Na,K-ATPase alpha4 isoform in male germ cell physiology

Na，K-ATPase转运体由一组相对普遍存在的质膜同工酶组成，它们利用ATP水解产生的能量将胞内Na+交换为胞外K+。Na，K-α酶的同工酶多样性是两种多肽的不同分子形式或异构体结合的结果，即催化的β和糖基化的ATPase亚基。在这些异构体中，α4多肽的表达模式最受限制，并且选择性地存在于雄性生殖细胞中。α4亚型表现出一些非常独特的、对精子功能至关重要的生化和功能特征。重要的是，α4是精子正常运动所必需的。支持其生物学重要性，我们已经证明了α4经历了显著的发育变化，并且它的表达水平和活性在精子减数分裂后显著增加。一旦释放，精子继续经历关键的成熟变化，这些变化是细胞获得受精能力所必需的。在这个称为获能的过程中，我们发现α4的活性被上调。虽然这些结果表明α4在精子功能中起着重要的作用，但该蛋白促进精子获能以调节精子受精率的确切机制(S)尚未完全确定。我们在这项研究中的总体目标是确定α4亚型活性和离子转运功能的调节机制(S)，以及这一事件在精子获能中的相关性。我们的中心假设是，α-4亚型在精子生理学中发挥着重要作用，以维持控制精子获能标志的pH、膜电位和活力变化的离子梯度。实验旨在确定导致α4活性上调的因素和机制，并确定这些因素和机制的贡献 精子获能的事件。这些结果将产生重要的积极影响，因为它们将有助于确定精子获能的分子基础，并将有助于未来针对α4亚型控制男性生育能力的药理学方法。

The Na,K-ATPase transporters comprise a group of relatively ubiquitous plasma membrane isozymes that use the energy from the hydrolysis of ATP to exchange cytoplasmic Na+ for extracellular K+. Isozyme diversity for the Na,K-ATPase results from the association of different molecular forms, or isoforms of two polypeptides, the catalytic α and glycosylated β subunits. Among these isoforms, the α4 polypeptide has the most restricted pattern of expression, and is selectively present in male germ cells. The α4 isoform exhibits several biochemical and functional characteristics that are highly unique and essential to sperm function. Importantly, α4 is necessary for normal motility of spermatozoa. Supporting its biological importance, we have shown that α4 undergoes significant developmental changes, and that its level of expression and activity increase dramatically after sperm meiosis. Once released, spermatozoa continue to undergo critical maturational changes that are essential for the cells to acquire their fertilizing ability. During this process, called capacitation, we found α4 activity to be up-regulated. While these results suggest an important role for α4 in sperm function, the precise mechanism(s) by which this protein contributes to sperm capacitation to regulate sperm fertility has yet to be fully defined. Our overall goal in this research is to determine the mechanism(s) by which the activity and ion transport function of the α4 isoform is regulated and the relevance of this event in sperm capacitation. Our central hypothesis is that the α4 isoform plays an important role in sperm physiology to maintain the ion gradients that control pH, membrane potential and motility changes that are hallmarks of sperm capacitation. Experiments are designed to identify the factors and mechanisms responsible for up-regulation of α4 activity, and to determine the contribution of these events to sperm capacitation. The results will have an important positive impact, because they will help to define the molecular basis of sperm capacitation and will contribute to future pharmacologic approaches that will target the α4 isoform to control male fertility.