Prorenin and its ancient receptor

Downregulation of the (pro)renin receptor alleviates ferroptosis-associated cardiac pathological changes via the NCOA 4-mediated ferritinophagy pathway in diabetic cardiomyopathy

Ferroptosis, characterized by the accumulation of reactive oxygen species and lipid peroxidation, is involved in various cardiovascular diseases. (Pro)renin receptor (PRR) in performs as ligands in the autophagic process, and its function in diabetic cardiomyopathy (DCM) is not fully understood. We investigated whether PRR promotes ferroptosis through the nuclear receptor coactivator 4 (NCOA 4)-mediated ferritinophagy pathway and thus contributes to DCM. We first established a mouse model of DCM with downregulated and upregulated PRR expression and used a ferroptosis inhibitor. Myocardial inflammation and fibrosis levels were then measured, cardiac function and ferroptosis-related indices were assessed. In vitro, neonatal rat ventricular primary cardiomyocytes were cultured with high glucose and transfected with recombinant adenoviruses knocking down or overexpressing the PRR, along with a ferroptosis inhibitor and small interfering RNA for the ferritinophagy receptor, NCOA4. Ferroptosis levels were measured in vitro. The results showed that the knockdown of PRR not only alleviated cardiomyocyte ferroptosis in vivo but also mitigated the HG-induced ferroptosis in vitro. Moreover, administration of Fer-1 can inhibit HG-induced ferroptosis. NCOA4 knockdown blocked the effect of PRR on ferroptosis and improved cell survival. Our result indicated that inhibition of PRR and NCOA4 expression provides a new therapeutic strategy for the treatment of DCM. The effect of PRR on the pathological process of DCM in mice may be in promoting cardiomyocyte ferroptosis through the NCOA 4-mediated ferritinophagy pathway.

Importance of the (Pro)renin Receptor in Activating the Renin-Angiotensin System During Normotensive and Preeclamptic Pregnancies

PURPOSE OF REVIEW

For a healthy pregnancy to occur, a controlled interplay between the maternal circulating renin-angiotensin-aldosterone system (RAAS), placental renin-angiotensin system (RAS) and intrarenal renin-angiotensin system (iRAS) is necessary. Functionally, both the RAAS and iRAS interact to maintain blood pressure and cardiac output, as well as fluid and electrolyte balance. The placental RAS is important for placental development while also influencing the maternal circulating RAAS and iRAS. This narrative review concentrates on the (pro)renin receptor ((P)RR) and its soluble form (s(P)RR) in the context of the hypertensive pregnancy pathology, preeclampsia.

RECENT FINDINGS

The (P)RR and the s(P)RR have become of particular interest as not only can they activate prorenin and renin, thus influencing levels of angiotensin II (Ang II), but s(P)RR has now been shown to directly interact with and stimulate the Angiotensin II type 1 receptor (AT1R). Levels of both placental (P)RR and maternal circulating s(P)RR are elevated in patients with preeclampsia. Furthermore, s(P)RR has been shown to increase blood pressure in non-pregnant and pregnant rats and mice. In preeclamptic pregnancies, which are characterised by maternal hypertension and impaired placental development and function, we propose that there is enhanced secretion of s(P)RR from the placenta into the maternal circulation. Due to its ability to both activate prorenin and act as an AT1R agonist, excess maternal circulating s(P)RR can act on both the maternal vasculature, and the kidney, leading to RAS over-activation. This results in dysregulation of the maternal circulating RAAS and overactivation of the iRAS, contributing to maternal hypertension, renal damage, and secondary changes to neurohumoral regulation of fluid and electrolyte balance, ultimately contributing to the pathophysiology of preeclampsia.

The renin-angiotensin-aldosterone system (RAAS) signaling pathways and cancer: foes versus allies

The renin-angiotensin-aldosterone system (RAAS), is an old system with new fundamental roles in cancer biology which influences cell growth, migration, death, and metastasis. RAAS signaling enhances cell proliferation in malignancy directly and indirectly by affecting tumor cells and modulating angiogenesis. Cancer development may be influenced by the balance between the ACE/Ang II/AT1R and the ACE2/Ang 1-7/Mas receptor pathways. The interactions between Ang II/AT1R and Ang I/AT2R as well as Ang1-7/Mas and alamandine/MrgD receptors in the RAAS pathway can significantly impact the development of cancer. Ang I/AT2R, Ang1-7/Mas, and alamandine/MrgD interactions can have anticancer effects while Ang II/AT1R interactions can be involved in the development of cancer. Evidence suggests that inhibitors of the RAAS, which are conventionally used to treat cardiovascular diseases, may be beneficial in cancer therapies.Herein, we aim to provide a thorough description of the elements of RAAS and their molecular play in cancer. Alongside this, the role of RAAS components in sex-dependent cancers as well as GI cancers will be discussed with the hope of enlightening new venues for adjuvant cancer treatment.

Association of angiotensin II and receptors in peri-implantation endometrium with microvessel density and pregnancy outcomes of women with recurrent implantation failure after embryo transfer

Purpose

Investigate whether local angiotensin II (AngII) and its AngII type 1 and 2 receptors (AT1R, AT2R) in the endometrium are different and correlate with microvessel density in women with reproductive failure and pregnancy outcomes.

Methods

Endometrium during the window of implantation from 40 women with recurrent miscarriage (RM) and 40 with recurrent implantation failure (RIF) were compared with 27 fertile women. Peri-implantation endometrium from 54 women prior to euploid embryo transfer were collected and compared in women with successful pregnancy and unsuccessful pregnancy.

Results

Compared with fertile women, expression of AT2R was significantly lower, while AT1R/AT2R expression ratio was significantly higher in the stroma of the RIF group. Endometrium arteriole MVD was significantly lower and negatively correlated with the AT1R/AT2R expression ratio in the stroma of the RIF group. No significant differences and correlations were found in the RM group. Compared with the pregnancy group, expression of AT1R and AT2R were significantly lower in all compartments, but only AT1R/AT2R ratio was significantly higher in the stroma of the non-pregnancy group. Similarly, endometrium arteriole MVD was also significantly lower and negatively correlated with the AT1R/AT2R ratio in the stroma of the non-pregnancy group.

Conclusion

Local renin-angiotensin system is dysregulated in peri-implantation endometrium and associated with abnormal angiogenesis in RIF and poor implantation outcome after embryo transfer.

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.

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.

