Glomerular localization and expression of Angiotensin-converting enzyme 2 and Angiotensin-converting enzyme: implications for albuminuria in diabetes

Expression of ACE and ACE2 in individuals with diabetic kidney disease and healthy controls

BACKGROUND

Angiotensin-converting enzyme (ACE) 2 (ACE2) is expressed mainly in the heart and kidney and forms angiotensin-1-7 from angiotensin II. ACE2 might act in a counterregulatory manner to ACE. There is little information about renal ACE and ACE2 expression in human diabetic nephropathy.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

Kidney tissue from 20 patients with type 2 diabetes and overt nephropathy and 20 healthy kidney donors.

PREDICTOR

Diabetes status.

OUTCOMES & MEASUREMENTS

Renal expression of ACE and ACE2 assessed by means of immunohistochemistry and in situ hybridization. Correlation between ACE and ACE2 expression and levels of various biochemical parameters.

RESULTS

Decreased ACE2 and increased ACE expression in both the tubulointerstitium and glomeruli resulted in a significant (P < 0.001) increase in ACE/ACE2 ratio in patients with diabetes with overt nephropathy compared with controls, although ACE messenger RNA in the tubulointerstitium did not significantly increase. ACE/ACE2 ratio correlated positively with values for mean blood pressure, fasting blood glucose, serum creatinine, proteinuria, and hemoglobin A(1c) and inversely with estimated glomerular filtration rate (P < 0.001).

LIMITATIONS

Inclusion of small number of human renal biopsy specimens with structural distortion of cortical tissue.

CONCLUSIONS

The high ACE/ACE2 ratio in kidneys of patients with type 2 diabetes with overt nephropathy may contribute to renal injury.

Recent advances in the angiotensin-converting enzyme 2-angiotensin(1-7)-Mas axis

In the past few years, the classical concept of the renin-angiotensin system (RAS) has experienced substantial conceptual changes. The identification of: the renin/prorenin receptor; the angiotensin-converting enzyme homologue, ACE2, as an angiotensin peptide-processing enzyme and a virus receptor for severe acute respiratory syndrome, the Mas as a receptor for angiotensin (1-7) [Ang(1-7)], and the possibility of signaling through ACE have contributed to switch our understanding of the RAS from the classical limited-proteolysis linear cascade to a cascade with multiple mediators, multiple receptors and multifunctional enzymes. With regard to Ang(1-7), the identification of ACE2 and of Mas as a receptor implicated in its actions contributed to decisively establish this heptapeptide as a biologically active member of the RAS cascade. In this review, we will focus on the recent findings related to the ACE2-Ang(1-7)-Mas axis and, in particular, on its putative role as an ACE-Ang II-AT(1) receptor counter-regulatory axis within the RAS.

Role of angiotensin-converting enzyme 2 and angiotensin(1-7) in 17beta-oestradiol regulation of renal pathology in renal wrap hypertension in rats

17beta-Oestradiol (E2)-mediated inhibition of angiotensin-converting enzyme (ACE) protects the E2-replete kidney from the progression of hypertensive renal disease. Angiotensin-converting enzyme 2 (ACE2), a homologue of ACE, counters the actions of ACE by catalysing the conversion of angiotensin II (Ang II) to angiotensin(1-7) [Ang(1-7)]. We investigated E2 regulation of ACE2 in the renal wrap (RW) model of hypertension in rats. After 6 weeks on a high-sodium diet (4% NaCl), the activity of ACE2 was reduced in the renal cortex by 31%, which was mirrored by similar decreases in ACE2 protein (30%) and mRNA expression (36%) in the ovariectomized RW rat (RW-OVX); E2 replacement prevented these effects. The RW-OVX rats exhibited greater renal injury, including 1.7-fold more tubulointerstitial fibrosis and 1.6-fold more glomerulosclerosis than E2-replete females (RW-Intact and RW-OVX+E2). Angiotensin(1-7) infusion prevented these exacerbating effects of ovariectomy on renal pathology; no differences in indicators of renal injury were observed between RW-OVX-Ang(1-7) and RW-Intact rats. These renal protective effects of Ang(1-7) infusion were not attributable to increased ACE2 activity or to changes in heart rate or body weight, since these parameters were unchanged by Ang(1-7) infusion. Furthermore, Ang(1-7) infusion did not attenuate renal injury by reducing mean arterial pressure (MAP), since infusion of the peptide did not lower MAP but rather caused a slight increase during a 6 week chronic treatment for Ang(1-7). These results suggest that E2-mediated upregulation of renal ACE2 and the consequent increased Ang(1-7) production contribute to E2-mediated protection from hypertensive renal disease. These findings have implications for E2-deficient women with hypertensive renal disease and suggest that therapeutics targeted towards increasing ACE2 activity and Ang(1-7) levels will be renal protective.

