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

Novel role of ouabain as a cystogenic factor in autosomal dominant polycystic kidney disease

The classic role of the Na-K-ATPase is that of a primary active transporter that utilizes cell energy to establish and maintain transmembrane Na(+) and K(+) gradients to preserve cell osmotic stability, support cell excitability, and drive secondary active transport. Recent studies have revealed that Na-K-ATPase located within cholesterol-containing lipid rafts serves as a receptor for cardiotonic steroids, including ouabain. Traditionally, ouabain was viewed as a toxin produced only in plants, and it was used in relatively high concentrations to experimentally block the pumping action of the Na-K-ATPase. However, the new and unexpected role of the Na-K-ATPase as a signal transducer revealed a novel facet for ouabain in the regulation of a myriad of cell functions, including cell proliferation, hypertrophy, apoptosis, mobility, and metabolism. The seminal discovery that ouabain is endogenously produced in mammals and circulates in plasma has fueled the interest in this endogenous molecule as a potentially important hormone in normal physiology and disease. In this article, we review the role of the Na-K-ATPase as an ion transporter in the kidney, the experimental evidence for ouabain as a circulating hormone, the function of the Na-K-ATPase as a signal transducer that mediates ouabain's effects, and novel results for ouabain-induced Na-K-ATPase signaling in cystogenesis of autosomal dominant polycystic kidney disease.

Generation of c-Myc transgenic pigs for autosomal dominant polycystic kidney disease

After several decades of research, autosomal dominant polycystic kidney disease (ADPKD) is still incurable and imposes enormous physical, psychological, and economic burdens on patients and their families. Murine models of ADPKD represent invaluable tools for studying this disease. These murine forms of ADPKD can arise spontaneously, or they can be induced via chemical or genetic manipulations. Although these models have improved our understanding of the etiology and pathogenesis of ADPKD, they have not led to effective treatment strategies. The mini-pig represents an effective biomedical model for studying human diseases, as the pig's human-like physiological processes help to understand disease mechanisms and to develop novel therapies. Here, we tried to generate a transgenic model of ADPKD in pigs by overexpressing c-Myc in kidney tissue. Western-blot analysis showed that c-Myc was overexpressed in the kidney, brain, heart, and liver of transgenic pigs. Immunohistochemical staining of kidney tissue showed that exogenous c-Myc predominantly localized to renal tubules. Slightly elevated blood urea nitrogen levels were observed in transgenic pigs 1 month after birth, but no obvious abnormalities were detected after that time. In the future, we plan to subject this model to renal injury in an effort to promote ADPKD progression.

Progressive development of polycystic kidney disease in the mouse model expressing Pkd1 extracellular domain

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by slow progression of multiple cysts in both kidneys that lead to renal insufficiency in mid-life or later. ADPKD is associated with mutations mainly in the PKD1 gene (encoding polycystin-1 or PC1) and less frequently in the PKD2 gene (encoding polycystin-2 or PC2). To mimic naturally occurring human PKD1 mutations and gain insight into the PC1 extracellular domain function, four transgenic mouse lines were established with exclusively the extracellular domain of the Pkd1 gene (Pkd1(extra)) under endogenous transcriptional regulation. Expression of the Pkd1(extra) transgene was 2- to 80-fold above endogenous levels. Strikingly, the Pc1(extra) protein was more abundant, proportionally to the endogenous levels. All four transgenic mouse lines consistently displayed progressive renal cystic phenotype. Consequently, these transgenic mice reproducibly developed renal functional alterations similar to human ADPKD with proteinuria, renal insufficiency, anemia and died of renal failure late in life. In precystic kidneys, the Pkd1(extra) transgene modulated Pc2 expression and thereby, uncovered a potential Pc1-mutant/Pc2 pathogenic crosstalk mechanism. Moreover, the pathophysiologic mechanism also implicates c-myc, a major modulator of cystogenesis. Altogether, the novel Pkd1(extra) mouse model is the first Pc1 extracellular mutant that reproduces human ADPKD clinical progression and physiopathology.

Tuberous sclerosis complex

Tuberous Sclerosis Complex, also known as Epiloia or Bourneville-Pringle disease is an autosomal dominant neurocutaneous syndrome with variable clinical expression. It is a multisystem disorder that may be associated with hamartomas in multiple organs in an unpredictable manner. The dermatologist plays an essential role in the history of the disease, since skin manifestations represent the most prevalent clinical features, enabling early diagnosis and intervention in its natural course. This article aims to inform the scientific community about advances made in the study of genetics and molecular biology. Recent findings regarding stimulation of tumor growth have been changing the history of this condition, making therapeutic trials with topical and systemic drugs possible. Knowledge of these topics enables better management of the patients affected, since tissue replacement by tumors can result in significant morbidity and mortality.

Autosomal dominant polycystic kidney disease: recent advances in pathogenesis and potential therapies

Autosomal dominant polycystic kidney disease (ADPKD) is the most common progressive hereditary kidney disease. In 85-90% of cases, ADPKD results from a mutation in the PKD1 gene, and the other 10-15% of the cases are accounted for by mutations in PKD2. PKD1 and PKD2 encode polycystin-1 and polycystin-2. Polycystin-1 may be a receptor that controls the channel activity of polycystin-2 as part of the polycystin signaling complex. ADPKD is characterized by the progressive development of fluid-filled cysts derived from renal tubular epithelial cells that gradually compress the parenchyma and compromise renal function. In recent years, considerable interest has developed in the primary cilia as a site of the proteins that are involved in renal cystogenesis. The pathological processes that facilitate cyst enlargement are hypothesized to result from two specific cellular abnormalities: (1) increased fluid secretion into the cyst lumen and (2) inappropriately increased cell division by the epithelium lining the cyst. Since there is no clinically approved specific or targeted therapy, current practice focuses on blood pressure control and statin therapy to reduce the cardiac mortality associated with chronic kidney disease. However, recent advances in our understanding of the pathways that govern renal cystogenesis have led to a number of intriguing possibilities in regard to therapeutic interventions. The purpose of this article is to review the pathogenesis of renal cyst formation and to review novel targets for the treatment of ADPKD.