Microglia-Mediated Neuroinflammation: A Potential Target for the Treatment of Cardiovascular Diseases

Microglia are tissue-resident macrophages of the central nervous system (CNS). In the CNS, microglia play an important role in the monitoring and intervention of synaptic and neuron-level activities. Interventions targeting microglia have been shown to improve the prognosis of various neurological diseases. Recently, studies have observed the activation of microglia in different cardiovascular diseases. In addition, different approaches that regulate the activity of microglia have been shown to modulate the incidence and progression of cardiovascular diseases. The change in autonomic nervous system activity after neuroinflammation may be a potential intermediate link between microglia and cardiovascular diseases. Here, in this review, we will discuss recent updates on the regulatory role of microglia in hypertension, myocardial infarction and ischemia/reperfusion injury. We propose that microglia serve as neuroimmune modulators and potential targets for cardiovascular diseases.

Ageing related thyroid deficiency increases brain-targeted transport of liver-derived ApoE4-laden exosomes leading to cognitive impairment

Alzheimer’s disease (AD) is the prevalent cause of dementia in the ageing world population. Apolipoprotein E4 (ApoE4) allele is the key genetic risk factor for AD, although the mechanisms linking ApoE4 with neurocognitive impairments and aberrant metabolism remains to be fully characterised. We discovered a significant increase in the ApoE4 content of serum exosomes in old healthy subjects and AD patients carrying ApoE4 allele as compared with healthy adults. Elevated exosomal ApoE4 demonstrated significant inverse correlation with serum level of thyroid hormones and cognitive function. We analysed effects of ApoE4-containing peripheral exosomes on neural cells and neurological outputs in aged or thyroidectomised young mice. Ageing-associated hypothyroidism as well as acute thyroidectomy augmented transport of liver-derived ApoE4 reach exosomes into the brain, where ApoE4 activated nucleotide-binding oligomerisation domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome by increasing cholesterol level in neural cells. This, in turn, affected cognition, locomotion and mood. Our study reveals pathological potential of exosomes-mediated relocation of ApoE4 from the periphery to the brain, this process can represent potential therapeutic target.

(Pro)renin Receptor Regulates Phosphate Homeostasis in Rats via Releasing Fibroblast Growth Factor-23

Phosphate (Pi) is one of the basic necessities required for sustenance of life and its metabolism largely relies on excretory function of the kidney, a process chiefly under the endocrine control of bone-derived fibroblast growth factor 23 (FGF23). However, knowledge gap exists in understanding the regulatory loop responsible for eliciting phophaturic response to Pi treatment. Here, we reported a novel role of (pro)renin receptor (PRR) in mediating phosphaturic response to Pi treatment via upregulation of FGF23 production. Male Sprague-Dawley rats were pretreated for 5 days via osmotic pump-driven infusion of a PRR antagonist PRO20 or vehicle, and then treated with high Pi (HP) solution as drinking fluid for the last 24 h. PRO20 reduced HP-induced Pi excretion by 42%, accompanied by blunted upregulation of circulating FGF23 and parathyroid hormone (PTH) and downregulation of renal Na/Pi-IIa expression. In cultured osteoblast cells, exposure to HP induced a 1.56-fold increase in FGF23 expression, which was blunted by PRO20 or siRNA against PRR. Together, these results suggest that activation of PRR promotes phosphaturic response through stimulation of FGF23 production and subsequent downregulation of renal Na/Pi-IIa expression.

(Pro)renin Receptor and Blood Pressure Regulation: A Focus on the Central Nervous System

The renin-angiotensin system (RAS) is classically described as a hormonal system in which angiotensin II (Ang II) is one of the main active peptides. The action of circulating Ang II on its cognate Ang II type-1 receptor (AT1R) in circumventricular organs has important roles in regulating the autonomic nervous system, blood pressure (BP) and body fluid homeostasis, and has more recently been implicated in cardiovascular metabolism. The presence of a local or tissue RAS in various tissues, including the central nervous system (CNS), is well established. However, because the level of renin, the rate-limiting enzyme in the systemic RAS, is very low in the brain, how endogenous angiotensin peptides are generated in the CNS-the focus of this review-has been the subject of considerable debate. Notable in this context is the identification of the (pro)renin receptor (PRR) as a key component of the brain RAS in the production of Ang II in the CNS. In this review, we highlight cellular and anatomical locations of the PRR in the CNS. We also summarize studies using gain- and loss-of function approaches to elucidate the functional importance of brain PRR-mediated Ang II formation and brain RAS activation, as well as PRR-mediated Ang II-independent signaling pathways, in regulating BP. We further discuss recent developments in PRR involvement in cardiovascular and metabolic diseases and present perspectives for future directions.

Blood Pressure Elevation of Tubular Specific (P)RR Transgenic Mice and Lethal Tubular Degeneration due to Possible Intracellular Interactions between (P)RR and Alternative Renin Products

The prorenin/renin receptor ((P)RR) is a multifunctional protein that is widely distributed in various organs. Despite intensive research for more than 20 years, this receptor has not been fully characterized. In this study, we generated mice overexpressing the tubular epithelial (P)RR gene ((P)RR-TG mice) to test the previously reported functional role of (P)RR by Ramkumar et al. in 2015 using tubular specific (P)RR KO mice. (P)RR-TG mice were maintained and analyzed in individual metabolic cages and were administered angiotensin II blocker (ARB), direct renin inhibitor (DRI), and bafilomycin, that is, vacuolar ATPase (V-ATPase) antagonist. (P)RR-TG mice were hypertensive and had alkalized urine with lower osmolality and Na⁺ excretion. ARB and DRI, but not bafilomycin, concurrently decreased blood pressure. Bafilomycin acidized urine of (P)RR-TG mice, or equivalently this phenomenon restored the effect of overexpressed transgene, suggesting that (P)RR functioned as a V-ATPase in renal tubules. Afterall, (P)RR-TG mice were mated with alternative renin transgenic mice (ARen2-TG), which we identified as intracellular renin previously, to generate double transgenic mice (DT-TG). Lethal renal tubular damage was observed in DT-TG mice, suggesting that intracellular renin may be a ligand for (P)RR in tubules. In summary, (P)RR did not substantially affect the tissue renin-angiotensin system (RAS) in our model of tubular specific (P)RR gene over-expression, but alternative intracellular renin may be involved in (P)RR signaling in addition to conventional V-ATPase function. Further investigations are warranted.

