Novel roles of integrin b1 signaling in regulating principal cell function andmaintaining collecting duct integrity

水通道水通道蛋白-2(Aquaporin-2，AQP2)是一种主要的水通道，在集合过程中调节水的运输 肾脏的导管(CDs)对抗利尿激素(ADH)，也称为加压素(VP)做出反应。我们和 其他人多年来对AQP2贩运及其调控机制(S)进行了广泛的研究。在 在过去的5年里，我们的研究发现了AQP2：1的几个以前没有被认识到的重要方面) 水通道蛋白2出人意料地与黏附分子和主要细胞外基质受体β1相互作用 整合素。通过与β1整合素的相互作用，AQP2调控β1整合素的转运，并促进 肾小管上皮细胞迁移；2)极化的AQP2向根尖膜的运输涉及基侧插入和 通过跨细胞作用进行重定向，因此可能受到来自ECM的调节信号的影响；3)更多 最近，我们发现整合素信号通路的一个主要下游靶点，整合素连接 激酶(ILK)通过调节肌动蛋白细胞骨架来调节AQP2的循环。这些数据开辟了一个新的方面 AQP2转运和整合素-ECM信号的密切相互作用及其相互作用的重要性 在调节上皮结构和功能方面。为了进一步了解它，我们用 肾脏集合管中的主细胞(PC)中β1整合素的特异性缺失。非常有趣的是， 我们已经发现，删除CD PC中的β1整合素会导致显著的肾小管损伤和间质纤维化 明显激活转化生长因子-β信号转导通路。KO小鼠在6-8岁时出现肾功能衰竭和早期死亡 只有几周大。此外，幼年KO小鼠和成年半合子KO小鼠表现出高度浓缩的 尿液和利水能力受损。有一层显著且持久的根尖膜。 β-1整合素KO小鼠CD细胞中水通道蛋白2的积聚。基于这两点 耐人寻味的是，我们提出了一个全面的研究计划，以1)确定 PC特异性β1整合素信号在维持集合管完整性中的作用，并具体解剖上皮 转化生长因子-β活化和随后的β-1整合素KO间质纤维化的机制(S) 以及2)表征β-1整合素信号在AQP2细胞和 肾脏中的尿液浓度。我们建议的研究在逻辑上是整合的，并集中在两个重要的 急性镉损伤/纤维化和水分滞留的过程。AQP2和β1整合素之间的串扰可以， 因此，应同时参与细胞损伤和水分重吸收的调节。他们将做出重要的贡献 更好地理解启动和促进从根本上至关重要但被忽视的上皮因素 肾脏纤维化。他们还将揭示一种新的ECM-整合素介导的水调节机制 在肾脏中的运输。它可以作为局部的水平衡调节器，对血流动力学作出反应 和音量的变化。

The water channel aquaporin-2 (AQP2) is a major water channel that mediates water transport in the collecting ducts (CDs) of the kidney in response to the antidiuretic hormone (ADH), also called vasopressin (VP). We and others have studied extensively the AQP2 trafficking and its regulatory mechanism(s) for many years. In the past 5 years, our studies have uncovered several important and previously unrecognized aspects of AQP2: 1) AQP2 unexpectedly interacts with the adhesion molecule and major extracellular matrix (ECM) receptor, β1 integrin. Through interaction with β1 integrin, AQP2 modulates the trafficking of β1 integrin and promotes tubular cell migration; 2) Polarized AQP2 trafficking to the apical membrane involves basolateral insertion and redirection via transcytosis, and therefore, is potentially subjected to regulatory cues from the ECM; 3) More recently, we have identified that a major downstream target of the integrin signaling pathway, integrin-linked kinase (ILK) regulates AQP2 recycling via modulating the actin cytoskeleton. These data open a novel aspect of a close interplay of AQP2 trafficking and integrin-ECM signaling, and the importance of their interaction in modulating epithelial structure and function. To understand it further, we generated transgenic animals with a deletion of β1 integrin specifically in the principal cells (PCs) in the kidney collecting ducts. Very interestingly, we have found that deleting β1 integrin in the CD PCs causes significant tubular injury and interstitial fibrosis with significantly activated TGF-β signaling cascade. KO mice develop renal failure and early mortality at 6-8 weeks of age. In addition, the young KO and adult hemizygous KO mice presented with highly concentrated urine and impaired capability of water diuresis. There was a significant and persistent apical membrane accumulation of AQP2 in the CD PCs in the homo- and hemizygous β1 integrin KO mice. Based on these two intriguing observations, we proposed a comprehensive research program to 1) determine the critical function of PC specific β1 integrin signaling in maintaining collecting duct integrity, and dissect specifically, the epithelial mechanism(s) contributing to TGF-β activation and subsequent interstitial fibrosis in the β1 integrin KO animals; and 2) characterize the novel regulatory role of β1 integrin signaling in AQP2 trafficking in cells and urine concentration in the kidney. Our proposed studies are logically integrated and focus on two important processes of acute CD injury/fibrosis and water retention. Cross talk between AQP2 and β1 integrin could, therefore, be involved in mediating both cell injury and water reabsorption. They will contribute importantly to better understanding the fundamentally critical, but overlooked epithelial factors that initiate and promote fibrogenesis in kidney. They will also uncover a novel ECM-integrin mediated regulatory mechanism for water transport in the kidney. It could serve as a local regulator of water homeostasis in response to hemodynamic and volume changes.