Recovery from release of ureteral obstruction in the rat: relationship to nephrogenesis

Hypertension and renal disease programming: focus on the early postnatal period

The developmental origin of hypertension and renal disease is a concept highly supported by strong evidence coming from both human and animal studies. During development there are periods in which the organs are more vulnerable to stressors. Such periods of susceptibility are also called 'sensitive windows of exposure'. It was shown that as earlier an adverse event occurs; the greater are the consequences for health impairment. However, evidence show that the postnatal period is also quite important for hypertension and renal disease programming, especially in rodents because they complete nephrogenesis postnatally, and it is also important during preterm human birth. Considering that the developing kidney is vulnerable to early-life stressors, renal programming is a key element in the developmental programming of hypertension and renal disease. The purpose of this review is to highlight the great number of studies, most of them performed in animal models, showing the broad range of stressors involved in hypertension and renal disease programming, with a particular focus on the stressors that occur during the early postnatal period. These stressors mainly include undernutrition or specific nutritional deficits, chronic behavioral stress, exposure to environmental chemicals, and pharmacological treatments that affect some important factors involved in renal physiology. We also discuss the common molecular mechanisms that are activated by the mentioned stressors and that promote the appearance of these adult diseases, with a brief description on some reprogramming strategies, which is a relatively new and promising field to treat or to prevent these diseases.

Comparative transcriptome analysis of miRNA in hydronephrosis male children caused by ureteropelvic junction obstruction with or without renal functional injury

MicroRNAs (miRNAs or miRs) are non-coding RNAs that contribute to pathological processes of various kidney diseases. Renal function injury represents a final common outcome of congenital obstructive nephropathy and has attracted a great deal of attention. However the molecular mechanisms are still not fully established. In this study, we compared transcriptome sequencing data of miRNAs of renal tissues from congenital hydronephrosis children with or without renal functional injury, in order to better understand whether microRNAs could play important roles in renal functional injury after ureteropelvic junction obstruction. A total of 22 microRNAs with significant changes in their expression were identified. Five microRNAs were up-regulated and 17 microRNAs were down-regulated in the renal tissues of the hydronephrosis patients with renal function injury compared with those without renal function injury. MicroRNA target genes were predicted by three major online miRNA target prediction algorithms, and all these mRNAs were used to perform the gene ontology analysis and Kyoto Encyclopedia of Gene and Genomes pathway analysis. Then, twelve candidate human and rat homologous miRNAs were selected for validation using RT-qPCR in vitro and in vivo; only miR-187-3p had a trend identical to that detected by the sequencing results among the human tissues, in vivo and in vitro experimental models. In addition, we found that the change of miR-187-3p in vivo was consistent with results in vitro models and showed a decrease trend in time dependence. These results provided a detailed catalog of candidate miRNAs to investigate their regulatory role in renal injury of congenital hydronephrosis, indicating that they may serve as candidate biomarkers or therapeutic targets in the future.

Timing urinary tract reconstruction in rats to avoid hydronephrosis and fibrosis in the transplanted fetal metanephros as assessed using imaging

Chronic kidney disease leads to high morbidity rates among humans. Kidney transplantation is often necessary for severe symptoms; however, options for new curative treatments are desired because of donor shortage. For example, it has been established that the kidneys can efficiently generate urine after transplantation of the metanephros, ureter, and bladder as a group. After transplantation, the urine can indirectly flow into the recipient's bladder using a stepwise peristaltic ureter system method where the anastomosis is created via the recipient's ureter for urinary tract reconstruction. However, the growth of the regenerated metanephros varies significantly, whereas the time window for successful completion of the stepwise peristaltic ureter system that does not cause hydronephrosis of the metanephros with bladder (ureter) is quite narrow. Therefore, this study was conducted to periodically and noninvasively evaluate the growth of the transplanted metanephros, ureter, and bladder in rats through computed tomography and ultrasonography. The ultrasonographic findings highly correlated to the computed tomography findings and clearly showed the metanephros and bladder. We found that the degree of growth of the metanephros and the bladder after transplantation differed in each case. Most of the rats were ready for urinary tract reconstruction within 21 days after transplantation. Optimizing the urinary tract reconstruction using ultrasonography allowed for interventions to reduce long-term tubular dilation of the metanephros due to inhibited overdilation of the fetal bladder, thereby decreasing the fibrosis caused possibly by transforming growth factor-β1. These results may be significantly related to the long-term maturation of the fetal metanephros and can provide new insights into the physiology of transplant regeneration of the metanephros in higher animals. Thus, this study contributes to the evidence base for the possibility of kidney regeneration in human clinical trials.

Decreased biventricular myocardial deformation in fetuses with lower urinary tract obstruction

BACKGROUND

To observe myocardial deformations in fetuses with isolated lower urinary tract obstruction (LUTO) and identify the correlation between myocardial deformation and the severity of obstruction.

METHODS

The strain (S), strain rate in systole (SRs) and strain rate in diastole (SRd) of the left and right ventricles at the first examination were prospectively analyzed and compared between fetuses with isolated LUTO and gestational age (GA)-matched normal control fetuses. Multiple regression analyses were used to assess the obstructive factors for impaired strain and strain rate, and the independent variables included bladder volume, sum of the bilateral pelvic diameters, sum of the bilateral ureteral diameters, mean bilateral renal artery pulsatility index, and amniotic fluid index.

RESULTS

Thirty-six fetuses with isolated LUTO and 36 normal controls were enrolled. Overall, decreased S, SRs and SRd of both ventricles were noted in fetuses with LUTO (p < 0.001). Moreover, S and SR were significantly negatively related to distended bladder volume (p < 0.001).

CONCLUSIONS

Fetuses with LUTO demonstrated decreased left and right myocardial deformation, and this impaired cardiac dysfunction was correlated with the urinary bladder volume. Evaluating the myocardial deformation in fetal LUTO could provide information to aid in parental counselling and intervention monitoring.

Clinical consequences of developmental programming of low nephron number

Nephron number in humans varies up to 13-fold, likely reflecting the impact of multiple factors on kidney development, including inherited body size and ethnicity, as well as maternal health and nutrition, fetal exposure to gestational diabetes or preeclampsia and other environmental factors, which may potentially be modifiable. Such conditions predispose to low or high offspring birth weight, growth restriction or preterm birth, which have all been associated with increased risks of higher blood pressures and/or kidney dysfunction in later life. Low birth weight, preterm birth, and intrauterine growth restriction are associated with reduced nephron numbers. Humans with hypertension and chronic kidney disease tend to have fewer nephrons than their counterparts with normal blood pressures or kidney function. A developmentally programmed reduction in nephron number therefore enhances an individual's susceptibility to hypertension and kidney disease in later life. A low nephron number at birth may not lead to kidney dysfunction alone except when severe, but in the face of superimposed acute or chronic kidney injury, a kidney endowed with fewer nephrons may be less able to adapt, and overt kidney disease may develop. Given that millions of babies are born either too small, too big or too soon each year, the population impact of altered renal programming is likely to be significant. Many gestational exposures are modifiable, therefore urgent attention is required to implement public health measures to optimize maternal, fetal, and child health, to prevent or mitigate the consequences of developmental programming, to improve the health future generations.

Alterations on a key nephrogenic/cardiogenic gene expression linked to hypertension development

The elevation of blood pressure produces specific organic lesions, including kidney and cardiac damage. On the other hand, cardiovascular disease usually leads to the development of hypertension. Thus, hypertension could be both a cause and a consequence of cardiovascular disease. Previous studies linked the lack of nitric oxide to cardiovascular abnormalities, including hypertension, arteriosclerosis, myocardial infarction, cardiac hypertrophy, diastolic heart failure, and reduced endothelium-derived hyperpolarizing factor responses, with shorter survival. The lack of this gas also leads to renal/cardiac abnormalities. It is widely known that nephrogenic deficiency is a risk factor for kidney disease. Besides, recent evidence suggests that alterations in WT-1, a key nephrogenic factor, could contribute to the development of hypertension. Moreover, some genes involved in the development of hypertension depend on WT-1. This knowledge makes it essential to investigate and understand the mechanisms regulating the expression of these genes during renal/cardiac development, and hypertension. As a consequence, the most in-depth knowledge of the complex aetiopathogenic mechanism responsible for the hypertensive disease will allow us to propose novel therapeutic tools.

siRNA-silencing of CD40 attenuates unilateral ureteral obstruction-induced kidney injury in mice

Background

The costimulatory CD40-CD40L pathway plays a role in kidney inflammation. We have previously reported that renal CD40 upregulation precedes cellular interstitial infiltrate and fibrosis in the unilateral ureteral obstruction (UUO) model. Here we sought to evaluate whether the administration of siRNA-CD40 has a therapeutic effect in a reversible unilateral ureteral obstruction (D-UUO) mice model.

