Kidney-specific enhancement of ANG II stimulates endogenous intrarenal angiotensinogen in gene-targeted mice

Urinary angiotensinogen as a marker of intrarenal angiotensin II activity in adolescents with primary hypertension

BACKGROUND

Experimental and epidemiological studies have demonstrated that urinary angiotensinogen (AGT) is a novel biomarker for the intrarenal activity of the renin-angiotensin system in hypertension (HT). Several large-scale epidemiological studies have shown that an elevated serum uric acid (SUA) level is associated with HT. The aim of our study was to assess urinary AGT excretion and its correlation with SUA level, the lipid profile, and the body mass index (BMI) Z-score in hypertensive adolescents.

METHODS

Participants were divided into two groups: (1) the group with confirmed HT consisting of 55 subjects with primary HT and (2) the reference (R) group consisting of 33 subjects with white-coat HT. A commercial enzyme-linked immunosorbent assay (ELISA) kit was used to determine urinary AGT concentration.

RESULTS

The urinary AGT/creatinine (cr.) ratio in subjects in the HT group was significantly higher than that in the reference group (p < 0.01) and showed a strong positive correlation with SUA (r = 0.47, p < 0.01). The relationship between the AGT/cr. ratio and SUA levels after controlling for age, gender and BMI Z-score continued to show a significant association.

CONCLUSIONS

The most obvious finding to emerge from this study is that in adolescents with primary HT, the increased urinary excretion of AGT correlated with hyperuricemia, although large, multicenter studies are needed to confirm this observation.

Early life stress induces renal dysfunction in adult male rats but not female rats

Maternal separation (MatSep) is a model of behavioral stress during early life. We reported that MatSep exacerbates ANG II-induced hypertension in adult male rats. The aims of this study were to determine whether exposure to MatSep in female rats sensitizes blood pressure to ANG II infusion similar to male MatSep rats and to elucidate renal mechanisms involved in the response in MatSep rats. Wistar Kyoto (WKY) pups were exposed to MatSep 3 h/day from days 2 to 14, while control rats remained with their mothers. ANG II-induced mean arterial pressure (MAP; telemetry) was enhanced in female MatSep rats compared with control female rats but delayed compared with male MatSep rats. Creatinine clearance (Ccr) was reduced in male MatSep rats compared with control rats at baseline and after ANG II infusion. ANG II infusion significantly increased T cells in the renal cortex and greater histological damage in the interstitial arteries of male MatSep rats compared with control male rats. Plasma testosterone was greater and estradiol was lower in male MatSep rats compared with control rats with ANG II infusion. ANG II infusion failed to increase blood pressure in orchidectomized male MatSep and control rats. Female MatSep and control rats had similar Ccr, histological renal analysis, and sex hormones at baseline and after ANG II infusion. These data indicate that during ANG II-induced hypertension, MatSep sensitizes the renal phenotype in male but not female rats.

Multiphoton imaging of the glomerular permeability of angiotensinogen

Patients and animals with renal injury exhibit increased urinary excretion of angiotensinogen. Although increased tubular synthesis of angiotensinogen contributes to the increased excretion, we do not know to what degree glomerular filtration of systemic angiotensinogen, especially through an abnormal glomerular filtration barrier, contributes to the increase in urinary levels. Here, we used multiphoton microscopy to visualize and quantify the glomerular permeability of angiotensinogen in the intact mouse and rat kidney. In healthy mice and Munich-Wistar-Frömter rats at the early stage of glomerulosclerosis, the glomerular sieving coefficient of systemically infused Atto565-labeled human angiotensinogen (Atto565-hAGT), which rodent renin cannot cleave, was only 25% of the glomerular sieving coefficient of albumin, and its urinary excretion was undetectable. In a more advanced phase of kidney disease, the glomerular permeability of Atto565-hAGT was slightly higher but still very low. Furthermore, unlike urinary albumin, the significantly higher urinary excretion of endogenous rat angiotensinogen did not correlate with either the Atto565-hAGT or Atto565-albumin glomerular sieving coefficients. These results strongly suggest that the vast majority of urinary angiotensinogen originates from the tubules rather than glomerular filtration.

Augmented intrarenal and urinary angiotensinogen in hypertension and chronic kidney disease

Activated intrarenal renin-angiotensin system plays a cardinal role in the pathogenesis of hypertension and chronic kidney disease. Angiotensinogen is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system. Because the levels of angiotensinogen are close to the Michaelis-Menten constant values for renin, angiotensinogen levels as well as renin levels can control the renin-angiotensin system activity, and thus, upregulation of angiotensinogen leads to an increase in the angiotensin II levels and ultimately increases blood pressure. Recent studies using experimental animal models have documented the involvement of angiotensinogen in the intrarenal renin-angiotensin system activation and development of hypertension. Enhanced intrarenal angiotensinogen mRNA and/or protein levels were observed in experimental models of hypertension and chronic kidney disease, supporting the important roles of angiotensinogen in the development and the progression of hypertension and chronic kidney disease. Urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-infused rats. Also, a direct quantitative method has been developed recently to measure urinary angiotensinogen using human angiotensinogen enzyme-linked immunosorbent assay. These data prompted us to measure urinary angiotensinogen in patients with hypertension and chronic kidney disease, and investigate correlations with clinical parameters. This short article will focus on the role of the augmented intrarenal angiotensinogen in the pathophysiology of hypertension and chronic kidney disease. In addition, the potential of urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertension and chronic kidney disease will be also discussed.

Urinary angiotensinogen levels in relation to renal involvement of Henoch-Schonlein purpura in children

AIM

To investigate whether urinary angiotensinogen (UAGT) levels are correlated with renal involvement of Henoch-Schonlein purpura (HSP) in children, and to explore whether UAGT has any relation to the severity of HSP.

METHODS

The study sample consisted of 107 patients (50 boys and 57 girls, 6.68±2.41 years) with clinical diagnosis of HSP. A 24 h urine sample was collected before treatment. UAGT levels were measured in patients with HSP in the acute and convalescent phases by enzyme linked immunosorbent assay.

RESULTS

Urinary angiotensinogen/urinary concentration of creatinine levels were significantly higher in proteinuric HSP in the acute phase and the convalescent phase (32.02±3.95 and 25.31±4.11 µg/g) compared with those with HSP without renal involvement (17.26±2.60 and 15.14±3.81 µg/g) and those with hematuric HSP (19.70±2.21 and 17.28±3.62 µg/g) (P<0.0001 and P<0.01, respectively). Using matched urine samples from the same patients, UAGT/urinary concentration of creatinine (UCr) levels of proteinuric HSP patients were significantly lower in the convalescent phase (25.31 ± 4.11 µg/g, P<0.01) than in the acute phase (32.02±3.95 µg/g). UAGT/UCr levels showed positive correlation with 24 h urine protein or serum creatinine in both hematuric HSP and proteinuric HSP groups during the acute phase (P<0.05).