Functions of the (pro)renin receptor (Atp6ap2) at molecular and system levels: pathological implications in hypertension, renal and brain development, inflammation, and fibrosis

The (pro)renin receptor [(P)RR, Atp6ap2] was initially discovered as a membrane-bound binding partner of prorenin and renin. A soluble (P)RR has additional paracrine effects and is involved in metabolic syndrome and kidney damage. Meanwhile it is clear that most of the effects of the (P)RR are independent of prorenin. In the kidney, (P)RR plays an important role in renal dysfunction by activating proinflammatory and profibrotic molecules. In the brain, (P)RR is expressed in cardiovascular regulatory nuclei and is linked to hypertension. (P)RR is known to be an essential component of the v-ATPase as a key accessory protein and plays an important role in kidney, brain and heart via regulating the pH of the extracellular space and intracellular compartments. V-ATPase and (P)RR together act on WNT and mTOR signalling pathways, which are responsible for cellular homeostasis and autophagy. (P)RR through its role in v-ATPase assembly and function is also important for fast recycling endocytosis by megalin. In the kidney, megalin together with v-ATPase and (P)RR is crucial for endocytic uptake of components of the RAS and their intracellular processing. In the brain, (P)RR, v-ATPases and megalin are important regulators both during development and in the adult. All three proteins are associated with diseases such as XLMR, XMRE, X-linked parkinsonism and epilepsy, cognitive disorders with Parkinsonism, spasticity, intellectual disability, and Alzheimer's Disease which are characterized by impaired neuronal function and/or neuronal loss. The present review focusses on the relevant effects of Atp6ap2 without assigning them necessarily to the RAS. Mechanistically, many effects can be well explained by the role of Atp6ap2 for v-ATPase assembly and function. Furthermore, application of a soluble (P)RR analogue as new therapeutic option is discussed.

Soluble (Pro)Renin Receptor as a Negative Regulator of NCC (Na+-Cl- Cotransporter) Activity

[Figure: see text].

The Renin-Angiotensin System in the Tumor Microenvironment of Glioblastoma

Simple Summary

Glioblastoma (GB) is the most aggressive brain cancer in humans. Patient survival outcomes have remained dismal despite intensive research over the past 50 years, with a median overall survival of only 14.6 months. We highlight the critical role of the renin–angiotensin system (RAS) on GB cancer stem cells and the tumor microenvironment which, in turn, influences cancer stem cells in driving tumorigenesis and treatment resistance. We present recent developments and underscore the need for further research into the GB tumor microenvironment. We discuss the novel therapeutic targeting of the RAS using existing commonly available medications and utilizing model systems to further this critical investigation.

Abstract

Glioblastoma (GB) is an aggressive primary brain tumor. Despite intensive research over the past 50 years, little advance has been made to improve the poor outcome, with an overall median survival of 14.6 months following standard treatment. Local recurrence is inevitable due to the quiescent cancer stem cells (CSCs) in GB that co-express stemness-associated markers and components of the renin–angiotensin system (RAS). The dynamic and heterogeneous tumor microenvironment (TME) plays a fundamental role in tumor development, progression, invasiveness, and therapy resistance. There is increasing evidence showing the critical role of the RAS in the TME influencing CSCs via its upstream and downstream pathways. Drugs that alter the hallmarks of cancer by modulating the RAS present a potential new therapeutic alternative or adjunct to conventional treatment of GB. Cerebral and GB organoids may offer a cost-effective method for evaluating the efficacy of RAS-modulating drugs on GB. We review the nexus between the GB TME, CSC niche, and the RAS, and propose re-purposed RAS-modulating drugs as a potential therapeutic alternative or adjunct to current standard therapy for GB.

Soluble (pro)renin receptor induces endothelial dysfunction and hypertension in mice with diet-induced obesity via activation of angiotensin II type 1 receptor

Until now, renin-angiotensin system (RAS) hyperactivity was largely thought to result from angiotensin II (Ang II)-dependent stimulation of the Ang II type 1 receptor (AT1R). Here we assessed the role of soluble (pro)renin receptor (sPRR), a product of site-1 protease-mediated cleavage of (pro)renin receptor (PRR), as a possible ligand of the AT1R in mediating: (i) endothelial cell dysfunction in vitro and (ii) arterial dysfunction in mice with diet-induced obesity. Primary human umbilical vein endothelial cells (HUVECs) treated with a recombinant histidine-tagged sPRR (sPRR-His) exhibited IκBα degradation concurrent with NF-κB p65 activation. These responses were secondary to sPRR-His evoked elevations in Nox4-derived H2O2 production that resulted in inflammation, apoptosis and reduced NO production. Each of these sPRR-His-evoked responses was attenuated by AT1R inhibition using Losartan (Los) but not ACE inhibition using captopril (Cap). Further mechanistic exploration revealed that sPRR-His activated AT1R downstream Gq signaling pathway. Immunoprecipitation coupled with autoradiography experiments and radioactive ligand competitive binding assays indicate sPRR directly interacts with AT1R via Lysine199 and Asparagine295. Important translational relevance was provided by findings from obese C57/BL6 mice that sPRR-His evoked endothelial dysfunction was sensitive to Los. Besides, sPRR-His elevated blood pressure in obese C57/BL6 mice, an effect that was reversed by concurrent treatment with Los but not Cap. Collectively, we provide solid evidence that the AT1R mediates the functions of sPRR during obesity-related hypertension. Inhibiting sPRR signaling should be considered further as a potential therapeutic intervention in the treatment and prevention of cardiovascular disorders involving elevated blood pressure.

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.

Soluble (pro)renin receptor promotes the fibrotic response in renal proximal tubule epithelial cells in vitro via the Akt/β-catenin/Snail signaling pathway

Tubulointerstitial fibrosis has been regarded as a critical event in the pathogenesis of chronic kidney disease. The soluble form of (pro)renin receptor (sPRR), generated by site-1 protease (S1P) cleavage of full-length PRR, can be detected in biological fluid and elevated under certain pathological conditions. The present study was designed to evaluate the potential role of sPRR in the regulation of the fibrotic response in a cultured human renal proximal tubular cell line (HK-2 cells) in the setting of transforming growth factor (TGF)-β or sPRR-His treatment. The TGF-β-induced fibrotic response of HK-2 cells was indicated by upregulation of fibronectin (FN) expression; meanwhile, TGF-β could also induce the generation of sPRR, due to enhanced cleavage of full-length PRR. To explore the role of sPRR in the fibrotic response of HK-2 cells, we blocked the production of sPRR with a the S1P inhibitor PF429242 and found that PF429242 remarkably suppressed TGF-β-induced sPRR generation and FN expression in HK-2 cells. Administration of sPRR-His restored the PF429242-attenuated FN expression in HK-2 cells, indicating that sPRR could promote the TGF-β-induced fibrotic response. Furthermore, sPRR-His alone also increased the abundance of FN in HK-2 cells. These data suggested that sPRR was sufficient and necessary for the TGF-β-induced fibrotic response of HK-2 cells. Mechanistically, sPRR activated the AKT and β-catenin pathway in HK-2 cells, and blockade of the AKT or β-catenin pathway significantly abrogated sPRR-induced FN and Snail expression. Taking together, sPRR promoted the fibrotic response of HK-2 cells by activating Akt/β-catenin/Snail signaling, and it may serve as a potential therapeutic target in renal fibrosis.