Methods

Eight week-old C57BL6J male mice were divided into four groups: Vehicle (Phosphate-buffered saline) (n = 8); siRNA SC (non-specific siRNA) (n = 6); siRNA-CD40 (n = 8) and WT (wild type) (n = 6) mice. UUO was performed with a microvascular clamp. At day 3 after surgery, the ureteral clamp was removed and nephrectomy of the contralateral kidney was performed. Immediately, PBS, siRNA SC (50μg) or siRNA-CD40 (50μg) was administrated via the tail vein. Mice were killed 48h hours after the siRNA or saline administration. Wild type (WT) mice were used as controls. Blood samples were collected for measuring creatinine and blood urea nitrogen (BUN). Histology and kidney mRNA expression were performed.

Results

The administration of siRNA-CD40 reduced significantly the severity of acute renal failure associated with UUO. Pathologic analysis showed reduction of tubular dilation, interstitial fibrosis, F4/80 macrophage and CD3 (T cell) infiltration in animals treated with siRNA-CD40. Furthermore, kidney mRNA gene expression analysis showed significantly lower levels of macrophage markers (F4/80 and Mannose receptor), fibrosis matrix proteins (Fibronectin, MMP-9, Collagen IV and α-SMA), pro-inflammatory cytokines (iNOS and MCP-1) and the pro-fibrotic molecule TGF-β1 in siRNA-CD40.

Conclusions

The administration of siRNA-CD40 therapy reduces the severity of the acute kidney injury induced by obstructive uropathy and promotes kidney repair. This strategy seems suitable to be tested in humans.

The Impact of Kidney Development on the Life Course: A Consensus Document for Action

Hypertension and chronic kidney disease (CKD) have a significant impact on global morbidity and mortality. The Low Birth Weight and Nephron Number Working Group has prepared a consensus document aimed to address the relatively neglected issue for the developmental programming of hypertension and CKD. It emerged from a workshop held on April 2, 2016, including eminent internationally recognized experts in the field of obstetrics, neonatology, and nephrology. Through multidisciplinary engagement, the goal of the workshop was to highlight the association between fetal and childhood development and an increased risk of adult diseases, focusing on hypertension and CKD, and to suggest possible practical solutions for the future. The recommendations for action of the consensus workshop are the results of combined clinical experience, shared research expertise, and a review of the literature. They highlight the need to act early to prevent CKD and other related noncommunicable diseases later in life by reducing low birth weight, small for gestational age, prematurity, and low nephron numbers at birth through coordinated interventions. Meeting the current unmet needs would help to define the most cost-effective strategies and to optimize interventions to limit or interrupt the developmental programming cycle of CKD later in life, especially in the poorest part of the world.

MMP9 overexpression is associated with good surgical outcome in children with UPJO: Preliminary results

BACKGROUND

Ureteropelvic junction obstruction (UPJO) diagnosed prenatally occurs in 1:150 - 1:1200 pregnancies. Although many studies investigating the molecular changes of this obstructed segment have been performed, the underlying mechanisms are still unclear. The role of extracellular matrix (ECM) components remains controversial, and the investigations in the field of ECM changes, might help the better understanding of the pathogenesis of this common condition. The aim of the present study was to investigate for the first time in the literature whether MMP9 and its specific inhibitors, TIMP1 and RECK, are expressed in a reproducible, specific pattern in UPJ.

METHODS

UPJO specimens were obtained from 16 children at the time of dismembered pyeloplasty due to intrinsic UPJ stenosis. Expression levels of the three genes (MMP9, TIMP1 and RECK) were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Then correlated the expression levels of the genes according to grade study population that was divided in 2 categories according to Society of Fetal Urology classification, grade 3 (moderate) and 4 (severe). For DTPA we subdivided the childrens in 2 groups, obstructive (T 1/2 more than 20 min) and partial obstructive (T 1/2 between 10 and 20 min) and success in a surgery was defined as decrease in T 1/2 to less than 20 min, absence of symptoms, improving renal function and decreasing dilatation on successive exams.

RESULTS

MMP9 was underexpressed and TIMP1 and RECK were overexpressed in children with obstructive DTPA but the differences were not statistically significant. Overexpression of MMP9 was higher among patients with severe grade of UPJ compared to those with moderate grade. Surprisingly expression levels of MMP-9 was three times higher in children who were successfully treated by surgery (n = 10) (p = 0.072), so those who were followed for at least 1 year after surgery and remained with improvement in renal function and decreasing dilation on intravenous urogram and TIMP-1 was underexpressed in 100 % of this cases (p = 0.00).

CONCLUSIONS

We showed an increase in expression of MMP9 and a decrease in expression of TIMP1 in children who improving renal function and decreasing dilation after surgery. We believe that the higher expression of MMP9 in these cases can reflect an increase in degradation and remodeling process that could be used as a marker for surgical outcome.

Changes in renal WT-1 expression preceding hypertension development

Background

Hypertension is a public health problem with mostly unknown causes, and where strong hereditary genetic alterations have not been fully elucidated. However, the use of experimental models has provided valuable information. Recent evidences suggest that alterations in key nephrogenic factors, such as Wilms’ tumor 1 transcription factor (WT-1), could contribute to the development of hypertension. The aim of this paper is to evaluate the expression of WT-1 and related genes in the nephrogenic process in connection with the development of hypertension as well as the corresponding anatomical and functional correlation.

Methods

Male spontaneously hypertensive and control rats were evaluated weekly from birth until week 8 of life. Their blood pressure was taken weekly using the tail-cuff blood pressure system. Weekly, 5 rats per group were sacrificed with a lethal injection of pentobarbital, and their kidneys were removed, decapsulated and weighed. The serum was collected for measuring biochemical parameters. The results were assessed using one-way analysis of variance for comparisons between groups.

Results

The relationship between renal weight/total body weights was established, without significantly different values. These data were compared with apoptosis, fibrosis, number and size of the glomeruli. The elevation of systolic blood pressure was significant since week 6. Biochemical values differed slightly. Histology showed a slight increase in deposits of collagen fibers since week 4. Additionally, in kidney cortices, the expression of WT-1, heat shock protein 70 (Hsp70) and vitamin D receptors (VDR) decreased since week 4. Finally, we demonstrated ultrastructural damage to mitochondria since week 4.

Conclusions

Our results would suggest an unprecedented link, possibly a regulatory mechanism, between WT-1 on nephrogenic alteration processes and their relationship with hypertension. Moreover, and previous to the increase in blood pressure, we demonstrated low expressions of WT-1, VDR and Hsp70 in kidneys from neonatal SHRs. If so, this may suggest that deregulation in the expression of WT-1 and its impact on nephrogenesis induction could be crucial in understanding the development and maintenance of hypertension.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0250-6) contains supplementary material, which is available to authorized users.

Current applications of in utero intervention for lower urinary tract obstruction

PURPOSE

Since the early 1980s with the inception of fetal intervention for obstructive uropathy, there have been creative attempts to improve both perinatal and long-term outcomes. Despite advances in technology and an improved understanding of lower urinary tract obstruction (LUTO) in the fetus, the results for these therapeutic interventions remain guarded and the long-term renal morbidity among survivors remains problematic.

RECENT FINDINGS

Fetal LUTO represents a range of disorders but the most common of these is posterior urethral valves (PUVs). Selection criteria for candidates of possible intervention have improved with our understanding of fetal renal physiology. Serial urinalysis has marginally improved our ability to predict those that may ultimately respond to treatment [1,2], but the potential in the development of biomarkers for renal development or maldevelopment holds greater promise [3]. Advancements in fetal surgery may result in less fetal and maternal morbidity, but limited long-term improvement in outcomes highlights the controversial nature of the various interventions [4-10]. We must counsel families that fetal surgery offers hope but we cannot allow them to hold unrealistic expectations for cure.

