Angiotensin-converting enzyme 2 (ACE2) expression has been shown to be altered in renal tubules from diabetic mice. This study examined the localization of ACE and ACE2 within the glomerulus of kidneys from control (db/m) and diabetic (db/db) mice and the effect of chronic pharmacologic ACE2 inhibition. ACE2 co-localized with glomerular epithelial cell (podocyte) markers, and its localization within the podocyte was confirmed by immunogold labeling. ACE, by contrast, was seen only in glomerular endothelial cells. By immunohistochemistry, in glomeruli from db/db mice, strong ACE staining was found more frequently than in control mice (db/db 64.6 ؎ 6.3 versus db/m 17.8 ؎ 3.4%; P < 0.005). By contrast, strong ACE2 staining in glomeruli from diabetic mice was less frequently seen than in controls (db/db 4.3 ؎ 2.4 versus db/m 30.6 ؎ 13.6%; P < 0.05). For investigation of the significance of reduced glomerular ACE2 expression, db/db mice were treated for 16 wk with a specific ACE2 inhibitor (MLN-4760) alone or combined with telmisartan, a specific angiotensin II type 1 receptor blocker. At the end of the study, glomerular staining for fibronectin, an extracellular matrix protein, was increased in both db/db and db/m mice that were treated with MLN-4760. Urinary albumin excretion (UAE) increased significantly in MLN-4760 -treated as compared with vehicle-treated db/db mice (743 ؎ 200 versus 247 ؎ 53.9 g albumin/mg creatinine, respectively; P < 0.05), and the concomitant administration of telmisartan completely prevented the increase in UAE associated with the ACE2 inhibitor (161 ؎ 56; P < 0.05). It is concluded that ACE2 is localized in the podocyte and that in db/db mice glomerular expression of ACE2 is reduced whereas glomerular ACE expression is increased. The finding that chronic ACE2 inhibition increases UAE suggests that ACE2, likely by modulating the levels of glomerular angiotensin II via its degradation, may be a target for therapeutic interventions that aim to reduce albuminuria and glomerular injury.

Abstract-Angiotensin (Ang)-converting enzyme 2 (ACE2) cleaves Ang II to form Ang-(1-7). Here we examined whether soluble human recombinant ACE2 (rACE2) can efficiently lower Ang II and increase Ang-(1-7) and whether rACE2 can prevent hypertension caused by Ang II infusion as a result of systemic versus local mechanisms of ACE2 activity amplification. rACE2 was infused via osmotic minipumps for 3 days in conscious mice or acutely in anesthetized mice. rACE2 caused a dose-dependent increase in serum ACE2 activity but had no effect on kidney or cardiac ACE2 activity. After Ang II infusion (40 pmol/min), rACE2 (1 mg/kg per day) resulted in normalization of systolic blood pressure and plasma Ang II. In acute studies, rACE2 (1 mg/kg) prevented the rapid hypertensive effect of Ang II (0.2 mg/kg), and this was associated with both a decrease in Ang II and an increase in Ang-(1-7) in plasma. Moreover, during infusion of Ang II, the effect of rACE2 on blood pressure was unaffected by a specific Ang-(1-7) receptor blocker, A779 (0.2 mg/kg), and infusing supraphysiologic levels of Ang-(1-7) (0.2 mg/kg) had no effect on blood pressure. We conclude that, during Ang II infusion, rACE2 effectively degrades Ang II and, in the process, normalizes blood pressure. The mechanism of rACE2 action results from an increase in systemic, not tissue, ACE2 activity and the lowering of plasma Ang II rather than the attendant increase in Ang-(1-7). Increasing ACE2 activity may provide a new therapeutic target in states of Ang II overactivity by enhancing its degradation, an approach that differs from the current focus on blocking Ang II formation and action. (Hypertension. 2010;55:90-98.)A ngiotensin (Ang)-converting enzyme 2 (ACE2) is the only known enzymatically active homologue of Angconverting enzyme (ACE). 1-3 ACE2 is a monocarboxypeptidase that removes single amino acids from the C terminus of its substrates. 1-3 ACE, by contrast, is a peptidyl dipeptidase that removes C-terminal dipeptides. ACE promotes Ang II formation from Ang I, whereas ACE2 converts Ang I to Ang-(1-9) and Ang II to Ang-(1-7), respectively. 1-3 The catalytic efficiency of human ACE2 is 400-fold higher with Ang II than with Ang I as a substrate. 3 Moreover, because the product of Ang I cleavage by ACE2, Ang-(1-9), has no known biological action, it seems logical to postulate that cleavage of Ang II to Ang-(1-7) is a major action of ACE2.There is increasing interest in the possible renoprotective effects of ACE2. 4 -9 A protective effect of ACE2 against acute lung injury 10,11 and cardiovascular disease 12,13 has also been proposed. Ang-(1-7) is a blood-vessel dilator identified as an endogenous ligand for a G protein-coupled Mas receptor. 14 -16 Ang II, among its many other known biological effects, is a potent vasoconstrictor and promotes renal sodium retention, both of which lead to hypertension.The blockade of steps leading to Ang II formation using ACE inhibitors and renin inhibitors or blocking the action of Ang II on the Ang II type 1 receptor using specific an...