Role of angiotensin in renal vascular development

Progressive Kidney Failure by Angiotensinogen Inactivation in the Germline

BACKGROUND

Autosomal recessive renal tubular dysgenesis is a rare, usually fatal inherited disorder of the renin-angiotensis system (RAS). Herein, we report an adolescent individual experiencing an unknown chronic kidney disease and aim to provide novel insights into disease mechanisms.

METHODS

Exome sequencing for a gene panel associated with renal disease was performed. The RAS was assessed by comprehensive biochemical analysis in blood. Renin expression was determined in primary tubular cells by quantitative polymerase chain reaction and in situ hybridization on kidney biopsy samples. Allele frequencies of heterozygous and biallelic deleterious variants were determined by analysis of the Genomics England 100,000 Genomes Project.

RESULTS

The patient was delivered prematurely after oligohydramnios was detected during pregnancy. Postnatally, he recovered from third-degree acute kidney injury but developed chronic kidney disease stage G3b over time. Exome sequencing revealed a previously reported pathogenic homozygous missense variant, p.(Arg375Gln), in the AGT (angiotensinogen) gene. Blood AGT concentrations were low, but plasma renin concentration and gene expression in kidney biopsy, vascular, and tubular cells revealed strong upregulation of renin. Angiotensin II and aldosterone in blood were not abnormally elevated.

CONCLUSIONS

Renal tubular dysgenesis may present as chronic kidney disease with a variable phenotype, necessitating broad genetic analysis for diagnosis. Functional analysis of the RAS in a patient with AGT mutation revealed novel insights regarding compensatory upregulation of renin in vascular and tubular cells of the kidney and in plasma in response to depletion of AGT substrate as a source of Ang II (similarly observed with hepatic AGT silencing for the treatment of hypertension).

Inhibition of the AT1R agonistic autoantibody in a rat model of preeclampsia improves fetal growth in late gestation

Placenta ischemia, the initiating event in preeclampsia (PE), is associated with fetal growth restriction. Inhibition of the agonistic autoantibody against the angiotensin type 1 receptor AT1-AA, using an epitope-binding inhibitory peptide ('n7AAc') attenuates increased blood pressure at gestational day (G)19 in the clinically relevant reduced uterine perfusion pressure (RUPP) model of PE. Thus we tested the hypothesis that maternal administration of 'n7AAc' does not transfer to the fetus, improves uterine blood flow and fetal growth, and attenuates elevated placental expression of miRNAs implicated in PE and FGR. Sham or RUPP surgery was performed at G14 with vehicle or 'n7AAc' (144 µg/day) administered via an osmotic pump from G14 to G20. Maternal plasma levels of the peptide on G20 were 16.28 ± 4.4 nM, and fetal plasma levels were significantly lower at 1.15 ± 1.7 nM (P = 0.0007). The uterine artery resistance index was significantly elevated in RUPP (P < 0.0001) but was not increased in 'n7AAc'-RUPP or 'n7AAc'-Sham versus Sham. A significant reduction in fetal weight at G20 in RUPP (P = 0.003) was not observed in 'n7AAc'-RUPP. Yet, percent survival was reduced in RUPP (P = 0.0007) and 'n7AAc'-RUPP (P < 0.0002). Correlation analysis indicated the reduction in percent survival during gestation was specific to the RUPP (r = 0.5342, P = 0.043) and independent of 'n7AAc'. Placental miR-155 (P = 0.0091) and miR-181a (P = 0.0384) expression was upregulated in RUPP at G20 but was not elevated in 'n7AAc'-RUPP. Collectively, our results suggest that maternal administration of 'n7AAc' does not alter fetal growth in the RUPP implicating its potential as a therapeutic for the treatment of PE.NEW & NOTEWORTHY The seven amino acid inhibitory peptide to the AT1-AA ('n7AAc') has limited transfer to the fetus at gestational day 20, improves uterine blood flow and fetal growth in the reduced uterine perfusion pressure model of preeclampsia (PE), and does not impair fetal survival during gestation in sham-operated or placental ischemic rats. Collectively, these findings suggest that maternal administration of 'n7AAc' as an effective strategy for the treatment of PE is associated with improved outcomes in the fetus.

Phylogeny and ontogeny of the renin-angiotensin system: Current view and perspectives

The renin-angiotensin system (RAS) evolved early among vertebrates and remains functioning throughout the vertebrate phylogeny and has adapted to various environments. The RAS is crucial for the regulation of blood pressure, fluid-electrolyte balance and tissue homeostasis. The RAS is also expressed during early ontogeny in renal and extra-renal tissues, and exerts unique vascular growth and differentiation functions. In this brief review, we describe advances from molecular-genetic and whole animal approaches and discuss similarities and unique aspects of the RAS in the context of embryonic development and vertebrates' phylogeny.

