Endothelial cells from humans and mice with polycystic kidney disease are characterized by polyploidy and chromosome segregation defects through survivin down-regulation

Identifying the roles of miR-17 in ciliogenesis and cell cycle

Emerging evidence suggests a significant contribution of primary cilia to cell division and proliferation. MicroRNAs, especially miR-17, contribute to cell cycle regulation and proliferation. Recent investigations have highlighted the dysregulated expression of miR-17 in various malignancies, underlining its potential role in cancer. However, the correlation between primary cilia and miR-17 has yet to be fully elucidated. The present study examines the presence of miR-17 in primary cilia. The miR-17 expression is studied in selected ciliary protein knockdown cells. Using in situ hybridization (ISH), we identified the subcellular localization of miR-17 in both cilium and cell body. We confirmed the importance of miR-17, progesterone receptor membrane component-2 (PGRMC2), and monosialodihexosylganglioside (GM3S) in cilia formation, as shown by the significant reduction in cilia and cilia length in knockdown cells compared to control. We also demonstrated the involvement of PGRMC2, GM3S, polycystin-2 (PKD2), and miR-17 in cellular proliferation and cell growth. Our studies revealed a hyperproliferative effect in the knockdown cells compared to control cells, suggesting the regulatory roles of PGRMC2/GM3S/PKD2/miR-17 in promoting cell proliferation. Overall, our studies conclude that ciliary proteins are involved in cell division and proliferation. We further hypothesize that primary cilia can serve as compartments to store and control genetic materials, further implicating their complex involvement in cellular processes.

The Mechanosensitive Pkd2 Channel Modulates the Recruitment of Myosin II and Actin to the Cytokinetic Contractile Ring

Cytokinesis, the last step in cell division, separates daughter cells through mechanical force. This is often through the force produced by an actomyosin contractile ring. In fission yeast cells, the ring helps recruit a mechanosensitive ion channel, Pkd2, to the cleavage furrow, whose activation by membrane tension promotes calcium influx and daughter cell separation. However, it is unclear how the activities of Pkd2 may affect the actomyosin ring. Here, through both microscopic and genetic analyses of a hypomorphic pkd2 mutant, we examined the potential role of this essential gene in assembling the contractile ring. The pkd2-81KD mutation significantly increased the counts of the type II myosin heavy chain Myo2 (+18%), its regulatory light chain Rlc1 (+37%) and actin (+100%) molecules in the ring, compared to the wild type. Consistent with a regulatory role of Pkd2 in the ring assembly, we identified a strong negative genetic interaction between pkd2-81KD and the temperature-sensitive mutant myo2-E1. The pkd2-81KD myo2-E1 cells often failed to assemble a complete contractile ring. We conclude that Pkd2 modulates the recruitment of type II myosin and actin to the contractile ring, suggesting a novel calcium-dependent mechanism regulating the actin cytoskeletal structures during cytokinesis.

The mechanosensitive Pkd2 channel modulates the recruitment of myosin II and actin to the cytokinetic contractile ring

Cytokinesis, the last step in cell division, separate daughter cells through the force produced by an actomyosin contractile ring assembled at the equatorial plane. In fission yeast cells, the ring helps recruit a mechanosensitive ion channel Pkd2 to the cleavage furrow, whose activation by membrane tension promotes calcium influx and daughter cell separation. However, it is unclear how the activities of Pkd2 may affect the actomyosin ring. Here, through both microscopic and genetic analyses of a hypomorphic mutant of the essential pkd2 gene, we examine its potential role in assembling and constricting the contractile ring. The pkd2-81KD mutation significantly increased the number of type II myosin heavy chain Myo2 (+20%), its regulatory light chain Rlc1 (+37%) and actin (+20%) molecules in the ring, compared to the wild type. Consistent with a regulatory role of Pkd2 in the ring assembly, we identified a strong negative genetic interaction between pkd2-81KD and the temperature-sensitive mutant myo2-E1 . The pkd2-81KD myo2-E1 cells often failed to assemble a complete contractile ring. We conclude that Pkd2 modulates the recruitment of type II myosin and actin to the contractile ring, suggesting a novel calcium- dependent mechanism regulating the actin cytoskeletal structures during cytokinesis.

Brain microvascular endothelial cells possess a second cilium that arises from the daughter centriole

Primary cilia from the brain microvascular endothelial cells (ECs) are specialized cell-surface organelles involved in mediating sensory perception, cell signaling, and vascular stability. Immunofluorescence (IF) analysis of human primary brain microvascular ECs reveals two cilia per cell. To confirm the in vitro observation of the two-cilia phenotype in human primary brain ECs, ECs isolated from mouse brain were cultured and stained for cilium. Indeed, brain ECs from a ciliopathic mouse (polycystic kidney disease or Pkd2 -/-) also possess more than one cilium. Primary cilium emerges from the mother centriole. Centriole analysis by IF suggests that in brain ECs, markers for the mother and daughter centrioles stain both cilia, suggesting that the second cilium in brain ECs arises from the daughter centriole. Further quantification of cilia size in brain ECs revealed that cilia arising from the mother centriole are bigger in size compared with cilia from the daughter centriole. Cell cycle analyses using immunoblotting and flow cytometry suggest that the ciliary proteins ARL13B and IFT88 involved in brain EC ciliogenesis are highly expressed only in the G0/G1 and S phases of the cell cycle. The IF analyses of cells arrested at different cell cycle stages indicate that the two-cilia phenotype is highly specific to the G0/G1 phase. Our findings suggest that in addition to the mother centriole, the daughter centriole also plays a role in ciliogenesis in primary cultured ECs.

Folate conjugated nanomedicines for selective inhibition of mTOR signaling in polycystic kidneys at clinically relevant doses

Although rapamycin is a very effective drug for rodents with polycystic kidney disease (PKD), it is not encouraging in the clinical trials due to the suboptimal dosages compelled by the off-target side effects. We here report the generation, characterization, specificity, functionality, pharmacokinetic, pharmacodynamic and toxicology profiles of novel polycystic kidney-specific-targeting nanoparticles (NPs). We formulated folate-conjugated PLGA-PEG NPs, which can be loaded with multiple drugs, including rapamycin (an mTOR inhibitor) and antioxidant 4-hydroxy-TEMPO (a nephroprotective agent). The NPs increased the efficacy, potency and tolerability of rapamycin resulting in an increased survival rate and improved kidney function by decreasing side effects and reducing biodistribution to other organs in PKD mice. The daily administration of rapamycin-alone (1 mg/kg/day) could now be achieved with a weekly injection of NPs containing rapamycin (379 μg/kg/week). This polycystic kidney-targeting nanotechnology, for the first time, integrated advances in the use of 1) nanoparticles as a delivery cargo, 2) folate for targeting, 3) near-infrared Cy5-fluorophore for in vitro and in vivo live imaging, 4) rapamycin as a pharmacological therapy, and 5) TEMPO as a combinational therapy. The slow sustained-release of rapamycin by polycystic kidney-targeting NPs demonstrates a new era of nanomedicine in treatment for chronic kidney diseases at clinically relevant doses.

