Multiple causes of human kidney malformations

Ultrasound Doppler renal pulsatility index is a predictive marker of arterial stiffness in children with solitary functioning kidney

INTRODUCTION

Patients with solitary functioning kidney (SFK) have glomerular hyperfiltration, hypertension, proteinuria and impaired renal function resulting in microvascular atherosclerotic abnormalities. This condition leads to an increase in arterial stiffness. In this study, we aimed to investigate the usefulness of non-invasive renal Doppler ultrasonography hemodynamic parameters in demonstrating arterial stiffness in pediatric patients with SFK.

METHODS

The study included 59 children aged 6-18 years who were diagnosed with SFK. Demographic, biochemical, anthropometric, and blood pressure data were recorded. The renal Doppler ultrasound hemodynamic parameters renal resistive index (RRI), renal pulsatility index (RPI), carotid-femoral pulse wave velocity (cfPWV), central augmentation index (cAIx) and carotid intima media thickness (cIMT) were evaluated.

RESULTS

Eighteen (30.5%) cases with acquired SFK and 41 (64.5%) cases with congenital SFK were detected. Central augmentation indices were higher in children with congenital SFK than in children with acquired SFK (p = 0.038). CkiD-eGFR-SCr-CysC was lower in patients with acquired SFK (p = 0.011). LDL cholesterol levels were higher in children with acquired SFK (p = 0.018). We found a significant correlation between RPI and cfPWV with a correlation coefficient (r) of 0.321 and a statistically significant p-value of 0.013.

CONCLUSIONS

Congenital SFK is associated with increased microvascular atherosclerotic burden. RPI assessment with renal Doppler ultrasound may be a non-invasive method to identify arterial stiffness.

Associations between maternal chronic diseases and congenital anomalies of the kidney and urinary tract in offspring: a population-based cohort study

Background

The relationship between maternal chronic diseases and congenital anomalies of the kidneys and urinary tract (CAKUT) in offspring still needs elucidation. This study aimed to comprehensively evaluate the associations between maternal chronic disease and CAKUT in their offspring.

Methods

Data of mothers and children were extracted from the Taiwan Maternal and Child Health Database and National Health Insurance Research Database. The concept of developmental origins of health and disease (DOHaD) was used to select maternal chronic diseases.

Results

The study cohort included 1 196 175 mothers and 1 628 706 offspring. Analysis showed that maternal chronic diseases, especially type 1 diabetes, type 2 diabetes, gestational diabetes, connective tissue disorders and CAKUT were highly associated with CAKUT in the offspring. Higher maternal age, abnormal birthweight (>3500 g or <2500 g), gestational age <36 weeks and birth order <2 were all associated with a higher risk of CAKUT. Maternal chronic hypertension and taking angiotensin-related drugs increased the odds ratios of obstructive kidney disease in the offspring. Offspring tended to have the same type of CAKUT as their mothers.

Conclusion

Maternal chronic diseases, older maternal age and abnormal birthweight are risk factors for CAKUT. Also, a percentage of patients with CAKUT were not full-term newborns. Results support prenatal counselling and health management of pregnant women with chronic diseases and extra care for infants with a high risk of anomalies. It is strongly recommended that prevention of CAKUT in offspring should start with care of the mothers' prenatal chronic diseases.

Current evidence on the use of anti-RAAS agents in congenital or acquired solitary kidney

RATIONAL

The inhibition of renin-angiotensin-aldosterone system (RAAS) is a major strategy for slowing the progression of chronic kidney disease (CKD). The utility of anti-RAAS agents in patients with congenital or acquired solitary kidney is still controversial.

OBJECTIVE

A systematic literature review was conducted.

MAIN FINDINGS

The conclusions of the few available studies on the topic are homogeneously in agreement with a long-term reno-protective activity of anti-RAAS drugs in patients with solitary kidney, especially if patients are hypertensive or proteinuric. However, angiotensin 2 (ANG2) levels permit a functional adaptation to a reduced renal mass in adults and is crucial for sustaining complete kidney development and maturation in children. A hormonal interference on ANG2 levels has been supposed in women. Consequently, at least in children and women, the use of ARBs appears more appropriate. Principle conclusions: Available data on this topic are limited; however, by their overall assessment, it would appear that anti-RAAS drugs might also be reno-protective in patients with solitary kidney. The use of ARBs, especially in children and in women, seems to be more appropriate. However, more experimental data would be strictly necessary to confirm this hypothesis.

