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

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is a rare disorder and one of the most severe forms of polycystic kidney disease, leading to end-stage renal disease (ESRD) in childhood. PKHD1 is the gene that is responsible for the vast majority of ARPKD. However, some cases have been related to a new gene that was recently identified (DZIP1L gene), as well as several ciliary genes that can mimic a ARPKD-like phenotypic spectrum. In addition, a number of molecular pathways involved in the ARPKD pathogenesis and progression were elucidated using cellular and animal models. However, the function of the ARPKD proteins and the molecular mechanism of the disease currently remain incompletely understood. Here, we review the clinics, treatment, genetics, and molecular basis of ARPKD, highlighting the most recent findings in the field.

Pharmacokinetic Evaluation of Nimotuzumab in Patients With Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by an overexpression and mislocalization of epidermal growth factor receptor (EGFR) to the apical membranes of cystic epithelial cells. Nimotuzumab is a humanized antibody that recognizes an extracellular domain III of human EGFR. The aim of this study was to assess the pharmacokinetic behavior of nimotuzumab in patients with ADPKD given as a single dose. A phase I, single-center, and noncontrolled open clinical study was conducted. Five patients were enrolled at each of the following fixed-dose levels: 50, 100, 200, and 400 mg. Intravenous continuous infusions of nimotuzumab were administered every 14 days during a year, except the first administration, when blood samples were drawn during 28 days for pharmacokinetic assessments. Subjects were closely monitored during the trial and at completion of the administration of nimotuzumab, including the anti-idiotypic response. For the first time, nimotuzumab was used for treating a nononcological disease. The administration of nimotuzumab showed dose-dependent kinetics. Nimotuzumab does not develop anti-idiotypic response against the murine portion present in the hypervariable region of the antibody present in the serum of the patients treated. No significant differences were found in the systemic clearance between the 100- and 400-mg dose, which indicates that the optimal biological dose is in this range of dose.

Emerging Therapies for Childhood Polycystic Kidney Disease

Cystic kidney diseases comprise a varied collection of hereditary disorders, where renal cysts comprise a major element of their pleiotropic phenotype. In pediatric patients, the term polycystic kidney disease (PKD) commonly refers to two specific hereditary diseases, autosomal recessive polycystic kidney disease (ARPKD) and autosomal dominant polycystic kidney disease (ADPKD). Remarkable progress has been made in understanding the complex molecular and cellular mechanisms of renal cyst formation in ARPKD and ADPKD. One of the most important discoveries is that both the genes and proteins products of ARPKD and ADPKD interact in a complex network of genetic and functional interactions. These interactions and the shared phenotypic abnormalities of ARPKD and ADPKD, the "cystic phenotypes" suggest that many of the therapies developed and tested for ADPKD may be effective in ARPKD as well. Successful therapeutic interventions for childhood PKD will, therefore, be guided by knowledge of these molecular interactions, as well as a number of clinical parameters, such as the stage of the disease and the rate of disease progression.

The epidermal growth factor receptor pathway in chronic kidney diseases

The epidermal growth factor receptor (EGFR) pathway has a critical role in renal development, tissue repair and electrolyte handling. Numerous studies have reported an association between dysregulation of this pathway and the initiation and progression of various chronic kidney diseases such as diabetic nephropathy, chronic allograft nephropathy and polycystic kidney disease through the promotion of renal cell proliferation, fibrosis and inflammation. In the oncological setting, compounds that target the EGFR pathway are already in clinical use or have been evaluated in clinical trials; in the renal setting, therapeutic interventions targeting this pathway by decreasing ligand availability with disintegrin and metalloproteinase inhibitors or with ligand-neutralizing antibodies, or by inhibiting receptor activation with tyrosine kinase inhibitors or monoclonal antibodies are only just starting to be explored in animal models of chronic kidney disease and in patients with autosomal dominant polycystic kidney disease. In this Review we focus on the role of the EGFR signalling pathway in the kidney under physiological conditions and during the pathophysiology of chronic kidney diseases and explore the clinical potential of interventions in this pathway to treat chronic renal diseases.

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.

Epidermal growth factor-induced proliferation of collecting duct cells from Oak Ridge polycystic kidney mice involves activation of Na+/H+ exchanger

Epidermal growth factor (EGF) is linked to the pathogenesis of polycystic kidney disease (PKD). We explored signaling pathways activated by EGF in orpk cilia (-) collecting duct cell line derived from a mouse model of PKD (hypomorph of the Tg737/Ift88 gene) with severely stunted cilia, and in a control orpk cilia (+) cell line with normal cilia. RT-PCR demonstrated mRNAs for EGF receptor subunits ErbB1, ErbB2, ErbB3, ErbB4, and mRNAs for Na(+)/H(+) exchangers (NHE), NHE-1, NHE-2, NHE-3, NHE-4, and NHE-5 in both cell lines. EGF stimulated proton efflux in both cell lines. This effect was significantly attenuated by MIA, 5-(n-methyl-N-isobutyl) amiloride, a selective inhibitor of NHE-1 and NHE-2, and orpk cilia (-) cells were more sensitive to MIA than control cells (P < 0.01). EGF significantly induced extracellular signal-regulated kinase (ERK) phosphorylation in both cilia (+) and cilia (-) cells (63.3 and 123.6%, respectively), but the effect was more pronounced in orpk cilia (-) cells (P < 0.01). MIA significantly attenuated EGF-induced ERK phosphorylation only in orpk cilia (-) cells (P < 0.01). EGF increased proliferation of orpk cilia (+) cells and orpk cilia (-) cells, respectively, and MIA at 1-5 μM attenuated EGF-induced proliferation in orpk cilia (-) cells without affecting proliferation of orpk cilia (+) cells. EGF-induced proliferation of both cell lines was significantly decreased by the EGFR tyrosine kinase inhibitor AG1478 and MEK inhibitor PD98059. These results suggest that EGF exerts mitogenic effects in the orpk cilia (-) cells via activation of growth-associated amiloride-sensitive NHEs and ERK.

