Contribution of nonproteolytically activated prorenin in glomeruli to hypertensive renal damage

Hormone-Dependent Regulation of Renin and Effects on Prorenin Receptor Signaling in the Collecting Duct

The production of renin by the principal cells of the collecting duct has widened our understanding of the regulation of intrarenal angiotensin II (Ang II) generation and blood pressure. In the collecting duct, Ang II increases the synthesis and secretion of renin by mechanisms involving the activation of Ang II type 1 receptor (AT1R) via stimulation of the PKCα, Ca²⁺, and cAMP/PKA/CREB pathways. Additionally, paracrine mediators, including vasopressin (AVP), prostaglandins, bradykinin (BK), and atrial natriuretic peptide (ANP), regulate renin in principal cells. During Ang II-dependent hypertension, despite plasma renin activity suppression, renin and prorenin receptor (RPR) are upregulated in the collecting duct and promote de novo formation of intratubular Ang II. Furthermore, activation of PRR by its natural agonists, prorenin and renin, may contribute to the stimulation of profibrotic factors independent of Ang II. Thus, the interactions of RAS components with paracrine hormones within the collecting duct enable tubular compartmentalization of the RAS to orchestrate complex mechanisms that increase intrarenal Ang II, Na+ reabsorption, and blood pressure.

Elevated serum leptin levels are associated with lower renal function among middle-aged and elderly adults in Taiwan, a community-based, cross-sectional study

BACKGROUND

Plasma leptin is considered a risk factor for obesity and cardio-metabolic disease, but the link between serum leptin and renal function is still under evaluation. In our study, we focused on the relationship between serum leptin and renal function, and we investigated the relationship in more detail.

METHODS

The 396 middle-aged and elderly Taiwanese adults recruited for our health survey were the subject of our research. All participants agreed to participate and signed a consent form before they joined and completed our study. We divided the participants into three groups according to eGFR tertiles and analyzed the parameters between each group. Then, we used Pearson's correlation test to investigate the relationship between eGFR levels and cardio-metabolic risk factors with adjustment for age. The scatter plot indicates the trend between serum leptin levels and eGFR levels. Participants were reclassified into three subgroups according to their leptin levels and the bar chart reveals the prevalence of chronic kidney disease (CKD) in each group. Finally, we used multivariate linear regression to evaluate the relationship between serum leptin and eGFR levels with adjustment for age, sex, smoking status, drinking status, body mass index (BMI), uric acid levels, hypertension (HTN), diabetes mellitus (DM), and dyslipidemia.

RESULTS

In our study, we analyzed the data from 396 eligible participants. A total of 41.4% of the participants were male, and the average age of all participants was 64.81 years ( ± 8.78). The participants in the high eGFR group were more likely to have lower serum leptin levels. Furthermore, eGFR values were negatively correlated with serum leptin levels even after adjustment for age. The prevalence of CKD in the high serum leptin group was higher than that in the low serum leptin group. Serum leptin levels showed significant negative correlations with eGFR levels (β=-0.14, p<0.01) in the multivariate linear regression after adjusting for age, sex, smoking status, drinking status, BMI, uric acid levels, HTN, DM, and dyslipidemia.

CONCLUSION

According to our study, serum leptin levels show a negative relationship with eGFR levels in middle-aged and elderly people in Taiwan. In addition, high serum leptin levels could be an novel marker to survey kidney failure in clinical practices.

The evolving complexity of the collecting duct renin-angiotensin system in hypertension

The intrarenal renin-angiotensin system is critical for the regulation of tubule sodium reabsorption, renal haemodynamics and blood pressure. The excretion of renin in urine can result from its increased filtration, the inhibition of renin reabsorption by megalin in the proximal tubule, or its secretion by the principal cells of the collecting duct. Modest increases in circulating or intrarenal angiotensin II (ANGII) stimulate the synthesis and secretion of angiotensinogen in the proximal tubule, which provides sufficient substrate for collecting duct-derived renin to form angiotensin I (ANGI). In models of ANGII-dependent hypertension, ANGII suppresses plasma renin, suggesting that urinary renin is not likely to be the result of increased filtered load. In the collecting duct, ANGII stimulates the synthesis and secretion of prorenin and renin through the activation of ANGII type 1 receptor (AT1R) expressed primarily by principal cells. The stimulation of collecting duct-derived renin is enhanced by paracrine factors including vasopressin, prostaglandin E2 and bradykinin. Furthermore, binding of prorenin and renin to the prorenin receptor in the collecting duct evokes a number of responses, including the non-proteolytic enzymatic activation of prorenin to produce ANGI from proximal tubule-derived angiotensinogen, which is then converted into ANGII by luminal angiotensin-converting enzyme; stimulation of the epithelial sodium channel (ENaC) in principal cells; and activation of intracellular pathways linked to the upregulation of cyclooxygenase 2 and profibrotic genes. These findings suggest that dysregulation of the renin-angiotensin system in the collecting duct contributes to the development of hypertension by enhancing sodium reabsorption and the progression of kidney injury.

High-salt intake accelerates functional and histological renal damage associated with renal tissue overexpression of (pro)renin receptors and AT1 receptors in spontaneously hypertensive rats

OBJECTIVE

This study aimed to investigate the effect of combination of high-salt intake and hypertension on renal functional and histological damage, associated with renal (pro)renin receptor [(P)RR] and AT1 receptor in rats.

METHODS

Wistar Kyoto rats (WKYs) and spontaneously hypertensive rats (SHRs) received regular rat chow (normal-salt diet 0.9%) or high-salt rat chow (high-salt diet 8.9%) for 6 weeks from 6 to 12 weeks of age. Systolic blood pressure, serum creatinine and blood urea nitrogen (BUN) were measured. Histological analysis of the kidney was performed. Western blot analysis was performed on the expressions of (P)RR, angiotensinogen and AT1 receptor in the kidney.

RESULTS

High-salt intake significantly increased systolic blood pressure in WKYs and especially in SHRs. High-salt intake significantly increased serum creatinine and BUN, and accelerated renal tubulointerstitial fibrosis and glomerular sclerosis in SHRs. High-salt intake significantly enhanced the renal tissue expressions of (P)RR, angiotensinogen and AT1 receptor in SHRs.

CONCLUSION

High-salt intake accelerates functional and histological renal damage associated with renal tissue overexpression of (P)RR and AT1 receptors in SHRs.

The (pro)renin receptor in health and disease

The (pro)renin receptor ((P)RR) was first identified as a single-transmembrane receptor in human kidneys and initially attracted attention owing to its potential role as a regulator of the tissue renin-angiotensin system (RAS). Subsequent studies found that the (P)RR is widely distributed in organs throughout the body, including the kidneys, heart, brain, eyes, placenta and the immune system, and has multifaceted functions in vivo. The (P)RR has roles in various physiological processes, such as the cell cycle, autophagy, acid-base balance, energy metabolism, embryonic development, T cell homeostasis, water balance, blood pressure regulation, cardiac remodelling and maintenance of podocyte structure. These roles of the (P)RR are mediated by its effects on important biological systems and pathways including the tissue RAS, vacuolar H⁺-ATPase, Wnt, partitioning defective homologue (Par) and tyrosine phosphorylation. In addition, the (P)RR has been reported to contribute to the pathogenesis of diseases such as fibrosis, hypertension, pre-eclampsia, diabetic microangiopathy, acute kidney injury, cardiovascular disease, cancer and obesity. Current evidence suggests that the (P)RR has key roles in the normal development and maintenance of vital organs and that dysfunction of the (P)RR is associated with diseases that are characterized by a disruption of the homeostasis of physiological functions.

