Wnt signaling in polycystic kidney disease

PALS1-dependent modulations of mRNA profiles in MDCK II cells grown in non-confluent monolayers and three-dimensional cysts

In epithelia, apicobasal cell polarization is closely linked to cell-cell contact formation, both controlled by the conserved Crumbs (CRB) complex, which includes the transmembrane protein Crumbs (CRB3a) and adapter proteins PALS1, PATJ, and LIN7c. In MDCK II cells, a model for cell polarization, depletion of PALS1 - which binds to all CRB components - leads to defective cell polarization and improper distribution of tight junction proteins, resulting in severe epithelial barrier defects in 3D cyst models. This study investigated whether this phenotype is associated with transcriptional changes by analyzing wildtype (WT) and PALS1 knockout (KO) MDCK II cell lines grown under non-confluent conditions and in 3D cyst cultures. Our results indicate that the transition from non-confluent cells to 3D cysts involves numerous differentially expressed genes (DEGs) in both WT and KO cells. Importantly, the analyses revealed significant overlaps between WT and KO cells in their maturation processes, suggesting that most identified DEGs are linked to differentiation from non-confluent to polarized MDCK cells and likely not a result of PALS1 deficiency. Gene Ontology (GO) enrichment and over-representation analyses using REACTOME and KEGG databases confirmed these similarities. In contrast, the direct comparison of WT and KO cells at the two stages showed fewer DEGs and overlaps in associated biological processes and signaling pathways. DEGs associated with the 3D stage, in which the phenotype manifests, contain DEGs and pathways that were predominantly linked to cell cycle linked processes, centromere assembly, or DNA replication. Furthermore, the transcription of genes encoding key junction proteins, additional polarity proteins, and cell-substrate interaction proteins is less affected by the loss of PALS1, indicating that PALS1 influences the transcriptional profiles in epithelial cells as a modulating factor.

Cross-Species Insights into Autosomal Dominant Polycystic Kidney Disease: Provide an Alternative View on Research Advancement

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a prevalent hereditary disorder that affects the kidneys, characterized by the development of an excessive number of fluid-filled cysts of varying sizes in both kidneys. Along with the progression of ADPKD, these enlarged cysts displace normal kidney tissue, often accompanied by interstitial fibrosis and inflammation, and significantly impair renal function, leading to end-stage renal disease. Currently, the precise mechanisms underlying ADPKD remain elusive, and a definitive cure has yet to be discovered. This review delineates the epidemiology, pathological features, and clinical diagnostics of ADPKD or ADPKD-like disease across human populations, as well as companion animals and other domesticated species. A light has been shed on pivotal genes and biological pathways essential for preventing and managing ADPKD, which underscores the importance of cross-species research in addressing this complex condition. Treatment options are currently limited to Tolvaptan, dialysis, or surgical excision of large cysts. However, comparative studies of ADPKD across different species hold promise for unveiling novel insights and therapeutic strategies to combat this disease.

Polycystin-2-dependent transcriptome reveals early response of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in polycystin genes, Pkd1 and Pkd2, but the underlying pathogenic mechanisms are poorly understood. To identify genes and pathways that operate downstream of polycystin-2 (PC2), a comprehensive gene expression database was created, cataloging changes in the transcriptome immediately following PC2 protein depletion. To explore cyst initiation processes, an immortalized mouse inner medullary collecting duct line was developed with the ability to knock out the Pkd2 gene conditionally. Genome-wide transcriptome profiling was performed using RNA sequencing in the cells immediately after PC2 was depleted and compared with isogenic control cells. Differentially expressed genes were identified, and a bioinformatic analysis pipeline was implemented. Altered expression of candidate cystogenic genes was validated in Pkd2 knockout mice. The expression of nearly 900 genes changed upon PC2 depletion. Differentially expressed genes were enriched for genes encoding components of the primary cilia, the canonical Wnt pathway, and MAPK signaling. Among the PC2-dependent ciliary genes, the transcription factor Glis3 was significantly downregulated. MAPK signaling formed a key node at the epicenter of PC2-dependent signaling networks. Activation of Wnt and MAPK signaling, concomitant with the downregulation of Glis3, was corroborated in Pkd2 knockout mice. The data identify a PC2 cilia-to-nucleus signaling axis and dysregulation of the Gli-similar subfamily of transcription factors as a potential initiator of cyst formation in ADPKD. The catalog of PC2-regulated genes should provide a valuable resource for future ADPKD research and new opportunities for drug development.NEW & NOTEWORTHY Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease. Mutations in polycystin genes cause the disease, but the underlying mechanisms of cystogenesis are unknown. To help fill this knowledge gap, we created an inducible cell model of ADPKD and assembled a catalog of genes that respond in immediate proximity to polycystin-2 depletion using transcriptomic profiling. The catalog unveils a ciliary signaling-to-nucleus axis proximal to polycystin-2 dysfunction, highlighting Glis, Wnt, and MAPK signaling.

Targeting the ADPKD methylome using nanoparticle-mediated combination therapy

DNA methylation aberrancies are found in autosomal dominant polycystic kidney disease (ADPKD), which suggests the methylome to be a promising therapeutic target. However, the impact of combining DNA methylation inhibitors (DNMTi) and ADPKD drugs in treating ADPKD and on disease-associated methylation patterns has not been fully explored. To test this, ADPKD drugs, metformin and tolvaptan (MT), were delivered in combination with DNMTi 5-aza-2'-deoxycytidine (Aza) to 2D or 3D cystic Pkd1 heterozygous renal epithelial cells (PKD1-Het cells) as free drugs or within nanoparticles to enable direct delivery for future in vivo applications. We found Aza synergizes with MT to reduce cell viability and cystic growth. Reduced representation bisulfite sequencing (RRBS) was performed across four groups: PBS, Free-Aza (Aza), Free-Aza+MT (F-MTAza), and Nanoparticle-Aza+MT (NP-MTAza). Global methylation patterns showed that while Aza alone induces a unimodal intermediate methylation landscape, Aza+MT recovers the bimodality reminiscent of somatic methylomes. Importantly, site-specific methylation changes associated with F-MTAza and NP-MTAza were largely conserved including hypomethylation at ADPKD-associated genes. Notably, we report hypomethylation of cancer-associated genes implicated in ADPKD pathogenesis as well as new target genes that may provide additional therapeutic effects. Overall, this study motivates future work to further elucidate the regulatory mechanisms of observed drug synergy and apply these combination therapies in vivo.

Enhanced primary ciliogenesis via mitochondrial oxidative stress activates AKT to prevent neurotoxicity in HSPA9/mortalin-depleted SH-SY5Y cells

The primary cilium, an antenna-like structure on the cell surface, acts as a mechanical and chemical sensory organelle. Primary cilia play critical roles in sensing the extracellular environment to coordinate various developmental and homeostatic signaling pathways. Here, we showed that the depletion of heat shock protein family A member 9 (HSPA9)/mortalin stimulates primary ciliogenesis in SH-SY5Y cells. The downregulation of HSPA9 enhances mitochondrial stress by increasing mitochondrial fragmentation and mitochondrial reactive oxygen species (mtROS) generation. Notably, the inhibition of either mtROS production or mitochondrial fission significantly suppressed the increase in primary ciliogenesis in HSPA9-depleted cells. In addition, enhanced primary ciliogenesis contributed to cell survival by activating AKT in SH-SY5Y cells. The abrogation of ciliogenesis through the depletion of IFT88 potentiated neurotoxicity in HSPA9-knockdown cells. Furthermore, both caspase-3 activation and cell death were increased by MK-2206, an AKT inhibitor, in HSPA9-depleted cells. Taken together, our results suggest that enhanced primary ciliogenesis plays an important role in preventing neurotoxicity caused by the loss of HSPA9 in SH-SY5Y cells.