Signal transduction in podocytes--spotlight on receptor tyrosine kinases

The mammalian kidney filtration barrier is a complex multicellular, multicomponent structure that maintains homeostasis by regulating electrolytes, acid-base balance, and blood pressure (via maintenance of salt and water balance). To perform these multiple functions, podocytes--an important component of the filtration apparatus--must process a series of intercellular signals. Integrating these signals with diverse cellular responses enables a coordinated response to various conditions. Although mature podocytes are terminally differentiated and cannot proliferate, they are able to respond to growth factors. It is possible that the initial response of podocytes to growth factors is beneficial and protective, and might include the induction of hypertrophic cell growth. However, extended and/or uncontrolled growth factor signalling might be maladaptive and could result in the induction of apoptosis and podocyte loss. Growth factors signal via the activation of receptor tyrosine kinases (RTKs) on their target cells and around a quarter of the 58 RTK family members that are encoded in the human genome have been identified in podocytes. Pharmacological inhibitors of many RTKs exist and are currently used in experimental and clinical cancer therapy. The identification of pathological RTK-mediated signal transduction pathways in podocytes could provide a starting point for the development of novel therapies for glomerular disorders.

Compensatory renal growth in uninephrectomized immature rats: proliferative activity and epidermal growth factor

Compensatory response to uninephrectomy in immature animals is stronger compared with that in adult ones and the response is due mainly to renal cell proliferation. The present study explored to show the growth pattern of the remaining kidney immediately after uninephrectomy in immature rats with special reference to proliferating activity and epidermal growth factor (EGF). Immunolocalizations of proliferating cell nuclear antigen (PCNA) and EGF in immature rat kidney were examined during the first three days after uninephrectomy. Semi-quantitative analysis of the expression of preproEGF mRNA was performed. One day after the operation, the PCNA positive cell ratios in the glomeruli and the proximal tubules were significantly higher in unilaterally nephrectomized (UNx) rats than in sham-operated (Sham) rats. In UNx and Sham rats, the proximal and distal tubular cells showed positive reactions to EGF antibody. The positive reaction of proximal tubules to EGF antibody was weaker in UNx than in Sham rats 1 day after the operation, while the degree of reactivity was not different between UNx and Sham rats 3 days after the operation. The level of expression of preproEGF mRNA in the kidney was significantly lower in UNx than in Sham rats 1 day after the operation. These results indicate that unilateral nephrectomy in immature rats causes increased proliferative activity and decreased expression of EGF in the remaining kidney during the early period of compensatory renal growth.

Epidermal growth factor activates Na(+/)H(+) exchanger in podocytes through a mechanism that involves Janus kinase and calmodulin

Sodium-proton exchanger type 1 (NHE-1) is ubiquitously expressed, is activated by numerous growth factors, and plays significant roles in regulating intracellular pH and cellular volume, proliferation and cytoskeleton. Despite its importance, little is known about its regulation in renal glomerular podocytes. In the current work, we studied the regulation of NHE-1 activity by the epidermal growth factor receptor (EGFR) in cultured podocytes. RT-PCR demonstrated mRNAs for NHE-1 and NHE-2 in differentiated podocytes, as well as for EGFR subunits EGFR/ErbB1, Erb3, and ErbB4. EGF induced concentration-dependent increases in proton efflux in renal podocytes as assessed using a Cytosensor microphysiometer, were diminished in the presence of 5-(N-methyl-N-isobutyl) amiloride or in a sodium-free solution. Furthermore, pharmacological inhibitors of Janus kinase (Jak2) and calmodulin (CaM) attenuated EGF-induced NHE-1 activity. Co-immunoprecipitation studies determined that EGF induced formation of complexes between Jak2 and CaM, as well as between CaM and NHE-1. In addition, EGF increased levels of tyrosine phosphorylation of Jak2 and CaM. The EGFR kinase inhibitor, AG1478, blocked activation of NHE-1, but did not block EGF-induced phosphorylation of Jak2 or CaM. These results suggest that EGF induces NHE-1 activity in podocytes through two pathways: (1) EGF-->EGFR-->Jak2 activation (independent of EGFR tyrosine kinase activity)-->tyrosine phosphorylation of CaM-->CaM binding to NHE-1-->conformational change of NHE-1-->activation of NHE-1; and (2) EGF-->EGFR-->EGFR kinase activation-->association of CaM with NHE-1 (independent of Jak2)-->conformational change of NHE-1-->activation of NHE-1.

Mitotic activation of Akt signalling pathway in Han:SPRD rats with polycystic kidney disease

AIM

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by an imbalance between tubular epithelial cell proliferation and apoptosis. We have previously shown that the mammalian target of rapamycin (mTOR) signalling pathway is aberrantly activated in the cystic kidneys of Han:SPRD rats with ADPKD. Because the Akt kinase is an upstream regulator of mTOR, we hypothesized that the activity of Akt could be enhanced in the kidneys of Han:SPRD rats.

METHODS

Reverse transcription-polymerase chain reaction, western blot, enzyme-linked immunosorbent assay and immunohistochemistry were used to analyse Akt expression in rat polycystic kidneys.

RESULTS

Wild-type (+/+) and heterozygous (Cy/+) Han:SPRD rats showed constitutive expression of Akt-1, -2 and -3 mRNA by reverse transcription-polymerase chain reaction analysis with no significant difference between Cy/+ and +/+ kidneys. Western blotting and enzyme-linked immunosorbent assay showed a significant increase in phosphorylated Akt in Cy/+ compared with +/+ kidneys. The pattern of immunoreactivity for phosphorylated Akt in kidney sections was the same in +/+ and in Cy/+ rats, with very low levels in interphase cells, but extremely bright signals in mitotic cells, beginning with the onset of the prophase. The in vivo incorporation of bromo-deoxyuridine revealed approximately a ninefold higher rate of proliferation in Cy/+ cyst epithelia compared with normal tubule epithelia in +/+ rats, while the expression of the cell cycle marker Ki67 revealed approximately a sixfold higher rate of proliferation. In summary, enhanced phosphorylation of Akt can be demonstrated in Cy/+ kidneys which correlates with a markedly elevated proliferation rate of epithelial cells in cysts. Mitotic but not resting cells display strong phosphorylation of Akt.

CONCLUSION

Because Akt is a proximal target of mTOR, its inhibition with specific antagonists could be useful to prevent or halt cystogenesis in ADPKD.

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.

