The Consortium of Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) recently showed that renal enlargement in autosomal-dominant polycystic kidney disease mimicked exponential growth. We determined the effects of cyst initiation rate, total number, and growth rate on the time-dependent change of total cyst volume (TCV). Mathematical models with equations integrating cyst surface area, volume, and an invariant growth rate constant were used to compute the time-dependent change in volume of solitary and multiple cysts. Multiple expanding cysts increased TCV in an exponential-like pattern even when individual cysts formed at different rates or exhibited different but constant growth rates. TCV depended on the rate of cyst initiation and on the total number of cysts; however, the compounding effect of exponential-like growth was the most powerful determinant of long-term cyst expansion. Extrapolation of TCV data plots for individual subjects back to an age of 18 predicted TCV values within an established range. We conclude that cysts started early in life were the main contributor to eventual TCV while their growth rate primarily determined renal size; although the rate of formation and the ultimate number of cysts also contributed. The good fit between the exponential models and the extrapolated CRISP data indicates that the TCV growth rate is a defining trait for individual patients and may be used as a prognostic marker.

EDITORIALCyclic AMP, at the hub of the cystic cycle Half a century after its discovery, new roles for adenosine 3 ,5 -cyclic monophosphate (cAMP) continue to be discovered. The article by Belibi et al [1] in this issue of Kidney International, implicates cAMP in the pathogenesis of autosomal-dominant and recessive polycystic kidney diseases (ADPKD and ARPKD) and provides a target for the pharmacologic treatment of these disorders.Cyclic AMP is a ubiquitous and versatile second messenger. Extracellular ligands bind to G proteincoupled receptors (GPCR) that positively (Gs) or negatively (Gi) regulate closely associated adenylyl cyclases (ACs). Cyclic AMP levels are controlled within specific cellular compartments by the activity of cAMP phosphodiesterases (PDEs), themselves subject to complex regulatory mechanisms. Maximal rates of degradation by PDEs exceed those of synthesis by ACs, pointing to the importance of PDEs in the regulation of cAMP signaling. Cyclic AMP may exit the cells by an energy-dependent transport mechanism, but in most cells efflux does not have a major effect on cAMP levels. Biological effects of cAMP are mediated by protein kinase A (PKA), cyclic nucleotide gated cation channels, and guanine nucleotide exchange factors. PKA is targeted to specific cellular compartments by A kinase-anchoring proteins (AKAPs). The specificity of cAMP signaling is achieved by the extraordinary diversity of ACs, PDEs, PKAs, and AKAPs. It also depends on cell-type specific cross-talk with other signaling systems, such as mitogenactivated protein kinase/extracellular-regulated kinase (MAPK/ERK) cascades that couple growth factor receptors and Ras to cell proliferation. They consist of three protein kinases acting in series, a MAP kinase kinase kinase (MAPKKK), which activates a MAP kinase kinase (MAPKK or MEK), which phosphorylates a MAP kinase (MAPK or ERK). In the ERK1/2 cascade, the Raf family of serine/threonine protein kinases (A-Raf, B-Raf, and Raf-1) function as MAPKKK. Activated PKA catalytic subunits and ERKs can translocate to the nucleus where they phosphorylate transcription factors. Calcium in intracellular compartments ([Ca 2+ ] i ) that may be directly affected by polycystic kidney disease (PKD)-causing genetic alterations can regulate positively and negatively cAMP and MAPK signaling.

We have produced continuous cell lines using retroviral transduction of SV40 large T antigen into epithelial cells removed from the lumen of liver cysts from four female patients with autosomal dominant polycystic kidney disease (ADPKD). Liver cyst-derived epithelial (LCDE) cell lines are grown in a hormonally supplemented medium in the presence of lethally irradiated NIH/3T3 fibroblast coculture. LCDE cells maintain their epithelial appearance and are positive for the biliary-specific markers cytokeratin 7 and 19 and gamma-glutamyl transpeptidase while being negative for hepatocyte markers. SV40 large T antigen is localized to the cell nucleus. LCDE cells have been grown continuously for periods exceeding 12 mo and 25 passages (170 population doublings). LCDE cells exhibit intracellular pH regulatory pathways that, with one exception, are similar to those found in normal intrahepatic biliary epithelium. These LCDE cell lines exhibit impaired alkalinization in response to Cl- substitution. This finding is suggestive of decreased function or abundance of a Cl-/HCO3- anion exchanger and could account for the failure of ADPKD hepatic cysts to secrete HCO3- in response to secretin.

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.

Liver and liver cyst volume measurements are important quantitative imaging biomarkers for assessment of disease progression in autosomal dominant polycystic kidney disease (ADPKD) and polycystic liver disease (PLD). To date, no study has presented automated segmentation and volumetric computation of liver and liver cysts in these populations. In this paper, we proposed an automated segmentation framework for liver and liver cysts from bounded abdominal MR images in patients with ADPKD. To model the shape and variations in ADPKD livers, the spatial prior probability map (SPPM) of liver location and the tissue prior probability maps (TPPMs) of liver parenchymal tissue intensity and cyst morphology were generated. Formulated within a three-dimensional level set framework, the TPPMs successfully captured liver parenchymal tissues and cysts, while the SPPM globally constrained the initial surfaces of the liver into the desired boundary. Liver cysts were extracted by combined operations of the TPPMs, thresholding, and false positive reduction based on spatial prior knowledge of kidney cysts and distance map. With cross-validation for the liver segmentation, the agreement between the radiology expert and the proposed method was 84% for shape congruence and 91% for volume measurement assessed by the intra-class correlation coefficient (ICC). For the liver cyst segmentation, the agreement between the reference method and the proposed method was ICC=0.91 for cyst volumes and ICC=0.94 for % cyst-to-liver volume.