Prorenin receptor is critical for nephron progenitors

Principle role of the (pro)renin receptor system in cardiovascular and metabolic diseases: An update

(Pro)renin receptor (PRR), along with its soluble form, sPRR, functions not only as a crucial activator of the local renin-angiotensin system but also engages with and activates various angiotensin II-independent signaling pathways, thus playing complex and significant roles in numerous physiological and pathophysiological processes, including cardiovascular and metabolic disorders. This article reviews current knowledge on the intracellular partners of the PRR system and explores its physiological and pathophysiological impacts on cardiovascular diseases as well as conditions related to glucose and lipid metabolism, such as hypertension, heart disease, liver disease, diabetes, and diabetic complications. Targeting the PRR system could emerge as a promising therapeutic strategy for treating these conditions. Elevated levels of circulating sPRR might indicate the severity of these diseases, potentially serving as a biomarker for diagnosis and prognosis in clinical settings. A comprehensive understanding of the functions and regulatory mechanisms of the PRR system could facilitate the development of novel therapeutic approaches for the prevention and management of cardiovascular and metabolic diseases.

Nephron specific ATP6AP2 knockout increases urinary excretion of fatty acids and decreases renal cortical megalin expression

ATP6AP2 knockout in the renal nephron impairs receptor-mediated endocytosis, increasing urinary albumin and glucose excretion and impairing weight gain. Nonesterified fatty acids (NEFA) in urine are bound to albumin and reabsorbed in the proximal tubule through receptor-mediated endocytosis by the megalin-cubilin complex. We hypothesized that ATP6AP2 knockout increases urinary NEFA excretion through a reduction in megalin. Ten-week-old male C57BL/6 mice with nephron specific inducible ATP6AP2 knockout and noninduced controls were fed either normal diet (ND 12% fat) or high fat diet (HFD 45% fat) for 6 months. ATP6AP2 knockout significantly increased urine albumin:creatinine ratio in both ND and HFD fed mice while normalized urine NEFA concentration increased 489% and 259% in ND and HFD knockout mice compared to respective controls. Knockout decreased renal cortical megalin mRNA by 47% on ND and 49% on HFD while megalin protein expression decreased by 36% and 44% respectively. At the same time, markers of mTOR activity were increased while autophagy was impaired. Our results indicate that nephron specific ATP6AP2 knockout increases urinary NEFA excretion in the setting of impaired receptor-mediated endocytosis. Further investigation should determine whether ATP6AP2 contributes to obesity related ectopic lipid deposition in the proximal tubule.

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.

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.

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

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

Renin-angiotensin system in mammalian kidney development

Mutations in the genes of the renin-angiotensin system result in congenital anomalies of the kidney and urinary tract (CAKUT), the main cause of end-stage renal disease in children. The molecular mechanisms that cause CAKUT are unclear in most cases. To improve the care of children with CAKUT, it is critical to determine the underlying mechanisms of CAKUT. In this review, we discuss recent advances that have helped to better understand how disruption of the renin-angiotensin system during kidney development contributes to CAKUT.

Role of the renin-angiotensin system in kidney development and programming of adult blood pressure

