The effects of different angiotensin II type 1 receptor blockers on the regulation of the ACE-AngII-AT1 and ACE2-Ang(1–7)-Mas axes in pressure overload-induced cardiac remodeling in male mice
Introduction
Cardiovascular diseases remain one of the most important causes of morbidity and mortality worldwide, and they continue to increase in prevalence [1]. The activation of the renin-angiotensin system (RAS) and the subsequent generation of angiotensin (Ang) II are important mediators of cardiovascular diseases [2]. Angiotensin Converting Enzyme (ACE), Angiotensin II (AngII), and the Angiotensin II type I receptor (AT1), otherwise known as the AngII-ACE-AT1 axis, are thought to constitute the classic RAS pathway [3], [4], [5]. Drugs that target AngII and the AngII type 1 (AT1) receptor are widely used clinically for the treatment of cardiovascular diseases [6], [7]. The ACE-AngII-AT1 axis has long been thought to be the main pathway of the RAS [8]. However, the understanding of the RAS has rapidly expanded in the past ten years. Specifically, the identification of ACE2 in 2000 opened a new chapter of research on the regulation of the RAS [8], [9].
Human ACE2 is an 805-amino-acid homolog of human ACE, which has a 42% identity in the catalytic domain to human ACE [8], [9]. ACE2 is able to cleave Ang I and AngII to Ang(1–9) and Ang(1–7), respectively, and Ang(1–9) can be further converted to Ang(1–7) [9], [10]. As the catalytic efficiency of ACE2 is approximately 400-fold higher with AngII as a substrate than with Ang I as a substrate, it is therefore believed that the main physiological function of ACE2 is to convert AngII to Ang(1–7) [8], [11]. Ang(1–7) is an endogenous ligand for the G protein-coupled Mas receptor (Mas1), which is a cell surface receptor that is highly expressed within the cardiovascular system [8], [12], [13]. The ACE2-Ang(1–7)-Mas axis is known as the non-classical axis of the RAS, which plays a pivotal role in regulating the occurrence and development of cardiovascular diseases [3], [14], [15]. Therefore, the study of the ACE2-Ang(1–7)-Mas axis has become a research hotspot distinct from the study of the AngII-ACE-AT1 axis.
Recent studies have indicated that the prevalence rate of myocardial remodeling and heart failure is much higher in ACE2 knockout (KO) mice and that the upregulation of the ACE2-Ang(1–7)-Mas axis in the heart prevented heart remodeling [16], [17], [18]. Although some ARBs have been reported to increase ACE2 and Ang(1–7) besides blocking the AT1 receptor [19], [20], the precise effects of different ARBs on the regulation of the ACE-AngII-AT1 axis and the ACE2-Ang(1–7)-Mas axis are not fully understood. It has been reported that Olmesartan could significantly increase all of the components of the ACE2-Ang(1–7)-Mas axis, while the other ARBs, such as Telmisartan and Valsartan, have also been shown to act on some components of the ACE2-Ang(1–7)-Mas axis [21], [22], [23]. In our previous study, we have reported the different effects and mechanisms of AT1R blockers [24]. Some of them inhibited pressure overload-induced cardiac hypertrophy independently of AngII, whereas others exerted inhibitory effects only in the presence of AngII. Therefore, we wondered whether there were differences in the effects on the ACE-AngII-AT1 axis and the ACE2-Ang(1–7)-Mas axis among the different ARBs. However, at present, no studies have directly compared the effects of the different ARBs on the two axes. Here, we designed this study to examine and compare the effects of several ARBs widely used in clinics, such as Olmesartan, Candesartan, Telmisartan, Losartan, Valsartan and Irbesartan, on the ACE-AngII-AT1 axis and the ACE2-Ang(1–7)-Mas axis during the development of cardiac remodeling after pressure overload. Moreover, it has been reported that AT1R blockers could protect against cardiac remodeling and improve cardiac function through modulation of ACE2 and Ang(1–7) expressions besides inhibition of AT1R [25], [26], [27]. Since some AT1R blockers exerted effects only in the presence of AngII, and we here want to compare the effects of different AT1R blockers on ACE2 and Ang(1–7) at the conditions of normal and lower levels of AngII, we therefore used the ATG knockdown method.
Section snippets
Antibodies and reagents
All of the ARBs administered to the mice, Olmesartan (Daiichi Sankyo Pharmaceutical, Shanghai, China), Candesartan (Takeda Pharmaceutical, Tianjin, China), Telmisartan (Boehringer Ingelheim Pharmaceutical, Shanghai, China), Losartan (Merck Pharmaceutical, Hangzhou, China), Valsartan (Novartis Pharmaceutical, Beijing, China) and Irbesartan (Sanofi Pharmaceutical, Hangzhou, China) were purchased commercially. For the cell experiments, Losartan was purchased from Sigma-Aldrich (St. Louis, MO), and
ATG expression following treatment with Ad-ATG siRNA in mice
First, three different sequences targeting the mouse ATG were used in mouse cardiomyocytes, and the most effective siRNA was selected and used in the mice (Supplemental Fig. 1). Then, the expression of ATG was detected to verify the effectiveness of the Ad-ATG siRNA used in vivo. As shown in Fig. 1, the mRNA expression of ATG in the siRNA-treated mouse hearts measured by quantitative real-time PCR was markedly reduced when compared with the control group 2 weeks and 4 weeks after virus injection.
Discussion
To the best of our knowledge, this represents the first study to demonstrate that the effects of different ARBs on the ACE-AngII-AT1 axis and the ACE2-Ang(1–7)-Mas axis are quite diverse. In the present study, we showed that in a similar hypertensive condition, Olmesartan, Candesartan, and Losartan alleviated cardiac dysfunction regardless of the knockdown of AngII, whereas Telmisartan, Valsartan and Irbesartan only exerted effects in the presence of AngII in vivo. We subsequently found that
Disclosures
None.
Acknowledgments
This study was supported by grants from the National Natural Science Foundation of China (81220108003, and 30930043), Natural Science Fund of Shanghai Committee of Science and Technology (12ZR1442100), and the Research Fund for Excellent Doctor of Shanghai Medical College of Fudan University (EZF152300002001). We thank Mr. Guoping Zhang, Mr. Chunjie Yang and Mr. Jianguo Jia for their excellent technical support and assistance with the experiments.
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These authors contributed equally.