Downregulation of Spry-1, an inhibitor of GDNF/Ret, causes angiotensin II-induced ureteric bud branching

Programmed Adult Kidney Disease: Importance of Fetal Environment

The Barker hypothesis strongly supported the influence of fetal environment on the development of chronic diseases in later life. Multiple experimental and human studies have identified that the deleterious effect of fetal programming commonly leads to alterations in renal development. The interplay between environmental insults and fetal genome can induce epigenetic changes and lead to alterations in the expression of renal phenotype. In this review, we have explored the renal development and its functions, while focusing on the epigenetic findings and functional aspects of the renin-angiotensin system and its components.

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

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

Duplex kidney formation: developmental mechanisms and genetic predisposition

Congenital abnormalities of the kidney and urinary tract (CAKUT) are a highly diverse group of diseases that together belong to the most common abnormalities detected in the new-born child. Consistent with this diversity, CAKUT are caused by mutations in a large number of genes and present a wide spectrum of phenotypes. In this review, we will focus on duplex kidneys, a relatively frequent form of CAKUT that is often asymptomatic but predisposes to vesicoureteral reflux and hydronephrosis. We will summarise the molecular programs responsible for ureter induction, review the genes that have been identified as risk factors in duplex kidney formation and discuss molecular and cellular mechanisms that may lead to this malformation.

Decreased H3K9ac level of AT2R mediates the developmental origin of glomerulosclerosis induced by prenatal dexamethasone exposure in male offspring rats

This study aimed to demonstrate that prenatal dexamethasone exposure (PDE) can induce kidney dysplasia in utero and adult glomerulosclerosis in male offspring, and to explore the underlying intrauterine programming mechanisms. Pregnant rats were subcutaneously administered dexamethasone 0.2 mg/kg.d from gestational day (GD) 9 to GD20. The male fetus on GD20 and the adult offspring at age of postnatal week 28 were analyzed. The adult offspring kidneys in the PDE group displayed glomerulosclerosis, elevated levels of serum creatinine and urine protein, ultrastructural damage of podocytes, the reduced expression levels of podocyte marker genes, nephrin and podocin. The histone 3 lysine 9 acetylation (H3K9ac) level in the promoter of renal angiotensin II receptor type 2 (AT2R) and its expression were reduced, whereas the angiotensin II receptor type 1a (AT1aR)/AT2R expression ratio was increased. The fetal kidneys in the PDE group displayed an enlarged Bowman's space and a shrunken glomerular tuft, a reduced cortex width and an increase in the nephrogenic zone/cortical zone ratio, reduced the expression level of glial-cell-line derived neurotrophic factor/c-Ret tyrosine kinase receptor (GDNF/c-Ret) signal pathway and podocyte marker genes. Moreover, the H3K9ac and H3K27ac levels of AT2R as well as the gene and protein expression levels of AT2R in fetal kidneys were inhibited by PDE. In vitro, primary metanephric mesenchyme stem cells (MMSCs) were treated with dexamethasone. Overexpression of AT2R reversed the inhibited expression of GDNF/c-Ret and podocin/nephrin induced by dexamethasone, and glucocorticoids receptor antagonist abolished the decreased H3K9ac level and gene expression of AT2R. In conclusion, PDE induced the offspring's kidney dysplasia as well as adult glomerulosclerosis, which was mediated by a sustained decrease in renal AT2R expression via decreasing the H3 K9ac level.

Adhesion GPCRs in Kidney Development and Disease

Chronic kidney disease (CKD) represents the fastest growing pathology worldwide with a prevalence of >10% in many countries. In addition, kidney cancer represents 5% of all new diagnosed cancers. As currently no effective therapies exist to restore kidney function after CKD- as well as cancer-induced renal damage, it is important to elucidate new regulators of kidney development and disease as new therapeutic targets. G protein-coupled receptors (GPCRs) represent the most successful class of pharmaceutical targets. In recent years adhesion GPCRs (aGPCRs), the second largest GPCR family, gained significant attention as they are present on almost all mammalian cells, are associated to a plethora of diseases and regulate important cellular processes. aGPCRs regulate for example cell polarity, mitotic spindle orientation, cell migration, and cell aggregation; all processes that play important roles in kidney development and/or disease. Moreover, polycystin-1, a major regulator of kidney development and disease, contains a GAIN domain, which is otherwise only found in aGPCRs. In this review, we assess the potential of aGPCRs as therapeutic targets for kidney disease. For this purpose we have summarized the available literature and analyzed data from the databases The Human Protein Atlas, EURExpress, Nephroseq, FireBrowse, cBioPortal for Cancer Genomics and the National Cancer Institute Genomic Data Commons data portal (NCIGDC). Our data indicate that most aGPCRs are expressed in different spatio-temporal patterns during kidney development and that altered aGPCR expression is associated with a variety of kidney diseases including CKD, diabetic nephropathy, lupus nephritis as well as renal cell carcinoma. We conclude that aGPCRs present a promising new class of therapeutic targets and/or might be useful as diagnostic markers in kidney disease.