Branching morphogenesis of the ureteric epithelium during kidney development is coordinated by the opposing functions of GDNF and Sprouty1

Branching of ureteric bud-derived epithelial tubes is a key morphogenetic process that shapes development of the kidney. Glial cell line-derived neurotrophic factor (GDNF) initiates ureteric bud formation and promotes subsequent branching morphogenesis. Exactly how GDNF coordinates branching morphogenesis is unclear. Here we show that the absence of the receptor tyrosine kinase antagonist Sprouty1 (Spry1) results in irregular branching morphogenesis characterized by both increased number and size of ureteric bud tips. Deletion of Spry1 specifically in the epithelium is associated with increased epithelial Wnt11 expression as well as increased mesenchymal Gdnf expression. We propose that Spry1 regulates a Gdnf/Ret/Wnt11-positive feedback loop that coordinates mesenchymal-epithelial dialogue during branching morphogenesis. Genetic experiments indicate that the positive (GDNF) and inhibitory (Sprouty1) signals have to be finely balanced throughout renal development to prevent hypoplasia or cystic hyperplasia. Epithelial cysts develop in Spry1-deficient kidneys that share several molecular characteristics with those observed in human disease, suggesting that Spry1 null mice may be useful animal models for cystic hyperplasia.

Renal cystic disease: new insights for the clinician

This article cannot comprehensively cover the enormous strides made in defining the molecular and cellular basis of renal cystic diseases over the last decade. Therefore, it provides a brief overview and categorization of inherited, developmental, and acquired renal cystic diseases, providing a relevant, up-to-date bibliography as well as a useful list of informative Internet Web sites. Its major focus is the translational biology of polycystic kidney disease. It demonstrates how emerging molecular and cellular knowledge of the pathophysiology of particular diseases such as autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ADPKD) can translate into innovative therapeutic insights.

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.

Molecular and cellular pathophysiology of autosomal recessive polycystic kidney disease (ARPKD)

Autosomal recessive polycystic kidney disease (ARPKD) belongs to a group of congenital hepatorenal fibrocystic syndromes characterized by dual renal and hepatic involvement of variable severity. Despite the wide clinical spectrum of ARPKD (MIM 263200), genetic linkage studies indicate that mutations at a single locus, PKHD1 (polycystic kidney and hepatic disease 1), located on human chromosome region 6p21.1-p12, are responsible for all phenotypes of ARPKD. Identification of cystic disease genes and their encoded proteins has provided investigators with critical tools to begin to unravel the molecular and cellular mechanisms of PKD. PKD cystic epithelia share common phenotypic abnormalities despite the different genetic mutations that underlie the disease. Recent studies have shown that many cyst-causing proteins are expressed in multimeric complexes at distinct subcellular locations within epithelia. This co-expression of cystoproteins suggests that cyst formation, regardless of the underlying disease gene, results from perturbations in convergent and/or integrated signal transduction pathways. To date, no specific therapies are in clinical use for ameliorating cyst growth in ARPKD. However, studies noted in this review suggest that therapeutic targeting of the cAMP and epidermal growth factor receptor (EGFR)-axis abnormalities in cystic epithelia may translate into effective therapies for ARPKD and, by analogy, autosomal dominant polycystic kidney disease (ADPKD). A particularly promising approach appears to be the targeting of downstream intermediates of both the cAMP and EGFR axis. This review focuses on ARPKD and presents a concise summary of the current understanding of the molecular genetics and cellular pathophysiology of this disease. It also highlights phenotypic and mechanistic similarities between ARPKD and ADPKD.

Androgen Receptor Pathway in Rats with Autosomal Dominant Polycystic Kidney Disease

Androgens have been implicated in mediating disease escalation in autosomal dominant polycystic kidney disease (ADPKD). Dihydrotestosterone (DHT), an agonist, and flutamide (FLT), an antagonist, were administered to Han:SPRD rats with ADPKD, and the role of androgen receptor (AR) abundance and activation on the enlargement and function of cystic kidneys was evaluated. Renal AR abundance determined by immunoblots in 8- to 10-wk-old Cy/+ male rats was naturally increased four-fold above that of littermate +/+ controls. In male Cy/+, castration decreased AR abundance below control +/+ by -89.4%, and AR expression within cyst mural epithelial cells was strikingly decreased. Castration of Cy/+ male rats also reduced the usual increases in kidney weight by -49.7%, kidney cyst area by -34.0%, and serum urea nitrogen by -72.8%; these indices were restored to precastration levels by DHT. In Cy/+ male rats, FLT administration reduced the increase in kidney weight by -27.6% and serum urea nitrogen by -53.7% and decreased the increment in AR expression by -84.2% in comparison with untreated +/+ controls. There was no effect of FLT in female rats. Immunoblot expression of phospho-extracellular signal-regulated kinase 1/2 (P-ERK) and B-Raf, key intermediates in the mitogen-activated protein kinase pathway that are abnormally elevated in Cy/+, was unaffected by castration and/or administration of DHT or FLT. AR was not expressed in renal epithelial cell nuclei of androgen-deficient rats but was displayed in most tubule and mural cyst cell nuclei of androgen-replete rats. In androgen-deficient Cy/+, 80.6% of renal epithelial cells that had entered the cell cycle (proliferating cell nuclear antigen positive) also expressed P-ERK. In androgen-replete rats, proliferating cell nuclear antigen-positive cells co-expressed AR (12.7%), P-ERK (36.4%), and P-ERK + AR (45.0%); 5.9% were probably stimulated by other mitogenic mechanisms. It is concluded that androgens potentiate renal cell proliferation and cyst enlargement through ERK1/2-dependent and ERK1/2-independent signaling mechanisms in Han:SPRD. It is suggested that the basal rate of cell proliferation is determined by ERK1/2 signaling to a major extent and that androgens have additive effects.

p38 kinase-mediated transactivation of the epidermal growth factor receptor is required for dedifferentiation of renal epithelial cells after oxidant injury