ACE2: a new target for cardiovascular disease therapeutics

The discovery of angiotensin-converting enzyme 2 (ACE2) in 2000 is an important event in the renin-angiotensin system (RAS) story. This enzyme, an homolog of ACE, hydrolyzes angiotensin (Ang) I to produce Ang-(1-9), which is subsequently converted into Ang-(1-7) by a neutral endopeptidase and ACE. ACE2 releases Ang-(1-7) more efficiently than its catalysis of Ang-(1-9) by cleavage of Pro(7)-Phe(8) bound in Ang II. Thus, the major biologically active product of ACE2 is Ang-(1-7), which is considered to be a beneficial peptide of the RAS cascade in the cardiovascular system. This enzyme has 42% identity with the catalytic domain of ACE, is present in most cardiovascular-relevant tissues, and is an ectoenzyme as ACE. Despite these similarities, ACE2 is distinct from ACE. Since it is a monocarboxypeptidase, it has only 1 catalytic site and is insensitive to ACE inhibitors. As a result, ACE2 is a central enzyme in balancing vasoconstrictor and proliferative actions of Ang II with vasodilatory and antiproliferative effects of Ang-(1-7). In this review, we will summarize the role of ACE2 in the cardiovascular system and discuss the importance of ACE2-Ang-(1-7) axis in the control of normal cardiovascular physiology and ACE2 as a potential target in the development of novel therapeutic agents for cardiovascular diseases.

Angiotensin-(1-7) prevents activation of NADPH oxidase and renal vascular dysfunction in diabetic hypertensive rats

BACKGROUND/AIM

We examined the influence of chronic treatment with angiotensin-(1-7) [Ang-(1-7)] on renox (renal NADPH oxidase, NOX-4) and the development of renal dysfunction in streptozotocin-treated spontaneously hypertensive rats (diabetic SHR).

METHODS

Mean arterial pressure, urinary protein and vascular responsiveness of the isolated renal artery to vasoactive agonists were studied in vehicle- or Ang-(1-7)-treated SHR and diabetic SHR.

RESULTS

Ang-(1-7) decreased the elevated levels of renal NADPH oxidase (NOX) activity and attenuated the activation of NOX-4 gene expression in the diabetic SHR kidney. Ang-(1-7) treatment increased sodium excretion but did not affect mean arterial pressure in diabetic SHR. There was a significant increase in urinary protein (266 +/- 22 mg/24 h) in the diabetic compared to control SHR (112 +/- 13 mg/24 h) and treatment of diabetic SHR with Ang-(1-7) reduced the degree of proteinuria (185 +/- 23 mg/24 h, p < 0.05). Ang-(1-7) treatment also attenuated the diabetes-induced increase in renal vascular responsiveness to endothelin-1, norepinephrine, and angiotensin II in SHR, but significantly increased the vasodilation of the renal artery of SHR and diabetic SHR to the vasodilator agonists.

CONCLUSION

These results suggest that treatment with Ang-(1-7) constitutes a potential therapeutic strategy to alleviate NOX-mediated oxidative stress and to reduce renal dysfunction in diabetic hypertensive rats.

Angiotensin-converting enzyme 2 and new insights into the renin-angiotensin system

Components of the renin–angiotensin system are well established targets for pharmacological intervention in a variety of disorders. Many such therapies abrogate the effects of the hypertensive and mitogenic peptide, angiotensin II, by antagonising its interaction with its receptor, or by inhibiting its formative enzyme, angiotensin-converting enzyme (ACE). At the turn of the millennium, a homologous enzyme, termed ACE2, was identified which increasingly shares the limelight with its better-known homologue. In common with ACE, ACE2 is a type I transmembrane metallopeptidase; however, unlike ACE, ACE2 functions as a carboxypeptidase, cleaving a single C-terminal residue from a distinct range of substrates. One such substrate is angiotensin II, which is hydrolysed by ACE2 to the vasodilatory peptide angiotensin 1–7. In this commentary we discuss the latest developments in the rapidly progressing study of the physiological and patho-physiological roles of ACE2 allied with an overview of the current understanding of its molecular and cell biology. We also discuss parallel developments in the study of collectrin, a catalytically inactive homologue of ACE2 with critical functions in the pancreas and kidney.

