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

水通道水通道蛋白-2（AQP 2）是介导收集中的水运输的主要水通道。 抗利尿激素（ADH）也称为血管加压素（VP），可刺激肾脏导管（CD）。我们和 其他人已经对AQP 2的运输及其调节机制进行了多年的广泛研究。在 在过去的5年里，我们的研究发现了AQP 2的几个重要的和以前未被认识的方面：1） AQP 2与粘附分子和主要细胞外基质（ECM）受体β1 整联蛋白通过与β1整合素的相互作用，AQP 2调节β1整合素的运输，并促进β1整合素的表达。 肾小管细胞迁移; 2）极化的AQP 2运输到顶膜涉及基底外侧插入， 通过转胞吞作用重定向，因此，可能受到ECM的调节提示; 3）更多 最近，我们已经确定了整合素信号通路的一个主要下游靶点，整合素相关的 激酶（ILK）通过调节肌动蛋白细胞骨架来调节AQP 2再循环。这些数据开启了一个新的视角 AQP 2运输和整合素-ECM信号传导的密切相互作用，以及它们相互作用的重要性， 调节上皮结构和功能。为了进一步了解它，我们产生了转基因动物， 肾集合管中的主细胞（PC）中特异性β1整联蛋白缺失。很有趣的是， 我们发现，CD PC中β1整合素的缺失会导致显著的肾小管损伤和间质纤维化 TGF-β信号级联反应显著激活。KO小鼠在6-8岁时发生肾衰竭和早期死亡 周的年龄。此外，年轻KO和成年半合子KO小鼠呈现高度集中的 尿和水的利尿能力受损。有一个明显的和持久的顶膜 在同源和半合子β1整联蛋白KO小鼠中，CD PC中AQP 2的积累。基于这两 有趣的观察，我们提出了一个全面的研究计划，以1）确定的关键功能， PC特异性β1整合素信号在维持集合管完整性中的作用，并具体解剖上皮细胞 在β1整合素KO中促进TGF-β活化和随后的间质纤维化的机制 动物;和2）表征β1整联蛋白信号传导在细胞中AQP 2运输中的新调节作用， 尿液在肾脏中的浓度。我们建议的研究是逻辑上的整合，并集中在两个重要的 急性CD损伤/纤维化和水潴留的过程。AQP 2和β1整合素之间的相互作用， 因此，参与介导细胞损伤和水重吸收。他们将做出重要贡献， 更好地理解从根本上至关重要，但被忽视的上皮因素，启动和促进 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 肾脏中的运输。它可以作为响应血流动力学的水稳态的局部调节器 和体积变化。

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.