Human monocyte subsets exhibit divergent angiotensin I-converting activity

Abstract

Immune cells may take part in the renin-angiotensin-aldosterone system (RAAS), which plays a pivotal role in the regulation of vascular tone and blood pressure. The aim of the study was to analyse the expression and activity of angiotensin-converting enzyme type 1 (ACE1) and ACE2 in human monocytes (MO) and their subsets. The highest relative level of ACE1-, as well as ACE2-mRNA expression, was observed in CD14(++)CD16(-) (classical) MO. Moreover, in these cells, mean level of ACE2-mRNA was almost two times higher than that of ACE1-mRNA (11.48 versus 7.073 relative units, respectively). In peripheral blood mononuclear cells (PBMC), MO and classical MO, ACE1 and ACE2 protein expression was stronger compared to other MO subpopulations. The highest level of Ang II generated from Ang I in vitro was observed in classical MO. In this setting, generation of Ang-(1-9) by PBMC and classical MO was higher when compared to the whole MO population (P < 0.05). The generation rate of vasoprotective Ang-(1-7) was comparable in all analysed cell populations. However, in CD14(+)CD16(++) (non-classical) MO, formation of Ang-(1-7) was significantly greater than Ang II (P < 0.001). We suggest that in physiological conditions MO (but also lymphocytes forming the rest of PBMC pool) may be involved in the regulation of vessel wall homeostasis via the RAAS-related mechanisms. Moreover, non-classical MO, which are associated preferentially with the vascular endothelium, express the vasoprotective phenotype.

Keywords: angiotensin; angiotensin-converting enzymes; monocyte subpopulations; renin-angiotensin-aldosterone system.

Figure 1

Simplified scheme of the rennin–angiotensin system (RAS). Angiotensin (Ang)II, -(1–9), and -(1–7) derived by C-terminal cleavage of their particular antecessors by angiotensin converting enzyme (ACE)1 or ACE2. ACE1/2 = angiotensin-converting enzyme type 1 or type 2; AT1/2 = angiotensin II receptor type 1 or type 2; MAS-1 = Mas oncogene, receptor for Ang-(1–7); aa = amino acids.

Figure 2

Expression level of angiotensin converting enzyme (ACE)1- (a) and ACE2-mRNA (b) in analysed cell subsets. The mRNA expression was analysed using the 2^-ΔΔCt method and presented as a fold difference of each sample compared to peripheral blood mononuclear cells (PBMC). Data represent the mean values ± standard error of the mean (s.e.m.) of 12 independent experiments. *P < 0·05; **P < 0·001.

Figure 3

Angiotensin-converting enzyme (ACE)1 and ACE2 protein expression analysed by the Western blotting method. Monochrome images show representative ACE1 and ACE2 protein immunoblots obtained from particular cell subsets. One representative experiment of four performed is presented.

Figure 4

Mean values of the concentration of angiotensin (Ang) II (a), Ang (1–9) (b) and Ang (1–7) (c) in the samples of: peripheral blood mononuclear cells (PBMC), dummy sorted whole monocyte (MO) population and three sorted particular MO subsets, measured using reversed-phase, high-performance liquid chromatography. The ratio of Ang-(1–7)/Ang II of the same cell populations is presented (d). Data represent the mean values ± standard error of the mean (s.e.m.) of five independent experiments. *P < 0·05; **P < 0·001.