Endothelial cells from humans and mice with polycystic kidney disease are characterized by polyploidy and chromosome segregation defects through survivin down-regulation (original) (raw)
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P olycystic kidney disease (PKD) is the most common hereditary kidney disorder, and formation of bilateral cystic kidneys is the hallmark of the disease. Among other extrarenal phenotypes, aneurysm formation is one of the deadliest vascular abnormalities observed in PKD patients. Unfortunately, there is no study that explains the formation of these "bulb-like structures" in both vasculatures and renal tubules. Abnormalities in primary cilia, 1-4 polyploidy, 5,6 and centrosomal number 5,7 have been independently studied in the vascular or renal systems. However, there is currently no unifying mechanism that explains these cellular phenotypes. Clinical Perspective on p 672 Survivin is a chromosomal passenger involved in coordinating proper chromosomal events during mitosis. 8 Because of its clinical manifestation in cancer, overexpression of survivin has always been the main focus of medical research. Whereas overexpression of survivin is associated with cancer formation and progression, the Survivin knockout mouse model is not viable beyond 4.5 days post coitum. 9 Interestingly, survivin homozygote cells isolated at 4.5 days post coitum show a cellular polyploidy phenotype similar to that of Pkd cells. 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. (Circulation. 2014;129:660-672.
Cilium, centrosome and cell cycle regulation in polycystic kidney disease
Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 2011
Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/ centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.
Role of Primary Cilia in the Pathogenesis of Polycystic Kidney Disease
Journal of the American Society of Nephrology, 2007
Cysts in the kidney are among the most common inherited human pathologies, and recent research has uncovered that a defect in cilia-mediated signaling activity is a key factor that leads to cyst formation. The cilium is a microtubule-based organelle that is found on most cells in the mammalian body. Multiple proteins whose functions are disrupted in cystic diseases have now been localized to the cilium or at the basal body at the base of the cilium. Current data indicate that the cilium can function as a mechanosensor to detect fluid flow through the lumen of renal tubules. Flow-mediated deflection of the cilia axoneme induces an increase in intracellular calcium and alters gene expression. Alternatively, a recent finding has revealed that the intraflagellar transport 88/polaris protein, which is required for cilia assembly, has an additional role in regulating cell-cycle progression independent of its function in ciliogenesis. Further research directed at understanding the relationship between the cilium, cell-cycle, and cilia-mediated mechanosensation and signaling activity will hopefully provide important insights into the mechanisms of renal cyst pathogenesis and lead to better approaches for therapeutic intervention.
Journal of Clinical Investigation, 2002
Polycystic kidney disease (PKD) represents a set of hereditary nephropathies characterized by progressive cyst formation, massive renal enlargement, and often, progression to end-stage renal disease. Autosomal dominant PKD (ADPKD) occurs in 1 in 1,000 individuals and, in addition to renal cystic disease, is associated with cyst formation in other epithelial organs, most notably the liver, as well as connective tissue defects, such as intracranial aneurysms, aortic dissection, and cardiac valve defects (1). Mutations in either of two genes, PKD1 and PKD2, cause ADPKD phenotypes that are virtually indistinguishable (2). In comparison, autosomal recessive PKD (ARPKD) is much less frequent (1 in 20,000 live births). The clinical phenotype is dominated by renal collecting duct ectasia, biliary dysgenesis, and portal tract fibrosis (3). The principal disease locus, PKHD1, has been mapped to chromosome 6p21.1-p12 (4, 5), but the gene has yet to be identified. In the mouse, several distinct, recessively acting mutations cause PKD phenotypes that mimic human disease (6). Among these models, the congenital polycystic kidney (cpk) mutation is the most extensively characterized. The cpk locus on chromosome 12 is defined by a single recessive mutation that arose spontaneously in the C57BL/6J strain (7). The renal phenotype is fully expressed in homozygotes and is strikingly similar to human ARPKD (8, 9), whereas genetic background modulates the penetrance of the corresponding defect in the developing biliary tree (10, 11). Multiple cellular and extracellular matrix abnormalities have been described in cpk/cpk kidneys. These changes include: (a) enhanced expression of the protooncogenes, c-myc, c-fos, c-Ki-ras (12-14); (b) increased expression of the transcriptional repressor, Cux-1, a putative inhibitor of terminal differentiation (15); (c) enhanced growth factor expression (16); (d) apical mislocation of a functional EGF receptor (17); (e) increased expression of basement membrane constituents, laminin β1, and γ1, α1/α2 chains of collagen IV, collagen I, and fibronectin (18, 19); (f) overexpression of the basement membrane remodeling enzymes, matrix metalloproteinases (MMPs), and their specific tissue inhibitors, TIMPs (20); (g) abnormal expression of epithelial cell adhesion molecules (21, 22); and (h) alterations in steroid metabolism and lipid composition (23-25). These numerous abnormalities involving a wide range of developmentally regulated cellular processes suggest that cpk/cpk mutant kidneys are unable to complete the terminal phases of tubuloepithelial differentiation (26).
2006
Primary cilia are implicated in the pathogenesis of autosomal-dominant polycystic kidney disease (ADPKD), which results from defects in polycystin-1 (PC1), but the function of PC1 remains poorly understood. Here, we show that PC1 undergoes proteolytic cleavage that results in nuclear translocation of its cytoplasmic tail. The PC1 tail interacts with the transcription factor STAT6 and the coactivator P100, and it stimulates STAT6-dependent gene expression. Under normal conditions, STAT6 localizes to primary cilia of renal epithelial cells. Cessation of apical fluid flow results in nuclear translocation of STAT6. Cyst-lining cells in ADPKD exhibit elevated levels of nuclear STAT6, P100, and the PC1 tail. Exogenous expression of the human PC1 tail results in renal cyst formation in zebrafish embryos. These results identify a novel mechanism of cilia function in the transduction of a mechanical signal to changes of gene expression involving PC1 and show that this pathway is inappropriately activated in ADPKD.