Adverse events during fetal life such as insufficient protein intake or elevated transfer of glucocorticoid to the fetus may impact cardiovascular and metabolic health later in adult life and are associated with increased incidence of type 2 diabetes, ischemic heart disease and hypertension. Several adverse factors converge and suppress the fetal renin-angiotensin-aldosterone system (RAAS). The aim of this review is to summarize data on the significance of RAAS for kidney development and adult hypertension. Genetic inactivation of RAAS in rodents at any step from angiotensinogen to angiotensin II (ANGII) type 1 receptor (AT1) receptors or pharmacologic inhibition leads to complex developmental injury to the kidneys that has also been observed in human case reports. Deletion of the 'protective' arm of RAAS, angiotensin converting enzyme (ACE) 2 (ACE-2) and G-protein coupled receptor for Angiotensin 1-7 (Mas) receptor does not reproduce the AT1 phenotype. The changes comprise fewer glomeruli, thinner cortex, dilated tubules, thicker arterioles and arteries, lack of vascular bundles, papillary atrophy, shorter capillary length and volume in cortex and medulla. Altered activity of systemic and local regulators of fetal-perinatal RAAS such as vitamin D and cyclooxygenase (COX)/prostaglandins are associated with similar injuries. ANGII-AT1 interaction drives podocyte and epithelial cell formation of vascular growth factors, notably vascular endothelial growth factor (VEGF) and angiopoietins (Angpts), which support late stages of glomerular and cortical capillary growth and medullary vascular bundle formation and patterning. RAAS-induced injury is associated with lower glomerular filtration rate (GFR), lower renal plasma flow, kidney fibrosis, up-regulation of sodium transporters, impaired sodium excretion and salt-sensitive hypertension. The renal component and salt sensitivity of programmed hypertension may impact dietary counseling and choice of pharmacological intervention to treat hypertension.

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

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

Stromal prorenin receptor is critical for normal kidney development

Formation of the metanephric kidney requires coordinated interaction among the stroma, ureteric bud, and cap mesenchyme. The transcription factor Foxd1, a specific marker of renal stromal cells, is critical for normal kidney development. The prorenin receptor (PRR), a receptor for renin and prorenin, is also an accessory subunit of the vacuolar proton pump V-ATPase. Global loss of PRR is embryonically lethal in mice, indicating an essential role of the PRR in embryonic development. Here, we report that conditional deletion of the PRR in Foxd1⁺ stromal progenitors in mice (cKO) results in neonatal mortality. The kidneys of surviving mice show reduced expression of stromal markers Foxd1 and Meis1 and a marked decrease in arterial and arteriolar development with the subsequent decreased number of glomeruli, expansion of Six2⁺ nephron progenitors, and delay in nephron differentiation. Intrarenal arteries and arterioles in cKO mice were fewer and thinner and showed a marked decrease in the expression of renin, suggesting a central role for the PRR in the development of renin-expressing cells, which in turn are essential for the proper formation of the renal arterial tree. We conclude that stromal PRR is crucial for the appropriate differentiation of the renal arterial tree, which in turn may restrict excessive expansion of nephron progenitors to promote a coordinated and proper morphogenesis of the nephrovascular structures of the mammalian kidney.

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

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

Interplay between the renin-angiotensin system, the canonical WNT/β-catenin pathway and PPARγ in hypertension

PURPOSE OF REVIEW

Heterogeneous causes can determinate hypertension.

RECENT FINDINGS

The renin-angiotensin system (RAS) has a major role in the pathophysiology of blood pressure. Angiotensin II and aldosterone are overexpressed during hypertension and lead to hypertension development and its cardiovascular complications. In several tissues, the overactivation of the canonical WNT/β-catenin pathway leads to inactivation of peroxisome proliferator-activated receptor gamma (PPARγ), while PPARγ stimulation induces a decrease of the canonical WNT/β-catenin pathway. In hypertension, the WNT/β-catenin pathway is upregulated, whereas PPARγ is decreased. The WNT/β-catenin pathway and RAS regulate positively each other during hypertension, whereas PPARγ agonists can decrease the expression of both the WNT/β-catenin pathway and RAS. We focus this review on the hypothesis of an opposite interplay between PPARγ and both the canonical WNT/β-catenin pathway and RAS in regulating the molecular mechanism underlying hypertension. The interactions between PPARγ and the canonical WNT/β-catenin pathway through the regulation of the renin-angiotensin system in hypertension may be an interesting way to better understand the actions and the effects of PPARγ agonists as antihypertensive drugs.

