Developmental expression of renal angiotensin II receptor genes in the mouse

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

Angiotensin II Type 2 Receptor: A Target for Protection Against Hypertension, Metabolic Dysfunction, and Organ Remodeling

The renin-angiotensin system is of vital significance not only in the maintenance of blood pressure but also because of its role in the pathophysiology of different organ systems in the body. Of the 2 Ang II (angiotensin II) receptors, the AT₁R (Ang II type 1 receptor) has been extensively studied for its role in mediating the classical functions of Ang II, including vasoconstriction, stimulation of renal tubular sodium reabsorption, hormonal secretion, cell proliferation, inflammation, and oxidative stress. The other receptor, AT₂R (Ang II type 2 receptor), is abundantly expressed in both immune and nonimmune cells in fetal tissue. However, its expression is increased under pathological conditions in adult tissues. The role of AT₂R in counteracting AT₁R function has been discussed in the past 2 decades. However, with the discovery of the nonpeptide agonist C21, the significance of AT₂R in various pathologies such as obesity, hypertension, and kidney diseases have been examined. This review focuses on the most recent findings on the beneficial effects of AT₂R by summarizing both gene knockout studies as well as pharmacological studies, specifically highlighting its importance in blood pressure regulation, obesity/metabolism, organ protection, and relevance in the treatment of coronavirus disease 2019 (COVID-19).

Renin-angiotensin system in mammalian kidney development

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

Localization of angiotensin II type 1 receptor gene expression in rodent and human kidneys

The kidneys are an important target for angiotensin II (ANG II). In adult kidneys, the effects of ANG II are mediated mainly by ANG II type 1 (AT₁) receptors. AT₁ receptor expression has been reported for a variety of different cell types within the kidneys, suggesting a broad spectrum of actions for ANG II. Since there have been heterogeneous results in the literature regarding the intrarenal distribution of AT₁ receptors, this study aimed to obtain a comprehensive overview about the localization of AT₁ receptor expression in mouse, rat, and human kidneys. Using the cell-specific and high-resolution RNAscope technique, we performed colocalization experiments with various cell markers to specifically discriminate between different segments of the tubular and vascular system. Overall, we found a similar pattern of AT₁ mRNA expression in mouse, rat, and human kidneys. AT₁ receptors were detected in mesangial cells and renin-producing cells. In addition, AT₁ mRNA was found in interstitial cells of the cortex and outer medulla. In rodents, late afferent and early efferent arterioles expressed AT₁ receptor mRNA, but larger vessels of the investigated species showed no AT₁ expression. Tubular expression of AT₁ mRNA was species dependent with a strong expression in proximal tubules of mice, whereas expression was undetectable in human tubular cells. These findings suggest that the (juxta)glomerular area and tubulointerstitium are conserved expression sites for AT₁ receptors across species and might present the main target sites for ANG II in adult human and rodent kidneys.NEW & NOTEWORTHY Angiotensin II (ANG II) type 1 (AT₁) receptors are essential for mediating the effects of ANG II in the kidneys. This study aimed to obtain a comprehensive overview about the cell-specific localization of AT₁ receptor expression in rodent and human kidneys using the novel RNAscope technique. We found that the conserved AT₁ receptor mRNA expression sites across species are the (juxta)glomerular areas and tubulointerstitium, which might present main target sites for ANG II in adult human and rodent kidneys.

Renal impairment induced by prenatal exposure to angiotensin II in male rat offspring

Suboptimal conditions during prenatal ontogeny can impair development of several physiological systems and result in cardiometabolic diseases in adulthood. The kidney has been identified as one of the most sensitive organs for developmental programming, but underlying mechanisms are not fully understood. Therefore, in our study we explored the consequences of prenatally increased angiotensin II (Ang II) on the structural development of the kidney and its damage by infiltrated immune cells under normal diet and after an increased salt intake, as a second insult representing a lifestyle factor in humans. Female rats were implanted with osmotic mini-pumps continuously releasing Ang II of dose 2 µg/kg/h during last two weeks of pregnancy, whereas control females were sham operated. Immunohistological and ultrastructural evaluations of the kidneys and their infiltration with immune cells were performed in mature male progeny kept either on a standard or increased salt (2% NaCl) diet. Glomerular volume decreased and the cortical tubulointerstitial injury increased in the offspring prenatally exposed to Ang II with no additional effect of increased salt. Ultrastructural examination demonstrated degenerative changes in proximal tubules, mainly fewer and shorter microvilli in the brush border, enlarged mitochondria, and an increased number of lysosomes in the epithelial cells in the progeny prenatally exposed to Ang II. Moreover, the treatment resulted in increased infiltration of T-cells and macrophages in the renal cortex compared to controls. These changes paralleled with reduced numbers of cytotoxic T-cells in circulation and higher oxidative burst of neutrophils in the progeny of Ang II-treated mothers compared to controls. Altogether, results suggest that prenatally increased Ang II promoted infiltration of immune cells in the kidney and subsequent oxidative stress, which induced a damage of renal glomerular and tubular system entailing negative consequences on the cardiovascular system.

Impact statement

Suboptimal prenatal conditions can contribute to development of cardiovascular diseases and an altered renin-angiotensin-aldosterone system (RAAS) can be involved in the process. In our study, increased angiotensin II in pregnant female rats resulted in renal cortical interstitial damage, and renal ultrastructural changes in the glomeruli, the brush border of proximal tubules and mitochondria in mature male offspring. The treatment promoted infiltration of T cells and macrophages in the kidneys and primed an oxidative burst of circulating neutrophils, indicating a pro-inflammatory state in the progeny of angiotensin II-treated mothers. Deregulated RAAS of mothers is involved in developmental programming of hypertension in adult male offspring via damaging kidney morphology and function. These findings suggest that preventing the activation of RAAS and oxidative stress during perinatal development might protect against hypertension development in adult male progeny.

