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.

Apelin-13: a novel approach to suppressing renin production in RVHT.

Renovascular hypertension (RVHT) is characterized by renal artery stenosis and overactivated renin-angiotensin system (RAS). Apelin, known for its negative modulation of RAS, has protective effects against cardiovascular diseases. The role and mechanisms of the primary active form of apelin, apelin-13, in RVHT are unclear. In this study, male Sprague-Dawley rats were divided into control, two-kidney one-clip (2K1C) model, and 2K1C with apelin-13 treatment groups. Renin expression was analyzed using immunohistochemistry and molecular techniques. Full-length (pro)renin receptor (fPRR) and soluble PRR (sPRR) levels were assessed via Western blotting, and cAMP levels were measured using ELISA. Plasma renin content, plasma renin activity (PRA), angiotensin II (ANG II), and sPRR levels were determined by ELISA. Human Calu-6 and mouse As4.1 cells were used to investigate renin production mechanisms. The 2K1C model exhibited increased systolic blood pressure, plasma renin content, PRA, sPRR, and ANG II levels, while apelin-13 treatment reduced these elevations. Apelin-13 inhibited cAMP production, renin mRNA expression, protein synthesis, and PRR/sPRR protein expression in renal tissue. In Calu-6 cells, cAMP-induced fPRR and site-1 protease (S1P)-derived sPRR expression, which was blocked by cAMP-responsive element-binding protein (CREB) inhibition. Apelin-13 suppressed cAMP elevation, CREB phosphorylation, fPRR/sPRR protein expression, and renin production. Recombinant sPRR (sPRR-His) stimulated renin production, which was inhibited by the PRR decoy peptide PRO20 and S1P inhibitor PF429242. These findings suggest that apelin-13 inhibits plasma renin expression through the cAMP/PKA/sPRR pathway, providing a potential therapeutic approach for RVHT. Understanding the regulation of renin production is crucial for developing effective treatments.NEW & NOTEWORTHY Our research elucidated that apelin-13 inhibits renin production through the cAMP/PKA/soluble (pro)renin receptor pathway, presenting a promising therapeutic approach for renovascular hypertension (RVHT) by targeting renin expression mechanisms. These findings underscore the potential of apelin-13 as a novel strategy to address RVHT.

Neuropilin-1 regulates renin synthesis in juxtaglomerular cells.

Renin is the key enzyme of the systemic renin-angiotensin-aldosterone system, which plays an essential role in regulating blood pressure and maintaining electrolyte and extracellular volume homeostasis. Renin is mainly produced and secreted by specialized juxtaglomerular (JG) cells in the kidney. In the present study, we report for the first time that the conserved transmembrane receptor neuropilin-1 (NRP1) participates in the development of JG cells and plays a key role in renin production. We used the myelin protein zero-Cre (P0-Cre) to abrogate Nrp1 constitutively in P0-Cre lineage-labelled cells of the kidney. We found that the P0-Cre precursor cells differentiate into renin-producing JG cells. We employed a lineage-tracing strategy combined with RNAscope quantification and metabolic studies to reveal a cell-autonomous role for NRP1 in JG cell function. Nrp1-deficient animals displayed abnormal levels of tissue renin expression and failed to adapt properly to a homeostatic challenge to sodium balance. These findings provide new insights into cell fate decisions and cellular plasticity operating in P0-Cre-expressing precursors and identify NRP1 as a novel key regulator of JG cell maturation. KEY POINTS: Renin is a centrepiece of the renin-angiotensin-aldosterone system and is produced by specialized juxtaglomerular cells (JG) of the kidney. Neuropilin-1 (NRP1) is a conserved membrane-bound receptor that regulates vascular and neuronal development, cancer aggressiveness and fibrosis progression. We used conditional mutagenesis and lineage tracing to show that NRP1 is expressed in JG cells where it regulates their function. Cell-specific Nrp1 knockout mice present with renin paucity in JG cells and struggle to adapt to a homeostatic challenge to sodium balance. The results support the versatility of renin-producing cells in the kidney and may open new avenues for therapeutic approaches.

An efficient inducible model for the control of gene expression in renin cells.

