Polycystic kidney disease: clues to pathogenesis

High-resolution melt as a screening method in autosomal dominant polycystic kidney disease (ADPKD)

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited condition caused by PKD1 and PKD2 mutations. Complete analysis of both genes is typically required in each patient. In this study, we explored the utility of High-Resolution Melt (HRM) as a tool for mutation analysis of the PKD2 gene in ADPKD families.

METHODS

HRM is a mismatch-detection method based on the difference of fluorescence absorbance behavior during the melting of the DNA double strand to denatured single strands in a mutant sample as compared to a reference control. Our families were previously screened by linkage analysis. Subsequently, HRM was used to characterize PKD2-linked families. Amplicons that produced an overlapping profile sample versus wild-type control were not further evaluated, while those amplicons with profile deviated from the control were consequently sequenced.

RESULTS

We analyzed 16 PKD2-linked families by HRM analysis. We observed ten different variations: six single-nucleotide polymorphisms and four mutations. The mutations detected by HRM and confirmed by sequencing were as follows: 1158T>A, 2159delA, 2224C>T, and 2533C>T. In particular, the same haplotype block and nonsense mutation 2533C>T was found in 8 of 16 families, so we suggested the presence of a founder effect in our province.

CONCLUSIONS

We have developed a strategy for rapid mutation analysis of the PKD2 gene in ADPKD families, which utilizes an HRM-based prescreening followed by direct sequencing of amplicons with abnormal profiles. This is a simple and good technique for PKD2 genotyping and may significantly reduce the time and cost for diagnosis in ADPKD.

Cystogenic potential of CD133+ progenitor cells of human polycystic kidneys

In autosomal dominant polycystic kidney disease, cysts arise focally and disrupt normal renal tissue leading to renal failure. In the present study, we show that cyst-lining cells express the stem cell marker CD133. CD133+ progenitor cells isolated from polycystic kidney, carrying mutations of PKD genes, showed a dedifferentiated phenotype similar to CD133+ progenitor cells from normal kidney. However, these cells were more proliferative and presented a defective epithelial differentiation phenotype with respect to normal renal CD133+ cells as they were not able to express all tubular epithelial cell markers when cultured in epithelial differentiation medium. Polycystic CD133+ cells, in contrast to normal renal CD133+ cells, formed cysts in vitro in a three-dimensional culture system and in vivo when injected subcutaneously within Matrigel in SCID mice. Rapamycin treatment reduced in vitro proliferation of polycystic CD133+ cells and decreased cystogenesis both in vitro and in vivo. The in vitro epithelial differentiation was only partially improved by rapamycin. These results indicate that polycystic CD133+ cells retain a dedifferentiated phenotype and the ability to generate cysts.

Polycystic kidney disease: the complexity of planar cell polarity and signaling during tissue regeneration and cyst formation

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is an inherited systemic disease with intrarenal cystogenesis as its primary characteristic. A variety of mouse models provided information on the requirement of loss of balanced polycystin levels for initiation of cyst formation, the role of proliferation in cystogenesis and the signaling pathways involved in cyst growth and expansion. Here we will review the involvement of different signaling pathways during renal development, renal epithelial regeneration and cyst formation in ADPKD, focusing on planar cell polarity (PCP) and oriented cell division (OCD). This will be discussed in context of the hypothesis that aberrant PCP signaling causes cyst formation. In addition, the role of the Hippo pathway, which was recently found to be involved in cyst growth and tissue regeneration, and well-known for regulating organ size control, will be reviewed. The fact that Hippo signaling is linked to PCP signaling makes the Hippo pathway a novel cascade in cystogenesis. The newly gained understanding of the complex signaling network involved in cystogenesis and disease progression, not only necessitates refining of the current hypothesis regarding initiation of cystogenesis, but also has implications for therapeutic intervention strategies. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

New mutations in the PKD1 gene in Czech population with autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease. The disease is caused by mutations of the PKD1 (affecting roughly 85% of ADPKD patients) and PKD2 (affecting roughly 14% of ADPKD patients) genes, although in several ADPKD families, the PKD1 and/or PKD2 linkage was not found. Mutation analysis of the PKD1 gene is complicated by the presence of highly homologous genomic duplications of the first two thirds of the gene.

