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

Situs inversus and ciliary abnormalities: 20 years later, what is the connection?

Heterotaxy (also known as situs ambiguous) and situs inversus totalis describe disorders of laterality in which internal organs do not display their typical pattern of asymmetry. First described around 1600 by Girolamo Fabrizio, numerous case reports about laterality disorders in humans were published without any idea about the underlying cause. Then, in 1976, immotile cilia were described as the cause of a human syndrome that was previously clinically described, both in 1904 by AK Siewert and in 1933 by Manes Kartagener, as an association of situs inversus with chronic sinusitis and bronchiectasis, now commonly known as Kartagener’s syndrome. Despite intense research, the underlying defect of laterality disorders remained unclear. Nearly 20 years later in 1995, Björn Afzelius discussed five hypotheses to explain the connection between ciliary defects and loss of laterality control in a paper published in the International Journal of Developmental Biology asking: ‘Situs inversus and ciliary abnormalities: What is the connection?’. Here, nearly 20 research years later, we revisit some of the key findings that led to the current knowledge about the connection between situs inversus and ciliary abnormalities.

The ciliary protein cystin forms a regulatory complex with necdin to modulate Myc expression

Cystin is a novel cilia-associated protein that is disrupted in the cpk mouse, a well-characterized mouse model of autosomal recessive polycystic kidney disease (ARPKD). Interestingly, overexpression of the Myc gene is evident in animal models of ARPKD and is thought to contribute to the renal cystic phenotype. Using a yeast two-hybrid approach, the growth suppressor protein necdin, known to modulate Myc expression, was found as an interacting partner of cystin. Deletion mapping demonstrated that the C-terminus of cystin and both termini of necdin are required for their mutual interaction. Speculating that these two proteins may function to regulate gene expression, we developed a luciferase reporter assay and observed that necdin strongly activated the Myc P1 promoter, and cystin did so more modestly. Interestingly, the necdin effect was significantly abrogated when cystin was co-transfected. Chromatin immunoprecipitation and electrophoretic mobility shift assays revealed a physical interaction with both necdin and cystin and the Myc P1 promoter, as well as between these proteins. The data suggest that these proteins likely function in a regulatory complex. Thus, we speculate that Myc overexpression in the cpk kidney results from the dysregulation of the cystin-necdin regulatory complex and c-Myc, in turn, contributes to cystogenesis in the cpk mouse.

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.

Identification and characterization of a novel polycystin family member, polycystin-L2, in mouse and human: sequence, expression, alternative splicing, and chromosomal localization

Polycystins-1, -2, -L, and -REJ are the four known members of the polycystin family of proteins. In this study, we describe a fifth member of the family, polycystin-L2, encoded by PKD2L2 in human and Pkd2l2 in mouse. Full-length cDNA sequences for both mouse and human polycystin-L2 were obtained from testis cDNA. Sequence analysis predicts that the mouse and human polycystin-L2 proteins consist of 621 and 624 amino acid residues, respectively. Polycystin-L2 has significant homology with polycystins-L and -2, with similarities of 58 and 59%, respectively. Both human and murine polycystin-L2 proteins are predicted to have seven putative transmembrane (TM) domains, and, by comparison with transient receptor potential channels, the six carboxyl-terminal TM domains are likely to constitute an ion channel subunit. Northern blot analysis indicated that mouse Pkd2l2 has an abundant approximately 2.5-kb transcript in testis and an approximately 2.2-kb transcript in heart. RT-PCR analysis showed that the full-length transcript is expressed in human brain, kidney, testis, and HepG2 cells, and there are three alternatively spliced variants that were differentially expressed. PKD2L2 consists of 17 exons spanning approximately 50 kb of genomic DNA. PKD2L2 was mapped to human chromosome 5q31 and Pkd2l2 to mouse chromosome 18 in band C.

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.

