PPAR-gamma agonist ameliorates kidney and liver disease in an orthologous rat model of human autosomal recessive polycystic kidney disease

In autosomal recessive polycystic kidney disease (ARPKD), progressive enlargement of fluid-filled cysts is due to aberrant proliferation of tubule epithelial cells and transepithelial fluid secretion leading to extensive nephron loss and interstitial fibrosis. Congenital hepatic fibrosis associated with biliary cysts/dilatations is the most common extrarenal manifestation in ARPKD and can lead to massive liver enlargement. Peroxisome proliferator-activated receptor γ (PPAR-γ), a member of the ligand-dependent nuclear receptor superfamily, is expressed in a variety of tissues, including the kidneys and liver, and plays important roles in cell proliferation, fibrosis, and inflammation. In the current study, we determined that pioglitazone (PIO), a PPAR-γ agonist, decreases polycystic kidney and liver disease progression in the polycystic kidney rat, an orthologous model of human ARPKD. Daily treatment with 10 mg/kg PIO for 16 wk decreased kidney weight (% of body weight), renal cystic area, serum urea nitrogen, and the number of Ki67-, pERK1/2-, and pS6-positive cells in the kidney. There was also a decrease in liver weight (% of body weight), liver cystic area, fibrotic index, and the number of Ki67-, pERK1/2-, pERK5-, and TGF-β-positive cells in the liver. Taken together, these data suggest that PIO inhibits the progression of polycystic kidney and liver disease in a model of human ARPKD by inhibiting cell proliferation and fibrosis. These findings suggest that PPAR-γ agonists may have therapeutic value in the treatment of the renal and hepatic manifestations of ARPKD.     

Effective treatment of an orthologous model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a leading cause of end-stage renal disease. The vasopressin V2 receptor (VPV2R) antagonist OPC31260 has been effective in two animal models of PKD with pathologies that are probably related. Here we show, in a mouse model of ADPKD (Pkd2(-/tm1Som)), a similar cellular phenotype and response to OPC31260 treatment, with reduction of renal cyclic AMP (cAMP) levels, prevention of renal enlargement, marked inhibition of cystogenesis and protection of renal function.     

The gene expression profile of cyst epithelial cells in autosomal dominant polycystic kidney disease patients

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder characterized by the formation of fluid-filled cysts in the kidney and progressive renal failure. Other manifestations of ADPKD include the formation of cysts in other organs (liver, pancreas, and spleen), hypertension, cardiac defects, and cerebral aneurysms. The loss of function of the polycystin -1 and -2 results in the formation of epithelium-lined cysts, a process that depends on initial epithelial proliferation. cDNA microarrays powerfully monitor gene expression and have led to the discoveries of pathways regulating complex biological processes. We undertook to profile the gene expression patterns of epithelial cells derived from the cysts of ADPKD patients using the cDNA microarray technique. Candidate genes that were differently expressed in cyst tissues were identified. 19 genes were up-regulated, and 6 down-regulated. Semi-quantitative RT-PCR results were consistent with the microarray findings. To distinguish between normal and epithelial cells, we used the hierarchical method. The results obtained may provide a molecular basis for understanding the biological meaning of cytogenesis.     

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

Summary 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. Both authors contributed equally to the work.     

Role of genetic modifiers in an orthologous rat model of ARPKD

Human data and animal models of autosomal recessive polycystic kidney disease (ARPKD) suggest that genetic factors modulate the onset and severity of the disease. We report here for the first time that ARPKD susceptibility is attenuated by introgressing the mutated Pkhd1 disease allele from the polycystic kidney (PCK) rat onto the FHH (Fawn-Hooded Hypertensive) genetic background. Compared with PCK, the FHH.Pkhd1 strain had significantly decreased renal cyst formation that coincided with a threefold reduction in mean kidney weights. Further analysis revealed that the FHH. Pkhd1 is protected from increased blood pressure as well as elevated plasma creatinine and blood urea nitrogen levels. On the other hand, liver weight and biliary cystogenesis revealed no differences between PCK and FHH.Pkdh1, indicating that genes within the FHH genetic background prevent the development of renal, but not hepatic, manifestations of ARPKD. Microarray expression analysis of kidneys from 30-day-old PCK rats revealed increased expression of genes previously identified in PKD renal expression profiles, such as inflammatory response, extracellular matrix synthesis, and cell proliferation genes among others, whereas the FHH.Pkhd1 did not show activation of these common markers of disease. This newly developed strain can serve as a tool to map modifier genes for renal disease in ARPKD and provides further insight into disease variability and pathophysiology.     

