Interacting molecule of AT1 receptor, ATRAP, is colocalized with AT1 receptor in the mouse renal tubules

The renin-angiotensin system in the kidney plays a critical role in the regulation of renal hemodynamics and sodium handling through the activation of vascular, glomerular and tubular angiotensin II type 1 (AT1) receptor-mediated signaling. We previously cloned a molecule that specifically bound to the AT1 receptor and modulated AT1 receptor signaling in vitro, which we named ATRAP (for AT1 receptor-associated protein). The purpose of this study is to analyze the renal distribution of ATRAP and to examine whether ATRAP is co-expressed with the AT1 receptor in the mouse kidney. We performed in situ hybridization, Western blot analysis, and immunohistochemistry to investigate the expression of ATRAP mRNA and protein in the mouse kidney. The results of Western blot analysis revealed the ATRAP protein to be abundantly expressed in the kidney. Employing in situ hybridization and immunohistochemistry, we found that both ATRAP mRNA and the protein were widely distributed along the renal tubules from Bowman's capsules to the inner medullary collecting ducts. ATRAP mRNA was also detected in the glomeruli, vasculature, and interstitial cells. In all tubular cells, the ATRAP protein colocalized with the AT1 receptor. Finally, we found that the dietary salt depletion significantly decreased the renal expression of ATRAP as well as AT1 receptor. These findings show ATRAP to be abundantly and broadly distributed in nephron segments where the AT1 receptor is expressed. Furthermore, this is the first report demonstrating a substantial colocalization of ATRAP and AT1 receptor in vivo.

Angiotensin II-induced calcium signaling in the afferent arteriole from rats with two-kidney, one-clip hypertension

The aim of this study was to investigate ANG II-induced Ca2+signaling in freshly isolated afferent arterioles (AA) from two-kidney, one-clip hypertensive (2K1C) rats, which have an elevated plasma and renal ANG II level, and different perfusion pressure and vascular tone in the clipped and nonclipped kidney. The Ca2+responses in vessels from 2K1C and control rats were similar in all groups ( P > 0.1). The intracellular Ca2+(Cai2+) response in the afferent arteriole after 10−8M ANG II stimulation was 0.57 ± 0.10, 0.50 ± 0.07, 0.48 ± 0.04, and 0.36 ± 0.05 in the control, sham, nonclipped, and clipped kidney, respectively. These data were consistent with the finding of unchanged AT1aR mRNA levels in AAs from all groups. Although the absolute values were similar, the dose-response curves to ANG II were different. In the control, sham, and nonclipped kidney from 2K1C, the dose-response curve leveled off between 10−8and 10−6M ANG II. In the clipped kidney, the dose-response curve was linear, with a significantly increased response at 10−6M compared with 10−8M ANG II ( P < 0.05). Inhibition of cyclooxygenase-1 (COX-1) with indomethacin enhanced the ANG II response in the nonclipped (Δ0.30 ± 0.09) and clipped (Δ0.30 ± 0.09) kidneys from 2K1C ( P < 0.005), but not in control rats (Δ−0.02 ± 0.11, P > 0.8). Conclusively, the ANG II-induced Cai2+response was reduced by COX-1-derived prostaglandins in 2K1C, in contrast to control animals, where the COX-1 inhibition had no effect. COX-2 inhibition with NS-398 did not increase the ANG II-mediated Cai2+response in any of the groups.

Angiotensin II production and distribution in the kidney--II. Model-based analysis of experimental data

Information on the regional concentrations of angiotensin (Ang) II and its type-1 and -2 receptors (AT(1)R, AT(2)R) in the kidney is still incomplete. Published data on the levels of arterially delivered Ang I and II (Ang Ia, Ang IIa) and intrarenally produced Ang I and II (Ang Ii, Ang IIi) in the renal vein and in whole tissue were analyzed by using a kinetic model of Ang production and distribution in the glomerular and peritubular cortical tissue regions (Glom, Pt). (1) 90% of Ang II is cell-associated, due to its binding to AT(1)R and AT(2)R; (2) most Ang II in the renal cortex is Ang IIi; (3) Ang IIa is mainly localized in Glom; (4) Ang Ii rather than Ang Ia is a substrate of renal angiotensin-converting enzyme; (5) Ang IIi is localized in Pt and its concentration in interstitial fluid is 5-15 times the Ang II concentration in arterial plasma; and (6) in Glom the interstitial concentration of cell surface-bound AT(1)R is above 200K(d), and in Pt the AT(1)R and AT(2)R concentrations are above 10K(d). In conclusion, endocrine Ang II mainly acts in Glom, whereas Pt is exposed to paracrine Ang II generated by the conversion of intrarenally produced Ang I. High AT(1)R concentrations in Glom and Pt favor diffusion-limited binding, so that the apparent binding rate constant at sites closest to the source of Ang II delivery is greatly increased. Results may explain why the kidney is responsive to low levels of endocrine Ang II, despite its high content of paracrine Ang II.

