Soluble form of the (pro)renin receptor is augmented in the collecting duct and urine of chronic angiotensin II-dependent hypertensive rats

Glaucoma and the ocular renin-angiotensin-aldosterone system: Update on molecular signalling and treatment perspectives

Glaucoma, a leading cause of blindness worldwide, encompasses a group of pathological conditions affecting the optic nerve and is characterized by progressive retinal ganglion cell loss, cupping of the optic nerve head, and distinct visual field defects. While elevated intraocular pressure (IOP) is the main risk factor for glaucoma, many patients do not have elevated IOP. Consequently, other risk factors, such as ocular blood flow abnormalities and immunological factors, have been implicated in its pathophysiology. Traditional therapeutic strategies primarily aim to reduce IOP, but there is growing interest in developing novel treatment approaches to improve disease management and reduce the high rates of severe visual impairment. In this context, targeting the ocular renin-angiotensin-aldosterone system (RAAS) has been found as a potential curative strategy. The RAAS contributes to glaucoma development through key effectors such as prorenin, angiotensin II, and aldosterone. Recent evidence has highlighted the potential of using RAAS modulators to combat glaucoma, yielding encouraging results. Our study aims to explore the molecular pathways linking the ocular RAAS and glaucoma, summarizing recent advances that elucidate the role of the RAAS in triggering oxidative stress, inflammation, and remodelling in the pathogenesis of glaucoma. Additionally, we will present emerging therapeutic approaches that utilize RAAS modulators and antioxidants to slow the progression of glaucoma.

Assessment of the (Pro)renin Receptor Protein Expression in Organs

The (pro)renin receptor ((P)RR) is an essential component of the renin-angiotensin system (RAS) as a specific single-pass transmembrane receptor for prorenin and renin and has now emerged as a multifunctional protein implicated in a wide variety of developmental and physio-pathological processes and pathways. The (P)RR may be of pathological significance in metabolic syndrome. The (P)RR has received much consideration; substantial efforts have been made to understand the localization, regulation, and function of the (P)RR at both a molecular and system level. (P)RR regulation of cell function depends on whether it is intact or cleaved into its constituent forms. Therefore, the present chapter describes immunohistochemical approaches to examine the expression of (P)RR in various organs. It was shown that different molecular forms of (P)RR could be present in different tissue compartments in almost all organs. Among them, the liver has high PRR activity. Our findings could elucidate more detailed distribution of different (P)RR molecular forms in different organs, which could provide useful information to further investigate the pathophysiological mechanisms of the development of various diseases in the future.

Inhibition of intrarenal PRR-RAS pathway by Ganoderma lucidum polysaccharide peptides in proteinuric nephropathy

Excessive proteinuria leads to renal dysfunction and damage. Ganoderma lucidum polysaccharide peptide (GL-PP) and Ganoderma lucidum polysaccharide peptide 2 (GL-PP2) are biologically active compounds extracted from Ganoderma lucidum. GL-PP has a relative molecular weight of 37,121 with 76.39 % polysaccharides and 16.35 % polypeptides, while GL-PP2 has a relative molecular weight of 31,130, composed of 64.14 % polysaccharides and 17.73 % polypeptides. The xylose: mannose: glucose monosaccharide ratios in GL-PP and GL-PP2 were 4.83:1:7.03 and 2.35:1:9.38, respectively. In this study, we investigated the protective effects of GL-PP and GL-PP2 on proteinuria-induced renal dysfunction and damage using rat and cell models. Both compounds reduced kidney injury, proteinuria, and inhibited the (pro)renin receptor (PRR)-renin-angiotensin system (RAS) pathway, inflammatory cell infiltration, oxidative stress, and fibrosis. GL-PP2 showed stronger inhibition of cyclooxygenase-2 and inducible nitric oxide synthase proteins compared to GL-PP. In cell models, both compounds displayed anti-inflammatory properties and improved cellular viability by inhibiting the PRR-RAS pathway. GL-PP2 has higher feasibility and productivity than GL-PP in pharmacology and industrial production. It shows promise in treating proteinuria-induced renal disease with superior anti-inflammatory effects and economic, safe industrial application prospects. Further research is needed to compare efficacy, mechanisms, clinical applications, and commercial feasibility of GL-PP and GL-PP2.

Sex differences in the renin-angiotensin-aldosterone system and its roles in hypertension, cardiovascular, and kidney diseases

Cardiovascular disease is a pathology that exhibits well-researched biological sex differences, making it possible for physicians to tailor preventative and therapeutic approaches for various diseases. Hypertension, which is defined as blood pressure greater than 130/80 mmHg, is the primary risk factor for developing coronary artery disease, stroke, and renal failure. Approximately 48% of American men and 43% of American women suffer from hypertension. Epidemiological data suggests that during reproductive years, women have much lower rates of hypertension than men. However, this protective effect disappears after the onset of menopause. Treatment-resistant hypertension affects approximately 10.3 million US adults and is unable to be controlled even after implementing ≥3 antihypertensives with complementary mechanisms. This indicates that other mechanisms responsible for modulating blood pressure are still unclear. Understanding the differences in genetic and hormonal mechanisms that lead to hypertension would allow for sex-specific treatment and an opportunity to improve patient outcomes. Therefore, this invited review will review and discuss recent advances in studying the sex-specific physiological mechanisms that affect the renin-angiotensin system and contribute to blood pressure control. It will also discuss research on sex differences in hypertension management, treatment, and outcomes.

High-plasma soluble prorenin receptor is associated with vascular damage in male, but not female, mice fed a high-fat diet

Plasma soluble prorenin receptor (sPRR) displays sexual dimorphism and is higher in women with type 2 diabetes mellitus (T2DM). However, the contribution of plasma sPRR to the development of vascular complications in T2DM remains unclear. We investigated if plasma sPRR contributes to sex differences in the activation of the systemic renin-angiotensin-aldosterone system (RAAS) and vascular damage in a model of high-fat diet (HFD)-induced T2DM. Male and female C57BL/6J mice were fed either a normal fat diet (NFD) or an HFD for 28 wk to assess changes in blood pressure, cardiometabolic phenotype, plasma prorenin/renin, sPRR, and ANG II. After completing dietary protocols, tissues were collected from males to assess vascular reactivity and aortic reactive oxygen species (ROS). A cohort of male mice was used to determine the direct contribution of increased systemic sPRR by infusion. To investigate the role of ovarian hormones, ovariectomy (OVX) was performed at 32 wk in females fed either an NFD or HFD. Significant sex differences were found after 28 wk of HFD, where only males developed T2DM and increased plasma prorenin/renin, sPRR, and ANG II. T2DM in males was accompanied by nondipping hypertension, carotid artery stiffening, and aortic ROS. sPRR infusion in males induced vascular thickening instead of material stiffening caused by HFD-induced T2DM. While intact females were less prone to T2DM, OVX increased plasma prorenin/renin, sPRR, and systolic blood pressure. These data suggest that sPRR is a novel indicator of systemic RAAS activation and reflects the onset of vascular complications during T2DM regulated by sex.NEW & NOTEWORTHY High-fat diet (HFD) for 28 wk leads to type 2 diabetes mellitus (T2DM) phenotype, concomitant with increased plasma soluble prorenin receptor (sPRR), nondipping blood pressure, and vascular stiffness in male mice. HFD-fed female mice exhibiting a preserved cardiometabolic phenotype until ovariectomy revealed increased plasma sPRR and blood pressure. Plasma sPRR may indicate the status of systemic renin-angiotensin-aldosterone system (RAAS) activation and the onset of vascular complications during T2DM in a sex-dependent manner.

