New perspectives on angiotensin-converting enzyme 2 and its related diseases

Table 1 List of animal studies on the high-sodium diet and angiotensin-converting enzyme 2

Animal	Study details	Main findings	Ref.
Zucker rats	Lean and obese Zucker rats were fed a normal-sodium diet (0.4%) or a high-sodium diet (8%) for 2 wk	ACE2 mRNA and protein expression was significantly reduced in HS-fed obese Zucker rats	Samuel et al[19]
Wistar rats	Rats were fed three salt concentrations (0.2%, 1.2%, 8.2%) for 4 wk after uninephrectomy of the left kidney	HS diet increased the glomerular ACE/ACE2 ratio	Bernardi et al[20]
Wistar rats	After 4 wk of induction of hypertension (2-kidney 1-clip model), rats were fed a normal-sodium diet (0.4%) or a high-sodium diet (8%) for 2 wk	HS diet decreased urinary angiotensinogen, ACE, and ACE2 expression in the clipped and unclipped kidneys	Shimoura et al[21]
SHR	Rats were fed three NaCl content diets (0.03%, 0.3%, 3%) for 6 mo	HS diet decreased ACE2 protein expression in kidney tissues	Berger et al[18]
SHR	Rats were fed an 8% salt diet for 5 wk	HS diet decreased cardiac ACE2 mRNA and protein levels	Varagic et al[22]
DS and DR rats	DS and DR rats were fed low-sodium chow (0.45%) or high-sodium chow (7%) for 8 wk and treated with or without eplerenone (100 mg/kg/d), candesartan (10 mg/kg/d), or both drugs for 8 wk	HS diet increased angiotensinogen mRNA and decreased ACE2 mRNA in the hearts of DS rats; candesartan increased ACE2 mRNA levels in the heart	Takeda et al[23]
SD rats	Rats were fed an 8% NaCl high-salt or 0.4% NaCl (normal-salt) diet for 3 wk, with or without antioxidant supplementation with tempol	HS diet decreased ACE2 expression; tempol reversed the imbalance of renal RAS components (decrease in Ang II and AT1R and increase in AT2, ACE2, Ang 1-7, and MasR staining intensity)	Cao et al[24]

SHR: Spontaneously hypertensive rats; DS rats: Dahl salt-sensitive hypertensive rats; DR rats: Dahl salt-resistant rats; SD rats: Sprague-Dawley rats; HS: High-sodium; ACE2: Angiotensin-converting enzyme 2; MasR: Mas receptor; AT1R: Angiotensin type 1 receptor; AT2: Angiotensin type 2; Ang 1-7: Angiotensin 1-7; RAS: Renin angiotensin system.

Table 2 List of animal studies on renin angiotensin system inhibitors and angiotensin-converting enzyme 2

Animal	Model	Study details	Main findings	Ref.
Lewis rats	Normotensive	Rats were assigned to drink water containing losartan or lisinopril at 10 mg/kg/d for 12 d	Lisinopril or losartan increased cardiac ACE2 mRNA, but the combination did not produce this effect	Ferrario et al[26]
SD rats	MI	Enalapril was given to rats after sham operation or LCA ligation	Enalapril prevented the decrease of ventricular ACE2 mRNA levels and activities post-MI	Ocaranza et al[27]
Lewis rats	MI	Losartan and olmesartan was administered for 28 d after coronary artery ligation	The level of ACE2 mRNA increased after treatment with losartan and olmesartan	Ishiyama et al[28]
C57BLKS/J mice	Normotensive	Mice were treated with telmisartan at 2 mg/kg/d for 2 wk	Telmisartan increased ACE2 expression in the tunica media of renal arterioles	Soler et al[29]
SD rats	MI	SD rats received ramipril at 1 mg/kg/d for 28 d after MI operation	Ramipril inhibited cardiac ACE but had no effect on cardiac ACE2 mRNA after MI	Burrell et al[30]
SD rats	MI	Ramipril (1 mg/kg/d) and valsartan (10 mg/kg/d) were given for 28 d after MI operation	Cardiac ACE2 expression was not augmented after either treatment alone or in combination	Burchill et al[31]

MI: Myocardial infarction; LCA: Left ventricular artery; SD rats: Sprague-Dawley rats; ACE2: Angiotensin-converting enzyme 2.

