Increased Urinary Angiotensin-Converting Enzyme 2 in Renal Transplant Patients with Diabetes

Angiotensin-converting enzyme 2 (ACE2) is expressed in the kidney and may be a renoprotective enzyme, since it converts angiotensin (Ang) II to Ang-(1-7). ACE2 has been detected in urine from patients with chronic kidney disease. We measured urinary ACE2 activity and protein levels in renal transplant patients (age 54 yrs, 65% male, 38% diabetes, n = 100) and healthy controls (age 45 yrs, 26% male, n = 50), and determined factors associated with elevated urinary ACE2 in the patients. Urine from transplant subjects was also assayed for ACE mRNA and protein. No subjects were taking inhibitors of the renin-angiotensin system. Urinary ACE2 levels were significantly higher in transplant patients compared to controls (p = 0.003 for ACE2 activity, and p≤0.001 for ACE2 protein by ELISA or western analysis). Transplant patients with diabetes mellitus had significantly increased urinary ACE2 activity and protein levels compared to non-diabetics (p<0.001), while ACE2 mRNA levels did not differ. Urinary ACE activity and protein were significantly increased in diabetic transplant subjects, while ACE mRNA levels did not differ from non-diabetic subjects. After adjusting for confounding variables, diabetes was significantly associated with urinary ACE2 activity (p = 0.003) and protein levels (p<0.001), while female gender was associated with urinary mRNA levels for both ACE2 and ACE. These data indicate that urinary ACE2 is increased in renal transplant recipients with diabetes, possibly due to increased shedding from tubular cells. Urinary ACE2 could be a marker of renal renin-angiotensin system activation in these patients

The effect of angiotensin-(1-7) in mouse unilateral ureteral obstruction

Angiotensin-(1-7) is a ligand for the Mas receptor and may protect against tissue injury associated with renin-angiotensin system activation. We determined the effects of endogenous or exogenous angiotensin-(1-7) in mice with unilateral ureteral obstruction (UUO). Mice with UUO were treated with or without the angiotensin-(1-7) antagonist A779 or with 6, 24, or 62 μg/kg per hour exogenous angiotensin-(1-7). After 10 days, kidneys were harvested for histology, immunoblots, and measurement of NADPH oxidase. Compared with controls, A779 treatment significantly increased fibronectin, transforming growth factor-β, and α-smooth muscle actin expression in obstructed kidneys and enhanced tubulointerstitial injury, apoptosis, and NADPH oxidase. Unexpectedly, administration of angiotensin-(1-7) to mice with UUO caused injury in obstructed kidneys compared with controls and increased macrophage infiltration. In obstructed kidneys from mice with gene deletion of Mas (Mas−/−), apoptosis and macrophage infiltration were increased compared with wild-type mice. Angiotensin-(1-7) (but not A779) further increased apoptosis and macrophage influx in obstructed kidneys from Mas−/− mice, compared with untreated Mas−/− mice. These data indicate that endogenous angiotensin-(1-7) protects against kidney injury in UUO. In mice with or without the Mas receptor, however, delivery of exogenous angiotensin-(1-7) worsens kidney damage. The results suggest dose-dependent effects of angiotensin-(1-7) in the kidney in UUO, with endogenous angiotensin-(1-7) promoting repair pathways via interaction with Mas and higher amounts exacerbating injury

Early diabetes mellitus stimulates proximal tubule renin mRNA expression in the rat

Early diabetes mellitus stimulates proximal tubule renin mRNA expression in the rat.BackgroundEnhanced intrarenal angiotensin II (Ang II) activity may contribute to diabetic nephropathy. The proximal tubule is a proposed site of significant intrarenal Ang II production. We determined the effect of early diabetes on mRNA expression of components of the proximal tubule renin-angiotensin system.MethodsThree groups of male Sprague-Dawley rats were studied after two weeks: (1) control (C), (2) streptozotocin-induced diabetes (STZ), and (3) STZ-induced diabetes, with normoglycemia maintained by insulin implants (STZ-I). Competitive reverse transcription-polymerase chain reaction was used to assay mRNA for renin, angiotensinogen, and angiotensin-converting enzyme in suspensions of proximal tubules; plasma and kidney levels of Ang II were measured by radioimmunoassay, and Western analysis of Ang II subtype 1 (AT1) receptors was performed.ResultsSTZ rats tended to have increased plasma and intrarenal levels of Ang II compared with C and STZ-I rats. In proximal tubules, mRNA for renin was significantly increased in STZ rats, with reversal to control values in STZ-I rats (C, 2432 ± 437 vs. STZ, 5688 ± 890 fg/0.25 μg RNA, P < 0.05 vs. C, N = 9, vs. STZ-I, 1676 ± 376 fg/0.25 μg RNA, P = NS vs. C). In STZ rats, the AT1 receptor antagonist losartan caused a further fivefold increase in proximal tubule renin mRNA, associated with proximal tubular renin immunostaining. STZ had no significant effect on mRNA expression for angiotensinogen or angiotensin-converting enzyme in proximal tubules. By Western blot analysis, cortical and proximal tubule AT1 receptor protein expression was significantly decreased in STZ rats.ConclusionsThese data suggest activation of the proximal tubule renin-angiotensin system in early STZ diabetes, mediated at least partly by enhanced expression of renin mRNA. Increased local production of Ang II could contribute to tubulointerstitial injury in this model

Immunoblot analysis of ACE2 protein in media and cell lysates from mouse PT cells.

<p>(A) Representative immunoblot for ACE2 protein in concentrated media (Lanes 1–3) and cell lysates (Lanes 4–6) from mouse PT cells. Lanes 1 and 4: wildtype cells, Lanes 2 and 5: ACE2 knockout (KO) cells, Lanes 3 and 6: ACE2 KO cells transfected with a human ACE2 expression vector, Lane 7: mouse kidney cortex showing a band at ∼100 kDa, used as a positive control. Lane 1 shows two bands in the media at ∼90 kDa and ∼70 kDa for mouse ACE2. Lane 3 shows two bands in the media for human ACE2 in transfected cells, at ∼110 kDa and ∼95 kDa. Lanes 4 and 6 show a single band in cell lysates at ∼100 kDa for mouse ACE2, and ∼120 kDa for human ACE2, respectively. Lanes 2 and 5 show no ACE2 bands detected on immunoblots of both media and cell lysates from untransfected ACE2 KO cells. (B) Increased ACE2 activity in the media from ACE2 KO cells transfected with a human ACE2 expression vector (HA-hACE2, 3.75 µg on 35 mm culture dishes). Untransfected cells and cells transfected with an empty pcDNA3 vector had no detectable ACE2 activity in the media. Numbers in parentheses represent mean values for ACE2 activity. *P<0.001 vs untransfected control or empty pcDNA3 vector, n = 4.</p