The renin angiotensin system and kidney development

Renin-angiotensin system: Basic and clinical aspects-A general perspective

The renin–angiotensin system (RAS) is one of the most complex hormonal regulatory systems, involving several organs that interact to regulate multiple body functions. The study of this system initially focused on investigating its role in the regulation of both cardiovascular function and related pathologies. From this approach, pharmacological strategies were developed for the treatment of cardiovascular diseases. However, new findings in recent decades have suggested that the RAS is much more complex and comprises two subsystems, the classic RAS and an alternative RAS, with antagonistic effects that are usually in equilibrium. The classic system is involved in pathologies where inflammatory, hypertrophic and fibrotic phenomena are common and is related to the development of chronic diseases that affect various body systems. This understanding has been reinforced by the evidence that local renin–angiotensin systems exist in many tissue types and by the role of the RAS in the spread and severity of COVID-19 infection, where it was discovered that viral entry into cells of the respiratory system is accomplished through binding to angiotensin-converting enzyme 2, which is present in the alveolar epithelium and is overexpressed in patients with chronic cardiometabolic diseases. In this narrative review, preclinical and clinical aspects of the RAS are presented and topics for future research are discussed some aspects are raised that should be clarified in the future and that call for further investigation of this system.

Renin-angiotensin system: Basic and clinical aspects-A general perspective

The renin–angiotensin system (RAS) is one of the most complex hormonal regulatory systems, involving several organs that interact to regulate multiple body functions. The study of this system initially focused on investigating its role in the regulation of both cardiovascular function and related pathologies. From this approach, pharmacological strategies were developed for the treatment of cardiovascular diseases. However, new findings in recent decades have suggested that the RAS is much more complex and comprises two subsystems, the classic RAS and an alternative RAS, with antagonistic effects that are usually in equilibrium. The classic system is involved in pathologies where inflammatory, hypertrophic and fibrotic phenomena are common and is related to the development of chronic diseases that affect various body systems. This understanding has been reinforced by the evidence that local renin–angiotensin systems exist in many tissue types and by the role of the RAS in the spread and severity of COVID-19 infection, where it was discovered that viral entry into cells of the respiratory system is accomplished through binding to angiotensin-converting enzyme 2, which is present in the alveolar epithelium and is overexpressed in patients with chronic cardiometabolic diseases. In this narrative review, preclinical and clinical aspects of the RAS are presented and topics for future research are discussed some aspects are raised that should be clarified in the future and that call for further investigation of this system.

Angiotensin-converting enzyme defines matrikine-regulated inflammation and fibrosis

The neutrophil chemoattractant proline-glycine-proline (PGP) is generated from collagen by matrix metalloproteinase-8/9 (MMP-8/9) and prolyl endopeptidase (PE), and it is concomitantly degraded by extracellular leukotriene A₄ hydrolase (LTA₄H) to limit neutrophilia. Components of cigarette smoke can acetylate PGP, yielding a species (AcPGP) that is resistant to LTA₄H-mediated degradation and can, thus, support a sustained neutrophilia. In this study, we sought to elucidate if an antiinflammatory system existed to degrade AcPGP that is analogous to the PGP-LTA₄H axis. We demonstrate that AcPGP is degraded through a previously unidentified action of the enzyme angiotensin-converting enzyme (ACE). Pulmonary ACE is elevated during episodes of acute inflammation, as a consequence of enhanced vascular permeability, to ensure the efficient degradation of AcPGP. Conversely, we suggest that this pathway is aberrant in chronic obstructive pulmonary disease (COPD) enabling the accumulation of AcPGP. Consequently, we identify a potentially novel protective role for AcPGP in limiting pulmonary fibrosis and suggest the pathogenic function attributed to ACE in idiopathic pulmonary fibrosis (IPF) to be a consequence of overzealous AcPGP degradation. Thus, AcPGP seemingly has very divergent roles: it is pathogenic in its capacity to drive neutrophilic inflammation and matrix degradation in the context of COPD, but it is protective in its capacity to limit fibrosis in IPF.

ACE degrades the collagen-derived matrikine, acetylate proline–glycine–proline, to limit pulmonary inflammation and promote repair.

The concept of crosstalk-directed embryological target mining and its application to essential hypertension treatment failures

This review aims to introduce the novel concept of embryological target mining applied to interorgan crosstalk network genesis, and applies embryological target mining to multidrug-resistant essential hypertension (a prototype, complex, undertreated, multiorgan systemic syndrome) to uncover new treatment targets and critique why existing strategies fail. Briefly, interorgan crosstalk pathways represent the next frontier for target mining in molecular medicine. This is because stereotyped stepwise organogenesis presents a unique opportunity to infer interorgan crosstalk pathways that may be crucial to discovering novel treatment targets. Insights gained from this review will be applied to patient management in a clinician-directed fashion.

