Polycystic kidney disease

Constitutive renal Rel/nuclear factor-κB expression in Lewis polycystic kidney disease rats

AIM: To determine the temporal expression and pattern of Rel/nuclear factor (NF)-κB proteins in renal tissue in polycystic kidney disease (PKD).

METHODS: The renal expression of Rel/NF-κB proteins was determined by immunohistochemistry, immunofluorescence and immunoblot analysis in Lewis polycystic kidney rats (LPK, a genetic ortholog of human nephronopthsis-9) from postnatal weeks 3 to 20. At each timepoint, renal disease progression and the mRNA expression of NF-κB-dependent genes (TNFα and CCL2) were determined. NF-κB was also histologically assessed in human PKD tissue.

RESULTS: Progressive kidney enlargement in LPK rats was accompanied by increased renal cell proliferation and interstitial monocyte accumulation (peaking at weeks 3 and 10 respectively), and progressive interstitial fibrosis (with α smooth muscle actin and Sirius Red deposition significantly increased compared to Lewis kidneys from weeks 3 to 6 onwards). Rel/NF-κB proteins (phosphorylated-p105, p65, p50, c-Rel and RelB) were expressed in cystic epithelial cells (CECs) of LPK kidneys as early as postnatal week 3 and sustained until late-stage disease at week 20. From weeks 10 to 20, nuclear p65, p50, RelB and cytoplasmic IκBα protein levels, and TNFα and CCL2 expression, were upregulated in LPK compared to Lewis kidneys. NF-κB proteins were consistently expressed in CECs of human PKD. The DNA damage marker γ-H2AX was also identified in the CECs of LPK and human polycystic kidneys.

CONCLUSION: Several NF-κB proteins are consistently expressed in CECs in human and experimental PKD. These data suggest that the upregulation of both the canonical and non-canonical pathways of NF-κB signaling may be a constitutive and early pathological feature of cystic renal diseases.

Combined liver-kidney transplantation for polycystic liver and kidney disease: analysis from the United Network for Organ Sharing dataset

BACKGROUND & AIMS

The purpose of this study was to evaluate predictors of outcomes in combined liver-kidney transplants for polycystic liver and kidney disease.

METHODS

We queried the United Network for Organ Sharing dataset for combined liver-kidney transplants performed from 1988 to 2013.

RESULTS

Out of 107 patients who had combined liver-kidney transplants for polycystic liver and kidney disease, 84 were women (78.5%) with a mean age of 54.9 ±7.2 years. Kaplan-Meier analysis demonstrated that patients undergoing liver-kidney transplantation for polycystic liver and kidney disease had better survival than patients with polycystic liver disease undergoing liver transplant alone and those undergoing liver-kidney transplantation for other indications. This group had a 1-, 3- and 5-year survival of 91%, 90% and 90%, respectively. Multivariable analysis demonstrated that an indication of polycystic liver and kidney disease for combined liver-kidney transplant (hazard ratio, 0.29; 95% confidence interval, 0.129-0.526; P < 0.001) and Model for End-Stage Liver Disease score (hazard ratio, 1.271; 95% confidence interval, 1.093-1.477; P = 0.002) are independently associated with patient survival. In a propensity score analysis adjusting for age, gender, cold ischaemia time and total bilirubin and excluding hepatitis C, we found that patients transplanted with combined liver-kidney for other indications have similar survival compared with our study group.

CONCLUSIONS

Combined liver-kidney transplantation for polycystic liver and kidney disease can achieve good outcomes in selected patients. On Cox regression analysis, patients with polycystic liver and kidney disease undergoing liver-kidney transplantation had better survival compared with patients with combined liver-kidney for other indications. After excluding hepatitis C patients, those transplanted for polycystic liver and kidney disease vs other indications had similar survival after combined liver-kidney transplantation. Interestingly, patients in the combined polycystic liver and kidney disease group have significantly better outcomes than patients with polycystic liver disease undergoing liver transplant alone.

Influence of the R823W mutation on the interaction of the ANKS6-ANKS3: insights from molecular dynamics simulation and free energy analysis

The sterile alpha motif (SAM) domain of the protein ANKS6, a protein-protein interaction domain, is responsible for autosomal dominant polycystic kidney disease. Although the disease is the result of the R823W point mutation in the SAM domain of the protein ANKS6, the molecular details are still unclear. We applied molecular dynamics simulations, the principal component analysis, and the molecular mechanics Poisson-Boltzmann surface area binding free energy calculation to explore the structural and dynamic effects of the R823W point mutation on the complex ANKS6-ANKS3 (PDB ID: 4NL9) in comparison to the wild proteins. The energetic analysis presents that the wild type has a more stable structure than the mutant. The R823W point mutation not only disrupts the structure of the ANKS6 SAM domain but also negatively affects the interaction of the ANKS6-ANKS3. These results further clarify the previous experiments to understand the ANKS6-ANKS3 interaction comprehensively. In summary, this study would provide useful suggestions to understand the interaction of these proteins and their fatal action on mediating kidney function.

Inhibition of histone deacetylase 6 activity reduces cyst growth in polycystic kidney disease

Abnormal proliferation of cyst-lining epithelium and increased intracystic fluid secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) are thought to contribute to cyst growth in autosomal dominant polycystic kidney disease (ADPKD). Histone deacetylase 6 (HDAC6) expression and activity are increased in certain cancers, neurodegenerative diseases, and in Pkd1-mutant renal epithelial cells. Inhibition of HDAC6 activity with specific inhibitors slows cancer growth. Here we studied the effect of tubacin, a specific HDAC6 inhibitor, on cyst growth in polycystic kidney disease. Treatment with tubacin prevented cyst formation in MDCK cells, an in vitro model of cystogenesis. Cyclic AMP stimulates cell proliferation and activates intracystic CFTR-mediated chloride secretion in ADPKD. Treatment with tubacin downregulated cyclic AMP levels, inhibited cell proliferation, and inhibited cyclic AMP-activated CFTR chloride currents in MDCK cells. We also found that tubacin reduced cyst growth by inhibiting proliferation of cyst-lining epithelial cells, downregulated cyclic AMP levels, and improved renal function in a Pkd1-conditional mouse model of ADPKD. Thus, HDAC6 could play a role in cyst formation and could serve as a potential therapeutic target in ADPKD.