Genetics, pathobiology and therapeutic opportunities of polycystic liver disease

Polycystic liver diseases (PLDs) are inherited genetic disorders characterized by progressive development of intrahepatic, fluid-filled biliary cysts (more than ten), which constitute the main cause of morbidity and markedly affect the quality of life. Liver cysts arise in patients with autosomal dominant PLD (ADPLD) or in co-occurrence with renal cysts in patients with autosomal dominant or autosomal recessive polycystic kidney disease (ADPKD and ARPKD, respectively). Hepatic cystogenesis is a heterogeneous process, with several risk factors increasing the odds of developing larger cysts. Depending on the causative gene, PLDs can arise exclusively in the liver or in parallel with renal cysts. Current therapeutic strategies, mainly based on surgical procedures and/or chronic administration of somatostatin analogues, show modest benefits, with liver transplantation as the only potentially curative option. Increasing research has shed light on the genetic landscape of PLDs and consequent cholangiocyte abnormalities, which can pave the way for discovering new targets for therapy and the design of novel potential treatments for patients. Herein, we provide a critical and comprehensive overview of the latest advances in the field of PLDs, mainly focusing on genetics, pathobiology, risk factors and next-generation therapeutic strategies, highlighting future directions in basic, translational and clinical research.

Association of the Transcription Factor 7-Like 2 (TCF7L2) rs7903146 Polymorphism with the Risk of Diabetic Nephropathy: A Meta-Analysis

Transcription factor 7-like 2 (TCF7L2) polymorphism plays an essential role in the occurrence and development of patients living with diabetes, but the current conclusions are inconsistent on the relationship between TCF7L2 polymorphism and the risk of diabetic nephropathy. This meta-analysis aims to explore the exact association between TCF7L2 rs7903146 locus polymorphism and susceptibility to diabetic nephropathy. PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), and China Wanfang databases were searched for studies on the relationship between single nucleotide polymorphism at TCF7L2 rs7903146 locus and susceptibility to diabetic nephropathy until January 10, 2022. The data were analyzed by Stata 15.0 software. A total of 7 articles were included, covering 1443 patients with diabetic nephropathy and 2129 diabetic non-nephropathy patients. The results showed that allele C at TCF7L2 rs7903146 locus, compared to allele T, the pooled odds ratio (OR)=0.69 (95% CI: 0.56-0.85, p≤0.05). In the dominant gene inheritance model, recessive gene inheritance model, homozygous genetic model, and heterozygous genetic model, the pooled OR was 0.47 (95% CI: 0.36-0.61), 0.63 (95% CI: 0.54-0.73), 0.39 (95% CI: 0.29-0.51), and 0.59 (95% CI: 0.45-0.78), respectively, and the differences were statistically significant. In conclusion, TCF7L2 rs7903146 polymorphism is associated with susceptibility to diabetic nephropathy. Allele T and genotype TT can increase the risk of diabetic nephropathy.

ROS-Influenced Regulatory Cross-Talk With Wnt Signaling Pathway During Perinatal Development

Over a century ago, it was found that a rapid burst of oxygen is needed and produced by the sea urchin oocyte to activate fertilization and block polyspermy. Since then, scientific research has taken strides to establish that Reactive Oxygen Species (ROS), besides being toxic effectors of cellular damage and death, also act as molecular messengers in important developmental signaling cascades, thereby modulating them. Wnt signaling pathway is one such developmental pathway, which has significant effects on growth, proliferation, and differentiation of cells at the earliest embryonic stages of an organism, apart from being significant role-players in the instances of cellular transformation and cancer when this tightly-regulated system encounters aberrations. In this review, we discuss more about the Wnt and ROS signaling pathways, how they function, what roles they play overall in animals, and mostly about how these two major signaling systems cross paths and interplay in mediating major cellular signals and executing the predestined changes during the perinatal condition, in a systematic manner.

Nephronophthisis-Pathobiology and Molecular Pathogenesis of a Rare Kidney Genetic Disease

The exponential rise in our understanding of the aetiology and pathophysiology of genetic cystic kidney diseases can be attributed to the identification of cystogenic genes over the last three decades. The foundation of this was laid by positional cloning strategies which gradually shifted towards next-generation sequencing (NGS) based screenings. This shift has enabled the discovery of novel cystogenic genes at an accelerated pace unlike ever before and, most notably, the past decade has seen the largest increase in identification of the genes which cause nephronophthisis (NPHP). NPHP is a monogenic autosomal recessive cystic kidney disease caused by mutations in a diverse clade of over 26 identified genes and is the most common genetic cause of renal failure in children. NPHP gene types present with some common pathophysiological features alongside a diverse range of extra-renal phenotypes associated with specific syndromic presentations. This review provides a timely update on our knowledge of this disease, including epidemiology, pathophysiology, anatomical and molecular features. We delve into the diversity of the NPHP causing genes and discuss known molecular mechanisms and biochemical pathways that may have possible points of intersection with polycystic kidney disease (the most studied renal cystic pathology). We delineate the pathologies arising from extra-renal complications and co-morbidities and their impact on quality of life. Finally, we discuss the current diagnostic and therapeutic modalities available for disease management, outlining possible avenues of research to improve the prognosis for NPHP patients.

Synergistic Antiproliferative Effects of All-Trans Retinoic Acid and Paclitaxel on Autosomal Dominant Polycystic Kidney Disease Epithelial Cells

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by uncontrollable epithelial cell growth, cyst formation, and kidney malfunction. In the present study, we investigated the antiproliferative effects of the treatment with the combination of paclitaxel (PAC) and all-trans retinoic acid (ATRA) on ADPKD epithelial cells. Our results show that the combined treatment with 1 nM PAC and 10 nM ATRA significantly suppressed ADPKD cell proliferation (20%), while the treatment with ATRA or PAC alone had no such effect. Treatment with PAC and ATRA induced cell cycle arrest at the G2/M phase and apoptosis by upregulating p53 and caspase-8 expression and increased the intracellular calcium (Ca²⁺) level possibly by enhancing Ca²⁺ uptake via plasma membrane channels. In addition, this treatment suppressed extracellular signal-regulated kinase signaling possibly through mitogen-activated protein kinase phosphatase-1 activation. Thus, the combination of PAC and ATRA can be explored as a potential treatment regimen for ADPKD.

Cadherin and Wnt signaling pathways as key regulators in diabetic nephropathy

AIM

A recent meta-analysis of genome-wide linkage studies (GWLS) has identified multiple genetic regions suggestive of linkage with DN harboring hundreds of genes. Moving this number of genetic loci forward into biological insight is truly the next step. Here, we approach this challenge with a gene ontology (GO) analysis in order to yield biological and functional role to the genes, an over-representation test to find which GO terms are enriched in the gene list, pathway analysis, as well as protein network analysis.