Foxd1 is an upstream regulator of the renin-angiotensin system during metanephric kidney development

BackgroundWe tested the hypothesis that Foxd1, a transcription factor essential for normal kidney development, is an upstream regulator of the renin-angiotensin system (RAS) during ureteric bud (UB)-branching morphogenesis.MethodsUB branching, RAS gene, and protein expression were studied in embryonic mouse kidneys. RAS mRNA expression was studied in mesenchymal MK4 cells.ResultsThe number of UB tips was reduced in Foxd1^-/- compared with that in Foxd1^+/+ metanephroi on embryonic day E12.5 (14±2.1 vs. 28±1.3, P<0.05). Quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) demonstrated that renin, angiotensin I-converting enzyme (ACE), and angiotensin (Ang) II receptor type 1 (AT₁R) mRNA levels were decreased in Foxd1^-/- compared with those in Foxd1^+/+ E14.5 metanephroi. Western blot analysis and immunohistochemistry showed decreased expression of AGT and renin proteins in Foxd1^-/- metanephroi compared with that in Foxd1^+/+ metanephroi. Foxd1 overexpression in mesenchymal MK4 cells in vitro increased renin, AGT, ACE, and AT₁R mRNA levels. Exogenous Ang II stimulated UB branching equally in whole intact E12.5 Foxd1^-/- and Foxd1^+/+ metanephroi grown ex vivo (+364±21% vs. +336±18%, P=0.42).ConclusionWe conclude that Foxd1 is an upstream positive regulator of RAS during early metanephric development and propose that the cross-talk between Foxd1 and RAS is essential in UB-branching morphogenesis.

Nephron number, hypertension, and CKD: physiological and genetic insight from humans and animal models

The kidneys play a vital role in the excretion of waste products and the regulation of electrolytes, maintenance of acid-base balance, regulation of blood pressure, and production of several hormones. Any alteration in the structure of the nephron (basic functional unit of the kidney) can have a major impact on the kidney's ability to work efficiently. Progressive decline in kidney function can lead to serious illness and ultimately death if not treated by dialysis or transplantation. While there have been numerous studies that implicate lower nephron numbers as being an important factor in influencing susceptibility to developing hypertension and chronic kidney disease, a direct association has been difficult to establish because of three main limitations: 1) the large variation in nephron number observed in the human population; 2) no established reliable noninvasive methods to determine nephron complement; and 3) to date, nephron measurements have been done after death, which doesn't adequately account for potential loss of nephrons with age or disease. In this review, we will provide an overview of kidney structure/function, discuss the current literature for both humans and other species linking nephron deficiency and cardio-renal complications, as well as describe the major molecular signaling factors involved in nephrogenesis that modulate variation in nephron number. As more detailed knowledge about the molecular determinants of nephron development and the role of nephron endowment in the cardio-renal system is obtained, it will hopefully provide clinicians the ability to accurately identify people at risk to develop CKD/hypertension and lead to a shift in patient care from disease treatment to prevention.

Prenatal nicotine exposure induced GDNF/c-Ret pathway repression-related fetal renal dysplasia and adult glomerulosclerosis in male offspring

Prenatal nicotine exposure could induce fetal renal dysplasia associated with the suppression of the GDNF/c-Ret pathway and adult glomerulosclerosis in male offspring, which might be mediated by alterations in angiotensin II receptors.

Chromatin dynamics in kidney development and function

Epigenetic mechanisms are fundamental key features of developing cells connecting developmental regulatory factors to chromatin modification. Changes in the environment during renal development can have long-lasting effects on the permanent tissue structure and the level of expression of important functional genes. These changes are believed to contribute to kidney disease occurrence and progression. Although the mechanisms of early patterning and cell fate have been well described for renal development, little is known about associated epigenetic modifications and their impact on how genes interact to specify the renal epithelial cells of nephrons and how this specification is relevant to maintaining normal renal function. A better understanding of the renal cell-specific epigenetic modifications and the interaction of different cell types to form this highly complex organ will not only help to better understand developmental defects and early loss of kidney function in children, but also help to understand and improve chronic disease progression, cell regeneration and renal aging.

