Recent advances in autosomal‐dominant polycystic kidney disease

Autosomal‐dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease in adults, affecting one in every 1000 Australians. It is caused by loss‐of‐function heterozygous mutations in either PKD1 or PKD2 , which encode the proteins, polycystin‐1 and polycystin‐2 respectively. The disease hallmark is the development of hundreds of microscopic fluid‐filled cysts in the kidney during early childhood, which grow exponentially and continuously through life at varying rates (between 2% and 10% per year), causing loss of normal renal tissue and up to a 50% lifetime risk of dialysis‐dependent kidney failure. Other systemic complications include hypertensive cardiac disease, hepatic cysts, intracranial aneurysms, diverticular disease and hernias. Over the last two decades, advances in the genetics and pathogenesis of this disease have led to novel treatments that reduce the rate of renal cyst growth and may potentially delay the onset of kidney failure. New evidence indicates that conventional therapies (such as angiotensin inhibitors and statins) have mild attenuating effects on renal cyst growth and that systemic levels of vasopressin are critical for promoting renal cyst growth in the postnatal period. Identifying and integrating patient‐centred perspectives in clinical trials is also being advocated. This review will provide an update on recent advances in the clinical management of ADPKD.     

Autosomal-dominante polyzystische Nierenerkrankung

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, and it is even one of the most common hereditary diseases in man. In 85% of the cases the disease is caused by mutations in the PKD1 gene, which encodes for the ciliary protein polycystin-1. A milder variant of the disease is caused by mutations in the PKD2 gene, which encodes for the calcium channel-related protein polycystin-2. The disease is characterized by the progressive development of innumerable cysts in both kidneys, which gradually replace the normal kidney tissue. In ADPKD patients the inexorable cyst growth leads to a progressive deterioration of renal function over decades, which ultimately can only be treated by renal replacement therapy or renal transplantation. Until now a causal treatment was not available, and treatment options were limited to regular clinical controls and treatment of complications (hypertension, cyst infections). Several promising clinical studies are currently examining new or even existing drugs as therapeutic options to retard cyst growth in ADPKD (vasopressin receptor-2 antagonists [V2RA], mammalian target of rapamycin [mTOR] inhibitors, somatostatin). It can be anticipated that ADPKD patients will benefit from these new treatment options in the near future.     

Inhibiting the HSP90 chaperone slows cyst growth in a mouse model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a progressive genetic syndrome with an incidence of 1:500 in the population, arising from inherited mutations in the genes for polycystic kidney disease 1 (PKD1) or polycystic kidney disease 2 (PKD2). Typical onset is in middle age, with gradual replacement of renal tissue with thousands of fluid-filled cysts, resulting in end-stage renal disease requiring dialysis or kidney transplantation. There currently are no approved therapies to slow or cure ADPKD. Mutations in the PKD1 and PKD2 genes abnormally activate multiple signaling proteins and pathways regulating cell proliferation, many of which we observe, through network construction, to be regulated by heat shock protein 90 (HSP90). Inhibiting HSP90 with a small molecule, STA-2842, induces the degradation of many ADPKD-relevant HSP90 client proteins in Pkd1^−/− primary kidney cells and in vivo. Using a conditional Cre-mediated mouse model to inactivate Pkd1 in vivo, we find that weekly administration of STA-2842 over 10 wk significantly reduces initial formation of renal cysts and kidney growth and slows the progression of these phenotypes in mice with preexisting cysts. These improved disease phenotypes are accompanied by improved indicators of kidney function and reduced expression and activity of HSP90 clients and their effectors, with the degree of inhibition correlating with cystic expansion in individual animals. Pharmacokinetic analysis indicates that HSP90 is overexpressed and HSP90 inhibitors are selectively retained in cystic versus normal kidney tissue, analogous to the situation observed in solid tumors. These results provide an initial justification for evaluating HSP90 inhibitors as therapeutic agents for ADPKD.     

