Characterization of the Han:SPRD rat model for hereditary polycystic kidney disease

The Han:SPRD Rat: A Preclinical Model of Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) stands as the most prevalent hereditary renal disorder in humans, ultimately culminating in end-stage kidney disease. Animal models carrying mutations associated with polycystic kidney disease have played an important role in the advancement of ADPKD research. The Han:SPRD rat model, carrying an R823W mutation in the Anks6 gene, is characterized by cyst formation and kidney enlargement. The mutated protein, named Samcystin, is localized in cilia of tubular epithelial cells and seems to be involved in cystogenesis. The homozygous Anks6 mutation leads to end-stage renal disease and death, making it a critical factor in kidney development and function. This review explores the utility of the Han:SPRD rat model, highlighting its phenotypic similarity to human ADPKD. Specifically, we discuss its role in preclinical trials and its importance for investigating the pathogenesis of the disease and developing new therapeutic approaches.

Ouabain enhances renal cyst growth in a slowly progressive mouse model of autosomal dominant polycystic kidney disease

Renal cyst progression in autosomal dominant polycystic kidney disease (ADPKD) is highly dependent on agents circulating in blood. We have previously shown, using different in vitro models, that one of these agents is the hormone ouabain. By binding to Na+-K+-ATPase (NKA), ouabain triggers a cascade of signal transduction events that enhance ADPKD cyst progression by stimulating cell proliferation, fluid secretion, and dedifferentiation of the renal tubular epithelial cells. Here, we determined the effects of ouabain in vivo. We show that daily administration of ouabain to Pkd1RC/RC ADPKD mice for 1-5 mo, at physiological levels, augmented kidney cyst area and number compared with saline-injected controls. Also, ouabain favored renal fibrosis; however, renal function was not significantly altered as determined by blood urea nitrogen levels. Ouabain did not have a sex preferential effect, with male and female mice being affected equally. By contrast, ouabain had no significant effect on wild-type mice. In addition, the actions of ouabain on Pkd1RC/RC mice were exacerbated when another mutation that increased the affinity of NKA for ouabain was introduced to the mice (Pkd1RC/RCNKAα1OS/OS mice). Altogether, this work highlights the role of ouabain as a procystogenic factor in the development of ADPKD in vivo, that the ouabain affinity site on NKA is critical for this effect, and that circulating ouabain is an epigenetic factor that worsens the ADPKD phenotype.NEW & NOTEWORTHY This work shows that the hormone ouabain enhances the progression of autosomal dominant polycystic kidney disease (ADPKD) in vivo. Ouabain augments the size and number of renal cysts, the kidney weight to body weight ratio, and kidney fibrosis in an ADPKD mouse model. The Na+-K+-ATPase affinity for ouabain plays a critical role in these effects. In addition, these outcomes are independent of the sex of the mice.

TRPV4 functional status in cystic cells regulates cystogenesis in autosomal recessive polycystic kidney disease during variations in dietary potassium

Mechanosensitive TRPV4 channel plays a dominant role in maintaining [Ca2+ ]i homeostasis and flow-sensitive [Ca2+ ]i signaling in the renal tubule. Polycystic kidney disease (PKD) manifests as progressive cyst growth due to cAMP-dependent fluid secretion along with deficient mechanosensitivity and impaired TRPV4 activity. Here, we tested how regulation of renal TRPV4 function by dietary K+ intake modulates the rate of cystogenesis and mechanosensitive [Ca2+ ]i signaling in cystic cells of PCK453 rats, a homologous model of human autosomal recessive PKD (ARPKD). One month treatment with both high KCl (5% K+ ) and KB/C (5% K+ with bicarbonate/citrate) diets significantly increased TRPV4 levels when compared to control (0.9% K+ ). High KCl diet caused an increased TRPV4-dependent Ca2+ influx, and partial restoration of mechanosensitivity in freshly isolated monolayers of cystic cells. Unexpectedly, high KB/C diet induced an opposite effect by reducing TRPV4 activity and worsening [Ca2+ ]i homeostasis. Importantly, high KCl diet decreased cAMP, whereas high KB/C diet further increased cAMP levels in cystic cells (assessed as AQP2 distribution). At the systemic level, high KCl diet fed PCK453 rats had significantly lower kidney-to-bodyweight ratio and reduced cystic area. These beneficial effects were negated by a concomitant administration of an orally active TRPV4 antagonist, GSK2193874, resulting in greater kidney weight, accelerated cystogenesis, and augmented renal injury. High KB/C diet also exacerbated renal manifestations of ARPKD, consistent with deficient TRPV4 activity in cystic cells. Overall, we demonstrate that TRPV4 channel activity negatively regulates cAMP levels in cystic cells thus attenuating (high activity) or accelerating (low activity) ARPKD progression.

Adult human kidney organoids originate from CD24+ cells and represent an advanced model for adult polycystic kidney disease

Adult kidney organoids have been described as strictly tubular epithelia and termed tubuloids. While the cellular origin of tubuloids has remained elusive, here we report that they originate from a distinct CD24+ epithelial subpopulation. Long-term-cultured CD24+ cell-derived tubuloids represent a functional human kidney tubule. We show that kidney tubuloids can be used to model the most common inherited kidney disease, namely autosomal dominant polycystic kidney disease (ADPKD), reconstituting the phenotypic hallmark of this disease with cyst formation. Single-cell RNA sequencing of CRISPR-Cas9 gene-edited PKD1- and PKD2-knockout tubuloids and human ADPKD and control tissue shows similarities in upregulation of disease-driving genes. Furthermore, in a proof of concept, we demonstrate that tolvaptan, the only approved drug for ADPKD, has a significant effect on cyst size in tubuloids but no effect on a pluripotent stem cell-derived model. Thus, tubuloids are derived from a tubular epithelial subpopulation and represent an advanced system for ADPKD disease modeling.

Pharmacological Effects of Panduratin A on Renal Cyst Development in In Vitro and In Vivo Models of Polycystic Kidney Disease

Renal cyst expansion in polycystic kidney disease (PKD) involves abnormalities in both cyst-lining-cell proliferation and fluid accumulation. Suppression of these processes may retard the progression of PKD. Evidence suggests that the activation of 5' AMP-activated protein kinase (AMPK) inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated chloride secretion, leading to reduced progression of PKD. Here we investigated the pharmacological effects of panduratin A, a bioactive compound known as an AMPK activator, on CFTR-mediated chloride secretion and renal cyst development using in vitro and animal models of PKD. We demonstrated that AMPK was activated in immortalized normal renal cells and autosomal dominant polycystic kidney disease (ADPKD) cells following treatment with panduratin A. Treatment with panduratin A reduced the number of renal cyst colonies corresponding with a decrease in cell proliferation and phosphorylated p70/S6K, a downstream target of mTOR signaling. Additionally, panduratin A slowed cyst expansion via inhibition of the protein expression and transport function of CFTR. In heterozygous Han:Sprague-Dawley (Cy/+) rats, an animal model of PKD, intraperitoneal administration of panduratin A (25 mg/kg BW) for 5 weeks significantly decreased the kidney weight per body weight ratios and the cystic index. Panduratin A also reduced collagen deposition in renal tissue. Intraperitoneal administration of panduratin A caused abdominal bleeding and reduced body weight. However, 25 mg/kg BW of panduratin A via oral administration in the PCK rats, another non-orthologous PKD model, showed a significant decrease in the cystic index without severe adverse effects, indicating that the route of administration is critical in preventing adverse effects while still slowing disease progression. These findings reveal that panduratin A might hold therapeutic properties for the treatment of PKD.

Kidney Injury Molecule-1 Is Specifically Expressed in Cystically-Transformed Proximal Tubules of the PKD/Mhm (cy/+) Rat Model of Polycystic Kidney Disease

Expression of kidney injury molecule-1 (Kim-1) is rapidly upregulated following tubular injury, constituting a biomarker for acute kidney damage. We examined the renal localization of Kim-1 expression in PKD/Mhm (polycystic kidney disease, Mannheim) (cy/+) rats (cy: mutated allel, +: wild type allel), an established model for autosomal dominant polycystic kidney disease, with chronic, mainly proximal tubulointerstitial alterations. For immunohistochemistry or Western blot analysis, kidneys of male adult heterozygously-affected (cy/+) and unaffected (+/+) littermates were perfusion-fixed or directly removed. Kim-1 expression was determined using peroxidase- or fluorescence-linked immunohistochemistry (alone or in combination with markers for tubule segments or differentiation). Compared to (+/+), only in (cy/+) kidneys, a chronic expression of Kim-1 could be detected by Western blot analysis, which was histologically confined to an apical cellular localization in areas of cystically-transformed proximal tubules with varying size and morphology, but not in distal tubular segments. Kim-1 was expressed by cystic epithelia exhibiting varying extents of dedifferentiation, as shown by double labeling with aquaporin-1, vimentin or osteopontin, yielding partial cellular coexpression. In this model, in contrast to other known molecules indicating renal injury and/or repair mechanisms, the chronic renal expression of Kim-1 is strictly confined to proximal cysts. Its exact role in interfering with tubulo-interstitial alterations in polycystic kidney disease warrants future investigations.