Apparently normal kidney development in mice with conditional disruption of ANG II-AT1 receptor genes in FoxD1-positive stroma cell precursors

An intact renin-angiotensin system involving ANG II type 1 (AT₁) receptors is crucial for normal kidney development. It is still unclear in which cell types AT₁ receptor signaling is required for normal kidney development, maturation, and function. Because all kidney cells deriving from stroma progenitor cells express AT₁ receptors and because stromal cells fundamentally influence nephrogenesis and tubular maturation, we investigated the relevance of AT₁ receptors in stromal progenitors and their descendants for renal development and function. For this aim, we generated and analyzed mice with conditional deletion of AT_1A receptor in the FoxD1 cell lineage in combination with global disruption of the AT_1B receptor gene. These FoxD1-AT1ko mice developed normally. Their kidneys showed neither structural nor functional abnormalities compared with wild-type mice, whereas in isolated perfused FoxD1-AT1ko kidneys, the vasoconstrictor and renin inhibitory effects of ANG II were absent. In vivo, however, plasma renin concentration and renal renin expression were normal in FoxD1-AT1ko mice, as were blood pressure and glomerular filtration rate. These findings suggest that a strong reduction of AT₁ receptors in renal stromal progenitors and their descendants does not disturb normal kidney development.

When Less or More Isn't Enough: Renal Maldevelopment Arising From Disequilibrium in the Renin-Angiotensin System

Environmental and nutritional factors during fetal and neonatal life can have long-lasting effects on renal functions and physiology and susceptibility to kidney disease in adulthood. All components of the renin-angiotensin system (RAS) are highly expressed in the kidneys during the period of renal development. The RAS plays a central role in the regulation of various cellular growth factors and stimulates adhesion molecules and cellular migration. The use of antagonists of this system during fetal development represents a major risk factor for hypertension, renal vascular dysfunction, and kidney medulla atrophy in adulthood. The inappropriate activation of the RAS by vitamin D (VitD) deficiency has been studied in recent years. Clinical and experimental studies have demonstrated an inverse relationship between circulating VitD levels and blood pressure, plasma and renin activity, and an increase in angiotensin II and the receptor AT₁. These data raise new questions about the importance of the integrity of the RAS during development since RAS pathway inhibitors and VitD deficiency have opposing functions. This is a literature review on the possible mechanisms by which antagonists of the RAS and VitD deficiency during fetal development provoke disturbances in kidney structure and function. Potential mechanisms are presented and discussed, and the possible pathways by which an imbalanced maternal RAS may negatively impact fetal development and have consequences in adulthood are also explored.

AT2 receptors in cardiovascular and renal diseases

The renin-angiotensin system (RAS) plays an important role in the initiation and progression of cardiovascular and renal diseases. These actions mediated by AT1 receptor (AT1R) are well established and led to development of selective AT1R blockers (ARBs). In contrast, there is scientific evidence that AT2 receptor (AT2R) mediates effects different from and often opposing those of the AT1R. Meagrely expressed in healthy tissue the AT2R is upregulated in injuries providing an endogenous protection to inflammatory, oxidative and apoptotic processes. Interestingly the beneficial effects mediated by AT2R can be further enhanced by pharmacological intervention using the recently developed AT2R agonists. This review article summarizes our current knowledge about regulation, signalling and effects mediated by AT2R in health and disease, with emphasis on cardiac and renal systems. At the end a novel concept of natural protective systems will be introduced and discussed as an attractive target in drug development.

Angiotensin II-AT1-receptor signaling is necessary for cyclooxygenase-2-dependent postnatal nephron generation

Deletion of cyclooxygenase-2 (COX-2) causes impairment of postnatal kidney development. Here we tested whether the renin angiotensin system contributes to COX-2-dependent nephrogenesis in mice after birth and whether a rescue of impaired renal development and function in COX-2^-/- mice was achievable. Plasma renin concentration in mouse pups showed a birth peak and a second peak around day P8 during the first 10 days post birth. Administration of the angiotensin II receptor AT1 antagonist telmisartan from day P1 to P3 did not result in cortical damage. However, telmisartan treatment from day P3 to P8, the critical time frame of renal COX-2 expression, led to hypoplastic glomeruli, a thinned subcapsular cortex and maturational arrest of superficial glomeruli quite similar to that observed in COX-2^-/- mice. In contrast, AT2 receptor antagonist PD123319 was without any effect on renal development. Inhibition of the renin angiotensin system by aliskiren and enalapril caused similar glomerular defects as telmisartan. Administration of the AT1 receptor agonist L162313 to COX-2^-/- pups improved kidney growth, ameliorated renal defects, but had no beneficial effect on reduced cortical mass. L162313 rescued impaired renal function by reducing serum urea and creatinine and mitigated pathologic albumin excretion. Moreover, glomerulosclerosis in the kidneys of COX-2^-/- mice was reduced. Thus, angiotensin II-AT1-receptor signaling is necessary for COX-2-dependent normal postnatal nephrogenesis and maturation.

Renal effects of angiotensin II in the newborn period: role of type 1 and type 2 receptors

BACKGROUND

Evidence suggests a critical role for the renin-angiotensin system in regulating renal function during postnatal development. However, the physiological relevance of a highly elevated renin-angiotensin system early in life is not well understood, nor which angiotensin receptors might be involved. This study was designed to investigate the roles of angiotensin receptors type 1 (AT1R) and type 2 (AT2R) in regulating glomerular and tubular function during postnatal development.

METHODS

The renal effects of the selective antagonist to AT1R, ZD 7155 and to AT2R, PD 1233319 were evaluated in two groups of conscious chronically instrumented lambs aged ~ one week (N = 8) and ~ six weeks (N = 10). Two experiments were carried out in each animal and consisted of the assessment of renal variables including glomerular and tubular function, for 30 min before (Control) and 60 min after infusion of ZD 7155 and PD 123319, respectively. Statistical significance was determined using parametric testing (Student t-test, analysis of variance ANOVA) as appropriate.

