A splice site variant in INPP5E causes diffuse cystic renal dysplasia and hepatic fibrosis in dogs

Ciliopathies presenting as inherited hepatorenal fibrocystic disorders are rare in humans and in dogs. We describe here a novel lethal ciliopathy in Norwich Terrier puppies that was diagnosed at necropsy and characterized as diffuse cystic renal disease and hepatic fibrosis. The histopathological findings were typical for cystic renal dysplasia in which the cysts were located in the straight portion of the proximal tubule, and thin descending and ascending limbs of Henle’s loop. The pedigree of the affected puppies was suggestive of an autosomal recessive inheritance and therefore, whole exome sequencing and homozygosity mapping were used for identification of the causative variant. The analyses revealed a case-specific homozygous splice donor site variant in a cilia related gene, INPP5E: c.1572+5G>A. Association of the variant with the defect was validated in a large cohort of Norwich Terriers with 3 cases and 480 controls, the carrier frequency being 6%. We observed that the identified variant introduces a novel splice site in INPP5E causing a frameshift and formation of a premature stop codon. In conclusion, our results suggest that the INPP5E: c.1572+5G>A variant is causal for the ciliopathy in Norwich Terriers. Therefore, genetic testing can be carried out in the future for the eradication of the disease from the breed.

Inhibition of Pkhd1 impairs tubulomorphogenesis of cultured IMCD cells

Fibrocystin/polyductin (FPC), the gene product of PKHD1, is responsible for autosomal recessive polycystic kidney disease (ARPKD). This disease is characterized by symmetrically large kidneys with ectasia of collecting ducts. In the kidney, FPC predominantly localizes to the apical domain of tubule cells, where it associates with the basal bodies/primary cilia; however, the functional role of this protein is still unknown. In this study, we established stable IMCD (mouse inner medullary collecting duct) cell lines, in which FPC was silenced by short hairpin RNA inhibition (shRNA). We showed that inhibition of FPC disrupted tubulomorphogenesis of IMCD cells grown in three-dimensional cultures. Pkhd1-silenced cells developed abnormalities in cell-cell contact, actin cytoskeleton organization, cell-ECM interactions, cell proliferation, and apoptosis, which may be mediated by dysregulation of extracellular-regulated kinase (ERK) and focal adhesion kinase (FAK) signaling. These alterations in cell function in vitro may explain the characteristics of ARPKD phenotypes in vivo.

Immature ovaries and polycystic kidneys in the congenital polycystic kidney mouse may be due to abnormal sex steroid metabolism

Ke 6 is a 17beta-hydroxysteroid dehydrogenase (17betaHSD) that is expressed in the kidneys and gonads. The expression of this gene is markedly reduced in three murine models of recessive polycystic kidney disease, a developmental disorder, where some nephrons within the affected kidneys develop into huge fluid-filled cysts while the non-cystic nephrons atrophies by apoptosis. Here, we show that in the cpk/cpk mouse, which have polycystic kidneys, the female reproductive organs also fail to mature properly and remain arrested at an early stage of development. Direct measurement of 17betaHSD activity showed a severe reduction in estrogen and androgen metabolism within gonadal and non-gonadal tissues of the cpk/cpk mouse. Using immunofluorescent staining we localized the expression of the Ke 6 protein within the female mouse reproductive organs. Our findings suggest that estrogen/androgen metabolism may play an important role in the development of the urogenital systems.

Mouse plasma glutathione peroxidase. cDNA sequence analysis and renal proximal tubular expression and secretion

A mouse kidney cDNA isolated by differential screening was found to be highly homologous to rat, human, and bovine plasma glutathione peroxidase (GPx) sequences. Analysis of the full-length coding region sequence demonstrated an in-frame selenocysteine-encoding opal codon and putative signal sequence, suggesting that the sequence represents the mouse homolog of plasma GPx. The level of expression of plasma GPx in various mouse tissues and during development was investigated by Northern blot analysis. Plasma GPx mRNA was observed to be very abundant in kidney compared with placenta, epididymis, intestine, lung, heart, testis, ovary, salivary gland, spleen, thymus, stomach, brain, and fetal kidney and could not be detected in pancreas or in liver except from pregnant mice. In addition, plasma GPx mRNA levels were shown to increase during postnatal development of the kidney. In situ hybridization localized plasma GPx mRNA to proximal tubules, while primary cell culture demonstrated that plasma GPx is synthesized and secreted by proximal tubular epithelial cells. The relative abundance of plasma GPx mRNA in mouse kidney suggests that proximal tubules may be the primary source of the enzyme detectable in plasma and further suggests that plasma GPx has an important function in protecting the kidney from oxidative damage.

Immunocytochemical studies of the distribution of alpha and pi isoforms of glutathione S-transferase in cystic renal diseases

We describe immunohistochemical studies of the expression of alpha and pi class glutathione S-transferases (GSTs) in normal fetal kidneys. These define, in greater detail, changes in expression of alpha isoforms in the proximal tubule. At about 36 weeks of gestation expression of alpha isoforms was down-regulated in the distal tubules and collecting ducts while pi was expressed throughout the nephron. Tubular expression of alpha isoforms was restricted to the part adjacent to the glomerulus; cells farthest from the glomerulus were negative. After 40 weeks of gestation, alpha isoforms were expressed along the entire proximal tubule, while pi was restricted to the distal tubule and collecting ducts. GST expression was also studied in multicystic renal dysplasia, autosomal recessive polycystic kidney disease, and autosomal dominant polycystic kidney disease to determine whether the patterns of expression of alpha and pi isoforms allow identification of the origin of the cysts that characterize these diseases. Cysts were lined by epithelia that were strongly positive for alpha and pi isoforms. The epithelia of noncystic nephrons in renal cystic dysplasia demonstrated delayed maturity, suggesting that GST expression was dependent on the stage of development and not length of gestation.

Epithelial polarity and differentiation in polycystic kidney disease

Renal cysts are central pathological features in a number of human congenital and acquired diseases, and produce significant morbidity and mortality. This review describes our laboratory's efforts to identify specific alterations in epithelial cell polarity and differentiation associated with renal tubular cyst formation and progressive enlargement. Studies in a murine model of human autosomal recessive polycystic kidney disease, the C57BL/6J cpk/cpk (CPK) mouse have demonstrated quantitative (increased activity) and qualitative (apical membrane distribution) alterations in Na+,K(+)-adenosine triphosphatase activity that mediate tubular cyst formation. Proximal tubular cyst formation in CPK kidneys is characterized by increased activity of a basolateral Na+,K(+)-ATPase, which drives organic anion secretion and consequent tubular fluid secretion. In contrast, collecting tubule cyst formation is characterized by increased apical membrane Na+,K(+)-ATPase expression, which may be a marker of the relatively undifferentiated phenotype of cyst lining cells. If such apically expressed enzyme is active, it may have pathogenic import in collecting tubule cyst formation and enlargement by mediating net basal to apical vectorial solute and fluid transport.