Development Of Renal Tubules Research Articles

Postnatal renal tubule development: roles of tubular flow and flux.

Postnatal renal tubule development is critical to adult kidney function. Several postnatal changes regulate the differentiation and proliferation of renal tubular cells. Here, we review the literature and our efforts on thick ascending limb (TAL) development in Bartter syndrome (BS). Glomerular filtrate quickly increases after birth, imposing fluid shear stress and circumferential stretch on immature renal tubules. Recent studies showed that kidney organoids under flow (superfusion) have better development of tubular structures and the expression of cilia and solute transporters. These effects are likely mediated by mechanosensors, such as cilia and the piezo1 channel. Improved renal oxygenation and sodium pump-dependent active transport can stimulate mitochondrial respiration and biogenesis. The functional coupling between transport and mitochondria ensures ATP supply for energy-demanding reactions in tubular cells, including cell cycle progression and proliferation. We recently discovered that postnatal renal medulla maturation and TAL elongation are impaired in Clc-k2-deficient BS mice. Primary cultured Clc-k2-deficient TAL cells have G1-S transition and proliferation delay. These developmental defects could be part of the early pathogenesis of BS and worsen the phenotype. Understanding how tubular flow and transepithelial ion fluxes regulate renal tubule development may improve the treatment of congenital renal tubulopathies.

Renal Tubular Dysgenesis Associated with Compound Heterozygous ACE Mutations

Inherited renal tubular dysgenesis(RTD), a rare, autosomal recessive disorder is caused by mutations in the genes encoding components of the renin-angiotensin pathway: angiotensinogen(AGT), renin (REN), angiotensin-converting enzyme(ACE), and angiotensin ?? receptor type 1(AGTR1). It characterized by the absence or poor development of renal tubules, and associated with oligohydramnios, Potter sequence and neonatal death due to renal or respiratory failure. We report a family with two mutations in the coding region of the ACE gene: a nonsense mutation in exon4 (c.538C>T) and a frameshift deletion at nucleotide 3073 and nucleotide 3074 in exon20(c.3073_3074delTC). The mutations were in the compound heterozygous state causing disease, because each parent had their own mutation.

Pectoral muscle transcriptome analyses reveal high-altitude adaptations in Tibetan chickens

Abstract The largest muscles in fowl are the pectorals, which provide the power required for birds to fly. Tibetan chickens show specific adaptations to high-altitude conditions, but changes in the muscle transcriptome associated with these adaptations have not been characterized yet. Therefore, in this study, we used next-generation sequencing technologies to generate eight libraries of mRNA sequences for four Tibetan chickens and four Beijing fatty chickens. A comprehensive transcriptome analysis was performed. In the eight samples, 12 333 annotated protein-coding genes were expressed. Among these, 48 differentially expressed genes were found; all of which were upregulated in Tibetan chickens. These differentially expressed genes were mainly involved in kidney morphogenesis, which indicates that hypoxia has an important effect on renal tubule development. Only nine genes were involved in Kyoto Encyclopedia of Genes and Genomes pathways, such as the endocytosis pathway, the MAPK signaling pathway, the calcium signaling pathway and the TGF-beta signaling pathway. The differentially expressed genes identified in this study will be used to facilitate future research into the Tibetan chicken.

Role of Core Planar Cell Polarity Vangl2 Gene in the Renal Tubule Development in Mice

