New Modulators of Na, K-ATPase in the CNS

描述(由申请人提供)：这项提案旨在测试一种调节中枢神经系统钠泵的创新新范式。钠泵(Na，K-ATPase)消耗的能量占大脑所用能量的一半。它在缺血组织中被稳定地抑制，从而增强了兴奋性毒性。它通过对钠和钾的调节以及对膜电位的电生成贡献，对神经和神经胶质细胞的生理学做出贡献。有许多证据表明，它受到递质和激素的积极调控，但令人沮丧的是，分子和生化水平上的机制仍然难以捉摸。我们最近发现，肾脏的Na，K-ATPase“伽马亚基”作为一种辅助蛋白，通过降低其对Na和K的亲和力来调节Na，K-ATPase。其他研究表明，同系物Chif对肾脏的钠泵特性具有相反的功能作用，这两种作用在不同的肾单位节段中表达。这些蛋白质不在大脑中表达，但我们已经确定了其他五个同源物。我们将检验新的假设，即它们都是Na，K-ATPase调节因子。这些同源基因(FXYD基因家族)共享一个保守的中央膜结构域，但具有不同的胞外和胞内结构域。这预示着它们具有不同的功能效应，并成为不同调控机制的靶点。在我们的初步数据中，我们发现其中一个同源物仅限于小脑皮质分子层，并且确实与Na，K-ATPase有关。我们将确定其他同系物是否具有不同的细胞分布，是否与不同的Na，K-ATPase亚型相互作用，以及是否对Na，K-ATPase特性有不同的功能影响。其中两个是在我们的基因组研究中首次发现的新基因产物，需要先导数据才能从序列过渡到生物学。这项工作有望在大脑运输和能量代谢的调节方面取得重大突破，并可能导致神经保护性治疗，从而恢复中风后高危组织的钠泵活动。

DESCRIPTION (provided by applicant): This proposal aims to test an innovative new paradigm for the regulation of the sodium pump in the CNS. The sodium pump (Na,K-ATPase) consumes half of all the energy used in the brain. It is stably inhibited in ischemic tissue, which potentiates excitotoxicity. It contributes to neural and glial physiology through its regulation of Na and K and its electrogenic contribution to membrane potential. There is much evidence that it is actively regulated by transmitters and hormones, but the mechanisms remain frustratingly elusive at the molecular and biochemical level. We have recently shown that the Na,K-ATPase "gamma subunit" of the kidney acts as an accessory protein, modulating the Na,K-ATPase by reducing its affinity for Na and K. Others have shown that a homologue, CHIF, has a functionally opposite effect on kidney sodium pump properties, and the two are expressed in different nephron segments. These proteins are not expressed in the brain, but we have identified five other homologs that are. We will test the new hypothesis that they are all Na,K-ATPase regulators. The homologs (the FXYD gene family) share a conserved central membrane domain, but have divergent extracellular and intracellular domains. This predicts that they have different functional effects and are targeted by different regulatory mechanisms. In our preliminary data we show that one of the homologs is restricted to the cerebellar cortex molecular layer, and that it indeed associates with Na, K-ATPase. We will determine whether the other homologs have different cellular distributions, interact with different Na,K-ATPase isoforms, and have different functional effects on Na, K-ATPase properties. Two of them are new gene products that were first identified in our genomic studies, and pilot data are needed to make the transition from sequence to biology. The work promises to provide a significant breakthrough in the regulation of transport and energy metabolism in the brain, and may lead to neuroprotective therapy that could restore sodium pump activity in tissue-at-risk after stroke.