Ontogeny of renin gene expression in the chicken, Gallus gallus

Renin or a renin-like enzyme evolved in ancestral vertebrates and is conserved along the vertebrate phylogeny. The ontogenic development of renin, however, is not well understood in nonmammalian vertebrates. We aimed to determine the expression patterns and relative abundance of renin mRNA in pre- and postnatal chickens (Gallus gallus, White Leghorn breed). Embryonic day 13 (E13) embryos show renal tubules, undifferentiated mesenchymal structures, and a small number of developing glomeruli. Maturing glomeruli are seen in post-hatch day 4 (D4) and day 30 (D30) kidneys, indicating that nephrogenic activity still exists in kidneys of 4-week-old chickens. In E13 embryos, renin mRNA measured by quantitative polymerase chain reaction in the adrenal glands is equivalent to the expression in the kidneys, whereas in post-hatch D4 and D30 maturing chicks, renal renin expressions increased 2-fold and 11-fold, respectively. In contrast, relative renin expression in the adrenals became lower than in the kidneys. Furthermore, renin expression is clearly visible by in situ hybridization in the juxtaglomerular (JG) area in D4 and D30 chicks, but not in E13 embryos. The results suggest that in chickens, renin evolved in both renal and extrarenal organs at an early stage of ontogeny and, with maturation, became localized to the JG area. Clear JG structures are not morphologically detectable in E13 embryos, but are visible in 30-day-old chicks, supporting this concept.

Angiotensin receptor blockade in juvenile male rat offspring: Implications for long-term cardio-renal health

Inhibition of the renin-angiotensin system in early postnatal life is a potential therapeutic approach to prevent long-term cardiovascular and kidney diseases in individuals born small. We determined the long-term effects of juvenile losartan treatment on cardiovascular and kidney function in control male rat offspring and those exposed to uteroplacental insufficiency and born small. Bilateral uterine vessel ligation (Restricted) or sham (Control) surgery was performed in late gestation in Wistar Kyoto rats. At weaning, male offspring were randomly assigned to receive losartan in their drinking water or drinking water alone from 5 to 8 weeks of age, and followed to 26 weeks of age. Systolic blood pressure and kidney function were assessed throughout the study. Pressure myography was used to assess passive mechanical wall properties in mesenteric and femoral arteries from 26-week-old offspring. Losartan treatment for three weeks lowered systolic blood pressure in both Control and Restricted groups but this difference was not sustained after the cessation of treatment. Losartan, irrespective of birth weight, mildly increased renal tubulointerstitial fibrosis when assessed at 26 weeks of age. Mesenteric artery stiffness was increased by the early losartan treatment, and was associated with increased collagen and decreased elastin content. Losartan also exerted long-term increases in fat mass and decreases in skeletal muscle mass. In this study, untreated Restricted offspring did not develop hypertension, vascular dysfunction or kidney changes as anticipated. Regardless, we demonstrate that short-term losartan treatment in the juvenile period negatively affects postnatal growth, and kidney and vascular parameters in adulthood, irrespective of birth weight. The long-term effects of early-life losartan treatment warrant further consideration in settings where the potential benefits may outweigh the risks; i.e. when programmed adulthood diseases are apparent and in childhood cardiovascular and kidney diseases.

Renin-angiotensin system in vertebrates: phylogenetic view of structure and function

Renin substrate, biological renin activity, and/or renin-secreting cells in kidneys evolved at an early stage of vertebrate phylogeny. Angiotensin (Ang) I and II molecules have been identified biochemically in representative species of all vertebrate classes, although variation occurs in amino acids at positions 1, 5, and 9 of Ang I. Variations have also evolved in amino acid positions 3 and 4 in some cartilaginous fish. Angiotensin receptors, AT₁ and AT₂ homologues, have been identified molecularly or characterized pharmacologically in nonmammalian vertebrates. Also, various forms of angiotensins that bypass the traditional renin-angiotensin system (RAS) cascades or those from large peptide substrates, particularly in tissues, are present. Nonetheless, the phylogenetically important functions of RAS are to maintain blood pressure/blood volume homeostasis and ion-fluid balance via the kidney and central mechanisms. Stimulation of cell growth and vascularization, possibly via paracrine action of angiotensins, and the molecular biology of RAS and its receptors have been intensive research foci. This review provides an overview of: (1) the phylogenetic appearance, structure, and biochemistry of the RAS cascade; (2) the properties of angiotensin receptors from comparative viewpoints; and (3) the functions and regulation of the RAS in nonmammalian vertebrates. Discussions focus on the most fundamental functions of the RAS that have been conserved throughout phylogenetic advancement, as well as on their physiological implications and significance. Examining the biological history of RAS will help us analyze the complex RAS systems of mammals. Furthermore, suitable models for answering specific questions are often found in more primitive animals.

Impaired angiogenesis in the enalapril-treated neonatal rat kidney

PURPOSE

Nephrogenesis is normally accompanied by a tightly regulated and efficient vascularization. We investigated the effect of angiotensin II inhibition on angiogenesis in the developing rat kidney.

METHODS

Newborn rat pups were treated with enalapril (30 mg/kg/day) or vehicle (control) for 7 days after birth. Renal histological changes were checked using Hematoxylin & Eosin staining. We also investigated the intrarenal expression of vascular endothelial growth factor (VEGF)-A, VEGF receptor 1 (VEGFR1), VEGFR2, platelet-derived growth factor (PDGF)-B, and PDGF receptor-β with Western blotting and immunohistochemical staining at postnatal day 8. Expression of the endothelial cell marker CD31 was examined to determine glomerular and peritubular capillary density.

