Li Ningjun, Zimpelmann Joseph, Cheng Keding, Wilkins John A, Burns Kevin D
Department of Medicine, Ottawa Hospital, and the Kidney Research Centre, Ottawa Health Research Institute, University of Ottawa, Ontario, Canada.
Am J Physiol Renal Physiol. 2005 Feb;288(2):F353-62. doi: 10.1152/ajprenal.00144.2004. Epub 2004 Oct 5.
ANG converting enzyme (ACE) 2 (ACE2) is a homologue of ACE, which is not blocked by conventional ACE inhibitors. ACE2 converts ANG 1-10 (ANG I) to ANG 1-9, which can be hydrolyzed by ACE to form the biologically active peptide ANG 1-7. ACE2 is expressed in the kidney, but its precise intrarenal localization is unclear, and the role of intrarenal ACE2 in the production of ANG 1-7 is unknown. The present studies determined the relative distribution of ACE2 in the rat kidney and defined its role in the generation of ANG 1-7 in proximal tubule. In microdissected rat nephron segments, semiquantitative RT-PCR revealed that ACE2 mRNA was widely expressed, with relatively high levels in proximal straight tubule (PST). Immunohistochemistry demonstrated ACE2 protein in tubular segments, glomeruli, and endothelial cells. Utilizing mass spectrometry, incubation of isolated PSTs with ANG I (10(-6) M) led to generation of ANG 1-7 (sensitivity of detection > 1 x 10(-9) M), accompanied by the formation of ANG 1-8 (ANG II) and ANG 1-9. The ACE2 inhibitor DX600 completely blocked ANG I-mediated generation of ANG 1-7. Incubation of PSTs with ANG 1-9 also led to generation of ANG 1-7, an effect blocked by the ACE inhibitor captopril or enalaprilat, but not by DX600. Incubation of PSTs with ANG II or luminal perfusion of ANG II did not result in detection of ANG 1-7. The results indicate that ACE2 is widely expressed in rat nephron segments and contributes to the production of ANG 1-7 from ANG I in PST. ANG II may not be a major substrate for ACE2 in isolated PST. The data suggest that ACE2-mediated production of ANG 1-7 represents an important component of the proximal tubular renin-ANG system.
血管紧张素转换酶（ACE）2（ACE2）是ACE的同源物，传统的ACE抑制剂不会对其产生抑制作用。ACE2可将血管紧张素1-10（ANG I）转化为血管紧张素1-9，血管紧张素1-9可被ACE水解形成生物活性肽血管紧张素1-7。ACE2在肾脏中表达，但其在肾脏内的确切定位尚不清楚，肾脏内ACE2在血管紧张素1-7生成中的作用也尚不明确。本研究确定了ACE2在大鼠肾脏中的相对分布，并明确了其在近端小管血管紧张素1-7生成中的作用。在显微解剖的大鼠肾单位节段中，半定量逆转录-聚合酶链反应（RT-PCR）显示ACE2信使核糖核酸（mRNA）广泛表达，在近端直小管（PST）中水平相对较高。免疫组织化学显示ACE2蛋白存在于肾小管节段、肾小球和内皮细胞中。利用质谱分析，将分离的PST与ANG I（10⁻⁶ M）孵育可导致血管紧张素1-7的生成（检测灵敏度>1×10⁻⁹ M），同时伴有血管紧张素1-8（ANG II）和血管紧张素1-9的形成。ACE2抑制剂DX600完全阻断了ANG I介导的血管紧张素1-7的生成。将PST与血管紧张素1-9孵育也可导致血管紧张素1-7的生成，这一作用被ACE抑制剂卡托普利或依那普利拉阻断，但未被DX600阻断。将PST与ANG II孵育或向管腔内灌注ANG II未检测到血管紧张素1-7。结果表明，ACE2在大鼠肾单位节段中广泛表达，并有助于在PST中由ANG I生成血管紧张素1-7。在分离的PST中，ANG II可能不是ACE2的主要底物。数据表明，ACE2介导的血管紧张素1-7的生成是近端小管肾素-血管紧张素系统的重要组成部分。