METHOD

GO analysis was performed using protein analysis through evolutionary relationships (PANTHER) version 14.0 software and P-values less than 0.05 were considered statistically significant. GO analysis was followed by over-representation test for the identification of enriched terms. Statistical significance was calculated by Fisher's exact test and adjusted using the false discovery rate (FDR) for correction of multiple tests. Cytoscape with the relevant plugins was used for the construction of the protein network and clustering analysis.

RESULTS

The GO analysis assign multiple GO terms to the genes regarding the molecular function, the biological process and the cellular component, protein class and pathway analysis. The findings of the over-representation test highlight the contribution of cell adhesion regarding the biological process, integral components of plasma membrane regarding the cellular component, chemokines and cytokines with regard to protein class, while the pathway analysis emphasizes the contribution of Wnt and cadherin signaling pathways.

CONCLUSIONS

Our results suggest that a core feature of the pathogenesis of DN may be a disturbance in Wnt and cadherin signaling pathways, whereas the contribution of chemokines and cytokines need to be studied in additional studies.

Ciclopirox olamine induces ferritinophagy and reduces cyst burden in polycystic kidney disease

Despite the recent launch of tolvaptan, the search for safer polycystic kidney disease (PKD) drugs continues. Ciclopirox (CPX) or its olamine salt (CPX-O) is contained in a number of commercially available antifungal agents. CPX is also reported to possess anticancer activity. Several mechanisms of action have been proposed, including chelation of iron and inhibition of iron-dependent enzymes. Here, we show that CPX-O inhibited in vitro cystogenesis of primary human PKD cyst-lining epithelial cells cultured in a 3D collagen matrix. To assess the in vivo role of CPX-O, we treated PKD mice with CPX-O. CPX-O reduced the kidney-to-body weight ratios of PKD mice. The CPX-O treatment was also associated with decreased cell proliferation, decreased cystic area, and improved renal function. Ferritin levels were markedly elevated in cystic kidneys of PKD mice, and CPX-O treatment reduced renal ferritin levels. The reduction in ferritin was associated with increased ferritinophagy marker nuclear receptor coactivator 4, which reversed upon CPX-O treatment in PKD mice. Interestingly, these effects on ferritin appeared independent of iron. These data suggest that CPX-O can induce ferritin degradation via ferritinophagy, which is associated with decreased cyst growth progression in PKD mice. Most importantly these data indicate that CPX-O has the potential to treat autosomal dominant PKD.

WNK regulates Wnt signalling and β-Catenin levels by interfering with the interaction between β-Catenin and GID

β-Catenin is an important component of the Wnt signalling pathway. As dysregulation or mutation of this pathway causes many diseases, including cancer, the β-Catenin level is carefully regulated by the destruction complex in the Wnt signalling pathway. However, the mechanisms underlying the regulation of β-Catenin ubiquitination and degradation remain unclear. Here, we find that WNK (With No Lysine [K]) kinase is a potential regulator of the Wnt signalling pathway. We show that WNK protects the interaction between β-Catenin and the Glucose-Induced degradation Deficient (GID) complex, which includes an E3 ubiquitin ligase targeting β-Catenin, and that WNK regulates the β-Catenin level. Furthermore, we show that WNK inhibitors induced β-Catenin degradation and that one of these inhibitors suppressed xenograft tumour development in mice. These results suggest that WNK is a previously unrecognized regulator of β-Catenin and a therapeutic target of cancer.

Sato et al. find that WNK (With No Lysine [K]) acts as a positive regulator of the Wnt signaling pathway by attenuating the interaction between β-Catenin and the Glucose Induce degradation Deficient (GID) complex, and show that a WNK inhibitor also functions as a Wnt inhibitor, suppressing xenograft tumor development in mice. These findings suggest that WNK is a regulator of β-Catenin and a potential therapeutic target

Targeting and therapeutic peptide-based strategies for polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by progressive cyst growth and is a leading cause of renal failure worldwide. Currently, there are limited therapeutic options available to PKD patients, and only one drug, tolvaptan, has been FDA-approved to slow cyst progression. Similar to other small molecule drugs, however, tolvaptan is costly, only moderately effective, and causes adverse events leading to high patient dropout rates. Peptides may mitigate many drawbacks of small molecule drugs, as they can be highly tissue-specific, biocompatible, and economically scaled-up. Peptides can function as targeting ligands that direct therapies to diseased renal tissue, or be potent as therapeutic agents themselves. This review discusses various aberrant signaling pathways in PKD and renal receptors that can be potential targets of peptide-mediated strategies. Additionally, peptides utilized in other kidney applications, but may prove useful in the context of PKD, are highlighted. Insights into novel peptide-based solutions that have potential to improve clinical management of PKD are provided.

The regulation effect of WNT-RAS signaling in hypothalamic paraventricular nucleus on renal fibrosis

Background

Abnormal activation of wnt/β-catenin signaling and renin-angiotensin system is known to play a vital role in the development and progression of CKD. We hypothesized that abnormal expression of central wnt/β-catenin signaling and renin-angiotensin system (WNT-RAS signaling) was tightly involved in CKD.

Methods

We established sham-operated and 5/6 nephrectomized (5/6 NX) rat model and blocked the central wnt signaling by intracerebroventricular injection of adeno-associated virus vector which can overexpress target gene DKK1. The central and renal expression level of wnt/β-catenin signaling and RAS and renal injury were assessed.

Results

The expression levels of the main wnt/β-catenin signaling components in both brain and kidney of 5/6NX rats, such as wnt3a and active-β-catenin, were elevated obviously and the up-regulation were inhibited by central blockade of the wnt signaling. Furthermore, the expression of the major components of RAS in both brain and kidney in 5/6NX rats, such as angiotensinogen (AGT), angiotensin converting enzyme (ACE-1), angiotensin II AT1-receptor (AT1R), was significantly up-regulated and the up-regulated expression was inhibited by central blockade of the wnt singling. Notably, central blockade of the wnt signaling improved renal function as indicated by decreased serum creatinine and 24 h urinary protein, and attenuated interstitial fibrosis as indicated by reduced Sirius red staining and expression of Fibronectin, Collagen-I and α-SMA.

Conclusion

These data suggest that the central WNT-RAS signaling plays a significant role in the development and progression of CKD.

Identifying cystogenic paracrine signaling molecules in cyst fluid of patients with polycystic kidney disease

In autosomal dominant polycystic kidney disease (ADPKD) paracrine signaling molecules in cyst fluid can induce proliferation and cystogenesis of neighboring renal epithelial cells. However, the identity of this cyst-inducing factor is still unknown. The aim of this study was to identify paracrine signaling proteins in cyst fluid using a 3D in vitro cystogenesis assay. We collected cyst fluid from 15 ADPKD patients who underwent kidney or liver resection (55 cysts from 13 nephrectomies, 5 cysts from 2 liver resections). For each sample, the ability to induce proliferation and cyst formation was tested using the cystogenesis assay (RPTEC/TERT1 cells in Matrigel with cyst fluid added for 14 days). Kidney cyst fluid induced proliferation and cyst growth of renal epithelial cells in a dose-dependent fashion. Liver cyst fluid also induced cystogenesis. Using size exclusion chromatography, 56 cyst fluid fractions were obtained of which only the fractions between 30 and 100 kDa showed cystogenic potential. Mass spectrometry analysis of samples that tested positive or negative in the assay identified 43 candidate cystogenic proteins. Gene ontology analysis showed an enrichment for proteins classified as enzymes, immunity proteins, receptors, and signaling proteins. A number of these proteins have previously been implicated in ADPKD, including secreted frizzled-related protein 4, S100A8, osteopontin, and cysteine rich with EGF-like domains 1. In conclusion, both kidney and liver cyst fluids contain paracrine signaling molecules that drive cyst formation. Using size exclusion chromatography and mass spectrometry, we procured a candidate list for future studies. Ultimately, cystogenic paracrine signaling molecules may be targeted to abrogate cystogenesis in ADPKD.

