Xia Weiliang, Mruk Dolores D, Lee Will M, Cheng C Yan
Population Council, Center for Biomedical Research, 1230 York Avenue, New York, NY 10021, USA.
J Biol Chem. 2006 Jun 16;281(24):16799-813. doi: 10.1074/jbc.M601618200. Epub 2006 Apr 13.
The biochemical basis that regulates the timely and selective opening of the blood-testis barrier (BTB) to migrating preleptotene/leptotene spermatocytes at stage VIII of the epithelial cycle in adult rat testes is virtually unknown. Recent studies have shown that cytokines (e.g. transforming growth factor (TGF)-beta3) may play a crucial role in this event. However, much of this information relies on the use of toxicants (e.g. CdCl(2)), making it difficult to relay these findings to normal testicular physiology. Here we report that overexpression of TGF-beta3 in primary Sertoli cells cultured in vitro indeed perturbed the tight junction (TJ) barrier with a concomitant decline in the production of BTB constituent proteins as follows: occludin, N-cadherin, and ZO-1. Additionally, local administration of TGF-beta3 to testes in vivo was shown to reversibly perturb the BTB integrity and Sertoli-germ cell adhesion via the p38 MAPK and ERK signaling pathways. Most importantly, the simultaneous activation of p38 and ERK signaling pathways is dependent on the association of the TGF-beta3-TbetaR1 complex with adaptors TAB1 and CD2AP because if TbetaR1 was associated preferentially with CD2AP, only Sertoli-germ cell adhesion was perturbed without compromising the BTB. Collectively, these data illustrate that local production of TGF-beta3, and perhaps other TGF-betas and cytokines, by Sertoli and germ cells into the microenvironment at the BTB during spermatogenesis transiently perturbs the BTB and Sertoli-germ cell adhesion to facilitate germ cell migration when the activated TbetaRI interacts with adaptors TAB1 and CD2AP. However, TGF-beta3 selectively disrupts Sertoli-germ cell adhesion in the seminiferous epithelium to facilitate germ cell migration without compromising BTB when TbetaRI interacts only with adaptor CD2AP.
成年大鼠睾丸上皮周期第八阶段，调控血睾屏障（BTB）适时且选择性地向迁移中的前细线期/细线期精母细胞开放的生化基础实际上仍不清楚。最近的研究表明，细胞因子（如转化生长因子（TGF）-β3）可能在此过程中起关键作用。然而，这些信息大多依赖于使用有毒物质（如CdCl₂），这使得难以将这些发现应用于正常睾丸生理学。在此我们报告，体外培养的原代支持细胞中TGF-β3的过表达确实扰乱了紧密连接（TJ）屏障，同时BTB组成蛋白（如闭合蛋白、N-钙黏蛋白和ZO-1）的产生也随之下降。此外，体内向睾丸局部施用TGF-β3被证明可通过p38丝裂原活化蛋白激酶（MAPK）和细胞外信号调节激酶（ERK）信号通路可逆地扰乱BTB完整性和支持细胞-生殖细胞黏附。最重要的是，p38和ERK信号通路的同时激活依赖于TGF-β3-TβR1复合物与衔接蛋白TAB1和CD2相关蛋白（CD2AP）的结合，因为如果TβR1优先与CD2AP结合，只会扰乱支持细胞-生殖细胞黏附，而不会损害BTB。总体而言，这些数据表明，在精子发生过程中，支持细胞和生殖细胞在BTB处向微环境局部产生TGF-β3，或许还有其他TGF-β和细胞因子，当活化的TβRI与衔接蛋白TAB1和CD2AP相互作用时，会短暂扰乱BTB和支持细胞-生殖细胞黏附，以促进生殖细胞迁移。然而，当TβRI仅与衔接蛋白CD2AP相互作用时，TGF-β3选择性地破坏生精上皮中的支持细胞-生殖细胞黏附，以促进生殖细胞迁移而不损害BTB。