SUMMARY

In appropriately selected fetuses, intervention may improve perinatal survival but not without risk to mother and fetus. Long-term renal outcomes remain problematic amongst survivors. In the case of PUV, postnatal primary valve ablation remains the cornerstone of treatment for nephron preservation; however, our ability to mimic these results in the prenatal population remains poor [11]. Disease severity has likely predetermined those that will survive through the perinatal period with or without intervention. Nonetheless, our drive to assess and manage fetal obstructive uropathy perseveres so that we may ultimately relieve obstruction and preserve renal and lung function. We must maintain optimism that continued advances will ultimately improve outcomes, but also be realistic with our current expectations. This paper reviews the status of current in utero interventions and outcomes.

Urine exoglycosidases are potential markers of renal tubular injury in children with ureteropelvic junction obstruction

AIM

Hydronephrosis caused by ureteropelvic junction obstruction (UPJO) is an important problem in children and young adults. The aim of this pilot study was to determine the urine profiles of a number of lysosomal exoglycosidases to see whether they indicated tubular renal damage in children with UPJO.

METHODS

We measured lysosomal exoglycosidases urine activities in 32 patients with UPJO, dividing them into three groups. The surgical group comprised 16 children with severe hydronephrosis who required surgery, the nonsurgical group comprised 16 patients with mild hydronephrosis, and the reference group comprised 42 healthy children. The following indicators were measured: N-acetyl-β-hexosaminidase and its A and B isoenzymes, α-fucosidase, β-galactosidase, α-mannosidase and β-glucuronidase.

RESULTS

The urine activities of all exoglycosidases were significantly higher in children with UPJO than children in the reference group (p < 0.01). A strong positive correlation was also found between most of the urine exoglycosidases and the urine albumin/creatinine ratio (p < 0.01).

CONCLUSION

Our findings demonstrated that children with UPJO showed increased renal activities of assessed exoglycosidases, which correlated positively with the urine albumin/creatinine ratio. A larger multicentre study is required to confirm the clinical applications of these observations.

Mediators and mechanisms of heat shock protein 70 based cytoprotection in obstructive nephropathy

Urinary heat shock protein 70 (Hsp70) is rapidly increased in patients with clinical acute kidney injury, indicating that it constitutes a component of the endogenous stress response to renal injury. Moreover, experimental models have demonstrated that Hsp70 activation is associated with the cytoprotective actions of several drugs following obstruction, including nitric oxide (NO) donors, geranylgeranylacetone, vitamin D, and rosuvastatin. Discrete and synergistic effects of the biological activities of Hsp70 may explain its cytoprotective role in obstructive nephropathy. Basic studies point to a combination of effects including inhibition of apoptosis and inflammation, repair of damaged proteins, prevention of unfolded protein aggregation, targeting of damaged protein for degradation, and cytoskeletal stabilization as primary effectors of Hsp70 action. This review summarizes our understanding of how the biological actions of Hsp70 may affect renal cytoprotection in the context of obstructive injury. The potential of Hsp70 to be of central importance to the mechanism of action of various drugs that modify the genesis of experimental obstructive nephropathy is considered.

The Fate of Nephrons in Congenital Obstructive Nephropathy: Adult Recovery is Limited by Nephron Number Despite Early Release of Obstruction

PURPOSE

Urinary tract obstruction and reduced nephron number often occur together as a result of maldevelopment of the kidneys and the urinary tract. We determined the role of nephron number on adaptation of the remaining nephrons of mice subjected to neonatal partial unilateral ureteral obstruction followed through adulthood.

MATERIALS AND METHODS

Wild-type and Os/+ mice (the latter with 50% fewer nephrons) underwent sham operation or partial unilateral ureteral obstruction in the first 2 days of life. Additional mice underwent release of unilateral ureteral obstruction at 7 days. All kidneys were harvested at 3 weeks (weaning) or 6 weeks (adulthood). Glomerular number and area, glomerulotubular junction integrity, proximal tubular volume fraction and interstitial fibrosis were measured by histomorphometry.

RESULTS

In the obstructed kidney unilateral ureteral obstruction caused additional nephron loss in Os/+ but not in wild-type mice. Glomerular growth from 3 to 6 weeks was impaired by ipsilateral obstruction and not preserved by release in wild-type or Os/+ mice. Proximal tubular growth was impaired and interstitial collagen was increased by ipsilateral obstruction in all mice. These conditions were attenuated by release of unilateral ureteral obstruction in wild-type mice but were not restored in Os/+ mice. Unilateral ureteral obstruction increased interstitial collagen in the contralateral kidney while release of obstruction enhanced tubular growth and reduced interstitial collagen.

CONCLUSIONS

Unilateral ureteral obstruction in early postnatal development impairs adaptation to reduced nephron number and induces additional nephron loss despite release of obstruction. Premature and low birth weight infants with congenital obstructive nephropathy are likely at increased risk for progression of chronic kidney disease.

Epigallocatechin-3-Gallate Attenuates Oxidative Stress and Inflammation in Obstructive Nephropathy via NF-κB and Nrf2/HO-1 Signalling Pathway Regulation

Oxidative stress and inflammation contribute importantly to the pathogenesis of chronic kidney disease (CKD). Epigallocatechin-3-gallate (EGCG), which is the most abundant and most active catechin polyphenol extracted from green tea, has been proved to have many bioactivities. In this study, the renoprotective effect of EGCG was evaluated in a widely used kidney disease model, the unilateral ureteral obstruction (UUO) mice model. After 14 days of EGCG administration, mean arterial blood pressure, body-weight and obstructed kidney weight were measured. Levels of blood urea nitrogen (BUN) and creatinine (CR) and activities of glutamic-pyruvic transaminase (GPT) and lactate dehydrogenase (LDH) in serum were estimated as indicators of renal function. Periodic acid-Schiff (PAS) staining was performed to observe the pathological changes of the obstructed kidney. Antioxidant enzymes and pro-inflammatory cytokine production were estimated to reflect the oxidative stress and inflammatory state in the obstructed kidney. Finally, the main proteins in the NF-κB and Nrf2 signalling pathway and DNA binding activity of NF-κB and Nrf2 were measured to investigate the effect of EGCG on these two pathways. The results demonstrated that EGCG could restore UUO-induced kidney weight loss and renal dysfunction. In addition, UUO-induced oxidative stress and inflammatory responses in the obstructed kidney were also prevented by EGCG. Furthermore, EGCG could induce both NF-κB and Nrf2 nuclear translocation in the UUO kidney and promote heme oxygenase-1 (HO-1) production. These results indicated that the renoprotective effect of EGCG might be through its NF-κB and Nrf2 signalling pathway regulations.

Birth weight, malnutrition and kidney-associated outcomes--a global concern

An adverse intrauterine environment is associated with an increased risk of elevated blood pressure and kidney disease in later life. Many studies have focused on low birth weight, prematurity and growth restriction as surrogate markers of an adverse intrauterine environment; however, high birth weight, exposure to maternal diabetes and rapid growth during early childhood are also emerging as developmental risk factors for chronic diseases. Altered programming of nephron number is an important link between exposure to developmental stressors and subsequent risk of hypertension and kidney disease. Maternal, fetal, and childhood nutrition are crucial contributors to these programming effects. Resource-poor countries experience the sequential burdens of fetal and childhood undernutrition and subsequent overnutrition, which synergistically act to augment the effects of developmental programming; this observation might explain in part the disproportionate burden of chronic disease in these regions. Numerous nutritional interventions have been effective in reducing the short-term risk of low birth weight and prematurity. Understanding the potential long-term benefits of such interventions is crucial to inform policy decisions to interrupt the developmental programming cycle and stem the growing epidemics of hypertension and kidney disease worldwide.

Testosterone changes bladder and kidney structure in juvenile male rats

PURPOSE

Testosterone affects male development, maturation and aging but limited data exist on testosterone effects on the juvenile genitourinary system. We hypothesized that testosterone has bladder and kidney developmental effects, and investigated this in juvenile male rats.

MATERIALS AND METHODS

To examine the testosterone effect 21-day-old prepubertal male Wistar rats were divided into 3 groups of 12 each, including sham orchiectomy as controls, and bilateral orchiectomy with vehicle and bilateral orchiectomy with testosterone. Starting at age 28 days (week 0) testosterone enanthate (5 mg/100 gm) or vehicle was injected weekly. Testosterone was measured at study week 0 before injection, and at weeks 1, 6 and 16. Whole bladders and kidneys were evaluated for androgen receptor, bladder collagen-to-smooth muscle ratio, and renal morphometry and immunohistochemistry.

