Aberrant 11beta-hydroxysteroid dehydrogenase-1 activity in the cpk mouse: implications for regulation by the Ke 6 gene

Glucocorticoids have been used to create experimental polycystic kidney disease in rodents and to induce cysts in embryonic kidneys cultures. In addition, the plasma corticosterone levels are higher in a heritable murine model of polycystic kidney disease, cpk mice, in the first postnatal week. Previously, we had shown that the 11beta-hydroxysteroid dehydrogenase-1 (11betaHSD-1) gene is down-regulated in the cpk mice in a coordinated pattern with the Ke 6 gene. In this study, we measured the level of 11betaHSD-1 activity in kidney and liver tissues of cpk homozygote mice and found a reduction in its activity only in the kidney, not in the liver. The activity of the 11betaHSD-1 enzyme appears to be tightly correlated to the level of Ke 6 protein in these tissues. We discuss the possibility that the activity of the 11betaHSD-1 enzyme may be regulated by the Ke 6 enzyme. Ke 6 gene expression has been located to the outer stripe region of rodent kidneys, which is the same region of expression as that for the 11betaHSD-1 gene. These results suggest that down-regulation of the Ke 6 gene may lead to elevated corticosterone levels, mediated through an inhibition of 11betaHSD-1 activity.     

Murine autosomal recessive polycystic kidney disease with multiorgan involvement induced by the cpk gene

BACKGROUND: Autosomal recessive (AR) polycystic kidney disease (PKD) is characterized in humans and mice as a rapidly progressive, collecting duct cystic disease usually leading to uremia in the neonatal or infantile period. In humans, ARPKD renal pathology can be variable in severity and is associated with the development of prominent bile duct and liver pathology. The C57BL/6J-cpk/cpk mouse model of ARPKD is the most extensively studied murine model of inherited infantile PKD; however, these mice lack extrarenal pathology. METHODS: In the present study, the cpk gene was backbreed onto CD1 mice to examine the development of cpk-induced ARPKD in this outbred mouse background. Resulting cystic offspring were examined morphologically and their serum urea nitrogen levels were assessed. RESULTS: The rapid development of PKD in CD1 mice homozygous for the cpk gene appears to be slightly more rapid but otherwise comparable to that seen in inbred C57BL/6J mice. In CD1-cpk/cpk mice, the principal renal pathological finding is collecting duct cysts, which are lined by a relatively uniform epithelium. This epithelium appears to be relatively undifferentiated based on almost total absence of intercalated cells. Proximal tubule cysts are prominent in the first postnatal week while collecting duct cysts predominate in the later stages of the disease. Extrarenal manifestations of the cpk gene are evident in the CD1 strain and include cysts of pancreatic, common bile, and major hepatic ducts. Intrahepatic bile ducts also have focal dilations. Primary (thymus) and secondary (spleen) lymphoid tissues become hypoplastic as azotemia progresses. The strain-related variability in renal and liver changes in cpk-induced ARPKD may reflect the influence of other genes (possibly modifier genes) expressed in this mouse strain. In older CD1-cpk/+ mice, renal (proximal tubular) cysts and prominent liver cysts (lined by a biliary epithelium) develop, indicating that the heterozygous state (cpk/+ genotype) causes renal and hepatic pathology. CONCLUSIONS: The cpk gene, when placed on an appropriate mouse strain background, causes multiorgan disease that more closely mimics human ARPKD than when the cpk gene is expressed on the C57BL/6J strain. A gene dose effect is present as cystic pathology is present in kidney and liver of both suckling homozygous (cpk/cpk) and old heterozygous (cpk/+) mice.     

Sodium pump distribution is not reversed in the DBA/2FG-pcy, polycystic kidney disease model mouse

Recently, it has been reported that Na,K-ATPase in the renal epithelia of human autosomal dominant polycystic kidney disease and cpk mouse, a murine model of autosomal recessive polycystic kidney disease, mislocates to apical plasma membrane and that mislocated Na,K-ATPase causes the cyst formation. Whether the DBA/2FG-pcy mice, which are presumably a suitable model for autosomal dominant polycystic kidney disease, also exhibit the reversal polarity of Na,K-ATPase localization was examined. Kidneys of newborn DBA/2FG-pcy mice, and those at early and late stages of cyst development were examined by immunohistochemical techniques. At any stage, abnormal distribution of Na,K-ATPase on the apical membranes of tubular epithelial cells could not be detected. It is suggested that cysts can be formed without reversed polarity of Na,K-ATPase distribution in pcy mice.     