Fate mapping and genetic manipulation of renin cells have relied on either noninducible Cre lines that can introduce the developmental effects of gene deletion or bacterial artificial chromosome transgene-based inducible models that may be prone to spurious and/or ectopic gene expression. To circumvent these problems, we generated an inducible mouse model in which CreERT2 is under the control of the endogenous Akr1b7 gene, an independent marker of renin cells that is expressed in a few extrarenal tissues. We confirmed the proper expression of Cre using Akr1b7CreERT2/+;R26RmTmG/+ mice in which Akr1b7+/renin+ cells become green fluorescent protein (GFP)+ upon tamoxifen administration. In embryos and neonates, GFP was found in juxtaglomerular cells, along the arterioles, and in the mesangium, and in adults, GFP was present mainly in juxtaglomerular cells. In mice treated with captopril and a low-salt diet to induce recruitment of renin cells, GFP extended along the afferent arterioles and in the mesangium. We generated Akr1b7CreERT2/+;Ren1cFl/-;R26RmTmG/+ mice to conditionally delete renin in adult mice and found a marked reduction in kidney renin mRNA and protein and mean arterial pressure in mutant animals. When subjected to a homeostatic threat, mutant mice were unable to recruit renin+ cells. Most importantly, these mice developed concentric vascular hypertrophy ruling out potential developmental effects on the vasculature due to the lack of renin. We conclude that Akr1b7CreERT2 mice constitute an excellent model for the fate mapping of renin cells and for the spatial and temporal control of gene expression in renin cells.NEW & NOTEWORTHY Fate mapping and genetic manipulation are important tools to study the identity of renin cells. Here, we report on a novel Cre mouse model, Akr1b7CreERT2, for the spatial and temporal regulation of gene expression in renin cells. Cre is properly expressed in renin cells during development and in the adult under basal conditions and under physiological stress. Moreover, renin can be efficiently deleted in the adult, leading to the development of concentric vascular hypertrophy.

Human soluble prorenin receptor expressed in mouse renal collecting duct shows sex-specific effect on cardiorenal function.

Soluble prorenin receptor (sPRR), a component of the renin-angiotensin system (RAS), has been identified as a plasma biomarker for hypertension and cardiovascular diseases in humans. Despite studies showing that sPRR in the kidney is produced by tubular cells in the renal collecting duct (CD), its biological actions modulating cardiorenal function in physiological conditions remain unknown. Therefore, the objective of our study was to investigate whether CD-derived human sPRR (HsPRR) expression influences cardiorenal function and examine sex and circadian differences. Thus, we investigated the status of the intrarenal RAS, water and electrolyte balance, renal filtration capacity, and blood pressure (BP) regulation in CD-HsPRR and control (CTL) mice. CD-HsPRR mice were generated by breeding human sPRR-Myc-tag mice with Hoxb7/Cre mice. Renal sPRR expression increased in CD-HsPRR mice, but circulating sPRR and RAS levels were unchanged compared with CTL mice. Only female littermates expressing CD-HsPRR showed 1) increased 24-h BP, 2) an impaired BP response to an acute dose of losartan and attenuated angiotensin II (ANG II)-induced hypertension, 3) reduced angiotensin-converting enzyme activity and ANG II content in the renal cortex, and 4) decreased glomerular filtration rate, with no changes in natriuresis and kaliuresis despite upregulation of the ß-subunit of the epithelial Na+ channel in the renal cortex. These cardiorenal alterations were displayed only during the active phase of the day. Taken together, these data suggest that HsPRR could interact with ANG II type 1 receptors mediating sex-specific, ANG II-independent renal dysfunction and a prohypertensive phenotype in a sex-specific manner.NEW & NOTEWORTHY We successfully generated a humanized mouse model that expresses human sPRR in the collecting duct. Collecting duct-derived human sPRR did not change circulating sPRR and RAS levels but increased daytime BP in female mice while showing an attenuated angiotensin II-dependent pressor response. These findings may aid in elucidating the mechanisms by which women show uncontrolled BP in response to antihypertensive treatments targeting the RAS, improving approaches to reduce uncontrolled BP and chronic kidney disease incidences in women.

