Epidermal growth factor (EGF) expression in the congenital polycystic mouse kidney

Proliferative signaling by ERBB proteins and RAF/MEK/ERK effectors in polycystic kidney disease

A primary pathological feature of polycystic kidney disease (PKD) is the hyperproliferation of epithelial cells in renal tubules, resulting in formation of fluid-filled cysts. The proliferative aspects of the two major forms of PKD-autosomal dominant PKD (ADPKD), which arises from mutations in the polycystins PKD1 and PKD2, and autosomal recessive PKD (ARPKD), which arises from mutations in PKHD1-has encouraged investigation into protein components of the core cell proliferative machinery as potential drivers of PKD pathogenesis. In this review, we examine the role of signaling by ERBB proteins and their effectors, with a primary focus on ADPKD. The ERBB family of receptor tyrosine kinases (EGFR/ERBB1, HER2/ERBB2, ERBB3, and ERBB4) are activated by extracellular ligands, inducing multiple pro-growth signaling cascades; among these, activation of signaling through the RAS GTPase, and the RAF, MEK1/2, and ERK1/2 kinases enhance cell proliferation and restrict apoptosis during renal tubuloepithelial cyst formation. Characteristics of PKD include overexpression and mislocalization of the ERBB receptors and ligands, leading to enhanced activation and increased activity of downstream signaling proteins. The altered regulation of ERBBs and their effectors in PKD is influenced by enhanced activity of SRC kinase, which is promoted by the loss of cytoplasmic Ca²⁺ and an increase in cAMP-dependent PKA kinase activity that stimulates CFTR, driving the secretory phenotype of ADPKD. We discuss the interplay between ERBB/SRC signaling, and polycystins and their depending signaling, with emphasis on thes changes that affect cell proliferation in cyst expansion, as well as the inflammation-associated fibrogenesis, which characterizes progressive disease. We summarize the current progress of preclinical and clinical trials directed at inhibiting this signaling axis, and discuss potential future strategies that may be productive for controlling PKD.

Evidence for a "Pathogenic Triumvirate" in Congenital Hepatic Fibrosis in Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is a severe monogenic disorder that occurs due to mutations in the PKHD1 gene. Congenital hepatic fibrosis (CHF) associated with ARPKD is characterized by the presence of hepatic cysts derived from dilated bile ducts and a robust, pericystic fibrosis. Cyst growth, due to cyst wall epithelial cell hyperproliferation and fluid secretion, is thought to be the driving force behind disease progression. Liver fibrosis is a wound healing response in which collagen accumulates in the liver due to an imbalance between extracellular matrix synthesis and degradation. Whereas both hyperproliferation and pericystic fibrosis are hallmarks of CHF/ARPKD, whether or not these two processes influence one another remains unclear. Additionally, recent studies demonstrate that inflammation is a common feature of CHF/ARPKD. Therefore, we propose a "pathogenic triumvirate" consisting of hyperproliferation of cyst wall growth, pericystic fibrosis, and inflammation which drives CHF/ARPKD progression. This review will summarize what is known regarding the mechanisms of cyst growth, fibrosis, and inflammation in CHF/ARPKD. Further, we will discuss the potential advantage of identifying a core pathogenic feature in CHF/ARPKD to aid in the development of novel therapeutic approaches. If a core pathogenic feature does not exist, then developing multimodality therapeutic approaches to target each member of the "pathogenic triumvirate" individually may be a better strategy to manage this debilitating disease.

Urinary EGF Receptor Ligand Excretion in Patients with Autosomal Dominant Polycystic Kidney Disease and Response to Tolvaptan

BACKGROUND AND OBJECTIVES

Recent animal experiments suggest that dysregulation of the EGF receptor pathway plays a role in the pathophysiology of autosomal dominant polycystic kidney disease (ADPKD). Research on EGF receptor ligands in humans with ADPKD is lacking. EGF receptor ligands were measured in patients with ADPKD at baseline and after treatment with a vasopressin V2 receptor antagonist (V2RA) because this information might provide a rationale for future V2RA combination therapy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Blood and urine concentrations of the EGF receptor ligands heparin-binding (HB)-EGF, EGF, and TGF-α were measured by ELISAs in 27 patients with ADPKD who participated in a single-center study investigating a V2RA in 2011-2013 and in 27 controls who were selected from a general population-based observational study. Cyst fluid concentrations were also measured. In patients with ADPKD, ligands were measured at baseline, after 3-week treatment with a V2RA, and 3 weeks after drug withdrawal. The measured GFR (mGFR) was determined by iothalamate infusion, and total kidney volume was measured by magnetic resonance imaging.

RESULTS

Urinary HB-EGF excretion and plasma concentration were higher in patients with ADPKD than in controls (median, 1.4 [interquartile range, 1.2-1.9] versus 0.6 [0.4-0.8] µg/24 hours [P<0.001] and 157.9 [83.1-225.9] versus 77.2 [37.2-174.3] pg/ml [P=0.04]). In contrast, urinary EGF excretion and plasma EGF concentration were lower in patients with ADPKD, whereas TGF-α did not differ between patients and controls. Higher HB-EGF excretion was correlated with more severe disease, assessed as lower mGFR (r=-0.39; P=0.05), higher total kidney volume (r=0.39; P=0.05), and higher urinary excretion of albumin and heart-type fatty acid-binding protein, whereas higher EGF excretion and TGF-α excretion were negatively correlated with disease severity. During V2RA treatment, HB-EGF excretion increased (from 1.4 [1.2-1.9] to 2.4 [2.1-3.1] µg/24 hours; P<0.001).

CONCLUSION

In patients with ADPKD, higher urinary HB-EGF excretion is correlated with more severe disease. Whether this association is causal needs to be investigated in intervention studies.

Urinary biomarkers of kidney diseases in HIV-infected children

A significant number of children infected with the human immunodeficiency virus 1 (HIV-1) virus all over the world are at risk of developing renal diseases that could have a significant impact on their treatment and quality of life. It is necessary to identify children undergoing the early stages of these renal diseases, as well as the potential renal toxicity that could be caused by antiretroviral drugs, in order to prevent the development of cardiovascular complications and chronic renal failure. This article describes the most common renal diseases seen in HIV-infected children, as well as the value and limitations of the clinical markers that are currently being used to monitor their renal function and histological damage in a noninvasive manner. In addition, we discuss the progress made during the last 10 years in the discovery and validation of new renal biomarkers for HIV-infected children and young adults. Although significant progress has been made during the early phases of the biomarkers discovery, more work remains to be done to validate the new biomarkers in a large number of patients. The future looks promising, however, the new knowledge needs to be integrated and validated in the context of the clinical environment where these children are living.