The use of aliskiren as an antifibrotic drug in experimental models: A systematic review

Aliskiren is an oral antihypertensive medication that acts by directly inhibiting renin. High levels of circulating renin and prorenin activate the pathological signaling pathway of fibrosis. This drug also reduces oxidative stress. Thus, the aim of this systematic review is to analyze experimental studies that show the actions of aliskiren on fibrosis. PubMed and LILACS databases were consulted using the keywords aliskiren and fibrosis within the period between 2005 and 2017. Fifty-three articles were analyzed. In the heart, aliskiren attenuated remodeling, hypertrophy, inflammatory cytokines, collagen deposition, and oxidative stress. In the kidneys, there was a reduction in interstitial fibrosis, the infiltration of inflammatory cells, apoptosis, proteinuria, and in the recruitment of macrophages. In diabetic models, an improvement in the albumin/creatinine relationship and in the insulin pathway in skeletal muscles was observed; aliskiren was beneficial to pancreatic function and glucose tolerance. In the liver, aliskiren reduced fibrosis, steatosis, inflammatory cytokines, and collagen deposition. In the lung and peritoneal tissues, there was a reduction in fibrosis. Many studies have reported on the beneficial effects of aliskiren on endothelial function and arterial rigidity. A reduction in fibrosis in different organs is cited by many authors, which complies with the results found in this review. However, studies diverge on the use of the drug in diabetic patients. Aliskiren has antifibrotic potential in several experimental models, interfering with the levels of fibrogenic cytokines and oxidative stress. Therefore, its use in diseases in which fibrosis plays an important pathophysiological role is suggested.

Expression of (Pro)renin Receptor During Rapamycin-Induced Erythropoiesis in K562 Erythroleukemia Cells and Its Possible Dual Actions on Erythropoiesis

(Pro)renin receptor ((P)RR), a specific receptor for renin and prorenin, is expressed in erythroblastic cells. (P)RR has multiple biological actions: prorenin activation, stimulation of the intracellular signaling including extracellular signal-regulated kinases, and functional complex formation with vacuolar H⁺-ATPase (v-ATPase). However, the functional implication of (P)RR in erythroblast cells has not been clarified. The aim of the present study was to clarify changes of (P)RR expression during erythropoiesis and a role of (P)RR in the heme synthesis. (P)RR expression was studied during rapamycin-induced erythropoiesis in a human erythroleukemia cell line, K562. Treatment with rapamycin (100 nM) for 48 hours significantly increased %number of hemoglobin-producing cells, γ-globin mRNA levels, erythroid specific 5-aminolevulinate synthase (ALAS2) mRNA levels, and heme content in K562 cells. Both (P)RR protein and mRNA levels increased about 1.4-fold during rapamycin-induced erythropoiesis. Suppression of (P)RR expression by (P)RR-specific small interference RNA increased ALAS2 mRNA levels about 1.6-fold in K562 cells, compared to control using scramble RNA, suggesting that (P)RR may down-regulate ALAS2 expression. By contrast, treatment with bafilomycin A1, an inhibitor of v-ATPase, decreased greatly % number of hemoglobin-producing cells and heme content in K562 cells, indicating that the v-ATPase function is essential for hemoglobinization and erythropoiesis. Treatment with bafilomycin A1 increased (P)RR protein and mRNA levels. In conclusion, we propose that (P)RR has dual actions on erythropoiesis: the promotion of erythropoiesis via v-ATPase function and the down-regulation of ALAS2 mRNA expression. Thus, (P)RR may contribute to the homeostatic control of erythropoiesis.

Pathologic Roles of Receptor-Associated Prorenin System in Idiopathic Epiretinal Membrane

Receptor-associated prorenin system (RAPS) refers to the pathogenic mechanism whereby prorenin binding to (pro)renin receptor [(P)RR] dually activates tissue renin-angiotensin system (RAS) and RAS-independent signaling via (P)RR. The aim of this study is to determine the association of RAPS with idiopathic epiretinal membrane (iERM). Reverse transcription-PCR indicated the expression of RAPS components, including (P)RR and Ang II type 1 receptor (AT1R), in iERM tissues and human Müller glial cell line. Double-labeling analyses demonstrated that (P)RR and AT1R were detected in cells positive for glial fibrillary acidic protein, a marker for glial cells, and co-localized with prorenin and angiotensinogen, respectively. Administration of prorenin to Müller glial cells enhanced mRNA expression of fibroblast growth factor 2, while Ang II application stimulated the expression of glial cell line-derived neurotrophic factor, nerve growth factor, and transforming growth factor-β1. These expression levels induced by prorenin or Ang II were reversed by (P)RR or AT1R blockade, respectively. Immunofluorescence revealed tissue co-localization of (P)RR and AT1R with the products of the upregulated genes in vitro. The present findings suggest the involvement of RAPS in the pathogenesis of iERM.

Ubiquitous expression and multiple functions of biologically active peptides

Biologically active peptides are widely expressed throughout in human bodies. For example, endothelin-1 and adrenomedullin are expressed in almost all types of cells, including neurons, glial cells, fibroblasts, macrophages, cardiomyocytes, vascular endothelial cells, epithelial cells and cancer cells of various origins. Expression of both these peptides is induced by stimuli, such as hypoxia and inflammatory cytokines. They have a variety of biological functions, such as effects on brain function, hormone secretion, the cardiovascular system and cell proliferation. By contrast, orexins (hypocretins) and melanin-concentrating hormone (MCH) are specifically expressed in the hypothalamus, particularly in the lateral hypothalamus, although very low concentrations of these peptides are found in the peripheral tissues. Orexins and MCH play coordinated, but distinct physiological roles in the regulation of sleep-wake cycle, appetite, emotion and other brain functions. The cardiovascular system is regulated by cardiovascular peptides, such as natriuretic peptides, endothelins and angiotensin II. The renin-angiotensin system (RAS) is one of the most classical regulatory systems on blood pressure, electrolytes and kidney. (Pro)renin receptor is a novel member of the RAS and may be related to the pathophysiology of microvascular complications of hypertension and diabetes mellitus. Moreover, (pro)renin receptor forms a functional complex with vacuolar-type H(+)-ATPase, which plays an important physiological role in maintaining the acidic environment of intracellular compartments including secretory vesicles. Perhaps, the complex of (pro)renin receptor and vacuolar-type H(+)-ATPase may be important for the post-translational processing and secretion of many biologically active peptides.

Renin and the (pro)renin receptor in the renal collecting duct: Role in the pathogenesis of hypertension

The intrarenal renin-angiotensin system (RAS) plays a critical role in the pathogenesis and progression of hypertension and kidney disease. In angiotensin (Ang) II-dependent hypertension, collecting duct renin synthesis and secretion are stimulated despite suppression of juxtaglomerular (JG) renin. This effect is mediated by the AngII type I receptor (AT1 R), independent of blood pressure. Although the regulation of JG renin has been extensively studied, the mechanisms by which renin is regulated in the collecting duct remain unclear. The augmentation of renin synthesis and activity in the collecting duct may provide a pathway for additional generation of intrarenal and intratubular AngII formation due to the presence of angiotensinogen substrate and angiotensin-converting enzyme in the nephron. The recently described (pro)renin receptor ((P)RR) binds renin or prorenin, enhancing renin activity and fully activating the biologically inactive prorenin peptide. Stimulation of (P)RR also activates intracellular pathways related to fibrosis. Renin and the (P)RR are augmented in renal tissues of AngII-dependent hypertensive rats. However, the functional contribution of the (P)RR to enhanced renin activity in the collecting duct and its contribution to the development of hypertension and kidney disease have not been well elucidated. This review focuses on recent evidence demonstrating the mechanism of renin regulation in the collecting ducts and its interaction with the (P)RR. The data suggest that renin-(P)RR interactions may induce stimulation of intracellular pathways associated with the development of hypertension and kidney disease.

Role of non-classical renin-angiotensin system axis in renal fibrosis

The renin–angiotensin system (RAS) is a major regulator of renal fibrosis. Besides the classical renin/Angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/AT1 and AT2 axis, multiple new axes have been recently described. The new members have added new dimensions to RAS, including the ACE2/Ang(1–7)/Mas receptor axis, the prorenin/(pro)renin receptor(PRR)/intracelluar pathway axis, and the Angiotensin A (Ang A), alamandine-Mas-related G protein coupled receptor D(MrgD) axis. This review summarized recent studies regarding role of the non-classical RAS axis in renal fibrosis, and its possible implications to the intervention of progression of chronic kidney disease.