Maternal Vitamin D Status at Week 30 of Gestation and Offspring Cardio-Metabolic Health at 20 Years: A Prospective Cohort Study over Two Decades

Background/Objectives

Vitamin D deficiency is common among pregnant women and since the fetus relies exclusively on maternal supply, deficiency could potentially interfere with fetal development. Vitamin D blood concentrations during pregnancy have been associated with offspring cardio-metabolic health in a few previous studies but the evidence is still inconsistent and only one previous study has followed the offspring into adulthood. The aim of the present study was to investigate the association between maternal serum concentration of vitamin D (25(OH)D) in week 30 of gestation and offspring cardio-metabolic risk factors at 20 years.

Subjects/Methods

A follow up study of a Danish birth cohort from 1988–89 (n = 965) was conducted. A blood sample was drawn from the women in week 30 of gestation. In 2008–2009, 95% of the original mother and child dyads could be identified in the central registration registry and were alive and living in Denmark. The offspring were followed up with self-reported anthropometrics (N = 629, 69%) and a clinical examination (N = 410, 45%). Multiple linear regression was used to estimate the association between maternal 25(OH)D and offspring cardio-metabolic risk factors adjusting for potential confounders.

Results

No overall association was observed between maternal 25(OH)D in week 30 of gestation and offspring cardio-metabolic risk factors. However, the analyses did suggest a possible inverse association with blood pressure in females.

Conclusions

No clear association between maternal 25(OH)D concentration in week 30 of gestation and cardio-metabolic risk factors in the 20 year old offspring was found.

Polyuria-associated hydronephrosis induced by xenobiotic chemical exposure in mice

Hydronephrosis is a commonly found disease state characterized by the dilation of renal calices and pelvis, resulting in the loss of kidney function in the severest cases. A generally accepted etiology of hydronephrosis involves the obstruction of urine flow along the urinary tract. In the recent years, we have developed a mouse model of hydronephrosis induced by lactational exposure to dioxin and demonstrated a lack of anatomical obstruction in this model. We also showed that prostaglandin E2 synthesis system plays a critical role in the onset of hydronephrosis. In the present study, we found that neonatal hydronephrosis was not likely to be associated with functional obstruction (impaired peristalsis) but was found to be associated with polyuria and low urine osmolality with the downregulation of proteins involved in the urine concentrating process. The administration of an antidiuretic hormone analog to the dioxin-exposed pups not only suppressed the increased urine output but also decreased the incidence and severity of hydronephrosis. In contrast to the case in pups, administration of dioxin to adult mice failed to induce polyuria and upregulation of prostaglandin E2 synthesis system, and the adult mice were resistant to develop hydronephrosis. These findings suggest the possibility that polyuria could induce hydronephrosis in the absence of anatomical or functional obstruction of the ureter. It is concluded that the present animal model provides a unique example of polyuria-associated type of hydronephrosis, suggesting a need to redefine this disease state.

Influence of gestational salt restriction in fetal growth and in development of diseases in adulthood

Recent studies reported the critical role of the intrauterine environment of a fetus in growth or the development of disease in adulthood. In this article we discussed the implications of salt restriction in growth of a fetus and the development of growth-related disease in adulthood. Salt restriction causes retardation of fatal growth or intrauterine death thereby leading to low birth weight or decreased birth rate. Such retardation of growth along with the upregulation of the renin angiotensin system due to salt restriction results in the underdevelopment of cardiovascular organs or decreases the number of the nephron in the kidney and is responsible for onset of hypertension in adulthood. In addition, gestational salt restriction is associated with salt craving after weaning. Moreover, salt restriction is associated with a decrease in insulin sensitivity. A series of alterations in metabolism due to salt restriction are probably mediated by the upregulation of the renin angiotensin system and an epigenetic mechanism including proinflammatory substances or histone methylation. Part of the metabolic disease in adulthood may be programmed through such epigenetic changes. The modification of gene in a fetus may be switched on through environment factors or life style after birth. The benefits of salt restriction have been assumed thus far; however, more precise investigation is required of its influence on the health of fetuses and the onset of various diseases in adulthood.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Feeding pregnant ewes a high-salt diet or saltbush suppresses their offspring's postnatal renin activity