Endothelin and tubulointerstitial renal disease

All components of the endothelin (ET) system are present in renal tubular cells. In this review, we summarize current knowledge about ET and the most common tubular diseases: acute kidney injury (AKI) and polycystic kidney disease. AKI originally was called acute tubular necrosis, pointing to the most prominent morphologic findings. Similarly, cysts in polycystic kidney disease, and especially in autosomal-dominant polycystic kidney disease, are of tubular origin. Preclinical studies have indicated that the ET system and particularly ETA receptors are involved in the pathogenesis of ischemia-reperfusion injury, although these findings have not been translated to clinical studies. The ET system also has been implicated in radiocontrast-dye-induced AKI, however, ET-receptor blockade in a large human study was not successful. The ET system is activated in sepsis models of AKI; the effectiveness of ET blocking agents in preclinical studies is variable depending on the model and the ET-receptor antagonist used. Numerous studies have shown that the ET system plays an important role in the complex pathophysiology associated with cyst formation and disease progression in polycystic kidney disease. However, results from selective targeting of ET-receptor subtypes in animal models of polycystic kidney disease have proved disappointing and do not support clinical trials. These studies have shown that a critical balance between ETA and ETB receptor action is necessary to maintain structure and function in the cystic kidney. In summary, ETs have been implicated in the pathogenesis of several renal tubulointerstitial diseases, however, experimental animal findings have not yet led to use of ET blockers in human beings.

Screen-based identification and validation of four new ion channels as regulators of renal ciliogenesis

To investigate the contribution of ion channels to ciliogenesis, we carried out a small interfering RNA (siRNA)-based reverse genetics screen of all ion channels in the mouse genome in murine inner medullary collecting duct kidney cells. This screen revealed four candidate ion channel genes: Kcnq1, Kcnj10, Kcnf1 and Clcn4. We show that these four ion channels localize to renal tubules, specifically to the base of primary cilia. We report that human KCNQ1 Long QT syndrome disease alleles regulate renal ciliogenesis; KCNQ1-p.R518X, -p.A178T and -p.K362R could not rescue ciliogenesis after Kcnq1-siRNA-mediated depletion in contrast to wild-type KCNQ1 and benign KCNQ1-p.R518Q, suggesting that the ion channel function of KCNQ1 regulates ciliogenesis. In contrast, we demonstrate that the ion channel function of KCNJ10 is independent of its effect on ciliogenesis. Our data suggest that these four ion channels regulate renal ciliogenesis through the periciliary diffusion barrier or the ciliary pocket, with potential implication as genetic contributors to ciliopathy pathophysiology. The new functional roles of a subset of ion channels provide new insights into the disease pathogenesis of channelopathies, which might suggest future therapeutic approaches.

Food Restriction Ameliorates the Development of Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by the accumulation of kidney cysts that ultimately leads to loss of renal function and kidney failure. At present, the treatment for ADPKD is largely supportive. Multiple studies have focused on pharmacologic approaches to slow the development of the cystic disease; however, little is known about the role of nutrition and dietary manipulation in PKD. Here, we show that food restriction (FR) effectively slows the course of the disease in mouse models of ADPKD. Mild to moderate (10%-40%) FR reduced cyst area, renal fibrosis, inflammation, and injury in a dose-dependent manner. Molecular and biochemical studies in these mice indicate that FR ameliorates ADPKD through a mechanism involving suppression of the mammalian target of the rapamycin pathway and activation of the liver kinase B1/AMP-activated protein kinase pathway. Our data suggest that dietary interventions such as FR, or treatment that mimics the effects of such interventions, may be potential and novel preventive and therapeutic options for patients with ADPKD.

Regulation of polycystin-1 ciliary trafficking by motifs at its C-terminus and polycystin-2 but not by cleavage at the GPS site

Failure to localize membrane proteins to the primary cilium causes a group of diseases collectively named ciliopathies. Polycystin-1 (PC1, also known as PKD1) is a large ciliary membrane protein defective in autosomal dominant polycystic kidney disease (ADPKD). Here, we developed a large set of PC1 expression constructs and identified multiple sequences, including a coiled-coil motif in the C-terminal tail of PC1, regulating full-length PC1 trafficking to the primary cilium. Ciliary trafficking of wild-type and mutant PC1 depends on the dose of polycystin-2 (PC2, also known as PKD2), and the formation of a PC1-PC2 complex. Modulation of the ciliary trafficking module mediated by the VxP ciliary-targeting sequence and Arf4 and Asap1 does not affect the ciliary localization of full-length PC1. PC1 also promotes PC2 ciliary trafficking. PC2 mutations truncating its C-terminal tail but not those changing the VxP sequence to AxA or impairing the pore of the channel, leading to a dead channel, affect PC1 ciliary trafficking. Cleavage at the GPCR proteolytic site (GPS) of PC1 is not required for PC1 trafficking to cilia. We propose a mutually dependent model for the ciliary trafficking of PC1 and PC2, and that PC1 ciliary trafficking is regulated by multiple cis-acting elements. As all pathogenic PC1 mutations tested here are defective in ciliary trafficking, ciliary trafficking might serve as a functional read-out for ADPKD.

Long-Term Follow-Up of Kidney Transplant Recipients With Polycystic Kidney Disease

OBJECTIVES

Patients with polycystic kidney disease are candidates for kidney transplant. We report the results of our single center study of 250 first transplant recipients with polycystic kidney disease (autosomal dominant [64%], medullary cystic [16%], autosomal recessive [6%], and nonspecified [14%]).

MATERIALS AND METHODS

Patient groups were divided and analyzed according to the origin of the graft (deceased donor or living donor). We also analyzed demographic data of donors and recipients, waiting time, duration of dialysis, transfusion, nephrectomy, hospitalization, morbidities, and graft and patient survival. The study was approved by the Ethical Review Committee of the Institute. All of the protocols conformed to the ethical guidelines of the 1975 Helsinki Declaration.

RESULTS

The deceased-donor group comprised 79% and the living-donor group comprised 21% of the cases. Nephrectomy was performed on 21% of the recipients. The deceased-donor group showed significantly higher values than the living-donor group regarding rate of hemodialysis (82% vs 68%), duration of dialysis (1571 vs 1002 days), waiting time (1129 vs 33 days), and blood transfusions (45% vs 27%). In deceased-donor versus living-donor transplant recipients, surgical complications included arterial stenosis (1% vs 0%), venous thrombosis (1% vs 0%), urine leakage (0.5% vs 1.9%), ureteral stenosis (0.5% vs 0%), reflux (0% vs 1.9%), lymphocele (11.7% vs 8.1%), and hernia (5.2% vs 8.1%), with no statistically significant differences shown between the groups. The living-donor group had graft and patient survival rates as high as the deceased-donor group.

CONCLUSIONS

The low rate of morbidity and excellent survival rates make kidney transplant an excellent option for patients with polycystic kidney disease. Although fear of future appearance of polycystic kidney disease may reduce the rate of related living donors, our study showed that graft and patient survival rates in the living-donor group were as high as in the deceased-donor group.