CONCLUSIONS

Urinary angiotensinogen levels were remarkably high in the acute phase in the patients with proteinuric HSP, suggesting increased UAGT may indicate a series of functional changes in the kidney and it may be used as a potential biomarker of severity of HSP to monitor the progression of HSP with renal involvement.

The establishment of a primary culture system of proximal tubule segments using specific markers from normal mouse kidneys

The proximal tubule contains the highest expression of angiotensinogen mRNA and protein within the kidney and plays a vital role in the renal renin-angiotensin system. To study the regulation of angiotensinogen expression in the kidney in more detail, the proximal tubule needs to be accurately isolated from the rest of the nephron and separated into its three segments. The purpose of this study was to design a novel protocol using specific markers for the separation of proximal tubule cells into the three proximal tubule segments and to determine angiotensinogen expression in each segment. Kidneys were removed from C57BL/6J mice. The proximal tubules were aspirated from region of a Percoll gradient solution of the appropriate density. The proximal tubule was then separated into its three segments using segment-specific membrane proteins, after which each segment was characterized by a different specific marker (sodium-glucose transporter 2 for Segment 1; carbonic anhydrase IV for Segment 2; ecto-adenosine triphosphatase for Segment 3). The isolation of proximal tubules into three segments was successful, and angiotensinogen mRNA in Segment 2 and 3 and angiotensinogen protein in all three segments were confirmed. This protocol will be helpful for future studies of the detailed mechanisms of the intrarenal renin-angiotensin system.

Liver angiotensinogen is the primary source of renal angiotensin II

Angiotensin II content in the kidney is much higher than in the plasma, and it increases more in kidney diseases through an uncertain mechanism. Because the kidney abundantly expresses angiotensinogen mRNA, transcriptional dysregulation of angiotensinogen within the kidney is one potential cause of increased renal angiotensin II in the setting of disease. Here, we observed that kidney-specific angiotensinogen knockout mice had levels of renal angiotensinogen protein and angiotensin II that were similar to those levels of control mice. In contrast, liver-specific knockout of angiotensinogen nearly abolished plasma and renal angiotensinogen protein and renal tissue angiotensin II. Immunohistochemical analysis in mosaic proximal tubules of megalin knockout mice revealed that angiotensinogen protein was incorporated selectively in megalin-intact cells of the proximal tubule, indicating that the proximal tubule reabsorbs filtered angiotensinogen through megalin. Disruption of the filtration barrier in a transgenic mouse model of podocyte-selective injury increased renal angiotensin II content and markedly increased both tubular and urinary angiotensinogen protein without an increase in renal renin activity, supporting the dependency of renal angiotensin II generation on filtered angiotensinogen. Taken together, these data suggest that liver-derived angiotensinogen is the primary source of renal angiotensinogen protein and angiotensin II. Furthermore, an abnormal increase in the permeability of the glomerular capillary wall to angiotensinogen, which characterizes proteinuric kidney diseases, enhances the synthesis of renal angiotensin II.

Interferon-γ biphasically regulates angiotensinogen expression via a JAK-STAT pathway and suppressor of cytokine signaling 1 (SOCS1) in renal proximal tubular cells

Renal inflammation modulates angiotensinogen (AGT) production in renal proximal tubular cells (RPTCs) via inflammatory cytokines, including interleukin-6, tumor necrosis factor α, and interferon-γ (IFN-γ). Among these, the effects of IFN-γ on AGT regulation in RPTCs are incompletely delineated. This study aimed to elucidate mechanisms by which IFN-γ regulates AGT expression in RPTCs. RPTCs were incubated with or without IFN-γ up to 48 h. AGT expression, STAT1 and STAT3 activities, and SOCS1 expression were evaluated. RNA interference studies against STAT1, SOCS1, and STAT3 were performed to elucidate a signaling cascade. IFN-γ decreased AGT expression at 6 h (0.61±0.05, ratio to control) and 12 h (0.47±0.03). In contrast, longer exposure for 24 and 48 h increased AGT expression (1.76±0.18, EC(50)=3.4 ng/ml, and 1.45±0.08, respectively). IFN-γ treatment for 6 h strongly induced STAT1 phosphorylation and SOCS1 augmentation, and decreased STAT3 activity. However, STAT1 phosphorylation and SOCS1 augmentation waned at 24 h, while STAT3 activity increased. RNA interference studies revealed that activation of STAT1-SOCS1 axis decreased STAT3 activity. Thus, IFN-γ biphasically regulates AGT expression in RPTCs via STAT3 activity modulated by STAT1-SOCS1 axis, suggesting the STAT1-SOCS1 axis is important in IFN-γ-induced activation of the intrarenal renin-angiotensin system.

Lessons from in vitro studies and a related intracellular angiotensin II transgenic mouse model

In the classical renin-angiotensin system, circulating ANG II mediates growth stimulatory and hemodynamic effects through the plasma membrane ANG II type I receptor, AT1. ANG II also exists in the intracellular space in some native cells, and tissues and can be upregulated in diseases, including hypertension and diabetes. Moreover, intracellular AT1 receptors can be found associated with endosomes, nuclei, and mitochondria. Intracellular ANG II can function in a canonical fashion through the native receptor and also in a noncanonical fashion through interaction with alternative proteins. Likewise, the receptor and proteolytic fragments of the receptor can function independently of ANG II. Participation of the receptor and ligand in alternative intracellular pathways may serve to amplify events that are initiated at the plasma membrane. We review historical and current literature relevant to ANG II, compared with other intracrines, in tissue culture and transgenic models. In particular, we describe a new transgenic mouse model, which demonstrates that intracellular ANG II is linked to high blood pressure. Appreciation of the diverse, pleiotropic intracellular effects of components of the renin-angiotensin system should lead to alternative disease treatment targets and new therapies.

Divergent mechanism regulating fluid intake and metabolism by the brain renin-angiotensin system

The purpose of this review is two-fold. First, I will highlight recent advances in our understanding of the mechanisms regulating angiotensin II (ANG II) synthesis in the brain, focusing on evidence that renin is expressed in the brain and is expressed in two forms: a secreted form, which may catalyze extracellular ANG I generation from glial or neuronal angiotensinogen (AGT), and an intracellular form, which may generate intracellular ANG in neurons that may act as a neurotransmitter. Second, I will discuss recent studies that advance the concept that the renin-angiotensin system (RAS) in the brain not only is a potent regulator of blood pressure and fluid intake but may also regulate metabolism. The efferent pathways regulating the blood pressure/dipsogenic effects and the metabolic effects of elevated central RAS activity appear different, with the former being dependent upon the hypothalamic-pituitary-adrenal axis, and the latter being dependent upon an interaction between the brain and the systemic (or adipose) RAS.