Attenuation of lipopolysaccharide-induced acute lung injury after (pro)renin receptor blockade

PURPOSE/AIM

We performed a randomized, prospective animal study to investigate whether inhibiting the renin-angiotensin system with a (pro)renin receptor blocker (PRRB) prevents acute lung injury (ALI) in a rodent model.

MATERIALS

We used Thirty-six male Sprague-Dawley rats. We administered lipopolysaccharide (LPS; 2 mg/kg) intratracheally with or without PRRB pretreatment (1 mg/kg/d).

METHODS

We performed bronchoalveolar lavage (BAL) and lung removal at 4 h after LPS administration and measured levels of inflammatory cytokines, high mobility group box 1 (HMGB-1) protein, and total protein in bronchoalveolar lavage fluid (BALF). Myeloperoxidase (MPO) activity was detected in lung tissue homogenates using a sensitive ELISA. We performed hematoxylin and eosin staining and immunohistochemical staining for nonproteolytically activated prorenin in the left lung.

RESULTS

The PRRB decreased leukocyte counts and total protein, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-2, IL-6, and IL-10 levels in the BALF and MPO activity in lung tissue. The PRRB reduced interstitial edema, hemorrhage, and the neutrophil count in the lung tissues. Consistent with the reduction in lung tissue damage, immunohistochemical staining showed that the PRRB decreased the amount of nonproteolytically activated prorenin.

CONCLUSIONS

The PRRB blocked LPS-induced inflammatory response in the lung and protected against ALI. Therefore, it is a potential therapeutic agent for preventing ALI.

Different effect of handle region peptide on β-cell function in different sexes of rats neonatally treated with sodium L-glutamate

BACKGROUND The (pro)renin receptor ((P)RR) was reported to be expressed in various tissues including the pancreas, and handle region peptide (HRP) is believed to block the function of (P)RR. This study aimed to investigate the effect of HRP on the glucose tolerance status and β-cell function of female rats, neonatally treated with sodium L-glutamate (MSG) and to compare with the previously reported HRP effect on male rats. MATERIAL AND METHODS Female MSG rats aged 8 weeks were divided into MSG control group and HRP treated group and the normal SD rats served as control. The MSG rats were treated with HRP by osmotic minipumps with dose of 1 mg/kg per day for total 28 days. Glucose tolerance status was evaluated at the end of the study. Islets α-cell and β-cell were marked with insulin antibody and glucagon antibody respectively. The proliferation of islet cells and expression of subunit of NADPH oxidase P22phox were marked by PCNA and P22phox antibody. Picrosirius red staining was performed for evaluating fibrosis of islets. RESULTS HRP improved the glucose status tolerance with decreasing α-cell mass, islets PCNA-positive cells, expression of P22phox and picrosirius red stained areas, and increasing β-cell mass in female MSG rats. The indexes with obviously interacted effect of sexes and HRP for the MSG rats were the AUC of blood glucose concentration (P<0.01), α-cell mass (P<0.05), proliferation of islet cells (P<0.01) and area of picrosirius red staining (P<0.01). CONCLUSIONS HRP improved the glucose tolerance status in the females although it was previously reported to worsen the glucose tolerance in male MSG rats. Different levels of sex hormones may partly account for the disparate effects observed for HRP in different sexes.

Expression of (pro)renin receptor and its upregulation by high salt intake in the rat nephron

A functional receptor for renin and prorenin ((P)RR) was identified as a new component of the renin-angiotensin system. The precise localization of (P)RR in the kidney has not been clarified. The present study was designed to determine the localization of (P)RR in the rat nephron and to investigate the regulation of renal (P)RR expression by high salt (HS) intake. (P)RR mRNA levels in the kidney sections and isolated nephron segments were examined using reverse transcription and polymerase chain reaction (RT-PCR), and (P)RR protein levels were examined by immunoblot and immunohistochemical analyses. Renal (P)RR mRNA and protein levels in rats fed a HS diet for 4 weeks were also compared with those fed a normal salt diet. (P)RR mRNA was expressed in various nephron segments of the cortex and medulla; glomeruli (Glm), proximal tubules (PT), thick ascending limbs (TAL) and collecting ducts (CD). (P)RR protein was highly expressed in the PT, medullary TAL (MTAL) and inner medullary CD (IMCD), and lowly in the preglomerular arterioles (Art) and Glm. HS intake increased (P)RR protein levels in the Glm, PT and tubules of medullary rays. These results indicated that (P)RR is expressed throughout various nephron segments and Art, and that (P)RR protein is expressed predominantly in the PT, MTAL and IMCD. HS intake appears to upregulate the (P)RR expression in the Glm, PT and tubules of medullary rays, suggesting that (P)RR may be involved in the regulation of renal function and HS-induced disorders.

DJ-1 regulates the expression of renal (pro)renin receptor via reactive oxygen species-mediated epigenetic modification

BACKGROUND

DJ-1 protein plays multifunctional roles including transcriptional regulation and scavenging oxidative stress; thus, it may be associated with the development of renal disorders. We investigated whether DJ-1 protein regulates the expression of (pro)renin receptor (PRR), a newly identified member of renin-angiotensin system.

METHODS

The levels of mRNA and protein were determined by real-time PCR and western blot, respectively. H2O2 production was tested by using fluorescence probe. Histone modification was determined by chromatin immunoprecipitation.

RESULTS

The expression of PRR was significantly higher in the kidney from DJ-1 knockout mice (DJ-1-/-) compared with wild-type mice (DJ-1+/+). Histone deacetylase 1 recruitment at the PRR promoter was lower, and histone H3 acetylation and RNA polymerase II recruitment were higher in DJ-1-/- than in DJ-1+/+. Knockdown or inhibition of histone deacetylase 1 restored PRR expression in mesangial cells from DJ-1+/+. H2O2 production was greater in DJ-1-/- cells compared with DJ-1+/+ cells. These changes in PRR expression and epigenetic modification in DJ-1-/- cells were induced by H2O2 treatment and reversed completely by addition of an antioxidant reagent. Prorenin-stimulated ERK1/2 phosphorylation was greater in DJ-1-/- than in DJ-1+/+ cells and this was inhibited by a PRR-inhibitory peptide, and by AT1 and AT2 receptor inhibitors. The expression of renal fibrotic genes was higher in DJ-1-/- than in DJ-1+/+ cells and decreased in PRR-knockdown DJ-1-/- cells.

CONCLUSIONS

We conclude that DJ-1 protein regulates the expression of renal PRR through H2O2-mediated epigenetic modification.

GENERAL SIGNIFICANCE

We suggest that renal DJ-1 protein may be an important molecule in the acceleration of renal pathogenesis through PRR regulation.

(Pro)renin receptor in skeletal muscle is involved in the development of insulin resistance associated with postinfarct heart failure in mice

We previously reported that insulin resistance was induced by the impairment of insulin signaling in the skeletal muscle from heart failure (HF) via NAD(P)H oxidase-dependent oxidative stress. (Pro)renin receptor [(P)RR] is involved in the activation of local renin-angiotensin system and subsequent oxidative stress. We thus examined whether (P)RR inhibitor, handle region peptide (HRP), could ameliorate insulin resistance in HF after myocardial infarction (MI) by improving oxidative stress and insulin signaling in the skeletal muscle. C57BL6J mice were divided into four groups: sham operated (Sham, n = 10), Sham treated with HRP (Sham+HRP, 0.1 mg·kg(-1)·day(-1), n = 10), MI operated (MI, n = 10), and MI treated with HRP (MI+HRP, 0.1 mg/kg/day, n = 10). After 4 wk, MI mice showed left ventricular dysfunction, which was not affected by HRP. (P)RR was upregulated in the skeletal muscle after MI (149% of sham, P < 0.05). The decrease in plasma glucose after insulin load was smaller in MI than in Sham (21 ± 2 vs. 44 ± 3%, P < 0.05), and was greater in MI+HRP (38 ± 2%, P < 0.05) than in MI. Insulin-stimulated serine phosphorylation of Akt and glucose transporter 4 translocation were decreased in the skeletal muscle from MI by 48 and 49% of Sham, both of which were ameliorated in MI+HRP. Superoxide production and NAD(P)H oxidase activities were increased in MI, which was inhibited in MI+HRP. HRP ameliorated insulin resistance associated with HF by improving insulin signaling via the inhibition of NAD(P)H oxidase-induced superoxide production in the skeletal muscle. The (P)RR pathway is involved in the development of insulin resistance, at least in part, via the impairment of insulin signaling in the skeletal muscle from HF.

