Polycystic Kidney Disease Gene Research Articles

Family‐based analysis identified CD 2 as a susceptibility gene for primary open angle glaucoma in Chinese Han population

Primary open angle glaucoma (POAG) is characterized by optic disc cupping and irreversible loss of retinal ganglion cells. Few genes have been detected that influence POAG susceptibility and little is known about its genetic architecture. In this study, we employed exome sequencing on three members from a high frequency POAG family to identify the risk factors of POAG in Chinese population. Text-mining method was applied to identify genes associated with glaucoma in literature, and protein–protein interaction networks were constructed. Furthermore, reverse transcription PCR and Western blot were performed to confirm the differential gene expression. Six genes, baculoviral inhibitors of apoptosis protein repeat containing 6 (BIRC6), CD2, luteinizing hormone/choriogonadotropin receptor (LHCGR), polycystic kidney and hepatic disease gene 1 (PKHD1), phenylalanine hydroxylase (PAH) and fucosyltransferase 7 (FUT7), which might be associated with POAG, were identified. Both the mRNA expression levels and protein expression levels of HSP27 were increased in astrocytes from POAG patients compared with those from normal control, suggesting that mutation in CD2 might pose a risk for POAG in Chinese population. In conclusion, novel rare variants detected by exome sequencing may hold the key to unravelling the remaining contribution of genetics to complex diseases such as POAG.

Fetal and Postnatal Magnetic Resonance Imaging of Unilateral Cystic Renal Dysplasia in a Neonate with Tuberous Sclerosis

Tuberous sclerosis (TS) is an autosomal dominant condition associated with mutations in the TSC1 and/or TSC2 genes. Clinical manifestations are multisystemic, and they often include lesions in the brain, skin, heart, kidneys, and bones. TSC2 gene mutations can be seen concomitantly with autosomal dominant polycystic kidney disease gene mutations. We present a case of a fetus with prenatal diagnosis of TS that had unique asymmetrical distribution of renal cystic disease. We describe the extensive work up with both fetal and neonatal magnetic resonance imaging with correlating images of the unilateral polycystic renal disease in addition to typical TS brain findings.

Genome-wide methylation profiling of ADPKD identified epigenetically regulated genes associated with renal cyst development

Autosomal dominant polycystic kidney disease (ADPKD) is a common human genetic disease characterized by the formation of multiple fluid-filled cysts in bilateral kidneys. Although mutations in polycystic kidney disease 1 (PKD1) are predominantly responsible for ADPKD, the focal and sporadic property of individual cystogenesis suggests another molecular mechanism such as epigenetic alterations. To determine the epigenomic alterations in ADPKD and their functional relevance, ADPKD and non-ADPKD individuals were analyzed by unbiased methylation profiling genome-wide and compared with their expression data. Intriguingly, PKD1 and other genes related to ion transport and cell adhesion were hypermethylated in gene-body regions, and their expressions were downregulated in ADPKD, implicating epigenetic silencing as the key mechanism underlying cystogenesis. Especially, in patients with ADPKD, PKD1 was hypermethylated in gene-body region and it was associated with recruitment of methyl-CpG-binding domain 2 proteins. Moreover, treatment with DNA methylation inhibitors retarded cyst formation of Madin-Darby Canine Kidney cells, accompanied with the upregulation of Pkd1 expression. These results are consistent with previous studies that knock-down of PKD1 was sufficient for cystogenesis. Therefore, our results reveal a critical role for hypermethylation of PKD1 and cystogenesis-related regulatory genes in cyst development, suggesting epigenetic therapy as a potential treatment for ADPKD.