Variants and haplotypes in angiotensinogen gene are associated with plasmatic angiotensinogen level in Mexican population

INTRODUCTION

The plasmatic angiotensinogen (AGT) level has been associated with essential hypertension. Linkage analysis has found a relationship between the AGT gene locus and hypertension in the Mexican-American population, but studies have failed to identify genetic variants associated with hypertension or plasma AGT levels. This study analyzes the relationship between polymorphisms in the AGT gene and plasmatic AGT levels in Mexican population.

METHODS

Nine polymorphisms in AGT gene were genotyped, and plasma AGT level was determined by enzyme-linked immunosorbent assay.

RESULTS

Differences in AGT plasma levels were associated with 2 polymorphisms: T-20G, TT = 25.3 ± 8.3 versus TG + GG = 21.6 ± 8.8 μg/mL; P = 0.008 and C3389T (T174M), CC = 25.8 ± 9.9 versus TC + TT = 20.5 ± 5.4 μg/mL; P = 0.0002. Haplotype 2 was associated with low plasma AGT (-5.1 μg/mL [95% confidence interval: -8.6 to -1.6], P = 0.004) and Haplotype 8 was associated with high plasma AGT (6.5 μg/mL [95% confidence interval: 2.5 to 10.6], P = 0.001). This association remained after adjustment for covariates. A Likelihood Ratio Test for haplotype-phenotype association adjusted for covariates resulted in χ = 38.9, P = 0.0005. The total effect of the haplotypes on plasma AGT level variance was 19.5%. No association was identified between haplotypes and quantitative traits of blood pressure.

CONCLUSIONS

Two polymorphisms (T-20G and C3389T) and 2 haplotypes (H2 and H8) showed an association with plasma AGT levels in Mexican population.

Urinary angiotensinogen as a biomarker of nephropathy in childhood

While most circulating angiotensinogen (AGT) is synthesized in the liver, the kidneys also produce AGT. Recently, we reported that urinary AGT is mainly originated from AGT. Using newly developed human AGT ELISA, we measured urinary AGT levels in chronic glomerulonephritis (GN) patients and patients with type 1 diabetes in childhood. Urinary AGT level was positively correlated with diastolic blood pressure, urinary albumin, urinary protein levels, and urinary occult blood in chronic GN patients. Furthermore, urinary AGT level was significantly increased in chronic GN patients not treated with renin-angiotensin system (RAS) blockers compared with control subjects. Importantly, patients treated with RAS blockers had a marked attenuation of this increase. Also, urinary AGT level was significantly higher in patients with diabetic nephropathy in the premicroalbuminuric phase than in control subjects. These results suggest that urinary AGT reflects intrarenal RAS status in chronic GN and may be an early marker of diabetic nephropathy.

Renal proximal tubule angiotensin AT1A receptors regulate blood pressure

All components of the renin angiotensin system necessary for ANG II generation and action have been reported to be present in renal proximal convoluted tubules. Given the close relationship between renal sodium handling and blood pressure regulation, we hypothesized that modulating the action of ANG II specifically in the renal proximal tubules would alter the chronic level of blood pressure. To test this, we used a proximal tubule-specific, androgen-dependent, promoter construct (KAP2) to generate mice with either overexpression of a constitutively active angiotensin type 1A receptor transgene or depletion of endogenous angiotensin type 1A receptors. Androgen administration to female transgenic mice caused a robust induction of the transgene in the kidney and increased baseline blood pressure. In the receptor-depleted mice, androgen administration to females resulted in a Cre recombinase-mediated deletion of angiotensin type 1A receptors in the proximal tubule and reduced blood pressure. In contrast to the changes observed at baseline, there was no difference in the blood pressure response to a pressor dose of ANG II in either experimental model. These data, from two separate mouse models, provide evidence that ANG II signaling via the type 1A receptor in the renal proximal tubule is a regulator of systemic blood pressure under baseline conditions.

Salt-induced renal injury in SHRs is mediated by AT1 receptor activation

OBJECTIVE

This study aimed to examine the effects of salt loading, with or without simultaneous angiotensin receptor blocker (ARB) treatment, on the systemic and tissue renin-angiotensin system (RAS) in spontaneously hypertensive rats (SHRs).

METHOD

Evaluation was performed early (4 weeks) in the course of salt loading in order to examine initial mediating events of cardiovascular and renal damage produced by salt excess. Four groups of rats were studied. Group 1 received regular rat chow (normal-salt diet); group 2 received normal-salt diet and an ARB (losartan, 30 mg/kg per day); group 3 received high-salt (8%) chow; and group 4 received high-salt diet and losartan.

RESULTS

High-salt diet increased systolic pressure to 193±1 mmHg compared to 180±2 in normal-salt diet group. Losartan reduced SBP in SHRs fed normal-salt diet but did not reduce SBP in the SHRs fed high-salt diet (192±2 mmHg). High-salt diet markedly increased urinary protein excretion from 27±4 to 64±13 mg/day and this increase was ameliorated by losartan (40±9 mg/day). In SHRs on high-salt diet, plasma angiotensin II concentration increased three to four-fold, whereas urinary angiotensinogen excretion increased 10-fold; and these changes were significantly reduced by losartan. High-salt diet accelerated glomerular injury and interstitial fibrosis in SHRs which were reduced by losartan.

CONCLUSION

These results demonstrate that the activity of RAS was either not suppressed or, even augmented, after 4 weeks of salt loading despite high salt intake and increased SBP. The data suggest that an augmented intrarenal RAS during high-salt diet may contribute to the development of renal injury in this experimental model.

Urinary angiotensinogen as a predictive marker in patients with immunoglobulin A nephropathy

BACKGROUND

The intrarenal renin-angiotensinogen system (RAS) plays a major role in the progression of chronic kidney disease. Urinary angiotensinogen (UAGT) provides a specific index of the intrarenal RAS status. This study was conducted to find the role of UAGT as a predictive marker in patients with immunoglobulin A nephropathy (IgAN).

METHODS

Thirty-six patients with IgAN, 14 non-IgAN and 15 healthy controls were included. The UAGT concentration was measured using human ELISA kits and adjusted by urinary creatinine.

RESULTS

UAGT levels were significantly higher in patients with IgAN and non-IgAN than in healthy subjects (104.96 vs. 6.71 ng/mgCr, p < 0.01). Using univariate regression analysis, UAGT was found to correlate with the urine protein-to-creatinine ratio (UPCR), serum creatinine, and systolic and diastolic blood pressure in patients with IgAN. Multivariate regression analysis revealed that UAGT correlated positively with UPCR. Patients with levels of UAGT >100 ng/mgCr showed higher serum creatinine after treatment than patients with UAGT levels <100 ng/mgCr.

CONCLUSION

This study showed that UAGT levels are increased and correlate positively with the UPCR in IgAN. Patients with high levels of UAGT may have poor renal function following treatment.