Influence of the R823W mutation on the interaction of the ANKS6-ANKS3: insights from molecular dynamics simulation and free energy analysis

The sterile alpha motif (SAM) domain of the protein ANKS6, a protein-protein interaction domain, is responsible for autosomal dominant polycystic kidney disease. Although the disease is the result of the R823W point mutation in the SAM domain of the protein ANKS6, the molecular details are still unclear. We applied molecular dynamics simulations, the principal component analysis, and the molecular mechanics Poisson-Boltzmann surface area binding free energy calculation to explore the structural and dynamic effects of the R823W point mutation on the complex ANKS6-ANKS3 (PDB ID: 4NL9) in comparison to the wild proteins. The energetic analysis presents that the wild type has a more stable structure than the mutant. The R823W point mutation not only disrupts the structure of the ANKS6 SAM domain but also negatively affects the interaction of the ANKS6-ANKS3. These results further clarify the previous experiments to understand the ANKS6-ANKS3 interaction comprehensively. In summary, this study would provide useful suggestions to understand the interaction of these proteins and their fatal action on mediating kidney function.

The SAM domain of ANKS6 has different interacting partners and mutations can induce different cystic phenotypes

The ankyrin repeat and sterile α motif (SAM) domain-containing six gene (Anks6) is a candidate for polycystic kidney disease (PKD). Originally identified in the PKD/Mhm(cy/+) rat model of PKD, the disease is caused by a mutation (R823W) in the SAM domain of the encoded protein. Recent studies support the etiological role of the ANKS6 SAM domain in human cystic diseases, but its function in kidney remains unknown. To investigate the role of ANKS6 in cyst formation, we screened an archive of N-ethyl-N-nitrosourea-treated mice and derived a strain carrying a missense mutation (I747N) within the SAM domain of ANKS6. This mutation is only six amino acids away from the PKD-causing mutation (R823W) in cy/+ rats. Evidence of renal cysts in these mice confirmed the crucial role of the SAM domain of ANKS6 in kidney function. Comparative phenotype analysis in cy/+ rats and our Anks6(I747N) mice further showed that the two models display noticeably different PKD phenotypes and that there is a defective interaction between ANKS6 with ANKS3 in the rat and between ANKS6 and BICC1 (bicaudal C homolog 1) in the mouse. Thus, our data demonstrate the importance of ANKS6 for kidney structure integrity and the essential mediating role of its SAM domain in the formation of protein complexes.

Impaired expression of key molecules of ammoniagenesis underlies renal acidosis in a rat model of chronic kidney disease

BACKGROUND

Advanced chronic kidney disease (CKD) is associated with the development of renal metabolic acidosis. Metabolic acidosis per se may represent a trigger for progression of CKD. Renal acidosis of CKD is characterized by low urinary ammonium excretion with preserved urinary acidification indicating a defect in renal ammoniagenesis, ammonia excretion or both. The underlying molecular mechanisms, however, have not been addressed to date.

METHODS

We examined the Han:SPRD rat model and used a combination of metabolic studies, mRNA and protein analysis of renal molecules involved in acid-base handling.

RESULTS

We demonstrate that rats with reduced kidney function as evident from lower creatinine clearance, lower haematocrit, higher plasma blood urea nitrogen, creatinine, phosphate and potassium had metabolic acidosis that could be aggravated by HCl acid loading. Urinary ammonium excretion was highly reduced whereas urinary pH was more acidic in CKD compared with control animals. The abundance of key enzymes and transporters of proximal tubular ammoniagenesis (phosphate-dependent glutaminase, PEPCK and SNAT3) and bicarbonate transport (NBCe1) was reduced in CKD compared with control animals. In the collecting duct, normal expression of the B1 H(+)-ATPase subunit is in agreement with low urinary pH. In contrast, the RhCG ammonia transporter, critical for the final secretion of ammonia into urine was strongly down-regulated in CKD animals.

CONCLUSION

In the Han:SPRD rat model for CKD, key molecules required for renal ammoniagenesis and ammonia excretion are highly down-regulated providing a possible molecular explanation for the development and maintenance of renal acidosis in CKD patients.

Characterization of the SAM domain of the PKD-related protein ANKS6 and its interaction with ANKS3

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disorder leading to end-stage renal failure in humans. In the PKD/Mhm(cy/+) rat model of ADPKD, the point mutation R823W in the sterile alpha motif (SAM) domain of the protein ANKS6 is responsible for disease. SAM domains are known protein-protein interaction domains, capable of binding each other to form polymers and heterodimers. Despite its physiological importance, little is known about the function of ANKS6 and how the R823W point mutation leads to PKD. Recent work has revealed that ANKS6 interacts with a related protein called ANKS3. Both ANKS6 and ANKS3 have a similar domain structure, with ankyrin repeats at the N-terminus and a SAM domain at the C-terminus.

RESULTS

The SAM domain of ANKS3 is identified as a direct binding partner of the ANKS6 SAM domain. We find that ANKS3-SAM polymerizes and ANKS6-SAM can bind to one end of the polymer. We present crystal structures of both the ANKS3-SAM polymer and the ANKS3-SAM/ANKS6-SAM complex, revealing the molecular details of their association. We also learn how the R823W mutation disrupts ANKS6 function by dramatically destabilizing the SAM domain such that the interaction with ANKS3-SAM is lost.

CONCLUSIONS

ANKS3 is a direct interacting partner of ANKS6. By structurally and biochemically characterizing the interaction between the ANKS3 and ANKS6 SAM domains, our work provides a basis for future investigation of how the interaction between these proteins mediates kidney function.

Aberrant expression of laminin-332 promotes cell proliferation and cyst growth in ARPKD

Basement membrane abnormalities have often been observed in kidney cysts of polycystic kidney disease (PKD) patients and animal models. There is an abnormal deposition of extracellular matrix molecules, including laminin-α3,β3,γ2 (laminin-332), in human autosomal dominant PKD (ADPKD). Knockdown of PKD1 paralogs in zebrafish leads to dysregulated synthesis of the extracellular matrix, suggesting that altered basement membrane assembly may be a primary defect in ADPKD. In this study, we demonstrate that laminin-332 is aberrantly expressed in cysts and precystic tubules of human autosomal recessive PKD (ARPKD) kidneys as well as in the kidneys of PCK rats, an orthologous ARPKD model. There was aberrant expression of laminin-γ2 as early as postnatal day 2 and elevated laminin-332 protein in postnatal day 30, coinciding with the formation and early growth of renal cysts in PCK rat kidneys. We also show that a kidney cell line derived from Oak Ridge polycystic kidney mice, another model of ARPKD, exhibited abnormal lumen-deficient and multilumen structures in Matrigel culture. These cells had increased proliferation rates and altered expression levels of laminin-332 compared with their rescued counterparts. A function-blocking polyclonal antibody to laminin-332 significantly inhibited their abnormal proliferation rates and rescued their aberrant phenotype in Matrigel culture. Furthermore, abnormal laminin-332 expression in cysts originating from collecting ducts and proximal tubules as well as in precystic tubules was observed in a human end-stage ADPKD kidney. Our results suggest that abnormal expression of laminin-332 contributes to the aberrant proliferation of cyst epithelial cells and cyst growth in genetic forms of PKD.

