Renal abnormalities in mutant mice

Structural effect of the H992D/H418D mutation of angiotensin-converting enzyme in the Indian population: implications for health and disease

The Non synonymous SNPs (nsSNPs) of the renin-angiotensin-system (RAS) pathway, unique to the Indian population were investigated in view of its importance as an endocrine system. nsSNPs of the RAS pathway genes were mined from the IndiGenome database. Damaging nsSNPs were predicted using SIFT, PredictSNP, SNP and GO, Snap2 and Protein Variation Effect Analyzer. Loss of function was predicted based on protein stability change using I mutant, PremPS and CONSURF. The structural impact of the nsSNPs was predicted using HOPE and Missense3d followed by modeling, refinement, and energy minimization. Molecular Dynamics studies were carried out using Gromacsv2021.1. 23 Indian nsSNPs of the RAS pathway genes were selected for structural analysis and 8 were predicted to be damaging. Further sequence analysis showed that HEMGH zinc binding motif changes to HEMGD in somatic ACE-C domain (sACE-C) H992D and Testis ACE (tACE) H418D resulted in loss of zinc coordination, which is essential for enzymatic activity in this metalloprotease. There was a loss of internal interactions around the zinc coordination residues in the protein structural network. This was also confirmed by Principal Component Analysis, Free Energy Landscape and residue contact maps. Both mutations lead to broadening of the AngI binding cavity. The H992D mutation in sACE-C is likely to be favorable for cardiovascular health, but may lead to renal abnormalities with secondary impact on the heart. H418D in tACE is potentially associated with male infertility.

Genetically altered animal models in the kallikrein-kinin system

Transgenic and gene-targeting technologies allowing the generation of genetically altered animal models have greatly advanced our understanding of the function of specific genes. This is also true for the kallikrein-kinin system (KKS), in which some, but not yet all, components have been functionally characterized using such techniques. The first genetically altered animal model for a KKS component was supplied by nature, the brown Norway rat carrying an inactivating mutation in the kininogen gene. Mice deficient in tissue kallikrein, B1 and B2 receptors, some kinin-degrading enzymes, and factor XII followed, together with transgenic rat and mouse strains overexpressing tissue kallikrein, B1 and B2 receptors, and degrading enzymes. There are still no animal models with genetic alterations in plasma kallikrein, kininases I and some other degrading enzymes. The models have confirmed an important role of the KKS in cardiovascular pathology, inflammation, and pain, and have partially elucidated the distinct function of the two receptors. This created the basis for rational decisions concerning the putative use of kinin receptor agonists and antagonists in therapeutic applications. However, a more thorough analysis of the existing models and the generation of new, more sophisticated transgenic models will be necessary to clarify the still elusive issue as to where and by which mechanisms the kinins exert their actions.

Cilia and centrosomes: a unifying pathogenic concept for cystic kidney disease?

Cystic kidney diseases are among the most frequent lethal genetic diseases. Positional cloning of novel cystic kidney disease genes revealed that their products (cystoproteins) are expressed in sensory organelles called primary cilia, in basal bodies or in centrosomes. Primary cilia link mechanosensory, visual, osmotic, gustatory and other stimuli to mechanisms of cell-cycle control and epithelial cell polarity. The ciliary expression of cystoproteins explains why many other organs might be also affected in patients with cystic kidney disease. Protein-protein interactions among cystoproteins, and their strong evolutionary conservation, provide a basis for a multidisciplinary approach to unravelling the novel signalling mechanisms that are involved in this disease group.

Knockout of renin-angiotensin system genes: effects on vascular development

Pharmacologic inhibition of the renin-angiotensin system (RAS) is a widely accepted and effective treatment for hypertension. However, in the past several years, much attention has been focused on additional roles of the RAS including the possibility that its end-product, angiotensin II, could elicit end-organ pathologies independent of its effect on blood pressure. The ability to selectively delete genes in mice (by homologous recombination or gene knockouts) has led to new--and sometimes surprising--insights into the roles of the RAS in the developmental modeling and pathologic remodeling of the heart and blood vessels.

