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

描述(申请人提供)：Na，K-ATPase由一组同工酶组成，负责维持大多数细胞质膜上的Na+和K+梯度。Na，K-ATPase同工酶的多样性源于组成该酶的催化α、α1、α2、α3和α4亚基和糖基化β亚基(β1、β2和β3)的不同分子形式的结合。不同的Na，K-ATPase同工酶以高度调控的方式表达，这取决于细胞类型、发育阶段、激素刺激和组织的病理状态。此外，Na，K-ATPase亚型具有独特的酶特性。A4亚型表现出最受限制的表达模式，它在大鼠睾丸中选择性表达，在生殖细胞中大量表达。它的功能约占精子总Na，K-ATPase活性的三分之二，其余的与普遍表达的ctl亚型相对应。在功能上，α4多肽具有不同于其他Na，K-ATPase亚型的酶性质。这暗示了异构体的生理作用，并且(4)可能被调整以满足雄性生殖细胞的离子需求。众所周知，Na+和K+梯度是影响精子活力的关键因素。此外，对于精子获能和顶体反应，这是可育精子生物发生所必需的步骤。目前，(4)在这些过程中的确切作用尚不清楚。本研究的主要目的是阐明Na，K-ATPaseα4亚型在男性生殖细胞功能中的生物学意义及其与男性生育能力的关系。其具体目的是：1)研究Na，K-ATPase(4种多肽)在男性生殖细胞发育过程中的表达和细胞定位；2)研究(4)在男性生殖细胞中的功能；3)研究Na，K-ATPase(4种异构体)在精子生理学中的作用；4)确定Na，K-ATPase(4种异构体)的酶性质和功能。这项研究对于了解睾丸特异的Na，K-ATPase亚型在男性生育和避孕中的生物学相关性具有重要意义。

DESCRIPTION (provided by applicant): The Na,K-ATPase comprises a group of isozymes responsible for maintaining the Na+ and K+ gradients across the plasma membrane of most cells. Isozyme diversity for the Na,K-ATPase results from the association of different molecular forms of the catalytic alpha, alpha1, alpha2, alpha3 and alpha4 and glycosylated beta (beta1,beta2 and beta3) subunits that constitute the enzyme. The various Na,K-ATPase isozymes are expressed in a highly regulated manner, depending on cell type, developmental stage, hormonal stimulation and pathological state of the tissue. In addition, Na,K-ATPase isoforms have enzymatic properties that are unique. The a4 isoform exhibits the most restricted pattern of expression, and it is selectively expressed in rat testes, where it is abundant in germ cells. Its function comprises approximately two thirds of the total Na,K-ATPase activity of spermatozoa, the rest corresponding to the ubiquitously expressed ctl isoform. Functionally, the alpha4 polypeptide has enzymatic properties different from those of the other Na,K-ATPase isoforms. This suggests a physiological role for the isoform, and (4 may be adapted to fulfill the ionic requirements of the male germ cells. It is well known that the Na+ and K+ gradients are key factors for sperm motility. Also, for spermatozoa capacitation and acrosomal reaction, which are required steps for the biogenesis of fertile spermatozoa. At present, the precise role of (4 in these processes remains unknown. The main objective of the present proposal is to elucidate the biological importance of the Na,K-ATPase alpha4 isoform in male germ cell function and its relevance to male fertility. Specifically the aims are: 1) to investigate expression and cell localization of the Na,K-ATPase (4 polypeptide in male germ cells during development, and in Sertoli cells, 2) to study the function of (4 in male germ cells during gametogenesis, epididymal maturation and acrosomal reaction, 3) to study the role of the Na,K-ATPase (4 isoform in sperm physiology, and 4) to determine the enzymatic properties and function of Na,K-ATPase (4 isoform from humans. This study will be important to understand the biological relevance of the testes specific isoform of the Na,K-ATPase in male fertility and contraception.