RESULTS

ZD 7155 infusion was associated with a significant decrease in glomerular filtration rate and filtration fraction at one but not six weeks; urinary flow rate decreased significantly in older animals, whereas sodium excretion and free water clearance were not altered. There was an age-dependent effect on potassium handling along the nephron, potassium excretion decreasing after ZD 7155 infusion in younger but not in older lambs. PD 123319 had no significant effects on glomerular filtration rate and tubular function in either age group.

CONCLUSIONS

These results provide evidence to support an important role for AT1Rs in mediating the renal effects of angiotensin II during postnatal maturation in conscious developing animals. In contrast to a role for AT2Rs later in life, there appears to be no role for AT2Rs in influencing the renal effects of Angiotensin II in the postnatal period.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

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.

Commercially available angiotensin II At₂ receptor antibodies are nonspecific

Commercially available angiotensin II At₂ receptor antibodies are widely employed for receptor localization and quantification, but they have not been adequately validated. In this study, we characterized three commercially available At₂ receptor antibodies: 2818-1 from Epitomics, sc-9040 from Santa Cruz Biotechnology, Inc., and AAR-012 from Alomone Labs. Using western blot analysis the immunostaining patterns observed were different for every antibody tested, and in most cases consisted of multiple immunoreactive bands. Identical immunoreactive patterns were present in wild-type and At₂ receptor knockout mice not expressing the target protein. In the mouse brain, immunocytochemical studies revealed very different cellular immunoreactivity for each antibody tested. While the 2818-1 antibody reacted only with endothelial cells in small parenchymal arteries, the sc-9040 antibody reacted only with ependymal cells lining the cerebral ventricles, and the AAR-012 antibody reacted only with multiple neuronal cell bodies in the cerebral cortex. Moreover, the immunoreactivities were identical in brain tissue from wild-type or At₂ receptor knockout mice. Furthermore, in both mice and rat tissue extracts, there was no correlation between the observed immunoreactivity and the presence or absence of At₂ receptor binding or gene expression. We conclude that none of these commercially available At₂ receptor antibodies tested met the criteria for specificity. In the absence of full antibody characterization, competitive radioligand binding and determination of mRNA expression remain the only reliable approaches to study At₂ receptor expression.

Hypothesis: a new role for the Renin-Angiotensin system in ureteric bud branching

Branching morphogenesis in the developing mammalian kidney involves growth and branching of the ureteric bud (UB), leading to formation of its daughter collecting ducts, calyces, pelvis and ureters. Even subtle defects in the efficiency and/or accuracy of this process have profound effects on the ultimate development of the kidney and result in congenital abnormalities of the kidney and urinary tract. This review summarizes current knowledge regarding a number of genes known to regulate UB development and emphasizes an emerging role for the renin-angiotensin system (RAS) in renal branching morphogenesis. Mutations in the genes encoding components of the RAS in mice cause renal papillary hypoplasia, hydronephrosis, and urinary concentrating defect. These findings imply that UB-derived epithelia are targets for angiotensin (ANG) II actions during metanephric kidney development. Here, it is proposed that papillary hypoplasia in RAS-deficient mice is secondary to an intrinsic defect in the development of the renal medulla. This hypothesis is based on the following observations: (a) UB and surrounding stroma express angiotensinogen (AGT) and ANG II AT(1) receptors in vivo; (b) ANG II stimulates UB cell process extension, branching and cord formation in collagen gel cultures in vitro; and (c) AT(1) blockade inhibits ANG II-induced UB cell branching. It is further postulated that ANG II is a novel stroma-derived factor involved in stroma/UB cross-talk which regulates UB branching morphogenesis.

A new transgenic rat model overexpressing the angiotensin II type 2 receptor provides evidence for inhibition of cell proliferation in the outer adrenal cortex

This study aimed to elucidate the role of the AT(2) receptor (AT(2)R), which is expressed and upregulated in the adrenal zona glomerulosa (ZG) under conditions of increased aldosterone production. We developed a novel transgenic rat (TGR; TGRCXmAT(2)R) that overexpresses the AT(2)R in the adrenal gland, heart, kidney, brain, skeletal muscle, testes, lung, spleen, aorta, and vein. As a consequence the total angiotensin II (Ang II) binding sites increased 7.8-fold in the kidney, 25-fold in the heart, and twofold in the adrenals. The AT(2)R number amounted to 82-98% of total Ang II binding sites. In the ZG of TGRCXmAT(2)R, the AT(2)R density was elevated threefold relative to wild-type (WT) littermates, whereas AT(1)R density remained unchanged. TGRCXmAT(2)R rats were viable and exhibited normal reproduction, blood pressure, and kidney function. Notably, a slightly but significantly reduced body weight and a moderate increase in plasma urea were observed. With respect to adrenal function, 24-h urinary and plasma aldosterone concentrations were unaffected in TGRCXmAT(2)R at baseline. Three and 14 days of Ang II infusion (300 ng·min(-1)·kg(-1)) increased plasma aldosterone levels in WT and in TGR. These changes were completely abolished by the AT(1)R blocker losartan. Of note, glomerulosa cell proliferation, as indicated by the number of Ki-67-positive glomerulosa cells, was stimulated by Ang II in TGR and WT rats; however, this increase was significantly attenuated in TGR overexpressing the AT(2)R. In conclusion, AT(2)R in the adrenal ZG inhibits Ang II-induced cell proliferation but has no obvious lasting effect on the regulation of the aldosterone production at the investigated stages.

