Renin-expressing Cells Research Articles

Fate and plasticity of renin precursors in development and disease

Renin-expressing cells appear early in the embryo and are distributed broadly throughout the body as organogenesis ensues. Their appearance in the metanephric kidney is a relatively late event in comparison with other organs such as the fetal adrenal gland. The functions of renin cells in extra renal tissues remain to be investigated. In the kidney, they participate locally in the assembly and branching of the renal arterial tree and later in the endocrine control of blood pressure and fluid-electrolyte homeostasis. Interestingly, this endocrine function is accomplished by the remarkable plasticity of renin cell descendants along the kidney arterioles and glomeruli which are capable of reacquiring the renin phenotype in response to physiological demands, increasing circulating renin and maintaining homeostasis. Given that renin cells are sensors of the status of the extracellular fluid and perfusion pressure, several signaling mechanisms (β-adrenergic receptors, Notch pathway, gap junctions and the renal baroreceptor) must be coordinated to ensure the maintenance of renin phenotype--and ultimately the availability of renin--during basal conditions and in response to homeostatic threats. Notably, key transcriptional (Creb/CBP/p300, RBP-J) and posttranscriptional (miR-330, miR125b-5p) effectors of those signaling pathways are prominent in the regulation of renin cell identity. The next challenge, it seems, would be to understand how those factors coordinate their efforts to control the endocrine and contractile phenotypes of the myoepithelioid granulated renin-expressing cell.

Conditional deletion of p53 and Rb in the renin-expressing compartment of the pancreas leads to a highly penetrant metastatic pancreatic neuroendocrine carcinoma

Efforts to model human pancreatic neuroendocrine tumors (PanNETs) in animals have been moderately successful, with minimal evidence for glucagonomas or metastatic spread. The renin gene, although classically associated with expression in the kidney, is also expressed in many other extrarenal tissues including the pancreas. To induce tumorigenesis within rennin-specific tissues, floxed alleles of p53 and Rb were selectively abrogated using Cre-recombinase driven by the renin promoter. The primary neoplasm generated is a highly metastatic islet cell carcinoma of the pancreas. Lineage tracing identifies descendants of renin-expressing cells as pancreatic alpha cells despite a lack of active renin expression in the mature pancreas. Both primary and metastatic tumors express high levels of glucagon; furthermore, an increased level of glucagon is found in the serum, identifying the pancreatic cancer as a functional glucagonoma. This new model is highly penetrant and exhibits robust frequency of metastases to the lymph nodes and the liver, mimicking human disease, and provides a useful platform for better understanding pancreatic endocrine differentiation and development, as well as islet cell carcinogenesis. The use of fluorescent reporters for lineage tracing of the cells contributing to disease initiation and progression provides an unique opportunity to dissect the timeline of disease, examining mechanisms of the metastatic process, as well as recovering primary and metastatic cells for identifying cooperating mutations that are necessary for progression of disease.

Development of renal renin-expressing cells does not involve PDGF-B-PDGFR-βsignaling

Apart from their endocrine functions renin-expressing cells play an important functional role as mural cells of the developing preglomerular arteriolar vessel tree in the kidney. The recruitment of renin-expressing cells from the mesenchyme to the vessel wall is not well understood. Assuming that it may follow more general lines of pericyte recruitment to endothelial tubes we have now investigated the relevance of the platelet-derived growth factor (PDGF)-B-PDGFR-β signaling pathway in this context. We studied renin expression in kidneys lacking PDGFR-β in these cells and in kidneys with reduced endothelial PDGF-B expression. We found that expression of renin in the kidneys under normal and stimulated conditions was not different from wild-type kidneys. As expected, PDGFR-β immunoreactivity was found in mesangial, adventitial and tubulo-interstitial cells but not in renin-expressing cells. These findings suggest that the PDGF-B-PDGFR-β signaling pathway is not essential for the recruitment of renin-expressing cells to preglomerular vessel walls in the kidney.

