Treatment prospects for autosomal-dominant polycystic kidney disease

Inhibiting Focal Adhesion Kinase Ameliorates Cyst Development in Polycystin-1-Deficient Polycystic Kidney Disease in Animal Model

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by numerous cysts originating from renal tubules and is associated with significant tubular epithelial cell proliferation. Focal adhesion kinase (FAK) promotes tumor growth by regulating multiple proliferative pathways.

METHODS

We established the forskolin (FSK)-induced three-dimensional (3D) Madin-Darby Canine Kidney cystogenesis model and 8-bromoadenosine-3`,5`-cyclic monophosphate-stimulated cyst formation in ex vivo embryonic kidney culture. Cultured human renal cyst-lining cells (OX-161) and normal tubular epithelial cells were treated with FAK inhibitors or transfected with green fluorescent protein-tagged FAK mutant plasmids for proliferation study. Furthermore, we examined the role of FAK in two transgenic ADPKD animal models, the kidney-specific Pkd1 knockout and the collecting duct-specific Pkd1 knockout mouse models.

RESULTS

FAK activity was significantly elevated in OX-161 cells and in two ADPKD mouse models. Inhibiting FAK activity reduced cell proliferation in OX-161 cells and prevented cyst growth in ex vivo and 3D cyst models. In tissue-specific Pkd1 knockout mouse models, FAK inhibitors retarded cyst development and mitigated renal function decline. Mechanically, FSK stimulated FAK activation in tubular epithelial cells, which was blocked by a protein kinase A (PKA) inhibitor. Inhibition of FAK activation by inhibitors or transfected cells with mutant FAK constructs interrupted FSK-mediated Src activation and upregulation of ERK and mTOR pathways.

CONCLUSIONS

Our study demonstrates the critical involvement of FAK in renal cyst development, suggests that FAK is a potential therapeutic target in treating patients with ADPKD, and highlights the role of FAK in cAMP-PKA-regulated proliferation.

Hippo signaling-a central player in cystic kidney disease?

Cystic transformation of kidney tissue is a key feature of various disorders including autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and disorders of the nephronophthisis spectrum (NPH). While ARPKD and NPH typically affect children and adolescents, pediatric onset of ADPKD is less frequently found. While both ADPKD and ARPKD are characterized by formation of hundreds of cysts accompanied by hyperproliferation of tubular epithelia with massive renal enlargement, NPH patients usually show kidneys of normal or reduced size with cysts limited to the corticomedullary border. Recent results suggest the hippo pathway to be a central regulator at the crossroads of the renal phenotype in both diseases. Hippo signaling regulates organ size and proliferation by keeping the oncogenic transcriptional co-activators Yes associated protein 1 (YAP) and WW domain containing transcription regulator 1 (TAZ) in check. Once this inhibition is released, nuclear YAP/TAZ interacts with TEAD family transcription factors and the consecutive transcriptional activation of TEA domain family members (TEAD) target genes mediates an increase in proliferation. Here, we review the current knowledge on the impact of NPHP and ADPKD mutations on Hippo signaling networks. Furthermore, we provide an outlook towards potential future therapeutic strategies targeting Hippo signaling to alleviate cystic kidney disease.

Increased water intake reduces long-term renal and cardiovascular disease progression in experimental polycystic kidney disease

Polycystic kidney disease (PKD) is the most common inherited cause of kidney failure and currently has limited treatment options. Increasing water intake reduces renal cyst growth in the pck rat (a genetic ortholog of autosomal recessive PKD) but it is not clear if this beneficial effect is present in other models of PKD. In this study, we tested the hypothesis that high water intake (HWI) reduces the progression of cystic renal disease in Lewis polycystic kidney (LPK) rats (a genetic ortholog of human nephronophthisis-9). Groups of female and male LPK (n = 8–10 per group) and Lewis (n = 4 per group) rats received water ad libitum supplemented with or without 5% glucose [to simulate HWI or normal water intake (NWI) respectively] from postnatal weeks 3 to 16. Water intake increased ~1.3-fold in the LPK+HWI group compared to LPK+NWI rats between weeks 3 to 10 but the differences were not significant at later timepoints. In LPK rats, HWI reduced the increases in the kidney to body weight ratio by 54% at week 10 and by 42% at week 16 compared to NWI (both p<0.01). The reduction in kidney enlargement was accompanied by decreases in the percentage renal cyst area, percentage renal interstitial collagen and proteinuria (all p<0.05). At week 16, HWI reduced systolic blood pressure and the heart to body to weight ratio by 16% and 21% respectively in males LPK rats (both p<0.01). In conclusion, a modest increase in water intake during the early phase of disease was sufficient to attenuate renal cystic disease in LPK rats, with secondary benefits on hypertension and cardiovascular disease. These data provide further preclinical evidence that increased water intake is a potential intervention in cystic renal diseases.

