Lai-Jiang Chen

The ACE2/Apelin Signaling, microRNAs, and Hypertension.

The renin-angiotensin aldosterone system (RAAS) plays a pivotal role in the development of hypertension. Angiotensin converting enzyme 2 (ACE2), which primarily metabolises angiotensin (Ang) II to generate the beneficial heptapeptide Ang-(1-7), serves as a negative regulator of the RAAS. Apelin is a second catalytic substrate for ACE2 and functions as an inotropic and cardiovascular protective peptide. The physiological effects of Apelin are exerted through binding to its receptor APJ, a seven-transmembrane G protein-coupled receptor that shares significant homology with the Ang II type 1 receptor (AT1R). The deregulation of microRNAs, a class of short and small noncoding RNAs, has been shown to involve cardiovascular remodeling and pathogenesis of hypertension via the activation of the Ang II/AT1R pathway. MicroRNAs are linked with modulation of the ACE2/Apelin signaling, which exhibits beneficial effects in the cardiovascular system and hypertension. The ACE2-coupled crosstalk among the RAAS, the Apelin system, and microRNAs provides an important mechanistic insight into hypertension. This paper focuses on what is known about the ACE2/Apelin signaling and its biological roles, paying particular attention to interactions and crosstalk among the ACE2/Apelin signaling, microRNAs, and hypertension, aiming to facilitate the exploitation of new therapeutic medicine to control hypertension.

ACE2/Ang-(1-7) signaling and vascular remodeling.

The renin-angiotensin system (RAS) regulates vascular tone and plays a critical role in vascular remodeling, which is the result of a complex interplay of alterations in vascular tone and structure. Inhibition of the RAS has led to important pharmacological tools to prevent and treat vascular diseases such as hypertension, diabetic vasculopathy and atherosclerosis. Angiotensin converting enzyme 2 (ACE2) was recently identified as a multifunctional monocarboxypeptidase responsible for the conversion of angiotensin (Ang) II to Ang-(1–7). The ACE2/Ang-(1–7) signaling has been shown to prevent cellular proliferation, pathological hypertrophy, oxidative stress and vascular fibrosis. Thus, the ACE2/Ang-(1–7) signaling is deemed to be beneficial to the cardiovascular system as a negative regulator of the RAS. The addition of the ACE2/Ang-(1–7) signaling to the complexities of the RAS may lead to the development of novel therapeutics for the treatment of hypertension and other vascular diseases. The present review considers recent findings regarding the ACE2/Ang-(1–7) signaling and focuses on its regulatory roles in processes related to proliferation, inflammation, vascular fibrosis and remodeling, providing proof of principle for the potential use of ACE2 as a novel therapy for vascular disorders related to vascular remodeling.

Angiotensin-converting enzyme 2 ameliorates renal fibrosis by blocking the activation of mTOR/ERK signaling in apolipoprotein E-deficient mice

Angiotensin-converting enzyme 2 (ACE2) has been shown to prevent atherosclerotic lesions and renal inflammation. However, little was elucidated upon the effects and mechanisms of ACE2 in atherosclerotic kidney fibrosis progression. Here, we examined regulatory roles of ACE2 in renal fibrosis in the apolipoprotein E (ApoE) knockout (KO) mice. The ApoEKO mice were randomized to daily deliver either angiotensin (Ang) II (1.5mg/kg) and/or human recombinant ACE2 (rhACE2; 2mg/kg) for 2 weeks. Downregulation of ACE2 and upregulation of phosphorylated Akt, mTOR and ERK1/2 levels were observed in ApoEKO kidneys. Ang II infusion led to increased tubulointerstitial fibrosis in the ApoEKO mice with greater activation of the mTOR/ERK1/2 signaling. The Ang II-mediated renal fibrosis and structural injury were strikingly rescued by rhACE2 supplementation, associated with reduced mRNA expression of TGF-β1 and collagen I and elevated renal Ang-(1-7) levels. In cultured mouse kidney fibroblasts, exposure with Ang II (100nmolL(-1)) resulted in obvious elevations in superoxide generation, phosphorylated levels of mTOR and ERK1/2 as well as mRNA levels of TGF-β1, collagen I and fibronectin 1, which were dramatically prevented by rhACE2 (1mgmL(-1)) or mTOR inhibitor rapamycin (10μmolL(-1)). These protective effects of rhACE2 were eradicated by the Ang-(1-7)/Mas receptor antagonist A779 (1μmolL(-1)). Our results demonstrate the importance of ACE2 in amelioration of kidney fibrosis and renal injury in the ApoE-mutant mice via modulation of the mTOR/ERK signaling and renal Ang-(1-7)/Ang II balance, thus indicating potential therapeutic strategies by enhancing ACE2 action for preventing atherosclerosis and fibrosis-associated kidney disorders.

OS 36-07 TREATMENT WITH APELIN-13 PREVENTS PRESSURE OVERLOAD-INDUCED AORTIC ADVENTITIAL REMODELING AND FIBROSIS IN HYPERTENSIVE RATS WITH TAC.