RESULTS

Testosterone was not detectable at week 0 in all groups. It remained undetectable at weeks 1, 6 and 16 in the orchiectomy plus vehicle group. Testosterone levels were physiological in controls and rats with orchiectomy plus testosterone but levels were higher in the latter than in the former group. Rats with orchiectomy plus testosterone had increased bladder-to-body and kidney-to-body weight ratios (p<0.01 and <0.05, respectively), and decreased collagen-to-smooth muscle ratio than the orchiectomy plus vehicle and control groups. Rats with orchiectomy plus testosterone had a lower renal total glomerular count (p<0.01) but increased androgen receptor density.

CONCLUSIONS

In juvenile male rats testosterone was associated with increased bladder and renal mass, and increased bladder smooth muscle. Testosterone associated kidneys also appeared to have fewer but larger glomeruli. These data support an important role for sex hormones in structural and functional development of the bladder and kidney.

Wt-1 Expression Linked to Nitric Oxide Availability during Neonatal Obstructive Nephropathy

The wt-1 gene encodes a zinc finger DNA-binding protein that acts as a transcriptional activator or repressor depending on the cellular or chromosomal context. The wt-1 regulates the expression of a large number of genes that have a critical role in kidney development. Congenital obstructive nephropathy disrupts normal renal development and causes chronic progressive interstitial fibrosis, which contributes to renal growth arrest, ultimately leading to chronic renal failure. Wt-1 is downregulated during congenital obstructive nephropathy, leading to apoptosis. Of great interest, nitric oxide bioavailability associated with heat shock protein 70 (Hsp70) interaction may modulate wt-1 mRNA expression, preventing obstruction-induced cell death during neonatal unilateral ureteral obstruction. Moreover, recent genetic researches have allowed characterization of many of the complex interactions among the individual components cited, but the realization of new biochemical, molecular, and functional experiments as proposed in our and other research labs allows us to establish a deeper level of commitment among proteins involved and the potential pathogenic consequences of their imbalance.

Evaluation of TGF-β1, CCL5/RANTES and sFas/Apo-1 urine concentration in children with ureteropelvic junction obstruction

INTRODUCTION

The aim of this study was to evaluate changes in expression of soluble biomarkers tumor factor growth-β1 (TGF-β1), CCL5/RANTES, and sFas/Apo-1 in the urine of patients undergoing ureteropyeloplasty for ureteropelvic junction (UPJ) obstruction. These factors are connected with different processes ongoing in the obstructive uropathy. If their urine concentrations correlate with AP diameter of the renal pelvis and differential function of the affected kidney, they can be helpful in making a decision on corrective surgery.

MATERIAL AND METHODS

Creatinine, TGF-β1, CCL5/RANTES, and sFas/Apo-1 levels were measured in the urine from the bladder and renal pelvis of 45 patients undergoing ureteropyeloplasty and from bladders of 25 patients undergoing inguinal herniorrhaphy.

RESULTS

LEVELS OF EXAMINED BIOMARKERS WERE HIGHER IN THE RENAL PELVIS AND BLADDER OF CHILDREN WITH UPJ OBSTRUCTION AS COMPARED TO CONTROLS: TGF-β1 in older children and adolescents (p < 0.05), CCL5/RANTES in the youngest and older children (p < 0.05), and sFas/Apo-1 in all patients (p < 0.05). Twelve months after surgery their levels in the bladder decreased: TGF-β1 in younger and older children (p < 0.05), CCL5/RANTES in the youngest patients and adolescents (p < 0.05), and sFas/Apo-1 in the youngest and older children (p < 0.05). A significant decrease in the AP diameter of the renal pelvis post-operatively (32.09 mm vs. 18.72 mm) (p < 0.01) and significant improvement in renal function (36.94% vs. 42.76%) (p < 0.05) were observed in the examined group.

CONCLUSIONS

Mean TGF-β1, CCL5/RANTES, and sFas/Apo-1 urine levels are significantly increased in patients with UPJ and decreased 1 year after ureteropyeloplasty. Bladder concentrations of examined factors may be clinically useful markers of obstruction.

Interactions between cytokines, congenital anomalies of kidney and urinary tract and chronic kidney disease

Fetal hydronephrosis is the most common anomaly detected on antenatal ultrasound, affecting 1-5% of pregnancies. Postnatal investigation has the major aim in detecting infants with severe urinary tract obstruction and clinically significant urinary tract anomalies among the heterogeneous universe of patients. Congenital uropathies are frequent causes of pediatric chronic kidney disease (CKD). Imaging techniques clearly contribute to this purpose; however, sometimes, these exams are invasive, very expensive, and not sufficient to precisely define the best approach as well as the prognosis. Recently, biomarkers have become a focus of clinical research as potentially useful diagnostic tools in pediatric urological diseases. In this regard, recent studies suggest a role for cytokines and chemokines in the pathophysiology of CAKUT and for the progression to CKD. Some authors proposed that the evaluation of these inflammatory mediators might help the management of postnatal uropathies and the detection of patients with high risk to developed chronic kidney disease. Therefore, the aim of this paper is to revise general aspects of cytokines and the link between cytokines, CAKUT, and CKD by including experimental and clinical evidence.

Maturational regression of glomeruli determines the nephron population in normal mice

BACKGROUND

Regression is an important process in the normal development of many organs. In this study, we investigated whether glomerular regression occurs after normal glomerulogenesis and determined the time course for this process.

METHODS

Glomerular number was analyzed in normal mouse kidneys at postnatal day (P)7, P10, P14, P18, P21, P25, and P28 by the gold standard fractionator/dissector method, which involves exhausting the kidney tissue. Vascular regression markers, angiopoietin 2 (ANGPT2), and thrombospondin 1 (THBS1), were examined by immunohistochemistry.

RESULTS

The maximum glomerular number was reached at P7 with 14,051 glomeruli per kidney (95% confidence interval: 12,084-16,018). This peak was followed by a progressive reduction, with a nadir of 11,060 (10,393-11,727) occurring at P18 (P < 0.05 as compared with P7). Thereafter, glomerular number remained constant. Complementary immunohistochemical examination of vascular regression markers showed peak expression of glomerular ANGPT2 and THBS1 at P14.

CONCLUSION

Our study reveals that the tissue- and time-saving Weibel-Gomez method commonly used to assess glomerular number is valid only after P18. The data indicate that regulation of glomerular number by regression occurs in normally maturing mouse kidneys. These findings suggest that the process of glomerular regression could be therapeutically targeted to prevent oligonephronia, which otherwise predisposes to chronic kidney disease.

Thrombospondin-1 plays a profibrotic and pro-inflammatory role during ureteric obstruction

Thrombospondin-1 (TSP-1) is an endogenous activator of transforming growth factor-β (TGF-β), and an anti-angiogenic factor, which may prevent kidney repair. Here we investigated whether TSP-1 is involved in the development of chronic kidney disease using rats with unilateral ureteral obstruction, a well-known model to study renal fibrosis. Obstruction of 10 days duration induced inflammation, tubular cell atrophy, dilation, apoptosis, and proliferation, leading to interstitial fibrosis. TSP-1 expression was increased in parallel to that of collagen III and TGF-β. Relief of the obstruction at day 10 produced a gradual improvement in renal structure and function, the reappearance of peritubular capillaries, and restoration of renal VEGF content over a 7- to 15-day post-relief period. TSP-1 expression decreased in parallel with that of TGF-β1 and collagen III. Mice in which the TSP-1 gene was knocked out displayed less inflammation and had better preservation of renal tissue and the peritubular capillary network compared to wild-type mice. Additional studies showed that the inflammatory effect of TSP-1 was mediated, at least in part, by monocyte chemoattractant protein-1 and activation of the Th17 pathway. Thus, TSP-1 is an important profibrotic and inflammatory mediator of renal disease. Blockade of its action may be a treatment against the development of chronic kidney disease.