Renin-angiotensin system in ureteric bud branching morphogenesis: implications for kidney disease

Failure of normal branching morphogenesis of the ureteric bud (UB), a key ontogenic process that controls organogenesis of the metanephric kidney, leads to congenital anomalies of the kidney and urinary tract (CAKUT), the leading cause of end-stage kidney disease in children. Recent studies have revealed a central role of the renin-angiotensin system (RAS), the cardinal regulator of blood pressure and fluid/electrolyte homeostasis, in the control of normal kidney development. Mice or humans with mutations in the RAS genes exhibit a spectrum of CAKUT which includes renal medullary hypoplasia, hydronephrosis, renal hypodysplasia, duplicated renal collecting system and renal tubular dysgenesis. Emerging evidence indicates that severe hypoplasia of the inner medulla and papilla observed in angiotensinogen (Agt)- or angiotensin (Ang) II AT 1 receptor (AT 1 R)-deficient mice is due to aberrant UB branching morphogenesis resulting from disrupted RAS signaling. Lack of the prorenin receptor (PRR) in the UB in mice causes reduced UB branching, resulting in decreased nephron endowment, marked kidney hypoplasia, urinary concentrating and acidification defects. This review provides a mechanistic rational supporting the hypothesis that aberrant signaling of the intrarenal RAS during distinct stages of metanephric kidney development contributes to the pathogenesis of the broad phenotypic spectrum of CAKUT. As aberrant RAS signaling impairs normal renal development, these findings advocate caution for the use of RAS inhibitors in early infancy and further underscore a need to avoid their use during pregnancy and to identify the types of molecular processes that can be targeted for clinical intervention.

How the kidney is impacted by the perinatal maternal environment to develop hypertension

Environmental conditions during perinatal development such as maternal undernutrition, maternal glucocorticoids, placental insufficiency, and maternal sodium overload can program changes in renal Na(+) excretion leading to hypertension. Experimental studies indicate that fetal exposure to an adverse maternal environment may reduce glomerular filtration rate by decreasing the surface area of the glomerular capillaries. Moreover, fetal responses to environmental insults during early life that contribute to the development of hypertension may include increased expression of tubular apical or basolateral membrane Na(+) transporters and increased production of renal superoxide leading to enhanced Na(+) reabsorption. This review will address the role of these potential renal mechanisms in the fetal programming of hypertension in experimental models induced by maternal undernutrition, fetal exposure to glucocorticoids, placental insufficiency, and maternal sodium overload in the rat.

Ontogeny of the (pro)renin receptor

BACKGROUND

This study examined temporal expression of the (pro)renin receptor ((P)RR), during renal, heart, lung, and brain organogenesis in the mouse.

METHODS

(P)RR expression was determined by quantitative reverse-transcription PCR, western blotting, and immunohistochemistry.

RESULTS

Brain, kidney, and lung (P)RR mRNA levels increased progressively during gestation and peak on postnatal day (P)10. (P)RR protein contents were high during gestation in all organs studied and declined with maturation. Brain (P)RR was expressed most prominently in the ependymal lining of the ventricles. In the embryonic day (E)16.5 and E18.5 metanephros, (P)RR was present in the ureteric bud and ureteric bud-derived collecting ducts. In the fetal heart, (P)RR was expressed diffusely in the myocardium, whereas pulmonary (P)RR was detected at highest levels in the epithelium of branching airways. Treatment of newborn kidneys with the angiotensin (Ang) II type 1 receptor (AT₁R) antagonist candesartan increased (P)RR mRNA levels.

CONCLUSION

(P)RR gene and protein expressions in the brain, kidney, heart, and lung are developmentally regulated in a tissue-specific manner. Endogenous Ang II, acting via the AT₁R, exerts a negative feedback on (P)RR in the newborn kidney. These findings suggest that high (P)RR protein levels observed during gestation may play a role in brain, kidney, heart, and lung organogenesis.

