Myocardial Infarction Research Laboratory, Department of Cardiology, Pulmonology, and Angiology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany.
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Nitric Oxide. 2022 Aug 1;125-126:69-77. doi: 10.1016/j.niox.2022.06.004. Epub 2022 Jun 23.
Arginase 1 (Arg1) is a ubiquitous enzyme belonging to the urea cycle that catalyzes the conversion of l-arginine into l-ornithine and urea. In endothelial cells (ECs), Arg1 was proposed to limit the availability of l-arginine for the endothelial nitric oxide synthase (eNOS) and thereby reduce nitric oxide (NO) production, thus promoting endothelial dysfunction and vascular disease. The role of EC Arg1 under homeostatic conditions is in vivo less understood. The aim of this study was to investigate the role of EC Arg1 on the regulation of eNOS, vascular tone, and endothelial function under normal homeostatic conditions in vivo and ex vivo. By using a tamoxifen-inducible EC-specific gene-targeting approach, we generated EC Arg1 KO mice. Efficiency and specificity of the gene targeting strategy was demonstrated by DNA recombination and loss of Arg1 expression measured after tamoxifen treatment in EC only. In EC Arg1 KO mice we found a significant decrease in Arg1 expression in heart and lung ECs and in the aorta, however, vascular enzymatic activity was preserved likely due to the presence of high levels of Arg1 in smooth muscle cells. Moreover, we found a downregulation of eNOS expression in the aorta, and a fully preserved systemic l-arginine and NO bioavailability, as demonstrated by the levels of l-arginine, l-ornithine, and l-citrulline as well as nitrite, nitrate, and nitroso-species. Lung and liver tissues from EC Arg1 KO mice showed respectively increase or decrease in nitrosyl-heme species, indicating that the lack of endothelial Arg1 affects NO bioavailability in these organs. In addition, EC Arg1 KO mice showed fully preserved acetylcholine-mediated vascular relaxation in both conductance and resistant vessels but increased phenylephrine-induced vasoconstriction. Systolic, diastolic, and mean arterial pressure and cardiac performance in EC Arg1 KO mice were not different from the wild-type littermate controls. In conclusion, under normal homeostatic conditions, lack of EC Arg1 expression is associated with a down-regulation of eNOS expression but a preserved NO bioavailability and vascular endothelial function. These results suggest that a cross-talk exists between Arg1 and eNOS to control NO production in ECs, which depends on both L-Arg availability and EC Arg1-dependent eNOS expression.
精氨酸酶 1（Arg1）是一种普遍存在的酶，属于尿素循环，可催化 l-精氨酸转化为 l-鸟氨酸和尿素。在内皮细胞（ECs）中，Arg1 被认为可限制内皮一氧化氮合酶（eNOS）中 l-精氨酸的可用性，从而减少一氧化氮（NO）的产生，从而促进内皮功能障碍和血管疾病。在体内，ECs 中 Arg1 的稳态条件下的作用理解得较少。本研究的目的是研究 EC Arg1 在体内和体外正常稳态条件下对 eNOS、血管张力和内皮功能的调节作用。通过使用他莫昔芬诱导的内皮细胞特异性基因靶向方法，我们生成了 EC Arg1 KO 小鼠。通过 DNA 重组证明了基因靶向策略的效率和特异性，并在仅 EC 中用他莫昔芬处理后测量了 Arg1 表达的丧失。在 EC Arg1 KO 小鼠中，我们发现心脏和肺 ECs 以及主动脉中的 Arg1 表达显著降低，但是血管酶活性得以保留，可能是由于平滑肌细胞中 Arg1 水平较高所致。此外，我们发现主动脉中 eNOS 表达下调，并且全身 l-精氨酸和 NO 生物利用度完全保留，这通过 l-精氨酸、l-鸟氨酸和 l-瓜氨酸以及亚硝酸盐、硝酸盐和亚硝酰基的水平来证明。EC Arg1 KO 小鼠的肺和肝组织分别显示出亚硝酰基血红素的增加或减少，表明内皮 Arg1 的缺乏会影响这些器官中的 NO 生物利用度。此外，EC Arg1 KO 小鼠在传导和阻力血管中均表现出乙酰胆碱介导的血管舒张完全保留，但对苯肾上腺素诱导的血管收缩作用增强。EC Arg1 KO 小鼠的收缩压、舒张压和平均动脉压以及心脏功能与野生型同窝对照无差异。总之，在正常稳态条件下，缺乏 EC Arg1 表达与 eNOS 表达下调有关，但 NO 生物利用度和血管内皮功能保留。这些结果表明，Arg1 和 eNOS 之间存在相互作用，以控制 ECs 中的 NO 产生，这取决于 l-精氨酸的可用性和 EC Arg1 依赖性 eNOS 表达。