Characterization of a novel polycystic kidney rat model with accompanying polycystic liver.

A polycystic kidney rat model is being established from a Crj:CD (SD) rat strain. Unlike existing animal models of polycystic kidney disease, this mutant rat has a completely polycystic liver. Mating experiments revealed that the phenotype is controlled by an autosomal recessive gene. We propose that this gene be tentatively called the "rpc" gene.     

Urinary biomarkers for monitoring disease progression in the Han:SPRD-cy rat model of autosomal-dominant polycystic kidney disease

The Han:SRPD-cy rat is a well-recognized model of human autosomal-dominant polycystic kidney disease. The disease is characterized by the development of progressive renal cysts, leading to declining renal function. Disease progression typically is monitored by measurement of plasma urea concentration. Although plasma urea may be an adequate measure of overall renal function, urinary biomarkers capable of accurately monitoring disease progression may be equally useful. The goal of this study was to assess several urinary biomarkers as potential markers of disease progression in male and female Han:SPRD-cy rats. These biomarkers were compared with changes in plasma urea concentration and morphometric changes as the disease progressed. Urinary activity of N-acetyl-β-D-glucosaminidase and concentration of α-glutathione S-transferase were measured as markers of proximal tubular dysfunction, glutathione S-transferase Yb1 as a distal tubular marker, and collagen IV as a biomarker for glomerular lesions. Urinary albumin was used as biomarker of glomerular or proximal tubular lesions. Albuminuria increased in male rats as the disease progressed, correlating with increasing plasma urea and morphologic changes. Urine concentrations of α-glutathione S-transferase decreased significantly in the male heterozygotic compared with wildtype rats in the later stages of the disease. Urinary concentrations of glutathione S-transferase Yb1 and collagen IV and activity of N-acetyl-β-D-glucosaminidase did not change during disease progression. Measurement of urinary albumin and concentrations of α-glutathione S-transferase may be useful for monitoring disease progression in the male Han:SPRD-cy rat model in future experiments.     

Lysophosphatidic acid is a modulator of cyst growth in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the slow growth of multiple fluid-filled cysts predominately in the kidney tubules and liver bile ducts. Elucidation of mechanisms that control cyst growth will provide the basis for rational therapeutic intervention. We used electrophysiological methods to identify lysophosphatidic acid (LPA) as a component of cyst fluid and serum that stimulates secretory Cl- transport in the epithelial cell type that lines renal cysts. LPA effects are manifested through receptors located on the basolateral membrane of the epithelial cells resulting in stimulation of channel activity in the apical membrane. Concentrations of LPA measured in human ADPKD cyst fluid and in normal serum are sufficient to maximally stimulate ion transport. Thus, cyst fluid seepage and/or leakage of vascular LPA into the interstitial space are capable of stimulating epithelial cell secretion resulting in cyst enlargement. These observations are particularly relevant to the rapid decline in renal function in late-stage disease and to the "third hit" hypothesis that renal injury exacerbates cyst growth.     

Autosomal dominant polycystic kidney disease--in vitro culture of cyst-lining epithelial cells.

The major form of autosomal dominant polycystic kidney disease (ADPKD) in humans is linked to the PKD1 gene on chromosome 16p. The identity of the gene and the underlying pathogenetic mechanisms are not yet defined. Cyst-lining epithelial cells derived from a polycystic kidney were successfully grown in culture and designated MZ-PKD-1 cells. By linkage analysis, the related pedigree of the nephrectomized patient could be linked to the PKD1 gene on chromosome 16p. Thus, these cells exhibit the genotype of a mutated PKD1 gene and represent an in vitro culture model for ADPKD involving chromosome 16p. The antigenic phenotype was characterized immunohistologically by epithelial differentiation antigens and markers of individual nephron segments. An essentially identical antigenic pattern of proximal tubular cells was observed both in vitro and in fresh frozen tissue. Electron microscopy showed the formation of a microvillous-like coating. During growth phases in vitro successive changes in the cell shape were observed. MZ-PKD-1 cells exhibited a limited lifespan ending in replicative senescence. Northern blot analysis of kidney-growth-related genes, c-myc, TGF-alpha, TGF-beta 1, and EGF receptor revealed abundant expression of all of these genes in MZ-PKD-1 cells.     