Cell biology of ureter development

The mammalian ureter contains two main cell types: a multilayered water-tight epithelium called the urothelium, surrounded by smooth muscle layers that, by generating proximal to distal peristaltic waves, pump urine from the renal pelvis toward the urinary bladder. Here, we review the cellular mechanisms involved in the development of these tissues, and the molecules that control the process. We consider the relevance of these biologic findings for understanding the pathogenesis of human ureter malformations.

Maternal exposure to di-(2-ethylhexyl)phthalate alters kidney development through the renin-angiotensin system in offspring

Di-(2-ethylhexyl)phthalate (DEHP) is a widely used industrial plasticizer to which humans are widely exposed. We investigated the consequences of maternal exposure to DEHP on nephron formation, examined the programming of renal function and blood pressure and explored the mechanism in offspring. Maternal rats were treated with vehicle, 0.25 and 6.25mg/kg body weight/day DEHP respectively from gestation day 0 to postnatal day 21. Maternal DEHP exposure resulted in lower number of nephrons, higher glomerular volume and smaller Bowman's capsule in the DEHP-treated offspring at weaning, as well as glomerulosclerosis, interstitial fibrosis and effacement of podocyte foot processes in adulthood. In the DEHP-treated offspring, the renal function was lower and the blood pressure was higher. The renal protein expression of renin and angiotensin II was reduced at birth day and increased at weaning. Maternal DEHP exposure also led to reduced mRNA expression of some renal development involved genes at birth day, including Foxd1, Gdnf, Pax2 and Wnt11. While, the mRNA expression of some genes was raised, including Bmp4, Cdh11, Calm1 and Ywhab. These data show that maternal DEHP exposure impairs the offspring renal development, resulting in a nephron deficit, and subsequently elevated blood pressure later in life. Our findings suggest that DEHP exposure in developmental periods may affect the development of nephrons and adult renal disease through inhibition of the renin-angiotensin system.

Ontogeny of angiotensin-converting enzyme 2

INTRODUCTION

This study examined the temporal expression of angiotensin (Ang)-converting enzyme 2 (ACE2) during renal, heart, lung, and brain organogenesis in the mouse.

RESULTS

We demonstrate that kidney ACE2 mRNA levels are low on embryonic day (E) 12.5, increase fourfold during development, and decline in adulthood. In extrarenal tissues, ACE2 mRNA levels are also low during early gestation, increase in perinatal period, and peak in adulthood. The lung shows the highest age-related increase in ACE2 mRNA levels followed by the brain, kidney, and heart. ACE2 protein levels and enzymatic activity are high in all organs studied during gestation and decline postnatally. Ang II decreases ACE2 mRNA levels and enzymatic activity in kidneys grown ex vivo. These effects of Ang II are blocked by the specific Ang II AT(1) receptor (AT(1)R) antagonist candesartan, but not by the AT(2) receptor (AT(2)R) antagonist PD123319.

DISCUSSION

We conclude that ACE2 gene and protein expression and enzymatic activity are developmentally regulated in a tissue-specific manner. Ang II, acting through AT(1)R, exerts a negative feedback on ACE2 during kidney development. We postulate that relatively high ACE2 protein levels and enzymatic activity observed during gestation may play a role in kidney, lung, brain, and heart organogenesis.

Alpha-tocopherol prevents intrauterine undernutrition-induced oligonephronia in rats

The role of α-tocopherol during nephrogenesis was investigated in rats subjected to maternal undernutrition, which reduces the number of nephrons. α-tocopherol (350 mg/kg, p.o.) was administered daily to well-nourished or malnourished Wistar dams during pregnancy, or to prenatal undernourished rats during lactation. The kidneys of 1- and 25-day-old offspring were removed to evaluate expression of angiotensin II (Ang II) and to correlate this with expression of proliferating cell nuclear antigen, α-smooth muscle actin, fibronectin and vimentin in the glomeruli and tubulointerstitial space. One-day-old prenatally undernourished rats had reduced expression of Ang II and of kidney development markers, and presented with an enlarged nephrogenic zone. Maternal administration of α-tocopherol restored the features of normal kidney development in undernourished rats. Twenty-five-day-old prenatally undernourished progeny had fewer glomeruli than the control group. Conversely, animals from mothers that received α-tocopherol during lactation presented with the same number of glomeruli and the same glomerular morphometrical profile as the control group. Analyzing the levels of thiobarbituric acid reactive substances in the liver in conjunction with kidney development markers, it is plausible that α-tocopherol had antioxidant and non-antioxidant actions. This study provides evidence that α-tocopherol treatment restored Ang II expression, and subsequently restored renal structural development.

