Research Express@NCKU - Articles Digest
Research Express@NCKU Volume 23 Issue 2 - January 11, 2013 [ http://research.ncku.edu.tw/re/articles/e/20130111/3.html ]
Angiotensin II inhibits neuronal nitric oxide synthase
activation through the ERK1/2-RSK signaling pathway
to modulate central control of blood pressure
Wen-Han Cheng
1,2,3, Pei-Jung Lu
*4, Wen-Yu Ho
5, Che-Se Tung
6, Pei-Wen Cheng
1, Michael
Hsiao
7, Ching-Jiunn Tseng
1,2,3,81Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung; 2Institute of Clinical Medicine, National Yang-Ming University, Taipei; 3Institute of Biomedical Sciences, National Sun Yat-sen University, Kaohsiung; 4Institute of Clinical Medicine, National Cheng-Kung University, Tainan; 5Department of Internal Medicine, Zuoying Armed Forces General Hospital, Kaohsiung; 6Department of Physiology, National Defense Medical Center, Taipei;
7Genomics Research Center, Academia Sinica, Taipei; and 8Department of Pharmacology, National Defense Medical Center, Taipei, Taiwan.
Circulation Research 2010;106:788-795.
R
ationale: Angiotensin (Ang) II exerts diverse physiological actions in both the peripheral and central neural systems. It was reported that the activity of Ang II is higher in the nucleus tractus solitarii (NTS) of spontaneously hypertensive rats (SHRs) and that angiotensin type-1 receptors are colocalized with NAD(P)H oxidase in the neurons of the NTS, resulting in the induction of local reactive oxygen species production by Ang II. However, the signaling mechanisms of Ang II that induce hypertension remain unclear. Objective: The aim of this study was to investigate the possible signaling pathways involved in Ang II–mediated blood pressure regulation in the NTS. Methods and Results:Male SHRs were treated with losartan or tempol for 2 weeks, after which systolic blood pressure was observed to decrease significantly. Dihydroethidium staining showed many cells with high reactive oxygen species in the NTS of SHRs. The addition of losartan or tempol decreased the numbers of reactive oxygen species–positive cells in the NTS. The systemic administration of losartan or tempol reduced the systolic blood pressure and increased NO production. Immunoblotting and immunohistochemical analysis further showed that inhibition of Ang II activity by losartan or tempol significantly increased the expression extracellular signal-regulated kinase (ERK)1/2, ribosomal protein S6 kinase (RSK), and also increased neuronal NO synthase (nNOS) phosphorylation. RSK was also found to bind directly to nNOS and induce phosphorylation at the Ser1416 position. Conclusions: Taken together, these results suggest that the ERK1/2-RSK-nNOS signaling pathway may play a significant role in Ang II–mediated central blood pressure regulation.
Figure 1. ROS production and cardiovascular effect on SHR after losartan and tempol treatment. (A) In situ
Research Express@NCKU - Articles Digest
evaluations of ROS (red fluorescence) production in cells (blue fluorescence) of the NTS after addition of Ang II inhibitors. (B) The systolic blood pressure of SHR mice (filled circles) and mice treated with losartan (open circles) or tempol (filled triangles) for two weeks was measured as time points indicated. Data are shown as means ±SEM (n=6).
Figure 2. Immunoblotting and immunohistochemical analysis of nNOSS1416 phosphorylation in the NTS following treatment with losartan or tempol. (A) Diagrammatic representation of the rat NTS. (B) Immunoblot and (C) densitometric analysis of P-nNOSS1416 level in the NTS of SHRs. Data are shown as means±SEM (n=6). *P<0.05 and #P<0.05 compared with SHR controls. (D) In situ immunohistochemical staining and (E) quantitative analysis of P-nNOSS1416-positive cells after treatment with losartan or tempol. The arrowhead indicates the central
canal. Arrows indicate the P-nNOSS1416-positive cells. The scale bar represents 200 μm.
Figure 3. Phosphorylation of nNOS, RSK, and Erk1/2 in the NTS. (A) Lysates from the NTS were assayed and used for coimmunoprecipitation of nNOS and RSK. (B) RSK-associated kinase activity was determined using nNOS as a substrate. (C) Quantitative immunoblotting analysis of RSK and ERK1/2 phosphorylation in the NTS following treatment with losartan or tempol. (D) The proposed Ang II–induced signaling pathway in the regulation of blood pressure in the NTS of SHRs.