Renal expression of FGF23 and peripheral resistance to elevated FGF23 in rodent models of polycystic kidney disease

Fibroblast growth factor 23 (FGF23) regulates phosphate homeostasis and is linked to cardiovascular disease and all-cause mortality in chronic kidney disease. FGF23 rises in patients with CKD stages 2-3, but in patients with autosomal dominant polycystic kidney disease, the increase of FGF23 precedes the first measurable decline in renal function. The mechanisms governing FGF23 production and effects in kidney disease are largely unknown. Here we studied the relation between FGF23 and mineral homeostasis in two animal models of PKD. Plasma FGF23 levels were increased 10-fold in 4-week-old cy/+ Han:SPRD rats, whereas plasma urea and creatinine concentrations were similar to controls. Plasma calcium and phosphate levels as well as TmP/GFR were similar in PKD and control rats at all time points examined. Expression and activity of renal phosphate transporters, the vitamin D3-metabolizing enzymes, and the FGF23 co-ligand Klotho in the kidney were similar in PKD and control rats through 8 weeks of age, indicating resistance to FGF23, although phosphorylation of the FGF receptor substrate 2α protein was enhanced. In the kidneys of rats with PKD, FGF23 mRNA was highly expressed and FGF23 protein was detected in cells lining renal cysts. FGF23 expression in bone and spleen was similar in control rats and rats with PKD. Similarly, in an inducible Pkd1 knockout mouse model, plasma FGF23 levels were elevated, FGF23 was expressed in kidneys, but renal phosphate excretion was normal. Thus, the polycystic kidney produces FGF23 but is resistant to its action.

Renal cyclooxygenase and lipoxygenase products are altered in polycystic kidneys and by dietary soy protein and fish oil treatment in the Han:SPRD-Cy rat

SCOPE

Dietary fish oil (FO) and soy protein (SP) are two interventions that slow disease progression in the Han:SPRD-Cy rat model of polycystic kidney disease (PKD). Inhibition of cyclooxygenase (COX)-derived eicosanoids also reduces disease progression, but the role of lipoxygenase (LOX) products in this disease is not known.

METHODS AND RESULTS

Since dietary FO and SP have been shown to alter eicosanoid formation via differing mechanisms, Han:SPRD-Cy rats were given diets containing either casein protein (CP) or SP, and soy oil (SO) or FO. Analysis of eicosanoids revealed that renal COX products were higher and LOX products were lower in diseased kidneys. SP feeding resulted in lower COX products, activity and COX1 protein and higher LOX products in the diseased kidneys in parallel with reduced renal cyst growth and fibrosis. By comparison, FO reduced both COX and LOX products produced from n-6 fatty acids and increased 3-series prostanoids in both normal and diseased cortex and medulla, but these differences did not parallel effects on disease.

CONCLUSION

Renal COX-derived eicosanoids are elevated and LOX products are reduced in this model of kidney disease. The effects of dietary SP, but not FO, on renal eicosanoids parallel the effects on disease.

Novel role of ouabain as a cystogenic factor in autosomal dominant polycystic kidney disease

The classic role of the Na-K-ATPase is that of a primary active transporter that utilizes cell energy to establish and maintain transmembrane Na(+) and K(+) gradients to preserve cell osmotic stability, support cell excitability, and drive secondary active transport. Recent studies have revealed that Na-K-ATPase located within cholesterol-containing lipid rafts serves as a receptor for cardiotonic steroids, including ouabain. Traditionally, ouabain was viewed as a toxin produced only in plants, and it was used in relatively high concentrations to experimentally block the pumping action of the Na-K-ATPase. However, the new and unexpected role of the Na-K-ATPase as a signal transducer revealed a novel facet for ouabain in the regulation of a myriad of cell functions, including cell proliferation, hypertrophy, apoptosis, mobility, and metabolism. The seminal discovery that ouabain is endogenously produced in mammals and circulates in plasma has fueled the interest in this endogenous molecule as a potentially important hormone in normal physiology and disease. In this article, we review the role of the Na-K-ATPase as an ion transporter in the kidney, the experimental evidence for ouabain as a circulating hormone, the function of the Na-K-ATPase as a signal transducer that mediates ouabain's effects, and novel results for ouabain-induced Na-K-ATPase signaling in cystogenesis of autosomal dominant polycystic kidney disease.

Inhibition of Comt with tolcapone slows progression of polycystic kidney disease in the more severely affected PKD/Mhm (cy/+) substrain of the Hannover Sprague-Dawley rat

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common human inherited diseases. Modifier genes seem to modulate the disease progression and might therefore be promising drug targets. Although a number of modifier loci have been already identified, no modifier gene has been proven to be a real modifier yet.

METHODS

Gene expression profiling of two substrains of the Han:SPRD rat, namely PKD/Mhm and PKD/US, both harboring the same mutation, was conducted in 36-day-old animals. Catechol-O-methyltransferase (Comt) was identified as a potential modifier gene. A 3-month treatment with tolcapone, a selective inhibitor of Comt, was carried out in PKD/Mhm and PKD/US (cy/+) animals.

RESULTS

Comt is localized within a known modifier locus of PKD (MOP2). The enzyme encoding gene was found upregulated in the more severely affected PKD/Mhm substrain and was hence presumed to be a putative modifier gene of PKD. The treatment with tolcapone markedly attenuated the loss of renal function, inhibited renal enlargement, shifted the size distribution of renal cysts and retarded cell proliferation, apoptosis, inflammation and fibrosis development in affected (cy/+) male and female PKD/Mhm and PKD/US rats.

CONCLUSIONS

Comt has been confirmed to be the first reported modifier gene for PKD and tolcapone offers a promising drug for treating PKD.

Parallel analysis of mRNA and microRNA microarray profiles to explore functional regulatory patterns in polycystic kidney disease: using PKD/Mhm rat model

Autosomal polycystic kidney disease (ADPKD) is a frequent monogenic renal disease, characterised by fluid-filled cysts that are thought to result from multiple deregulated pathways such as cell proliferation and apoptosis. MicroRNAs (miRNAs) are small non-coding RNAs that regulate the expression of many genes associated with such biological processes and human pathologies. To explore the possible regulatory role of miRNAs in PKD, the PKD/Mhm (cy/+) rat, served as a model to study human ADPKD. A parallel microarray-based approach was conducted to profile the expression changes of mRNAs and miRNAs in PKD/Mhm rats. 1,573 up- and 1,760 down-regulated genes were differentially expressed in PKD/Mhm. These genes are associated with 17 pathways (such as focal adhesion, cell cycle, ECM-receptor interaction, DNA replication and metabolic pathways) and 47 (e.g., cell proliferation, Wnt and Tgfβ signaling) Gene Ontologies. Furthermore, we found the similar expression patterns of deregulated genes between PKD/Mhm (cy/+) rat and human ADPKD, PKD1^L3/L3, PKD1^−/−, Hnf1α-deficient, and Glis2^lacZ/lacZ models. Additionally, several differentially regulated genes were noted to be target hubs for miRNAs. We also obtained 8 significantly up-regulated miRNAs (rno-miR-199a-5p, −214, −146b, −21, −34a, −132, −31 and −503) in diseased kidneys of PKD/Mhm rats. Additionally, the binding site overrepresentation and pathway enrichment analyses were accomplished on the putative targets of these 8 miRNAs. 7 out of these 8 miRNAs and their possible interactions have not been previously described in ADPKD. We have shown a strong overlap of functional patterns (pathways) between deregulated miRNAs and mRNAs in the PKD/Mhm (cy/+) rat model. Our findings suggest that several miRNAs may be associated in regulating pathways in ADPKD. We further describe novel miRNAs and their possible targets in ADPKD, which will open new avenues to understand the pathogenesis of human ADPKD. Furthermore they could serve as a useful resource for anti-fibrotic therapeutics.

Polycystins and cellular Ca2+ signaling

The cystic phenotype in autosomal dominant polycystic kidney disease is characterized by a profound dysfunction of many cellular signaling patterns, ultimately leading to an increase in both cell proliferation and apoptotic cell death. Disturbance of normal cellular Ca²⁺ signaling seems to be a primary event and is clearly involved in many pathways that may lead to both types of cellular responses. In this review, we summarize the current knowledge about the molecular and functional interactions between polycystins and multiple components of the cellular Ca²⁺-signaling machinery. In addition, we discuss the relevant downstream responses of the changed Ca²⁺ signaling that ultimately lead to increased proliferation and increased apoptosis as observed in many cystic cell types.