The macula densa prorenin receptor is essential in renin release and blood pressure control

The prorenin receptor (PRR) was originally proposed to be a member of the renin-angiotensin system (RAS); however, recent work questioned their association. The present paper describes a functional link between the PRR and RAS in the renal juxtaglomerular apparatus (JGA), a classic anatomical site of the RAS. PRR expression was found in the sensory cells of the JGA, the macula densa (MD), and immunohistochemistry-localized PRR to the MD basolateral cell membrane in mouse, rat, and human kidneys. MD cell PRR activation led to MAP kinase ERK1/2 signaling and stimulation of PGE₂ release, the classic pathway of MD-mediated renin release. Exogenous renin or prorenin added to the in vitro microperfused JGA-induced acute renin release, which was inhibited by removing the MD or by the administration of a PRR decoy peptide. To test the function of MD PRR in vivo, we established a new mouse model with inducible conditional knockout (cKO) of the PRR in MD cells based on neural nitric oxide synthase-driven Cre-lox recombination. Deletion of the MD PRR significantly reduced blood pressure and plasma renin. Challenging the RAS by low-salt diet + captopril treatment caused further significant reductions in blood pressure, renal renin, cyclooxygenase-2, and microsomal PGE synthase expression in cKO vs. wild-type mice. These results suggest that the MD PRR is essential in a novel JGA short-loop feedback mechanism, which is integrated within the classic MD mechanism to control renin synthesis and release and to maintain blood pressure.

The prorenin receptor in the cardiovascular system and beyond

Since the prorenin receptor (PRR) was first reported, its physiological role in many cellular processes has been under intense scrutiny. The PRR is currently recognized as a multifunctional receptor with major roles as an accessory protein of the vacuolar-type H+-ATPase and as an intermediary in the Wnt signaling pathway. As a member of the renin-angiotensin system (RAS), the PRR has demonstrated to be of relevance in cardiovascular diseases (CVD) because it can activate prorenin and enhance the enzymatic activity of renin, thus promoting angiotensin II formation. Indeed, there is an association between PRR gene polymorphisms and CVD. Independent of angiotensin II, the activation of the PRR further stimulates intracellular signals linked to fibrosis. Studies using tissues and cells from a variety of organs and systems have supported its roles in multiple functions, although some remain controversial. In the brain, the PRR appears to be involved in the central regulation of blood pressure via activation of RAS- and non-RAS-dependent mechanisms. In the heart, the PRR promotes atrial structural and electrical remodeling. Nonetheless, animals overexpressing the PRR do not exhibit cardiac injury. In the kidney, the PRR is involved in the development of ureteric bud branching, urine concentration, and regulation of blood pressure. There is great interest in the PRR contributions to T cell homeostasis and to the development of visceral and brown fat. In this mini-review, we discuss the evidence for the pathophysiological roles of the PRR with emphasis in CVD.

Renin cells in homeostasis, regeneration and immune defence mechanisms

An accumulating body of evidence suggests that renin-expressing cells have developed throughout evolution as a mechanism to preserve blood pressure and fluid volume homeostasis as well as to counteract a number of homeostatic and immunological threats. In the developing embryo, renin precursor cells emerge in multiple tissues, where they differentiate into a variety of cell types. The function of those precursors and their progeny is beginning to be unravelled. In the developing kidney, renin-expressing cells control the morphogenesis and branching of the renal arterial tree. The cells do not seem to fully differentiate but instead retain a degree of developmental plasticity or molecular memory, which enables them to regenerate injured glomeruli or to alter their phenotype to control blood pressure and fluid-electrolyte homeostasis. In haematopoietic tissues, renin-expressing cells might regulate bone marrow differentiation and participate in a circulating leukocyte renin-angiotensin system, which acts as a defence mechanism against infections or tissue injury. Furthermore, renin-expressing cells have an intricate lineage and functional relationship with erythropoietin-producing cells and are therefore central to two endocrine systems - the renin-angiotensin and erythropoietin systems - that sustain life by controlling fluid volume and composition, perfusion pressure and oxygen delivery to tissues. However, loss of the homeostatic control of these systems following dysregulation of renin-expressing cells can be detrimental, with serious pathological events.