The Triad Na+ Activated Na+ Channel (Nax)-Salt Inducible KINASE (SIK) and (Na+ + K+)-ATPase: Targeting the Villains to Treat Salt Resistant and Sensitive Hypertension

The Na⁺-activated Na⁺ channel (Nax) and salt-inducible kinase (SIK) are stimulated by increases in local Na⁺ concentration, affecting (Na⁺ + K⁺)-ATPase activity. To test the hypothesis that the triad Nax/SIK/(Na⁺ + K⁺)-ATPase contributes to kidney injury and salt-sensitive hypertension (HTN), uninephrectomized male Wistar rats (200 g; n = 20) were randomly divided into 4 groups based on a salt diet (normal salt diet; NSD-0.5% NaCl-or high-salt diet; HSD-4% NaCl) and subcutaneous administration of saline (0.9% NaCl) or deoxycorticosterone acetate (DOCA, 8 mg/kg), as follows: Control (CTRL), CTRL-Salt, DOCA, and DOCA-Salt, respectively. After 28 days, the following were measured: kidney function, blood pressure, (Na⁺ + K⁺)-ATPase and SIK1 kidney activities, and Nax and SIK1 renal expression levels. SIK isoforms in kidneys of CTRL rats were present in the glomerulus and tubular epithelia; they were not altered by HSD and/or HTN. CTRL-Salt rats remained normotensive but presented slight kidney function decay. HSD rats displayed augmentation of the Nax/SIK/(Na⁺ + K⁺)-ATPase pathway. HTN, kidney injury, and kidney function decay were present in all DOCA rats; these were aggravated by HSD. DOCA rats presented unaltered (Na⁺ + K⁺)-ATPase activity, diminished total SIK activity, and augmented SIK1 and Nax content in the kidney cortex. DOCA-Salt rats expressed SIK1 activity and downregulation in (Na⁺ + K⁺)-ATPase activity in the kidney cortex despite augmented Nax content. The data of this study indicate that the (Na⁺ + K⁺)-ATPase activity response to SIK is attenuated in rats under HSD, independent of HTN, as a mechanism contributing to kidney injury and salt-sensitive HTN.

(Pro)Renin Receptor Decoy Peptide PRO20 Protects against Oxidative Renal Damage Induced by Advanced Oxidation Protein Products

Chronic kidney disease (CKD) is associated with advanced oxidation protein products (AOPPs). A recent study has shown that AOPP-induced renal tubular injury is mediated by the (pro)renin receptor (PRR). However, it is unclear whether the PRR decoy inhibitor PRO20 can protect against renal damage related to AOPPs in vivo. In this study, we examined the role of the PRR in rats with AOPP-induced renal oxidative damage. Male SD rats were subjected to unilateral nephrectomy, and after a four-day recuperation period, they were randomly divided into four groups (n = 6/group) for four weeks: control (CTR), unmodified rat serum albumin (RSA, 50 mg/kg/day via tail-vein injection), AOPPs-RSA (50 mg/kg/day via tail-vein injection), and AOPPs-RSA + PRO20 (50 mg/kg/day via tail-vein injection + 500 μg/kg/day via subcutaneous injection) groups. PRO20 was administered 3 days before AOPPs-RSA injection. Renal histopathology evaluation was performed by periodic acid–Schiff (PAS) staining, and biochemical parameters related to renal injury and oxidative stress biomarkers were evaluated. The expression of related indicators was quantified by RT-qPCR and immunoblotting analysis. In the results, rats in the AOPPs-RSA group exhibited higher levels of albuminuria, inflammatory cell infiltration, and tubular dilation, along with upregulation of oxidative stress, profibrotic and proinflammatory factors, and elevation of AOPP levels. Meanwhile, in the PRO20 group, these were significantly reduced. Moreover, the levels of almost all components of the renin-angiotensin system (RAS) and Nox4-dependent H2O2 production in urine and the kidneys were elevated by AOPPs-RSA, while they were suppressed by PRO20. Furthermore, AOPPs-RSA rats showed elevated kidney expression of the PRR and soluble PRR (sPRR) and increased renal excretion of sPRR. In summary, these findings suggest that PRR inhibition may serve as a protective mechanism against AOPP-induced nephropathy by inhibiting the intrarenal RAS and Nox4-derived H2O2 mechanisms.

Mutagenesis of the cleavage site of (pro)renin receptor abrogates aldosterone-salt-induced hypertension and renal injury in mice

Soluble (pro)renin receptor (sPRR), the extracellular domain of (pro)renin receptor (PRR), is primarily generated by site-1 protease and furin. It has been reported that sPRR functions as an important regulator of intrarenal renin contributing to angiotensin II (ANG II)-induced hypertension. Relatively, less is known for the function of sPRR in ANG II-independent hypertension such as mineralocorticoid excess. In the present study, we used a novel mouse model with mutagenesis of the cleavage site in PRR (termed as PRRR279V/L282V or mutant) to examine the phenotype during aldosterone (Aldo)-salt treatment. The hypertensive response of mutant mice to Aldo-salt treatment was blunted in parallel with the attenuated response of plasma volume expansion and renal medullary α-epithelial Na+ channel expression. Moreover, Aldo-salt-induced hypertrophy in the heart and kidney as well as proteinuria were improved, accompanied by blunted polydipsia and polyuria. Together, these results represent strong evidence favoring endogenous sPRR as a mediator of Aldo-salt-induced hypertension and renal injury.NEW & NOTEWORTHY We used a novel mouse model with mutagenesis of the cleavage site of PRR to support soluble PRR as an essential mediator of aldosterone-salt-induced hypertension and also as a potential therapeutic target for patients with mineralocorticoid excess. We firstly report that soluble PRR-dependent pathway medicates the Na+-retaining action of aldosterone in the distal nephron, which opens up a new area for a better understanding of the molecular basis of renal handling of Na+ balance and blood pressure.

Potential of soluble (pro)renin receptor in kidney disease: can it go beyond a biomarker?

(Pro)renin receptor (PRR), also termed ATPase H+-transporting accessory protein 2 (ATP6AP2), is a type I transmembrane receptor and is capable of binding and activating prorenin and renin. Apart from its association with the renin-angiotensin system, PRR has been implicated in diverse developmental, physiological, and pathophysiological processes. Within the kidney, PRR is predominantly expressed in the distal nephron, particularly the intercalated cells, and activation of renal PRR contributes to renal injury in various rodent models of chronic kidney disease. Moreover, recent evidence demonstrates that PRR is primarily cleaved by site-1 protease to produce 28-kDa soluble PRR (sPRR). sPRR seems to mediate most of the known pathophysiological functions of renal PRR through modulating the activity of the intrarenal renin-angiotensin system and provoking proinflammatory and profibrotic responses. Not only does sPRR activate renin, but it also directly binds and activates the angiotensin II type 1 receptor. This review summarizes recent advances in understanding the roles and mechanisms of sPRR in the context of renal pathophysiology.

Soluble (Pro)Renin Receptor Levels Are Regulated by Plasma Renin Activity and Correlated with Edema in Mice and Humans with HFrEF

Symptomatic heart failure with reduced ejection fraction (HFrEF) is characterized by edema and chronic pathological activation of the classical renin–angiotensin–aldosterone system (RAAS). The soluble (pro)renin receptor (s(P)RR) is released into circulation by proteolytic cleavage of tissue expressed (P)RR and is a candidate biomarker of RAAS activation. However, previous studies linked elevated levels of s(P)RR in patients with HFrEF to renal dysfunction. Utilizing prospectively enrolled patients with comparable rEF, we show that increased plasma levels of s(P)RR are associated with symptomatic HF (characterized by edema), independent of chronic renal dysfunction. We also found that s(P)RR levels were positively correlated with patient plasma renin activity (PRA). Normotensive mice with dilated cardiomyopathy (DCM) and HFrEF, without renal dysfunction, showed plasma s(P)RR and PRA patterns similar to human HFrEF patients. Plasma s(P)RR levels positively correlated with PRA and systemic edema, but not with EF, resembling findings in patients with HFrEF without chronic kidney dysfunction. In female DCM mice with elevated PRA levels and plasma s(P)RR levels, a randomized, blinded trial comparing the direct renin inhibitor, aliskiren vs. vehicle control, showed that direct renin inhibition normalized PRA, lowered s(P)RR, and prevented symptomatic HFrEF. Considered in light of previous findings, these data suggest that, in HFrEF, in the absence of renal dysfunction, elevation of plasma s(P)RR levels is caused by increased PRA and associated with the development of systemic edema.