Polycystin-1 Interacting Protein-1 (CU062) Interacts with the Ectodomain of Polycystin-1 (PC1)

The PKD1 gene, encoding protein polycystin-1 (PC1), is responsible for 85% of cases of autosomal dominant polycystic kidney disease (ADPKD). PC1 has been shown to be present in urinary exosome-like vesicles (PKD-ELVs) and lowered in individuals with germline PKD1 mutations. A label-free mass spectrometry comparison of urinary PKD-ELVs from normal individuals and those with PKD1 mutations showed that several proteins were reduced to a degree that matched the decrease observed in PC1 levels. Some of these proteins, such as polycystin-2 (PC2), may be present in a higher-order multi-protein assembly with PC1-the polycystin complex (PCC). CU062 (Q9NYP8) is decreased in ADPKD PKD-ELVs and, thus, is a candidate PCC component. CU062 is a small glycoprotein with a signal peptide but no transmembrane domain and can oligomerize with itself and interact with PC1. We investigated the localization of CU062 together with PC1 and PC2 using immunofluorescence (IF). In nonconfluent cells, all three proteins were localized in close proximity to focal adhesions (FAs), retraction fibers (RFs), and RF-associated extracellular vesicles (migrasomes). In confluent cells, primary cilia had PC1/PC2/CU062 + extracellular vesicles adherent to their plasma membrane. In cells exposed to mitochondrion-decoupling agents, we detected the development of novel PC1/CU062 + ring-like structures that entrained swollen mitochondria. In contact-inhibited cells under mitochondrial stress, PC1, PC2, and CU062 were observed on large, apically budding extracellular vesicles, where the proteins formed a reticular network on the membrane. CU062 interacts with PC1 and may have a role in the identification of senescent mitochondria and their extrusion in extracellular vesicles.

Tubular-specific expression of HIV protein Vpr leads to severe tubulointerstitial damage accompanied by progressive fibrosis and cystic development

Chronic kidney disease (CKD) is a common cause of morbidity in human immunodeficiency virus (HIV)-positive individuals. HIV infection leads to a wide spectrum of kidney cell damage, including tubular epithelial cell (TEC) injury. Among the HIV-1 proteins, the pathologic effects of viral protein R (Vpr) are well established and include DNA damage response, cell cycle arrest, and cell death. Several in vitro studies have unraveled the molecular pathways driving the cytopathic effects of Vpr in tubular epithelial cells. However, the in vivo effects of Vpr on tubular injury and CKD pathogenesis have not been thoroughly investigated. Here, we use a novel inducible tubular epithelial cell-specific Vpr transgenic mouse model to show that Vpr expression leads to progressive tubulointerstitial damage, interstitial inflammation and fibrosis, and tubular cyst development. Importantly, Vpr-expressing tubular epithelial cells displayed significant hypertrophy, aberrant cell division, and atrophy; all reminiscent of tubular injuries observed in human HIV-associated nephropathy (HIVAN). Single-cell RNA sequencing analysis revealed the Vpr-mediated transcriptomic responses in specific tubular subsets and highlighted the potential multifaceted role of p53 in the regulation of cell metabolism, proliferation, and death pathways in Vpr-expressing tubular epithelial cells. Thus, our study demonstrates that HIV Vpr expression in tubular cells is sufficient to induce HIVAN-like tubulointerstitial damage and fibrosis, independent of glomerulosclerosis and proteinuria. Additionally, as this new mouse model develops progressive CKD with diffuse fibrosis and kidney failure, it can serve as a useful tool to examine the mechanisms of kidney disease progression and fibrosis in vivo.

Single-cell RNA sequencing reveals differential cell cycle activity in key cell populations during nephrogenesis

The kidney is a complex organ composed of more than 30 terminally differentiated cell types that all are required to perform its numerous homeostatic functions. Defects in kidney development are a significant cause of chronic kidney disease in children, which can lead to kidney failure that can only be treated by transplant or dialysis. A better understanding of molecular mechanisms that drive kidney development is important for designing strategies to enhance renal repair and regeneration. In this study, we profiled gene expression in the developing mouse kidney at embryonic day 14.5 at single-cell resolution. Consistent with previous studies, clusters with distinct transcriptional signatures clearly identify major compartments and cell types of the developing kidney. Cell cycle activity distinguishes between the "primed" and "self-renewing" sub-populations of nephron progenitors, with increased expression of the cell cycle-related genes Birc5, Cdca3, Smc2 and Smc4 in "primed" nephron progenitors. In addition, augmented expression of cell cycle related genes Birc5, Cks2, Ccnb1, Ccnd1 and Tuba1a/b was detected in immature distal tubules, suggesting cell cycle regulation may be required for early events of nephron patterning and tubular fusion between the distal nephron and collecting duct epithelia.

OFD Type I syndrome: lessons learned from a rare ciliopathy

The OFD1 gene was initially identified as the gene responsible for the X-linked dominant male lethal OFD type I syndrome, a developmental disorder ascribed to cilia disfunction. The transcript has been subsequently associated to four different X-linked recessive conditions, namely Joubert syndrome, retinitis pigmentosa, primary ciliary dyskinesia and Simpson-Golabi-Behmel type 2 syndrome. The centrosomal/basal body OFD1 protein has indeed been shown to be required for primary cilia formation and left-right asymmetry. The protein is also involved in other tasks, e.g. regulation of cellular protein content, constrain of the centriolar length, chromatin remodeling at DNA double strand breaks, control of protein quality balance and cell cycle progression, which might be mediated by non-ciliary activities. OFD1 represents a paradigmatic model of a protein that performs its diverse actions according to the cell needs and depending on the subcellular localization, the cell type/tissue and other possible factors still to be determined. An increased number of multitask protein, such as OFD1, may represent a partial explanation to human complexity, as compared with less complex organisms with an equal or slightly lower number of proteins.

Epithelial proliferation and cell cycle dysregulation in kidney injury and disease

Various cellular insults and injury to renal epithelial cells stimulate repair mechanisms to adapt and restore the organ homeostasis. Renal tubular epithelial cells are endowed with regenerative capacity, which allows for a restoration of nephron function after acute kidney injury. However, recent evidence indicates that the repair is often incomplete, leading to maladaptive responses that promote the progression to chronic kidney disease. The dysregulated cell cycle and proliferation is also a key feature of renal tubular epithelial cells in polycystic kidney disease and HIV-associated nephropathy. Therefore, in this review, we provide an overview of cell cycle regulation and the consequences of dysregulated cell proliferation in acute kidney injury, polycystic kidney disease, and HIV-associated nephropathy. An increased understanding of these processes may help define better targets for kidney repair and combat chronic kidney disease progression.

Differential modulation of SK channel subtypes by phosphorylation

Small-conductance Ca2+-activated K+ (SK) channels are voltage-independent and are activated by Ca2+ binding to the calmodulin constitutively associated with the channels. Both the pore-forming subunits and the associated calmodulin are subject to phosphorylation. Here, we investigated the modulation of different SK channel subtypes by phosphorylation, using the cultured endothelial cells as a tool. We report that casein kinase 2 (CK2) negatively modulates the apparent Ca2+ sensitivity of SK1 and IK channel subtypes by more than 5-fold, whereas the apparent Ca2+ sensitivity of the SK3 and SK2 subtypes is only reduced by ∼2-fold, when heterologously expressed on the plasma membrane of cultured endothelial cells. The SK2 channel subtype exhibits limited cell surface expression in these cells, partly as a result of the phosphorylation of its C-terminus by cyclic AMP-dependent protein kinase (PKA). SK2 channels expressed on the ER and mitochondria membranes may protect against cell death. This work reveals the subtype-specific modulation of the apparent Ca2+ sensitivity and subcellular localization of SK channels by phosphorylation in cultured endothelial cells.