Implications of Dysfunction of Mechanosensory Cilia in Polycystic Kidney Disease
2015
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a multisystemic disorder characterized by numerous fluid-filled renal cysts that eventually destroy the kidney architecture and lead to end-stage kidney disease (ESKD). Although the formation of bilateral cystic kidneys is the hallmark of the disease, patients with ADPKD also suffer from extra-renal manifestations and cardiovascular complications. ADPKD is considered a ciliopathy disease due to defects in mechanosensory polycystins, localized to primary cilia, which have been recognized as mechanosensory organelles due to their involvement in ADPKD only within the past decade. Our recent studies focus on the fluid mechanosensory functions of primary cilia using cultured cells, animal models, and tissue from ADPKD patients. Growing evidence from these studies suggests that aberrant expression or localization of polycystins to cilia could promote high blood pressure due to the inability to synthesize nitric oxide in response to a...
LRRC50, a Conserved Ciliary Protein Implicated in Polycystic Kidney Disease
Journal of the American Society of Nephrology, 2008
Cilia perform essential motile and sensory functions central to many developmental and physiological processes. Disruption of their structure or function can have profound phenotypic consequences, and has been linked to left-right patterning and polycystic kidney disease. In a forward genetic screen for mutations affecting ciliary motility, we isolated zebrafish mutant hu255H. The mutation was found to disrupt an ortholog of the uncharacterized highly conserved human SDS22-like leucine-rich repeat (LRR)-containing protein LRRC50 (16q24.1) and Chlamydomonas Oda7p. Zebrafish lrrc50 is specifically expressed in all ciliated tissues. lrrc50 hu255H mutants develop pronephric cysts with an increased proliferative index, severely reduced brush border, and disorganized pronephric cilia manifesting impaired localized fluid flow consistent with ciliary dysfunction. Electron microscopy analysis revealed ultrastructural irregularities of the dynein arms and misalignments of the outer-doublet microtubules on the ciliary axonemes, suggesting instability of the ciliary architecture in lrrc50 hu255H mutants. The SDS22-like leucine-rich repeats present in Lrrc50 are necessary for proper protein function, since injection of a deletion construct of the first LRR did not rescue the zebrafish mutant phenotype. Subcellular distribution of human LRRC50-EGFP in MDCK and HEK293T cells is diffusely cytoplasmic and concentrated at the mitotic spindle poles and cilium. LRRC50 RNAi knock-down in human proximal tubule HK-2 cells thoroughly recapitulated the zebrafish brush border and cilia phenotype, suggesting conservation of LRRC50 function between both species. In summary, we present the first genetic vertebrate model for lrrc50 function and propose LRRC50 to be a novel candidate gene for human cystic kidney disease, involved in regulation of microtubule-based cilia and actin-based brush border microvilli.
Cilia-Localized Counterregulatory Signals as Drivers of Renal Cystogenesis
Frontiers in Molecular Biosciences
Primary cilia play counterregulatory roles in cystogenesis—they inhibit cyst formation in the normal renal tubule but promote cyst growth when the function of polycystins is impaired. Key upstream cilia-specific signals and components involved in driving cystogenesis have remained elusive. Recent studies of the tubby family protein, Tubby-like protein 3 (TULP3), have provided new insights into the cilia-localized mechanisms that determine cyst growth. TULP3 is a key adapter of the intraflagellar transport complex A (IFT-A) in the trafficking of multiple proteins specifically into the ciliary membrane. Loss of TULP3 results in the selective exclusion of its cargoes from cilia without affecting their extraciliary pools and without disrupting cilia or IFT-A complex integrity. Epistasis analyses have indicated that TULP3 inhibits cystogenesis independently of the polycystins during kidney development but promotes cystogenesis in adults when polycystins are lacking. In this review, we di...
Human Molecular Genetics, 2008
Polycystic kidney disease (PKD) is an inherited disorder that is characterized by the accumulation of cysts in the renal parenchyma and progressive decline in renal function. Recent studies suggest that PKD arises from abnormalities of the primary cilium. We have previously shown that kidney-specific inactivation of the ciliogenic gene Kif3a during embryonic development produces kidney cysts and renal failure. Here, we used tamoxifen-inducible, kidney-specific gene targeting to inactivate Kif3a in the postnatal mouse kidney. Kidney-specific inactivation of Kif3a in newborn mice resulted in the loss of primary cilia and produced kidney cysts primarily in the loops of Henle, whereas inactivation in adult mice did not lead to the rapid development of cysts despite a comparable loss of primary cilia. The age-dependence and locations of the cysts suggested that cyst formation required increased rates of cell proliferation. To test this possibility, we stimulated cell proliferation in the adult kidney by inducing acute kidney injury and tubular regeneration. Acute kidney injury induced cyst formation in adult Kif3a mutant mice. Analysis of pre-cystic tubules in Kif3a mutant mice showed that the loss of cilia did not stimulate cell proliferation but instead resulted in aberrant planar cell polarity as manifested by abnormalities in the orientation of cell division. We conclude that primary cilia are required for the maintenance of planar cell polarity in the mammalian kidney and that acute kidney injury exacerbates cystic disease.