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

描述(申请人提供)：项目摘要：Na，K-ATPaseα4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。用心脏糖苷哇巴因抑制这种Na，K-ATPase亚型的特异性药理作用已被证明完全抑制大鼠精子的活力。Na，K-ATPaseα4抑制的精子失去活力的机制尚不清楚，但间接证据表明，细胞内[H+]增加是原因之一。Na，K-ATPase本身不转运H+，因此，与抑制Na，K-ATPaseα4亚型相关的细胞内[H+]增加可能是由于精子中发现的Na+/H+交换器(NHE)亚型之一的继发性抑制。NHEs使用Na，K-ATPase建立的Na+梯度将H+从细胞中排出，以换取细胞外的Na+。以大鼠和小鼠为模型，观察Na，K-ATPase抑制精子过程中细胞内离子浓度的变化，探讨NHE和其他Na，K-ATPase亚型在维持精子活力中的作用。我们还将描述人类Na，K-ATPaseα4亚型的组织分布及其作为功能性Na，K-ATPaseα亚型的特性。这些研究不仅对确定Na，K-ATPase和NHE亚型在精子活力中的作用很重要，而且可能具有医学上的相关意义：如果人的Na，K-ATPaseα4亚型在人类精子中起到与大鼠精子中相同的作用，那么很可能1)由于Na，K-ATPaseα4基因的失活突变而导致一部分不育男性不育，以及2)Na，K-ATPaseα4亚型的特异性抑制剂可以作为男性避孕药开发出来。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的根本原因，并有助于确定针对男性的避孕措施。

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.