Elevated plasma levels of soluble (pro)renin receptor in patients with obstructive sleep apnea syndrome: association with polysomnographic parameters

(Pro)renin receptor ((P)RR) is a specific receptor for both renin and its precursor prorenin. (P)RR was shown to be involved in pathophysiology of cardiovascular and renal diseases. Soluble (pro)renin receptor (s(P)RR), which is generated by furin from full length (P)RR, is present in blood. The aim of the present study is to clarify the association of plasma s(P)RR levels and the severity of OSAS. Plasma levels of s(P)RR were measured by ELISA in 58 male patients diagnosed as OSAS based on polysomnography, and 14 age-matched male control subjects. Blood samples were obtained at 6:00 a.m. just after overnight polysomnography. Plasma s(P)RR levels were significantly higher in patients with OSAS (9.0±2.0 ng/mL, mean ± SD) than in control subjects (7.4±1.5 ng/mL) (P=0.0026). Plasma s(P)RR levels showed a significant negative correlation with % stage rapid eye movement (REM) sleep (r=-0.377, p<0.005), and significant positive correlations with % stage 1 (r=0.374, p<0.005), arousal index (r=0.341, p<0.01), apnea hypopnea index (AHI) (r=0.352, p<0.01) and desaturation index (r=0.302, p<0. 05). In 12 OSAS patients with AHI ≥20, plasma levels of s(P)RR were studied after 3-month treatment with nasal continuous positive airway pressure (nCPAP). Plasma s(P)RR levels were significantly decreased after the nCPAP treatment (p=0.0016). The present study has shown for the first time elevated plasma s(P)RR levels in patients with OSAS. Plasma s(P)RR levels were associated with the severity of OSAS. Soluble (P)RR may serve as a plasma marker reflecting the severity of OSAS.

Deterioration of kidney function by the (pro)renin receptor blocker handle region peptide in aliskiren-treated diabetic transgenic (mRen2)27 rats

Dual renin-angiotensin system (RAS) blockade in diabetic nephropathy is no longer feasible because of the profit/side effect imbalance. (Pro)renin receptor [(P)RR] blockade with handle region peptide (HRP) has been reported to exert beneficial effects in various diabetic models in a RAS-independent manner. To what degree (P)RR blockade adds benefits on top of RAS blockade is still unknown. In the present study, we treated diabetic TGR(mREN2)27 rats, a well-established nephropathy model with high prorenin levels [allowing continuous (P)RR stimulation in vivo], with HRP on top of renin inhibition with aliskiren. Aliskiren alone lowered blood pressure and exerted renoprotective effects, as evidenced by reduced glomerulosclerosis, diuresis, proteinuria, albuminuria, and urinary aldosterone levels as well as diminished renal (P)RR and ANG II type 1 receptor expression. It also suppressed plasma and tissue RAS activity and suppressed cardiac atrial natriuretic peptide and brain natriuretic peptide expression. HRP, when given on top of aliskiren, did not alter the effects of renin inhibition on blood pressure, RAS activity, or aldosterone. However, it counteracted the beneficial effects of aliskiren in the kidney, induced hyperkalemia, and increased plasma plasminogen activator-inhibitor 1, renal cyclooxygenase-2, and cardiac collagen content. All these effects have been linked to (P)RR stimulation, suggesting that HRP might, in fact, act as a partial agonist. Therefore, the use of HRP on top of RAS blockade in diabetic nephropathy is not advisable.

Binding of prorenin to (pro)renin receptor induces the proliferation of human umbilical artery smooth muscle cells via ROS generation and ERK1/2 activation

INTRODUCTION

Since the discovery of the (pro)renin receptor (PRR), it has been considered as a novel bioactive molecule of the renin-angiotensin system (RAS). The activation of PRR can elicit a series of angiotensin II (AngII)-independent effects.

MATERIALS AND METHODS

In this study, we investigated the effects of prorenin and PRR on the proliferation of human umbilical artery smooth muscle (HUASM) cells and explored the possible mechanisms underlying these effects.

RESULTS

The binding of prorenin to PRR can promote proliferation and upregulate the anti-apoptotic protein Bcl-2 and downregulate the pro-apoptotic protein Bax independently of AngII in HUASM cells. In addition, the binding of prorenin to PRR can also increase the production of reactive oxygen species (ROS) and the phosphorylation of extracellular signal-regulated kinase (ERK1/2) independently of AngII. The pretreatment of HUASM cells with an NADPH oxidase inhibitor DPI decreased the production of ROS and also decreased the phosphorylation of ERK1/2. Furthermore, pretreatment of HUASM cells with DPI and the ERK1/2 inhibitor PD98059 significantly attenuated the prorenin-induced proliferation and regulation of apoptosis factors.

CONCLUSION

Binding of prorenin to PRR can induce HUASM cell proliferation via the ROS generation and ERK1/2 activation.

Cardiac function and architecture are maintained in a model of cardiorestricted overexpression of the prorenin-renin receptor

The (pro)renin-renin receptor, (P)RR has been claimed to be a novel element of the renin-angiotensin system (RAS). The function of (P)RR has been widely studied in renal and vascular pathology but the cardio-specific function of (P)RR has not been studied in detail. We therefore generated a transgenic mouse (Tg) with cardio-restricted (P)RR overexpression driven by the alpha-MHC promotor. The mRNA expression of (P)RR was ∼170-fold higher (P<0.001) and protein expression ∼5-fold higher (P<0.001) in hearts of Tg mice as compared to non-transgenic (wild type, Wt) littermates. This level of overexpression was not associated with spontaneous cardiac morphological or functional abnormalities in Tg mice. To assess whether (P)RR could play a role in cardiac hypertrophy, we infused ISO for 28 days, but this caused an equal degree of cardiac hypertrophy and fibrosis in Wt and Tg mice. In addition, ischemia-reperfusion injury was performed in Langendorff perfused isolated mouse hearts. We did not observe differences in parameters of cardiac function or damage between Wt and Tg mouse hearts under these conditions. Finally, we explored whether the hypoxia sensing response would be modulated by (P)RR using HeLa cells with and without (P)RR overexpression. We did not establish any effect of (P)RR on expression of genes associated with the hypoxic response. These results demonstrate that cardio-specific overexpression of (P)RR does not provoke phenotypical differences in the heart, and does not affect the hearts’ response to stress and injury. It is concluded that increased myocardial (P)RR expression is unlikely to have a major role in pathological cardiac remodeling.

The role of individual domains and the significance of shedding of ATP6AP2/(pro)renin receptor in vacuolar H(+)-ATPase biogenesis

The ATPase 6 accessory protein 2 (ATP6AP2)/(pro)renin receptor (PRR) is essential for the biogenesis of active vacuolar H⁺-ATPase (V-ATPase). Genetic deletion of ATP6AP2/PRR causes V-ATPase dysfunction and compromises vesicular acidification. Here, we characterized the domains of ATP6AP2/PRR involved in active V-ATPase biogenesis. Three forms of ATP6AP2/PRR were found intracellularly: full-length protein and the N- and C-terminal fragments of furin cleavage products, with the N-terminal fragment secreted extracellularly. Genetic deletion of ATP6AP2/PRR did not affect the protein stability of V-ATPase subunits. The extracellular domain (ECD) and transmembrane domain (TM) of ATP6AP2/PRR were indispensable for the biogenesis of active V-ATPase. A deletion mutant of ATP6AP2/PRR, which lacks exon 4-encoded amino acids inside the ECD (Δ4M) and causes X-linked mental retardation Hedera type (MRXSH) and X-linked parkinsonism with spasticity (XPDS) in humans, was defective as a V-ATPase-associated protein. Prorenin had no effect on the biogenesis of active V-ATPase. The cleavage of ATP6AP2/PRR by furin seemed also dispensable for the biogenesis of active V-ATPase. We conclude that the N-terminal ECD of ATP6AP2/PRR, which is also involved in binding to prorenin or renin, is required for the biogenesis of active V-ATPase. The V-ATPase assembly occurs prior to its delivery to the trans-Golgi network and hence shedding of ATP6AP2/PRR would not affect the biogenesis of active V-ATPase.

