Sox9 sustains chondrocyte survival and hypertrophy in part through Pik3ca-Akt pathways
Sox9 sustains chondrocyte survival and hypertrophy in part through Pik3ca-Akt pathways
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DOI：
10.1242/dev.057802
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发表时间：
2011-04-15
期刊：
影响因子：
4.6
通讯作者：
Tsumaki, Noriyuki
中科院分区：
文献类型：
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作者：
Ikegami, Daisuke;Akiyama, Haruhiko;Tsumaki, Noriyuki
在软骨内骨形成过程中，Sox 9表达始于间充质祖细胞，在圆形和扁平软骨细胞阶段以高水平持续，并在肥大软骨细胞阶段之前停止。Sox 9在间充质祖细胞分化为软骨细胞中是重要的，但其分化后的功能尚未确定。为了研究Sox 9在软骨细胞中的功能，我们在软骨细胞分化后的两个不同步骤中删除小鼠Sox 9。Sox9在圆形软骨细胞中的失活导致Col2a1表达的丧失和细胞凋亡。扁平软骨细胞中的Sox9失活导致立即的终末成熟，而没有肥大和过度凋亡。在最后几个细胞层中Sox 9的失活导致Col10a1表达的缺失，这表明在肥大之前Sox 9的持续表达对于软骨细胞肥大是必要的。SOX9基因敲低也可引起人软骨肉瘤SW1353细胞凋亡。这些表型与Akt磷酸化减少相关。通过Pten失活的Akt的强制磷酸化部分恢复了Sox 9（Aphrodel/Aphrodel）小鼠软骨细胞中Col10a1的表达和细胞存活，表明磷酸化Akt介导了Sox 9诱导的软骨细胞存活和肥大。当研究Sox 9诱导的Akt磷酸化的分子机制时，我们发现在Sox 9（p110 del/p110 del）小鼠软骨细胞中PI3K亚基Pik3ca（p110 alpha）的表达降低。Sox 9与Pik3ca的启动子结合并增强Pik3ca的转录活性。因此，分化的软骨细胞中Sox 9的持续表达对于随后的肥大是必不可少的，并且通过与Pik3ca启动子结合，诱导Akt磷酸化来维持软骨细胞特异性存活机制。
During endochondral bone formation, Sox9 expression starts in mesenchymal progenitors, continues in the round and flat chondrocyte stages at high levels, and ceases just prior to the hypertrophic chondrocyte stage. Sox9 is important in mesenchymal progenitors for their differentiation into chondrocytes, but its functions post-differentiation have not been determined. To investigate Sox9 function in chondrocytes, we deleted mouse Sox9 at two different steps after chondrocyte differentiation. Sox9 inactivation in round chondrocytes resulted in a loss of Col2a1 expression and in apoptosis. Sox9 inactivation in flat chondrocytes caused immediate terminal maturation without hypertrophy and with excessive apoptosis. Inactivation of Sox9 in the last few cell layers resulted in the absence of Col10a1 expression, suggesting that continued expression of Sox9 just prior to hypertrophy is necessary for chondrocyte hypertrophy. SOX9 knockdown also caused apoptosis of human chondrosarcoma SW1353 cells. These phenotypes were associated with reduced Akt phosphorylation. Forced phosphorylation of Akt by Pten inactivation partially restored Col10a1 expression and cell survival in Sox9(floxdel/floxdel) mouse chondrocytes, suggesting that phosphorylated Akt mediates chondrocyte survival and hypertrophy induced by Sox9. When the molecular mechanism of Sox9-induced Akt phosphorylation was examined, we found that expression of the PI3K subunit Pik3ca (p110 alpha) was decreased in Sox9(floxdel/floxdel) mouse chondrocytes. Sox9 binds to the promoter and enhances the transcriptional activities of Pik3ca. Thus, continued expression of Sox9 in differentiated chondrocytes is essential for subsequent hypertrophy and sustains chondrocyte-specific survival mechanisms by binding to the Pik3ca promoter, inducing Akt phosphorylation.