Elevated V-ATPase Activity Following PTEN Loss Is Required for Enhanced Oncogenic Signaling in Breast Cancer

PTEN loss-of-function contributes to hyperactivation of the PI3K pathway and to drug resistance in breast cancer. Unchecked PI3K pathway signaling increases activation of the mechanistic target of rapamycin complex 1 (mTORC1), which promotes tumorigenicity. Several studies have suggested that vacuolar (H⁺)-ATPase (V-ATPase) complex activity is regulated by PI3K signaling. In this study, we showed that loss of PTEN elevated V-ATPase activity. Enhanced V-ATPase activity was mediated by increased expression of the ATPase H+ transporting accessory protein 2 (ATP6AP2), also known as the prorenin receptor (PRR). PRR is cleaved into a secreted extracellular fragment (sPRR) and an intracellular fragment (M8.9) that remains associated with the V-ATPase complex. Reduced PTEN expression increased V-ATPase complex activity in a PRR-dependent manner. Breast cancer cell lines with reduced PTEN expression demonstrated increased PRR expression. Similarly, PRR expression became elevated upon PTEN deletion in a mouse model of breast cancer. Interestingly, concentration of sPRR was elevated in the plasma of patients with breast cancer and correlated with tumor burden in HER2-enriched cancers. Moreover, PRR was essential for proper HER2 receptor expression, localization, and signaling. PRR knockdown attenuated HER2 signaling and resulted in reduced Akt and ERK 1/2 phosphorylation, and in lower mTORC1 activity. Overall, our study demonstrates a mechanism by which PTEN loss in breast cancer can potentiate multiple signaling pathways through upregulation of the V-ATPase complex. IMPLICATIONS: Our study contributed to the understanding of the role of the V-ATPase complex in breast cancer cell tumorigenesis and provided a potential biomarker in breast cancer.

MicroRNA mimics that target the placental renin-angiotensin system inhibit trophoblast proliferation

In early gestation, the human placental renin-angiotensin system (RAS) is upregulated and plays a role in placental development. Among other functions, signalling through the angiotensin II type 1 receptor (AT1R) initiates proliferation. Many microRNAs (miRNAs) targeting placental RAS mRNAs are downregulated at this time. We propose that in early gestation miRNAs that target the placental RAS are downregulated, allowing for the increased RAS expression and proliferation required for adequate placentation. HTR-8/SVneo cells (an immortalized human trophoblast cell line) were used to assess the effect of nine miRNA mimics (at 0.08, 0.16, 0.32 and 0.64 ng/μL) on trophoblast cell proliferation and predicted RAS target mRNAs. The effect of the miRNA mimics on the rate of cell proliferation was assessed using the xCELLigence real-time cell analysis system over 48 h. Levels of miRNAs and predicted RAS target mRNAs were determined by RT-PCR (qPCR, n = 9/group). Statistically different levels of expression were determined (P < 0.05). All nine miRNA mimics significantly affected the proliferation rates of HTR-8/SVneo cells. Five of the miRNA mimics (miR-181a-5p (predicted to target: renin (REN), angiotensin converting enzyme (ACE)), miR-378 (REN, ACE), miR-663 (REN), miR-483-3p (ACE, ACE2, angiotensinogen (AGT), angiotensin II type 1 receptor (AGTR1)) and miR-514 (AGT)) were associated with a dose-dependent reduction in cell proliferation. Seven of the mimics significantly decreased expression of at least one of their predicted target RAS mRNAs. Our study shows that miRNAs targeting placental RAS mRNAs play a role in controlling trophoblast proliferation. As placentation is largely a process of proliferation, changes in expression of these miRNAs may be partly responsible for the expression of the placental RAS, proliferation and placentation.

Maternal high-fructose intake induces hypertension through activating histone codes on the (pro)renin receptor promoter

High-fructose intake induces hypertension via the renal expression of (pro)renin receptor (PRR) that stimulates the expression of sodium/hydrogen exchanger 3, Na/K/2Cl cotransporter 2, and genes of the intrarenal renin-angiotensin system. We hypothesize that maternal high-fructose intake induces hypertension in subsequent generation offspring through activating histone codes on the PRR promoter. Mice dams were offered 20% fructose solution during pregnancy and lactation, while the subsequent 1st to 4th generation offspring were raised without fructose. Blood pressure was measured via tail-cuff method. The mRNA and protein expression were determined using quantitative real-time polymerase chain reaction and western blotting, respectively. Histone modification was evaluated using a chromatin immunoprecipitation assay. Maternal high-fructose intake statistically significantly increased blood pressure in the 1st and 2nd generations of offspring compared to the control group. Expression levels of sodium transporters and PRR were increased in the kidneys of the 1st to 3rd generation offspring. Increased enrichment of active histone codes such as H3Ac and H3K4me2 but decreased enrichment of repressive histone codes such as H3K9me3 and H3K27me3 on the PRR promoter were observed in the 1st to 3rd not the 4th generation. Moreover, there was increased the mRNA expression for histone acetyltransferase and methyl transferases for H3K4 in the 1st and 2nd generation offspring compared to the control group. This study implicates that maternal high-fructose intake induces hypertension in multigenerational offspring through activating histone codes on the PRR promoter.

Structure of V-ATPase from the mammalian brain

In neurons, the loading of neurotransmitters into synaptic vesicles uses energy from proton-pumping vesicular- or vacuolar-type adenosine triphosphatases (V-ATPases). These membrane protein complexes possess numerous subunit isoforms, which complicates their analysis. We isolated homogeneous rat brain V-ATPase through its interaction with SidK, a Legionella pneumophila effector protein. Cryo-electron microscopy allowed the construction of an atomic model, defining the enzyme's ATP:proton ratio as 3:10 and revealing a homolog of yeast subunit f in the membrane region, which we tentatively identify as RNAseK. The c ring encloses the transmembrane anchors for cleaved ATP6AP1/Ac45 and ATP6AP2/PRR, the latter of which is the (pro)renin receptor that, in other contexts, is involved in both Wnt signaling and the renin-angiotensin system that regulates blood pressure. This structure shows how ATP6AP1/Ac45 and ATP6AP2/PRR enable assembly of the enzyme's catalytic and membrane regions.