METHODS

The direct detection of mutations in the non-duplicated region of the PKD1 gene was performed in 90 unrelated individuals, consisting of 58 patients with end-stage renal failure (manifesting before their 50th year of life) and 32 individuals from families where the disease was clearly linked to the PKD1 gene. Mutation screening was performed using denaturing gradient gel electrophoresis (DGGE). DNA fragments showing an aberrant electrophoretic banding pattern were sequenced.

RESULTS

In the non-duplicated region of the PKD1 gene, 19 different likely pathogenic germline sequence changes were identified in 19 unrelated families/individuals. Fifteen likely pathogenic sequence changes are unique for the Czech population. The following probable mutations were identified: 9 nonsense mutations, 6 likely pathogenic missense mutations, 2 frameshifting mutations, one in-frame deletion and probable splice site mutation. In the non-duplicated region of the PKD1 gene, 16 different polymorphisms or unclassified variants were detected.

CONCLUSION

Twenty probable mutations of the PKD1 gene in 90 Czech individuals (fifteen new probable mutations) were detected. The establishment of localization and the type of causal mutations and their genotype phenotype correlation in ADPKD families will improve DNA diagnosis and could help in the assessment of the clinical prognosis of ADPKD patients.

Lixazinone stimulates mitogenesis of Madin-Darby canine kidney cells

Polycystic kidney diseases (PKD) are characterized by excessive proliferation of renal tubular epithelial cells, development of fluid-filled cysts, and progressive renal insufficiency. cAMP inhibits proliferation of normal renal tubular epithelial cells but stimulates proliferation of renal tubular epithelial cells derived from patients with PKD. Madin-Darby canine kidney (MDCK) epithelial cells, which are widely used as an in vitro model of cystogenesis, also proliferate in response to cAMP. Intracellular cAMP levels are tightly regulated by phosphodiesterases (PDE). Isoform-specific PDE inhibitors have been developed as therapeutic agents to regulate signaling pathways directed by cAMP. In other renal cell types, we have previously demonstrated that cAMP is hydrolyzed by PDE3 and PDE4, but only PDE3 inhibitors suppress proliferation by inhibiting Raf-1 activity (Cheng J, Thompson MA, Walker HJ, Gray CE, Diaz Encarnacion MM, Warner GM, Grande JP. Am J Physiol Renal Physiol 287:F940-F953, 2004.) A potential role for PDE isoform(s) in cAMP-mediated proliferation of MDCK cells has not previously been established. Similar to what we have previously found in several other renal cell types, cAMP hydrolysis in MDCK cells is directed primarily by PDE4 (85% of total activity) and PDE3 (15% of total activity). PDE4 inhibitors are more effective than PDE3 inhibitors in increasing intracellular cAMP levels in MDCK cells. However, only PDE3 inhibitors, and not PDE4 inhibitors, stimulate mitogenesis of MDCK cells. PDE3 but not PDE4 inhibitors activate B-Raf but not Raf-1, as assessed by an in vitro kinase assay. PDE3 but not PDE4 inhibitors activate the ERK pathway and activate cyclins D and E, as assessed by histone H1 kinase assay. We conclude that mitogenesis of MDCK cells is regulated by a functionally compartmentalized intracellular cAMP pool directed by PDE3. Pharmacologic agents that stimulate PDE3 activity may provide the basis for new therapies directed toward reducing cystogenesis in patients with PKD.

Autosomal dominant polycystic kidney disease presenting as subarachnoid hemorrhage

Intracranial aneurysms occur in patients with autosomal dominant polycystic kidney disease (ADPKD) approximately five times more often than in the general population, and in the same patient group, subarachnoid hemorrhage from rupture of aneurysms occurs about a decade earlier than in the general population. We present a case of unsuspected ADPKD presenting as spontaneous subarachnoid hemorrhage from a ruptured intracranial aneurysm.

A "two-hit" model of cystogenesis in autosomal dominant polycystic kidney disease?

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic nature of individual cyst formation. Typically, only a few renal cysts are detectable in an affected individual during the first two decades of life. By the fifth decade, however, hundreds to thousands of renal cysts can be found in most patients. Additionally, significant intra-familial variability of ADPKD has been well documented. Taken together, these findings suggest that factor(s) in addition to the germline mutation of a polycystic kidney disease gene might be required for individual cyst formation. Indeed, recent studies have provided compelling evidence in support of a "two-hit" model of cystogenesis in ADPKD. In this model, inactivation of both copies of a polycystic kidney disease gene by germline and somatic mutations within an epithelial cell provides growth advantages for it to proliferate clonally into a cyst. This article highlights key findings of these recent studies and discusses the controversies and implications of the "two-hit" model in ADPKD.