If ewes consumed a high-salt diet or saltbush during the last 3 months of pregnancy and for 3 weeks after birth, we expected the renin activity of their lamb to be suppressed at birth and at 3 weeks of age. We also expected an increase in the concentration of cations other than sodium in the ewe's milk and an increase in the plasma Na concentration of the lamb at birth. To test these hypotheses, Merino ewes were fed a high-salt diet (14% NaCl) in an animal house and compared to control ewes eating a control diet (2% NaCl). In addition, we compared ewes grazing saltbush (about 13% salt in diet) to ewes grazing pasture from day 60 of pregnancy to 3 weeks after birth. Lambs born to ewes consuming saltbush had 85% lower (P < 0.001) renin activity than offspring from ewes consuming pasture at 3 weeks of age. Similarly, lambs born to ewes consuming a high-salt diet had 20% lower renin activity at birth and 3 weeks (P = 0.07). Feeding ewes a high-salt diet or saltbush altered the mineral composition of the milk; the largest change was a 10% increase in K levels (P 0.05). Consuming a high-salt diet or saltbush lowered the plasma Na of ewes at 130 days of gestation (by 3-5 mmol/l; P < 0.001), but only lambs from ewes fed the high-salt diet had a lower plasma Na at birth (P < 0.05). Suppression of the renin activity of lambs could lead to permanent physiological changes in salt balance in later life.

Angiotensin II type 2 receptor is critical for the development of human fetal pancreatic progenitor cells into islet-like cell clusters and their potential for transplantation

Local renin-angiotensin systems (RASs) regulate the differentiation of tissue progenitors. However, it is not known whether such systems can regulate the development of pancreatic progenitor cells (PPCs). To address this issue, we characterized the expression profile of major RAS components in human fetal PPC preparations and examined their effects on the differentiation of PPCs into functional islet-like cell clusters (ICCs). We found that expression of RAS components was highly regulated throughout PPC differentiation and that locally generated angiotensin II (Ang II) maintained PPC growth and differentiation via Ang II type 1 and type 2 (AT(1) and AT(2)) receptors. In addition, we observed colocalization of AT(2) receptors with critical β-cell phenotype markers in PPCs/ICCs, as well as AT(2) receptor upregulation during differentiation, suggesting that these receptors may regulate β-cell development. In fact, we found that AT(2) , but not AT(1) , receptor was a key mediator of Ang II-induced upregulation of transcription factors important in β-cell development. Furthermore, lentivirus-mediated knockdown of AT(2) receptor suppressed the expression of these transcription factors in ICCs. Transplantation of AT(2) receptor-depleted ICCs into immune-privileged diabetic mice failed to ameliorate hyperglycemia, implying that AT(2) receptors are indispensable during ICC maturation in vivo. These data strongly indicate that a local RAS is involved in governing the functional maturation of pancreatic progenitors toward the endocrine lineage.

Programmed hypertension in rats treated with a NF-κB inhibitor during nephrogenesis: renal mechanisms

Suppression of the renin-angiotensin system (RAS) during murine lactation causes progressive renal injury, indicating a physiological action of angiotensin II on nephrogenesis. The nuclear factor NF-κB system is one of the main intracellular mediators of angiotensin II. We investigated whether inhibition of this system with pyrrolidine dithiocarbamate (PDTC) during rat nephrogenesis would lead to similar hypertension and renal injury as observed with RAS suppressors. Immediately after delivery, 32 Munich-Wistar dams, each nursing 6 male pups, were divided into 2 groups: C, untreated, and PDTC, receiving PDTC, 280 mg kg(-1) day(-1) orally, during 21 days. After weaning, the offspring were followed until 10 months of age without treatment. Adult rats that received neonatal PDTC exhibited stable hypertension and myocardial injury, without albuminuria. To gain additional insight into this process, the renal expression of RAS components and sodium transporters were determined by quantitative real-time PCR (qRT-PCR) at 3 and 10 months of life. Renal renin and angiotensinogen were upregulated at 3 and downregulated at 10 months of age, suggesting a role for early local RAS activation. Likewise, there was early upregulation of the proximal sodium/glucose and sodium/bicarbonate transporters, which abated later in life, suggesting that additional factors sustained hypertension in the long run. The conclusions drawn from the findings were as follows: (1) an intact NF-κB system during nephrogenesis may be essential to normal renal and cardiovascular function in adult life; (2) neonatal PDTC represents a new model of hypertension, lacking overt structural injury or functional impairment of the kidneys; and (3) hypertension in this model seems associated with early temporary activation of renal RAS and sodium transporters.