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.

The Role of (Pro)Renin Receptor in the Metabolic Syndrome

The prorenin receptor (PRR) is a complex multi-functional single transmembrane protein receptor that is ubiquitously expressed in organs and tissues throughout the body. PRR is involved in different cellular mechanisms that comprise the generation of Angiotensin II, the activation of Wnt/β-catenin signaling, the stimulation of ERK 1/2 pathway, and the proper functioning of the vacuolar H+-ATPase. Evidence supports the role of PRR and its soluble form, sPRR, in the classical features of the metabolic syndrome, including obesity, hypertension, diabetes, and disruption of lipid homeostasis. This review summarizes our current knowledge and highlights new advances in the pathophysiological function of PRR and sPRR in adipogenesis, adipocyte differentiation, lipolysis, glucose and insulin resistance, lipid homeostasis, energy metabolism, and blood pressure regulation.

Soluble (Pro)Renin Receptor in Hypertension

The (pro)renin receptor (PRR) was originally cloned as a specific single-transmembrane receptor for prorenin and renin and has now emerged as a multifunctional protein implicated in a wide variety of developmental and physiopathological processes. Activation of PRR in the kidney causes Na+ and water retention, contributing to elevation of blood pressure in response to various hypertensive stimuli. Part of the renal action of PRR depends on activation of intrarenal renin-angiotensin system. In recent years, accumulating evidence suggests that the prohypertensive action of renal PRR was largely mediated by production of the 28-kDa soluble (pro)renin receptor through protease-mediated cleavage of the extracellular domain of PRR. The generation of multiple isoforms of PRR due to the protease-mediated cleavage partially explains diversified actions of PRR. The current review will summarize recent advances in understanding the roles of sPPR in animal models of hypertension.

Kidney Angiotensin in Cardiovascular Disease: Formation and Drug Targeting

The concept of local formation of angiotensin II in the kidney has changed over the last 10-15 years. Local synthesis of angiotensinogen in the proximal tubule has been proposed, combined with prorenin synthesis in the collecting duct. Binding of prorenin via the so-called (pro)renin receptor has been introduced, as well as megalin-mediated uptake of filtered plasma-derived renin-angiotensin system (RAS) components. Moreover, angiotensin metabolites other than angiotensin II [notably angiotensin-(1-7)] exist, and angiotensins exert their effects via three different receptors, of which angiotensin II type 2 and Mas receptors are considered renoprotective, possibly in a sex-specific manner, whereas angiotensin II type 1 (AT1) receptors are believed to be deleterious. Additionally, internalized angiotensin II may stimulate intracellular receptors. Angiotensin-converting enzyme 2 (ACE2) not only generates angiotensin-(1-7) but also acts as coronavirus receptor. Multiple, if not all, cardiovascular diseases involve the kidney RAS, with renal AT1 receptors often being claimed to exert a crucial role. Urinary RAS component levels, depending on filtration, reabsorption, and local release, are believed to reflect renal RAS activity. Finally, both existing drugs (RAS inhibitors, cyclooxygenase inhibitors) and novel drugs (angiotensin receptor/neprilysin inhibitors, sodium-glucose cotransporter-2 inhibitors, soluble ACE2) affect renal angiotensin formation, thereby displaying cardiovascular efficacy. Particular in the case of the latter three, an important question is to what degree they induce renoprotection (e.g., in a renal RAS-dependent manner). This review provides a unifying view, explaining not only how kidney angiotensin formation occurs and how it is affected by drugs but also why drugs are renoprotective when altering the renal RAS. SIGNIFICANCE STATEMENT: Angiotensin formation in the kidney is widely accepted but little understood, and multiple, often contrasting concepts have been put forward over the last two decades. This paper offers a unifying view, simultaneously explaining how existing and novel drugs exert renoprotection by interfering with kidney angiotensin formation.

Cardiovascular aspects of the (pro)renin receptor: Function and significance

Cardiovascular diseases (CVDs), including all types of disorders related to the heart or blood vessels, are the major public health problems and the leading causes of mortality globally. (Pro)renin receptor (PRR), a single transmembrane protein, is present in cardiomyocytes, vascular smooth muscle cells, and endothelial cells. PRR plays an essential role in cardiovascular homeostasis by regulating the renin-angiotensin system and several intracellular signals such as mitogen-activated protein kinase signaling and wnt/β-catenin signaling in various cardiovascular cells. This review discusses the current evidence for the pathophysiological roles of the cardiac and vascular PRR. Activation of PRR in cardiomyocytes may contribute to myocardial ischemia/reperfusion injury, cardiac hypertrophy, diabetic or alcoholic cardiomyopathy, salt-induced heart damage, and heart failure. Activation of PRR promotes vascular smooth muscle cell proliferation, endothelial cell dysfunction, neovascularization, and the progress of vascular diseases. In addition, phenotypes of animals transgenic for PRR and the hypertensive actions of PRR in the brain and kidney and the soluble PRR are also discussed. Targeting PRR in local tissues may offer benefits for patients with CVDs, including heart injury, atherosclerosis, and hypertension.

Renin-Angiotensin System Induced Secondary Hypertension: The Alteration of Kidney Function and Structure

Long-term hypertension is known as a major risk factor for cardiovascular and chronic kidney disease (CKD). The Renin-angiotensin system (RAS) plays a key role in hypertension pathogenesis. Angiotensin II (Ang II) enhancement in Ang II-dependent hypertension leads to progressive CKD and kidney fibrosis. In the two-kidney one-clip model (2K1C), more renin is synthesized in the principal cells of the collecting duct than juxtaglomerular cells (JGCs). An increase of renal Ang I and Ang II levels and a decrease of renal cortical and medullary Ang 1–7 occur in both kidneys of the 2K1C hypertensive rat model. In addition, the activity of the angiotensin-converting enzyme (ACE) increases, while ACE2's activity decreases in the medullary region of both kidneys in the 2K1C hypertensive model. Also, the renal prolyl carboxypeptidase (PrCP) expression and its activity reduce in the clipped kidneys. The imbalance in the production of renal ACE, ACE2, and PrCP expression causes the progression of renal injury. Intrarenal angiotensinogen (AGT) expression and urine AGT (uAGT) excretion rates in the unclipped kidney are greater than the clipped kidney in the 2K1C hypertensive rat model. The enhancement of Ang II in the clipped kidney is related to renin secretion, while the elevation of intrarenal Ang II in the unclipped kidney is related to stimulation of AGT mRNA and protein in proximal tubule cells by a direct effect of systemic Ang II level. Ang II-dependent hypertension enhances macrophages and T-cell infiltration into the kidney which increases cytokines, and AGT synthesis in proximal tubules is stimulated via cytokines. Accumulation of inflammatory cells in the kidney aggravates hypertension and renal damage. Moreover, Ang II-dependent hypertension alters renal Ang II type 1 & 2 receptors (AT₁R & AT₂R) and Mas receptor (MasR) expression, and the renal interstitial fluid bradykinin, nitric oxide, and cGMP response to AT₁R, AT₂R, or BK B₂-receptor antagonists. Based on a variety of sources including PubMed, Google Scholar, Scopus, and Science-Direct, in the current review, we will discuss the role of RAS-induced secondary hypertension on the alteration of renal function.

The Soluble (Pro)Renin Receptor in Health and Diseases: Foe or Friend?

The (pro)renin receptor (PRR) is a single-transmembrane protein that regulates the local renin-angiotensin system and participates in various intracellular signaling pathways, thus exhibiting a significant physiopathologic relevance in cellular homeostasis. A soluble form of PRR (sPRR) is generated through protease-mediated cleavage of the full-length PRR and secreted into extracellular spaces. Accumulating evidence indicates pivotal biologic functions of sPRR in various physiopathological processes. sPRR may be a novel biomarker for multiple diseases. SIGNIFICANCE STATEMENT: Circulating sPRR concentrations are elevated in patients and animals under various physiopathological conditions. This minireview highlights recent advances in sPRR functions in health and pathophysiological conditions. Results suggest that sPRR may be a novel biomarker for multiple diseases, but further studies are needed to determine the diagnostic value of sPRR.