Angiotensin II regulates growth of the developing papillas ex vivo

We tested the hypothesis that lack of angiotensin (ANG) II production in angiotensinogen (AGT)-deficient mice or pharmacologic antagonism of ANG II AT(1) receptor (AT(1)R) impairs growth of the developing papillas ex vivo, thus contributing to the hypoplastic renal medulla phenotype observed in AGT- or AT(1)R-null mice. Papillas were dissected from Hoxb7(GFP+) or AGT(+/+), (+/-), (-/-) mouse metanephroi on postnatal day P3 and grown in three-dimentional collagen matrix gels in the presence of media (control), ANG II (10(-5) M), or the specific AT(1)R antagonist candesartan (10(-6) M) for 24 h. Percent reduction in papillary length was attenuated in AGT(+/+) and in AGT(+/-) compared with AGT(-/-) (-18.4 ± 1.3 vs. -32.2 ± 1.6%, P < 0.05, -22.8 ± 1.3 vs. -32.2 ± 1.6%, P < 0.05, respectively). ANG II blunted the decrease in papilla length observed in respective media-treated controls in Hoxb7(GFP+) (-1.5 ± 0.3 vs. -10.0 ± 1.4%, P < 0.05) or AGT(+/+), (+/-), and (-/-) papillas (-12.8 ± 0.7 vs. -18.4 ± 1.3%, P < 0.05, -16.8 ± 1.1 vs. -23 ± 1.2%, P < 0.05; -26.2 ± 1.6 vs. -32.2 ± 1.6%, P < 0.05, respectively). In contrast, percent decrease in the length of Hoxb7(GFP+) papillas in the presence of the AT(1)R antagonist candesartan was higher compared with control (-24.3 ± 2.1 vs. -10.5 ± 1.8%, P < 0.05). The number of proliferating phospho-histone H3 (pH3)-positive collecting duct cells was lower, whereas the number of caspase 3-positive cells undergoing apoptosis was higher in candesartan- vs. media-treated papillas (pH3: 12 ± 1.4 vs. 21 ± 2.1, P < 0.01; caspase 3: 3.8 ± 0.5 vs. 1.7 ± 0.2, P < 0.01). Using quantitative RT-PCR, we demonstrate that AT(1)R signaling regulates the expression of genes implicated in morphogenesis of the renal medulla. We conclude that AT(1)R prevents shrinkage of the developing papillas observed ex vivo via control of Wnt7b, FGF7, β-catenin, calcineurin B1, and α3 integrin gene expression, collecting duct cell proliferation, and survival.

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 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.

A new role for the renin-angiotensin system in the development of the ureteric bud and renal collecting system

The renin-angiotensin system (RAS) plays a critical role in kidney development. Mutations in the genes encoding components of the RAS or pharmacological inhibition of RAS in mice or humans cause a spectrum of congenital abnormalities of the kidney and urinary tract (CAKUT). The observed defects include renal vascular abnormalities, abnormal glomerulogenesis, renal papillary hypoplasia, hydronephrosis, aberrant ureteric bud (UB) budding, duplicated collecting system and renal tubular dysgenesis. Little is known about the potential role of Ang II and its receptors in the morphogenesis of the UB and renal collecting system. This review emphasizes a novel role for the RAS in the development of the UB, collecting ducts and renal medulla. We observe that UB and surrounding stroma express angiotensinogen and Ang II AT1 receptors (AT1R) in vivo. Ang II stimulates UB cell branching in collagen gel cultures in vitro and induces UB morphogenesis in intact whole embryonic metanephroi grown ex vivo. In contrast, treatment of metanephroi with the AT1R antagonist candesartan inhibits UB branching. In addition, Ang II induces tyrosine phosphorylation of the epidermal growth factor receptor (EGFR) in UB cells. Furthermore, Ang II-stimulated UB morphogenesis is abrogated by inhibition of EGFR tyrosine kinase activity. In summary: 1) Ang II, acting via the AT1R, stimulates UB branching; 2) This process depends on tyrosine phosphorylation of the EGFR. Together, these data indicate that cooperation of AT1R and EGFR signaling performs essential functions during renal collecting system development via control of UB branching morphogenesis.

Deficiency of intrarenal angiotensin II type 2 receptor impairs paired homeo box-2 and N-myc expression during nephrogenesis

We previously demonstrated that angiotensin II (Ang II) stimulates paired homeo box-2 (Pax-2) via the Ang II type 2 receptor (AT(2)R). The Pax-2 gene and N-myc play pivotal roles in renal morphogenesis via their effects on cell proliferation and differentiation in embryonic mesenchymal cells and embryonic mouse kidneys. Since AT(2)R knock-out (KO) mice have a phenotype that is similar to that of humans with congenital renal and urinary tract anomalies (CAKUT) and develop hypertension in adulthood, these mice and wild-type controls were used for this study. Embryonic kidneys isolated from E12 to term gestation were cultured in Dulbecco's modified Eagle's medium (DMEM) with or without Ang II (10(-6) M) for 24 h ex vivo. Renal morphogenesis was histologically assessed. Mean glomerular tuft volume was determined by the method of Weibel and Gomez with the aid of image analysis software. Pax-2 and N-myc gene expression were determined by immunostaining as well as by Western blotting and real-time-quantitative polymerase chain reaction (RT-qPCR). Glomerular size was significantly smaller, and Pax-2 and N-myc expression down-regulated, in kidneys of AT(2)R KO mice compared with those of wild-type mice. In ex vivo studies, Ang II stimulated Pax-2 and N-myc mRNA expression in embryonic kidneys of wild-type mice, but this stimulatory effect was absent in embryonic kidneys of AT(2)R KO mice. Taken together, these data indicate that intrarenal AT(2)R plays an important role in nephrogenesis. Deficiency of AT(2)R may impair both Pax-2 and N-myc expression, eventually resulting in glomerular hyperfiltration that may, ultimately, lead to later development of hypertension.