Implementing Patch Clamp and Live Fluorescence Microscopy to Monitor Functional Properties of Freshly Isolated PKD Epithelium

Cyst initiation and expansion during polycystic kidney disease is a complex process characterized by abnormalities in tubular cell proliferation, luminal fluid accumulation and extracellular matrix formation. Activity of ion channels and intracellular calcium signaling are key physiologic parameters which determine functions of tubular epithelium. We developed a method suitable for real-time observation of ion channels activity with patch-clamp technique and registration of intracellular Ca2+ level in epithelial monolayers freshly isolated from renal cysts. PCK rats, a genetic model of autosomal recessive polycystic kidney disease (ARPKD), were used here for ex vivo analysis of ion channels and calcium flux. Described here is a detailed step-by-step procedure designed to isolate cystic monolayers and non-dilated tubules from PCK or normal Sprague Dawley (SD) rats, and monitor single channel activity and intracellular Ca2+ dynamics. This method does not require enzymatic processing and allows analysis in a native setting of freshly isolated epithelial monolayer. Moreover, this technique is very sensitive to intracellular calcium changes and generates high resolution images for precise measurements. Finally, isolated cystic epithelium can be further used for staining with antibodies or dyes, preparation of primary cultures and purification for various biochemical assays.

Comparative Study of Outcomes among Patients with Polycystic Kidney Disease on Hemodialysis and Peritoneal Dialysis

Polycystic kidney disease (PCKD) is the most common hereditary cause of end-stage renal disease, the complications of which may prevent the choice of peritoneal dialysis (PD). The aim of this study was to explore the effects of dialysis modality on outcomes in patients with PCKD. We extracted a cohort of 1417 adult patients with PCKD initiating long-term dialysis therapy in 1999-2010 from the Taiwan National Health Insurance Research Database, among which 125 patients chose PD. The patients on HD were older and had a higher comorbidity index compared to those on PD. We compared the risks for death, hospitalization and medical expenditures between the patients on PD and propensity-score matched patients on hemodialysis (HD). The overall survival did not differ between the patients on PD and HD. The patients on PD tended to have higher hazard ratios (HR) for the first episode of hospitalization (adjusted HR 1.34 [95% CI, 1.04-1.79]). The annual medical expenses were 10% lower for the patients on PD. PD is an equivalent choice of renal replacement therapy to HD for patients with PCKD in terms of survival. Although the patients on PD had a higher risk for hospitalization, the medical expenditure for PD was 10% lower.

Comprehensive PKD1 and PKD2 Mutation Analysis in Prenatal Autosomal Dominant Polycystic Kidney Disease

Prenatal forms of autosomal dominant polycystic kidney disease (ADPKD) are rare but can be recurrent in some families, suggesting a common genetic modifying background. Few patients have been reported carrying, in addition to the familial mutation, variation(s) in polycystic kidney disease 1 (PKD1) or HNF1 homeobox B (HNF1B), inherited from the unaffected parent, or biallelic polycystic kidney and hepatic disease 1 (PKHD1) mutations. To assess the frequency of additional variations in PKD1, PKD2, HNF1B, and PKHD1 associated with the familial PKD mutation in early ADPKD, these four genes were screened in 42 patients with early ADPKD in 41 families. Two patients were associated with de novo PKD1 mutations. Forty patients occurred in 39 families with known ADPKD and were associated with PKD1 mutation in 36 families and with PKD2 mutation in two families (no mutation identified in one family). Additional PKD variation(s) (inherited from the unaffected parent when tested) were identified in 15 of 42 patients (37.2%), whereas these variations were observed in 25 of 174 (14.4%, P=0.001) patients with adult ADPKD. No HNF1B variations or PKHD1 biallelic mutations were identified. These results suggest that, at least in some patients, the severity of the cystic disease is inversely correlated with the level of polycystin 1 function.

Improved Structure and Function in Autosomal Recessive Polycystic Rat Kidneys with Renal Tubular Cell Therapy

Autosomal recessive polycystic kidney disease is a truly catastrophic monogenetic disease, causing death and end stage renal disease in neonates and children. Using PCK female rats, an orthologous model of autosomal recessive polycystic kidney disease harboring mutant Pkhd1, we tested the hypothesis that intravenous renal cell transplantation with normal Sprague Dawley male kidney cells would improve the polycystic kidney disease phenotype. Cytotherapy with renal cells expressing wild type Pkhd1 and tubulogenic serum amyloid A1 had powerful and sustained beneficial effects on renal function and structure in the polycystic kidney disease model. Donor cell engraftment and both mutant and wild type Pkhd1 were found in treated but not control PCK kidneys 15 weeks after the final cell infusion. To examine the mechanisms of global protection with a small number of transplanted cells, we tested the hypothesis that exosomes derived from normal Sprague Dawley cells can limit the cystic phenotype of PCK recipient cells. We found that renal exosomes originating from normal Sprague Dawley cells carried and transferred wild type Pkhd1 mRNA to PCK cells in vivo and in vitro and restricted cyst formation by cultured PCK cells. The results indicate that transplantation with renal cells containing wild type Pkhd1 improves renal structure and function in autosomal recessive polycystic kidney disease and may provide an intra-renal supply of normal Pkhd1 mRNA.

Stem cells and fluid flow drive cyst formation in an invertebrate excretory organ

Cystic kidney diseases (CKDs) affect millions of people worldwide. The defining pathological features are fluid-filled cysts developing from nephric tubules due to defective flow sensing, cell proliferation and differentiation. The underlying molecular mechanisms, however, remain poorly understood, and the derived excretory systems of established invertebrate models (Caenorhabditis elegans and Drosophila melanogaster) are unsuitable to model CKDs. Systematic structure/function comparisons revealed that the combination of ultrafiltration and flow-associated filtrate modification that is central to CKD etiology is remarkably conserved between the planarian excretory system and the vertebrate nephron. Consistently, both RNA-mediated genetic interference (RNAi) of planarian orthologues of human CKD genes and inhibition of tubule flow led to tubular cystogenesis that share many features with vertebrate CKDs, suggesting deep mechanistic conservation. Our results demonstrate a common evolutionary origin of animal excretory systems and establish planarians as a novel and experimentally accessible invertebrate model for the study of human kidney pathologies.

Laparoscopic Nephrectomy versus Open Nephrectomy for Patients with Autosomal Dominant Polycystic Kidney Disease: A Systematic Review and Meta-Analysis

Objective

To compare efficacy and safety of laparoscopicnephrectomy (LN) versusopen nephrectomy (ON) in the management of autosomal dominant polycystic kidney disease (ADPKD), we conducted a systematic review and meta-analysis.

Methods

A systematic search of the electronic databases PubMed, Scopus, and the Cochrane Library was performed up to October 2014.This systematic review was performed based on observational comparative studies that assessed the two techniques. The weighted mean difference (WMD) and risk ratio (RR), with their corresponding 95% confidence interval (CI), were calculated to compare continuous and dichotomous variables, respectively.

Results

Seven studies were identified, including 195 cases (118 LN / 77 ON). Although LN was associated with longer operative time (WMD 30.236, 95%CI 14.541 −45.932, P<0.001) and the specimen might not have been resected as heavy as the ON group (WMD -986.516, 95%CI -1883.24–-89.795, P = 0.031), patients in this group might benefit from a shorter length of hospital stay (WMD -3.576, 95%CI 4.976–-2.176, P <0.001), less estimated blood loss (WMD -180.245, 95%CI -317.939–-42.556, P = 0.010), and lower need of transfusion (RR 0.345, 95%CI 0.183–0.650, P = 0.001). The LN group also had less overall complications (RR 0.545, 95%CI 0.329–0.903, P = 0.018). The need of narcotic analgesics between the two groups might have no significant difference (WMD -54.66, 95%CI -129.76–20.44, P = 0.154).

