Roles of I-2(PP2A) in the downregulation of eNOS Ser1177 phosphorylation by angiotensin II-activated PP2A

摘要

The chronic elevation of angiotensin II (Ang II) is an important cause of endothelial dysfunction (ED). The Ang II/type 1 receptor (AT(1)R) signaling pathway can cause endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) dysfunction through various mechanisms leading to ED. The modulation of eNOS phosphorylated at Ser1177 is an important mechanism upregulating eNOS activity. Protein phosphatase 2 A (PP2A) has been reported to dephosphorylate eNOS at Ser1177. The PP2A inhibitor 2 protein (I-2(PP2A)) is a specific endogenous inhibitor that binds the catalytic subunit of PP2A and directly inhibits PP2A activity. Therefore, we hypothesized that Ang II might attenuate I-2(PP2A) expression to activate PP2A, which downregulates eNOS Ser 1177 phosphorylation, leading to eNOS dysfunction. In our study, we used Ang II-treated human umbilical vein endothelial cells (HUVECs) and, found that the eNOS Ser1177 phosphorylation levels were downregulated, the activity of PP2A was increased, and I-2(PP2A) expression was decreased. Furthermore, these effects were blocked by candesartan (CAN). The phosphorylation levels of eNOS Ser1177 were decreased after I-2(PP2A) was knocked down by specific siRNA but increased after I-2(PP2A) overexpression. We also found that the Ang II treatment decreased the association of I-2(PP2A) with PP2A but increased the association between PP2A and eNOS. Taken together, our results suggest that Ang II activates PP2A by downregulating the I-2(PP2A) expression through the AT(1)R signaling pathway leading to the loss of eNOS Ser1177 phosphorylation and ED. (C) 2019 Elsevier Inc. All rights reserved.