Inhibition of Angiotensin II receptors during pregnancy induces malformations in developing rat kidney

Evidence suggests that Angiotensin II plays an important role in the complex process of renal organogenesis. Rat kidney organogenesis starts between E13-14 and lasts up to 2 weeks after birth. The present study demonstrates histologic modifications and changes in receptor localisation in animals born from mothers treated with Angiotensin II, Losartan or PD123319 (1.0 mg/kg/day) during late pregnancy. Angiotensin II-treated animals exhibited very well developed tubules in the renal medulla in coincidence with higher AT(1) binding. Control animals exhibited angiotensin AT(2) binding in the outer stripe of the outer medulla, while in the Angiotensin II-treated animals binding was observed to the inner stripe. In Angiotensin II-treated 1-week-old animals, the nephrogenic zone contained fewer immature structures, and more developed collecting tubules than control animals. Treatment with Losartan resulted in severe renal abnormalities. For newborn and 1-week-old animals, glomeruli exhibited altered shape and enlarged Bowman spaces, in concordance with a loss of [(125)I]Angiotensin II binding in the cortex. Blockade with PD123319 led to an enlarged nephrogenic zone with increased number of immature glomeruli, and less glomeruli in the juxtamedullary area. Autoradiography showed a considerable loss of AT(1) binding in the kidney cortex of PD123319-treated animals at both ages. The present results show for the first time histomorphological and receptor localisation alterations following treatment with low doses of Losartan and PD123319 during pregnancy. These observations confirm previous assumptions that in the developing kidney Angiotensin II exerts stimulatory effects through AT(1) receptors that might be counterbalanced by angiotensin AT(2) receptors.

Targeting genes in the renin-angiotensin system

PURPOSE OF REVIEW

The renin-angiotensin system plays a key role in the regulation of blood pressure and fluid homeostasis. Owing to its critical contribution to blood pressure control, abnormalities of any component in this system can lead to hypertension and cardiovascular diseases. In this review, we will highlight studies using this approach to uncover new perspectives on the physiology of the renin-angiotensin system.

RECENT FINDINGS

Over the past decade, application of techniques for manipulating the genome of living animals, including gene targeting through homologous recombination in embryonic stem cells, has provided unique insights into the complex biology of the renin-angiotensin system. Along with advances in understanding functions of the classical components of the system, gene targeting has clarified the functions of newly discovered angiotensin-converting enzyme homologues.

SUMMARY

Since pharmacological antagonists of the renin-angiotensin system are widely used in clinical medicine, advances in the gene-targeting experiments of the system have helped to clarify the mechanisms of action of these agents and may provide clues for improved approaches for the treatment of hypertension and kidney diseases.

Tissue-specific regulation of ACE/ACE2 and AT1/AT2 receptor gene expression by oestrogen in apolipoprotein E/oestrogen receptor-alpha knock-out mice

Angiotensin-converting enzyme (ACE) and ACE2 and the AT1 and AT2 receptors are pivotal points of regulation in the renin-angiotensin system. ACE and ACE2 are key enzymes in the formation and degradation of angiotensin II (Ang II) and angiotensin-(1-7)(Ang-(1-7)). Ang II acts at either the AT1 or the AT2 receptor to mediate opposing actions of vasoconstriction or vasodilatation respectively. While it is known that oestrogen acts to downregulate ACE and the AT(1) receptor, its regulation of ACE2 and the AT2 receptor and the involvement of a specific oestrogen receptor subtype are unknown. To investigate the role of oestrogen receptor-alpha (ERalpha) in the regulation by oestrogen of ACE/ACE2 and AT1/AT2 mRNAs in lung and kidney, ovariectomized female mice lacking apolipoprotein E (ee) with the ERalpha (AAee) or without the ERalpha (alphaalphaee) were treated with 17beta-oestradiol (6 microg day(-1)) or placebo for 3 months. ACE, ACE2, AT1 receptor and AT2 receptor mRNAs were measured using reverse transcriptase, real-time polymerase chain reaction. In the kidney, 17beta-oestradiol showed 1.7-fold downregulation of ACE mRNA in AAee mice, with 2.1-fold upregulation of ACE mRNA in alphaalphaee mice. 17beta-Oestradiol showed 1.5- and 1.8-fold downregulation of ACE2 and AT1 receptor mRNA in AAee mice; this regulation was lost in alphaalphaee mice. 17beta-Oestradiol showed marked (81-fold) upregulation of the AT(2) receptor mRNA in AAee mice. In the lung, 17beta-oestradiol treatment had no effect on AT1 receptor mRNA in AAee mice, but resulted in a 1.5-fold decreased regulation of AT1 mRNA in alphaalphaee mice. There was no significant interaction of oestrogen with ERalpha in the lung for ACE, ACE2 and AT2 receptor genes. These studies reveal tissue-specific regulation by 17beta-oestradiol of ACE/ACE2 and AT1/AT2 receptor genes, with the ERalpha receptor being primarily responsible for the regulation of kidney ACE2, AT1 receptor and AT2 receptor genes.

Dynamics of the epithelium during canalization of the rat ventral prostate

Outgrowth and branching of solid cords are the initial events in postnatal prostatic morphogenesis. These processes involve cell proliferation and their projection into the stroma and precede epithelial canalization. The purpose of the present study was to examine the dynamics of the prostate epithelium during canalization of the rat ventral prostate in the first week of postnatal development using histological, stereological, and ultrastructural analyses. The terminal deoxynucleotidyltransferase [TdT]-mediated deoxy-UTP nick end labeling assay was used to investigate the occurrence of DNA fragmentation. Our results demonstrate that canalization of the prostate epithelium starts as early as on day 1 (24 hr after birth) and progresses thereafter. By the end of the first week (day 6), luminal volume density reached approximately 3% (P < 0.05) of the organ. Canalization was the result of epithelial cell differentiation and apoptosis. The former involved organization of the epithelial cells into a single layer sitting on the basement membrane, polarization, enlargement of secretory organelles and accumulation of secretory vesicles, microvilli formation, and establishment of the adult pattern of cell junctions. The latter was observed to occur mostly to epithelial cells not in contact with the basement membrane. Structures of variable electron density were observed in the developing lumen. In conclusion, different phenomena seem to be involved in the canalization of the rat ventral prostate. However, it was evident from the present results that complex epithelial cell fate decisions take place during this process.