(Pro)renin Receptor Is an Amplifier of Wnt/β-Catenin Signaling in Kidney Injury and Fibrosis

The (pro)renin receptor (PRR) is a transmembrane protein with multiple functions. However, its regulation and role in the pathogenesis of CKD remain poorly defined. Here, we report that PRR is a downstream target and an essential component of Wnt/β-catenin signaling. In mouse models, induction of CKD by ischemia-reperfusion injury (IRI), adriamycin, or angiotensin II infusion upregulated PRR expression in kidney tubular epithelium. Immunohistochemical staining of kidney biopsy specimens also revealed induction of renal PRR in human CKD. Overexpression of either Wnt1 or β-catenin induced PRR mRNA and protein expression in vitro Notably, forced expression of PRR potentiated Wnt1-mediated β-catenin activation and augmented the expression of downstream targets such as fibronectin, plasminogen activator inhibitor 1, and α-smooth muscle actin (α-SMA). Conversely, knockdown of PRR by siRNA abolished β-catenin activation. PRR potentiation of Wnt/β-catenin signaling did not require renin, but required vacuolar H+ ATPase activity. In the mouse model of IRI, transfection with PRR or Wnt1 expression vectors promoted β-catenin activation, aggravated kidney dysfunction, and worsened renal inflammation and fibrotic lesions. Coexpression of PRR and Wnt1 had a synergistic effect. In contrast, knockdown of PRR expression ameliorated kidney injury and fibrosis after IRI. These results indicate that PRR is both a downstream target and a crucial element in Wnt signal transmission. We conclude that PRR can promote kidney injury and fibrosis by amplifying Wnt/β-catenin signaling.

Wnt signaling, a novel pathway regulating blood pressure? State of the art review

Recent antihypertensive trials show conflicting results on blood pressure (BP) targets in patient populations with different metabolic profiles, with lowest benefit from tight BP control observed in patients with type 2 diabetes mellitus. This paradox could arise from the heterogeneity of study populations and underscores the importance of precision medicine initiatives towards understanding and treating hypertension. Wnt signaling pathways and genetic variations in its signaling peptides have been recently associated with metabolic syndrome, hypertension and diabetes, generating a breakthrough for advancement of precision medicine in the field of hypertension. We performed a review of PubMed for publications addressing the contributions of Wnt to BP regulation and hypertension. In addition, we performed a manual search of the reference lists for relevant articles, and included unpublished observations from our laboratory. There is emerging evidence for Wnt's role in BP regulation and its involvement in the pathogenesis of hypertension. Wnt signaling has pleiotropic effects on distinct pathways that involve vascular smooth muscle plasticity, and cardiac, renal, and neural physiology. Hypertension is a heterogeneous disease with unique molecular pathways regulating its response to therapy. Recognition of these pathways is a prerequisite to identify novel targets for drug development and personalizing medicine. A review of Wnt signaling reveals its emerging role in BP regulation and as a target for novel drug development that has the potential to transform the therapy of hypertension in specific populations.

(Pro)renin receptor as a therapeutic target for the treatment of cardiovascular diseases?

The discovery of the (pro)renin receptor [(P)RR] 15years ago stimulated ideas on prorenin being more than renin's inactive precursor. Indeed, binding of prorenin to the (P)RR induces a conformational change in the prorenin molecule, allowing it to display angiotensin-generating activity, and additionally results in intracellular signaling in an angiotensin-independent manner. However, the prorenin levels required to observe these angiotensin-dependent and -independent effects of the (P)RR are many orders above its in vivo concentrations, both under normal and pathological conditions. Given this requirement, the idea that the (P)RR has a function within the renin-angiotensin system (RAS) is now being abandoned. Instead, research is now focused on the (P)RR as an accessory protein of vacuolar H⁺-ATPase (V-ATPase), potentially determining its integrity. Acting as an adaptor between Frizzled co-receptor LRP6 and V-ATPase, the (P)RR appears to be indispensable for Wnt/β-catenin signaling, thus explaining why (P)RR deletion (unlike renin deletion) is lethal even when restricted to specific cells, such as cardiomyocytes, podocytes and smooth muscle cells. Furthermore, recent studies suggest that the (P)RR may play important roles in lipoprotein metabolism and overall energy metabolism. In this review, we summarize the controversial RAS-related effects of the (P)RR, and critically review the novel non-RAS-related functions of the (P)RR, ending with a discussion on the potential of targeting the (P)RR to treat cardiovascular diseases.