Pathophysiology of childhood polycystic kidney diseases: new insights into disease-specific therapy

Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are significant causes of morbidity and mortality in children and young adults. ADPKD, with an incidence of 1:400 to 1:1,000, affects more than 13 million individuals worldwide and is a major cause of end-stage renal disease in adults. However, symptomatic disease is increasingly recognized in children. ARPKD is a dual-organ hepatorenal disease with an incidence of 1:20,000 to 1:40,000 and a heterozygote carrier rate of 1 in 70. Currently, no clinically significant disease-specific therapy exists for ADPKD or ARPKD. The genetic basis of both ADPKD and ARPKD have been identified, and delineation of the basic molecular and cellular pathophysiology has led to the discovery that abnormal ADPKD and ARPKD gene products interact to create "polycystin complexes" located at multiple sites within affected cells. The extracellular matrix and vessels produce a variety of soluble factors that affect the biology of adjacent cells in many dynamic ways. This review will focus on the molecular and cellular bases of the abnormal cystic phenotype and discuss the clinical translation of such basic data into new therapies that promise to alter the natural history of disease for children with genetic PKDs.

Mechanisms underlying rapid aldosterone effects in the kidney

The steroid hormone aldosterone is a key regulator of electrolyte transport in the kidney and contributes to both homeostatic whole-body electrolyte balance and the development of renal and cardiovascular pathologies. Aldosterone exerts its action principally through the mineralocorticoid receptor (MR), which acts as a ligand-dependent transcription factor in target tissues. Aldosterone also stimulates the activation of protein kinases and secondary messenger signaling cascades that act independently on specific molecular targets in the cell membrane and also modulate the transcriptional action of aldosterone through MR. This review describes current knowledge regarding the mechanisms and targets of rapid aldosterone action in the nephron and how aldosterone integrates these responses into the regulation of renal physiology.

Protein kinase D stabilizes aldosterone-induced ERK1/2 MAP kinase activation in M1 renal cortical collecting duct cells to promote cell proliferation

Aldosterone elicits transcriptional responses in target tissues and also rapidly stimulates the activation of protein kinase signalling cascades independently of de novo protein synthesis. Here we investigated aldosterone-induced cell proliferation and extra-cellular regulated kinase 1 and 2 (ERK1/2) mitogen activated protein (MAP) kinase signalling in the M1 cortical collecting duct cell line (M1-CCD). Aldosterone promoted the proliferative growth of M1-CCD cells, an effect that was protein kinase D1 (PKD1), PKCdelta and ERK1/2-dependent. Aldosterone induced the rapid activation of ERK1/2 with peaks of activation at 2 and 10 to 30 min after hormone treatment followed by sustained activation lasting beyond 120 min. M1-CCD cells suppressed in PKD1 expression exhibited only the early, transient peaks in ERK1/2 activation without the sustained phase. Aldosterone stimulated the physical association of PKD1 with ERK1/2 within 2 min of treatment. The mineralocorticoid receptor (MR) antagonist RU28318 inhibited the early and late phases of aldosterone-induced ERK1/2 activation, and also aldosterone-induced proliferative cell growth. Aldosterone induced the sub-cellular redistribution of ERK1/2 to the nuclei at 2 min and to cytoplasmic sites, proximal to the nuclei after 30 min. This sub-cellular distribution of ERK1/2 was inhibited in cells suppressed in the expression of PKD1.

A urinary biomarker profile for children with HIV-associated renal diseases

Human immunodeficiency virus (HIV)-infected children are at risk of developing several types of renal diseases, including HIV-associated nephropathy (HIVAN), which is usually seen during late stages of infection in children with a high viral load. This disease is defined by the presence of proteinuria associated with mesangial hyperplasia and/or global-focal segmental glomerulosclerosis combined with microcystic transformation of the renal tubules. Because HIVAN can have an insidious clinical onset, renal biopsy is the only definitive way of establishing a diagnosis. Given the risk of performing this procedure in HIV-infected children with other AIDS-defining illness, we sought to identify informative biomarkers such as growth factors in the urine of 55 HIV-infected children that might be predictive of the extent and activity of the renal lesions characteristic of HIVAN. We found that the levels of epidermal growth factor were lower in the urine of children with renal disease, whereas levels of fibroblast growth factor-2 and metalloproteinase-2 were higher as compared with those levels in infected children without renal disease. Similar changes were observed in HIV-Tg26 mice correlating with the progression of renal disease in this model of HIVAN. Our findings suggest that this urinary growth factor profile may be useful in facilitating the diagnosis of HIV-infected children at risk of developing HIVAN when interpreted in the appropriate clinical setting.

Potential pharmacological interventions in polycystic kidney disease

Polycystic kidney diseases (autosomal dominant and autosomal recessive) are progressive renal tubular cystic diseases, which are characterised by cyst expansion and loss of normal kidney structure and function. Autosomal dominant polycystic kidney disease (ADPKD) is the most common life- threatening, hereditary disease. ADPKD is more prevalent than Huntington's disease, haemophilia, sickle cell disease, cystic fibrosis, myotonic dystrophy and Down's syndrome combined. Early diagnosis and treatment of hypertension with inhibitors of the renin-angiotensin-aldosterone system (RAAS) and its potential protective effect on left ventricular hypertrophy has been one of the major therapeutic goals to decrease cardiac complications and contribute to improved prognosis of the disease. Advances in the understanding of the genetics, molecular biology and pathophysiology of the disease are likely to facilitate the improvement of treatments for these diseases. Developments in describing the role of intracellular calcium ([Ca(2+)](i)) and its correlation with cellular signalling systems, Ras/Raf/mitogen extracellular kinase (MEK)/extracellular signal-regulated protein kinase (ERK), and interaction of these pathways with cyclic adenosine monophosphate (cAMP) levels, provide new insights on treatment strategies. Blocking the vasopressin V(2) receptor, a major adenylyl cyclase agonist, demonstrated significant improvements in inhibiting cytogenesis in animal models. Because of activation of the mammalian target of rapamycin (mTOR) pathway, the use of sirolimus (rapamycin) an mTOR inhibitor, markedly reduced cyst formation and decreased polycystic kidney size in several animal models. Caspase inhibitors have been shown to decrease cytogenesis and renal failure in rats with cystic disease. Cystic fluid secretion results in cyst enlargement and somatostatin analogues have been shown to decrease renal cyst progression in patients with ADPKD. The safety and efficacy of these classes of drugs provide potential interventions for experimental and clinical trials.

Polycystic kidney disease: genes, proteins, animal models, disease mechanisms and therapeutic opportunities

An increased understanding of the genetic, molecular and cellular mechanisms responsible for the development of polycystic kidney disease has laid out the foundation for the development of rational therapies. Many animal models where these therapies can be tested are currently available. This review summarizes the rationale for these treatments, the results of preclinical trials and the prospects for clinical trials, some already in early phases of implementation.

Mechanisms of Disease: autosomal dominant and recessive polycystic kidney diseases

Autosomal dominant polycystic kidney disease and autosomal recessive polycystic kidney disease are the best known of a large family of inherited diseases characterized by the development of renal cysts of tubular epithelial cell origin. Autosomal dominant and recessive polycystic kidney diseases have overlapping but distinct pathogeneses. Identification of the causative mutated genes and elucidation of the function of their encoded proteins is shedding new light on the mechanisms that underlie tubular epithelial cell differentiation. This review summarizes recent literature on the role of primary cilia, intracellular calcium homeostasis, and signaling involving Wnt, cyclic AMP and Ras/MAPK, in the pathogenesis of polycystic kidney disease. Improved understanding of pathogenesis and the availability of animal models orthologous to the human diseases provide an excellent opportunity for the development of pathophysiology-based therapies. Some of these have proven effective in preclinical studies, and clinical trials have begun.