RESULTS

Enalapril-treated rat kidneys showed disrupted tubules and vessels when compared with the control rat kidneys. In the enalapril-treated group, intrarenal VEGF-A protein expression was significantly higher, whereas VEGFR1 protein expression was lower than that in the control group (P<0.05). The expression of VEGFR2, PDGF-B, and PDGF receptor-β was not different between the 2 groups. The increased capillary CD31 expression on the western blots of enalapril-treated rat kidneys indicated that the total endothelial cell protein level was increased, while the cortical capillary density, assessed using CD31 immunohistochemical staining, was decreased.

CONCLUSION

Impaired VEGF-VEGFR signaling and altered capillary repair may play a role in the deterioration of the kidney vasculature after blocking of angiotensin II during renal development.

Vascular versus tubular renin: role in kidney development

Renin, the key regulated enzyme of the renin-angiotensin system regulates blood pressure, fluid-electrolyte homeostasis, and renal morphogenesis. Whole body deletion of the renin gene results in severe morphological and functional derangements, including thickening of renal arterioles, hydronephrosis, and inability to concentrate the urine. Because renin is found in vascular and tubular cells, it has been impossible to discern the relative contribution of tubular versus vascular renin to such a complex phenotype. Therefore, we deleted renin independently in the vascular and tubular compartments by crossing Ren1(c fl/fl) mice to Foxd1-cre and Hoxb7-cre mice, respectively. Deletion of renin in the vasculature resulted in neonatal mortality that could be rescued with daily injections of saline. The kidneys of surviving mice showed the absence of renin, hypertrophic arteries, hydronephrosis, and negligible levels of plasma renin. In contrast, lack of renin in the collecting ducts did not affect kidney morphology, intra-renal renin, or circulating renin in basal conditions or in response to a homeostatic stress, such as sodium depletion. We conclude that renin generated in the renal vasculature is fundamental for the development and integrity of the kidney, whereas renin in the collecting ducts is dispensable for normal kidney development and cannot compensate for the lack of renin in the vascular compartment. Further, the main source of circulating renin is the kidney vasculature.

Unwrapping the origins and roles of the renal endothelium

The renal vasculature, like all vessels, is lined by a thin layer of simple squamous epithelial cells called an endothelium. These endothelial-lined vessels can be subdivided into four major compartments: arteries, veins, capillaries and lymphatics. The renal vasculature is a highly integrated network that forms through the active processes of angiogenesis and vasculogenesis. Determination of the precise contribution of these two processes and of the molecular signaling that governs the differentiation, specification and maturation of these critical cell populations is the focus of an actively evolving field of research. Although much of the focus has concentrated on the origin of the glomerular capillaries, in this review we extend the investigation to the origins of the endothelial cells throughout the entire kidney and the signaling events that cause their distinct functional and molecular profiles. A thorough understanding of endothelial cell biology may play a critical role in a better understanding of renal vascular diseases.

Organic Anion Transporter 4-Mediated Transport of Olmesartan at Basal Plasma Membrane of Human Placental Barrier

Mechanisms regulating fetal transfer of olmesartan, an angiotensin-II receptor type 1 antagonist, are important as potential determinants of life-threatening adverse fetal effects. The purpose of this study was to examine the olmesartan transport mechanism through the basal plasma membrane (BM) of human syncytiotrophoblasts forming the placental barrier. Uptake of olmesartan by human placental BM vesicles was potently inhibited by dehydroepiandrosterone sulfate (DHEAS), estrone 3-sulfate, and bromosulfophthalein, which are all typical substrates of organic anion transporter (OAT) 4 localized at the BM of syncytiotrophoblasts, and was increased in the absence of chloride. In tetracycline-inducible OAT4-expressing cells, [(3) H]olmesartan uptake was increased by tetracycline treatment. Olmesartan uptake via OAT4 was concentration dependent with a Km of 20 μM, and was increased in the absence of chloride. [(3) H]Olmesartan efflux via OAT4 was also observed and was trans-stimulated by extracellular chloride and DHEAS. Thus, OAT4 mediates bidirectional transport of olmesartan and appears to regulate fetal transfer of olmesartan at the BM of syncytiotrophoblasts. Efflux transport of olmesartan via OAT4 from syncytiotrophoblasts to the fetal circulation might be facilitated in the presence of an inwardly directed physiological chloride gradient and extracellular DHEAS.

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.

Control of renin [corrected] gene expression

Renin, as part of the renin-angiotensin system, plays a critical role in the regulation of blood pressure, electrolyte homeostasis, mammalian renal development, and progression of fibrotic/hypertrophic diseases. Renin gene transcription is subject to complex developmental and tissue-specific regulation. Initial studies using the mouse As4.1 cell line, which has many characteristics of the renin-expressing juxtaglomerular cells of the kidney, have identified a proximal promoter region (-197 to -50 bp) and an enhancer (-2,866 to -2,625 bp) upstream of the Ren-1(c) gene, which are critical for renin gene expression. The proximal promoter region contains several transcription factor binding sites including a binding site for the products of the developmental control genes Hox. The enhancer consists of at least 11 transcription factor binding sites and is responsive to various signal transduction pathways including cAMP, retinoic acid, endothelin-1, and cytokines, all of which are known to alter renin mRNA levels. Furthermore, in vivo models have validated several of these key components found within the proximal promoter region and the enhancer as well as other key sites necessary for renin gene transcription.

