RU38486 prolongs survival in murine congenital polycystic kidney disease

The cpk/cpk mutant mouse develops a lethal infantile polycystic kidney disease that is associated with disregulation of post natal glucocorticoid production. To establish if the observed endocrine abnormality is involved in the pathophysiology of polycystic kidney disease, blockade of glucocorticoid action during the immediate post-natal period was attempted. The steroid antagonist, RU38486, when administered from day 3 to day 12 of post-natal life, prolonged survival in affected animals. This finding supports a role for steroid hormones in the pathogenesis of this form of polycystic kidney disease.     

The mouse polycystic kidney disease mutation (cpk) is located on proximal chromosome 12

The mouse congenital polycystic kidney (cpk) mutation produces a condition that resembles human autosomal recessive polycystic kidney disease (ARPKD) in its pattern of inheritance, clinical progression, and histopathology. Inheritance of this mouse mutation in crosses segregating the Rb(12.14)8Rma translocation chromosome and various DNA markers of Chromosome 12 have localized cpk to a site near D12Nyu2, approximately 7 cM from the centromere of Chromosome 12. This result suggests that the homologous PKD2 gene should be localized to either human chromosome 2p23-p25 or chromosome 7q22-q31.     

Linkage analysis of two murine polycystic kidney disease genes, pcy and cpk.

Two murine models of polycystic kidney disease (PKD) in humans are currently available: the infant-type cpk in mice and the adult-type pcy mutation in mice. Our linkage analysis was to determine whether these genes are allelic forms of the same gene, or infant-type and adult-type PKD resulting from homozygous and heterozygous mutation, as in the rat Cy gene. We found that the pcy gene in the mice was linked with the d gene on chromosome 9, but the cpk gene was not. A segregation test indicated that the two genes are inherited independently. This indicates that the cpk and pcy genes are not alleles and that the genetic mechanism of PKD pathogenesis in the mouse is different from that in the Cy rat.     

Hypoxia-inducible factor-1α (HIF-1α) and autophagy in polycystic kidney disease (PKD)

Cyst expansion in polycystic kidney disease (PKD) results in localized hypoxia in the kidney that may activate hypoxia-inducible factor-1α (HIF-1α). HIF-1α and autophagy, a form of programmed cell repair, are induced by hypoxia. The purposes were to determine HIF-1α expression and autophagy in rat and mouse models of PKD. HIF-1α was detected by electrochemiluminescence. Autophagy was visualized by electron microscopy (EM). LC3 and beclin-1, markers of autophagy, were detected by immunoblotting. Eight-week-old male heterozygous (Cy/+) and 4-wk-old homozygous (Cy/Cy) Han:SPRD rats, 4-wk-old cpk mice, and 112-day-old Pkd2WS25/- mice with a mutation in the Pkd2 gene were studied. HIF-1α was significantly increased in massive Cy/Cy and cpk kidneys and not smaller Cy/+ and Pkd2WS25/- kidneys. On EM, features of autophagy were seen in wild-type (+/+), Cy/+, and cpk kidneys: autophagosomes, mitophagy, and autolysosomes. Specifically, autophagosomes were found on EM in the tubular cells lining the cysts in cpk mice. The increase in LC3-II, a marker of autophagosome production and beclin, a regulator of autophagy, in Cy/Cy and cpk kidneys, followed the same pattern of increase as HIF-1α. To determine the role of HIF-1α in cyst formation and/or growth, Cy/+ rats, Cy/Cy rats, and cpk mice were treated with the HIF-1α inhibitor 2-methoxyestradiol (2ME2). 2ME2 had no significant effect on kidney volume or cyst volume density. In summary, HIF-1α is highly expressed in the late stages of PKD and is associated with an increase in LC3-II and beclin-1. The first demonstration of autophagosomes in PKD kidneys is reported. Inhibition of HIF-1α did not have a therapeutic effect.     