Cardiovascular, skeletal, and renal defects in mice with a targeted disruption of the Pkd1 gene

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by cyst formation in the kidney, liver, and pancreas and is associated often with cardiovascular abnormalities such as hypertension, mitral valve prolapse, and intracranial aneurysms. It is caused by mutations in PKD1 or PKD2, encoding polycystin-1 and -2, which together form a cell surface nonselective cation ion channel. Pkd2-/- mice have cysts in the kidney and pancreas and defects in cardiac septation, whereas Pkd1(del34) -/- and Pkd1(L) -/- mice have cysts but no cardiac abnormalities, although vascular fragility was reported in the latter. Here we describe mice carrying a targeted mutation in Pkd1 (Pkd1(del17-21betageo)), which defines its expression pattern by using a lacZ reporter gene and may identify novel functions for polycystin-1. Although Pkd1(del17-21betageo) +/- adult mice develop renal and hepatic cysts, Pkd1(del17-21betageo) -/- embryos die at embryonic days 13.5-14.5 from a primary cardiovascular defect that includes double outflow right ventricle, disorganized myocardium, and abnormal atrio-ventricular septation. Skeletal development is also severely compromised. These abnormalities correlate with the major sites of Pkd1 expression. During nephrogenesis, Pkd1 is expressed in maturing tubular epithelial cells from embryonic day 15.5. This expression coincides with the onset of cyst formation in Pkd1(del34) -/-, Pkd1(L) -/-, and Pkd2-/- mice, supporting the hypothesis that polycystin-1 and polycystin-2 interact in vivo and that their failure to do so leads to abnormalities in tubule morphology and function.     

Chronic pancreatitis with polycystic kidney disease: A rare coincidence?

IntroductionIn children, chronic pancreatitis (CP) is usually associated with anatomical anomalies of the pancreas and biliary tract or is genetically determined. Autosomal dominant polycystic kidney disease (ADPKD) may present with extrarenal cyst formation, sometimes involving the pancreas. Large enough, these cysts may cause pancreatitis in ADPKD patients.Case presentationHerein, we present a case of a 12-year-old Caucasian girl with recurrent pancreatitis with no identifiable traumatic, metabolic, infectious, drug, or immunologic causes. Structural anomalies of the pancreas, including cysts, were ruled out by imaging. However, bilateral cystic kidneys were found as an incidental finding. Her family history was negative for pancreatitis, but positive for polycystic kidney disease. Molecular analysis of ADPKD-causing mutations revealed a novel c.9659C>A (p.Ser3220*) mutation in the PKD1 gene confirming the clinical suspicion of ADPKD. Although CP may rarely occur as an extrarenal manifestation of ADPKD with pancreatic cysts, it is unusual in their absence. Thus, molecular analysis of pancreatitis susceptibility genes was performed and a homozygous pathologic c.180C>T (p.G60=) variant of the CTRC gene, known to increase the risk of CP, was confirmed.ConclusionThis is the first reported case of a pediatric patient with coincidence of genetically determined CP and ADPKD. Occurrence of pancreatitis in children with ADPKD without pancreatic cysts warrants further investigation of CP causing mutations.     

Cardiovascular polycystins: insights from autosomal dominant polycystic kidney disease and transgenic animal models

Mutations in the PKD1 and PKD2 polycystin genes are responsible for autosomal dominant polycystic kidney disease (ADPKD), one of the most prevalent genetic kidney disorders. ADPKD is a multisystem disease characterized by the formation of numerous fluid-filled cysts in the kidneys, the pancreas, and the liver. Moreover, major cardiovascular manifestations are common complications in ADPKD. Intracranial aneurysms and arterial hypertension are among the leading causes of mortality in this disease. In the present review, we summarize our current understanding of the role of polycystins in the development, maintenance, and function of the cardiovascular system.     

Mutational analysis of the PKD1 and PKD2 (type 1 and 2 dominant autosomal polycystic kidney) genes

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease. It is caused by mutations in at least two different genes: PKD1 and PKD2. The study of mutations in these genes is very difficult nowadays. In this study we have analyzed the non reiterated region of the PKD1 gene and all the exons and intron exon boundaries of the PKD2 gene. The technique used to study these genes have been single strand conformation analysis and heteroduplex. We have found 25 differences within the DNA sequence of the PKD1 gene with respect to the published sequence. Seven of these changes correspond to nonsense, missense, frameshifting and splicing mutations. The rest of changes correspond to polymorphisms or rare DNA variants. In the PKD2 gene we have identified 8 new mutations and one polymorphism. Six of these mutations are frameshifting, one is missense and the other one is a large deletion of the PKD2 gene. The rate of mutation detection within the PKD1 gene has been 4% and the rate for PKD2 has been 100%. We have not observed any correlation between genotype and phenotype either in the PKD1 nor in the PKD2 gene. The mutation analysis of ADPKD genes is very difficult, specially for the PKD1 gene. The rate of mutation detection is higher in the PKD2 gene but the global efficacy of the technique is very low as PKD2 represents only 15% of ADPKD patients. Nowadays linkage analysis is still the most useful technique for the molecular diagnosis of ADPKD patients.     

