尚不清楚。为了研究Smad 7在软骨细胞分化过程中不同阶段的不同作用，我们通过使用Cre/loxP系统产生了一系列在软骨细胞分化的各个阶段过表达Smad 7的条件转基因小鼠。建立Col 11 a2-lacZ（floxed）-Smad 7转基因小鼠，并与3种Cre转基因小鼠交配，获得Smad 7（Prx 1）、Smad 7（11 Enh）和Smad 7（11 Prom）条件转基因小鼠。Smad 7（Prx 1）小鼠过度表达Smad 7在凝聚间充质细胞表现出紊乱的间充质凝聚与减少Sox 9的表达，导致不良的软骨形成。Smad 7（11 Enh）小鼠在圆形软骨细胞中过表达Smad 7，显示软骨细胞增殖率降低。在扁平软骨细胞中过表达Smad 7的Smad 7（11 Prom）小鼠显示软骨细胞向肥大的成熟受到抑制。间充质细胞的微团培养表明，BMP诱导的软骨结节形成下调Smad 7的过表达，但不是Smad 6。Smad 7的过表达下调了p38 MAPK的磷酸化，而Smad 6则没有。我们的数据提供了在体内的证据，在软骨细胞分化的不同阶段的Smad 7的不同影响，并建议在prechondrogenic细胞中的Smad 7抑制软骨细胞分化可能通过下调BMP-激活的p38 MAPK途径。
Bone morphogenetic proteins (BMPs) play critical roles at various stages in endochondral bone formation. In vitro studies have demonstrated that Smad7 regulates transforming growth factor-beta and BMP signals by inhibiting Smad pathways in chondrocytes. However, the in vivo roles of Smad7 during cartilage development are unknown. To investigate distinct effects of Smad7 at different stages during chondrocyte differentiation, we generated a series of conditional transgenic mice that overexpress Smad7 in chondrocytes at various steps of differentiation by using the Cre/loxP system. Wegenerated Col11a2-lacZ(floxed)-Smad7 transgenic mice and mated them with three types of Cre transgenic mice to obtain Smad7(Prx1), Smad7(11Enh), and Smad7(11Prom) conditional transgenic mice. Smad7(Prx1) mice overexpressing Smad7 in condensing mesenchymal cells showed disturbed mesenchymal condensation associated with decreased Sox9 expression, leading to poor cartilage formation. Smad7(11Enh) mice overexpressing Smad7 in round chondrocytes showed decreased chondrocyte proliferation rates. Smad7(11Prom) mice overexpressing Smad7 in flat chondrocytes showed inhibited maturation of chondrocytes toward hypertrophy. Micromass culture of mesenchymal cells showed that BMP-induced cartilaginous nodule formation was down-regulated by overexpression of Smad7, but not Smad6. Overexpression of Smad7, but not Smad6, down-regulated the phosphorylation of p38 MAPKs. Our data provide in vivo evidence for distinct effects of Smad7 at different stages during chondrocyte differentiation and suggest that Smad7 in prechondrogenic cells inhibits chondrocyte differentiation possibly by down- regulating BMP- activated p38 MAPK pathways.