NADPH oxidases are in part responsible for increased cardiovascular superoxide production during aging

The aim of our study was to examine in rats, age-related differences in myocardial ischemic recovery and to determine the possible relationship with modification of cardiac and vascular oxidative stress. Isolated perfused hearts from young (2 months), adult (6 months), and old (21 months) Wistar rats were subjected to a ischemia-reperfusion sequence. Vascular histomorphological analyses were performed and NADPH oxidase was studied. The expression of angiotensin AT(1) receptors was evaluated using immunostaining. During the preischemic period, but also after ischemia, an aged-related decrease in myocardial functional parameters was observed, and was associated with an increased release of reactive oxygen species. In aortas, the activity and expression of NADPH oxidase increased with age according to the ESR, fluorescence microscopy, and immunohistochemistry; the NADPH oxidase involved was localized in endothelial cells. We found an age-related increase in the expression of endothelial angiotensin AT(1). Our study suggests that myocardial function and adaptation to ischemia-reperfusion declined during aging and are related to a higher level of oxidative stress. Endothelial NADPH oxidase is a major contributor to age-related cardiovascular deterioration. One of the regulators of vascular NADPH oxidase activity, the renin-angiotensin system, may be involved in the modulation of vascular superoxide production during the aging process.

Intravenous insulin-like growth factor-I receptor antisense treatment reduces angiotensin receptor expression and function in spontaneously hypertensive rats

The present study investigated the effects of a functional deficit in insulin-like growth factor-I signaling via chronic intravenous administration of insulin-like growth factor-I (IGF-I) receptor antisense in the conscious spontaneously hypertensive rat cardiovascular system. Insulin-like growth factor-I receptor (IGF-IR) antisense, but not full mismatch treatment, decreased IGF-IR expression in both conductance and resistance blood vessels. Aortic IGF-IR density was reduced by 67.4 +/- 6.0% in antisense-treated spontaneously hypertensive rat (SHR) compared with untreated animals, whereas mismatch treatment had no effect (analysis of variance, n = 3, P < 0.01). Aortic and tail artery angiotensin II type 1 receptor expression was significantly reduced by IGF-IR antisense treatment, whereas angiotensin II type 2 receptor expression was unaffected by administration of antisense and mismatch oligonucleotides. IGF-I receptor antisense treatment caused a significant decrease in pressor responses to angiotensin II in comparison with full-length mismatch treatment (E(max) was reduced to 65 +/- 7 mm Hg compared with 99 +/- 6 mm Hg, p < 0.05). Likewise, a reduction in pressor responses to noradrenaline was observed in hypertensive rats treated with IGF-IR antisense compared with full mismatch-treated rats (E(max) was reduced to 60 +/- 6 mm Hg compared with 108 +/- 5 mm Hg, p < 0.01). There was no clear antisense effect on resting blood pressure and no effect at on aortic medial thickness. These results suggest that although the proliferative and vasodilator effects of IGF-I are impaired in SHR, the effects on angiotensin receptor expression remain profound.

Renin-angiotensin system is an important factor in hormone refractory prostate cancer

BACKGROUND

The aim of this study was to perform a comprehensive evaluation of the renin-angiotensin system (RAS) in prostate cancer.

METHODS

We investigated the expression of RAS components in prostate cancer cells treated with hormonal agents. Real-time PCR data showed the expression of the AT1 receptor, angiotensin I converting enzyme (ACE), and angiotensin I/II (Ang-I/II) precursor in all 87 prostate tissue samples.

RESULTS

Expression of these genes in hormone refractory prostate cancer (HRPC) was significantly higher than that in normal prostate tissue and untreated prostate cancer tissue. Western blot showed that protein expression of the AT1 receptor and Ang-I/II was enhanced in LNCaP cells cultivated in steroid-free medium. When LNCaP cells were stimulated with dihydrotestosterone (DHT), estradiol (E2), dexamethasone (DEX), or anti-androgen drugs, protein expression of the AT1 receptor and Ang-I/II was augmented.

CONCLUSIONS

The present data suggest that prostatic RAS is overexpressed in HRPC tissue, and expression of its components is influenced by several kinds of hormonal stimulation.

Exercise-induced apoptosis in rat kidney is mediated by both angiotensin II AT1 and AT2 receptors

Excessive physical exercise may lead to disturbance of the entire homeostasis in the body, including damage not only in skeletal muscles but also in many distant organs. The mechanisms responsible for the exercise-induced changes could include oxidative stress or angiotensin II. We previously showed that acute exercise led to apoptosis in kidney but not as a result of oxidative stress. In this study, we examined the role of angiotensin II and its AT1 and AT2 receptors in mediation of exercise-induced apoptosis in kidney. We clearly demonstrated that acute physical exercise induced apoptosis in renal cells of distal convoluted tubuli and cortical and medullary collecting ducts. Moreover, the cells displayed an increased expression of both AT1 and AT2 angiotensin II receptors and of p53 protein. The results suggest that angiotensin II could upregulate p53 expression in renal distal convoluted tubular cells and in the cells collecting ducts via both AT1 and AT2 receptors, which might be the crucial apoptosis-mediating mechanism in kidneys after excessive exercise.

