Update on the Angiotensin converting enzyme 2-Angiotensin (1-7)-MAS receptor axis: fetal programing, sex differences, and intracellular pathways

Abstract

The renin-angiotensin-system (RAS) constitutes an important hormonal system in the physiological regulation of blood pressure. Indeed, dysregulation of the RAS may lead to the development of cardiovascular pathologies including kidney injury. Moreover, the blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or antagonism of the angiotensin type 1 receptor (AT1R) constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS that the system is comprised of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, sodium retention, and other mechanisms to maintain blood pressure, as well as increased oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the non-classical RAS composed of the ACE2-Ang-(1-7)-Mas receptor axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and oxidative stress. Thus, a reduced tone of the Ang-(1-7) system may contribute to these pathologies as well. Moreover, the non-classical RAS components may contribute to the effects of therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury. The review considers recent studies on the ACE2-Ang-(1-7)-Mas receptor axis regarding the precursor for Ang-(1-7), the intracellular expression and sex differences of this system, as well as an emerging role of the Ang1-(1-7) pathway in fetal programing events and cardiovascular dysfunction.

Keywords: ACE; ACE2; Ala1-Ang-(1–7); Ang-(1–7); Mas receptor; Mas-related receptor D; fetal programing.

Figure 1

Enzymatic cascade of angiotensin peptide formation and metabolism. Renin cleaves the precursor protein angiotensinogen to angiotensin-(1–10) (Ang I) which is further processed to the biologically active peptides Ang-(1–8) (Ang II) by angiotensin converting enzyme (ACE) and Ang-(1–7) by endopeptidases such as neprilysin (NEP). Ang II undergoes further processing at the carboxyl terminus by the carboxypeptidase ACE2 to yield Ang-(1–7) (Ang 7). Ang-(1–7) undergoes decarboxylation (DC) of the aspartic acid residue to form Ala¹-Ang-(1–7) (Ala¹-Ang 7). The dodecapeptide Ang-(1–12) is derived from the hydrolysis of the Tyr¹²-Tyr¹³ bond of rat angiotensinogen by an unknown enzymatic pathway. Ang II recognizes both AT₁ and AT₂ receptors. Ang-(1–7) activates the Mas receptor and Ala¹-Ang-(1–7) recognizes the Mas-D related receptor (Mrg).

Figure 2

Scheme for the interaction of ACE2 and ADAMs on the apical surface of the proximal tubules in the diabetic kidney. Ang II binds to the AT₁ receptor (AT₁R) and stimulates MAP kinase (MAPK) pathways and production of reactive oxygen species (ROS). The Ang II-AT₁-receptor axis may attenuate ACE2 expression but increase ADAM levels. ACE2 is anchored to the apical membrane and directly converts Ang II to Ang-(1–7) (Ang 7); ACE also anchored to the membrane metabolizes Ang-(1–7) to Ang-(1–5) (Ang 5). Ang-(1–7) recognizes the AT₇/Mas receptor (AT₇R) to antagonize the actions of the Ang II-AT₁R by stimulation of protein phosphatases (PTP) and nitric oxide synthase (NOS) to form nitric oxide (NO) and cGMP. In pathological conditions, increased expression of ADAMs may hydrolyze ACE2 away from the apical surface to increase local concentrations of Ang II and reduce the levels of Ang-(1–7).

Figure 3

Expression of intracellular components of the renin-angiotensin system in NRK-52E renal epithelial cells. Immunofluorescent (IMF) staining and protein immunoblot for rat angiotensinogen (Aogen) and renin. Immunoblots of Aogen and renin in nuclei (lanes 1–3) and cytosol (lanes 4–6) were from three separate passages of NRK-52E cells. Major bands for Aogen and renin were identified at approximately 55 kDa. Renin activity (conversion of Aogen to Ang I) in isolated nuclear fractions was increased threefold following activation by trypsin (TRP) and was essentially abolished by the renin inhibitor aliskiren (ALK). Conversion of ¹²⁵I-Ang I to ¹²⁵I-Ang-(1–7) in the isolated nuclear fraction was predominantly blocked by the thimet oligopeptidase inhibitor CPP. Renin activity data are mean ± SEM; n = 4; *P < 0.05. Ang I metabolism representative of data from n = 4 separate cell passages. Adapted from Alzayadneh and Chappell (107).

Figure 4

Betamethasone-exposed (BMS) offspring exhibit higher mean arterial pressure (MAP) and CSF endopeptidase activity than non-exposed sheep. Blood pressure (MAP) was higher in BMS animals at 6 months of age. CSF peptidase activity was twofold higher in BMS animals as compared to controls. CSF Ang-(1–7) peptide levels were lower in BMS animals. Ang-(1–7) peptide levels negatively correlate with peptidase activity in the CSF (r = −0.81, P = 0.01). Data are mean ± SEM; 4–5 per group; *P < 0.05 or ***P < 0.001 vs. controls. Adapted from Marshall et al. (70).

Figure 5

Sex differences in systolic blood pressure and RAS components in the renal cortex of 15-week-old hemizygous mRen2.Lewis congenic rats. Systolic blood pressure (mmHg) is higher in males. Intrarenal concentrations (femtomole peptide per milligram protein – fmol/mg) of Ang II are higher in males, but Ang-(1–7) content is lower. ACE2 activity (femtomole product per milligram protein per minute – fmol/mg/min) is higher in males, but neprilysin (NEP) activity is lower in males. NEP expression assessed by Western blot was lower in males (M) as compared to females (F). Data are mean ± SEM; n = 4–8 per group; *P < 0.05 or **P < 0.01. Adapted from Pendergrass et al. (81).