(Pro)renin receptor and insulin resistance: possible roles of angiotensin II-dependent and -independent pathways

A growing body of evidence has suggested the potential role of (pro)renin receptor [(P)RR] in the pathogenesis of cardiovascular and renal injuries during the development of hypertension and diabetes. However, there is very little information on the contribution of (P)RR to the pathophysiology of insulin resistance. In this regard, our preliminary data showed that the development of insulin resistance was associated with nonproteolytic activation of prorenin as well as local angiotensin II generation in skeletal muscle and adipose tissues of obese Otsuka Long-Evans Tokushima Fatty rats. In fructose-fed rats, insulin resistance was also associated with nonproteolytic activation of prorenin and skeletal muscle angiotensin II generation. Furthermore, inhibition of (P)RR with handle region decoy peptide (HRP) improved the development of fructose-induced insulin resistance. However, in other animal model, such as transgenic rats overexpressing the human renin gene, HRP failed to ameliorate glucose intolerance. In this review, we will summarized the current knowledge regarding the possible contribution of (P)RR to the pathophysiology of insulin resistance.

(Pro)renin receptor blocker improves survival of rats with sepsis

BACKGROUND

The renin-angiotensin system (RAS) affects inflammatory responses during sepsis. Nonproteolytic activation of prorenin by the (pro)renin receptor has recently been shown to stimulate the tissue RAS. In the present study, the effect of (pro)renin receptor blocker (PRRB) pretreatment on sepsis in a rat cecal ligation and puncture (CLP) model was investigated.

MATERIALS AND METHODS

Male Sprague-Dawley rats underwent CLP and were randomly divided into two groups: PRRB-treated group and control peptide-treated group. Survival was analyzed for 7 d after CLP. The serum concentrations of cytokines and high-mobility group box chromosomal protein 1 (HMGB1) were measured at three time points (0, 3, and 6 h after CLP). Hematoxylin-eosin staining and immunohistochemical staining for nonproteolytically activated prorenin and HMGB1 were performed on the cecum to assess pathologic changes found 6 h after CLP.

RESULTS

Treatment with PRRB improved the survival rate of the post-CLP septic rats (P = 0.023). PRRB also significantly reduced serum tumor necrosis factor-α, interleukin-1β, and HMGB1 levels 6 h after CLP. In CLP rats that were treated with control peptide, the expression of activated prorenin was elevated in peritoneal foam cells. Moreover, expression of HMGB1 was increased in peritoneal inflammatory cells. In contrast, both were markedly suppressed in CLP rats that were treated with PRRB.

CONCLUSIONS

PRRB significantly improved the survival rate of rats with clinically relevant sepsis, possibly by attenuating a sepsis-induced systemic inflammatory response. We propose that overactivation of the RAS by activation of prorenin in foam cells may be a significant contributor to sepsis.

(Pro)renin receptor and vacuolar H(+)-ATPase

The (pro)renin receptor [(P)RR] is a molecule that binds prorenin and renin in tissues, leading not only to their activation, but also carrying out intracellular signaling. As a key player in the tissue renin-angiotensin system, (P)RR activation plays an important role in the development of end-organ damage in hypertension and diabetes. One fragment of (P)RR is also known as ATP6AP2 because it is associated with vacuolar H(+)-ATPase (V-ATPase). V-ATPase is a multi-subunit proton pump involved in diverse and fundamental aspects of cellular physiology, including receptor-mediated endocytosis and recycling, processing of proteins and signaling molecules, membrane sorting and trafficking, and activation of lysosomal/autophagosomal enzymes. The role of (P)RR in the function of V-ATPase has been investigated in recent studies using conditional knockout mice. Furthermore, the novel function of (P)RR as an adaptor protein between the Wnt receptor complex and V-ATPase has been demonstrated. Thus, (P)RR is a multi-functional molecule that has complex structure and functionality. This review focuses on current insights into the possibility of (P)RR acting as a modulator of V-ATPase and future perspectives in translational research.

Handle Region Peptide Ameliorating Insulin Resistance but Not β Cell Functions in Male Rats Neonatally Treated with Sodium L-Glutamate

Handle region peptide (HRP), which was recognized as a blocker of (pro)renin receptor ((P)RR), may block the function of (P)RR. The aim of this study was to investigate the effect of HRP with a large dose of 1 mg/kg/d on glucose status in the rats treated neonatally with monosodium L-glutamate (MSG). At the age of 8 weeks, the MSG rats were randomly divided into MSG control group, HRP treated group with minipump (MSG-HRP group), losartan treated group (MSG-L group), and HRP and losartan cotreated group (MSG-HRP-L group) and fed with high-fat diet for 4 weeks. Losartan but not HRP increased the levels of insulin releasing and ameliorate glucose status although both losartan and HRP improved insulin sensitivity. On the one hand, both losartan and HRP decreased levels of pancreatic local Ang-II and NADPH oxidase activity as well as its subunits P(22phox). On the other hand, losartan but not HRP decreased α -cell mass and number of PCNA-positive cells located periphery of the islets and decreased picrosirius red stained area in islets. HRP ameliorating insulin resistance but not β -cell functions leads to hyperglycemia in the end in male MSG rats, and the dual characters of HRP may partly account for the phenomenon.

In vivo regulation of renal expression of (pro)renin receptor by a low-sodium diet

Effects of low salt (LS) on (pro)renin receptor (PRR) expression are not well established. We hypothesized that LS enhances renal PRR expression via the cGMP-protein kinase G (PKG) signaling pathway. Sprague-Dawley rats were fed a normal-salt (NS) or LS diet associated with intrarenal cortical administration of vehicle (V), the nitric oxide (NO) synthase inhibitor nitro-l-arginine methyl ester (l-NAME), the NO donor S-nitroso-N-acetyl-dl-penicillamine (SNAP), the cGMP analog 8-bromoguanosine (8-Br)-cGMP, the guanylyl cyclase inhibitor 1H-[1, 2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), or a PKG inhibitor (PKGi) for 6 days via osmotic minipump. We evaluated the effects of each treatment on renal interstitial fluid (RIF) levels of nitrate/nitrite and cGMP and renal PRR expression. There were no significant changes in blood pressure with any of the treatments. Urinary sodium excretion was significantly lower in rats given a LS diet. Compared with NS + V, RIF nitrate/nitrite and cGMP levels increased in LS + V rats. In NS groups, RIF nitrate/nitrite and cGMP levels did not change with l-NAME, ODQ, or PKGi and increased in response to SNAP. 8-Br-cGMP increased RIF cGMP but not RIF nitrate/nitrite. In LS groups, RIF nitrate/nitrite decreased with l-NAME and did not change with ODQ or PKGi whereas RIF cGMP decreased with l-NAME, ODQ, and PKGi. PRR mRNA and protein increased in LS + V. In NS rats, PRR mRNA and protein increased in response to 8-Br-GMP and were not affected by any of other treatments. In LS rats, PRR mRNA and protein decreased significantly in response to l-NAME, ODQ, and PKGi. We conclude that LS intake enhances renal expression of PRR via cGMP-PKG signaling pathway.

