Aminopeptidase-A (APA) is a less well-studied enzyme of the renin angiotensin system. We propose that it is involved in cardiac Angiotensin (Ang) metabolism and its pathologies. Ang-(1-7) can ameliorate remodeling after myocardial injury. The aims of this study are to (1)Develop mass spectrometric (MS) approaches for the assessment of Ang processing by APA within the myocardium; (2)Investigate the role of APA in cardiac Ang-(1-7) metabolism after myocardial infarction (MI) using sensitive MS techniques. MI was induced in C57Bl/6 male mice by ligating the left anterior descending (LAD) artery. Frozen mouse heart sections (in situ assay) or myocardial homogenates (in vitro assay) were incubated with the endogenous APA substrate, AngII. Results showed concentration and time-dependent cardiac formation of AngIII from AngII which was inhibited by the specific APA inhibitor, 4-amino-4-phosphonobutyric acid. Myocardial APA activity was significantly increased 24 hrs after LAD ligation (0.82±0.02 vs 0.32±0.02 ρmol/min/µg, MI vs sham, p<0.01). Both MS enzyme assays identified the presence of a new peptide Ang-(2-7), m/z 784, which accumulated in the MI (146.45±6.4 vs 72.96±7.0%, MI vs sham, p<0.05). Use of recombinant APA enzyme revealed that APA is responsible for Ang-(2-7) formation from Ang-(1-7). APA exhibited similar substrate affinity for Ang-(1-7) compared to AngII (Km[AngII]=14.67±1.6 vs Km[Ang-(1-7)]=6.07±1.12 µmol/L, p<0.05). Results demonstrate a novel role of APA in Ang-(1-7) metabolism and suggest that the upregulation of APA, which occurs after MI may deprive the heart of cardioprotective Ang-(1-7). Thus, APA may serve as a potentially novel therapeutic target for management of tissue remodeling after MI.
- renin angiotensin system
- angiotensin peptides
- myocardial infarction
- Copyright © 2014, American Journal of Physiology - Heart and Circulatory Physiology