Targeted deletion of Dicer from proximal tubules protects against renal ischemia-reperfusion injury

MicroRNAs are endogenous, noncoding, small RNAs that regulate expression and function of genes, but little is known about regulation of microRNA in the kidneys under normal or pathologic states. Here, we generated a mouse model in which the proximal tubular cells lack Dicer, a key enzyme for microRNA production. These mice had normal renal function and histology under control conditions despite a global downregulation of microRNAs in the renal cortex; however, these animals were remarkably resistant to renal ischemia-reperfusion injury (IRI), showing significantly better renal function, less tissue damage, lower tubular apoptosis, and improved survival compared with their wild-type littermates. Microarray analysis showed altered expression of specific microRNAs during renal IRI. Taken together, these results demonstrate evidence for a pathogenic role of Dicer and associated microRNAs in renal IRI.

Tissue renin-angiotensin-aldosterone systems: Targets for pharmacological therapy

The renin-angiotensin-aldosterone system is one of the most important systems in cardiovascular control and in the pathogenesis of cardiovascular diseases. Therefore, it is already a very successful drug target for the therapy of these diseases. However, angiotensins are generated not only in the plasma but also locally in tissues from precursors and substrates either locally expressed or imported from the circulation. In most areas of the brain, only locally generated angiotensins can exert effects on their receptors owing to the blood-brain barrier. Other tissue renin-angiotensin-aldosterone systems are found in cardiovascular organs such as kidney, heart, and vessels and play important roles in the function of these organs and in the deleterious actions of hypertension and diabetes on these tissues. Novel components with mostly opposite actions to the classical renin-angiotensin-aldosterone systems have been described and need functional characterization to evaluate their suitability as novel drug targets.

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.

Programming sheep production on saltbush: adaptations of offspring from ewes that consumed high amounts of salt during pregnancy and early lactation

We investigated if feeding a high salt diet (pellet containing 14% NaCl) or saltbush (Atriplex nummularia) to ewes between day 60 of gestation and day 21 of lactation would allow their offspring to gain more weight, and produce more wool, when grazing saltbush as adults compared to offspring from ewes that were fed a control diet (2% NaCl) or grazed pasture. At 10 months of age, offspring grazed saltbush for 8 weeks then dry pasture for 2 weeks. Throughout this time, liveweights, plasma renin activity and wool growth (g/day) were measured. Greasy and clean fleece weights, and fleece characteristics were measured at 14 months of age, and greasy fleece weight was measured again at 22 months after grazing pasture. Offspring from ewes that consumed the high salt pellet had an 8 and 10% increased fleece weight at 14 and 22 months of age, respectively (P ≤ 0.01). Offspring of ewes that consumed saltbush also showed an 8% increase in greasy fleece weight at 22 months of age (P ≤ 0.05). Offspring from ewes that consumed saltbush had lower plasma renin activity and gained tissue weight when grazing saltbush (P ≤ 0.05), whereas the other three treatment groups all lost weight (P > 0.05). Grazing pregnant ewes on saltbush induces important adaptations in plasma renin activity of their offspring, which allows them to gain weight when grazing saltbush as adults and may also increase the density of their wool follicles. Grazing pregnant ewes on saltbush can profit farmers in three main ways: (i) ability to utilise salt-affected land; (ii) increase weight gain of sheep when grazing saltbush; and (iii) increase fleece weight.

Update on tissue renin-angiotensin systems

Angiotensin (Ang) II is not only generated in the circulation by renin and angiotensin-converting enzyme (ACE) but also is produced locally in numerous organs including kidney, vessels, heart, adrenal gland, eye, testis, and brain. Furthermore, widely distributed mast cells have been shown to be a production site. Local Ang II production process is commonly termed the result of a "tissue" renin-angiotensin system (RAS). Because pharmacological experiments do not easily allow targeting of specific tissues, many novel findings about the functional importance of tissue RAS have been collected from transgenic rodent models. These animals either overexpress or lack RAS components in specific tissues and thereby elucidate their local functions. The data to date show that in most tissues local RAS amplify the actions of circulating Ang II with important implications for physiology and pathophysiology of cardiovascular diseases. This review summarizes the recent findings on the importance of tissue RAS in the most relevant cardiovascular organs.

Development of renin expression in the mouse kidney

During metanephric kidney development, renin is expressed in the walls of larger intrarenal arteries, but is restricted to the terminal part of the preglomerular arterioles in the adult kidney. Our study describes the three-dimensional development of renin expression in mouse kidneys during fetal and postnatal life. Renin immunoreactivity first appeared at day 14 of development in the cells expressing alpha-smooth muscle actin (alphaSMA) in the arcuate arteries. Before adulthood, the branching of the arcuate arterial tree increased exponentially and renin expression shifted from proximal to distal parts of the tree. Renin expression at branching points or in the cones of growing vessels was not seen. Instead, renin expression appeared after vessel walls and branches were already established, disappeared a few days later, and remained only in the juxtaglomerular regions of afferent arterioles. In these arterioles, coexpression of renin and alphaSMA disappeared gradually, with the terminal cells expressing only renin. At all stages of kidney development, renin expression among comparable vessel segments was heterogeneous. Renin expression remained stable after it reached the terminal parts of afferent arterioles.

