Ang II (Angiotensin II) Conversion to Angiotensin-(1-7) in the Circulation Is POP (Prolyloligopeptidase)-Dependent and ACE2 (Angiotensin-Converting Enzyme 2)-Independent

Abstract

The Angiotensin II-Angiotensin-(1-7) axis of the Renin Angiotensin System (RAS) encompasses three enzymes that form Angiotensin-(1-7) [Ang(1-7)] directly from Angiotensin II (Ang II): Angiotensin Converting Enzyme 2 (ACE2), Prolyl Carboxypeptidase (PRCP) and Prolyl Oligopeptidase (POP). We investigated their relative contribution to Ang-(1-7) formation in-vivo and also ex-vivo in serum, lungs and kidneys using models of genetic ablation coupled with pharmacological inhibitors. In WT mice infusion of Ang II resulted in a rapid increase of plasma Ang-(1-7). In ACE2 −/− / PRCP −/− mice, Ang II infusion resulted in a similar increase in Ang-(1-7) as in WT (563 ± 48 vs 537 ± 70 fmol/ml, respectively), showing that the bulk of Ang-(1-7) formation in circulation is essentially independent of ACE2 and PRCP. By contrast, a POP inhibitor, Z-Pro-Prolinal (ZPP) reduced the rise in plasma Ang-(1-7) after infusing Ang II to control WT mice. In POP −/− mice, the increase in Ang-(1-7) was also blunted as compared to WT mice (309 ± 46 and 472 ± 28 fmol/ml, respectively p=0.01), and moreover, the rate of recovery from acute Ang II-induced hypertension was delayed (p=0.016). In ex vivo studies POP inhibition with ZZP reduced Ang-(1-7) formation from Ang II markedly in serum and in lung lysates. By contrast, in kidney lysates the absence of ACE2, but not POP, obliterated Ang-(1-7) formation from added Ang II. We conclude that POP is the main enzyme responsible for Ang II conversion to Ang-(1-7) in the circulation and in the lungs, whereas Ang-(1-7) formation in the kidney is mainly ACE2-dependent. This study demonstrates the relevance of the POP/Ang-(1-7) axis in the circulation and in the lungs while confirming the importance of ACE2 in kidney Ang-(1-7) formation from Ang II.