An update on the islet renin-angiotensin system

The traditional renin-angiotensin system (RAS) components have been studied extensively since the rate-limiting component of RAS, renin, was first characterized. The ongoing identification of various novel RAS components and signaling pathways continues to elaborate the complexity of this system. Regulation of RAS according to the conventional and contemporary views of its functions in various tissues under pathophysiological conditions is a main treatment strategy for many metabolic diseases. The local pancreatic RAS, first proposed to exist in pancreatic islets two decades ago, could regulate islet function and glycemic control via influences on islet cell mass, inflammation, and ion channels. Insulin secretion, the major function of pancreatic islets, is controlled by numerous factors. Among these factors and of particular interest are glucagon-like peptide-1 (GLP-1) and vitamin D, which may regulate islet function by directly binding receptors on islet beta cells. These factors may work with local RAS signaling in islets to protect and maintain islet function under diabetic and hyperglycemic conditions. In this concise review, the local islet RAS will be discussed with particular attention being paid to recent notable findings.

Intrarenal angiotensin-converting enzyme induces hypertension in response to angiotensin I infusion

The contribution of the intrarenal renin-angiotensin system to the development of hypertension is incompletely understood. Here, we used targeted homologous recombination to generate mice that express angiotensin-converting enzyme (ACE) in the kidney tubules but not in other tissues. Mice homozygous for this genetic modification (ACE 9/9 mice) had low BP levels, impaired ability to concentrate urine, and variable medullary thinning. In accord with the ACE distribution, these mice also had reduced circulating angiotensin II and high plasma renin concentration but maintained normal kidney angiotensin II levels. In response to chronic angiotensin I infusions, ACE 9/9 mice displayed increased kidney angiotensin II, enhanced rate of urinary angiotensin II excretion, and development of hypertension. These findings suggest that intrarenal ACE-derived angiotensin II formation, even in the absence of systemic ACE, increases kidney angiotensin II levels and promotes the development of hypertension.

Intrarenal angiotensin II and its contribution to the genesis of chronic hypertension

The increased activity of intrarenal renin-angiotensin system (RAS) in a setting of elevated arterial pressure elicits renal vasoconstriction, increased sodium reabsorption, proliferation, fibrosis and renal injury. Increases in intrarenal and interstitial angiotensin (Ang) II levels are due to increased AT(1) receptor mediated Ang II uptake and stimulation of renal angiotensinogen (AGT) mRNA and protein expression. Augmented proximal tubule AGT production increases tubular AGT secretion and spillover of AGT into the distal nephron and urine. Increased renin formation by principal cells of the collecting ducts forms Ang I from AGT thus increasing Ang II. The catalytic actions of renin and prorenin are enhanced by prorenin receptors (PRRs) on the intercalated cells. The resultant increased intrarenal Ang II levels contribute to the genesis of chronic hypertension.

Contribution of a nuclear factor-kappaB binding site to human angiotensinogen promoter activity in renal proximal tubular cells

Intrarenal angiotensinogen (AGT) is expressed highly in renal proximal tubular cells (RPTCs) and contributes to the regulation of intrarenal angiotensin II levels. Inhibition of nuclear factor (NF)-κB suppressed human (h)AGT expression in human RPTCs. However, the presence and localization of an NF-κB binding site in the hAGT promoter region have not been determined. Therefore, this study was performed to demonstrate that an NF-κB binding site in the hAGT promoter region contributes to hAGT promoter activity in human RPTCs. The hAGT promoter region was cloned from -4358 to +122 and deletion analysis was performed. A possible NF-κB binding site was removed from the hAGT promoter region (M1) and mutated (M2). Human RPTCs were transfected, and hAGT promoter activity was determined by luciferase assay. The identity of DNA binding proteins from binding assays were determined by Western blot. Progressive 5'-end deletions demonstrated removal of a distal promoter element in hAGT_-2414/+122 reduced promoter activity (0.61 ± 0.12, ratio to hAGT_-4358/+122). Inhibition of NF-κB suppressed promoter activity in hAGT_-4358/+122 (0.51 ± 0.14, ratio to control) and hAGT_-3681/+122 (0.48 ± 0.06, ratio to control) but not in the construct without the NF-κB binding site. Promoter activity was reduced in the domain mutants M1 (0.57 ± 0.08, ratio to hAGT_-4358/+122) and M2 (0.61 ± 0.16, ratio to hAGT_-4358/+122). DNA binding levels of NF-κB protein were reduced in M1. These data demonstrate the functional importance of an NF-κB binding site in the hAGT promoter region, which contributes to hAGT promoter activity in human RPTCs.

Angiotensinogen Expression Is Enhanced in the Progression of Glomerular Disease

Intrarenal renin-angiotensin system (RAS) activation plays a critical role in the development and progression of renal injury. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by multiple independent mechanisms. Angiotensinogen (AGT) is the only known substrate for renin that is a rate-limiting enzyme of the RAS. Recently, enhanced intrarenal AGT levels have been shown to reflect the intrarenal RAS status in hypertension, chronic glomerular disease and diabetic nephropathy. In this review, we focus on AGT expression of the diseased glomeruli in the progression of glomerular disease. An anti-glomerular basement membrane nephritis rat model developed progressive proteinuria and glomerular crescent formation, accompanied by increased macrophage infiltration and glomerular expression of AGT and Ang II. The addition of Ang II type 1 receptor blocker to CC-chemokine recaptor 2 antagonist markedly attenuated the induction of macrophage infiltration, AGT and Ang II, and reduced glomerular crescent formation. Next, the levels of glomerular AGT expression and marker of reactive oxygen species in Zucker diabetic fatty (ZDF) obese rats were higher than those in ZDF lean rats. Hydrogen peroxide (H(2)O(2)) induced an increase in the AGT expression in primary rat mesangial cells. Furthermore, the H(2)O(2)-induced upregulation of AGT was inhibited by a mitogen-activated protein kinase kinase and a c-Jun N-terminal kinase inhibitor. These data suggest the potential contribution of enhanced AGT expression in glomeruli to the intrarenal RAS activation for the development of glomerular disease.

Molecular and Pathophysiological Features of Angiotensinogen: A Mini Review

The renin-angiotensin system is an essential regulatory system for blood pressure and fluid homeostasis. Angiotensinogen is the only known precursor of all the peptides generated in this system. While many of the basic understandings of angiotensinogen have come from research efforts to define its role in blood pressure regulation, novel pathophysiological functions of angiotensinogen have been discovered in the last two decades including kidney developmental abnormalities, atherosclerosis, and obesity. Despite the impressive advance in the understanding of angiotensinogen gene structure and protein functions, some fundamental questions remain unanswered. In this short review, we provide contemporary insights into the molecular characteristics of angiotensinogen and its pathophysiological features. In light of the recent progress, we emphasize some newly recognized functional features of angiotensinogen other than its regulation on blood pressure.