The (pro)renin receptor: a novel biomarker and potential therapeutic target for various cancers

BACKGROUND

The (pro) renin receptor ((P)RR) plays important roles in various pathways, such as the Wnt/β-catenin, renin-angiotensin system (RAS), MAPK/ERK and PI3K/AKT/mTOR pathways, that are involved in a wide range of physiological and pathological processes incorporating the tumorigenesis. However, our knowledge about (P) RR was mostly limited to its roles in cardiovascular and renal physiological functions and diseases. In the past 5 years, however, compelling evidence has revealed that (P) RR is aberrantly expressed in and contributes to the development of various cancers by different means. For instance, (P) RR was recently demonstrated to induce the oncogenesis of pancreatic, colorectal and brain cancers via the Wnt signaling, while promote the endometrial cancer and glioblastoma through the RAS.

METHODS

Combining with the deep analysis of big data from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases, this review updates and summarizes the recent studies about the newly recognized roles of (P) RR in the pathophysiological processes of cancer development and its detailed functions through related pathways, as well as the novel research progress of (P) RR in related fields including the development and application of soluble (P) RR detection kit and monoclonal (P) RR antibody.

RESULTS

This review provides an overview of the essential roles of (P) RR in the tumorigenesis and progression of various cancers and offers a translational outlook for the future research and clinical practices.

CONCLUSION

(P) RR in the tumor tissues and/or body fluids of patients may be a novel and promising biomarker and potential therapeutic target for diagnosis, treatment and prognosis prediction in various cancers. Video Abstract.

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.

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.

(Pro)renin receptor knockdown in the paraventricular nucleus of the hypothalamus attenuates hypertension development and AT1 receptor-mediated calcium events

Activation of the brain renin-angiotensin system (RAS) is a pivotal step in the pathogenesis of hypertension. The paraventricular nucleus (PVN) of the hypothalamus is a critical part of the angiotensinergic sympatho-excitatory neuronal network involved in neural control of blood pressure and hypertension. However, the importance of the PVN (pro)renin receptor (PVN-PRR)-a key component of the brain RAS-in hypertension development has not been examined. In this study, we investigated the involvement and mechanisms of the PVN-PRR in DOCA-salt-induced hypertension, a mouse model of hypertension. Using nanoinjection of adeno-associated virus-mediated Cre recombinase expression to knock down the PRR specifically in the PVN, we report here that PVN-PRR knockdown attenuated the enhanced blood pressure and sympathetic tone associated with hypertension. Mechanistically, we found that PVN-PRR knockdown was associated with reduced activation of ERK (extracellular signal-regulated kinase)-1/2 in the PVN and rostral ventrolateral medulla during hypertension. In addition, using the genetically encoded Ca²⁺ biosensor GCaMP6 to monitor Ca²⁺-signaling events in the neurons of PVN brain slices, we identified a reduction in angiotensin II type 1 receptor-mediated Ca²⁺ activity as part of the mechanism by which PVN-PRR knockdown attenuates hypertension. Our study demonstrates an essential role of the PRR in PVN neurons in hypertension through regulation of ERK1/2 activation and angiotensin II type 1 receptor-mediated Ca²⁺ activity. NEW & NOTEWORTHY PRR knockdown in PVN neurons attenuates the development of DOCA-salt hypertension and autonomic dysfunction through a decrease in ERK1/2 activation in the PVN and RVLM during hypertension. In addition, PRR knockdown reduced AT_1aR expression and AT₁R-mediated calcium activity during hypertension. Furthermore, we characterized the neuronal targeting specificity of AAV serotype 2 in the mouse PVN and validated the advantages of the genetically encoded calcium biosensor GCaMP6 in visualizing neuronal calcium activity in the PVN.

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.

(Pro)renin receptor: Involvement in diabetic retinopathy and development of molecular targeted therapy

The renin-angiotensin system (RAS), a crucial regulator of systemic blood pressure (circulatory RAS), plays distinct roles in pathological angiogenesis and inflammation in various organs (tissue RAS), such as diabetic microvascular complications. Using ocular clinical samples and animal disease models, we elucidated molecular mechanisms in which tissue RAS excites the expression of vascular endothelial growth factor (VEGF)-A responsible for retinal inflammation and angiogenesis, the two major pathological events in diabetic retinopathy (DR). Furthermore, we showed the involvement of (pro)renin receptor [(P)RR] in retinal RAS activation and its concurrent intracellular signal transduction (e.g., extracellular signal-regulated kinase); namely, the (P)RR-induced dual pathogenic bioactivity referred to as the receptor-associated prorenin system. Indeed, neovascular endothelial cells in the fibrovascular tissue collected from eyes with proliferative DR were immunoreactive for the receptor-associated prorenin system components including prorenin, (P)RR, phosphorylated extracellular signal-regulated kinase and VEGF-A. Protein levels of soluble (P)RR increased with its positive correlations with prorenin, renin enzymatic activity and VEGF in the vitreous of proliferative DR eyes, suggesting a close link between (P)RR and VEGF-A-driven angiogenic activity. Furthermore, we revealed an unsuspected, PAPS-independent role of (P)RR in glucose-induced oxidative stress. Recently, we developed an innovative single-strand ribonucleic acid interference molecule selectively targeting human and mouse (P)RR, and confirmed its efficacy in suppressing diabetes-induced retinal inflammation in mice. Our data using clinical samples and animal models suggested the significant implication of (P)RR in the pathogenesis of DR, and the potential usefulness of the ribonucleic acid interference molecule as a therapeutic agent to attenuate ocular inflammation and angiogenesis.

Enzymatic sources and physio-pathological functions of soluble (pro)renin receptor

PURPOSE OF REVIEW

(Pro)renin receptor (PRR) belongs to type I transmembrane receptor family and binds both prorenin and renin, representing a potential regulator of the activity of the renin-angiotensin system. Soluble form of PRR (sPRR) is generated by intracellular protease-mediated cleavage of full-length PRR. The purpose of this review is to highlight recent advances in understanding the mechanisms of action and production of sPRR.

RECENT FINDINGS

It has recently been demonstrated that site-1-protease (S1P) plays a dominant role in the generation of sPRR. New evidence is also emerging to support a biological function of sPRR in the physiological regulation of fluid homeostasis as well as pathogenesis of chronic kidney disease.

SUMMARY

sPRR is a 28 kDa product of PRR cleavage via S1P-mediated protease activity. Not only does sPRR regulate renal tubular water transport, but it also mediates pathogenic responses to renal cellular injury. sPRR is likely involved in a wide range of physio-pathological processes.