Conclusion

LN for giant symptomatic ADPKD was feasible, safe and efficacious. Morbidity was significantly reduced compared with the open approach. For an experienced laparoscopist, LN might be a better alternative.

AMP-activated Protein Kinase Suppresses Biosynthesis of Glucosylceramide by Reducing Intracellular Sugar Nucleotides

The membrane glycolipid glucosylceramide (GlcCer) plays a critical role in cellular homeostasis. Its intracellular levels are thought to be tightly regulated. How cells regulate GlcCer levels remains to be clarified. AMP-activated protein kinase (AMPK), which is a crucial cellular energy sensor, regulates glucose and lipid metabolism to maintain energy homeostasis. Here, we investigated whether AMPK affects GlcCer metabolism. AMPK activators (5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside and metformin) decreased intracellular GlcCer levels and synthase activity in mouse fibroblasts. AMPK inhibitors or AMPK siRNA reversed these effects, suggesting that GlcCer synthesis is negatively regulated by an AMPK-dependent mechanism. Although AMPK did not affect the phosphorylation or expression of GlcCer synthase, the amount of UDP-glucose, an activated form of glucose required for GlcCer synthesis, decreased under AMPK-activating conditions. Importantly, the UDP-glucose pyrophosphatase Nudt14, which degrades UDP-glucose, generating UMP and glucose 1-phosphate, was phosphorylated and activated by AMPK. On the other hand, suppression of Nudt14 by siRNA had little effect on UDP-glucose levels, indicating that mammalian cells have an alternative UDP-glucose pyrophosphatase that mainly contributes to the reduction of UDP-glucose under AMPK-activating conditions. Because AMPK activators are capable of reducing GlcCer levels in cells from Gaucher disease patients, our findings suggest that reducing GlcCer through AMPK activation may lead to a new strategy for treating diseases caused by abnormal accumulation of GlcCer.

4D MRI of polycystic kidneys from rapamycin-treated Glis3-deficient mice

Polycystic kidney disease (PKD) is a life-threatening disease that leads to a grotesque enlargement of the kidney and significant loss of function. Several imaging studies with MRI have demonstrated that cyst size in polycystic kidneys can determine disease severity and progression. In the present study, we found that, although kidney volume and cyst volume decreased with drug treatment, renal function did not improve with treatment. Here, we applied dynamic contrast-enhanced MRI to study PKD in a Glis3 (GLI-similar 3)-deficient mouse model. Cysts from this model have a wide range of sizes and develop at an early age. To capture this crucial stage and assess cysts in detail, we imaged during early development (3-17 weeks) and applied high spatiotemporal resolution MRI (125 × 125 × 125 cubic microns every 7.7 s). A drug treatment with rapamycin (also known as sirolimus) was applied to determine whether disease progression could be halted. The effect and synergy (interaction) of aging and treatment were evaluated using an analysis of variance (ANOVA). Structural measurements, including kidney volume, cyst volume and cyst-to-kidney volume ratio, changed significantly with age. Drug treatment significantly decreased these metrics. Functional measurements of time-to-peak (TTP) mean and TTP variance were determined. TTP mean did not change with age, whereas TTP variance increased with age. Treatment with rapamycin generally did not affect these functional metrics. Synergistic effects of treatment and age were not found for any measurements. Together, the size and volume ratio of cysts decreased with drug treatment, whereas renal function remained the same. The quantification of renal structure and function with MRI can comprehensively assess the pathophysiology of PKD and response to treatment.

Complete heart block with diastolic heart failure and pulmonary edema secondary to enlarging previously diagnosed thrombosed aneurysm of sinus of valsalva in a patient with history of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is associated with vascular aneurysms that can affect any part of the vascular tree, like ascending aorta or coronary arteries. Sinus of Valsalva is known as an anatomical dilation at the root of aorta above the aortic valve and very few cases show aneurysm at that site in patients with ADPKD. Sinus of Valsalva aneurysm (SVA) can present with rupture and acute heart failure and infective endocarditis or could be asymptomatic accidentally discovered during cardiac catheterization. We report a case of a 76-year-old male with a unique constellation of cardiovascular anomalies associated with ADPKD. Patient was previously diagnosed with aneurysms affecting ascending aorta, sinus of Valsalva, and coronary arteries. Several years later, he came with complete heart block which was discovered later to be secondary to enlargement of his previously diagnosed thrombosed SVA. His case was complicated with acute heart failure and pulmonary edema. Conclusion. Patients with ADPKD can present with extrarenal manifestations. In our case, aneurysm at sinus of Valsalva was progressively enlarging and presented with complete heart block.

Hospital-based inpatient resource utilization associated with autosomal dominant polycystic kidney disease in the US

OBJECTIVE

Polycystic kidney disease (PKD) is a clinically and genetically heterogeneous class of genetic disorders characterized by development of renal cysts leading to renal failure and end stage renal disease (ESRD). Autosomal dominant polycystic kidney disease (ADPKD) accounts for the majority of PKD cases and is the predominant monogenic cause of ESRD. Limited information on patient characteristics and healthcare resource utilization is available in this population. This study assessed hospital-based inpatient utilization of patients with ADPKD in the US to help further understand the disease, which may lead to treatments that delay progression and reduce healthcare resource utilization.

METHODS

A cross-sectional analysis was conducted using MedAssets Health System Data to investigate inpatient resource utilization for a total of 1876 patients hospitalized with ADPKD or chronic kidney disease (CKD). Patient characteristics and inpatient resource utilization were compared between hospitalized patients with ADPKD and CKD, including demographic and clinical characteristics, overall health, rates of complications and surgical interventions, and average length of hospital and intensive care unit stay.

RESULTS

Compared with patients with CKD, patients with ADPKD were more likely to have commercial insurance as their primary payer (36.1 vs 17.8%) and were significantly younger (mean age 57.9 vs 69.5 years) and generally healthier (Charlson Comorbidity Score of 2.0 vs 3.3). Patients with ADPKD also had a substantially shorter average length of hospital stay (6.3 vs 10.3 days). However, patients with ADPKD experienced more kidney-related complications and a higher surgical procedure rate (mainly for transplant and complete nephrectomy).

CONCLUSIONS

Although patients with ADPKD were generally healthier than patients with CKD, specific kidney function complications were more frequent. Patients with ADPKD had a higher rate of major kidney procedures, which may contribute to the high burden of ADPKD-related hospital-based inpatient resource utilization.