Background: Polycystic kidney disease (PKD) is a common kidney disease that affects the development and maintenance of renal tubules, leads to cyst formation, and often progresses to end-stage kidney disease. It has been postulated that defective planar cell polarity (PCP) signaling contributes to initiation of cyst formation in PKD via controlling both convergent extension (CE, a process of directional cell movements) and oriented cell division (OCD, a process of directional cell divisions during tubular elongation post-natally). Indeed, mutations of the key PCP gene, Van Gogh-like 2 (Vangl2), lead to abnormal renal tubules in murine embryonic kidneys, correlating with the original postulate. Methods: In order to further understand the influence of the Vangl2 gene on renal morphogenesis and cystogenesis, control and Vangl2 mutant embryos—as well as post-natal Vangl2 mice with conditional excision of the Vangl2 gene in renal collecting tubules—were generated, then analyzed using immunostaining and fluorescence microscopy. Results: Our results show that Vangl2 plays a role in CE and apical constriction (AC) during embryonic stage of tubulogenesis. Compared to control animals, mutant Vangl2Δ/Δ and conditional Vangl2Δ/CD embryos displayed: i) a significant dilation in the diameter of renal tubules seen as an increased tubule cross-section area and a larger number of cells per cross-section; and ii) changes in cell shape indicative of defective AC. Surprisingly, post-natal mice showed virtually no difference in any of these aspects comparing to control mice, suggesting that other pathways may compensate for the lack of PCP signaling in maintenance of the tubule architecture. Limitations: a) The analysis of the renal tubules at the specific time points does not account for the dynamics of tubular movement and growth in real time; b) a mechanistic and morphological distinction between mice and humans may exist in the renal collecting duct tubules, pertaining to the Vangl2 gene’s influence in the PCP pathway; and c) the degree of mosaicism resulting from the gene excision by Cre-recombinase may correlate with the severity of the phenotype. Conclusion: We conclude that the PCP pathway is required for normal tubule development during embryogenesis. Our results, however, indicate that the cystogenesis seen in PKD postnatally may not be directly attributed to the disrupted PCP signaling, and requires the derangement of additional pathways.

Renal tubular dysgenesis: An unusual cause of anhydramnios

We present case of renal tubular dysgenesis, a rare fetal disorder of abnormal renal tubule development which causes anhydramnios and neonatal death. Kidneys are of normal size, with non-specific, subtle, ultrasound abnormalities, but show absence or incomplete differentiation of proximal tubules due to abnormalities of the renin angiotensin system. We highlight the need for post-mortem for accurate diagnosis, targeted genetic testing, genetic counselling and subsequent antenatal screening for this usually autosomal recessive condition.

Epithelial–mesenchymal transition of renal tubules: Divergent processes of repairing in acute or chronic injury?

Epithelial–mesenchymal transition (EMT) of tubular epithelial cells (TECs) is commonly considered as the major mechanism leading to renal fibrosis in chronic kidney diseases (CKD) injury. We raise the hypothesis that EMT in adult kidney may be an event of “atavistic” phenotypic transition, which mimics but reverses the genetic and cellular processes of development of renal tubules. Transformed TECs may be regarded as induced mesenchymal stem-like cells, representing a cellular self-adaptation when in acute or chronic injury. The reasons are as follows: (1) Embryonic gene WT1 and Pax2, which govern tubule development, have been found to re-express during tubular EMT when facing injury. (2) The common factors that induce EMT in vitro, like IL-1, angiotension II and hypoxia could also promote WT1 and/or Pax2 re-expression. (3) Expression of WT1 and Pax2 are found to be associated with progenitor cells. (4) Beside embryonic gene WT1 and Pax2, we also found that some stem cell markers like CD133 were expressed during EMT process. (5) The process of EMT is not only take place in chronic kidney injury (CKD), but also in acute kidney injury (AKI) as well. (6) The phenotype transition of TECs and genetic event during AKI are entirely consistent with what happened in CKD, but the outcome is completely different. Thus, we thought tubular injury of CKD and AKI may share a common initiative repair mechanism: tubular EMT, that is TECs are transformed into induced mesenchymal stem-like cells, and then interpret the injurious signal differently in acute versus chronic conditions, so as to possess a divergent fates, tubular regeneration or fibrosis formation, depending on a different microenvironment or the duration of the injury. In this sense, tubular EMT could be purposefully orientated into a constructively pathway that repair kidney injury via tubular regeneration, matrix remodeling and tissue structure and function restoration.

