Cyst-derived cells do not exhibit accelerated growth or features of transformed cells in vitro

Fundamental insights into autosomal dominant polycystic kidney disease from human-based cell models

Several animal- and human-derived models are used in autosomal dominant polycystic kidney disease (ADPKD) research to gain insight in the disease mechanism. However, a consistent correlation between animal and human ADPKD models is lacking. Therefore, established human-derived models are relevant to affirm research results and translate findings into a clinical set-up. In this review, we give an extensive overview of the existing human-based cell models. We discuss their source (urine, nephrectomy and stem cell), immortalisation procedures, genetic engineering, kidney segmental origin and characterisation with nephron segment markers. We summarise the most studied pathways and lessons learned from these different ADPKD models. Finally, we issue recommendations for the derivation of human-derived cell lines and for experimental set-ups with these cell lines.

A telomerase immortalized human proximal tubule cell line with a truncation mutation (Q4004X) in polycystin-1

Autosomal dominant polycystic kidney disease (ADPKD) is associated with a variety of cellular phenotypes in renal epithelial cells. Cystic epithelia are secretory as opposed to absorptive, have higher proliferation rates in cell culture and have some characteristics of epithelial to mesenchymal transitions [1], [2]. In this communication we describe a telomerase immortalized cell line that expresses proximal tubule markers and is derived from renal cysts of an ADPKD kidney. These cells have a single detectable truncating mutation (Q4004X) in polycystin-1. These cells make normal appearing but shorter cilia and fail to assemble polycystin-1 in the cilia, and less uncleaved polycystin-1 in membrane fractions. This cell line has been maintained in continuous passage for over 35 passages without going into senescence. Nephron segment specific markers suggest a proximal tubule origin for these cells and the cell line will be useful to study mechanistic details of cyst formation in proximal tubule cells.

Adult human CD133/1(+) kidney cells isolated from papilla integrate into developing kidney tubules

Approximately 60,000 patients in the United States are waiting for a kidney transplant due to genetic, immunologic and environmentally caused kidney failure. Adult human renal stem cells could offer opportunities for autologous transplant and repair of damaged organs. Current data suggest that there are multiple progenitor types in the kidney with distinct localizations. In the present study, we characterize cells derived from human kidney papilla and show their capacity for tubulogenesis. In situ, nestin(+) and CD133/1(+) cells were found extensively intercalated between tubular epithelia in the loops of Henle of renal papilla, but not of the cortex. Populations of primary cells from the renal cortex and renal papilla were isolated by enzymatic digestion from human kidneys unsuited for transplant and immuno-enriched for CD133/1(+) cells. Isolated CD133/1(+) papillary cells were positive for nestin, as well as several human embryonic stem cell markers (SSEA4, Nanog, SOX2, and OCT4/POU5F1) and could be triggered to adopt tubular epithelial and neuronal-like phenotypes. Isolated papillary cells exhibited morphologic plasticity upon modulation of culture conditions and inhibition of asymmetric cell division. Labeled papillary cells readily associated with cortical tubular epithelia in co-culture and 3-dimensional collagen gel cultures. Heterologous organ culture demonstrated that CD133/1(+) progenitors from the papilla and cortex became integrated into developing kidney tubules. Tubular epithelia did not participate in tubulogenesis. Human renal papilla harbor cells with the hallmarks of adult kidney stem/progenitor cells that can be amplified and phenotypically modulated in culture while retaining the capacity to form new kidney tubules. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Processing of tissue culture cells

Live cells are often studied, in vitro, bathed in nutrient growth media. It is sometimes necessary to study individual compounds produced by these cells and antibodies work well for this purpose. These cells must first be concentrated and fixed before testing. There are a couple of ways to study cells in culture using antibodies. One is to fix the cells in place as they adhere to a solid surface and then test them as though they were cells on a slide. Another is to retrieve them and pellet the cells, fixing them in a test tube and then embedding and sectioning them as though they were a solid tissue. Fixatives can be mild to moderate depending on the antigens to be studied. Sectioned cells can be tested following mild pretreatment steps. Cells fixed in the culture dish can be tested following mild pretreatment steps in buffers containing 0.25% Triton X-100 and 5% dimethylsulfoxide (DMSO) to allow for easier antibody penetration. The endogenous peroxidase enzyme or oxidative compounds can be quenched in a mild hydrogen peroxide solution. The sections are then ready to test with antibody after an incubation in a normal serum solution blocks any available charged sites.