Polycystin 1 is required for the structural integrity of blood vessels

Autosomal dominant polycystic kidney disease (ADPKD), often caused by mutations in the PKD1 gene, is associated with life-threatening vascular abnormalities that are commonly attributed to the frequent occurrence of hypertension. A previously reported targeted mutation of the mouse homologue of PKD1 was not associated with vascular fragility, leading to the suggestion that the vascular lesion may be of a secondary nature. Here we demonstrate a primary role of PKD1 mutations in vascular fragility. Mouse embryos homozygous for the mutant allele (Pkd1(L)) exhibit s.c. edema, vascular leaks, and rupture of blood vessels, culminating in embryonic lethality at embryonic day 15.5. Kidney and pancreatic ductal cysts are present. The Pkd1-encoded protein, mouse polycystin 1, was detected in normal endothelium and the surrounding vascular smooth muscle cells. These data reveal a requisite role for polycystin 1 in maintaining the structural integrity of the vasculature as well as epithelium and suggest that the nature of the PKD1 mutation contributes to the phenotypic variance in ADPKD.     

A Pilot Clinical Study to Evaluate Changes in Urine Osmolality and Urine cAMP in Response to Acute and Chronic Water Loading in Autosomal Dominant Polycystic Kidney Disease

Background and objectives: Autosomal dominant polycystic kidney disease (ADPKD) leads to kidney failure in half of those affected. Increased levels of adenosine 3′:5′-cyclic monophosphate (cAMP) play a critical role in disease progression in animal models. Water loading, by suppressing arginine vasopressin (AVP)-stimulated cAMP production, is a proposed therapy for ADPKD.Design, setting, participants, & measurements: The effects of acute and sustained water loading on levels of urine osmolality (Uosm) and cAMP in 13 subjects with ADPKD and 10 healthy controls were studied. Uosm and cAMP concentrations were measured before and after water loading.Results: Urine [cAMP] indexed to Uosm significantly decreased with acute water loading in both groups (58% in controls and 35% in ADPKD). Chronic water loading resulted in a nonsignificant 13% decrease in 24-hour urine cAMP excretion in ADPKD participants, despite an increase in 24-hour urine volume by 64% to 3.14 ± 0.32 L and decrease in mean Uosm by 46%, to below that of plasma (270 ± 21 mOsm/L).Conclusions: Increased water intake of 3 L per day decreased Uosm in most ADPKD subjects. While urine [cAMP] accurately reflects changes in Uosm during acute water loading in ADPKD subjects, chronic water loading did not lower 24-hour urine cAMP excretion, although subjects with higher baseline [cAMP] (>2 nmol/mg Cr) responded best. Decreases in urine [cAMP] and osmolality are consistent with decreased AVP activity. These results support the need for a larger study to evaluate the effect of chronic water loading on ADPKD progression.Autosomal dominant polycystic kidney disease (ADPKD) is the most common, lethal, human genetic disease inherited as a dominant trait as a result of mutations in a single gene. With an estimated prevalence of 1:750, it affects nearly 600,000 individuals in the United States (1). In recent years, substantial progress has been made toward understanding the molecular genetics and biology of this disease that now makes it possible to design translational studies. Although rates of progression vary, 50% of ADPKD patients will develop ESRD.ADPKD is caused by mutations in PKD1 in 85% of patients or in PKD2 in 15% of patients. The polycystins are membrane proteins that interact with other membrane proteins, the cytoskeleton, and each other to transduce extracellular stimuli into intracellular signaling cascades (2,3). Disrupting the integrity of this system results in the pathologic sequelae of cyst formation. Cyst generation and growth depend on epithelial proliferation and fluid secretion. The molecular events leading to these changes have been partially identified. Earlier studies have demonstrated the important role of adenosine 3′:5′-cyclic monophosphate (cAMP) in promoting ADPKD renal tubule epithelial proliferation and cyst growth via B-Raf and extracellular-regulated kinase activation (4). cAMP also drives ADPKD renal epithelial fluid secretion into the cyst by regulation of the cystic fibrosis transmembrane conductance regulator chloride channel (1).Arginine vasopressin (AVP) is the major stimulus that leads to increased levels of cAMP in renal distal tubule epithelial cells. AVP is an antidiuretic hormone that stimulates cAMP production by activating G-protein-coupled vasopressin 2 receptors (V2Rs). A critical role for AVP and cAMP in the pathogenesis of ADPKD has been demonstrated by the finding that V2R antagonism or genetic loss of AVP markedly slows progression of disease in a number of animal models of ADPKD (5–9). Water loading, by suppressing plasma AVP levels, is another potential way to inhibit V2R signaling. In fact, previous studies in murine models of PKD have demonstrated that water loading also slows disease progression by inhibiting V2R-stimulated production of cAMP (10).As an autosomal dominant trait, single germline mutations in either PKD1 or PKD2 are sufficient to cause disease. Although cystogenesis is stochastic on a tissue level, on a molecular level this is the result of a second somatic “hit” inactivating the second PKD allele (11). Other variables are known to modulate disease progression, such as hypertension, male sex, and environment. Most recently, a “third-hit” hypothesis has been tested in an animal model of PKD, where ischemia-reperfusion injury accelerated cyst formation (12,13).One possible environmental factor that may affect disease progression is water intake. Increased water intake, by suppressing plasma AVP levels, may have a beneficial effect in patients with ADPKD. Human studies of high water intake to modulate renal cAMP levels and as therapy for ADPKD have not been reported. In this study, we sought to evaluate changes in urine osmolality and urine cAMP in human ADPKD and healthy subjects with acute water loading and also to assess the efficacy of sustained high water intake in decreasing urine osmolality and urine cAMP levels in ADPKD patients.     