Renal programming: cause for concern?

Development of the kidney can be altered in utero in response to a suboptimal environment. The intrarenal factors that have been most well characterized as being sensitive to programming events are kidney mass/nephron endowment, the renin-angiotensin system, tubular sodium handling, and the renal sympathetic nerves. Newborns that have been subjected to an adverse intrauterine environment may thus begin life at a distinct disadvantage, in terms of renal function, at a time when the kidney must take over the primary role for extracellular fluid homeostasis from the placenta. A poor beginning, causing renal programming, has been linked to increased risk of hypertension and renal disease in adulthood. However, although a cause for concern, increasingly, evidence demonstrates that renal programming is not a fait accompli in terms of future cardiovascular and renal disease. A greater understanding of postnatal renal maturation and the impact of secondary factors (genes, sex, diet, stress, and disease) on this process is required to predict which babies are at risk of increased cardiovascular and renal disease as adults and to be able to devise preventative measures.

Using enteral sterile water feeds for hypernatremia in extremely low birth-weight infants

Extremely low birth-weight infants are prone to fluid and electrolyte imbalance due to multiple etiologies. Hypernatremia can occur in this gestational age group during the first week of life. One therapy that many NICUs initiate to treat hypernatremia is enteral sterile water feeds (SWFs). The use of free water is an adjunct therapy in place of large volumes of intravenous fluids. This article presents a review of renal physiology and 3 case studies of infants, less than 27 weeks' gestational age and less than 1000-g birth weight, treated with SWFs for hypernatremia. Commonalities and differences in treatment are addressed. There is limited evidence-based research using enteral SWFs for the treatment of hypernatremia.

Plasma and renal renin concentrations in adult sheep after prenatal betamethasone exposure

This study examined whether renin expression and secretion and plasma angiotensin II (Ang II) levels were altered in adult sheep exposed to antenatal betamethasone. Pregnant sheep received injections of 0.17 mg/kg betamethasone or vehicle, at 80 and 81 days of gestation, and offspring were studied at 6 and 18 months of age. At 6 months, plasma prorenin concentrations were significantly lower in betamethasone animals (4.63 +/- 0.64 vs 7.09 +/- 0.83 ng angiotensin I/mL/h, P < .01). The percentage of plasma active renin was significantly higher in the betamethasone group (31.93 +/- 4.09% vs 18.57 +/- 2.79%, P < .01). Plasma and renocortical renin levels were similar in both groups at 18 months, but plasma renin activity was lower than at 6 months. Ang II levels were suppressed by betamethasone. The data indicate that prenatal exposure to betamethasone alters processing and secretion of renin in offspring at 6 months, but that this difference is not apparent at 18 months.

Nitric oxide synthase and renin-angiotensin gene expression and NOS function in the postnatal renal resistance vasculature

Nitric oxide (NO), produced by nitric oxide synthase (NOS), critically counteracts angiotensin-II-enhanced vascular resistance in the immature kidney, perhaps due to the developmental regulation of NOS expression and function in the postnatal preglomerular resistance vessels (PRV). Our experiments measured the messenger ribonucleic acid (mRNA) gene expression of neuronal NOS (nNOS), endothelial NOS (eNOS), and components of the renin-angiotensin system (renin, AT1 and AT2 receptors), by real-time RT-PCR, as well as NOS enzymatic activity by citrulline assay in PRVs (afferent, interlobular, and arcuate arterioles) obtained from swine ages newborn, 7 and 21 days, and adult. NOS enzymatic activity was upregulated in PRVs immediately after birth but decreased to adult levels with maturation. Neuronal NOS, renin, and AT2 receptor expression in PRVs were upregulated in the newborn and decreased with age to lowest levels in the adult. In contrast, eNOS and AT1 receptor expression were downregulated at birth but increased to the highest levels in the adult. Upregulated NOS enzymatic activity in newborn PRVs supports the critical neonatal role for NO renal vascular vasodilation. Upregulated nNOS gene expression, concomitant with downregulated eNOS gene expression in neonatal PRVs, suggests that the nNOS isoform may be responsible for counteracting angiotensin II increased vascular resistance in immature porcine PRVs.

In vivo analysis of key elements within the renin regulatory region

Renin is responsible for initiating the enzymatic cascade that results in the production of angiotensin II, the major effector molecule of the renin-angiotensin system (RAS). Extensive information on the regulatory region of the renin gene has been derived by transient transfection studies in vitro, particularly using the As4.1 cell line. To verify key factors within the regulatory region of renin in vivo, homologous recombination was used to introduce a green fluorescent protein (GFP) cassette into exon one of the renin gene contained within a 240 kb bacterial artificial chromosome (BAC) to create a construct that has GFP expression controlled by the renin regulatory region (RenGFP BAC). Within the regulatory region of the RenGFP BAC construct we independently deleted the enhancer, as well as mutated the HOX-PBX site within the proximal promoter element. Transgenic lines were generated for each of these BAC constructs and GFP expression was analyzed throughout a spectrum of tissues positive for renin expression including the kidney, adrenal gland, gonadal artery, and submandibular gland. The results described within this manuscript support the interpretation that the renin enhancer is critical for regulating baseline expression where as the Hox/Pbx site is important for the tissue specificity of renin expression.