Loss of angiotensin-converting enzyme-2 (Ace2) accelerates diabetic kidney injury

Diabetic nephropathy is one of the most common causes of end-stage renal failure, but the factors responsible for the development of diabetic nephropathy have not been fully elucidated. We examined the effect of deletion of the angiotensin-convert-ing enzyme 2 (Ace2) gene on diabetic kidney injury. Ace2(-/-) mice were crossed with Akita mice (Ins2(WT/C96Y)), a model of type 1 diabetes mellitus, and four groups of mice were studied at 3 months of age: Ace2(+/y)Ins2(WT/WT), Ace2(-/y)Ins2(WT/WT), Ace2(+/y) Ins2(WT/C96Y), and Ace2(-/y)Ins2(WT/C96Y). Ace2(-/y) Ins2(WT/C96Y) mice exhibited a twofold increase in the urinary albumin excretion rate compared with Ace2(+/y)Ins2(WT/C96Y) mice despite similar blood glucose levels. Ace2(-/y)Ins2(WT/C96Y) mice were the only group to exhibit increased mesangial matrix scores and glomerular basement membrane thicknesses compared with Ace2(+/y)Ins2(WT/WT) mice, accompanied by increased fibronectin and alpha-smooth muscle actin immunostaining in the glomeruli of Ace2(-/y) Ins2(WT/C96Y) mice. There were no differences in blood pressure or heart function to account for the exacerbation of kidney injury. Although kidney levels of angiotensin (Ang) II were not increased in the diabetic mice, treatment with an Ang II receptor blocker reduced urinary albumin excretion rate in Ace2(-/y)Ins2(WT/C96Y) mice, suggesting that acceleration of kidney injury in these mice is Ang II-mediated. We conclude that ACE2 plays a protective role in the diabetic kidney, and ACE2 is an important determinant of diabetic nephropathy.

ACE2 inhibition worsens glomerular injury in association with increased ACE expression in streptozotocin-induced diabetic mice

Angiotensin converting enzyme 2 (ACE2) is localized to the glomerular epithelial cells. Since ACE2 promotes the degradation of angiotensin II, a decrease in ACE2 activity could lead to the development of glomerular injury. We gave a specific ACE2 inhibitor, MLN-4760, for 4 weeks to mice rendered diabetic with streptozotocin. The urinary albumin/creatinine ratio was increased along with expansion of the glomerular matrix in diabetic mice treated with the inhibitor compared to the vehicle-treated mice. Glomerular staining of ACE was increased in the diabetic group and was further significantly increased in the diabetic group treated with MLN-4760. In renal vessels, ACE expression was also increased in the diabetic mice and, again, further increased in those diabetic mice treated with the ACE2 inhibitor. Our study shows that chronic pharmacologic ACE2 inhibition worsens glomerular injury in streptozotocin-induced diabetic mice in association with increased ACE expression.

The emerging role of ACE2 in physiology and disease

The renin–angiotensin–aldosterone system (RAAS) is a key regulator of systemic blood pressure and renal function and a key player in renal and cardiovascular disease. However, its (patho)physiological roles and its architecture are more complex than initially anticipated. Novel RAAS components that may add to our understanding have been discovered in recent years. In particular, the human homologue of ACE (ACE2) has added a higher level of complexity to the RAAS. In a short period of time, ACE2 has been cloned, purified, knocked‐out, knocked‐in; inhibitors have been developed; its 3D structure determined; and new functions have been identified. ACE2 is now implicated in cardiovascular and renal (patho)physiology, diabetes, pregnancy, lung disease and, remarkably, ACE2 serves as a receptor for SARS and NL63 coronaviruses. This review covers available information on the genetic, structural and functional properties of ACE2. Its role in a variety of (patho)physiological conditions and therapeutic options of modulation are discussed. Copyright © 2007 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Angiotensin-converting enzyme I/D and alpha-adducin Gly460Trp polymorphisms: from angiotensin-converting enzyme activity to cardiovascular outcome