Prevalence of Cysts in Seminal Tract and Abnormal Semen Parameters in Patients with Autosomal Dominant Polycystic Kidney Disease

Background and objectives: Autosomal dominant polycystic kidney disease is a systemic disorder with a wide range of extrarenal involvement. The scope of this study was to analyze the prevalence of seminal cysts and to correlate these findings with the sperm parameters in patients with autosomal dominant polycystic kidney disease.Design, setting, participants, & measurements: A prospective study enrolled 30 adult men with autosomal dominant polycystic kidney disease. Of these 30 patients, 22 agreed to provide a semen sample for analysis, and 28 of 30 agreed to undergo an ultrasound rectal examination. Data obtained from the semen tests and from the ultrasound study were compared.Results: Cysts in the seminal tract were present in 10 (43.47%) of 28 individuals. Twenty of 22 patients showed abnormal semen parameters, with asthenozoospermia as the most common finding. No correlation between ultrasound findings and sperm abnormalities was observed.Conclusions: The presence of cysts in the seminal tract is remarkably high (43.47%); however, this finding does not correlate with sperm abnormalities, which are also a frequent finding, especially asthenozoospermia. This semen abnormality is probably related to the abnormal function of polycystins. More attention should be paid to reproductive aspects in the initial evaluation of patients with autosomal dominant polycystic kidney disease before their ability to conceive is further impaired by uremia.Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited disorders, occurring in approximately one of 1000 individuals in the general population. ADPKD is a genetically heterogeneous disorder caused by mutations in either the PKD1 or the PKD2 gene, which encode for the proteins polycystin-1 and polycystin-2, respectively. Most ADPKD cases (>80%) are due to mutations of the PKD1 gene and are associated with an earlier onset and faster disease progression than the PKD2 phenotype. ADPKD has been widely studied during the past decade, having shed new light on polycystin structure and function. Polycystin-1 and -2 are highly conserved ubiquitous transmembrane proteins that, in the kidney, are located in epithelial cells of renal tubules, in particular in the primary cilia at the luminal side of the tubules, as well as in other areas of the renal cell epithelium. Polycystin-1 is a large protein with a long extracellular N-terminal region, 11 transmembrane domains, and a short intracellular C-terminal tail. Polycystin-2 is structurally related to the transient receptor potential channel family, and it is known to function as a nonselective cation channel permeable to Ca². Polycystin-1 and -2 form heteromeric complexes and co-localize in the primary cilium of renal epithelial cells. The primary cilium is a long nonmotile tubular structure located in the apical surface of epithelial cells in renal tubules. Its function was unknown for a long time; however, recent studies proposed a role of the primary cilium as a mechanoreceptor that may sense changes in apical fluid flow and may be able to transduce them into an intracellular Ca²⁺ signaling response (1). This model involves the participation of polycystin-1 as a mechanical sensor of ciliary bending induced by luminal fluid flow. Bending of the cilium would cause a conformational change in polycystin-1 that would in turn activate polycystin-2–associated Ca²⁺ channel, increasing the intracellular Ca²⁺ concentration and triggering intracellular signaling pathways leading to normal kidney development.Many extrarenal features are well known in ADPKD. Hepatic cysts are the most common extrarenal manifestation of ADPKD. More than 75% of individuals who have ADPKD and are older than 60 yr have hepatic cysts (2). The prevalence of intracranial aneurysms is approximately 10%, and the prevalence of pancreatic cysts is 6 to 9%; however, other extrarenal organ involvement, such as aortic abdominal aneurysms, colonic diverticulae, and cardiac valve abnormalities, has been questioned for ADPKD. Other rare associations have been reported, but their prevalence remains unknown. This could be the case for thoracic aortic aneurysm, hernias, and seminal tract cysts.There have been several case reports on cysts in epididymis, seminal vesicles, prostate, and testes in patients with ADPKD. Also some cases of infertility have been reported. Even a structural abnormality in the sperm from some patients with ADPKD has been reported; however, ADPKD is not a disease that is considered to cause infertility. Fewer than 10% of cases are sporadic, and in the remaining 90%, the disease has been inherited independently from the mother or the father. Moreover, large pedigrees are frequent. The aim of this study was to determine the prevalence of cysts in the seminal tract and to correlate it with sperm parameters.     