Loss of heterozygosity is present in SEC63 germline carriers with polycystic liver disease

Polycystic liver disease (PCLD) is an autosomal dominant disorder characterised by multiple fluid filled cysts in the liver. This rare disease is caused by heterozygous germline mutations in PRKCSH and SEC63. We previously found that, in patients with a PRKCSH mutation, over 76% of the cysts acquired a somatic 'second-hit' mutation in the wild type PRKCSH allele. We hypothesise that somatic second-hit mutations are a general mechanism of cyst formation in PCLD which also plays a role in PCLD patients carrying a SEC63 germline mutation. We collected cyst epithelial cells from 52 liver cysts from three different SEC63 patients using laser microdissection. DNA samples were sequenced to identify loss of heterozygosity (LOH) mutations and other somatic mutations in cyst epithelial DNA. We discovered somatic SEC63 mutations in patient 3 (1/14 cysts), but not in patient 1 and 2 (38 cysts). Upon review we found that the germline mutation of patient 1 and 2 (SEC63 c.1703_1705delAAG) was present in the same frequency in DNA samples from healthy controls, suggesting that this variant is not causative of PCLD. In conclusion, as somatic second-hit mutations also play a role in cyst formation in patients with a SEC63 germline mutation, this appears to be a general mechanism of cyst formation in PCLD.

Functional polycystin-1 dosage governs autosomal dominant polycystic kidney disease severity

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations to PKD1 or PKD2, triggering progressive cystogenesis and typically leading to end-stage renal disease in midlife. The phenotypic spectrum, however, ranges from in utero onset to adequate renal function at old age. Recent patient data suggest that the disease is dosage dependent, where incompletely penetrant alleles influence disease severity. Here, we have developed a knockin mouse model matching a likely disease variant, PKD1 p.R3277C (RC), and have proved that its functionally hypomorphic nature modifies the ADPKD phenotype. While Pkd1+/null mice are normal, Pkd1RC/null mice have rapidly progressive disease, and Pkd1RC/RC animals develop gradual cystogenesis. These models effectively mimic the pathophysiological features of in utero-onset and typical ADPKD, respectively, correlating the level of functional Pkd1 product with disease severity, highlighting the dosage dependence of cystogenesis. Additionally, molecular analyses identified p.R3277C as a temperature-sensitive folding/trafficking mutant, and length defects in collecting duct primary cilia, the organelle central to PKD pathogenesis, were clearly detected for the first time to our knowledge in PKD1. Altogether, this study highlights the role that in trans variants at the disease locus can play in phenotypic modification of dominant diseases and provides a truly orthologous PKD1 model, optimal for therapeutic testing.

Conditional mesenchymal disruption of pkd1 results in osteopenia and polycystic kidney disease

Conditional deletion of Pkd1 in osteoblasts using either Osteocalcin(Oc)-Cre or Dmp1-Cre results in defective osteoblast-mediated postnatal bone formation and osteopenia. Pkd1 is also expressed in undifferentiated mesenchyme that gives rise to the osteoblast lineage. To examine the effects of Pkd1 on prenatal osteoblast development, we crossed Pkd1^flox/flox and Col1a1(3.6)-Cre mice, which has been used to achieve selective inactivation of Pkd1 earlier in the osteoblast lineage. Control Pkd1^flox/flox and Pkd1^flox/+, heterozygous Col1a1(3.6)-Cre;Pkd1^flox/+ and Pkd1^flox/null, and homozygous Col1a1(3.6)-Cre;Pkd1^flox/flox and Col1a1(3.6)-Cre;Pkd1^flox/null mice were analyzed at ages ranging from E14.5 to 8-weeks-old. Newborn Col1a1(3.6)-Cre;Pkd1^flox/null mice exhibited defective skeletogenesis in association with a greater reduction in Pkd1 expression in bone. Conditional Col1a1(3.6)-Cre;Pkd1^flox/+ and Col1a1(3.6)-Cre;Pkd1^flox/flox mice displayed a gene dose-dependent decrease in bone formation and increase in marrow fat at 6 weeks of age. Bone marrow stromal cell and primary osteoblast cultures from homozygous Col1a1(3.6)-Cre;Pkd1^flox/flox mice showed increased proliferation, impaired osteoblast development and enhanced adipogenesis ex vivo. Unexpectedly, we found evidence for Col1a1(3.6)-Cre mediated deletion of Pkd1 in extraskeletal tissues in Col1a1(3.6)-Cre;Pkd1^flox/flox mice. Deletion of Pkd1 in mesenchymal precursors resulted in pancreatic and renal, but not hepatic, cyst formation. The non-lethality of Col1a1(3.6)-Cre;Pkd1^flox/flox mice establishes a new model to study abnormalities in bone development and cyst formation in pancreas and kidney caused by Pkd1 gene inactivation.

Secondary, somatic mutations might promote cyst formation in patients with autosomal dominant polycystic liver disease

BACKGROUND & AIMS

Heterozygous germline mutations in PRKCSH cause autosomal dominant polycystic liver disease (PCLD), but it is not clear how they lead to cyst formation. We investigated whether mutations in cyst epithelial cells and corresponding loss of the PRKCSH gene product (hepatocystin) contributed to cyst development.

METHODS

Liver cyst material was collected through laparoscopic cyst fenestration from 8 patients with PCLD who had a heterozygous germline mutation in PRKCSH. Tissue sections from 71 cysts (2-14 per patient) were obtained for hepatocystin staining and mutation analysis. Cyst epithelium was acquired using laser microdissection; DNA was isolated and analyzed for loss of heterozygosity (LOH) and somatic mutations using restriction analysis and sequencing. Common single nucleotide polymorphisms (SNPs) in a 70-kilobase region surrounding the germline mutation were used to determine variations in the genomic region with LOH.

RESULTS

The wild-type allele of PRKCSH was lost (LOH) in 76% of cysts (54/71). Hepatocystin was not detected in cyst epithelia with LOH, whereas heterozygous cysts still expressed hepatocystin. The variation observed in the LOH region analysis indicates that cysts develop independently. We also detected somatic mutations in PRKCSH in 17% (2/12) of the cysts without LOH. Trans-heterozygous mutations in SEC63 were not observed.

CONCLUSIONS

Among patients with PCLD who have a heterozygous germline mutation in PRKCSH, we found secondary, somatic mutations (second hits) in more than 76% of the liver cyst epithelia. PCLD is recessive at the cellular level, and loss of functional PRKCSH is an important step in cystogenesis.

A mosaic activating mutation in AKT1 associated with the Proteus syndrome

BACKGROUND

The Proteus syndrome is characterized by the overgrowth of skin, connective tissue, brain, and other tissues. It has been hypothesized that the syndrome is caused by somatic mosaicism for a mutation that is lethal in the nonmosaic state.

METHODS

We performed exome sequencing of DNA from biopsy samples obtained from patients with the Proteus syndrome and compared the resultant DNA sequences with those of unaffected tissues obtained from the same patients. We confirmed and extended an observed association, using a custom restriction-enzyme assay to analyze the DNA in 158 samples from 29 patients with the Proteus syndrome. We then assayed activation of the AKT protein in affected tissues, using phosphorylation-specific antibodies on Western blots.