Angiotensin II type 2 receptor gene polymorphism in Caucasian children with a wide spectrum of congenital anomalies of the kidney and urinary tract

The A-1332G transition of the angiotensin II type 2 receptor (AT2R) gene was found to occur more often in males with ureteropelvic (UPJO) or ureterovesical junction obstruction (UVJO). However, other studies have shown controversial results. Tauhe frequency of this polymorphism was investigated in 275 Caucasian children (153 boys, 122 girls) with a wide spectrum of congenital anomalies both of upper (165) and lower (110) urinary tract system and in 200 controls (100 boys, 100 girls). Among the included malformations, renal agenesis and duplex collecting system (DCS) were studied for the first time. The frequency of the G allele did not differ among patients (193 of 397 total alleles, 48.6%) and controls (146 of 300, 48.7%). No significant difference was also found in the frequency of the G allele in subgroups of congenital uropathies compared with controls. When analysis was performed in males and females separately, no significant difference was found in the frequency of the G allele in male (45.1%) or female (50.8%) patients compared with male (57.0%) or female (44.5%) controls. Our data indicate that the AT2R gene A-1332G transition is not associated with the development of human congenital uropathies and further investigations should be carried out to unravel their etiology.

Effects of dietary protein restriction on nephron number in the mouse

In rats, maternal protein restriction reduces nephron endowment and often leads to adult hypertension. Sex differences in these responses have been identified. The molecular and genetic bases of these phenomena can best be identified in a mouse model, but effects of maternal protein restriction on kidney development have not been examined in mice. Therefore, we determined how combined prenatal and postnatal protein restriction in mice affects organ weight, glomerular number and dimensions, and renal expression of angiotensin receptor mRNA, in both male and female offspring. C57/BL6/129sv mice received either a normal (20% wt/wt; NP) or low (9% wt/wt; LP) protein diet during gestation and postnatal life. Offspring were examined at postnatal day 30. Protein restriction retarded growth of the kidney, liver, spleen, heart, and brain. All organs except the brain weighed less in female than male offspring. Protein restriction increased normalized (to body weight) brain weight, with females having relatively heavier brains than males. The effects of protein restriction were not sex dependent, except that normalized liver weight was reduced in males but increased in females. Glomerular volume, but not number, was greater in female than in male mice. Maternal protein restriction reduced nephron endowment similarly in male and female mice. Renal expression of AT1A receptor mRNA was approximately sixfold greater in female than male NP mice, but similar in male LP and female LP mice. We conclude that maternal protein restriction reduces nephron endowment in mice. This effect provides a basis for future studies of developmental programming in the mouse.

The aetiology and pathogenesis of chronic allograft nephropathy

Renal transplantation is the ultimate form of renal replacement therapy, and is the treatment of choice for many patients with end-stage renal failure. The advent of calcineurin inhibitor based immunosuppression resulted in the 1-year renal allograft failure rate dropping from around 50% twenty years ago to less than 10% in more recent times. Despite a massive improvement in renal allograft survival in the first year following transplantation 10-year graft survival can be as low as 50%. Chronic allograft nephropathy (CAN) is recognised as the main cause of renal allograft failure following the first year after transplantation. The diagnosis of CAN can only be made histologically. Typically biopsy specimens in grafts with CAN demonstrate an overall fibrotic appearance effecting the vascular endothelium, renal tubules, interstitium, and glomerulus. The risk factors for CAN are divided into alloimmune and alloimmune independent. Alloimmune dependent factors include acute cellular rejection, severity of rejection, subclinical rejection and HLA mismatch. Alloimmune independent factors such as delayed graft function, donor age, Cytomegalovirus infection, donor/recipient co-morbidity and of course calcineurin inhibitor toxicity are important in the development of CAN. The pathogenesis of CAN is complex, multifactorial, and unfortunately incompletely understood. There are a number of pivotal steps in the initiation and propagation of the fibrosis seen in biopsy specimens from kidneys with CAN. Endothelial activation in response to one or more of the aforementioned risk factors stimulates leukocyte activation and recruitment. Recruited leukocytes subsequently infiltrate through the endothelium and induce key effector cells to secrete excessive and abnormal extracellular matrix (ECM). Enhanced deposition of ECM is a histological hallmark of CAN. This paper aims to present a concise yet accurate and up-to-date review of the literature concerning the aetiological factors and pathological processes which are present in the generation of CAN.

No evidence for angiotensin type 2 receptor gene polymorphism in intron 1 in patients with coarctation of the aorta and Ullrich-Turner syndrome

In male patients with congenital anomalies of the kidney and urinary tract, an increased incidence of a polymorphism in the angiotensin type 2 receptor gene (AT2R) has been identified. The AT2R has been shown to be involved in apoptosis, particularly during embryogenesis. The aim of this study was to examine the A-->1675G transition polymorphism in intron 1 of the AT2R gene that is located on the X chromosome in patients with coarctation of the aorta (CoA) with and without Ullrich-Turner syndrome (UTS). Screening of DNA samples was performed with restriction fragment length polymorphism analysis. Ninety-seven patients with CoA, 28 girls with UTS, 10 girls with UTS and CoA, and 96 control individuals were studied. There was no significant difference in the distribution of A and G-genotypes in any of the patient groups compared to controls. An A-->1675G transition in the AT2R gene seems not to be involved in the pathogenesis of aortic coarctation.

Different Effects of Angiotensin Receptor Blockade on End-Organ Damage in Salt-Dependent and Salt-Independent Hypertension

Background— Although angiotensin II type 1 receptor blockers have emerged as effective antihypertensive agents, it is not known how efficacious these agents are in treating hypertension-associated target organ damage.

