The renin-angiotensin system: going beyond the classical paradigms

Abstract

Thirty years ago, a novel axis of the renin-angiotensin system (RAS) was unveiled by the discovery of angiotensin-(1-7) [ANG-(1-7)] generation in vivo. Later, angiotensin-converting enzyme 2 (ACE2) was shown to be the main mediator of this reaction, and Mas was found to be the receptor for the heptapeptide. The functional analysis of this novel axis of the RAS that followed its discovery revealed numerous protective actions in particular for cardiovascular diseases. In parallel, similar protective actions were also described for one of the two receptors of ANG II, the ANG II type 2 receptor (AT₂R), in contrast to the other, the ANG II type 1 receptor (AT₁R), which mediates deleterious actions of this peptide, e.g., in the setting of cardiovascular disease. Very recently, another branch of the RAS was discovered, based on angiotensin peptides in which the amino-terminal aspartate was replaced by alanine, the alatensins. Ala-ANG-(1-7) or alamandine was shown to interact with Mas-related G protein-coupled receptor D, and the first functional data indicated that this peptide also exerts protective effects in the cardiovascular system. This review summarizes the presentations given at the International Union of Physiological Sciences Congress in Rio de Janeiro, Brazil, in 2017, during the symposium entitled "The Renin-Angiotensin System: Going Beyond the Classical Paradigms," in which the signaling and physiological actions of ANG-(1-7), ACE2, AT₂R, and alatensins were reported (with a focus on noncentral nervous system-related tissues) and the therapeutic opportunities based on these findings were discussed.

Keywords: alamandine; angiotensin-(1−7); angiotensin-(1−9); angiotensin-converting enzyme 2; heart failure.

Fig. 1.

Enzymatic cascade involving the renin-angiotensin system, key receptor systems, and biological effects. A: renin-angiotensin system cascade showing the angiotensin peptide metabolic pathway. ANG I is cleaved by angiotensin-converting enzyme (ACE) to ANG II, which is metabolized by ACE2 to ANG-(1−7). ANG II binds to ANG II type 1 receptors (AT₁Rs) and ANG II type 2 receptors (AT₂Rs), whereas ANG-(1−7) binds to Mas receptors (MasRs) and opposes ANG II/AT₁R actions. B: decreased ACE2 shifts the balance in the renin-angiotensin system toward the ANG II/AT₁R axis, resulting in the progression of cardiovascular disease. Increased ACE2 shifts the balance to the ANG-(1−7)/Mas axis, leading to protection from cardiovascular disease. ADH, antidiuretic hormone; APA, aminopeptidase A; PCP, prolyl carboxypeptidase (also known as angiotensinase C). [Reproduced with permission from Ref. .]

Fig. 2.

Signaling pathways for nitric oxide (NO) formation. ANG-(1−7)/Mas and ANG II/ANG II type 2 receptors (AT₂Rs) induce NO formation via phosphatidylinositol 3-kinase (PI3K)/Akt signaling, whereas alamandine/Mas-related G protein-coupled receptor D (MrgD) leads to NO formation through AMP-activated protein kinase (AMPK) activation.

Fig. 3.

Effect of alamandine on blood pressure in nonanesthetized 12-wk-old Sprague-Dawley male rats. Administration of drugs and blood pressure measurement were performed with a cannula inserted in the femoral vein and artery, respectively. Alamandine was administered intravenously in bolus in increasing amounts (0.02, 0.2, 1, 5, 20, and 80 ng). A subsequent alamandine amount was administrated only when mean arterial pressure (MAP) returned to the basal level. Losartan (5 mg/kg) was administrated intravenously in bolus 30 min before intravenous administration of alamandine. A U-shaped effect of alamandine was observed. *P < 0.05 vs. saline; #P < 0.05 vs. alamandine. Statistical significance was obtained by two-way ANOVA followed by a Bonferroni test. Each bar represents the mean ± SE.

Fig. 4.

Phosphoproteomic approach to study signaling pathways. A: activation or inhibition of a given receptor leads to phosphorylation and dephosphorylation of target proteins from the plasma membrane toward the nucleus in a time-dependent manner. B: general phosphoproteomic workflow for temporal cell signaling studies. To study phosphorylation and dephosphorylation dynamics, experimental groups are divided based on treatment duration (e.g., from seconds to days). Untreated cells are used as controls and are considered time = 0 min (i). Cells are lysed to extract proteins and phosphoproteins and then digested using specific proteases (e.g., trypsin) (ii). Generated peptides are labeled with nonradioactive isotopes for multiplexing analysis (iii). Phosphopeptides are enriched to reduce sample dynamic range (iv). Samples are analyzed using liquid chromatography coupled to mass spectrometry (LC-MS), and bioinformatics tools are used to identify and quantify phosphoproteins, including their phosphorylation sites, to ultimately build dynamic signaling networks affected by the given treatment (v).