A polycystin multiprotein complex constitutes a cholesterol-containing signalling microdomain in human kidney epithelia

Polycystins are plasma membrane proteins that are expressed in kidney epithelial cells and associated with the progression of ADPKD (autosomal dominant polycystic kidney disease). A polycystin multiprotein complex, including adherens junction proteins, is thought to play an important role in cell polarity and differentiation. Sucrose gradient analyses and immunoprecipitation studies of primary human kidney epithelial cells showed the polycystins and their associated proteins E-cadherin and beta-catenin distributed in a complex with the raft marker flotillin-2, but not caveolin-1, in high-density gradient fractions. The integrity of the polycystin multiprotein complex was sensitive to cholesterol depletion, as shown by cyclodextrin treatment of immunoprecipitated complexes. The overexpressed C-terminus of polycystin-1 retained the ability to associate with flotillin-2. Flotillin-2 was found to contain CRAC (cholesterol recognition/interaction amino acid) cholesterol-binding domains and to promote plasma membrane cholesterol recruitment. Based on co-association of signalling molecules, such as Src kinases and phosphatases, we propose that the polycystin multiprotein complex is embedded in a cholesterol-containing signalling microdomain specified by flotillin-2, which is distinct from classical light-buoyant-density, detergent-resistant domains.

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

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

New insights into ADPKD molecular pathways using combination of SAGE and microarray technologies

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 or PKD2 gene, but cellular mechanisms of cystogenesis remain unclear. In an attempt to display the array of cyst-specific molecules and to elucidate the disease pathway, we have performed comprehensive high-throughput expression analysis of normal and ADPKD epithelia in a two-step fashion. First, we generated expression profiles of normal and cystic epithelia derived from kidney and liver using serial analysis of gene expression (SAGE). We found 472 and 499 differentially expressed genes with fivefold difference in liver and kidney libraries, respectively. These genes encode growth factors, transcription factors, proteases, apoptotic factors, molecules involved in cell-extracellular matrix interactions, and ion channels. As a second step, we constructed a custom cDNA microarray using a subset of the differentially regulated genes identified by SAGE and interrogated ADPKD patient samples. Subsequently, a set of differentially expressed genes was refined to 26 up-regulated and 48 down-regulated genes with ap value of <0.01. This study may provide valuable insights into the pathophysiology of ADPKD and suggest potential therapeutic targets.

A polycystin-1 multiprotein complex is disrupted in polycystic kidney disease cells

Autosomal dominant polycystic kidney disease (ADPKD) is typified by the accumulation of fluid-filled cysts and abnormalities in renal epithelial cell function. The disease is principally caused by mutations in the gene encoding polycystin-1, a large basolateral plasma membrane protein expressed in kidney epithelial cells. Our studies reveal that, in normal kidney cells, polycystin-1 forms a complex with the adherens junction protein E-cadherin and its associated catenins, suggesting a role in cell adhesion or polarity. In primary cells from ADPKD patients, the polycystin-1/polycystin-2/E-cadherin/beta-catenin complex was disrupted and both polycystin-1 and E-cadherin were depleted from the plasma membrane as a result of the increased phosphorylation of polycystin-1. The loss of E-cadherin was compensated by the transcriptional upregulation of the normally mesenchymal N-cadherin. Increased cell surface N-cadherin in the disease cells in turn stabilized the continued plasma membrane localization of beta-catenin in the absence of E-cadherin. The results suggest that enhanced phosphorylation of polycystin-1 in ADPKD cells precipitates changes in its localization and its ability to form protein complexes that are critical for the stabilization of adherens junctions and the maintenance of a fully differentiated polarized renal epithelium.

Molecular genetics and pathogenesis of autosomal dominant polycystic kidney disease

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

Compromised cytoarchitecture and polarized trafficking in autosomal dominant polycystic kidney disease cells