Chemical modifier screen identifies HDAC inhibitors as suppressors of PKD models

Polycystic kidney disease (PKD) is a common human genetic disease with severe medical consequences. Although it is appreciated that the cilium plays a central role in PKD, the underlying mechanism for PKD remains poorly understood and no effective treatment is available. In zebrafish, kidney cyst formation is closely associated with laterality defects and body curvature. To discover potential drug candidates and dissect signaling pathways that interact with ciliary signals, we performed a chemical modifier screen for the two phenotypes using zebrafish pkd2^hi4166 and ift172^hi2211 models. pkd2 is a causal gene for autosomal dominant PKD and ift172 is essential for building and maintaining the cilium. We identified trichostatin A (TSA), a pan-HDAC (histone deacetylase) inhibitor, as a compound that affected both body curvature and laterality. Further analysis verified that TSA inhibited cyst formation in pkd2 knockdown animals. Moreover, we demonstrated that inhibiting class I HDACs, either by valproic acid (VPA), a class I specific HDAC inhibitor structurally unrelated to TSA, or by knocking down hdac1, suppressed kidney cyst formation and body curvature caused by pkd2 deficiency. Finally, we show that VPA was able to reduce the progression of cyst formation and slow the decline of kidney function in a mouse ADPKD model. Together, these data suggest body curvature may be used as a surrogate marker for kidney cyst formation in large-scale high-throughput screens in zebrafish. More importantly, our results also reveal a critical role for HDACs in PKD pathogenesis and point to HDAC inhibitors as drug candidates for PKD treatment.     

Isolated polycystic liver disease as a distinct genetic disease,unlinked to polycystic kidney disease 1 and polycystic kidney disease 2

Polycystic liver disease (PLD) is proven to occur either sporadically or in association with autosomal dominant polycystic kidney disease (ADPKD), whereas the existence of an isolated (i.e., without any kidney cyst) familial form is disputed. We describe a family with definitely isolated PLD transmitted through three generations and exclude the linkage of the disease to the genetic markers of PKD1 and PKD2, the two main loci responsible for ADPKD. These findings strongly support the existence of PLD as a genetic disease distinct from the known forms of ADPKD. (Hepatology 1996 Feb;23(2):249-52)     

Interpretation of renal volume in autosomal dominant polycystic kidney disease and relevant clinical implications

Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening hereditary disease of the kidney. It presents with progressive enlargement of the kidneys with numerous cysts that distort the parenchyma and result in progressive decline in kidney function. Autosomal dominant polycystic kidney disease is genetically modified with the responsible genes localized to separate loci on chromosome 16 (PKD1 gene), accounting for the majority of ADPKD cases, and chromosome 4 (PKD2 gene), accounting for the remainder. This review discusses the current understanding of the pathogenesis of ADPKD, focusing on renal volume and its pivotal role on the manifestations of the disease. Specifically, activation of the renin-angiotensin-aldosterone system, hypertension, left ventricular hypertrophy, kidney function deterioration, pain, and hematuria are examined as consequences of renal volume increase. Recent developments on diagnostic modalities and criteria of the ADPKD are also discussed.     