MDCT and MR Urogram Spectrum of Congenital Anomalies of the Kidney and Urinary Tract Diagnosed in Adulthood

OBJECTIVE

Congenital anomalies of the kidneys and urinary tract (CAKUT) encompass a spectrum of anomalies that result from genetic, epigenetic, environmental, and molecular signal aberrations at key stages of urinary tract development. CAKUT can be seen incidentally on cross-sectional imaging of the abdomen or can be a cause for adult-onset chronic kidney disease, posing new challenges for nephrologists, urologists, and radiologists.

CONCLUSION

Awareness of CAKUT and familiarity with their imaging findings permit optimal patient management and thorough workup to prevent hypertension and progression from CAKUT to renal failure. The purpose of this article is to review the cross-sectional imaging findings of CAKUT that may present in adulthood.

Atlas of Cellular Dynamics during Zebrafish Adult Kidney Regeneration

The zebrafish is a useful animal model to study the signaling pathways that orchestrate kidney regeneration, as its renal nephrons are simple, yet they maintain the biological complexity inherent to that of higher vertebrate organisms including mammals. Recent studies have suggested that administration of the aminoglycoside antibiotic gentamicin in zebrafish mimics human acute kidney injury (AKI) through the induction of nephron damage, but the timing and details of critical phenotypic events associated with the regeneration process, particularly in existing nephrons, have not been characterized. Here, we mapped the temporal progression of cellular and molecular changes that occur during renal epithelial regeneration of the proximal tubule in the adult zebrafish using a platform of histological and expression analysis techniques. This work establishes the timing of renal cell death after gentamicin injury, identifies proliferative compartments within the kidney, and documents gene expression changes associated with the regenerative response of proliferating cells. These data provide an important descriptive atlas that documents the series of events that ensue after damage in the zebrafish kidney, thus availing a valuable resource for the scientific community that can facilitate the implementation of zebrafish research to delineate the mechanisms that control renal regeneration.

Prenatal risk factors for childhood CKD

Development of CKD may be programmed prenatally. We sought to determine the association of childhood CKD with prenatal risk factors, including birth weight, maternal diabetes mellitus (DM), and maternal overweight/obesity. We conducted a population-based, case-control study with 1994 patients with childhood CKD (<21 years of age at diagnosis) and 20,032 controls in Washington state. We linked maternal and infant characteristics in birth records from 1987 to 2008 to hospital discharge data and used logistic regression analysis to assess the association of prenatal risk factors with childhood CKD. The prevalence of CKD was 126.7 cases per 100,000 births. High birth weight and maternal pregestational DM associated nominally with CKD, with respective crude odds ratios (ORs) of 1.17 (95% confidence interval [95% CI], 1.03 to 1.34) and 1.97 (95% CI, 1.15 to 3.37); however, adjustment for maternal confounders attenuated these associations to 0.97 (95% CI, 0.79 to 1.21) and 1.19 (95% CI, 0.51 to 2.81), respectively. The adjusted ORs for CKD associated with other prenatal factors were 2.88 (95% CI, 2.28 to 3.63) for low birth weight, 1.54 (95% CI, 1.13 to 2.09) for maternal gestational DM, 1.24 (95% CI, 1.05 to 1.48) for maternal overweight, and 1.26 (95% CI, 1.05 to 1.52) for maternal obesity. In subgroup analysis by CKD subtype, low birth weight and maternal pregestational DM associated significantly with increased risk of renal dysplasia/aplasia. Low birth weight, maternal gestational DM, and maternal overweight/obesity associated significantly with obstructive uropathy. These data suggest that prenatal factors may impact the risk of CKD. Future studies should aim to determine if modification of these factors could reduce the risk of childhood CKD.

Hyperglycemia: GDNF-EGR1 pathway target renal epithelial cell migration and apoptosis in diabetic renal embryopathy

Maternal hyperglycemia can inhibit morphogenesis of ureteric bud branching, Glial cell line-derived neurotrophilic factor (GDNF) is a key regulator of the initiation of ureteric branching. Early growth response gene-1 (EGR-1) is an immediate early gene. Preliminary study found EGR-1 persistently expressed with GDNF in hyperglycemic environment. To evaluate the potential relationship of hyperglycemia-GDNF-EGR-1 pathway, in vitro human renal proximal tubular epithelial (HRPTE) cells as target and in vivo streptozotocin-induced mice model were used. Our in vivo microarray, real time-PCR and confocal morphological observation confirmed apoptosis in hyperglycemia-induced fetal nephropathy via activation of the GDNF/MAPK/EGR-1 pathway at E12-E15. Detachment between ureteric branch and metanephrons, coupled with decreasing number and collapse of nephrons on Day 1 newborn mice indicate hyperglycemic environment suppress ureteric bud to invade metanephric rudiment. In vitro evidence proved that high glucose suppressed HRPTE cell migration and enhanced GDNF-EGR-1 pathway, inducing HRPTE cell apoptosis. Knockdown of EGR-1 by siRNA negated hyperglycemic suppressed GDNF-induced HRPTE cells. EGR-1 siRNA also reduced GDNF/EGR-1-induced cRaf/MEK/ERK phosphorylation by 80%. Our findings reveal a novel mechanism of GDNF/MAPK/EGR-1 activation playing a critical role in HRPTE cell migration, apoptosis and fetal hyperglycemic nephropathy.