Activation of the MEK5/ERK5 cascade is responsible for biliary dysgenesis in a rat model of Caroli's disease

Polycystic kidney (PCK) rats exhibit a multiorgan cyst pathology similar to human autosomal recessive polycystic kidney disease, and are proposed as an animal model of Caroli's disease with congenital hepatic fibrosis (CHF). This study investigated the expression and function of selected components of the mitogen activated protein kinase (MAPK) pathway in cultured intrahepatic biliary epithelial cells (BECs) of PCK rats. Compared to the proliferative activity of cultured BECs of control rats, those of the PCK rats were hyperresponsive to epidermal growth factor (EGF). The increase in BEC proliferation was accompanied by overexpression of MAPK/extracellular signal-regulated protein kinase (ERK) kinase 5 (MEK5), and subsequent phosphorylation of ERK5 in vitro. The increased proliferative activity was significantly inhibited by the transfection of short interfering RNA against MEK5 mRNA. An EGF receptor tyrosine kinase inhibitor, gefitinib ("Iressa", ZD1839), also significantly inhibited the abnormal growth of cultured BECs of PCK rats. By contrast, treatment with PD98059 and U0126, inhibitors for MEK1/2, was less effective. These results suggest that the activation of the MEK5-ERK5 cascade plays a pivotal role in the biliary dysgenesis of PCK rats, and also provide insights into the pathogenesis of Caroli's disease with CHF. As the MEK5-ERK5 interaction is highly specific, it may represent a potential target of therapy.

Epidermal growth factor receptor tyrosine kinase inhibition is not protective in PCK rats

BACKGROUND

Advances in the understanding of cystogenesis, identification of the PKHD1 gene and availability of a rat model (the PCK rat) caused by a Pkhd1 mutation facilitate testing of therapies for autosomal-recessive polycystic kidney disease (ARPKD). Considerable support exists for the importance of the epidermal growth factor (EGF)/transforming growth factor-alpha (TGF-alpha)/EGF receptor (EGFR) axis and of the adenylyl cyclase-adenosine 3',5'-cyclic monophosphate (cAMP) pathway in the pathogenesis of cyst formation and progressive enlargement.

METHODS

To determine whether EGFR tyrosine kinase inhibition is protective in the PCK rat, male and female animals were treated with EKI-785 or EKB-569 or with vehicle alone between 3 and 10 weeks of age. Biochemical and histomorphometric analysis, immunohistochemistry, immunoblotting, enzyme immunoassay, and quantitative reverse transcription-polymerase chain reaction (RT-PCR) were used to ascertain the effects of treatment.

RESULTS

Contrary to other murine models of ARPKD, overexpression and apical mislocalization of EGFR were not detected in the PCK rats. Consistent with these expression results, EKI-785 or EKB-569 administration had no effect or worsened PKD, and had no effect on the development of fibrocystic liver disease. Increased renal cAMP and vasopressin V2 receptor expression were observed in the EKI-785-treated animals.

CONCLUSION

EGFR tyrosine kinase inhibition did not protect PCK rats from the development of PKD. This may be due to effects on collecting duct cAMP that counteract possible beneficial effects on the extracellular-regulated protein kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway, particularly in the absence of EGFR overexpression or mislocalization. The relevance of these observations to the treatment of human cystic kidney diseases deserves further study.

Murine models of polycystic kidney disease: molecular and therapeutic insights

Numerous murine (mouse and rat) models of polycystic kidney disease (PKD) have been described in which the mutant phenotype results from a spontaneous mutation or engineering via chemical mutagenesis, transgenic technologies, or gene-specific targeting in mouse orthologs of human PKD genes. These murine phenotypes closely resemble human PKD, with common abnormalities observed in tubular epithelia, the interstitial compartment, and the extracellular matrix of cystic kidneys. In both human and murine PKD, genetic background appears to modulate the renal cystic phenotype. In murine models, these putative modifying effects have been dissected into discrete factors called quantitative trait loci and genetically mapped. Several lines of experimental evidence support the hypothesis that PKD genes and their modifiers may define pathways involved in cystogenesis and PKD progression. Among the various pathway abnormalities described in murine PKD, recent provocative data indicate that structural and/or functional defects in the primary apical cilia of tubular epithelia may play a key role in PKD pathogenesis. This review describes the most widely studied murine models; highlights the data regarding specific gene defects and genetic modifiers; summarizes the data from these models that have advanced our understanding of PKD pathogenesis; and examines the effect of various therapeutic interventions in murine PKD.

EGF receptor tyrosine kinase inhibition attenuates the development of PKD in Han:SPRD rats

BACKGROUND

Increasing evidence supports an important role for the epidermal growth factor (EGF)/transforming growth factor-alpha (TGF-alpha)/EGF receptor (EGFR) axis in promoting tubular epithelial cell proliferation and cyst formation in polycystic kidney disease (PKD).

METHODS

To determine whether the inhibition of EGFR tyrosine kinase activity can attenuate the development of PKD in the Han:SPRD rat, a frequently used animal model of autosomal-dominant slowly progressive PKD (ADPKD), wild-type and cy/+ rats were treated with EKI-785 or EKB-569 or with vehicle alone. Western analysis, immunoprecipitation, and immunohistochemistry were used to ascertain the expression, activation, and localization of EGFR.

RESULTS

Overexpression, activation and apical mislocalization of EGFR were observed in the cy/+ rats. The intraperitoneal administration of EKI-785 reversed the activation of the EGFR to the level observed in wild-type animals. The intraperitoneal administration of EKI-785 (90 mg/kg body weight every third day) or of EKB-569 (20 mg/kg body weight every third day) to cy/+ rats resulted in lower kidney weights, serum concentrations of blood urea nitrogen (BUN), cyst volumes, and fibrosis scores. The administration of EKB-569 by gavage was less effective probably because of lower bioavailability.

CONCLUSION

These results support a significant role for the EGF/TGF-alpha/EGFR axis in the development of PKD in the Han:SPRD rat and the therapeutic potential of EGFR tyrosine kinase inhibition in ADPKD.

Recent advances in the cell biology of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a significant familial disorder, crossing multiple ethnicities as well as organ systems. The goal of understanding and, ultimately, curing ADPKD has fostered collaborative efforts among many laboratories, mustered on by the opportunity to probe fundamental cellular biology. Here we review what is known about ADPKD including well-accepted data such as the identification of the causative genes and the fact that PKD1 and PKD2 act in the same pathway, fairly well-accepted concepts such as the "two-hit hypothesis," and somewhat confusing information regarding polycystin-1 and -2 localization and protein interactions. Special attention is paid to the recently discovered role of the cilium in polycystic kidney disease and the model it suggests. Studying ADPKD is important, not only as an evaluation of a multisystem disorder that spans a lifetime, but as a testament to the achievements of modern biology and medicine.

Multiorgan mRNA misexpression in murine autosomal recessive polycystic kidney disease

BACKGROUND

BALB/c mice homozygous for the cpk mutation develop a form of polycystic kidney disease (PKD) with multiorgan pathology similar to human autosomal recessive PKD. Messenger RNA expression in multiple affected organs was analyzed to determine if common gene cascades were misexpressed in the cystic kidney and extrarenal sites of disease. In cystic kidneys, misexpressed mRNAs were found in one of four general groups: proliferation/cell growth, apoptosis, differentiation or extracellular matrix.