Extracellular matrix formation by epithelial cells from human polycystic kidney cysts in culture

Cells from the cysts of patients with autosomal dominant polycystic kidney disease (PKD) were grown in vitro under standard conditions without the aid of collagen-pretreated surfaces, and both the synthesis and composition of the extracellular matrix were investigated. At confluence, PKD cells presented the typical features of epithelial cells, but showed a different collagen composition from fibroblasts. Compared with normal tubular epithelia (NTE), PKD monolayers produced an excess of extracellular matrix, which accounted for 30% of the total incorporation of [³H] proline, although this value was considerably lower (by a factor of 10) in the case of NTE. Immunohistochemical and electrophoretic techniques revealed a complex collagen composition in the extracellular matrix which included [α(III)]₃ and collagen IV. However, part of the collagen components remained unidentified in spite of the fact that they exhibited a typical M_r of α₁(I) and α₂(I) in the presence of urea. Immunoprecipitation with monospecific antibodies and Northern blotting with specific probes failed to recognize α₁(I) and α₂(I), but demonstrated their presence in fibroblasts. Purification and cyanogen bromide digestion demonstrated a strong interhomology in fingerprint peptide composition among the uncharacterized collagens synthesized by PKD cells, thus suggesting a common identity. These observations document a markedly augmented production of extracellular matrix by PKD cultured cells in vitro, and show the presence of collagens which do not share homologies with the major collagen molecules. A better characterization of extracellular matrix composition is central to any comprehension of the cystogenetic mechanisms in vivo.     

Heightened epithelial Na+ channel-mediated Na+ absorption in a murine polycystic kidney disease model epithelium lacking apical monocilia

The Tg737°^rpk autosomal recessive polycystic kidney disease (ARPKD) mouse carries a hypomorphic mutation in the Tg737 gene. Because of the absence of its protein product Polaris, the nonmotile primary monocilium central to the luminal membrane of ductal epithelia, such as the cortical collecting duct (CCD) principal cell (PC), is malformed. Although the functions of the renal monocilium remain elusive, primary monocilia or flagella on neurons act as sensory organelles. Thus we hypothesized that the PC monocilium functions as a cellular sensor. To test this hypothesis, we assessed the contribution of Polaris and cilium structure and function to renal epithelial ion transport electrophysiology. Properties of Tg737°^rpk mutant CCD PC clones were compared with clones genetically rescued with wild-type Tg737 cDNA. All cells were grown as polarized cell monolayers with similarly high transepithelial resistance on permeable filter supports. Three- to fourfold elevated transepithelial voltage (V_te) and short-circuit current (I_sc) were measured in mutant orpk monolayers vs. rescued controls. Pharmacological and cell biological examination of this enhanced electrical end point in mutant monolayers revealed that epithelial Na⁺ channels (ENaCs) were upregulated. Amiloride, ENaC-selective amiloride analogs (benzamil and phenamil), and protease inhibitors (aprotinin and leupeptin) attenuated heightened V_te and I_sc. Higher concentrations of additional amiloride analogs (ethylisopropylamiloride and dimethylamiloride) also revealed inhibition of V_te. Cell culture requirements and manipulations were also consistent with heightened ENaC expression and function. Together, these data suggest that ENaC expression and/or function are upregulated in the luminal membrane of mutant, cilium-deficient orpk CCD PC monolayers vs. cilium-competent controls. When the genetic lesion causes loss or malformation of the monocilium, ENaC-driven Na⁺ hyperabsorption may explain the rapid emergence of severe hypertension in a majority of patients with ARPKD. cilia; hypertension; ion transport; epithelial cells     

