Renal endosomes contain angiotensin peptides, converting enzyme, and AT_1Areceptors

Abstract

Kidney cortex and proximal tubular angiotensin II (ANG II) levels are greater than can be explained on the basis of circulating ANG II, suggesting intrarenal compartmentalization of these peptides. One possible site of intracellular accumulation is the endosomes. In the present study, we tested for endosomal ANG I, ANG II, angiotensin type 1A receptor (AT1A), and angiotensin converting enzyme (ACE) activity and determined whether these levels are regulated by salt intake. Male Sprague-Dawley rats were fed chow containing either high or low dietary sodium for 10–14 days. Blood and kidneys were harvested and processed for measurement of plasma, kidney, and renal intermicrovillar cleft and endosomal angiotensin levels. Kidney ANG I averaged 179 ± 20 fmol/g and ANG II averaged 258 ± 36 fmol/g in rats fed a high-sodium diet and were significantly higher, averaging 347 ± 58 fmol/g and 386 ± 55 fmol/g, respectively, in rats fed a low-salt diet. Renal intermicrovillar clefts and endosomes contained ANG I and ANG II. Intermicrovillar cleft ANG I and ANG II levels averaged 8.4 ± 2.6 and 74 ± 26 fmol/mg, respectively, in rats fed a high-salt diet and 7.6 ± 1.7 and 70 ± 25 fmol/mg in rats fed a low-salt diet. Endosomal ANG I and ANG II levels averaged 12.3 ± 4.4 and 43 ± 19 fmol/mg, respectively, in rats fed a high-salt diet, and these levels were similar to those observed in rats fed a low-salt diet. Renal endosomes from rats fed a low-salt diet demonstrated significantly more AT1A receptor binding compared with rats fed a high-salt diet. ACE activity was detectable in renal intermicrovillar clefts and was 2.5-fold higher than the levels observed in renal endosomes. Acute enalaprilat treatment decreased ACE activity in renal intermicrovillar clefts by 90% and in renal endosomes by 84%. Likewise, intermicrovillar cleft and endosomal ANG II levels decreased by 61% and 52%, respectively, in enalaprilat-treated animals. These data demonstrate the presence of intact angiotensin peptides and ACE activity in renal intermicrovillar clefts and endosomes, indicating that intact angiotensin peptides are formed and/or trafficked through intracellular endosomal compartments and are dependent on ACE activity.

High-affinity prorenin binding to cardiac man-6-P/IGF-II receptors precedes proteolytic activation to renin

“…Alternatively and perhaps more likely in view of the rapid activation process, cell-activated prorenin may contribute to intracellular angiotensin generation before its destruction. Several studies have provided evidence for intracellular angiotensin generation (17,32,42), and ANG II is known to activate intracellular AT 1 receptors in the cytosol and nucleus (23,27). In the absence of local renin synthesis, such intracellular angiotensin generation will depend on the uptake of circulating renin or prorenin.…”

Review: Novel roles of intracrine angiotensin II and signalling mechanisms in kidney cells

“…There is indirect evidence suggesting proximal tubule cells as potential sites of intrarenal Ang II accumulation. 92 For example, we recently demonstrated increased intracellular uptake of Ang II in renal endosomes of Ang II-infused rats isolated primarily from renal cortical tubules, and this uptake was prevented by the ARB candesartan (figure 2). 36 Ang II has also been shown to stimulate AT 1a -receptor internalisation 95,96 we showed that intracellular Ang II levels were increased more than two-fold when they were incubated with exogenous Ang II, and this response was inhibited by the ARB losartan and the cytoskeleton microtubule inhibitor colchicine or the tyrosine phosphatase inhibitor phenylarsine oxide (PAO).…”

Redox Control of Renal Function and Hypertension

“…Further, recent data also identified renin expression along other parts of the nephron, such as the proximal tubules and collecting ducts (165). Angiotensinogen expression was thought to originate from the liver; however, evidence now exists for strong angiotensinogen expression in kidney cortices, proximal tubules, distal convoluted tubules, and renal endosomes (132,134). It is also expressed weakly in the glomerular endothelial cells (165).…”

“…It is also expressed weakly in the glomerular endothelial cells (165). ACE was thought to originate in the pulmonary epithelium; however, ACE also is expressed abundantly on the brush-border membrane of the PTC, in addition to renal endosomes (132). Furthermore, ACE activity has been detected throughout the nephron by others (25).…”