Non-invasive markers of ureteropelvic junction obstruction

Non-invasive prognosis of the clinical progression of disease is of high interest, especially in newborn and children. Neonatal ureteropelvic (UPJ) junction obstruction needs close and invasive surveillance to determine the necessity of pyeloplasty. A number of groups have initiated research with the aim to find non-invasive biomarkers for UPJ obstruction. Two different strategies have been followed. One strategy, based on the knowledge obtained in animal models of UPJ obstruction, has identified a number of individual urinary markers of severe UPJ obstruction. Combining these markers might allow prediction of which patients will require surgery and in which patients UPJ obstruction will spontaneously resolve. The other strategy is based on urinary proteomics. In this strategy the entire urinary proteome is probed for a set of biomarkers that correlates with the degree of UPJ obstruction. In subsequent steps, these sets of urinary biomarkers are used for prediction of the clinical evolution of UPJ obstruction patients. This proteomic-based strategy allowed prediction, several months in advance, of the clinical evolution of neonates with UPJ-obstruction. Both strategies will be complementary and will hopefully replace in the near future the invasive follow-up of newborns with UPJ obstruction.

Enhanced TGF-beta/Smad signaling in the early stage of diabetic nephropathy is independent of the AT1a receptor

BACKGROUND

Angiotensin II (AII) and transforming growth factor-beta (TGF-beta) are closely involved in the pathogenesis of diabetic nephropathy (DN). AII is known to induce TGF-beta production in resident renal cells, including glomerular mesangial cells and tubular epithelial cells. TGF-beta receptor types I and II (TGF-betaRI, II) are up-regulated in the diabetic kidney. The aim of this study was to clarify the role of AII in the regulation of the TGF-beta system in the early stage of DN using AII type1a receptor-deficient(AT1a(-/-)) mice.

METHODS

We investigated the expression of TGF-beta1, TGF-betaRI, II, and Smad signaling in AT1a(-/-) mice with streptozotocin (STZ)-induced DN. Mice were killed 10 and 20 days after the induction of hyperglycemia. The expression of TGF-beta receptors was analyzed by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR). TGF-beta-specific Smad signaling was analyzed by electrophoretic mobility shift assay and Western blotting.

RESULTS

The expression of both TGF-betaRI and RII was up-regulated in the glomerular tufts and vasculature in diabetic AT1a(+/+) mice kidney by immunohistochemistry. RT-PCR revealed that mRNAs for TGF-betaRI and RII were also up-regulated. Smad2 and 4 protein levels were reduced in the renal cortex after the induction of diabetes, with an increase of Smad 3/4 complex in the nucleus. The expression of TGF-beta receptors increased in both diabetic AT1a(-/-) and AT1a(+/+) mice. Smad signaling in AT1a(-/-) mice was also enhanced.

CONCLUSIONS

Our results suggest that the complete blockade of the AT1a-mediated pathway has a minimal effect on the enhanced TGF-beta/Smad signaling in the early stage of DN, at least in the AT1a(-/-) model.

Renin-angiotensin system affects endothelial morphology and permeability of renal afferent arteriole

The afferent arteriole (AA) is an important regulatory site of renal function and blood pressure. We have demonstrated endothelial fenestration and high permeability in the vicinity of renin granulated epithelioid cells in the juxtaglomerular portion of the afferent arteriole in different mammals. The permeability of fenestrated endothelium of afferent arteriole may be important in connection to various physiologic and pathophysiologic processes. We have assumed that the permeable fenestration may serve as a communication channel between the intravascular circulation and a pathway for renin secretion. Utilising the multiphoton image technique we were able to visualise the endothelial fenestration and renin granules of the in vitro microperfused AA and in vivo AA. We demonstrated that ferritin-positive, i.e., permeable portion of the afferent arteriole, under control conditions is on average 45 microm, which is about one-third to half of the total length of the afferent arteriole. The length of this portion is not constant and can change by physiologic and pharmacologic manipulation of renin formation. The permeability of the afferent arteriole is not changing only parallel with the pharmacologically stimulated renin secretion as already demonstrated in adult rats, but also with the change of renin appearance in afferent arteriole within the very first few days of life after birth. Independently from the age there is a significant correlation between the renin-positive and permeable portion of the AA. Further studies are necessary to clarify the physiological significance of afferent arteriolar permeability and its changes in the postnatal development of the kidney, as well as in correlation with activity of renin- angiotensin system.