Novel mutations of the PKD1 gene in Korean patients with autosomal dominant polycystic kidney disease

The gene for the most common form of autosomal dominant polycystic kidney disease (ADPKD), PKD1, has recently been characterized and shown to encode an integral membrane protein, polycystin-1, which is involved in cell-cell and cell-matrix interactions. Until now, approximately 30 mutations of the 3' single copy region of the PKD1 gene have been reported in European and American populations. However, there is no report of mutations in Asian populations. Using the polymerase chain reaction and single-strand conformation polymorphism (SSCP) analysis, 91 Korean patients with ADPKD were screened for mutation in the 3' single copy region of the PKD1 gene. As a result, we have identified and characterized six mutations: three frameshift mutations (11548del8bp, 11674insG and 12722delT), a nonsense mutation (Q4010X), and two missense mutations (R3752W and D3814N). Five mutations except for Q4010X are reported here for the first time. Our findings also indicate that many different mutations are likely to be responsible for ADPKD in the Korean population. The detection of additional disease-causing PKD1 mutations will help in identifying the location of the important functional regions of polycystin-1 and help us to better understand the pathophysiology of ADPKD.

Somatic PKD2 mutations in individual kidney and liver cysts support a "two-hit" model of cystogenesis in type 2 autosomal dominant polycystic kidney disease

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic formation of renal and extrarenal cysts. Recent documentation of somatic PKD1 mutations in cystic epithelia of patients with germ-line PKD1 mutations suggests a "two-hit" model for cystogenesis in type 1 ADPKD. This study tests whether the same mechanism for cystogenesis might also occur in type 2 ADPKD. Genomic DNA was obtained from 54 kidney and liver cysts from three patients with known germ-line PKD2 mutations, using procedures that minimize contamination of cells from noncystic tissue. Using intragenic and microsatellite markers, these cyst samples were screened for loss of heterozygosity. The same samples were also screened for somatic mutations in five of the 15 exons in PKD2 by single-stranded conformational polymorphism analysis. Loss of heterozygosity was found in five cysts, and unique intragenic mutations were found in seven other cysts. In 11 of these 12 cysts, it was also determined that the somatic mutation occurred nonrandomly in the copy of PKD2 inherited from the unaffected parent. These findings support the "two-hit" model as a unified mechanism for cystogenesis in ADPKD. In this model, the requirement of a somatic mutation as the rate-limiting step for individual cyst formation has potential therapeutic implications.

Mutational analysis within the 3' region of the PKD1 gene

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic diseases in humans, affecting 1 out of 1000 individuals. At least three different genes are involved in this disease. The search for mutations in PKD1 is complicated because most of the transcript is encoded by a genomic region reiterated more proximally on chromosome 16, and no prevalent mutation has been reported.

METHODS

We have screened DNA from exon 43 through exon 46 and intron 40 of the PKD1 sequence by single-stranded conformational polymorphism (SSCP) analysis in 175 ADPKD patients.

RESULTS

We have found 25 differences with respect to the reported PKD1 DNA sequence, seven of which are mutations (Q4041X, Q4124X, IVS44-1G-->C, IVS45-1G-->A, 12801del28, R4275W, and Q4224P). We found different phenotypical expressions of the same mutation in the families studied. We have detected several common polymorphisms, and some of them cosegregate, suggesting a common origin of these alleles in PKD1.

CONCLUSIONS

The detection of only seven mutations in 175 unrelated ADPKD patients for this region of the PKD1 analyzed suggests that mutations could be widespread throughout all of the gene and that a prevalent mutation is not expected to occur. The identified PKD1 missense mutations may help to refine critical regions of the protein. Until a quicker and more sensitive method for the detection of mutations becomes available, linkage studies will continue to be the basis for the molecular diagnosis of ADPKD families.

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.