Soluble (pro)renin receptor and blood pressure during pregnancy: a prospective cohort study

The renin-angiotensin system is believed to influence blood pressure (BP) during pregnancy, but the associations between BP during pregnancy and the soluble form of the (pro)renin receptor (s[P]RR), a new component of the tissue renin-angiotensin system, remain undetermined. In this prospective cohort study of 437 pregnant women with normal BP (systolic <140 mm Hg and diastolic <90 mm Hg) during early pregnancy (<16 weeks of gestation) regression analysis was performed to examine the associations between plasma s(P)RR concentrations and BP in 3 gestational stages (20-24, 28-32, and 36-40 weeks of gestation) and logistic regression analysis to evaluate the incidence of preeclampsia. Plasma s(P)RR concentrations at early, middle (16-28 weeks), and late pregnancy (>28 weeks) and at delivery averaged 29.7 ± 10.0, 31.3 ± 12.0, 39.2 ± 8.9, and 40.4 ± 10.2 ng/mL (mean ± SD), respectively. A 1-ng/mL increase in plasma s(P)RR concentration in early pregnancy predicted systolic/diastolic BP elevation in the later 3 gestational stages: 0.11 (95% CI, 0.014-0.20)/0.093 (0.027-0.16) mm Hg for 20 to 24 weeks, 0.11 (0.029-0.19)/0.088 (0.027-0.15) mm Hg for 28 to 32 weeks, and 0.16 (0.058-0.26)/0.12 (0.043-0.19]) mm Hg for 36 to 40 weeks, respectively. Plasma s(P)RR concentrations in middle and late pregnancy were not associated with BP. Adjusted models revealed that women with plasma s(P)RR concentrations above the 75th percentile at delivery had a significantly increased risk of preeclampsia (odds ratio, 22.5 [95% CI, 1.8-279.9]). In conclusion, high circulating levels of s(P)RR at early pregnancy predicted a subsequent elevation in BP, and high concentrations at delivery were significantly associated with preeclampsia.

Critical roles of (pro)renin receptor-bound prorenin in diabetes and hypertension: sallies into therapeutic approach

High plasma prorenin levels in diabetic patients predict microvascular complications, but the mechanism of the connection between them has remained unclear. (Pro)renin receptors were recently found in the human kidney, and their distribution in various organs, including the heart, has been identified. Binding of prorenin to the (pro)renin receptor triggers two major pathways: the angiotensin II-dependent pathway as a result of conversion of prorenin to the active form of prorenin by a conformational change, and the angiotensin II-independent intracellular pathway via the (pro)renin receptor. To investigate whether the (pro)renin-receptor-dependent pathways contribute to the pathophysiology of the end-organ damage that occurs in diabetes and hypertension, a (pro)renin receptor blocker (PRRB), which binds to the receptor and competitively inhibits prorenin binding to the receptor, was administered to rats with streptozotocin-induced diabetes and to stroke-prone spontaneously hypertensive rats. PRRB significantly inhibited the development and progression of end-organ damage in these animal models of diabetes and hypertension, and it was of greater benefit than conventional inhibitors in relation to the renin-angiotensin system in diabetic angiotensin II-type 1a-receptor-deficient mice. The (pro)renin receptor may prove useful as an important therapeutic target for the prevention and regression of end-organ damage in diabetes and hypertension.

Inhibition of renin and the (pro)renin receptor system

Renin is the rate-limiting step of the renin-angiotensin system (RAS) and can induce hypertension and cardiovascular diseases (CVDs) through the over-activated renin-angiotensin-converting enzyme (ACE)-angiotensin (Ang) II-Ang II type 1 receptor (AT(1)R) axis. Prorenin and renin bound to the (pro)renin receptor [(P)RR] not only increase the catalytic conversion of angiotensinogen (AGT) to Ang I, but also upregulate the expression of profibrotic genes. This review will discuss the inhibition of renin and the (P)RR system pharmacologically and nutritionally.

Chemotactic effect of prorenin on human aortic smooth muscle cells: a novel function of the (pro)renin receptor

AIMS

The discovery of a specific prorenin receptor (PRR) suggests a biological function of prorenin that is independent of angiotensin I production. In the present study, we investigated the role of PRR on smooth muscle cell (SMC) migration.

METHODS AND RESULTS

PRR was expressed in human mammary arteries and in cultured human aortic SMCs. Prorenin induced SMC migration in a dose-dependent manner, as assessed by Boyden chamber chemotaxis assay, and increased SMC random motility, as determined by video microscopy. The prorenin decoy peptide inhibited SMC migration in response to prorenin, and knockdown of PRR by small interfering RNA completely inhibited the migratory response to prorenin, demonstrating that the chemotactic action of prorenin is mediated by the PRR. Prorenin induced cytoskeleton reorganization and lamellipodia formation and increased the intracellular levels of both RhoA-GTP and Rac1-GTP through PRR. These effects were required for SMC migration, because the suppression by small interfering RNA of either Rac1 or RhoA GTP-bound forms completely blocked the PRR-mediated chemotactic effect. Prorenin also induced the formation of larger focal adhesions and cleavage of the focal adhesion kinase (pp125(FAK)) into two main fragments with molecular weights of 50 and 90 kDa. The generation of these two fragments of pp125(FAK) was reduced by the calpain inhibitor ALLN, which also inhibited SMC migration in response to prorenin.

CONCLUSIONS

These results demonstrate that prorenin is a chemotactic factor for human aortic SMCs expressing PRR. This effect is elicited through reorganization of the cytoskeleton and focal adhesion, activation of RhoA and Rac1, and calpain-mediated cleavage of pp125(FAK).

Three key proteases--angiotensin-I-converting enzyme (ACE), ACE2 and renin--within and beyond the renin-angiotensin system

The discovery of angiotensin-I-converting enzyme 2 (ACE2) and a (pro)renin receptor has renewed interest in the physiology of the renin-angiotensin system (RAS). Through the ACE2/angiotensin-(1–7)/Mas counter-regulatory axis, ACE2 balances the vasoconstrictive, proliferative, fibrotic and proinflammatory effects of the ACE/angiotensin II/AT1 axis. The (pro)renin receptor system shows an angiotensin-dependent function related to increased generation of angiotensin I, and an angiotensin-independent aspect related to intracellular signalling. Activation of ACE2 and inhibition of ACE and renin have been at the core of the RAS regulation. The aim of this review is to discuss the biochemistry and biological functions of ACE, ACE2 and renin within and beyond the RAS, and thus provide a perspective for future bioactives from natural plant and/or food resources related to the three proteases.

The interaction between prorenin, renin and the (pro)renin receptor: time to rethink the role in hypertension

PURPOSE OF REVIEW

Elevated prorenin levels are seen in diabetics with microvascular disease. The discovery of a receptor capable of binding renin and prorenin [(P)RR] and triggering an intracellular signal in the laboratory setting raised the expectation that prorenin might be directly responsible for these vascular disorders. However, there has been substantial disagreement concerning the signaling properties of renin and prorenin and it has been impossible to inactivate the (P)RR gene in mouse to define its function.

RECENT FINDINGS

Mouse and rat models in which prorenin is highly overexpressed do not demonstrate the glomerulosclerosis typically seen in severe diabetic nephropathy, but do exhibit an increase in blood pressure that is angiotensin II-dependent. (P)RR has been shown to colocalize with other subunits of the vacuolar ATPase in the kidney and heart and to be necessary for Wnt signaling in a renin-independent manner. Although whole-body inactivation of the (P)RR gene is lethal, tissue-specific inactivation results in severe disorders associated with massive cell death.

SUMMARY

These results do not support a role of direct prorenin or renin signaling through (P)RR in vascular disorders. Rather, they suggest that the main role of (P)RR is as a subunit of the vacuolarATPase complex. Whether or not (P)RR is responsible for the ability of prorenin to generate angiotensin II in tissues has not been resolved.