MiR-17∼92 miRNA cluster promotes kidney cyst growth in polycystic kidney disease

Polycystic kidney disease (PKD), the most common genetic cause of chronic kidney failure, is characterized by the presence of numerous, progressively enlarging fluid-filled cysts in the renal parenchyma. The cysts arise from renal tubules and are lined by abnormally functioning and hyperproliferative epithelial cells. Despite recent progress, no Food and Drug Administration-approved therapy is available to retard cyst growth. MicroRNAs (miRNAs) are short noncoding RNAs that inhibit posttranscriptional gene expression. Dysregulated miRNA expression is observed in PKD, but whether miRNAs are directly involved in kidney cyst formation and growth is not known. Here, we show that miR-17∼92, an oncogenic miRNA cluster, is up-regulated in mouse models of PKD. Kidney-specific transgenic overexpression of miR-17∼92 produces kidney cysts in mice. Conversely, kidney-specific inactivation of miR-17∼92 in a mouse model of PKD retards kidney cyst growth, improves renal function, and prolongs survival. miR-17∼92 may mediate these effects by promoting proliferation and through posttranscriptional repression of PKD genes Pkd1, Pkd2, and hepatocyte nuclear factor-1β. These studies demonstrate a pathogenic role of miRNAs in mouse models of PKD and identify miR-17∼92 as a therapeutic target in PKD. Our results also provide a unique hypothesis for disease progression in PKD involving miRNAs and regulation of PKD gene dosage.

Mutations in NEK8 link multiple organ dysplasia with altered Hippo signalling and increased c-MYC expression

Mutations affecting the integrity and function of cilia have been identified in various genes over the last decade accounting for a group of diseases called ciliopathies. Ciliopathies display a broad spectrum of phenotypes ranging from mild manifestations to lethal combinations of multiple severe symptoms and most of them share cystic kidneys as a common feature. Our starting point was a consanguineous pedigree with three affected fetuses showing an early embryonic phenotype with enlarged cystic kidneys, liver and pancreas and developmental heart disease. By genome-wide linkage analysis, we mapped the disease locus to chromosome 17q11 and identified a homozygous nonsense mutation in NEK8/NPHP9 that encodes a kinase involved in ciliary dynamics and cell cycle progression. Missense mutations in NEK8/NPHP9 have been identified in juvenile cystic kidney jck mice and in patients suffering from nephronophthisis (NPH), an autosomal-recessive cystic kidney disease. This work confirmed a complete loss of NEK8 expression in the affected fetuses due to nonsense-mediated decay. In cultured fibroblasts derived from these fetuses, the expression of prominent polycystic kidney disease genes (PKD1 and PKD2) was decreased, whereas the oncogene c-MYC was upregulated, providing potential explanations for the observed renal phenotype. We furthermore linked NEK8 with NPHP3, another NPH protein known to cause a very similar phenotype in case of null mutations. Both proteins interact and activate the Hippo effector TAZ. Taken together, our study demonstrates that NEK8 is essential for organ development and that the complete loss of NEK8 perturbs multiple signalling pathways resulting in a severe early embryonic phenotype.

Síndrome de deleción de genes contiguos TSC2/PKD1

The TSC2 gene responsible for Tuberous Sclerosis, is located in chromosome 16p 13.3, adjacent to the gene for autosomal dominant polycystic kidney disease. A large deletion can involve both genes, causing the so-called TSC2/PKD1 contiguous gene syndrome (MIM#600273). It is characterized by congenital renal cysts, or their early onset in patients with tuberous sclerosis, and implies a worst prognosis in renal disease. We report the case of a five year-old boy with tuberous sclerosis, who presented with multiple large bilateral renal cysts in the neonatal period. A genetic confirmation study was later performed using the multiple ligation probe amplification (MLPA) technique.

Conditional loss of kidney microRNAs results in congenital anomalies of the kidney and urinary tract (CAKUT)

MicroRNAs have emerged as essential regulators of gene expression and may play important roles in a variety of human disorders. To understand the role of microRNA-mediated gene regulation in the kidney, we deleted the microRNA-processing enzyme Dicer in developing renal tubules and parts of the ureteric bud in mice. Genetic deletion of Dicer resulted in renal failure and death of the animals at 4-6 weeks of age. Interestingly, the kidneys of microRNA-deficient animals were small due to a reduced number of nephrons and showed massive hydronephrosis due to ureteropelvic junction obstruction. This phenotype is reminiscent of congenital anomalies of the kidney and urinary tract (CAKUT), an important group of human disorders characterized by a combination of renal hypoplasia with congenital abnormalities of the urinary tract. We used metanephric kidney cultures to examine the developmental defects underlying these pathologies. Dicer knockout kidneys showed a significant reduction of tubular branching explaining renal hypoplasia. Moreover, the ureters of these kidneys showed an altered morphology and impaired motility. These functional changes went along with altered expression of smooth muscle actin implying a defect in the differentiation of ureteric smooth muscle cells. In addition, we show the polycystic kidney disease gene Pkd1 to be a target of miR-20 implying that this interaction may contribute to the molecular basis for the cystogenesis in our model. In conclusion, these data demonstrate an essential role for microRNA-dependent gene regulation in mammalian kidney development and suggest that deregulation of microRNAs may underlie CAKUT, the most important group of renal disorders in humans.