RESULTS

Of 29 patients with the Proteus syndrome, 26 had a somatic activating mutation (c.49G→A, p.Glu17Lys) in the oncogene AKT1, encoding the AKT1 kinase, an enzyme known to mediate processes such as cell proliferation and apoptosis. Tissues and cell lines from patients with the Proteus syndrome harbored admixtures of mutant alleles that ranged from 1% to approximately 50%. Mutant cell lines showed greater AKT phosphorylation than did control cell lines. A pair of single-cell clones that were established from the same starting culture and differed with respect to their mutation status had different levels of AKT phosphorylation.

CONCLUSIONS

The Proteus syndrome is caused by a somatic activating mutation in AKT1, proving the hypothesis of somatic mosaicism and implicating activation of the PI3K-AKT pathway in the characteristic clinical findings of overgrowth and tumor susceptibility in this disorder. (Funded by the Intramural Research Program of the National Human Genome Research Institute.).

A non-synonymous mutation in the canine Pkd1 gene is associated with autosomal dominant polycystic kidney disease in Bull Terriers

Polycystic Kidney Disease is an autosomal dominant disease common in some lines of Bull Terriers (BTPKD). The disease is linked to the canine orthologue of human PKD1 gene, Pkd1, located on CFA06, but no disease-associated mutation has been reported. This study sequenced genomic DNA from two Bull Terriers with BTPKD and two without the disease. A non-synonymous G>A transition mutation in exon 29 of Pkd1 was identified. A TaqMan® SNP Genotyping Assay was designed and demonstrated the heterozygous detection of the mutation in 47 Bull Terriers with BTPKD, but not in 102 Bull Terriers over one year of age and without BTPKD. This missense mutation replaces a glutamic acid residue with a lysine residue in the predicted protein, Polycystin 1. This region of Polycystin 1 is highly conserved between species, and is located in the first cytoplasmic loop of the predicted protein structure, close to the PLAT domain and the second transmembrane region. Thus, this change could alter Polycystin 1 binding or localization. Analytic programs PolyPhen 2, Align GVGD and SIFT predict this mutation to be pathogenic. Thus, BTPKD is associated with a missense mutation in Pkd1, and the application of this mutation specific assay could reduce disease transmission by allowing diagnosis of disease in young animals prior to breeding.

Autosomal dominant polycystic kidney disease: genetics, mutations and microRNAs

Autosomal dominant polycystic kidney disease (ADPKD) is a common, monogenic multi-systemic disorder characterized by the development of renal cysts and various extrarenal manifestations. Worldwide, it is a common cause of end-stage renal disease. ADPKD is caused by mutation in either one of two principal genes, PKD1 and PKD2, but has large phenotypic variability among affected individuals, attributable to PKD genic and allelic variability and, possibly, modifier gene effects. Recent studies have generated considerable information regarding the genetic basis and molecular diagnosis of this disease, its pathogenesis, and potential strategies for targeted treatment. The purpose of this article is to provide a comprehensive review of the genetics of ADPKD, including mechanisms responsible for disease development, the role of gene variations and mutations in disease presentation, and the putative role of microRNAs in ADPKD etiology. The emerging and important role of genetic testing and the advent of novel molecular diagnostic applications also are reviewed. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

The cell biology of polycystic kidney disease

Polycystic kidney disease is a common genetic disorder in which fluid-filled cysts displace normal renal tubules. Here we focus on autosomal dominant polycystic kidney disease, which is attributable to mutations in the PKD1 and PKD2 genes and which is characterized by perturbations of renal epithelial cell growth control, fluid transport, and morphogenesis. The mechanisms that connect the underlying genetic defects to disease pathogenesis are poorly understood, but their exploration is shedding new light on interesting cell biological processes and suggesting novel therapeutic targets.

TRPP channels and polycystins

The founding member of the TRPP family, TRPP2, was identified as one of the disease genes causing autosomal dominant polycystic kidney disease (ADPKD). ADPKD is the most prevalent, potentially lethal, monogenic disorder in humans, with an average incidence of one in 400 to one in 1,000 individuals worldwide. Here we give an overview of TRPP ion channels and Polycystin-1 receptor proteins focusing on more recent studies. We include the Polycystin-1 family since these proteins are functionally linked to TRPP channels.

Cyclic AMP-mediated cyst expansion

In polycystic kidney disease (PKD), intracellular cAMP promotes cyst enlargement by stimulating mural epithelial cell proliferation and transepithelial fluid secretion. The proliferative effect of cAMP in PKD is unique in that cAMP is anti-mitogenic in normal renal epithelial cells. This phenotypic difference in the proliferative response to cAMP appears to involve cross-talk between cAMP and Ca(2+) signaling to B-Raf, a kinase upstream of the MEK/ERK pathway. In normal cells, B-Raf is repressed by Akt (protein kinase B), a Ca(2+)-dependent kinase, preventing cAMP activation of ERK and cell proliferation. In PKD cells, disruption of intracellular Ca(2+) homeostasis due to mutations in the PKD genes relieves Akt inhibition of B-Raf, allowing cAMP stimulation of B-Raf, ERK and cell proliferation. Fluid secretion by cystic cells is driven by cAMP-dependent transepithelial Cl(-) secretion involving apical cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channels. This review summarizes the current knowledge of cAMP-dependent cyst expansion, focusing on cell proliferation and Cl(-)-dependent fluid secretion, and discusses potential therapeutic approaches to inhibit renal cAMP production and its downstream effects on cyst enlargement. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Progressive renal distortion by multiple cysts in transgenic mice expressing artificial microRNAs against Pkd1

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common life-threatening inherited diseases, and the PKD1 gene is responsible for most cases of this disease. Previous efforts to establish a mouse model that recapitulates the phenotypic characteristics of ADPKD, which have used conventional or conditional knockout of the mouse orthologue Pkd1, have been unsuccessful or unreliable. In a previous study, we described the generation of a novel Pkd1 hypomorphic allele, in which Pkd1 expression was significantly reduced but not totally blocked. These Pkd1 homozygous mutant mice rapidly developed renal cystic disease, supporting the hypothesis that 'haploinsufficiency' explains development of the ADPKD phenotype. In the present study, we further investigated the Pkd1 haploinsufficiency effect by generating Pkd1 knockdown transgenic mice with co-cistronic expression of two miRNA hairpins specific to Pkd1 transcript and an Emerald GFP reporter driven by a human ubiquitin B promoter. Two transgenic lines which had ∼60-70% reduction of Pkd1 expression developed severe renal cystic disease at a rate similar to that of human ADPKD. These results further support the haploinsufficiency hypothesis, and suggest that the onset and progression of the renal cystic diseases are correlated with the level of Pkd1 expression. The two novel mutant lines of mice appear to be ideal models for the study of ADPKD.