Portal hypertension: An uncommon presentation of Caroli's syndrome

Portal hypertension is not a classical presentation of Caroli's syndrome. However, some young children can present with overt signs and symptoms indicative of advanced disease state despite the improvement in imaging technology which has decreased its diagnostic age. High index of clinical suspicion can help in timely diagnosis and management.

Exploring Key Challenges of Understanding the Pathogenesis of Kidney Disease in Bardet-Biedl Syndrome

Bardet–Biedl syndrome (BBS) is a rare pleiotropic inherited disorder known as a ciliopathy. Kidney disease is a cardinal clinical feature; however, it is one of the less investigated traits. This study is a comprehensive analysis of the literature aiming to collect available information providing mechanistic insights into the pathogenesis of kidney disease by analyzing clinical and basic science studies focused on this issue. The analysis revealed that the syndrome is either clinically and genetically heterogenous, with 24 genes discovered to date, but with 3 genes (BBS1, BBS2, and BBS10) accounting for almost 50% of diagnoses; genotype–phenotype correlation studies showed that patients with BBS1 mutations have a less severe renal phenotype than the other 2 most common loci; in addition, truncating rather than missense mutations are more likely to cause kidney disease. However, significant intrafamilial clinical variability has been described, with no clear explanation to date. In mice kidneys, Bbs genes have relative low expression levels, in contrast with other common affected organs, like the retina; surprisingly, Bbs1 is the only locus with basal overexpression in the kidney. In vitro studies indicate that signalling pathways involved in embryonic kidney development and repair are affected in the context of BBS depletion; in mice, kidney disease does not have a full penetrance; when present, it resembles human phenotype and shows an age-dependent progression. Data on the exact contribution of local versus systemic consequences of Bbs dysfunction are scanty and further investigations are required to get firm conclusions.

Rapamycin treatment correlates changes in primary cilia expression with cell cycle regulation in epithelial cells

Primary cilia are sensory organelles that regulate cell cycle and signaling pathways. In addition to its association with cancer, dysfunction of primary cilia is responsible for the pathogenesis of polycystic kidney disease (PKD) and other ciliopathies. Because the association between cilia formation or length and cell cycle or division is poorly understood, we here evaluated their correlation in this study. Using Spectral Karyotyping (SKY) technique, we showed that PKD and the cancer/tumorigenic epithelial cells PC3, DU145, and NL20-TA were associated with abnormal ploidy. We also showed that PKD and the cancer epithelia were highly proliferative. Importantly, the cancer epithelial cells had a reduction in the presence and/or length of primary cilia relative to the normal kidney (NK) cells. We then used rapamycin to restore the expression and length of primary cilia in these cells. Our subsequent analyses indicated that both the presence and length of primary cilia were inversely correlated with cell proliferation. Collectively, our data suggest that restoring the presence and/or length of primary cilia may serve as a novel approach to inhibit cancer cell proliferation.

Collateral Vessels Have Unique Endothelial and Smooth Muscle Cell Phenotypes

Collaterals are unique blood vessels present in the microcirculation of most tissues that, by cross-connecting a small fraction of the outer branches of adjacent arterial trees, provide alternate routes of perfusion. However, collaterals are especially susceptible to rarefaction caused by aging, other vascular risk factors, and mouse models of Alzheimer’s disease—a vulnerability attributed to the disturbed hemodynamic environment in the watershed regions where they reside. We examined the hypothesis that endothelial and smooth muscle cells (ECs and SMCs, respectively) of collaterals have specializations, distinct from those of similarly-sized nearby distal-most arterioles (DMAs) that maintain collateral integrity despite their continuous exposure to low and oscillatory/disturbed shear stress, high wall stress, and low blood oxygen. Examination of mouse brain revealed the following: Unlike the pro-inflammatory cobble-stoned morphology of ECs exposed to low/oscillatory shear stress elsewhere in the vasculature, collateral ECs are aligned with the vessel axis. Primary cilia, which sense shear stress, are present, unexpectedly, on ECs of collaterals and DMAs but are less abundant on collaterals. Unlike DMAs, collaterals are continuously invested with SMCs, have increased expression of Pycard, Ki67, Pdgfb, Angpt2, Dll4, Ephrinb2, and eNOS, and maintain expression of Klf2/4. Collaterals lack tortuosity when first formed during development, but tortuosity becomes evident within days after birth, progresses through middle age, and then declines—results consistent with the concept that collateral wall cells have a higher turnover rate than DMAs that favors proliferative senescence and collateral rarefaction. In conclusion, endothelial and SMCs of collaterals have morphologic and functional differences from those of nearby similarly sized arterioles. Future studies are required to determine if they represent specializations that counterbalance the disturbed hemodynamic, pro-inflammatory, and pro-proliferative environment in which collaterals reside and thus mitigate their risk factor-induced rarefaction.

The Role of the Primary Cilium in Sensing Extracellular pH

Biosensors on the membrane of the vascular endothelium are responsible for sensing mechanical and chemical signals in the blood. Transduction of these stimuli into intracellular signaling cascades regulate cellular processes including ion transport, gene expression, cell proliferation, and/or cell death. The primary cilium is a well-known biosensor of shear stress but its role in sensing extracellular pH change has never been examined. As a cellular extension into the immediate microenvironment, the cilium could be a prospective sensor for changes in pH and regulator of acid response in cells. We aim to test our hypothesis that the primary cilium plays the role of an acid sensor in cells using vascular endothelial and embryonic fibroblast cells as in vitro models. We measure changes in cellular pH using pH-sensitive 2',7'-biscarboxyethy1-5,6-carboxyfluorescein acetoxy-methylester (BCECF) fluorescence and mitogen-activated protein kinase (MAPK) activity to quantify responses to both extracellular pH (pH_o) and intracellular pH (pH_i) changes. Our studies show that changes in pH_o affect pH_i in both wild-type and cilia-less Tg737 cells and that the kinetics of the pH_i response are similar in both cells. Acidic pH_o or pH_i was observed to change the length of primary cilia in wild-type cells while the cilia in Tg737 remained absent. Vascular endothelial cells respond to acidic pH through activation of ERK1/2 and p38-mediated signaling pathways. The cilia-less Tg737 cells exhibit delayed responsiveness to pH_o dependent and independent pH_i acidification as depicted in the phosphorylation profile of ERK1/2 and p38. Otherwise, intracellular pH homeostatic response to acidic pH_o is similar between wild-type and Tg737 cells, indicating that the primary cilia may not be the sole sensor for physiological pH changes. These endothelial cells respond to pH changes with a predominantly K⁺-dependent pH_i recovery mechanism, regardless of ciliary presence or absence.