Pathophysiological regulation of the AT1-receptor and implications for vascular disease

BACKGROUND

Numerous studies have demonstrated that activation of the angiotensin II type 1 (AT1) receptor plays an important role in the pathogenesis of cardiovascular diseases.

RESULTS

AT1-receptor activation by angiotensin II is not only involved in the regulation of blood pressure, water and sodium homeostasis, and control of other neurohumoral systems, but also leads to excessive production of reactive oxygen species and to hypertrophy, proliferation, migration, and apoptosis of vascular cells. AT1-receptor-induced oxidative stress may cause nitric oxide inactivation, lipid oxidation, and activation of redox-sensitive genes, such as chemotaxis and adhesion molecules, pro-inflammatory cytokines, and matrix metalloproteinases, all of which are involved in the initiation and progression of endothelial dysfunction and manifested atherosclerosis. The expression levels of the AT1-receptor define the biological efficacy of angiotensin II. Many agonists, such as, for example, angiotensin II, growth factors, low-density lipoprotein cholesterol, insulin, glucose, estrogen, progesterone, reactive oxygen species, cytokines, nitric oxide, and many others, are known to regulate AT1-receptor expression in vascular cells. The pathophysiological relevance of dysregulated AT1-receptor expression has been demonstrated in many cell culture and animal studies and interventional trials in humans. Hypercholesterolemia, estrogen deficiency, and diabetes mellitus are associated with enhanced vascular AT1-receptor expression, increased oxidative stress, and endothelial dysfunction. Importantly, treatment with AT1-receptor blockers may inhibit the onset and progression of vascular oxidative stress and inflammation, endothelial dysfunction, atherosclerosis, and related organ damage.

CONCLUSION

Inhibition of AT1-receptor activation is presumably a primary treatment goal in patients suffering from cardiovascular risk factors or manifested atherosclerotic diseases.

Intravenous IGF-I receptor antisense reduces IGF-IR expression and diminishes pressor responses to angiotensin II in conscious normotensive rats

Given the variety of cardiovascular effects of insulin-like growth factor-I (IGF-I), we investigated the effects of a functional deficit in IGF-I signalling in the conscious rat cardiovascular system using intravenous IGF-I receptor antisense (AS, 0.5 nmol) treatment.Insulin-like growth factor-I receptor (IGF-IR) immunoreactivity was reduced in IGF-IR AS-treated tail arteries. Western immunoblot analysis demonstrated a decrease in cardiac IGF-IR in IGF-IR AS-treated rats; treatment reduced the expression of IGF-IR to 83+/-6% of that in samples from vehicle-treated rats, compared to 99+/-3% for a control, full-mismatch oligonucleotide (MM-18) or 100% (vehicle).IGF-IR AS treatment had no effect on resting blood pressure during the 14-day treatment period. Pressor responses (as measured by increase in systolic arterial pressure) to angiotensin II (AngII) gradually decreased over 2 weeks treatment with IGF-IR AS (5 x 0.5 nmol per intravenous injection, 2 weeks), and were significantly reduced at treatment day 14 compared to day 7 (2.7-fold rightward shift). IGF-IR AS treatment caused a significant rightward shift in the angiotensin II (AngII) dose-response compared to both vehicle and full-mismatch treated rats (4.0-fold shift compared to vehicle, P<0.01, n=6-14). There was a significant decrease in cardiac angiotensin II type 1 receptor (AT(1)R) expression in AS-treated rats compared to vehicle-treated rats; cardiac AT(1)R was decreased to 80+/-6% in comparison to 100%. AT(1)R immunoreactivity was also reduced in IGF-IR AS-treated tail arteries.IGF-IR AS treatment resulted in structural changes in both the heart and aortae, with small but significant differences observed between left ventricle/bodyweight ratios of AS and both vehicle- and MM-18-treated rats (n=8, P<0.05). Aortic cross-sectional areas of AS-treated rats were significantly lower than MM-18- and vehicle-treated rats (27.4+/-5.7% reduction of vehicle-treated samples, n=8, P<0.01). The results of this study suggest that an induced loss of IGF-IR, while not affecting resting blood pressure, has a predominantly inhibitory effect on vascular response to vasoconstrictor agents including angiotensin II. This may occur through downstream effects on AT1R expression, via modulation of the expression of receptors for other vasoactive signalling molecules, or via changes in myocyte proliferation.

Differential expression of nuclear AT1 receptors and angiotensin II within the kidney of the male congenic mRen2. Lewis rat