Table 3 List of animal studies on the role of angiotensin-converting enzyme 2 in diabetes, hypertension, cardiovascular disease, and acute lung injury

Disease	Animal	Study details	Main findings	Ref.
Diabetes	db/db mice	Mice were randomly assigned to four treatment groups: (1) Control group fed normal chow; (2) Control group fed rosiglitazone diet; (3) db/db group fed normal chow; and (4) db/db group fed rosiglitazone diet	Protein expression of glomerular ACE2 was decreased in the kidneys of db/db mice, while tubular ACE2 and ADAM17 were increased. Rosiglitazone treatment of db/db mice normalized hyperglycemia, attenuated renal injury, and decreased urinary ACE2 and renal ADAM17 protein expression	Chodavarapu et al[45]
	db/db mice	Mice were treated for 16 wk with a specific ACE2 inhibitor (MLN-4760) alone or combined with telmisartan.	ACE and ACE2 colocalized on the apical surface of the proximal tubules, whereas in glomeruli, ACE2 is present in podocytes and, to a lesser extent, in glomerular mesangial cells, whereas ACE is present only in endothelial cells. Telmisartan prevented the increase in UAE associated with the ACE2 inhibitor	Ye et al[46]
	db/db mice	ACE and ACE 2 expression was measured in the kidney and heart	ACE2 protein in renal cortical tubules was increased, whereas ACE protein was decreased. In heart tissue, there were no significant differences between db/db and db/m mice in either ACE or ACE2 expression	Ye et a l[48]
	STZ-induced diabetic SD rats	ACE2 and ACE gene and protein expression was measured in the kidney	ACE2 and ACE mRNA levels were decreased in diabetic renal tubules by approximately 50% and were not influenced by ramipril	Tikellis et al[47]
	STZ-induced diabetic Wistar rats	Diabetic Wistar rats were treated with DIZE	Treatment with DIZE restored ACE2 expression in glomeruli and increased the expression of AT2 receptors in whole kidney and isolated glomeruli	Goru et al[44]
	Akita and Ace2-/- mice	Ace2-/- mice were crossed with Akita mice (Ins2WT/C96Y), and four groups of mice were studied: Ace2+/yIns2WT/WT, Ace2-/yIns2WT/WT, Ace2+/yIns2WT/C96Y, and Ace2-/y Ins2WT/C96Y. The Ace2+/yIns2WT/C96Y and Ace2-/y Ins2WT/C96Y mice were treated with the ARB (irbesartan)	Deletion of the ACE2 gene was associated with accelerated kidney injury and reduced ACE2 expression in diabetic mice. Irbesartan reduced urinary albumin excretion rate in Ace2-/y Ins2WT/C96Y mice	Wong et al[49]
	STZ-induced diabeticC57BL/6J mice and ACE2 knockout (KO) mice	Control and diabetic C57BL/6J and ACE2 KO mice, after 5 wk without treatment, were randomized to receive the ACE inhibitor perindopril. Wild-type mice were further randomized to receive the selective ACE2 inhibitor MLN-4760	Induction of diabetes in wild-type mice was associated with a reduction in renal ACE2 expression and decreased Ang 1-7. In diabetic mice receiving MLN-4760 and in ACE2 KO mice, diabetes-associated albuminuria was enhanced	Tikellis et al[50]
	Akita mice	Male diabetic Akita mice (Ins2 (WT/C96Y)) and control C57BL/6J mice (Ins2(WT/WT)) were injected daily with placebo or with rhACE2 (2 mg/kg) for 4 wk	Treatment with rhACE2 increased plasma ACE2 activity, normalized blood pressure, and reduced the urinary albumin excretion	Oudit et al[51]
	STZ-induced diabetic Wistar rats	Diabetic Wistar rats were divided into 5 groups: No-treatment group, adenoviral (Ad)-ACE2 group, Ad-green fluorescent protein (GFP) group, ACEI group receiving benazepril and Ad-ACE2 + ACEI group	Rats in Ad-ACE2 group exhibited reduced SBP, urinary albumin excretion, creatinine clearance, glomeruli sclerosis index, and renal malondialdehyde level; downregulated transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF), and collagen IV protein expression; and increased renal superoxide dismutase activity. Ad-ACE2 and ACEI had similar effects, whereas combined use of Ad-ACE2 and ACEI offered no additional benefits	Liu et al[52]
Hypertension	Salt-sensitive Sabra hypertensive rats, SHR, and SHRSP	ACE2 expression levels were determined in the kidneys	ACE2 levels were reduced in all of these hypertensive rat strains	Crackower et al[56]
	ACE2-deficient mice	Ang II peptide was administered by i.v. infusion in wild-type and ACE2-deficient mice	Blood pressure measurements were substantially higher in the ACE2-deficient mice	Gurley et al[57]