Caroli syndrome: a clinical case with detailed histopathological analysis

Herein we present a clinical case of the Caroli syndrome caused by the compound heterozygous mutation in the PKHD1 gene. Histopathological assessment of liver detected biliary cirrhosis, numerous dilated bile ducts of various sizes, hyperplastic cholangiocytes containing a large amount of acid mucopolysaccharides, decreased ß-tubulin expression and increased proliferation of cholangiocytes. A significant proportion of hepatic tissue was composed of giant cysts lined with a single layer of cholangiocytes, containing pus and bile in its lumen and surrounded by granulation tissue. An accumulation of neutrophils in the lumen of the bile ducts was observed, as well as an infiltration of the ducts and cysts surrounding connective tissue by CD4⁺ and to a lesser extent CD8⁺ lymphocytes. This may be caused by the expression of HLA-DR by cholangiocytes. Atrophy and desquamation of the epithelium of collecting tubules with the formation of microcysts were detected in the kidneys without a clinically significant loss of renal function. Morphopathogenetic mechanisms of the Caroli syndrome can be targets for a potential pathogenetic therapy and prevention of its manifestations and complications.

Role of endothelial primary cilia as fluid mechanosensors on vascular health

Primary cilia are microtubule-based organelles that protrude from the cell surface of many mammalian cell types, including endothelial and epithelial cells, osteoblasts, and neurons. These antennal-like projections enable cells to detect extracellular stimuli and elicit responses via intracellular signaling mechanisms. Primary cilia on endothelial cells lining blood vessels function as calcium-dependent mechanosensors that sense blood flow. In doing so, they facilitate the regulation of hemodynamic parameters within the vascular system. Defects in endothelial primary cilia result in inappropriate blood flow-induced responses and contribute to the development of vascular dysfunctions, including atherosclerosis, hypertension, and aneurysms. This review examines the current understanding of vascular endothelial cilia structure and function and their role in the vascular system. Future directions for primary cilia research and treatments for ciliary-based pathologies are discussed.

IFT proteins spatially control the geometry of cleavage furrow ingression and lumen positioning

Cytokinesis mediates the physical separation of dividing cells and, in 3D epithelia, provides a spatial landmark for lumen formation. Here, we unravel an unexpected role in cytokinesis for proteins of the intraflagellar transport (IFT) machinery, initially characterized for their ciliary role and their link to polycystic kidney disease. Using 2D and 3D cultures of renal cells, we show that IFT proteins are required to correctly shape the central spindle, to control symmetric cleavage furrow ingression and to ensure central lumen positioning. Mechanistically, IFT88 directly interacts with the kinesin MKLP2 and is essential for the correct relocalization of the Aurora B/MKLP2 complex to the central spindle. IFT88 is thus required for proper centralspindlin distribution and central spindle microtubule organization. Overall, this work unravels a novel non-ciliary mechanism for IFT proteins at the central spindle, which could contribute to kidney cyst formation by affecting lumen positioning.

Cytokinesis relies on central spindle organization and provides a spatial landmark for lumen formation. Here, the authors show that intraflagellar transport proteins are required for the localization of the cytokinetic regulator Aurora B and subsequent cleavage furrow ingression and lumen positioning.

Recent advances in the molecular diagnosis of polycystic kidney disease

INTRODUCTION

Polycystic kidney disease (PKD) is clinically and genetically heterogeneous and constitutes the most common heritable kidney disease. Most patients are affected by the autosomal dominant form (ADPKD) which generally is an adult-onset multisystem disorder. By contrast, the rarer recessive form ARPKD usually already manifests perinatally or in childhood. In some patients, however, ADPKD and ARPKD can phenotypically overlap with early manifestation in ADPKD and only late onset in ARPKD. Progressive fibrocystic renal changes are often accompanied by severe hepatobiliary changes or other extrarenal abnormalities. Areas covered: A reduced dosage of disease proteins disturbs cell homeostasis and explains a more severe clinical course in some PKD patients. Cystic kidney disease is also a common feature of other ciliopathies and genetic syndromes. Genetic diagnosis may guide clinical management and helps to avoid invasive measures and to detect renal and extrarenal comorbidities early in the clinical course. Expert Commentary: The broad phenotypic and genetic heterogeneity of cystic and polycystic kidney diseases make NGS a particularly powerful approach. Interpretation of data becomes the challenge and bench and bedside benefit from digitized multidisciplinary interrelationships.

Polycystin and calcium signaling in cell death and survival

Mutations in polycystin-1 (PC1) and polycystin-2 (PC2) result in a commonly occurring genetic disorder, called Autosomal Dominant Polycystic Kidney Disease (ADPKD), that is characterized by the formation and development of kidney cysts. Epithelial cells with loss-of-function of PC1 or PC2 show higher rates of proliferation and apoptosis and reduced autophagy. PC1 is a large multifunctional transmembrane protein that serves as a sensor that is usually found in complex with PC2, a calcium (Ca²⁺)-permeable cation channel. In addition to decreased Ca²⁺ signaling, several other cell fate-related pathways are de-regulated in ADPKD, including cAMP, MAPK, Wnt, JAK-STAT, Hippo, Src, and mTOR. In this review we discuss how polycystins regulate cell death and survival, highlighting the complexity of molecular cascades that are involved in ADPKD.

RAPAMYCIN INCREASES LENGTH AND MECHANOSENSORY FUNCTION OF PRIMARY CILIA IN RENAL EPITHELIAL AND VASCULAR ENDOTHELIAL CELLS

Primary cilia arebiophysically-sensitive organelles responsible for sensing fluid-flow and transducing this stimulus into intracellular responses. Previous studies have shown that the primary cilia mediate flow-induced calcium influx, and sensitivity of cilia function to flow is correlated to cilia length. Cells with abnormal cilia length or function can lead to a host of diseases that are collectively termed as ciliopathies. Rapamycin, a potent inhibitor of mTOR (mammalian target of rapamycin), has been demonstrated to be a potential pharmacological agent against the aberrant mTOR signaling seen in ciliopathies such as polycystic kidney disease (PKD) and tuberous sclerosis complex (TSC). Here we look at the effects of rapamycin on ciliary length and function for the first time. Compared to controls, primary cilia in rapamycin-treated porcine renal epithelial and mouse vascular endothelial cells showed a significant increase in length. Graded increases in fluid-shear stress further indicates that rapamycin enhances cilia sensitivity to fluid flow. Treatment with rapamycin led to G0 arrest in porcine epithelial cells while no significant change in cell cycle were observed in rapamycin-treated mouse epithelial or endothelial cells, indicating a species-specific effect of rapamycin. Given the previousin vitro and in vivo studies establishing rapamycin as a potential therapeutic agent for ciliopathies, such as PKD and TSC, our studies show that rapamycin enhances ciliary function and sensitivity to fluid flow. The results of our studies suggest a potential ciliotherapeutic effect of rapamycin.

Capillary endothelia from two ADPKD patients are polyploidy

Bilateral renal cyst formation is the main feature of autosomal dominant polycystic kidney disease (ADPKD). We and other laboratories have previously shown that cyst-lining epithelia of kidneys from ADPKD patients are characterized by polyploidy. In this report, we show that endothelia from the renal capillary beds of two ADPKD patients are also polyploidy. Spectral karyotyping study further confirms our flow cytometry analyses. We suggest that polyploidy may be used as a potential cellular marker in ADPKD.