Clinical utility of PKD2 mutation testing in a polycystic kidney disease cohort attending a specialist nephrology out-patient clinic

ABSTRACT: BACKGROUND: ADPKD affects approximately 1:1000 of the worldwide population. It is caused by mutations in two genes, PKD1 and PKD2. Although allelic variation has some influence on disease severity, genic effects are strong, with PKD2 mutations predicting later onset of ESRF by up to 20 years. We therefore screened a cohort of ADPKD patients attending a nephrology out-patient clinic for PKD2 mutations, to identify factors that can be used to offer targeted gene testing and to provide patients with improved prognostic information. METHODS: 142 consecutive individuals presenting to a hospital nephrology out-patient service with a diagnosis of ADPKD and CKD stage 4 or less were screened for mutations in PKD2, following clinical evaluation and provision of a detailed family history (FH). RESULTS: PKD2 mutations were identified in one fifth of cases. 12% of non-PKD2 patients progressed to ESRF during this study whilst none with a PKD2 mutation did (16-88 months of follow-up, p < 0.03). However, the overall age to development of CKD3 was not predicted by mutation status. A significant difference was found in age at ESRF of affected family members (non-PKD2 vs. PKD2, 54 yrs vs. 65 yrs; p < 0.0001). No PKD2 mutations were identified in patients with a FH of ESRF occurring before age 50 yrs, whereas a PKD2 mutation was predicted by a positive FH without ESRF. CONCLUSIONS: PKD2 testing has a clinically significant detection rate in the pre-ESRF population. It did not accurately distinguish those individuals with milder renal disease defined by stage of CKD but did identify a group less likely to progress to ESRF. When used with detailed FH, it also offers useful prognostic information for individuals and their families. It can usefully be offered to all but those whose relatives have developed ESRF before the sixth decade.     

Polycystic kidney disease

Polycystic kidney disease, an inherited systemic disorder, is characterized by the development of multiple cysts in the kidneys and other organs. Patients can present at any age, but more often come to clinical attention (unless there is a family history) after age 30. Patients who are diagnosed before age 30 have a worse renal survival. Although palpation of the abdomen occasionally provides a clue to the presence of polycystic kidney disease, radiographic procedures most often suggest the diagnosis. Mutations in the PKD1 or PKD2 genes give rise to cyst formation. Flank pain, hematuria, polyuria, nephrolithiasis, urinary tract infections, and hypertension may be part of the syndrome of polycystic kidney disease. It is the fourth most common cause of end-stage renal disease. Blood pressure treatment goals are less than 130/80 mm Hg. Treatment should include the use of angiotensin-converting enzyme inhibitors.     

Cyst Infections in Patients with Autosomal Dominant Polycystic Kidney Disease

Background and objectives: Cyst infection is a complex diagnostic and therapeutic issue in patients with autosomal dominant polycystic kidney disease (ADPKD); however, published data regarding the diagnosis and the management of cyst infections in patients with ADPKD are sparse.Design, setting, participants, & measurements: A retrospective study was conducted in a referral center for patients with ADPKD in Paris, France. We identified using a computerized database all patients who had ADPKD and were admitted in the nephrology department of Hôpital Necker between January 1998 and August 2008 with likely or definite renal and/or hepatic cyst infection. Medical files of all included patients were reviewed.Results: Among 389 identified patients with ADPKD, 33 (8.4%) had 41 episodes of cyst infection, including eight definite and 33 likely cases. The incidence of cyst infections in patients with ADPKD was 0.01 episode per patient per year. Microbiological documentation was available for 31 episodes (75%), Escherichia coli accounting for 74% of all retrieved bacterial strains. Positron emission tomography scan proved superior to ultrasound, Computed tomography scan, and magnetic resonance imaging for the detection of infected cysts. Clinical efficacy of initial antibiotic treatment was noted in 71% of episodes. Antibiotic treatment modification was more frequently required for patients who were receiving initial monotherapy compared with those who were receiving bitherapy. Large (diameter >5 cm) infected cysts frequently required drainage.Conclusions: Positron emission tomography scan will probably make the diagnosis of cyst infections easier and more accurate. Antibiotic association, including a fluoroquinolone, and the drainage of large infected cysts remain the main treatment for cyst infections.Autosomal dominant polycystic kidney disease (ADPKD) represents the most common inherited disorder affecting one in 500 to one in 1000 live births and accounting for 4 to 10% of dialysis patients. The most striking feature of ADPKD is the occurrence of numerous renal and hepatic cysts, which arise from various renal tubule segments and lead to an increased kidney size. Cysts are also associated with some of the most common complications of ADPKD: Intracystic bleeding, gross hematuria, obstruction mainly caused by liver cysts, and, most important, infections. Kidney and liver cyst infection is a complex diagnostic and therapeutic challenge; however, the literature on the diagnosis and the management of urinary tract infections and particularly cyst infections in patients with ADPKD is relatively sparse. The clinical, microbiological, and radiologic features of cyst infections as well as treatment regimens remain ill-defined (1–3). We conducted a retrospective, single-center study to assess the clinical and radiologic presentation and treatment outcomes of cyst infections in patients with ADPKD.     