Fluorescence activated cell sorting of transiently transfected As4.1 cells shows renin enhancer directs on/off switching of renin promoter in vitro

1. The proximal promoter of the renin gene is weak and its activity is influenced by a strong, far-upstream enhancer. This and the ability of renin expression in renal afferent arteriolar cells to be 'recruited' under chronic stimulation is consistent with the on/off switching (variegation) model of gene expression. If true, this would provide an example in which variegation controls a physiologically regulable gene. 2. The present study tested the hypothesis that renin promoter activity may accord with the variegation model, at least in individual juxtaglomerular (mouse As4.1) cells in vitro. 3. As4.1 cells were transiently transfected with constructs containing the mouse renin (Ren-1c) enhancer adjacent to the Ren-1c promoter and a linked reporter gene encoding enhanced green fluorescent protein (EGFP). The EGFP signal from individual cells was monitored by fluorescence activated cell sorting. 4. In the presence of the renin enhancer there was 10-fold higher EGFP expression in transfected cells compared with cells transfected with EGFP constructs containing the promoter alone. There was, moreover, an 8-fold increase in the number of EGFP expressing cells. However, EGFP expression in individual transfected cells was similar in the presence or absence of the enhancer. 5. Results from the in vitro system used suggest that the Ren-1c enhancer does not regulate the rate of promoter activity, but rather increases the probability of achieving an active transcriptional state. Limitations of these findings are discussed.

Nephrogenesis and the renal renin-angiotensin system in fetal sheep: effects of intrauterine growth restriction during late gestation

Previous studies have shown that intrauterine growth restriction (IUGR) can impair nephrogenesis, but uncertainties remain about the importance of the gestational timing of the insult and the effects on the renal renin-angiotensin system (RAS). We therefore hypothesized that induction of IUGR during late gestation alters the RAS, and this is associated with a decrease in nephron endowment. Our aims were to determine the effects of IUGR induced during the later stages of nephrogenesis on 1) nephron number; 2) mRNA expression of angiotensin AT(1) and AT(2) receptors, angiotensinogen, and renin genes in the kidney; and 3) the size of maculae densae. IUGR was induced in fetal sheep (n = 7) by umbilical-placental embolization from 110 to 130 days of the approximately 147-day gestation; saline-infused fetuses served as controls (n = 7). Samples of cortex from the left kidney were frozen, and the right kidney was perfusion fixed. Total kidney volume, nephron number, renal corpuscle volume, total maculae densae volume, and the volume of macula densa per glomerulus were stereologically estimated. mRNA expression of AT(1) and AT(2) receptors, angiotensinogen, and renin in the renal cortex was determined. In IUGR fetuses at 130 days, body and kidney weights were significantly reduced and nephron number was reduced by 24%. There was no difference in renin, angiotensinogen, or AT(1) and AT(2) receptor mRNA expression levels in the IUGR kidneys compared with controls. We conclude that fetal growth restriction late in nephrogenesis can lead to a marked reduction in nephron endowment but does not affect renal corpuscle or macula densa size, or renal RAS gene expression.

AT1 receptor blockade prevents interstitial and glomerular apoptosis but not fibrosis in pigs with neonatal induced partial unilateral ureteral obstruction

Obstruction-induced fibrosis is a leading cause of end-stage renal failure in children. The pathophysiological mechanisms may involve apoptosis and the renin-angiotensin system. We studied apoptosis and fibrosis in a well-established neonatal pig model with unilateral partial ureteral obstruction (PUUO) induced during ongoing nephrogenesis in 2-day-old piglets. The role of angiotensin II (ANG II) was studied using the AT(1) receptor blocker CV-11974 (0.12 mg/h candesartan from age 23 to 30 days). At day 30 the kidneys were perfusion fixed and fibrosis, apoptosis, and tubular lengths were quantitated using stereological methods, picro Sirius red staining, and immunohistochemical techniques identifying activated caspase 3, aquaporin-2 (AQP2), and von Willebrand factor. The collagen content was assessed by hydroxyproline density. Neonatal induced PUUO increased interstitial and glomerular cell apoptosis and fibrosis. At this stage, PUUO did not increase tubular cell apoptosis or decrease tubular length and cell number. AT(1) receptor blockade prevented the PUUO-induced interstitial and glomerular cell apoptosis but did not attenuate fibrosis. In conclusion, AT(1) receptor blockade after the end of nephrogenesis may prevent interstitial and glomerular cell apoptosis but not fibrosis, suggesting that pathways not involving AT(1) receptor stimulation contribute to neonatal obstruction-induced fibrosis or that prevention of interstitial cell apoptosis counteracts a potential antifibrotic effect of AT(1) receptor blockade in this pig model of congenital obstructive nephropathy. Our results demonstrate that ANG II plays a role in PUUO-induced glomerular cell apoptosis.

