Molecular mechanism of bone-resorption in osteoclasts through microtubule regulation

我们研究了磷脂酰肌醇3-激酶的下游效应因子Akt在成熟破骨细胞骨吸收活性中的作用。用一种特定的Akt抑制剂治疗可破坏封闭区形成并降低破骨细胞的骨吸收活性。正常的微管结构丢失，Akt抑制剂减少了乙酰化微管蛋白的数量，这反映了微管的稳定，而通过腺病毒载体强制激活Akt则产生相反的效果。Akt的强制激活增加了微管相关蛋白APC、APC结合蛋白末端结合蛋白1 （EB1）和动力蛋白激活物复合物（dynactin）与微管的结合。Akt1和Akt2的缺失导致APC/EB1连接断开，骨吸收活性降低，封闭区形成减少，在添加GSK-3ss抑制剂flicl后，这两种情况都得到了恢复。Akt1和Akt2双敲除小鼠由于骨吸收减少而表现出骨质硬化。这些发现表明Akt通过调节微管相关蛋白的结合来稳定微管，从而控制破骨细胞的骨吸收活性。

We investigated the role of Akt, a downstream effector of phosphatidylinositol 3-kinase, in bone-resorbing activity of mature osteoclasts. Treatment with a specific Akt inhibitor disrupted sealing zone formation and decreased the bone-resorbing activity of osteoclasts. The normal microtubule structures were lost and the Akt inhibitor reduced the amount of acetylated tubulin, which reflects stabilized microtubules, whereas forced Akt activation by adenovirus vectors resulted in the opposite effect. Forced Akt activation increased the binding of themicrotubule-associated protein APC, the APC-binding protein end-binding protein 1 (EB1) and dynactin, a dynein activator complex, with microtubules. Depletion of Akt1 and Akt2 resulted in a disconnection of APC/EB1 and a decrease in bone-resorbing activity along with reduced sealing zone formation, both of which were recovered upon the addition ofLiCl, a GSK-3ss inhibitor. The Akt1 and Akt2 double knock-out mice exhibitedosteosclerosis due to reduced bone resorption. These findings indicate that Akt controls the bone-resorbing activity of osteoclasts by stabilizing microtubules via a regulationof the binding of microtubule associated proteins.