Urinary angiotensinogen reflects the activity of intrarenal renin-angiotensin system in patients with IgA nephropathy

BACKGROUND

A potential contribution of local activation of the renin-angiotensin system (RAS) to the pathogenesis of renal injury has been indicated by evidence for blood pressure-independent renoprotective effects of angiotensin II (AngII) receptor blockers (ARBs). The present study was performed to test the hypothesis that urinary angiotensinogen provides a specific index of intrarenal RAS status in patients with immunoglobulin A (IgA) nephropathy.

METHODS

This paper is a survey of urine specimens from three groups: healthy volunteers, patients with IgA nephropathy and patients with minor glomerular abnormality (MGA). Patients with hypertension, diabetes, reduced glomerular filtration rate and/or who were under any medication were excluded from this study. Urinary angiotensinogen levels were measured by a sandwich enzyme-linked immunosorbent assay system.

RESULTS

Urinary angiotensinogen levels were not different between healthy volunteers and patients with MGA. However, urinary angiotensinogen levels, renal tissue angiotensinogen expression and AngII immunoreactivity were significantly higher in patients with IgA nephropathy than in patients with MGA. Baseline urinary angiotensinogen levels were positively correlated with renal angiotensinogen gene expression and AngII immunoreactivity but not with plasma renin activity or the urinary protein excretion rate. In patients with IgA nephropathy, treatment with an ARB, valsartan (40 mg/day), significantly increased renal plasma flow and decreased filtration fraction, which were associated with reductions in urinary angiotensinogen levels.

CONCLUSION

These data indicate that urinary angiotensinogen is a powerful tool for determining intrarenal RAS status and associated renal derangement in patients with IgA nephropathy.

Urinary Angiotensinogen as a Novel Biomarker of Intrarenal Renin-Angiotensin System in Chronic Kidney Disease

An activated intrarenal reninangiotensin system (RAS) plays a crucial role in the pathogenesis of hypertension and chronic kidney diseases (CKD). Angiotensinogen (AGT) is the only known substrate for renin, which is the rate-limiting enzyme of the RAS. Because the levels of AGT are close to the Michaelis-Menten constant for renin, AGT levels can also control the RAS activity, and upregulation of AGT may lead to elevated angiotensin peptide levels and increases in blood pressure. Recent studies on experimental animal models have documented the involvement of AGT in the intrarenal RAS activation and development of hypertension. Enhanced intrarenal AGT mRNA and/or protein levels occur in experimental models of hypertension and kidney diseases supporting important roles in the development and progression of hypertension and kidney diseases. Urinary excretion rates of AGT provide a specific index of intrarenal RAS status in angiotensin II-infused rats. Also, a direct quantitative method was recently developed to measure urinary AGT using human AGT ELISA. These data prompted us to measure urinary AGT in patients with hypertension and CKD, and investigate correlations with clinical parameters. This brief review will address the potential of urinary AGT as a novel biomarker of the intrarenal RAS status in hypertension and CKD.

Urinary angiotensinogen is correlated with blood pressure in men (Bogalusa Heart Study)

BACKGROUND

The Bogalusa Heart Study is a long-term study on cardiovascular disease and has followed a biracial (black/white) population from childhood. Risk factor data pertaining to many patients have been collected over 35 years, and the time course of hypertension has been documented by repeated examinations and measurements. Considerable sex and racial differences have been found to be related to cardiovascular disease. Urinary angiotensinogen (UAGT) is a novel biomarker for the intrarenal activity of the renin-angiotensin system in hypertension and kidney disease. We aimed to determine the relationship of UAGT with traditional cardiovascular disease risk factors in asymptomatic young adults in this biracial population.

METHOD

We recruited 251 individuals and collected a single random spot urine sample from each one. Because UAGT is significantly increased in diabetic patients and the use of antihypertensive drugs affects UAGT levels, we excluded patients who had diabetes, who were receiving antihypertensive treatment, or both. Consequently, 190 participants were included for this analysis.

RESULTS

UAGT levels did not differ with race or sex, but were significantly correlated with SBP (r = +0.23, P = 0.0015) and DBP (r = +0.24, P = 0.0012). Moreover, high correlations were shown in men, especially in black men (SBP, r = +0.85, P = 0.0005 and DBP, r = +0.72, P = 0.0079). Thus, UAGT is correlated with blood pressure in men, even when they do not show overt proteinuria or albuminuria.

CONCLUSION

The biomarker, UAGT, may facilitate the identification of individuals that are at increased risk for the development of hypertension and early asymptomatic renal disease.

Tumor necrosis factor-{alpha} suppresses angiotensinogen expression through formation of a p50/p50 homodimer in human renal proximal tubular cells

Angiotensinogen (AGT) expression in renal proximal tubular cells (RPTCs) and intrarenal tumor necrosis factor-α (TNF-α) levels are increased in hypertension and renal diseases However, the contribution of TNF-α to AGT expression in RPTCs has not been established. Therefore, the objective of the present study was to determine influence of TNF-α on AGT expression in RPTCs. Human kidney-2 (HK-2) cells, immortalized human RPTCs, were treated with several concentrations of TNF-α up to 24 h. AGT mRNA and protein expression were evaluated by RT-PCR and ELISA, respectively. Activation of nuclear factor-κB (NF-κB) by TNF-α was evaluated by Western blot analysis, immunocytochemistry, and electrophoretic mobility shift assay (EMSA). TNF-α suppressed AGT mRNA expression in a dose- and time-dependent manner. Maximum AGT mRNA reduction was caused by 40 ng/ml of TNF-α (0.52 ± 0.09, ratio to control, at 24 h) and at 24 h (0.66 ± 0.05, ratio to control, by 10 ng/ml TNF-α). TNF-α reduced AGT protein accumulation in the medium between 8 and 24 h (0.62 ± 0.13 by 40 ng/ml TNF-α, ratio to control). TNF-α activated and induced translocalization of p50 and p65, which are NF-κB subunits. Elevated formation of p50/p65 and p50/p50 dimers by TNF-α were observed by EMSA and supershift assay. Gene silencing of p50, but not p65, attenuated the effect of TNF-α on reduction of AGT expression in RPTCs. These results indicate that TNF-α suppresses AGT expression through p50/p50 homodimer formation in human RPTCs, suggesting a possible counteracting mechanism that limits excessive intrarenal AGT production.

Tissue renin-angiotensin-aldosterone systems: Targets for pharmacological therapy

The renin-angiotensin-aldosterone system is one of the most important systems in cardiovascular control and in the pathogenesis of cardiovascular diseases. Therefore, it is already a very successful drug target for the therapy of these diseases. However, angiotensins are generated not only in the plasma but also locally in tissues from precursors and substrates either locally expressed or imported from the circulation. In most areas of the brain, only locally generated angiotensins can exert effects on their receptors owing to the blood-brain barrier. Other tissue renin-angiotensin-aldosterone systems are found in cardiovascular organs such as kidney, heart, and vessels and play important roles in the function of these organs and in the deleterious actions of hypertension and diabetes on these tissues. Novel components with mostly opposite actions to the classical renin-angiotensin-aldosterone systems have been described and need functional characterization to evaluate their suitability as novel drug targets.