Cystogenesis associated with autosomal dominant polycystic kidney disease (ADPKD) is characterized by perturbations in the polarized phenotype and function of cyst-lining epithelial cells. The polycystins, the protein products of the genes mutated in the majority of ADPKD cases, have been described recently, but the pathological mechanism by which causal mutations result in the mislocalization of cell membrane proteins has remained unclear. This report documents the dissociation from the ADPKD cell basolateral membrane of three molecules essential for spatial organization and exocytosis. The adherens junction protein E-cadherin, the subcellular disposition of which governs intercellular and intracellular architecture, was discovered sequestered in an internal ADPKD cell compartment. At the same time, sec6 and sec8, components of a complex critical for basolateral cargo delivery normally arrayed at the apico-lateral apex, were depleted from the ADPKD cell plasma membrane. An analysis of membrane transport revealed that basolateral trafficking of proteins and lipids was impaired as a result of delayed cargo exit from the ADPKD cell Golgi apparatus. Apical transport proceeded normally. Taken together with recent documentation of an association between polycystin-1 and E-cadherin (Huan and van Adelsberg 1999), the data suggest that causal mutations disrupt E-cadherin-dependent cytoarchitecture, adversely affecting protein assemblies crucial for basolateral trafficking.

Loss of the polycystic kidney disease (PKD1) region of chromosome 16p13 in renal cyst cells supports a loss-of-function model for cyst pathogenesis

It is not known whether mutations in the PKD1 gene cause autosomal dominant polycystic kidney disease (PKD) by an activating (gain-of-function) or an inactivating (loss-of-function) model. We analyzed DNA from cyst epithelial cells for loss of heterozygosity (LOH) in the PKD1 region of chromosome 16p13 using microsatellite markers. 29 cysts from four patients were studied. Five cysts from three patients had chromosome 16p13 LOH. Four of the cysts had loss of two chromosome 16p13 markers that flank the PKD1 gene. In two patients, microsatellite analysis of family members was consistent with loss of the wild-type copy of PKD1 in the cysts. In the third patient, 16p13 LOH was detected in three separate cysts, all of which showed loss of the same alleles. Chromosome 3p21 LOH was detected in one cyst. No LOH was detected in four other genomic regions. These results demonstrate that some renal cyst epithelial cells exhibit clonal chromosomal abnormalities with loss of the wild-type copy of PKD1. This supports a loss-of-function model for autosomal dominant PKD, with a germline mutation inactivating one copy of PKD1 and somatic mutation or deletion inactivating the remaining wild-type copy.

Comparison of the morphology of renal cysts and cystic renal tumors

Renal tumors appear uncommonly with cystic changes. They may develop due to necrosis though well-formed real cysts are also known. Such lesions may present problems in distinguishing them from benign renal cysts. Conditions leading to cyst formation are not known, however cell proliferation, altered extracellular matrix production and oncoprotein expression have been reported in cystic renal disorders. In the present study, we analysed the morphological features of 23 cystic renal tumors in comparison with 16 benign cysts using immunohistochemical and lectin binding methods. By our knowledge there has not been any piblication on such studies. The cystic renal tumors were represented predominantly in males and the size of the cysts was slightly larger than that of benign cysts. Tumorous cysts shared similar morphological appearance to solitary and multilocular cysts. They all showed strong epithelial membrane antigen reactivity on the luminal surface of the cells indicating distal tubular origin. Cell proliferation and p53 expression proved to be low excluding their role in the formation of the cysts. The amount of extracellular matrix and basement membrane was increased with an elevated type IV collagen and reduced fibronectin content. Polycystic kidney disease is different from tumorous cysts as cell proliferation, p53 oncoprotein expression and the composiition of extracellular matrix proved to be the opposite. As renal cell tumors arise from proximal tubules, neoplastic or metaplastic differentiation toward distal tubular direction seems to be the key even in cyst formation. Altered cell-matrix or cell-cell contact can modulate this transformation providing a basis for further results.

The etiology, pathogenesis, and treatment of autosomal dominant polycystic kidney disease: recent advances

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in at least three different genes: PKD1, PKD2, and PKD3. ADPKD1 is an inherited disorder that has led to the discovery of a novel protein, polycystin. Polycystin, a 460 kd protein with a host of domains implicating a potential role in cell-cell and cell-matrix regulation, is encoded by a 52 kb gene with a 14 kb mRNA. The PKD2 protein is also large (110 kd) and is thought to interact with polycystin. ADPKD1 is caused by mutated DNA that encodes an abnormal form of polycystin. Polycystin appears to have a normal role in the differentiation of epithelial cells, and when defective, these cells fail to maturate fully. These incompletely differentiated cells proliferate abnormally and express altered amounts of otherwise normal electrolyte transport proteins that result in excessive secretion of solute and fluid into the cysts. The proliferation of the cells and the associated apoptosis, and the secretion of the fluid into the cysts created by the enlarging tubule segments appear to be regulated by growth factors, hormones, and cytokines that can alter the extent to which the disease is clinically expressed among individuals. The formation of the cysts is associated with complex changes in the extracellular matrix of the kidneys and other organs that may be directly or indirectly tied to mutated polycystin. The summation of these pathogenetic elements leads to renal interstitial infiltration, with monocytes, macrophages, and fibroblasts culminating in fibrosis and progressive loss of renal function. The modem understanding of cyst pathogenesis opens opportunities to develop treatments that may diminish or halt altogether the progression of this disease.

