From the British Heart Foundation Centre of Research Excellence, Division of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
Hypertension. 2014 Sep;64(3):530-40. doi: 10.1161/HYPERTENSIONAHA.114.03089. Epub 2014 Apr 28.
Tetrahydrobiopterin (BH4) is an essential cofactor for endothelial nitric oxide synthase (eNOS) function and NO generation. Augmentation of BH4 levels can prevent eNOS uncoupling and can improve endothelial dysfunction in vascular disease states. However, the physiological requirement for de novo endothelial cell BH4 biosynthesis in eNOS function remains unclear. We generated a novel mouse model with endothelial cell-specific deletion of GCH1, encoding GTP cyclohydrolase 1, an essential enzyme for BH4 biosynthesis, to test the cell-autonomous requirement for endothelial BH4 biosynthesis in vivo. Mice with a floxed GCH1 allele (GCH1(fl/fl)) were crossed with Tie2cre mice to delete GCH1 in endothelial cells. GCH1(fl/fl)Tie2cre mice demonstrated virtually absent endothelial NO bioactivity and significantly greater O2 (•-) production. GCH1(fl/fl)Tie2cre aortas and mesenteric arteries had enhanced vasoconstriction to phenylephrine and impaired endothelium-dependent vasodilatations to acetylcholine and SLIGRL. Endothelium-dependent vasodilatations in GCH1(fl/fl)Tie2cre aortas were, in part, mediated by eNOS-derived hydrogen peroxide (H2O2), which mediated vasodilatation through soluble guanylate cyclase. Ex vivo supplementation of aortic rings with the BH4 analogue sepiapterin restored normal endothelial function and abolished eNOS-derived H2O2 production in GCH1(fl/fl)Tie2cre aortas. GCH1(fl/fl)Tie2cre mice had higher systemic blood pressure than wild-type littermates, which was normalized by NOS inhibitor, NG-nitro-L-arginine methyl ester. Taken together, these studies reveal an endothelial cell-autonomous requirement for GCH1 and BH4 in regulation of vascular tone and blood pressure and identify endothelial cell BH4 as a pivotal regulator of NO versus H2O2 as alternative eNOS-derived endothelial-derived relaxing factors.
四氢生物蝶呤（BH4）是内皮型一氧化氮合酶（eNOS）功能和 NO 生成的必需辅助因子。增加 BH4 水平可以防止 eNOS 解偶联，并可以改善血管疾病状态下的内皮功能障碍。然而，eNOS 功能中内源性细胞 BH4 生物合成的生理需求尚不清楚。我们生成了一种新型的小鼠模型，内皮细胞特异性缺失编码 BH4 生物合成必需酶——GTP 环水解酶 1（GCH1）的基因，以在体内测试内皮细胞 BH4 生物合成的细胞自主需求。具有 floxed GCH1 等位基因（GCH1(fl/fl)）的小鼠与 Tie2cre 小鼠杂交，使 GCH1 在内皮细胞中缺失。GCH1(fl/fl)Tie2cre 小鼠表现出几乎不存在的内皮一氧化氮生物活性和显著增加的 O2(•-)生成。GCH1(fl/fl)Tie2cre 主动脉和肠系膜动脉对苯肾上腺素的血管收缩增强，对乙酰胆碱和 SLIGRL 的内皮依赖性血管舒张受损。GCH1(fl/fl)Tie2cre 主动脉的内皮依赖性血管舒张部分由 eNOS 衍生的过氧化氢（H2O2）介导，H2O2 通过可溶性鸟苷酸环化酶介导血管舒张。在 GCH1(fl/fl)Tie2cre 主动脉的 ex vivo 补充 BH4 类似物 sepiapterin 恢复了正常的内皮功能，并消除了 GCH1(fl/fl)Tie2cre 主动脉中 eNOS 衍生的 H2O2 产生。GCH1(fl/fl)Tie2cre 小鼠的系统血压高于野生型同窝仔鼠，NOS 抑制剂 NG-硝基-L-精氨酸甲酯可使其正常化。综上所述，这些研究揭示了 GCH1 和 BH4 在调节血管张力和血压中的内皮细胞自主需求，并确定了内皮细胞 BH4 是作为替代 eNOS 衍生的内皮衍生松弛因子的 NO 与 H2O2 的关键调节剂。