Variable partial unilateral ureteral obstruction and its release in the neonatal and adult mouse

Obstructive nephropathy is the most important cause of renal failure in children. Unilateral ureteral obstruction (UUO) in the neonatal mouse provides a useful model to investigate the response of the developing kidney to urine flow obstruction. Creation of reversible variable partial UUO (compared to complete UUO) more closely approximates congenital lesions, and permits the study of recovery following release of the obstruction. Implementation of this technique requires the appropriate optical, surgical, and anesthetic equipment, as well as adaptations appropriate to the very small animals undergoing surgical procedures. Care of the pups must include minimizing trauma to delicate tissues, close monitoring of anesthesia and body temperature, and ensuring acceptance of the pups by the mother. It is important to document the severity and patency of the partial UUO by ureteral measurement and pelvic injection of India ink. Finally, removal of kidneys for histologic examination should be accomplished with gentle handling and processing.

Rosuvastatin preserves renal structure following unilateral ureteric obstruction in the neonatal rat

BACKGROUND/AIMS

Unilateral ureteric obstruction (UUO) in neonatal rodents can be used as a paradigm for in utero obstruction in humans and a platform for studying the potential of novel therapies for congenital obstructive nephropathy. The present study examined the effect of rosuvastatin (Ros) on key morphometric measures of renal injury and corresponding gene expression correlates following neonatal UUO in the rat.

METHODS

Neonatal rats subjected to UUO and controls were treated daily with vehicle or Ros for 14 days. Quantification of tubular dilatation, glomerular size and number and tubulointerstitial fibrotic area was performed and changes validated by reference to appropriate renal gene expression correlates.

RESULTS

UUO increased tubular diameter and interstitial fibrosis by 2.7- and 7-fold, respectively, in parallel with increases in renal transforming growth factor-β(1) (TGF-β(1)) and tumor necrosis factor-α (TNF-α) mRNA levels. Glomerular number and size were reduced by 52 and 33%, respectively. Reductions in WT-1 mRNA and protein expression were noted following obstruction occurring in tandem with reduced mRNA levels for BMP-7 and E-cadherin. Ros attenuated tubular dilatation (33%) and interstitial fibrosis (72%) in association with the normalization of renal TGF-β(1) and TNF-α mRNA levels. Ros improved glomerular number and size (30 and 50%), and preserved mRNA and protein expression levels of WT-1 and normalized mRNA levels for BMP-7 and E-cadherin.

CONCLUSIONS

Ros treatment attenuated all changes, most notably the increase in interstitial fibrosis. Notably, Ros treatment was unable to completely salvage glomerular development. Together these data highlight the therapeutic potential and limitations of Ros in neonatal obstruction.

Stimulation of soluble guanylate cyclase improves renal recovery after relief of unilateral ureteral obstruction

PURPOSE

The antifibrotic effects of soluble guanylate cyclase stimulation and cyclic guanosine monophosphate production have been observed in cases of anti-thy1-induced renal disease. We analyzed the action of the specific soluble guanylate cyclase stimulator BAY 41-8543 on the renal recovery phase in rats with unilateral ureteral obstruction after obstruction was relieved.

MATERIALS AND METHODS

Sprague-Dawley® rats underwent reversible unilateral ureteral obstruction for 5 days, after which obstruction was relieved. Rats were randomly assigned to unilateral ureteral obstruction and unilateral ureteral obstruction plus BAY 41-8543 (10 mg/kg body weight daily). Seven days after relief of obstruction we determined treatment effects on renal atrophy, apoptosis, fibrosis and nitric oxide/cyclic guanosine monophosphate signaling.

RESULTS

Untreated obstructed rats showed mildly increased systolic blood pressure, marked tubular atrophy and apoptosis, tubulointerstitial macrophage infiltration and fibrosis. Plasma cyclic guanosine monophosphate levels were unaltered in untreated rats with obstruction while renal soluble guanylate cyclase mRNA expression was increased. BAY 41-8543 administration significantly increased plasma cyclic guanosine monophosphate, which was paralleled by significant decreases in systolic blood pressure, renal tubular diameter, apoptosis and renal macrophage infiltration. Also, soluble guanylate cyclase stimulation decreased tubulointerstitial fibrosis, as shown by tubulointerstitial volume, matrix protein accumulation, α-smooth muscle actin expression, collagen IV deposition and transforming growth factor-β1 mRNA expression.

CONCLUSIONS

Soluble guanylate cyclase stimulation by BAY 41-8543 increases cyclic guanosine monophosphate production and subsequently enhances renal recovery after unilateral ureteral obstruction relief through an array of pathways. This finding suggests that soluble guanylate cyclase stimulation may serve as a novel treatment approach to restore or preserve renal structure and function in cases of obstructive kidney disease.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin-angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short-coming is the absence of data on the impact of UPJ obstruction on long-term adult renal function to elucidate whether these animal data are also valid in humans.

Mechanisms of renal injury and progression of renal disease in congenital obstructive nephropathy

Congenital obstructive nephropathy accounts for the greatest fraction of chronic kidney disease in children. Genetic and nongenetic factors responsible for the lesions are largely unidentified, and attention has been focused on minimizing obstructive renal injury and optimizing long-term outcomes. The cellular and molecular events responsible for obstructive injury to the developing kidney have been elucidated from animal models. These have revealed nephron loss through cellular phenotypic transition and cell death, leading to the formation of atubular glomeruli and tubular atrophy. Altered renal expression of growth factors and cytokines, including angiotensin, transforming growth factor-beta, and adhesion molecules, modulate cell death by apoptosis or phenotypic transition of glomerular, tubular, and vascular cells. Mediators of cellular injury include hypoxia, ischemia, and reactive oxygen species, while fibroblasts undergo myofibroblast transformation with increased deposition of extracellular matrix. Progression of the lesions involves interstitial inflammation and interstitial fibrosis, both of which impair growth of the obstructed kidney and result in compensatory growth of the contralateral kidney. The long-term outcome depends on timing and severity of the obstruction and its relief, minimizing ongoing injury, and enhancing remodeling. Advances will depend on new biomarkers to evaluate the severity of obstruction, to determine therapy, and to follow the evolution of lesions.

tPA protects renal interstitial fibroblasts and myofibroblasts from apoptosis

Activation and expansion of interstitial fibroblasts and myofibroblasts play an essential role in the evolution of renal fibrosis. After obstructive injury, mice lacking tissue-type plasminogen activator (tPA) have fewer myofibroblasts and less interstitial fibrosis than wild-type controls. This suggests that tPA controls the size of the fibroblast/myofibroblast population in vivo, and this study sought to determine the underlying mechanism. In vitro, tPA inhibited staurosporine or H(2)O(2)-induced caspase-3 activation, prevented cellular DNA fragmentation, and suppressed the release of cytochrome C from mitochondria into the cytosol in a rat interstitial fibroblast cell line (NRK-49F). tPA also protected TGF-beta1-activated myofibroblasts from apoptosis. This antiapoptotic effect of tPA was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). Deletion or knockdown of LRP-1 abolished tPA-mediated cell survival, whereas re-introduction of an LRP-1 minigene in a mouse LRP-1-deficient fibroblast cell line (PEA-13) restored the cytoprotective ability of tPA. tPA triggered a cascade of survival signaling involving extracellular signal-regulated kinase 1/2 (Erk1/2), p90RSK, and phosphorylation of Bad. Blockade of Erk1/2 activation abrogated the antiapoptotic effect of tPA, whereas expression of constitutively active MEK1 promoted cell survival similar to tPA. In vivo, compared with wild-type controls, apoptosis of interstitial myofibroblasts was increased in tPA(-/-) mice after obstructive injury, and myofibroblasts were completely depleted 4 wk after relief of the obstruction. Together, these findings illustrate that tPA is a survival factor that prevents apoptosis of renal interstitial fibroblasts and myofibroblasts through an LRP-1-, Erk1/2-, p90RSK-, and Bad-dependent mechanism.

Chronic partial ureteral obstruction and the developing kidney

Although congenital urinary tract obstruction is a common disorder, its pathophysiology remains poorly understood and clinical practice is controversial. Animal models have been used to elucidate the mechanisms responsible for obstructive nephropathy, and the models reveal that renal growth and function are impaired in proportion to the severity and duration of obstruction. Ureteral obstruction in the neonatal rat or mouse leads to activation of the renin-angiotensin system, renal infiltration by macrophages, and tubular apoptosis. Nephrons are lost by glomerular sclerosis and the formation of atubular glomeruli, and progressive injury leads to tubular atrophy and interstitial fibrosis. Recovery following release of obstruction depends on the timing, severity, and duration of obstruction. Growth factors and cytokines are produced by the hydronephrotic kidney, including MCP-1 and TGF-beta1, which are excreted in urine and can serve as biomarkers of renal injury. Because MRI can be used to monitor renal morphology, blood flow, and filtration rate, its use might supplant current imaging modalities (ultrasonography and diuretic renography), which have significant drawbacks. Combined use of MRI and new urinary biomarkers should improve our understanding of human congenital obstructive nephropathy and should lead to new approaches to evaluation and management of this challenging group of patients.