Urinary soluble (pro)renin receptor excretion is associated with urine pH in humans

The (pro)renin receptor [(P)RR] binds to renin and its precursor prorenin to activate the tissue renin-angiotensin system. It is cleaved to generate soluble (P)RR and M8–9, a residual hydrophobic truncated protein. The (pro)renin receptor also functions as an intracellular accessory protein of vacuolar-type H⁺-ATPase, which plays an essential role in controlling the intracellular vesicular acid environment. Thus, in the kidney, (P)RR may play a role in transporting H⁺ to urine in the collecting duct. Although blood soluble (P)RR has been recognized as a biomarker reflecting the status of the tissue renin-angiotensin system and/or tissue (P)RR, the significance of urinary soluble (P)RR excretion has not been determined. Therefore, this study aimed to investigate the characteristics of urinary soluble (P)RR excretion. Urinary soluble (P)RR excretion was measured, and its association with background factors was investigated in 441 patients. Relationships between changes in urine pH due to vitamin C treatment, which reduce urine pH, and urinary soluble (P)RR excretion were investigated in 10 healthy volunteers. Urinary soluble (P)RR excretion was 1.46 (0.44–2.92) ng/gCre. Urine pH showed a significantly positive association with urinary soluble (P)RR excretion, independent of other factors. Changes in urine pH and urinary soluble (P)RR excretion due to vitamin C treatment were significantly and positively correlated (ρ = 0.8182, p = 0.0038). These data showed an association between urinary soluble (P)RR excretion and urine pH in humans, suggesting that (P)RR in the kidney might play a role in urine pH regulation.

High glucose induces trafficking of prorenin receptor and stimulates profibrotic factors in the collecting duct

Growing evidence indicates that prorenin receptor (PRR) is upregulated in collecting duct (CD) of diabetic kidney. Prorenin is secreted by the principal CD cells, and is the natural ligand of the PRR. PRR activation stimulates fibrotic factors, including fibronectin, collagen, and transforming growth factor-β (TGF-β) contributing to tubular fibrosis. However, whether high glucose (HG) contributes to this effect is unknown. We tested the hypothesis that HG increases the abundance of PRR at the plasma membrane of the CD cells, thus contributing to the stimulation of downstream fibrotic factors, including TGF-β, collagen I, and fibronectin. We used streptozotocin (STZ) male Sprague–Dawley rats to induce hyperglycemia for 7 days. At the end of the study, STZ-induced rats showed increased prorenin, renin, and angiotensin (Ang) II in the renal inner medulla and urine, along with augmented downstream fibrotic factors TGF-β, collagen I, and fibronectin. STZ rats showed upregulation of PRR in the renal medulla and preferential distribution of PRR on the apical aspect of the CD cells. Cultured CD M-1 cells treated with HG (25 mM for 1 h) showed increased PRR in plasma membrane fractions compared to cells treated with normal glucose (5 mM). Increased apical PRR was accompanied by upregulation of TGF-β, collagen I, and fibronectin, while PRR knockdown prevented these effects. Fluorescence resonance energy transfer experiments in M-1 cells demonstrated augmented prorenin activity during HG conditions. The data indicate HG stimulates profibrotic factors by inducing PRR translocation to the plasma membrane in CD cells, which in perspective, might be a novel mechanism underlying the development of tubulointerstitial fibrosis in diabetes mellitus.

Mutagenesis of the Cleavage Site of Pro Renin Receptor Abrogates Angiotensin II-Induced Hypertension in Mice

[Figure: see text].

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.

Loss of Soluble (Pro)renin Receptor Attenuates Angiotensin-II Induced Hypertension and Renal Injury

[Figure: see text].

α-Ketoglutarate Upregulates Collecting Duct (Pro)renin Receptor Expression, Tubular Angiotensin II Formation, and Na+ Reabsorption During High Glucose Conditions

Diabetes mellitus (DM) causes high glucose (HG) levels in the plasma and urine. The (pro)renin receptor (PRR) is a key regulator of renal Na+ handling. PRR is expressed in intercalated (IC) cells of the collecting duct (CD) and binds renin to promote angiotensin (Ang) II formation, thereby contributing to Na+ reabsorption. In DM, the Kreb's cycle is in a state of suppression in most tissues. However, in the CD, expression of glucose transporters is augmented, boosting the Kreb's cycle and consequently causing α-ketoglutarate (αKG) accumulation. The αKG receptor 1 (OXGR1) is a Gq-coupled receptor expressed on the apical membrane of IC cells of the CD. We hypothesize that HG causes αKG secretion and activation of OXGR1, which increases PRR expression in CD cells. This effect then promotes intratubular AngII formation and Na+ reabsorption. To test this hypothesis, streptozotocin (STZ)-induced diabetic mice were treated with or without montelukast (ML), an OXGR1 antagonist, for 6 days. STZ mice had higher urinary αKG and PRR expression along with augmented urinary AngII levels and Na+ retention. Treatment with ML prevented all these effects. Similarly, primary cultured inner medullary CD cells treated with HG showed increased PRR expression, while OXGR1 antagonist prevented this effect. αKG increases PRR expression, while treatments with ML, PKC inhibition, or intracellular Ca2+ depletion impair this effect. In silico analysis suggested that αKG binds to mouse OXGR1. These results indicate that HG conditions promote increased levels of intratubular αKG and OXGR1-dependent PRR upregulation, which impact AngII formation and Na+ reabsorption.

Sex differences in soluble prorenin receptor in patients with type 2 diabetes

BACKGROUND

The soluble prorenin receptor (sPRR), a member of the renin-angiotensin system (RAS), is elevated in plasma of patients with preeclampsia, hypertension, chronic kidney disease (CKD), and type 2 diabetes. Our goal was to examine the relationship between sPRR and RAS activation to define whether sexual dimorphisms in sPRR might explain sex disparities in renal outcomes in patients with type 2 diabetes.

METHODS

Two hundred sixty-nine participants were included in the study (mean age, 48 ± 16 years; 42% men, 58% women), including 173 controls and 96 subjects with type 2 diabetes. In plasma and urine, we measured sPRR, plasma renin activity (PRA), and prorenin. In the urine, we also measured angiotensinogen along with other biomarkers of renal dysfunction.

RESULTS

Plasma sPRR and PRA were significantly higher in women with type 2 diabetes compared to men. In these women, plasma sPRR was positively correlated with PRA, age, and body mass index (BMI). In contrast, in men the sPRR in urine but not in plasma positively correlated with eGFR in urine, but negatively correlated with urine renin activity, plasma glucose, age, and BMI.

CONCLUSIONS

In patients with type 2 diabetes, sPRR contributes to RAS stimulation in a sex-dependent fashion. In diabetic women, increased plasma sPRR parallels the activation of systemic RAS; while in diabetic men, decreased sPRR in urine matches intrarenal RAS stimulation. sPRR might be a potential indicator of intrarenal RAS activation and renal dysfunction in men and women with type 2 diabetes.

The Pathological Role of Pro(Renin) Receptor in Renal Inflammation

(Pro)renin receptor (PRR) is the recently discovered component of the renin-angiotensin-aldosterone system (RAS). Many organs contain their own RAS, wherein PRR can exert organ-specific localized effects. The Binding of prorenin/renin to PRR activates angiotensin-dependent and independent pathways which leads to the development of physiological and pathological effects. Continued progress in PRR research suggests that the upregulation of PRR contributes to the development of hypertension, glomerular injury, and progression of kidney disease and inflammation. In the current review, we highlight the function of the PRR in renal inflammation in pathophysiological conditions.