Renal proximal tubular cell (RPTC) dedifferentiation is thought to be a prerequisite for regenerative proliferation and migration after renal injury. However, the specific mediators and the mechanisms that regulate RPTC dedifferentiation have not been elucidated. Because epidermal growth factor (EGF) receptor activity is required for recovery from acute renal failure, we examined the role of the EGF receptor in dedifferentiation and the mechanisms of EGF receptor transactivation in primary cultures of RPTCs after oxidant injury. Exposure of confluent RPTCs to H2O2 resulted in 40% cell death, and surviving RPTCs acquired a dedifferentiated phenotype (e.g. elongated morphology and vimetin expression). The EGF receptor, p38, Src, and MKK3 were activated after oxidant injury and inhibition of the EGF receptor or p38 with specific inhibitors (AG1478 and SB203580, respectively) blocked RPTC dedifferentiation. Treatment with SB203580 or adenoviral overexpression of dominant negative p38alpha or its upstream activator, MKK3, inhibited EGF receptor phosphorylation induced by oxidant injury, whereas AG1478 had no effect on p38 phosphorylation. Inhibition of Src with 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine (PP1) blocked MKK3 and p38 activation, and inhibition of MKK3 blocked p38 activation. In addition, inactivation of Src, MKK3, p38, or the EGF receptor blocked tyrosine phosphorylation of beta-catenin, a key signaling intermediate that is involved in the epithelial-mesenchymal transition and vimentin expression. These results reveal that p38 mediates EGF receptor activation after oxidant injury; that Src activates MMK3, which, in turn, activates p38; and that the EGF receptor signaling pathway plays a critical role in RPTC dedifferentiation.

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.

Cloning and characterization of a novel gene promoting ureteric bud branching in the metanephros

BACKGROUND

The ureteric buds and metanephric mesenchymal cells reciprocally induce each other's maturation during kidney development, and implicated transcription factors, secreted growth factors, and cell surface signaling peptides are critical regulators of renal branching morphogenesis. Protein kinase C (PKC) is a key enzyme in the signal transduction mechanisms in various biologic processes, including development, because it regulates growth and differentiation. Inhibition of PKC by the sphingolipid product ceramide interferes with nephron formation in the developing kidney, but the molecule that controls ureteric bud branching downstream of PKC is still unknown.

METHODS

Differential display polymerase chain reaction (PCR) of metanephroi cultured with a PKC activator and inhibitor was performed. We also examined the role of a novel gene in kidney development with organ culture system.

RESULTS

A novel gene encoding a 759 bp mRNA was identified, and we named it metanephros-derived tubulogenic factor (MTF)/L47. Inhibition of MTF with antisense oligonucleotide impaired ureteric bud branching by cultured metanephroi, and addition of recombinant MTF protein promoted ureteric bud branching in cultured metanephroi and increased cell proliferation.

CONCLUSION

We identified a novel molecule in developing kidney that is capable of modulating ureteric bud branching and kidney differentiation.

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.

Importance of Functional EGF Receptors in Recovery from Acute Nephrotoxic Injury

ABSTRACT. Previous studies have demonstrated increased renal expression of EGF receptor (EGFR) and EGFR ligands in response to acute toxic or ischemic renal tubular injury and have indicated that exogenous administration of EGF accelerates recovery from such injury. However, no studies to date have proved definitively an essential role for EGFR-mediated responses in regeneration after tubule injury. To this end, waved-2 (wa-2) mice, which contain a point mutation in EGFR that reduces receptor tyrosine kinase activity by >90%, were studied. These mice have a mild phenotype (wavy coat, curly whiskers, and runted stature) and normally developed kidneys. Acute nephrotoxic injury was induced in wa-2 and wild-type mice with HgCl2. One day after HgCl2 injection, functional renal compromise was comparable in wild-type and wa-2 mice. However, the rates of recovery of serum blood urea nitrogen and creatinine levels were markedly slower in wa-2 mice. Histologic evidence of tubular injury also was more severe and persisted longer in wa-2 mice. Furthermore, their kidneys demonstrated reduced levels of DNA synthesis and increased TdT-mediated dUTP nick-end labeling staining. These studies indicate that functional EGFR activity is an essential component of the kidney’s ability to recover from acute injury and that EGFR may regulate genes involved in growth, repair, and cell survival in the kidney.

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.

Decreased amiloride-sensitive Na+ absorption in collecting duct principal cells isolated from BPK ARPKD mice

The main feature of polycystic kidney diseases (PKD) is formation and progressive enlargement of renal cysts. Alterations in epithelial cell proliferation, extracellular matrix, and ion transport are thought to contribute to cyst enlargement and loss of renal function. Abnormal Cl- secretion is implicated in cyst enlargement in autosomal dominant PKD (ADPKD), but little is known about transport abnormalities in autosomal recessive PKD (ARPKD). We developed a method to isolate collecting duct (CD) principal cells (site of the lesion in ARPKD) from normal and ARPKD mice. A transgenic mouse (Hoxb7/GFP) in which enhanced green fluorescent protein (GFP) is expressed in CDs was bred with an ARPKD mouse (BPK), and GFP-positive cells from normal and cystic mice were selected by fluorescence-activated cell sorting. GFP-positive CD cells (>95 +/- 3%) obtained from either normal or cystic mice formed high-resistance, polarized epithelial monolayers. Expression patterns for marker proteins and the presence of a central cilium confirmed that the monolayers are composed of principal cells. Under basal conditions, the Cl- secretory responses elicited by elevation of cAMP or calcium were not significantly different between normal and cystic monolayers. In contrast, the amiloride-sensitive short-circuit current was significantly reduced in monolayers of cells isolated from cystic mice (12.9 +/- 1.6 microA/cm2; n = 10) compared with monolayers of cells isolated from normal mice (27.3 +/- 3.4 microA/cm2; n = 12). The results of these studies suggest that epithelial sodium channel-mediated sodium absorption is decreased in principal cells of ARPKD CD cysts and that the reduction in sodium absorption may contribute to the accumulation of luminal fluid.

Combination treatment of PKD utilizing dual inhibition of EGF-receptor activity and ligand bioavailability

BACKGROUND

We have previously demonstrated an essential role for increased epidermal growth factor receptor (EGFR) activity in mediating renal cyst formation and biliary ductal ectasia (BDE) in murine models of autosomal-recessive polycystic kidney disease (ARPKD) such as the BPK mouse. The current study was designed to determine (1). if treatment with a second-generation inhibitor of EGFR tyrosine kinase activity, EKB-569, was effective in treatment of ARPKD; (2). if tyrosine kinase inhibitor therapy used in combination with pharmacologic reduction of the availability of transforming growth factor-alpha (TGF-alpha), using WTACE2, could provide improved therapeutic efficacy and/or decrease potential toxicity; and (3). if effectiveness of treatment could be monitored noninvasively in murine ARPKD models by use of serial ultrasonography.