The novel and independent association between single-point SNP of NPHP4 gene and renal function in non-diabetic Japanese population: the Takahata study

Nephronophthisis (NPHP) 4 gene coding nephrocystin-4 is involved in the development of renal tubules and its congenital mutations cause juvenile end-stage renal disease, NPHP. To investigate the association between single-point single-nucleotide polymorphism (SNP) of NPHP4 gene and renal function, we conducted a cross-sectional study in Japanese population. The subjects of this study were non-diabetic general population consisting of 2604 individuals >40 years in Takahata town, Japan. We genotyped 11 SNPs within NPHP4 gene that displayed frequent minor allele frequencies (>0.1) in Japanese general population. Among 11 SNPs in NPHP4 gene, only rs1287637 that induces amino acid substitution (A (Gln)/T (Leu)), located in the acceptor site of exon 21, showed a significant association with estimated glomerular filtration rate (eGFR; T/T: 81.3±15.6 (n=1886), A/T: 82.0±15.5 (n=652) and A/A: 87.4±21.4 ml min(-1) per 1.73m(2) (n=66); mean±s.d., P=0.006). This SNP was not in linkage disequilibrium with the surrounding SNPs. The multivariate analysis adjusted with possible confounders showed that the A/T+T/T genotype of rs1287637 was independently associated with reduced renal function (eGFR <90 ml min(-1) per 1.73m(2); odds ratio (OR) 1.75, 95% confidence interval (CI) 1.05-2.94, P=0.033). These results indicate the novel and independent association between single-point SNP rs1287637 in NPHP4 gene and renal function in non-diabetic Japanese population.

Angiotensin I-Converting Enzyme Gln1069Arg Mutation Impairs Trafficking to the Cell Surface Resulting in Selective Denaturation of the C-Domain

BackgroundAngiotensin-converting enzyme (ACE; Kininase II; CD143) hydrolyzes small peptides such as angiotensin I, bradykinin, substance P, LH-RH and several others and thus plays a key role in blood pressure regulation and vascular remodeling. Complete absence of ACE in humans leads to renal tubular dysgenesis (RTD), a severe disorder of renal tubule development characterized by persistent fetal anuria and perinatal death.Methodology/Principal FindingsPatient with RTD in Lisbon, Portugal, maintained by peritoneal dialysis since birth, was found to have a homozygous substitution of Arg for Glu at position 1069 in the C-terminal domain of ACE (Q1069R) resulting in absence of plasma ACE activity; both parents and a brother who are heterozygous carriers of this mutation had exactly half-normal plasma ACE activity compared to healthy individuals. We hypothesized that the Q1069R substitution impaired ACE trafficking to the cell surface and led to accumulation of catalytically inactive ACE in the cell cytoplasm. CHO cells expressing wild-type (WT) vs. Q1069R-ACE demonstrated the mutant accumulates intracellularly and also that it is significantly degraded by intracellular proteases. Q1069R-ACE retained catalytic and immunological characteristics of WT-ACE N domain whereas it had 10–20% of the nativity of the WT-ACE C domain. A combination of chemical (sodium butyrate) or pharmacological (ACE inhibitor) chaperones with proteasome inhibitors (MG 132 or bortezomib) significantly restored trafficking of Q1069R-ACE to the cell surface and increased ACE activity in the cell culture media 4-fold.Conclusions/SignificanceHomozygous Q1069R substitution results in an ACE trafficking and processing defect which can be rescued, at least in cell culture, by a combination of chaperones and proteasome inhibitors. Further studies are required to determine whether similar treatment of individuals with this ACE mutation would provide therapeutic benefits such as concentration of primary urine.

Characteristics of Genomic Signatures Derived Using Univariate Methods and Mechanistically Anchored Functional Descriptors for Predicting Drug- and Xenobiotic-Induced Nephrotoxicity