Nonselective Cyclooxygenase Inhibition Retards Cyst Progression in a Murine Model of Autosomal Dominant Polycystic Kidney Disease

Aim: Autosomal dominant polycystic kidney disease is one of the most common genetic renal diseases. Cyclooxygenase plays an important role in epithelial cell proliferation and may contribute to the mechanisms underlying cyst formation. The aim of the present study was to evaluate the role of cyclooxygenase inhibition in the cyst progression in polycystic kidney disease. Method: Pkd2^WS25/- mice, a murine model which harbors a compound cis-heterozygous mutation of the Pkd2 gene were used. Cyclooxygenase expression was assessed in both human and murine kidney specimens. Pkd2^WS25/- mice were treated with Sulindac (a nonselective cyclooxygenase inhibitor) or vehicle for 8 months starting at three weeks age, and then renal cyst burden was assessed by kidney weight and volume. Results: Cyclooxygenase-2 expression was up-regulated compared to control kidneys as shown by RNase protection in human polycystic kidneys and immunoblot in mouse Pkd2^WS25/- kidneys. Cyclooxygenase-2 expression was up-regulated in the renal interstitium as well as focal areas of the cystic epithelium (p<0.05). Basal Cyclooxygenase-1 levels were unchanged in both immunohistochemistry and real-time PCR. Administration of Sulindac to Pkd2^WS25/- mice and to control mice for 8 months resulted in reduced kidney weights and volume in cystic mice. Renal function and electrolytes were not significantly different between groups. Conclusion: Thus treatment of a murine model of polycystic kidney disease with Sulindac results in decreased kidney cyst burden. These findings provide additional implications for the use of Cyclooxygenase inhibition as treatment to slow the progression of cyst burden in patients with polycystic kidney disease.

Polycystic kidney disease

Cystic kidneys are common causes of end-stage renal disease, both in children and in adults. Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are cilia-related disorders and the two main forms of monogenic cystic kidney diseases. ADPKD is a common disease that mostly presents in adults, whereas ARPKD is a rarer and often more severe form of polycystic kidney disease (PKD) that usually presents perinatally or in early childhood. Cell biological and clinical research approaches have expanded our knowledge of the pathogenesis of ADPKD and ARPKD and revealed some mechanistic overlap between them. A reduced 'dosage' of PKD proteins is thought to disturb cell homeostasis and converging signalling pathways, such as Ca²⁺, cAMP, mechanistic target of rapamycin, WNT, vascular endothelial growth factor and Hippo signalling, and could explain the more severe clinical course in some patients with PKD. Genetic diagnosis might benefit families and improve the clinical management of patients, which might be enhanced even further with emerging therapeutic options. However, many important questions about the pathogenesis of PKD remain. In this Primer, we provide an overview of the current knowledge of PKD and its treatment.

Retinoic acid-dependent activation of the polycystic kidney disease-1 (PKD1) promoter

The retinoic acids all-trans retinoic acid (AT-RA) and 9-cis retinoic acid (9C-RA) and the retinoic acid receptors RAR and RXR significantly induce transcriptional activity from a 200-bp PKD1 proximal promoter in transfected mammalian cells. This PKD1 promoter region contains Ets, p53, and GC box motifs, but lacks a canonical RAR/RXR motif. Mutagenesis of the Ets sites did not affect RA induction. In contrast, GC box mutations completely blocked stimulation by AT-RA and by RXRbeta or RARbeta. Mithramycin A, which prevents Sp1 binding, significantly reduced basal promoter activity and suppressed upregulation by AT-RA and RXR. The 200-bp proximal promoter could not be induced by AT-RA in Drosophila SL2 cells, which lack Sp1, but could be activated in these cells transfected with exogenous Sp1. Small interfering RNA knockdown of Sp1 in mammalian cells completely blocked RXRbeta upregulation of the promoter. These data indicate that induction of the PKD1 promoter by retinoic acid is mediated through Sp1 elements. RT-PCR showed that AT-RA treatment of HEK293T cells increased the levels of endogenous PKD1 RNA, and chromatin immunoprecipitation showed the presence of both RXR and Sp1 at the PKD1 proximal promoter. These results suggest that retinoids and their receptors may play a role in PKD1 gene regulation.