The Raf kinase inhibitor PLX5568 slows cyst proliferation in rat polycystic kidney disease but promotes renal and hepatic fibrosis

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common cause of renal failure. Aberrant epithelial cell proliferation is a major cause of progressive cyst enlargement in ADPKD. Since activation of the Ras/Raf signaling system has been detected in cyst-lining epithelia, inhibition of Raf kinase has been proposed as an approach to retard the progression of ADPKD. Methods and results. PLX5568, a novel selective small molecule inhibitor of Raf kinases, attenuated proliferation of human ADPKD cyst epithelial cells. It reduced in vitro cyst growth of Madin-Darby Canine Kidney cells and of human ADPKD cells within a collagen gel. In male cy/+ rats with polycystic kidneys, PLX5568 inhibited renal cyst growth along with a significant reduction in the number of proliferating cell nuclear antigen- and phosphorylated extracellular signal-regulated kinase-positive cyst-lining epithelial cells. Furthermore, treated animals showed increased capacity to concentrate urine. However, PLX5568 did not lead to a consistent improvement of renal function. Moreover, although relative cyst volume was decreased, total kidney-to-body weight ratio was not significantly reduced by PLX5568. Further analyses revealed a 2-fold increase of renal and hepatic fibrosis in animals treated with PLX5568.

CONCLUSIONS

PLX5568 attenuated cyst enlargement in vitro and in a rat model of ADPKD without improving kidney function, presumably due to increased renal fibrosis. These data suggest that effective therapies for the treatment of ADPKD will need to target fibrosis as well as the growth of cysts.

Transgenic overexpression of Anks6(p.R823W) causes polycystic kidney disease in rats

The PKD/Mhm(cy/+) rat is a widely used animal model for the study of human autosomal dominant polycystic kidney disease, one of the most common genetic disorders, affecting one in 1000 individuals. We identified a new gene, Anks6, which is mutated (Anks6((p.R823W))) in PKD/Mhm(cy/+) rats. The evidence for a causal link between Anks6((p.R823W)) and cystogenesis is still lacking, and the function of Anks6 is presently unknown. This study presents a novel transgenic rat model that overexpresses the mutated 2.8-kb Anks6((p.R823W)) cDNA in the renal tubular epithelium. The transgenic Anks6((p.R823W)) acts in a dominant-negative fashion and causes a predictable polycystic phenotype that largely mimics the general characteristics of the PKD/Mhm(cy/+) rats. Cyst development is accompanied by enhanced c-myc expression and continuous proliferation, apoptosis, and de-differentiation of the renal tubular epithelium as well as by a lack of translational up-regulation of p21 during aging. Using Northern blot analysis and in situ hybridization studies, we identified the first 10 days of age as the period during which transgene expression precedes and initiates cystic growth. Thus, we not only provide the first in vivo evidence for a causal link between the novel Anks6((p.R823W)) gene mutation and polycystic kidney disease, but we also developed a new transgenic rat model that will serve as an important resource for further exploration of the still unknown function of Anks6.

Apoptosis in polycystic kidney disease

Apoptosis is the process of programmed cell death. It is a ubiquitous, controlled process consuming cellular energy and designed to avoid cytokine release despite activation of local immune cells, which clear the cell fragments. The process occurs during organ development and in maintenance of homeostasis. Abnormalities in any step of the apoptotic process are associated with autoimmune diseases and malignancies. Polycystic kidney disease (PKD) is the most common inherited kidney disease leading to end-stage renal disease (ESRD). Cyst formation requires multiple mechanisms and apoptosis is considered one of them. Abnormalities in apoptotic processes have been described in various murine and rodent models of PKD as well as in human PKD kidneys. The purpose of this review is to outline the role of apoptosis in progression of PKD as well as to describe the mechanisms involved. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Global gene expression profiling in early-stage polycystic kidney disease in the Han:SPRD Cy rat identifies a role for RXR signaling

Han:SPRD Cy is a spontaneous rat model of polycystic kidney disease (PKD) caused by a missense mutation in Pkdr1. Cystogenesis in this model is not clearly understood. In the current study, we performed global gene expression profiling in early-stage PKD cyst development in Cy/Cy kidneys and normal (+/+) kidneys at 3 and 7 days of postnatal age. Expression profiles were determined by microarray analysis, followed by validation with real-time RT-PCR. Genes were selected with over 1.5-fold expression changes compared with age-matched +/+ kidneys for canonical pathway analysis. We found nine pathways in common between 3- and 7-day Cy/Cy kidneys. Three significantly changed pathways were designated "Vitamin D Receptor (VDR)/Retinoid X Receptor (RXR) Activation," "LPS/IL-1-Mediated Inhibition of RXR Function," and "Liver X Receptor (LXR)/RXR Activation." These results suggest that RXR-mediated signaling is significantly altered in developing kidneys with mutated Pkdr1. In gene ontology analysis, the functions of these RXR-related genes were found to be involved in regulating cell proliferation and organ morphogenesis. With real-time RT-PCR analysis, the upregulation of Ptx2, Alox15b, OSP, and PCNA, major markers of cell proliferation associated with the RXR pathway, were confirmed in 3- and 7-day Cy/Cy kidneys compared with 3-day +/+ kidneys. The increased RXR protein was observed in both the nucleus and cytoplasm of cystic epithelial cells in early-stage Cy/Cy kidneys, and the RXR-positive cells were strongly positive for PCNA staining. Taken together, cell proliferation and organ morphogenesis signals transduced by RXR-mediated pathways may have important roles for cystogenesis in early-stage PKD in this Pkdr1-mutated Cy rat.

mTORC1/2 and rapamycin in female Han:SPRD rats with polycystic kidney disease

Rapamycin slows disease progression in the male Han:SPRD (Cy/+) rat with polycystic kidney disease (PKD). The aim of this study was to determine the effect of rapamycin on PKD and the relative contributions of the proproliferative mammalian target of rapamycin complexes 1 and 2 (mTORC1 and mTORC2) in female Cy/+ rats. Female Cy/+ rats were treated with rapamycin from 4 to 12 wk of age. In vehicle-treated Cy/+ rats, kidney volume increased by 40% and cyst volume density (CVD) was 19%. Phosphorylated S6 (p-S6) ribosomal protein, a marker of mTORC1 activity, was increased in Cy/+ rats compared with normal littermate controls (+/+) and decreased by rapamycin. Despite activation of mTORC1 in female Cy/+ rats, rapamycin had no effect on kidney size, CVD, number of PCNA-positive cystic tubular cells, caspase-3 activity, or the number of terminal deoxynucleotidyl transferase dUTP-mediated nick-end label-positive apoptotic cells. To determine a reason for the lack of effect of rapamycin, we studied the mTORC2 signaling pathway. On immunoblot of kidney, phosphorylated (Ser473) Akt (p-Akt), a marker of mTORC2 activity, was increased in female Cy/+ rats treated with rapamycin. Phosphorylated (Ser657) PKCα, a substrate of mTORC2, was unaffected by rapamycin in females. In contrast, in male rats, where rapamycin significantly decreases PKD, p-Akt (Ser473) was decreased by rapamcyin. PKCα (Ser657) was increased in male Cy/+ rats but was unaffected by rapamycin. In summary, in female Cy/+ rats, rapamycin had no effect on PKD and proproliferative p-Akt (Ser473) activity was increased by rapamycin. There were differential effects of rapamycin on mTORC2 signaling in female vs. male Cy/+ rats.

Elevated TGFbeta-Smad signalling in experimental Pkd1 models and human patients with polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited renal disease characterized by many fluid-filled cysts and interstitial fibrosis in the kidneys, leading to chronic renal failure. During cystogenesis the renal tubules undergo extensive structural alterations that are accompanied by altered cellular signalling, directly and/or indirectly regulated by the PKD1 and PKD2 proteins. Since transforming growth factor (TGF)-beta signalling modulates cell proliferation, differentiation, apoptosis, adhesion and migration of various cell types, we studied the activation of this signalling pathway in Pkd1-mutant mouse models at different stages of the disease. Therefore, we analysed expression of the TGFbeta-Smad signalling pathway and its target genes in different Pkd1 mutant mouse models in various stages of polycystic disease. Nuclear accumulation of P-Smad2 in cyst lining epithelial cells was not observed in the initiation phase but was observed at mild and more advanced stages of PKD. This coincides with mild fibrosis and increased mRNA levels of TGFbeta target genes, such as fibronectin, collagen type I, plasminogen activator inhibitor 1 and matrix metalloproteinase-2. At this stage many interstitial fibroblasts were found around cysts, which also showed nuclear localization for P-Smad2. However, bone morphogenetic protein (BMP) signalling, which can antagonize TGFbeta signalling, is not affected, since nuclear expression of P-Smad1/5/8 and expression of the BMP target gene, inhibitor of DNA binding/differential-1 (ID-1) is not altered compared to wild-type controls. Also, human kidneys with progressive ADPKD showed increased nuclear localization of P-Smad2, while in general expression of P-Smad1/5/8 was weak. These results exclude TGFbeta signalling at the initiation of cystogenesis, but indicate an important role during cyst progression and in fibrogenesis of progressive ADPKD.