Berberine slows cell growth in autosomal dominant polycystic kidney disease cells

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary monogenic disorder characterized by development and enlargement of kidney cysts that lead to loss of renal function. It is caused by mutations in two genes (PKD1 and PKD2) encoding for polycystin-1 and polycystin-2 proteins which regulate different signals including cAMP, mTOR and EGFR pathways. Abnormal activation of these signals following PC1 or PC2 loss of function causes an increased cell proliferation which is a typical hallmark of this disease. Despite the promising findings obtained in animal models with targeted inhibitors able to reduce cystic cell growth, currently, no specific approved therapy for ADPKD is available. Therefore, the research of new more effective molecules could be crucial for the treatment of this severe pathology. In this regard, we have studied the effect of berberine, an isoquinoline quaternary alkaloid, on cell proliferation and apoptosis in human and mouse ADPKD cystic cell lines. Berberine treatment slows cell proliferation of ADPKD cystic cells in a dose-dependent manner and at high doses (100 μg/mL) it induces cell death in cystic cells as well as in normal kidney tubule cells. However, at 10 μg/mL, berberine reduces cell growth in ADPKD cystic cells only enhancing G₀/G₁ phase of cell cycle and inhibiting ERK and p70-S6 kinases. Our results indicate that berberine shows a selected antiproliferative activity in cellular models for ADPKD, suggesting that this molecule and similar natural compounds could open new opportunities for the therapy of ADPKD patients.     

Ultrasound detection and characterization of polycystic kidney disease in a mouse model

We sought to use ultrasonography to quantify renal size and echogenicity in a mouse model of polycystic kidney disease. We imaged 36 wild-type (WT) and juvenile cystic kidney (jck) mice by using a standard ultrasound unit and 10-5 MHz linear transducer. Mice were imaged at 3 (6 WT, 7 jck), 6 (7 WT, 5 jck), and 9 (6 WT, 5 jck) wk of age. Kidney length, width, and height were recorded for volume calculation. Sagittal images of both kidneys were recorded for assessment of intensity. Quantitative values were obtained from areas of similar depth and gain settings. Kidney and liver intensities were determined for calculation of their ratio. Representative histologic kidney sections were stained with hematoxylin and eosin and digitized for calculation of cyst number, mean cyst area, and percentage cystic area. We found that renal volume was greater in jck than WT mice at 3 (P < 0.0001), 6 (P < 0.0001), and 9 (P < 0.0001) wk of age. In addition, kidney intensity and kidney:liver ratio were higher in jck than WT mice at 3 (P < 0.002 for both parameters), 6 (P < 0.04), and 9 wk (P < 0.008). Kidneys with smaller mean cyst size and less percentage cystic space had higher intensity values. We therefore conclude that ultrasound measures of renal volume and intensity can noninvasively identify jck-affected mice as early as 3 wk of age. Cortical intensity is greater in jck versus WT mice and appears affected by percentage cyst area and mean cyst size.     

Uric acid activates NRLP3 inflammasome in an in-vivo model of epithelial to mesenchymal transition in the kidney

Uric acid (UA) has been associated with renal fibrosis and progression of chronic kidney disease. However, the underlying mechanisms of this process have still not been identified. Here, we studied the role of the innate imunity receptor NLRP3/ASC in UA induced epithelial-mesenchymal transition (EMT) in kidney. Wistar rats were fed with oxonic acid 2% and UA 2% (OXA?+?U), OXA?+?U plus allopurinol (ALL) or regular chow (C) for 7 weeks. We analyzed the presence of EMT markers, the expression of NLRP3, ASC, Caspase-1 and Smad 2/3 molecules and the mitochondrial morphological and functional characteristics. High UA induced renal fibrosis, mild chronic inflammation, as well as morphological and biochemical evidence of EMT. High UA also increased the expression of NLRP3/ASC with activation of both inflammasome related caspase-1 and inflammasome unrelated Smad 2/3 pathways. Ultrastructural co-localization of NLRP3 and Smad 2/3 indicated physical interaction between the two molecules. No morphological or functional changes were found between mitochondria exposed to high UA. In conclusion, kidney epithelial NLRP3/ASC expression was increased in high UA state in rats and both inflammasome related caspase-1 and non-inflammasome related P-Smad 2/3 pathways were associated with the observed EMT, inflammation and fibrosis induced by UA in the kidney.     