METHODS

RNA was isolated from kidney, liver and pancreas of cystic and normal BALB/c-cpk mice. Using Northern blot hybridization and ribonuclease protection assays (RPA), the expression of several genes thought to be associated with PKD, namely c-myc, epidermal growth factor receptor (EGF-R) and PKD-1, were evaluated. RPAs were used to assess mRNA expression of cyclins and members of the bax/bcl-2 family. In addition, kidney, liver and pancreas were immunostained for c-Myc and PCNA.

RESULTS

Cystic kidney, liver and pancreas all exhibited similar patterns of mRNA misexpression of c-myc, EGF-R and PKD-1. In addition, a number of cell proliferation and apoptosis-related mRNAs also were elevated in cystic kidney and pancreas. Renal epithelial cells expressing proliferation-associated proteins [c-Myc and proliferating cell nuclear antigen (PCNA)] were nearly absent in normal kidney; however, cells of cystic and non-cystic renal tubules plus liver and pancreatic cyst exhibited an increased number of nuclei labeled with antibodies to these proteins.

CONCLUSIONS

These data suggest that similar pathologic mechanisms (including the expression of c-myc, EGF-R, PKD-1, cyclin, and bax/bcl-2 family mRNAs) may be responsible for the development of cystic changes in kidney, liver and pancreas in murine autosomal recessive PKD. Treatments targeting these similarly misexpressed mRNAs may be efficacious in ameliorating the cystic pathology in the kidney as well as the other affected organs in ARPKD.

Overexpression of kidney phosphatidylinositol 4-kinasebeta and phospholipase C(gamma1) proteins in two rodent models of polycystic kidney disease

Our studies of renal phosphoinositide levels and metabolism in the pcy mouse with polycystic kidney disease (PKD) suggest that phosphatidylinositol kinase (PtdInsK) and phospholipase C (PLC) are elevated in this renal disorder. Therefore, the steady-state levels of select isoforms of these enzymes were examined in renal cytosolic and particulate (detergent-soluble) fractions in male and female normal and CD1-pcy/pcy (pcy) mice at 60, 120 and 180 days of age, and in male and female normal and diseased (Han:SPRD-cy) rats at 28 and 70 days of age. Disease-related increases in phosphatidylinositol 4-kinasebeta (PtdIns4Kbeta) and PLC(gamma1) levels were present in both models. PtdIns4Kbeta levels were higher by as much as 233% in pcy mice and by 95% in diseased Han:SPRD-cy rats compared to normals of the same age and gender. Steady-state levels of PLC(gamma1) were as much as 74% and 35% higher in pcy mice and diseased Han:SPRD-cy rats, respectively, compared to their controls. The consistency of these alterations in two accepted models of PKD indicates the importance of the phosphoinositide signalling pathway in the evolution of this disorder, and represents a potential site for therapeutic intervention.

Deficiency of phospholipase C-γ1 impairs renal development and hematopoiesis

Phospholipase C-γ1 (PLC-γ1) is involved in a variety of intracellular signaling via many growth factor receptors and T-cell receptor. To explore the role of PLC-γ1 in vivo, we generated the PLC-γ1-deficient (plc-γ1–/–) mice, which died of growth retardation at embryonic day 8.5-9.5 in utero. Therefore, we examined plc-γ1–/– chimeric mice generated with plc-γ1–/– embryonic stem (ES) cells for further study. Pathologically, plc-γ1–/– chimeras showed multicystic kidney due to severe renal dysplasia and renal tube dilation. Flow cytometric analysis and glucose phosphate isomerase assay revealed very few hematopoietic cells derived from the plc-γ1–/– ES cells in the mutant chimeras. However, differentiation of plc-γ1–/– ES cells into erythrocytes and monocytes/macrophages in vitro was observed to a lesser extent compared with control wild-type ES cells. These data suggest that PLC-γ1 plays an essential role in the renal development and hematopoiesis in vivo.

Urinary epidermal growth factor in different renal conditions in children

Several studies have demonstrated the important role of growth factors, particularly epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha), in cellular growth after renal damage. EGF is mainly synthesized by the kidney. Many studies indicate that urinary EGF concentration significantly decreases in patients with acute and chronic renal failure. In this study we determined urinary EGF concentrations in children with renal and/or urological pathologies. We investigated 38 patients, 17 males and 21 females, of 3.34+/-2.96 years (mean +/- standard deviation), who were followed in the Nephrologic Unit of the Pediatric Department of the University of Verona for recurrent urinary tract infections: seven of these had vesicoureteric reflux and 4 had hypodysplasia. The results were compared with those from a healthy age-matched group of 44 children. In all patients, we assessed renal function including an examination of the urine with a microbiological evaluation. Moreover, a renal ultrasound and a voiding cystourethrogram were performed.

Molecular genetics and pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common and systemic disease characterized by formation of focal cysts. Of the three potential causes of cysts, downstream obstruction, compositional changes in extracellular matrix, and proliferation of partially dedifferentiated cells, evidence strongly supports the latter as the primary abnormality. In the vast majority of cases, the disease is caused by mutations in PKD1 or PKD2, and appears to be recessive at the cellular level. Somatic second hits in the normal allele of cells containing the germ line mutation initiate or accelerate formation of cysts. The intrinsically high frequency of somatic second hits in epithelia appears to be sufficient to explain the frequent occurrence of somatic second hits in the disease-causing genes. PKD1 and PKD2 encode a putative adhesive/ion channel regulatory protein and an ion channel, respectively. The two proteins interact directly in vitro. Their cellular and subcellular localization suggest that they may also function independently in a common signaling pathway that may involve the membrane skeleton and that links cell-cell and cell-matrix adhesion to the development of cell polarity.

Development of autosomal recessive polycystic kidney disease in BALB/c-cpk/cpk mice

Autosomal recessive polycystic kidney disease (ARPKD) is a rare but devastating inherited disease in humans. Various strains of mice that are homozygous for the cpk gene display renal pathology similar to that seen in human ARPKD. The PKD progresses to renal insufficiency, azotemia, and ultimately a uremic death by approximately 3 wk of age. This study characterizes PKD in mice that are homozygous for the cpk gene on a BALB/c inbred mouse background. The BALB/c-cpk/cpk murine model displays renal as well as extrarenal pathology similar to that found in human ARPKD. The renal pathology includes the well-characterized early proximal tubule and, later, massive collecting duct cysts. The extrarenal defects in this murine model include common bile duct dilation, intrahepatic biliary duct cysts with periductal hyperplasia, and pancreatic dysplasia with cysts. Renal mRNA expression of c-myc, a proto-oncogene, and clusterin (SGP-2), a marker associated with immature collecting ducts, decreases during normal development but is upregulated in murine ARPKD. Expression of epidermal growth factor (EGF) mRNA is significantly diminished, whereas EGF receptor mRNA is upregulated in the BALB/c-cpk/cpk kidney compared with phenotypically normal littermates. To determine whether the altered EGF expression contributes to the development of PKD, neonatal mice were treated with exogenous EGF (1 microg/g body wt injected subcutaneously on postnatal days 3 through 9). EGF treatment reduced the relative kidney weight and common bile duct dilation and downregulated renal expression of clusterin and EGF receptor. However, exogenous EGF did not affect the degree of renal failure, the pancreatic pathology, or the misregulated renal expression of c-myc. In summary, the present study characterizes the renal and extrarenal pathology in the BALB/c-cpk/cpk murine model of ARPKD. Renal mRNA expression of EGF is diminished in this mouse model. EGF treatment did not prevent renal failure but ameliorated pathologic changes in the kidney and the biliary ducts of the BALB/c-cpk/cpk mouse.