Renin-angiotensin system in ureteric bud branching morphogenesis: insights into the mechanisms

Branching morphogenesis of the ureteric bud (UB) is a key developmental process that controls organogenesis of the entire metanephros. Notably, aberrant UB branching may result in a spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). Genetic, biochemical and physiological studies have demonstrated that the renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans cause diverse types of CAKUT which include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, abnormal glomerulogenesis and urinary concentrating defect. Despite widely accepted role of the RAS in metanephric kidney and renal collecting system (ureter, pelvis, calyces and collecting ducts) development, the mechanisms by which an intact RAS exerts its morphogenetic actions are incompletely defined. Emerging evidence indicates that defects in UB branching morphogenesis may be causally linked to the pathogenesis of renal collecting system anomalies observed under conditions of aberrant RAS signaling. This review describes the role of the RAS in UB branching morphogenesis and highlights emerging insights into the cellular and molecular mechanisms whereby RAS regulates this critical morphogenetic process.

Angiotensin II stimulates in vitro branching morphogenesis of the isolated ureteric bud

Mutations in the renin-angiotensin system (RAS) genes are associated with congenital anomalies of the kidney and urinary tract (CAKUT). As angiotensin (Ang) II, the principal effector peptide growth factor of the RAS, stimulates ureteric bud (UB) branching in whole intact embryonic (E) metanephroi, defects in UB morphogenesis may be causally linked to CAKUT observed under conditions of disrupted RAS. In the present study, using the isolated intact UB (iUB) assay, we tested the hypothesis that Ang II stimulates UB morphogenesis by directly acting on the UB, identified Ang II target genes in the iUB by microarray and examined the effect of Ang II on UB cell migration in vitro. We show that isolated E11.5 mouse iUBs express Ang II AT(1) and AT(2) receptor mRNA. Treatment of E11.5 iUBs grown in collagen matrix gels with Ang II (10(-5)M) increases the number of iUB tips after 48h of culture compared to control (4.8±0.4 vs. 2.4±0.2, p<0.01). A number of genes required for UB branching as well as novel genes whose role in UB development is currently unknown are targets of Ang II signaling in the iUB. In addition, Ang II increases UB cell migration (346±5.1 vs. 275±4.4, p<0.01) in vitro. In summary, Ang II stimulates UB cell migration and directly induces morphogenetic response in the iUB. We conclude that Ang II-regulated genes in the iUB may be important mediators of Ang II-induced UB branching. We hypothesize that Ang II-dependent cell movements play an important role in UB branching morphogenesis.

Receptor tyrosine kinases in kidney development

The kidney plays a fundamental role in the regulation of arterial blood pressure and fluid/electrolyte homeostasis. As congenital anomalies of the kidney and urinary tract (CAKUT) constitute one of the most common human birth defects, improved understanding of the cellular and molecular mechanisms that lead to CAKUT is critical. Accumulating evidence indicates that aberrant signaling via receptor tyrosine kinases (RTKs) is causally linked to CAKUT. Upon activation by their ligands, RTKs dimerize, undergo autophosphorylation on specific tyrosine residues, and interact with adaptor proteins to activate intracellular signal transduction pathways that regulate diverse cell behaviours such as cell proliferation, survival, and movement. Here, we review the current understanding of role of RTKs and their downstream signaling pathways in the pathogenesis of CAKUT.

Genetics of congenital anomalies of the kidney and urinary tract

Congenital anomalies of the kidney and urinary tract (CAKUT) occur in 1 in 500 births and are a major cause of morbidity in children. Notably, CAKUT account for the most cases of pediatric end-stage renal disease and predispose the individual to hypertension and cardiovascular disease throughout life. Although some forms of CAKUT are a part of a syndrome or are associated with a positive family history, most cases of renal system anomalies are sporadic and isolated to the urinary tract. Broad phenotypic spectrum of CAKUT and variability in genotype-phenotype correlation indicate that pathogenesis of CAKUT is a complex process that depends on interplay of many factors. This review focuses on the genetic mechanisms (single-gene mutations, modifier genes) leading to renal system anomalies in humans and discusses emerging insights into the role of epigenetics, in utero environmental factors, and micro-RNAs (miRNAs) in the pathogenesis of CAKUT. Common gene networks that function in defined temporospatial fashion to orchestrate renal system morphogenesis are highlighted. Derangements in cellular, molecular, and morphogenetic mechanisms that direct normal renal system development are emphasized as a major cause of CAKUT. Integrated understanding of how morphogenetic process disruptions are linked to CAKUT will enable improved diagnosis, treatment, and prevention of congenital renal system anomalies and their consequences.