METHODS

BPK litters were treated with EKB-569 by intraperitoneal injection from postnatal day 7 to postnatal day 21. EKB-569's effectiveness alone or in combination with WTACE2 was measured by reduction in kidney weight/body weight ratios, morphometric renal cystic index, and evaluation of renal function. Renal ultrasound was performed on normal and cystic animals, under different therapeutic regimens, utilizing a 15 mHz linear array transducer, and ultrasound data were compared with histology and renal functional data.

RESULTS

Treatment of BPK mice with EKB-569 alone resulted in a marked reduction of kidney weight/body weight ratios, dramatically reduced collecting tubule cystic index, as well as BDE, and improved renal function. The combined treatment with EKB-569 and WTACE2 permitted a 67% reduction in EKB-569 dosage necessary to achieve results equivalent to those produced with EKB-569 alone. Untreated cystic animals died of renal failure, on average, at postnatal day 24 with a collecting tubule cystic index of 4.8, significant BDE, and maximal urine osmolarity of 361 mOsm. Cystic animals treated with EKB-569 and WTACE2 to postnatal day 21 were alive and well with normal renal function, a reduced collecting tubule cystic index of 1.7 (P < 0.02), improvement in BDE, and a threefold increase in maximum urinary concentrating ability (P < 0.01). Renal ultrasound could reliably detect cystic kidneys as early as postnatal day 7 and the natural history as well as effects of therapeutic intervention were clearly delineated by ultrasound evaluation.

CONCLUSION

This study demonstrates that in murine ARPKD (1). EKB-569 is as effective as first-generation EGFR tyrosine kinase inhibitors in reducing cyst formation and preserving renal function; (2). combination therapy with EKB-569 and WTACE2 provides maximum efficacy in improving renal and biliary abnormalities, at lower doses, thereby minimizing potential toxicity; and (3). renal ultrasound provides a simple, reliable, noninvasive method of following natural history and effect of treatment regimens.

Expression of human mucin genes during normal and abnormal renal development

Human mucin genes encode large O-glycoproteins, which are expressed in various epithelial tissues. The proteins are the main components of mucus, but also might be involved in morphogenesis of or carcinogenesis in many organs. We studied the expression of human mucin genes during fetal kidney development and in malformed cystic renal diseases in 10 normal fetal kidneys and 12 malformed kidneys by in situ hybridization and immunohistochemical analysis. MUC1, MUC3, and MUC6 were expressed in normal fetal kidney. MUC1 was expressed from 7.5 weeks of gestation in the metanephric blastema and throughout fetal life in the ureteric buds, distal convoluted tubules, and collecting ducts. MUC3 was expressed weakly in immature tubules from 8 weeks of gestation, after which it was expressed weakly and focally in the proximal convoluted tubules. MUC6 was expressed at 9.5 weeks of gestation in the tips of the ureteric buds and later in the collecting ducts. In malformative cystic diseases, only MUC1 expression was retained; no expression of MUC6 and MUC3 was observed. These results implicate human mucin genes (MUC1, MUC3, and MUC6) in renal morphogenesis processes.

Delayed cystogenesis and increased ciliogenesis associated with the re-expression of polaris in Tg737 mutant mice

BACKGROUND

Renal cysts and shortened cilia on renal tubular epithelia have been observed in Tg737orpk (orpk) mutant mice, suggesting a potential connection between cystogenesis and ciliogenesis. To further test this hypothesis we have characterized the progression of cystic disease and cilia expression in orpk, orpk;Tg737Rsq (orpk rescue), and Tg737 Delta 2-3 beta Gal;Tg737Rsq (KO rescue) mice. Methods. Orpk, orpk rescue, and KO rescue animals were generated and analyzed from postnatal day (P) 0 to P21 (orpk mutants) or from P0 to P210 (orpk rescue and KO rescue animals). Proximal tubules (PT) and collecting tubules (CT) were identified by immunohistochemistry using segment-specific lectins and a segment-specific cystic index was calculated. Scanning electron microscopy was utilized to observe and measure cilia expression in cysts from orpk, orpk rescue, and KO rescue animals.

RESULTS

KO rescue and orpk rescue animals develop adult-onset autosomal-recessive polycystic kidney disease (ARPKD). Ultrastructural analysis of cilia expression revealed that cysts from orpk expressed short cilia, whereas cysts from KO rescue animals expressed normal length cilia and cysts from orpk rescue animals expressed cilia that are two to five times longer than wild type.

CONCLUSION

While this data is consistent with a role for polaris in ciliogenesis, it does not support a direct connection between ciliogenesis and cystic disease. Similarities in cyst formation and striking differences in cilia expression associated with these ARPKD mouse models indicates that cyst formation and cilia expression are independent phenotypic features regulated by polaris.

Evidence that soyasaponin Bb retards disease progression in a murine model of polycystic kidney disease

BACKGROUND

We reported a lessened cyst growth in the pcy mouse model of polycystic kidney disease (PKD) when mice were fed a soy protein isolate (SPI)-based diet and hypothesized that the soyasaponins may be associated with this therapeutic effect. The effects of feeding a saponin-enriched alcohol extract (SEAE) from SPI, an isoflavone- and saponin-enriched soy supplement (Novasoy 400), or a 99.5% pure soyasaponin Bb powder on cyst growth are reported here.

METHODS

The therapeutic effects of the soyasaponins were studied in 60-day-old male pcy mice in two separate, 90-day feeding trials. In the first study, mice were fed either a casein-based (control) diet, a diet in which SPI replaced the casein or the control diet supplemented with SEAE. In the second study, mice were fed the control diet unsupplemented or supplemented with either a soyasaponin- and isoflavone-enriched soy product (Novasoy 400) or a 99.5% pure soyasaponin Bb powder.

RESULTS

In study 1, kidney weight, water content, and plasma creatinine and urea levels were markedly reduced in the SEAE-fed animals compared to tissues from the control group; likewise, mice fed the SPI-based diet showed a decreased plasma creatinine, but only a slightly reduced plasma urea. In study 2, kidney weight, water content, plasma creatinine and urea levels were significantly reduced in mice fed the soyasaponin Bb powder and the Novasoy-400 supplement, compared to controls.