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.

Growth characteristics of cells cultured from two murine models of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by multiple renal cysts that are lined by epithelium and filled with fluid. PKD may result from one of a number of factors, either inherited or environmental. In this study, we have compared two mouse models in which PKD results from a genetic cause. In the C57BL/6J-cpk model, the mutated gene is unknown. In the other model, an SV40 large T antigen transgene causes renal cysts. We examined cultured cells from the kidneys of these mouse models, comparing growth characteristics. Although several features of PKD lead one to expect that the epithelial cells lining the cysts would have an increased rate of proliferation in culture, we found that they did not. The implications of these findings are discussed.

Renal expression of a transforming growth factor-alpha transgene accelerates the progression of inherited, slowly progressive polycystic kidney disease in the mouse

Polycystic kidney disease (PKD) is a prevalent inherited disease in human beings. The pathogenesis of PKD is as yet unclear. The epidermal growth factor family of proteins has been implicated in PKD based largely on in vitro data. To determine whether these growth factors contribute to the progression of inherited PKD in vivo, we crossed mice with a transgene for human transforming growth factor-alpha (TGF-alpha, a member of the epidermal growth factor (EGF) family) and mice with the pcy gene (which causes a slowly progressive form of PKD very similar to human autosomal dominant PKD). Renal expression of the TGF-alpha transgene in cystic mice (homozygous for the pcy gene) accelerated the development of PKD as shown by an increased kidney weight as a percent of body weight and an increased volume density of renal cysts at 8.5 weeks of age. However, renal expression of the TGF-alpha transgene did not appear to precociously initiate cyst development (at 6.5 weeks), nor did it cause an increase in the final degree of renal enlargement (at 29 weeks). Thus TGF-alpha accelerated the enlargement of cysts once initiated. At 8.5 weeks of age, renal expression of the TGF-alpha mRNA correlated positively with the amount of renal enlargement. At all time points studied, cystic kidneys exhibited increased expression of c-myc mRNA as compared with phenotypic normal kidneys, consistent with PKD being a hyperplastic disease of renal tubules. However, the renal expression of c-myc in 8.5 week cystic kidneys, with or without the transgene, did not correlate with the degree of renal enlargement. The results of this study suggest that EGF-like proteins may accelerate the progression of inherited renal cystic disease. However, the final degree of cystic change is dictated by the primary disease process rather than by the continued presence of growth factor.

Isolation of pepsin-resistant laminin fragments from human placenta: effect on epithelial cells cultured from the kidneys of patients with autosomal dominant polycystic kidney disease (ADPKD)

Laminin isolated from human placenta was subjected to prolonged pepsin digestion. Seven peptide fragments (designated N1 to N7) were separated by ion-exchange chromatography and gel filtration and characterised by SDS-polyacrylamide gel electrophoresis and immunoblotting. The molecular size of the laminin fragments varied from approx. 900,000 (N1) to 28,000 (N7). Epithelial cells obtained from normal kidneys and patients with autosomal dominant polycystic kidney disease (ADPKD) were cultured. The incorporation of [3H]thymidine was measured over 96 h to determine the effect of the addition of the different fragments and whole laminin from EHS tumour to the cells. The rate of growth of both normal and polycystic cells was increased in the presence of the laminin fragments but this effect was more pronounced in the ADPKD cells.