Commensal microbiota regulate aldosterone.

The gut microbiome regulates many important host physiological processes associated with cardiovascular health and disease; however, the impact of the gut microbiome on aldosterone is unclear. Investigating whether gut microbiota regulate aldosterone can offer novel insights into how the microbiome affects blood pressure. In this study, we aimed to determine whether gut microbiota regulate host aldosterone. We used enzyme-linked immunosorbent assays (ELISAs) to assess plasma aldosterone and plasma renin activity (PRA) in female and male mice in which gut microbiota are intact, suppressed, or absent. In addition, we examined urinary aldosterone. Our findings demonstrated that when the gut microbiota is suppressed following antibiotic treatment, there is an increase in plasma and urinary aldosterone in both female and male mice. In contrast, an increase in PRA is seen only in males. We also found that when gut microbiota are absent (germ-free mice), plasma aldosterone is significantly increased compared with conventional animals (in both females and males), but PRA is not. Understanding how gut microbiota influence aldosterone levels could provide valuable insights into the development and treatment of hypertension and/or primary aldosteronism. This knowledge may open new avenues for therapeutic interventions, such as probiotics or dietary modifications to help regulate blood pressure via microbiota-based changes to aldosterone.NEW & NOTEWORTHY We explore the role of the gut microbiome in regulating aldosterone, a hormone closely linked to blood pressure and cardiovascular disease. Despite the recognized importance of the gut microbiome in host physiology, the relationship with circulating aldosterone remains largely unexplored. We demonstrate that suppression of gut microbiota leads to increased levels of plasma and urinary aldosterone. These findings underscore the potential of the gut microbiota to influence aldosterone regulation, suggesting new possibilities for treating hypertension.

Renin and renin blockade have no role in complement activity.

Renin, an aspartate protease, regulates the renin-angiotensin system by cleaving its only known substrate angiotensinogen to angiotensin. Recent studies have suggested that renin may also cleave complement component C3 to activate complement or contribute to its dysregulation. Typically, C3 is cleaved by C3 convertase, a serine protease that uses the hydroxyl group of a serine residue as a nucleophile. Here, we provide seven lines of evidence to show that renin does not cleave C3. First, there is no association between renin plasma levels and C3 levels in patients with C3 Glomerulopathies (C3G) and atypical Hemolytic Uremic Syndrome (aHUS), implying that serum C3 consumption is not increased in the presence of high renin. Second, in vitro tests of C3 conversion to C3b do not detect differences when sera from patients with high renin levels are compared to sera from patients with normal/low renin levels. Third, aliskiren, a renin inhibitor, does not block abnormal complement activity introduced by nephritic factors in the fluid phase. Fourth, aliskiren does not block dysregulated complement activity on cell surfaces. Fifth, recombinant renin from different sources does not cleave C3 even after 24 hours of incubation at 37 °C. Sixth, direct spiking of recombinant renin into sera samples of patients with C3G and aHUS does not enhance complement activity in either the fluid phase or on cell surfaces. And seventh, molecular modeling and docking place C3 in the active site of renin in a position that is not consistent with a productive ground state complex for catalytic hydrolysis. Thus, our study does not support a role for renin in the activation of complement.

Spontaneous and evoked angiotensin II sniffer cell activity in the lamina terminalis in vitro.