Extracellular matrix formation by epithelial cells from human polycystic kidney cysts in culture.

Cells from the cysts of patients with autosomal dominant polycystic kidney disease (PKD) were grown in vitro under standard conditions without the aid of collagen-pretreated surfaces, and both the synthesis and composition of the extracellular matrix were investigated. At confluence, PKD cells presented the typical features of epithelial cells, but showed a different collagen composition from fibroblasts. Compared with normal tubular epithelia (NTE), PKD monolayers produced an excess of extracellular matrix, which accounted for 30% of the total incorporation of [3H] proline, although this value was considerably lower (by a factor of 10) in the case of NTE. Immunohistochemical and electrophoretic techniques revealed a complex collagen composition in the extracellular matrix which included [alpha (III)]3 and collagen IV. However, part of the collagen components remained unidentified in spite of the fact that they exhibited a typical M(r) of alpha 1(I) and alpha 2(I) in the presence of urea. Immunoprecipitation with monospecific antibodies and Northern blotting with specific probes failed to recognize alpha 1(I) and alpha 2(I), but demonstrated their presence in fibroblasts. Purification and cyanogen bromide digestion demonstrated a strong interhomology in fingerprint peptide composition among the uncharacterized collagens synthesized by PKD cells, thus suggesting a common identity. These observations document a markedly augmented production of extracellular matrix by PKD cultured cells in vitro, and show the presence of collagens which do not share homologies with the major collagen molecules. A better characterization of extracellular matrix composition is central to any comprehension of the cytogenetic mechanisms in vivo.     

Contribution of renal innervation to hypertension in rat autosomal dominant polycystic kidney disease

The kidney has both afferent (sensory) and efferent (sympathetic) nerves that can influence renal function. Renal innervation has been shown to play a role in the pathogenesis of many forms of hypertension. Hypertension and flank pain are common clinical manifestations of autosomal dominant (AD) polycystic kidney disease (PKD). We hypothesize that renal innervation contributes to the hypertension and progression of cystic change in rodent PKD. In the present study, the contribution of renal innervation to hypertension and progression of renal histopathology and dysfunction was assessed in male Han:SPRD-Cy/+ rats with ADPKD. At 4 weeks of age, male offspring from crosses of heterozygotes (Cy/+) were randomized into either 1) bilateral surgical renal denervation, 2) surgical sham denervation control, or 3) nonoperated control groups. A midline laparotomy was performed to allow the renal denervation (i.e., physical stripping of the nerves and painting the artery with phenol/alcohol). Blood pressure (tail cuff method), renal function (BUN) and histology were assessed at 8 weeks of age. Bilateral renal denervation reduced the cystic kidney size, cyst volume density, systolic blood pressure, and improved renal function (BUN) as compared with nonoperated controls. Operated control cystic rats had kidney weights, cyst volume densities, systolic blood pressures, and plasma BUN levels that were intermediate between those in the denervated animals and the nonoperated controls. The denervated group had a reduced systolic blood pressure compared with the operated control animals, indicating that the renal innervations was a major contributor to the hypertension in this model of ADPKD. Renal denervation was efficacious in reducing some pathology, including hypertension, renal enlargement, and cystic pathology. However, sham operation also affected the cystic disease but to a lesser extent. We hypothesize that the amelioration of hypertension in Cy/+ rats was due to the effects of renal denervation on the renin angiotensin system.     