Renal content and output of epidermal growth factor in long-term adrenergic agonist-treated rats

This study investigates the renal and urinary levels of epidermal growth factor (EGF) in rats under long-term treatment with alpha- or beta-adrenergic agonists. Urine samples were obtained on days 7, 14 and 21, and renal tissue samples on day 21. EGF was quantified by ELISA and tissue sections were used for immunohistochemistry and in situ hybridization. Fractional kidney weight was increased in the alpha-adrenergic agonist-treated group by 35% when compared with controls. Histological examination of the kidney revealed well-defined wedge-shaped areas of tubular dilatations and luminal amorphous material in the distal tubules. Concomitantly, reduced levels of EGF and EGF mRNA were observed, and also the urinary levels of EGF were reduced. Together, these observations indicate alpha-adrenergic treatment to affect the distal tubules. Treatment with the beta-adrenergic agonist did not change fractional kidney weight, but initially the urinary excretion of EGF was reduced. The data add further evidence to the suggestion that activity of the sympathetic nervous system influences renal homeostasis of EGF, either directly or indirectly through renal histopathological changes.

Developmental expression of urine concentration-associated genes and their altered expression in murine infantile-type polycystic kidney disease

Currently, there is little understanding of what factors regulate the development of urine concentrating capability in normal or polycystic kidney. The present study examined the developmental expression of genes associated with urine concentration in developing mice, including C57BL/6J-cpk/cpk mice with autosomal recessive-infantile (AR) polycystic kidney disease (PKD). Concentration of urine requires: 1) medullary collecting ducts (CD) located within a hypertonic interstitium, 2) CD cell expression of functional arginine vasopressin V2 receptors (AVP-V2R), and 3) the presence of appropriate CD water channels (aquaporins, AQP 2 and 3). An increase in urine osmolarity, normally seen between 1 and 3 weeks of age, was absent in cpk cystic mice. Aldose reductase mRNA expression (a gene upregulated by medullary hyperosmolarity) increased in normal mice, but remained low in the cystic kidney, suggesting the absence of a hypertonic medullary interstitium. AVP-V2R, AQP2, and AQP3 mRNA expression normally increase between 7 and 14 days. However, all were dramatically overexpressed even at 7 days of age in the cpk kidney in vivo, but decreased in vitro. Activation of the AVP-V2 receptor stimulates the production of cAMP, a substance known to promote cyst enlargement. To determine if CD cAMP, generated from increased AVP-V2Rs, was accelerating the PKD, cystic mice and their normal littermates were treated with OPC31260, a relatively specific AVP-V2R antagonist. OPC31260 treatment of cystic mice led to an amelioration of the cystic enlargement and azotemia. Treatment also decreased renal AQP2 mRNA but increased AVP-V2R and AQP3 mRNA expression in vivo. AVP upregulates the expression of AVP-V2R, AQP2, and AQP3 mRNAs in vitro. Renal EGF, known to inhibit AVP-V2R activity, downregulates AVP-V2R mRNA in vitro. Brief in vivo EGF treatment, known to decrease PKD in cpk mice, led to increased expression of AVP-V2R, AQP2, and AQP3 mRNAs at 2 weeks in both normal and cystic mice but no change was evident at 3 weeks of age. In conclusion, the development of urinary concentration ability correlates with the development of an increased medullary osmotic gradient which is diminished in murine ARPKD. However, CD genes associated with this process are overexpressed in vivo but underexpressed in vitro in the cystic kidney. The overexpression and/or overactivity of the AVP-V2R appears to contribute to the progression of PKD since an AVP-V2R antagonist inhibits cystic renal enlargement in the cpk mouse.

A new in vitro bioassay for cyst formation by renal cells from an autosomal dominant rat model of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most frequent human inherited diseases. The main feature of the disease is the development of renal cysts, first occurring in the proximal tubules, and with time, dominating all segments of the nephron, leading to end-stage renal disease in 50% of the patients in their fifth decade of life. A therapy for polycystic kidney disease (PKD) has not yet been developed. Patients coming to end-stage ADPKD require long-term dialysis and/or transplantation. A suitable animal model to study ADPKD is the spontaneously mutated Han:SPRD (cy/+) rat, but a method to cultivate Han:SPRD (cy/+) derived renal cells which preserves their ability to form cyst-like structures in vitro has previously not been reported. Based on this well-characterized animal model, we developed a cell culture model of renal cyst formation in vitro. When renal cells of the Han:SPRD (cy/+) rat were isolated and cultured under conditions that prevent cell-substratum adhesion, large amounts of cyst-like structures were formed de novo from Han:SPRD (cy/+) derived renal cells, but only a few from control rat renal cells. In contrast, when cultivated on plastic as monolayer cultures, Han:SPRD (cy/+)-derived and control rat-derived renal cells were indistinguishable and did not form cyst-like structures. Immunohistochemical characterization of the cyst-like structures suggests tubular epithelial origin of the cyst-forming cells. The amount of cysts formed from Han:SPRD (cy/+)-derived renal cells grown in a stationary suspension culture is susceptible to modulation by different conditions. Human cyst fluid and epidermal growth factor both stimulated the formation of cysts from Han:SPRD (cy/+)-derived renal cells whereas taxol inhibited cystogenesis. In contrast, neither human cyst fluid nor epidermal growth factor affected the amount of cysts formed by control rat renal cells. As the culture model reported here allows not only the distinction of PKD-derived tubular epithelium from its normal counterpart, but also the modulation of cyst formation especially by Han:SPRD (cy/+)-derived renal cells, it might be a useful prescreening protocol for potential treatments for PKD and thus reduce the need for animal experiments.

Functional activity of epidermal growth factor receptors in autosomal recessive polycystic kidney disease

Evidence from a number of laboratories suggests a potential role for the epidermal growth factor (EGF)-transforming growth factor-alpha-epidermal growth factor receptor (EGF-R) axis in promoting epithelial hyperplasia and cyst formation in autosomal recessive polycystic kidney disease (ARPKD). As previously reported, in the C57BL-6Jcpk/cpk (CPK), BALB/c-bpk/bpk (BPK), and C3H-orpk/orpk (ORPK) murine models of ARPKD, as well as in human ARPKD and human ADPKD, the EGF-R is mislocated to the apical surface of cystic collecting tubule (CT) epithelial cells. The present studies demonstrate that cells from cystic and control CTs can be isolated and that these cells maintain their in vivo EGF-R phenotype in vitro. Domain-specific high-affinity ligand binding was assessed by standard Scatchard analysis, and selective ligand stimulation of apical vs. basolateral EGF-R in these cells was followed by measurement of receptor autophosphorylation and determination of cell proliferation. These studies demonstrate that in vitro apically expressed EGF-Rs exhibit high-affinity binding for EGF, autophosphorylate in response to EGF, and transmit a mitogenic signal when stimulated by the appropriate ligand.