Angiotensin II (ANG II) has been shown to have central nervous system effects. Although tissue renin-angiotensin systems (RAS) have been demonstrated in multiple tissues, the existence of a brain RAS is still a matter of debate. These studies test for angiotensin release from brain slices prepared from adult male Sprague-Dawley rats and male and female renin knock-out rats using Chinese hamster ovary cells modified to express both the angiotensin II type 1 receptor and a fluorescent calcium indicator. Sniffer cells were placed on the slices and calcium transients were measured from those located on or adjacent to the median preoptic nucleus with and without stimulation of the subfornical organ. Bath application of tetrodotoxin (1 µM) significantly attenuated spontaneous events while abolishing evoked sniffer cell activity. Bath application of dl-AP4 (10 µM, glutamatergic antagonist) did not affect either spontaneous or evoked release. Incubating the slices with fluorocitrate to inactive astrocytes did not influence sniffer cell activity in the MnPO. Pharmacological experiments indicate that ANG II release is largely both renin (aliskiren 10 µM) and ACE-1 (captopril 100 µM) dependent. However, experiments with brain slices prepared from male and female Renin knock-out rats suggest that alternative synthetic pathways may exist. Finally, these studies demonstrate that increases in ANG II release are observed following 7 days of chronic intermittent hypoxia. These studies suggest the existence of a tissue-specific RAS in the brain that involves canonical and alternative ANG II synthetic pathways and is upregulated in an animal model of sleep apnea.NEW & NOTEWORTHY These studies used Chinese hamster ovary cells that were cloned to express an angiotensin receptor (At1ra) and a calcium indicator (R-GECO) to detect the release of angiotensin from brain slices containing the lamina terminalis of rats. Some of the experiments use tissue from renin knockout rats. The results support the existence of an angiotensin system in the brain that may involve alternative synthetic pathways and is upregulated by intermittent hypoxia.

Diagnostic challenges in patients with reninomas and extrarenal renin-producing tumours.

Renin-secreting tumours are rare causes of secondary hypertension and hypokalaemia. They are usually surgically curable, hence proper diagnostic work-up and tumour localisation is essential. In this paper, we present three Swedish patients recently diagnosed with renin secreting tumours, two with reninomas and one with an extrarenal renin-producing tumour, to illustrate diagnostic challenges. We also discuss the biochemical work-up, the pros and cons of different imaging techniques (computer tomography [CT], magnetic resonance imaging and [18F]fluorodeoxyglucose-positron emission tomography-CT), as well as how renal vein sampling (RVC) may contribute to localisation of the tumour.

Haemodynamic, hormonal and renal actions of osteocrin in normal sheep.

Osteocrin (OSTN) is an endogenous protein sharing structural similarities with the natriuretic peptides [NPs; atrial (ANP), B-type (BNP) and C-type (CNP) NP], which are hormones known for their crucial role in maintaining pressure/volume homeostasis. Osteocrin competes with the NPs for binding to the receptor involved in their clearance (NPR-C). In the present study, having identified, for the first time, the major circulating form of OSTN in human and ovine plasma, we examined the integrated haemodynamic, endocrine and renal effects of vehicle-controlled incremental infusions of ovine proOSTN (83-133) and its metabolism in eight conscious normal sheep. Incremental i.v. doses of OSTN produced stepwise increases in circulating concentrations of the peptide, and its metabolic clearance rate was inversely proportional to the dose. Osteocrin increased plasma levels of ANP, BNP and CNP in a dose-dependent manner, together with concentrations of their intracellular second messenger, cGMP. Increases in plasma cGMP were associated with progressive reductions in arterial pressure and central venous pressure. Plasma cAMP, renin and aldosterone were unchanged. Despite significant increases in urinary cGMP levels, OSTN administration was not associated with natriuresis or diuresis in normal sheep. These results support OSTN as an endogenous ligand for NPR-C in regulating plasma concentrations of NPs and associated cGMP-mediated bioactivity. Collectively, our findings support a role for OSTN in maintaining cardiovascular homeostasis.

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.

Targeting Angiotensinogen With N-Acetylgalactosamine-Conjugated Small Interfering RNA to Reduce Blood Pressure.

Blood pressure management involves antihypertensive therapies blocking the renin-angiotensin system (RAS). Yet, it might be inadequate due to poor patient adherence or the so-called RAS escape phenomenon, elicited by the compensatory renin elevation upon RAS blockade. Recently, evidence points toward targeting hepatic AGT (angiotensinogen) as a novel approach to block the RAS pathway that could circumvent the RAS escape phenomenon. Removing AGT, from which all angiotensins originate, should prevent further angiotensin generation, even when renin rises. Furthermore, by making use of a trivalent N-acetylgalactosamine ligand-conjugated small interfering RNA that specifically targets the degradation of hepatocyte-produced mRNAs in a highly potent and specific manner, it may be possible in the future to manage hypertension with therapy that is administered 1 to 2× per year, thereby supporting medication adherence. This review summarizes all current findings on AGT small interfering RNA in preclinical models, making a comparison versus classical RAS blockade with either ACE (angiotensin-converting enzyme) inhibitors or AT1 (angiotensin II type 1) receptor antagonists and AGT suppression with antisense oligonucleotides. It ends with discussing the first-in-human study with AGT small interfering RNA.