Structural and functional analyses of liver cysts from the BALB/c-cpk mouse model of polycystic kidney disease

Liver cysts arising from hepatic bile ducts are a common extra-renal pathology associated with both autosomal dominant and recessive polycystic kidney disease in humans. To elucidate the functional and structural changes inherent in cyst formation and growth, hepatic bile duct epithelia were isolated from the BALB/ c-cpk mouse model of polycystic kidney disease. Light and transmission electron microscopy revealed substantial fibrosis in the basal lamina surrounding hepatic bile duct cysts isolated from heterozygous (BALB/c-cpk/+) and homozygous (BALB/c-cpk/cpk) animals. Scanning electron microscopy and length analysis of normal, precystic and cystic bile ducts provided the unique observation that primary cilia in cholangiocytes isolated from bile ducts and cysts of animals expressing the mutated cpk gene had lengths outside the minimal and maximal ranges of those in cells lining bile ducts of wild-type animals. Based on the hypothesis that PKD is one of several diseases characterized as ciliopathies, this abnormal variability in the length of the primary cilia may have functional implications. Electrophysiological analyses of freshly isolated cysts indicate that the amiloride-sensitive epithelial Na(+) channel (ENaC) is inactive/absent and cAMP-mediated anion secretion is the electrogenic transport process contributing to cyst fluid accumulation. Anion secretion can be stimulated by the luminal stimulation of adenylyl cyclase.     

Protein composition of liver cyst fluid from the BALB/c‐cpk/+ mouse model of autosomal recessive polycystic kidney disease

Cysts arising from hepatic bile ducts are a common extra‐renal pathology associated with polycystic kidney disease in humans. As an initial step in identifying active components that could contribute to disease progression, we have investigated the protein composition of hepatic cyst fluid in an orthologous animal model of autosomal recessive polycystic kidney disease, heterozygous (BALB/c‐cpk/+) mice. Proteomic analysis of cyst fluid tryptic digests using LC‐MS/MS identified 303 proteins, many of which are consistent with enhanced inflammatory cell processes, cellular proliferation, and basal laminar fibrosis associated with the development of hepatic bile duct cysts. Protein identifications have been submitted to the PRIDE database ( http://www.ebi.ac.uk/pride ), accession number 9227.     

Defective epidermal growth factor gene expression in mice with polycystic kidney disease

The C57BL/6J-cpk mouse has an inheritable form of polycystic kidney disease similar to the autosomal recessive disorder seen in humans. Between approximately 1 and 3 weeks of age, affected cpk mice develop numerous large cysts in the collecting tubule segment of kidney nephrons. The present study examined the ontogeny of renal and submandibular gland prepro-epidermal growth factor (preproEGF) gene expression in the cpk mouse using Northern blot hybridization and immunohistochemistry. There was a virtual absence of renal preproEGF gene expression in cystic kidneys over the 3-week postnatal period, during which time renal preproEGF mRNA and proEGF/EGF protein normally reach significant levels. PreproEGF mRNA was expressed in salivary glands of cystic mice; however, this mRNA could not be further elevated with testosterone suggesting that there are abnormalities in the regulation of the preproEGF gene in the submandibular gland, as well as in the kidney. Since renal preproEGF expression during the early postnatal period occurs when collecting duct cysts form, it is possible that a deficiency in renal proEGF or EGF contributes to the rapid development of collecting duct cysts and the concomitant renal failure in the C57BL/6J-cpk cystic mouse.     

Apoptosis in polycystic kidney disease: involvement of caspases

Polycystic kidney disease (PKD) is characterized by the development of large renal cysts and progressive loss of renal function. Although the cause of the development of renal cysts is unknown, recent evidence suggests that excessive apoptosis occurs in PKD. With the use of terminal deoxynucleotidyl transferase dUTP nick-end labeling staining, we have confirmed the presence of apoptotic bodies in cystic kidneys of congenital polycystic kidney (cpk) disease mice carrying a homozygous mutation at 3 wk of age. Apoptosis was localized primarily to the interstitium with little evidence of cell death in cyst epithelium or noncystic tubules. In addition, we observed that the expression of various caspases, bax and bcl-2, was upregulated in cystic kidneys. With the use of various substrates in enzyme activity assays, we have demonstrated a greater than sevenfold increase in caspase 4 activity and a sixfold increase in caspase 3 activity. These data suggest that there is a caspase-dependent apoptosis pathway associated with PKD and support the hypothesis that apoptotic cell death contributes to cyst formation in PKD.     