Compromised cytoarchitecture and polarized trafficking in autosomal dominant polycystic kidney disease cells

Cystogenesis associated with autosomal dominant polycystic kidney disease (ADPKD) is characterized by perturbations in the polarized phenotype and function of cyst-lining epithelial cells. The polycystins, the protein products of the genes mutated in the majority of ADPKD cases, have been described recently, but the pathological mechanism by which causal mutations result in the mislocalization of cell membrane proteins has remained unclear. This report documents the dissociation from the ADPKD cell basolateral membrane of three molecules essential for spatial organization and exocytosis. The adherens junction protein E-cadherin, the subcellular disposition of which governs intercellular and intracellular architecture, was discovered sequestered in an internal ADPKD cell compartment. At the same time, sec6 and sec8, components of a complex critical for basolateral cargo delivery normally arrayed at the apico-lateral apex, were depleted from the ADPKD cell plasma membrane. An analysis of membrane transport revealed that basolateral trafficking of proteins and lipids was impaired as a result of delayed cargo exit from the ADPKD cell Golgi apparatus. Apical transport proceeded normally. Taken together with recent documentation of an association between polycystin-1 and E-cadherin (Huan and van Adelsberg 1999), the data suggest that causal mutations disrupt E-cadherin-dependent cytoarchitecture, adversely affecting protein assemblies crucial for basolateral trafficking.     

The effect of trehalose on autophagy-related proteins and cyst growth in a hypomorphic Pkd1 mouse model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disorder characterized by kidney cyst growth often resulting in end-stage renal disease. There is growing attention on understanding the role of impaired autophagy in ADPKD. Trehalose (TRE) has been shown to increase both protein stability and aggregate clearance and induce autophagy in neurodegenerative diseases. TRE treatment in wild type mice compared to vehicle resulted in increased expression in the kidney of Atg12–5 complex and increased Rab9a, autophagy-related proteins that play a role in the formation of autophagosomes. Thus, the aim of the study was to determine the effect of TRE on cyst growth and autophagy-related proteins, in the hypomorphic Pkd1^RC/RC mouse model of ADPKD. Pkd1^RC/RC mice were treated 2% TRE in water from days 50 to 120 of age. TRE did not slow cyst growth or improve kidney function or affect proliferation and apoptosis in Pkd1^RC/RC kidneys. In Pkd1^RC/RC vs. wild type kidneys, expression of the Atg12–5 complex was inhibited by TRE resulting in increased free Atg12 and TRE was unable to rescue the deficiency of the Atg12–5 complex. Rab9a was decreased in Pkd1^RC/RC vs. wild type kidneys and unaffected by TRE. The TRE-induced increase in p62, a marker of autophagic cargo, that was seen in normal kidneys was blocked in Pkd1^RC/RC kidneys. In summary, the autophagy phenotype in Pkd1^RC/RC kidneys was characterized by decreases in crucial autophagy-related proteins (Atg12–5 complex, Atg5, Atg16L1), decreased Rab9a and increased mTORC1 (pS6^S240/244, pmTOR^S2448) proteins. TRE increased Atg12–5 complex, Rab9a and p62 in normal kidneys, but was unable to rescue the deficiency in autophagy proteins or suppress mTORC1 in Pkd1^RC/RC kidneys and did not protect against cyst growth.     

Expression of Nek1 during kidney development and cyst formation in multiple nephron segments in the Nek1-deficient kat2J mouse model of polycystic kidney disease

Background

Neks, mammalian orthologs of the fungal protein kinase never-in-mitosis A, have been implicated in the pathogenesis of polycystic kidney disease. Among them, Nek1 is the primary protein inactivated in kat2J mouse models of PKD.

Result

We report the expression pattern of Nek1 and characterize the renal cysts that develop in kat2J mice. Nek1 is detectable in all murine tissues but its expression in wild type and kat2J heterozygous kidneys decrease as the kidneys mature, especially in tubular epithelial cells. In the embryonic kidney, Nek1 expression is most prominent in cells that will become podocytes and proximal tubules. Kidney development in kat2J homozygous mice is aberrant early, before the appearance of gross cysts: developing cortical zones are thin, populated by immature glomeruli, and characterized by excessive apoptosis of several cell types. Cysts in kat2J homozygous mice form postnatally in Bowman’s space as well as different tubular subtypes. Late in life, kat2J heterozygous mice form renal cysts and the cells lining these cysts lack staining for Nek1. The primary cilia of cells lining cysts in kat2J homozygous mice are morphologically diverse: in some cells they are unusually long and in others there are multiple cilia of varying lengths.

Conclusion

Our studies indicate that Nek1 deficiency leads to disordered kidney maturation, and cysts throughout the nephron.