Nuclear localization of beta-catenin and loss of apical brush border actin in cystic tubules of bcl-2 -/- mice

Tight regulation of the rates of cell proliferation and apoptosis is critical for normal nephrogenesis. Nephrogenesis is profoundly affected by the loss of bcl-2 expression. Bcl-2-deficient (bcl-2 -/-) mice are born with renal hypoplasia and succumb to renal failure secondary to renal multicystic disease. Cell-cell and cell-matrix interactions impact tissue architecture by modulating cell proliferation, migration, differentiation, and apoptosis. E-cadherin mediates calcium-dependent homotypic cell-cell interactions that are stabilized by its association with catenins and the actin cytoskeleton. The contribution of altered cell-cell interactions to renal cystic disease has not been delineated. Cystic kidneys from bcl-2 -/- mice displayed nuclear localization of beta-catenin and loss of apical brush border actin staining. The protein levels of alpha-catenin, beta-catenin, actin, and E-cadherin were not altered in cystic kidneys compared with normal kidneys. Therefore, an altered distribution of beta-catenin and actin, in kidneys from bcl-2 -/- mice, may indicate improper cell-cell interactions interfering with renal maturation and contributing to renal cyst formation.

The use of ultrasonography and linkage studies for early diagnosis of autosomal dominant polycystic kidney disease (ADPKD)

To define possibly affected members of 69 families and to identify the factors influencing the progression of autosomal dominant polycystic kidney disease (ADPKD), 276 subjects at risk of having inherited the mutant gene underwent ultrasonographic scanning (US), using an ultrasound real-time scanner. At a mean age of 26 +/- 12 years (range 4-71), 85/276 individuals (31%) presented ultrasound evidence of the disease (at least two cysts in one kidney and one cyst in the other) (US: positive), while only 19/85 (22%) had one or more manifestations of ADPKD prior to diagnosis. The prevalence of the disease in subjects at risk aged < 30 years was 53/154 (34%), while hepatic cysts were also detected in 7/85 ADPKD probands (8%) (five females) at a mean age of 40 +/- 6 years (range 30-45) and their frequency correlated with the number of pregnancies. History was proved to be important in suspecting the disease since symptoms were more common in US positive as compared to negative subjects (22% vs 6%, p < 0.001). On the other hand, physical examination and routine laboratory data at presentation revealed abnormal signs mainly in US positive individuals aged 30-39 years. Forty ADPKD families met the criterion for genetic study (at least two members affected) but in three of them (7.5%), no linkage to DNA-markers for the short arm of chromosome 16 was detected ("unlinked" or ADPKD2). DNA-analysis in the rest 37 "linked" (ADPKD1) families identified the gene-carrier state in 18/123 (15%) US negative subjects at risk, at a mean age of 13 +/- 7 years (range 3-25). There were significantly more US positive subjects aged > or = 30 years in ADPKD2 as compared to ADPKD1 families (83% vs 35%, p < 0.05) suggesting that the progression of the disease is slower in the former families. During a 5-year follow-up, 6/18 gene-carriers (33%) had already developed distinct renal cysts on US, at a mean age of 20 +/- 9 years (range 8-29). On the contrary, none of the ADPKD1 non-carriers and the US negative ADPKD2 subjects had shown any ultrasound findings of cystic renal disease at that period.

LOH at 16p13 is a novel chromosomal alteration detected in benign and malignant microdissected papillary neoplasms of the breast

Papillary carcinoma of the breast is a variant of predominantly intraductal carcinoma characterized by a papillary growth pattern with fibrovascular support. Loss of heterozygosity (LOH) was evaluated at multiple chromosomal loci (including loci reported to show frequent genetic alterations in breast cancer) to determine the frequency of genetic mutations in these tumors and their precursors. Thirty-three papillary lesions of the breast (6 papillary carcinomas, 12 carcinomas arising in a papilloma, and 15 intraductal papillomas with florid epithelial hyperplasia) were retrieved from the files of the Armed Forces Institute of Pathology (AFIP). Tumor cells and normal tissue were microdissected in each case and screened for LOH at INT-2 and p53 as well as several loci on chromosome 16p13 in the TSC2/PKD1 gene region (D16S423, D16S663, D16S665). LOH on chromosome 16p13 was present in 10 of 16 (63%) informative cases of either papillary carcinoma or carcinoma arising in a papilloma as well as in 6 of 10 (60%) informative cases of intraductal papilloma with florid epithelial hyperplasia (IDH). One case showed simultaneous LOH in both the florid IDH and carcinoma components of a papilloma. LOH was not observed at either INT-2 or p53 in any of the papillary carcinomas or papillomas with florid IDH. In conclusion, a high frequency of LOH at chromosome 16p13 (the TSC2/PKD1 gene region) is in both papillary carcinomas of the breast as well as in papillomas with florid IDH, including a case with LOH present simultaneously in both components. These findings suggest that chromosome 16p contains a tumor suppressor gene that frequently is mutated early in papillary neoplasia.

