Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
Proc Natl Acad Sci U S A. 2011 Jan 11;108(2):644-9. doi: 10.1073/pnas.1016902108. Epub 2010 Dec 27.
Regulation of ion balance in spermatozoa has been shown to be essential for sperm motility and fertility. Control of intracellular ion levels requires the function of distinct ion-transport mechanisms at the cell plasma membrane. Active Na(+) and K(+) exchange in sperm is under the control of the Na,K-ATPase. Two molecular variants of the catalytic subunit of the Na,K-ATPase, α1 and α4, coexist in sperm. These isoforms exhibit different biochemical properties; however, their function in sperm fertility is unknown. In this work, we show that Na,K-ATPase α4 is essential for sperm fertility. Knockout male mice lacking α4 are completely sterile and spermatozoa from these mice are unable of fertilizing eggs in vitro. Furthermore, α4 deletion results in severe reduction in sperm motility and hyperactivation typical of sperm capacitation. In addition, absence of α4 causes a characteristic bend in the sperm flagellum, indicative of abnormal sperm ion regulation. Accordingly, α4-null sperm present increased intracellular Na(+) and cell plasma membrane depolarization. These results are unique in demonstrating the absolute requirement of α4 for sperm fertility. Moreover, the inability of α1 to compensate for α4 suggests that α4 is the Na,K-ATPase-α isoform directly involved in sperm fertility. Our findings show α4 as an attractive target for male contraception and open the possibility for the potential use of this Na,K-ATPase isoform as a biomarker for male fertility.
精子中离子平衡的调节对于精子的运动能力和生育能力至关重要。细胞内离子水平的控制需要细胞膜上不同的离子转运机制来实现。精子中的主动 Na(+)和 K(+)交换受 Na,K-ATPase 的控制。Na,K-ATPase 的催化亚基 α1 和 α4 两种分子变异体共存于精子中。这些同工酶表现出不同的生化特性；然而，它们在精子生育能力中的功能尚不清楚。在这项工作中，我们表明 Na,K-ATPase α4 对于精子生育能力是必需的。缺乏 α4 的雄性 knockout 小鼠完全不育，并且这些小鼠的精子无法在体外受精卵子。此外，α4 的缺失导致精子运动能力严重下降和超激活，这是精子获能的典型特征。此外，α4 的缺失会导致精子鞭毛出现特征性弯曲，表明精子离子调节异常。因此，α4 缺失的精子表现出细胞内 Na(+)增加和细胞膜去极化。这些结果独特地证明了 α4 对精子生育能力的绝对要求。此外，α1 不能补偿 α4 表明 α4 是直接参与精子生育能力的 Na,K-ATPase-α 同工酶。我们的研究结果表明，α4 是男性避孕的一个有吸引力的靶点，并为这种 Na,K-ATPase 同工酶作为男性生育能力的生物标志物的潜在用途开辟了可能性。