Connexin 43 is not essential for the control of renin synthesis and secretion

The juxtaglomerular areas of mammalian kidneys express the gap junction proteins connexin 37, 40, 43, and 45. Among these, Cx40 plays a major role for the function of juxtaglomerular renin-expressing cells, while Cx37 and Cx45 appear to be less relevant in this context. Since the role of the remaining Cx43 for the function of renin expression is not well understood, this study aimed to systematically characterize the direct role of Cx43 for renin expression and secretion. For this aim, we generated mice with endothelium and with renin cell-specific deletions of Cx43, and we characterized the regulation of renin expression and renin secretion in the kidneys of these mice on normal salt diet and during chronic challenge of the renin system by pretreatment of mice with a low-salt diet in combination with an angiotensin I-converting enzyme inhibitor. We found that renal renin mRNA abundance, plasma renin concentration, and systolic blood pressure did not differ between wild-type, Cx43(fl/fl) Ren1d(+/Cre) mice as well as Cx43(fl/fl) Tie-2(+/Cre) mice under basal conditions nor under chronic stimulation by salt depletion. The localization of renin-expressing cells was also regular in kidneys of all genotypes, and moreover, regulation of renin secretion by beta-adrenergic stimulation and renal perfusion pressure measured in isolated perfused kidneys of Cx43(fl/fl) Ren1d(+/Cre) and Cx43(fl/fl) Tie-2(+/Cre) mice was not different from control. We infer from these results that Cx43 plays if at all only a minor role for the functional control of renin-producing cells in the kidney.

Procollagen I-expressing renin cell precursors

Renin-expressing cells in the kidney normally appear as mural cells of developing preglomerular vessels and finally impose as granulated juxtaglomerular cells in adult kidneys. The differentiation of renin-expressing cells from the metanephric mesenchyme in general and the potential role of special precursor stages in particular is not well understood. Therefore, it was the aim of this study to search for renin cell precursors in the kidney. As an experimental model, we used kidneys of aldosterone synthase-deficient mice, which display a prominent compensatory overproduction of renin cells that are arranged in multilayered perivascular cell clusters. We found that the perivascular cell clusters contained two apparently distinct cell types, one staining positive for renin and another one staining positive for type I procollagen (PC1). It appeared as if PC1 and renin expression were inversely related at the cellular level. The proportion of renin-positive to PC1-positive cells in the clusters was inversely linked to the rate of salt intake, as was overall renin expression. Our findings suggest that the cells in the perivascular cell clusters can reversibly switch between PC1 and renin expression and that PC1-expressing cells might be precursors of renin cells. A few of those PC1-positive cells were found also in adult wild-type kidneys in the juxtaglomerular lacis cell area, in which renin expression can be induced on demand.

Adult Renal Mesenchymal Stem Cell–Like Cells Contribute to Juxtaglomerular Cell Recruitment

The renin-angiotensin-aldosterone system (RAAS) regulates BP and salt-volume homeostasis. Juxtaglomerular (JG) cells synthesize and release renin, which is the first and rate-limiting step in the RAAS. Intense pathologic stresses cause a dramatic increase in the number of renin-producing cells in the kidney, termed JG cell recruitment, but how this occurs is not fully understood. Here, we isolated renal CD44(+) mesenchymal stem cell (MSC)-like cells and found that they differentiated into JG-like renin-expressing cells both in vitro and in vivo. Sodium depletion and captopril led to activation and differentiation of these cells into renin-expressing cells in the adult kidney. In summary, CD44(+) MSC-like cells exist in the adult kidney and can differentiate into JG-like renin-producing cells under conditions that promote JG cell recruitment.