Receptor-mediated nonproteolytic activation of prorenin and induction of TGF-β1 and PAI-1 expression in renal mesangial cells

While elevated plasma prorenin levels are commonly found in diabetic patients and correlate with diabetic nephropathy, the pathological role of prorenin, if any, remains unclear. Prorenin binding to the (pro)renin receptor [(p)RR] unmasks prorenin catalytic activity. We asked whether elevated prorenin could be activated at the site of renal mesangial cells (MCs) through receptor binding without being proteolytically converted to renin. Recombinant inactive rat prorenin and a mutant prorenin that is noncleavable, i.e., cannot be activated proteolytically, are produced in 293 cells. After MCs were incubated with 10(-7) M native or mutant prorenin for 6 h, cultured supernatant acquired the ability to generate angiotensin I (ANG I) from angiotensinogen, indicating both prorenins were activated. Small interfering RNA (siRNA) against the (p)RR blocked their activation. Furthermore, either native or mutant rat prorenin at 10(-7) M alone similarly and significantly induced transforming growth factor-β(1), plasminogen activator inhibitor-1 (PAI-1), and fibronectin mRNA expression, and these effects were blocked by (p)RR siRNA, but not by the ANG II receptor antagonist, saralasin. When angiotensinogen was also added to cultured MCs with inactive native or mutant prorenin, PAI-1 and fibronectin were further increased significantly compared with prorenin or mutant prorenin alone. This effect was blocked partially by treatment with (p)RR siRNA or saralasin. We conclude that prorenin binds the (p)RR on renal MCs and is activated nonproteolytically. This activation leads to increased expression of PAI-1 and transforming growth factor-β(1) via ANG II-independent and ANG II-dependent mechanisms. These data provide a mechanism by which elevated prorenin levels in diabetes may play a role in the development of diabetic nephropathy.

Enhanced intrarenal receptor-mediated prorenin activation in chronic progressive anti-thymocyte serum nephritis rats on high salt intake

Despite suppression of the circulating renin-angiotensin system (RAS), high salt intake (HSI) aggravates kidney injury in chronic kidney disease. To elucidate the effect of HSI on intrarenal RAS, we investigated the levels of intrarenal prorenin, renin, (pro)renin receptor (PRR), receptor-mediated prorenin activation, and ANG II in chronic anti-thymocyte serum (ATS) nephritic rats on HSI. Kidney fibrosis grew more severe in the nephritic rats on HSI than normal salt intake. Despite suppression of plasma renin and ANG II, marked increases in tubular prorenin and renin proteins without concomitant rises in renin mRNA, non-proteolytically activated prorenin, and ANG II were noted in the nephritic rats on HSI. Redistribution of PRR from the cytoplasm to the apical membrane, along with elevated non-proteolytically activated prorenin and ANG II, was observed in the collecting ducts and connecting tubules in the nephritic rats on HSI. Olmesartan decreased cortical prorenin, non-proteolytically activated prorenin and ANG II, and apical membranous PRR in the collecting ducts and connecting tubules, and attenuated the renal lesions. Cell surface trafficking of PRR was enhanced by ANG II and was suppressed by olmesartan in Madin-Darby canine kidney cells. These data suggest the involvement of the ANG II-dependent increase in apical membrane PRR in the augmentation of intrarenal binding of prorenin and renin, followed by nonproteolytic activation of prorenin, enhancement of renin catalytic activity, ANG II generation, and progression of kidney fibrosis in the nephritic rat kidneys on HSI. The origin of the increased tubular prorenin and renin remains to be clarified. Further studies measuring the urinary prorenin and renin are needed.

Prorenin receptor is essential for normal podocyte structure and function

The prorenin receptor is an accessory subunit of the vacuolar H(+)-ATPase, suggesting that it has fundamental functions beyond activation of the local renin-angiotensin system. Podocytes express the prorenin receptor, but its function in these cells is unknown. Here, podocyte-specific, conditional, prorenin receptor-knockout mice died of kidney failure and severe proteinuria within 4 weeks of birth. The podocytes of these mice exhibited foot process effacement with reduced and altered localization of the slit-diaphragm proteins nephrin and podocin. Furthermore, the podocytes contained numerous autophagic vacuoles, confirmed by enhanced accumulation of microtubule-associated protein 1 light chain 3-positive intracellular vesicles. Ablation of the prorenin receptor selectively suppressed expression of the V(0) c-subunit of the vacuolar H(+)-ATPase in podocytes, resulting in deacidification of intracellular vesicles. In conclusion, the prorenin receptor is important for the maintenance of normal podocyte structure and function.

The cardiac (pro)renin receptor is primarily expressed in myocyte transverse tubules and is increased in experimental diabetic cardiomyopathy

BACKGROUND

The pro(renin) receptor is a 350 amino acid transmembrane protein, that on ligand binding, increases the catalytic efficiency of angiotensinogen cleavage by both prorenin and renin, augmenting angiotensin I formation at the cell surface. While implicated in a broad range of diseases, studies to date have focused on the kidney, particularly in the diabetic context. We sought to examine the site-specific expression of the pro(renin) receptor within the heart.

METHODS

Using confocal microscopy, site-specific markers and transmission electron microscopy we assessed the location of the pro(renin) receptor in the heart at both cellular/sub-cellular levels. We assessed pro(renin) receptor expression in the setting of disease and blockade of the renin-angiotensin system, using the TGR[m(Ren2)-27] model of diabetic cardiomyopathy and the direct renin inhibitor, aliskiren.

RESULTS

The pro(renin) receptor was found predominantly at the Z-disc and dyad of cardiac myocytes coinciding closely with the distributions of the vacuolar H⁺-ATPase and ryanodine receptor, known to be located within T-tubules and the sarcoplasmic reticulum's terminal cisternae, respectively. Pro(renin) receptor mRNA/protein abundance were increased ∼3-fold in the hearts of diabetic rats in association with diastolic dysfunction, myocyte hypertrophy and interstitial fibrosis (all P < 0.01). Direct renin inhibition reduced cardiac pro(renin) receptor expression in association with improved cardiac structure/function (all P < 0.05).

CONCLUSION

Together, these findings are consistent with the notion that the pro(renin) receptor is a component of the vacuolar H⁺-ATPase, and that like the latter, is increased in the setting of cardiac stress and lowered by the administration of an ostensibly cardioprotective agent.

Prognostic value of renin and prorenin in heart failure patients with decreased kidney function

BACKGROUND

The renin-angiotensin-aldosterone system (RAAS) plays a key role in the progression of heart failure (HF) and concomitant kidney dysfunction. Despite the use of RAAS blockade, sustained activation of RAAS has been suggested to link with adverse outcome. We aimed to investigate the prognostic value of active plasma renin concentration (APRC) and prorenin in patients with HF treated with RAAS-blocking agents and its relationship with kidney function parameters.

METHODS

One hundred clinically stable patients with HF, treated with RAAS-blocking agents, were studied. Renal function parameters including effective renal plasma flow and glomerular filtration rate were measured invasively. The combined end point consisted of all-cause mortality, heart transplantation, and admission to hospital for HF.

RESULTS

Mean age was 58 ± 12 years, and 76% were men. Mean left ventricular ejection fraction was 28 ± 9, and median APRC levels were 24.3 ng/mL per hour. Active plasma renin concentration was most strongly associated with mean arterial pressure (r = 0.60, P < .001). In multivariate linear regression analysis, age, mean arterial pressure, angiotensin II concentration, and use of aldosterone antagonists were significantly related with APRC (adjusted R(2) = 0.53). Patients in the highest quartile of APRC had a worse prognosis. In multivariate analysis, APRC remained associated with worse prognosis: HR 2.87 (95% CI 1.14-7.20), P = .025. Prorenin did not show prognostic value. The prognostic value of APRC was strongest in patients with decreased kidney function.

CONCLUSIONS

Our data indicate that APRC is a strong prognostic factor in patients with HF in the presence of RAAS inhibition, especially in patients with kidney dysfunction.