Responding to threats to the kidney

Here's what you need to know about polycystic kidney disease and renal artery stenosis.

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.

Development of polycystic kidney disease in juvenile cystic kidney mice: insights into pathogenesis, ciliary abnormalities, and common features with human disease

Significant progress in understanding the molecular mechanisms of polycystic kidney disease (PKD) has been made in recent years. Translating this understanding into effective therapeutics will require testing in animal models that closely resemble human PKD by multiple parameters. Similar to autosomal dominant PKD, juvenile cystic kidney (jck) mice develop cysts in multiple nephron segments, including cortical collecting ducts, distal tubules, and loop of Henle. The jck mice display gender dimorphism in kidney disease progression with more aggressive disease in male mice. Gonadectomy experiments show that testosterone aggravates the severity of the disease in jck male mice, while female gonadal hormones have protective effects. EGF receptor is overexpressed and mislocalized in jck cystic epithelia, a hallmark of human disease. Increased cAMP levels in jck kidneys and activation of the B-Raf/extracellular signal-regulated kinase pathway are demonstrated. The effect of jck mutation on the expression of Nek8, a NIMA-related (never in mitosis A) kinase, and polycystins in jck cilia is shown for the first time. Nek8 overexpression and loss of ciliary localization in jck epithelia are accompanied by enhanced expression of polycystins along the cilia. The primary cilia in jck kidneys are significantly more lengthened than the cilia in wild-type mice, suggesting a role for Nek8 in controlling ciliary length. Collectively, these data demonstrate that the jck mice should be useful for testing potential therapies and for studying the molecular mechanisms that link ciliary structure/function and cystogenesis.

Renal cystic diseases: a review

This review aims to assist in the categorization of inherited, developmental, and acquired cystic disease of the kidney as well as to provide a pertinent, up-to-date bibliography. The conditions included are autosomal-dominant polycystic kidney disease, autosomal-recessive polycystic kidney disease, unilateral renal cystic disease (localized cystic disease), renal simple cysts, multicystic dysplastic kidney, pluricystic kidney of the multiple malformation syndromes, juvenile nephronophthisis and medullary cystic disease, medullary sponge kidney, primary glomerulocystic kidney disease, and glomerulocystic kidney associated with several systemic disorders mainly of genetic or chromosomal etiology, cystic kidney in tuberous sclerosis, and in von Hippel-Lindau syndrome, cystic nephroma, cystic variant of congenital mesoblastic nephroma, mixed epithelial stromal tumor of the kidney, renal lymphangioma, pyelocalyceal cyst, peripylic cyst and perinephric pseudocyst, acquired renal cystic disease of long-term dialysis, and cystic renal cell carcinoma and sarcoma. Whereas the gross and histologic appearance of some of these conditions may be diagnostic, clinical and sometimes molecular studies may be necessary to define other types.

A comparative study of three kidney biomarker tests in autosomal-dominant polycystic kidney disease

BACKGROUND

The relationship between the progress of tubular damage and renal insufficiency in autosomal-dominant polycystic kidney disease (ADPKD) is a subject of doubtless interest, and is the object of this present work.

METHODS

A total of 92 adult ADPKD patients of both genders were studied, none of which presented end-stage renal disease (ESRD), and classified according to an ultrasound score based on kidney size and number of cysts. Urinary albumin and beta-N-acetylhexosaminidase (Hex) and its isoenzymes were determined, together with serum glutathione peroxidase, cystatin C, creatinine, and urea.

RESULTS

A frequent elevation of the urinary Hex was found and an alteration of its isoenzymatic profile, with 31% of the normotensive patients with normoalbuminuria already presenting an increased proportion of Hex B isoenzyme. Keeping age constant, a partial significant correlation was found between the ultrasound score and the proportion of Hex B (r = 0.352, P < 0.05), but not with albuminuria or cystatin C. In 42 patients the different biochemical variables were again determined after 1 year, finding that in the 13 normotensive patients with normoalbuminuria there had been a significant decrease in the concentration of cystatin C (P < 0.05), and a significant increase in the urinary excretion of albumin and Hex B isoenzyme (P < 0.05). By the other hand, in the other 29 patients with micro- or macroalbuminuria and hypertension, no significant differences were found.