Severe Hyperaldosteronism in Neonatal Task3 Potassium Channel Knockout Mice Is Associated With Activation of the Intraadrenal Renin-Angiotensin System

Task3 K(+) channels are highly expressed in the adrenal cortex and contribute to the angiotensin II and K(+) sensitivity of aldosterone-producing glomerulosa cells. Adult Task3(-/-) mice display a partially autonomous aldosterone secretion, subclinical hyperaldosteronism, and salt-sensitive hypertension. Here, we investigated the age dependence of the adrenal phenotype of Task3(-/-) mice. Compared with adults, newborn Task3(-/-) mice displayed a severe adrenal phenotype with strongly increased plasma levels of aldosterone, corticosterone, and progesterone. This adrenocortical dysfunction was accompanied by a modified gene expression profile. The most strongly up-regulated gene was the protease renin. Real-time PCR corroborated the strong increase in adrenal renin expression, and immunofluorescence revealed renin-expressing cells in the zona fasciculata. Together with additional factors, activation of the local adrenal renin system is probably causative for the severely disturbed steroid hormone secretion of neonatal Task3(-/-) mice. The changes in gene expression patterns of neonatal Task3(-/-) mice could also be relevant for other forms of hyperaldosteronism.

Deletion of von Hippel–Lindau Protein Converts Renin-Producing Cells into Erythropoietin-Producing Cells

States of low perfusion pressure of the kidney associate with hyperplasia or expansion of renin-producing cells, but it is unknown whether hypoxia-triggered genes contribute to these changes. Here, we stabilized hypoxia-inducible transcription factors (HIFs) in mice by conditionally deleting their negative regulator, Vhl, using the Cre/loxP system with renin-1d promoter-driven Cre expression. Vhl (−/−(REN)) mice were viable and had normal BP. Deletion of Vhl resulted in constitutive accumulation of HIF-2α in afferent arterioles and glomerular cells and HIF-1α in collecting duct cells of the adult kidney. The preglomerular vascular tree developed normally, but far fewer renin-expressing cells were present, with more than 70% of glomeruli not containing renin cells at the typical juxtaglomerular position. Moreover, these mice had an attenuated expansion of renin-producing cells in response to a low-salt diet combined with an ACE inhibitor. However, renin-producing cells of Vhl (−/−(REN)) mice expressed the erythropoietin gene, and they were markedly polycythemic. Taken together, these results suggest that hypoxia-inducible genes, regulated by VHL, are essential for normal development and physiologic adaptation of renin-producing cells. In addition, deletion of Vhl shifts the phenotype of juxtaglomerular cells from a renin- to erythropoietin-secreting cell type, presumably in response to HIF-2 accumulation.

Nitric Oxide Can Directly Mediate Renin Cell Recruitment

See related article, pp 400–407 In this issue of Hypertension , Neubauer et al1 fit missing pieces into the puzzle of how renin production is controlled, when the demand for renin is high. Our understanding of the acute release of renin is much more complete than what we know about the long-term adaptations to stimuli of renin. Our scarce knowledge of the mechanisms mediating long-term renin stimulation is remarkable with regard to the clinical importance of renin. Hypertension, fluid and electrolyte homeostasis, as well as inflammation and fibrosis all may involve chronic renin stimulation.2 More than 400 million years ago, renin first appeared in organisms,3 and renin is often seen as the first hormone discovered. Shortly before the 20th century, Tigerstedt and Bergman showed that kidney extracts can elevate blood pressure, when intravenously infused.4 Today, we recognize that the actions of renin go far beyond that of controlling blood pressure, and we have detailed insight into how renin is released into the circulation.5 The major stimuli of short-term renin release are blood pressure decreases, β1-adrenergic stimulation, and low salt, whereas …

Endothelium-Derived Nitric Oxide Supports Renin Cell Recruitment Through the Nitric Oxide–Sensitive Guanylate Cyclase Pathway