The prorenin receptor and its soluble form contribute to lipid homeostasis

Obesity is associated with alterations in hepatic lipid metabolism. We previously identified the prorenin receptor (PRR) as a potential contributor to liver steatosis. Therefore, we aimed to determine the relative contribution of PRR and its soluble form, sPRR, to lipid homeostasis. PRR-floxed male mice were treated with an adeno-associated virus with thyroxine-binding globulin promoter-driven Cre to delete PRR in the liver [liver PRR knockout (KO) mice]. Hepatic PRR deletion did not change the body weight but increased liver weights. The deletion of PRR in the liver decreased peroxisome proliferator-activated receptor gamma (PPARγ) and triglyceride levels, but liver PRR KO mice exhibited higher plasma cholesterol levels and lower hepatic low-density lipoprotein receptor (LDLR) and Sortilin 1 (SORT1) proteins than control (CTL) mice. Surprisingly, hepatic PRR deletion elevated hepatic cholesterol, and up-regulated hepatic sterol regulatory element-binding protein 2 (SREBP2) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA-R) genes. In addition, the plasma levels of sPRR were significantly higher in liver PRR KO mice than in controls. In vitro studies in HepG2 cells demonstrated that sPRR treatment upregulated SREBP2, suggesting that sPRR could contribute to hepatic cholesterol biosynthesis. Interestingly, PRR, total cleaved and noncleaved sPRR contents, furin, and Site-1 protease (S1P) were elevated in the adipose tissue of liver PRR KO mice, suggesting that adipose tissue could contribute to the circulating pool of sPRR. Overall, this work supports previous works and opens a new area of investigation concerning the function of sPRR in lipid metabolism and adipose tissue-liver cross talk.NEW & NOTEWORTHY Hepatic PRR and its soluble form, sPRR, contribute to triglyceride and cholesterol homeostasis and hepatic inflammation. Deletion of hepatic PRR decreased triglyceride levels through a PRR-PPARγ-dependent mechanism but increased hepatic cholesterol synthesis through sPRR-medicated upregulation of SREBP-2. Our study highlighted a new paradigm of cross talk between the liver and the adipose tissue involving cholesterol and sPRR.

Clinical Implications of (Pro)renin Receptor (PRR) Expression in Renal Tumours

(1) Background: Renal cancer is one of the most frequent malignancies in Western countries, with an unpredictable clinical outcome, partly due to its high heterogeneity and the scarcity of reliable biomarkers of tumour progression. (Pro)renin receptor (PRR) is a novel receptor of the renin–angiotensin system (RAS) that has been associated with the development and progression of some solid tumours by RAS-dependent and -independent mechanisms. (2) Methods: In this study, we analysed the immunohistochemical expression of PRR at the centre and border in a series of 83 clear-cell renal cell (CCRCCs), 19 papillary (PRCC) and 7 chromophobe (ChRCC) renal cell carcinomas, and the benign tumour renal oncocytoma (RO, n = 11). (3) Results: PRR is expressed in all the tumour subtypes, with higher mean staining intensity in ChRCCs and ROs. A high expression of PRR at the tumour centre and at the infiltrative front of CCRCC tissues is significantly associated with high grade, tumour diameter, local invasion and stage, and with high mortality risk by UCLA integrated staging system (UISS) scale. (4) Conclusions: These findings indicate that PRR is associated with the development and progression of renal tumours. Its potential as a novel biomarker for RCC diagnosis/prognosis and as a promising therapeutic target should be taken into account in the future.

Site-1 Protease-Derived Soluble (Pro)Renin Receptor Contributes to Angiotensin II-Induced Hypertension in Mice

Activation of PRR ([pro]renin receptor) contributes to enhancement of intrarenal RAS and renal medullary α-ENaC and thus elevated blood pressure during Ang II (angiotensin II) infusion. The goal of the present study was to test whether such action of PRR was mediated by sPRR (soluble PRR), generated by S1P (site-1 protease), a newly identified PRR cleavage protease. F1 B6129SF1/J mice were infused for 6 days with control or Ang II at 300 ng/kg per day alone or in combination with S1P inhibitor PF-429242 (PF), and blood pressure was monitored by radiotelemetry. S1P inhibition significantly attenuated Ang II-induced hypertension accompanied with suppressed urinary and renal medullary renin levels and expression of renal medullary but not renal cortical α-ENaC expression. The effects of S1P inhibition were all reversed by supplement with histidine-tagged sPRR termed as sPRR-His. Ussing chamber technique was performed to determine amiloride-sensitive short-circuit current, an index of ENaC activity in confluent mouse cortical collecting duct cell line cells exposed for 24 hours to Ang II, Ang II + PF, or Ang II + PF + sPRR-His. Ang II-induced ENaC activity was blocked by PF, which was reversed by sPRR-His. Together, these results support that S1P-derived sPRR mediates Ang II-induced hypertension through enhancement of intrarenal renin level and activation of ENaC.

(Pro)renin receptor in the kidney: function and significance

(Pro)renin receptor (PRR), a 350-amino acid receptor initially thought of as a receptor for the binding of renin and prorenin, is multifunctional. In addition to its role in the renin-angiotensin system (RAS), PRR transduces several intracellular signaling molecules and is a component of the vacuolar H⁺-ATPase that participates in autophagy. PRR is found in the kidney and particularly in great abundance in the cortical collecting duct. In the kidney, PRR participates in water and salt balance, acid-base balance, and autophagy and plays a role in development and progression of hypertension, diabetic retinopathy, and kidney fibrosis. This review highlights the role of PRR in the development and function of the kidney, namely, the macula densa, podocyte, proximal and distal convoluted tubule, and the principal cells of the collecting duct, and focuses on PRR function in body fluid volume homeostasis, blood pressure regulation, and acid-base balance. This review also explores new advances in the molecular mechanism involving PRR in normal renal health and pathophysiological states.

Relationship between Soluble (pro)Renin Receptor and Renin Activity in Patients with Severe Heart Failure

The (pro)renin receptor ((P)RR), which evokes renin activity with prorenin, is secreted extracellularly as soluble (P)RR (s(P)RR) and may participate in tissue renin-angiotensin system (RAS) activity in severe heart failure (HF) patients. The aim of this study was to determine whether s(P)RR is an adequate marker in severe HF patients treated with RAS inhibitors, beta-blockers, and tolvaptan. We enrolled 11 patients with severe HF between May 2013 and June 2014. First of all, furosemide of all patients was changed to tolvaptan with hydrochlorothiazide and then the treatment had been changed according to the patient's condition. After 1, 3, 6, and 12 months, the variance of s(P)RR, plasma renin activity (PRA), plasma renin concentration (PRC), brain natriuretic peptide (BNP) and their association was investigated. Furosemide was restarted in five patients and two patients suffered cardiac death. PRA/PRC and s(P)RR were unchanged (PRA: 10.7 ± 13.9 to 12.8 ± 8.5 ng/mL/h; PRC: 347.1 ± 577.5 to 148.3 ± 123.8 pg/mL; s(P)RR: 28.2 ± 19.3 to 33.4 ± 22.4 ng/mL) and had no significant correlations (PRA and s(P)RR: p = 0.36; PRC and s(P)RR: p = 0.35). There was a significant positive correlation with a high correlation coefficient (CC) between PRA and PRC (p < 0.0001, CC = 0.76), and a negative correlation with weak CC between BNP and s(P)RR (p = 0.01, CC = -0.45). In conclusion, s(P)RR was always high and had no correlations with disease state and PRA/PRC in severe HF patients.