MicroRNAs Regulate Renal Tubule Maturation through Modulation of Pkd1

MicroRNAs (miRNAs) contribute to the regulation of early kidney development, but their role during later stages of renal tubule maturation is not well understood. Here, we found that ablation of the miRNA-processing enzyme Dicer from maturing renal tubules produces tubular and glomerular cysts in mice. Inactivation of Dicer is associated with downregulation of miR-200, a kidney-enriched miRNA family, and upregulation of the polycystic kidney disease gene Pkd1. Inhibition of miR-200 in cultured renal epithelial cells disrupted tubulogenesis and led to upregulation of Pkd1. Using bioinformatic and in vitro approaches, we found that miR-200b/c/429 induce post-transcriptional repression of Pkd1 through two conserved binding sites in the 3'-Untranslated regions of Pkd1. Overexpression of PKD1 in renal epithelial cells was sufficient to disrupt tubulogenesis and produce cyst-like structures. In conclusion, miRNAs are essential for the maturation of renal tubules, and Pkd1 is a target of miR-200. These results also suggest that miRNAs may modulate PKD1 gene dosage and play a role in the initiation of cystogenesis.

Polycystic kidney disease gene in the Lewis polycystic kidney rat is mapped to chromosome 10q21–q26

Correspondence: Jada Pasquale Yengkopiong Dr John Garang Memorial University of Science and Technology, Faculty of Science and Technology, Bor, Jonglei State, Republic of South Sudan Tel +211 955 621 320 Email jadalojuka@yahoo.com.au Background: Polycystic kidney disease (PKD) is a life-threatening disorder that affects the kidneys of millions of people across the world. The disease is normally inherited, but it can also be acquired, and leads to development of many cysts in the renal nephrons. In this study, the aim was to characterize PKD in the Lewis polycystic kidney (LPK) rat, the newest model for human PKD. Methods: Mating experiments were performed between male LPK rats with PKD and female Brown Norway and Wistar Kyoto rats without PKD to raise second filial (F2) and backcross 1 (BC1) progeny, respectively. Rats that developed PKD were identified. Histological examination of the kidneys and liver was performed. Liver tissue samples were collected from each rat and used to extract DNA. The extracted DNA was amplified, and mapping and linkage analyses were performed to identify the quantitative trait locus that controlled the disease phenotypes. Results: It was established that the disease was controlled by a recessive mutation in a single gene (F2: PKD = 42, non-PKD = 110, χ = 0.53; BC1: PKD = 67, non-PKD = 72, χ = 0.18, P . 0.05) and that the disease was inherited as autosomal recessive polycystic kidney disease (ARPKD). The rats with PKD developed larger fluid-filled cystic kidneys, higher systolic blood pressure, and anemia. However, there were no extrarenal cysts and no pup deaths. Mapping studies and linkage analyses associated the disease phenotypes in both the F2 and BC1 rats to chromosome 10q21–q26, giving a maximum LOD score of 7.9 (P = 0.00001) between peak markers D10Rat180 and D10Rat26. Conclusion: The quantitative trait locus on chromosome 10q21–q26 does not contain the Pkhd-1 gene, and it is different from quantitative trait loci that control ARPKD in other murine models. The candidate genes located in the quantitative trait locus are important in signal transduction, cell growth, cell proliferation, and cell differentiation. Although expression of PKD in the LPK rat shares common phenotypic traits with ARPKD caused by mutation in Pkhd-1, the gene responsible for ARPKD in the LPK rat is different and unknown, or a mechanism yet to be identified is responsible for development of the disease.