Canonical Wnt inhibitors ameliorate cystogenesis in a mouse ortholog of human ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) can be caused by mutations in the PKD1 or PKD2 genes. The PKD1 gene product is a Wnt cell-surface receptor. We previously showed that a lack of the PKD2 gene product, PC2, increases β-catenin signaling in mouse embryonic fibroblasts, kidney renal epithelia, and isolated renal collecting duct cells. However, it remains unclear whether β-catenin signaling plays a role in polycystic kidney disease phenotypes or if a Wnt inhibitor can halt cyst formation in ADPKD disease models. Here, using genetic and pharmacologic approaches, we demonstrated that the elevated β-catenin signaling caused by PC2 deficiency contributes significantly to disease phenotypes in a mouse ortholog of human ADPKD. Pharmacologically inhibiting β-catenin stability or the production of mature Wnt protein, or genetically reducing the expression of Ctnnb1 (which encodes β-catenin), suppressed the formation of renal cysts, improved renal function, and extended survival in ADPKD mice. Our study clearly demonstrates the importance of β-catenin signaling in disease phenotypes associated with Pkd2 mutation. It also describes the effects of two Wnt inhibitors, XAV939 and LGK974, on various Wnt signaling targets as a potential therapeutic modality for ADPKD, for which there is currently no effective therapy.

Myc cooperates with β-catenin to drive gene expression in nephron progenitor cells

For organs to achieve their proper size, the processes of stem cell renewal and differentiation must be tightly regulated. We previously showed that in the developing kidney, Wnt9b regulates distinct β-catenin-dependent transcriptional programs in the renewing and differentiating populations of the nephron progenitor cells. How β-catenin stimulated these two distinct programs was unclear. Here, we show that β-catenin cooperates with the transcription factor Myc to activate the progenitor renewal program. Although in multiple contexts Myc is a target of β-catenin, our characterization of a cell type-specific enhancer for the Wnt9b/β-catenin target gene Fam19a5 shows that Myc and β-catenin cooperate to activate gene expression controlled by this element. This appears to be a more general phenomenon as we find that Myc is required for the expression of every Wnt9b/β-catenin progenitor renewal target assessed as well as for proper nephron endowment in vivo This study suggests that, within the developing kidney, tissue-specific β-catenin activity is regulated by cooperation with cell type-specific transcription factors. This finding not only provides insight into the regulation of β-catenin target genes in the developing kidney, but will also advance our understanding of progenitor cell renewal in other cell types/organ systems in which Myc and β-catenin are co-expressed.

Dickkopf-1 Is a Biomarker for Systemic Lupus Erythematosus and Active Lupus Nephritis

An early diagnosis of lupus nephritis (LN) has an important clinical implication in guiding treatments of systemic lupus erythematosus (SLE) in clinical settings. In this study, the concentrations of Wnt-3A, Frizzled-8 (FZD-8), and Dickkopf-1 (DKK-1) of Wnt signaling, as well as their diagnostic values for accessing LN, were evaluated by ELISA in sera and urine of 111 SLE patients (31 with LN and 80 without LN) and 70 healthy cohorts. Significantly more abundances of DKK-1 protein were determined in both of sera and urine of SLE patients compared to healthy cohorts (p < 0.0001); in particular the serum DKK-1 concentration was even higher in LN-SLE patients relative to non-LN SLE subjects (p < 0.0001). Intriguingly, concentrations of above examined proteins in SLE patients showed no correlation between serum and urine. Moreover, a combination of DKK-1 with anti-dsDNA and/or levels of complement C3 and C4 could not increase the specificity and/or sensitivity for identification of patients with LN diseases, but both ROC curve and multiple-factor nonconditional logistic regression analysis showed that serum DKK-1 was considered better positive biomarker for identification of LN in SLE patients. These results imply that serum and/or urine DKK-1 may be a valuable and independent biomarker for identification of SLE patients with LN.

Phosphorylation-dependent Akt-Inversin interaction at the basal body of primary cilia

A primary cilium is a microtubule‐based sensory organelle that plays an important role in human development and disease. However, regulation of Akt in cilia and its role in ciliary development has not been demonstrated. Using yeast two‐hybrid screening, we demonstrate that Inversin (INVS) interacts with Akt. Mutation in the INVS gene causes nephronophthisis type II (NPHP2), an autosomal recessive chronic tubulointerstitial nephropathy. Co‐immunoprecipitation assays show that Akt interacts with INVS via the C‐terminus. In vitro kinase assays demonstrate that Akt phosphorylates INVS at amino acids 864–866 that are required not only for Akt interaction, but also for INVS dimerization. Co‐localization of INVS and phosphorylated form of Akt at the basal body is augmented by PDGF‐AA. Akt‐null MEF cells as well as siRNA‐mediated inhibition of Akt attenuated ciliary growth, which was reversed by Akt reintroduction. Mutant phosphodead‐ or NPHP2‐related truncated INVS, which lack Akt phosphorylation sites, suppress cell growth and exhibit distorted lumen formation and misalignment of spindle axis during cell division. Further studies will be required for elucidating functional interactions of Akt–INVS at the primary cilia for identifying the molecular mechanisms underlying NPHP2.

Molecular pathways and therapies in autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most prevalent inherited renal disease, characterized by multiple cysts that can eventually lead to kidney failure. Studies investigating the role of primary cilia and polycystins have significantly advanced our understanding of the pathogenesis of PKD. This review will present clinical and basic aspects of ADPKD, review current concepts of PKD pathogenesis, evaluate potential therapeutic targets, and highlight challenges for future clinical studies.

Wnt/β-catenin signaling in kidney injury and repair: a double-edged sword

The Wnt/β-catenin signaling cascade is an evolutionarily conserved, highly complex pathway that is known to be involved in kidney injury and repair after a wide variety of insults. Although the kidney displays an impressive ability to repair and recover after injury, these repair mechanisms can be overwhelmed, leading to maladaptive responses and eventual development of chronic kidney disease (CKD). Emerging evidence demonstrates that Wnt/β-catenin signaling possesses dual roles in promoting repair/regeneration or facilitating progression to CKD after acute kidney injury (AKI), depending on the magnitude and duration of its activation. In this review, we summarize the expression, intracellular modification, and secretion of Wnt family proteins and their regulation in a variety of kidney diseases. We also explore our current understanding of the potential mechanisms by which transient Wnt/β-catenin activation positively regulates adaptive responses of the kidney after AKI, and discuss how sustained activation of this signaling triggers maladaptive responses and causes destructive outcomes. A better understanding of these mechanisms may offer important opportunities for designing targeted therapy to promote adaptive kidney repair/recovery and prevent progression to CKD in patients.

