Characterization of Renal Angiotensin-Converting Enzyme 2 in Diabetic Nephropathy

Abstract

Abstract-ACE2, initially cloned from a human heart, is a recently described homologue of angiotensin-converting enzyme (ACE) but contains only a single enzymatic site that catalyzes the cleavage of angiotensin I to angiotensin 1-9 [Ang(1-9)] and is not inhibited by classic ACE inhibitors. It also converts angiotensin II to Ang(1-7). Although the role of ACE2 in the regulation of the renin-angiotensin system is not known, the renin-angiotensin system has been implicated in the pathogenesis of diabetic complications and in particular in diabetic nephropathy. Therefore, the aim of this study was to assess the possible involvement of this new enzyme in the kidney from diabetic Sprague-Dawley rats to compare and contrast it to ACE. ACE2 and ACE gene and protein expression were measured in the kidney after 24 weeks of streptozocin diabetes. ACE2 and ACE mRNA levels were decreased in diabetic renal tubules by Ϸ50% and were not influenced by ACE inhibitor treatment with ramipril. By immunostaining, both ACE2 and ACE protein were localized predominantly to renal tubules. In the diabetic kidney, there was reduced ACE2 protein expression that was prevented by ACE inhibitor therapy. The identification of ACE2 in the kidney, its modulation in diabetes, and the recent description that this enzyme plays a biological role in the generation and degradation of various angiotensin peptides provides a rationale to further explore the role of this enzyme in various pathophysiological states including diabetic complications. Key Words: angiotensin-converting enzyme Ⅲ diabetic nephropathy Ⅲ angiotensin Ⅲ diabetes mellitus A ngiotensin-converting enzyme (ACE) is a key enzyme in the renin-angiotensin system (RAS). 1 It contains 2 active domains and converts angiotensin I to angiotensin II, which is a potent vasoconstrictor, growth modulator, and proinflammatory peptide. In addition, this enzyme degrades bradykinin, a vasodilator. 1 A chemically related enzyme, ACE-related carboxypeptidase, also known as ACE2, has recently been cloned and identified by 2 different groups. 2,3 ACE2 has 42% homology with ACE at the metalloprotease catalytic domain 2,3 but differs from ACE in having only one enzymatic site. In humans, ACE2 transcripts have been identified in the heart, kidney, and testis. 2,3 It has been shown that recombinant ACE2 hydrolyses the carboxy terminal leucine from angiotensin I to generate angiotensin(1-9). 2,3 ACE2 also has a high affinity for angiotensin II, 4 resulting in its degradation to the vasodilator, angiotensin(1-7). 2 Furthermore, ACE2 is not inhibited by classic ACE inhibitors such as captopril and lisinopril. 2 A rat homologue of ACE2 has been cloned (GenBank No. AF291820) that allows exploration of this metalloprotease in rodents in normal and disease states such as diabetes, in which the RAS is considered to play a pivotal role in the development of complications. 5

Polymorphisms in the gene encoding angiotensin I converting enzyme 2 and diabetic nephropathy

“…Given that ACE2 expression is altered not only in the rat diabetic kidney [4] but also in human kidney disease [5], an association between gene variants and diabetic nephropathy could be expected. However, the present study did not detect any such association.…”

“…ACE2 is highly expressed in kidney, testis and heart and has been implicated in hypertension and cardiovascular disease [3]. Interestingly, ACE2 production is decreased in rat diabetic kidney [4] and is altered in human kidney disease such that neo-expression of ACE2 occurs in glomerular and peritubular capillary endothelium [5]. The only study published to date on ACE2 polymorphisms and essential hypertension reported no association [6].…”

The contribution of hypertension to diabetic nephropathy and retinopathy: the role of inflammation and oxidative stress

“…128 In the kidney, ACE2 has a distribution similar to ACE, with major localization in renal tubules. [128][129][130] It has been suggested that both mRNA and protein expression of ACE2 are reduced in kidney biopsy specimens from type 2 diabetic patients with nephropathy compared with normal controls or patients with other renal disease. 131 In another study, ACE2 levels in kidney biopsy of diabetic patients were reduced only at the protein level, not at the mRNA level, and only in the tubulointerstitial region, not in the glomeruli, compared with non-diabetic controls.…”

“…131 In another study, ACE2 levels in kidney biopsy of diabetic patients were reduced only at the protein level, not at the mRNA level, and only in the tubulointerstitial region, not in the glomeruli, compared with non-diabetic controls. 132 In experimental models of diabetes-associated kidney disease, it has been shown that ACE2 may be reduced 129 or elevated. 133 Reasons for this discrepancy may be attributed to the duration of diabetes and different methodology in assessing ACE2, gene or protein expression, or their activity.…”

A developmental nephron deficit in rats is associated with increased susceptibility to a secondary renal injury due to advanced glycation end-products

“…The samples from the control kidneys were used as the calibrator and given an arbitrary value of 1, and the treatment groups were compared with this calibrator [26].…”