	SHR and Wistar Kyoto (WKY) rats	Expression of ACE2 was examined in the kidney from SHR and normotensive WKY rats	The tubular expression of ACE2 fell while glomerular expression of ACE2 was paradoxically increased in the SHR	Tikellis et al[60]
	Sheep	Sheep were administered with betamethasone or vehicle at the 80th day of gestation and delivered at term	Antenatal steroid treatment resulted in the chronic alteration of ACE and ACE2 in the circulatory and tubular compartments of adolescent sheep, which may contribute to the higher blood pressure in this model of fetal programming–induced hypertension	Shaltout et al[61]
	Transgenic rats	Transgenic rats were generated in an SHRSP genetic background expressing human ACE2 in vascular smooth muscle cells by the use of the SM22 promoter (SHRSP-ACE2 model)	Mean arterial blood pressure was reduced in SHRSP-ACE2, and the vasoconstrictive response to intraarterial administration of angiotensin II was attenuated	Rentzsch et al[62]
	SHR	Male WKY rats were randomized to receive either placebo or rhACE2 and were subsequently infused with Ang II	Treatment with rhACE2 partly corrected the hypertension, NADPH oxidase activation, and increased superoxide generation in the heart, kidney, and blood vessels	Lo et al[63]
	Mice	ACE2 activity was measured in kidney cortex from mice that had received injection of MLN-4760 or DX600	A marked increase in serum ACE2 activity. Mouse ACE2 abolished the hypertension induced by Ang II infusion. These effects were blocked by MLN-4760 but not by DX600	Ye et al[64]
Cardiovascular disease	ACE2-deficient mice	ACE2 mutant mice were generated, and heart parameters were measured	Genetic inactivation of ACE2 using homologous recombination resulted in increased AngII peptide levels, upregulation of hypoxia genes in the heart, and severe cardiac dysfunction	Crackower et al[56]
	ACE2-deficient mice	Ang II peptide was administered by i.v. infusion in WT and ACE2-deficient mice	No evidence for a role of ACE2 in the regulation of cardiac structure or function was found	Gurley et al[57]
	SD rats	Lentiviral vector encoding mouse ACE2 (lenti-mACE2) or GFP was injected intracardially in Sprague–Dawley rats	ACE2 overexpression resulted in protective effects on AngII-induced cardiac hypertrophy and fibrosis	Huentelman et al[71]
	SHR	Lentiviral vector encoding mouse ACE2 (lenti-mACE2) or GFP was injected intracardially in SHR and normotensive WKY rats	ACE2 overexpression exerted protective effects on high BP and cardiac pathophysiology induced by hypertension in the SHR	Díez-Freire et al[72]
	Rabbits	66 male New Zealand white rabbits were fed an atherogenic chow and were randomly divided into three groups: Treatment with a suspension of Ad-ACE2, treatment with a suspension of Ad-EGFP, and no treatment	ACE2 inhibited the development of early atherosclerotic lesions by suppressing the growth of VSMCs and improving endothelial function	Zhang et al[73]
Acute lung injury	ACE2 mutant mice	Acid aspiration-induced, sepsis-induced, and endotoxin-induced acute lung injury animal models were generated. Mice received intraperitoneal injections of rhACE2 protein	ACE2 and AT2 protected mice from severe acute lung injury. rhACE2 can protect mice from severe acute lung injury	Imai et al[82]
	ACE2 knockout mice	Mice were intranasally inoculated with SARS-CoV virus	SARS-CoV receptor ACE2 had a protective role in acute lung failure	Kuba et al[84]
	BALB/c mice	LPS-induced acute lung injury mice were treated with ACE2 activator resorcinolnaphthalein (RES) or ACE2 inhibitor MLN-4760	ACE2 activation can reduce the severity of LPS-induced acute lung injury via the AMPK/mTOR pathway	Zhang et al[87]
	c57BL/6J mice	Transgenic mice expressing the human ACE2 receptor driven by the cytokeratin-18 (K18) gene promoter (K18-hACE2)	Intranasal inoculation of SARS-CoV-2 in K18-hACE2 mice resulted in high levels of viral infection in lungs	Winkler et al[91]
	c57BL/6J mice	Mice expressing hACE2 in the lung were transduced by oropharyngeal delivery of the recombinant human adenovirus type 5 that expresses hACE2 (Ad5-hACE2)	Mice were infected with SARS-CoV-2 and developed interstitial pneumonia associated with perivascular inflammation, accompanied by a higher viral load in the lungs	Han et al[92]