CONCLUSION

Soyasaponin Bb can impede kidney enlargement and cyst growth in the pcy mouse model of PKD. Further studies are needed to determine its most effective dose and mechanism of action.

Role of membrane-bound heparin-binding epidermal growth factor-like growth factor (HB-EGF) in renal epithelial cell branching

Role of membrane-bound heparin-binding epidermal growth factor-like growth factor (HB-EGF) in renal epithelial cell branching.

BACKGROUND

The developing metanephros is characterized by growth and differentiation of the ureteric bud and the surrounding mesenchymal tissue. These processes can be influenced by several growth factors, including epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). We examined whether another member of the EGF family of growth factors, heparin-binding epidermal growth factor (HB-EGF), might act as a morphogen in renal epithelial tubulogenesis.

METHODS

Expression of HB-EGF mRNA and immunoreactive protein were examined in fetal, neonatal and adult rat kidneys. For in vitro studies of tubulogenesis, a rat renal epithelial cell line (NRK52E) stably transfected with proHB-EGF (NRKproHB-EGF) was treated with TPA for 30 minutes, washed with 2 mol/L NaCl to remove soluble HB-EGF trapped by cell surface heparan sulfate proteoglycan and replated onto plastic dishes in the absence of fetal calf serum. In further experiments, NRKproHB-EGF were suspended in a type I collagen gel in serum-free media.

RESULTS

Northern blot analysis indicated that HB-EGF was strongly expressed in embryonic rat kidney (embryonic days 18-20) and was still increased in the neonatal kidney (day 10), compared to the low basal levels in adult kidney. Immunohistochemical analysis confirmed that immunoreactive HB-EGF expression in the fetal rat kidney was localized predominantly to the ureteric bud. When NRKproHB-EGF were plated onto plastic substrata, they became progressively flattened and enlarged and exhibited filopoidia. By 10 hours after plating, NRKproHB-EGF began to migrate and subsequently developed cell-cell contact and fully established tubular-like structures. Immunoelectron microscopy revealed that the initial recovery of cellular proHB-EGF was localized predominantly to areas of cell-cell attachment. No tubule-like structures were observed in similarly treated NRK52E cells transfected with the vector alone. In collagen gels, NRKproHB-EGF developed short tubule-like structures in the absence of TPA treatment, but with simultaneous TPA treatment, longer and more arborized structures developed. MMP-1 mRNA and immunoreactive protein increased in the TPA-treated cells, suggesting that protein kinase C-mediated collagenase activity was important for the observed tubulogenesis. However, inhibition of EGF receptor tyrosine kinase with AG 1478 significantly blunted the TPA-induced tubulogenesis by NRKproHB-EGF grown in collagen gels.

CONCLUSIONS

These results indicate that membrane-bound HB-EGF can mediate both epithelial cell branching and cell motility. Localization of proHB-EGF to the site of cell-cell contact and development of tubule-like structures in collagen gels suggests that proHB-EGF may be an important morphogen for renal epithelial cells.

cAMP-dependent protein kinase and proliferation differ in normal and polycystic kidney epithelia

Developmental control of cell proliferation is crucial, and abnormal principal cell proliferation may contribute to cystogenesis in polycystic kidney disease. This study investigates roles of cAMP and its primary effector, cAMP-dependent protein kinase (protein kinase A; PKA), in control of cell proliferation in filter-grown noncystic (NC) and cystic (CY)-derived principal cell cultures. These cultures had similar cAMP pathway characteristics upstream of PKA subunit distribution but differed in predicted PKA subtype distribution. Functionally, cultures were proliferative before polarization, with constitutively higher proliferation in CY cultures. NC cultures achieved levels similar to those of CY cultures on pharmacological manipulation of cAMP production or PKA activation or inhibition of PKA subtype I activity. Inhibition of overall PKA activity, or of PKA subtype II anchoring, diminished cAMP/PKA-mediated proliferation in NC cultures but had no effect on CY cultures. Polarized CY monolayers remained proliferative, but NC monolayers lost responsiveness. No large proliferation changes resulted from treatments of polarized cultures; however, polarized NC and CY cultures differed in poststimulation handling of PKA catalytic and type IIalpha regulatory subunits. Our results support PKA subtype regulation of prepolarization proliferation in NC principal cells and altered regulation of PKA in CY cells and suggest that differences at or downstream of PKA can contribute to altered proliferation in a developmental renal disease.

Treatment prospects for autosomal-dominant polycystic kidney disease

An increased understanding of the molecular genetic and cellular pathophysiologic mechanisms responsible for the development of autosomal-dominant polycystic kidney disease (ADPKD), made possible by the advances in molecular biology and genetics of the last three decades, has laid the foundation for the development of effective therapies. As the concept that a polycystic kidney is a neoplasm in disguise is becoming increasingly accepted, the development of therapies for ADPKD may benefit greatly from the expanding body of information on cancer chemoprevention and chemosuppression. This review summarizes the observations that already have been made and discusses therapies for PKD that deserve investigation.

Role of CFTR in autosomal recessive polycystic kidney disease

An extensive body of in vitro data implicates epithelial chloride secretion, mediated through cystic fibrosis transmembrane conductance regulator (CFTR) protein, in generating or maintaining fluid filled cysts in MDCK cells and in human autosomal dominant polycystic kidney disease (ADPKD). In contrast, few studies have addressed the pathophysiology of fluid secretion in cyst formation and enlargement in autosomal recessive polycystic kidney disease (ARPKD). Murine models of targeted disruptions or deletions of specific genes have created opportunities to examine the role of individual gene products in normal development and/or disease pathophysiology. The creation of a murine model of CF, which lacks functional CFTR protein, provides the opportunity to determine whether CFTR activity is required for renal cyst formation in vivo. Therefore, this study sought to determine whether renal cyst formation could be prevented by genetic complementation of the BPK murine model of ARPKD with the CFTR knockout mouse. The results of this study reveal that in animals that are homozygous for the cystic gene (bpk), the lack of functional CFTR protein on the apical surface of cystic epithelium does not provide protection against cyst growth and subsequent decline in renal function. Double mutant mice (bpk -/-; cftr -/-) developed massively enlarged kidneys and died, on average, 7 d earlier than cystic, non-CF mice (bpk -/-; cftr +/+/-). This suggests fundamental differences in the mechanisms of transtubular fluid secretion in animal models of ARPKD compared with ADPKD.