The angiotensin-converting enzyme (ACE) I/D and the alpha-adducin (ADD1) Gly460Trp polymorphisms are associated with cardiovascular risk factors. In a prospective population study and in cell models, we investigated the combined effects of these 2 polymorphisms. We randomly recruited 1287 white subjects (women: 50.0%; mean age: 55.9 years). We obtained outcomes from registries and repeat examinations (median 3). Over 9.0 years (median), 178 fatal or nonfatal cardiovascular events occurred. In ADD1 Trp allele carriers, the multivariate-adjusted hazard ratios associated with ACE DD versus I were 1.72 (P=0.007) for total mortality, 2.35 (P=0.02) for cardiovascular mortality, 2.02 (P=0.005) for all cardiovascular events, and 2.59 (P=0.03) for heart failure. In contrast, these hazard ratios did not reach significance in ADD1 GlyGly homozygotes (0.08<or=P<or=0.90). The positive predictive value and attributable risk associated with ACE DD homozygosity combined with mutated ADD1 were 36.2% and 10.3%, respectively. To clarify our epidemiological observations, we investigated the effects of mutated human ADD1 on the membrane-bound ACE activity in fibroblasts from 51 volunteers and in transfected human embryonic kidney cells (31 experiments). In fibroblasts (5.10 versus 3.63 nanomoles of generated hippuric acid per milligram of protein per minute; P=0.0021) and human embryonic kidney cells (1.086 versus 0.081 nmol/mg per minute; P=0.017), the membrane-bound ACE activity increased in the presence but not absence of the ADD1 Trp allele. In conclusion, the combination of ACE DD homozygosity and mutated ADD1 worsened cardiovascular prognosis to a similar extent as classic risk factors, possibly because of increased membrane-bound ACE activity in subjects carrying the ADD1 Trp allele.

Characterization of renin-angiotensin system enzyme activities in cultured mouse podocytes

Intraglomerular ANG II has been linked to glomerular injury. However, little is known about the contribution of podocytes (POD) to intraglomerular ANG II homeostasis. The aim of the present study was to examine the processing of angiotensin substrates by cultured POD. Our approach was to use matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry for peptide determination from conditioned cell media and customized AQUA peptides for quantification. Immortalized mouse POD were incubated with 1-2 microM ANG I, ANG II, or the renin substrate ANG-(1-14) for different time intervals and coincubated in parallel with various inhibitors. Human mesangial cells (MES) were used as controls. POD incubated with 1 microM ANG I primarily formed ANG-(1-9) and ANG-(1-7). In contrast, MES incubated with ANG I primarily generated ANG II. In POD, ANG-(1-7) was the predominant product, and its formation was inhibited by a neprilysin inhibitor. Modest angiotensin-converting enzyme (ACE) activity was also detected in POD, although only after cells were incubated with 2 microM ANG I. In addition, we observed that POD degraded ANG II into ANG III and ANG-(1-7). An aminopeptidase A inhibitor inhibited ANG III formation, and an ACE2 inhibitor led to ANG II accumulation. Furthermore, we found that POD converted ANG-(1-14) to ANG I and ANG-(1-7). This conversion was inhibited by a renin inhibitor. These findings demonstrate that POD express a functional intrinsic renin-angiotensin system characterized by neprilysin, aminopeptidase A, ACE2, and renin activities, which predominantly lead to ANG-(1-7) and ANG-(1-9) formation, as well as ANG II degradation. These findings may reflect a specific role of POD in maintenance of intraglomerular renin-angiotensin system balance.

Angiotensin-(1-7) and the renin-angiotensin system

PURPOSE OF REVIEW

In this review we will focus on the recent findings related to angiotensin-(1-7) as an angiotensin II counter-regulatory peptide within the renin-angiotensin system.

RECENT FINDINGS

The identification of the angiotensin-converting enzyme homologue ACE2 as an angiotensin peptide processing enzyme and of Mas as a receptor for angiotensin-(1-7) has contributed to establishing this heptapeptide as a biologically active member of the renin-angiotensin system cascade.

SUMMARY

The previously unsuspected complexity of the renin-angiotensin system, unmasked by novel findings, has revealed new possibilities for exploring its physiological and pathophysiological roles. In addition, the ACE2-angiotensin-(1-7)-Mas axis may be seriously considered as a putative target for the development of new cardiovascular drugs.