Low Nitric Oxide Bioavailability Increases Renin Production in the Collecting Duct

In the kidney, the stimulation of renin production by the collecting duct (CD-renin) contributes to the development of hypertension. The CD is a major nephron segment for the synthesis of nitric oxide (NO), and low NO bioavailability in the renal medulla is associated with hypertension. However, it is unknown whether NO regulates renin production in the CD. To test the hypothesis that low intrarenal NO levels stimulate the production of CD-renin, we first examined renin expression in the distal nephron segments of CD-eNOS deficient mice. In these mice, specific CD-renin immunoreactivity was increased compared to wild-type littermates; however, juxtaglomerular (JG) renin was not altered. To further assess the intracellular mechanisms involved, we then treated M-1 cells with either 1 mM L-NAME (L-arginine analog), an inhibitor of NO synthase activity, or 1 mM NONOate, a NO donor. Both treatments increased intracellular renin protein levels in M-1 cells. However, only the inhibition of NOS with L-NAME stimulated renin synthesis and secretion as reflected by the increase in Ren1C transcript and renin protein levels in the extracellular media, respectively. In addition, NONOate induced a fast mobilization of cGMP and intracellular renin accumulation. These response was partially prevented by guanylyl cyclase inhibition with ODQ (1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1]. Accumulation of intracellular renin was blocked by protein kinase G (PKG) and protein kinase C (PKC) inhibitors. Our data indicate that low NO bioavailability increases CD-renin synthesis and secretion, which may contribute to the activation of intrarenal renin angiotensin system.

COX-2-independent activation of renal (pro)renin receptor contributes to DOCA-salt hypertension in rats

It has been shown that cyclooxygenase (COX)-2-dependent activation of renal (pro)renin receptor (PRR) contributes to angiotensin II (ANG II)-induced hypertension. However, less is known about the involvement of this mechanism in ANG II-independent hypertension. The goal of the present study was to test whether or not COX-2-dependent upregulation of PRR serves as a universal mechanism contributing to ANG II-dependent and -independent hypertension. Here, we examined the association between renal COX-2 and PRR during deoxycorticosterone acetate (DOCA)-salt hypertension in rats. By immunoblot analysis and immunofluorescence, renal protein expression of PRR was remarkably upregulated by DOCA-salt treatment. Surprisingly, this upregulation of renal PRR expression was unaffected by a COX-2 inhibitor, celecoxib. To address the role of renal PRR to the pathogenesis of DOCA-salt hypertension, a decoy PRR inhibitor, PRO20, was infused to the renal medulla of uninephrectomized Sprague-Dawley rats for 14 days. Radiotelemetry demonstrated effective attenuation of DOCA-salt hypertension by intramedullary infusion of a PRR inhibitor, PRO20. In parallel, DOCA-salt-induced hypertrophy in the heart and kidney as well as proteinuria were improved, accompanied with blunted polydipsia and polyuria. In contrast, intravenous infusion of PRO20 was less effective in attenuating DOCA-salt hypertension and cardiorenal injury. Together, these results suggest that COX-2-independent activation of renal PRR contributes to DOCA-salt hypertension.

High Salt Intake-Increased (Pro)renin Receptor Expression Is Exaggerated in the Kidney of Dahl Salt-Sensitive Rats

The (P)RR ([pro]renin receptor) was identified as a new component of the renin-angiotensin system. We previously reported that high salt (HS) intake increased the (P)RR expression in several nephron segments of Sprague-Dawley rats. Other studies reported HS intake increased the XO (xanthine oxidase) activity and an MR (mineralocorticoid receptor) antagonist inhibited HS intake-increased (P)RR expression in the kidneys of Dahl salt-sensitive (DS) rats. The present study examined the effects of HS intake on (P)RR expression in the kidney of DS rats. Male DS rats were fed a normal salt diet or an HS diet for 4 weeks. Some of the rats fed on the HS diet were treated with the XO inhibitor, febuxostat, and the MR antagonist, spironolactone. Immunoblot and immunohistochemical analyses showed that HS intake increased (P)RR expression in the renal cortex by 22.6-fold, the proximal tubules by 4.9-fold and the distal tubules, respectively. Both febuxostat and spironolactone inhibited HS intake-increased (P)RR expression in the renal cortex. Febuxostat inhibited HS intake-increased (P)RR expression in the proximal tubules, whereas spironolactone inhibited HS intake-increased (P)RR expression in the distal tubules. Additionally, deoxycorticosterone acetate increased (P)RR expression in the renal cortex and distal tubules but not in the proximal tubules of DS rats fed the normal salt diet. These results indicate that HS intake greatly increases (P)RR expression in the renal cortex of DS rats. The mechanisms of HS intake-increased (P)RR expression may work in an XO-dependent manner in the proximal tubules and an MR-dependent manner in the distal tubules.

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.

Evaluation of Renin and Soluble (Pro)renin Receptor in Patients with IPF. A Comparison with Hypersensitivity Pneumonitis

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a lethal disease with an unclear pathogenic mechanism. Components of the renin-angiotensin system (RAS) have a role in the pathogenesis of IPF, specifically, the aspartyl protease renin acts as a profibrotic factor in the lung. However, the concentration of the RAS components renin and soluble (pro)renin receptor (sPRR) have not been previously evaluated neither in serum nor in bronchoalveolar lavage fluid (BAL) of patients with IPF or chronic Hypersensitivity pneumonitis (cHP), a disease which may be confused with IPF.

METHODS

The serum levels of renin [IPF patients (n = 70), cHP patients (n = 83), and controls (n = 26)] and sPRR [IPF (n = 28), cHP (37), and controls (n = 20)] were measured by ELISA. Renin was also quantified in BALs of IPF patients and controls by Western blot.

RESULTS

We found that the levels of renin were higher in serum samples from IPF patients when compared with cHP patients and controls. Furthermore, BALs from IPF patients had more renin than BALs from controls. Unlike renin, the serum levels of sPRR were lower in IPF and cHP patients than in control individuals.

CONCLUSIONS

The high levels of renin in sera and BALs of IPF patients suggest that renin might play a major role in the pathogenesis of IPF. Results from BAL confirm that renin is produced locally in the lung. Serum levels of renin could be used to differentiate IPF from cHP.

Soluble Prorenin Receptor Increases Blood Pressure in High Fat-Fed Male Mice

Obesity-related hypertension is a major public health concern. We recently demonstrated that plasma levels of the soluble form of the prorenin receptor (sPRR) were elevated in obesity-associated hypertension. Therefore, in the present study, we investigated the contribution of sPRR to blood pressure (BP) elevation in the context of obesity. High fat-fed C57BL/6 male mice were infused with vehicle or sPRR (30 µg/kg per day) via subcutaneously implanted osmotic minipump for 4 weeks. BP parameters were recorded using radiotelemetry devices. Male mice infused with sPRR exhibited higher systolic BP and mean arterial pressure and lower spontaneous baroreflex sensitivity than mice infused with vehicle. To define mechanisms involved in systolic BP elevation, mice were injected with an AT1R (Ang II [angiotensin II] type 1 receptor) antagonist (losartan), a muscarinic receptor antagonist (atropine), a β-adrenergic antagonist (propranolol), and a ganglionic blocker (chlorisondamine). Losartan did not blunt sPRR-induced elevation in systolic BP. Chlorisondamine treatment exacerbated the decrease in mean arterial pressure in male mice infused with sPRR. These results demonstrated that sPRR induced autonomic nervous dysfunction. Interestingly, plasma leptin levels were increased in high fat-fed C57BL/6 male mice infused with sPRR. Overall, our results indicated that sPRR increased systolic BP through an impairment of the baroreflex sensitivity and an increase in the sympathetic tone potentially mediated by leptin in high fat-fed C57BL/6 male mice.

Atp6ap2 deletion causes extensive vacuolation that consumes the insulin content of pancreatic β cells

Pancreatic β cells store insulin within secretory granules which undergo exocytosis upon elevation of blood glucose levels. Crinophagy and autophagy are instead responsible to deliver damaged or old granules to acidic lysosomes for intracellular degradation. However, excessive consumption of insulin granules can impair β cell function and cause diabetes. Atp6ap2 is an essential accessory component of the vacuolar ATPase required for lysosomal degradative functions and autophagy. Here, we show that Cre recombinase-mediated conditional deletion of Atp6ap2 in mouse β cells causes a dramatic accumulation of large, multigranular vacuoles in the cytoplasm, with reduction of insulin content and compromised glucose homeostasis. Loss of insulin stores and gigantic vacuoles were also observed in cultured insulinoma INS-1 cells upon CRISPR/Cas9-mediated removal of Atp6ap2. Remarkably, these phenotypic alterations could not be attributed to a deficiency in autophagy or acidification of lysosomes. Together, these data indicate that Atp6ap2 is critical for regulating the stored insulin pool and that a balanced regulation of granule turnover is key to maintaining β cell function and diabetes prevention.