Cilia - the prodigal organelle

Cilia - the prodigal organelle

Amplification of real-time high resolution melting analysis PCR method for polycystic kidney disease (PKD) gene mutations in autosomal dominant polycystic kidney disease patients

PKD1 and PKD2 are the two genes responsible for the development of autosomal dominant polycystic kidney disease (ADPKD). PKD1 gene mutations accounts for ≈85% of all ADPKD cases, while the remaining ≈15% of cases is caused by mutations in the PKD2 gene. Genotyping for PKD1 and PKD2 mutations was usually identified using conventional polymerase chain reaction (PCR) or PCR-single stranded conformation polymorphisms (SSCP) methods. In this study, we assessed the usefulness of eight common primers amplifying the respective genes in real-time high resolution melting analysis PCR (real-time HRMA PCR) in terms of time, cost and sensitivity with respect to PCR-SSCP method. We found that case sample can easily be differentiated from control sample by melting curve profile difference, although a primer was found to be less useful. We concluded that real-time HRMA PCR is a rapid and sensitive method to categorize samples based on the melting curve profiles with comparable sensitivity to conventional PCR-SSCP.

PKHD1 post‐transcriptionally modulated by miR‐365‐1 inhibits cell‐cell adhesion

Autosomal recessive polycystic kidney disease (ARPKD) is a severe inherited disorder with an incidence of 1/20 000 live births. Mutations of PKHD1 (polycystic kidney and hepatic disease gene 1) gene were identified to be responsible for ARPKD. However, the underlying molecular mechanisms remain largely unknown. MicroRNAs (miRNAs) are an abundant class of small RNAs with global effect on gene expression. Up to 30% of human protein coding genes may be regulated by miRNAs. However, to date, nothing is known regarding the role of miRNAs in PKHD1. In this study, we exploited bioinformatics to analyse the 3'UTR of PKHD1 gene and illustrated that the 3'UTR region of the gene is highly conserved in evolution. We identified about 35 candidate miRNAs within a 3738 bp window of the 3'UTR region. Of the 35 potential miRNAs, miR-365-1 emerged to post-transcriptionally modulate the expression of PKHD1. Furthermore, we demonstrated that miR-365-1 modulated PKHD1 suppressed cell-cell adhesion in part through E-cadherin.

It’s not all in the cilium, but on the road to it: Genetic interaction network in polycystic kidney and liver diseases and how trafficking and quality control matter

Autosomal dominant polycystic liver disease results from mutations in PRKCSH or SEC63. The respective gene products, glucosidase IIb and SEC63p, function in protein translocation and quality control pathways in the endoplasmic reticulum. Here we show that glucosidase IIb and Sec63p are required in mice for adequate expression of a functional complex of the polycystic kidney disease gene products, polycystin-1 and polycystin-2. We find that polycystin-1 is the rate-limiting component of this complex and that there is a dose–response relationship between cystic dilation and levels of functional polycystin-1 following mutation of Prkcsh or Sec63.Reduced expression of polycystin-1 also serves to sensitize the kidney to cyst formation resulting from mutations in Pkhd1, the recessive polycystic kidney disease gene. Finally, we show that proteasome inhibition increases steady-state levels of polycystin-1 in cells lacking glucosidase IIb and that treatment with a proteasome inhibit or reduces cystic disease in orthologous gene models of human autosomal dominant polycystic liver.

A genetic interaction network of five genes for human polycystic kidney and liver diseases defines polycystin-1 as the central determinant of cyst formation

Autosomal dominant polycystic liver disease results from mutations in PRKCSH or SEC63. The respective gene products, glucosidase IIβ and SEC63p, function in protein translocation and quality control pathways in the endoplasmic reticulum. Here we show that glucosidase IIβ and Sec63p are required in mice for adequate expression of a functional complex of the polycystic kidney disease gene products, polycystin-1 and polycystin-2. We find that polycystin-1 is the rate-limiting component of this complex and that there is a dose-response relationship between cystic dilation and levels of functional polycystin-1 following mutation of Prkcsh or Sec63. Reduced expression of polycystin-1 also serves to sensitize the kidney to cyst formation resulting from mutations in Pkhd1, the recessive polycystic kidney disease gene. Finally, we show that proteasome inhibition increases steady-state levels of polycystin-1 in cells lacking glucosidase IIβ and that treatment with a proteasome inhibitor reduces cystic disease in orthologous gene models of human autosomal dominant polycystic liver disease.