MAP/ERK kinase kinase 1 (MEKK1) mediates transcriptional repression by interacting with polycystic kidney disease-1 (PKD1) promoter-bound p53 tumor suppressor protein

Mitogen-activated protein kinase (MAPK) cascades regulate a wide variety of cellular processes that ultimately depend on changes in gene expression. We have found a novel mechanism whereby one of the key MAP3 kinases, Mekk1, regulates transcriptional activity through an interaction with p53. The tumor suppressor protein p53 down-regulates a number of genes, including the gene most frequently mutated in autosomal dominant polycystic kidney disease (PKD1). We have discovered that Mekk1 translocates to the nucleus and acts as a co-repressor with p53 to down-regulate PKD1 transcriptional activity. This repression does not require Mekk1 kinase activity, excluding the need for an Mekk1 phosphorylation cascade. However, this PKD1 repression can also be induced by the stress-pathway stimuli, including TNFα, suggesting that Mekk1 activation induces both JNK-dependent and JNK-independent pathways that target the PKD1 gene. An Mekk1-p53 interaction at the PKD1 promoter suggests a new mechanism by which abnormally elevated stress-pathway stimuli might directly down-regulate the PKD1 gene, possibly causing haploinsufficiency and cyst formation.

Determinants of renal disease variability in ADPKD

In common with other Mendelian diseases, the presentation and progression of autosomal dominant polycystic kidney disease (ADPKD) vary widely in the population. The typical course is of adult-onset disease with ESRD in the 6th decade. However, a small proportion has adequate renal function into the 9th decade, whereas others present with enlarged kidneys as neonates. ADPKD is genetically heterogeneous, and the disease gene is a major determinant of severity; PKD1 on average is associated with ESRD 20 years earlier than PKD2. The majority of PKD1 and PKD2 mutations are likely fully inactivating although recent studies indicate that some alleles retain partial activity (hypomorphic alleles). Homozygotes for such alleles are viable and in combination with an inactivating allele can result in early-onset disease. Hypomorphic alleles and mosaicism may also account for some cases with unusually mild disease. The degree of phenotypic variation detected in families indicates that genetic background influences disease severity. Genome-wide association studies are planned to map common variants associated with severity. Although ADPKD is a simple genetic disease, fully understanding the phenotypic variability requires consideration of influences at the genic, allelic, and genetic background level, and so, ultimately, it is complex.

Molecular advances in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic disease (ADPKD) is the most common form of inherited kidney disease that results in renal failure. The understanding of the pathogenesis of ADPKD has advanced significantly since the discovery of the 2 causative genes, PKD1 and PKD2. Dominantly inherited gene mutations followed by somatic second-hit mutations inactivating the normal copy of the respective gene result in renal tubular cyst formation that deforms the kidney and eventually impairs its function. The respective gene products, polycystin-1 and polycystin-2, work together in a common cellular pathway. Polycystin-1, a large receptor molecule, forms a receptor-channel complex with polycystin-2, which is a cation channel belonging to the TRP family. Both polycystin proteins have been localized to the primary cilium, a nonmotile microtubule-based structure that extends from the apical membrane of tubular cells into the lumen. Here we discuss recent insights in the pathogenesis of ADPKD including the genetics of ADPKD, the properties of the respective polycystin proteins, the role of cilia, and some cell-signaling pathways that have been implicated in the pathways related to PKD1 and PKD2.

Unravelling the genetic basis of renal diseases; from single gene to multifactorial disorders

Chronic kidney disease is common with up to 5% of the adult population reported to have an estimated glomerular filtration rate of < 60 ml/min/1.73 m(2). A large number of pathogenic mutations have been identified that are responsible for 'single gene' renal disorders, such as autosomal dominant polycystic kidney disease and X-linked Alport syndrome. These single gene disorders account for < 15% of the burden of end-stage renal disease that requires dialysis or kidney transplantation. It has proved more difficult to identify the genetic susceptibility underlying common, complex, multifactorial kidney conditions, such as diabetic nephropathy and hypertensive nephrosclerosis. This review describes success to date and explores strategies currently employed in defining the genetic basis for a number of renal disorders. The complementary use of linkage studies, candidate gene and genome-wide association analyses are described and a collation of renal genetic resources highlighted.

Pkd1 transgenic mice: adult model of polycystic kidney disease with extrarenal and renal phenotypes

While high levels of Pkd1 expression are detected in tissues of patients with autosomal dominant polycystic kidney disease (ADPKD), it is unclear whether enhanced expression could be a pathogenetic mechanism for this systemic disorder. Three transgenic mouse lines were generated from a Pkd1-BAC modified by introducing a silent tag via homologous recombination to target a sustained wild-type genomic Pkd1 expression within the native tissue and temporal regulation. These mice specifically overexpressed the Pkd1 transgene in extrarenal and renal tissues from approximately 2- to 15-fold over Pkd1 endogenous levels in a copy-dependent manner. All transgenic mice reproducibly developed tubular and glomerular cysts leading to renal insufficiency. Interestingly, Pkd1(TAG) mice also exhibited renal fibrosis and calcium deposits in papilla reminiscent of nephrolithiasis as frequently observed in ADPKD. Similar to human ADPKD, these mice consistently displayed hepatic fibrosis and approximately 15% intrahepatic cysts of the bile ducts affecting females preferentially. Moreover, a significant proportion of mice developed cardiac anomalies with severe left-ventricular hypertrophy, marked aortic arch distention and/or valvular stenosis and calcification that had profound functional impact. Of significance, Pkd1(TAG) mice displayed occasional cerebral lesions with evidence of ruptured and unruptured cerebral aneurysms. This Pkd1(TAG) mouse model demonstrates that overexpression of wild-type Pkd1 can trigger the typical adult renal and extrarenal phenotypes resembling human ADPKD.

Autosomal dominant polycystic kidney disease and transplantation

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited disorder affecting 1 in 1,000 people and responsible for 10% of cases of the end stage renal disease (ESRD). Apart from renal manifestations, changes in other organs may be present. In the absence of contraindications, patients with ADPKD and ESRD should be referred to renal transplantation. The ADPKD patient may also need liver transplantation, or combined liver and kidney transplantation. Also, the patient with ADPKD may become a potential organ donor. The aim of our paper is to review the problems that the physicians deal with in ADPKD patients in pre- and post-transplant period.