We established a new congenic model of hypertension, the mRen(2). Lewis rat and assessed the intracellular expression of angiotensin peptides and receptors in the kidney. The congenic strain was established from the backcross of the (mRen2)27 transgenic rat that expresses the mouse renin 2 gene onto the Lewis strain. The 20-wk-old male congenic rats were markedly hypertensive compared with the Lewis controls (systolic blood pressure: 195 +/- 2 vs. 107 +/- 2 mmHg, P < 0.01). Although plasma ANG II levels were not different between strains, circulating levels of ANG-(1-7) were 270% higher and ANG I concentrations were 40% lower in the mRen2. Lewis rats. In contrast, both cortical (CORT) and medullary (MED) ANG II concentrations were 60% higher in the mRen2. Lewis rats, whereas tissue ANG I was 66 and 84% lower in CORT and MED. For both strains, MED ANG II, ANG I, and ANG-(1-7) were significantly higher than CORT levels. Intracellular ANG II binding distinguished nuclear (NUC) and plasma membrane (PM) receptor using the ANG II radioligand 125I-sarthran. Isolated CORT nuclei exhibited a high density (Bmax >200 fmol/mg protein) and affinity for the sarthran ligand (KD<0.5 nM); the majority of these sites (>95%) were the AT1 receptor subtype. CORT ANG II receptor Bmax and KD values in nuclei were 75 and 50% lower, respectively, for the mRen2. Lewis vs. the Lewis rats. In the MED, the PM receptor density (Lewis: 50 +/- 4 vs. mRen2. Lewis: 21 +/- 5 fmol/mg protein) and affinity (Lewis: 0.31 +/- 0.1 vs. 0.69 +/- 0.1 nM) were lower in the mRen2. Lewis rats. In summary, the hypertensive mRen2. Lewis rats exhibit higher ANG II in both CORT and MED regions of the kidney. Evaluation of intracellular ANG II receptors revealed lower CORT NUC and MED PM AT1 sites in the mRen2. Lewis. The downregulation of AT1 sites in the mRen2. Lewis rats may reflect a compensatory response to dampen the elevated levels of intrarenal ANG II.

Intracellular ANG II induces cytosolic Ca2+ mobilization by stimulating intracellular AT1 receptors in proximal tubule cells

Intracellular ANG II induces biological effects in nonrenal cells, but it is not known whether it plays a physiological role in renal proximal tubule cells (PTCs). PTCs express angiotensinogen, renin, and angiotensin-converting enzyme mRNAs, suggesting the presence of high levels of intracellular ANG II. We determined if microinjection of ANG II directly in single PTCs increases intracellular calcium concentration ([Ca2+]i) and, if so, elucidated the cellular mechanisms involved. Changes in [Ca2+]i responses were studied by fluorescence imaging using the Ca2+ indicator fluo 3. ANG II (1 nM) was microinjected directly in the cells, whereas cell-surface angiotensin type 1 (AT1) receptors were blocked by losartan (10 microM). When ANG II (1 nM) was added to the perfusate, there was a marked increase in [Ca2+]i that was blocked by extracellular losartan. With losartan in the perfusate, intracellular microinjection of ANG II elicited a robust increase in cytoplasmic [Ca2+]i that peaked at 30 s (basal: 2.2 +/- 0.3 vs. ANG II: 14.9 +/- 0.4 relative fluorescence units; P < 0.01). Chelation of extracellular Ca2+ with EGTA (2 mM) did not alter microinjected ANG II-induced [Ca2+]i responses (Ca2+ free + ANG II: 12.3 +/- 2.6 relative fluorescence units, not significant vs. ANG II); however, pretreatment with thapsigargin to deplete intracellular Ca2+ stores or with U-73122 to inhibit phospholipase C (1 microM each) markedly attenuated microinjected ANG II-induced [Ca2+]i responses. Combined microinjection of ANG II and losartan abolished [Ca2+]i responses, whereas a combination of ANG II and PD-123319 had no effect. These data demonstrate for the first time that direct microinjection of ANG II in single PTCs increases [Ca2+]i by stimulating intracellular AT1 receptors and releases Ca2+ from intracellular stores, suggesting that intracellular ANG II may play a physiological role in PTC function.

Upregulation of angiotensin II type 1 receptor, inflammatory mediators, and enzymes of arachidonate metabolism in obese Zucker rat kidney: reversal by angiotensin II type 1 receptor blockade

BACKGROUND

Severe obesity can result in proteinuria and progressive glomerulosclerosis in humans and experimental animals. The associated renal disease is ameliorated by weight reduction and/or blockade of the renin-angiotensin system. Various growth factors, cytokines, and lipid mediators are implicated in the pathogenesis of renal disease. To explore the possible involvement of these mediators in obesity-induced renal disease, we examined the expression of key enzymes of arachidonate metabolism and inflammatory genes in untreated and losartan-treated obese Zucker rats, a model of obesity, insulin resistance, and renal injury.

METHODS AND RESULTS

Seven-week-old male obese Zucker rats were randomized to losartan-treated (100 mg/L drinking H2O) and untreated groups, with lean Zucker rats as controls. After 4 months, RNA and protein were obtained from renal cortical tissue for relative reverse transcription-polymerase chain reaction, Western blots, and immunohistochemistry. Compared with the lean controls, obese Zucker rats showed significant glomerular matrix expansion and increased mRNA expression of the extracellular matrix protein fibronectin, inflammatory mediators interleukin-6 and monocyte chemoattractant protein-1, and 2 major enzymes of arachidonate metabolism, namely, 12/15-lipoxygenase and cyclooxygenase-2. This was associated with significant increases in p38 and extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase activities and marked upregulation of angiotensin II type 1 receptor (AT1R) mRNA and protein expression. These abnormalities and the associated glomerulopathy and proteinuria were prevented by administration of the AT1R blocker losartan.