Estrogen receptor does not directly regulate the murine Muc-1 promoter

Muc-1 is a heavily O-glycosylated, type 1 membrane glycoprotein present on the surface of polarized secretory uterine epithelial cells. Previous studies have shown that treatment of ovariectomized mice with 17-beta-estradiol (E2) strongly induces Muc-1 mRNA expression in an estrogen receptor (ER)-mediated fashion in the uterus. In this study, the 5.4 kb Muc-1 gene promoter has been isolated from a mouse genomic library and the proximal 1.85 kb region has been sequenced. Sequence analysis revealed the presence of one potential full estrogen response element (ERE) (GCTCGCGGTGACC) located at -748 to -735 bp in the Muc-1 promoter and several potential ERE half sites. Electrophoretic mobility shift assays (EMSA) showed that neither ERalpha nor ERbeta bind efficiently to this sequence. Transient cotransfection assays using constructs containing various deletion mutations of the 5' Muc-1 flanking sequences showed that E2 had no direct stimulation on promoter-driven reporter in NMuMG cells or primary mouse uterine epithelial cells, but did stimulate a consensus ERE CAT-reporter gene activity. In addition, E2-treatment of Weg-ER cells, a mouse uterine epithelial cell line stably expressing human ERalpha, did not restore endogenous Muc-1 expression or activate Muc-1 promoter-driven CAT activity. These results indicate that regions of the Muc-1 gene promoter within -1838 to +43 bp do not respond to E2 and ER stimulation and that ER alone is not sufficient to restore Muc1 gene expression. Deletion analyses also revealed that the sequence between -73 and +43 bp of the Muc-1 promoter is the minimal promoter region required for maximal Muc-1 promoter activity. Collectively, these results demonstrate that ER does not directly regulate the 1.85 kb murine Muc-1 gene promoter. Therefore, E2 control of uterine Muc-1 gene expression is likely to be indirect, i.e. mediated by stromal cell-derived factors.     

Cystic kidney diseases

Among all inherited cystic kidney diseases, the commonest are polycystic kidney diseases, which include 2 diseases characterized by their pathological characteristics and their mode of inheritance, namely autosomal dominant or recessive. Autosomal dominant polycystic kidney disease is usually diagnosed in adulthood and is related at least to 2 different genes; PKD1 gene on chromosome 16 accounts for 85% of cases. This frequent disease (1 in 1,000 people) leads to end-stage renal failure in most patients at a mean age of 55 years. Renal ultrasonography allows its detection at an early stage, during childhood or adolescence, and even in utero in some cases. Autosomal recessive polycystic kidney disease, related to a single gene mapped to chromosome 6, is a rare disease, usually diagnosed during infancy because of enlarged kidneys and hypertension. The early occurrence of advanced renal failure is uncommon and only 1/3 of patients require renal replacement therapy during childhood. The term "polycystic kidney disease" should be limited to these 2 diseases; however there are many other inherited conditions including renal cysts like tuberous sclerosis or Hippel-Lindau's disease in adults, and several malformative syndromes in children.     

The molecular biology of polycystic kidney disease

In recent years there have been a number of developments in polycystic kidney disease (PKD) research. The genes associated with the predominant forms of autosomal dominant PKD have been cloned, and the gene associated with a mouse model for autosomal recessive PKD has been identified and characterized. Other studies have yielded new information regarding the role of the epidermal growth factor receptor gene in promoting renal cyst formation. In this review article we summarize recent published data on the molecular genetics of autosomal dominant and autosomal recessive PKD and provide a working model of how multiple genes participate in the PKD disease pathway.     

Molecular cloning, cDNA sequence analysis, and chromosomal localization of mouse Pkd2

The gene responsible for the second form of autosomal dominant polycystic kidney disease, PKD2, has recently been identified. We now describe the cloning, genomic localization, cDNA sequence, and expression analysis of its murine homologue, Pkd2. The cloned cDNA sequence is 5134 bp long and is predicted to encode a 966-amino-acid integral membrane protein with six membrane-spanning domains and intracellular NH2 and COOH termini. Pkd2 is highly conserved with 91% identity and 98% similarity to polycystin-2 at the amino acid level. Pkd2 mRNA is widely expressed in mouse tissues. Pkd2 maps to mouse Chromosome 5 and is excluded as a candidate gene for previously mapped mouse mutations resulting in a polycystic kidney phenotype.