Urinary angiotensinogen accurately reflects intrarenal Renin-Angiotensin system activity

BACKGROUND

We recently reported that immunoreactivity of intrarenal angiotensinogen (AGT) is significantly increased in IgA nephropathy patients. Meanwhile, we have developed direct enzyme-linked immunosorbent assays to measure plasma and urinary AGT (UAGT) in humans. This study was performed to test the hypothesis that UAGT levels are increased in chronic glomerulonephritis patients.

METHODS

We analyzed 100 urine samples from 70 chronic glomerulonephritis patients (26 from IgA nephropathy, 24 from purpura nephritis, 8 from lupus nephritis, 7 from focal segmental glomerulosclerosis, and 5 from non-IgA mesangial proliferative glomerulonephritis) and 30 normal control subjects.

RESULTS

UAGT-creatinine ratio (UAGT/UCre) was correlated positively with diastolic blood pressure (p = 0.0326), urinary albumin-creatinine ratio (p < 0.0001), urinary protein-creatinine ratio (p < 0.0001) and urinary occult blood (p = 0.0094). UAGT/UCre was significantly increased in chronic glomerulonephritis patients not treated with renin-angiotensin system (RAS) blockers compared with control subjects (p < 0.0001). Importantly, glomerulonephritis patients treated with RAS blockers had a marked attenuation of this augmentation (p = 0.0021).

CONCLUSION

These data indicate that UAGT are increased in chronic glomerulonephritis patients and treatment with RAS blockers suppressed UAGT. The efficacy of RAS blockade to reduce the intrarenal RAS activity can be confirmed by measurement of UAGT in chronic glomerulonephritis patients.

IL-6 augments angiotensinogen in primary cultured renal proximal tubular cells

In human kidneys, the mechanisms underlying angiotensinogen (AGT) augmentation by interleukin 6 (IL-6) are poorly understood and the only information available is in HK-2, immortalized human renal proximal tubular epithelial cells. Therefore, the present study was performed to elucidate the effects of IL-6 on AGT expression in primary cultured human renal proximal tubular epithelial cells (RPTEC) after characterization of HK-2 and RPTEC. RPTEC showed low basal AGT mRNA (11+/-1%) and protein (7.0+/-0.9%) expression, high IL-6 receptor (IL-6R) expression (282+/-17%), and low basal NF-kappaB (43+/-7%) and STAT3 (43+/-7%) activities compared to those in HK-2. In RPTEC, AGT mRNA and protein expressions were enhanced by IL-6 (172+/-31% and 378+/-39%, respectively). This AGT augmentation was attenuated by an IL-6R antibody. STAT3 phosphorylation (366+/-55% at 30min) and translocation were enhanced by IL-6. The AGT augmentation was attenuated by a STAT3 inhibitor. These data indicate that IL-6 increases AGT expression via STAT3 pathway in RPTEC.

Contribution of chymase-dependent angiotensin II formation to the progression of tubulointerstitial fibrosis in obstructed kidneys in hamsters

Recent studies indicate a role of chymase in the regulation of angiotensin II (AngII) formation in cardiovascular and renal tissues. We investigated a possible contribution of chymase to AngII formation and to renal fibrosis in unilateral ureteral obstruction (UUO). Eight-week-old Syrian hamsters were subjected to UUO and treated with vehicle, the specific chymase inhibitor (CI) 4-[1-(4-methyl-benzo[b]thiophen-3-ylmethyl)-1H-benzimidazol-2-ylsulfanyl]-butyric acid (50 mg/kg, twice a day, p.o.), or the selective AT(1)-receptor blocker olmesartan (10 mg/kg per day, p.o.) for 14 days. UUO-induced renal interstitial fibrosis was associated with increases in renal mRNA levels of alpha-smooth muscle actin (SMA), type I collagen, and transforming growth factor (TGF)-beta. The UUO hamsters showed markedly higher AngII contents and increased AT(1)-receptor mRNA level in the obstructed kidney than sham-operated ones. In contrast, angiotensin-converting enzyme (ACE) protein expression was significantly lower in UUO hamsters. In UUO hamsters, treatment with CI or olmesartan significantly decreased AngII levels in renal tissue and mRNA levels of alpha-SMA, type I collagen, and TGF-beta and ameliorated tubulointerstitial injury. On the other hand, neither CI nor olmesartan changed systolic blood pressure, renal ACE, and AT(1)-receptor protein levels. These data suggest that chymase-dependent intrarenal AngII formation contributes to the pathogenesis of interstitial fibrosis in obstructed kidneys of hamsters.

Role of activated intrarenal reactive oxygen species and renin-angiotensin system in IgA nephropathy model mice

1. Using HIGA (high IgA of ddY) mice as an IgA nephropathy model and BALB/c mice as controls, we demonstrated that reactive oxygen species (ROS) and the renin-angiotensin system (RAS) were activated in kidneys of HIGA mice. However, it was difficult to establish an association between renal damage and changes in ROS and the RAS. Therefore, the present study was performed to determine whether renal injury is associated with changes in ROS and the RAS in HIGA mice. 2. Male HIGA mice were divided into four groups of 10 each: (i) untreated mice (HIGA + null); (ii) mice treated with the angiotensin AT(1) receptor antagonist olmesartan (5 mg/kg per day; HIGA + OLM); (iii) mice treated with the superoxide dismutase mimetic tempol (50 mg/kg per day; HIGA + Tempol); and (iv) mice treated with RAS-independent antihypertensive drugs (30 mg/kg per day hydralazine, 0.6 mg/kg per day reserpine and 12 mg/kg per day hydrochlorothiazide; HIGA + HRH). Mice were treated for 5 weeks. 3. Systolic blood pressure decreased significantly in the HIGA + OLM and HIGA + HRH groups, but not in the HIGA + Tempol group, compared with HIGA + null mice. The expression of two ROS markers (4-hydroxy-2-nonenal and heme oxygenase-1) and angiotensin II as a marker of the RAS decreased significantly in HIGA + OLM and HIGA + Tempol mice, but not in HIGA + HRH mice, compared with HIGA + null mice. As a marker of renal damage, mesangial matrix expansion and the desmin-positive area decreased significantly in the HIGA + OLM and HIGA + Tempol groups, but not in HIGA + HRH group, compared with the HIGA + null group. 4. These data suggest that intrarenal ROS and RAS activation play a pivotal role in the development of IgA nephropathy model mice, from the early phase, independent of blood pressure.