Distinctive cyclic AMP-dependent protein kinase subunit localization is associated with cyst formation and loss of tubulogenic capacity in Madin-Darby canine kidney cell clones

Polycystic kidney disease is characterized by abnormal morphological development. Mechanisms that regulate cyst development may involve multiple signaling pathways. Cyst formation by Madin-Darby canine kidney (MDCK) cells in three-dimensional culture is assumed to be cyclic AMP-dependent and due to cyclic AMP-dependent protein kinase (cAPK) activation based on pharmacological responsiveness. To determine if different cyclic AMP (cAMP) pathways are associated with morphological development, the role of cAMP in regulating morphological change was examined in MDCK clones that form tumor-like or tubular structures under basal conditions. Pharmacological cAMP pathway activators induce cyst formation and diminish formation of other structures in three clones, whereas one clone is unaffected. Tyrosine kinase-mediated morphogens have little effect. Although all clones have intact cAMP signaling pathways, each has a unique subcellular distribution of cAPK regulatory subunits. This may reflect distinct mechanisms for cAPK anchoring, allowing cAPK subtype regulation of the unique phenotypic character of each clone through preferential access to substrates. These observations suggest a molecular basis for differential cAMP responsiveness in cells that develop distinct morphological phenotypes. This evidence establishes these MDCK clones as models for understanding the mechanism and functional significance of cAPK subunit localization and may have broader implications for cystogenesis in polycystic kidney disease.

Epidermal growth factor induces oxidative neuronal injury in cortical culture

Recently, we have demonstrated that certain neurotrophic factors can induce oxidative neuronal necrosis by acting at the cognate tyrosine kinase-linked receptors. Epidermal growth factor (EGF) has neurotrophic effects via the tyrosine kinase-linked EGF receptor (EGFR), but its neurotoxic potential has not been studied. Here, we examined this possibility in mouse cortical culture. Exposure of cortical cultures to 1-100 ng/ml EGF induced gradually developing neuronal death, which was complete in 48-72 h; no injury to astrocytes was noted. Electron microscopic findings of EGF-induced neuronal death were consistent with necrosis; severe mitochondrial swelling and disruption of cytoplasmic membrane occurred, whereas nuclei appeared relatively intact. The EGF-induced neuronal death was accompanied by increased free radical generation and blocked by the anti-oxidant Trolox. Suggesting mediation by the EGFR, an EGFR tyrosine kinase-specific inhibitor, C56, attenuated EGF-induced neuronal death. In addition, inhibitors of extracellular signal-regulated protein kinase 1/2 (Erk-1/2) (PD98056), protein kinase A (H89), and protein kinase C (GF109203X) blocked EGF-induced neuronal death. A p38 mitogen-activated protein kinase inhibitor (SB203580) or glutamate antagonists (MK-801 and 6-cyano-7-nitroquinoxaline-2,3-dione) showed no protective effect. The present results suggest that prolonged activation of the EGFR may trigger oxidative neuronal injury in central neurons.

Proximal tubular cysts in fetal human autosomal recessive polycystic kidney disease

Standard texts describe human autosomal recessive polycystic kidney disease (ARPKD) as a cystic kidney disease in which lesions are localized to collecting tubules. Murine models of ARPKD consistently demonstrate an early phase of proximal tubular (PT) cystic involvement, which disappears shortly after birth. This is followed by a phase of collecting tubular (CT) cyst formation and progressive enlargement leading to compromise of renal function and death. Because the description of cystic lesions in human ARPKD has been largely based on postnatal specimens, PT cyst formation was hypothesized to be a characteristic feature of fetal human, as well as murine, ARPKD. This study examines nephron segment-specific cyst localization histochemically by lectin binding in 11 human ARPKD specimens obtained at different fetal and postnatal ages. PT cysts were found in human fetal specimens from gestational age 14 wk to 26 wk. The percentage of cysts involving PT segments ranged from 2 to 41%. The cystic index of PT cysts ranged from 2 to 5. In all specimens in which PT cysts were found, both the percentage of CT cysts and their cystic index were equal to or greater than the percentage of PT cysts and the associated PT cystic index. PT cysts were absent in all kidney specimens older than 34 wk gestational age. It is concluded that human ARPKD, like murine ARPKD, has a transient phase of PT cyst formation during early fetal development.

Treatment of polycystic kidney disease with a novel tyrosine kinase inhibitor

Treatment of polycystic kidney disease with a novel tyrosine kinase inhibitor.

BACKGROUND

We have previously demonstrated an essential role for increased epidermal growth factor receptor (EGFR) activity in mediating renal cyst formation and biliary epithelial hyperplasia in murine models of autosomal recessive polycystic kidney disease (ARPKD). This study was designed to determine whether or not treatment with a newly developed inhibitor of EGFR tyrosine kinase activity (EKI-785) would reduce renal and biliary abnormalities in murine ARPKD.

METHODS

Balb/c-bpk/bpk (BPK) litters were treated with EKI-785, an EGFR-specific tyrosine kinase inhibitor. Animals were treated by intraperitoneal injection beginning at postnatal day 7 and were treated until postnatal day 24 or 48. EKI-785's effectiveness was measured by a reduction in the renal cystic index, an increased life span, and maintenance of normal renal function.

RESULTS

Treatment of BPK mice with EKI-785 resulted in a marked reduction of collecting tubule (CT) cystic lesions, improved renal function, decreased biliary epithelial abnormalities, and an increased life span. Untreated cystic animals died of renal failure at postnatal day 24 (P-24) with a CT cystic index of 4.8, a maximal urine osmolarity of 361 mOsm, and moderate to severe biliary abnormalities. Cystic animals treated with EKI-785 to postnatal day 48 (P-48) were alive and well with normal renal function, a reduced CT cystic index of 2.0 (P < 0.02), a threefold increased in maximum urinary concentrating ability (P < 0.01), and a significant decrease in biliary epithelial proliferation/fibrosis (P < 0.01).

CONCLUSION

This study demonstrates that EKI-785 has therapeutic effectiveness in improving histopathologic abnormalities and decreasing mortality in murine ARPKD.

