MTA2在睾丸支持细胞（Sertoli cells）中的功能和机制研究

Sertoli cells (SCs),characterized as the only somatic cells possessing close structural relationship with germ cells inside the seminiferous tubules, have drawn much attention of reproductive researchers because of their pivotal roles in the regulation of spermatogenic proliferation and differentiation. Accumulated evidences have demonstrated that deacetylation serves as a key modulator of the function of the genes predominantly expressed in SCs. We previously found that Metastasis associated protein 2 (MTA2), a recruiter of histone deacetylases, was exclusively expresssed in SCs.Its expression could be regulated by androgen pathway. MTA2 was involved in the homologous down-regulation of transcription of the FSH receptor gene in SCs. Furthermore, an attenuated expression patter of MTA2 was detected in pathological human testis with severe spermatogenic failure such as Sertoli cell only syndrome(SCOS), indicating a potential involvement of this histone modifier during the pathogenesis. These data collectively suggest that MTA2 may be an important regulator in SCs during spermatogenesis. An investigation is therefore to be initiated to futher study the potential relationship between MTA2, FSH-pathway and androgen signaling.We also try to observe the effect of ablation of MTA2 on the development and differentiatin of various spermatogenic cells by in vivo siRNA treatment, and to reveal the possible underlying mechanism, especially regarding the association with HDACs. Our systematic study would be helpful to elucidate the function and mechanism of SCs-specific expression of MTA2 during spermatogenesis, which will certainly shed novel light on the underlying mechanism by which SCs modulate spermatogenesis via MTA signaling pathway.

精子发生过程中，作为生精小管内唯一与生精细胞接触的体细胞，支持细胞（SCs）对生精细胞的发育分化起着重要的干预调节作用。大量文献表明，机体可以通过去乙酰化修饰机制对SCs关键性基因进行重要调控。我们前期研究显示组蛋白去乙酰化酶募集分子MTA2在SCs中特异性表达，这种表达受雄激素调节；MTA2参与了FSH对其受体的转录抑制调节；在以唯支持细胞综合征为代表的严重生精障碍的睾丸病理组织中MTA2的表达锐减，提示后者可能参与其病理发生。本课题拟在此基础上进一步研究MTA2与FSH、雄激素信号通路的作用关系，体外、体内干涉MTA2的表达后观察对各级生精细胞发育、分化的影响，继而深入研究其作用机制，尤其是与组蛋白去乙酰化酶HDACs的作用关系。这些研究可以阐明MTA2在SCs上特异性表达的功能意义，揭示其作用机制，并有助于发现SCs通过MTA信号通路调控生精细胞增殖分化的新机制，具有重要理论意义。

去乙酰化修饰是精子发生过程中调控支持细胞（Sertoli cells，SCs）中某些重要基因活性的关键机制之一，由于去乙酰化作用异常致SCs上关键基因表达异常进而引起SCs功能紊乱是诱发精子生成障碍的重要原因之一，但其具体分子机制还远不清楚。肿瘤转移相关蛋白2 (Metastasis Associated Protein 2， MTA2)是近年来发现的一类重要的核受体调节分子，它是核小体重建-去乙酰化酶复合物的核心成分之一，主要通过募集组蛋白去乙酰化酶于靶基因的方式来调节靶基因的转录活性及其功能，前期工作中，我们发现MTA2特异性表达于SCs，此表达受雄激素和FSH信号通路交叉调控，由于后二者是调节SCs功能的关键激素，我们推测MTA2的特异性表达对SCs具有重要功能意义。我们的研究结果显示，FSH受体（FSHR）是MTA2的靶基因之一，在FSH刺激下，MTA2通过直接结合于FSHR启动子序列而调节FSHR的表达水平，进而间接的影响FSH在睾丸的内分泌调节作用；在体外利用分离纯化的生精细胞残余小体与SCs共培养，SCs上的MTA2表达水平随时间增长逐渐上升，对MTA2表达水平最有效的刺激底物是残余小体或者凋亡精母细胞；在利用特异性siRNA在体抑制MTA2表达后，睾丸形态、精子密度和活动度、生育能力并未产生明显影响；然而利用annexin V封闭SCs吞噬功能后，睾丸内凋亡生精细胞数量在Ctrl siRNA处理组显著升高，而MTA2 siRNA处理组无明显变化，提示内源性MTA2对于SCs吞噬功能的正常维持是必需条件。我们还深入分析了MTA2同源基因MTA1、MTA2相关作用信号EGF、Ghrelin和α-taxilin在SCs的作用情况及其相应机制，我们的系统分析显示，MTA2很可能是通过 “募集”HDACs的方式来调节支持细胞上某些关键基因的转录活性，组成一个对生殖细胞的分化增殖起到重要调控作用的网络；MTA2在支持细胞中的作用受雄激素通路、FSH通路和相邻生精细胞分化状态的影响，它很可能参与了内分泌信号调节生精细胞发育功能的关键性“介导”作用。我们的研究系统揭示了SCs特异性表达MTA2的功能意义及其作用机制，并有助于进一步完善MTA家族在男性生殖系统功能的整体研究。