Genetic Modification of the Heart The use of knockout mouse technology to achieve tissue selective expression of angiotensin converting enzyme Hong D. Xiao, Sebastien Fuchs, Kristen Frenzel, Lu Teng, Ping Li, Xiao Z. Shen, Jonathan Adams, Hui Zhao, George T. Keshelava, Kenneth E. Bernstein *, Justin M. Cole Department of Pathology and Laboratory Medicine, Rm. 7107A WMB, Emory University, Atlanta, GA 30322, USA Received 6 January 2004; accepted 26 February 2004 Abstract The resin angiotensin system (RAS) plays an essential role in blood pressure regulation and electrolyte homeostasis. The effecter peptide of the RAS, angiotensin II, is produced by angiotensin converting enzyme (ACE) in multiple tissues. Genetic deletion ofACE in mice resulted a phenotype of low blood pressure, anemia and kidney defects. However, it is not clear whether the lack of the systemic or the local production of angiotensin II caused these defects. To understand the role of local angiotensin II production, we developed a method to achieve tissue specific ACE expression through homologous recombination. In this review, we discuss mouse models in which endothelial ACE was eliminated and replaced by hepatic ACE. These studies suggest that both circulating angiotensin II and local angiotensin II production play a role in angiotensin II generation; the elimination of local angiotensin II generation up-regulates systemic production and maintains physiologic homeostasis. © 2004 Elsevier Ltd. All rights reserved. Keywords: Knockout mouse technology; ACE 1. Introduction The first indication that something in the kidney partici- pated in the control of blood pressure was studies by Tiger- stedt in 1898 [1]. Tigerstedt had discovered renin, but his experiments were difficult to reproduce and, more impor- tantly, the clinical appreciation of blood pressure was so limited that these studies were not expanded. Barely 15 years later, the clinical measurement of human blood pressure had become routine. When Goldblatt et al. [2] identified the kidney as a central regulator of blood pressure in 1934, the modern era of blood pressure investigation began. And like many areas of science, increased understanding paralleled the development of new scientific tools. For instance, the identification of angiotensin converting enzyme (ACE) in the production of angiotensin II, published in 1956, derived from the development of new techniques for separating small peptides, such as angiotensin I and angiotensin II [3,4]. Also, the development in 1977 of captopril, the first non-peptidic inhibitor of ACE led to a much greater understanding of the physiology of the renin–angiotensin system (RAS) [5]. Fi- nally, the onset of the molecular era in the 1980s led to the cloning of all the individual components of the RAS, includ- ing the first cloning of angiotensin receptors [6,7]. We now live in the genetic age where DNA is easily manipulated. Now, targeted homologous recombination in mouse embryonic stem (ES) cells is a unique tool that allows us to manipulate the mouse genome such that virtually any genetic change imagined can be created in a mouse [8]. In turn, this allows us to ask new questions about blood pressure control. Consider ACE, a protein expressed on the surface of vascular endothelial cells where it makes angiotensin II in immediate proximity to vascular smooth muscle, a critical target organ for this vasoconstrictor. Other tissues make ACE, including activated macrophages, ciliated gut epithe- lium, and areas of the brain. In the midst of this complexity, how can we investigate the specific physiologic role of ACE expression by a single tissue such as endothelium. ACE inhibitors could be used, but these pharmaceuticals are sys- temic in their effects. ACE could be genetically eliminated through knockout mutation of the ACE gene but this too would eliminate all protein production and not help us to understand the specific role of ACE made by endothelium. * Corresponding author. Tel.: +1-404-727-3134; fax: +1-404-727-8540. E-mail address: kbernst@emory.edu (K.E. Bernstein). Journal of Molecular and Cellular Cardiology 36 (2004) 781–789 www.elsevier.com/locate/yjmcc © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.yjmcc.2004.02.013