Foetal kidney maldevelopment in maternal use of angiotensin II type I receptor antagonists

We report renal lesions observed in a foetus exposed throughout pregnancy to angiotensin II type I (AT 1) receptor antagonists. The mother suffered from essential hypertension and was treated with Cozaar (losartan 50 mg). Autopsy examination of the foetus revealed severe renal lesions, including tubular dysgenesis, hypertrophy of the endothelial and medial cells lining the arterial and arteriolar walls, hyperplasia of the juxtaglomerular apparatus and poorly developed vasa recta. Similar lesions have already been observed in foetuses of women treated with angiotensin-converting enzyme antagonists and also in foetuses and neonates of animals undergoing experimental blockade of the renin-angiotensin system. The purpose of this report is to describe structural lesions observed in the kidneys, and, particularly, vascular lesions. Our results suggest that the use of AT 1 receptor antagonists during pregnancy may have a severe deleterious effect on kidney development in the foetus.

Ontogeny and effects of thyroid hormone on beta1-adrenergic receptor mRNA expression in ovine fetal kidney cortex

OBJECTIVE

Previous studies indicate that thyroidectomy (TX) decreases renin gene expression in ovine fetal renal cortex in late gestation. Fetal ovine renin-containing renocortical cells become increasingly responsive to beta-adrenergic stimulation as gestation proceeds. Increases in plasma thyroid hormone concentrations parallel this change, suggesting that there is a positive developmental relationship between the two. To examine this hypothesis, we determined the ontogeny of beta1-adrenergic receptor (beta1R) mRNA expression, and the effect of thyroid hormone on in vivo and in vitro expression in fetal sheep.

METHODS

Renocortical tissue was obtained from naive, TX, and sham-operated fetuses to determine beta1R mRNA levels. Renin-containing renocortical cells from TX or sham fetuses were treated with isoproterenol (Iso) or forskolin (FSK) for analysis of cellular cyclic adenosine monophosphate (cAMP) levels. Renocortical cells from naive fetuses were treated with triiodothyronine (T3) to assess cellular beta1R mRNA levels. Fetal plasma thyroxine (T4) level was determined.

RESULTS

Renocortical beta1R mRNA expression increased significantly between 100 and 140 days' gestational age (dGA), while TX attenuated this increase (P <.01). Renocortical cellular cAMP levels were higher in sham compared to TX fetuses following incubation with Iso or FSK (P <.05). Cells incubated with T3 exhibited significantly increased beta1R mRNA expression (P <.05).

CONCLUSION

The data suggest that thyroid hormone may be involved in modulating ovine fetal renocortical beta1R gene expression during development. We speculate that the increased beta1R mRNA expression in renal cortical cells as development progresses may mediate the increases in renin gene response to beta-adrenergic stimulation in late gestation.

Oligonephropathy, developmental programming and nutritional management of low-gestation newborns

Intrauterine growth retardation is associated with oligonephropathy and the risk of hypertension and renal disease in adulthood. Animal study data show that nephron density is directly related to protein nutrition status during nephrogenesis. Among infants born at low gestation, postnatal growth retardation and major deficits in energy and protein intake have been reported.

CONCLUSION

Since nephrogenesis occurs mainly in late gestation, increasing protein intake during nephrogenesis could minimize the risk of long-term morbidities associated with oligonephropathy.

A single chinese center investigation of renal artery stenosis in 141 consecutive cases with coronary angiography

BACKGROUND

There is an increasing prevalence of ischemic nephropathy in the aging population of the world. However, the exact incidence of ischemic nephropathy in the Chinese population is still uncertain. The present study investigated the incidence of renal artery stenosis (RAS) in patients with suspected coronary artery disease (CAD) using renal angiography.

METHODS

Renal angiography was performed immediately after coronary artery angiography in 141 patients with suspected CAD, including 59 males and 82 females whose mean ages were 59 +/- 10 years. Comorbidities included hypertension (n = 69), diabetes mellitus (n = 21), hyperlipidemia (n = 19), hypokalemia (n = 7) and preoperative renal insufficiency (Cr >132 micromol/l; n = 14). The patients were divided into CAD (luminal narrowing of > or =50%) and non-CAD (luminal narrowing of <50%) subgroups, and RAS (luminal narrowing of > or =50%) and non-RAS subgroups. In the RAS group, there were 11 patients (5 males, 6 females) in whom percutaneous transluminal renal angioplasty was performed in conjunction with stent implantation due to refractory hypertension.

RESULTS

The incidence of RAS was 18.4% (26/141) in all cases and 30.8% (16/52) in patients with CAD identified by coronary artery angiography. Ten cases with RAS were found among the 89 cases with normal coronary arteries (11.2%). The incidence of RAS in patients with CAD was higher than that in patients without CAD (30.8 vs. 11.2%, p< 0.05). In 52 cases with CAD, the incidence of RAS with three vessel lesions was significantly higher than that with one or two vessel lesions. Hypertension, CAD, renal insufficiency, hyperlipidemia and hypokalemia were associated with a higher risk of RAS.

CONCLUSIONS

This study suggests that RAS is very common in the elderly Chinese population, specifically for those with three vessel lesions in CAD. For early detection of potential ischemic nephropathy, renal angiography is necessary in patients who receive coronary artery angiography.