The hallmarks of cancer: relevance to the pathogenesis of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a progressive inherited disorder in which renal tissue is gradually replaced with fluid-filled cysts, giving rise to chronic kidney disease (CKD) and progressive loss of renal function. ADPKD is also associated with liver ductal cysts, hypertension, chronic pain and extra-renal problems such as cerebral aneurysms. Intriguingly, improved understanding of the signalling and pathological derangements characteristic of ADPKD has revealed marked similarities to those of solid tumours, even though the gross presentation of tumours and the greater morbidity and mortality associated with tumour invasion and metastasis would initially suggest entirely different disease processes. The commonalities between ADPKD and cancer are provocative, particularly in the context of recent preclinical and clinical studies of ADPKD that have shown promise with drugs that were originally developed for cancer. The potential therapeutic benefit of such repurposing has led us to review in detail the pathological features of ADPKD through the lens of the defined, classic hallmarks of cancer. In addition, we have evaluated features typical of ADPKD, and determined whether evidence supports the presence of such features in cancer cells. This analysis, which places pathological processes in the context of defined signalling pathways and approved signalling inhibitors, highlights potential avenues for further research and therapeutic exploitation in both diseases.

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.

ARPKD and early manifestations of ADPKD: the original polycystic kidney disease and phenocopies

Renal cysts are clinically and genetically heterogeneous conditions. Polycystic kidney disease (PKD) is common and its characterization has paved the way for the identification of a growing number of cilia-related disorders (ciliopathies) of which most show cystic kidneys. While the recessive form of PKD (ARPKD) virtually always presents in childhood, early onset can, in some instances, also occur in the dominant form (ADPKD). Both ADPKD genes (PKD1 and PKD2) can also be inherited in a recessive way, making the story more complex with evidence for a dosage-sensitive network. Several phenocopies are known, and mutations in HNF1ß or genes that typically cause other ciliopathies, such as nephronophthisis, Bardet-Biedl, Joubert syndrome and related disorders, can mimic PKD. An accurate genetic diagnosis is crucial for genetic counseling, prenatal diagnostics, and the clinical management of patients and their families. The increasing number of genes that have to be considered in patients with cystic kidney disease is challenging to address by conventional techniques and largely benefits from next-generation sequencing-based approaches. The parallel analysis of targeted genes considerably increases the detection rate, allows for better interpretation of identified variants, and avoids genetic misdiagnoses.

[Non-ciliary functions of cilia proteins]

Cilia proteins have long been characterized for their role in cilia formation and function, and their implications in ciliopathies. However, several cellular defects induced by cilia proteins deregulation suggest that they could have non-ciliary roles. Indeed, several non-ciliary functions have been recently characterized for cilia proteins including roles in intra-cellular and in vesicular transport, in spindle orientation or in the maintenance of genomic stability. These observations thus raise the crucial question of the contribution of non-ciliary functions of cilia proteins to the pathological manifestations associated with ciliopathies such as polycystic kidney disease.

Endothelial dysfunction and oxidative stress in polycystic kidney disease

Cardiovascular disease (CVD) is the leading cause of premature mortality in ADPKD patients. The aim was to identify potential serum biomarkers associated with the severity of ADPKD. Serum samples from a homogenous group of 61 HALT study A ADPKD patients [early disease group with estimated glomerular filtration rate (eGFR) >60 ml·min(-1)·1.73 m(-2)] were compared with samples from 49 patients from the HALT study B group with moderately advanced disease (eGFR 25-60 ml·min(-1)·1.73 m(-2)). Targeted tandem-mass spectrometry analysis of markers of endothelial dysfunction and oxidative stress was performed and correlated with eGFR and total kidney volume normalized to the body surface area (TKV/BSA). ADPKD patients with eGFR >60 ml·min(-1)·1.73 m(-2) showed higher levels of CVD risk markers asymmetric and symmetric dimethylarginine (ADMA and SDMA), homocysteine, and S-adenosylhomocysteine (SAH) compared with the healthy controls. Upon adjustments for age, sex, systolic blood pressure, and creatinine, SDMA, homocysteine, and SAH remained negatively correlated with eGFR. Resulting cellular methylation power [S-adenosylmethionine (SAM)/SAH ratio] correlated with the reduction of renal function and increase in TKV. Concentrations of prostaglandins (PGs), including oxidative stress marker 8-isoprostane, as well as PGF2α, PGD₂, and PGE₂, were markedly elevated in patients with ADPKD compared with healthy controls. Upon adjustments for age, sex, systolic blood pressure, and creatinine, increased PGD₂ and PGF₂α were associated with reduced eGFR, whereas 8-isoprostane and again PGF₂α were associated with an increase in TKV/BSA. Endothelial dysfunction and oxidative stress are evident early in ADPKD patients, even in those with preserved kidney function. The identified pathways may provide potential therapeutic targets for slowing down the disease progression.

L-type calcium channel modulates cystic kidney phenotype

In polycystic kidney disease (PKD), abnormal proliferation and genomic instability of renal epithelia have been associated with cyst formation and kidney enlargement. We recently showed that L-type calcium channel (CaV1.2) is localized to primary cilia of epithelial cells. Previous studies have also shown that low intracellular calcium level was associated with the hyperproliferation phenotype in the epithelial cells. However, the relationship between calcium channel and cystic kidney phenotype is largely unknown. In this study, we generated cells with somatic deficient Pkd1 or Pkd2 to examine ciliary CaV1.2 function via lentiviral knockdown or pharmacological verapamil inhibition. Although inhibition of CaV1.2 expression or function did not change division and growth patterns in wild-type epithelium, it led to hyperproliferation and polyploidy in mutant cells. Lack of CaV1.2 in Pkd mutant cells also decreased the intracellular calcium level. This contributed to a decrease in CaM kinase activity, which played a significant role in regulating Akt and Erk signaling pathways. Consistent with our in vitro results, CaV1.2 knockdown in zebrafish and Pkd1 heterozygous mice facilitated the formation of kidney cysts. Larger cysts were developed faster in Pkd1 heterozygous mice with CaV1.2 knockdown. Overall, our findings emphasized the importance of CaV1.2 expression in kidneys with somatic Pkd mutation. We further suggest that CaV1.2 could serve as a modifier gene to cystic kidney phenotype.

Ciliotherapy: a novel intervention in polycystic kidney disease

Background

Ciliopathies are a group of diseases associated with abnormal structure or function of primary cilia. Ciliopathies include polycystic kidney disease (PKD), a pathology associated with vascular hypertension. We previously showed that cilia length regulates cilia function, and cilia function is required for nitric oxide (NO) biosynthesis in endothelial cells. Because patients with PKD show abnormal sensory cilia function, the aim of our current study was to search for a targeted therapy focused on primary cilia, which we refer to as ‘ciliotherapy’.

Methods and Results

In the present studies, our in vitro analyses refined fenoldopam as an equipotent and more specific dopaminergic agonist to regulate cilia length and function. Our in vivo studies indicated that fenoldopam increased cilia length and serum NO thereby reducing blood pressure in a PKD mouse model. Our crossover, multicenter, double-blind and placebo-controlled clinical study further indicated that cilia-targeting therapy showed an overall reduction in mean arterial pressure in PKD patients.

Conclusions

Overall, our studies provide the first evidence of ciliotherapy as an innovative intervention in patients with abnormal primary cilia.