CONCLUSIONS

These findings indicate that obesity-induced glomerulopathy is associated with upregulation of key inflammatory mediators. These events are associated with and perhaps in part due to upregulation of AT1R, as evidenced by their reversal with AT1R blocker treatment.

Effect of losartan pretreatment on kidney lipid content after unilateral obstruction in rats

Intrarenal concentration of angiotensin II increases after the onset of ureteral obstruction in the obstructed kidney. The effect of pretreatment with losartan, a specific angiotensin II AT1 receptor antagonist, on lipid contents, which were previously modified by unilateral ureteral obstruction (UUO), was studied in renal cortex of rats. Adult Wistar Kyoto rats were subjected to either UUO for 24 hr or control sham operation after being treated with losartan in the drinking water at 10 mg/kg rat/day for 15 days. In the cortex of obstructed kidney the increased free and esterified cholesterol concentrations were associated with the increased cholesterol synthesis measured by incorporation of 14C-acetate (0.001>p), compared with control and contralateral kidneys. The increased amount of phosphatidylcholine was related with the increased incorporation of 14C-choline into phosphatidylcholine (0.01>p). Phosphatidylethanolamine and sphingomyelin decreased slightly but total phospholipid content did not change. The level of AT1 receptor mRNA in obstructed kidney was significantly lower than in control and contralateral kidneys. Losartan pretreatment attenuated (0.01>p) the increase in cholesterol content and synthesis and restored and enhanced the AT1 angiotensin II receptor gene expression. The interference in the renin-angiotensin system before UUO may modify renal cortex cholesterol content.

Matrix metalloproteinases and atrial remodeling in patients with mitral valve disease and atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with extracellular matrix remodeling involving atrial fibrosis and atrial dilatation. Angiotensin II mediated pathways and matrix metalloproteinases (MMPs) have been implicated in these processes. Our aim was to study atrial structural remodeling and the expression of the angiotensin receptor subtypes and MMPs and their inhibitors (TIMPs) in patients with mitral valve disease with and without AF.

METHODS AND RESULTS

Biopsies from right and left atrial appendages (RA and LA) were taken from patients undergoing CABG (n=9, all in sinus rhythm (SR)) or mitral valve surgery (MVS; n=19; 9 with permanent AF and 10 in SR). Patients with MVS and AF had significantly larger atria (versus MVS and SR: p=0.02; versus CABG: p<0.01). The MVS patients had significantly more fibrosis than the control CABG group. Fibrosis was increased in both the AF and SR MVS groups in the LA, but only in the MVS-AF group in the RA. These AF patients had significantly more tricuspid regurgitation than SR patients. MMP-1 was down-regulated in LA of MVS patients (p=0.02) independent of the underlying rhythm (SR or AF; p=0.95). In RA biopsies, MMP-1 was down-regulated only in the MVS and AF group. MMP-9 was down-regulated in the MVS patients compared to CABG both in the RA and LA, and without a difference between the SR and AF groups. Protein expression of AT-1, AT-2, MMP-2, TIMP-1, -2 and -4, TNF-alpha, and TNF-alpha-converting enzyme did not differ significantly between the 3 groups.

CONCLUSIONS

Concordant changes between MMP-expression and fibrosis during mitral valve disease, both in LA and RA, suggest involvement of MMPs in structural atrial remodeling. AF itself did not contribute to altered fibrosis or MMP-expression in the LA. The association between AF and RA changes may be precipitated by greater hemodynamic load due to tricuspid regurgitation in these patients.

DIFFERENTIAL REGULATION OF ANGIOTENSIN II RECEPTORS DURING RENAL INJURY AND COMPENSATORY HYPERTROPHY IN THE RAT

1. The renin-angiotensin system may be involved in the compensatory adaptations occurring after the reduction of renal mass and during the consecutive changes leading to chronic renal failure. We therefore investigated the regulation of angiotensin II receptors in two models of renal hypertrophy in the rat: hypertrophy following uninephrectomy (UNx) or subtotal nephrectomy (STNx). The level of angiotensin type 1 (AT1A-R and AT1B-R) and type 2 (AT2-R) receptor mRNA was quantified by competitive reverse transcription-polymerase chain reaction (RT-PCR) in specific renal zones and the intrarenal distribution of angiotensin II receptors was analysed by immunohistochemistry. 2. In the UNx rats, AT1-R mRNA expression was not modified in the cortex or in the inner stripe of the outer medulla of the residual kidney at any time after the surgery (1, 4 and 12 weeks). In contrast, AT1-R mRNA expression was significantly reduced in these zones in STNx rats (-33% and -40%, respectively). This downregulation was organ-specific, as AT1-R mRNA levels were not modified in the liver. The proportions of AT1-R subtype (AT1A and AT1B) mRNA were unchanged by UNx or STNx. Very low levels of AT2-R mRNA were found in the cortex of all groups. Immunostaining revealed a similar localization of AT1-R in mesangial cells, proximal tubule, basolateral membrane of thick ascending limb, in both models of hypertrophy. AT1-R labelling was also detected in the apical membrane of intercalated cells of cortical collecting ducts. 3. This differential mRNA expression of angiotensin II receptors during compensatory hypertrophy and renal injury suggests that the development of renal hypertrophy is independent of AT1-R and AT2-R gene expression levels.