A new in vitro bioassay for cyst formation by renal cells from an autosomal dominant rat model of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most frequent human inherited diseases. The main feature of the disease is the development of renal cysts, first occurring in the proximal tubules, and with time, dominating all segments of the nephron, leading to end-stage renal disease in 50% of the patients in their fifth decade of life. A therapy for polycystic kidney disease (PKD) has not yet been developed. Patients coming to end-stage ADPKD require long-term dialysis and/or transplantation. A suitable animal model to study ADPKD is the spontaneously mutated Han:SPRD (cy/+) rat, but a method to cultivate Han:SPRD (cy/+) derived renal cells which preserves their ability to form cyst-like structures in vitro has previously not been reported. Based on this well-characterized animal model, we developed a cell culture model of renal cyst formation in vitro. When renal cells of the Han:SPRD (cy/+) rat were isolated and cultured under conditions that prevent cell-substratum adhesion, large amounts of cyst-like structures were formed de novo from Han:SPRD (cy/+) derived renal cells, but only a few from control rat renal cells. In contrast, when cultivated on plastic as monolayer cultures, Han:SPRD (cy/+)-derived and control rat-derived renal cells were indistinguishable and did not form cyst-like structures. Immunohistochemical characterization of the cyst-like structures suggests tubular epithelial origin of the cyst-forming cells. The amount of cysts formed from Han:SPRD (cy/+)-derived renal cells grown in a stationary suspension culture is susceptible to modulation by different conditions. Human cyst fluid and epidermal growth factor both stimulated the formation of cysts from Han:SPRD (cy/+)-derived renal cells whereas taxol inhibited cystogenesis. In contrast, neither human cyst fluid nor epidermal growth factor affected the amount of cysts formed by control rat renal cells. As the culture model reported here allows not only the distinction of PKD-derived tubular epithelium from its normal counterpart, but also the modulation of cyst formation especially by Han:SPRD (cy/+)-derived renal cells, it might be a useful prescreening protocol for potential treatments for PKD and thus reduce the need for animal experiments.

Matrix metalloproteinase-2 in a murine model of infantile-type polycystic kidney disease

It was previously found that elevated levels of matrix metalloproteinase (MMP)-2 (gelatinase A) and -9 (gelatinase B) were synthesized and secreted into the medium by cultured kidney tubules derived from cystic C57BL/6J-cpk mice. To determine whether increased synthesis and secretion occur in vivo in this mouse model of polycystic kidney disease, kidney protein extracts, mRNA, and tissue sections were compared for expression and activity of MMP-2 and -9. Although both MMP were detected in tissue extracts, the differences in expression levels and activity in normal and cystic kidneys were far greater for MMP-2. High levels of MMP-2 seemed to result from increased expression by the cystic kidneys predominantly in the second and third postnatal weeks (a time when the kidneys are undergoing rapid cystic enlargement). Much of the increased MMP was present in the inactive zymogen form, although active enzyme was readily detected by sodium dodecyl sulfate-polyacrylamide gel zymography and in situ zymography. MMP-2 was abnormally localized to the interstitium and to foci between cysts, suggesting that MMP-2 may regulate collagen accumulation at those sites, thus allowing cyst enlargement and limiting the severity of interstitial fibrosis.

Kid-1 expression is high in differentiated renal proximal tubule cells and suppressed in cyst epithelia

The cDNA coding for the transcriptional repressor protein Kid-1 was cloned in a screen for zinc finger proteins, which are regulated during renal development and after renal ischemia. Kid-1 mRNA levels increase in the course of postnatal renal development and decrease after acute renal injury caused by ischemia or administration of folic acid. We have raised a monoclonal anti-Kid-1 antibody and demonstrate that the Kid-1 protein is strongly expressed in the proximal tubule of the adult rat kidney. During nephron development, the Kid-1 protein appears after the S-shaped body stage concomitantly with the brush-border enzyme alkaline phosphatase. In two animal models of polycystic kidney disease, the expression of Kid-1 is downregulated. The loss of expression of Kid-1 in cyst wall cells correlates with the loss of alkaline phosphatase histochemical staining. Kid-1 mRNA levels are also reduced in rodent renal cell carcinomas, another condition characterized by epithelial cell dedifferentiation and increased proliferation. We propose that Kid-1 plays an important role during the differentiation of the proximal tubule.