ABSTRACTThe ideal toxicity biomarker is composed of the properties of prediction (is detected prior to traditional pathological signs of injury), accuracy (high sensitivity and specificity), and mechanistic relationships to the endpoint measured (biological relevance). Gene expression-based toxicity biomarkers (“signatures”) have shown good predictive power and accuracy, but are difficult to interpret biologically. We have compared different statistical methods of feature selection with knowledge-based approaches, using GeneGo's database of canonical pathway maps, to generate gene sets for the classification of renal tubule toxicity. The gene set selection algorithms include four univariate analyses: t-statistics, fold-change, B-statistics, and RankProd, and their combination and overlap for the identification of differentially expressed probes. Enrichment analysis following the results of the four univariate analyses, Hotelling T-square test, and, finally out-of-bag selection, a variant of cross-validation, were used to identify canonical pathway maps—sets of genes coordinately involved in key biological processes—with classification power. Differentially expressed genes identified by the different statistical univariate analyses all generated reasonably performing classifiers of tubule toxicity. Maps identified by enrichment analysis or Hotelling T-square had lower classification power, but highlighted perturbed lipid homeostasis as a common discriminator of nephrotoxic treatments. The out-of-bag method yielded the best functionally integrated classifier. The map “ephrins signaling” performed comparably to a classifier derived using sparse linear programming, a machine learning algorithm, and represents a signaling network specifically involved in renal tubule development and integrity. Such functional descriptors of toxicity promise to better integrate predictive toxicogenomics with mechanistic analysis, facilitating the interpretation and risk assessment of predictive genomic investigations.

The role of polyester interstitium and aldosterone during structural development of renal tubules in serum-free medium

Little knowledge is available regarding the development of renal stem/progenitor cells into functional parenchyme. To investigate the environmental mechanisms during this maturation process, we elaborated an advanced culture technique to follow renal tubule development. Embryonic stem/progenitor cells derived from neonatal rabbit kidney were placed in a perfusion culture container at the interphase of an artificial polyester interstitium. Tissue culture was carried out in IMDM without serum or protein supplementation and without coating with extracellular matrix proteins. Development of tubules was registered histochemically on cryosections labeled with soybean agglutinin (SBA) and tissue-specific antibodies. The experiments revealed that the development of renal tubules depends exclusively on the administration of aldosterone. The use of 1×10 −7 m aldosterone for 13 days generated numerous SBA-labeled tubules, while no tubules developed in the absence of the steroid hormone. To obtain further information about the action of the hormone on the cognate receptor, molecular precursors of the aldosterone synthesis pathway were tested. Surprisingly, application of cholesterol, pregnenolone, progesterone, 11-deoxycorticosterone (DOCA) and corticosterone failed to form numerous tubules. Only 11-DOCA and progesterone induced a few tubules, which were barely SBA-labeled. Furthermore, application of aldosterone antagonists such as 1×10 −4 m spironolactone and 1×10 −4 m canrenoate completely inhibited the development of tubules. We conclude that specifically aldosterone promotes the development of tubules via the mineralocorticoid receptor whereas its precursors have no effect.

Modulating the Development of Renal Tubules Growing in Serum-Free Culture Medium at an Artificial Interstitium

Little information on the structural growth of renal tubules is available. A major problem is the technical limitation of culturing intact differentiated tubules over prolonged periods of time. Consequently, we developed an advanced culture method to follow tubule development. Isolated tissue containing renal progenitor cells was placed in a perfusion culture container at the interphase of an artificial polyester interstitium. Iscove's modified Dulbecco's medium without serum or protein supplementation was used for culture, and the culture period was 13 days. Tissue growth was not supported by addition of extracellular matrix proteins. The development of tubules was registered on cryosections labeled with soybean agglutinin (SBA) and tissue-specific antibodies. Multiple SBA-labeled tubules were found when aldosterone was added to the culture medium. In contrast, culture without aldosterone supplementation displayed completely disintegrated tissue. The development of tubules depended on the applied aldosterone concentration. The use of 1 x 10(-6) M and 1 x 10(-7) M aldosterone produced numerous tubules, while application of 1 x 10(-8) M to 1 x 10(-10) M led to a continuous decrease and finally a loss of tubule formation. The development of labeled tubules in aldosterone-treated specimens took an unexpectedly long period of at least 8 days. The morphogenic effect of aldosterone appeared to be mineralocorticoid hormone-specific since spironolactone and canrenoate abolished the development. Finally, dexamethasone induced widely distributed cell clusters instead of tubules.