Soluble (pro)renin receptor as a potential therapy for diabetes insipidus

The antidiuretic hormone vasopressin (VP) is produced by the hypothalamus and is stored and secreted from the posterior pituitary. VP acts via VP type 2 receptors (V2Rs) on the basolateral membrane of principal cells of the collecting duct (CD) to regulate fluid permeability. The VP-evoked endocrine pathway is essential in determining urine concentrating capability. For example, a defect in any component of the VP signaling pathway can result in polyuria, polydipsia, and hypotonic urine, collectively termed diabetes insipidus (DI). A lack of VP production precipitates central diabetes insipidus (CDI), which can be managed effectively by VP supplementation. A majority of cases of nephrogenic diabetes insipidus (NDI) result from V2R mutations that impair receptor sensitivity. No specific therapy is currently available for management of NDI. Evidence is evolving that (pro)renin receptor (PRR), a newly identified member of the renin-angiotensin system, is capable of regulating VP production and action. As such, PRR should be considered strongly as a therapeutic target for treating CDI and NDI. The current review will summarize recent advances in understanding the physiology of renal and central PRR as it relates to the two types of DI.

Increased (pro)renin receptor expression in the subfornical organ of hypertensive humans

The central nervous system plays an important role in essential hypertension in humans and in animal models of hypertension through modulation of sympathetic activity and Na⁺ and body fluid homeostasis. Data from animal models of hypertension suggest that the renin-angiotensin system in the subfornical organ (SFO) of the brain is critical for hypertension development. We recently reported that the brain (pro)renin receptor (PRR) is a novel component of the brain renin-angiotensin system and could be a key initiator of the pathogenesis of hypertension. Here, we examined the expression level and cellular distribution of PRR in the SFO of postmortem human brains to assess its association with the pathogenesis of human hypertension. Postmortem SFO tissues were collected from hypertensive and normotensive human subjects. Immunolabeling for the PRR and a retrospective analysis of clinical data were performed. We found that human PRR was prominently expressed in most neurons and microglia, but not in astrocytes, in the SFO. Importantly, PRR levels in the SFO were elevated in hypertensive subjects. Moreover, PRR immunoreactivity was significantly correlated with systolic blood pressure but not body weight, age, or diastolic blood pressure. Interestingly, this correlation was independent of antihypertensive drug therapy. Our data indicate that PRR in the SFO may be a key molecular player in the pathogenesis of human hypertension and, as such, could be an important focus of efforts to understand the neurogenic origin of hypertension. NEW & NOTEWORTHY This study provides evidence that, in the subfornical organ of the human brain, the (pro)renin receptor is expressed in neurons and microglia cells but not in astrocytes. More importantly, (pro)renin receptor immunoreactivity in the subfornical organ is increased in hypertensive humans and is significantly correlated with systolic blood pressure.

Sodium butyrate suppresses angiotensin II-induced hypertension by inhibition of renal (pro)renin receptor and intrarenal renin-angiotensin system

OBJECTIVES

Butyrate, a short-chain fatty acid, is the end product of the fermentation of complex carbohydrates by the gut microbiota. Recently, sodium butyrate (NaBu) has been found to play a protective role in a number of chronic diseases. However, it is still unclear whether NaBu has a therapeutic potential in hypertension. The present study was aimed to investigate the role of NaBu in angiotensin II (Ang II)-induced hypertension and to further explore the underlying mechanism.

METHODS

Ang II was infused into uninephrectomized Sprague-Dawley rats with or without intramedullary infusion of NaBu for 14 days. Mean arterial blood pressure was recorded by the telemetry system. Renal tissues, serum samples, and 24-h urine samples were collected to examine renal injury and the regulation of the (pro)renin receptor (PRR) and renin.

RESULTS

Intramedullary infusion of NaBu in Sprague-Dawley rats lowered the Ang II-induced mean arterial pressure from 129 ± 6 mmHg to 108 ± 4 mmHg (P < 0.01). This corresponded with an improvement in Ang II-induced renal injury, including urinary albumin, glomerulosclerosis, and renal fibrosis, as well as the expression of inflammatory mediators tumor necrosis factor α, interleukin 6. The renal expression of PRR, angiotensinogen, angiotensin I-converting enzyme and the urinary excretion of soluble PRR, renin, and angiotensinogen were all increased by Ang II infusion but decreased by NaBu treatment. In cultured innermedullary collecting duct cells, NaBu treatment attenuated Ang II-induced expression of PRR and renin.

CONCLUSION

These results demonstrate that NaBu exerts an antihypertensive action, likely by suppressing the PRR-mediated intrarenal renin-angiotensin system.

Atp6ap2 ablation in adult mice impairs viability through multiple organ deficiencies

ATP6AP2 codes for the (pro)renin receptor and is an essential component of vacuolar H+ ATPase. Activating (pro)renin for conversion of Angiotensinogen to Angiotensin makes ATP6AP2 attractive for drug intervention. Tissue-specific ATP6AP2 inactivation in mouse suggested a strong impact on various organs. Consistent with this, we found that embryonic ablation of Atp6ap2 resulted in both male hemizygous lethality and female haploinsufficiency. Next, we examined the phenotype of an induced inactivation in the adult animal, most akin to detect potential effect of functional interference of ATP6AP2 through drug therapy. Induced ablation of Atp6ap2, even without equal efficiency in all tissues (aorta, brain and kidney), resulted in rapid lethality marked by weight loss, changes in nutritional as well as blood parameters, leukocyte depletion, and bone marrow hypoplasia. Upon Atp6ap2 ablation, the colon demonstrated a rapid disruption of crypt morphology, aberrant proliferation, cell-death activation, as well as generation of microadenomas. Consequently, disruption of ATP6AP2 is extremely poorly tolerated in the adult, and severely affects various organ systems demonstrating that ATP6AP2 is an essential gene implicated in basic cellular mechanisms and necessary for multiple organ function. Accordingly, any potential drug targeting of this gene product must be strictly assessed for safety.

Physiology and Pathophysiology of the Intrarenal Renin-Angiotensin System: An Update

The renin-angiotensin system (RAS) has a pivotal role in the maintenance of extracellular volume homeostasis and blood pressure through complex mechanisms. Apart from the well known systemic RAS, occurrence of a local RAS has been documented in multiple tissues, including the kidney. A large body of recent evidence from pharmacologic and genetic studies, particularly those using various transgenic approaches to manipulate intrarenal levels of RAS components, has established the important role of intrarenal RAS in hypertension. Recent studies have also begun to unravel the molecular mechanisms that govern intrarenal RAS activity. This local system is under the control of complex regulatory networks consisting of positive regulators of (pro)renin receptor, Wnt/β-catenin signaling, and PGE₂/PGE₂ receptor EP₄ subtype, and negative regulators of Klotho, vitamin D receptor, and liver X receptors. This review highlights recent advances in defining the regulation and function of intrarenal RAS as a unique entity separate from systemic angiotensin II generation.