Genomic characterization and expression analysis of the first nonmammalian renin genes from zebrafish and pufferfish

Renin is a key enzyme in the renin-angiotensin system (RAS), a pathway which plays an important physiological role in blood pressure and electrolyte homeostasis. The origin of the RAS is believed to have accompanied early evolution of vertebrates. However, renin genes have so far only been unequivocally identified in mammals. Whether or not a bona fide renin gene exists in nonmammalian vertebrates has been an intriguing question of physiological and evolutionary interest. Using a genomic analytical approach, we identified renin genes in two nonmammalian vertebrates, zebrafish (Danio rerio) and pufferfish (Takifugu rubripes). Phylogenetic analysis demonstrates that the predicted fish renins cluster together with mammalian renins to form a distinct subclass of vertebrate aspartyl proteases. RT-PCR results confirm generation of the predicted zebrafish mRNA and its expression in association with the opisthonephric kidney of adult zebrafish. Comparative in situ hybridization analysis of wild-type and developmental mutants indicates that renin expression is first detected bilaterally in cells of the interrenal primordia at 24 h postfertilization, which subsequently migrate to lie adjacent to, but distinct from, the glomerulus of the developing pronephric kidney. Our report provides the first molecular evidence for the existence of renin genes in lower vertebrates. The observation that the earliest renin-expressing cells, arising during ontogeny of this teleost vertebrate, are of adrenocortical lineage raises an interesting hypothesis as regards the origin of renin-expressing cells in the metanephric kidney of higher vertebrates.

The role of angiotensin II in kidney embryogenesis and kidney abnormalities

PURPOSE OF REVIEW

The renin-angiotensin system has a major role in the control of blood pressure and homeostasis balance. It also plays a fundamental role in kidney development. Recent insights into how the angiotensin-generating cascade controls developmental processes and homeostasis, and, when defective, causes disease, are discussed.

RECENT FINDINGS

The role of the renin-angiotensin system in kidney development is now widely accepted. New findings discussed in this review include the discovery of the capacity of the kidney to produce its own blood cells simultaneously with in-situ blood vessel formation, a process referred to as hemo-vasculogenesis. In addition, the role of the renin-angiotensin system in hematopoiesis is reviewed. Also discussed are the effects of angiotensin on branching morphogenesis and the development of hypertension in the adult as a result of a reduction in nephron number during nephrogenesis. Furthermore, the relationship between angiotensin and transdifferentiation of epithelial cells into fibroblasts is described.

SUMMARY

The aforementioned advances help to clarify pathological processes such as extramedullary hematopoiesis, post-transplant erythrocytosis, the relationship between nephron number and hypertension, and the role of angiotensin and other growth factors in renal fibrosis. The molecules and pathways whereby angiotensin contributes to the processes mentioned above are beginning to be elucidated.

Effects of AT(1A) receptor deletion on blood pressure and sodium excretion during altered dietary salt intake

The present study was performed to investigate the role of type 1A ANG II (AT(1A)) receptors in regulating sodium balance and blood pressure maintenance during chronic dietary sodium variations in AT(1A) receptor-deficient (-/-) mice. Groups of AT(1A) (-/-) and wild-type mice were placed on a low (LS)-, normal (NS)-, or high-salt (HS) diet for 3 wk. AT(1A) (-/-) mice on an LS diet had high urinary volume and low blood pressure despite increased renin and aldosterone levels. On an HS diet, (-/-) mice demonstrated significant diuresis, yet blood pressure increased to levels greater than control littermates. There was no effect of dietary sodium intake on systolic blood pressures in wild-type animals. The pressure-natriuresis relationship in AT(1A) (-/-) mice demonstrated a shift to the left and a decreased slope compared with wild-type littermates. These studies demonstrate that mice lacking the AT(1A) receptor have blood pressures sensitive to changes in dietary sodium, marked alterations of the pressure-natriuresis relationship, and compensatory mechanisms capable of maintaining normal sodium balance across a wide range of sodium intakes.

An Abd-B class HOX.PBX recognition sequence is required for expression from the mouse Ren-1c gene

Expression from the mouse Ren-1(c) gene in As4.1 cells is dependent on a proximal promoter element (PPE) located at approximately -60 and a 241-base pair enhancer region located at -2625 relative to the transcription start site. The PPE (TAATAAATCAA) is identical to a consensus HOX.PBX binding sequence. Further, PBX1b has been shown to be a component of a PPE-specific binding complex present in nuclear extracts from As4.1 cells. The binding affinities of different paralog HOX members to the PPE were examined in the absence or presence of PBX1b. HOXB6, -B7, and -C8 failed to bind the PPE alone but showed weak affinity in the presence of PBX1b. In contrast, HOXD10 and to a lesser degree HOXB9 bound the PPE with high affinities regardless of whether PBX1b was present. Abd-B HOX members, including HOXD10, -A10, -A9, -B9, and -C9, are expressed in As4.1 cells. The ability of HOX and PBX1b to form a ternary complex with PREP1 on the PPE is also demonstrated both in vivo and in vitro. Point mutations in either the HOX or PBX half-site of the PPE disrupted the formation of the HOX.PBX complex and dramatically decreased transcriptional activity of the Ren-1(c) gene demonstrating that both the HOX and PBX half-sites are critical for mouse renin gene expression. These results strongly implicate Abd-B class Hox genes and their cofactors as major determinants of the sites of renin expression.