The novel angiotensin II type 1 receptor (AT1R)-associated protein ATRAP downregulates AT1R and ameliorates cardiomyocyte hypertrophy

Activation of angiotensin II (Ang II) type 1 receptor (AT1R) signaling is reported to play an important role in cardiac hypertrophy. We previously cloned a novel molecule interacting with the AT1R, which we named ATRAP (for Ang II type 1 receptor-associated protein). Here, we report that overexpression of ATRAP significantly decreases the number of AT1R on the surface of cardiomyocytes, and also decreases the degree of p38 mitogen-activated protein kinase phosphorylation, the activity of the c-fos promoter and protein synthesis upon Ang II treatment. These results indicate that ATRAP significantly promotes downregulation of the AT1R and further attenuates certain Ang II-mediated hypertrophic responses in cardiomyocytes.

Angiotensin AT2 receptor protects against cerebral ischemia-induced neuronal injury

Several lines of clinical and experimental evidence suggest an important role of the renin-angiotensin system in ischemic brain injury although the cellular regulation of the angiotensin AT1 and AT2 receptors and their potential relevance in this condition have not yet been clearly defined. We first assessed the regulation of brain AT1 and AT2 receptors in response to transient unilateral medial cerebral artery occlusion in rats by real-time RT-PCR, Western blot, and immunofluorescence labeling. AT2 receptors in the peri-infarct zone were significantly upregulated 2 days after transient focal cerebral ischemia. Increased AT2 receptors, which were abundantly distributed in a large number of brain regions adjacent to the infarct area including cerebral frontal cortex, piriform cortex, striatum, and hippocampus, were exclusively expressed in neurons. By contrast, AT1 receptors, which remained unaltered, were mainly expressed in astrocytes. In neurons of ischemic striatum, increased AT2 receptors were associated with intense neurite outgrowth. Blockade of central AT2 receptors with PD123177 abolished the neuroprotective effects of central AT1 receptor blockade with irbesartan on infarct size and neurological outcome. In primary cortical neurons, stimulation of AT2 receptors supported neuronal survival and neurite outgrowth. Our data indicate that cerebral AT2 receptors exert neuroprotective actions in response to ischemia-induced neuronal injury, possibly by supporting neuronal survival and neurite outgrowth in peri-ischemic brain areas.

Possible Involvement of Adipocyte-Derived Leucine Aminopeptidase via Angiotensin II in Endometrial Carcinoma

OBJECTIVE

It has recently been appreciated that a local autocrine or paracrine renin-angiotensin system (RAS) may exist in a number of tissues. Angiotensin II (AngII) is a potent RAS-derived vasoconstrictor peptide, and it is involved in tumor angiogenesis. We have cloned human adipocyte-derived leucine aminopeptidase (A-LAP), which degrades Ang II. This study investigated whether the expression of A-LAP, Ang II, angiotensin type I receptor (AT1R) and vascular endothelial growth factor (VEGF) correlates with clinicopathologic factors and prognosis in patients with endometrial endometrioid adenocarcinoma.

METHODS

Histologic sections of formalin-fixed, paraffin-embedded specimens from 94 primary endometrial carcinomas were stained for A-LAP, AngII, AT1R and VEGF using each antibody. Disease-free survival (DFS) and other clinicopathologic characteristics were analyzed according to the intensity of each staining.

RESULTS

Of 94 cases, 91 (96.8%) showed specific A-LAP immunostaining. A-LAP expression demonstrated negative correlations with myometrial invasion (p = 0.01) and vascular infiltration (p = 0.01). Of 94 cases, 77 (81.9%) showed specific AngII immunostaining. We found a positive correlation between AngII expression and surgical stage (p = 0.01). Of 94 cases, 56 (59.6%) showed specific AT1R immunostaining and 73 (77.7%) specific VEGF immunostaining. We found a positive correlation between VEGF expression and lymph node metastasis (p = 0.05). AngII and AT1R expression predicted a significantly poorer prognosis. Contrarily, A-LAP expression indicated a significantly more favorable prognosis in endometrial endometrioid adenocarcinoma patients. Multivariate analysis demonstrated that A-LAP expression (odds ratio, 0.12; 95% confidence interval, 0.025-0.618; p = 0.01) was an independent prognostic factor.

CONCLUSIONS

In this study, we demonstrated the existence of local RAS and A-LAP in endometrial endometrioid adenocarcinoma as prognostic predictors of clinical outcome. These findings suggest that the assessment of RAS and A-LAP status provides clinically useful prognostic information in patients with endometrial carcinoma.