Molecular genetics of nephronophthisis and medullary cystic kidney disease

Nephronophthisis (NPH) and medullary cystic kidney disease (MCKD) constitute a group of renal cystic diseases that share the macroscopic feature of cyst development at the corticomedullary border of the kidneys. The disease variants also have in common a characteristic renal histologic triad of tubular basement membrane disintegration, tubular atrophy with cyst development, and interstitial cell infiltration with fibrosis. NPH and, in most instances, MCKD lead to chronic renal failure with an onset in the first two decades of life for recessive NPH and onset in adult life for autosomal dominant MCKD. There is extensive genetic heterogeneity with at least three different loci for NPH (NPHP1, NPHP2, and NPHP3) and two different loci for MCKD (MCKD1 and MCKD2). Juvenile nephronophthisis, in addition, can be associated with extrarenal organ involvement. As a first step toward understanding the pathogenesis of this disease group, the gene (NPH1) for juvenile nephronophthisis (NPH1) has been identified by positional cloning. Its gene product, nephrocystin, is a novel protein of unknown function that contains a src-homology 3 domain. It is hypothesized that the pathogenesis of NPH might be related to signaling processes at focal adhesions (the contact points between cells and extracellular matrix) and/or adherens junctions (the contact points between cells). This hypothesis is based on the fact that most src-homology 3-containing proteins are part of focal adhesion signaling complexes, on animal models that exhibit an NPH-like phenotype, and on the recent finding that nephrocystin binds to the protein p130(cas), a major mediator of focal adhesion signaling.

Angiotensin-converting enzyme gene insertion/deletion polymorphism and renal damage in childhood uropathies

BACKGROUND

The activation of the renin-angiotensin system in various renal disorders is well established. Congenital urological abnormalities, such as obstruction and reflux, are common causes of renal failure in children contributing to approximately 25% of chronic renal failure in this age group. While the outlook relates to the severity of initial renal damage, there is considerable heterogeneity in renal parenchymal destruction among individuals and the reasons for this heterogeneity are not fully understood. A polymorphism within intron 16 of the angiostensin-converting enzyme (ACE) gene has been shown to influence the activity of the renin-angiotensin system, thus, it may also have an impact on the expression of renal disorders. We have determined the incidence of this ID polymorphism of the ACE gene in 47 Kuwaiti children with different urological abnormalities leading to variable degrees of renal impairment and in 48 healthy control subjects with a similar ethnic background.

METHODS

Blood samples were collected from the patients (n = 47) and controls (n = 48), total genomic DNA extracted and the ACE genotypes were determined using a polymerase chain reaction-based method.

RESULTS

The DD genotype was detected in 27/47 (57%) cases compared with 25/48 (52%) controls (P = 0.439). The heterozygous genotype ID was found in 14/47 (29%) cases compared with 22/48 (46%) controls (P = 0.0138). The homozygous II genotype was detected in 6/47 (13%) cases compared with 1/48 (2%) controls (P = 0.0247). The D allele of ACE gene was detected in 41/47 (87%) uropathy cases when individuals with homozygous DD and heterozygous ID genotypes were considered collectively. The incidence of parenchymal damage was considerably higher in uropathy cases with DD genotype (62%) compared with those having ID (26%) and II (12%) genotypes.

CONCLUSIONS

Our data suggest an association of D allele of the ACE gene insertion/deletion polymorphism and congenital urological abnormalities, which result in parenchymal damage in Kuwaiti Arab children.

An intact renin-angiotensin system is a prerequisite for normal renal development

All components of the renin-angiotensin system (RAS) are highly expressed in the developing kidney in a pattern that suggests a role for angiotensin II in renal development In support of this notion, pharmacological interruption of angiotensin II type-1 (AT1) receptor-mediated effects in animals with an ongoing nephrogenesis produces specific renal abnormalities characterized by papillary atrophy, abnormal wall thickening of intrarenal arterioles, tubular atrophy associated with expansion of the interstitium, and a marked impairment in urinary concentrating ability. Similar changes in renal morphology and function also develop in mice with targeted inactivation of the genes that encode angiotensinogen, angiotensin converting enzyme, or both AT1 receptor isoforms simultaneously. Taken together, these results clearly indicate that an intact signalling through AT1 receptors is a prerequisite for normal renal development In a recent study, an increased incidence of congenital anomalies of the kidney and urinary tract was detected in mice deficient in the angiotensin II type-2 receptor, suggesting that this receptor subtype is also involved in the development of the genitourinary tract The present report mainly reviews the renal abnormalities that have been induced by blocking the RAS pharmacologically or by gene targeting in experimental animal models. In addition, pathogenetic mechanisms and clinical implications are discussed.