Renin and (pro)renin receptors induce vascular smooth muscle cell proliferation and neointimal hyperplasia by activating oxidative stress and inflammation.

Introduction: Renin and prorenin promote the proliferation of vascular smooth muscle cells (VSMCs) through the (pro)renin receptor, or (P)RR, to promote restenosis occurrence. This study aimed to explore whether prorenin promoted the proliferation of VSMCs in a (P)RR-mediated Ang II-independent manner. Methods: Losartan and PD123319 were used to block the interaction between (P)RR and angiotensin in vitro. Cells were treated with renin, platelet-derived growth factor (PDGF), or RNAi-(P)RR, either jointly or individually. Cell proliferation was measured via Cell Counting Kit-8 (CCK-8) and flow cytometry methods; moreover, real-time polymerase chain reaction (RT-PCR) and Western blot (WB) assays were used to detect the expression of cyclin D1, proliferating cell nuclear antigen (PCNA), (P)RR, NOX1, and phosphatidylinositol 3-kinase (PI3K)/AKT signaling proteins. Immunofluorescence staining was conducted to measure the expression of (P)RR, and the levels of renin, PDGF-BB, inflammatory factors, and oxidative stress were determined by using enzyme-linked immunosorbent assay (ELISA). Moreover, a balloon catheter was used to enlarge the carotid artery of the Sprague Dawley rats. PRO20 was applied to identify angiotensin II (Ang II). The hematoxylin and eosin, RT-PCR, and WB results validated the cell assay results. Results: Renin promoted the proliferation of rat VSMCs by enhancing cell viability and cell cycle protein expression when Ang II was blocked, but silencing (P)RR inhibited this effect. Furthermore, renin enhanced NOX1-mediated oxidative stress and inflammation by activating the extracellular signal-regulated kinase 1/2 (ERK1/2)-AKT pathway in vitro. Similarly, the inhibition of (P)RR resulted in the opposite phenomenon. Importantly, the inhibition of (P)RR inhibited neointimal hyperplasia in vivo after common carotid artery injury by restraining NOX1-mediated oxidative stress through the downregulation of the ERK1/2-AKT pathway. The animal study confirmed these findings. Conclusion: Renin and (P)RR induced VSMC proliferation and neointimal hyperplasia by activating oxidative stress, inflammation, and the ERK1/2-AKT pathway in an Ang II-independent manner.

Case-inspired exploration of renin mutations in autosomal dominant tubulointerstitial kidney disease: not all paths lead to the endoplasmic reticulum.

BACKGROUND: Autosomal dominant tubulointerstitial kidney disease (ADTKD) results from mutations in various genes, including REN, UMOD, MUC1, and HNF1B. ADTKD due to REN mutations (ADTKD-REN) is often characterized as a proteinopathy that triggers the endoplasmic reticulum stress (ERS) cascade, potentially sharing similarities with ADTKD-UMOD and ADTKD-MUC1 at the cellular level. This study, inspired by a patient harboring a W17R mutation, investigates ERS activation by this mutation alongside two other renin variants, W10R and L381P. METHODS: We established stable cell lines expressing both wild-type and mutated renin forms (W17R, W10R, and L381P). Using luciferase reporter assays, RT-qPCR, and confocal microscopy, we evaluated ERS activation, determined the cellular localization of the renin variants, and characterized the mitochondrial network in the W17R line. RESULTS: The L381P line exhibited ERS activation, including transcriptional upregulation of MANF and CRELD2. No ERS activation was observed in the W17R line, while the W10R line exhibited intermediate characteristics. Notably, the W17R variant was misrouted to the mitochondria resulting in changes of the mitochondrial network organisation. CONCLUSIONS: ERS activation is not a universal response to different renin mutations in ADTKD-REN. The pathogenesis of the W17R mutation may involve mitochondrial dysfunction rather than the ER pathway, albeit further research is needed to substantiate this hypothesis fully. Testing CRELD2 and MANF as targeted therapy markers for a specific subgroup of ADTKD-REN patients is recommended. Additionally, fludrocortisone treatment has shown efficacy in stabilizing the renal function of our patient over a four-year period without significant side effects.