Angiotensin II stimulates cAMP production and protein tyrosine phosphorylation in mouse spermatozoa

Angiotensin II (AII), found in seminal plasma, has been shown to stimulate capacitation in uncapacitated mammalian spermatozoa. The present study investigated the location of AII receptors on spermatozoa and AII's mechanism of action. AT1 type receptors for AII are present on the acrosomal cap region and along the whole of the flagellum of both mouse and human spermatozoa. Because combinations of low concentrations of AII and either calcitonin or fertilization-promoting peptide (FPP), both known to regulate the adenylyl cyclase (AC)/cAMP signal transduction pathway, elicited a significant response, this study investigated the hypothesis that these peptides act on the same pathway. AII was shown to significantly stimulate cAMP production in both uncapacitated and capacitated mouse spermatozoa and this was associated with increases in protein tyrosine phosphorylation. Using an anti-phosphotyrosine antibody to visualize the location of tyrosine phosphoproteins within individual cells, AII significantly stimulated phosphorylation within 20 min in both the head, especially in the acrosomal cap region, and the flagellum, especially in the principal piece, of uncapacitated mouse spermatozoa; combined AII + FPP was stimulatory within 5 min. In addition, Western blotting revealed that AII stimulation increased phosphorylation in a number of tyrosine phosphoproteins in both uncapacitated and capacitated mouse spermatozoa, with some being altered only in the latter category of cells. These results support the hypothesis that AII stimulates AC/cAMP in mammalian spermatozoa.

Translational regulation of angiotensin type 1a receptor expression and signaling by upstream AUGs in the 5' leader sequence

Rat angiotensin type 1a receptor (AT(1a)R) is regulated by four upstream AUGs present in the 5' leader sequence (5'-LS). Disruption of all four upstream AUGs (QM) results in 2-3-fold higher levels of angiotensin type 1 receptor (AT(1)R) densities in transiently transfected rat aortic smooth muscle cells (A10 cells) and stably transfected Chinese hamster ovary cells. Cells expressing QM have 5-fold higher levels of angiotensin II-induced inositol phosphate production than wild type (WT). Polysome analysis showed that QM mRNA is present in heavier fractions than the WT transcript, and 5.7-fold more AT(1)R protein is produced by in vitro translation from QM transcripts compared with WT transcripts. The AT(1a)R comprises 3 exons. Exon 3 (E3) encodes the entire open reading frame and 3'-untranslated region. Exons 1 and 2 (E1 and E2) and 52 nucleotides of E3 encode the 5'-LS. The AUGs in both exons contribute to the inhibitory effect on AT(1)R expression but not to the same degree. Disruption of the AUGs in exon 2 (DM2) relieves half of the inhibition, whereas disruption of the AUGs in exon 1 (DM1) is without effect. Disruption of the AUGs in exon 2 results in levels of receptor expression and translation that are indistinguishable from the alternative splice variant E1,3, which we previously showed was more efficiently translated than the E1,2,3 transcript. Individual mutations revealed that only the fourth AUG increased AT(1)R translation. In conclusion, all four AUGs present in the 5'-LS function cumulatively to suppress AT(1a)R expression and signaling by inhibiting translation. These data also show that both AUGs in E2 contribute to the inhibitory cis element present in this alternatively spliced exon.

Study on the expression of angiotensin II (ANG II) receptor subtype 1 (AT1R) in the placenta of pregnancy-induced hypertension

OBJECTIVE

To study the expression of angiotensin II (ANG II) receptor subtype 1 (AT(1)R) in the human placenta with pregnancy-induced hypertension (PIH).

METHODS

Immunohistochemistry was used to detect the expression of AT(1)R in placental tissues of 30 patients with PIH and 10 patients with normal pregnancies (control group). The PIH tissues were further divided into 3 groups: mild PIH group, moderate PIH group and severe PIH group. Each group consisted of 10 patients. A high-resolution pathological image analysis system (HPIAS-1000) was used to determine the quantity of AT(1)R expression.

RESULTS

The integral optical density and area of staining in the syncytiotrophoblast (STB) layer and villous endothelium of the placenta were significantly increased in PIH patients, in the moderate and severe PIH groups, as compared with the control group (P < 0.05), indicating that the expression of AT(1)R was highly increased in PIH. However, there was no significant difference between normal pregnancy and the mild PIH group (P > 0.05). Furthermore, statistically significant differences in AT(1)R expression were observed between mild, moderate and severe PIH groups (P < 0.05).

CONCLUSION

The expression of AT(1)R is statistically significantly increased in the STB layer and villous endothelium of human placenta with PIH. Expression increases with the severity of the disease. Increased expression may be involved in the pathogenesis of PIH.

Pulmonary injury follows systemic inflammatory reaction in infrarenal aortic surgery

OBJECTIVE

To investigate whether an inflammatory response occurs in patients undergoing infrarenal aortic abdominal aneurysm repair, the localization and timing (ischemia and/or reperfusion) of this activation, and finally whether it affects postoperative pulmonary function.

DESIGN

Prospective, observational study.

SETTING

Academic referral center in Italy.

PATIENTS

We included 12 patients undergoing infrarenal aortic abdominal aneurysm repair and 12 patients undergoing major abdominal surgery.