CONCLUSION

The results point toward an important participation of tubular damage in the pathogenesis of this disease. It may also be suggested that in normotensive and normoalbuminuric ADPKD patients, a gradual increase of glomerular filtration would be produced. After the start of hypertension and microalbuminuria, the glomerular filtration rate (GFR) would decrease progressively, although more slowly.

Functional imaging in small animals using X-ray computed tomography--study of physiologic measurement reproducibility

X-ray computed tomography (CT) has been traditionally used for morphologic analysis and in the recent past has been used for physiology imaging. This paper seeks to demonstrate functional CT as an effective tool for monitoring changes in tissue physiology associated with disease processes and cellular and molecular level therapeutic processes. We investigated the effect of noise and sampling time on the uncertainty of tissue physiologic parameters. A whole body compartmental model of mouse was formulated to simulate tissue time density curves and study the deviation of tissue physiologic parameters from their true values. These results were then used to determine the appropriate scanning protocols for the experimental studies. Dynamic contrast enhanced CT (DCE-CT) was performed in mice following the injection of hydrophilic iodinated contrast agent (CA) at three different injection rates, namely 0.5 ml/min, 1 ml/min, and 2.0 ml/min. These experiments probed the Nyquist sampling limit for reproducibility of tissue physiologic parameters. Separate experiments were performed with three mice at four different X-ray tube currents corresponding to different image noise values. A two-compartment model (2CM) model was formulated to describe the contrast kinematics in the kidney cortex. Three different 2CMs were implemented namely the 4-parameter (4P), 5-parameter (5P), and the 6-parameter (6P) model. The tissue kinematics is fitted to the models by using the Levenberg-Marquardt algorithm implemented in IDL (RSI Inc.) programming language to minimize the weighted sum of squares. The relevant tissue physiologic parameters extracted from the models are the renal blood flow (RBF), glomerular filtration rate (GFR), fractional plasma volume, fractional tubular volumes and urine formation rates. The experimental results indicate that the deviation of the tissue physiologic parameters is within the limits required for tracking disease physiology in vivo and thus small animal functional X-ray CT would be able to determine changes in tissue physiology in vivo.

Dietary potassium citrate does not harm the pcy mouse

Formation of multiple cysts in the kidneys occurs in several inherited diseases and often leads to terminal kidney failure. Because there is no definitive therapy to halt or slow the progression of renal cystic disease in people, numerous studies have examined possible therapies in animal models. Autosomal-dominant polycystic kidney disease (ADPKD) in the Han:SPRD rat is ameliorated when alkalinizing citrate salts are provided in drinking solutions. By contrast, pcy mice with cystic disease fare worse with the same treatment. We tested the hypothesis that pcy mice ingesting citrate salts in the feed would not be adversely affected by this treatment. Male homozygous pcy mice were given regular feed or 6% potassium citrate-supplemented feed and ad libitum access to water starting at 3 weeks of age. The survival curves of the treated and untreated mice were not significantly different. We conclude that treatment with potassium citrate in the feed does not affect the progression of renal cystic disease in the pcy mouse. This model closely resembles human adolescent nephronophthisis (NPHP3). Based on these findings, citrate treatment cannot be recommended for NPHP3. The fact that it did no harm, however, removes a significant barrier to its consideration as a therapy for ADPKD.

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.

Polycystin-1 activates the calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway

Regulation of intracellular Ca(2+) mobilization has been associated with the functions of polycystin-1 (PC1) and polycystin-2 (PC2), the protein products of the PKD1 and PKD2 genes. We have now demonstrated that PC1 can activate the calcineurin/NFAT (nuclear factor of activated T-cells) signaling pathway through Galpha(q) -mediated activation of phospholipase C (PLC). Transient transfection of HEK293T cells with an NFAT promoter-luciferase reporter demonstrated that membrane-targeted PC1 constructs containing the membrane proximal region of the C-terminal tail, which includes the heterotrimeric G protein binding and activation domain, can stimulate NFAT luciferase activity. Inhibition of glycogen synthase kinase-3beta by LiCl treatment further increased PC1-mediated NFAT activity. PC1-mediated activation of NFAT was completely inhibited by the calcineurin inhibitor, cyclosporin A. Cotransfection of a construct expressing the Galpha(q) subunit augmented PC1-mediated NFAT activity, whereas the inhibitors of PLC (U73122) and the inositol trisphosphate and ryanodine receptors (xestospongin and 2-aminophenylborate) and a nonspecific Ca(2+) channel blocker (gadolinium) diminished PC1-mediated NFAT activity. PC2 was not able to activate NFAT. An NFAT-green fluorescent protein nuclear localization assay demonstrated that PC1 constructs containing the C-tail only or the entire 11-transmembrane spanning region plus C-tail induced NFAT-green fluorescent protein nuclear translocation. NFAT expression was demonstrated in the M-1 mouse cortical collecting duct cell line and in embryonic and adult mouse kidneys by reverse transcriptase-PCR and immunolocalization. These data suggest a model in which PC1 signaling leads to a sustained elevation of intracellular Ca(2+) mediated by PC1 activation of Galpha(q) followed by PLC activation, release of Ca(2+) from intracellular stores, and activation of store-operated Ca(2+) entry, thus activating calcineurin and NFAT.

Direct block of the cystic fibrosis transmembrane conductance regulator Cl(-) channel by niflumic acid

Niflumic acid is widely used to inhibit Ca(2+) -activated Cl(-) channels. However, the chemical structure of niflumic acid resembles that of diphenylamine-2-carboxylate, a drug that inhibits the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. To investigate how niflumic acid inhibits CFTR Cl(-) channel, we studied recombinant wild-type human CFTR in excised inside-out membrane patches. When added to the intracellular solution, niflumic acid caused a concentration- and voltage-dependent decrease of CFTR Cl(-) current with half-maximal inhibitory concentration (K(i)) of 253 microM and Hill co-efficient of approximately 1, at -50 mV. Niflumic acid inhibition of single CFTR Cl(-) channels was characterized by a very fast, flickery block that decreased dramatically current amplitude without altering open-probability. Consistent with these data, spectral analysis of CFTR Cl(-) currents suggested that channel block by niflumic acid was described by the closed <--> open <--> blocked kinetic scheme with blocker on rate (k(on)) = 13.9 x 10(6) M(-1)s(-1), off rate (k(off))=3348 s(-1) and dissociation constant (K(d)) = 241 microM, at -50 mV. Based on these data, we tested the effects of niflumic acid on transepithelial Cl(-) secretion and cyst growth using type I MDCK epithelial cells. Niflumic acid (200 microM) inhibited cAMP-stimulated, bumetanide-sensitive short-circuit current by 55%. Moreover, the drug potently retarded cyst growth. We conclude that niflumic acid is an open-channel blocker of CFTR that inhibits Cl(-) permeation by plugging the channel pore. It or related agents might be of value in the development of new therapies for autosomal dominant polycystic kidney disease.

Genes and geneticization? The social construction of autosomal dominant polycystic kidney disease

Critics of the new genetics argue that contemporary understandings of health and illness are becoming increasingly 'geneticized.' Salient implications of this critique are explored here within the context of Autosomal Dominant Polycystic Kidney Disease (PKD), a life-threatening genetic disease that causes fluid-filled cysts in the kidneys and progressive loss of renal function. Although PKD is very common, public awareness of the disease remains low and there is little clinical emphasis on hereditary aspects. Drawing upon qualitative interviews with 16 healthcare providers, 13 patients and 15 family members, this paper examines the social construction and clinical management of PKD. In particular, interviewees' perceptions of the role of genetics in PKD and views on presymptomatic testing are considered. Finding little impetus toward early diagnosis and/or presymptomatic identification of mutation carriers, we conclude that careful empirical study of PKD (or other neglected hereditary conditions) contributes new insights into factors mitigating geneticization.

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.

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.