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

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

Lifetime treatment with captopril improves renal function in spontaneously hypertensive rats

Lifetime treatment with captopril prevents the development of hypertension in spontaneously hypertensive rats (SHR). This study tests the hypothesis that compared to untreated hypertensive SHR, captopril-treated SHR display similar diuretic and natriuretic responses to an isotonic saline infusion despite significantly lower arterial pressure. Eight-week-old, male SHR were instrumented with femoral arterial, venous, and bladder catheters. Forty-eight hours later, each rat was infused intravenously with an isotonic saline load (5% of body weight; 0.5 ml/min). Lifetime captopril-treated SHR and untreated control SHR displayed nearly identical natriuretic and diuretic responses to the saline infusion. Thus, although lifetime captopril treatment significantly reduces mean arterial pressure in SHR, renal excretory responses appear to be unaltered. Moreover, histological examination of the kidneys of the lifetime captopril-treated SHR did not reveal significant structural damage in the kidneys at either 8 weeks of age or at 12 months of age. Together, the data suggest that lifetime captopril treatment does not adversely affect renal function and structure in SHR.

Exclusion of the candidate genes ACE and Bcl-2 for six families with nephronophthisis not linked to the NPH1 locus

BACKGROUND

Nephronophthisis (NPH) is an autosomal recessively transmitted kidney disease, characterized by cyst formation at the cortico-medullary junction, and a sclerosing tubulointerstitial nephropathy. Juvenile nephronophthisis (NPH1) is the most common genetic cause of renal failure in children and maps to chromosome 2q12-q13. The responsible gene NPHP1 has been identified and encodes for nephrocystin. Not all families with NPH demonstrate linkage to that locus.

METHODS

We studied six families with NPH without linkage to the NPH1 locus. In order to attempt identification of a new causative gene, the candidate genes ACE (angiotensin converting enzyme) and Bcl-2 (B cell leukaemia/lymphoma 2 gene) originating from mouse models, were examined. For the six families highly polymorphic microsatellites covering the whole candidate gene regions were haplotyped and linkage analysis was performed.

RESULTS

Haplotype analyses of all families examined were incompatible with linkage of the disease status to ACE or Bcl-2. Linkage analysis excluded both candidate gene regions with a LOD-score of < -2.

CONCLUSIONS

This study excluded the candidate genes ACE and Bcl-2 for NPH. Additional linkage studies need to be performed in order to identify further genes responsible for nephronophthisis.

The renal lesions that develop in neonatal mice during angiotensin inhibition mimic obstructive nephropathy

BACKGROUND

Inhibition of angiotensin action, pharmacologically or genetically, during the neonatal period leads to renal anomalies involving hypoplastic papilla and dilated calyx. Recently, we documented that angiotensinogen (Agt -/-) or angiotensin type 1 receptor nullizygotes (Agtr1 -/-) do not develop renal pelvis nor ureteral peristaltic movement, both of which are essential for isolating the kidney from the high downstream ureteral pressure. We therefore examined whether these renal anomalies could be characterized as "obstructive" nephropathy.

METHODS

Agtr1 -/- neonatal mice were compared with wild-type neonates, the latter subjected to surgical complete unilateral ureteral ligation (UUO), by analyzing morphometrical, immunohistochemical, and molecular indices. Agtr1 -/- mice were also subjected to a complete UUO and were compared with wild-type UUO mice by quantitative analysis. To assess the function of the urinary tract, baseline pelvic and ureteral pressures were measured.

RESULTS

The structural anomalies were qualitatively indistinguishable between the Agtr1 -/- without surgical obstruction versus the wild type with complete UUO. Thus, in both kidneys, the calyx was enlarged, whereas the papilla was atrophic; tubulointerstitial cells underwent proliferation and also apoptosis. Both were also characterized by interstitial macrophage infiltration and fibrosis, and within the local lesion, transforming growth factor-beta 1, platelet-derived growth factor-A and insulin-like growth factor-1 were up-regulated, whereas epidermal growth factor was down-regulated. Moreover, quantitative differences that exist between mutant kidneys without surgical obstruction and wild-type kidneys with surgical UUO were abolished when both underwent the same complete surgical UUO. The hydraulic baseline pressure was always lower in the pelvis than that in the ureter in the wild type, whereas this pressure gradient was reversed in the mutant.

CONCLUSION

The abnormal kidney structure that develops in neonates during angiotensin inhibition is attributed largely to "functional obstruction" of the urinary tract caused by the defective development of peristaltic machinery.

Angiotensin II, type 2 receptor in the development of vesico-ureteric reflux

OBJECTIVE

To investigate if mutation of the angiotensin II (Ang II) receptors AT2 is involved in primary vesico-ureteric reflux (VUR) in humans.