Epidermal growth factor receptor activity mediates renal cyst formation in polycystic kidney disease

A consistent phenotype observed in both human patients and several different mouse models of autosomal recessive polycystic kidney disease (ARPKD) is an increased activity of the epidermal growth factor receptor (EGFR) in the affected kidneys. To determine whether this increased activity of the EGFR is a functional event that is directly part of the disease pathway of renal cyst formation, we used a genetic approach to introduce a mutant EGFR with decreased tyrosine kinase activity into a murine model of ARPKD. We found that the modified form of the EGFR could block the increase in EGFR-specific tyrosine kinase activity that normally accompanies the development of renal cysts, and this correlated with an improvement in kidney function and a substantial decrease in cyst formation in the collecting ducts. These results suggest that changes in the expression of the EGFR contribute to the formation of cysts in the collecting ducts, and that drugs that target the tyrosine kinase activity of the EGFR may potentially be therapeutic in ARPKD.

Microtubule active taxanes inhibit polycystic kidney disease progression in cpk mice

Homozygous cpk/cpk mice develop polycystic kidney disease and die of uremia between the fourth and fifth weeks of age. Cpk/cpk mice treated weekly with paclitaxel (Taxol) can live to over six months of age. This dramatic moderation of polycystic kidney disease progression has been postulated to be a result of paclitaxel's ability to stabilize microtubules. In this study, the ability of taxanes with differing abilities to promote spontaneous in vitro assembly of tubulin dimers into microtubules were tested for their ability to inhibit the progression of polycystic kidney disease in polycystic cpk/cpk mice. We found that taxanes that are active in promoting microtubule assembly, including paclitaxel, 10-deactyl-taxol and cephalomannine increased the survival of polycystic cpk/cpk mice significantly longer than control animals. In contrast, the microtubule inactive taxane baccatin-III has no effect on the progression of renal failure in cpk/cpk mice. We conclude that the ability to promote microtubule assembly may be necessary for paclitaxel and related taxanes to modulate the progression of polycystic kidney progression in cpk/cpk mice.

Functional correction of renal defects in a mouse model for ARPKD through expression of the cloned wild-type Tg737 cDNA

Autosomal recessive polycystic kidney disease (ARPKD) is characterized by the formation of large collecting tubule and ductular cysts that often result in renal insufficiency within the first decade of life. Understanding the process leading to cyst formation will require the identification and characterization of genes involved in the etiology of this disease. In this regard, we previously described the generation of a mouse model (TgN737Rpw) for ARPKD and the cloning of a candidate gene. Here we show direct involvement of the Tg737 gene in collecting duct cyst formation by expressing the wild-type Tg737 cDNA as a transgene in TgN737Rpw mutants. In contrast to TgN737Rpw mutants, the "rescued" animals survive longer, have normal renal function and normal localization of the EGFr to the basolateral surfaces of collecting duct epithelium.

Dietary fish oil prevents the development of renal damage in salt-loaded stroke-prone spontaneously hypertensive rats

1. Stroke-prone spontaneously hypertensive rats (SHRSP) fed a high salt diet rapidly develop proteinuria, a marker of renal damage. We have recently shown that supplementing the diet of these rats with pure omega-3 fatty acids can inhibit the development of proteinuria. The aim of the present study was to examine the underlying renal pathology and to see whether a similar benefit could be obtained with fish oil or canola oil. 2. Diets containing sodium (2% by weight) and 5% fish oil, canola oil, olive oil or safflower oil (the latter two serving as controls) were fed to groups of eight young SHRSP and the development of hypertension and proteinuria was monitored. After 9 weeks, rats were killed and their kidneys were taken for histological examination and fatty acid analysis. Urinary protein was characterized electrophoretically. 3. Patterns of protein excretion were consistent with the appearance of pathological changes in both glomeruli and tubules. Fish oil inhibited the elevation of blood pressure, prevented the development of proteinuria and minimized histological lesions. However, in rats fed canola oil, hypertension and renal damage were equally severe as in rats fed olive or safflower oil. 4. The prevention of hypertensive renal damage by dietary fish oil may be attributable to the increased incorporation of long-chain omega-3 fatty acids in the kidney.

Transforming growth factor alpha and epidermal growth factor expression in experimental murine polycystic kidney disease

Cystic change in polycystic kidney disease (PKD) is associated with epithelial hyperplasia, altered fluid and electrolyte transport, and de-differentiation of renal tubular epithelium. The role of polypeptide growth factors as potential modulators of cystic change remains an area of controversy. In this study, the expression of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) were assessed by immunohistochemistry and image analysis in glucocorticoid-induced PKD in the newborn mouse. Newborn C3H mice received either 200 mg/kg methylprednisolone acetate (MPA) or 0.9% saline as a control. EGF expression was not detected in significant quantities in either MPA-treated or control animals. TGF alpha, however, was expressed in immature control kidney in a largely basolateral distribution. Expression increased significantly in association with cystic change in MPA-treated animals and was localized to the apical cell surface, implying altered polarity of secretion. There is no evidence that EGF is a mitogen in this early developmental model of PKD. TGF alpha, however, may be an important mediator of cystic change in immature or de-differentiated renal tubular epithelium.

Deregulation of cell survival in cystic and dysplastic renal development

Various aberrations of cell biology have been reported in polycystic kidney diseases and in cystic renal dysplasias. A common theme in these disorders is failure of maturation of renal cells which superficially resemble embryonic tissue. Apoptosis is a feature of normal murine nephrogenesis, where it has been implicated in morphogenesis, and fulminant apoptosis occurs in the small, cystic kidneys which develop in mice with null mutations of bcl-2. Therefore, we examined the location and extent of apoptosis in pre- and postnatal samples of human polycystic and dysplastic kidney diseases using propidium iodide staining, in situ end-labeling and electron microscopy. In dysplastic kidneys cell death was prominent in undifferentiated cells around dysplastic tubules and was occasionally found in cystic epithelia. The incidence of apoptosis was significantly greater than in normal controls of comparable age both pre- and postnatally. In the polycystic kidneys there was widespread apoptosis in the interstitium around undilated tubules distant from cysts, in undilated tubules between cysts and in cystic epithelia. The level of apoptosis compared to controls was significantly increased postnatally. A similar increase of cell death was also noted in the early and late stages of renal disease in the polycystic cpk/cpk mouse model. We speculate that deregulation of cell survival in these kidneys may reflect incomplete tissue maturation, and may contribute to the progressive destruction of functional kidney tissue in polycystic kidneys and the spontaneous involution reported in cystic dysplastic kidneys.