HIV-1 genes vpr and nef synergistically damage podocytes, leading to glomerulosclerosis

This study aimed to identify the causative gene for HIV-1 associated nephropathy, a paradigmatic podocytopathy. A previous study demonstrated that transgenic expression of nonstructural HIV-1 genes selectively in podocytes in mice with FVB/N genetic background resulted in podocyte injury and glomerulosclerosis. In this study, transgenic mice that expressed individual HIV-1 genes in podocytes were generated. Five of six transgenic mice that expressed vpr developed podocyte damage and glomerulosclerosis. Analysis of an established vpr transgenic line revealed that transgenic mice on FVB/N but not on C57BL/6 genetic background developed podocyte injury by 8 wk of age, with later glomerulosclerosis. Four of 11 transgenic mice that expressed nef also developed podocyte injury. One transgenic line was established from the nef founder mouse with the mildest phenotype. Transgenic mice in this line developed mesangial expansion at 3 wk of age and mild focal podocyte damage at 10 wk of age. Mating with FVB/N mice did not augment nephropathy. None of the transgenic mice that expressed vif, tat, rev, or vpu in podocytes, even with the FVB/N genetic background, developed podocyte injury. For testing effects of simultaneous expression of vpr and nef, these two lines were mated. All nef:vpr double-transgenic mice showed severe podocyte injury and glomerulosclerosis by 4 wk of age. In contrast, all vpr or nef single-transgenic mice in the same litter uniformly showed no or much milder podocyte injury. These findings indicate that vpr and nef each can induce podocyte injury with a prominent synergistic interaction.

Implication of genetic variations in congenital obstructive nephropathy

The renin-angiotensin system (RAS) has long been implicated in kidney development, and it has been reported that disruption of angiotensin type 2 receptor (AGTR2) results in a wide range of congenital anomalies of the kidney and urinary tract. We investigated the allele frequencies of the AGTR2 and other RAS genes in Korean patients with ureteropelvic junction obstruction, multicystic dysplastic kidney (MCDK), and unilateral renal agenesis (RA). Fifty-three Korean children were enrolled: 37 boys and 16 girls, 27 with hydronephrosis, 23 with MCDK, and 3 with RA. Among 100 healthy Koreans, the frequencies of A and G alleles at the A-G transition site of intron 1 of the AGTR2 gene were 70% (140/200) and 30% (60/200), respectively. In the patient group, the A allele frequency was 57% (60/106) and the G allele frequency was 43% (46/106), significantly higher than in the general population (P=0.024). There was no significant difference of allele frequency between boys and girls. Angiotensin-converting enzyme insertion/deletion, angiotensinogen M235T, and the angiotensin 2 type 1 receptor A1166C genotype distribution showed no difference from those of the control subjects. These findings indicate that the AGTR2 gene may play a major role in the development of congenital obstructive nephropathy.

Renal haemodynamics and function in weanling rats treated with enalapril from birth

1. Inhibition of the renin-angiotensin system (RAS) during kidney development produces chronic alterations in renal morphology and function that have been characterized in detail in adult animals. The aim of the present study was to determine the consequences of neonatal angiotensin-converting enzyme (ACE) inhibition on renal haemodynamics and function in rats at a much earlier age, namely 3-4 weeks. 2. Male Wistar pups received daily intraperitoneal injections of enalapril (10 mg/kg) or isotonic saline from birth until 24-28 days of age, when renal haemodynamics and function were assessed using clearance techniques under pentobarbital anaesthesia. 3. Enalapril-treated rats showed significant reductions in glomerular filtration rate (GFR; -44 +/- 6%; P < 0.05), effective renal plasma flow (ERPF; -33 +/- 6%; P < 0.05) and filtration fraction (-16 +/- 3%; P < 0.05) compared with saline-treated controls. Although mean arterial pressure tended to be lower in enalapril-treated rats, this group demonstrated a significant increase in renal vascular resistance compared with control rats (RVR; 46 +/- 6 vs 32 +/- 3 mmHg/mL per.min per g.kidney weight, respectively; P < 0.05). In enalapril-treated rats, urine osmolality was reduced (-59 +/- 5%; P < 0.05) and urine flow rate and fractional urinary excretion rates of sodium and potassium were markedly elevated compared with controls (P < 0.05). Enalapril-treated rats showed severe renal histological abnormalities, including wall thickening of cortical arterioles, papillary atrophy and tubulointerstitial alterations, mimicking those described previously in similarly treated rats examined in adulthood. 4. In conclusion, neonatal ACE inhibition in rats induces pronounced alterations in renal haemodynamics and function, characterized by reductions in ERPF and GFR, increased RVR and impaired tubular sodium and water reabsorption, which are evident at weaning.

