Division of Nephrology and Hypertension, Department of Medicine, Oregon Health and Science University, Portland, OR 97239, USA.
Clin Sci (Lond). 2012 Dec;123(11):635-47. doi: 10.1042/CS20120003.
In the present study, we investigated the activity of the thiazide-sensitive NCC (Na(+)-Cl(-) co-transporter) in experimental metabolic syndrome and the role of insulin in NCC activation. Renal responses to the NCC inhibitor HCTZ (hydrochlorothiazide), as a measure of NCC activity in vivo, were studied in 12-week-old ZO (Zucker obese) rats, a model of the metabolic syndrome, and in ZL (Zucker lean) control animals, together with renal NCC expression and molecular markers of NCC activity, such as localization and phosphorylation. Effects of insulin were studied further in mammalian cell lines with inducible and endogenous expression of this molecule. ZO rats displayed marked hyperinsulinaemia, but no differences in plasma aldosterone, compared with ZL rats. In ZO rats, natriuretic and diuretic responses to NCC inhibition with HCTZ were enhanced compared with ZL rats, and were associated with a decrease in BP (blood pressure). ZO rats displayed enhanced Thr(53) NCC phosphorylation and predominant membrane localization of both total and phosphorylated NCC, together with a different profile in expression of SPAK (Ste20-related proline/alanine-rich kinase) isoforms, and lower expression of WNK4. In vitro, insulin induced NCC phosphorylation, which was blocked by a PI3K (phosphoinositide 3-kinase) inhibitor. Insulin-induced reduction in WNK4 expression was also observed, but delayed compared with the time course of NCC phosphorylation. In summary, we report increased NCC activity in hyperinsulinaemic rodents in conjunction with the SPAK expression profile consistent with NCC activation and reduced WNK4, as well as an ability of insulin to induce NCC stimulatory phosphorylation in vitro. Together, these findings indicate that hyperinsulinaemia is an important driving force of NCC activity in the metabolic syndrome with possible consequences for BP regulation.
在本研究中，我们研究了噻嗪类敏感的 NCC（钠-氯共转运蛋白）在实验性代谢综合征中的活性以及胰岛素在 NCC 激活中的作用。我们研究了 12 周龄 ZO（Zucker 肥胖）大鼠（代谢综合征模型）和 ZL（Zucker 瘦）对照动物的 NCC 抑制剂 HCTZ（氢氯噻嗪）肾反应，作为体内 NCC 活性的衡量标准，同时研究了肾 NCC 表达和 NCC 活性的分子标志物，如定位和磷酸化。我们还在具有该分子诱导和内源性表达的哺乳动物细胞系中进一步研究了胰岛素的作用。与 ZL 大鼠相比，ZO 大鼠表现出明显的高胰岛素血症，但血浆醛固酮没有差异。与 ZL 大鼠相比，ZO 大鼠对 NCC 抑制的 HCTZ 的排钠和利尿反应增强，并且与血压（BP）降低相关。ZO 大鼠表现出增强的 Thr（53）NCC 磷酸化和总 NCC 及其磷酸化形式的主要膜定位，同时 SPAK（Ste20 相关脯氨酸/丙氨酸丰富激酶）同工型的表达谱不同，WNK4 的表达水平较低。在体外，胰岛素诱导了 NCC 的磷酸化，而这种磷酸化被 PI3K（磷酸肌醇 3-激酶）抑制剂所阻断。还观察到胰岛素诱导的 WNK4 表达减少，但与 NCC 磷酸化的时间过程相比延迟。总之，我们报告了高胰岛素血症的啮齿动物中 NCC 活性增加，与 SPAK 的表达谱一致，提示 NCC 激活和 WNK4 减少，以及胰岛素在体外诱导 NCC 刺激性磷酸化的能力。这些发现表明，高胰岛素血症是代谢综合征中 NCC 活性的重要驱动力，可能对血压调节产生影响。