Polycystic kidney disease in Han:SPRD Cy rats is associated with elevated expression and mislocalization of SamCystin

Polycystic kidney disease (PKD) in Han:SPRD Cy rats is caused by a missense mutation in Anks6 (also called Pkdr1), leading to an R823W substitution in SamCystin, a protein that contains ankyrin repeats and a sterile alpha motif (SAM). The cellular function of SamCystin and the role of the Cy (R823W) mutation in cyst formation are unknown. In normal SPRD rats, SamCystin was found to be expressed in proximal tubules and glomeruli; protein expression was highest at 7 days of age and declined by ∼50-60% at 45-84 days of age. In Cy/+ and Cy/Cy kidneys, expression of SamCystin was lower than in +/+ kidneys at 3 and 7 days but became elevated at 21 days. Immunohistochemical analysis revealed that SamCystin was distributed on the brush border of proximal tubules in normal rat kidneys. In Cy/+ kidneys, there were robust SamCystin staining in cyst-lining epithelial cells and loss of apical localization, and increased number of PCNA-positive cells in cyst-lining epithelia. Verapamil, an L-type Ca(2+) channel blocker, accelerated PKD progression in this model and caused a further increase in the expression and abnormal distribution of SamCystin. We conclude that aberrant expression and mislocalization of R823W SamCystin lead to increased cell proliferation and renal cyst formation.

Dietary soy protein selectively reduces renal prostanoids and cyclooxygenases in polycystic kidney disease

Increasing evidence in human chronic kidney disease and in animal models indicates the potential utility of dietary soy protein in the treatment of this disorder. A model in which a beneficial soy protein effect has been consistently demonstrated is the Han:SPRD-cy rat model of polycystic kidney disease. Therefore, since dietary soy protein alters renal hemodynamics and prostanoid production, the effects of dietary soy protein on renal prostanoids and related rate-limiting enzymes were examined. Normal and diseased weanling rats were given diets containing casein or soy protein for 7 wk. At 10 wk of age, renal levels of thromboxane B(2) (TXB(2), stable metabolite of TXA(2)), prostaglandin E(2) (PGE(2)) and 6-keto PGF(1alpha) (stable metabolite of PGI(2)) and activities of cyclooxygenase 1 (COX1) and COX2 were elevated in diseased compared to normal kidneys. Soy protein feeding resulted in 49% lower in vitro steady-state levels of TXB(2), and 76% less 6-keto PGF(1alpha) produced by COX1 activity in diseased kidneys, while not altering these parameters in normal kidneys. It also resulted in 47% less TXB(2) and 36% lower 6-keto PGF(1alpha) produced by COX2 activity in diseased kidneys. The relative effect of soy protein feeding on COX2 activity was in the order of TXB(2) > 6-keto PGF(1alpha) > PGE(2). Diseased kidneys had elevated protein and mRNA levels of cytosolic phospholipase A(2) (cPLA(2)) and COX1 and lower levels of COX2. Dietary soy protein attenuated the protein levels of cPLA(2) in diseased kidneys, and reduced COX2 mRNA expression in both normal and diseased kidneys. Dietary soy protein therefore reduced the levels of specific renal prostanoids, cPLA(2) and COX enzymes in this model of polycystic kidney disease, a model in which soy protein has been demonstrated to reduce disease progression.

Long-term rapamycin therapy in the Han:SPRD rat model of polycystic kidney disease (PKD)

BACKGROUND

Short-term studies have demonstrated that rapamycin or everolimus treatment decreases cyst formation and improves renal function in animal models of polycystic kidney disease (PKD). Autosomal dominant polycystic kidney disease (ADPKD) patients would likely require life-long treatment with rapamycin.

METHODS

Male Han:SPRD rats with PKD (Cy/+) were treated with rapamycin (0.2 mg/kg/day IP) or vehicle from 1 to 12 months of age. Mean trough levels of rapamycin (ng/mL) were 6.6 +/- 0.1 at 8 weeks of age. Twelve-month-old littermates (+/+) were used as normal controls.

RESULTS

Twelve-month-old male Cy/+ rats treated with the vehicle had a more than doubling of kidney volume, severe chronic renal failure, severe hypertension and increased heart weight compared to normal littermate controls (+/+). After rapamycin treatment, 12-month-old Cy/+ rats had markedly improved kidney volume, renal function, blood pressure and heart weight not statistically different from controls. Rapamycin reduced the cyst volume density (CVD) by 72%. Mammalian target of rapamycin (mTOR) activation in the heart, as evidenced by a marked increase in the phospho-S6 protein that was inhibited by rapamycin, was demonstrated in 12-month-old Cy/+ rats.

CONCLUSION

In conclusion, long-term rapamycin treatment in Cy/+ rats results in a normalization of kidney volume, renal function, blood pressure and heart weight. The novel finding that rapamycin decreases hypertension, heart enlargement and mTOR signalling in the heart in PKD rats is reported. The only side effect of rapamycin treatment was an 11% decrease in body weight.

Identification of phosphoproteins in kidney tissues from patients with autosomal dominant polycystic kidney disease

Protein phosphorylation is a very important PTM. Phosphorylation/dephosphorylation of a protein can alter its behavior in almost every conceivable way. Previous studies indicate that abnormal phosphorylation is involved in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). However, large-scale proteomic analysis of altered phosphoproteins in ADPKD has not been reported. In this study, total proteins from ADPKD cystic kidney tissues (n = 5) and normal kidney tissues (n = 5) were extracted and phosphoproteins were enriched by phosphate metal affinity chromatography, then separated by 2-DE and identified by LC-MS/MS. Between the two groups, 48 protein spots showing more than a twofold difference were detected. Among them, 28 spots were up-regulated and 20 down-regulated in ADPKD kidney tissues. Of these, 38 different proteins were identified including cell signaling proteins, cytoskeleton proteins, mitochondria metabolic enzymes, antioxidant proteins, molecular chaperones, transcription factors and regulators. Two differential phosphoproteins, annexin II and tropomyosin, were further confirmed by immunoprecipitation and Western blot analysis. The results show that there are many kinds of abnormal phosphoproteins in ADPKD cystic kidney tissues. More studies on the functions of the differential phosphoproteins may provide us new clues for ADPKD pathogenesis and treatment.

Genomic organization and mutation screening of the human ortholog of Pkdr1 associated with polycystic kidney disease in the rat

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common inherited disorders in humans. Although disease-causing mutations have been found in two genes, PKD1 and PKD2, a small number of ADPKD families exist that are unlinked to either of these genes, suggesting involvement of a third, as yet unidentified PKD3 gene. Susceptibility to renal cyst formation in the (cy/+) rat is caused by a missense mutation in Pkdr1 encoding the novel protein SamCystin. To initiate studies of the human orthologous gene, we determined the location and the organization of human PKDR1. We genotyped microsatellite markers flanking the human ortholog in PKD families that either are unlinked to known PKD genes, or in which mutations have not yet been identified and carried out mutation analysis in PKD patients. We identified eight novel single nucleotide polymorphisms, including three leading to amino acid changes. These variants are unlikely to account for PKD in these patients, yet the screening of other affected populations may provide information about the involvement of PKDR1 as a modifier gene in cystic kidney disease.

Modeling ciliopathies: Primary cilia in development and disease

Primary (nonmotile) cilia are currently enjoying a renaissance in light of novel ascribed functions ranging from mechanosensory to signal transduction. Their importance for key developmental pathways such as Sonic Hedgehog (Shh) and Wnt is beginning to emerge. The function of nodal cilia, for example, is vital for breaking early embryonic symmetry, Shh signaling is important for tissue morphogenesis and successful Wnt signaling for organ growth and differentiation. When ciliary function is perturbed, photoreceptors may die, kidney tubules develop cysts, limb digits multiply and brains form improperly. The etiology of several uncommon disorders has recently been associated with cilia dysfunction. The causative genes are often similar and their cognate proteins certainly share cellular locations and/or pathways. Animal models of ciliary gene ablation such as Ift88, Kif3a, and Bbs have been invaluable for understanding the broad function of the cilium. Herein, we describe the wealth of information derived from the study of the ciliopathies and their animal models.