Glomerulotubular disconnection in neonatal mice after relief of partial ureteral obstruction

Ureteropelvic junction obstruction is a common cause of congenital obstructive nephropathy. To study the pathogenesis of nephropathy, a variable-partial, complete or a sham unilateral ureteral obstruction (UUO) was produced in mice within 2 days of birth. The obstruction was released in some animals at 7 days and kidneys harvested at 7-42 days of age for histologic and morphometric study. Renal parenchymal growth was stunted by partial UUO with the impairment proportional to the duration and severity of obstruction. Proximal tubule apoptosis and glomerulotubular disconnection led to nephron loss. Relief of partial UUO arrested glomerulotubular disconnection, resolved tubule atrophy, and interstitial fibrosis with remodeling of the renal architecture. Relief of severe UUO did not result in recovery. Compensatory growth of the contralateral kidney depended on the severity of obstruction. Our studies indicate that relief of moderate UUO will minimize nephron loss. Application of this technique to mutant mice will help develop future therapies to enhance nephron recovery.

Leukocytes induce epithelial to mesenchymal transition after unilateral ureteral obstruction in neonatal mice

Urinary tract obstruction during renal development leads to tubular apoptosis, tubular atrophy, and interstitial fibrosis. Epithelial to mesenchymal transition (EMT) has been proposed as a key mechanism of myofibroblast accumulation in renal fibrosis. We studied the interplay of leukocyte infiltration, tubular apoptosis, and EMT in renal fibrosis induced by unilateral ureteral obstruction (UUO) in neonatal mice. We show that leukocytes mediate tubular apoptosis and EMT in the developing kidney with obstructive nephropathy. Blocking leukocyte recruitment by using the chemokine receptor-1 antagonist BX471 protected against tubular apoptosis and interstitial fibrosis, as evidenced by reduced monocyte influx, a decrease in EMT, and attenuated collagen deposition. EMT was rapidly induced within 24 hours after UUO along with up-regulation of the transcription factors Snail1 and Snail2/Slug, preceding the induction of alpha-smooth muscle actin and vimentin. In the presence of BX471, the expression of chemokines, as well as of Snail1 and Snail2/Slug, in the obstructed kidney was completely attenuated. This was associated with reduced macrophage and T-cell infiltration, tubular apoptosis, and interstitial fibrosis in the developing kidney. Our findings provide evidence that leukocytes induce EMT and renal fibrosis after UUO and suggest that chemokine receptor-1 antagonism may prove beneficial in obstructive nephropathy.

Clinical and molecular markers of chronic interstitial nephropathy in congenital unilateral ureteropelvic junction obstruction

PURPOSE

We evaluated clinical and biological variables, and their meaning as reliable markers of chronic interstitial nephropathy in a selected group of children with prenatally detected hydronephrosis who underwent pyeloplasty because of congenital unilateral ureteropelvic junction obstruction.

MATERIALS AND METHODS

We reviewed the clinical, prenatal and postnatal ultrasonographic, and scintigraphic records of children for whom intraoperative biopsy records were available. We performed histological analysis, and evaluated tubulointerstitial immunostaining for vimentin and alpha-smooth muscle actin, and the immunohistochemical and mRNA expression of the renin-angiotensin system peptides and transforming growth factor-beta1.

RESULTS

The children were divided in 2 groups according to the absence (group 1) or presence (group 2) of chronic interstitial nephropathy in the biopsy. Patients in group 2 were significantly younger at prenatal diagnosis (p = 0.031), and had decreased split renal function (p = 0.005) and worse drainage (p = 0.035) on preoperative diuretic renography. No differences were found in terms of degree of hydronephrosis, or its prenatal and postnatal variation. Group 2 biopsies exhibited greater immunostaining for alpha-smooth muscle actin and vimentin (p = 0.004 and p = 0.047, respectively), and transforming growth factor-beta1 mRNA levels (p = 0.06). Vimentin and alpha-smooth muscle actin positivity correlated with renin, angiotensin II receptors 1 and 2, and transforming growth factor-beta1 mRNA levels, and all correlated with preoperative split renal function and post-void washout.

CONCLUSIONS

In congenital unilateral ureteropelvic junction obstruction chronic interstitial nephropathy and poor postoperative recovery seem to be associated with an earlier diagnosis of hydronephrosis, functional loss greater than 10% and worse scintigraphic drainage. Moreover, there is a strong correlation between molecular fibrogenic markers and histologically and scintigraphically demonstrated renal damage.

Angiotensin-converting enzyme inhibition aggravates renal interstitial injury resulting from partial unilateral ureteral obstruction in the neonatal rat

Congenital urinary tract obstruction is the most important cause of renal insufficiency in infants and children, and angiotensin-converting enzyme (ACE) inhibitors attenuate the progression of renal disease in adults. ACE inhibitors are increasingly utilized in children with progressive renal disease. Because angiotensin is necessary for normal renal development, we examined the effects of ACE inhibition both during and immediately following the period of postnatal nephrogenesis in the neonatal rat subjected to sham operation or partial unilateral ureteral obstruction (UUO) under general anesthesia within the first 48 h of life. Rats in group I received enalapril 30 mg/kg body wt (or vehicle) daily for the first 10 days, while in group II, the 10 days of treatment began 10 days after surgery. Kidneys were harvested at day 21 and analyzed for apoptosis (TUNEL), interstitial macrophages (ED-1 immunohistochemistry), myofibroblasts (alpha-smooth muscle actin), and collagen (Sirius red). Partial UUO delayed glomerular maturation and increased ipsilateral renal macrophage infiltration, alpha-smooth muscle actin and Sirius red staining. In group I, enalapril increased myofibroblast accumulation in sham-operated kidneys, but not in obstructed kidneys. In contrast, in group II, enalapril further increased macrophage, myofibroblast, and collagen accumulation following partial UUO. The relative abundance of components of the kallikrein-kinin system, measured by Western blot, was not altered by partial UUO in the 14- and 28-day-old rat. Thus, in contrast to its salutary effects at later ages, ACE inhibition can worsen injury to the partially obstructed kidney during renal maturation even after the completion of nephrogenesis.

Renal vascular endothelial growth factor in neonatal obstructive nephropathy. II. Exogenous VEGF

Chronic unilateral ureteral obstruction (UUO) in the neonatal rat causes delayed renal maturation, tubular apoptosis, and interstitial inflammation. Vascular endothelial growth factor (VEGF) acts as a survival factor for tubular cells and reduces renal injury in several models of renal disease. To determine whether exogenous VEGF attenuates renal injury from UUO, rats were subjected within the first 48 h of life to sham operation, partial UUO, or complete UUO. Saline vehicle or VEGF(121) (50 mg/kg) was injected twice daily for 7 days, after which kidneys were harvested for histological study. The density of peritubular capillaries was measured with platelet-endothelial cell adhesion molecule-1 immunostaining, proliferating nuclei were detected by proliferating-cell nuclear antigen staining, apoptosis by the transferase-mediated dUTP nick end-labeling technique, macrophages by ED-1 immunostaining, and collagen by Sirius red staining. Glomerular number and maturation index were also determined in each group. Following chronic complete UUO in the neonatal rat, peritubular capillary density was significantly decreased. Cortical capillary density was further reduced by exogenous VEGF in the partially obstructed kidney. While UUO also decreased glomerular number and delayed glomerular maturation, exogenous VEGF exerted no additional effects. Cellular proliferation and tubular apoptosis increased in proportion to the severity of obstruction, but exogenous VEGF had no additional effects on proliferation, tubular apoptosis, or macrophage infiltration. However, VEGF reduced interstitial apoptosis in the kidney with partial UUO. We conclude that VEGF does not have salutary effects on the renal lesions caused by chronic UUO in the neonatal rat and may actually worsen obstructive nephropathy by aggravating the interstitial lesions.