Modulating the Development of Renal Tubules Growing in Serum-Free Culture Medium at an Artificial Interstitium

Modulating the Development of Renal Tubules Growing in Serum-Free Culture Medium at an Artificial Interstitium

Early Embryonic Renal Tubules of Wild-Type and Polycystic Kidney Disease Kidneys Respond to cAMP Stimulation with Cystic Fibrosis Transmembrane Conductance Regulator/Na+,K+,2Cl− Co-Transporter–Dependent Cystic Dilation

Metanephric organ culture has been used to determine whether embryonic kidney tubules can be stimulated by cAMP to form cysts. Under basal culture conditions, wild-type kidneys from embryonic day 13.5 to 15.5 mice grow in size and continue ureteric bud branching and tubule formation over a 4- to 5-d period. Treatment of these kidneys with 8-Br-cAMP or the cAMP agonist forskolin induced the formation of dilated tubules within 1 h, which enlarged over several days and resulted in dramatically expanded cyst-like structures of proximal tubule and collecting duct origin. Tubule dilation was reversible upon withdrawal of 8-Br-cAMP and was inhibited by the cAMP-dependent protein kinase inhibitor H89 and the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR(inh)172. For further testing of the role of CFTR, metanephric cultures were prepared from mice with a targeted mutation of the Cftr gene. In contrast to kidneys from wild-type mice, those from Cftr -/- mice showed no evidence of tubular dilation in response to 8-Br-cAMP, indicating that CFTR Cl(-) channels are functional in embryonic kidneys and are required for cAMP-driven tubule expansion. A requirement for transepithelial Cl(-) transport was demonstrated by inhibiting the basolateral Na(+),K(+),2Cl(-) co-transporter with bumetanide, which effectively blocked all cAMP-stimulated tubular dilation. For determination of whether cystic dilation occurs to a greater extent in PKD kidneys in response to cAMP, Pkd1(m1Bei) -/- embryonic kidneys were treated with 8-Br-cAMP and were found to form rapidly CFTR- and Na(+),K(+),2Cl(-) co-transporter-dependent cysts that were three- to six-fold larger than those of wild-type kidneys. These results suggest that cAMP can stimulate fluid secretion early in renal tubule development during the time when renal cysts first appear in PKD kidneys and that PKD-deficient renal tubules are predisposed to abnormally increased cyst expansion in response to elevated levels of cAMP.

VEGF receptor 2 blockade leads to renal cyst formation in mice

Polycystic kidney disease (PKD) is associated with mutations in PKD1 and PKD2 and vascular abnormalities. The links between the epithelial and vascular defects, however, are poorly understood. Vascular endothelial growth factor (VEGF) has been shown to be critical for normal kidney development. In animal models, blockade of VEGF in the perinatal period can lead to abnormal glomerular development, impaired nephrogenesis, proteinuria, and renal failure. We hypothesized that brief blockade of VEGF signaling during early postnatal kidney development can lead to renal cyst development. On days 2 and 4 of life, CD-1 mice were treated with antibodies generated against the extracellular portion of the VEGF receptor 2 (DC101), the area of the receptor where VEGF binding occurs. Mice developed renal cysts between 2 and 3 weeks. The DC101-treated mice also had increased cell proliferation in the renal tubule epithelium. In addition, mice receiving DC101 developed abnormal glomeruli, proteinuria, and patchy cellular infiltrates. Early disruption of VEGFR-2 signaling during the perinatal period results in renal cyst formation, impaired glomerulogenesis, and inflammation. VEGF could be a key link between vascular and cystic changes in kidney cyst formation.

Development of hydrogen peroxide (H 2O 2)-generating oxidases in chick organs with special reference to kidneys