VEGF receptor inhibition slows the progression of polycystic kidney disease

Although the receptors for vascular endothelial growth factor (VEGF) exert their effects on vasculogenesis and angiogenesis through receptors located on endothelial cells, recent studies have shown that these receptors are also present on renal tubular epithelial cells. We investigated the role of VEGF on increased tubule cell proliferation in the Han:SPRD heterozygous (Cy/+) rat model of polycystic kidney disease. The levels of VEGF in the kidneys and the serum, and the expression of the two receptors on tubules were increased in Cy/+ rats. These rats were given ribozymes that specifically inhibited VEGFR1 and VEGFR2 mRNA expression. Tubule cell proliferation within the cysts was significantly decreased in the ribozyme-treated animals leading to decreased cystogenesis, blunted renal enlargement, and prevented the loss of renal function. Our studies show that inhibition of VEGF function may be an important therapeutic option to delay the progression of polycystic kidney disease.

Faster rates of post-puberty kidney deterioration in males is correlated with elevated oxidative stress in males vs females at early puberty

Background

Post-puberty deterioration of kidneys is more rapid in males than in females. To reveal the underlying molecular mechanisms for this difference, we analyzed gender-dependent gene expression in kidneys of three groups of 36 day-old rats.

Results

The number of genes exhibiting gender-dependent expression was highly influenced by the genetic background of the rat group examined. 373, 288 and 79 genes showed differential gene expression between males and females (p = 0.001) in US, Mhm and Mhm*BN rats, respectively. Of all gender dependently expressed genes, only 39 genes were differentially expressed in all tested groups and the direction of expression change was the same for those genes for all groups. The gene expression profile suggests higher metabolic and transport activities, enhanced cell proliferation, elevated oxidative stress, and altered vascular biology in males. Furthermore, elevated levels of superoxide anion (two- to three-fold) in males compared to females were detected at early puberty, but neither at pre-puberty nor at late puberty/early adulthood.

Conclusion

Our data suggest that early puberty, with gender-related elevation in oxidative stress in males, is a key compromising factor on kidneys in males.

Effect of statin and angiotensin-converting enzyme inhibition on structural and hemodynamic alterations in autosomal dominant polycystic kidney disease model

Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening hereditary disease and is the fourth most common cause of end-stage kidney disease. Preclinical studies to identify effective interventions to prevent or slow progression of PKD nephropathy are therefore direly needed. Heterozygous Han:SPRD rats are an autosomal dominant PKD model with many of the characteristics of ADPKD in humans. In the present study, parameters known to antedate the decrease in renal function, namely, renal structure, renal blood flow (RBF), and mean arterial pressure (MAP), were evaluated with three different interventions, namely, HMG-CoA reductase inhibition with lovastatin, angiotensin-converting enzyme (ACE) inhibition with enalapril, and a combination of these two treatments. The statin therapy demonstrated structural and functional benefits, including increased RBF and decreased BUN, independently of a change in MAP, while the ACE inhibition therapy demonstrated structural benefit in association with a decrease in MAP. An enhancement of these protective interventions in this autosomal dominant PKD model was not demonstrated with the combined treatment.

Involvement of hypoxia-inducible transcription factors in polycystic kidney disease

In polycystic kidney disease (PKD), erythropoietin (EPO) production and interstitial vascularization are increased compared with other kidney diseases. EPO and several angiogenic factors are controlled by hypoxia-inducible transcription factors (HIFs), which are composed of a constitutive beta-subunit and two alternative alpha-subunits (HIF-1alpha, HIF-2alpha). We hypothesized that cyst expansion may result in pericystic hypoxia and consecutive up-regulation of HIF and thus examined the expression of HIF-alpha and HIF target genes in human PKD and in a rodent PKD model. HIF-1alpha and HIF-2alpha were found to be up-regulated in cyst epithelium and cells of cyst walls, respectively. The distinct expression pattern of the HIF-alpha isoforms closely resembles the respective pattern in normal kidneys under systemic hypoxia. Pimonidazole staining, a marker for tissue hypoxia, confirmed the existence of regional hypoxia in polycystic kidneys. Immunohistochemistry for selected target genes implicated a role for HIF-1alpha in vascular endothelial growth factor and Glut-1 activation and HIF-2alpha in endoglin and EPO stimulation. Polycystin-deficient cells showed physiological, oxygen-dependent HIF-alpha modulation, excluding a direct influence of polycystin deficiency on HIF-alpha regulation. In conclusion, HIF accumulation in human and rat PKD seems to be responsible for increased EPO production and pericystic hypervascularity and may have an impact on progression of PKD.

Endothelin B receptor blockade accelerates disease progression in a murine model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease that causes kidney failure and accounts for 10% of all patients who are on renal replacement therapy. However, the marked phenotypic variation between patients who carry the same PKD1 or PKD2 mutation suggests that nonallelic factors may have a greater influence on the cystic phenotype. Endothelin-1 (ET-1) transgenic mice have been reported to develop profound renal cystic disease and interstitial fibrosis without hypertension. The hypothesis that ET-1 acts as a modifying factor for cystic disease progression was tested in an orthologous mouse model of ADPKD (Pkd2(WS25/-)). Four experimental groups (n = 8 to 11) were treated from 5 to 16 wk of age with the highly selective orally active receptor antagonists ABT-627 (ETA) and A-192621 (ETB) singly or in combination. Unexpected, ETB blockade led to accelerated cystic kidney disease. Of significance, this was associated with a reduction in urine volume and sodium excretion and increases in urine osmolarity and renal cAMP and ET-1 concentrations. The deleterious effect of chronic ETB blockade was neutralized by simultaneous ETA blockade. ETA blockade alone resulted in a significant increase in tubular cell proliferation but did not alter the cystic phenotype. It is concluded that the balance between ETA and ETB signaling is critical for maintaining tubular structure and function in the cystic kidney. These results implicate ET, acting via vasopressin-dependent and independent pathways, as a major modifying factor for cystic disease progression in human ADPKD.

Transcriptome analysis of a rat PKD model: Importance of genes involved in extracellular matrix metabolism

Transcriptome analysis of a rat polycystic kidney disease (PKD) model: importance of genes involved in extracellular matrix metabolism. PKD is a common genetic cause of chronic renal failure, and is characterized by the accumulation of fluid-filled cysts in the kidneys and other organs. Abnormalities in the expression of selected genes thought to be involved in cystogenesis have been described, but no systematic analysis of the global transcriptomal pattern has been reported. With this aim, a rat oligomicroarray was used to identify variations in gene expression in Han:Sprague-Dawley Cy/Cy rats, an animal model presenting a severe PKD phenotype. Some upregulated genes were validated using real-time polymerase chain reaction in Cy/Cy and Cy/+ rats. Among the 350 genes identified as being upregulated, we found about 30 genes involved in extracellular matrix metabolism. These genes encoded proteins or peptides that could be implicated into two different biological processes: molecules involved in fibrosis and proteins involved in adhesion to the extracellular matrix. In heterozygotes, some genes (glypican 3, fibronectin 1) were already upregulated in early stages of the disease. We conclude that differential regulation of genes linked to extracellular matrix metabolism may be one of the first events leading to tubule enlargement and subsequent cyst formation in PKD.

Biochemical validation of a rat model for polycystic kidney disease: Comparison of guanidino compound profile with the human condition

Polycystic kidney disease (PKD) accounts for 7-10% of all dialyzed renal insufficient patients. Accumulation of specific guanidino compounds (GCs) has been related to neurological, cardiovascular, hematological, and immunological complications of renal failure. In this study, we investigate whether the PKD/Mhm rat model can be used as a biochemical model for human PKD. For the validation of the rat model, we performed the first detailed evaluation of the concentrations of GCs in serum and urine of patients with PKD in addition to the GC patterns in the plasma, urine, and tissues of the PKD/Mhm rat model. The GCs were determined after separation on a cation exchange resin and fluorescence detection. The GC levels and changes observed in blood and urine of patients with PKD are comparable with those found in patients with renal insufficiency due to different etiologies. The PKD/Mhm rat model can be used as a biochemical model for human PKD as the obvious increases of urea, guanidinosuccinic acid, creatinine, guanidine, methylguanidine, and N(G)N(G)-dimethylarginine (symmetrical dimethylarginine) seen in blood of oldest heterozygous and younger homozygous PKD rats were largely within the same range as those found in the studied human PKD population, especially in patients with a glomerular filtration rate below 60 ml/min/1.73 m(2). The decreased levels of plasma guanidinoacetic acid seen at end-stage renal disease in homozygous and oldest heterozygous rats were also observed in serum of patients with a glomerular filtration rate below 20 ml/min/1.73 m(2). The PKD/Mhm rat model has, besides similar disease characteristics with human PKD, comparable GC alterations.