Association of (pro)renin receptor gene polymorphism with blood pressure in Caucasian men

The renin-angiotensin system is a major regulatory system of cardiovascular and renal function. Recently, (pro)renin receptor [(P)RR] was identified as new component of the renin-angiotensin system. The IVS5+169C>T polymorphism of the (P)RR gene was shown to be associated with blood pressure (BP) in Japanese men, but no data are available for Caucasians. Hence, we genotyped the IVS5+169C>T polymorphism of the (P)RR gene in 266 Caucasian men with normal or mildly elevated BP and without any medication. Office BP was measured according to current guidelines. Office and resting systolic BP was lower in C-allele than in T-allele carriers (P<0.05) of the (P)RR gene, with no difference in diastolic BP and heart rate. Serum aldosterone was also lower in C-allele than in T-allele carriers (P<0.05). These findings indicate that C-allele carriers have lower systolic BP than T-allele carriers. Thus, our data suggest that (P)RR influences BP regulation in Caucasian men, potentially through altered aldosterone release.

Renal (pro)renin receptor contributes to development of diabetic kidney disease through transforming growth factor-β1-connective tissue growth factor signalling cascade

1. Transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) are expressed in renal glomeruli, and contribute to the development of diabetic nephropathy. Recently, we showed that (pro)renin receptor (PRR) is upregulated in the kidneys of the streptozocin (STZ)-induced diabetes rat model. We hypothesized that in the presence of hyperglycaemia, increased renal PRR expression contributes to enhanced TGF-β1-CTGF signalling activity, leading to the development of diabetic kidney disease. 2. In vivo and in vitro studies were carried out in Sprague-Dawley rats and rat mesangial cells (RMC). PRR blockade was achieved in vivo by treating STZ induced diabetes rats with the handle region peptide (HRP) of prorenin and in vitro by HRP or PRR siRNA in RMC. Angiotensin AT1 receptor blockade was achieved by valsartan treatment. 3. Results showed that expression of PRR, TGF-β1 and CTGF were upregulated in diabetic kidneys and RMC exposed to high glucose. Glucose exposure also induced PRR phosphorylation, a process that was inhibited by HRP, valsartan or PRR siRNA. HRP and valsartan significantly attenuated renal TGF-β1 and CTGF expression in diabetic animals and high glucose treated RMC. Similar results were observed in high glucose exposed RMC in response to PRR siRNA. TGF-β receptor blockade decreased CTGF expression in RMC. Combined administration of valsartan and PRR siRNA showed further reduction of TGF-β1 and CTGF expression in RMC. 4. In conclusion, PRR contributes to kidney disease in diabetes through an enhanced TGF-β1-CTGF signalling cascade.

(Pro)renin Receptor in Kidney Development and Disease

The renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the developing metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans are associated with a broad spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). These forms of CAKUT include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, and aberrant glomerulogenesis. Emerging evidence indicates that (pro)renin receptor (PRR), a novel component of the RAS, is essential for proper kidney development and that aberrant PRR signaling is causally linked to cardiovascular and renal disease. This paper describes the role of the RAS in kidney development and highlights emerging insights into the cellular and molecular mechanisms by which the PRR may regulate this critical morphogenetic process.

Aliskiren ameliorates renal inflammation and fibrosis induced by unilateral ureteral obstruction in mice

PURPOSE

Renin-angiotensin system activation is involved in inflammation and fibrosis in the kidney. Aliskiren, a direct renin inhibitor, decreases renin-angiotensin system activation, including plasma renin activity and angiotensin II, but increases the prorenin level, which may promote inflammation and fibrosis in renal tissue. Thus, we evaluated whether inhibiting the renin-angiotensin system by aliskiren would decrease renal inflammation and fibrosis in a mouse model of unilateral ureteral obstruction.

MATERIALS AND METHODS

Ten-week-old male C57BL/6 mice (Samtako, Kyoung Gi-Do, Korea) weighing 30 to 33 gm were divided into 4 groups, including vehicle or aliskiren treated sham operated and vehicle or aliskiren treated unilateral ureteral obstruction groups. We evaluated plasma renin activity, and plasma renin and renal mRNA expression levels of renin and (pro)renin receptor. To evaluate inflammation and fibrosis renal mRNA expression of monocyte chemotactic protein-1, osteopontin and transforming growth factor-β was measured. Hematoxylin and eosin, Masson's trichrome staining, and immunohistochemical staining for CD68, transforming growth factor-β and α-smooth muscle actin were performed.

RESULTS

Plasma renin activity was significantly lower in the aliskiren treated obstruction group than in the vehicle treated obstruction group. Aliskiren treatment increased renal mRNA expression of renin. The number of CD68 positive cells, and renal monocyte chemotactic protein-1 and osteopontin mRNA levels were significantly higher in mice with unilateral ureteral obstruction than in sham operated mice. Aliskiren decreased the increased levels of these inflammation markers. Aliskiren also decreased renal transforming growth factor-β mRNA expression, transforming growth factor-β and α-smooth muscle actin immunostaining, and Masson's trichrome stained areas of unilateral ureteral obstruction kidneys.

CONCLUSIONS

Aliskiren has anti-inflammatory and antifibrotic effects in an experimental unilateral ureteral obstruction mouse model.

Direct renin inhibition: update on clinical investigations with aliskiren

The renin–angiotensin–aldosterone system (RAAS) plays a pivotal role in regulating blood pressure, volume, and electrolytes. The final product of RAAS cascade is angiotensin II, which exerts diverse biological activities via binding to one of three known receptor types, with different binding consequences. Despite the success with conventional strategies to limit angiotensin II production and action, these agents promote a reflex rise in plasma renin activity, which is thought to be associated with an increased incidence of cardiovascular events. Several renin inhibitors have been synthesized in order to counteract deleterious consequences of renin activity and RAAS activation; aliskiren is the first of these new non-peptide direct renin inhibitors to be approved for the treatment of hypertension. The paper reviews pharmacokinetics of aliskiren and its role in hypertension, with particular regard to those studies that compared clinical efficacy of aliskiren in comparison and in addition to other antihypertensive drug strategies.

Renin and cardiovascular disease: Worn-out path, or new direction

Inhibition of the renin angiotensin system has beneficial effects in cardiovascular prevention and treatment. The advent of orally active direct renin inhibitors adds a novel approach to antagonism of the renin-angiotensin system. Inhibition of the first and rate-limiting step of the renin angiotensin cascade offers theoretical advantages over downstream blockade. However, the recent discovery of the (pro)renin receptor which binds both renin and prorenin, and which can not only augment catalytic activity of both renin and prorenin in converting angiotensinogen to angiotensin I, but also signal intracellularly via various pathways to modulate gene expression, adds a significant level of complexity to the field. In this review, we will examine the basic and clinical data on renin and its inhibition in the context of cardiovascular pathophysiology.

(Pro)renin promotes fibrosis gene expression in HEK cells through a Nox4-dependent mechanism

The (pro)renin receptor (PRR) has recently been demonstrated to bind equally well renin and its precursor, prorenin, leading to a similar intracellular signaling independent of angiotensin II. In this study, we report that human embryonic kidney cells (HEK) exposed to renin or prorenin for 24 h in the presence of a blocking concentration of the angtiotensin-converting enzyme inhibitor perindoprilate increased superoxide anion production as measured by luminescence (lucigenin) and electron spin resonance spectroscopy (hydroxylamine radical transition). Also, both renin and prorenin increased Nox4 expression while Nox2, p47(phox), and p67(phox) remained unchanged. In an investigation of the effects of renin and prorenin on fibrosis genes, it appeared that both proteins stimulated transforming growth factor-β (TGF-β), fibronectin, and plasminogen activator inhibitor type 1 (PAI-1) expression and therefore participated to an overall switch toward a profibrotic state of the kidney cells. When the cells were transfected with a siRNA targeting the PRR, Nox4 expression was efficiently prevented as well as the increase in superoxide production, TGF-β, fibronectin, and PAI-1. Finally, we demonstrated that transfection of the cells with a Nox4-specific small interfering (si) RNA also prevented fibrosis gene expression following treatment with renin or prorenin. The results demonstrate that renin and prorenin, through their specific membrane receptor and independently of angiotensin II, promote fibrosis gene expression via a Nox4-dependent mechanism.