Matrix metalloproteinases and TIMPS in cultured C57BL/6J-cpk kidney tubules

Restructuring of basement membranes is a hallmark of the pathology of renal cystic disorders. Here, we present findings consistent with the view that basement membrane degradation by matrix metallo-proteinases (MMPs) may contribute to abnormal basement membrane structure in polycystic kidney disease. Cells from cystic kidney tubules embedded in collagen gels appeared to migrate through the gel. This migration through collagen indicated that these cells could degrade the matrix. To examine this activity, we cultured cystic kidney tubules derived from the C57BL/6J cpk/cpk mouse, a hereditary model of polycystic kidney disease, and assayed conditioned medium for the presence of MMPs and tissue inhibitors of metalloproteinases (TIMPs). The conditioned medium from the cystic tubules contained higher than normal levels of MMP-9, MMP-2, and MMP-3 as well as TIMP-1 and TIMP-2. A 101 kDa protease was present equally in cystic and control cultures and although inhibited by EDTA, it was not inhibited by TIMPs, nor activated by the mercurial compound APMA. These data suggest that cystic kidney tubules synthesize and secrete high levels of MMPs which may then participate in the restructuring of the tubular basement membrane.

Alterations of cathepsins B, H and L in proximal tubules from polycystic kidneys of the Han:SPRD rat

Abnormalities of tubular matrix metalloproteinases have been shown recently to occur early in the course of polycystic kidney disease (PKD). The present study was conducted to determine whether lysosomal cysteine proteinases were altered in proximal tubules from 2-month-old, heterozygous Han:SPRD rats. The activities of cathepsins B (-45%), H (-39%) and L (-37%) were significantly lower in proximal tubules from PKD rats as compared to healthy offspring. Enzyme proteins were also decreased (cath. B, 2.4 +/- 0.7-fold; cath. H, 1.9 +/- 0.6-fold; N = 4, P < 0.05), while mRNA levels for cathepsins B, H and L were not different. Tubular cystatin C, a major inhibitor of cathepsins, was normal with regard to protein and mRNA levels in PKD animals. The decrease in cathepsins in PKD was specific for tubules, as enzyme activities in glomeruli and liver tissue were unchanged and limited to the lysosomal compartment, since marker enzymes for cytoplasm, endoplasmatic reticulum and mitochondria were all normal. Intralysosomally, soluble enzymes like cathepsins and beta-NAG were decreased, while membrane-bound acid phosphatase was unchanged. The presence of cathepsins could be demonstrated in cyst fluid from homozygous PKD rats and urinary excretion of cathepsins was enhanced in heterozygous animals. Taken together, these findings indicate that the reduction in tubular cathepsins B, H and L was neither due to decreased gene expression nor to upregulation of specific inhibitors, but was likely due to enhanced apical secretion of these enzymes.

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.

Tubular gelatinase A (MMP-2) and its tissue inhibitors in polycystic kidney disease in the Han:SPRD rat

Thickening of the tubular basement membrane is one of the hallmarks of the polycystic kidney disease (PKD). The present study was conducted to investigate the potential role of the matrix metalloproteinase-2 (MMP-2) and its specific tissue inhibitors (TIMP-1 and TIMP-2) in the accumulation of matrix components in PKD. As a model of PKD, two-month-old heterozygous Han:SPRD rats, which are at an early stage of cystogenesis, were used. MMP-2, but not MMP-9 (gelatinase B) nor MMP-3 (stromelysin) could be detected in proximal tubules of the normal rat kidney. The presence of the inhibitors TIMP-1 and TIMP-2 was confirmed on the mRNA level. In tubules from PKD rats MMP-2 activity was lower (31 +/- 8 vs. 58 +/- 7 U/prep., N = 9, P < 0.05), mRNA of MMP-2 was reduced 4.2 +/- 0.6-fold (N = 4, P < 0.05) and enzyme protein was depressed 3.8 +/- 0.8-fold (N = 4, P < 0.05). By contrast, TIMP-1 mRNA was 9.0 +/- 1.1-fold and TIMP-2 mRNA 3.8 +/- 0.7-fold (N = 4, P < 0.05) elevated over controls. Cyst fluid from homozygous rats contained MMP-2 protein and activity. These findings indicate that tubular MMP-2 activity is reduced in PKD, due to down-regulation of MMP-2, up-regulation of TIMP-1 and TIMP-2, and luminal secretion of the enzyme. It is conceivable that these alterations relate to the enhanced matrix accumulation observed in the evolution of PKD.