A novel PKD2L1 C-terminal domain critical for trimerization and channel function

As a transient receptor potential (TRP) superfamily member, polycystic kidney disease 2-like-1 (PKD2L1) is also called TRPP3 and has similar membrane topology as voltage-gated cation channels. PKD2L1 is involved in hedgehog signaling, intestinal development, and sour tasting. PKD2L1 and PKD1L3 form heterotetramers with 3:1 stoichiometry. C-terminal coiled-coil-2 (CC2) domain (G699-W743) of PKD2L1 was reported to be important for its trimerization but independent studies showed that CC2 does not affect PKD2L1 channel function. It thus remains unclear how PKD2L1 proteins oligomerize into a functional channel. By SDS-PAGE, blue native PAGE and mutagenesis we here identified a novel C-terminal domain called C1 (K575-T622) involved in stronger homotrimerization than the non-overlapping CC2, and found that the PKD2L1 N-terminus is critical for dimerization. By electrophysiology and Xenopus oocyte expression, we found that C1, but not CC2, is critical for PKD2L1 channel function. Our co-immunoprecipitation and dynamic light scattering experiments further supported involvement of C1 in trimerization. Further, C1 acted as a blocking peptide that inhibits PKD2L1 trimerization as well as PKD2L1 and PKD2L1/PKD1L3 channel function. Thus, our study identified C1 as the first PKD2L1 domain essential for both PKD2L1 trimerization and channel function, and suggest that PKD2L1 and PKD2L1/PKD1L3 channels share the PKD2L1 trimerization process.

A novel PKD1 variant demonstrates a disease-modifying role in trans with a truncating PKD1 mutation in patients with autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common form of Polycystic Kidney Disease (PKD) and occurs at a frequency of 1/800 to 1/1000 affecting all ethnic groups worldwide. ADPKD shows significant intrafamilial phenotypic variability in the rate of disease progression and extra-renal manifestations, which suggests the involvement of heritable modifier genes. Here we show that the PKD1 gene can act as a disease causing and a disease modifier gene in ADPKD patients.

METHODS

Clinical evaluation of a family with ADPKD was performed to diagnose and assess disease progression in each individual. PKD1 was genotyped in each individual by targeted sequencing.

RESULTS

Targeted screening analysis showed that the patients with ADPKD in the family had the PKD1: p.Q2243X nonsense mutation. A more severe disease phenotype, in terms of estimated Glomerular Filtration Rate (eGFR) and total kidney volume, was observed in two patients where in addition to the mutation, they carried a novel PKD1 variant (p.H1769Y). Other patients from the same family carrying only the (p.Q2243X) mutation showed milder disease manifestations.

CONCLUSION

ADPKD shows significant intrafamilial phenotypic variability that is generally attributed to other modifier genes. In this rare case, we have shown that a variant at PKD1, in trans with the PKD1 mutation, can also act as a modifier gene in ADPKD patients. Understanding the molecular mechanism through which the gene exerts its disease modifying role may aid our understanding of the pathogenesis of ADPKD.

PKD1 mono-allelic knockout is sufficient to trigger renal cystogenesis in a mini-pig model

PKD1 and PKD2 mutations could lead to autosomal dominant polycystic kidney disease (ADPKD), which afflicts millions of people worldwide. Due to the marked differences in the lifespan, size, anatomy, and physiology from humans, rodent ADPKD models cannot fully mimic the disease. To obtain a large animal model that recapitulates the disease, we constructed a mini-pig model by mono-allelic knockout (KO) of PKD1 using zinc finger nuclease. The mono-allelic KO pigs had lower PKD1 expression than their wild-type littermates at both the transcriptional and translational levels. After approximately six months, renal cysts appeared and grew progressively in the KO pigs. Histological analysis showed that renal cysts were scatteredly distributed in the mutant pig kidneys and were lined by either cuboidal or flattened epithelial cells. Contrast-enhanced computed tomography confirmed that all of the mutant pigs had renal and hepatic cysts, when they were 11-month-old. Immunohistochemical analysis revealed that most of the cysts were derived from the proximal tubules and collecting ducts. Therefore, the PKD1 mono-allelic knockout is sufficient to trigger renal cystogenesis, and this pig model may provide a platform for future study of renal cyst formation.

Exon sequencing of PKD1 gene in an Iranian patient with autosomal-dominant polycystic kidney disease

Introduction: Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic kidney disorders with the incidence of 1 in 1,000 births. ADPKD is genetically heterogeneous with two genes identified: PKD1 (16p13.3, 46 exons) and PKD2 (4q21, 15 exons). Eighty five percent of the patients with ADPKD have at least one mutation in the PKD1 gene. Genetic studies have demonstrated an important allelic variability among patients, but very few data are known about the genetic variation among Iranian populations. Methods: In this study, exon direct sequencing of PKD1 was performed in a seven-year old boy with ADPKD and in his parents. The patient’s father was ADPKD who was affected without any kidney dysfunction, and the patient’s mother was congenitally missing one kidney. Results: Molecular genetic testing found a mutation in all three members of this family. It was a missense mutation GTG>ATG at position 3057 in exon 25 of PKD1. On the other hand, two novel missense mutations were reported just in the 7-year-old boy: ACA>GCA found in exon 15 at codon 2241 and CAC>AAC found in exon 38 at codon 3710. For checking the pathogenicity of these mutations, exons 15, 25, and 38 of 50 unrelated normal cases were sequenced. Conclusion: our findings suggested that GTG>ATG is a polymorphism with high frequency (60%) as well as ACA>GCA and CAC>AAC are polymorphisms with frequencies of 14% and 22%, respectively in the population of Southwest Iran.

The role of an out-patient renal clinic in renal disease management

The out-patient renal clinic (ORC) represents an important part of the nephrology service in general hospitals. The majority of renal diseases are chronic and patients need a systematic follow-up according to the severity and progression of kidney failure. The most important clinical manifestation is chronic renal failure (CRF) or chronic renal disease (CKD) The management of CKD, apart from medical and nursing services, also involves a number of community structures and financial resources. CRF treatment is costly and is a serious problem for the health systems in the western world. Effective treatment in the early stages aims to decrease the progression of kidney damage and, therefore, to prolong kidney function. Patients with renal failure can be managed as out-patients. The increased number of patients and the complexity of kidney diseases demand the collaboration of other out-patient clinics. The ORC may play an important role in this process. In this article. we present a literature review of the role of ORCs in the management of renal diseases around the world and we also present data based on our experience in our ORC.

Impaired epithelial Na+ channel activity contributes to cystogenesis and development of autosomal recessive polycystic kidney disease in PCK rats

BACKGROUND

Autosomal recessive polycystic kidney disease is a genetic disorder characterized by the development of renal cysts of tubular epithelial cell origin. Epithelial Na(+) channel (ENaC) is responsible for sodium reabsorption in the aldosterone-sensitive distal nephron. Here, we investigated the ENaC expression and activity in cystic tissue taken from rats with autosomal recessive polycystic kidney disease.

METHODS

Polycystic kidney (PCK) rats were treated with the selective ENaC inhibitor benzamil given in the drinking water, and after 4 or 12 wk, the severity of morphological malformations in the kidneys was assessed. ENaC and aquaporin-2 expression and ENaC activity were tested with immunohistochemistry and patch-clamp electrophysiology, respectively.