Human polycystin-2 transgene dose-dependently rescues ADPKD phenotypes in Pkd2 mutant mice

Although much is known about the molecular genetic mechanisms of autosomal-dominant polycystic kidney disease (ADPKD), few effective treatment is currently available. Here, we explore the in vivo effects of causal gene replacement in orthologous gene models of ADPKD in mice. Wild-type mice with human PKD2 transgene (PKD2(tg)) overexpressed polycystin (PC)-2 in several tissues, including the kidney and liver, and showed no significant cyst formation in either organ. We cross-mated PKD2(tg) with a Pkd2-null mouse model, which is embryonically lethal and forms renal and pancreatic cysts. Pkd2(-/-) mice with human PKD2 transgene (Pkd2(-/-);PKD2(tg)) were born in expected Mendelian ratios, indicating that the embryonic lethality of the Pkd2(-/-) mice was rescued. Pkd2(-/-);PKD2(tg) mice survived up to 12 months and exhibited moderate to severe cystic phenotypes of the kidney, liver, and pancreas. Moreover, Pkd2(-/-) mice with homozygous PKD2(tg)-transgene alleles (Pkd2(-/-);PKD2(tg/tg)) showed significant further amelioration of the cystic severity compared to that in Pkd2(-/-) mice with a hemizygous PKD2(tg) allele (Pkd2(-/-);PKD2(tg)), suggesting that the ADPKD phenotype was improved by increased transgene dosage. On further analysis, cystic improvement mainly resulted from reduced proliferation, rather apoptosis, of cyst-prone epithelial cells in the mouse model. The finding that the functional restoration of human PC2 significantly rescued ADPKD phenotypes in a dose-dependent manner suggests that increasing PC2 activity may be beneficial in some forms of ADPKD.

Association of TCF7L2 Polymorphism with Diabetic Nephropathy in the South Indian Population

The transcription factor 7-like 2 (TCF7L2) gene plays a significant role in the development of type 2 diabetes and diabetic nephropathy. The aim of this study was to investigate the association of TCF7L2 rs12255372 (G/T)polymorphism with type 2 diabetic nephropathy in the South Indian population. A total of 2102 subjects, 927 normal glucose tolerant (NGT) subjects, 598 type 2 diabetic subjects without nephropathy (DM), and 577 type 2 diabetic subjects with nephropathy (DN) were genotyped by MassARRAY. As compared to the NGT group, the odds ratio (adjusted for age, sex, BMI, HbA1c, and systolic BP) computed for the GT/TT genotype taking the GG genotype as reference was found to be 2.02 (95% CI: 1.16-3.51, p = 0.013) for DN and 1.94 (95% CI: 1.36-2.78, p = 0.0002) for DM. The genotype frequency was not significantly different between the DM and DN groups. In conclusion, the rs12255372 polymorphism in the TCF7L2 gene is associated with type 2 diabetes and DN but its association with DN is mediated through diabetes.

Genome-wide analysis of positively selected genes in seasonal and non-seasonal breeding species

Some mammals breed throughout the year, while others breed only at certain times of year. These differences in reproductive behavior can be explained by evolution. We identified positively-selected genes in two sets of species with different degrees of relatedness including seasonal and non-seasonal breeding species, using branch-site models. After stringent filtering by sum of pairs scoring, we revealed that more genes underwent positive selection in seasonal compared with non-seasonal breeding species. Positively-selected genes were verified by cDNA mapping of the positive sites with the corresponding cDNA sequences. The design of the evolutionary analysis can effectively lower the false-positive rate and thus identify valid positive genes. Validated, positively-selected genes, including CGA, DNAH1, INVS, and CD151, were related to reproductive behaviors such as spermatogenesis and cell proliferation in non-seasonal breeding species. Genes in seasonal breeding species, including THRAP3, TH1L, and CMTM6, may be related to the evolution of sperm and the circadian rhythm system. Identification of these positively-selected genes might help to identify the molecular mechanisms underlying seasonal and non-seasonal reproductive behaviors.

Urinary extracellular vesicles as reservoirs of altered proteins during the pathogenesis of polycystic kidney disease

PURPOSE

Recent findings indicate that urinary extracellular vesicles (EVs) might reflect the pathophysiological state of urinary system; and that EVs-induced ciliary signaling is a possible mechanism of intercellular communication within the tract. Here, we aimed to analyze the protein expression of urinary EVs during autosomal dominant polycystic kidney disease (ADPKD).

EXPERIMENTAL DESIGN

EVs were isolated from pooled urine samples of healthy control and ADPKD patients at two different stages of the disease and under tolvaptan treatment using the double-cushion ultracentrifugation method. Proteins were identified and quantified by iTRAQ and multidimensional protein identification technology (MudPIT)-based quantitative proteomics.

RESULTS

Quantitative analyses identified 83 differentially expressed EV proteins. Many of these have apical membrane origin and are involved in signal transduction pathways of primary cilia, Ca(2+) -activated signaling, cell-cycle regulation, and cell differentiation.

CONCLUSIONS AND CLINICAL RELEVANCE

The reduced AQP-2 and the increased APO-A1 levels observed in all ADPKD-affected groups may reflects the impaired renal concentrating capability of these patients and correlated with estimated glomerular filtration rate decline. The levels of some upregulated proteins involved in Ca(2+) -activated signaling declined upon tolvaptan treatment. The results obtained suggest that the quantitative proteomics of urinary EVs might be useful to monitor proteins difficult to access noninvasively, and thus advance our understanding of urinary tract physiology and pathology.

Polycystic liver diseases: advanced insights into the molecular mechanisms

Polycystic liver diseases are genetic disorders characterized by progressive bile duct dilatation and/or cyst development. The large volume of hepatic cysts causes different symptoms and complications such as abdominal distension, local pressure with back pain, hypertension, gastro-oesophageal reflux and dyspnea as well as bleeding, infection and rupture of the cysts. Current therapeutic strategies are based on surgical procedures and pharmacological management, which partially prevent or ameliorate the disease. However, as these treatments only show short-term and/or modest beneficial effects, liver transplantation is the only definitive therapy. Therefore, interest in understanding the molecular mechanisms involved in disease pathogenesis is increasing so that new targets for therapy can be identified. In this Review, the genetic mechanisms underlying polycystic liver diseases and the most relevant molecular pathways of hepatic cystogenesis are discussed. Moreover, the main clinical and preclinical studies are highlighted and future directions in basic as well as clinical research are indicated.

Vangl2 regulates E-cadherin in epithelial cells

E-cadherin belongs to the classic cadherin subfamily of calcium-dependent cell adhesion molecules and is crucial for the formation and function of epithelial adherens junctions. In this study, we demonstrate that Vangl2, a vertebrate regulator of planar cell polarity (PCP), controls E-cadherin in epithelial cells. E-cadherin co-immunoprecipitates with Vangl2 from embryonic kidney extracts, and this association is also observed in transfected fibroblasts. Vangl2 enhances the internalization of E-cadherin when overexpressed. Conversely, the quantitative ratio of E-cadherin exposed to the cell surface is increased in cultured renal epithelial cells derived from Vangl2(Lpt/+) mutant mice. Interestingly, Vangl2 is also internalized through protein traffic involving Rab5- and Dynamin-dependent endocytosis. Taken together with recent reports regarding the transport of Frizzled3, MMP14 and nephrin, these results suggest that one of the molecular functions of Vangl2 is to enhance the internalization of specific plasma membrane proteins with broad selectivity. This function may be involved in the control of intercellular PCP signalling or in the PCP-related rearrangement of cell adhesions.

