REGULATION OF THE RENAL SALT AND WATER TRANSPORTERS

Carolyn Ecelbarger博士，博士他同时接受过营养学家和肾脏生理学家的培训，处于一个独特的位置，可以弥合这些领域之间的差距。她的长期职业目标包括研究营养因素如何影响肾功能，特别是这与肾脏盐和水转运蛋白的表达和调节的关系。指导的研究职业奖（KO 1）将为建议的受指导者提供机会，Ecelbarger博士，在乔治敦大学Joseph Verbalis博士（建议的导师）的指导和专业知识下，扩大她在生理学方面的培训。在美国国立卫生研究院Mark Knepper博士的实验室进行博士后培训期间，她的研究主要集中在了解在尿液浓缩机制中重要的蛋白质，包括肾脏水通道蛋白和Na- K-2Cl协同转运蛋白。Ecelbarger博士与Verbalis博士实验室合作完成的一个关键项目涉及评估水通道蛋白表达在加压素逃逸生理现象中的作用。患有这种疾病的患者最初保留水分并成为低钠血症。然而，如果水负荷继续，最终他们开始排泄更大体积的相当稀释的尿液，尽管高循环水平的加压素。这种“加压素逃逸”的过程困扰了肾脏生理学家几十年，尽管对其中的机制知之甚少。在大鼠模型中，Ecelbarger等人能够显示水通道蛋白-2蛋白（水稳态中的关键蛋白）的显著下调。钠尿是加压素逃逸的另一种生理成分，但对其了解甚少。因此，该建议的具体目标概括如下：（1）评估在加压素的抗利尿作用的生理性“逃逸”过程中，钠转运蛋白在肾脏表达和细胞分布的变化;（2）研究加压素逃逸和慢性加压素暴露模型中水通道蛋白-2表达调控中涉及的信号传导事件，以及（3）评估长期加压素暴露对水通道蛋白-2表达的影响。长期肠外营养（TPN）对肾脏盐和水转运蛋白表达和调节的影响。主要假设是，直接调节几个关键的肾小管盐和水转运蛋白的表达和细胞分布是维持体内整体盐和水稳态的手段，尽管有生理扰动，如血液加压素水平的变化。研究建议简要概述了每个具体的目标，分别：（1）评估加压素逃逸的时间过程中的表达和调控的关键钠转运蛋白沿着肾小管免疫印迹和免疫组织化学;（2）利用多种生物化学和免疫学方法，以评估V2受体/腺苷酰-腺苷酸受体中的重要调节事件。在TPN大鼠模型中，评估全肠外营养对肾功能、肾血流动力学指标以及盐和水转运蛋白表达和调节的影响。

Dr. Carolyn Ecelbarger, Ph.D. who has trained as both a nutritionist and a renal physiologist is in a unique position to bridge the gap between these fields. Her long-term career goals include investigating how nutritional factors affects renal function and especially how this relates to expression and regulation of salt and water transporters of the kidney. The mentored Research Career Award (KO1) will provide the proposed mentee, Dr. Ecelbarger, with the opportunity to broaden her training in physiology, under the guidance and expertise of Dr. Joseph Verbalis (proposed mentor), at Georgetown University. During her post-doctoral training at the National Institutes of Health in Dr. Mark Knepper's laboratory, her research focussed mainly on understanding those proteins which are important in the urinary concentrating mechanism, including the renal aquaporins and the Na- K-2Cl cotransporter. A key project of Dr. Ecelbarger's, done in collaboration with Dr. Verbalis' laboratory, involved assessing the role of aquaporin expression in the physiological phenomenon of vasopressin escape. Patients with this disorder initially retain water and become hyponatremic. However, if water loading continues, eventually they begin to excrete larger volumes of fairly dilute urine, despite the high circulating levels of vasopressin. This process of "vasopressin escape" has puzzled renal physiologists for decades, although little is actually understood about the mechanisms involved. In a rat model, Ecelbarger et al. were able to show dramatic down-regulation of aquaporin-2 protein, a critical protein in water homeostasis. Naturesis is another physiologic component of vasopressin escape of which little is understood. Thus, the specific aims of the proposal are summarized as follows: (1) to evaluate changes in renal expression and cellular distribution of sodium transporters during physiologic "escape" from the antidiuretic action of vasopressin; (2) to investigate signaling events involved in regulation of aquaporin-2 expression in models of vasopressin escape and chronic vasopressin exposure and (3) to assess the impact of long-term parenteral nutrition (TPN) on the expression and regulation of renal salt and water transporters. The main hypothesis is that direct regulation of expression and cellular distribution of several critical kidney tubule salt and water transporters is the means by which overall salt and water homeostasis is maintained in the body, despite physiological perturbations such as changes in blood vasopressin levels. The study proposals are briefly outlined for each specific aim, respectively; (1) to evaluate the time course of vasopressin escape with regard to expression and regulation of critical sodium transporters along the kidney tubule by immunoblotting and immunohistochemistry; (2) to utilize a variety of biochemical and immunolological approaches in order to assess important regulatory events in the V2-receptor/adenylyl-cyclase signaling cascade and determine how they relate to aquaporin-2 abundance; (3) to assess the effects of total parenteral nutrition on renal function, measures of renal hemodynamics, and expression and regulation of salt and water transporters in a rat model of TPN.