Renal-retinal ciliopathy gene Sdccag8 regulates DNA damage response signaling

Nephronophthisis-related ciliopathies (NPHP-RCs) are developmental and degenerative kidney diseases that are frequently associated with extrarenal pathologies such as retinal degeneration, obesity, and intellectual disability. We recently identified mutations in a gene encoding the centrosomal protein SDCCAG8 as causing NPHP type 10 in humans. To study the role of Sdccag8 in disease pathogenesis, we generated a Sdccag8 gene-trap mouse line. Homozygous Sdccag8(gt/gt) mice lacked the wild-type Sdccag8 transcript and protein, and recapitulated the human phenotypes of NPHP and retinal degeneration. These mice exhibited early onset retinal degeneration that was associated with rhodopsin mislocalization in the photoreceptors and reduced cone cell numbers, and led to progressive loss of vision. By contrast, renal histologic changes occurred later, and no global ciliary defects were observed in the kidneys. Instead, renal pathology was associated with elevated levels of DNA damage response signaling activity. Cell culture studies confirmed the aberrant activation of DNA damage response in Sdccag8(gt/gt)-derived cells, characterized by elevated levels of γH2AX and phosphorylated ATM and cell cycle profile abnormalities. Our analysis of Sdccag8(gt/gt) mice indicates that the pleiotropic phenotypes in these mice may arise through multiple tissue-specific disease mechanisms.

Survivin-induced abnormal ploidy contributes to cystic kidney and aneurysm formation

BACKGROUND

Cystic kidneys and vascular aneurysms are clinical manifestations seen in patients with polycystic kidney disease, a cilia-associated pathology (ciliopathy). Survivin overexpression is associated with cancer, but the clinical pathology associated with survivin downregulation or knockout has never been studied before. The present studies aim to examine whether and how cilia function (Pkd1 or Pkd2) and structure (Tg737) play a role in cystic kidney and aneurysm through survivin downregulation.

METHODS AND RESULTS

Cysts and aneurysms from polycystic kidney disease patients, Pkd mouse, and zebrafish models are characterized by chromosome instability and low survivin expression. This triggers cytokinesis defects and formation of nuclear polyploidy or aneuploidy. In vivo conditional mouse and zebrafish models confirm that survivin gene deletion in the kidneys results in a cystic phenotype. As in hypertensive Pkd1, Pkd2, and Tg737 models, aneurysm formation can also be induced in vascular-specific normotensive survivin mice. Survivin knockout also contributes to abnormal oriented cell division in both kidney and vasculature. Furthermore, survivin expression and ciliary localization are regulated by flow-induced cilia activation through protein kinase C, Akt and nuclear factor-κB. Circumventing ciliary function by re-expressing survivin can rescue polycystic kidney disease phenotypes.

CONCLUSIONS

For the first time, our studies offer a unifying mechanism that explains both renal and vascular phenotypes in polycystic kidney disease. Although primary cilia dysfunction accounts for aneurysm formation and hypertension, hypertension itself does not cause aneurysm. Furthermore, aneurysm formation and cyst formation share a common cellular and molecular pathway involving cilia function or structure, survivin expression, cytokinesis, cell ploidy, symmetrical cell division, and tissue architecture orientation.

SIRT2 regulates ciliogenesis and contributes to abnormal centrosome amplification caused by loss of polycystin-1

The mechanisms underlying many of the human disease phenotypes associated with ciliary dysfunction and abnormal centrosome amplification have yet to be fully elucidated. Here, we present for the first time that SIRT2, a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, regulates ciliogenesis and centrosome amplification. Overexpression of SIRT2 in renal epithelial cells appeared to disrupt cilia formation, causing decreased numbers of cells with cilia and decreased cilia length, while inhibition of SIRT2 activity by nicotinamide treatment or knockdown of SIRT2 with siRNA was shown to block cilia disassembly during the cell cycle. Overexpression of SIRT2 in zebrafish decreased cilia numbers in Kupffer's vesicle, while morpholino knock down of SIRT2 increased cilia length. Aberrant centrosome amplification and polyploidy were seen with overexpression of SIRT2 in mouse inner medullary collecting duct 3 cells, similar to that observed following Pkd1 knockdown. SIRT2 was up-regulated in both Pkd1 mutant and knockdown cells. Depletion of SIRT2 prevented the abnormal centrosome amplification and polyploidy associated with loss of polycystin-1 (PC1) alone. Thus, we conclude that the aberrant centrosome amplification and polyploidy in Pkd1 mutant or depleted cells was mediated through overexpression of SIRT2. Our results suggest a novel function of SIRT2 in cilia dynamics and centrosome function, and in ciliopathy-associated disease progression.

Centrosomal abnormalities characterize human and rodent cystic cholangiocytes and are associated with Cdc25A overexpression

Hepatic cystogenesis in polycystic liver diseases is associated with abnormalities of cholangiocyte cilia. Given the crucial association between cilia and centrosomes, we tested the hypothesis that centrosomal defects occur in cystic cholangiocytes of rodents (Pkd2(WS25/-) mice and PCK rats) and of patients with polycystic liver diseases, contributing to disturbed ciliogenesis and cyst formation. We examined centrosomal cytoarchitecture in control and cystic cholangiocytes, the effects of centrosomal abnormalities on ciliogenesis, and the role of the cell-cycle regulator Cdc25A in centrosomal defects by depleting cholangiocytes of Cdc25A in vitro and in vivo and evaluating centrosome morphology, cell-cycle progression, proliferation, ciliogenesis, and cystogenesis. The cystic cholangiocytes had atypical centrosome positioning, supernumerary centrosomes, multipolar spindles, and extra cilia. Structurally aberrant cilia were present in cystic cholangiocytes during ciliogenesis. Depletion of Cdc25A resulted in i) a decreased number of centrosomes and multiciliated cholangiocytes, ii) an increased fraction of ciliated cholangiocytes with longer cilia, iii) a decreased proportion of cholangiocytes in G1/G0 and S phases of the cell cycle, iv) decreased cell proliferation, and v) reduced cyst growth in vitro and in vivo. Our data support the hypothesis that centrosomal abnormalities in cholangiocytes are associated with aberrant ciliogenesis and that accelerated cystogenesis is likely due to overexpression of Cdc25A, providing additional evidence that pharmacological targeting of Cdc25A has therapeutic potential in polycystic liver diseases.

Radiation-induced mitotic cell death and glioblastoma radioresistance: a new regulating pathway controlled by integrin-linked kinase, hypoxia-inducible factor 1 alpha and survivin in U87 cells

We have previously shown that integrin-linked kinase (ILK) regulates U87 glioblastoma cell radioresistance by modulating the main radiation-induced cell death mechanism in solid tumours, the mitotic cell death. To decipher the biological pathways involved in these mechanisms, we constructed a U87 glioblastoma cell model expressing an inducible shRNA directed against ILK (U87shILK). We then demonstrated that silencing ILK enhanced radiation-induced centrosome overduplication, leading to radiation-induced mitotic cell death. In this model, ionising radiations induce hypoxia-inducible factor 1 alpha (HIF-1α) stabilisation which is inhibited by silencing ILK. Moreover, silencing HIF-1α in U87 cells reduced the surviving fraction after 2 Gy irradiation by increasing cell sensitivity to radiation-induced mitotic cell death and centrosome amplification. Because it is known that HIF-1α controls survivin expression, we then looked at the ILK silencing effect on survivin expression. We show that survivin expression is decreased in U87shILK cells. Furthermore, treating U87 cells with the specific survivin suppressor YM155 significantly increased the percentage of giant multinucleated cells, centrosomal overduplication and thus U87 cell radiosensitivity. In consequence, we decipher here a new pathway of glioma radioresistance via the regulation of radiation-induced centrosome duplication and therefore mitotic cell death by ILK, HIF-1α and survivin. This work identifies new targets in glioblastoma with the intention of radiosensitising these highly radioresistant tumours.