Abstract SY14-02: From disease genetics to diagnostics to functional biology: High-throughput proteomics and protein interaction network building guides discovery of novel disease genes in ciliopathies, cystic disease, and cancer

Abstract With the advent of deep sequencing, genome-wide association studies, and rapid advances in human genetics, extensive genomic data linking human gene variants to specific diseases, including cancer, neurological disease, and metabolic syndromes, is rapidly accumulating. These disease associations, especially mutations, provide a definitive link between protein function and disease state, and can provide critical diagnostics for the disease. However, in many cases, the disease links are unclear and fail to 1) connect individual mutations to specific biological pathways, 2) provide functional hypotheses for understanding disease mechanism, or 3) identify targets for therapeutic intervention. Bioinformatic analyses can provide key clues to specific experimental tests, but a more extensible methodology is required to build from genomic hits to functional links. We have developed and implemented automated, a recombination-driven “tandem-affinity” proteomic probes, called the g-LAP (Gateway-Location and Affinity Purification) system. This approach is amenable to high-throughput and allows us to purify proteins associated with disease-related “bait” proteins and thus identify protein complexes and networks with high confidence. We have also established similarly high-throughput tools for studying protein localization, protein-protein interaction both in vivo and in vitro, and for testing interactions among biochemical complexes and activities. To date, we have tagged over 100 new human genetic disease genes, which have lent insight into a number of important pathways, notably in ciliary diseases or ciliopathies, neurological disease, and for novel tumor suppressors. Within the ciliopathies, the identification of assembly and regulatory complexes has provided new insight into the cell biology and signaling pathways associated with primary cilia. In the case of Bardet-Biedl syndrome, patients present with retinal degeneration, olfactory and hearing loss, polydactyly, neurological problems, and obesity linked to hyperphagia. Purifying proteins associated with LAP-tagged BBS proteins, we discovered seven of fourteen known BBS disease genes were present in the highly conserved BBSome complex, important to activate Rab8 vesicles for ciliary membrane formation1. In the tubby/Tubby-like (TULP) family of proteins, we recently purified the Hedgehog regulatory TULP3 protein and found the protein forms a complex together with the complete, six-component intraflagellar transport A (IFT-A) complex, which function together at the base of the cilia to regulate entry of G-protein coupled receptors into cilia2. A link between cilia and cancer was demonstrated by the link between cilia, Hedgehog signaling, and specific receptor tyrosine kinases, including the PDGF receptor α. Among cancers and proliferative diseases, specific ciliary pathways function in the kidney to limit polycystic kidney disease and renal cell carcinoma. Notably, the Von Hippel-Lindau (VHL) tumor suppressor protein and autosomal dominant polycystic kidney disease genes PKD1 and PKD2 proteins are present in primary cilia. Among ciliopathies, several may control the polarity and function of ductal structures of the kidney, but also of the pancreas, and liver. Do ciliary genes play an important role in cancer progression in these tissues? The molecular mechanism suppressing formation of cysts is poorly understood, but may include changes in the apical-basal polarity of cells, cell cycle, or secretory behavior of cells. Specific changes in ciliary signaling mechanisms may be important for cyst suppression. Among cystic regulators, nephronophthisis (NPHP), Joubert (JBTS), and Meckel-Gruber (MKS) syndromes are autosomal-recessive ciliopathies presenting with cystic kidneys, retinal degeneration, and cerebellar/neural tube malformation. Nephronophthisis (NPHP) is a rare pediatric autosomal cystic kidney disease caused by mutations of nine known genes, NPHP1-9. NPHP patients also show cerebellar defects, situs inversus, and retinitis pigmentosa (RP). The pediatric Joubert (JBST) and Meckel-Gruber (MKS) syndromes also present nephronophthisis and RP, but are characterized by cerebellar malformation or severe neural tube defects. There are nine JBST and seven MKS genes, with considerable allelism among NPHP, JBST, and MKS genes. We used high-confidence proteomics to identify over 200 interactors copurifying with nine NPHP/JBTS/MKS proteins and discovered three connected modules functioning at the apical cell surface and ciliary “transition zone” (NPHP1/4/8), at the basal body (NPHP5/6), or in a novel Hedgehog pathway (Mks1/Mks6/Tectonic). We employed assays for ciliogenesis and cell polarity defects using 3-D renal cultures to demonstrate that renal cystic disease links primarily to apical organization defects, whereas ciliary and Hedgehog pathway defects appear central to neural malformations. Using 38 interactors as candidates, linkage and sequencing analysis of 250 NPHP patients identified TCTN2 as a new Joubert syndrome disease gene, plus two other novel NPHP human. Our Tctn2 mouse knockout showed neural tube and Hedgehog signaling defects. Our studies demonstrate the power of linking proteomic networks and human genetics to uncover critical disease pathways. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr SY14-02. doi:10.1158/1538-7445.AM2011-SY14-02