A Possible Link between Cell Plasticity and Renin Expression in the Collecting Duct: A Narrative Review.

The hormone renin is produced in the kidney by the juxtaglomerular cells. It is the rate-limiting factor in the circulating renin-angiotensin-aldosterone system (RAAS), which contributes to electrolyte, water, and blood pressure homeostasis. In the kidneys, the distal tubule and the collecting duct are the key target segments for RAAS. The collecting duct is important for urine production and also for salt, water, and acid-base homeostasis. The critical functional role of the collecting duct is mediated by the principal and the intercalated cells and is regulated by different hormones like aldosterone and vasopressin. The collecting duct is not only a target for hormones but also a place of hormone production. It is accepted that renin is produced in the collecting duct at a low level. Several studies have described that the cells in the collecting duct exhibit plasticity properties because the ratio of principal to intercalated cells can change under specific circumstances. This narrative review focuses on two aspects of the collecting duct that remain somehow aside from mainstream research, namely the cell plasticity and the renin expression. We discuss the link between these collecting duct features, which we see as a promising area for future research given recent findings.

Pseudohyperaldosteronism Due to Licorice: A Practice-Based Learning from a Case Series.

Pseudohyperaldosteronism (PHA) is characterized by hypertension, hypokalemia, and a decrease in plasma renin and aldosterone levels. It can be caused by several causes, but the most frequent is due to excess intake of licorice. The effect is mediated by the active metabolite of licorice, glycyrrhetinic acid (GA), which acts by blocking the 11-hydroxysteroid dehydrogenase type 2 and binding to the mineralocorticoid receptor (MR) as an agonist. The management of licorice-induced PHA depends on several individual factors, such as age, gender, comorbidities, duration and amount of licorice intake, and metabolism. The clinical picture usually reverts upon licorice withdrawal, but sometimes mineralocorticoid-like effects can be critical and persist for several weeks, requiring treatment with MR blockers and potassium supplements. Through this case series of licorice-induced PHA, we aim to increase awareness about exogenous PHA, and the possible risk associated with excess intake of licorice. An accurate history is mandatory in patients with hypertension and hypokalemia to avoid unnecessary testing. GA is a component of several products, such as candies, breath fresheners, beverages, tobacco, cosmetics, and laxatives. In recent years, the mechanisms of action of licorice and its active compounds have been better elucidated, suggesting its benefits in several clinical settings. Nevertheless, licorice should still be consumed with caution, considering that licorice-induced PHA is still an underestimated condition, and its intake should be avoided in patients with increased risk of licorice toxicity due to concomitant comorbidities or interfering drugs.

Renal Expression and Localization of the Receptor for (Pro)renin and Its Ligands in Rodent Models of Diabetes, Metabolic Syndrome, and Age-Dependent Focal and Segmental Glomerulosclerosis.

The (pro)renin receptor ((P)RR), a versatile protein found in various organs, including the kidney, is implicated in cardiometabolic conditions like diabetes, hypertension, and dyslipidemia, potentially contributing to organ damage. Importantly, changes in (pro)renin/(P)RR system localization during renal injury, a critical information base, remain unexplored. This study investigates the expression and topographic localization of the full length (FL)-(P)RR, its ligands (renin and prorenin), and its target cyclooxygenase-2 and found that they are upregulated in three distinct animal models of renal injury. The protein expression of these targets, initially confined to specific tubular renal cell types in control animals, increases in renal injury models, extending to glomerular cells. (P)RR gene expression correlates with protein changes in a genetic model of focal and segmental glomerulosclerosis. However, in diabetic and high-fat-fed mice, (P)RR mRNA levels contradict FL-(P)RR immunoreactivity. Research on diabetic mice kidneys and human podocytes exposed to diabetic glucose levels suggests that this inconsistency may result from disrupted intracellular (P)RR processing, likely due to increased Munc18-1 interacting protein 3. It follows that changes in FL-(P)RR cellular content mechanisms are specific to renal disease etiology, emphasizing the need for consideration in future studies exploring this receptor's involvement in renal damage of different origins.