PATIENTS AND METHODS

Genetic polymorphisms in the AT1 and AT2 receptors was evaluated in 23 patients having the most common congenital urological abnormality, namely primary congenital VUR. The occurrence of the A1166C transition in the AT1 receptor gene and the A-1332G transition in the AT2 receptor gene were evaluated and compared with the incidence in normal controls with no urological abnormalities.

RESULT

The distribution of the AT1 receptor genotypes was no different between patients with VUR and healthy controls. Furthermore, 10 of 23 (44%) patients with VUR and seven of 19 (42%) controls carried the AT2 receptor gene variation. These results contrast with our previous finding of an association between the A-1332G transition in the AT2 receptor gene and primary obstructive megaureter, and pelvi-ureteric junction obstruction.

CONCLUSIONS

We propose that while the AT2 receptor is crucial for the normal development of the ureter, it does not contribute to the processes which culminate in VUR, which is primarily an abnormality in the bladder trigone.

Angiotensin induces the urinary peristaltic machinery during the perinatal period

The embryonic development of mammalian kidneys is completed during the perinatal period with a dramatic increase in urine production, as the burden of eliminating nitrogenous metabolic waste shifts from the placenta to the kidney. This urine is normally removed by peristaltic contraction of the renal pelvis, a smooth muscle structure unique to placental mammals. Mutant mice completely lacking angiotensin type 1 receptor genes do not develop a renal pelvis, resulting in the buildup of urine and progressive kidney damage. In mutants the ureteral smooth muscle layer is hypoplastic and lacks peristaltic movements. We show that angiotensin can induce the ureteral smooth muscles in organ cultures of wild-type, but not mutant, ureteral tissues and that, in wild-type mice, expression of both renal angiotensin and the receptor are transiently upregulated at the renal outlet at birth. These results reveal a new role for angiotensin in the unique cellular adaptations of the mammalian kidney to the physiological stresses of postnatal life.

Determination of right ventricular structure and function in normoxic and hypoxic mice: a transesophageal echocardiographic study

BACKGROUND

Noninvasive cardiac evaluation is of great importance in transgenic mice. Transthoracic echocardiography can visualize the left ventricle well but has not been as successful for the right ventricle (RV). We developed a method of transesophageal echocardiography (TEE) to evaluate murine RV size and function.

METHODS AND RESULTS

Normoxic and chronically hypoxic mice (F(IO2)=0.11, 3 weeks) and agarose RV casts were scanned with a rotating 3.5F/30-MHz intravascular ultrasound probe. In vivo, the probe was inserted in the mouse esophagus and withdrawn to obtain contiguous horizontal planes at 1-mm intervals. In vitro, the probe was withdrawn along the left ventricular posterior wall of excised hearts. The borders of the RV were traced on each plane, allowing calculation of diastolic and systolic volumes, RV mass, RV ejection fraction, stroke volume, and cardiac output. RV wall thickness was measured. Echo volumes obtained in vitro were compared with cast volumes. Echo-derived cardiac output was compared with measurements of an ascending aortic Doppler flow probe. Echo-derived RV free wall mass was compared with true RV free wall weight. There was excellent agreement between cast and TEE volumes (y=0.82x+6.03, r=0.88, P<0.01) and flow-probe and echo cardiac output (y=1.00x+0.45, r=0.99, P<0.0001). Although echo-derived RV mass and wall thickness were well correlated with true RV weight, echo-derived RV mass underestimated true weight (y=0.53x+2.29, r=0.81, P<0.0001). RV mass and wall thickness were greater in hypoxic mice than in normoxic mice (0.78+/-0.19 versus 0.51+/-0.14 mg/g, P<0.03, 0.50+/-0.03 versus 0.38+/-0.03 mm, P<0.04).

CONCLUSIONS

TEE with an intravascular ultrasound catheter is a simple, accurate, and reproducible method to study RV size and function in mice.

Transgenic animal models for the functional analysis of vasoactive peptides

The interplay of vasoactive peptide systems is an essential determinant of blood pressure regulation in mammals. While the endothelin and the renin-angiotensin systems raise blood pressure by inducing vasoconstriction and sodium retention, the kallikrein-kinin and the natriuretic-peptide systems reduce arterial pressure by eliciting vasodilatation and natriuresis. Transgenic technology has proven to be very useful for the functional analysis of vasoactive peptide systems. As an outstanding example, transgenic rats overexpressing the mouse Ren-2 renin gene in several tissues become extremely hypertensive. Several other transgenic rat and mouse strains with genetic modifications of components of the renin-angiotensin system have been developed in the past decade. Moreover, in recent years gene-targeting technology was employed to produce mouse strains lacking these proteins. The established animal models as well as the main insights gained by their analysis are summarized in this review.