Downregulated microRNA‑133a induces HUVECs injury: Potential role of the (pro) renin receptor in angiotensin II‑dependent hypertension

The renin‑angiotensin system (RAS) serves an essential role in hypertension. MicroRNAs (miRs) have been reported to be important regulators in angiotensin (Ang) II‑dependent hypertension. We aimed to explore the roles of Ang II and miR‑133a in the mechanism underlying hypertension. Human umbilical vein endothelial cells (HUVECs) were identified by immunofluorescence staining. Cell viability and miR‑133a expression under the inhibition of Ang II of various concentrations were determined by an MTT assay and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR), respectively. The effects of HUVECs transfected with miR‑133a mimic or inhibitor on Ang II‑induced apoptosis were measured using flow cytometry. The potential targeting of miR‑133a to the 3' untranslated region of (pro) renin receptor (PRR) was assessed using TargetScan and a dual‑luciferase assay. The effects of PRR interference using small interfering (si)RNA on PRR expression and the rate of apoptosis were determined by RT‑qPCR, western blotting and flow cytometry, respectively. Ang II at a concentration of 10‑5 M significantly inhibited the cell viability (P<0.05) and miR‑133a expression (P<0.01); Downregulation of miR‑133a suppressed cell viability. HUVECs transfected with miR‑133a mimic reduced the rate of Ang II‑induced apoptosis from 21.99 to 12.38%, but miR‑133a inhibitor promoted Ang II‑induced apoptosis (apoptosis rate, 28.9%). PRR was predicted to be a target gene of miR‑133a. Transfection with siPRR decreased the apoptotic rate in Ang II + negative control and Ang II + miR‑133a inhibitor group to 11.39 and 12.94%, respectively. Our findings also suggested that Ang II promoted PRR expression to enhance the apoptotic rate of HUVECs via the suppression of miR‑133a. Furthermore, siPRR efficiently decreased the Ang II‑induced apoptosis.

(Pro)renin Receptor-Dependent Induction of Profibrotic Factors Is Mediated by COX-2/EP4/NOX-4/Smad Pathway in Collecting Duct Cells

The binding of prorenin to the (pro)renin receptor (PRR) triggers the activation of MAPK/ERK1/2 pathway, induction of cyclooxygenase-2 (COX-2), NOX-4-dependent production of reactive oxygen species (ROS), and the induction of transforming growth factor β (TGF-β) and profibrotic factors connecting tissue growth factor (CTGF) and plasminogen activator inhibitor (PAI-I) in collecting duct (CD) cells. However, the role of COX-2 and the intracellular pathways involved are not clear. We hypothesized that the PRR activation increases profibrotic factors through COX-2-mediated PGE2 activation of E prostanoid receptor 4 (EP4), upregulation of NOX-4/ROS production, and activation of Smad pathway in mouse CD cells. Recombinant prorenin increased ROS production and protein levels of CTGF, PAI-I, and TGF-β in M-1 CD cell line. Inhibition of MAPK, NOX-4, and COX-2 prevented this effect. Inhibition of MEK, COX-2, and EP4 also prevented the upregulation of NOX-4. Because TGF-β activates Smad pathway, we evaluate the phosphorylation of Smad2 and 3. COX-2 inhibition or EP4 antagonism significantly prevented phosphorylation of Smad 2/3. Mice that were infused with recombinant prorenin showed an induction in the expression of CTGF, PAI-I, TGF-β, fibronectin, and collagen I in isolated collecting ducts as well as the expression of alpha smooth muscle actin (α-SMA) in renal tissues. COX-2 inhibition prevented this induction. These results indicate that the induction of TGF-β, CTGF, PAI-I, and ROS occurs through PRR-dependent activation of MAPK and NOX-4; however, this mechanism depends on COX-2-derived PGE2 production and the activation of EP4 and Smad pathway.

Conditional ablation of the prorenin receptor in nephron progenitor cells results in developmental programming of hypertension

Nephron induction during kidney development is driven by reciprocal interactions between progenitor cells (NPCs) of the cap mesenchyme (CM) and the ureteric bud (UB). The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump V‐ATPase. Previously, we demonstrated that conditional ablation of the PRR in Six2⁺NPCs in mice (Six2^PRR−/−) causes early neonatal death. Here, we identified genes that are regulated by PRR in Six2⁺NPCs FACS‐isolated from Six2^PRR−/− and control kidneys on embryonic day E15.5 using whole‐genome expression analysis. Seven genes with expression in CM cells previously shown to direct kidney development, including Notch1, β‐catenin, Lef1, Lhx1, Jag1, and p53, were downregulated. The functional groups within the downregulated gene set included genes involved in embryonic and cellular development, renal regeneration, cellular assembly and organization, cell morphology, death and survival. Double‐transgenic Six2^PRR−/−/BatGal⁺ mice, a reporter strain for β‐catenin transcriptional activity, showed decreased β‐catenin activity in the UB in vivo. Reduced PRR gene dosage in heterozygous Six2^PRR+/− mice was associated with decreased glomerular number, segmental thickening of the glomerular basement membrane with focal podocyte foot process effacement, development of hypertension and increased soluble PRR (sPRR) levels in the urine at 2 months of age. Together, these data demonstrate that NPC PRR performs essential functions during nephrogenesis via control of hierarchy of genes that regulate critical cellular processes. Both reduced nephron endowment and augmented urine sPRR likely contribute to programming of hypertension in Six2^PRR+/− mice.

Effects of the (Pro)renin Receptor on Cardiac Remodeling and Function in a Rat Alcoholic Cardiomyopathy Model via the PRR-ERK1/2-NOX4 Pathway

Alcoholic cardiomyopathy (ACM) caused by alcohol consumption manifests mainly as by maladaptive myocardial function, which eventually leads to heart failure and causes serious public health problems. The (pro)renin receptor (PRR) is an important member of the local tissue renin-angiotensin system and plays a vital role in many cardiovascular diseases. However, the mechanism responsible for the effects of PRR on ACM remains unclear. The purpose of this study was to determine the role of PRR in myocardial fibrosis and the deterioration of cardiac function in alcoholic cardiomyopathy. Wistar rats were fed a liquid diet containing 9% v/v alcohol to establish an alcoholic cardiomyopathy model. Eight weeks later, rats were injected with 1 × 10⁹v.g./100 μl of recombinant adenovirus containing EGFP (scramble-shRNA), PRR, and PRR-shRNA via the tail vein. Cardiac function was assessed by echocardiography. Cardiac histopathology was measured by Masson's trichrome staining, immunohistochemical staining, and dihydroethidium staining. In addition, cardiac fibroblasts (CFs) were cultured to evaluate the effects of alcohol stimulation on the production of the extracellular matrix and their underlying mechanisms. Our results indicated that overexpression of PRR in rats with alcoholic cardiomyopathy exacerbates myocardial oxidative stress and myocardial fibrosis. Silencing of PRR expression with short hairpin RNA (shRNA) technology reversed the myocardial damage mediated by PRR. Additionally, PRR activated phosphorylation of ERK1/2 and increased NOX4-derived reactive oxygen species and collagen expression in CFs with alcohol stimulation. Administration of the ERK kinase inhibitor (PD98059) significantly reduced NOX4 protein expression and collagen production, which indicated that PRR increases collagen production primarily through the PRR-ERK1/2-NOX4 pathway in CFs. In conclusion, our study demonstrated that PRR induces myocardial fibrosis and deteriorates cardiac function through ROS from the PRR-ERK1/2-NOX4 pathway during ACM development.

