The absence of intrarenal ACE protects against hypertension

Abstract

Activation of the intrarenal renin-angiotensin system (RAS) can elicit hypertension independently from the systemic RAS. However, the precise mechanisms by which intrarenal Ang II increases blood pressure have never been identified. To this end, we studied the responses of mice specifically lacking kidney angiotensin-converting enzyme (ACE) to experimental hypertension. Here, we show that the absence of kidney ACE substantially blunts the hypertension induced by Ang II infusion (a model of high serum Ang II) or by nitric oxide synthesis inhibition (a model of low serum Ang II). Moreover, the renal responses to high serum Ang II observed in wild-type mice, including intrarenal Ang II accumulation, sodium and water retention, and activation of ion transporters in the loop of Henle (NKCC2) and distal nephron (NCC, ENaC, and pendrin) as well as the transporter activating kinases SPAK and OSR1, were effectively prevented in mice that lack kidney ACE. These findings demonstrate that ACE metabolism plays a fundamental role in the responses of the kidney to hypertensive stimuli. In particular, renal ACE activity is required to increase local Ang II, to stimulate sodium transport in loop of Henle and the distal nephron, and to induce hypertension. IntroductionHypertension affects more than 1.5 billion people worldwide and is a key contributor to stroke and cardiovascular and kidney disease. The importance of the renin-angiotensin system (RAS) in the origins of this disorder is underscored by the blood pressure-lowering effects of angiotensin-converting enzyme (ACE) inhibitors and Ang II receptor blockers. However, plasma renin activity, the clinical index used to determine systemic RAS status, is distributed over a wide range in hypertensive subjects (1, 2). This observation prompts the suggestion that alterations in tissue-specific RAS, not detected by plasma renin activity, may underlie hypertension. The kidneys play a central role in long-term blood pressure control through their regulation of sodium and fluid balance. Because renal salt retention is strongly influenced by Ang II and there is a complete RAS along the nephron, it has been suggested that increased local Ang II formation may induce hypertension. Indeed, using gene-targeted mice, we and others have shown that increased intrarenal Ang II formation results in hypertension (3-6). As a whole, these observations suggest that renal Ang II synthesis has important consequences for nephron function and the development of hypertension. However, precisely how the intrarenal generation of Ang II elevates blood pressure is not known. Therefore, we tested the hypothesis that, in conditions in which the intrarenal RAS becomes activated, local Ang II synthesis enhances sodium and water reabsorption along the nephron. In addition, we postulated that inhibiting intrarenal Ang II formation effectively protects against hypertension.

Renal Angiotensin-Converting Enzyme Is Essential for the Hypertension Induced by Nitric Oxide Synthesis Inhibition

“…19 Finally, we validated our assay by measuring the renal angiotensin II content in histologic samples from angiotensin II-infused mice whose contralateral kidney was used to determine angiotensin II concentration by radioimmunoanalysis (Supplemental Figure 5). 8 As previously reported, baseline renal angiotensin II content was similar in wild-type and ACE 10/10 mice ( Figure 5, A and B, Supplemental Figure 6). Importantly, renal angiotensin II content increased significantly in wild-type mice after L-NAME treatment (1.6-fold increase over nontreated mice; P,0.01 by radioimmunoassay), but not in the ACE 10/10 mice ( Figure 5B).…”

“…Second, we quantified angiotensin II concentration in kidney homogenates by radioimmunoanalysis ( Figure 5B). 8 For the IHC protocol, preabsorption experiments demonstrated the absence of cross-reactivity with other relevant RAS peptides/proteins, including angiotensin-(1-7) and angiotensinogen. 18 We also confirmed minimal anti-angiotensin II staining on kidneys of systemic ACE knockout mice, a mouse strain with very little systemic and kidney angiotensin II (Supplemental Figure 4).…”

“…In a recent report, we investigated the responses of mice lacking renal ACE, termed ACE 3/3 and ACE 10/10 mice, to experimental hypertension. 8 Specifically, wild-type and mutant mice were subject to chronic angiotensin II infusion, an experimental model in which the "exogenous" infusion of angiotensin II activates the local renin-angiotensin system (RAS) and induces "endogenous" angiotensin II formation. 9 Remarkably, the absence of renal ACE blunted the hypertension induced by angiotensin II infusion.…”

“…9 Remarkably, the absence of renal ACE blunted the hypertension induced by angiotensin II infusion. 8 This was attributed to the absence of the renal responses observed in wild-type mice, including local angiotensin II accumulation; sodium and water retention; and activation of several key sodium transporters, namely the loop of Henle Na + -K + -2Cl -cotransporter (NKCC2), the distal tubule NaCl cotransporter (NCC), the epithelial sodium channel (ENaC), and pendrin. 8 Thus, these findings support the concept that the renal ACE/angiotensin II pathway works as an important regulator of sodium transport along the nephron, and that activation of this pathway plays an obligatory role in the development of experimental hypertension, even in the presence of high plasma angiotensin II levels.…”

Angiotensin II signaling via protein kinase C phosphorylates Kelch-like 3, preventing WNK4 degradation

“…It is increasingly recognized, however, that AII also directly affects renal epithelia. AT1R is present throughout the nephron (40), and signaling increases activities of the sodium hydrogen exchanger 3 in the proximal tubule, NKCC2 in the TAL, NCC of the DCT, and ENaC in the CNT and CD (41)(42)(43)(44). AII also regulates phosphorylation and activity of MR in renal intercalated cells, allowing induction of a transcellular Cl − reabsorption pathway (14).…”