RESULTS

Treatment with benzamil exacerbated development of cysts compared with the vehicle-treated animals. In contrast, the 12 wk of treatment with the loop diuretic furosemide had no effect on cystogenesis. Single-channel patch-clamp analysis revealed that ENaC activity in the freshly isolated cystic epithelium was significantly lower than that in the noncystic collecting ducts isolated from PCK or normal Sprague-Dawley rats. Immunohistochemical analysis confirmed that β-ENaC and aquaporin-2 expressions in cysts are decreased compared with nondilated tubules from PCK rat kidneys.

CONCLUSION

We demonstrated that cystic epithelium exhibits low ENaC activity and this phenomenon can contribute to cyst progression.

A Case of New Familiar Genetic Variant of Autosomal Dominant Polycystic Kidney Disease-2: A Case Study

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by renal cyst formation due to mutations in genes coding for polycystin-1 [PKD1 (85-90% of cases), on ch 16p13.3] and polycystin-2 [PKD2 (10-15% of cases), on ch 4q13-23] and PKD3 gene (gene unmapped). It is also associated with TSC2/PKD1 contiguous gene syndrome. ADPKD is usually inherited, but new mutations without a family history occur in approximately 10% of the cases.

CASE PRESENTATION

A 17-year-old boy was followed up for bilateral cystic kidney disease, hypertension, and obesity since he was 13 years old. The diagnosis was an accidental finding during abdominal CT at age 13 to rule out appendicitis. A renal ultrasonogram also demonstrated a multiple bilateral cysts. Because of parental history of bilateral renal cysts, PKD1 and PKD2, genetic testing was ordered. Results showed, PKD2 variant 1:3 bp deletion of TGT; nucleotide position: 1602-1604; codon position: 512-513; mRNA reading frame maintained. The same mutation was later identified in his father.

CONCLUSION

A smaller number of patients have a defect in the PKD2 locus on chromosome 4 (resulting in PKD2 disease). There are no known published cases on this familiar genetic variant of ADPKD-2 cystic kidney disease. In this case, the disease is present unusually early in life.

Renal artery embolization-indications, technical approaches and outcomes

Owing to improvements in catheters and embolic agents, renal artery embolization (RAE) is increasingly used to treat nephrological and urological disease. RAE has become a useful adjunct to medical resuscitation in severe penetrating, iatrogenic or blunt renal traumatisms with active bleeding, and might avoid surgical intervention, particularly among patients that are haemodynamically stable. The role of RAE in pre-operative or palliative management of advanced malignant renal tumours remains debated; however, RAE is recommended as a first-line therapy for bleeding angiomyolipomas and can be used as a preventative treatment for angiomyolipomas at risk of bleeding. RAE represents an alternative to nephrectomy in various medical conditions, including severe uncontrolled hypertension among patients with end-stage renal disease, renal graft intolerance syndrome or autosomal dominant polycystic kidney disease. RAE is increasingly used to treat renal artery aneurysms or symptomatic renal arteriovenous malformations, with a low complication rate as compared with surgical alternatives. This Review highlights the potential use of RAE as an adjunct in the management of renal disease. We first compare and contrast the technical approaches of RAE associated with the various available embolization agents and then discuss the complications associated with RAE and alternative procedures.

Antisense-mediated angiotensinogen inhibition slows polycystic kidney disease in mice with a targeted mutation in Pkd2

Renal cyst enlargement is associated with the activation of both the circulating and intrarenal renin-angiotensin systems. Angiotensinogen (AGT) is the substrate for renin. The aim of the present study was to determine the effect of AGT inhibition on renal cyst enlargement. An AGT antisense oligonucleotide (ASO) that selectively inhibits AGT mRNA was injected once weekly in PKD2WS25 mice [an orthologous model of human autosmal dominant polycystic kidney disease (PKD) involving mutation of the Pkd2 gene] from 4 to 16 wk of age. The AGT ASO resulted in a 40% decrease in AGT RNA in the kidney, a 60% decrease in AGT RNA in the liver, and a significant decrease in AGT protein in the kidney and serum. The AGT ASO resulted in a significant decrease in kidney size, cyst volume density, and blood urea nitrogen. The AGT ASO resulted in a significant decrease in transforming growth factor-β and interstitial fibrosis in the kidney. Mice treated with the AGT ASO had a significant decrease in proinflammatory cytokines [chemokine (C-X-C motif) ligand (CXCL)1 and IL-12] in the kidney. Cluster of differentiation (CD)36 is a scavenger receptor found on tubular cells that can activate the renin-angiotensin system. Administration of a CD36 ASO had no effect on PKD and kidney function, suggesting that the effect of the AGT ASO is independent of CD36. In summary, AGT inhibition resulted in significant decreases in kidney size and cyst volume and an improvement in kidney function in PKD mice. The AGT ASO resulted in a decrease in transforming growth factor-β, interstitial fibrosis, and the proinflammatory cytokines CXCL1 and IL-12 in the kidney.

Polycystin-1 and Gα12 regulate the cleavage of E-cadherin in kidney epithelial cells

Interaction of polycystin-1 (PC1) and Gα12 is important for development of kidney cysts in autosomal dominant polycystic kidney disease (ADPKD). The integrity of cell polarity and cell-cell adhesions (mainly E-cadherin-mediated adherens junction) is altered in the renal epithelial cells of ADPKD. However, the key signaling pathway for this alteration is not fully understood. Madin-Darby canine kidney (MDCK) cells maintain the normal integrity of epithelial cell polarity and adherens junctions. Here, we found that deletion of Pkd1 increased activation of Gα12, which then promoted the cystogenesis of MDCK cells. The morphology of these cells was altered after the activation of Gα12. By using liquid chromatography-mass spectrometry, we found several proteins that could be related this change in the extracellular milieu. E-cadherin was one of the most abundant peptides after active Gα12 was induced. Gα12 activation or Pkd1 deletion increased the shedding of E-cadherin, which was mediated via increased ADAM10 activity. The increased shedding of E-cadherin was blocked by knockdown of ADAM10 or specific ADAM10 inhibitor GI254023X. Pkd1 deletion or Gα12 activation also changed the distribution of E-cadherin in kidney epithelial cells and caused β-catenin to shift from cell membrane to nucleus. Finally, ADAM10 inhibitor, GI254023X, blocked the cystogenesis induced by PC1 knockdown or Gα12 activation in renal epithelial cells. Our results demonstrate that the E-cadherin/β-catenin signaling pathway is regulated by PC1 and Gα12 via ADAM10. Specific inhibition of this pathway, especially ADAM10 activity, could be a novel therapeutic regimen for ADPKD.