Functional aspects of primary cilia in signaling, cell cycle and tumorigenesis

Dysfunctional cilia underlie a broad range of cellular and tissue phenotypes and can eventually result in the development of ciliopathies: pathologically diverse diseases that range from clinically mild to highly complex and severe multi-organ failure syndromes incompatible with neonatal life. Given that virtually all cells of the human body have the capacity to generate cilia, it is likely that clinical manifestations attributed to ciliary dysfunction will increase in the years to come. Disputed but nevertheless enigmatic is the notion that at least a subset of tumor phenotypes fit within the ciliopathy disease spectrum and that cilia loss may be required for tumor progression. Contending for the centrosome renders ciliation and cell division mutually exclusive; a regulated tipping of balance promotes either process. The mechanisms involved, however, are complex. If the hypothesis that tumorigenesis results from dysfunctional cilia is true, then why do the classic ciliopathies only show limited hyperplasia at best? Although disassembly of the cilium is a prerequisite for cell proliferation, it does not intrinsically drive tumorigenesis per se. Alternatively, we will explore the emerging evidence suggesting that some tumors depend on ciliary signaling. After reviewing the structure, genesis and signaling of cilia, the various ciliopathy syndromes and their genetics, we discuss the current debate of tumorigenesis as a ciliopathy spectrum defect, and describe recent advances in this fascinating field.

The Roles of Primary cilia in Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited genetic disorder that results in progressive renal cyst formation with ultimate loss of renal function and other systemic disorders. These systemic disorders include abnormalities in cardiovascular, portal, pancreatic and gastrointestinal systems. ADPKD is considered to be among the ciliopathy diseases due to the association with abnormal primary cilia function. In order to understand the full course of primary cilia and its association with ADPKD, the structure, functions and role of primary cilia have been meticulously investigated. As a result, the focus on primary cilia has emerged to support the vital roles of primary cilia in ADPKD. The primary cilia have been shown to have not only a mechanosensory function but also a chemosensory function. Both structural and functional defects in primary cilia result in cystic kidney disease and vascular hypertension. Thus, the mechanosenory and chemosensory functions will be analyzed in regards to ADPKD.

Non-motile primary cilia as fluid shear stress mechanosensors

Primary cilia are sensory organelles that transmit extracellular signals into intracellular biochemical responses. Structural and functional defects in primary cilia are associated with a group of human diseases, known as ciliopathies, with phenotypes ranging from cystic kidney and obesity to blindness and mental retardation. Primary cilia mediate mechano- and chemosensation in many cell types. The mechanosensory function of the primary cilia requires the atypical G-protein-coupled receptor polycystin-1 and the calcium-permeable nonselective cation channel polycystin-2. Mechanical stimulations such as fluid-shear stress of the primary cilia initiate intracellular calcium rise, nitric oxide release, and protein modifications. In this review, we describe a set of protocols for cell culture to promote ciliation, mechanical stimulations of the primary cilia, and measurements of calcium rise and nitric oxide release induced by fluid shear stress.

Cilostazol prevents endothelin-induced smooth muscle constriction and proliferation

Cilostazol is a phosphodiesterase inhibitor that has been shown to inhibit platelet activation. Endothelin is known to be the most potent endogenous growth promoting and vasoactive peptide. In patients and animal models with stroke, the level of circulating endothelin increases and complicates the recovery progress contributed by vascular constriction (an immediate pathology) and vascular proliferation (a long-term pathology). However, the effects of cilostazol on endothelin have not been explored. To demonstrate the dual-antagonizing effects of cilostazol on vasoconstriction and cell proliferation induced by endothelin, we used primary culture of mouse vascular smooth muscle cells in vitro, mouse femoral artery ex vivo, and intracranial basilar artery ex vivo. We show that the dual-inhibition effects of cilostazol are mediated by blocking endothelin-induced extracellular calcium influx. Although cilostazol does not inhibit endothelin-induced intraorganellar calcium release, blockade of extracellular calcium influx is sufficient to blunt endothelin-induced vasoconstriction. We also show that cilostazol inhibits endothelin-induced cellular proliferation by blocking extracellular calcium influx. Inhibition of cAMP-dependent protein kinase (PKA) can block anti-proliferation activity of cilostazol, confirming the downstream role of PKA in cellular proliferation. To further demonstrate the selectivity of the dual-antagonizing effects of cilostazol, we used a different phosphodiesterase inhibitor. Interestingly, sildenafil inhibits endothelin-induced vasoconstriction but not cellular proliferation in smooth muscle cells. For the first time, we show selective dual-antagonizing effects of cilostazol on endothelin. We propose that cilostazol is an excellent candidate to treat endothelin-associated diseases, such as stroke.

The role of the cilium in normal and abnormal cell cycles: emphasis on renal cystic pathologies

The primary cilium protrudes from the cell surface and acts as a sensor for chemical and mechanical growth cues, with receptors for a number of growth factors (PDGFα, Hedgehog, Wnt, Notch) concentrated within the ciliary membrane. In normal tissues, the cilium assembles after cells exit mitosis and is resorbed as part of cell cycle re-entry. Although regulation of the cilium by cell cycle transitions has been appreciated for over 100 years, only recently have data emerged to indicate the cilium also exerts influence on the cell cycle. The resorption/protrusion cycle, regulated by proteins including Aurora-A, VHL, and GSK-3β, influences cell responsiveness to growth cues involving cilia-linked receptors; further, resorption liberates the ciliary basal body to differentiate into the centrosome, which performs discrete functions in S-, G2-, and M-phase. Besides these roles, the cilium provides a positional cue that regulates polarity of cell division, and thus directs cells towards fates of differentiation versus proliferation. In this review, we summarize the specific mechanisms mediating the cilia-cell cycle dialog. We then emphasize the examples of polycystic kidney disease (PKD), nephronopthisis (NPHP), and VHL-linked renal cysts as cases in which defects of ciliary function influence disease pathology, and may also condition response to treatment.

Spectral karyotyping to study chromosome abnormalities in humans and mice with polycystic kidney disease

