Abstract 019: Specific Knockdown of Renal Tubular Epithelial Ace Prevents Salt Sensitivity
We previously showed that mice lacking renal angiotensin-converting enzyme (ACE) do not accumulate angiotensin (Ang) II in the kidney and are protected against different forms of experimental hypertension, including salt sensitivity. However, these studies did not identify the locus of renal Ang II generation. Since ACE expression is high in the renal epithelium, we hypothesize that tubular epithelial ACE is the main source of renal Ang II and, is responsible for salt sensitivity. To study this, we designed an inducible tubular ACE knockdown mouse (it-ACE) that has three transgenes: one encoding the transcription factor tTA (Tet-off transactivator) that is under the control of the KSP-cadherin promoter only expressed in renal tubular cells. The second and third transgenes are activated by tTA and encode a short-hairpin RNAs (sh-RNA) degrading ACE mRNA in renal tubules. We found a lower basal ACE expression in the kidney of it-ACE compared to WT mice (19 ± 4 vs. 100 ± 26 AU; p<0.01 by Western blot). Selective tubular ACE suppression was confirmed by immunohistochemistry. At baseline, it-ACE mice display normal systolic blood pressure (SBP; 108 ± 4 mmHg), GFR (1288 ± 24 μl/min/100g b.w.) and urine concentration (2516 ± 184 mOsm/Kg after 12h water deprivation) compared to WT mice. To test the response of it-ACE mice to salt-sensitivity, we used a post L-NAME salt sensitivity protocol: L-NAME (0.5 mg/mL; 4 weeks), washout (1 week), high salt diet (HS, NaCl 4%, 3 weeks). In WT mice, L-NAME increased SBP from 109 ± 5 to 139 ± 4 mmHg (p<0.01; n=5). SBP then returned to baseline during the washout and increased again in response to the HS diet (135 ± 3 mmHg; p<0.01). Thus, WT mice, previously salt resistant, became salt sensitive. Remarkably, it-ACE mice, despite being as hypertensive as WT during the L-NAME phase, were still protected against salt sensitivity (110 ± 3 mmHg; p<0.01 vs. WT; n=6). Finally, we treated it-ACE mice with doxycycline (a tTA blocker) to restore tubular ACE specifically during the HS phase. Restoring tubular ACE in the mutant mice induced the development of salt sensitivity (134 ± 6 mmHg; p<0.01 vs. baseline; n=5). In conclusion, our data indicate that tubular epithelial ACE, and not ACE expression in endothelium or other locations, is essential for salt sensitivity.
Author Disclosures: J.F. Giani: None. S. Fuchs: None. E.A. Bernstein: None. K.E. Bernstein: None. R.A. Gonzalez-Villalobos: None.
This research has received full or partial funding support from the American Heart Association, Western States Affiliate (California, Nevada & Utah).
- © 2015 by American Heart Association, Inc.