INTERVENTIONS

Timed measurement of gene activation (angiotensinogen, angiotensin type 1 receptor, angiotensin-converting enzyme, and interleukin-6 genes) in muscle biopsies by reverse transcriptase-polymerase chain reaction (RT-PCR), and prospective assessment of interleukin-6 plasma concentration and pulmonary function (Pao2/FIO2 and Pao2/PAO2 ratios).

MEASUREMENTS AND MAIN RESULTS

After 30 mins of aortic clamping, angiotensinogen, angiotensin type 1 receptor, angiotensin-converting enzyme, and interleukin-6 genes were all overexpressed at RT-PCR studies in quadriceps muscle of patients undergoing aortic abdominal aneurysm repair, and the overexpression persisted after reperfusion. In situ hybridization and immunohistochemistry revealed that the inflammatory response was localized in endothelial cells. A significant increase in plasma interleukin-6 concentrations was then detectable at 6 and 12 hrs after reperfusion in aortic abdominal aneurysm surgery compared with patients undergoing abdominal surgery (p < .05). The increase in interleukin-6 plasma concentration was then followed (12 and 24 hrs after surgery) by a significant reduction of Pao2/ FIO2 and Pao2/PAO2 ratios (p < .05 vs. abdominal surgery).

CONCLUSIONS

The present study shows that a) during aortic surgery, the genes for interleukin-6 and for the components of the local renin-angiotensin system (angiotensinogen, angiotensin-converting enzyme, and angiotensin type 1 receptor subtype) are activated early in the ischemic muscle, and activation persists during reperfusion; b) interleukin-6 plasma concentration increases only in patients with tissue ischemia (aortic abdominal aneurysm), whereas no changes are detectable in patients with abdominal surgery; and finally c) the occurrence of systemic inflammatory reaction with increased interleukin-6 plasma concentrations is followed by impaired pulmonary function.

A lower ratio of AT1/AT2 receptors of angiotensin II is found in female than in male spontaneously hypertensive rats

OBJECTIVE

Sexual dimorphism has been observed in arterial hypertension. Blood pressure levels are lower in female than in male spontaneously hypertensive rats (SHR). Angiotensin II (Ang II) plays a major role in the regulation of blood pressure. The aim of this study was to compare Ang II vascular reactivity and AT(1) and AT(2) receptor gene expression in female and male SHR.

METHODS

SHR animals were divided into four groups: (I) male, (II) female in physiological estrus, (III) ovariectomized and (IV) ovariectomized treated with estrogen. Arterial blood pressure, AT(1) and AT(2) mRNA expression were determined. Ang II responses in aorta and mesenteric vessels were also evaluated.

RESULTS

In female SHR, aorta and mesenteric microvessels were hyporeactive to Ang II in comparison to male SHR. In ovariectomized females, Ang II vasoconstriction was similar to that of males. Estrogen treatment abolished this difference. The mRNA expression for AT(1) was higher in aorta and mesenteric vessels from males than in females. In ovariectomized SHR, mRNA expression for AT(1) was comparable to that of males. Treatment with estrogen reversed the over expression observed. Whereas AT(2) gene expression did not differ, a lower ratio AT(1)/AT(2) was found in female than in male vessels. A higher mRNA expression for AT(1) was observed in kidney from male than in female. Ovariectomy resulted in up-regulation of this subtype receptor. Treatment with estrogen reversed the overexpression. AT(2) gene expression was higher in kidney from female than male SHR. Ovariectomy reduced AT(2) gene expression and estrogen treatment reversed the alteration observed in kidney.

CONCLUSION

There is sexual dimorphism in vascular reactivity and in receptor gene expression to Ang II in SHR. We conclude that estrogen modulates AT(1) and AT(2) receptor gene expression and that this might explain at least partially the lower blood pressure observed in female SHR.

Renin-angiotensin system expression in rat bone marrow haematopoietic and stromal cells

The existence of a bone marrow renin-angiotensin system (RAS) is evidenced by the association of renin, angiotensin converting enzyme (ACE), and angiotensin (Ang) II and its AT(1) and AT(2) receptors with both normal and disturbed haematopoiesis. The expression of RAS components by rat unfractionated bone marrow cells (BMC), haematopoietic-lineage BMC and cultured marrow stromal cells (MSC) was investigated to determine which specific cell types may contribute to a local bone marrow RAS. The mRNAs for angiotensinogen, renin, ACE, and AT(1a) and AT(2) receptors were present in BMC and in cultured MSC; ACE2 mRNA was detected only in BMC. Two-colour flow fluorocytometry analysis showed immunodetectable angiotensinogen, ACE, AT(1) and AT(2) receptors, and Ang II, as well as binding of Ang II to AT(1) and AT(2) receptors, in CD4(+), CD11b/c(+), CD45R(+) and CD90(+) BMC and cultured MSC; renin was found in all cell types with the exception of CD4(+) BMC. Furthermore, Ang II was detected by radioimmunoassay in MSC homogenates as well as conditioned culture medium. The presence of Ang II receptors in both haematopoietic-lineage BMC and MSC, and the de novo synthesis of Ang II by MSC suggest a potential autocrine-paracrine mechanism for local RAS-mediated regulation of haematopoiesis.