Department of Pathophysiology, Guizhou Medical University, Guiyang, China; Guizhou Provincial Key Laboratory of Pathogenesis & Drug Research on Common Chronic Diseases, Guizhou Medical University, Guiyang, China.
Key Laboratory of Endemic and Ethnic Diseases, Ministry of Education, Guizhou Medical University, Guiyang, China.
Exp Cell Res. 2024 Apr 1;437(1):113998. doi: 10.1016/j.yexcr.2024.113998. Epub 2024 Mar 20.
Plasma saturated free fatty acid (FFA)-induced endothelial dysfunction (ED) contributes to the pathogenesis of atherosclerosis and cardiovascular diseases. However, the mechanism underlying saturated FFA-induced ED remains unclear. This study demonstrated that palmitic acid (PA) induced ED by activating the NADPH oxidase (NOX)/ROS signaling pathway to activate protein phosphatase 4 (PP4) and protein phosphatase 2A (PP2A), thereby reducing endothelial nitric oxide synthase (eNOS) phosphorylation at Ser633 and Ser1177, respectively. Okadaic acid (OA) and fostriecin (FST), which are inhibitors of PP2A, inhibited the PA-induced decreases in eNOS phosphorylation at Ser633 and Ser1177. The antioxidants N-acetylcysteine (NAC) and apocynin (APO) or knockdown of gp91phox or p67phox (NOX subunits) restored PA-mediated downregulation of PP4R2 protein expression and eNOS Ser633 phosphorylation. Knockdown of the PP4 catalytic subunit (PP4c) specifically increased eNOS Ser633 phosphorylation, while silencing the PP2A catalytic subunit (PP2Ac) restored only eNOS Ser1177 phosphorylation. Furthermore, PA dramatically decreased the protein expression of the PP4 regulatory subunit R2 (PP4R2) but not the other regulatory subunits. PP4R2 overexpression increased eNOS Ser633 phosphorylation, nitric oxide (NO) production, cell migration and tube formation but did not change eNOS Ser1177 phosphorylation levels. Coimmunoprecipitation (Co-IP) suggested that PP4R2 and PP4c interacted with the PP4R3α and eNOS proteins. In summary, PA decreases PP4R2 protein expression through the Nox/ROS pathway to activate PP4, which contributes to ED by dephosphorylating eNOS at Ser633. The results of this study suggest that PP4 is a novel therapeutic target for ED and ED-associated vascular diseases.
血浆饱和游离脂肪酸（FFA）诱导的内皮功能障碍（ED）是动脉粥样硬化和心血管疾病发病机制的关键因素。然而，饱和FFA 诱导 ED 的机制尚不清楚。本研究表明，软脂酸（PA）通过激活 NADPH 氧化酶（NOX）/ROS 信号通路诱导 ED，从而激活蛋白磷酸酶 4（PP4）和蛋白磷酸酶 2A（PP2A），进而分别降低内皮型一氧化氮合酶（eNOS）丝氨酸 633 和丝氨酸 1177 的磷酸化。作为 PP2A 抑制剂的 okadaic acid（OA）和 fostriecin（FST）抑制了 PA 诱导的 eNOS 丝氨酸 633 和丝氨酸 1177 磷酸化减少。抗氧化剂 N-乙酰半胱氨酸（NAC）和 apocynin（APO）或 gp91phox 或 p67phox（NOX 亚基）的敲低恢复了 PA 介导的 PP4R2 蛋白表达和 eNOS 丝氨酸 633 磷酸化的下调。PP4 催化亚基（PP4c）的敲低特异性增加 eNOS 丝氨酸 633 磷酸化，而沉默 PP2A 催化亚基（PP2Ac）仅恢复 eNOS 丝氨酸 1177 磷酸化。此外，PA 显著降低了 PP4 调节亚基 R2（PP4R2）的蛋白表达，但不影响其他调节亚基。PP4R2 过表达增加 eNOS 丝氨酸 633 磷酸化、一氧化氮（NO）产生、细胞迁移和管形成，但不改变 eNOS 丝氨酸 1177 磷酸化水平。免疫共沉淀（Co-IP）表明 PP4R2 和 PP4c 与 PP4R3α 和 eNOS 蛋白相互作用。总之，PA 通过 Nox/ROS 途径降低 PP4R2 蛋白表达，激活 PP4，通过去磷酸化 eNOS 丝氨酸 633 导致 ED。本研究结果表明，PP4 是 ED 和 ED 相关血管疾病的新的治疗靶点。