Animal models of polycystic kidney disease

Polycystic kidney disease (PKD) is one of the most prevalent causes of heritable renal failure. The disease is characterized by the occurrence of numerous fluid-filled cysts within the parenchyma of kidney. The cysts are epithelial in origin and expand in size, leading to crowding of normal kidney tissue. Ultimately, there is gross enlargement of the kidneys with loss of normal functions, and death usually occurs because of complications related to renal failure. Animal models of polycystic kidney disease are proving to be extremely useful for studying the molecular basis of renal cyst formation and for the isolation of genes carrying the mutations. This article describes the various animal models of polycystic kidney disease, spontaneously and experimentally derived, that have recently been identified.

Tyrosine kinase activity of the EGF receptor in murine metanephric organ culture

Epidermal growth factor (EGF) and its fetal form, transforming growth factor alpha (TGF-alpha) are renal mitogens which induce epithelial hyperplasia, proximal tubular cyst formation (TC), and accelerated distal nephron differentiation in metanephric organ culture. To delineate the intracellular mechanisms mediating these growth factor effects, we studied the specific role of the epidermal growth factor receptor (EGF-R), the common receptor for both ligands, as an activated tyrosine kinase in TC formation and nephrogenesis. Fetal murine metanephric explants were incubated for 120 hours in control, and EGF (15 ng/ml)/TGF-alpha (10 ng/ml) supplemented medium with and without EGF-R blocking monoclonal antibody (50 mg/ml), or tyrosine kinase inhibitor. EGF-R tyrosine kinase inhibition was achieved by incubation with a synthetic tyrphostin (TP B42) (0.1 microM) or genestein (5.5 micrograms/ml). The following parameters were assessed: (a) segment-specific nephron development using morphometry and immunohistology; (b) tubular epithelial hyperplasia by protein content and BrdU uptake; and (c) TC formation by morphometric cystic index. Both growth factors produced hyperplastic proximal TC, significantly increased explant growth, and significantly increased distal nephron differentiation. Inhibiting the ligand-EGF-R interaction with EGF-R blocking monoclonal antibody abolished all growth factor-induced effects and resulted in increased amounts of undifferentiated mesenchyme and decreased distal nephron differentiation. Inhibition of EGF-R tyrosine kinase activity with either Tyrphostin B42 or genestein blocked TC formation and produced nodular blastemal hyperplasia and decreased distal nephron differentiation.

Epidermal growth factor precursor is present in a variety of human renal cyst fluids

Progressive human renal cystic diseases are characterized by proliferation of the epithelial cells lining the cyst. The kidney synthesizes epidermal growth factor and its presence in renal cyst fluid might contribute to renal epithelial cell proliferation. We screened autosomal dominant polycystic kidney disease, acquired renal cystic disease, the von Hippel-Lindau syndrome, multilocular cystic nephroma, multicystic dysplastic kidney disease and simple cyst fluids for the presence of epidermal growth factor by radioreceptor assay, specific radioimmunoassay, immunoprecipitation and immunoblotting. Multiple epidermal growth factor immunoreactive species of approximately 180 kD. and lower molecular weights were present in almost all cyst fluids examined, suggesting endogenous synthesis and limited proteolysis of epidermal growth factor precursor protein in cyst fluid. Tamm-Horsfall protein was detected by enzyme-linked immunosorbent assay in most cysts (for example 55 of 59 autosomal dominant polycystic kidney disease samples). The majority of simple and autosomal dominant polycystic kidney disease renal cysts contained high sodium ion concentration, epidermal growth factor precursor protein and Tamm-Horsfall protein, characteristic of the early thick ascending limb. Rather than the mere presence of epidermal growth factor in renal cyst fluids, increased sensitivity to epidermal growth factor or other mitogens present in renal cyst fluid may be pathogenic in progressive renal cystic disease.

Impaired tubulogenesis of cyst-derived cells from autosomal dominant polycystic kidneys

Under appropriate growth factor or hormonal influence, renal epithelial cells cultured in collagen gels form branching tubular elements, reminiscent of metanephric tubulogenesis. This study evaluates the phenotypic characteristics of normal human renal epithelial cells (NK) and epithelial cells from cysts of autosomal dominant polycystic kidneys (ADPKD) grown in collagen gels under the influence of the growth factors (GFs) epidermal (EGF), transforming (TGF-alpha), hepatocyte (HGF) and fibroblast (FGF). All GFs induced cell proliferation with the formation of cell aggregates in both group of cells, however, NK cells exhibited proliferation at a much higher rate compared to ADPKD. All GFs induced formation of branching tubular elements with cell-polarity characteristics in NK cells. Such organized tubular elements were essentially absent in ADPKD cell cultures. Both NK and ADPKD cells expressed cell adhesion and matrix macromolecules. Expression of heparan sulfate-proteoglycan was diminished but enhanced for fibronectin in ADPKD cells. Receptor expression for EGF and FGF was similar. These findings indicate an impairment in tubulogenesis of ADPKD cells, perhaps related to the aberrant morphogenetic cell aggregation. Alternatively, this differentiation arrest may relate to abnormal biosynthesis of secretory matrix glycoproteins rather than those expressed on the plasmalemma.

Epidermal growth factor receptor expression is abnormal in murine polycystic kidney

Renal tubular cyst formation and progressive enlargement in autosomal recessive polycystic kidney disease (ARPKD) are mediated by increased epithelial cell proliferation and altered transtubular fluid transport. Epidermal growth factor (EGF)-like peptides have been proposed to play roles in normal nephrogenesis and cystic tubular mitogenesis. Therefore, renal expression of EGF receptor (EGFR) protein and mRNA was examined in an animal model for ARPKD, the C57BL/6Jcpk/cpk (CPK) mouse. Both quantitative and qualitative abnormalities of EGFR expression were demonstrated. While both control and cystic proximal tubules, as well as control collecting tubules, demonstrated exclusive basalateral EGFR protein expression, cystic collecting tubules exhibited significant apical-lateral receptor localization. During nephrogenesis, EGFR protein expression was elevated in CPK renal tissue when compared to developmentally staged controls. Control and CPK kidneys expressed the same species of EGFR mRNA. Levels increased with developmental age, but were significantly higher at each stage of development in CPK kidneys. Overexpression of both EGFR protein and mRNA in CPK mice suggests altered control of EGFR protein and/or gene expression. EGFR mislocalization and overexpression may be mechanisms whereby the EGF-like factors in cyst fluid stimulate cystogenesis through an autocrine-paracrine cycle in ARPKD.

Polycystic kidney disease--a truly pediatric problem

Polycystic kidney disease (PKD) represents the most common inherited cause of chronic renal failure. PKD is a relatively uncommon cause of chronic renal failure or mortality in childhood and adolescence, but is nevertheless often responsible for symptoms of renal disease. Current research into the pathogenesis of PKD suggests that disturbance of the normal regulation of growth and development of tubular epithelium is intrinsic to cyst formation and growth. Features of cystic epithelium that are analogous to earlier stages of renal development include altered composition of the extracellular matrix, abnormal cell proliferation, and the persistence of a secretory pattern of fluid and electrolyte transport. The potential for early diagnosis and intervention in PKD makes it an area of great interest to the pediatric nephrologist. Animal and in vitro studies have achieved modification of cyst growth by reduction of dietary protein, use of amiloride and its analogs, antagonism of the epidermal growth factor receptor system, anti-inflammatory therapy, and most recently with the use of taxol, an agent that inhibits microtubule assembly. PKD may represent an area in which childhood diagnosis and intervention will have a significant impact on the prevalence of chronic renal failure in adult life.

