Role of the Na, K-ATPase Alpha4 Isoform in Sperm Motility

描述（由申请人提供）：项目概述：Na，K-ATP酶α 4亚型仅在大鼠雄性生殖细胞膜中发现，在成熟精子中含量最高。使用强心苷哇巴因对该Na，K-ATP酶亚型进行特异性药理学抑制已显示可完全抑制大鼠精子的活动性。Na，K-ATP酶α 4抑制精子运动力丧失的机制尚不清楚，但间接证据表明细胞内[H+]增加是原因。Na，K-ATP酶本身不转运H+，因此，与Na，K-ATP酶α 4亚型抑制相关的细胞内[H+]增加可能是由于精子中发现的一种Na+/H+交换器（NHE）亚型的继发性抑制。NHE使用由Na，K-ATP酶建立的Na+梯度从细胞中挤出H+以交换细胞外Na+。以大鼠和小鼠为模型，观察了Na，K-ATP酶抑制精子细胞内离子浓度的变化，并探讨了NHE亚型和其他Na，K-ATP酶亚型在维持精子活力中的作用。我们还将表征来自人类的Na，K-ATP酶α 4同种型的组织分布及其作为功能性Na，K-ATP酶α同种型的特性。这些研究不仅对确定Na，K-ATP酶和NHE亚型在精子活力中的作用很重要，而且可能具有医学相关意义：如果人Na，K-ATP酶α 4同种型在人精子中发挥与大鼠同种型在大鼠精子中相同的作用，则可能1）不育男性的子集由于Na，K-ATP酶α 4中的失活突变而不育，K-ATP酶α 4基因和2）Na，K-ATP酶α 4亚型的特异性抑制剂可开发为男性避孕药。相关性：了解这些蛋白质之间的相互作用将进一步加深我们对精子基本生物学的理解，并将影响人类生殖生物学。这些研究可能有助于了解某些形式的男性不育症的根本原因，并确定男性专用避孕药。

DESCRIPTION (provided by applicant): Project Summary: The Na,K-ATPase alpha4 isoform has been found only in the membrane of male germ cells of rats and is most abundant in mature sperm. Specific pharmacological inhibition of this Na,K-ATPase isoform using the cardiac glycoside ouabain has been shown to completely inhibit the motility of rat sperm. The mechanism underlying the loss of motility of Na,K-ATPase alpha4 inhibited sperm is unclear, however indirect evidence suggests that an increase in intracellular [H+] is responsible. The Na,K-ATPase does not transport H+ itself therefore, the increase in intracellular [H+] associated with inhibition of the Na,K-ATPase alpha4 isoform is likely due to secondary inhibition of one of the Na+/H+ exchanger (NHE) isoforms found in sperm. The NHEs use the Na+ gradient established by the Na,K-ATPase to extrude H+ from the cell in exchange for extracellular Na+. Using rats and mice as models we w II asses the changes in intracellular ion concentrations in Na,K-ATPase inhibited sperm and examine the role that isoforms of the NHE and other Na,K-ATPase isoforms play in maintaining sperm motility. We will also characterize the Na,K-ATPase alpha4 isoform from humans with respect to its tissue distribution and its identity as a functional Na,K- ATPase alpha isoform. These studies will not only be important for defining the role that isoforms of the Na,K-ATPase and the NHE play in sperm motility but also may have medically relevant implications: If the human Na,K-ATPase alpha4 isoform plays the same role in human sperm as the rat isoform does in rat sperm it is likely that 1) a subset of infertile men are infertile due to inactivating mutations in the Na,K- ATPase alpha4 gene and 2) specific inhibitors of the Na,K-ATPase alpha4 isoform could be developed as male contraceptive agents. Relevance: Understanding the interactions between these proteins will further our understanding of the basic biology of sperm and will impact human reproductive biology. These studies could lead to understanding the underlying reasons for some forms of male infertility as well as to identifying male-specific contraceptives.