Activation of reactive oxygen species and the renin-angiotensin system in IgA nephropathy model mice

1. Although IgA nephropathy is the most common form of primary glomerulopathy, the detailed mechanisms underlying its development remain uncertain. 2. In the present study, we used male high IgA strain of ddY (HIGA) mice as the IgA nephropathy model and age-matched male BALB/c mice as the control. Recent studies have demonstrated that reactive oxygen species (ROS)-dependent enhancement of the renin-angiotensin system (RAS) plays a potential role in the development and progression of renal injury. Therefore, in the present study we periodically measured the systolic blood pressure (SBP) of mice over the period 21-25 weeks of age and estimated markers for ROS, RAS and renal damage after mice had been killed at 25 weeks of age. 3. Markers for ROS (urinary 8-isoprostane excretion and renal 4-hydroxy-2-nonenal accumulation), RAS (renal angiotensinogen protein expression, urinary angiotensinogen excretion and renal angiotensin II) and renal damage (desmin-positive area and urinary protein excretion), as well as SBP, were significantly increased in HIGA mice compared with control BALB/c mice. 4. The data suggest that both ROS and the RAS are activated at an early phase in IgA nephropathy model mice.

Renin-angiotensin-aldosterone system-mediated redox effects in chronic kidney disease

The renin-angiotensin-aldosterone system (RAAS) is central to the pathogenesis of hypertension, cardiovascular disease, and kidney disease. Evidence supports various pathways through which a local renal RAAS can affect kidney function, hypertension, and cardiovascular disease. A prominent mechanism seems to be the loss of reduction-oxidation (redox) homeostasis and the formation of excessive free radicals. Free radicals such as reactive oxygen species (ROS) are necessary in normal physiologic processes, which include the development of nephrons, erythropoeisis, and tubular sodium transport. However, the loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney that in turn lead to decreased vascular compliance, podocyte pathology, and proteinuria. Both the blockade of the RAAS and the oxidative stress produce salutary effects on hypertension and glomerular filtration barrier injury. Thus, the focus of current research is on understanding the pathophysiology of chronic kidney disease in the context of an increased RAAS and unbalanced redox mechanisms.

Urinary angiotensinogen as a novel biomarker of the intrarenal renin-angiotensin system status in hypertensive patients

We reported previously that urinary angiotensinogen (UAGT) levels provide a specific index of the intrarenal renin-angiotensin system (RAS) status in angiotensin II-dependent hypertensive rats. To study this system in humans, we recently developed a human angiotensinogen ELISA. To test the hypothesis that UAGT is increased in hypertensive patients, we recruited 110 adults. Four subjects with estimated glomerular filtration levels <30 mL/min per 1.73 m(2) were excluded because previous studies have already shown that UAGT is highly correlated with estimated glomerular filtration in this stage of chronic kidney disease. Consequently, 106 paired samples of urine and plasma were analyzed from 70 hypertensive patients (39 treated with RAS blockers [angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor blockers; systolic blood pressure: 139+/-3 mm Hg] and 31 not treated with RAS blockers [systolic blood pressure: 151+/-4 mm Hg]) and 36 normotensive subjects (systolic blood pressure: 122+/-2 mm Hg). UAGT, normalized by urinary concentrations of creatinine, were not correlated with race, gender, age, height, body weight, body mass index, fractional excretion of sodium, plasma angiotensinogen levels, or estimated glomerular filtration. However, UAGT/urinary concentration of creatinine was significantly positively correlated with systolic blood pressure, diastolic blood pressure, urinary albumin:creatinine ratio (r=0.5994), and urinary protein:creatinine ratio (r=0.4597). UAGT/urinary concentration of creatinine was significantly greater in hypertensive patients not treated with RAS blockers (25.00+/-4.96 microg/g) compared with normotensive subjects (13.70+/-2.33 microg/g). Importantly, patients treated with RAS blockers exhibited a marked attenuation of this augmentation (13.26+/-2.60 microg/g). These data indicate that UAGT is increased in hypertensive patients, and treatment with RAS blockers suppresses UAGT, suggesting that the efficacy of RAS blockade to reduce the intrarenal RAS activity can be assessed by measurements of UAGT.

Angiotensin-converting enzyme-derived angiotensin II formation during angiotensin II-induced hypertension

The extent to which endogenous angiotensin (Ang) II formation is responsible for increasing kidney Ang II content and blood pressure during Ang II-induced hypertension is unknown. To address this, mice were treated with an Ang-converting enzyme (ACE) inhibitor (ACEi) to block endogenous Ang II formation during chronic Ang II infusions. C57BL/6J male mice (8 to 12 weeks) were subjected to Ang II infusions (400 ng/kg per minute) with or without an ACEi (lisinopril, 100 mg/L in the drinking water) for 12 days. Blood pressure was monitored by tail-cuff method and telemetry. Ang II content was determined by radioimmunoanalysis. Ang II infusions increased 24-hour mean arterial pressure significantly (141.0+/-3.7 mm Hg) versus controls (110.0+/-1.0 mm Hg). ACEi prevented the increase in concentration in Ang II-infused mice (Ang II+ACEi; 114.0+/-7.4 mm Hg; P value not significant). Plasma Ang II content was significantly increased by Ang II (367+/-60 fmol/mL) versus controls (128+/-22 fmol/mL; P<0.05); plasma Ang II was not altered by ACEi alone (90+/-31) or in combination with Ang II infusions (76+/-27). Intrarenal Ang II content was significantly increased by Ang II (998+/-143 fmol/g) versus controls (524+/-60 fmol/g; P<0.05), and this was prevented by ACEi (Ang II+ACEi; 484+/-102 fmol/g; P value not significant). Thus, ACEi ameliorates the increases in blood pressure and intrarenal Ang II content caused by Ang II infusions, indicating that endogenous ACE-mediated Ang II formation plays a significant role in the increases of blood pressure and intrarenal Ang II during Ang II-induced hypertension.

Intrarenal angiotensin II and angiotensinogen augmentation in chronic angiotensin II-infused mice

The objectives of this study were to determine the effects of chronic angiotensin II (ANG II) infusions on ANG II content and angiotensinogen expression in the mouse kidney and the role of the angiotensin II type 1 receptor (AT(1)R) in mediating these changes. C57BL/6J male mice were subjected to ANG II infusions at doses of 400 or 1,000 ng.kg(-1).min(-1) either alone or with an AT(1)R blocker (olmesartan; 3 mg.kg(-1).day(-1)) for 12 days. Systolic and mean arterial pressures were determined by tail-cuff plethysmography and radiotelemetry. On day 13, blood and kidneys were collected for ANG II determinations by radioimmunoanalysis and intrarenal angiotensinogen expression studies by quantitative RT-PCR, Western blotting, and immunohistochemistry. ANG II infusions at the low dose elicited progressive increases in systolic blood pressure (135 +/- 2.5 mmHg). In contrast, the high dose induced a rapid increase (152 +/- 2.5, P < 0.05 vs. controls, 109 +/- 2.8). Renal ANG II content was increased by ANG II infusions at the low dose (1,203 +/- 253 fmol/g) and the high dose (1,258 +/- 173) vs. controls (499 +/- 40, P < 0.05). Kidney angiotensinogen mRNA and protein were increased only by the low dose to 1.13 +/- 0.02 and 1.26 +/- 0.10, respectively, over controls (1.00, P < 0.05). These effects were not observed in mice infused at the high dose and those receiving olmesartan. The results indicate that chronic ANG II infusions augment mouse intrarenal ANG II content with AT(1)R-dependent uptake occurring at both doses, but only the low dose of infusion, which elicited a slow progressive response, causes an AT(1)R-dependent increase in intrarenal angiotensinogen expression.