Primary cilium regulates CaV1.2 expression through Wnt signaling

Primary cilia are sensory organelles that provide a feedback mechanism to restrict Wnt signaling in the absence of endogenous Wnt activators. Abnormal Wnt signaling has been shown to result in polycystic kidney disease (PKD) although the exact mechanism has been debated. Previously, we reported that the calcium channel CaV1.2 functions in primary cilia. In this study, we show that CaV1.2 expression level is regulated by Wnt signaling. This occurs through modulation of mitochondrial mass and activity resulting in increased reactive oxygen species which generate oxidative DNA lesions. We found that the subsequent cellular DNA damage response triggers increased CaV1.2 expression. In the absence of primary cilia where Wnt signaling is upregulated, we found that CaV1.2 is overexpressed as a compensatory mechanism. We show for the first time that CaV1.2 knockdown in zebrafish results in classic primary cilia defects including renal cyst formation, hydrocephalus, and left-right asymmetry defects. Our study shows that suppressed Wnt signaling prevents CaV1.2 expression ultimately resulting in PKD phenotypes. Thus, CaV1.2 expression is tightly regulated through Wnt signaling and plays an essential sensory role in primary cilia necessary for cellular homeostasis.

Identification of people with autosomal dominant polycystic kidney disease using routine data: a cross sectional study

Background

Autosomal dominant polycystic kidney disease (ADPKD) causes progressive renal damage and is a leading cause of end-stage renal failure. With emerging therapies it is important to devise a method for early detection. We aimed to identify factors from routine clinical data which can be used to distinguish people with a high likelihood of having ADPKD in a primary health care setting.

Method

A cross-sectional study was undertaken using data from the Quality Intervention in Chronic Kidney Disease trial extracted from 127 primary care practices in England. The health records of 255 people with ADPKD were compared to the general population. Logistic regression was used to identify clinical features which distinguish ADPKD. These clinical features were used to stratify individual risk using a risk score tool.

Results

Renal impairment, proteinuria, haematuria, a diastolic blood pressure over 90 mmHg and multiple antihypertensive medications were more common in ADPKD than the general population and were used to build a regression model (area under the receiver operating characteristic curve; 0.79). Age, gender, haemoglobin and urinary tract infections were not associated with ADPKD. A risk score (range −3 to +10) of ≥0 gave a sensitivity of 70.2% and specificity 74.9% of for detection.

Conclusions

Stratification of ADPKD likelihood from routine data may be possible. This approach could be a valuable component of future screening programs although further longitudinal analyses are needed.

INPP5E interacts with AURKA, linking phosphoinositide signaling to primary cilium stability

Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) cause the ciliopathies known as Joubert and MORM syndromes; however, the role of INPP5E in ciliary biology is not well understood. Here, we describe an interaction between INPP5E and AURKA, a centrosomal kinase that regulates mitosis and ciliary disassembly, and we show that this interaction is important for the stability of primary cilia. Furthermore, AURKA phosphorylates INPP5E and thereby increases its 5-phosphatase activity, which in turn promotes transcriptional downregulation of AURKA, partly through an AKT-dependent mechanism. These findings establish the first direct link between AURKA and phosphoinositide signaling and suggest that the function of INPP5E in cilia is at least partly mediated by its interactions with AURKA.

An mTOR kinase inhibitor slows disease progression in a rat model of polycystic kidney disease

BACKGROUND

The mTOR pathway, which consists of mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), is activated in polycystic kidney disease (PKD) kidneys. Sirolimus and everolimus indirectly bind and inhibit mTORC1. A novel group of drugs, the mTOR kinase inhibitors, directly bind to mTOR kinase, thus inhibiting both mTORC1 and 2. The aim of the study was to determine the therapeutic effect of an mTOR kinase inhibitor, PP242, in the Han:SPRD rat (Cy/+) model of PKD.

METHODS

Male rats were treated with PP242 5 mg/kg/day IP or vehicle for 5 weeks.

RESULTS

PP242 significantly reduced the kidney enlargement, the cyst density and the blood urea nitrogen in Cy/+ rats. On immunoblot of kidneys, PP242 resulted in a decrease in pS6, a marker of mTORC1 signaling and pAkt(Ser473), a marker of mTORC2 signaling. mTORC plays an important role in regulating cytokine production. There was an increase in IL-1, IL-6, CXCL1 and TNF-α in Cy/+ rat kidneys that was unaffected by PP242. Apoptosis or proliferation is known to play a causal role in cyst growth. PP242 had no effect on caspase-3 activity, TUNEL positive or active caspase-3-positive tubular cells in Cy/+ kidneys. PP242 reduced the number of proliferating cells per cyst and per non-cystic tubule in Cy/+ rats.

CONCLUSIONS

In a rat model of autosomal dominant polycystic kidney disease, PP242 treatment (i) decreases proliferation in cystic and non-cystic tubules; (ii) inhibits renal enlargement and cystogenesis and (iii) significantly reduces the loss of kidney function.

Polycystic kidneys and GM2 gangliosidosis-like disease in neonatal springboks (Antidorcas marsupialis)

Clinical, gross, histopathologic, electron microscopic findings and enzymatic analysis of 4 captive, juvenile springboks (Antidorcas marsupialis) showing both polycystic kidneys and a storage disease are described. Springbok offspring (4 of 34; 12%) were affected by either one or both disorders in a German zoo within a period of 5 years (2008-2013). Macroscopic findings included bilaterally severely enlarged kidneys displaying numerous cysts in 4 animals and superior brachygnathism in 2 animals. Histopathologically, kidneys of 4 animals displayed cystic dilation of the renal tubules. In addition, abundant cytoplasmic vacuoles with a diameter ranging from 2 to 10 μm in neurons of the central and peripheral nervous system, hepatocytes, thyroid follicular epithelial cells, pancreatic islets of Langerhans and renal tubular cells were found in 2 springbok neonates indicative of an additional storage disease. Ultrastructurally, round electron-lucent vacuoles, up to 4 μm in diameter, were present in neurons. Enzymatic analysis of liver and kidney tissue of 1 affected springbok revealed a reduced activity of total hexosaminidase (Hex) with relatively increased HexA activity at the same level of total Hex, suggesting a hexosaminidase defect. Pedigree analysis suggested a monogenic autosomal recessive inheritance for both diseases. In summary, related springboks showed 2 different changes resembling both polycystic kidney and a GM2 gangliosidosis similar to the human Sandhoff disease. Whether the simultaneous occurrence of these 2 entities represents an incidental finding or has a genetic link needs to be investigated in future studies.

Renal transplant in patients with polycystic disease: the Italian experience

We analyzed the results of kidney transplantation in autosomal dominent polycystic kidney disease (ADPKD) patients in Italy, including 14,305 transplantations performed from January 2002 to December 2010, including: 12,859 first single or double kidneys from cadaveric donors (13% polycystic), 172 combined liver-kidney cases (22% polycystic), and 1,303 living-donor organs (7% polycystic). Among the first transplantations (12,008 single, 851 double), with follow-ups ranging from 16 to 120 months, polycystic patients demonstrated better graft survival compared with other kidney diseases (86% vs 82% at 5 years; P < .01); mortality was not different (92% vs 79% at 1 year). A better trend was obtained also among combined liver-kidney transplantations in ADPKD. Regarding pretransplantation management of polycystic patients, we noticed a conservative attitude in 32/35 transplant centers. The main indication for nephrectomy was for the lack of abdominal space. Regarding instrumental studies, 86% of centers asked for second-level investigations computerized tomography for kidney dimensions. Radiologic investigations for vasculocerebral malformations were required in 97% of the centers: 74% as a routine and 23% in the presence of familial history of cerebral hemorrhage. Polycystic patients are good candidates for kidney transplantation with correct management before transplantation.