High glucose promotes nascent nephron apoptosis via NF-kappaB and p53 pathways

A hyperglycemic environment in utero reduces kidney size and nephron number due to nascent nephron apoptosis. However, the underlying mechanisms are incompletely understood. The present study investigated whether the nascent nephron apoptosis promoted by high glucose is mediated via the transcription factor NF-κB and p53 signaling pathways. Neonatal mouse kidneys from the offspring of nondiabetic, diabetic, and insulin-treated diabetic dams were used for in vivo studies, and MK4 cells, an embryonic metanephric mesenchymal (MM) cell line, were used for in vitro studies. Neonatal kidneys of the offspring of diabetic mothers exhibited an increased number of apoptotic cells and reactive oxygen species (ROS) generation, enhanced NF-κB activation, and nuclear translocation of its subunits (p50 and p65 subunits) as well as phosphorylation (Ser 15) of p53 compared with kidneys of offspring of nondiabetic mothers. Insulin treatment of diabetic dams normalized these parameters in the offspring. In vitro, high-glucose (25 mM) induced ROS generation and significantly increased MK4 cell apoptosis and caspase-3 activity via activation of NF-κB pathway, with p53 phosphorylation and nuclear translocation compared with normal glucose (5 mM). These changes in a high-glucose milieu were prevented by transient transfection of small interfering RNAs for dominant negative IκBα or IKK or p53. Our data demonstrate that high glucose-induced nascent nephron apoptosis is mediated, at least in part, via ROS generation and the activation of NF-κB and p53 pathways.

Management and etiology of the unilateral multicystic dysplastic kidney: a review

In children, unilateral multicystic dysplastic kidney (MCDK) is one of the most frequently identified urinary tract abnormalities. A variety of proposed etiologies has been associated with the underlying pathogenesis of MCDK. These include genetic disturbances, teratogens, in utero infections, and urinary outflow tract obstruction. From 5-43% of the time, MCDK has associated genito-urinary anomalies, both structural and functional in nature. A review of the literature reveals that involution rates are reported to be 19-73%, compensatory hypertrophy of the contralateral kidney occurs from 24-81% of the time, and estimated glomerular filtration rates (GFRs) (by the Schwartz formula) range from 86-122 ml/min per 1.73 m(2) body surface area. Most authors suggest serial ultrasonography to monitor contralateral growth, routine blood pressure monitoring, and a serum creatinine monitoring algorithm. The risk of hypertension in those with MCDKs does not appear to be greater than that of the general population, and the rates of malignant transformation of MCDK are small, if at all increased, in comparison with those in the general population. If the patient develops a urinary tract infection or has abnormalities of the contralateral kidney, shown on ultrasound, a voiding cystourethrogram is recommended. Finally, the body of literature does not support the routine surgical removal of MCDKs.

Maternal diabetes modulates renal morphogenesis in offspring

Maternal diabetes leads to an adverse in utero environment, but whether maternal diabetes impairs nephrogenesis is unknown. Diabetes was induced with streptozotocin in pregnant Hoxb7-green fluorescence protein mice at embryonic day 13, and the offspring were examined at several time points after birth. Compared with offspring of nondiabetic controls, offspring of diabetic mice had lower body weight, body size, kidney weight, and nephron number. The observed renal dysmorphogenesis may be the result of increased apoptosis, because immunohistochemical analysis revealed significantly more apoptotic podocytes as well as increased active caspase-3 immunostaining in the renal tubules compared with control mice. Regarding potential mediators of these differences, offspring of diabetic mice had increased expression of intrarenal angiotensinogen and renin mRNA, upregulation of NF-kappaB isoforms p50 and p65, and activation of the NF-kappaB pathway. In conclusion, maternal diabetes impairs nephrogenesis, possibly via enhanced intrarenal activation of the renin-angiotensin system and NF-kappaB signaling.