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

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

Epidermal growth factor receptor expression is abnormal in murine polycystic kidney

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

Polycystic kidney disease--a truly pediatric problem

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

Characterization of the Han:SPRD rat model for hereditary polycystic kidney disease

The Han:SPRD rat model for inherited polycystic kidney disease (PKD) was characterized (clinical parameters, morphology, immunohistochemistry and in situ hybridization). Homozygous animals died of uremia after three to four weeks with severe cystic transformation of virtually all nephrons and collecting ducts (serum urea: 616 +/- 195 mg/dl; kidney-to-body weight ratio: > 20%). In heterozygotes, slow progression of the disease led to death between the 12th and 21st month (median: 17 months; serum urea levels above 200 mg/dl). Kidney enlargement was moderate, and cysts were restricted to the cortex and outer medulla. Immunohistochemical markers showed that approximately 75% of the cysts were derived from the proximal tubule. Cystic transformation started in the proximal tubule with a sharp onset of basement membrane alteration and a loss of epithelial differentiation restricted to small focal areas. In these areas, alpha 1(IV) collagen and laminin B1 mRNA were enhanced as revealed by isotopic and non-isotopic in situ hybridization. Fibroblasts underlying the affected tubular portions were involved in matrix overexpression resulting in subepithelial accumulation of immunoreactive collagen IV and laminin. In later stages of cystic transformation distal nephron segments were affected as well. A reversal in epithelial polarity as judged from Na,K-ATPase-immunoreactivity was not observed. Renal immunoreactive renin-status was significantly decreased. Hematocrit was lowered in heterozygotes (40.4 +/- 5.8 vol% compared to 46.7 +/- 1.99 vol% in controls; P < 0.05) and total renal EPO mRNA was reduced to 36 +/- 14% of the mean value of control animals, whereas serum EPO levels were not significantly altered. We conclude that the Han:SPRD rat is a useful model for the study of human ADPKD since both diseases are similar in several aspects. The model is particularly suitable for the study of epithelial-mesenchymal interactions at the beginning of tubular cystic transformation.

Taxol inhibits progression of congenital polycystic kidney disease

Polycystic kidney diseases (PKD) are the most common hereditary diseases of the human kidney and account for ten per cent of patients requiring renal transplantation or dialysis. Renal cyst formation has been attributed to enhanced cell proliferation, unbalanced cell death, abnormal targeting of membrane proteins, aberrant kidney development and tubular obstruction, but there is no treatment that blocks the formation and enlargement of renal cysts. We have now developed an in vitro model of spontaneous cyst formation that distinguishes polycystic kidney epithelium from its normal counterpart. Inhibitors of DNA, RNA and protein synthesis did not prevent in vitro cyst formation, but this was reversibly inhibited by ouabain, amiloride and the microtubule-specific agents colchicine, vinblastine and taxol. The cpk mouse is a well-characterized recessive PKD model and we find that cpk/cpk mice develop PKD and die from uraemia by 4-5 weeks of age, but when treated weekly with taxol they survive for more than 200 days with minimal loss of renal function, show limited collecting-dust cyst enlargement, and attain adult size. Our results indicate that the microtubule cytoskeleton has a central role in the pathogenesis of PKD in cpk mice and that taxol may also be useful in treating human PKD.

Extracellular matrix formation by epithelial cells from human polycystic kidney cysts in culture

Cells from the cysts of patients with autosomal dominant polycystic kidney disease (PKD) were grown in vitro under standard conditions without the aid of collagen-pretreated surfaces, and both the synthesis and composition of the extracellular matrix were investigated. At confluence, PKD cells presented the typical features of epithelial cells, but showed a different collagen composition from fibroblasts. Compared with normal tubular epithelia (NTE), PKD monolayers produced an excess of extracellular matrix, which accounted for 30% of the total incorporation of [3H] proline, although this value was considerably lower (by a factor of 10) in the case of NTE. Immunohistochemical and electrophoretic techniques revealed a complex collagen composition in the extracellular matrix which included [alpha (III)]3 and collagen IV. However, part of the collagen components remained unidentified in spite of the fact that they exhibited a typical M(r) of alpha 1(I) and alpha 2(I) in the presence of urea. Immunoprecipitation with monospecific antibodies and Northern blotting with specific probes failed to recognize alpha 1(I) and alpha 2(I), but demonstrated their presence in fibroblasts. Purification and cyanogen bromide digestion demonstrated a strong interhomology in fingerprint peptide composition among the uncharacterized collagens synthesized by PKD cells, thus suggesting a common identity. These observations document a markedly augmented production of extracellular matrix by PKD cultured cells in vitro, and show the presence of collagens which do not share homologies with the major collagen molecules. A better characterization of extracellular matrix composition is central to any comprehension of the cytogenetic mechanisms in vivo.