Cleavage of arginyl-arginine and lysyl-arginine from the C-terminus of pro-hormone peptides by human germinal angiotensin I-converting enzyme (ACE) and the C-domain of human somatic ACE

Mammalian germinal angiotensin I-converting enzyme (gACE) is a single-domain dipeptidyl carboxypeptidase found exclusively in male germ cells, which has almost identical sequence and enzymic properties with the C-domain of the two-domain somatic ACE. Mutant mice that do not express gACE are infertile, suggesting a role for the enzyme in the processing of undefined peptides involved in fertilization. A number of spermatid peptides [e.g. cholecystokinin (CCK) and gastrin] are processed from pro-hormones by endo- and exo-proteolytic cleavages which might generate substrates for gACE. We have shown that peptide hormone intermediates with Lys/Arg-Arg at the C-terminus are high-affinity substrates for human gACE. gACE from human sperm cleaved Arg-Arg from the C-terminus of the CCK5-GRR (GWMDFGRR), a peptide corresponding to the C-terminus of a CCK-gastrin prohormone intermediate. Hydrolysis of CCK5-GRR by recombinant human C-domain ACE was Cl- dependent, with maximal activity achieved in 5-10 mM NaCl at pH 6.4. C-Domain ACE cleaved Lys/Arg-Arg from the C-terminus of dynorphin-(1-7), a pro-TRH peptide KRQHPGKR, and two insect peptides FSPRLGKR and FSPRLGRR. C-Domain ACE displayed high affinity towards all these substrates with Vmax/Km values between 14 and 113 times greater than the Vmax/Km for the conversion of the best known ACE substrate, angiotensin I, into angiotensin II. In conclusion, we have identified a new class of substrates for human gACE, and we suggest that gACE might be an alternative to carboxypeptidase E for the trimming of basic dipeptides from the C-terminus of intermediates generated from pro-hormones by subtilisin-like convertases in human male germ cells.

Fashioning the vertebrate heart: earliest embryonic decisions

Our goal here is to set out the types of unitary decisions made by heart progenitor cells, from their appearance in the heart field until they form the simple heart tube. This provides a context to evaluate cell fate, lineage and, finally, morphogenetic decisions that configure global heart form and function. Some paradigms for cellular differentiation and for pattern generation may be borrowed from invertebrates, but neither Drosophila nor Caenorhabditis elegans suffice to unravel higher order decisions. Genetic analyses in mouse and zebrafish may provide one entrance to these pathways.

Neonatal angiotensin-converting enzyme inhibition in the rat induces persistent abnormalities in renal function and histology

Recently, we reported that neonatal blockade of the renin-angiotensin system in the rat produces irreversible abnormalities in renal histology associated with increased diuresis. In the present study, we assessed the long-term consequences of neonatal angiotensin-converting enzyme inhibition on renal function. Rats were injected with 10 mg.kg-1.d-1 enalapril or vehicle from day 3 to day 24 after birth. Urine concentrating ability, renal function, and renal histology were assessed in 16-week-old rats. There was a twofold increase in diuresis and water intake in enalapril-treated rats throughout the study course. Urine osmolality after 24 hours of water deprivation was 1008 +/- 108 and 2549 +/- 48 mOsm.kg-1 (P < .05) in enalapril- and vehicle-treated rats, respectively. Glomerular filtration rate (0.54 +/- 0.03 versus 0.75 +/- 0.06 mL.min-1x100 g body wt-1, P < .05) and effective renal plasma flow (1.76 +/- 0.09 versus 2.19 +/- 0.14 mL.min-1x100 g body wt-1, P < .05) were reduced in neonatally enalapril-treated versus control rats. Absolute and fractional urinary sodium excretion values were elevated (P < .05) in enalapril-treated rats. Semiquantitative assessment of renal histology demonstrated statistically significant degrees of papillary atrophy, interstitial fibrosis and inflammation, tubular atrophy and dilatation, and focal glomerulosclerosis in neonatally enalapril-treated rats. In conclusion, neonatal angiotensin-converting enzyme inhibition in the rat produces irreversible alterations in renal function and morphology, demonstrating the importance of an intact renin-angiotensin system neonatally for normal renal development.