Chronic challenge of renin-angiotensin causes recruitment of renin-producing cells in the kidney along the media layer of afferent arterioles and hypertrophy of cells in the juxtaglomerular apparatus. This study aimed to define the role of nitric oxide (NO) with regard to the recruitment pattern of renin-producing cells and to the possible pathways along which NO could act. We considered the hypothesis that endothelium-derived NO acts via NO-sensitive guanylate cyclase. Mice were treated with low-salt diet in combination with the angiotensin I-converting enzyme inhibitor enalapril for 3 weeks, which led to a 13-fold increase in renin expression associated with marked recruitment of renin cells in afferent arterioles and hypertrophy of the juxtaglomerular apparatus in wild-type mice. In wild-type mice additionally treated with the nonselective NO synthase inhibitor L-NAME, the recruitment of renin-expressing cells along the afferent arterioles was absent and juxtaglomerular hypertrophy was diminished. An almost identical attenuation of renin cell recruitment as with L-NAME treatment in wild-type mice was found in mice lacking the endothelial isoform of NO synthase. Treatment of mice lacking NO-sensitive guanylate cyclase in renin-expressing cells and preglomerular smooth muscle cells with low-salt diet in combination with the angiotensin I-converting enzyme inhibitor enalapril for 3 weeks produced juxtaglomerular hypertrophy like in wild-type mice, but no recruitment in afferent arterioles. These findings suggest that endothelium-derived NO and concomitant formation of cGMP in preglomerular renin cell precursors supports recruitment of renin-expressing cells along preglomerular vessels, but not in the juxtaglomerular apparatus.

Histone acetyl transferases CBP and p300 are necessary for maintenance of renin cell identity and transformation of smooth muscle cells to the renin phenotype.

In response to a homeostatic threat circulating renin increases by increasing the number of cells expressing renin by dedifferentiation and re-expression of renin in arteriolar smooth muscle cells (aSMCs) that descended from cells that expressed renin in early life. However, the mechanisms that govern the maintenance and reacquisition of the renin phenotype are not well understood. The cAMP pathway is important for renin synthesis and release: the transcriptional effects are mediated by binding of cAMP responsive element binding protein with its co-activators, CBP and p300, to the cAMP response element in the renin promoter. We have shown previously that mice with conditional deletion of CBP and p300 (cKO) in renin cells had severely reduced renin expression in adult life. In this study we investigated when the loss of renin-expressing cells in the cKO occurred and found that the loss of renin expression becomes evident after differentiation of the kidney is completed during postnatal life. To determine whether CBP/p300 is necessary for re-expression of renin we subjected cKO mice to low sodium diet + captopril to induce retransformation of aSMCs to the renin phenotype. The cKO mice did not increase circulating renin, their renin mRNA and protein expression were greatly diminished compared with controls, and only a few aSMCs re-expressed renin. These studies underline the crucial importance of the CREB/CBP/p300 complex for the ability of renin cells to retain their cellular memory and regain renin expression, a fundamental survival mechanism, in response to a threat to homeostasis.

Role of blood pressure in mediating the influence of salt intake on renin expression in the kidney

The salt intake of an organism controls the number of renin-producing cells in the kidney by yet undefined mechanisms. This study aimed to assess a possible mediator role of preglomerular blood pressure in the control of renin expression by oral salt intake. We used wild-type (WT) mice and mice lacking angiotensin II type 1a receptors (AT(1a)-/-) displaying an enhanced salt sensitivity to renin expression. In WT kidneys, we found renin-expressing cells at the ends of all afferent arterioles. A low-salt diet (0.02%) led to a moderate twofold increase in renin-expressing cells along afferent arterioles. In AT(1a)-/- mice, lowering of salt content led to a 12-fold increase in renin expression. Here, the renin-expressing cells were distributed along the preglomerular vascular tree in a typical distal-to-proximal distribution gradient which was most prominent at high salt intake and was obliterated at low salt intake by the appearance of renin-expressing cells in proximal parts of the preglomerular vasculature. While lowering of salt intake produced only a small drop in blood pressure in WT mice, the marked reduction of systolic blood pressure in AT(1a)-/- mice was accompanied by the disappearance of the distribution gradient from afferent arterioles to arcuate arteries. Unilateral renal artery stenosis in AT(1a)-/- mice on a normal salt intake produced a similar distribution pattern of renin-expressing cells as did low salt intake. Conversely, increasing blood pressure by administration of the NOS inhibitor N-nitro-l-arginine methyl ester or of the adrenergic agonist phenylephrine in AT(1a)-/- mice kept on low salt intake produced a similar distribution pattern of renin-producing cells as did normal salt intake alone. These findings suggest that changes in preglomerular blood pressure may be an important mediator of the influence of salt intake on the number and distribution of renin-producing cells in the kidney.

