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

Na，K-ATP酶转运蛋白包括一组相对普遍存在的质膜同工酶，其使用来自ATP水解的能量将细胞质Na+交换为细胞外K+。Na，K-ATP酶的同工酶多样性来自于不同分子形式或两种多肽的同工酶，催化α和糖基化β亚基的缔合。在这些亚型中，α4多肽具有最有限的表达模式，并且选择性地存在于雄性生殖细胞中。α4亚型表现出几种生化和功能特征，这些特征是非常独特的，对精子功能至关重要。重要的是，α4是精子正常活动所必需的。支持其生物学重要性，我们已经表明，α4经历了显着的发育变化，其表达水平和活性在精子减数分裂后显着增加。一旦释放，精子继续经历关键的成熟变化，这对于细胞获得其可再生性至关重要。在这个被称为获能的过程中，我们发现α4活性被上调。虽然这些结果表明α4在精子功能中发挥重要作用，但这种蛋白质有助于精子获能以调节精子生育力的确切机制尚未完全确定。本研究的总体目标是确定调节α4亚型活性和离子转运功能的机制以及该事件与精子获能的相关性。我们的中心假设是α4亚型在精子生理学中起着重要作用，以维持控制pH值、膜电位和运动性变化的离子梯度，这些变化是精子获能的标志。实验旨在确定负责α4活性上调的因素和机制，并确定这些因素的贡献。 精子获能事件。这些结果将产生重要的积极影响，因为它们将有助于定义精子获能的分子基础，并将有助于未来靶向α4亚型控制男性生育力的药理学方法。

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.