Adipocyte (Pro)Renin-Receptor Deficiency Induces Lipodystrophy, Liver Steatosis and Increases Blood Pressure in Male Mice

Adipose tissue dysfunction related to obesity is overwhelmingly associated with increased risk of developing cardiovascular diseases. In the setting of obesity, (pro)renin receptor (PRR) is increased in adipose tissue of mice. We sought to determine the physiological consequences of adipocyte-PRR deficiency using adiponectin-Cre mice. We report a unique model of adipocyte-PRR-deficient mice (PRR(Adi/Y)) with almost no detectable white adipose tissues. As a consequence, the livers of PRR(Adi/Y) mice were enlarged and demonstrated a marked accumulation of lipids. Adipocyte-specific deficiency of PRR increased systolic blood pressure and the concentration of soluble PRR in plasma. To determine whether adipocyte-PRR was involved in the development of obesity-induced hypertension, mice were fed a low-fat or a high-fat diet for 16 weeks. Adipocyte-PRR-deficient mice were resistant to diet-induced obesity. Both high-fat- and low-fat-fed PRR(Adi/Y) mice had elevated insulin levels. Interestingly, adipocyte-PRR deficiency improved glucose tolerance in high-fat-fed PRR(Adi/Y) mice. In response to feeding either low-fat or high-fat diets, systolic blood pressure was greater in PRR(Adi/Y) mice than in control mice. High-fat feeding elevated soluble PRR concentration in control and PRR(Adi/Y) mice. In vitro knockdown of PRR by siRNA significantly decreased mRNA abundance of PPARγ (peroxisome proliferator-activated receptor gamma), suggesting an important role for PRR in adipogenesis. Our data indicate that adipocyte-PRR is involved in lipid homeostasis and glucose and insulin homeostasis, and that soluble PRR may be a predictor of metabolic disturbances and play a role in systolic blood pressure regulation.

Collecting duct (pro)renin receptor targets ENaC to mediate angiotensin II-induced hypertension

The (pro)renin receptor (PRR) is abundantly expressed in the collecting duct (CD) and the expression is further induced by angiotensin II (ANG II). The present study was conducted to investigate the role of CD PRR during ANG II-induced hypertension and to further explore the underlying mechanism. Radiotelemetry demonstrated that a 1-wk ANG II infusion gradually and significantly induced hypertensive response in floxed mice and this response was significantly attenuated in mice lacking PRR in the CD (termed CD PRR KO). ANG II infusion in floxed mice increased urinary renin activity and selectively induced renal medullary α-epithelial sodium channel (α-ENaC) mRNA and protein expression, all of which were blunted in the null mice. In cultured mpkCCD cells grown in Transwells, transepithelial Na⁺ transport as measured by using a volt-ohmmeter was transiently stimulated by acute ANG II treatment, which was abolished by a PRR antagonist, PRO20. In a chronic setting, ANG II treatment induced α-ENaC mRNA expression in mpkCCD cells, which was similarly blocked by PRO20. Chronic intramedullary infusion of an ENaC inhibitor amiloride in rats significantly attenuated ANG II-induced hypertension. Overall, the present study suggests that CD PRR contributes to ANG II-induced hypertension at least partially via activation of renal medullary ENaC.

Activation of ENaC in collecting duct cells by prorenin and its receptor PRR: involvement of Nox4-derived hydrogen peroxide

The collecting duct (CD) has been recognized as an important source of prorenin/renin, and it also expresses (pro)renin receptor (PRR). The goal of this study was to examine the hypothesis that prorenin or renin via PRR regulates epithelial Na(+) channel (ENaC) activity in mpkCCD cells. Transepithelial Na(+) transport was measured by using a conventional epithelial volt-ohmmeter and was expressed as the calculated equivalent current (Ieq). Amiloride-inhibitable Ieq was used as a reflection of ENaC activity. Administration of prorenin in the nanomolar range induced a significant increase in Ieq that was detectable as early as 1 min, peaked at 5 min, and gradually returned to baseline within 15 min. These changes in Ieq were completely prevented by a newly developed PRR decoy inhibitor, PRO20. Prorenin-induced Ieq was inhibitable by amiloride. Compared with prorenin, renin was less effective in stimulating Ieq Prorenin-induced Ieq was attenuated by apocynin but enhanced by tempol, the latter effect being prevented by catalase. In response to prorenin treatment, the levels of total reactive oxygen species and H2O2 were both increased, as detected by spin-trap analysis and reactive oxygen species (ROS)-Glo H2O2 assay, respectively. Both siRNA-mediated Nox4 knockdown and the dual Nox1/4 inhibitor GKT137892 attenuated prorenin-induced Ieq Overall, our results demonstrate that activation of PRR by prorenin stimulates ENaC activity in CD cells via Nox4-derived H2O2.

Renal medullary (pro)renin receptor contributes to angiotensin II-induced hypertension in rats via activation of the local renin-angiotensin system

BACKGROUND

(Pro)renin receptor (PRR) is a new component of the renin-angiotensin system and regulates renin activity in vitro. Within the kidney, PRR is highly expressed in the renal medulla where its expression is induced by angiotensin II infusion. The objective of the present study was to test a potential role of renal medullary PRR during angiotensin II-induced hypertension.

METHODS

A rat AngII infusion model (100 ng/kg/min) combined with renal intramedullary infusion of PRO20, a specific inhibitor of PRR, was builded. And the intravenous PRO20 infusion serve as control. Mean arterial pressure was recorded by radiotelemetry for one week. Further analysis of kidney injury, inflammation, biochemical indices and protein localization were performed in vivo or in vitro.

RESULTS

Radiotelemetry demonstrated that AngII infusion elevated the mean arteria pressure from 108 ± 5.8 to 164.7 ± 6.2 mmHg. Mean arterial pressure decreased to 128.6 ± 5.8 mmHg (P < 0.05) after intramedullary infusion of PRO20, but was only modestly affected by intravenous PRO20 infusion. Indices of kidney injury, including proteinuria, glomerulosclerosis, and interstitial fibrosis, inflammation, and increased renal medullary and urinary renin activity following angiotensin II infusion were all remarkably attenuated by intramedullary PRO20 infusion. Following one week of angiotensin II infusion, increased PRR immunoreactivity was found in vascular smooth muscle cells. In cultured rat vascular smooth muscle cells, angiotensin II induced parallel increases in soluble PRR and renin activity, and the latter was significantly reduced by PRO20.