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.

Loss of polycystin-1 causes centrosome amplification and genomic instability

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenetic disease predominantly caused by alteration or dysregulation of the PKD1 gene, which encodes polycystin-1 (PC1). The disease is characterized by the progressive expansion of bilateral fluid-filled renal cysts that ultimately lead to renal failure. Individual cysts, even within patients with germline mutations, are genetically heterogeneous, displaying diverse chromosomal abnormalities. To date, the molecular mechanisms responsible for this genetic heterogeneity remain unknown. Using a lentiviral-mediated siRNA expression model of Pkd1 hypomorphism, we show that loss of PC1 function is sufficient to produce centrosome amplification and multipolar spindle formation. These events lead to genomic instability characterized by gross polyploidism and mitotic catastrophe. Following these dramatic early changes, the cell population rapidly converges toward a stable ploidy in which centrosome amplification is significantly decreased, though cytological abnormalities such as micronucleation, chromatin bridges and aneuploidy remain common. In agreement with our in vitro findings, we provide the first in vivo evidence that significant centrosome amplification occurs in kidneys from conditional Pkd1 knockout mice at early and late time during the disease progression as well as in human ADPKD patients. These findings establish a novel function of PC1 in ADPKD pathogenesis and a genetic mechanism that may underlie the intrafamilial variability of ADPKD progression.

RecQ and RecG helicases have distinct roles in maintaining the stability of polypurine.polypyrimidine sequences

DNA triplex structures can block the replication fork and result in double-stranded DNA breaks (DSBs). RecQ and RecG helicases may be important for replication of such sequences as RecQ resolves synthetic triplex DNA structures and RecG mediates replication restart by fork regression. Primer extension on an 88 bp triplex-forming polypurine.polypyrimidine (Pu.Py) tract from the PKD1 gene demonstrated that RecQ, but not RecG, facilitated primer extension by T7 DNA polymerase. A high-throughput, dual plasmid screening system using isogenic bacterial lines deficient in RecG, RecQ, or both, revealed that RecQ deficiency increased mutation to sequence flanking this 88 bp tract by eight to ten-fold. Although RecG facilitated small deletions in an 88 bp mirror repeat-containing sequence, it was absolutely required to maintain a 2.5 kb Pu.Py tract containing multiple mirror repeats. These results support a two-tiered model where RecQ facilitates fork progression through triplex-forming tracts and, failing processivity, RecG is critical for replication fork restart.

Analysis of PKD1 for genomic deletion by multiplex ligation-dependent probe assay: absence of hot spots

Autosomal dominant polycystic kidney disease is largely due to mutations in PKD1. PKD1 has an unusual genomic structure, including a 2.5-kb polypyrimidine sequence in intron 21, which has been postulated to lead to a high rate of spontaneous genomic mutation events. In addition, the majority of the gene is duplicated three to six times at 97-99% identity elsewhere in the genome. To identify genomic mutations in PKD1, we developed a multiplex ligation-dependent probe assay (MLPA) in which sites of variation between PKD1 and its copies were positioned at the ligation sites of the MLPA probe sets. Thirteen probe sets covered PKD1 exons 2 through 46, at an average spacing of 2.5 kb. Analysis of 27 independent PKD patient samples showed no evidence for genomic deletions confined to PKD1. Analysis of 15 tuberous sclerosis patient samples in which deletions in TSC2 extended into PKD1 showed no evidence of clustering of breakpoints near the polypyrimidine tract.

Determinants of renal volume in autosomal-dominant polycystic kidney disease

The Consortium of Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) recently showed that renal enlargement in autosomal-dominant polycystic kidney disease mimicked exponential growth. We determined the effects of cyst initiation rate, total number, and growth rate on the time-dependent change of total cyst volume (TCV). Mathematical models with equations integrating cyst surface area, volume, and an invariant growth rate constant were used to compute the time-dependent change in volume of solitary and multiple cysts. Multiple expanding cysts increased TCV in an exponential-like pattern even when individual cysts formed at different rates or exhibited different but constant growth rates. TCV depended on the rate of cyst initiation and on the total number of cysts; however, the compounding effect of exponential-like growth was the most powerful determinant of long-term cyst expansion. Extrapolation of TCV data plots for individual subjects back to an age of 18 predicted TCV values within an established range. We conclude that cysts started early in life were the main contributor to eventual TCV while their growth rate primarily determined renal size; although the rate of formation and the ultimate number of cysts also contributed. The good fit between the exponential models and the extrapolated CRISP data indicates that the TCV growth rate is a defining trait for individual patients and may be used as a prognostic marker.

Prognosis of autosomal dominant polycystic kidney disease diagnosed in utero or at birth

The use of prenatal ultrasonography has resulted in increased numbers of fetuses being diagnosed with autosomal dominant polycystic kidney disease (ADPKD), but the long-term prognosis is still not well-known. Between 1981 and 2006 we followed 26 consecutive children with enlarged hyperechoic kidneys detected between the 12th week of pregnancy and the first day of life (Day 1) as well as one affected parent. Three other fetuses were excluded following the termination of the pregnancy. The mother was the transmitting parent in 16 of the 26 children (ns, p=0.1). Clinical features that presented during follow-up were oligoamnios (5/26), neonatal pneumothorax (3/26), pyelonephritis (5/26), gross hematuria (2/26), hypertension (5/26), proteinuria (2/26) and chronic renal insufficiency (CRI) (2/26). At the last follow-up (mean duration of follow-up: 76 months; range: 0.5-262 months), 19 children (mean age: 5.5 years) were asymptomatic, five (mean age: 8.5 years) had hypertension, two (mean age: 9.7 years) had proteinuria and two (mean age: 19 years) had CRI. Children presenting enlarged kidneys postnatally tended to have more clinical manifestations than their counterparts who did not. Of 25 siblings of the patients, seven had renal cysts; these were detected during childhood in five siblings and in utero in two siblings. In conclusion, prognosis is favourable in most children with prenatal ADPKD, at least during childhood. The sex of the transmitting parent is not a risk factor of prenatal ADPKD. A high proportion of siblings develop early renal cysts. Abnormalities visualized by ultrasonography appear to be associated to more clinical manifestations.