Conventional method to identify and classify individual chromosomes depends on the unique banding pattern of each chromosome in a specific species being analyzed (1, 2). This classical banding technique, however, is not reliable in identifying complex chromosomal aberrations such as those associated with cancer. To overcome the limitations of the banding technique, Spectral Karyotyping (SKY) is introduced to provide much reliable information on chromosome abnormalities. SKY is a multicolor fluorescence in-situ hybridization (FISH) technique to detect metaphase chromosomes with spectral microscope (3, 4). SKY has been proven to be a valuable tool for the cytogenetic analysis of a broad range of chromosome abnormalities associated with a large number of genetic diseases and malignancies (5, 6). SKY involves the use of multicolor fluorescently-labelled DNA probes prepared from the degenerate oligonucleotide primers by PCR. Thus, every chromosome has a unique spectral color after in-situ hybridization with probes, which are differentially labelled with a mixture of fluorescent dyes (Rhodamine, Texas Red, Cy5, FITC and Cy5.5). The probes used for SKY consist of up to 55 chromosome specific probes (7-10). The procedure for SKY involves several steps (Figure 1). SKY requires the availability of cells with high mitotic index from normal or diseased tissue or blood. The chromosomes of a single cell from either a freshly isolated primary cell or a cell line are spread on a glass slide. This chromosome spread is labeled with a different combination of fluorescent dyes specific for each chromosome. For probe detection and image acquisition,the spectral imaging system consists of sagnac interferometer and a CCD camera. This allows measurement of the visible light spectrum emitted from the sample and to acquire a spectral image from individual chromosomes. HiSKY, the software used to analyze the results of the captured images, provides an easy identification of chromosome anomalies. The end result is a metaphase and a karyotype classification image, in which each pair of chromosomes has a distinct color (Figure 2). This allows easy identification of chromosome identities and translocations. For more details, please visit Applied Spectral Imaging website (http://www.spectral-imaging.com/). SKY was recently used for an identification of chromosome segregation defects and chromosome abnormalities in humans and mice with Autosomal Dominant Polycystic Kidney Disease (ADPKD), a genetic disease characterized by dysfunction in primary cilia (11-13). Using this technique, we demonstrated the presence of abnormal chromosome segregation and chromosomal defects in ADPKD patients and mouse models (14). Further analyses using SKY not only allowed us to identify chromosomal number and identity, but also to accurately detect very complex chromosomal aberrations such as chromosome deletions and translocations (Figure 2).

Mechanisms regulating cilia growth and cilia function in endothelial cells

The primary cilium is an important sensory organelle present in most mammalian cells. Our current studies aim at examining intracellular molecules that regulate cilia length and/or cilia function in vitro and ex vivo. For the first time, we show that intracellular cAMP and cAMP-dependent protein kinase (PKA) regulate both cilia length and function in vascular endothelial cells. Although calcium-dependent protein kinase modulates cilia length, it does not play a significant role in cilia function. Cilia length regulation also involves mitogen-activated protein kinase (MAPK), protein phosphatase-1 (PP-1), and cofilin. Furthermore, cofilin regulates cilia length through actin rearrangement. Overall, our study suggests that the molecular interactions between cilia function and length can be independent of one another. Although PKA regulates both cilia length and function, changes in cilia length by MAPK, PP-1, or cofilin do not have a direct correlation to changes in cilia function. We propose that cilia length and function are regulated by distinct, yet complex intertwined signaling pathways.

Educational paper: ciliopathies

Cilia are antenna-like organelles found on the surface of most cells. They transduce molecular signals and facilitate interactions between cells and their environment. Ciliary dysfunction has been shown to underlie a broad range of overlapping, clinically and genetically heterogeneous phenotypes, collectively termed ciliopathies. Literally, all organs can be affected. Frequent cilia-related manifestations are (poly)cystic kidney disease, retinal degeneration, situs inversus, cardiac defects, polydactyly, other skeletal abnormalities, and defects of the central and peripheral nervous system, occurring either isolated or as part of syndromes. Characterization of ciliopathies and the decisive role of primary cilia in signal transduction and cell division provides novel insights into tumorigenesis, mental retardation, and other common causes of morbidity and mortality, including diabetes mellitus and obesity. New technologies ("Next generation sequencing/NGS") have considerably improved genetic research and diagnostics by allowing simultaneous investigation of all disease genes at reduced costs and lower turn-around times. This is undoubtedly a result of the dynamic development in the field of human genetics and deserves increased attention in genetic counselling and the management of affected families.

Polycystic diseases in visceral organs

Primary cilia are nonmotile, microtubule-based, antenna-like organelles projecting from the apical surface of most mammalian cells. Elegant studies have established the importance of ciliary structure and function in signal transduction and the sensory roles of cilia in maintaining healthy cellular state. In particular, dysfunctional cilia have been implicated in a large number of diseases mainly characterized by the presence of fluid-filled cysts in various organs. Aside from polycystic kidney disease (PKD), however, the roles of cilia in polycystic liver disease (PLD), polycystic pancreas disease (PPD), and polycystic ovarian syndrome (PCOS) are still very vague. In addition, although gender and sex hormones are known to regulate cyst formation, their roles in regulating physiological functions of cilia need to be further explored.

Chronic fluid flow is an environmental modifier of renal epithelial function

Although solitary or sensory cilia are present in most cells of the body and their existence has been known since the sixties, very little is been known about their functions. One suspected function is fluid flow sensing- physical bending of cilia produces an influx of Ca(++), which can then result in a variety of activated signaling pathways. Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a progressive disease, typically appearing in the 5(th) decade of life and is one of the most common monogenetic inherited human diseases, affecting approximately 600,000 people in the United States. Because ADPKD is a slowly progressing disease, I asked how fluid flow may act, via the primary cilium, to alter epithelial physiology during the course of cell turnover. I performed an experiment to determine under what conditions fluid flow can result in a change of function of renal epithelial tissue. A wildtype epithelial cell line derived the cortical collecting duct of a heterozygous offspring of the Immortomouse (Charles River Laboratory) was selected as our model system. Gentle orbital shaking was used to induce physiologically relevant fluid flow, and periodic measurements of the transepithelial Sodium current were performed. At the conclusion of the experiment, mechanosensitive proteins of interest were visualized by immunostaining. I found that fluid flow, in itself, modifies the transepithelial sodium current, cell proliferation, and the actin cytoskeleton. These results significantly impact the understanding of both the mechanosensation function of primary cilia as well as the understanding of ADPKD disease progression.

Dopamine receptor type 5 in the primary cilia has dual chemo- and mechano-sensory roles

Polycystic kidney disease is characterized by cardiovascular irregularities, including hypertension. Dopamine, a circulating hormone, is implicated in essential hypertension in humans and animal models. Vascular endothelial primary cilia are known to function as mechano-sensory organelles. Although both primary cilia and dopamine receptors play important roles in vascular hypertension, their relationship has never been explored. To determine the roles of the dopaminergic system and mechano-sensory cilia, we studied the effects of dopamine on ciliary length and function in wild-type and mechano-insensitive polycystic mutant cells (Pkd1(-/)(-) and Tg737(orpk/orpk)). We show for the first time that mouse vascular endothelia exhibit dopamine receptor-type 5 (DR5), which colocalizes to primary cilia in cultured cells and mouse arteries in vivo. DR5 activation increases cilia length in arteries and endothelial cells through cofilin and actin polymerization. DR5 activation also restores cilia function in the mutant cells. In addition, silencing DR5 completely abolishes mechano-ciliary function in WT cells. We found that DR5 plays very important roles in ciliary length and function. Furthermore, the chemo-sensory function of cilia can alter the mechano-sensory function through changes in sensitivity to fluid-shear stress. We propose that ciliary DR5 has functional chemo- and mechano-sensory roles in endothelial cells.

The mechanosensory role of primary cilia in vascular hypertension

Local regulation of vascular tone plays an important role in cardiovascular control of blood pressure. Aside from chemical or hormonal regulations, this local homeostasis is highly regulated by fluid-shear stress. It was previously unclear how vascular endothelial cells were able to sense fluid-shear stress. The cellular functions of mechanosensory cilia within vascular system have emerged recently. In particular, hypertension is insidious and remains a continuous problem that evolves during the course of polycystic kidney disease (PKD). The basic and clinical perspectives on primary cilia are discussed with regard to the pathogenesis of hypertension in PKD.