Survival of AA and ANA Rats During Lifelong Ethanol Exposure

BACKGROUND

Study of the long-term effects of chronic alcohol consumption in human populations is confounded by genetic and environmental factors.

METHODS

The study was intended to investigate the effects on morbidity and survival of lifetime forced ethanol consumption in male and female AA (Alko, Alcohol) and ANA (Alko, Non-Alcohol) rats. The ethanol-exposed rats had 12% ethanol as the only available fluid from 3 to 24 months of age. The control groups had water. Rats that died during the experiment and those that were killed at 24 months of age were all autopsied, and the pathologic findings were recorded.

RESULTS

Lifelong ethanol consumption did not change the survival rate of the rats, and had no significant effect on the rates of any of the pathologic measures in either the AA or ANA line of rats, suggesting that this may not be a good animal model for studying the detrimental effects of chronic alcohol. An unexpected, highly significant finding was observed: the AA rats, bred for high voluntary ethanol drinking, lived much longer than the ANA rats, bred for ethanol avoidance. The death rate by 24 months in the AA line was less than one-third of that in the ANA line. This difference was found regardless of whether the animals were maintained on alcohol or water, and in both genders. The AA rats had significantly lower rates of kidney disease, benign tumors, and cardiovascular disease than the ANA animals.

CONCLUSIONS

Lifelong ethanol consumption increased neither the mortality nor the morbidity of AA and ANA line of rats. Genes selected in the development of the high drinking AA line have additional effects producing rats that are healthier and living longer than the ANA rats possessing genes resulting in alcohol avoidance.

Selectivity of cyclooxygenase isoform activity and prostanoid production in normal and diseased Han:SPRD-cy rat kidneys

Renal prostanoids are important regulators of normal renal function and maintenance of renal homeostasis. In diseased kidneys, renal cylooxygenase (COX) expression and prostanoid formation are altered. With the use of the Han:Sprague-Dawley-cy rat, the aim of this study was to determine the relative contribution of renal COX isoforms (protein, gene expression, and activity) on renal prostanoid production [thromboxane B(2) (TXB(2), stable metabolite of TXA(2)), prostaglandin E(2) (PGE(2)), and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha), stable metabolite of PGI(2))] in normal and diseased kidneys. In diseased kidneys, COX-1-immunoreactive protein and mRNA levels were higher and COX-2 levels were lower compared with normal kidneys. In contrast, COX activities were higher in diseased compared with normal kidneys for both COX-1 [0.05 +/- 0.02 vs. 0.45 +/- 0.11 ng prostanoids x min(-1) x mg protein(-1) (P < 0.001)] and COX-2 [0.64 +/- 0.10 vs. 2.32 +/- 0.22 ng prostanoids x min(-1).mg protein(-1) (P < 0.001)]. As the relative difference in activity was greater for COX-1, the ratio of COX-1/COX-2 was higher in diseased compared with normal kidneys, although the predominant activity was still due to the COX-2 isoform in both genotypes. Endogenous and steady-state in vitro levels of prostanoids were approximately 2-10 times higher in diseased compared with normal kidneys. The differences between normal and diseased kidney prostanoids were in the order of TXB(2) > 6-keto-PGF(1alpha) > PGE(2), as determined by higher renal prostanoid levels and COX activity ratios of TXB(2)/6-keto-PGF(1alpha), TXB(2)/PGE(2), and 6-keto-PGF(1alpha)/PGE(2). This specificity in both the COX isoform type and for the prostanoids produced has implications for normal and diseased kidneys in treatments involving selective inhibition of COX isoforms.

Missense mutation in sterile alpha motif of novel protein SamCystin is associated with polycystic kidney disease in (cy/+) rat

Autosomal dominant polycystic kidney disease (PKD) is the most common genetic disease that leads to kidney failure in humans. In addition to the known causative genes PKD1 and PKD2, there are mutations that result in cystic changes in the kidney, such as nephronophthisis, autosomal recessive polycystic kidney disease, or medullary cystic kidney disease. Recent efforts to improve the understanding of renal cystogenesis have been greatly enhanced by studies in rodent models of PKD. Genetic studies in the (cy/+) rat showed that PKD spontaneously develops as a consequence of a mutation in a gene different from the rat orthologs of PKD1 and PKD2 or other genes that are known to be involved in human cystic kidney diseases. This article reports the positional cloning and mutation analysis of the rat PKD gene, which revealed a C to T transition that replaces an arginine by a tryptophan at amino acid 823 in the protein sequence. It was determined that Pkdr1 is specifically expressed in renal proximal tubules and encodes a novel protein, SamCystin, that contains ankyrin repeats and a sterile alpha motif. The characterization of this protein, which does not share structural homologies with known polycystins, may give new insights into the pathophysiology of renal cyst development in patients.

Altered ATP-sensitive P2 receptor subtype expression in the Han:SPRD cy/+ rat, a model of autosomal dominant polycystic kidney disease

The effects of extracellular ATP on fluid secretion and reabsorption by renal epithelial cells, as well as its known effects on cell proliferation and death, are potentially important contributory factors in the development and growth of renal cysts. In this study, we have investigated the protein and mRNA expression of several P2Y receptor subtypes (P2Y(1,2,4,6)), as well as the P2X(5) and P2X(7) receptors, in kidney tissue from the Han:SPRD (cy/+) rat model of polycystic kidney disease. All of the P2Y receptors tested for, and the P2X(5) and P2X(7) subtypes, were located on the cyst-lining cells of Han:SPRD (cy/+) rat polycystic kidneys; most immunostaining was cytosolic and we could not confidently localize it to one or other membrane. However, the staining pattern for P2Y(6) was uniquely granular when compared with the other P2 receptors. P2Y(2) and P2Y(6) receptor mRNA was increased in both homozygote (cy/cy) and heterozygote (cy/+) rat kidneys when compared with unaffected littermates. The protein levels of P2Y(2) and P2Y(6) receptors were also increased, being undetectable or at a low level, respectively, in control tissue. Finally, P2X(7) receptor mRNA was increased in cy/+, but not in cy/cy rat kidneys. Our results show that a number of P2Y receptor subtypes, as well as the P2X(5) and P2X(7) receptors, are clearly expressed in cyst-lining cells in the Han:SPRD (cy/+) rat model of renal cystic disease. Furthermore, P2Y(2) and P2Y(6) receptor mRNA and protein levels are markedly increased in cystic rat kidneys compared with normal rats of the same genetic background. Thus, the most consistent findings were an increase in the expression of P2Y(2), P2Y(6) and P2X(7) receptors in cystic tissue. Given the widely reported effects of stimulating these P2 receptor subtypes in epithelial and other renal cells, they could contribute to the development and growth of renal cysts: extracellular ATP and its products 'trapped' in cyst fluid may activate P2 receptors expressed by cyst-lining cells, causing cyst expansion from increased fluid secretion and/or reduced reabsorption, as well as an increase in cell turnover (re-modeling).