Renal vascular endothelial growth factor in neonatal obstructive nephropathy. I. Endogenous VEGF

Obstructive nephropathy constitutes a major cause of renal impairment in children. Chronic unilateral ureteral obstruction (UUO) impairs maturation of the developing kidney and leads to tubular apoptosis and interstitial inflammation. Vascular endothelial growth factor (VEGF) is involved in recovery from various forms of renal injury. We questioned whether the renal expression of endogenous VEGF and its receptor (VEGFR2/Flk-1) is modified by UUO in early development. Neonatal rats were subjected to partial or complete UUO or sham operation. The distribution of immunoreactive VEGF in each kidney was examined after 7, 14, or 28 days. Adult rats were also subjected to sham operation or complete UUO. Tubular VEGF increased between 14 and 28 days in sham-operated rats and in some partially obstructed neonatal rats but decreased with complete UUO. Parallel changes were found by Western blotting, but not by RT-PCR. Immunoreactive VEGF colocalized with mitochondria in proximal and distal tubules and also appeared in type A intercalated cells, glomerular vascular endothelium, and podocytes. While neonatal microvascular renal VEGFR2 receptor staining was strongly positive regardless of UUO, staining was weak in sham-operated adults but increased following UUO. Parallel changes in VEGFR2 expression were verified by RT-PCR and Western blotting. We conclude that endogenous renal VEGF is developmentally regulated in the neonatal rat and is differentially regulated by partial and complete UUO. Following UUO in the adult, the VEGF receptor is upregulated. Endogenous VEGF may serve an adaptive role in responding to tubular injury caused by UUO and may modulate adaptation by the contralateral kidney.

Distinct roles of Mac-1 and its counter-receptors in neonatal obstructive nephropathy

Urinary tract obstruction during renal development leads to tubular atrophy and interstitial fibrosis. Inflammatory macrophages are crucial in this process, and beta2-integrins play a major role in leukocyte recruitment. We investigated the role of beta2-integrins and their major counter-receptors (intercellular adhesion molecule-1 (ICAM-1), receptor for advanced glycation endproducts (RAGE), junctional adhesion molecule (JAM)-C) in obstructive nephropathy in neonatal mice. Two-day-old beta2-integrin-deficient mice (Mac-1-/- and LFA-1-/-(deficient for leukocyte function-associated antigen-1)) and wild-type mice (C57BL/6) underwent unilateral ureteral obstruction (UUO) or sham operation. After 1, 5 or 12 days of obstruction, renal macrophage infiltration and tubulointerstitial damage were quantitated. Tissue abundance of Mac-1 and its ligands ICAM-1, RAGE and JAM-C was examined by Western blot and immunoprecipitation. Deficiency of either integrin was associated with reduced early macrophage invasion into the obstructed kidney. After 12 days of UUO, macrophage infiltration and tubulointerstitial injury were reduced only in Mac-1-/- but not in LFA-1-/- mice. Besides ICAM-1, an upregulation of two novel Mac-1 ligands, RAGE and JAM-C were observed, however, with distinct time courses. We conclude that beta2-integrins mediate macrophage infiltration in UUO. Mac-1 is the predominant leukocyte integrin involved in leukocyte recruitment after obstruction. ICAM-1 and its new ligands RAGE and JAM-C are sequentially activated in UUO. Blocking of Mac-1 and its ligands may confer synergistic renoprotective effects in neonatal obstructive nephropathy.

Compensatory renal growth due to neonatal ureteral obstruction: implications for clinical studies

In response to unilateral ureteral obstruction (UUO), the contralateral kidney undergoes compensatory renal growth, which is enhanced in early development. We investigated the renal growth response to UUO in the neonatal rat. Within 2 days of birth, animals were subjected to sham-operation, complete UUO, or variable partial UUO, and kidneys were harvested 3-60 days later. Contralateral kidney weight increased after only 7 days of complete UUO. Increase in contralateral kidney weight was not significant for partial UUO until 45 days, but kidney/body weight ratio increased after only 14 days of 0.3 mm partial UUO. The rate of contralateral renal growth increased with age and with increasing severity of UUO. In rats subjected to 45 days UUO, glomerular area was proportional to kidney/body weight ratio (r =0.61, p <0.01). We conclude that the rate of compensatory renal growth is dependent on the severity and duration of obstruction, and takes place at the single nephron level. The results suggest that biologic variability limits the early detection of compensatory renal growth, which is compounded by limitations in measuring renal size by clinical imaging. Factoring kidney length (or volume) by intervertebral length (or body surface area) should improve the precision of tracking renal growth.

Obstructive nephropathy: insights from genetically engineered animals

Congenital obstructive nephropathy is the primary cause for end-stage renal disease (ESRD) in children. An increasingly used animal model of obstructive nephropathy is unilateral ureteral obstruction (UUO). This model mimics, in an accelerated manner, the different stages of obstructive nephropathy leading to tubulointerstitial fibrosis: cellular infiltration, tubular proliferation and apoptosis, epithelial-mesenchymal transition (EMT), (myo)fibroblast accumulation, increased extracellular matrix (ECM) deposition, and tubular atrophy. During the last decade genetically modified animals are increasingly used to study the development of obstructive nephropathy. Although the use of these animals (mainly knockouts) has highlighted some pitfalls of this approach (compensation by closely related gene products, absence of temporal knockouts) it has brought important information about the role of specific gene-products in the pathogenesis of obstructive nephropathy. Besides confirming the important pathologic role for angiotensin II (Ang II) and transforming growth factor-beta (TGF-beta) in obstructive nephropathy, these animals have shown the complexity of the development of tubulointerstitial fibrosis involving a large number of closely functionally related molecules. More interestingly, the use of these animals has led to the discovery of unexpected and contradictory roles (both potentially pro- and antifibrotic) for Ang II, for ECM degrading enzymes matrix metalloproteinase 9 (MMP-9) and tissue plasminogen activators (PAs), for plasminogen activator inhibitor 1 (PAI-1), and for the adhesion molecule osteopontin (OPN) in obstructive nephropathy. Further use of these animals, especially in combination with pharmacologic tools, should help to better identify potential antifibrotic strategies in obstructive nephropathy.

Obstructive uropathy

Routine second trimester ultrasound screening has resulted in more infants diagnosed with antenatal hydronephrosis. Current recommendations suggest postnatal evaluation of all infants with a renal pelvic diameter >5 mm with ultrasound and voiding cystourethrogram (VCUG.) There are many etiologies of obstructive uropathy including ureteropelvic junction (UPJ) obstruction, ureterovesical junction (UVJ) obstruction, posterior urethral valves (PUV), prune belly syndrome, and vesicoureteral reflux (VUR). Obstructive uropathy can result in tubular damage and decreased nephron number. Tubular damage can result in sodium wasting, hyperkalemic acidosis, and nephrogenic diabetes insipidus. Most patients do not require renal replacement therapy in the neonatal period; however, chronic renal insufficiency can occur if the neonate has a significant reduction in nephron number or progressive renal damage from obstruction or infection.

Epidermal growth factor potentiates renal cell death in hydronephrotic neonatal mice, but cell survival in rats

BACKGROUND

Epidermal growth factor (EGF) markedly attenuates tubular apoptosis induced by unilateral ureteral obstruction (UUO) in the neonatal rat, and reduces apoptosis induced by mechanical stretch of cultured rat tubular cells.

METHODS

To investigate the role of EGF in modulating apoptosis resulting from UUO, neonatal wild type and mutant mice lacking EGF (knockout), or with diminished EGF receptor activity (waved-2 mutant) were compared to control mice for tubular apoptosis and atrophy. Rat and mouse kidneys were compared for localization of the EGF receptor. Apoptosis was also measured in cultured mouse tubular cells subjected to stretch and exposed to EGF.

RESULTS

UUO reduced endogenous renal EGF expression in wild-type mice. Unlike the rat, exogenous EGF did not decrease tubular apoptosis or atrophy in the obstructed kidney, and significantly increased stretch-induced apoptosis of cultured mouse tubular cells. Tubular apoptosis was 50% lower in the obstructed kidney of EGF knockout and waved-2 mice relative to wild type and heterozygous animals. Exogenous EGF increased tubular apoptosis and doubled atrophy in the obstructed kidney of waved-2 mice. Species differences in EGF receptor localization were detected in 3-day-old kidneys.

CONCLUSION

EGF acts as a survival factor in the neonatal rat, but potentiates tubular cell death in the neonatal mouse. Species differences are maintained in cultured cells, suggesting that differences in EGF receptor signaling underlie these opposing effects.

