Department of Clinical and Experimental Medicine, Clinica Medica 4, University of Padova, Padova, Italy.
J Hypertens. 2010 Jan;28(1):111-8. doi: 10.1097/HJH.0b013e328332b738.
Angiotensin II (Ang II) signaling via type 1 receptor (AT1R) has been extensively characterized, whereas Ang II signaling via type 2 receptors (AT2R), although counteracts actions mediated by AT1R, is still not completely understood. Bartter's/Gitelman's patients (BS/GS) have intrinsically blunted AT1R signaling, making them a good model to examine Ang II signaling via AT2R with particular emphasis on mitogen-activated protein kinase phosphatase 1 (MKP-1) that interacts with the Ang II-stimulated ERK pathway of cell signaling.
BS/GS and healthy controls fibroblasts AT1R and AT2R level and the time course of Ang II's effect on MKP-1 levels and ERK1/2 phosphorylation over 1-h time course were assessed by western blot. The time course of Ang II's effect on MKP-1 levels and ERK1/2 phosphorylation alone or in the presence of either PD123319, an AT2R blocker, or Losartan, an AT1R blocker, or in combination was characterized.
AT1R and AT2R levels did not differ between BS/GS and healthy controls. Ang II induced ERK1/2 phosphorylation in BS/GS fibroblasts, but peak ERK1/2 phosphorylation declined more rapidly than that in control and BS/GS fibroblasts also exhibited increased MKP-1 levels at 30-min incubation. PD123319, an AT2R blocker in BS/GS fibroblasts, abolished the increased MKP-1 and ERK1/2 phosphorylation time course became same as that for control. Losartan, an AT1R blocker, alone altered the time course of control fibroblast MKP-1 to mimic the increase seen in BS/GS fibroblasts, whereas ERK1/2 declined concomitantly. Treatment with Losartan and PD123319 in controls reduced MKP-1 and elevated ERK1/2 phosphorylation to the level observed in BS/GS patients treated with PD123319.
ERK1/2 phosphorylation time course found in BS/GS fibroblasts tracked changes in MKP-1 levels and incubation with an AT2R blocker, PD123319, abrogated those responses. Losartan, an AT1R blocker, reproduced these changes in healthy controls, whereas the presence of both AT1R and AT2R inhibitors in controls abolished these changes. These data strongly suggest that MKP-1 is a major effector in altering ERK1/2 phosphorylation status. Moreover, the results provide insight into the blunted responses in BS/GS reported for Ang II short-term and long-term effects, the mechanisms responsible, and thereby yield additional support for the role of AT2R signaling in the proposed effects of Ang II AT1R blockers beyond AT1R blockade.
血管紧张素 II（Ang II）通过 1 型受体（AT1R）的信号转导已得到广泛研究，而 Ang II 通过 2 型受体（AT2R）的信号转导，尽管与 AT1R 介导的作用相反，但仍未完全理解。巴特氏/吉尔曼氏病（BS/GS）患者的 AT1R 信号转导固有地减弱，使他们成为研究 Ang II 通过 AT2R 信号转导的良好模型，特别强调丝裂原活化蛋白激酶磷酸酶 1（MKP-1），它与 Ang II 刺激的细胞信号 ERK 通路相互作用。
通过 Western blot 评估 BS/GS 和健康对照成纤维细胞 AT1R 和 AT2R 水平以及 Ang II 在 1 小时时间过程中对 MKP-1 水平和 ERK1/2 磷酸化的作用的时间过程。还描述了 Ang II 对 MKP-1 水平和 ERK1/2 磷酸化的作用的时间过程，单独或存在 PD123319（AT2R 阻滞剂）或 Losartan（AT1R 阻滞剂）或两者组合的时间过程。
BS/GS 和健康对照之间的 AT1R 和 AT2R 水平没有差异。Ang II 在 BS/GS 成纤维细胞中诱导 ERK1/2 磷酸化，但峰值 ERK1/2 磷酸化的下降速度快于对照和 BS/GS 成纤维细胞，并且在 30 分钟孵育时也表现出增加的 MKP-1 水平。PD123319（BS/GS 成纤维细胞中的 AT2R 阻滞剂）消除了增加的 MKP-1，并且 ERK1/2 磷酸化的时间过程变得与对照相同。AT1R 阻滞剂 Losartan 单独改变了对照成纤维细胞 MKP-1 的时间过程，使其类似于 BS/GS 成纤维细胞中观察到的增加，而 ERK1/2 则同时下降。在对照中用 Losartan 和 PD123319 处理降低了 MKP-1 并升高了 ERK1/2 磷酸化水平，达到 PD123319 处理的 BS/GS 患者的水平。
BS/GS 成纤维细胞中发现的 ERK1/2 磷酸化时间过程与 MKP-1 水平的变化相关，并且用 AT2R 阻滞剂 PD123319 孵育消除了这些反应。AT1R 阻滞剂 Losartan 在健康对照中复制了这些变化，而在对照中存在 AT1R 和 AT2R 抑制剂则消除了这些变化。这些数据强烈表明 MKP-1 是改变 ERK1/2 磷酸化状态的主要效应物。此外，这些结果提供了对 Ang II 短期和长期作用中报告的 BS/GS 中减弱反应的深入了解，其机制，并为 Ang II AT1R 阻滞剂的拟议作用中的 AT2R 信号转导提供了额外的支持，而不仅仅是 AT1R 阻断。