Control of Renin Synthesis and Secretion

The aspartyl protease renin is the rate limiting activity of the renin-angiotensin-aldosterone system (RAAS). Renin is synthesized as an enzymatically inactive proenzyme which is constitutively secreted from several tissues. Only renin-expressing cells in the kidney are capable of generating active renin from prorenin, which is stored in prominent vesicles and which is released into the circulation upon demand. The acute release of renin is controlled by cyclic adenosine monophosphate (cAMP) and by calcium signaling pathways, which in turn are activated by a number of systemic and local factors. Longer lasting challenges of renin secretion lead to changes in the number of renin-producing cells, which occur by a metaplastic transformation of renin cell precursors such as preglomerular vascular smooth muscle or extraglomerular mesangial cells. This review aims to briefly address the state of knowledge of these various aspects of renin synthesis and secretion and attempts to relate them to the in vivo situation, in particular in men.

Genes that Confer the Identity of the Renin Cell

Renin-expressing cells modulate BP, fluid-electrolyte homeostasis, and kidney development, but remarkably little is known regarding the genetic regulatory network that governs the identity of these cells. Here we compared the gene expression profiles of renin cells with most cells in the kidney at various stages of development as well as after a physiologic challenge known to induce the transformation of arteriolar smooth muscle cells into renin-expressing cells. At all stages, renin cells expressed a distinct set of genes characteristic of the renin phenotype, which was vastly different from other cell types in the kidney. For example, cells programmed to exhibit the renin phenotype expressed Akr1b7, and maturing cells expressed angiogenic factors necessary for the development of the kidney vasculature and RGS (regulator of G-protein signaling) genes, suggesting a potential relationship between renin cells and pericytes. Contrary to the plasticity of arteriolar smooth muscle cells upstream from the glomerulus, which can transiently acquire the embryonic phenotype in the adult under physiologic stress, the adult juxtaglomerular cell always possessed characteristics of both smooth muscle and renin cells. Taken together, these results identify the gene expression profile of renin-expressing cells at various stages of maturity, and suggest that juxtaglomerular cells maintain properties of both smooth muscle and renin-expressing cells, likely to allow the rapid control of body fluids and BP through both contractile and endocrine functions.

Transcriptional regulator RBP-J regulates the number and plasticity of renin cells

Renin-expressing cells are crucial in the control of blood pressure and fluid-electrolyte homeostasis. Notch receptors convey cell-cell signals that may regulate the renin cell phenotype. Because the common downstream effector for all Notch receptors is the transcription factor RBP-J, we used a conditional knockout approach to delete RBP-J in cells of the renin lineage. The resultant RBP-J conditional knockout (cKO) mice displayed a severe reduction in the number of renin-positive juxtaglomerular apparatuses (JGA) and a reduction in the total number of renin positive cells per JGA and along the afferent arterioles. This reduction in renin protein was accompanied by a decrease in renin mRNA expression, decreased circulating renin, and low blood pressure. To investigate whether deletion of RBP-J altered the ability of mice to increase the number of renin cells normally elicited by a physiological threat, we treated RBP-J cKO mice with captopril and sodium depletion for 10 days. The resultant treated RBP-J cKO mice had a 65% reduction in renin mRNA levels (compared with treated controls) and were unable to increase circulating renin. Although these mice attempted to increase the number of renin cells, the cells were unusually thin and had few granules and barely detectable amounts of immunoreactive renin. As a consequence, the cells were incapable of fully adopting the endocrine phenotype of a renin cell. We conclude that RBP-J is required to maintain basal renin expression and the ability of smooth muscle cells along the kidney vasculature to regain the renin phenotype, a fundamental mechanism to preserve homeostasis.