Pax-2 and N-myc regulate epithelial cell proliferation and apoptosis in a positive autocrine feedback loop

Both paired homeo box-2 (Pax-2) and N-myc genes play pivotal roles in renal morphogenesis via their effects on cell proliferation and differentiation, but whether and how they interact have not been addressed. In the present study, we investigated such a potential interaction using embryonic renal cells in vitro. Mouse embryonic mesenchymal (MK4) cells stably transfected with Pax-2 cDNA in sense (+) or antisense (-) orientation were used for experiments. Pax-2 promoter activity was monitored by luciferase assay. Reactive oxygen species (ROS) generation, cell proliferation, and cell apoptosis were evaluated. We found that Pax-2 and N-myc gene expression were upregulated and downregulated in Pax-2 (+) and Pax-2 (-) stable transformants, respectively. ROS generation and apoptosis were significantly reduced both in Pax-2 (+) transformants compared with Pax-2 (-) transformants and in naïve MK4 cells cultured in either normal- (5 mM) or high-glucose (25 mM) medium. Transient transfection of N-myc cDNA into Pax-2 (-) stable transformants restored Pax-2 gene expression and prevented ROS generation induced by high glucose. Our data demonstrate that Pax-2 gene overexpression prevents hyperglycemia-induced apoptosis, and N-myc appears to provide a positive autocrine feedback on Pax-2 gene expression in embryonic mesenchymal cells.

Reactive oxygen species and nuclear factor-kappa B pathway mediate high glucose-induced Pax-2 gene expression in mouse embryonic mesenchymal epithelial cells and kidney explants

Diabetic mellitus confers a major risk of congenital malformations, and is associated with diabetic embryopathy, affecting multiple organs including the kidney. The DNA paired box-2 (Pax-2) gene is essential in nephrogenesis. We investigated whether high glucose alters Pax-2 gene expression and aimed to delineate its underlying mechanism(s) of action using both in vitro (mouse embryonic mesenchymal epithelial cells (MK4) and ex vivo (kidney explant from Hoxb7-green florescent protein (GFP) mice) approaches. Pax-2 gene expression was determined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunofluorescent staining. A fusion gene containing the full-length 5'-flanking region of the human Pax-2 promoter linked to a luciferase reporter gene, pGL-2/hPax-2, was transfected into MK4 cells with or without dominant negative IkappaBalpha (DN IkappaBalpha) cotransfection. Fusion gene expression level was quantified by cellular luciferase activity. Reactive oxygen species (ROS) generation was measured by lucigenin assay. Embryonic kidneys from Hoxb7-GFP mice were cultured ex vivo. High D(+) glucose (25 mM), compared to normal glucose (5 mM), specifically induced Pax-2 gene expression in MK4 cells and kidney explants. High glucose-induced Pax-2 gene expression is mediated, at least in part, via ROS generation and activation of the nuclear factor kappa B signaling pathway, but not via protein kinase C, p38 mitogen-activated protein kinase (MAPK), and p44/42 MAPK signaling.

Novel therapy of focal glomerulosclerosis with mycophenolate and angiotensin blockade

Steroid-resistant nephrotic syndrome of childhood poses a dilemma in attempting to balance toxicity of medications against long-term prognosis. This report presents our preliminary experience with the novel use of combined mycophenolate mofetil (MMF) and angiotensin blockade (AB) in the treatment of nine children and young adults with focal glomerulosclerosis (FSGS). All patients were steroid resistant and had failed conventional treatment regimens. Prior to the initiation of the MMF-AB protocol, the patients were pre-treated with weekly intravenous methylprednisolone (MP) (15 mg/kg per week) for 4-8 weeks. Angiotensin-converting-enzyme inhibitors and/or angiotensin receptor blockers were begun when intravascular volume was restored. MMF was given at a dose of 250-500 mg/m(2) per day. Proteinuria, as measured by urine protein/creatinine ratios (Up/c), decreased by 43% following MP ( P<0.05). After 6 months of MMF-AB protocol, the Up/c was 72% below baseline ( P<0.01). This level was maintained for a minimum of 24 months of observation. Similarly, hyperlipidemia, as measured by total cholesterol and triglycerides, improved significantly with treatment (536+/-163 to 265+/-70 mg/dl, 447+/-168 to 230+/-92 mg/dl, respectively, P<0.01). Our data support the use of MMF and AB for treatment of steroid-resistant FSGS when other conventional treatments have failed and/or induced toxicity.