Down-regulation of PKHD1 induces cell apoptosis through PI3K and NF-κB pathways

Mutations in PKHD1 (polycystic kidney and hepatic disease gene 1) gene cause the autosomal recessive polycystic kidney disease (ARPKD). Fibrocystin/polyductin (FPC), encoded by PKHD1, is a membrane-associated receptor-like protein. Although it is widely accepted that cystogenesis is mostly due to aberrant cell proliferation and apoptosis, it is still unclear how apoptosis is regulated. The aim of this study is to analyze the relationship among apoptosis, phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor κB (NF-κB) in FPC knockdown kidney cells. We show that PKHD1-silenced HEK293 cells demonstrate a higher PI3K/Akt activity. Selective inhibition of PI3K/Akt using LY294002 or wortmannin in these cells increases serum starvation-induced HEK293 cell apoptosis with a concomitant decrease in cell proliferation and higher caspase-3 activity. PI3K/Akt inhibition also leads to increased NF-κB activity in these cells. We conclude that the PI3K/Akt pathway is involved in apoptotic function in PKHD1-silenced cells, and PI3K/Akt inhibition correlates with upregulation of NF-κB activity. These observations provide a potential platform for determining FPC function and therapeutic investigation of ARPKD.

Germline PKHD1 mutations are protective against colorectal cancer

The autosomal recessive polycystic kidney disease (ARPKD) gene, PKHD1, has been implicated in the genesis or growth of colorectal adenocarcinoma, as a high level of somatic mutations was found in colorectal tumor tissue. To determine whether carriers of a single PKHD1 mutation are at increased risk of colorectal carcinoma, we assessed the prevalence of the commonest European mutation, T36M. First, we assayed a European cohort of ARPKD patients and found T36M was responsible for 13.1% of mutations. We then investigated two European cohorts with colorectal adenocarcinoma versus two control cohorts of similar age and gender. Screening for the most common PKHD1 mutation, T36M, we detected 15:3,603 (0.42%) controls versus 1:3,767 (0.027%) colorectal cancer individuals, indicating that heterozygous PKHD1 mutations are not a risk factor and are protective (p=0.0002). We also show that the carriage rate for PKHD1 mutations in the European population is higher than previous accepted at 3.2% (1:31 genomes).