Renal cystic neoplasms and renal neoplasms associated with cystic renal diseases: pathogenetic and molecular links

Cystic renal neoplasms represent an isolated cystic mass not accompanied by cystic change of the renal parenchyma. Although cystic change may be seen in any type of renal neoplasm, a few (i.e., cystic renal cell carcinoma, cystic nephroma, cystic partially differentiated nephroblastoma, mixed epithelial and stromal tumor) are characterized by constant cystic change that may involve the entire tumor. Cystic kidney disease is characterized by cystic change, which usually involves the kidneys in a bilateral and diffuse pattern, does not create a discreet mass, and is due to hereditary or developmental conditions. Some of the cystic kidney diseases are not known to give rise to renal neoplasm; others such as autosomal polycystic kidney disease or multicystic dysplastic kidney may fortuitously coexist with renal neoplasms. Three conditions (acquired cystic kidney disease, tuberous sclerosis, and von Hippel-Lindau disease) are associated with renal neoplasms with such a high frequency that they are considered preneoplastic. This article reviews the differential diagnoses among cystic neoplasms. It also focuses on the underlying genetic and molecular mechanisms for the relationship between cystic renal diseases and renal neoplasms.

ETA receptor blockade induces tubular cell proliferation and cyst growth in rats with polycystic kidney disease

Tissue concentrations of ET-1 are markedly elevated in the kidneys of Han:Sprague-Dawley (Han:SPRD) rats, a model of human autosomal dominant polycystic kidney disease (ADPKD). This study analyzed whether disease progression might be attenuated by endothelin receptor antagonists. Heterozygous Han:SPRD rats received an ETA receptor antagonist (LU 135252), a combined ETA/ETB receptor antagonist (LU 224332), or placebo for 4 mo. Glomerulosclerosis, protein excretion, and GFR remained unchanged, whereas interstitial fibrosis was enhanced by both compounds. BP was not reduced by both compounds in Han:SPRD rats. Renal blood flow (RBF) decreased in ADPKD rats treated with the ETA receptor antagonist. Long-term ETA receptor blockade furthermore increased markedly the number of renal cysts (ADPKD rats, 390 +/- 119 [cysts/kidney section +/- SD]; LU 135252-treated APKD rats, 1084 +/- 314; P < 0.001), cyst surface area (ADPKD rats, 7.97 +/- 2.04 [% of total section surface +/- SD]; LU 135252-treated ADPKD rats, 33.83 +/- 10.03; P < 0.001), and cell proliferation of tubular cells (ADPKD rats, 42.2 +/- 17.3 [BrdU-positive cells/1000 cells]; LU 135252-treated ADPKD rats, 339.4 +/- 286.9; P < 0.001). The additional blockade of the ETB receptor attenuated these effects in Han:SPRD rats. Both endothelin receptor antagonists had no effect on BP, protein excretion, GFR, and kidney morphology in Sprague-Dawley rats without renal cysts. It is concluded that ETA receptor blockade enhances tubular cell proliferation, cyst number, and size and reduces RBF in Han:SPRD rats. This is of major clinical impact because endothelin receptor antagonists are upcoming clinically used drugs.

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.

Pathogenesis and treatment of hypertension in polycystic kidney disease

PURPOSE OF REVIEW

Hypertension is common in patients with autosomal dominant polycystic kidney disease. It may contribute to cardiovascular risk and to progression of renal failure.

RECENT FINDINGS

Apart from fluid overload and renin activation, hypertensive patients with autosomal dominant polycystic kidney disease also have increased sympathetic activity, regardless of renal function. Sympathetic hyperactivity not only contributes to the hypertension but may also increase cardiovascular risk independent of blood pressure.

SUMMARY

Treatment for normalizing blood pressure and sympathetic activity should be started early in the course of the disease.

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.

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.

Chronic caffeine consumption exacerbates hypertension in rats with polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder frequently associated with renal failure, hypertension, and other abnormalities. The present study determined whether chronic caffeine intake in an animal model of this disease would affect renal structure and function and blood pressure. Heterozygous male Han:Sprague-Dawley rats with ADPKD and normal littermates were provided with either tap water or solutions of caffeine to drink, starting at 1 month of age. When rats were aged 6 months, glomerular filtration rate (GFR) and mean arterial blood pressure (MAP) were measured under Inactin (Byk Gulden, Konstanz, Germany) anesthesia. Caffeine intake had no effect on GFR or cyst development in rats with PKD. MAP was greater in rats with PKD than normal rats and was increased more by caffeine. The hypertensive effect of chronic caffeine intake could not be ascribed to direct pressor effects of angiotensin II. Based on our finding that caffeine exacerbates hypertension in rats with PKD, it may be prudent for patients with ADPKD to limit coffee consumption to four or fewer cups of caffeinated coffee per day, pending studies of humans.