The developmental pattern of H2O2-producing oxidases (OX) was studied in chick kidneys (mesonephros, metanephros), intestine, liver, yolk sac and adrenal glands between embryonic days (ED) 5-20 as well as in chick organs after hatching. Sections from snap frozen tissue fixed in cold cacodylate-buffered 2% glutaraldehyde were processed by cerium-DAB-Co-H2O2 methods for benzylamine OX, diamine OX, histamine OX, alpha-hydroxyacid OX, D-amino acid OX (AAOX) and monoamine OX (MAOX). Prenatally, only activities of AAOX and MAOX could be demonstrated. AAOX appeared primarily in the proximal tubular cells of both types of kidneys. In the metanephros the enzyme was also detected in the thick ascending limbs of Henle's loops. The amount of reaction product in tubular cells increased with their maturation. MAOX activity was detected in immature enterocytes, in smooth muscle cells of large systemic arteries (on ED 5-6) as well as in proximal tubular cells of the mesonephros and adrenal gland. Later the enzyme appeared also in smooth muscle cells of the intestinal wall and in endothelial and smooth muscle cells of arterioles of the mesonephros. In the metanephros MAOX was detected at the same locations with a time delay because of a developmental shift of the kidney. Inhibition tests revealed that MAOX differs in epithelial cells from that in smooth muscle cells. Benzylamine OX, diamine OX and histamine OX were detected postnatally in smooth muscle cells of the arterial media and muscularis externa of the intestinal wall with low activities. It is concluded that MAOX and AAOX activities represent useful markers in the development of renal tubules. In addition, MAOX activity can be considered an indicator of maturation of components of the vascular wall.

Proceedings of the Symposium ‘Angiotensin AT1 Receptors: From Molecular Physiology to Therapeutics’: ANGIOTENSIN RECEPTORS AND DEVELOPMENT: THE KIDNEY

SUMMARY This brief review examines the evidence that angiotensin II (AngII) is essential for kidney development. Several components of the renin‐angiotensin system (RAS) are detected in the foetal kidney early in development. Angiotensin II is essential for normal foetal and neonatal renal function. Angiotensin II receptors transduce important signals leading to growth and development. Angiotensin receptor subtypes show spatial and temporal specificity of localization throughout renal development. Angiotensin converting enzyme (ACE) inhibition or AngII receptor blockade (specifically AT1 subtype blockade) results in functional and structural abnormalities of the developing kidney in both experimental and clinical situations. While chronic postnatal RAS blockade in rats is associated with structural damage to tubules and blood vessels of the kidney, reports differ on whether treatment also affects glomerular induction and growth. In metanephric organ culture, glomerular induction proceeds despite AngII receptor blockade. In summary, the evidence suggests that AngII is not essential for nephron induction and glomerular development in the rat kidney. However, AngII is essential for normal growth and development of renal tubules and vasculature.

Expression of connexin 32 gap junction protein in the kidneys during fetal development of the hamster (Mesocricetus auratus).

The expression of gap junction protein was examined immunohistochemically using affinity-purified antibody against rat liver gap junction protein, connexin 32 (Cx32), in the kidneys of fetal (gestation days 13-16) and adult Syrian golden hamsters. Phalloidin histochemical staining, PNA- and RCA I-lectin staining, NCAM immunostaining, and alkaline phosphatase and Na(+)-K(+)-ATPase enzyme-histochemical staining were performed in combination with Cx32 immunostaining. The kidney sections were observed with a confocal scanning laser microscope. By gestation day 13, Cx32 immunoreactivity was observed in the differentiating tubules. The Cx32 staining was localized on the lateral cell membrane of the cells lining the developing proximal tubules, while the S-shaped bodies, developing distal tubules, and collecting tubules showed no positive immunostaining. As the kidney developed, the density of Cx32 immunoreactivity increased. As the gap junction provides pathways for cell-cell communication, the development of Cx32 expression may imply that this structure plays an important role in renal tubule development. Confocal scanning laser microscopy provided a clear image of the fluorescence-labeled cell structures, free from out-of-focus blur. Using the same sections, stereoscopic images were easily reconstructed from serial optical sections, and were helpful in understanding the spatial distribution of Cx32 expression in the developing fetal proximal tubules.

Aldosterone and sodium HOMEOSTASIS in preterm infants.

A specific mass spectrometric method was used for tetrahydroaldosterone determination in urine of preterm infants (26-34 weeks gestational age) up to 9 weeks of age. Hyponatraemia during the first 2 weeks of life was associated with an excretion of tetrahydroaldosterone (5-50 mug/24 h) comparable with full-term infants. Excretion of tetrahydroaldosterone was significantly elevated in all infants studied during the third week of life (80-350 mug/24 h) and this was associated with establishment of positive sodium balance. The excretion of tetrahydro aldosterone remained high for 2 or 3 weeks. The results are discussed in relation to the development of renal tubules and control mechanism for sodium homeostasis.