Microtubule active taxanes inhibit polycystic kidney disease progression in cpk mice

Homozygous cpk/cpk mice develop polycystic kidney disease and die of uremia between the fourth and fifth weeks of age. Cpk/cpk mice treated weekly with paclitaxel (Taxol) can live to over six months of age. This dramatic moderation of polycystic kidney disease progression has been postulated to be a result of paclitaxel's ability to stabilize microtubules. In this study, the ability of taxanes with differing abilities to promote spontaneous in vitro assembly of tubulin dimers into microtubules were tested for their ability to inhibit the progression of polycystic kidney disease in polycystic cpk/cpk mice. We found that taxanes that are active in promoting microtubule assembly, including paclitaxel, 10-deactyl-taxol and cephalomannine increased the survival of polycystic cpk/cpk mice significantly longer than control animals. In contrast, the microtubule inactive taxane baccatin-III has no effect on the progression of renal failure in cpk/cpk mice. We conclude that the ability to promote microtubule assembly may be necessary for paclitaxel and related taxanes to modulate the progression of polycystic kidney progression in cpk/cpk mice.

Identification and genetic mapping of a new polycystic kidney disease on mouse chromosome 8

We report here a new mouse mutation, kat, that causes pleiotropic effects including facial dysmorphism, dwarfing, male sterility, anemia, and progressive polycystic kidney disease. kat (kidney anemia and testis) and a second allele, kat2J, that occurred on C57BL/ 6J were mapped to mouse chromosome (Chr) 8 using intra- and intersubspecific intercrosses. A high-resolution map for kat2J on Chr 8 was constructed using the F2 progeny from a cross between C57BL/6J-kat2J/+ and an inbred strain of Mus musculus castaneus (CAST/Ei). The kat2J mutation was localized between D8Mit129 and D8Mit128 with the gene order centromere-D8Mit100-(1.2 +/- 0.26 cM)-D8Mit231-(0.17 +/- 0.09 cM)-D8Mit129-(0.28 +/- 0.12 cM)-D8Mit128-(0.98 +/- 0.23 cM)-D8Mit25/D8Mit8. This segment is homologous to human Chr 19p. The two mutations at this locus that have occurred at The Jackson Laboratory will be invaluable for positional cloning and subsequent functional analysis of the mutated gene.

Molecular therapy for renal diseases

The introduction of molecular therapy through the delivery of nucleic acids either as oligonucleotides or genetic constructs holds enormous promise for the treatment of renal disease. Significant barriers remain, however, before successful organ-specific molecular therapy can be applied to the kidney. These include the development of methods to target the kidney selectively, the definition of vectors that transduce renal tissue, the identification of appropriate molecular targets, the development of constructs that are regulated and expressed for long periods of time, the demonstration of efficacy in vivo, and the demonstration of safety in humans. As the genetic and pathophysiologic basis of renal disease is clarified, obvious targets for therapy will be defined, for example, polycystin in polycystic kidney disease, human immunodeficiency virus (HIV) type 1 in HIV-associated nephropathy, alpha-galactosidase A in Fabry's disease, insulin in diabetic nephropathy, and the "minor" collagen IV chains in Alport's syndrome. In addition, several potential mediators of progressive renal disease may be amenable to molecular therapeutic strategies, such as interleukin-6, basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and transforming growth factor-beta(TGF-beta). To test the in vivo efficacy of molecular therapy, appropriate animal models for these disease states must be developed, an area that has received too little attention. For the successful delivery of genetic constructs to the kidney, both viral and nonviral vector systems will be required. The kidney has a major advantage over other solid organs since it is accessible by many routes, including intrarenal artery infusion, retrograde delivery through the uroexcretory pathways, and ex vivo during transplantation. To further restrict expression to the kidney, tropic vectors and tissue-specific promoters also must be developed. For the purpose of inhibition of endogenous or exogenous genes, current therapeutic modalities include the delivery of antisense oligodeoxynucleotides or ribozymes. For these approaches to succeed, we must gain a much better understanding of the nature of their transport into the kidney, requirements for specificity, and in vivo mechanisms of action. The danger of a rush to clinical application is that superficial approaches to these issues will likely fail and enthusiasm will be lost for an area that should be one of the most exciting developments in therapeutics in the next decade.