Maturation of malfunctioning kidneys

Because loss of functional renal mass is compensated by hyperfiltration of remaining tissue, one could hypothesize that a damaged kidney might not have the same rate of maturation as the contralateral one. To verify this, maturation was evaluated in children with asymmetrical renal function during early life. Twenty-five children were selected having had 2 (99m)Tc-MAG3 renograms combined with (51)Cr-EDTA clearance measurement, enabling estimation of glomerular filtration rate (GFR), split renal function (SRF), and single kidney GFR (SKGFR). The first test had to be performed before the age of 18 months and SRF on the affected side had to be < or =40%. Moreover, GFR had to increase between the 2 tests by > or =10 mL(-1) min/1.73 m(2), reflecting maturation due to age. For 18 children SRF changed by between -5% and +5%. For 4 children an increase of > or =5% was observed whereas for the remaining 3 a decrease of > or =5% occurred. For the first 22 kidneys, mean increase of SKGFR was +6.3 mL(-1) min/1.73 m(2)(SD: 6). For the 3 kidneys with > or =5% SRF decrease, SKGFR remained unchanged in 2 (+0.3 and -3 mL min(-1)/1.73 m(2)) and increased in the third patient (+15 mL min(-1)/1.73 m(2)). In conclusion, renal maturation is comparable in both the malfunctioning kidney and the contralateral normal functioning side.

Variable chronic partial ureteral obstruction in the neonatal rat: a new model of ureteropelvic junction obstruction

BACKGROUND

Congenital ureteropelvic junction (UPJ) obstruction is a common developmental anomaly. To elucidate the mechanisms underlying the renal consequences of congenital UPJ obstruction, we have developed a new model of variable partial unilateral ureteral obstruction (UUO) in the neonatal rat.

METHODS

Rat pups were subjected to sham-operation, complete UUO, or variable partial UUO within the first day of life. After 14 or 28 days, the relative number of glomeruli, cell proliferation, tubular apoptosis, tubular atrophy, and interstitial fibrosis were quantitated in histologic sections. Glomerular filtration rate (GFR) was determined after 28 days of partial or complete UUO.

RESULTS

Following 70% to 75% reduction in ureteral diameter, renal growth from 14 to 28 days was reduced by 60%, and the number of glomeruli decreased by 50%. Renal pelvic diameter increased in proportion to the severity of obstruction following 14 days of partial UUO, and by 28 days, was maximally dilated regardless of the luminal diameter. Renal proliferation was increased, while tubular apoptosis, tubular atrophy, and interstitial fibrosis were less severe 14 days following partial UUO than in complete UUO. GFR was reduced by 80%, and proteinuria developed following 28 days of partial UUO.

CONCLUSION

Renal function is impaired by chronic ipsilateral partial UUO, which reduces the number of nephrons, and leads to progressive renal pelvic dilatation. Tubular atrophy and interstitial fibrosis develop prior to significant renal pelvic dilatation. Correlation of clinically measurable parameters with renal morphometry or imaging studies in this model may lead to new approaches to the management of congenital UPJ obstruction.

A2A adenosine receptor agonist and PDE4 inhibition delays inflammation but fails to reduce injury in experimental obstructive nephropathy

BACKGROUND

Renal interstitial inflammation is a consequence of unilateral ureteral obstruction (UUO). Following ischemia/reperfusion, adenosine reduces renal inflammation and injury, effects which are potentiated by type 4 phosphodiesterase inhibitors. We therefore studied the effects of A2A adenosine receptor agonist (ATL146e), and PDE4 inhibitor (rolipram) in mice subjected to UUO.

METHODS

Mice were subjected to UUO or sham operation, and received either vehicle or ATL146e + rolipram by osmotic minipump for 1 or 7 days. At 1, 3, 7, or 14 days after operation, renal macrophage infiltration, apoptosis, proliferation, tubular atrophy, and interstitial fibrosis were quantitated, and expressions of IL-6 and TGF-beta mRNA were determined.

RESULTS

ATL146e + rolipram reduced macrophage infiltration by 40% after 3 days UUO (p < 0.05). Tubular apoptosis, tubular atrophy, and interstitial fibrosis were increased by 7 or 14 days UUO, but were unaffected by ATL146e + rolipram. However, cellular proliferation was increased by ATL146e + rolipram in the obstructed kidney. ATL146e + rolipram had no effect on the renal expression of IL-6 and TGF-beta mRNA.

CONCLUSIONS

A2A receptor activation and PDE4 inhibition transiently reduce renal macrophage infiltration, but do not ameliorate the renal response to UUO. We speculate that the persistent stimulus for inflammation triggered by UUO cannot be reversed by agents that suppress inflammatory cell activation alone.

Perinatal obstructive nephropathy

Significant advances have been made recently in elucidating the cellular consequences of urinary tract obstruction during renal development. Urinary tract obstruction impairs growth and maturation of the kidney, and can also cause renal maldevelopment. This includes a reduction in the number of nephrons, tubular atrophy, and progressive interstitial fibrosis. Apoptosis (programmed cell death) accounts for much of the loss of tubular epithelial cells. Factors contributing to apoptosis include stretching of cells in dilated tubules, altered renal production of growth factors, and infiltration of the renal interstitium by macrophages. Two major controversies remain regarding the surgical management of congenital obstructive nephropathy: first, which fetuses with bladder outlet obstruction should undergo prenatal intervention, and second, which infants should undergo early pyeloplasty for ureteropelvic junction obstruction? Even after successful surgery for congential obstructive nephropathy, all patients should be followed for hypertension, proteinuria, or renal deterioration.

Early release of neonatal ureteral obstruction preserves renal function

The incidence of congenital hydronephrosis is approximately 1% and is often associated with renal insufficiency. It is unknown whether early release is essential to prevent deterioration of renal function. Rats were subjected to partial unilateral ureteral obstruction (PUUO) on postnatal day 2. The obstruction was left in place or released after 1 or 4 wk. Renal blood flow (RBF) and kidney size were measured sequentially over 24 wk using MRI. In rats in which the obstruction was left in place, RBF of the obstructed kidney was progressively reduced to 0.92 +/- 0.17 vs. 1.79 +/- 0.12 ml.min(-1).100 g body wt(-1) (P < 0.05) after 24 wk. Similarly, glomerular filtration rate of the obstructed kidney was severely reduced at 24 wk: 172 +/- 36 vs. 306 +/- 42 microl.min(-1).100 g body wt(-1) (P < 0.05). These changes were preceded by development of severe hydronephrosis and obstructive nephropathy with a reduction in total protein content: 45 +/- 3 vs. 58 +/- 4 mg/kidney. Moreover, nonreleased PUUO caused a marked natriuresis (0.32 +/- 0.07 vs. 0.11 +/- 0.02 micromol.min(-1).100 g body wt(-1), P < 0.05) and impaired solute free water reabsorption (0.47 +/- 0.16 vs. 2.71 +/- 0.67 microl.min(-1).100 g body wt(-1), P < 0.05), consistent with a significant downregulation of Na-K-ATPase to 62 +/- 7%, aquaporin-1 to 53 +/- 3%, and aquaporin-3 to 53 +/- 7% of sham levels. Release after 1 wk completely prevented development of hydronephrosis, reduction in RBF and glomerular filtration rate, and downregulation of renal transport proteins, whereas release after 4 wk had no effect. These results suggest that early release of neonatal obstruction provides dramatically better protection of renal function than release of obstruction after the maturation process is completed.

[Experimental ureteral obstruction and knockout animals]

Obstructive uropathies caused by congenital malformations of the urinary tract are relatively frequent in newborn. These obstructive lesions are the main cause for renal disease in infancy. Most of these uropathies are treated by surgical interventions restoring the drainage function of the urinary tract. Clinically these patients are cured but the question remains wether these patients will develop renal disease in adult life, since it has been recently shown in animal models that transient, neonatal and prenatal, ureteral obstruction induces significant renal deterioration later in life. Except for angiotensin converting enzyme inhibitors that slow down the progression of renal disease, no specific drugs reducing renal fibrosis exist. Animal models of ureteral obstruction have allowed to clearly identify the events leading to tubulointerstitial fibrosis. Furthermore, more recently, the use of ureteral obstruction in genetically engineered animals has shown pro- and anti-fibrotic properties of a large number of molecules. These studies using genetically engineered animals have suggested several new future promising therapeutic directions to treat renal fibrosis.