Caspase inhibition reduces tubular apoptosis and proliferation and slows disease progression in polycystic kidney disease

We have previously demonstrated an increase in proapoptotic caspase-3 in the kidney of Han:SPRD rats with polycystic kidney disease (PKD). The aim of the present study was to determine the effect of caspase inhibition on tubular cell apoptosis and proliferation, cyst formation, and renal failure in the Han:SPRD rat model of PKD. Heterozygous (Cy/+) and littermate control (+/+) male rats were weaned at 3 weeks of age and then treated with the caspase inhibitor IDN-8050 (10 mg/kg per day) by means of an Alzet (Palo Alto, CA) minipump or vehicle [polyethylene glycol (PEG 300)] for 5 weeks. The two-kidney/total body weight ratio more than doubled in Cy/+ rats compared with +/+ rats. IDN-8050 significantly reduced the kidney enlargement by 44% and the cyst volume density by 29% in Cy/+ rats. Cy/+ rats with PKD have kidney failure as indicated by a significant increase in blood urea nitrogen. IDN-8050 significantly reduced the increase in blood urea nitrogen in the Cy/+ rats. The number of proliferating cell nuclear antigen-positive tubular cells and apoptotic tubular cells in non-cystic and cystic tubules was significantly reduced in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. On immunoblot, the active form of caspase-3 (20 kDa) was significantly decreased in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. In summary, in a rat model of PKD, caspase inhibition with IDN-8050 (i) decreases apoptosis and proliferation in cystic and noncystic tubules; (ii) inhibits renal enlargement and cystogenesis, and (iii) attenuates the loss of kidney function.

Rapamycin markedly slows disease progression in a rat model of polycystic kidney disease

Increased tubular epithelial cell proliferation is a prerequisite for cyst formation and expansion in polycystic kidney disease (PKD). Rapamycin is a potent antiproliferative agent. The aim of the present study was to determine the effect of rapamycin on tubular cell proliferation, cyst formation, and renal failure in the Han:SPRD rat model of PKD. Heterozygous (Cy/+) and littermate control (+/+) male rats were weaned at 3 wk of age and then treated with rapamycin 0.2 mg/kg per d intraperitoneally or vehicle (ethanol) for 5 wk. Vehicle-treated Cy/+ rats had a more than doubling of kidney size compared with +/+ rats. Rapamycin reduced the kidney enlargement by 65%. Rapamycin significantly reduced the cyst volume density in Cy/+ rats by >40%. Blood urea nitrogen was 59% increased in vehicle-treated Cy/+ rats compared with +/+ rats. Rapamycin reduced the blood urea nitrogen to normal in Cy/+ rats. The number of proliferating cell nuclear antigen (PCNA)-positive cells per noncystic tubule was eightfold increased in vehicle-treated Cy/+ compared with +/+ rats. Rapamycin significantly reduced the number of PCNA-positive cells in noncystic tubules of Cy/+ rats. In addition, the number of PCNA-positive cells per cyst in Cy/+ rats was significantly reduced by rapamycin. In summary, in a rat model of PKD, rapamycin treatment (1) decreases proliferation in cystic and noncystic tubules, (2) markedly inhibits renal enlargement and cystogenesis, and (3) prevents the loss of kidney function.

Urinary excretion of monocyte chemoattractant protein-1 in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) progresses to renal insufficiency in >50% of patients and is characterized by interstitial inflammation and fibrosis in the end stage. In a rat model of ADPKD, monocytes accumulate within the renal interstitium in association with increased levels of monocyte chemoattractant protein-1 (MCP-1) in cyst mural cells and increased excretion of this chemokine into the urine. For determining the extent to which this chemokine is abnormally expressed in patients with ADPKD, a cross-section study was performed of MCP-1 in urine, serum, and cyst fluid and MCP-1 production by mural epithelial cells cultured from the cysts of human patients with ADPKD. Upper boundaries for urinary MCP-1 excretion (>263 pg/mg creatinine) and serum creatinine concentration (>1.5 mg/dl) determined in 19 normal individuals were used to sort 55 ADPKD patients into three groups. In group 1 (n = 13), urine MCP-1 excretion (136 +/- 14 pg/mg creatinine) was not different from normal volunteers (152 +/- 16 pg/mg); serum creatinine levels and urine total protein excretion were normal as well. In group 2 (n = 27), urine MCP-1 excretion was increased (525 +/- 39 pg/mg creatinine), but serum creatinine levels and urine protein excretion were not different from normal. In group 3 (n = 15), urine MCP-1 excretion increased further (1221 +/- 171 pg/mg), serum creatinine levels increased to 4.3 +/- 0.8 mg/dl, and urine protein excretion rose to 0.64 +/- 0.28 mg/mg creatinine. Serum MCP-1 levels of ADPKD patients (84 +/- 9.9 pg/ml; n = 15) did not differ from normal. Levels of MCP-1 much higher than in serum or urine were found in cyst fluids obtained from nephrectomy specimens (range, 767 to 40,860 pg/ml; mean, 6434 +/- 841 pg/ml; n = 73). Polarized, confluent cultures of ADPKD cyst epithelial cells secreted MCP-1 into the apical fluid to levels eightfold greater than in the basolateral medium. Similar results were obtained with tubule epithelial cells cultured from normal human renal cortex. On the basis of these results, it is concluded that urinary excretion of MCP-1 is increased in the majority of adult patients with ADPKD and that the source of some of this chemokine may be the mural epithelium of cysts. Furthermore, it seemed that urinary MCP-1 excretion may have increased in these ADPKD patients before appreciable increases in serum creatinine concentration or urine protein excretion were detected. It is reasonable to include urine MCP-1 excretion among candidate surrogate markers in controlled, longitudinal studies of ADPKD.

The expression and activity of renal nitric oxide synthase and circulating nitric oxide in polycystic kidney disease rats

Nitric oxide (NO) influences tubular fluid and electrolyte transport, and hence possibly also fluid accumulation in renal cysts. The expression and activity of intrarenal constitutive NO synthase (cNOS) [neuronal NOS, nNOS and endothelial NOS, eNOS] and inducible NOS (iNOS) and plasma nitrite/nitrate (PNOx) concentration were assessed in homozygous Han:SPRD polycystic kidney disease (PKD) rats (cy/cy), heterozygous Han:SPRD PKD rats (cy/+), homozygous normal Han:SPRD littermates (+/+) and Sprague Dawley rats (sd). The results showed: 1) nNOS expression was decreased in proximal tubules and thick ascending limbs of the loop of Henle in cy/cy and cy/+ rats compared to +/+ and sd rats (p<0.05). nNOS was weakly expressed in the epithelium of small cysts and unexpressed in epithelium of large cysts. 2) iNOS expression was increased in proximal tubular epithelial cells in cy/+ rats compared to +/+ rats and sd rats (p<0.01). iNOS expression in cyst epithelium was decreased in cy/+ rats (p<0.05) and absent in cy/cy rats. 3) eNOS expression was similar in the endothelium of intrarenal arteries in all groups. 4) The activity of renal cNOS was decreased in cy/cy and cy/+ rats; the activity of iNOS was decreased only in cy/cy rats, with no significant difference among the other three groups. 5) PNOx concentration was higher in cy/cy rats than in the other three groups, and correlated positively with plasma creatinine and urea. In conclusion, NOS expression and activity decreased as cysts developed, suggesting that NO downregulation is involved in the pathogenesis of PKD.

Two-photon in vivo microscopy of sulfonefluorescein secretion in normal and cystic rat kidneys

Sulfonefluorescein (SF) is a fluorescent organic anion secreted by kidney proximal tubules. The purposes of this study were 1) to quantify accumulation of SF in normal and cystic rat kidneys in vivo and 2) to test whether SF accumulation could be used as a marker for cysts derived from proximal tubules. Male Munich-Wistar rats, normal Han:SPRD rats, and heterozygous Han:SPRD rats with autosomal-dominant polycystic kidney disease were anesthetized with Inactin and solutions containing SF were administered by constant intravenous infusion. In Munich-Wistar rats, SF fluorescence in the urinary space of Bowman's capsule averaged 0.15 +/- 0.04 (n = 17) times that of glomerular capillary plasma, consistent with extensive plasma protein binding of SF. In normal Han:SPRD rats, steady-state cell cytoplasm SF fluorescence in proximal tubule and distal tubule cells averaged, respectively, 2.7 +/- 1.4 (n = 99 tubules) and 0.2 +/- 0.2 (n = 17) times that of peritubular capillary plasma. No punctate SF fluorescence was seen in proximal tubule cell cytoplasm. Probenecid reduced proximal tubule cell SF fluorescence to 0.64 +/- 0.40 (n = 64) times that of plasma. Ureteral obstruction decreased the proximal tubule cell-to-lumen SF fluorescence gradient, suggesting that tubule fluid flow normally sweeps away secreted SF. In cystic kidneys, cysts derived from proximal tubules could be identified by their uptake of SF, but cell uptake was patchy. We conclude that in vivo two-photon microscopy is a powerful tool for quantifying glomerular and tubular handling of SF, and SF can be used to identify proximal tubule-derived cysts.