A mouse kidney- and liver-expressed cDNA having homology with a prokaryotic parathion hydrolase (phosphotriesterase)-encoding gene: abnormal expression in injured and polycystic kidneys

To investigate abnormalities in gene expression associated with cyst formation in polycystic kidney disease, differential cDNA library screening was carried out using RNA from normal and cystic kidneys of the C57BL/6J-cpk mouse. Among a number of genes found to be abnormally expressed was one (cDNA clone 56-1) that was significantly underexpressed in cystic kidneys. Hybridization analyses revealed that the 56-1 mRNA is expressed primarily in kidney and liver, and that the kidney expression begins postnatally and continues in the adult. Expression of this mRNA was found to be significantly decreased upon acute renal injury induced by a single intraperitoneal injection of folic acid, and to return to normal levels upon recovery of kidney function. Analysis of the cDNA sequence predicted a protein of 349 amino acids (aa), which was confirmed by in vitro translation of a sense-strand transcript, producing a protein of approx. 39 kDa. The aa sequence shows similarity to Flavobacterium sp. and Pseudomonas diminuta parathion hydrolase (phosphotriesterase or PTE), an enzyme that hydrolyzes toxic organophosphates and other phosphotriesters, and to the predicted product of an Escherichia coli open reading frame of unknown function (phosphotriesterase homology protein or PHP). Use of optimal alignment programs demonstrated a significant overall homology between the bacterial and mouse sequences, with greater than 50% aa sequence similarity. This cDNA represents the first eukaryotic sequence showing similarity to these prokaryotic genes. Based on this apparent homology, it has been named mpr56-1 (for mouse phosphotriesterase-related 56-1).

Growth characteristics of cells cultured from two murine models of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by multiple renal cysts that are lined by epithelium and filled with fluid. PKD may result from one of a number of factors, either inherited or environmental. In this study, we have compared two mouse models in which PKD results from a genetic cause. In the C57BL/6J-cpk model, the mutated gene is unknown. In the other model, an SV40 large T antigen transgene causes renal cysts. We examined cultured cells from the kidneys of these mouse models, comparing growth characteristics. Although several features of PKD lead one to expect that the epithelial cells lining the cysts would have an increased rate of proliferation in culture, we found that they did not. The implications of these findings are discussed.

Animal models of polycystic kidney disease

Polycystic kidney disease (PKD) is one of the most prevalent causes of heritable renal failure. The disease is characterized by the occurrence of numerous fluid-filled cysts within the parenchyma of kidney. The cysts are epithelial in origin and expand in size, leading to crowding of normal kidney tissue. Ultimately, there is gross enlargement of the kidneys with loss of normal functions, and death usually occurs because of complications related to renal failure. Animal models of polycystic kidney disease are proving to be extremely useful for studying the molecular basis of renal cyst formation and for the isolation of genes carrying the mutations. This article describes the various animal models of polycystic kidney disease, spontaneously and experimentally derived, that have recently been identified.

New mouse model for polycystic kidney disease with both recessive and dominant gene effects

In the course of studying the genetics of chlorambucil mutagenesis, we have uncovered a new model for autosomal polycystic kidney disease (PKD). In the homozygous condition, the gene, jcpk, causes a very severe disease characterized by cysts in all segments of the nephron. Death usually occurs before 10 days of age. Extrarenal involvement was also noted; enlarged bile ducts, pancreatic ducts, and gall bladder often accompanied the PKD. In addition, approximately 25% of the aged +/jcpk heterozygotes show evidence of glomerulocystic disease. This gene maps to Chromosome 10 between two DNA markers, D10Mit20 and D10Mit42. Because this gene causes extrarenal abnormalities and because it has a heterozygote effect, it may be an informative animal model for the commonly occurring human adult dominant PKD.

Juvenile cystic kidneys (jck): a new mouse mutation which causes polycystic kidneys

We have characterized a new recessive mutation in the mouse which predisposes to the development of polycystic kidney disease. This mutation, called juvenile cystic kidneys (jck), arose in a transgenic line of mice, but appears unrelated to the transgene since it segregates freely from it. While focal cysts are evident in affected animals as early as three days of life and the disease is progressive, the mice are fertile and generally survive to four or more months of age. Complementation analysis indicates that the jck mutation is not allelic with three other known recessive polycystic kidney mutations (cpk and two as yet unnamed mutations), and linkage studies demonstrate it is unlikely to be allelic with a fourth (pcy). The study of these five mutations and their interactions should prove useful for understanding the mechanisms required to maintain the normal integrity of renal tubules.