MicroRNAs in Cholangiopathies

Cholangiocytes, the cells lining bile ducts, comprise a small fraction of the total cellular component of the liver, yet perform the essential role of bile modification and transport of biliary and blood constituents. Cholangiopathies are a diverse group of biliary disorders with the cholangiocyte as the target cell; the etiopathogenesis of most cholangiopathies remains obscure. MicroRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression. These small RNAs may not only be involved in the etiopathogenesis of disease, but are showing promise as diagnostic and prognostic tools. In this brief review, we summarize recent work regarding the role of microRNAs in the etiopathogenesis of several cholangiopathies, and discuss their utility as prognostic and diagnostic tools.

Vasopressin-2 receptor signaling and autosomal dominant polycystic kidney disease: from bench to bedside and back again

Blockade of the vasopressin-2 receptor (V2R) in the kidney has recently emerged as a promising therapeutic strategy in autosomal dominant polycystic kidney disease. The pathophysiologic basis of V2R-dependent cyst proliferation and disease progression, however, is not fully understood. Recent evidence suggests that polycystic kidney disease is characterized by defects in urinary concentrating mechanisms and subsequent deregulation of vasopressin excretion by the neurohypophysis. On the cellular level, several recent studies revealed unexpected crosstalk of signaling pathways downstream of V2R activation in the kidney epithelium. This review summarizes some of the unexpected roles of V2R signaling and suggests that vasopressin signaling itself may contribute crucially to loss of polarity and enhanced proliferation in cystic kidney epithelium.

Gpr48 deficiency induces polycystic kidney lesions and renal fibrosis in mice by activating Wnt signal pathway

G protein-coupled receptor 48 (Gpr48/Lgr4) is essential to regulate the development of multiple tissues in mice. The notion that Gpr48 functions in renal development prompted us to investigate the relation between Gpr48 and renal diseases. Using a Gpr48 knockout mice model, we observed that 66.7% Gpr48 null mice developed polycystic lesions in the kidney, while no cysts were observed in the kidneys of wild-type mice. Polycystic kidney disease 1 (PKD1) and PKD2 expressions were also markedly decreased in the Gpr48 knockout mice. Abnormal expressions of exra-cellular matrix protein lead to the progression of polycystic kidney disease and the formation of renal fibrosis in the Gpr48 null mice. The expressions of several Wnt molecules and its receptors were increased and marked β-catenin nuclear accumulation was observed in the Gpr48 null mice. The inhibitors of Wnt/β-catenin signal pathway such as GSK3β and axin2 were loss of function. The Wnt/PCP signaling pathway is also activated in Gpr48 null mice. However, TGF-β expression and phosphorylated Smad2/3 levels were not altered. Collectively, our results showed that Gpr48 null mice are at a greater risk of suffering from polycystic lesions and renal fibrosis. Moreover, the formation of polycystic lesions and renal fibrosis induced by Gpr48 deficiency involves the activation of Wnt signaling pathway but not the TGF-β/Smad pathway.

Transcription factor 7-like 2 (TCF7L2) gene polymorphism and clinical phenotype in end-stage renal disease patients

Variants of the transcription factor 7-like 2 gene (TCF7L2) have been associated with type 2 diabetes and cardiovascular disease in different populations. Here we investigated the potential association of the rs7903146 polymorphism in the TCF7L2 gene with clinical profile of end-stage renal disease (ESRD) patients. We examined a cohort of 1065 ESRD patients with diabetic and non-diabetic renal disease. The control group consisted of 924 healthy individuals. All subjects were genotyped for the rs7903146 single nucleotide polymorphism by polymerase chain reaction. The genotype distribution and allele frequencies were significantly different between ESRD patients and controls (p < 0.01). The OR for the TT genotype was 2.81 (95 % CI 2.08–3.79). Genotype and allele frequencies were compared between subgroups of patients with different clinical phenotypes. The frequency of the T allele was significantly higher in patients with diabetic nephropathy versus non-diabetic renal disease (p = 0.007, OR 1.70, 95 % CI 1.36–2.11). The statistically significant differences were demonstrated between patients with and without cardiovascular disease, with the OR for T allele 1.57 (95 % CI 1.31–1.90). The odds ratio for TT genotype was 2.38 (95 % CI 1.62–3.51). In our study the T allele of the rs7903146 SNP in the TCF7L2 gene confers the risk of developing diabetic nephropathy. We described for the first time a strong relationship between the TCF7L2 gene variant rs7903146 and cardiovascular disease in end-stage renal disease patients.

A glimpse of the pathogenetic mechanisms of Wnt/β-catenin signaling in diabetic nephropathy

The Wnt family of proteins belongs to a group of secreted lipid-modified glycoproteins with highly conserved cysteine residues. Prior results indicate that Wnt/β-catenin signaling plays a prominent role in cell differentiation, adhesion, survival, and apoptosis and is involved in organ development, tumorigenesis, and tissue fibrosis, among other functions. Accumulating evidence has suggested that Wnt/β-catenin exhibits a pivotal function in the progression of diabetic nephropathy (DN). In this review, we focused on discussing the dual role of Wnt/β-catenin in apoptosis and epithelial mesenchymal transition (EMT) formation of mesangial cells. Moreover, we also elucidated the effect of Wnt/β-catenin in podocyte dysfunction, tubular EMT formation, and renal fibrosis under DN conditions. In addition, the molecular mechanisms involved in this process are introduced. This information provides a novel molecular target of Wnt/β-catenin for the protection of kidney damage and in delay of the progression of DN.

Inversin modulates the cortical actin network during mitosis

Mutations in inversin cause nephronophthisis type II, an autosomal recessive form of polycystic kidney disease associated with situs inversus, dilatation, and kidney cyst formation. Since cyst formation may represent a planar polarity defect, we investigated whether inversin plays a role in cell division. In developing nephrons from inv-/- mouse embryos we observed heterogeneity of nuclear size, increased cell membrane perimeters, cells with double cilia, and increased frequency of binuclear cells. Depletion of inversin by siRNA in cultured mammalian cells leads to an increase in bi- or multinucleated cells. While spindle assembly, contractile ring formation, or furrow ingression appears normal in the absence of inversin, mitotic cell rounding and the underlying rearrangement of the cortical actin cytoskeleton are perturbed. We find that inversin loss causes extensive filopodia formation in both interphase and mitotic cells. These cells also fail to round up in metaphase. The resultant spindle positioning defects lead to asymmetric division plane formation and cell division. In a cell motility assay, fibroblasts isolated from inv-/- mouse embryos migrate at half the speed of wild-type fibroblasts. Together these data suggest that inversin is a regulator of cortical actin required for cell rounding and spindle positioning during mitosis. Furthermore, cell division defects resulting from improper spindle position and perturbed actin organization contribute to altered nephron morphogenesis in the absence of inversin.

Novel antilithiatic cationic proteins from human calcium oxalate renal stone matrix identified by MALDI-TOF-MS endowed with cytoprotective potential: an insight into the molecular mechanism of urolithiasis

BACKGROUND

No substantial work has been conducted to date in context to cationic proteins with antilithiatic activity. We explored the antilithiatic cationic proteins present in human calcium oxalate (CaOx) stones and also examined their molecular interactions with calcium oxalate crystals in silico.

METHODS

Proteins were isolated from the matrix of human CaOx containing kidney stones. Proteins having MW>3 kDa were subjected to cation exchange chromatography followed by molecular-sieve chromatography. The effect of these purified cationic proteins was tested against CaOx nucleation and growth and on oxalate injured MDCK cells for their activity. Proteins were identified by MALDI-TOF MS. Molecular interaction studies with COM crystals in silico were also investigated.