The absence of prostaglandin e1 returned confluent cultures of highly proliferative murine polycystic kidney principal cells to a normal proliferation level

Constitutively high proliferation, loss of cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA)-regulated proliferation, and half-normal cAMP levels were observed previously in principal cells from the C57BL/6J- Cyc1\[cf12\]cpk\[cf1\] (cpk) model of autosomal recessive polycystic kidneys disease (PKD) cultured in defined medium supplemented with prostaglandin E1 (PGE1). Because PGE1 can up- or down-regulate renal cAMP production depending upon its receptor coupling; cAMP exerted both PKA-dependent and PKA-independent effects on cell proliferation; proliferation is considered to be a component of cystogenesis; and PGE1 resulted in loss of tubular structures and formation of cystic structures in gel culture of Madin Darby Canine Kidney cells; the effect of removing PGE1 on murine principal cell proliferation was examined. Proliferation was measured in filter-grown cultures of cystic (cpk) and noncystic (C57) principal cells from cpk and C57BL/6J mice, respectively. Lack of PGE1 had no effect on subconfluent C57 and cpk cultures or confluent C57 cultures but had a dramatic effect on confluent cpk cultures. Without PGE1, cpk proliferation was comparable with the low C57 level. In PGE1-deficient medium, differences were observed between confluence conditions and cell types for responses to a cAMP analog and a PKA activity inhibitor that suggested altered regulation of both PKA-dependent and PKA-independent cell proliferation. Cyclic adenosine monophosphate-dependent differences reported here, and previously, support the idea that the combination of mutant PKD gene product, altered PGE1 responsiveness, and altered PKA targeting contributes to activation of a cystogenic signaling pathway that regulates principal cell proliferation and is involved in pathogenesis.     

C-fos expression is hypersensitive to serum-stimulation in cultured cystic kidney cells from the C57BL/6J-cpk mouse.

Cystic kidneys of the C57BL/6J-cpk murine model of polycystic kidney disease show a marked overexpression of the proto-oncogenes c-fos, c-myc, and c-Ki-ras, consistent with an increased rate of cell proliferation and an altered state of differentiation. To determine if cystic cells have increased responsiveness to stimulation with mitogenic agents, quiescent primary cultures from normal and cystic cpk kidneys were treated with fetal bovine serum (FBS), 8-bromo-cAMP (cAMP), or epidermal growth factor (EGF). The level of c-fos induction following stimulation by FBS was found to be dramatically higher in cystic cells than in normal cells; whereas induction by cAMP or EGF was essentially the same in both cell types and much less than that seen in FBS-stimulated cells. To determine if this serum hypersensitivity reflects an increased proliferative state in vivo, c-fos induction was examined in cultures derived from normal kidneys stimulated to regenerate by folic acid-induced acute renal injury. As with cystic kidneys, the folic acid-injured kidneys showed increased c-fos responsiveness to FBS in cell culture. These experiments suggest that cystic and regenerating kidneys have an altered phenotypic state in vivo that is manifested in cell culture by serum hypersensitivity. However, whereas the folic acid-injured kidneys ultimately reestablish normal kidney function, cystic kidneys further progress to renal failure, suggesting that cystic epithelial cells are locked in this altered state of differentiation.     

Autosomal recessive polycystic kidney disease does not map to the second gene locus for autosomal dominant polycystic kidney disease on chromosome 4

Linkage analysis in 19 families with autosomal recessive polycystic kidney disease (ARPKD) has shown that ARPKD is not linked to the recently assigned second gene locus for autosomal dominant polycystic kidney disease (ADPKD) on chromosome 4q (PKD2). Thus, there is strong evidence that ADPKD and ARPKD have different gene loci.     

<Emphasis Type="Italic">Arabidopsis</Emphasis> Ca<Superscript>2+</Superscript>-dependent protein kinase CPK3 mediates relationship of putative inositol triphosphate receptor with slow-type anion channel