Autosomal dominant polycystic kidney disease--in vitro culture of cyst-lining epithelial cells

The major form of autosomal dominant polycystic kidney disease (ADPKD) in humans is linked to the PKD1 gene on chromosome 16p. The identity of the gene and the underlying pathogenetic mechanisms are not yet defined. Cyst-lining epithelial cells derived from a polycystic kidney were successfully grown in culture and designated MZ-PKD-1 cells. By linkage analysis, the related pedigree of the nephrectomized patient could be linked to the PKD1 gene on chromosome 16p. Thus, these cells exhibit the genotype of a mutated PKD1 gene and represent an in vitro culture model for ADPKD involving chromosome 16p. The antigenic phenotype was characterized immunohistologically by epithelial differentiation antigens and markers of individual nephron segments. An essentially identical antigenic pattern of proximal tubular cells was observed both in vitro and in fresh frozen tissue. Electron microscopy showed the formation of a microvillous-like coating. During growth phases in vitro successive changes in the cell shape were observed. MZ-PKD-1 cells exhibited a limited lifespan ending in replicative senescence. Northern blot analysis of kidney-growth-related genes, c-myc, TGF-alpha, TGF-beta 1, and EGF receptor revealed abundant expression of all of these genes in MZ-PKD-1 cells.

Expression of differentiation antigens and growth-related genes in normal kidney, autosomal dominant polycystic kidney disease, and renal cell carcinoma

Cellular differentiation and mRNA levels of genes involved in kidney growth were investigated in normal kidney cells, cyst-lining epithelial cells of polycystic kidney disease, and renal carcinoma cells (RCC). All cells comparatively studied exhibited an antigenic phenotype of proximal tubular cells as shown by the expression of a panel of brush border membrane enzymes and kidney-associated cell surface antigens. The epithelial developmental antigen Exo-1 was expressed in 50% to 80% of cyst-lining epithelia in polycystic kidney tissue and in 20% to 30% of polycystic kidney cells cultured in vitro. Normal kidney cells and RCC were negative under identical culture conditions. The expression of antigen Exo-1 is associated with hyperproliferation in an epithelial tissue compartment composed of cells which have not yet reached their terminal differentiation state. Increased amounts of mRNA of the growth factor receptor system of epidermal growth factor (EGF) receptor and its ligand transforming growth factor (TGF)-alpha were associated with the malignant phenotype of RCC. Increased expression of EGF receptor and TGF-alpha, although less prominent, were also observed in polycystic kidney cells compared with normal kidney cells. In conclusion, the expression of Exo-1 in cyst-lining epithelial cells of autosomal dominant polycystic kidney disease (ADPKD) and the altered regulation of TGF-alpha and EGF receptor in these cells contribute to the hypothesis that hyperproliferation is an underlying pathogenic mechanism of ADPKD.

Comparison of proteoglycans synthesized by porcine normal and polycystic renal tubular epithelial cells in vitro

Newly synthesized porcine tubular epithelial cell proteoglycans were labeled in vitro with Na2[35S]SO4. At the beginning of the labeling period (24 h) [35S] sulfate incorporated into macromolecules was measured following PD-10 chromatography. There was a significant reduction in the amount of 35S-labeled macromolecules isolated from polycystic cells compared to that from normal cells. The distribution of recovered radiolabeled material among the medium, cell surface, and intracellular fractions was similar for both normal and polycystic cells. Analysis of the proteoglycans in polycystic cells demonstrated that 86 and 73% of 35S-labeled macromolecules were of the heparan sulfate type in polycystic and normal cells, respectively. The remainder was chondroitin sulfate. Proteoglycans were characterized using DEAE-Sephacel ion-exchange chromatography, chondroitinase ABC, heparitinase, and nitrous acid digestion followed by Sepharose CL-4B gel permeation chromatography. The majority of radiolabeled material in the medium, cell surface, and intracellular fractions eluted between 0.35 and 0.39 M NaCl. However, a second peak (peak II) that eluted at 0.25 M NaCl was found in the medium from polycystic cells. This peak accounted for 27% of the total macromolecules secreted into the medium. Proteoglycans in the major peak were susceptible to nitrous acid and chondroitinase ABC digestion. A similar proportion of peak II was degraded by chondroitinase ABC. However, the remainder was only slightly susceptible to treatment with nitrous acid or heparitase. In normal cells a small amount of material eluted at a similar low charge; the proteoglycans were the same as those found in the major peak and appeared as a shoulder on this peak.

