Abstract 088: Angiotensin Converting Enzyme 2 (ACE2) in the Kidney: Soluble ACE2 Restores Blood Pressure Regulation

Abstract

Angiotensin converting enzyme 2 (ACE2) is a carboxypeptidase that metabolizes angiotensin II (AngII) to Ang(1-7). ACE2 can be cleaved by metalloproteinases to generate soluble ACE2 (sACE2), which remains catalytically active. The objective of this study is to determine if sACE2, acting in the kidney, could modulate the BP response to AngII infusion.Data from our kidney cross-transplant study using male (129/SvEv x C57BL/6)F 1 ACE2 KO and WT mice suggest that sACE2 can reach the urinary compartment even when not expressed in kidney cells. For these experiments, we generated 4 experimental groups: 1) WT, 2) Kidney ACE2KO, 3) Systemic ACE2KO, and 4) Total ACE2KO. Mean arterial pressures (MAP) were measured with radiotelemetry. AngII was infused chronically at 1ug/kg/min. Enzymatic activity was determined using an ACE2-specific quenched fluorescent substrate assay. ACE2 protein in the urine was confirmed by western blots using a specific N-terminus antibody. Total ACE2KO mice had an enhanced hypertensive response to AngII compared to WT (152±6 vs.144±7 mmHg; p =0.03). The presence of ACE2 in either kidney or systemic tissues restored MAPs to levels similar to WT (kidney ACE2KO 140±7mmHg, systemic ACE2 KO 140±5 mmHg, p<0.01 vs. total ACE2KO). However, Kidney ACE2KO mice had similar urinary ACE2 activity as systemic ACE2KO (76±32 and 108±52 RFU/ul/hr, respectively, p=NS). We confirmed this was ACE2 with immunoblotting of urine samples. As expected, we detected a 92kDa band in WT and systemic KO mice, which represents full length ACE2. A smaller band (70kDa) was present in the WT, systemic KO, and kidney KO groups, and absent in total KO mice. This likely represents sACE2. Moreover, the presence of the smaller band correlated with urine ACE2 activity and was associated with attenuated BPs. Our studies demonstrate that the exaggerated hypertensive phenotype seen in total ACE2 deficiency can be rescued when ACE2 is restored either in the kidney or in systemic tissues. Since the Kidney KO group demonstrated ACE2 activity and protein in the urine, we suggest that soluble ACE2 can be filtered in hypertensive renal injury and may provide an additional source of balance against upregulation of the RAS within the kidney, with the overall goal of regulating BP.