Constitutive heterochromatin of chromosome 1 and Duffy blood group alleles in schizophrenia

Cytogenetic analysis was carried out in unrelated schizophrenic patients, unrelated controls and patients and family members in multiplex families. The size distribution of chromosome 1 heterochromatic region (1qH, C-band variants) among 21 unrelated schizophrenic patients was different from that found in a group of 46 controls. The patient group had 1qH variants of smaller size than the control group (P < 0.01). Incubation of phytohemagglutinin-treated blood lymphocytes with 5-azacytidine (which causes decondensation and extension of the heterochromatin) led to a lesser degree of heterochromatin decondensation in a group of patients than in the controls (7 schizophrenic, 9 controls, P < 0.01). The distribution of phenotypes of Duffy blood group system [whose locus is linked to the 1qH region (Donahue et al.: Proc Natl Acad Sci USA 61:949-955, 1968; Rouleau et al.: Genomics 7:313-318, 1990)] among 28 schizophrenic patients was also different from that in the general population. Cosegregation of schizophrenia with a 1qH (C-band) variant and Duffy blood group allele was observed in one of six multiplex families. The overall results suggest that alterations within the Duffy/1qH region are involved in schizophrenia in some cases. This region contains the locus of D5 dopamine receptor pseudogene 2 (1q21.1), which is transcribed in normal lymphocytes (Takahashi et al.: FEBS Lett 314:23-25, 1992).

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

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

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.

Prenatal testing in a fetus at risk for autosomal dominant polycystic kidney disease and autosomal recessive junctional epidermolysis bullosa with pyloric atresia

Amniocentesis and fetal skin biopsies were performed at 18 weeks of gestation in a fetus at risk for autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive junctional epidermolysis bullosa (EBJ) with pyloric atresia. A previous son of the couple under investigation had died at 3 months of EBJ. The mother of the propositus has ADPKD. Genetic linkage studies were carried out in 11 relatives (4 with ADPKD), and on fetal DNA obtained from cultured amniocytes, using 8 flanking DNA markers tightly linked to the PKD1 locus on chromosome 16p, and a DNA marker linked to another putative ADPKD locus on chromosome 2p. The linkage results indicated that the fetus had not inherited the ADPKD chromosome from the affected mother, with a diagnostic accuracy of > 99%. Ultrastructural and immunohistochemical analyses of multiple fetal skin biopsies showed no EBJ-associated abnormalities. Thus, combining recent morphological and molecular diagnostic methods, we could show that the fetus was free from both diseases. After 40 weeks of gestation, a normal male infant was delivered.

Autosomal dominant polycystic kidney disease in Toronto

This study describes the Toronto, Ontario experience with autosomal dominant polycystic kidney disease (ADPKD). Patients were divided into three groups: Group 1, 19 families studied with genetic markers; Group 2, 80 pre-dialysis ADPKD patients followed by Toronto nephrologists in whom the incidence of non-renal complications and the mean age of onset of symptomatology is documented; Group 3, 4,449 individuals who entered end-stage renal failure (ESRF) in the Toronto region between the years 1981 and 1992, 320 with ADPKD and 4129 with other diseases. In this third group age of onset of ESRF, frequency, age and cause of death is compared between ADPKD and non-ADPKD. ADPKD caused by a gene different from that linked to chromosome 16 short-arm probes occurred at a frequency of between 8 and 17%. Incidence of hepatic cysts in ADPKD was similar to that of previous series, other organ involvement was underdiagnosed without deliberate screening, and incidence of symptomatic intracranial aneurysm was 1.25%. A 5% excess of patients with ADPKD died of cerebro-vascular accident. Years of survival after ESRF measured by life table analysis was significantly greater for ADPKD patients than for non-ADPKD patients. A high frequency of death due to infection still exists in ADPKD despite the reduction of invasive procedures in diagnosis and treatment, and despite the presumably improved recent methods of managing infection. The average age of onset of ESRF has been delayed by over six years, and average age of death of ADPKD patients at 63.9 years-old by 12.4 years since 1960.