Methods and Results— The present study was undertaken to compare the effect of angiotensin type 1 receptor inhibition on the progression of the organ damage observed in 2 models of hypertension, namely, salt-sensitive and nitric oxide synthase inhibition–mediated hypertension. Effective (16.4 μmol/kg) and ineffective (0.8 to 4.9 μmol/kg) antihypertensive doses of candesartan cilexetil were initiated after hypertension was established. Both low- and high-dose candesartan cilexetil significantly reduced cardiac and renal damage in the nitric oxide synthase inhibitor model of hypertension ( P <0.05 versus untreated); however, high-dose candesartan caused a significant increase in renal damage in the Dahl salt-sensitive model of hypertension ( P <0.05 versus untreated). Interestingly, the beneficial end-organ effects of candesartan in the nitric oxide synthase inhibition model were independent of sustained antihypertensive actions of candesartan, whereas the exacerbation of renal injury with candesartan in the Dahl salt-sensitive model was inversely related to its blood pressure–lowering effect.

Conclusions— These data show that angiotensin type 1 blockade reduces injury in the l -nitroarginine methyl ester model but increases tissue injury in the salt-sensitive model. These data suggest that angiotensin II via angiotensin type 1 receptor activation contributes to organ damage in nitric oxide–deficient salt-independent hypertension but is protective in salt-induced hypertension. These data further suggest that (1) renal injury may evolve independently of blood pressure and (2) the effectiveness of an antihypertensive agent in ameliorating renal injury may depend on the etiology of the hypertension.

Dose-dependent systemic and renal haemodynamic effects of angiotensin II in conscious lambs: role of angiotensin AT1and AT2receptors

The present experiments were designed to measure the effects of acute administration of angiotensin (ANG) II on mean arterial pressure (MAP) and renal blood flow (RBF) in conscious, chronically instrumented lambs at two different stages of postnatal maturation, and to determine the receptors through which these effects of ANG II are elicited. Experiments consisted of haemodynamic measurements for 10 s before (Control) and for 60 s after intravenous (i.v.) administration of one of 11 doses of ANG II (0-200 ng kg(-1)). Administration of ANG II was associated with a dose-dependent increase in MAP to a maximal effective concentration (EC100) of 100 ng kg(-1) in lambs aged 1 and 6 weeks. Administration of ANG II has caused a dose-dependent decrease in RBF, with EC100 values of 50 ng kg(-1) in 1-week-old lambs, and 25 ng kg(-1) in 6-week-old lambs. Responses to ANG II at the EC(50) were also measured in the presence of the specific ANG II AT(1) receptor antagonist, ZD 7155, the specific AT2 receptor antagonist, PD 123319, and vehicle. Administration of ZD 7155, but not PD 123319 or vehicle, abolished the MAP and RBF responses to ANG II in both age groups. In addition, MAP decreased and RBF increased in both age groups after administration of ZD 7155, but not PD 123319; the effects were similar in both age groups. These data provide new information that pressor and renal vasoconstrictor effects of ANG II during the first 6 weeks of postnatal life in lambs are elicited by activation of AT1 but not AT2 receptors.

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.

Low renin-angiotensin system activity gene polymorphism and dysplasia associated with posterior urethral valves

PURPOSE

Obstructive uropathies, including posterior urethral valves (PUVs) and kidney hypodysplasia, are the most frequent cause of renal failure in children. The role of renin-angiotensin system genes in renal and urinary tract development has been observed in experimental models. The aim of this study was to investigate the distribution of angiotensin converting enzyme (ACE), angiotensinogen (AGT) and angiotensin receptor type 1 (ATR1) genetic polymorphisms in children affected by chronic renal failure due to renal hypodysplasia associated with posterior urethral valves or without urethral abnormalities.

MATERIALS AND METHODS

The study included 50 children (21 with hypodysplasia associated with PUVs, 7 with obstructive uropathy and 22 with pure hypodysplasia) and 50 healthy subjects matched for sex and geographic origin. ACE ID, AGT TC and ATR1 AC gene polymorphisms were assayed in all patients with standard polymerase chain reaction techniques.

RESULTS

ACE II was expressed more in patients with PUVs compared to those with other dysplasias and controls (43% vs 7% and 10%, respectively, chi-square test p <0.05), while ATR1 AA was significantly less represented in patients with hypodysplasia compared to controls (38% vs 56%, chi-square test p <0.05). ACE DD and AGT genotypes were not distributed differently in patients with PUVs compared to those with other dysplasias and controls.

CONCLUSIONS

To our knowledge this is the first report associating severe congenital uropathies and renal hypodysplasia with decreased renin-angiotensin system activity associated with the ACE II genotype and a possible functional imbalance among ATR1 receptors.

Role of the renin-angiotensin system in the development of the ureteric bud and renal collecting system

Genetic, biochemical and physiological studies have demonstrated that the renin-angiotensin system (RAS) plays a fundamental role in kidney development. All of the components of the RAS are expressed in the metanephros. Mutations in the genes encoding components of the RAS in mice or pharmacological inhibition of RAS in animals or humans cause diverse congenital abnormalities of the kidney and lower urinary tract. The latter include renal vascular abnormalities, abnormal glomerulogenesis, renal papillary hypoplasia, hydronephrosis, aberrant UB budding, duplicated collecting system, and urinary concentrating defect. Thus, the actions of angiotensin (ANG) II during kidney development are pleiotropic both spatially and temporally. Whereas the role of ANG II in renovascular and glomerular development has received much attention, little is known about the potential role of ANG II and its receptors in the morphogenesis of the collecting system. In this review, we discuss recent genetic and functional evidence gathered from transgenic knockout mice and in vitro organ and cell culture implicating the RAS in the development of the ureteric bud and collecting ducts. A novel conceptual framework has emerged from this body of work which states that stroma-derived ANG II elicits activation of AT(1)/AT(2) receptors expressed on the ureteric bud to stimulate branching morphogenesis as well as collecting duct elongation and papillogenesis.