Angiotensin-Converting Enzyme and Renin-Inhibitory Activities of Protein Hydrolysates Produced by Alcalase Hydrolysis of Peanut Protein.

Hypertension is a major controllable risk factor associated with cardiovascular disease (CVD) and overall mortality worldwide. Most people with hypertension must take medications that are effective in blood pressure management but cause many side effects. Thus, it is important to explore safer antihypertensive alternatives to regulate blood pressure. In this study, peanut protein concentrate (PPC) was hydrolyzed with 3-5% Alcalase for 3-10 h. The in vitro angiotensin-converting enzyme (ACE) and renin-inhibitory activities of the resulting peanut protein hydrolysate (PPH) samples and their fractions of different molecular weight ranges were determined as two measures of their antihypertensive potentials. The results show that the crude PPH produced at 4% Alcalase for 6 h of hydrolysis had the highest ACE-inhibitory activity with IC50 being 5.45 mg/mL. The PPH samples produced with 3-5% Alcalase hydrolysis for 6-8 h also displayed substantial renin-inhibitory activities, which is a great advantage over the animal protein-derived bioactive peptides or hydrolysate. Remarkably higher ACE- and renin-inhibitory activities were observed in fractions smaller than 5 kDa with IC50 being 0.85 and 1.78 mg/mL. Hence, the PPH and its small molecular fraction produced under proper Alcalase hydrolysis conditions have great potential to serve as a cost-effective anti-hypertensive ingredient for blood pressure management.

The role of Gata3 in renin cell identity.

Renin cells are precursors for other cell types in the kidney and show high plasticity in postnatal life in response to challenges to homeostasis. Our previous single-cell RNA-sequencing studies revealed that the dual zinc-finger transcription factor Gata3, which is important for cell lineage commitment and differentiation, is expressed in mouse renin cells under normal conditions and homeostatic threats. We identified a potential Gata3-binding site upstream of the renin gene leading us to hypothesize that Gata3 is essential for renin cell identity. We studied adult mice with conditional deletion of Gata3 in renin cells: Gata3fl/fl;Ren1dCre/+ (Gata3-cKO) and control Gata3fl/fl;Ren1d+/+ counterparts. Gata3 immunostaining revealed that Gata3-cKO mice had significantly reduced Gata3 expression in juxtaglomerular, mesangial, and smooth muscle cells, indicating a high degree of deletion of Gata3 in renin lineage cells. Gata3-cKO mice exhibited a significant increase in blood urea nitrogen, suggesting hypovolemia and/or compromised renal function. By immunostaining, renin-expressing cells appeared very thin compared with their normal plump shape in control mice. Renin cells were ectopically localized to Bowman's capsule in some glomeruli, and there was aberrant expression of actin-α2 signals in the mesangium, interstitium, and Bowman's capsule in Gata3-cKO mice. Distal tubules showed dilated morphology with visible intraluminal casts. Under physiological threat, Gata3-cKO mice exhibited a lower increase in mRNA levels than controls. Hematoxylin-eosin, periodic acid-Schiff, and Masson's trichrome staining showed increased glomerular fusion, absent cubical epithelial cells in Bowman's capsule, intraglomerular aneurysms, and tubular dilation. In conclusion, our results indicate that Gata3 is crucial to the identity of cells of the renin lineage.NEW & NOTEWORTHY Gata3, a dual zinc-finger transcription factor, is responsible for the identity and localization of renin cells in the kidney. Mice with a conditional deletion of Gata3 in renin lineage cells have abnormal kidneys with juxtaglomerular cells that lose their characteristic location and are misplaced outside and around arterioles and glomeruli. The fundamental role of Gata3 in renin cell development offers a new model to understand how transcription factors control cell location, function, and pathology.

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.