Functional Specialization of Sensory Cilia by an RFX Transcription Factor Isoform

In animals, RFX transcription factors govern ciliogenesis by binding to an X-box motif in the promoters of ciliogenic genes. In Caenorhabditis elegans, the sole RFX transcription factor (TF) daf-19 null mutant lacks all sensory cilia, fails to express many ciliogenic genes, and is defective in many sensory behaviors, including male mating. The daf-19c isoform is expressed in all ciliated sensory neurons and is necessary and sufficient for activating X-box containing ciliogenesis genes. Here, we describe the daf-19(n4132) mutant that is defective in expression of the sensory polycystic kidney disease (PKD) gene battery and male mating behavior, without affecting expression of ciliogenic genes or ciliogenesis. daf-19(n4132) disrupts expression of a new isoform, daf-19m (for function in male mating). daf-19m is expressed in male-specific PKD and core IL2 neurons via internal promoters and remote enhancer elements located in introns of the daf-19 genomic locus. daf-19m genetically programs the sensory functions of a subset of ciliated neurons, independent of daf-19c. In the male-specific HOB neuron, DAF-19(M) acts downstream of the zinc finger TF EGL-46, indicating that a TF cascade controls the PKD gene battery in this cell-type specific context. We conclude that the RFX TF DAF-19 regulates ciliogenesis via X-box containing ciliogenic genes and controls ciliary specialization by regulating non-X-box containing sensory genes. This study reveals a more extensive role for RFX TFs in generating fully functional cilia.

Sirolimus attenuates disease progression in an orthologous mouse model of human autosomal dominant polycystic kidney disease

In autosomal dominant polycystic kidney disease (ADPKD), abnormal proliferation of tubular cells drives cyst development and growth. Sirolimus, an inhibitor of the protein kinase mammalian target of rapamycin (mTOR) and a potent anti-proliferative agent, decreases cyst growth in several genetically distinct rodent models of polycystic kidney disease (PKD). We determined here the effect of sirolimus on renal cyst growth in Pkd2WS25/- mice; an ortholog of human ADPKD involving mutation of the Pkd2 gene. In Pkd2WS25/- mice treated with sirolimus, both the two kidney/total body weight (2K/TBW) ratio and the cyst volume density (CVD) were significantly decreased by over half compared with untreated mice suffering with PKD. However, there was no effect on the increased blood urea nitrogen (BUN) levels as an index of kidney function. There are two distinct complexes containing mTOR depending on its binding partners: mTORC1 and mTORC2. Western blot analysis of whole kidney lysates and immunohistochemistry of the cysts found that phospho-S6 ribosomal protein, a marker of mTORC1 activity, was increased in Pkd2WS25/- mice and its phosphorylation was decreased by sirolimus treatment. Phospho-Akt at serine 473, a marker associated with mTORC2 activity, was not different between Pkd2WS25/- mice and normal littermate controls. Hence, our study found that inhibition of mTORC1 by sirolimus correlated with decreased renal cyst growth in this model of human ADPKD but had no effect on the decline in renal function.

Regulation of cell proliferation and apoptosis through fibrocystin–prosaposin interaction

Mutations in PKHD1 (polycystic kidney and hepatic disease gene 1) gene cause the autosomal recessive polycystic kidney disease (ARPKD). It is widely accepted that cystogenesis is owing to aberrant cell proliferation and apoptosis, increased fluid secretion, and extracellular matrix abnormality. Fibrocystin/polyductin (FPC), the encoded protein product by PKHD1, is a single transmembrane protein and believed to be a novel receptor-like molecule. FPC has been located mainly on the plasma membrane and cilium/basal body. However, its biological functions remain poorly understood. To investigate the roles of FPC in the pathogenesis of ARPKD, we searched for FPC-interacting proteins by yeast two-hybrid assay, and found a novel partner, prosaposin. Prosaposin is a glycoprotein with multiple functions. With GST pull-down assay and co-immunoprecipitation, we confirmed the interaction between FPC and prosaposin. In order to study the effects of FPC–prosaposin interaction on cell proliferation and apoptosis, we have made stable cell lines in which FPC was overexpressed or knocked down alone or in combination with prosaposin overexpression. By MTT assay, we found that FPC knockdown and prosaposin overexpression increased cell proliferation, respectively, while overexpression of FPC C-tail did the opposite. With apoptosis assay, we found that overexpression of FPC C-tail promoted cell apoptosis. However, overexpression of prosaposin significantly enhanced cell survival in FPC knockdown cells. All these findings indicated that FPC and prosaposin may play significant roles in regulation of cell proliferation and apoptosis. Taken together, we have disclosed a novel signaling pathway of FPC, which may be important for the pathogenesis of ARPKD.