In vitro modulation of cyst formation by a novel tyrosine kinase inhibitor

BACKGROUND

Recessively transmitted polycystic kidney disease (PKD) in many murine models is characterized by the initial formation of proximal tubular cysts (stage 1), followed by growth and enlargement of renal collecting tubule (CT) cysts (stage 2). Previous studies have reported that stage 1 cyst formation and growth could be manipulated in vitro by using embryonic kidney explants and newborn explant microslices in organ culture.

METHODS

Microslices of postnatal kidneys cultured on Transwell tissue culture inserts allow experimental manipulation of stage 2 CT cyst development and growth. This system was used to test a potential therapeutic compound for treatment of PKD. This compound, EKI-785, modulates altered epidermal growth factor receptor (EGFR) expression in CT cysts by inhibition of EGFR autophosphorylation.

RESULTS

These studies demonstrate that: (a) minor modifications of the previously described organ culture system permit successful culture of more mature renal tissue, and (b) cystic explants treated with EGF and EKI-785 demonstrated a marked reduction in CT cystic lesions compared with cystic explants treated with EGF alone.

CONCLUSIONS

This study suggests that pharmacological strategies can be used to decrease EGFR tyrosine kinase activity and CT cyst formation and enlargement in murine PKD.

New insights into the molecular pathophysiology of polycystic kidney disease

Polycystic kidney diseases are characterized by the progressive expansion of multiple cystic lesions, which compromise the function of normal parenchyma. Throughout the course of these diseases, renal tubular function and structure are altered, changing the tubular microenvironment and ultimately causing the formation and progressive expansion of cystic lesions. Renal tubules are predisposed to cystogenesis when a germ line mutation is inherited in either the human PKD1 or PKD2 genes in autosomal dominant polycystic kidney disease (ADPKD) or when a homozygous mutation in Tg737 is inherited in the orpk mouse model of autosomal recessive polycystic kidney disease (ARPKD). Recent information strongly suggests that the protein products of these disease genes may form a macromolecular signaling structure, the polycystin complex, which regulates fundamental aspects of renal epithelial development and cell biology. Here, we re-examine the cellular pathophysiology of renal cyst formation and enlargement in the context of our current understanding of the molecular genetics of ADPKD and ARPKD.

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.

Soy protein modification of rat polycystic kidney disease

We undertook a study to determine whether soy protein feeding would ameliorate renal injury in the Han:SPRD-cy rat model of polycystic kidney disease (PKD). Male offspring of Han:SPRD-cy heterozygotes received isocaloric diets based on 20% casein or 20% heat-treated soy protein at weaning ad libitum for 8 wk. Soy-fed animals demonstrated lower serum creatinine (66 vs. 125 mumol/l; P = 0.002), lower urinary ammonium excretion (0.080 vs. 0.173 mmol/kg; P = 0.01), reduced renal cysts (0.98 vs. 4.92 ml/kg body wt, P < 0.0001), renal fibrosis (0.79 vs. 1.4 ml/kg; P = 0.016), macrophage infiltration, renal tubular cell proliferation, and apoptosis. Proton nuclear magnetic resonance (1H-NMR) studies of urine demonstrated that soy diet was associated with increased losses of citric acid cycle organic anions. 1H-NMR of perchloric acid-extracted tissue found that levels of succinate were not depleted in soy-fed animals, despite increased urinary losses. Soy-fed animals had marked elevation of tissue betaine (P < 0.001), with reduced taurine and cholines, compared with casein-fed animals (P < 0.001). Soy feeding dramatically reduces both tubular and interstitial pathology in the Han:SPRD-cy rat model of PKD, through mechanisms that remain to be determined.

New insights into polycystic kidney disease and its treatment

Major advances in the understanding of the genetics and pathogenesis of autosomal dominant polycystic kidney disease have occurred within the past year. The proteins encoded by the PKD1 and PKD2 genes, polycystin 1 and polycystin 2, are membrane proteins, capable of interacting physically in vitro, and are likely components of a complex signalling pathway. The majority of PKD1 and PKD2 mutations so far identified are unique inactivating mutations dispersed over the entire genes. Immunohistochemical studies have shown that polycystin 1 and polycystin 2 are developmentally regulated and are overexpressed in polycystic kidneys. The cysts probably result from clonal expansions of single cells. The demonstration of loss of heterozygosity for PKD1 and the absence of immunoreactive polycystin 1 in approximately 20% of the cysts supports a two-hit tumor suppressor gene model of cystogenesis. Regardless of the nature of the initial pathogenic mechanism, the cysts in autosomal dominant polycystic kidney disease are accompanied by partial dedifferentiation of the epithelial cells, disregulation of epithelial cell proliferation, expression of a secretory phenotype, and disarray of cell matrix interactions which leads to interstitial inflammation and matrix accumulation. Recent observations in animal models of inherited polycystic kidney disease have implicated oxidative stress in its pathogenesis. These downstream pathogenetic events have been targeted for intervention, and an increasing number of studies have demonstrated that the course of polycystic kidney disease in rodents can be altered by environmental and pharmacological interventions. Nevertheless, these experimental observations cannot be extrapolated to human autosomal dominant polycystic kidney disease. The recent generation of mice with PKD1 or PKD2 targeted mutations will help to bridge this gap.

The role of hepatocyte growth factor (HGF) at progressive stages of metanephric development

Several lines of evidence suggest that hepatocyte growth factor (HGF), a soluble protein secreted by mesenchymal cells, may elicit a morphogenic response in the developing metanephros. We investigated the role of HGF at three different stages of murine metanephric development utilizing serum-free organ culture. Cultures were initiated at E-13, E-15, and E-17; treated with exogenous HGF or antibodies to HGF (to block endogenous HGF) for 120 h in vitro; and evaluated for growth and differentiation in comparison to control explants cultured for 120 h in basal medium. HGF treatment of E-13 explants resulted in a reduction of growth and differentiation compared to control explants. Treatment of E-13 explants with antibodies to HGF produced explant growth and differentiation indistinguishable from control explants. In contrast to the results of E-13 cultures, explants initiated at E-15 and E-17 demonstrated an increased growth and differentiation profile when treated with HGF compared to controls. Treatment of E-15 and E-17 explants with antibodies to HGF resulted in a decrease growth and differentiation profile compared to control or HGF-treated explants. These data demonstrate that HGF has differential effects on renal morphogenesis at progressive developmental stages of metanephric development.

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.