Cyst number but not the rate of cystic growth is associated with the mutated gene in autosomal dominant polycystic kidney disease

Data from serial renal magnetic resonance imaging of the Consortium of Radiologic Imaging Study of PKD (CRISP) autosomal dominant polycystic kidney disease (PKD) population showed that cystic expansion occurs at a consistent rate per individual, although it is heterogeneous in the population, and that larger kidneys are associated with more rapid disease progression. The significance of gene type to disease progression is analyzed in this study of the CRISP cohort. Gene type was determined in 183 families (219 cases); 156 (85.2%) had PKD1, and 27 (14.8%) had PKD2. PKD1 kidneys were significantly larger, but the rate of cystic growth (PKD1 5.68%/yr; PKD2 4.82%/yr) was not different (P = 0.24). Cyst number increased with age, and more cysts were detected in PKD1 kidneys (P < 0.0001). PKD1 is more severe because more cysts develop earlier, not because they grow faster, implicating the disease gene in cyst initiation but not expansion. These insights will inform the development of targeted therapies in autosomal dominant PKD.

Loss of polycystin-1 in human cyst-lining epithelia leads to ciliary dysfunction

A "two-hit" hypothesis predicts a second somatic hit, in addition to the germline mutation, as a prerequisite to cystogenesis and has been proposed to explain the focal nature for renal cyst formation in autosomal dominant polycystic kidney disease (ADPKD). It was reported previously that Pkd1(null/null) mouse kidney epithelial cells are unresponsive to flow stimulation. This report shows that Pkd1(+/null) cells are capable of responding to mechanical flow stimulation by changing their intracellular calcium concentration in a manner similar to that of wild-type cells. This paper reports that human renal epithelia require a higher level of shear stress to evoke a cytosolic calcium increase than do mouse renal epithelia. Both immortalized and primary cultured renal epithelial cells that originate from normal and nondilated ADPKD human kidney tubules display normal ciliary expression of the polycystins and respond to fluid-flow shear stress with the typical change in cytosolic calcium. In contrast, immortalized and primary cultured cyst-lining epithelial cells from ADPKD patients with mutations in PKD1 or with abnormal ciliary expression of polycystin-1 or -2 were not responsive to fluid shear stress. These data support a two-hit hypothesis as a mechanism of cystogenesis. This report proposes that calcium response to fluid-flow shear stress can be used as a readout of polycystin function and that loss of mechanosensation in the renal tubular epithelia is a feature of PKD cysts.

Overexpression of PKD1 causes polycystic kidney disease

The pathogenetic mechanisms underlying autosomal dominant polycystic kidney disease (ADPKD) remain to be elucidated. While there is evidence that Pkd1 gene haploinsufficiency and loss of heterozygosity can cause cyst formation in mice, paradoxically high levels of Pkd1 expression have been detected in the kidneys of ADPKD patients. To determine whether Pkd1 gain of function can be a pathogenetic process, a Pkd1 bacterial artificial chromosome (Pkd1-BAC) was modified by homologous recombination to solely target a sustained Pkd1 expression preferentially to the adult kidney. Several transgenic lines were generated that specifically overexpressed the Pkd1 transgene in the kidneys 2- to 15-fold over Pkd1 endogenous levels. All transgenic mice reproducibly developed tubular and glomerular cysts and renal insufficiency and died of renal failure. This model demonstrates that overexpression of wild-type Pkd1 alone is sufficient to trigger cystogenesis resembling human ADPKD. Our results also uncovered a striking increased renal c-myc expression in mice from all transgenic lines, indicating that c-myc is a critical in vivo downstream effector of Pkd1 molecular pathways. This study not only produced an invaluable and first PKD model to evaluate molecular pathogenesis and therapies but also provides evidence that gain of function could be a pathogenetic mechanism in ADPKD.

Defining a link with autosomal-dominant polycystic kidney disease in mice with congenitally low expression of Pkd1

Mouse models for autosomal-dominant polycystic kidney disease (ADPKD), derived from homozygous targeted disruption of Pkd1 gene, generally die in utero or perinatally because of systemic defects. We introduced a loxP site and a loxP-flanked mc1-neo cassette into introns 30 and 34, respectively, of the Pkd1 locus to generate a conditional, targeted mutation. Significantly, before excision of the floxed exons and mc1-neo from the targeted locus by Cre recombinase, mice homozygous for the targeted allele appeared normal at birth but developed polycystic kidney disease with a slower progression than that of Pkd-null mice. Further, the homozygotes continued to produce low levels of full-length Pkd1-encoded protein, suggesting that slight Pkd1 expression is sufficient for renal cyst formation in ADPKD. In this viable model, up-regulation of heparin-binding epidermal growth factor-like growth factor accompanied increased epidermal growth factor receptor signaling, which may be involved in abnormal proliferation of the cyst-lining epithelia. Increased apoptosis in cyst epithelia was only observed in the later period that correlated with the cyst regression. Abnormalities in Na(+)/K(+)-ATPase, aquaporin-2, and vasopressin V2 receptor expression were also identified. This mouse model may be suitable for further studies of progression and therapeutic interventions of ADPKD.

Ets factors regulate the polycystic kidney disease-1 promoter

The Ets family of transcription factors consists of a group of highly conserved sequence-specific DNA binding proteins that functionally cooperate with other transcription factors to regulate a number of diverse cellular processes including proliferation, differentiation, and apoptosis. We have analyzed a 3.3kb 5'-upstream region of the human PKD1 promoter, using transient transfection in HEK293T cells and Drosophila SL2 cells, to demonstrate that the PKD1 promoter is a target of Ets family transcription factors. Our studies showed that PKD1 promoter-luciferase reporter gene expression is downregulated by cotransfected Fli-1 and is upregulated by cotransfected Ets-1. Using deletion constructs, we demonstrated that the sequences responding to Fli-1 and Ets-1 lie within the -200 to +33bp proximal promoter. This region was found to contain two putative Ets response elements (EREs): an upstream (Ets-A) sequence 5'-CGGAA-3' (-181 to -185) and a downstream (Ets-B) sequence 5'-CGGAT-3' (-129 to -133). Site-directed mutagenesis indicated that both EREs are functional. A Fli-1 DNA binding domain mutant construct (W321R), which is incapable of binding DNA, was unable to inhibit basal promoter activity. In contrast, a Fli-1 DNA binding domain truncation mutant construct, which only contains the DNA binding domain and lacks the transactivation domain, was able to inhibit. These results suggest that the effect of Fli-1 is through direct binding to these EREs. Direct binding of Fli-1 and Ets-1 to the Ets-A and Ets-B sites was supported by electrophoretic mobility shift assays. Lastly, competition between Fli-1 and Ets-1 for the two EREs was demonstrated by showing that increasing amounts of Ets-1 could overcome Fli-1 repression of promoter activity. Taken together, these experiments define the proximal PKD1 promoter region as a potential target of Ets family transcription factors.