Prorenin receptor in kidney development

Prorenin receptor (PRR), a receptor for renin and prorenin and an accessory subunit of the vacuolar proton pump H⁺-ATPase, is expressed in the developing kidney. Global loss of PRR is lethal in mice, and PRR mutations are associated with a high blood pressure, left ventricular hypertrophy and X-linked mental retardation in humans. With the advent of modern gene targeting techniques, including conditional knockout approaches, several recent studies have demonstrated critical roles for the PRR in several lineages of the developing kidney. PRR signaling has been shown to be essential for branching morphogenesis of the ureteric bud (UB), nephron progenitor survival and nephrogenesis. PRR regulates these developmental events through interactions with other transcription and growth factors. Several targeted PRR knockout animal models have structural defects mimicking congenital anomalies of the kidney and urinary tract observed in humans. The aim of this review, is to highlight new insights into the cellular and molecular mechanisms by which PRR may regulate UB branching, terminal differentiation and function of UB-derived collecting ducts, nephron progenitor maintenance, progression of nephrogenesis and normal structural kidney development and function.

(Pro)renin and (pro)renin receptor expression during kidney development in neonates

Although a recent study demonstrated that the (pro)renin receptor ((P)RR) was highly expressed in the developing kidney during the mouse embryonic development, the mechanism by which (P)RR supports renal development in humans is not fully understood. In this study, we examined the plasma levels of (pro)renin and soluble (P)RR (s(P)RR) in cord blood and neonates as well as (P)RR expression in human kidney tissues. Samples were collected from 57 preterm and 67 full-term human neonates. (Pro)renin and s(P)RR levels were measured using enzyme-linked immunosorbent assays. Additionally, we performed an immunohistochemical (IHC) analysis of kidney tissues from neonates and minor glomerular abnormalities in order to assess (P)RR expression in the kidney. Plasma (pro)renin and s(P)RR levels in cord blood were significantly higher in preterm neonates than in full-term neonates. Four weeks after birth, these differences were no longer evident for either plasma (pro)renin or s(P)RR levels between the two groups. Importantly, plasma (pro)renin and s(P)RR levels in cord blood were inversely correlated with gestational age. Furthermore, IHC indicated that renal expression levels of (P)RR in neonates were stronger than those in minor glomerular abnormalities.

CONCLUSION

(P)RR may play a pivotal role in prenatal renal development in humans. What is Known: • Renal renin-angiotensin system (RAS) has several pathophysiologic functions not only in blood pressure regulation but also in pediatric renal disease. • Renal RAS activation plays a key role of renal development during gestation. What is New : • Plasma (pro)renin and soluble (pro)renin receptor (s(P)RR) levels in cord blood were significantly higher in preterm neonates than in full-term neonates. • Immunohistochemical analysis of kidney tissue indicated that renal expression levels of (P)RR in neonates were stronger than in minor glomerular abnormalities.

The nephron (pro)renin receptor: function and significance

The (pro)renin receptor (PRR) is a multifunctional protein that is part of the renin-angiotensin system and is an important accessory molecule for the vacuolar H+-ATPase. The PRR is widely expressed in the kidney with relatively high abundance in the distal nephron. Determining the physiological relevance of the PRR has been challenging due to early lethality in whole animal and cell-specific PRR knockout models. Recently, viable renal cell-specific PRR knockout mice have been developed; these studies suggest that PRR in the nephron can modulate renal function via angiotensin II (ANG II)-dependent and -independent cell signaling pathways. In this mini-review, we highlight new developments in nephron PRR function in health and in pathophysiological conditions.