Effects of glial cell line-derived neurotrophic factor on cultured murine retinal progenitor cells

PURPOSE

Glial cell line-derived neurotrophic factor (GDNF) is neuroprotective of retinal neurons, and transduced retinal progenitor cells (RPCs) can deliver this cytokine for the treatment of retinal diseases, yet the potential effects of GDNF on RPCs have received little attention.

METHODS

Murine RPCs were assessed under multiple conditions in the presence or absence of epidermal growth factor (EGF, 20 ng/ml) and/or GDNF (10 ng/ml) using a variety of techniques, including live-cell imaging, caspase-3 activity assay, whole genome microarray, quantitative polymerase chain reaction (qPCR), and western blotting.

RESULTS

Live monitoring revealed that formation of initial aggregates resulted largely from the collision and adherence of dissociated RPCs, as opposed to clonal proliferation. Spheres enlarged in size and number, with more reaching the threshold criteria for cross-sectional areas in the EGF+GDNF condition. Proliferation was measurably augmented in association with EGF+GDNF, and K(i)-67 expression was modestly increased (1.07 fold), as were hairy and enhancer of split 5 (Hes5), mammalian achaete-scute homolog 1 (Mash1), and Vimentin. However, global gene expression did not reveal a notable treatment-related response, and the expression of the majority of progenitor and lineage markers examined remained stable. GDNF reduced RPC apoptosis, compared to complete growth-factor withdrawal, although it could not by itself sustain mitotic activity.

CONCLUSIONS

These data support the feasibility of developing GDNF-transduced RPCs as potential therapeutic agents for use in retinal diseases.

Histone deacetylases are critical regulators of the renin-angiotensin system during ureteric bud branching morphogenesis

Mutations in the genes encoding components of the renin-angiotensin system (RAS) in mice or humans cause congenital abnormalities of the kidney and urinary tract. We hypothesized that absence of angiotensin (Ang) II in angiotensinogen (AGT)-deficient mice leads to defects in ureteric bud (UB) branching and that RAS genes are critically dependent on histone deacetylase (HDAC) activity. The number of UB tips was lower in AGT-/- compared with AGT+/+ embryonic (E) day E13.5 metanephroi (24+/-1.5 versus 36+/-3.7, p<0.05). Real-time RT-PCR demonstrated that pharmacological inhibition of HDAC activity with Scriptaid increases AGT, renin, angiotensin-converting enzyme (ACE), and AT1 receptor (AT1R) mRNA levels in E12.5 mouse metanephroi and early mesenchymal (MK3) cells. Furthermore, Scriptaid enhanced Ang II induced decrease in Sprouty (Spry) 1 gene expression in cultured UB cells. Treatment of intact E12.5 mouse metanephroi grown ex vivo with Ang II (10(-5) M, 24 h) increased HDAC-1 and decreased total acetylated histone H3 protein levels. These findings indicate that lack of endogenous Ang II in AGT-deficient mice inhibits UB branching. We conclude that intact RAS is critical in structural integrity of the renal collecting system and that UB morphogenetic program genes, such as AGT, renin, ACE, AT1R, or Spry1, are epigenetically controlled via HDACs.