No evidence for AT2R gene derangement in human urinary tract anomalies

BACKGROUND

It has been recently found that mice, especially males, with a disrupted angiotensin type 2 receptor (AT2R) gene, which is located on the X-chromosome, often have a range of congenital anomalies of the kidney and urinary tract (CAKUT), including renal hypoplasia, and that Caucasian male patients with ureteropelvic junction stenosis (UPJ) and multicystic dysplastic kidneys frequently have A-G transition in intron 1 of the AT2R gene. We have previously found that renal hypoplasia is remarkably predominant in Japanese boys.

METHODS

We investigated sex ratios for the frequency of each CAKUT. The frequency of the A-G transition between the controls and 66 Japanese boys with CAKUT were compared. There was renal hypoplasia in 16, UPJ in 17, vesicoureteral in 20, and other anomalies in 13. We also investigated whether any mutations in AT2R genes were detectable in patients with renal hypoplasia.

RESULTS

In contrast to mice with a disruption of the AT2R gene, the male-to-female ratios in human patients proved to be considerably variable: 16 for renal hypoplasia, 2.1 for UPJ, 0.8 for vesicoureteral, and 1.2 for others. The frequency of the A-G transition was not different between the control population and the patients with CAKUT [31 of 102 (30%) vs. 23 of 66 (35%), respectively]. A sequencing study disclosed no mutations in nine boys with renal hypoplasia.

CONCLUSIONS

These findings indicate that the AT2R gene may not play a major role in the development of renal hypoplasia and other CAKUT in humans, at least in the Japanese population.

Fetal obstructive uropathy: patterns of renal pathology

Fetal obstructive uropathy (FOU) is characterized by obstruction of the urethra, renal anomalies, ureterovesical dilatation, oligohydramnios, cryptorchidism, and abdominal muscle wall changes. The main objective of the present study was to better understand the relationship between FOU and renal pathology using a series of 15 male autopsy cases. A total of 11 cases with patent anus and 4 with imperforate anus were analyzed. Of the first group, most cases showed obstruction at the level of prostatic urethra. Seven cases showed obstruction at the level of the prostatic urethra and histologic study revealed scarring and partial or complete absence of the prostate, while in the remaining four cases the prostate was present. Of the cases with imperforate anus, two showed obstruction at the level of prostatic urethra, one showed posterior urethral valves, and one was obstructed at the proximal urethra. In all cases the kidneys showed mixed (dysplastic and cystic) changes with no significant differences between the two groups. An inverse correlation was observed between degree of renal dysplasia and gestational age, whereas the opposite was true for cystic changes. Distal and collecting tubules were more intensely immunoreactive to the anti-cytokeratin antibody when compared to proximal tubules. Moreover, anti-cytokeratin immunoreactivity was more prominent in tubules displaying cystic dilatation. DNA fragmentation analysis of renal tissue revealed a higher apoptosis of mesenchymal and tubular cells in the FOU cases, compared to gestational aged-matched controls. These results suggest that renal anomalies in FOU might be related to the gestational age at which the injury occurred and to the duration of the obstruction.

Short-term urinary flow impairment deregulates PAX2 and PCNA expression and cell survival in fetal sheep kidneys

Renal malformations account for most children with chronic renal failure and are often associated with urinary tract anatomical obstruction. We examined cellular and molecular events after experimental urinary flow impairment in fetal sheep. Ovine gestation lasts 144 to 150 days with the metanephros appearing at 27 to 30 days. We generated complete unilateral ureteric anatomical obstruction at 90 days when a few layers of glomeruli had formed. After 10 days, we recorded ureteric and pelvic dilatation with renal parenchymal weight greater than contralateral organs or those from unoperated fetuses. The nephrogenic cortex was replaced by disorganized cells separated by edema and prominent vascular spaces. Cortical histology was dominated by cysts associated with malformed glomerular tufts. Cystic epithelia expressed PAX2, a growth-stimulating transcription factor down-regulated during normal maturation, and proliferating cell nuclear antigen, a surrogate marker of cycling cells. Detection of apoptosis using propidium iodide and in situ end labeling showed a significant increase of the point prevalence of death in the obstructed cortex. Hence, PAX2 and proliferating cell nuclear antigen expression as well as death were deregulated, as we previously reported in human kidney malformations. Medullary collecting ducts and loops of Henle were also disrupted, correlating with impaired urinary dilution and sodium reabsorption. Therefore, complex aberrations of morphogenesis, gene expression, cell turnover, and urine composition occur relatively early after experimental impairment of fetal urinary flow.