Cyst formation in the PKD2 (1-703) transgenic rat precedes deregulation of proliferation-related pathways

Background

Polycystic Kidney Disease is characterized by the formation of large fluid-filled cysts that eventually destroy the renal parenchyma leading to end-stage renal failure. Although remarkable progress has been made in understanding the pathologic mechanism of the disease, the precise orchestration of the early events leading to cyst formation is still unclear. Abnormal cellular proliferation was traditionally considered to be one of the primary irregularities leading to cyst initiation and growth. Consequently, many therapeutic interventions have focused on targeting this abnormal proliferation, and some have even progressed to clinical trials. However, the role of proliferation in cyst development was primarily examined at stages where cysts are already visible in the kidneys and therefore at later stages of disease development.

Methods

In this study we focused on the cystic phenotype since birth in an attempt to clarify the temporal contribution of cellular proliferation in cyst development. Using a PKD2 transgenic rat model (PKD2 (1-703)) of different ages (0-60 days after birth) we performed gene expression profiling and phenotype analysis by measuring various kidney parameters.

Results

Phenotype analysis demonstrated that renal cysts appear immediately after birth in the PKD2 transgenic rat model (PKD2 (1-703)). On the other hand, abnormal proliferation occurs at later stages of the disease as identified by gene expression profiling. Interestingly, other pathways appear to be deregulated at early stages of the disease in this PKD model. Specifically, gene expression analysis demonstrated that at day 0 the RAS system is involved. This is altered at day 6, when Wnt signaling and focal adhesion pathways are affected. However, at and after 24 days, proliferation, apoptosis, altered ECM signaling and many other factors become involved.

Conclusions

Our data suggest that cystogenesis precedes deregulation of proliferation-related pathways, suggesting that proliferation abnormalities may contribute in cyst growth rather than cyst formation.     

Evidence for Pathogenicity of Atypical Splice Mutations in Autosomal Dominant Polycystic Kidney Disease