CONCLUSION

Renal medullary PRR mediates angiotensin II-induced hypertension, likely by amplifying the local renin response.

New role for the (pro)renin receptor in T-cell development

The (pro)renin receptor (PRR) was originally thought to be important for regulating blood pressure via the renin-angiotensin system. However, it is now emerging that PRR has instead a generic role in cellular development. Here, we have specifically deleted PRR from T cells. T-cell-specific PRR-knockout mice had a significant decrease in thymic cellularity, corresponding with a 100-fold decrease in the number of CD4(+) and CD8(+) thymocytes, and a large increase in double-negative (DN) precursors. Gene expression analysis on sorted DN3 thymocytes indicated that PRR-deficient thymocytes have perturbations in key cellular pathways essential at the DN3 stage, including transcription and translation. Further characterization of DN T-cell progenitors leads us to propose that PRR deletion affects thymocyte survival and development at multiple stages; from DN3 through to DN4, double-positive, and single-positive CD4 and CD8. Our study thus identifies a new role for PRR in T-cell development.

ATP6AP2/(pro)renin receptor contributes to glucose metabolism via stabilizing the pyruvate dehydrogenase E1 β subunit

Aerobic glucose metabolism is indispensable for metabolically active cells; however, the regulatory mechanism of efficient energy generation in the highly evolved mammalian retina remains incompletely understood. Here, we revealed an unsuspected role for (pro)renin receptor, also known as ATP6AP2, in energy metabolism. Immunoprecipitation and mass spectrometry analyses identified the pyruvate dehydrogenase (PDH) complex as Atp6ap2-interacting proteins in the mouse retina. Yeast two-hybrid assays demonstrated direct molecular binding between ATP6AP2 and the PDH E1 β subunit (PDHB). Pdhb immunoreactivity co-localized with Atp6ap2 in multiple retinal layers including the retinal pigment epithelium (RPE). ATP6AP2 knockdown in RPE cells reduced PDH activity, showing a predilection to anaerobic glycolysis. ATP6AP2 protected PDHB from phosphorylation, thus controlling its protein stability. Down-regulated PDH activity due to ATP6AP2 knockdown inhibited glucose-stimulated oxidative stress in RPE cells. Our present data unraveled the novel function of ATP6AP2/(P)RR as a PDHB stabilizer, contributing to aerobic glucose metabolism together with oxidative stress.

Intracellular retention of the extracellular domain of the (pro)renin receptor in mammalian cells

As a component of the renin-angiotensin system, the (pro)renin receptor [(P)RR] activates prorenin along with intracellular signaling pathways. In this study, the glutathione S-transferase-fused extracellular domain of (P)RR expressed in mammalian cells was recovered in the detergent phase in detergent-based two-phase separation experiments, and intracellular localization was observed by immunocytochemistry, suggesting retention inside the cell through stable membrane association.

Significant roles of the (pro)renin receptor in integrity of vascular smooth muscle cells

The (pro)renin receptor ((P)RR) is known to play an important role in the pathogenesis of vascular complications in diabetes mellitus and hypertension through its function in activating the local renin-angiotensin system. Recent studies have shown that the (P)RR is an accessory protein of the vacuolar H(+)-ATPase, suggesting a more fundamental and developmental function. In this study, smooth muscle cell-specific (P)RR/Atp6ap2 conditional knockout mice were generated. Smooth muscle cell-specific ablation of the (P)RR resulted in nonatherogenic sclerosis in the abdominal aorta. The deletion of the (P)RR did not affect ambulatory blood pressure levels. In cultured murine vascular smooth muscle cells (VSMCs), ablation of the (P)RR suppressed the expression of the Vo subunit c of the vacuolar H(+)-ATPase and impaired the cell recycling system, leading to autophagic cell death. In addition, loss of the (P)RR in VSMCs induced the expression of monocyte chemotactic protein-1 and interleukin-6 mRNAs. These results suggest that the (P)RR is essential for cell survival and downregulation of vascular inflammation in murine VSMCs through maintaining normal function of the vacuolar H(+)-ATPase.

(Pro)renin receptor and V-ATPase: from Drosophila to humans

A decade ago, the (P)RR [(pro)renin receptor] was discovered and depicted as a potential activator of the tissue renin-angiotensin system. For this reason, the role of the (P)RR in cardiovascular diseases and diabetes has been particularly studied. However, the discovery of embryonic lethality after (P)RR gene deletion in mouse and zebrafish paved the way for additional roles of (P)RR in cell homoeostasis. Indeed, the (P)RR has been shown to associate with vacuolar H+-ATPase, hence its other name ATP6ap2. Developmental studies in Xenopus and Drosophila have revealed an essential role of this association to promote the canonical and non-canonical Wnt signalling pathways, whereas studies with tissue-specific gene deletion have pointed out a role in autophagy. The present review aims to summarize recent findings on the cellular functions of (P)RR emerging from various mutated and transgenic animal models.

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.

Increased expression of (pro)renin receptor in aldosterone-producing adenomas

(Pro)renin receptor ((P)RR) is a specific receptor for renin and prorenin. The aim of the present study is to clarify expression and possible pathophysiological roles of (P)RR in aldosterone-producing adenomas (APAs) and other adrenal tumors. Expression of (P)RR was studied by immunocytochemistry, western blot analysis and real-time RT-PCR in adrenal tumor tissues obtained at surgery. Immunocytochemistry showed that (P)RR was expressed in normal adrenal glands and tumor tissues of adrenocortical tumors including APAs. In the normal adrenal glands, positive (P)RR immunostaining was observed in both adrenal cortex and medulla, with higher (P)RR immunostaining observed in zona glomerulosa and zona reticularis. Positive (P)RR immunostaining was also observed in the adrenocortical tumors, with elevated (P)RR immunostaining found in APAs, particularly in compact cells. By contrast, no apparent (P)RR immunostaining was observed in pheochromocytomas. Western blot analysis showed a band of (P)RR protein in normal adrenal glands and adrenocortical tumors at the position of 35 kDa. The relative expression levels of (P)RR protein were higher in tumor tissues of APAs than in attached non-neoplastic adrenal tissues of APAs. Real-time RT-PCR showed that expression levels of (P)RR mRNA were significantly increased in tumor tissues of APAs compared with other adrenal tumor tissues and attached non-neoplastic adrenal tissues of APAs. The present study has shown for the first time that expression of (P)RR is elevated in tumor tissues of APAs, raising the possibility that (P)RR may play pathophysiological roles in APAs, such as aldosterone secretion and cell proliferation.