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

Na，K-ATP酶转运体包括一组相对普遍存在的质膜同工酶，它们利用ATP水解产生的能量将胞质Na+交换为胞外K+。Na， k - atp酶的同工酶多样性是由于两种多肽、催化α和糖基化β亚基的不同分子形式或同工形式的结合。在这些亚型中，α4多肽的表达模式最受限制，并选择性地存在于男性生殖细胞中。α4异构体表现出一些对精子功能非常独特和必要的生化和功能特征。重要的是，α4对于精子的正常运动是必需的。我们发现α4在精子减数分裂后发生了显著的发育变化，其表达水平和活性急剧增加，这也支持了其生物学重要性。一旦被释放，精子继续经历关键的成熟变化，这对细胞获得受精能力至关重要。在这个过程中，我们发现α4的活性被上调。虽然这些结果表明α4在精子功能中起重要作用，但这种蛋白质对精子获能调节精子生育能力的确切机制尚未完全确定。我们在这项研究中的总体目标是确定α4亚型的活性和离子转运功能被调控的机制，以及这一事件在精子获能中的相关性。我们的中心假设是α4亚型在精子生理中发挥重要作用，维持离子梯度，控制pH值、膜电位和运动变化，这些都是精子获能的标志。实验旨在确定α4活性上调的因素和机制，并确定这些因素的贡献

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.