Epidermal growth factor and endothelin in cyst fluid from autosomal dominant polycystic kidney disease cases: possible evidence of heterogeneity in cystogenesis

We determined the concentrations of immunoreactive epidermal growth factor (EGF), endothelin (ET), and cyclic adenosine monophosphate (cAMP) in cyst fluid from 10 nondialyzed patients with autosomal dominant polycystic kidney disease (ADPKD). The concentrations of ET and cAMP in low-sodium cyst fluid (cyst sodium concentration < 100 mEq/L) were significantly increased compared with those in high-sodium cyst fluid (cyst sodium concentration > or = 100 mEq/L), but the concentration of EGF did not differ between the two. There was no relationship between cyst fluid volume and EGF, ET, cAMP values in ADPKD cases. Significant variations of cyst fluid concentrations of EGF, ET, and cAMP were observed among the patients. However, the differences of these variables between the right and left kidney of the individual subjects were unremarkable. Serum levels of creatinine and urea nitrogen showed significant negative correlations with EGF, but not with ET and cAMP. The present data demonstrate the differences in cytokine activity among cysts in ADPKD cases, suggesting the heterogeneity of cystogenesis along the tubular segments in this particular disease.

Polycystic renal disease

Renal cystic disease is a relatively common disorder whose development and progression currently appear to be due to an interaction between an abnormal basement membrane matrix, a potentially immature, hyperproliferative epithelium, and an abnormal epithelial secretory apparatus. RCC risk in cystic kidneys is the most controversial sequela of PKD. Currently, RCC risk in ESRD patients appears to be close to that present in the general population and only coincidentally associated with renal cysts. Screening of all ESRD patients for RCC and prophylactic native nephrectomy in dialysis and transplant patients does not seem to be indicated.

Altered growth factor expression during toxic proximal tubular necrosis and regeneration

Growth factor expression was investigated during the regenerative response after toxic proximal tubular necrosis. Therefore, gentamicin was administered to rats to achieve an experimental model, characterized by the appearance of segment-specific proximal tubular necrosis, that is followed by a regenerative response leading to functional and morphological recovery in a limited time. Four days after the administration of the highest dose, serum creatinine rose to a mean value of 5.8 mg/dl and returned to normal values ten days after the treatment. The S1-S2 segment of the proximal tubules in the cortex became clearly affected by severe toxic necrosis one day after the treatment, while maximal necrosis was observed at days 2 to 4. Only minor injuries were noticed in the other renal compartments. The proliferative response started in the interstitial cells first. The major proliferative wave was localized in the convoluted part of the proximal tubules at days 6 to 8, although proliferation was also prominent among non-proximal tubular cells. A profound interstitial infiltration of leukocytes, including macrophages and T lymphocytes, was observed. Ten days after the treatment the functional and morphological recovery were completed. Slot blot hybridization revealed a decreased EGF and IGF-I mRNA expression from the start of the observation period. While IGF-I mRNA had regained its normal expression at day 10, EGF mRNA was still below control levels. The PDGF-B transcript became more abundant towards the end of our observation. No major changes in the expression of TGF-alpha, TGF-beta 1 and c-fos were detected. Renal EGF-immunoreactivity disappeared from the luminal plasma membrane of the distal tubular cells analogous to the results obtained at the messenger level. However, EGF-staining was lost in the cortex first, hence a topographical association between the loss of EGF-immunoreactivity in the distal tubules and the observed necrotic lesions in the proximal tubules was found. Immunoreactive EGF was never observed in proximal tubular cells from normal, injured or regenerating rat kidneys. We conclude that in this experimental rat model, EGF and IGF-I mRNA expression is decreased during the regenerative response upon severe toxic tubular necrosis. No evidence for a participation of EGF or IGF-I of renal origin in the recovery of the kidney is found.

Normal and abnormal nephrogenesis

During the past decade, exciting advances in the fields of cell and molecular biology have provided new insight into the processes of normal and abnormal nephron induction and renal morphogenesis. Although the specific molecular signals that control renal mesenchymal-epithelium inductive interaction remain unknown, recent data suggest that postinductive nephrogenesis may be regulated by the overall balance of a number of local autocrine and/or paracrine growth factor systems. Alterations in the critical balance of regulatory factors might produce a variety of hypoplastic and dysplastic nephropathies or hyperplastic lesions such as tubular cysts. Additional studies demonstrate that extracellular matrix components and cell surface integrins have important regulatory roles in ureteric bud development and branching. Perturbations in matrix or integrin expression due to altered gene activity or toxin exposure would be expected to produce a variety of renal abnormalities ranging from failure of nephron induction (aplasia) to focal disruptions of differentiation (segmental dysplasia). Finally, several groups of genes encoding transcriptional regulatory proteins have been identified that appear to regulate aspects of cell proliferation, pattern formation, and segment-specific differentiation during normal and abnormal nephrogenesis. Future studies will elucidate the roles that specific genes and proteins play in renal development and will ultimately reveal the manner in which their dysregulation or dysfunction causes a variety of developmental renal disorders.

Gastrointestinal complications of gastrocystoplasty

The cases are reported of five children with chronic renal failure who underwent gastrocystoplasty for a variety of urological disorders. Gastrocystoplasty comprises the transplantation of a vascularised segment of stomach to the bladder to form an augmented neobladder. The patients had gastrointestinal complications after the operation, including considerable weight loss in all five patients, accompanied by marked failure to thrive in four of the five patients, and food aversion, feeding intolerance, dumping syndrome, delayed gastric emptying, and oesophagitis in two patients. Three of the five patients developed severe abdominal pain and haemorrhagic cystitis secondary to gastric acid secretion in the neobladder from the transplanted gastric pedicle. Nutritional and pharmacological interventions were used to manage the gastrointestinal problems. Explanations are offered for the pathophysiology of the observed complications of gastrocystoplasty. It is believed that the use of this procedure in infants and children, particularly those with chronic renal failure and uraemia, warrants caution until successful long term follow up and experience with this procedure have been reported.

In vivo formation of polyphosphoinositide isomers and association with progression of murine polycystic kidney disease

Polyphosphoinositide isomers have been demonstrated to be important mediators of cell proliferation in vitro. The present study demonstrates, for the first time, the in vivo formation of the novel isomer, phosphatidylinositol(3)phosphate, in the kidney and liver of intact animals following intraperitoneal administration of [3H]myo-inositol. The formation of renal [3H]phosphatidylinositol(3)phosphate relative to total [3H]phosphatidylinositol-phosphate was positively correlated with cyst proliferation and renal enlargement in a murine model of polycystic kidney disease. Furthermore, despite no difference in the formation of renal [3H]phosphatidylinositol(4)phosphate, a markedly lower accumulation (by 48%) of [3H]phosphatidylinositol(4,5)bisphosphate was observed in the diseased animals as compared to controls. These results indicate that further studies on the in vivo formation of specific polyphosphoinositide isomers in disease states characterized by abnormal growth and oncogene expression are warranted.