A gene for familial juvenile nephronophthisis (recessive medullary cystic kidney disease) maps to chromosome 2p

Familial juvenile nephronophthisis (NPH) is a chronic autosomal recessive kidney disease responsible for 15% of end stage renal failure in children. NPH is frequently (16% of cases) associated with Leber amaurosis (termed Senior-Løken syndrome, SLS). Linkage analyses, performed in 22 multiplex NPH families (18 without and 4 with ocular abnormalities), have localized the gene to a region between D2S48 and D2S51 on chromosome 2p. This was confirmed using adjacent microsatellite markers, one of which (AFM220ze3 at the D2S160 locus) gave a lod score of 4.78 at theta = 0.05 in the 18 families with isolated NPH, whereas the same marker excluded linkage with SLS. These results demonstrate linkage of the purely renal form of NPH to chromosome 2p, and suggest that there may be genetic heterogeneity between NPH and SLS.

Downregulation of Ke 6, a novel gene encoded within the major histocompatibility complex, in murine polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by progressive enlargement of the kidneys due to numerous expanding cysts ultimately leading to renal failure. We have identified a gene, Ke 6, located within the H-2K/tw5 region on mouse chromosome 17, which is downregulated in two distinct murine models of heritable PKD. Ke 6 is a member of the short-chain alcohol dehydrogenase family and possess remarkable amino acid sequence conservation with several bacterial proteins with oxidoreductase function. The Ke 6 gene gives rise to two transcripts--a 1-kb Ke 6a mRNA which is abundant in kidney and liver tissue and a 1.4-kb Ke 6b mRNA which is found at a moderate level in spleen tissue. We report here the complete nucleotide sequence of Ke 6a cDNA and the expression of the Ke 6 gene in murine models of PKD. The Ke 6 gene may be intimately involved in the manifestation of these cystic kidney diseases.

Downregulation of Ke 6, a novel gene encoded within the major histocompatibility complex, in murine polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by progressive enlargement of the kidneys due to numerous expanding cysts ultimately leading to renal failure. We have identified a gene, Ke 6, located within the H-2K/tw5 region on mouse chromosome 17, which is downregulated in two distinct murine models of heritable PKD. Ke 6 is a member of the short-chain alcohol dehydrogenase family and possess remarkable amino acid sequence conservation with several bacterial proteins with oxidoreductase function. The Ke 6 gene gives rise to two transcripts--a 1-kb Ke 6a mRNA which is abundant in kidney and liver tissue and a 1.4-kb Ke 6b mRNA which is found at a moderate level in spleen tissue. We report here the complete nucleotide sequence of Ke 6a cDNA and the expression of the Ke 6 gene in murine models of PKD. The Ke 6 gene may be intimately involved in the manifestation of these cystic kidney diseases.

Polycystic kidney disease: primary extracellular matrix abnormality or defective cellular differentiation?

Polycystic kidney disease (PKD) is inherited as a dominant or recessive trait or can be provoked by environmental factors. The disease is characterized by the growth of large epithelial-lined cysts derived from the nephrons and collecting ducts of affected kidneys. Cysts are thought to initiate as small dilations in renal tubules, which then expand into fluid-filled cavities of relatively large size. Cyst formation appears to involve increased cell proliferation, reversal of tubular epithelial polarity, and epithelial fluid secretion. In addition, a number of pronounced extracellular matrix changes have been found in the cystic kidneys of several animal models and in human autosomal dominant PKD. These abnormalities include thickened, laminated basement membrane, increased expression of alpha 1 type IV collagen and laminins B1 and B2, and changes in heparan sulfate proteoglycan and fibronectin. Some of these changes can also be seen in vitro, reflecting intrinsic abnormalities, and may be associated with abnormal tubular morphogenesis early in cyst formation as well as later in cyst expansion. We have been investigating gene expression in the C57BL/6J-cpk mouse, which has an autosomal recessive form of PKD, to determine the genetic basis of the abnormal tubule cell growth and morphology manifested during cyst formation.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Human-mouse homologies in the region of the polycystic kidney disease gene (PKD1)

Autosomal dominant polycystic kidney disease (PKD1) is linked to the alpha-globin locus near the telomere of chromosome 16p. We established the existence of a conserved linkage group in mouse by mapping conserved sequences and cDNAs from the region surrounding the PKD1 gene in the mouse genome. Results obtained with the BXD recombinant strain system and somatic cell hybrids show the homologous region to be located on mouse chromosome 17 near the globin pseudogene Hba-ps4, an unprocessed alpha-like globin gene. The markers we mapped are widely distributed over the region known to contain the PKD1 gene, and it is therefore likely that the mouse homologue of PKD1 is also located on mouse chromosome 17.