RESULTS

Three antilithiatic cationic proteins were identified as histone-lysine N-methyltransferase, inward rectifier K channel and protein Wnt-2 (MW~53, ~44, and ~42 kDa respectively) by MALDI-TOF MS based on database search with MASCOT server. Further molecular modeling calculations revealed the mode of interaction of these proteins with CaOx at the molecular level.

CONCLUSION

We identified histone-lysine N-methyltransferase, inward rectifier K channel and protein Wnt-2 as novel antilithiatic proteins which play a vital role in the kidney function and have been associated with various kidney diseases.

Polycystin-1 regulates the stability and ubiquitination of transcription factor Jade-1

Autosomal-dominant polycystic kidney disease (ADPKD) and von Hippel-Lindau (VHL) disease lead to large kidney cysts that share pathogenetic features. The polycystin-1 (PC1) and pVHL proteins may therefore participate in the same key signaling pathways. Jade-1 is a pro-apoptotic and growth suppressive ubiquitin ligase for beta-catenin and transcriptional coactivator associated with histone acetyltransferase activity that is stabilized by pVHL in a manner that correlates with risk of VHL renal disease. Thus, a relationship between Jade-1 and PC1 was sought. Full-length PC1 bound, stabilized and colocalized with Jade-1 and inhibited Jade-1 ubiquitination. In contrast, the cytoplasmic tail or the naturally occurring C-terminal fragment of PC1 (PC1-CTF) promoted Jade-1 ubiquitination and degradation, suggesting a dominant-negative mechanism. ADPKD-associated PC1 mutants failed to regulate Jade-1, indicating a potential disease link. Jade-1 ubiquitination was mediated by Siah-1, an E3 ligase that binds PC1. By controlling Jade-1 abundance, PC1 and the PC1-CTF differentially regulate Jade-1-mediated transcriptional activity. A key target of PC1, the cyclin-dependent kinase inhibitor p21, is also up-regulated by Jade-1. Through Jade-1, PC1 and PC1 cleaved forms may exert fine control of beta-catenin and canonical Wnt signaling, a critical pathway in cystic renal disease. Thus, Jade-1 is a transcription factor and ubiquitin ligase whose activity is regulated by PC1 in a manner that is physiologic and may correlate with disease. Jade-1 may be an important therapeutic target in renal cystogenesis.

c-Met and NF-κB-dependent overexpression of Wnt7a and -7b and Pax2 promotes cystogenesis in polycystic kidney disease

The mechanisms of cystogenesis in autosomal dominant polycystic kidney disease (ADPKD) are not fully understood. Hyperactivation of the tyrosine kinase c-Met contributes to cyst formation, but we do not know the downstream mediators. Here, we found that hyperactivated c-Met led to increased NF-κB signaling, which in turn, drove de novo expression of Wnt7a and overexpression of Wnt7b in Pkd1(-/-) mouse kidneys. Hyperactivated Wnt signaling increased expression of the transcription factor Pax2 in the cells lining cysts. Furthermore, blocking Wnt signaling with DKK1 decreased cyst formation in an organ culture model of ADPKD. In summary, these results suggest that the c-Met/NF-κB/Wnt/Pax2 signaling transduction axis may provide pharmacological targets for the treatment of ADPKD.

Regulation of KCNQ1/KCNE1 by β-catenin

β-catenin, a multifunctional protein expressed in all tissues including the heart stimulates the expression of several genes important for cell proliferation. Signaling involving ß-catenin participates in directing cardiac development and in the pathophysiology of cardiac hypertrophy. Nothing is known, however, on the role of β-catenin in the regulation of cardiac ion channels. The present study explored the functional interaction of β-catenin and KCNE1/KCNQ1, the K⁺ channel complex underlying the slowly activating outwardly rectifying K⁺ current. To this end, KCNE1/KCNQ1 was expressed in Xenopus oocytes with and without β-catenin and the depolarization (up to + 80 mV) induced current (I(Ks)) was determined using the two-electrode voltage clamp. As a result, β-catenin enhanced I(Ks) by 30%. The effect of β-catenin on I(Ks) was not affected by actinomycin D (10 μM), an inhibitor of transcription, indicating that β-catenin was not effective as transcription factor. Confocal microscopy revealed that β-catenin enhanced the KCNE1/KCNQ1 protein abundance in the cell membrane. Exposure of the oocytes to brefeldin A (5 μM), an inhibitor of vesicle insertion, was followed by a decline of I(Ks), which was then similar in oocytes expressing KCNE1/KCNQ1 together with β-catenin and in oocytes expressing KCNE1/KCNQ1 alone. In conclusion, β-catenin enhances I(Ks) by increasing the KCNE1/KCNQ1 protein abundance in the cell membrane, an effect requiring vesicle insertion into the cell membrane.

Ciliogenesis in Caenorhabditis elegans requires genetic interactions between ciliary middle segment localized NPHP-2 (inversin) and transition zone-associated proteins

The cystic kidney diseases nephronophthisis (NPHP), Meckel-Gruber syndrome (MKS) and Joubert syndrome (JBTS) share an underlying etiology of dysfunctional cilia. Patients diagnosed with NPHP type II have mutations in the gene INVS (also known as NPHP2), which encodes inversin, a cilia localizing protein. Here, we show that the C. elegans inversin ortholog, NPHP-2, localizes to the middle segment of sensory cilia and that nphp-2 is partially redundant with nphp-1 and nphp-4 (orthologs of human NPHP1 and NPHP4, respectively) for cilia placement within the head and tail sensilla. nphp-2 also genetically interacts with MKS ciliopathy gene orthologs, including mks-1, mks-3, mks-6, mksr-1 and mksr-2, in a sensilla-dependent manner to control cilia formation and placement. However, nphp-2 is not required for correct localization of the NPHP- and MKS-encoded ciliary transition zone proteins or for intraflagellar transport (IFT). We conclude that INVS/NPHP2 is conserved in C. elegans and that nphp-2 plays an important role in C. elegans cilia by acting as a modifier of the NPHP and MKS pathways to control cilia formation and development.

Axonemal positioning and orientation in three-dimensional space for primary cilia: what is known, what is assumed, and what needs clarification

Two positional characteristics of the ciliary axoneme--its location on the plasma membrane as it emerges from the cell, and its orientation in three-dimensional (3D) space--are known to be critical for optimal function of actively motile cilia (including nodal cilia), as well as for modified cilia associated with special senses. However, these positional characteristics have not been analyzed to any significant extent for primary cilia. This review briefly summarizes the history of knowledge of these two positional characteristics across a wide spectrum of cilia, emphasizing their importance for proper function. Then the review focuses what is known about these same positional characteristics for primary cilia in all major tissue types where they have been reported. The review emphasizes major areas that would be productive for future research for understanding how positioning and 3D orientation of primary cilia may be related to their hypothesized signaling roles within different cellular populations.

