哺乳类精子发生过程中，支持细胞（Sertoli cells，SCs）通过吞噬作用清除脱落的细胞成分和凋亡的生精细胞，维持生精小管内环境稳态，但其作用机制很不清楚。我们前期工作显示一类重要的组蛋白去乙酰化酶募集分子MTA2可特异性表达于SCs且对后者关键基因FSHR起重要的转录调节作用；凋亡生精细胞或残余小体与SCs共培养可以明显上调MTA2在SCs中的表达水平，从而有效抑制吞噬过程中FSHR mRNA表达。FSH是调节SCs吞噬功能的重要激素，我们的结果提示MTA2很可能直接参与了这一过程。本课题拟在体外特异性抑制MTA2的表达后，深入观察对SCs吞噬功能和精子发生的影响；系统研究MAPK信号通路、酪氨酸激酶家族以及ROS信号途径对MTA2在吞噬过程中的调控效应,以期明确MTA2在SCs吞噬过程中表达上调的生物学意义。

During mammalian spermatogenesis, more than 75% of developing spermatogenic cells are estimated to undergo apoptosis before they mature into spermatozoa. In the last stage of spermatogenesis, the cytoplasmic portions of elongated spermatids are shed and form residual bodies (RBs) before extrusion of differentiated sperm into the lumen of the seminiferous tubules. The apoptotic germ cells and RBs are selectively phagocytosed by Sertoli cells (SCs), which is essential for healthy spermatogenic cells to proceed through spermatogenesis. However, the underlying mechanisms remain largely unknown. We have previously shown that Metastasis associated protein 2 (MTA2), an essential component of the nucleosome remodeling and histone deacetylation (NuRD) complex, can regulate the SCs function via its chromatin remodeling ability through transcriptional regulation of follicle-stimulating hormone receptor (FSHR) gene. Recently, we have found that co-culture of RBs and SCs significantly upregulated the expression of MTA2 in SCs. One major result of this response is the transcriptional repression of FSHR mRNA expression during phagocytosis, suggesting a potential involvement of MTA2 in SCs phagocytosis because FSH signaling fundamentally regulates this process. On these bases, we aim to further investigate the role of MTA2 in the phagocytosis by SCs and its relevant mechanism (including potential regulation by MAPK pathway, tyrosine kinases family and ROS signaling). The effect of ablation of endogenous MTA2 on phagocytosis by SCs will be assessed using specific siRNA treatment. Our systematic analysis will shed light on the role of MTA2 in the complicated process of phagocytosis by SCs.

在复杂的哺乳动物精子发生过程中，凋亡的生精细胞和残余小体需要被睾丸支持细胞（Sertoli cells，SCs）及时清除，这一生理现象被称为“SCs的吞噬功能”，后者对于维持生精小管内稳态至关重要，但其分子调控机制还很不清楚。肿瘤转移相关蛋白2 （Metastasis Associated Protein 2， MTA2）是核小体重建-去乙酰化酶复合物（Nucleosome remodeling and deacetylation，NuRD）的核心成分之一，可以通过募集组蛋白去乙酰化酶（Histone deacetylases，HDACs）于靶基因的方式来调节靶基因的转录活性，在细胞增殖、分化过程中发挥了重要作用。我们前期工作显示，MTA2在睾丸SCs中特异性表达，这一表达受FSH信号调节；FSH受体（FSHR）基因是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。此外，与残余小体或凋亡的生精细胞混合培养可以显著上调SCs中MTA2的表达水平；对MTA2刺激作用最强的是残余小体和凋亡的精母细胞，提示MTA2可能参与到了SCs的吞噬活动中。在本研究中，当利用MTA2 siRNA特异性抑制TM4内源性MTA2的表达后，观察到SCs吞噬活性明显降低；雄激素信号通路关键基因Pem表达有明显降低，同时CREB的磷酸化水平显著被抑制，这些结果提示内源性MTA2对于SCs吞噬功能的正常维持是必需条件，且其调节功能很可能由FSH、雄激素信号通路共同调节。进一步在体水平深入研究MTA2在SCs吞噬活动中的作用特点及其相关调控机制将为理解SCs这一复杂生理活动提供重要新线索。