The Connexin40 A96S Mutation Causes Renin-Dependent Hypertension

Deletion of the gap-junction-forming protein connexin40 leads to renin-dependent hypertension in mice, but whether observed human variants in connexin40, such as A96S, promote hypertension is unknown. Here, we generated mice with the A96S variant in the mouse connexin40 gene. Although mice homozygous for the A96S mutations had normal expression patterns of connexin40 in the kidney, they were hypertensive, had sixfold higher plasma renin concentrations, and had 40% higher levels of renin mRNA than controls. Renin-expressing cells were aberrantly located outside the media layer of afferent arterioles, and increased renal perfusion pressure did not inhibit renin secretion from kidneys isolated from homozygous A96S mice. Treatment with a low-salt diet in combination with an ACE inhibitor increased renin mRNA levels, plasma renin concentrations, and the number of aberrantly localized renin-producing cells. Taken together, these findings suggest that the A96S mutation in connexin40 leads to renin-dependent hypertension in mice. Modulation of renin secretion by BP critically depends on functional connexin40; with the A96S mutation, the aberrant extravascular localization of renin-secreting cells in the kidney likely impairs the pressure-mediated inhibition of renin secretion.

Reciprocal expression of connexin 40 and 45 during phenotypical changes in renin-secreting cells

Gap junctional coupling of renin-producing cells is of major functional importance for the control of renin synthesis and release. This study was designed to determine the relevance of the vascular gap junction protein connexin 45 (Cx45) for the control of renin expression and secretion. By crossbreeding mice which drive Cre recombinase under the control of the endogenous renin promoter with mice harboring floxed Cx45 gene alleles, we generated viable mice with a deletion of Cx45 in the renin cell lineage. These mice were normotensive, and renin cells in their kidneys were normal with regard to localization and number. Sodium deficiency induced typical recruitment of renin-producing cells along afferent arterioles, whereas sodium overload resulted in a decrease in the number of cells expressing renin. Regulation of renin secretion by perfusion pressure, catecholamines, and angiotensin II from isolated kidneys of mice with renin cell-specific deletion of Cx45 was normal. Analyzing Cx45 promoter activity in cells of the preglomerular arteriolar tree by using mice driving the reporter gene LacZ under the control of the Cx45 promoter revealed strong staining in smooth muscle cells of the media, whereas renin-expressing cells were almost devoid of LacZ staining. Conversely, renin-producing cells, but not vascular smooth muscle cells expressed the gap junction protein Cx40. These findings suggest that Cx45 plays no major functional role in renin-producing cells, probably because the expression of Cx45 is downregulated in these cells. Since renin-producing cells in the adult kidney can reversibly transform into vascular smooth muscle cells and vice versa, our findings on connexin expression indicate that these phenotype switches are paralleled by characteristic reciprocal changes in the transcriptional activity of Cx40 and Cx45 genes.