Costimulation with angiotensin II and interleukin 6 augments angiotensinogen expression in cultured human renal proximal tubular cells

Augmented intrarenal ANG II stimulates IL-6, which contributes to renal injury. The expression of intrarenal angiotensinogen (AGT) is enhanced by increased intrarenal ANG II in human renin/human AGT double transgenic mice. ANG II also augments AGT expression in hepatocytes and cardiac myocytes. However, the mechanisms underlying AGT augmentation by ANG II and the contribution of IL-6 to this system are poorly understood. This study was performed in human renal proximal tubular epithelial cells (HRPTECs) to test the hypothesis that IL-6 contributes to the upregulation of AGT expression by ANG II. Human kidney-2 (HK-2) cells, immortalized HRPTECs, were incubated with 10(-7) M ANG II and/or 10 ng/ml IL-6 for up to 24 h. AGT mRNA and protein expressions were measured by real-time RT-PCR and ELISA, respectively. The activities of NF-kappaB and STAT3 were evaluated by Western blotting and EMSA. Stimulation with either ANG II or IL-6 did not significantly alter AGT mRNA or protein expression. In contrast, costimulation with ANG II and IL-6 significantly increased AGT mRNA and protein expressions (1.26 +/- 0.10 and 1.16 +/- 0.13 over control, respectively). Olmesartan, an ANG II type 1 receptor blocker, and an IL-6 receptor antibody individually inhibited this synergistic effect. NF-kappaB was also activated by costimulation with ANG II and IL-6. Phosphorylation and activity of STAT3 were increased by stimulation with IL-6 alone and by costimulation. The present study indicates that IL-6 plays an important role in ANG II-mediated augmentation of AGT expression in human renal proximal tubular cells.

Determination of plasma and urinary angiotensinogen levels in rodents by newly developed ELISA

We recently reported that urinary excretion rates of angiotensinogen provide a specific index of the intrarenal renin-angiotensin system status in angiotensin II-dependent hypertensive rats. Angiotensinogen concentrations in mouse plasma are thought to be much lower than those in rat plasma; however, detailed information is deficient due to lack of direct quantitative measurements of rodent angiotensinogen. To elucidate this issue, we have developed a quantitative method for measurement of rodent angiotensinogen using a sandwich-type ELISA. The standard curve for mouse and rat angiotensinogen exhibited a high linearity at 0.16-10 and 0.08-5 ng/ml, respectively, with correlation coefficients >0.99. While plasma angiotensinogen concentrations of male high serum IgA (HIGA) mice (IgA nephritis model animals, 1,308 +/- 47 ng/ml; n = 10) were lower than those of control BALB/c mice (1,620 +/- 384; n = 12), urinary angiotensinogen concentrations of HIGA mice (14.6 +/- 1.5 ng/ml; n = 34) were higher than those of BALB/c mice (4.6 +/- 0.1; n = 2). In a similar manner, while plasma angiotensinogen concentrations of Zucker diabetic fatty (ZDF) obese rats (type 2 diabetic model animals, 1,789 +/- 50 ng/ml; n = 5) were lower than those of control ZDF lean rats (2,296 +/- 47; n = 5), urinary angiotensinogen concentrations of ZDF obese rats (88.2 +/- 11.4 ng/ml; n = 15) were higher than those of ZDF lean rats (31.3 +/- 1.9; n = 15). These data indicate that plasma and urinary angiotensinogen concentrations are less in mice than rats. However, these data suggest that urinary angiotensinogen levels are different from plasma angiotensinogen levels in rodents. The development of rodent angiotensinogen ELISA allows quantitative comparisons in mouse and rat angiotensinogen levels in models of hypertension and cardiovascular and kidney diseases.

Update on tissue renin-angiotensin systems

Angiotensin (Ang) II is not only generated in the circulation by renin and angiotensin-converting enzyme (ACE) but also is produced locally in numerous organs including kidney, vessels, heart, adrenal gland, eye, testis, and brain. Furthermore, widely distributed mast cells have been shown to be a production site. Local Ang II production process is commonly termed the result of a "tissue" renin-angiotensin system (RAS). Because pharmacological experiments do not easily allow targeting of specific tissues, many novel findings about the functional importance of tissue RAS have been collected from transgenic rodent models. These animals either overexpress or lack RAS components in specific tissues and thereby elucidate their local functions. The data to date show that in most tissues local RAS amplify the actions of circulating Ang II with important implications for physiology and pathophysiology of cardiovascular diseases. This review summarizes the recent findings on the importance of tissue RAS in the most relevant cardiovascular organs.

Renal (pro)renin receptor upregulation in diabetic rats through enhanced angiotensin AT1 receptor and NADPH oxidase activity

Recent studies have demonstrated the presence of the (pro)renin receptor (PRR) in the glomerular mesangium and the subendothelial layer of the renal arteries. We hypothesized that diabetes upregulates PRR expression through enhanced angiotensin subtype 1 (AT1) receptor-NADPH oxidase cascade activity. Using real-time polymerase chain reaction, Western blot analysis and immunostaining, we studied renal localization of the PRR in the streptozotocin-induced diabetic rat model and in response to 1 week of treatment with the AT1 receptor blocker valsartan (10 mg kg(-1) day(-1)), the angiotensin AT2 receptor blocker PD123319 (0.5 mg kg(-1) day(-1)) or the NADPH oxidase inhibitor diphenylene iodonium (DPI; 0.5 mg kg(-1) day(-1)) 6 weeks post-induction of diabetes. Both PRR mRNA and protein were expressed constitutively in the kidneys of normal rat renal cortex and medulla, mainly in glomerular mesangium, proximal, distal and collecting tubules. Compared with normal rats (100%), diabetic rats demonstrated an increase in renal PRR mRNA (184%), protein (228%) and immunostaining. Valsartan and DPI prevented the increase in the PRR mRNA (106 and 126%, respectively), protein (97 and 140%, respectively) and immunostaining that was seen in the kidneys of diabetic rats. The AT2 blocker PD123319 did not have significant effects on PRR mRNA (157%) or protein expression (200%) in the kidneys of diabetic rats. These results demonstrate that the PRR is constitutively expressed in renal glomeruli and tubules. Expression of the PRR is upregulated in diabetes via enhancement of AT1 receptor-NADPH oxidase activity.