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

描述（由申请人提供）：Na，K- atp酶包括一组同工酶，负责维持大多数细胞的质膜上Na+和K+的梯度。Na， k - atp酶的同工酶多样性是由不同分子形式的催化α， α 1, α 2， α 3和α 4以及构成该酶的糖基化β （β a1， β a2和β a3）亚基的结合引起的。各种Na、k - atp酶同工酶的表达受细胞类型、发育阶段、激素刺激和组织病理状态的高度调控。此外，Na， k - atp酶异构体具有独特的酶性质。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，在生殖细胞中含量丰富。其功能约占精子总Na， k - atp酶活性的三分之二，其余部分对应于普遍表达的ctl亚型。在功能上，α 4多肽具有不同于其他Na， k - atp酶同工型的酶性质。这表明该异构体具有生理作用，并且(4)可能适应于满足雄性生殖细胞的离子需求。众所周知，Na+和K+梯度是精子活力的关键因素。精子获能和顶体反应是可育精子生物发生的必要步骤。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 - atp酶α 4亚型在男性生殖细胞功能中的生物学重要性及其与男性生育能力的相关性。具体目的是：1)研究Na，K-ATPase（4)多肽在男性生殖细胞发育和支持细胞中的表达和细胞定位；2)研究（4)在配子体发生、附睾成熟和顶体反应过程中在男性生殖细胞中的功能；3）研究Na，K-ATPase(4)异构体在精子生理中的作用；4）确定Na，K-ATPase(4)异构体在人体内的酶学性质和功能。这项研究将对了解Na， k - atp酶在男性生育和避孕中的睾丸特异性异构体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.