An evolving story of angiotensin-II-forming pathways in rodents and humans

Abstract

Lessons learned from the characterization of the biological roles of Ang-(1-7) [angiotensin-(1-7)] in opposing the vasoconstrictor, proliferative and prothrombotic actions of AngII (angiotensin II) created an underpinning for a more comprehensive exploration of the multiple pathways by which the RAS (renin-angiotensin system) of blood and tissues regulates homoeostasis and its altered state in disease processes. The present review summarizes the progress that has been made in the novel exploration of intermediate shorter forms of angiotensinogen through the characterization of the expression and functions of the dodecapeptide Ang-(1-12) [angiotensin-(1-12)] in the cardiac production of AngII. The studies reveal significant differences in humans compared with rodents regarding the enzymatic pathway by which Ang-(1-12) undergoes metabolism. Highlights of the research include the demonstration of chymase-directed formation of AngII from Ang-(1-12) in human left atrial myocytes and left ventricular tissue, the presence of robust expression of Ang-(1-12) and chymase in the atrial appendage of subjects with resistant atrial fibrillation, and the preliminary observation of significantly higher Ang-(1-12) expression in human left atrial appendages.

Figure 1

Correlative changes in plasma (top panel) and left ventricular (bottom panel) content of angiotensin II (Ang II) at the completion of a 14-day therapy with either vehicle, lisinopril, losartan or both drugs combined shows significant divergency of the effects of the therapies on plasma versus cardiac Ang II levels. Data are means ± SEM in Wistar rats. *P < 0.05 vs. vehicle; #P <0.05 vs. lisinopril; ◆P < 0.05 vs losartan. Adapted from our reference .

Figure 2

Metabolism of ¹²⁵I-Ang-(1-12) (1 nmol/L) expressed as percent of the peptides remaining in the cultured medium of neonatal cardiac myocytes following 60 min incubation at 37°C in Wistar Kyoto and Spontaneously Hypertensive Rats. RAS cocktail includes lisinopril, a neprilysin inhibitor (SCH39370), an ACE2 inhibitor (MLN-4760), and a chymase inhibitor (chymostatin) all added at a concentration of 10 μM. Data from our reference .

Figure 3

Processing of ¹²⁵I-Ang-(1-12) by plasma membranes isolated from the human left atrial appendage of subjects undergoing heart surgery for the treatment of resistant atrial fibrillation shows a primary role of chymase as the Ang-(1-12) processing enzyme. Data drawn from Table 1 of our reference .

Figure 4

Schematic diagram of biotransformation pathways for Ang-(1-12) in the human circulation and cardiac myocytes. The sequence of Ang-(1-12) is that of the human form which differs from that expressed in rodents in terms of the substitution of valine (Val) for leucine (Leu) in position 11 and the presence of histidine (His) instead of tyrosine (Tyr) in position 12. Chymase either produced in cardiac myocytes or released by mast cells during ischemia reperfusion/injury (I/R) or increased oxidative stress generates Ang II intracellularly from Ang-(1-12) [93;94]. ACE, angiotensin converting enzyme; NEPs, angiotensin-(1-7) forming enzymes (prolyl endopeptidase 24.26 and neprilysin) [95].

Figure 5

Representative example of immunohistochemistry of left atria (LA) from a subject with mitral regurgitation. From left to right, the LA demonstrates infiltration of mast cells with chymase (red) in various stages of degranulation. A) intact mast cell, B) mast cell release of chymase into interstitium, C) mast cell chymase located within atrial myocyte as well as in the interstitium in magnified inset with degranulating mast cell in lower right corner. Green: desmin, Blue: 4′,6-diamidino-2-phenylindole (DAPI).

Figure 6

Immunohistochemistry fluorescent staining for desmin and Ang-(1-12) in normal and mitral regurgitation (MR) left atrium (LA). MR LA has a loss of desmin (green) in the intercalated disc (white arrow) along with an increase in Ang-(1-12) (red) compared to normal LA. DAPI for nucleus: blue