Mouse ovary developmental RNA and protein markers from gene expression profiling

To identify genes involved in morphogenetic events during mouse ovary development, we started with microarray analyses of whole organ RNA. Transcripts for 60% of the 15,000 gene NIA panel were detected, and about 2000 were differentially expressed in nascent newborn compared to adult ovary. Highly differentially expressed transcripts included noncoding RNAs and newly detected genes involved in transcription regulation and signal transduction. The phased pattern of newborn mouse ovary differentiation allowed us to (1) extend information on activity and stage specificity of cell type-specific genes; and (2) generate a list of candidate genes involved in primordial follicle formation, including podocalyxin (Podxl), PDGFR-beta, and a follistatin-domain-encoding gene Flst1. Oocyte-specific transcripts included many (e.g., Deltex2, Bicd2, and Zfp37) enriched in growing oocytes, as well as a novel family of untranslated RNA's (RLTR10) that is selectively expressed in early stage follicles. The results indicate that global expression profiling of whole organ RNA provides sensitive first-line information about ovarian histogenesis for which no in vitro cell models are currently available.

Molecular biology of ureteral bud and trigonal development

Advances in molecular biology have provided valuable insight into the development of the urinary tract, particularly ureteral bud formation. Reciprocal inductive signals between the ureteral bud and growing kidney are crucial for normal development. The Wolffian duct serves as the site of origin of the ureteral bud and forms distal excretory ducts that are incorporated into the developing bladder to become the trigone. Vesicoureteral reflux and renal dysplasia can result from abnormal position of the ureteral orifice on the trigone. The presumed origin of trigone formation is based largely on evaluation of human and animal models performed nearly a century ago. The trigone is thought to develop from the mesodermal germ cell layer; however, several recent studies have shown that endoderm may be the tissue of origin. This review highlights important discoveries in the field of molecular biology as it relates to the development of normal and abnormal ureteral bud formation. It also describes the anatomic relationship between the developing bud and trigone as it pertains to clinically relevant urinary tract anomalies, including recent discoveries that attempt to prove the origin of the trigone.

Tissue-specific expression of renin-angiotensin system components in IgA nephropathy

BACKGROUND

The renin-angiotensin II system (RAS) has been implicated in the development of glomerulonephritis. The aims of this study were to determine (1) the expression of RAS components, angiotensin (Ang II)-forming enzymes [angiotensin-I-converting enzyme (ACE) and chymase], and Ang II receptors, and (2) the correlation between RAS expression and severity of tissue injury in IgA nephropathy (IgAN).

METHODS

The expression levels of ACE, chymase, and Ang II type 1 and type 2 receptor (AT1R and AT2R) mRNAs were determined by in situ hybridization in renal specimens from 18 patients with IgAN, 5 patients with non-IgA mesangial proliferative glomerulonephritis (non-IgAN) and 10 patients with nonmesangial proliferative glomerulonephritis (minimal change nephrotic syndrome, n = 5, and membranous nephropathy, n = 5). Normal portions of surgically resected kidney served as control.

RESULTS

In normal kidney, a few mesangial cells and glomerular and tubular epithelial cells weakly expressed ACE, chymase and AT1R mRNAs. In IgAN and non-IgAN samples, ACE, chymase, AT1R and AT2R mRNAs were expressed in resident glomerular cells, including mesangial cells, glomerular epithelial cells and cells of Bowman's capsule. The glomerular expressions in IgAN were stronger than in minimal change nephrotic syndrome and membranous nephropathy. In IgAN, the expressions in glomeruli correlated with the degree of mesangial hypercellularity, whereas the expression levels were weaker at the area of mesangial expansion. IgAN with severe tubulointerstitial injury showed expression of ACE, chymase, AT1R and AT2R mRNAs in atrophic tubules and infiltrating cells and such expression correlated with the degree of tubulointerstitial damage.

CONCLUSION

Our results suggest that renal cells can produce RAS components and that locally synthesized Ang II may be involved in tissue injury in IgAN through Ang II receptors in the kidney.

Angiotensin-converting enzyme and angiotensin type 2 receptor gene genotype distributions in Italian children with congenital uropathies

Angiotensin I-converting enzyme (ACE) and angiotensin type 2 receptor (AT2R) gene polymorphisms have been associated with an increased incidence of congenital anomalies of the kidney and urinary tract (CAKUT). We investigated the genotype distribution of these polymorphisms in Italian children with CAKUT. We also evaluated the association between the ACE insertion/deletion and the AT2R gene polymorphisms with the progression of renal damage in subgroups of CAKUT patients. We recruited 102 Italian children with CAKUT; 27 with vesicoureteral reflux; 12 with hypoplastic kidneys; 20 with multicystic dysplastic kidneys; 13 with ureteropelvic junctions stenosis/atresia; 18 with nonobstructed, nonrefluxing primary megaureters; and 12 with posterior urethral valves and compared them with 92 healthy control subjects. ACE and AT2R gene polymorphisms were analyzed by PCR. The identification of AT2R gene polymorphisms in intron 1 and in exon 3 was revealed by enzymatic digestion. ACE genotype distribution in children with CAKUT was no different from that of the control subjects, but the subgroup of patients with radiographic renal parenchymal abnormalities showed an increased occurrence of the D/D genotype. The frequency of the G allele of AT2R gene in children with CAKUT was increased in respect to that of the control subjects. By contrast, no significant difference in the frequency of the C and A alleles of the AT2R gene was found. Our findings indicate that the ACE gene can be a risk factor in the progression of renal parenchymal damage in CAKUT patients. Moreover, a major role of the AT2R gene in the development of CAKUT has been found, at least in Italian children.

Exploring type I angiotensin (AT1) receptor functions through gene targeting

The renin-angiotensin system (RAS) modulates a diverse set of physiological processes including development, blood pressure, renal function and inflammation. The principal effector molecule of this system, angiotensin II, mediates most of these actions. The classically recognized functions of the RAS are triggered via the type 1 (AT(1)) class of angiotensin receptors. Pharmacological blockade of the AT(1) receptor lowers blood pressure and slows the progression of cardiovascular and renal diseases. Gene-targeting technology provides an experimental approach for precisely dissecting the physiological functions of the RAS. Here, we review how gene-targeting experiments have elucidated AT(1) receptor functions.