Differential interactions between transforming growth factor-β3/ TβR1, TAB1, and CD2AP disrupt blood-testis barrier and sertoli-germ cell adhesion
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)-β3) may play a crucial role in this event. However, much of this information relies on the use of toxicants (e.g. CdCl2), making it difficult to relay these findings to normal testicular physiology. Here we report that overexpression of TGF-β3 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-β3 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-β3-TβR1 complex with adaptors TAB1 and CD2AP because if TβR1 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-β3, and perhaps other TGF-βs 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 TβRI interacts with adaptors TAB1 and CD2AP. However, TGF-β3 selectively disrupts Sertoli-germ cell adhesion in the seminiferous epithelium to facilitate germ cell migration without compromising BTB when TβRI interacts only with adaptor CD2AP.
Xia, Weiliang, Dolores D. Mruk, Will M. Lee, and C. Yan Cheng. 2006. "Differential interactions between transforming growth factor-β3/TβR1, TAB1, and CD2AP disrupt blood-testis barrier and Sertoli-germ cell adhesion," Journal of Biological Chemistry 281(24): 16799–16813.