Superimposing a high-fat diet on Schistosoma mansoni infection affects renin-angiotensin system components in the mouse kidney

INTRODUCTION

The levels of the full-length form of the (pro)renin receptor (PRR), a component of the renin-angiotensin system (RAS), may be reduced in the membranes of kidneys in renal diseases. This study aimed to investigate the RAS components in the kidneys of mice submitted to a combination of a high-fat diet and Schistosoma mansoni infection.

METHODS

Female BALB/c mice were maintained on a control or high-fat diet from 3 weeks of age. After 10 weeks on the designated diets, half the mice in each group were infected with S. mansoni cercariae. The blood and kidneys were harvested 8 weeks after infection.

RESULTS

The high-fat diet increased the number of eggs in the feces and the number of adult worms in the mesenteric bed. Schistosoma mansoni infection reduced the plasma levels of glucose, triglycerides, and HDL cholesterol in the control and high-fat diet groups. In mice on the control diet, S. mansoni infection resulted in increased expression of IL-6 in the kidneys; however, in mice on the high-fat diet, the levels of IL-6 were reduced and those of superoxide anions were increased. The RAS components evaluated were ACE2, renin, PRR, AT1R, and AT2R, and the levels of PRR were found to be reduced in the kidneys of infected mice on the high-fat diet.

CONCLUSIONS

The finding regarding PRR is not yet clear. However, combining a high-fat diet and S. mansoni infection resulted in increased oxidative stress in the kidney that can aggravate hypertension as well as its associated complications.

The (pro)renin receptor: an emerging player in hypertension and metabolic syndrome

The (pro)renin receptor (PRR) is a multifunctional protein that is expressed in multiple organs. Binding of prorenin/renin to the PRR activates angiotensin II-dependent and angiotensin II-independent pathways. The PRR is also involved in autophagy and Wnt/ß catenin signaling, functions that are not contingent on prorenin binding. Emerging evidence suggests that the PRR plays an important role in blood pressure regulation and glucose and lipid metabolism. Herein, we review PRR function in health and disease, with particular emphasis on hypertension and the metabolic syndrome.

Elevated plasma soluble (pro)renin receptor levels are associated with left ventricular remodeling and renal function in chronic heart failure patients with reduced ejection fraction

Soluble (pro)renin receptor [s(P)RR], which is generated from cleavage of (P)RR, can be detected in plasma and urine. s(P)RR levels can reflect the severity of some diseases, such as renal lesions, gestational diabetes mellitus or hypertension, and obstructive sleep apnea syndrome. However, the relationship between s(P)RR levels and the severity of chronic heart failure remains undetermined. We studied s(P)RR levels in 118 patients with chronic heart failure with reduced ejection fraction (HFrEF), including 86 without renal dysfunction (HF) and 32 with renal dysfunction (HF + RF), and 28 healthy subjects (HS) to reveal the relationship between s(P)RR levels and other HFrEF parameters. Plasma s(P)RR levels were 22.2 ± 4.1 ng/mL (HS), 26.4 ± 5.3 ng/ mL (HF) and 30.0 ± 5.3 ng/mL (HF + RF). Plasma s(P)RR levels were significantly higher in the HF group than in the HS group (P < 0.001) and even more increased in the HF + RF group (P < 0.001 vs. the HS group and P < 0.05 vs. the HF group). Multivariate regression analysis revealed that the left ventricular mass index (LVMI) and estimated glomerular filtration rate (eGFR) were independently related to s(P)RR levels in HFrEF patients. In conclusion, high plasma s(P)RR levels are associated with left ventricular remodeling and, especially, with renal dysfunction. Therefore, s(P)RR is a promising evaluative indicator for the severity of HFrEF patients.

Aliskiren reduces the release of soluble (pro)renin receptor from human umbilical vein endothelial cells

(Pro)renin receptor [(P)RR] has been implicated in diverse biological processes through binding to its ligands, which include renin, prorenin, Wnt signaling molecules and subunits of vascular H⁺-ATPase. Recent studies have reported that (P)RR is implicated in pathophysiological conditions including retinopathy and pancreatic ductal adenocarcinoma, and the soluble form of this receptor [s(P)RR] is considered as a useful biomarker for diseases. The present study examined the effect of aliskiren, the first orally active direct renin inhibitor, on the protein levels of (P)RR using cultured human umbilical vein endothelial cells (HUVECs). The cells were treated with or without aliskiren (10 nM) at 37°C for different durations (0, 8, 16 and 24 h). Aliskiren-treated HUVECs exhibited reduced proliferation compared with those treated without the drug. Furthermore, aliskiren treatment decreased not only the level of exogenous prorenin that bound to the membranes of HUVECs, but also the renin activity derived from this binding activity. These results indicate that the quantity of full-length (P)RR was reduced by aliskiren treatment, and furthermore, that the level of s(P)RR released from HUVECs was decreased with the treatment. Recent study has reported that s(P)RR exerted antidiuretic function. The current study suggests that the levels of s(P)RR, as a potential antidiuretic molecule and prospective disease biomarker, may be decreased during anti-hypertensive treatments with aliskiren.

Collecting duct principal, but not intercalated, cell prorenin receptor regulates renal sodium and water excretion

The collecting duct is the predominant nephron site of prorenin and prorenin receptor (PRR) expression. We previously demonstrated that the collecting duct PRR regulates epithelial Na+ channel (ENaC) activity and water transport; however, which cell type is involved remains unclear. Herein, we examined the effects of principal cell (PC) or intercalated cell (IC) PRR deletion on renal Na+ and water handling. PC or IC PRR knockout (KO) mice were obtained by crossing floxed PRR mice with mice harboring Cre recombinase under the control of the AQP2 or B1 subunit of the H+ ATPase promoters, respectively. PC KO mice had reduced renal medullary ENaC-α abundance and increased urinary Na+ losses on a low-Na+ diet compared with controls. Conversely, IC KO mice had no apparent differences in Na+ balance or ENaC abundance compared with controls. Acute treatment with prorenin increased ENaC channel number and open probability in acutely isolated cortical collecting ducts from control and IC PRR KO, but not PC PRR KO, mice. Furthermore, compared with controls, PC KO, but not IC KO mice, had increased urine volume, reduced urine osmolality, and reduced abundance of renal medullary AQP2. Taken together, these findings indicate that PC, but not IC, PRR modulates ENaC activity, urinary Na+ excretion, and water transport.

(Pro)Renin receptor mediates obesity-induced antinatriuresis and elevated blood pressure via upregulation of the renal epithelial sodium channel

Recent studies have demonstrated that the renal (pro)renin receptor (PRR) regulates expression of the alpha subunit of the epithelial sodium channel (α-ENaC). In this study we hypothesized that the renal PRR mediates high fat diet (HFD)-induced sodium retention and elevated systolic blood pressure (SBP) by enhancing expression of the epithelial sodium channel (α-ENaC). In our study we used a recently developed inducible nephron specific PRR knockout mouse. Mice (n = 6 each group) were allocated to receive regular diet (RD, 12 kcal% fat) or a high-fat diet (HFD, 45 kcal% fat) for 10 weeks. Body weight (BW), SBP, urine volume (UV) and urine sodium (U_NaV), as well as renal interstitial Angiotensin II (Ang II), and renal medullary expression of PRR, p-SGK-1, α-ENaC were monitored in RD and HFD mice with or without PRR knockout. At baseline, there were no significant differences in BW, BP, UV or U_NaV between different animal groups. At the end of the study, HFD mice had significant increases in SBP, BW, and significant reductions in UV and U_NaV. Compared to RD, HFD significantly increased mRNA and protein expression of PRR, α-ENaC, p-SGK-1, and Ang II. Compared to HFD alone, PRR knockout mice on HFD had reduced mRNA and protein expression of PRR, p-SGK-1, and α-ENaC, as well as increased UV, U_NaV and significantly reduced SBP. RIF Ang II was significantly increased by HFD and did not change in response to PRR knockout. We conclude that obesity induced sodium retention and elevated SBP are mediated by the PRR-SGK-1- α-ENaC pathway independent of Ang II.