Ren1cHomozygous Null Mice Are Hypotensive and Polyuric, but Heterozygotes Are Indistinguishable from Wild-Type

Mice lacking Ren1c were generated using C57BL/6-derived embryonic stem cells. Mice homozygous for Ren1c disruption (Ren1c-/-) are born at the expected ratio, but approximately 80% die of dehydration within a few days. The surviving Ren1c-/- mice have no renin mRNA expression in the kidney, hydronephrosis, thickening of renal arterial walls, and fibrosis in the kidney. Plasma renin and angiotensins I and II are undetectable. Urinary aldosterone is 6% wild-type. They have low tail-cuff BP (84 +/- 4 versus 116 +/- 5 mmHg in +/+) and excrete large amounts of urine (5.2 +/- 0.8 ml/d, 725 +/- 34 mOsm versus 1.1 +/- 0.1 ml/d, 2460 +/- 170 mOsm in +/+). After 5 d of drinking 5% dextrose, desmopressin does not increase the osmolality of the urine in -/- mice (624 +/- 19 to 656 +/- 25 mOsm), whereas in +/+, it increases severalfold (583 +/- 44 to 2630 +/- 174 mOsm). Minipump infusion of angiotensin II to Ren1c-/- mice restores BP to wild-type level, but preexisting damage to the medulla prevents complete restoration of the ability of the kidney to concentrate urine. Heterozygous Ren1c+/- mice, in contrast, are indistinguishable from +/+ in BP, urine volume, and osmolality. Kidney renin mRNA, the number of kidney cells producing renin, and plasma renin concentration in the Ren1c+/- mice are also indistinguishable from +/+. These results demonstrate that renin is the only enzyme capable of maintaining plasma angiotensins and that renin expression in the kidney is very tightly regulated at the mRNA level.

Angiotensin-converting enzyme inhibitors in the therapy of renal diseases

Renal diseases, especially chronic renal failure (CRF), are common in canine and feline medicine. The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in these conditions in the development of renal lesions and the progression of kidney dysfunction. Angiotensin-converting enzyme inhibitors (ACEI) are currently considered as the most efficient agents in therapeutic strategies. The benefit of an ACEI treatment can be explained by at least three mechanisms: ACEI limit systemic and glomerular capillary hypertension, have an antiproteinuric effect, and retard the development of glomerulosclerosis and tubulointerstitial lesions. These effects have been studied in dogs and cats, and there is now some evidence to support the recommendation of ACEI therapy in dogs and cats with CRF. Nevertheless the prescription of ACEI in such patients should take into account the potential influence of renal impairment on ACEI disposition, and adverse effects on the renal function itself (especially hypotension and acute reductions in glomerular filtration rate). The risk of drug interaction with diuretics, nonsteroidal anti-inflammatory drugs and anesthetics, should not be overestimated. Furthermore, hypotension may occur in patients on a low sodium diet.

Calcineurin is required in urinary tract mesenchyme for the development of the pyeloureteral peristaltic machinery

Congenital obstructive nephropathy is the principal cause of renal failure in infants and children. The underlying molecular and cellular mechanisms of this disease, however, remain largely undetermined. We generated a mouse model of congenital obstructive nephropathy that resembles ureteropelvic junction obstruction in humans. In these mice, calcineurin function is removed by the selective deletion of Cnb1 in the mesenchyme of the developing urinary tract using the Cre/lox system. This deletion results in reduced proliferation in the smooth muscle cells and other mesenchymal cells in the developing urinary tract. Compromised cell proliferation causes abnormal development of the renal pelvis and ureter, leading to defective pyeloureteral peristalsis, progressive renal obstruction, and, eventually, fatal renal failure. Our study demonstrates that calcineurin is an essential signaling molecule in urinary tract development and is required for normal proliferation of the urinary tract mesenchymal cells in a cell-autonomous manner. These studies also emphasize the importance of functional obstruction, resulting from developmental abnormality, in causing congenital obstructive nephropathy.

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.

Genetic disorders of human congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital abnormalities of the kidney and urinary tract, CAKUT are common in humans, occurring at a frequency of approximately 1 in 500 fetal ultrasound examinations. CAKUT are major causes of chronic renal failure in infants and young children, but little is known about the molecular pathogenesis of these disorders. To date, several gene mutations have been identified as a cause of human CAKUT: these include PAX2, KAL, EYA1, AGTR2 and HNF-1beta. At present, there is only limited information regarding how mutations alter gene expression during development to cause some CAKUT. The most convincing information comes from the multiorgan malformation syndromes with specific gene mutations. However, these syndromes are relatively rare, and most CAKUT appear to occur in isolation. The goal of this review is to provide an overview of these genetic disorders for CAKUT. An understanding of the genetic aspects of human CAKUT will help to unravel the pathogenesis of these disorders and may facilitate the design of genetic screening tests for early diagnosis and appropriate genetic counseling. Moreover, a deeper insight into the relationship between abnormal genes and the pathogenesis of abnormalities of CAKUT will provide an etiological classification of CAKUT. In addition, the importance of developing a registry of patients with various forms of CAKUT is discussed. This information will allow us to combine molecular biology and classical epidemiologic methods, and to continue expanding our knowledge regarding CAKUT.