Objective: The Apelin/APJ system has recently been implicated in pathologies of hypertension. However, little was elucidated upon effects of Apelin on vascular adventitial remodeling progression. Here, we examined regulatory roles of Apelin in pressure overload-induced adventitial remodeling and fibrosis in hypertensive rats. Design and Method: The male Sprague–Dawley rats were performed with transverse aortic constriction (TAC). The rats with TAC were randomized to daily deliver either pyroglutamyl Apelin-13 (50 &mgr;g/kg) or saline for 4 weeks. Results: Histomorphometric analysis by HE and Masson trichrome staining revealed increased medial and adventitial thicknesses, especially in the adventitia, in ascending aortas in rats with TAC when compared with the sham-operated rats. Downregulation of APJ receptor and elevations in systolic blood pressure, phosphorylated mTOR and ERK1/2 levels were observed in hypertensive rats with TAC. Pressure overload-mediated by TAC led to marked increases in heart weight (HW), HW/body weight ratio, malonyldialdehyde (MDA) contents and aortic fibrosis in the hypertensive rats with enhanced activation of NADPH oxidase activity. The pressure overload-mediated pathological adventitial remodeling was strikingly rescued by Apelin-13 supplementation, associated with attenuation of aortic fibrosis and reduced mRNA expression of TGF-ß1 and collagen I. In cultured rat adventitial fibroblasts, exposure with Ang II (100 nmol L−1) resulted in obvious increases in MDA, phosphorylated levels of mTOR and ERK1/2 and mRNA levels of TGF-ß1, collagen I and fibronectin 1, which were dramatically prevented by Apelin-13 (100 nmol L−1) or mTOR inhibitor rapamycin (10 &mgr;mol L−1). However, Apelin-13 had no effect on collagen III levels. Conclusions: Our results demonstrate the importance of Apelin-13 in amelioration of aortic oxidative stress, adventitial remodeling and fibrosis in hypertensive rats with TAC via modulation of the mTOR/ERK signaling, thus indicating potential therapeutic strategies by enhancing Apelin/APJ action for preventing hypertensive vascular adventitial remodeling and fibrosis and pressure overload-associated cardiovascular disorders.

Ascending aortic adventitial remodeling and fibrosis are ameliorated with Apelin-13 in rats after TAC via suppression of the miRNA-122 and LGR4-β-catenin signaling

Apelin has been proved to be a critical mediator of vascular function and homeostasis. Here, we investigated roles of Apelin in aortic remodeling and fibrosis in rats with transverse aortic constriction (TAC). Male Sprague-Dawley rats were subjected to TAC and then randomized to daily deliver Apelin-13 (50μg/kg) or angiotensin type 1 receptor (AT1) blocker Irbesartan (50mg/kg) for 4 weeks. Pressure overload resulted in myocardial hypertrophy, systolic dysfunction, aortic remodeling and adventitial fibrosis with reduced levels of Apelin in ascending aortas of rat after TAC compared with sham-operated group. These changes were associated with marked increases in levels of miRNA-122, TGFβ1, CTGF, NFAT5, LGR4, and β-catenin. More importantly, Apelin and Irbesartan treatment strikingly prevented TAC-mediated aortic remodeling and adventitial fibrosis in pressure overloaded rats by blocking AT1 receptor and miRNA-122 levels and repressing activation of the CTGF-NFAT5 and LGR4-β-catenin signaling. In cultured primary rat adventitial fibroblasts, exposure to angiotensin II (100nmolL-1) led to significant increases in cellular migration and levels of TGFβ1, CTGF, NFAT5, LGR4 and β-catenin, which were effectively reversed by pre-treatment with Apelin (100nmolL-1) and miRNA-122 inhibitor (50nmolL-1). In conclusion, Apelin counterregulated against TAC-mediated ascending aortic remodeling and angiotensin II-induced promotion of cellular migration by blocking AT1 receptor and miRNA-122 levels and preventing activation of the TGFβ1-CTGF-NFAT5 and LGR4-β-catenin signaling, ultimately contributing to attenuation of aortic adventitial fibrosis. Our data point to Apelin as an important regulator of aortic remodeling and adventitial fibrosis and a promising target for vasoprotective therapies.

8D.01: EFFECTS OF ANGIOTENSIN-CONVERTING ENZYME 2 ON RENAL OXIDATIVE STRESS LEVELS IN APOLIPOPROTEIN E-DEFICIENT MICE.

Objective: The renin-angiotensin system (RAS) has been known for more than a century as a cascade that regulates body fluid balance, renal functions and blood pressure. Angiotensin-converting enzyme 2 (ACE2) is now known as a negative regulator of RAS, and activation of the ACE2 is a possible alternative target for new drugs, since some protective influences on renal and cardiovascular function have been revealed. We hypothesized that ACE2 would exert beneficial effects on oxidative stress levels and renal injury in apolipoprotein E (ApoE) -knockout (KO) mice. Design and method: In this study, we used 12-week-old wild-type, ApoEKO, and ACE2/ApoE double KO mice. The ApoEKO mice were treated with recombinant human ACE2 (hrACE2) with the daily dose of 2 mg/kg. We characterized the functional, structural and molecular signaling changes in mice kidneys. Results: Compared with the ApoEKO mice, ACE2 deficiency led to greater increases in renal oxidative stress levels and expression of oxidative stress-inducible proteins NADPH oxidase 4 (NOX4) in the ACE2/ApoE double KO mice. These changes were associated with exacerbation of renal tubule ultrastructure injury and greater activation of Akt and ERK1/2 phosphorylated signaling. Conversely, treatment with hrACE2 significantly attenuated renal oxidative stress levels and ultrastructure injury, and prevented the expression of NOX4 and phosphorylated level of Akt and ERK1/2 in ApoEKO mouse kidneys. However, there were no changes in renal expression of NOX2 and Mas receptor among groups. Conclusions: Deletion of ACE2 triggers greater increases in renal oxidative stress and tubular ultrastructure injury in the ACE2/ApoE double mutant mice with greater activation of Akt-ERK1/2 phosphorylated signaling. While ACE2 overexpression alleviates renal tubular injury in ApoE-mutant mice with suppression of superoxide generation and downregulation of the Akt-ERK phosphorylated signaling. Strategies aimed at enhancing ACE2 action may have important therapeutic potential for atherosclerosis and renal diseases.