Genetic evidence that lethality in angiotensinogen-deficient mice is due to loss of systemic but not renal angiotensinogen

Angiotensinogen (AGT)-deficient mice die shortly after birth presumably due to renal dysfunction caused by the presence of severe vascular and tubular lesions in the kidney. Because AGT is expressed in renal proximal tubule cells, we hypothesized that its loss may be the primary mediator of the lethal phenotype. We generated two models to test this hypothesis by breeding transgenic mice expressing human renin with mice expressing human AGT (hAGT) either systemically or kidney-specifically. We then bred double transgenic mice with AGT+/- mice, intercrossed the compound heterozygotes, and examined the offspring. We previously reported that the presence of the human renin and systemically expressed hAGT transgene complemented the lethality observed in AGT-/- mice. On the contrary, we show herein that the presence of the human renin and kidney-specific hAGT transgene cannot rescue lethality in AGT-/- mice. An analysis of newborns indicated that AGT-/- mice were born in normal numbers, and collection of dead 10-day old pups revealed an enrichment in AGT-/-. Importantly, we demonstrated that angiotensinogen protein and functional angiotensin II was generated in the kidney, and the kidney-specific transgene was temporally expressed during renal development similar to the endogenous AGT gene. These data strongly support the notion that the loss of systemic AGT, but not intrarenal AGT, is responsible for death in the AGT-/- mouse model. Taken together with our previous studies, we conclude that the intrarenal renin-angiotensin system located in the proximal tubule plays an important role in blood pressure regulation and may cause hypertension if overexpressed, but may not be required for continued development of the kidney after birth.

Expression of a renin/GFP transgene in mouse embryonic, extra-embryonic, and adult tissues

A reporter construct was assembled with 4-kb of renin 5'-flanking sequence fused to humanized green fluorescent protein (GFP) cDNA. Transgenic mice carrying this construct were produced and assayed for GFP expression. In the adult, expression was detected in juxtaglomerular (JG) cells of the kidney and granular convoluted tubular cells of the submandibular gland. Furthermore, treatment of mice with captopril induced GFP expression in renal vascular smooth muscle cells. During embryogenesis, GFP expression was first detected at embryonic day E13 in the adrenal gland and Wolffian duct. Expression was also seen in the developing renal vasculature as early as E14 and remained detectable through birth. Renal GFP expression became restricted to JG cells in adults. Fetal adrenal and gonadal arteries also expressed GFP. In the placenta, GFP was observed in giant cell trophoblasts, consistent with reports of renin expression in chorionic cells of both humans and mice. We conclude that 4 kb of renin 5' flank is sufficient to direct multiple known renin expression patterns. Furthermore, the renin-GFP construct characterized here will provide a useful vital reporter for renin expression.

Nephrocystin: gene expression and sequence conservation between human, mouse, and Caenorhabditis elegans

Juvenile nephronophthisis, an autosomal recessive cystic kidney disease, is the primary genetic cause for chronic renal failure in children. The gene (NPHP1) for nephronophthisis type 1 has recently been identified. Its gene product, nephrocystin, is a novel protein of unknown function, which contains a src-homology 3 domain. To study tissue expression and analyze amino acid sequence conservation of nephrocystin, the full-length murine Nphp1 cDNA sequence was obtained and Northern and in situ hybridization analyses were performed for extensive expression studies. The results demonstrate widespread but relatively weak NPHP1 expression in the human adult. In the adult mouse there is strong expression in testis. This expression occurs specifically in cell stages of the first meiotic division and thereafter. In situ hybridization to whole mouse embryos demonstrated widespread and uniform expression at all developmental stages. Amino acid sequence conservation studies in human, mouse, and Caenorhabditis elegans show that in nephrocystin the src-homology 3 domain is embedded in a novel context of other putative domains of protein-protein interaction, such as coiled-coil and E-rich domains. It is concluded that for multiple putative protein-protein interaction domains of nephrocystin, sequence conservation dates back at least to Caenorhabditis elegans. The previously described discrepancy between widespread tissue expression and the restriction of symptoms to the kidney has now been confirmed by an in-depth expression study.

Developmental changes in renal renin mRNA half-life and responses to stimulation in fetal lambs

In the perinatal period there is increased renin gene expression in the kidney compared with other stages of development. This may be related to changes in responsiveness of the renin gene to stimulation and/or differences in renin mRNA stability as development progresses. To ascertain if either responsiveness or stability changes in fetal life, we studied renin mRNA levels in primary cultures of renal cortical cells obtained from fetal lamb kidneys at two stages (0.7 and 0.9) of gestation after stimulation with isoproterenol, forskolin, or isobutyl methylxanthine and after inhibition of transcription with actinomycin D. Forskolin and isobutyl methylxanthine rapidly increased renin mRNA by at least twofold in the cultured cells from fetuses of both ages, with the sensitivity to stimulation higher in the cells from the mature fetal kidneys. Isoproterenol was effective only in mature fetal cells. In addition, the decay of renin mRNA after cessation of transcription was slower in mature cells compared with immature cells, the half-life being 11.6 +/- 0.8 h in mature cells and 6.6 +/- 0.6 h in immature cells (P < 0.05). The data suggest that increases in both renin mRNA sensitivity to stimulation and in stability can contribute to the enhanced renin expression in the perinatal period.