STAT proteins mediate angiotensin II-induced production of TIMP-1 in human proximal tubular epithelial cells

BACKGROUND

Angiotensin II and tissue type inhibitor metalloproteinase-1 (TIMP-1) have been implicated in renal tubulointerstitial fibrosis, but the exact mediating signaling pathway is still unknown. Angiotensin II has been reported to activate signal transducers and activators of transcription (STAT) and induce proliferation of myocyte and vascular smooth muscle cells (VSMC). We hypothesized that the STAT signal pathway is involved in the process of renal tubulointerstitial fibrosis. Therefore, we designed the present study to explore whether angiotensin II could induce TIMP-1 expression in human proximal tubular epithelial cells, and whether it was mediated through the STAT signaling pathway.

METHODS

Electrophoretic mobility shift assay (EMSA) was employed to determine the DNA-STAT binding activity. Supershift assay was used to test the components of activated STAT proteins. Nuclear translocation of activated STATs was observed with laser scanning confocal microscopy. TIMP-1 expression was analyzed with Northern and Western blots. Valsartan and PD123319 were used to block the effects of angiotensin II type 1 (AT1) and angiotensin II type 2 (AT2) receptors of angiotensin II, respectively.

RESULTS

Cultured human proximal tubular epithelial cells constitutively expressed TIMP-1. Angiotensin II induced TIMP-1, mRNA, and protein expressions in time- and dose-dependent manners, which could be inhibited by the AT1 receptor antagonist valsartan, but not by the AT2 antagonist PD123319. Angiotensin II also activated STAT-DNA binding activity in both dose-dependent and biphasic time-dependent manners, and increased the phosphorylation and nuclear translocation of STAT proteins. To examine the role of STAT in angiotensin II-induced TIMP-1 expression, STAT1 and STAT3 antisense oligonucleotides were used. Northern and Western blots showed that STAT1 and STAT3 antisense oligonucleotides could inhibit angiotensin II-induced TIMP-1 expressions, and STAT1 and STAT3 proteins, respectively, could be supershifted by their polyclonal antibodies.

CONCLUSION

STAT1 and STAT3 may, at least in part, mediate angiotensin II-induced TIMP-1 mRNA expression in human renal proximal tubular epithelial cells, implicating a role of the STAT signaling pathway in pathogenesis of renal tubulointerstitial fibrosis.

Kidney development and the fetal programming of adult disease

Recent evidence, from both epidemiological and animal experimental studies, suggest that the very first environment, the intrauterine, is extremely important in determining the future health of the individual. Genetic and 'lifestyle' factors impinge on, and can exacerbate, a 'programming' effect of an adverse fetal environment. In this review, we present compelling evidence to suggest that one of the major organs affected by an unfavourable prenatal environment is the kidney. Many of the factors that can affect fetal renal development (i.e. exposure to excess glucocorticoids, insufficient vitamin A, protein/calorie malnutrition (in rats) and alterations in the intrarenal renin angiotensinogen system), also produce hypertension in the adult animal. When nephron number is compromised during kidney development, maladaptive functional changes occur and can lead, eventually, to hypertension and/or renal disease. Surprisingly, it is during the very earliest stages of kidney development that the vulnerability to these effects occurs.

Brain-specific restoration of angiotensin II corrects renal defects seen in angiotensinogen-deficient mice

Mice deficient for angiotensinogen (AGT), or other components of the renin-angiotensin system, show a high rate of neonatal mortality correlated with severe renal abnormalities including hydronephrosis, hypertrophy of renal arteries, and an impaired ability to concentrate urine. Although transgenic replacement of systemic or adipose, but not renal, AGT in AGT-deficient mice has previously been reported to correct some of these renal abnormalities, the tissue target for this complementation has not been defined. In the current study, we have used a novel transgenic strategy to restore the peptide product of the renin-angiotensin system, angiotensin II, exclusively in the brain of AGT-deficient mice and demonstrate that brain-specific angiotensin II can correct the hydronephrosis and partially correct renal dysfunction seen in AGT-deficient mice. Taken together, these results suggest that the renin-angiotensin system affects renal development and function through systemically accessible targets in the brain.