ADPKD: molecular characterization and quest for treatment

Autosomal-dominant polycystic kidney disease (ADPKD) is a common hereditary disease that features multiple cystogenesis in various organs and vascular defects. The genes responsible for ADPKD, PKD1, and PKD2 have been identified, and the pathological processes of the disease are becoming clearer. This review focuses on recent findings about the molecular and cellular biology of ADPKD, and especially on PKD1. PKD1 and its product, polycystin-1, play pivotal roles in cellular differentiation because they regulate the cell cycle and because polycystin-1 is a component of adherens junctions. A possible link between polycystin-1 and PPARgamma is discussed. The extraordinarily fast research progress in this area in the last decade has now reached a stage where the development of a remedy for ADPKD might become possible in the near future.

Calcium Restores a Normal Proliferation Phenotype in Human Polycystic Kidney Disease Epithelial Cells

Polycystic kidney disease (PKD) is a lethal disorder characterized by progressive expansion of renal cysts. Genetic mutations associated with PKD are thought to disrupt intracellular Ca2+ regulation, leading to abnormal proliferation of tubule epithelial cells. cAMP stimulates the B-Raf/MEK/extracellular signal-regulated kinase (B-Raf/MEK/ERK) pathway and accelerates the proliferation of cells that are cultured from PKD cysts. By contrast, cAMP inhibits the proliferation of cells from normal human kidneys (NHK) and M-1 mouse collecting duct cells. Previously, it was found that a sustained reduction of intracellular Ca2+ levels in NHK and M-1 cells that were treated with Ca2+ entry blockers allowed cAMP activation of the B-Raf/MEK/ERK pathway, switching the cells to a cAMP-growth stimulated phenotype. In this study, primary cultures of cyst epithelial cells from autosomal dominant (ADPKD) and recessive (ARPKD) PKD kidneys were used to determine whether controlled addition of Ca2+ could reverse the aberrant mitogenic response to cAMP. Steady-state intracellular Ca2+ levels were found to be 20 nM lower in cyst-derived ADPKD cells (57 +/- 2 nM) compared with NHK cells (77 +/- 2 nM). Treatment of ADPKD cells or ARPKD cells with either Bay K8644, a Ca2+ channel activator, or A23187, a Ca2+ ionophore, caused sustained increases in intracellular Ca2+ levels and completely reversed the mitogenic response to cAMP. Elevation of intracellular Ca2+ levels in ADPKD cells increased Akt activity and blocked cAMP-dependent B-Raf and ERK activation. Thus, increases in [Ca2+]i are able to restore the normal anti-mitogenic response to cAMP in cells that are derived from two genetically distinct forms of PKD.

Molecular pathogenesis of ADPKD: the polycystin complex gets complex

Autosomal-dominant polycystic kidney disease (ADPKD) is one of the most common human monogenic diseases with an incidence of 1:400 to 1:1000. It is characterized by the progressive development and enlargement of focal cysts in both kidneys, typically resulting in end-stage renal disease (ESRD) by the fifth decade. The cystogenic process is highly complex with a cellular phenotype consistent with "dedifferentiation" (i.e., a high proliferative rate, increased apoptosis, altered protein sorting, changed secretory characteristics, and disorganization of the extracellular matrix). Although cystic renal disease is the major cause of morbidity, the occurrence of nonrenal cysts, most notably in the liver (occasionally resulting in clinically significant polycystic liver disease) and the increased prevalence of other abnormalities including intracranial aneurysms, indicate that ADPKD is a systemic disorder. Following the identification of the first ADPKD gene, PKD1, 10 years ago and PKD2 2 years later, considerable progress has been made in defining the etiology and understanding the pathogenesis of this disorder, knowledge that is now leading to the development of several promising new therapies. The purpose of this review is to summarize our current state of knowledge as to the structure and function of the PKD1 and PKD2 proteins, polycystin-1 and -2, respectively, and explore how mutation at these loci results in the spectrum of changes seen in ADPKD.

Hereditary hormone excess: genes, molecular pathways, and syndromes

Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.

Tuberous sclerosis and the kidney: from mesenchyme to epithelium, and beyond

The renal manifestations of tuberous sclerosis complex (TSC) are remarkably diverse, including polycystic kidney disease, oncocytomas, renal cell carcinomas, and both benign and malignant angiomyolipomas. All of these occur in children as well as adults with TSC. Benign angiomyolipomas, which can cause spontaneous life-threatening hemorrhage, are by far the most prevalent and the greatest source of morbidity. What is particularly unusual about TSC, setting it apart from virtually all other inherited forms of renal disease, is the abnormalities of both mesenchymal cells (angiomyolipomas) and epithelial cells (cysts, oncocytomas, and carcinomas). Recently, the TSC1/TSC2 protein complex was shown to inhibit the kinase mTOR (mammalian target of rapamycin). This places TSC1/TSC2 at center stage in signaling pathways that regulate cell growth. Furthermore, recent advances in TSC1/TSC2 signaling open the door for targeted therapy for TSC patients. Here, we will address the genetic, cellular and biochemical mechanisms that may contribute to the unusually broad spectrum of renal disease in cells with TSC1 or TSC2 mutations, and consider how the TSC signaling pathways may be linked to other renal diseases such as polycystic kidney disease and renal cell carcinoma.

A mechanistic approach to inherited polycystic kidney disease

There are approximately six and a half million people, of the estimated world population of six billion, with inherited polycystic kidney disease. Polycystic kidney diseases have a broad spectrum of associated findings that distinguish and define them as specific disease states. The dysregulation of renal tubular epithelial cell biology, including cell polarity, cell signaling, proliferation and apoptosis, basement membrane and matrix abnormalities, and fluid transport, has been postulated to contribute to cystogenesis. Evidence is currently accumulating that supports an association of the primary cilium and basal body, as well as the focal adhesion assembly, with polycystic kidney diseases. Renal cystogenesis may be the result of a disruption of a critical feedback loop that regulates tissue morphology based on the epithelial cell environment.