Expression of Nek1 during kidney development and cyst formation in multiple nephron segments in the Nek1-deficient kat2J mouse model of polycystic kidney disease

BACKGROUND

Neks, mammalian orthologs of the fungal protein kinase never-in-mitosis A, have been implicated in the pathogenesis of polycystic kidney disease. Among them, Nek1 is the primary protein inactivated in kat2J mouse models of PKD.

RESULT

We report the expression pattern of Nek1 and characterize the renal cysts that develop in kat2J mice. Nek1 is detectable in all murine tissues but its expression in wild type and kat2J heterozygous kidneys decrease as the kidneys mature, especially in tubular epithelial cells. In the embryonic kidney, Nek1 expression is most prominent in cells that will become podocytes and proximal tubules. Kidney development in kat2J homozygous mice is aberrant early, before the appearance of gross cysts: developing cortical zones are thin, populated by immature glomeruli, and characterized by excessive apoptosis of several cell types. Cysts in kat2J homozygous mice form postnatally in Bowman's space as well as different tubular subtypes. Late in life, kat2J heterozygous mice form renal cysts and the cells lining these cysts lack staining for Nek1. The primary cilia of cells lining cysts in kat2J homozygous mice are morphologically diverse: in some cells they are unusually long and in others there are multiple cilia of varying lengths.

CONCLUSION

Our studies indicate that Nek1 deficiency leads to disordered kidney maturation, and cysts throughout the nephron.

Characterization of the SAM domain of the PKD-related protein ANKS6 and its interaction with ANKS3

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disorder leading to end-stage renal failure in humans. In the PKD/Mhm(cy/+) rat model of ADPKD, the point mutation R823W in the sterile alpha motif (SAM) domain of the protein ANKS6 is responsible for disease. SAM domains are known protein-protein interaction domains, capable of binding each other to form polymers and heterodimers. Despite its physiological importance, little is known about the function of ANKS6 and how the R823W point mutation leads to PKD. Recent work has revealed that ANKS6 interacts with a related protein called ANKS3. Both ANKS6 and ANKS3 have a similar domain structure, with ankyrin repeats at the N-terminus and a SAM domain at the C-terminus.

RESULTS

The SAM domain of ANKS3 is identified as a direct binding partner of the ANKS6 SAM domain. We find that ANKS3-SAM polymerizes and ANKS6-SAM can bind to one end of the polymer. We present crystal structures of both the ANKS3-SAM polymer and the ANKS3-SAM/ANKS6-SAM complex, revealing the molecular details of their association. We also learn how the R823W mutation disrupts ANKS6 function by dramatically destabilizing the SAM domain such that the interaction with ANKS3-SAM is lost.

CONCLUSIONS

ANKS3 is a direct interacting partner of ANKS6. By structurally and biochemically characterizing the interaction between the ANKS3 and ANKS6 SAM domains, our work provides a basis for future investigation of how the interaction between these proteins mediates kidney function.

Novel roles of Pkd2 in male reproductive system development

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited genetic diseases, caused by mutations in PKD1 and/ or PKD2. Infertility and reproductive tract abnormalities in male ADPKD patients are very common and have higher incidence than in the general population. In this work, we reveal novel roles of Pkd2 for male reproductive system development. Disruption of Pkd2 caused dilation of mesonephric tubules/efferent ducts, failure of epididymal coiling, and defective testicular development. Deletion of Pkd2 in the epithelia alone was sufficient to cause reproductive tract defects seen in Pkd2(-/-) mice, suggesting that epithelial Pkd2 plays a pivotal role for development and maintenance of the male reproductive tract. In the testis, Pkd2 also plays a role in interstitial tissue and testicular cord development. In-depth analysis of epithelial-specific knockout mice revealed that Pkd2 is critical to maintain cellular phenotype and developmental signaling in the male reproductive system. Taken together, our data for the first time reveal novel roles for Pkd2 in male reproductive system development and provide new insights in male reproductive system abnormality and infertility in ADPKD patients.

Genetic mechanisms and signaling pathways in autosomal dominant polycystic kidney disease

Recent advances in defining the genetic mechanisms of disease causation and modification in autosomal dominant polycystic kidney disease (ADPKD) have helped to explain some extreme disease manifestations and other phenotypic variability. Studies of the ADPKD proteins, polycystin-1 and -2, and the development and characterization of animal models that better mimic the human disease, have also helped us to understand pathogenesis and facilitated treatment evaluation. In addition, an improved understanding of aberrant downstream pathways in ADPKD, such as proliferation/secretion-related signaling, energy metabolism, and activated macrophages, in which cAMP and calcium changes may play a role, is leading to the identification of therapeutic targets. Finally, results from recent and ongoing preclinical and clinical trials are greatly improving the prospects for available, effective ADPKD treatments.

An mTOR anti-sense oligonucleotide decreases polycystic kidney disease in mice with a targeted mutation in Pkd2

Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening hereditary disease in the USA. In human ADPKD studies, sirolimus, a mammalian target of rapamycin complex 1 (mTORC1) inhibitor, had little therapeutic effect. While sirolimus robustly inhibits mTORC1, it has a minimal effect on mTOR complex 2 (mTORC2). Polycystic kidneys of Pkd2WS25/- mice, an orthologous model of human ADPKD caused by a mutation in the Pkd2 gene, had an early increase in pS6 (marker of mTORC1) and pAktSer(473) (marker of mTORC2). To investigate the effect of combined mTORC1 and 2 inhibition, Pkd2WS25/- mice were treated with an mTOR anti-sense oligonucleotide (ASO) that blocks mTOR expression thus inhibiting both mTORC1 and 2. The mTOR ASO resulted in a significant decrease in mTOR protein, pS6 and pAktSer(473). Pkd2WS25/- mice treated with the ASO had a normalization of kidney weights and kidney function and a marked decrease in cyst volume. The mTOR ASO resulted in a significant decrease in proliferation and apoptosis of tubular epithelial cells. To demonstrate the role of mTORC2 on cyst growth, Rictor, the functional component of mTORC2, was silenced in Madin-Darby canine kidney cell cysts grown in 3D cultures. Silencing Rictor significantly decreased cyst volume and expression of pAktSer(473). The decreased cyst size in the Rictor silenced cells was reversed by introduction of a constitutively active Akt1. In vitro, combined mTORC1 and 2 inhibition reduced cyst growth more than inhibition of mTORC1 or 2 alone. In conclusion, combined mTORC1 and 2 inhibition has therapeutic potential in ADPKD.