Background and objectives: Mutation-based molecular diagnostics of autosomal dominant polycystic kidney disease (ADPKD) is complicated by locus and allelic heterogeneity, large multi-exon gene structure and duplication in PKD1, and a high level of unclassified variants. Comprehensive screening of PKD1 and PKD2 by two recent studies have shown that atypical splice mutations account for 3.5% to 5% of ADPKD. We evaluated the role of bioinformatic prediction of atypical splice mutations and determined the pathogenicity of an atypical PKD2 splice variant from a multiplex ADPKD (TOR101) family.Design, setting, participants, & measurements: Using PubMed, we identified 17 atypical PKD1 and PKD2 splice mutations. We found that bioinformatics analysis was often useful for evaluating the pathogenicity of these mutations, although RT-PCR is needed to provide the definitive proof.Results: Sequencing of both PKD1 and PKD2 in an affected subject of TOR101 failed to identify a definite mutation, but revealed several UCVs, including an atypical PKD2 splice variant. Linkage analysis with microsatellite markers indicated that TOR101 was PKD2-linked and IVS8 + 5G→A was shown to cosegregate only with affected subjects. RT-PCR of leukocyte mRNA from an affected subject using primers from exons 7 and 9 revealed six splice variants that resulted from activation of different combinations of donor and acceptor cryptic splice sites, all terminating with premature stop codons.Conclusions: The data provide strong evidence that IVS8 + 5G→A is a pathogenic mutation for PKD2. This case highlights the importance of functional analysis of UCVs.Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disorder worldwide, affecting approximately one in 500 live births. It is characterized by focal development and progressive enlargement of renal cysts, leading to end-stage renal disease (ESRD) in late middle age. Typically, only a few renal cysts are detected in most affected subjects before 30 yr of age. However, by the fifth decade of life, hundreds to thousands of renal cysts are found in most patients. Overall, ADPKD accounts for 5% to 8% of end-stage renal disease (ESRD) in developed countries (1,2). Extrarenal complications of ADPKD are variable and include inguinal hernias, colonic diverticulae, valvular heart disease, and intracranial arterial aneurysms (1).Mutations of two genes, PKD1 (MIM 601313) and PKD2 (MIM 173910), account for approximately 85% and 15% of all cases of ADPKD in linkage-characterized European populations (3,4). Although the clinical manifestations of PKD1 and PKD2 overlap completely, a strong locus effect on renal disease severity is evident with more severe renal disease in PKD1 than PKD2 (median age at ESRD: 54 yr versus 74, respectively) (5). PKD1 is a large gene consisting of 46 exons with an open reading frame of approximately 13 kb and is predicted to encode a protein of 4302 amino acids. Its entire 5′ region up to exon 33 has been duplicated six times proximally on chromosome 16p, and the presence of these highly homologous pseudogenes has made genetic analysis of PKD1 difficult (1,2). Recent availability of protocols for long-range and locus-specific amplification of PKD1 has enabled the complete mutation screening of this complex gene (6–9). In contrast, PKD2 is a single-copy gene consisting of 15 exons with an open reading frame of approximately 3 kb and is predicted to encode a protein of 968 amino acids (1,2).The diagnosis of ADPKD is straightforward in affected subjects with a positive family history and enlarged kidneys with multiple cysts (6). Renal ultrasound is a useful method for this purpose, and age-dependant criteria based on cyst number have been derived for subjects born with 50% risk of PKD1 or PKD2 (6,10). However, ultrasound diagnosis of ADPKD in younger at-risk subjects with equivocal or negative findings and in subjects affected by PKD2 or de novo disease remains a challenge (6). For these reasons, molecular screening is a useful tool in the clinical setting. However, marked allelic heterogeneity is evident, with over 200 different PKD1 and over 50 different PKD2 mutations reported to date (2,6–9,11–13). The majority of these mutations are unique and scattered throughout both genes. Although the majority of these mutations are predicted to be protein truncating (frame-shift deletion/insertion, nonsense or canonical splice changes), a large number of unclassified variants (UCVs; in-frame deletions, mis-sense and atypical splice changes) has also been reported (7–9). Comprehensive screening of both PKD1 and PKD2 by two recent studies identified definitive and probable mutations in 42% to 63% and 26% to 37% of patients, respectively (8,9). These two studies also reported that atypical splice mutations account for approximately 3.5% to 5% of ADPKD (8,9). In the current study, we performed and evaluated the utility of bioinformatics analysis on 17 reported atypical PKD1 and PKD2 splice mutations. We also determine the pathogenicity of an atypical splice variant found in a family affected by PKD2 and highlight the importance of functional analysis of UCVs in molecular diagnostic testing.     

Mutant polycystin-2 induces proliferation in primary rat tubular epithelial cells in a STAT-1/p21-independent fashion accompanied instead by alterations in expression of p57KIP2 and Cdk2

Background

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is characterized by the formation of multiple fluid-filled cysts that destroy the kidney architecture resulting in end-stage renal failure. Mutations in genes PKD1 and PKD2 account for nearly all cases of ADPKD. Increased cell proliferation is one of the key features of the disease. Several studies indicated that polycystin-1 regulates cellular proliferation through various signaling pathways, but little is known about the role played by polycystin-2, the product of PKD2. Recently, it was reported that as with polycystin-1, polycystin-2 can act as a negative regulator of cell growth by modulating the levels of the cyclin-dependent kinase inhibitor, p21 and the activity of the cyclin-dependent kinase 2, Cdk2.

Methods

Here we utilized different kidney cell-lines expressing wild-type and mutant PKD2 as well as primary tubular epithelial cells isolated from a PKD transgenic rat to further explore the contribution of the p21/Cdk2 pathway in ADPKD proliferation.

Results

Surprisingly, over-expression of wild-type PKD2 in renal cell lines failed to inactivate Cdk2 and consequently had no effect on cell proliferation. On the other hand, expression of mutated PKD2 augmented proliferation only in the primary tubular epithelial cells of a rat model but this was independent of the STAT-1/p21 pathway. On the contrary, multiple approaches revealed unequivocally that expression of the cyclin-dependent kinase inhibitor, p57^KIP2, is downregulated, while p21 remains unchanged. This p57 reduction is accompanied by an increase in Cdk2 levels.

Conclusion

Our results indicate the probable involvement of p57^KIP2 on epithelial cell proliferation in ADPKD implicating a new mechanism for mutant polycystin-2 induced proliferation. Most importantly, contrary to previous studies, abnormal proliferation in cells expressing mutant polycystin-2 appears to be independent of STAT-1/p21.