Loss of the basement membrane matrix molecule, bamin, in diphenylamine-treated mice

Polycystic kidney disease (PKD) is a life-threatening disease characterized by focal dilatations or cysts in certain kidney tubules. Changes (i.e. thickening) in the support structure for these tubules, the basement membrane, have been related to the development of the cysts. Analysis of changes in basement membranes of humans with PKD is difficult, however, due to the restricted amount of material available for study. Several genetic and induced animal models, including diphenylamine-treated rats, have been employed to study the effects of PKD on basement membrane synthesis. While all these studies agree that PKD has a significant influence on basement membranes, no clear understanding as to how PKD effects basement membrane composition has emerged. Here, we report our findings of the effect of diphenylamine treatment on the composition of the basement membrane. Our immunohistological studies indicate that bamin, a recently described glycoprotein associated with glomerular basement membranes (Robinson et al., 1989), is not present in the glomerular basement membranes of diphenylamine-treated mice. This finding was confirmed by analysis of the composition of the basement membrane matrix synthesized by EHS tumors grown in control and diphenylamine-treated mice. The possible role of bamin in the pathogenesis of renal cysts is discussed.

Autosomal-dominant polycystic kidney disease in the rat

Kaspareit-Rittinghausen described a rodent model of inherited polycystic kidney disease (PKD), the Han:SPRD rat [1, 2], in which heterozygotes develop renal cysts and renal failure (in males) over several months, whereas homozygous animals develop rapidly progressive renal enlargement that leads to death in a few weeks. In this study, we examined selected elements of the pathogenesis of this disease in heterozygotes and homozygotes from birth to advanced disease. Heterozygous male rats developed slowly progressive renal cystic disease with interstitial fibrosis and azotemia seen by six months of age. Female heterozygotes developed slowly progressive renal cystic disease, but did not develop interstitial fibrosis or azotemia. Epithelial cells lining cyst cavities showed various degrees of morphologic immaturity. Cyst walls also developed basement membrane thickening, especially in areas of cellular immaturity, suggesting an interrelationship between this basement membrane thickening and cellular dedifferentiation. Thickened basement membranes were associated with increased immunoreactivity for type IV collagen, laminin, and fibronectin. Homozygous rats developed massive renal enlargement, marked azotemia, and died near three weeks of age. Renal c-myc proto-oncogene expression was elevated in homozygous cystic infants and in adult heterozygotes. In situ hybridization showed high levels of c-myc mRNA in cyst epithelia, suggesting abnormal regulation of cellular proliferation in the cells lining cysts, as seen in other models of PKD. The Han:SPRD rat is the only well-documented animal model of inherited PKD with an autosomal-dominant inheritance pattern and appears to have several features which resemble human ADPKD.

Polycystic kidney disease: primary extracellular matrix abnormality or defective cellular differentiation?

Polycystic kidney disease (PKD) is inherited as a dominant or recessive trait or can be provoked by environmental factors. The disease is characterized by the growth of large epithelial-lined cysts derived from the nephrons and collecting ducts of affected kidneys. Cysts are thought to initiate as small dilations in renal tubules, which then expand into fluid-filled cavities of relatively large size. Cyst formation appears to involve increased cell proliferation, reversal of tubular epithelial polarity, and epithelial fluid secretion. In addition, a number of pronounced extracellular matrix changes have been found in the cystic kidneys of several animal models and in human autosomal dominant PKD. These abnormalities include thickened, laminated basement membrane, increased expression of alpha 1 type IV collagen and laminins B1 and B2, and changes in heparan sulfate proteoglycan and fibronectin. Some of these changes can also be seen in vitro, reflecting intrinsic abnormalities, and may be associated with abnormal tubular morphogenesis early in cyst formation as well as later in cyst expansion. We have been investigating gene expression in the C57BL/6J-cpk mouse, which has an autosomal recessive form of PKD, to determine the genetic basis of the abnormal tubule cell growth and morphology manifested during cyst formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Autosomal recessive polycystic kidney disease

Autosomal recessive polycystic kidney disease is a rare inherited disorder which usually becomes clinically manifest in early childhood, whereas autosomal dominant polycystic kidney disease usually is a disorder of adult onset. With increasing knowledge and improving diagnostic techniques, it becomes evident that the spectrum of both entities is much more variable than generally known. The presentation of autosomal recessive polycystic kidney disease at later ages and survival into adulthood have been reported. The diagnostic criteria, clinical course, genetics and differential diagnosis of autosomal recessive polycystic kidney disease will be presented.