Cilia, adenomatous polyposis coli and associated diseases

Cilium is a conservative cell organelle, found in many types of cell surfaces. Cilia are tail-like prominence protruding out of the cell surface, capable of locomotion and acting as the cell's signal transduction sensory organs with their complex structures and ingenious function. Studies have shown that ciliary pathological changes and defects are related to the development of many diseases, including renal cysts, infertility, organ reversal, obesity and so on. The inactivation and mutation of cilia-related proteins can cause tumors, such as neoplasms, intestinal cancer, myeloma, rhabdomyosarcoma and adenocarcinoma. Adenomatous polyposis coli (APC) is a kind of multifunctional protein encoded by the APC gene that participates in many vital activities of organisms. The mutation of APC can lead to familial adenomatous polyposis, and also has a role in the development of human tumors, such as gastric cancer, esophageal cancer and breast carcinoma. Recent studies indicate that the abnormal mutation of APC may lead to some diseases caused by abnormal growth of cilia. Herein, the development of studies on cilia, APC and associated diseases are summarized in brief.

Cilia and cell cycle re-entry: more than a coincidence

With the exception of the final stages of spermatogenesis in butterfly and some unicellular ciliates and flagellates, ciliated cells undergo cell division without cilia. This reciprocal relationship between cilia formation and cell division has prompted investigators to propose that ciliogenesis and cell cycle progression are mutually exclusive processes. Early work in fibroblasts showed that deciliation occurs in two waves, as cells depart from quiescence. The first wave of deciliation occurs before entry into S, while the second wave occurs between S and mitosis. Since then, it has remained a mystery whether and how (de)ciliation is coupled to the cell cycle and further, whether ciliation can affect cell cycle progression. Several recent publications provide evidence for a causative role of ciliary resorption in influencing the duration of the G1 phase of the cell cycle impacting on several developmental processes, including left-right patterning, kidney, skeletal and brain development. This body of work argues for the existence of a molecular crosstalk between ciliary factors and regulators of the cell cycle. Here, we review the evidence connecting primary cilia and the cell cycle and evaluate the idea that the primary cilium may function as a physical checkpoint in cell cycle re-entry.

Ectopic expression of cadherin 8 is sufficient to cause cyst formation in a novel 3D collagen matrix renal tubule culture

While a variety of genetic mutations have been shown to be associated with renal cyst formation, mechanisms of renal cyst formation are largely unknown. In prior communications we described alterations in E-cadherin assembly in cultured cystic epithelial cells (Charron AJ, Nakamura S, Bacallao R, Wandinger-Ness A. J Cell Biol 149: 111-124, 2000). Using the same cell line we assayed cadherin expression by RT-PCR using primer pairs that anneal to highly conserved sequences of cadherin genes but flank informative regions of cadherins. Using this approach we found that autosomal dominant polycystic kidney disease (ADPKD) cells express cadherin 8, a neuronal cadherin with limited expression in the kidney. Immunohistochemistry confirmed cadherin 8 expression in cystic epithelia. To test the functional significance of cadherin 8 expression in renal epithelial cells, we adapted a three-dimensional collagen culture method in which HK-2 cells form tubule structures and microinjected adenovirus into the matrix space surrounding tubule structures. Adenovirus expressing cadherin 8 under the control of a tet promoter caused cyst structures to grow out of the tubules when coinjected with adenovirus expressing a tet transactivator. Microinjection of single adenovirus expressing either tet transactivator or cadherin 8 failed to cause cyst formation. When doxycycline was added to the culture, following coinjection of adenovirus, there was a dose-response reduction in cadherin 8 expression and cyst formation. Similarly, HK-2 cells transfected with Flag-tagged cadherin 8 form cysts in addition to tubular structures. HK-2 cells transfected with Flag-tagged N-cadherin do not form cysts. These data suggest that ectopic expression of cadherin 8 in renal epithelial cells is sufficient to cause the morphogenic pattern of cyst formation.

Molecular genetics and pathogenic mechanisms for the severe ciliopathies: insights into neurodevelopment and pathogenesis of neural tube defects

Meckel-Gruber syndrome (MKS) is a severe autosomal recessively inherited disorder characterized by developmental defects of the central nervous system that comprise neural tube defects that most commonly present as occipital encephalocele. MKS is considered to be the most common syndromic form of neural tube defect. MKS is genetically heterogeneous with six known disease genes: MKS1, MKS2/TMEM216, MKS3/TMEM67, RPGRIP1L, CEP290, and CC2D2A with the encoded proteins all implicated in the correct function of primary cilia. Primary cilia are microtubule-based organelles that project from the apical surface of most epithelial cell types. Recent progress has implicated the involvement of cilia in the Wnt and Shh signaling pathways and has led to an understanding of their role in normal mammalian neurodevelopment. The aim of this review is to provide an overview of the molecular genetics of the human disorder, and to assess recent insights into the etiology and molecular cell biology of severe ciliopathies from mammalian animal models of MKS.

Epithelial-to-mesenchymal transition in cyst lining epithelial cells in an orthologous PCK rat model of autosomal-recessive polycystic kidney disease

In polycystic kidney disease (PKD), cyst lining cells show polarity abnormalities. Recent studies have demonstrated loss of cell contact in cyst cells, suggesting induction of epithelial-to-mesenchymal transition (EMT). Recently, EMT has been implicated in the pathogenesis of PKD. To explore further evidence of EMT in PKD, we examined age- and segment-specific expression of adhesion molecules and mesenchymal markers in PCK rats, an orthologous model of human autosomal-recessive PKD. Kidneys from 5 male PCK and 5 control rats each at 0 days, 1, 3, 10, and 14 wk, and 4 mo of age were serially sectioned and stained with segment-specific markers and antibodies against E-cadherin, Snail1, β-catenin, and N-cadherin. mRNAs for E-cadherin and Snail1 were quantified by real-time PCR. Vimentin, fibronectin, and α-smooth muscle actin (α-SMA) expressions were assessed as mesenchymal markers. E-cadherin expression pattern was correlated with the disease pathology in that tubule segments showing the highest expression in control had much severer cyst formation in PCK rats. In PCK rats, E-cadherin and β-catenin in cystic tubules was attenuated and localized to lateral areas of cell-cell contact, whereas nuclear expression of Snail1 increased in parallel with cyst enlargement. Some epithelial cells in large cysts derived from these segments, especially in adjacent fibrotic areas, showed positive immunoreactivity for vimentin and fibronectin. In conclusion, these findings suggest that epithelial cells in cysts acquire mesenchymal features in response to cyst enlargement and participate in progressive renal fibrosis. Our study clarified the nephron segment-specific cyst profile related to EMT in PCK rats. EMT may play a key role in polycystic kidney disease.

Inversin relays Frizzled-8 signals to promote proximal pronephros development

Mutations of inversin cause type II nephronophthisis, an infantile autosomal recessive disease characterized by cystic kidney disease and developmental defects. Inversin regulates Wnt signaling and is required for convergent extension movements during early embryogenesis. We now show that Inversin is essential for Xenopus pronephros formation, involving two distinct and opposing forms of cell movements. Knockdown of Inversin abrogated both proximal pronephros extension and distal tubule differentiation, phenotypes similar to that of Xenopus deficient in Frizzled-8. Exogenous Inversin rescued the pronephric defects caused by lack of Frizzled-8, indicating that Inversin acts downstream of Frizzled-8 in pronephros morphogenesis. Depletion of Inversin prevents the recruitment of Dishevelled in response to Frizzled-8 and impeded the accumulation of Dishevelled at the apical membrane of tubular epithelial cells in vivo. Thus, defective tubule morphogenesis seems to contribute to the renal pathology observed in patients with nephronophthisis type II.