It has been suggested in Arabidopsis thaliana (L.) Heynh. cv. Columbia that, contrary to 30 μM abscisic acid (ABA), 20 μM ABA induces guard cell Ca²⁺ mobilization through activating phosphoinositide-specific phospholipase C (PI-PLC)-dependent inositol 1,4,5-triphosphate (IP₃) production. Here, it was investigated whether Ca²⁺-dependent protein kinase, CPK3 or CPK6 would mediate ABA-induced stomatal closure downstream of IP₃ production. In the knockout cpk3-1 mutant, the PLC inhibitor (U73122) adjusted 20 μM ABA-induced stomatal closure to the extent observed in the knockout cpk6-1 and cpk3-1cpk6-1 mutants and the wild type, whereas, in the wild type, the inhibitor of IP₃-induced Ca²⁺ mobilization, xestospongin C (XeC), adjusted this closure to the extent observed in the cpk3-1 mutant. The Ca²⁺ buffer, EGTA and XeC positively interacted with the slow anion channel blocker, anthracene-9-carboxylic acid (9-AC) to inhibit 20 μM ABA-induced stomatal closure, which was suppressed in the dexamethasone-inducible AtPLC1 antisense transgene or the knockout cpk3-1, cpk6-1, cpk3-1cpk6-1 and NADPH oxidase atrbohD/F mutants. Discrete concentrations of 9-AC or another slow anion channel blocker (probenecid) negatively interacted with the Ca²⁺ buffer, BAPTA or the inhibitor of cyclic ADP-ribose-induced Ca²⁺ mobilization, ruthenium red, to inhibit 30 μM ABAinduced stomatal closure in the wild type but not in the cpk6-1, cpk3-1cpk6-1 and atrbohD/F mutants. Based on so far revealed features of the tested compounds and plant materials, interpretation of the results confirmed that guard cell ABA concentration discriminates between two Ca²⁺ mediations and outlined that one of them sequentially implicates CPK6, PLC1, a putative IP₃ receptor homologue, CPK3, and the slow anion channel, whereas the other one excludes AtPLC1-dependent IP₃ production and CPK3.     

A new mouse model for autosomal recessive polycystic kidney disease

In the course of large-scale mutagenesis studies, we discovered a mutant that provides a new mouse model for human autosomal recessive polycystic kidney disease. Animals homozygous for this mutation, T(2;10)67Gso, present evidence of grossly cystic renal and hepatic tissue at birth and a limited survival time of 3-4 days. The recessively expressed phenotype is associated with inheritance of a reciprocal translocation involving mouse chromosomes 2 and 10. Here we describe the pathology and phenotype of this new mutation. The mapping of the chromosomal breakpoint to the 1.0-cM critical region defined for another mouse autosomal recessive polycystic kidney disease model, juvenile congenital polycystic kidney disease (jcpk), led us to undertake the complementation testing that confirmed T(2;10)67Gso and jcpk are allelic. Because of the strong resemblance between the phenotype associated with these mouse mutations and early childhood polycystic kidney disease, and because of advantages offered by reciprocal translocations for gene mapping and cloning, T(2;10)67Gso should prove a valuable asset for studies concerning this fatal disease.     

The SGP-2 gene is developmentally regulated in the mouse kidney and abnormally expressed in collecting duct cysts in polycystic kidney disease.

Sulfated glycoprotein-2 (SGP-2) is a secreted, dimeric, glycosylated protein synthesized by a number of different epithelial cell types. Although its function is not yet understood, SGP-2 has been hypothesized to be involved in such diverse processes as the promotion of cell-cell interactions, spermatogenesis, modulation of the complement system, and programmed cell death. We have now found that the SGP-2 gene is developmentally regulated in the mouse kidney. SGP-2 gene expression is first detected in the condensing nephrogenic mesenchyme and is subsequently down-regulated during the maturation of the glomerular epithelia, proximal tubules, and collecting ducts. SGP-2 continues to be expressed in the mature kidney in distal tubules and in the urothelial lining of the calyx and papilla. We have also examined the expression of the SGP-2 gene in polycystic kidneys of the C57BL/6J-cpk mouse, a model of autosomal recessive polycystic kidney disease in which there is development of epithelial-lined cysts arising primarily from the collecting duct system. Abnormally high levels of SGP-2 mRNA were found in the cyst wall epithelium of polycystic kidneys. The expression of the SGP-2 gene in normal development suggests that it plays a role in differentiating epithelial structures; and the abnormally high levels of SGP-2 gene expression in polycystic kidneys suggests that the cells lining cysts are not fully differentiated. It is possible, therefore, that polycystic kidney disease is caused by a defective developmental process in which there is a delay in terminal differentiation.     