Developmental renin expression in mice with a defective renin-angiotensin system

During nephrogenesis, renin expression shifts from the vessel walls of interlobular arteries to the terminal portions of afferent arterioles in a wavelike pattern. Since the mechanisms responsible for the developmental deactivation of renin expression are as yet unknown, we hypothesized that the developing renin-angiotensin system (RAS) may downregulate itself via negative feedback to prevent overactivity of renin. To test for a possible role of angiotensin II in the developmental deactivation of renin expression, we studied the development of intrarenal renin expression in mice lacking ANG II AT1a, AT1b, or AT2 receptors and in animals with abolished circulating ANG II due to deletion of the gene for angiotensin I-converting enzyme (ACE). The development of intrarenal renin expression was normal in mice lacking ANG II AT1b or AT2 receptors. In animals lacking both ANG II AT1a and AT1b receptors, ACE, or ANG II AT1a receptors, renin expression was normal early and renin disappeared from mature vessels until development of cortical interlobular and afferent arterioles began. The development of cortical vessels in these genotypes was accompanied by a markedly increased number of renin-expressing cells, many of which were ectopically located and attached in a grapelike fashion to the outer vessel perimeter. Although the number of renin-expressing cells declined during final maturation of the kidneys, the atypical distribution pattern of renin cells was maintained. These findings suggest that ANG II does not play a central role in the typical developmental shift in renin expression from the arcuate vessels to the afferent arterioles. During postnatal maturation of mouse kidneys, interruption of the RAS causes severe hyperplasia of renin cells via a mechanism that centrally involves AT(1a) receptors. However, the distribution pattern of renin cells in adult kidneys with an interrupted RAS does not mimic any normal developmental stage since renin expression is frequently found in cells outside the arteriolar vessel walls in RAS mutants.

Connexin 37 is dispensable for the control of the renin system and for positioning of renin-producing cells in the kidney

Within the juxtaglomerular apparatus, renin-producing cells and endothelial cells of the afferent arterioles express connexin (Cx)37 and Cx40, which form abundant gap junctions among these cells. Deletion of Cx40 leads to strong hyperreninemia and ectopic localization of renin-producing cells; however, the relevance of Cx37 for the renin system in the kidney has not been investigated. We therefore studied renin expression and renin secretion in kidneys from Cx37-deficient mice, both on normal salt diet and during chronic challenge of the renin system by pretreatment of mice with a low-salt diet in combination with an angiotensin I-converting enzyme inhibitor. This treatment procedure strongly enhances renin gene expression and renin secretion. We found that renal renin mRNA abundance and plasma renin concentration did not differ between wild-type and Cx37-/- mice under normal conditions. The stimulation of renin gene expression and renin secretion by salt depletion was even more pronounced in Cx37-/- as compared to wild-type mice. The regulation of renin secretion from isolated perfused kidneys by perfusion pressure and by angiotensin II was normal in Cx37-/- mice. In addition, the localization of renin-expressing cells was also regular in Cx37-/- kidneys. Finally, the expression pattern of other vascular Cxs such as Cx40, Cx43, and Cx45 was not altered in Cx37-/- kidneys. Our findings suggest that Cx37 is not essential for normal development and function of renin-producing cells. As a consequence, it appears unlikely that Cx40 exerts its important function in renin-producing cells via Cx37/Cx40 heteromeric gap junctions.

Dominant Renin Gene Mutations Associated with Early-Onset Hyperuricemia, Anemia, and Chronic Kidney Failure

Through linkage analysis and candidate gene sequencing, we identified three unrelated families with the autosomal-dominant inheritance of early onset anemia, hypouricosuric hyperuricemia, progressive kidney failure, and mutations resulting either in the deletion (p.Leu16del) or the amino acid exchange (p.Leu16Arg) of a single leucine residue in the signal sequence of renin. Both mutations decrease signal sequence hydrophobicity and are predicted by bioinformatic analyses to damage targeting and cotranslational translocation of preprorenin into the endoplasmic reticulum (ER). Transfection and in vitro studies confirmed that both mutations affect ER translocation and processing of nascent preprorenin, resulting either in reduced (p.Leu16del) or abolished (p.Leu16Arg) prorenin and renin biosynthesis and secretion. Expression of renin and other components of the renin-angiotensin system was decreased accordingly in kidney biopsy specimens from affected individuals. Cells stably expressing the p.Leu16del protein showed activated ER stress, unfolded protein response, and reduced growth rate. It is likely that expression of the mutant proteins has a dominant toxic effect gradually reducing the viability of renin-expressing cells. This alters the intrarenal renin-angiotensin system and the juxtaglomerular apparatus functionality and leads to nephron dropout and progressive kidney failure. Our findings provide insight into the functionality of renin-angiotensin system and stress the importance of renin analysis in families and individuals with early onset hyperuricemia, anemia, and progressive kidney failure.