Department of General and Environmental Physiology, University of Bari, Bari, Italy.
Am J Hypertens. 2011 Jul;24(7):822-8. doi: 10.1038/ajh.2011.47. Epub 2011 Mar 31.
Sodium-sensitive hypertension is caused by renal tubular dysfunction, leading to increased retention of sodium and water. Previous findings have suggested that single-nucleotide polymorphisms of the cytoskeletal protein, α-adducin, are associated with increased membrane expression of the Na/K pump and abnormal renal sodium transport in Milan hypertensive strain (MHS) rats and in humans. However, the possible contribution of renal aquaporins (AQPs) to water retention remains undefined in MHS rats.
Kidneys from MHS rats were analyzed and compared with those from age-matched Milan normotensive strain (MNS) animals by quantitative-PCR, immunoblotting, and immunoperoxidase. Endocytosis assay was performed on renal cells stably expressing AQP4 and co-transfected either with wild-type normotensive (NT) or with mutated hypertensive (HT) α-adducin.
Semiquantitative immunoblotting revealed that AQP1 abundance was significantly decreased only in HT MHS whereas AQP2 was reduced in both young pre-HT and adult-HT animals. On the other hand, AQP4 was dramatically upregulated in MHS regardless of the age. These results were confirmed by immunoperoxidase microscopy. Endocytosis assays clearly showed that the expression of mutated adducin strongly reduced the rate of constitutive AQP4 endocytosis, thereby increasing its abundance at the plasma membrane.
We provide here the first evidence that AQP1, AQP2, and AQP4 are dysregulated in the kidneys of MHS animals. In particular, we provide evidence that α-adducin mutations may be responsible for AQP4 upregulation. The downregulation of AQP1 and AQP2 and the upregulation of AQP4 may be relevant for the onset and maintenance of salt-sensitive hypertension.
钠敏性高血压是由肾小管功能障碍引起的，导致钠和水的潴留增加。先前的研究结果表明，细胞骨架蛋白α-辅肌动蛋白的单核苷酸多态性与米兰高血压大鼠（MHS）和人类中 Na/K 泵的膜表达增加和异常肾脏钠转运有关。然而，在 MHS 大鼠中，肾脏水通道蛋白（AQP）对水潴留的可能贡献仍未定义。
通过定量 PCR、免疫印迹和免疫过氧化物酶分析，比较了 MHS 大鼠和年龄匹配的米兰正常血压大鼠（MNS）肾脏，并进行了内吞测定。AQP4 稳定表达的肾细胞进行了内吞测定，并用野生型正常血压（NT）或突变型高血压（HT）α-辅肌动蛋白共转染。
半定量免疫印迹显示，仅在 HT MHS 中 AQP1 的丰度显著降低，而在年轻的 pre-HT 和成年-HT 动物中 AQP2 减少。另一方面，AQP4 在 MHS 中无论年龄大小均显著上调。免疫过氧化物酶显微镜证实了这些结果。内吞测定清楚地表明，突变辅肌动蛋白的表达强烈降低了 AQP4 的组成性内吞作用的速率，从而增加了其在质膜上的丰度。
我们在这里首次提供证据表明，AQP1、AQP2 和 AQP4 在 MHS 动物的肾脏中失调。特别是，我们提供了证据表明，α-辅肌动蛋白突变可能导致 AQP4 的上调。AQP1 和 AQP2 的下调以及 AQP4 的上调可能与盐敏感性高血压的发生和维持有关。