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

The mechanisms responsible for renal cyst formation in congenital polycystic kidney disease remain unknown, although abnormalities of cellular metabolism, basement membrane components, and growth factors have been suggested. In the present study, we examined a potential role for epidermal growth factor (EGF) in cyst formation in a mouse model. We measured growth factor activity and concentration in renal cyst fluid, urine, and serum obtained from mice with congenital polycystic kidney disease (cpk). In affected mice, both growth factor activity of urine and the urinary EGF concentration were much lower than unaffected littermate controls even when corrected for creatinine concentration. Although the growth factor activity was much lower in affected mice, there were significant differences in the regional distribution of EGF in animals with cysts. Both growth factor activity and EGF concentration were greater in cyst fluid when compared to urine. Growth factor activity in cysts was completely inhibited by anti-EGF antibody using BALB/MK epithelial keratinocytes as targets. The expression of EGF mRNA in kidneys from affected mice was markedly decreased when compared to littermate controls. These results suggest that decreased EGF production and local differences in EGF concentration may contribute to cyst formation.

Human renal biopsies as source of cells for glomerular and tubular cell cultures

Glomerular and tubular cells were obtained from normal and pathological human renal biopsies. Single nephron structures were isolated by microdissection for culture. Proximal and distal tubular cells were cultivated for 5-6 weeks (three passages), whereas outgrowth of glomerular cells was sparse and after three weeks infiltrated by mesangial cells. The morphology of cultures obtained from pathological tissue was comparable with the morphology of normal cells, although cultures were more often overgrown by fibroblasts. In culture, both proximal and distal tubular cells retained physiological responses characteristic of their origin. Epidermal growth factor induced growth of proximal tubular cells. The proximal tubular cells were furthermore characterized by cAMP response to parathyroid hormone (PTH) stimulation. The distal tubular cells showed cAMP response to both PTH and vasopressin stimulation. Twelve of 17 cultures obtained from patients with no tubular injuries showed cAMP response to PTH stimulation compared with 2 of 9 cultures from renal tissue with tubular injuries.

Autosomal dominant polycystic kidney disease--more than a renal disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease, affecting a half million Americans. The clinical phenotype can result from at least two different gene defects. One gene that can cause ADPKD has been located on the short arm of chromosome 16. This discovery has made possible new methods for diagnosing the disorder in gene carriers prior to the development of renal cysts. Although renal cysts are clearly an important manifestation of the gene defect, other systemic manifestations are both common and clinically important. Cardiac valvular lesions, intracranial aneurysms, hepatic cysts, and diverticula are included in the array of systemic manifestations. Moreover, renal cysts are only one of a myriad of renal manifestations. Although ADPKD was long considered an adult cystic disease, it is also a common cause of childhood cystic disease and must be considered in the differential diagnosis in that setting.

Autosomal recessive polycystic kidney disease: characterization of human peritoneal and cystic kidney cells in vitro

Renal cystic epithelia and peritoneal mesothelia from two humans with autosomal recessive polycystic kidney disease (ARPKD) were grown in culture. Cystic epithelial and mesothelial cells formed continuous monolayers in vitro. By electron microscopy, cystic renal cells exhibited a single apical cilium and numerous short, stubby microvilli, both in situ and in vitro. Mesothelial cells exhibited intra- and extracellular membrane-limited, lipid-filled vesicles and surface microvilli. Cystic kidney cells in vitro stained positive for lectins from Cancanavalia ensiformis (concanavalin A), Triticum vulgaris, Erythrina cristagalli, Ulex europeaus, and Arachis hypogaea. Immunocytochemical and lectin staining revealed the renal and peritoneal cells to be of collecting tubule and mesothelial origin, respectively. Both cell types showed large depositions of glycogen granules in the cytoplasm during propagation in certain culture media; in kidney cells, dibutyryl cyclic adenosine monophosphate (cAMP) abolished glycogen depositions. Glycogen deposition also was observed in liver tissue obtained by needle biopsy from one patient. No bacteria were cultured from nor endotoxin detected in the renal cyst fluid. Relative to serum, the cyst fluids contained low sodium, potassium, and chloride levels. Thus, cultured ARPKD cells demonstrate a number of characteristics that are different from cells derived from the autosomal dominant form of renal cystic disease (ADPKD).