Role of vasopressin in regulating renal medullary gene expression

描述（由申请人提供）：糖尿病和充血性心力衰竭是与肾脏处理盐和水的缺陷有关的疾病。在患有这些疾病的个体中常见的是血管加压素循环水平升高，血管加压素是一种调节肾脏水排泄的肽激素。循环加压素在高血压的细胞外液扩张和发展中起关键作用，从而有助于疾病的发病机制。抗利尿激素在肾脏中具有明确的长期作用，与抗利尿激素受体激活过程和转录调节有关。循环加压素也通过激活逆流机制增加肾髓质的浓缩能力。其结果是髓质渗透应激的增加，可以直接激活肾细胞信号通路和基因转录。因此，抗利尿激素对基因表达的特定影响不能从与髓质渗透压变化相关的继发性改变中描述出来。来自小鼠体内研究的初步数据确定了加压素在收集管细胞中激活内质网应激（ER应激）的作用。内质网应激可能是收集管细胞在抗利尿过程中髓质渗透应激大量增加时存活的关键。因此，我们将确定加压素是否在髓质中发挥预处理作用，以保护收集管细胞免于凋亡，同时继续上调水通道蛋白-2的表达并增加收集管的水通透性。我们还发现了一种新的抗利尿激素信号通路，它可以降低收集管中类固醇激素失活酶的表达，并提出这种抗利尿激素介导的通路可能间接增强ENaC的表达。我们的研究将利用三种互补的模型系统，细胞，小管悬浮液和动物模型来解决我们的中心假设，即加压素通过直接（V2R）和间接（渗透应激）机制促进AQP2和enac依赖通路。具体目的是：1)确定局部溶质浓度的增加是否激活内质网应激蛋白并保护收集管细胞免受进一步的渗透胁迫；2)确定抗利尿激素是否通过V2受体途径直接介导内质网应激蛋白的上调；3)确定抗利尿激素是否通过V2受体途径直接介导类固醇激素酶的下调。

DESCRIPTION (provided by applicant): Diabetes and congestive heart failure are diseases that have been associated with defects in the handling of salt and water by the kidney. Common in individuals with these disorders are elevated circulating levels of vasopressin, the peptide hormone that regulates renal water excretion. Circulating vasopressin plays a critical role in extra-cellular fluid expansion and development of hypertension, thus contributes to the pathogenesis of the disease. Vasopressin has clear long-term actions in the kidney, associated with vasopressin receptor activated processes and transcriptional regulation. Circulating vasopressin also increases the concentrating capacity of the renal medulla by activating the counter current mechanism. The result is an increase in medullary osmotic stress that can directly activate renal cell signaling pathways and gene transcription. Thus specific effects of vasopressin on gene expression are not delineated from secondary alterations associated with this change in medullary osmolality. Preliminary data, from in vivo studies in mice, identifies a role for vasopressin in activating endoplasmic reticulum stress (ER stress) in collecting duct cells. ER stress may be the key to how collecting duct cells survive large increases in medullary osmotic stress during anti-diuresis. Thus we will determine if vasopressin plays a preconditioning role in the medulla to protect collecting duct cells from apoptosis while continuing to upregulate aquaporin-2 expression and increase collecting duct water permeability. We have also identified a novel vasopressin- signaling pathway that decreases the expression of steroid hormone inactivating enzymes in the collecting duct and propose that this vasopressin-mediated pathway may indirectly enhance ENaC expression. Our studies will utilize three complementary model systems, cells, tubule suspensions and animal models to address our central hypothesis that vasopressin promotes AQP2- and ENaC-dependent pathways through direct (V2R) and indirect (osmotic stress) mechanisms. Specific Aims are: 1) To determine if increases in local solute concentrations activate ER stress proteins and protect collecting duct cells from further osmotic stress 2) To determine if vasopressin directly mediates the up-regulation of ER stress proteins via a V2 receptor pathway 3) To determine if vasopressin directly mediates the down-regulation of steroid hormone enzymes via a V2 receptor pathway.