Angiotensin II AT2 receptor regulates ureteric bud morphogenesis

ANG II AT2 receptor (AT2R)-deficient mice exhibit abnormal ureteric bud (UB) budding, increased incidence of double ureters, and vesicoureteral reflux. However, the role of the AT2R during UB morphogenesis and the mechanisms by which aberrant AT2R signaling disrupts renal collecting system development have not been fully defined. In this study, we mapped the expression of the AT2R during mouse metanephric development, examined the impact of disrupted AT2R signaling on UB branching, cell proliferation, and survival, and investigated the cross talk of the AT2R with the glial-derived neurotrophic factor (GDNF)/c-Ret/Wnt11 signaling pathway. Embryonic mouse kidneys express AT2R in the branching UB and the mesenchyme. Treatment of embryonic day 12.5 (E12.5) metanephroi with the AT2R antagonist PD123319 or genetic inactivation of the AT2R in mice inhibits UB branching, decreasing the number of UB tips compared with control (34 +/- 1.0 vs. 43 +/- 0.6, P < 0.01; 36 +/- 1.8 vs. 48 +/- 1.3, P < 0.01, respectively). In contrast, treatment of metanephroi with the AT2R agonist CGP42112 increases the number of UB tips compared with control (48 +/- 1.8 vs. 39 +/- 12.3, P < 0.05). Using real-time quantitative RT-PCR and whole mount in situ hybridization, we demonstrate that PD123319 downregulates the expression of GDNF, c-Ret, Wnt11, and Spry1 mRNA levels in E12.5 metanephroi grown ex vivo. AT(2)R blockade or genetic inactivation of AT2R stimulates apoptosis and inhibits proliferation of the UB cells in vivo. We conclude that AT2R performs essential functions during UB branching morphogenesis via control of the GDNF/c-Ret/Wnt11 signaling pathway, UB cell proliferation, and survival.

Angiotensin II-induced activation of c-Ret signaling is critical in ureteric bud branching morphogenesis

The renin-angiotensin system (RAS) plays a critical role in ureteric bud (UB) and kidney morphogenesis. Mutations in the genes encoding components of the RAS cause a spectrum of congenital abnormalities of the kidney and urinary tract (CAKUT). However, the mechanisms by which aberrations in the RAS result in CAKUT are poorly understood. Given that c-Ret receptor tyrosine kinase (RTK) is a major inducer of UB branching, the present study tested the hypothesis that angiotensin (Ang) II-induced activation of c-Ret plays a critical role in UB branching morphogenesis. E12.5 mice metanephroi were grown for 24h in the presence or absence of Ang II, Ang II AT(1) receptor (AT(1)R) antagonist candesartan, phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 or ERK1/2 inhibitor PD98059. Ang II increased the number of UB tips (61+/-2.4 vs. 45+/-4.3, p<0.05) compared with control. Quantitative RT-PCR analysis demonstrated that Ang II increased c-Ret mRNA levels in the kidney (1.35+/-0.05 vs. 1.0+/-0, p<0.01) and in the UB cells (1.28+/-0.04 vs. 1.0+/-0, p<0.01) compared to control. This was accompanied by increased Tyr(1062)Ret phosphorylation by Ang II (5.5+/-0.9 vs. 1.8+/-0.4 relative units, p<0.05). In addition, treatment of UB cells with Ang II (10(-5)M) increased phosphorylation of Akt compared to control (213+/-16 vs. 100+/-20%, p<0.05). In contrast, treatment of metanephroi or UB cells with candesartan decreased c-Ret mRNA levels (0.72+/-0.06 vs. 1.0+/-0, p<0.01; 0.68+/-0.07 vs. 1.0+/-0, p<0.05, respectively) compared with control. Ang II-induced UB branching was abrogated by LY294002 (24+/-2.6 vs. 37+/-3.0, p<0.05) or PD98059 (33+/-2.0 vs. 48+/-2.2, p<0.01). These data demonstrate that Ang II-induced UB branching depends on activation of Akt and ERK1/2. We conclude that cross-talk between the RAS and c-Ret signaling plays an important role in the development of the renal collecting system.

Renin-angiotensin system-growth factor cross-talk: a novel mechanism for ureteric bud morphogenesis

The renin-angiotensin system (RAS) plays a critical role in kidney development. Mutations in the genes encoding components of the RAS cause a spectrum of congenital abnormalities of the kidney and renal collecting system, ranging from hypoplasia of the renal medulla and hydronephrosis in mice to renal tubular dysgenesis in humans. However, the mechanisms by which an intact RAS controls proper renal system development and how aberrations in the RAS result in abnormal kidney and renal collecting system development are poorly understood. The renal collecting system originates from the ureteric bud (UB). A number of transcription and growth factors regulate UB branching morphogenesis to ultimately form the ureter, pelvis, calyces, medullary, and cortical collecting ducts. Importantly, UB morphogenesis is a key developmental process that controls organogenesis of the entire metanephros. This review emphasizes emerging insights into the role for the RAS in UB morphogenesis and explores the mechanisms whereby RAS regulates this important process. A conceptual framework derived from recent work indicates that cooperation between the angiotensin II AT(1) receptor and receptor tyrosine kinase signaling performs essential functions during renal collecting system development via control of UB branching morphogenesis.