Pkd1 regulates immortalized proliferation of renal tubular epithelial cells through p53 induction and JNK activation

Autosomal dominant polycystic kidney disease (ADPKD) is the most common human monogenic genetic disorder and is characterized by progressive bilateral renal cysts and the development of renal insufficiency. The cystogenesis of ADPKD is believed to be a monoclonal proliferation of PKD-deficient (PKD(-/-)) renal tubular epithelial cells. To define the function of Pkd1, we generated chimeric mice by aggregation of Pkd1(-/-) ES cells and Pkd1(+/+) morulae from ROSA26 mice. As occurs in humans with ADPKD, these mice developed cysts in the kidney, liver, and pancreas. Surprisingly, the cyst epithelia of the kidney were composed of both Pkd1(-/-) and Pkd1(+/+) renal tubular epithelial cells in the early stages of cystogenesis. Pkd1(-/-) cyst epithelial cells changed in shape from cuboidal to flat and replaced Pkd1(+/+) cyst epithelial cells lost by JNK-mediated apoptosis in intermediate stages. In late-stage cysts, Pkd1(-/-) cells continued immortalized proliferation with downregulation of p53. These results provide a novel understanding of the cystogenesis of ADPKD patients. Furthermore, immortalized proliferation without induction of p53 was frequently observed in 3T3-type culture of mouse embryonic fibroblasts from Pkd1(-/-) mice. Thus, Pkd1 plays a role in preventing immortalized proliferation of renal tubular epithelial cells through the induction of p53 and activation of JNK.

Atypical 18p- syndrome associated with partial trisomy 16p in a chromosomally unbalanced child of consanguineous parents with an identical balanced translocation

A 2 month old male infant was found to have mild growth retardation, prominent forehead, low set ears, low nasal bridge, rounded facies, cleft palate, webbed neck, shawl scrotum, and absent right kidney. The propositus, a product of a consanguineous marriage, had extremely rare abnormal cytogenetic findings. His karyotype contained three derivative chromosomes that originated from a familial translocation, t(16;18)(p13.3;p11.2) carried by both parents. Based on parental studies, the infant's unbalanced karyotype was defined as: [46,XY,t(16;18)(p13.3;p11.2), der(18)t(16;18).ish t(16;18)(16ptel-,16qtel+,18ptel+,wcp16+,wcp18+;16ptel+,18ptel-,wcp16+,wcp18+), der(18)t(16;18)(16ptel+,18ptel-,wcp16+,wcp18+)]. We describe this child at 2 months of age with a follow up at 4 1/2 years, exhibiting a mixed clinical picture with features of both 18p- and partial trisomy 16p13.3.

Urinary excretion of monocyte chemoattractant protein-1 in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) progresses to renal insufficiency in >50% of patients and is characterized by interstitial inflammation and fibrosis in the end stage. In a rat model of ADPKD, monocytes accumulate within the renal interstitium in association with increased levels of monocyte chemoattractant protein-1 (MCP-1) in cyst mural cells and increased excretion of this chemokine into the urine. For determining the extent to which this chemokine is abnormally expressed in patients with ADPKD, a cross-section study was performed of MCP-1 in urine, serum, and cyst fluid and MCP-1 production by mural epithelial cells cultured from the cysts of human patients with ADPKD. Upper boundaries for urinary MCP-1 excretion (>263 pg/mg creatinine) and serum creatinine concentration (>1.5 mg/dl) determined in 19 normal individuals were used to sort 55 ADPKD patients into three groups. In group 1 (n = 13), urine MCP-1 excretion (136 +/- 14 pg/mg creatinine) was not different from normal volunteers (152 +/- 16 pg/mg); serum creatinine levels and urine total protein excretion were normal as well. In group 2 (n = 27), urine MCP-1 excretion was increased (525 +/- 39 pg/mg creatinine), but serum creatinine levels and urine protein excretion were not different from normal. In group 3 (n = 15), urine MCP-1 excretion increased further (1221 +/- 171 pg/mg), serum creatinine levels increased to 4.3 +/- 0.8 mg/dl, and urine protein excretion rose to 0.64 +/- 0.28 mg/mg creatinine. Serum MCP-1 levels of ADPKD patients (84 +/- 9.9 pg/ml; n = 15) did not differ from normal. Levels of MCP-1 much higher than in serum or urine were found in cyst fluids obtained from nephrectomy specimens (range, 767 to 40,860 pg/ml; mean, 6434 +/- 841 pg/ml; n = 73). Polarized, confluent cultures of ADPKD cyst epithelial cells secreted MCP-1 into the apical fluid to levels eightfold greater than in the basolateral medium. Similar results were obtained with tubule epithelial cells cultured from normal human renal cortex. On the basis of these results, it is concluded that urinary excretion of MCP-1 is increased in the majority of adult patients with ADPKD and that the source of some of this chemokine may be the mural epithelium of cysts. Furthermore, it seemed that urinary MCP-1 excretion may have increased in these ADPKD patients before appreciable increases in serum creatinine concentration or urine protein excretion were detected. It is reasonable to include urine MCP-1 excretion among candidate surrogate markers in controlled, longitudinal studies of ADPKD.

A patient with TSC1 germline mutation whose clinical phenotype was limited to lymphangioleiomyomatosis

BACKGROUND

Lymphangioleiomyomatosis (LAM) can occur as in isolated form (sporadic LAM) or as a pulmonary manifestation of tuberous sclerosis complex (TSC) (TSC-associated LAM). Recent studies, however, revealed that both forms of LAM are genetically related but that sporadic LAM is a distinct clinical entity caused by somatic mutations of TSC2 (not TSC1) rather than a forme fruste of TSC carrying either of the TSC1 or TSC2 germline mutations.

METHOD

Case presentation and in-depth molecular and histopathological examinations. A 34-year-old Japanese woman was diagnosed as having pulmonary lymphangioleiomyomatosis (LAM) when bilateral pneumothoraces were surgically treated in 1992. Although slowly progressive renal disfunction was observed due to bilateral multiple renal cysts during the past 4 years, she had no other clinical features of TSC and was diagnosed as having sporadic LAM with multiple renal cysts of undetermined aetiology. Her subsequent clinical course was complicated by an endobrochial carcinoid tumour, which eventually resulted in her death in June 1999 due to massive haemoptysis.

RESULTS

Postmortem examination revealed the presence of LAM lesions in the lungs, mediastinal lymph nodes, kidneys and uterus. Diffuse renal LAM lesions are presumed to generate multiple renal cysts by constricting the nephron rather than epithelial hyperplasia obstructing lumina, which is analysis of the TSC genes demonstrated that she did not have TSC2/PKD1 contiguous gene syndrome but had a TSC1 germline mutation (Sato T et al. J Hum Genet 2002; 47: 20-8) that had occured de novo.

CONCLUSION

This patient therefore illustrates that clinical manifestations of TSC are sufficiently diverse as to allow a forme fruste of TSC that mimics sporadic LAM and that TSC1 mutation can cause multiple renal cysts resulting in renal failure.