Salt-Sensitive Hypertension: Role of renal superoxide

由粗大的上行支（THAL）引起的异常盐潴留导致盐敏感性高血压。流量升高 拉伸和剪切应力均刺激NADPH氧化酶4（NOX 4）和NO合成塔尔O2 NO合成酶3（NOS 3）。我们报道了血流刺激的塔尔Na重吸收 依赖于O2-和蛋白激酶C α（PKCα），但流动诱导的NO缓冲流动刺激的NaCl 重吸收通过直接抑制NaCl运输和钝化流动诱导的O2-。高盐饮食会增加塔尔 我们报道了它通过增加NOS 3的表达和活性来增强塔尔NO的产生， 在苏氨酸495（T495）处的磷酸化，这是由PKC修饰的抑制位点。因此，盐诱导的 血流通过NO预防盐敏感性高血压：血流诱导的拉伸和剪切的机械转导 上皮细胞中应激可通过TRPV 4通道和/或纤毛和TRPV 4-TRPP 2通道发生。我们发现 流动诱导的牵张刺激TRPV 4，增加细胞内Ca（Cai）并刺激O2-。我们还展示 TRPV 4介导流动诱导的Cai和NO增加。 剪切应力，两者都可能参与NO的产生。如果是这样的话，拉伸和剪切应力可能会不同地激活 TRPV 4通道和纤毛/TRPV 4-TRPP 2通道。这将使细胞能够区分拉伸- 和剪切应力升高的Cai。在Dahl盐敏感大鼠（SS）中，O2-和NO之间的失衡有利于 前者导致盐引起的血压升高，但原因不明。我们的数据显示， TRPV 4依赖的Cai增加和流动诱导的O2产生在SS中比耐盐（SR）更大 然而，流动诱导的NO产生减少。这种减少不是由于O2-或 NOS 3表达的差异。我们还表明，高盐饮食增加了流动诱导的差异， Cai和O2-在SS和SR THAL之间起作用，并导致NOS 3表达的差异。因此，我们假设 SS THAL显示TRPV 4通道活性增加，以响应盐增强的管腔流动， 异常升高的Cai和O2-生产的NOX 4。慢性升高的O2-钝化血流诱导的NO 由于盐刺激的NOS 3表达减少，T495的NOS 3磷酸化增强， 减少四氢生物蝶呤（BH 4），导致THL的盐保留和BP的盐敏感性。我们建议3 目标。目的1：升高血流和牵张刺激SS中TRPV 4通道活性高于SR THAL 导致Cai、NOX 4产生的O2-、PKCα激活和NaCl重吸收的显著增加。目标二： SS THALs中慢性升高的O2-减弱了流动诱导的剪切应力刺激NO合成的能力 由于T495处NOS 3磷酸化增强，BH 4减少，盐刺激NOS 3减少， 而不是通过清除或影响纤毛信号传导。目的3：流量诱导的O2-和 随后SS THAL中NO产生的减少导致盐潴留和盐敏感性高血压。这 建议可以提供一个根本的解释不同的数据有关盐敏感性的BP在SS。

Abnormal salt retention by thick ascending limbs (THALs) causes salt-sensitive hypertension. Flow elevates both stretch and shear stress which stimulates THAL O2- synthesis by NADPH oxidase 4 (NOX4) and NO production by NO synthase 3 (NOS3), respectively. We reported that flow-stimulated THAL Na reabsorption depends on O2- and protein kinase C α (PKCα) but that flow-induced NO buffers flow-stimulated NaCl reabsorption by directly inhibiting NaCl transport and blunting flow-induced O2-. A high-salt diet increases THAL flow and we reported it enhances THAL NO production by increasing NOS3 expression and activity via de- phosphorylation at threonine 495 (T495), an inhibitory site modified by PKC. Thus salt-induced increases in flow prevent salt-sensitive hypertension via NO. Mechano-transduction of flow-induced stretch and shear stress in epithelia may occur via TRPV4 channels and/or cilia and TRPV4-TRPP2 channels. We showed that flow-induced stretch stimulates TRPV4, increases intracellular Ca (Cai) and stimulates O2-. We also showed that TRPV4 mediates flow-induced increases in Cai and NO. Since cilia and TRPV4-TRPP2 channels sense shear stress, both may be involved in NO production. If so, stretch and shear stress may differentially activate TRPV4 channels and cilia/TRPV4-TRPP2 channels, respectively. This would allow cells to distinguish stretch- and shear stress-elevated Cai. In Dahl salt-sensitive rats (SS) an imbalance between O2- and NO favoring the former causes salt-induced increases in BP but the cause is unknown. Our data show that stretch-induced TRPV4-dependent increases in Cai and flow-induced O2- production are greater in SS than salt-resistant (SR) THALs; however flow-induced NO production is reduced. This decrease is NOT due to scavenging by O2- or differences in NOS3 expression. We also show that a high-salt diet augments the differences in flow-induced Cai and O2- between SS and SR THALs, and causes a difference in NOS3 expression. Thus, we hypothesize that SS THALs display increased TRPV4 channel activity in response to salt-enhanced luminal flow causing abnormally elevated Cai and O2- production by NOX4. Chronically elevated O2- blunts flow-induced NO synthesis due to diminished salt-stimulated NOS3 expression, enhanced NOS3 phosphorylation at T495 and reduced tetrahydrobiopterin (BH4) resulting in salt retention by THALs and salt-sensitivity of BP. We propose 3 aims. Aim 1: Elevating flow and stretch stimulates TRPV4 channel activity more in SS than SR THALs resulting in greater increases in Cai, O2- production by NOX4, PKCα activation and NaCl reabsorption. Aim 2: Chronically elevated O2- in SS THALs blunts the ability of flow-induced shear stress to stimulate NO synthesis as a result of enhanced phosphorylation of NOS3 at T495, reduced BH4, and diminished salt-stimulated NOS3 expression rather than by scavenging or affecting ciliary signaling. Aim 3: Elevated flow-induced O2- and consequent reduced NO production in SS THALs cause salt retention and salt-sensitive hypertension. This proposal may provide a fundamental explanation for disparate data concerning salt-sensitivity of BP in SS.