UAE: Urinary albumin excretion; STZ: Streptozotocin; SD rats: Sprague-Dawley rats; SHR: Spontaneously hypertensive rats; SHRSP: Stroke-prone spontaneously hypertensive rats; SM22: Smooth muscle 22α; LPS: Lipopolysaccharide; SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2; ACE2: Angiotensin-converting enzyme 2.

Table 4 List of epidemiological studies on the role of angiotensin-converting enzyme 2 in diabetes, hypertension, cardiovascular disease, and acute lung injury

Disease	Source country	Patients	Main findings	Ref.
Diabetes	Canada	Renal biopsies from 13 diabetic and 8 control patients	ACE2 mRNA and protein expression were significantly reduced in both the glomeruli and proximal tubules of the diabetic patients	Reich et al[53]
	Japan	66 nondiabetic and 8 diabetic patients with biopsy-proven renal diseases	ACE2 mRNA expression was not significantly changed in the diabetic patients	Konoshita et al[54]
	China	275 Uygur T2D patients and 272 nondiabetic Uygur individuals	ACE2 SNPs rs1978124, rs2048683, rs2074192, rs233575, rs4240157, rs4646156, rs4646188, and rs879922 were associated with T2D	Liu et al[55]
Hypertension	Australia	503 Caucasian subjects with type 2 diabetes	Genetic variation in ACE2 was associated with hypertension and reduced systolic function in men, and hypertension and increased LV mass in women	Patel et al[65]
	China	275 Uygur T2D patients and 272 nondiabetic Uygur individuals	ACE2 SNPs rs2048683, rs233575, rs4240157, rs4646156, rs4646188, and rs879922 were associated with increased SBP, while rs2074192, rs4646188, and rs879922 were associated elevated DBP	Liu et al[55]
	China	402 hypertensive patients and 233 normotensive individuals	ACE2 variant rs2074192 was associated with EH, while rs4240157, rs4646155, and rs4830542 were associated with EH- and hypertension-related atrial fibrillation and left atrial remodeling	Luo et al[66]
	China	3408 untreated hypertensive patients	The T allele of ACE2 rs2106809 was found to confer a 1.6-fold risk for hypertension in women	Fan et al[67]
	China	96 patients with EH and 96 healthy controls	Aberrant methylation of the ACE2 promoter may be associated with EH risk	Fan et al[68]
Cardiovascular disease	United States	11 individuals with dilated cardiomyopathy, 15 individuals with hypertrophic cardiomyopathy, and 16 controls with nonfailing hearts from the Penn Human Heart Tissue Biobank	ACE2 expression was downregulated in fibroblasts, pericytes, and vascular smooth muscle but upregulated in cardiomyocytes in dilated cardiomyopathy and hypertrophic cardiomyopathy	Fan et al[67]
	Hungary	45 healthy individuals, 239 hypertensiveindividuals,141 patients with heart failure (HF) and reduced ejection fraction (HFrEF), and 47 patients with HF and preserved ejection fraction (HFpEF)	ACE2 activity was further increased in HFrEF patients. Serum ACE2 activity was negatively correlated with left ventricular systolic function in HFrEF	Úri et al[74]
	United States	113 patients with chronic systolic heart failure	Elevated plasma soluble ACE2 (sACE2) activity was associated with greater severity of myocardial dysfunction and was an independent predictor of adverse clinical events	Epelman et al[75]
	14 countries across five continents	10753 Prospective Urban Rural Epidemiology participants	Increased concentration of plasma ACE2 was associated with a higher risk of incident heart failure, myocardial infarction, stroke, and diabetes	Narula et al[76]
	Italy	Healthy subjects (C) and EH and Bartter's/Gitelman's (BS/GS) patients	ACE2 was significantly elevated in BS/GS compared with either C or EH	Calò et al[77]
	China	275 Uygur T2D patients and 272 nondiabetic Uygur individuals	ACE2 SNPs rs2074192 and rs879922 were associated with carotid arteriosclerosis stenosis and ACE2 SNPs rs2048683, rs4240157, rs4646156, rs4646188, and rs879922 were linked to heavier left heart remodeling	Liu et al[55]
Acute lung injury	United States	44 patients with acute respiratory distress syndrome (ARDS)	GSK2586881, a rhACE2, was well-tolerated in patients with ARDS, and has been found to reduce Ang II levels and increase Ang 1-7 levels	Khan et al[94]

T2D: type 2 diabetes; EH: Essential hypertension; ACE2: Angiotensin-converting enzyme 2; ARDS: Acute respiratory distress syndrome; SNP: Single nucleotide polymorphism; HF: Heart failure; HFrEF: Heart failure and reduced ejection fraction; HFpEF: Heart failure and preserved ejection fraction; Ang 1-7: Angiotensin 1-7.