Identification of a new target molecule for a cascade therapy of polycystic kidney

Autosomal dominant polycystic kidney disease is a systemic disorder that primary affects the kidney which is characterized by the formation of fluid-filled cysts in both kidneys that leads to progressive renal failure. Mutated genes, polycystin-1 and polycystin-2, are identified, and evidence has emerged that polycystins are ion channels or regulators of ion channels. In spite of extensive characterization of polycystins, how polycystin channel signaling may be involved in cyst formation in ADPKD is still unclear. We found a mutant mouse which exhibits polycystic kidney and bone deformity in the course of making a transgenic mouse carrying the Drosophila sex-lethal gene. We identified a mutated gene Makorin1 by positional cloning. Makorin1 carries a typical RING-finger motif, suggesting that Makorin1 belongs to ubiquitinase E3 family. Makorin1 would open a new avenue to understand pathogenesis of polycystic kidney, and become a new therapeutic target of polycystic kidney.     

Glucocorticoid teratogenesis in the developing nephron

Although the induction of polycystic kidney disease by neonatal glucocorticoid treatment has been extensively documented, there are no data on induction of polycystic kidney disease with fetal exposure to glucocorticoids. We injected groups of pregnant Swiss Webster albino mice subcutaneously with 250 mg/kg of hydrocortisone acetate on individual days from days 1 to 19 of gestation. A control group received an equal volume of saline. Histologic analysis of 1,522 kidneys from the offspring of these animals revealed no evidence of polycystic kidneys in the control group or in offspring of animals injected before day 11 of pregnancy. A bimodal distribution of cystic kidney disease was noted in the remaining animals, with highest prevalence after injection on day 12 (50.8%) and day 17 (34.3%). We conclude that 250 mg/kg of glucocorticoids may induce polycystic kidney disease in utero, but possibly only during critical periods of metanephric development.     

An ever-expanding story of cyst formation

Autosomal-dominant polycystic kidney disease represents one of the most common monogenetic human disorders. The cloning of the PKD1 and PKD2 genes, which are mutated in far more than 90% of the patients affected by this disease, has generated high hopes for a quick understanding of the pathogenesis of cyst formation. However, these expectations have not yet been fulfilled, since the function of both polycystin-1 and polycystin-2, the two proteins encoded by PKD1 and PKD2, still remains a puzzle. In this review, we will highlight some of the characteristics of polycystic kidney disease, briefly touch on polycystin-1, and then go on to describe recent results of experiments with polycystin-2, since the latter is the major focus of our work. We will discuss new evidence which suggests that autosomal-dominant polycystic kidney disease actually behaves recessively on a cellular level. Finally, a model will be presented that tries to explain the available data.     

Molecular pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the commonest inherited human disorders yet remains relatively unknown to the wider medical, scientific and public audience. ADPKD is characterised by the development of bilateral enlarged kidneys containing multiple fluid-filled cysts and is a leading cause of end-stage renal failure (ESRF). ADPKD is caused by mutations in two genes: PKD1 and PKD2. The protein products of the PKD genes, polycystin-1 and polycystin-2, form a calcium-regulated, calcium-permeable ion channel. The polycystin complex is implicated in regulation of the cell cycle via multiple signal transduction pathways as well as the mechanosensory function of the renal primary cilium, an enigmatic cellular organelle whose role in normal physiology is still poorly understood. Defects in cilial function are now documented in several other human diseases including autosomal recessive polycystic kidney disease, nephronophthisis, Bardet-Biedl syndrome and many animal models of polycystic kidney disease. Therapeutic trials in these animal models of polycystic kidney disease have identified several promising drugs that ameliorate disease severity. However, elucidation of the function of the polycystins and the primary cilium will have a major impact on our understanding of renal cystic diseases and will create exciting new opportunities for the design of disease-specific therapies.     

Tuberin-dependent membrane localization of polycystin-1: a functional link between polycystic kidney disease and the TSC2 tumor suppressor gene

The PKD1 gene accounts for 85% of autosomal dominant polycystic kidney disease (ADPKD), the most common human genetic disorder. Rats with a germline inactivation of one allele of the Tsc2 tumor suppressor gene developed early onset severe bilateral polycystic kidney disease, with similarities to the human contiguous gene syndrome caused by germline codeletion of PKD1 and TSC2 genes. Polycystic rat renal cells retained two normal Pkd1 alleles but were null for Tsc2 and exhibited loss of lateral membrane-localized polycystin-1. In tuberin-deficient cells, intracellular trafficking of polycystin-1 was disrupted, resulting in sequestration of polycystin-1 within the Golgi and reexpression of Tsc2 restored correct polycystin-1 membrane localization. These data identify tuberin as a determinant of polycystin-1 functional localization and, potentially, ADPKD severity.