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Autosomal dominant polycystic kidney disease (ADPKD), primarily due to PKD1 or PKD2 mutations, causes progressive kidney cyst development and kidney failure. There is significant intrafamilial variability likely due to the genetic background and environmental/lifestyle factors; variability that can be modeled in PKD mice. Here, we characterized mice homozygous for the PKD1 hypomorphic allele, p.Arg3277Cys (Pkd1(RC/RC)), inbred into the BALB/cJ (BC) or the 129S6/SvEvTac (129) strains, plus F1 progeny bred with the previously characterized C57BL/6J (B6) model; F1(BC/B6) or F1(129/B6). By one-month cystic disease in both the BC and 129 Pkd1(RC/RC) mice was more severe than in B6 and continued with more rapid progression to six to nine months. Thereafter, the expansive disease stage plateaued/declined, coinciding with increased fibrosis and a clear decline in kidney function. Greater severity correlated with more inter-animal and inter-kidney disease variability, especially in the 129-line. Both F1 combinations had intermediate disease severity, more similar to B6 but progressive from one-month of age. Mild biliary dysgenesis, and an early switch from proximal tubule to collecting duct cysts, was seen in all backgrounds. Preclinical testing with a positive control, tolvaptan, employed the F1(129/B6)-Pkd1(RC/RC) line, which has moderately progressive disease and limited isogenic variability. Magnetic resonance imaging was utilized to randomize animals and provide total kidney volume endpoints; complementing more traditional data. Thus, we show how genetic background can tailor the Pkd1(RC/RC) model to address different aspects of pathogenesis and disease modification, and describe a possible standardized protocol for preclinical testing.

BACKGROUND and AIMSExtra-hepatic biliary atresia (BA) is a pediatric liver disease with no approved medical therapy. Recent studies using human samples and experimental modeling suggest that glutathione redox metabolism and heterogeneity play a role in disease pathogenesis. We sought to dissect the mechanistic basis of liver redox variation and explore how other stress responses affect cholangiocyte injury in BA.METHODSWe performed quantitative in situ hepatic glutathione redox mapping in zebrafish larvae carrying targeted mutations in glutathione metabolism genes and correlated these findings with sensitivity to the plant-derived BA-linked toxin biliatresone. We also determined whether genetic disruption of HSP90 protein quality control pathway genes implicated in human BA altered biliatresone toxicity in zebrafish and human cholangiocytes. An in vivo screen of a known drug library was performed to identify novel modifiers of cholangiocyte injury in the zebrafish experimental BA model with subsequent validation.RESULTSGlutathione metabolism gene mutations caused regionally distinct changes in the redox potential of cholangiocytes that differentially sensitized them to biliatresone. Disruption of human BA-implicated HSP90 pathway genes sensitized zebrafish and human cholangiocytes to biliatresone-induced injury independent of glutathione. Phosphodiesterase-5 inhibitors (PDE5i) and other cGMP signaling activators worked synergistically with the glutathione precursor N- acetylcysteine (NAC) in preventing biliatresone-induced injury in zebrafish and human cholangiocytes. PDE5i enhanced proteasomal degradation and required intact HSP90 chaperone.CONCLUSIONRegional variation in glutathione metabolism underlies sensitivity to the biliary toxin biliatresone, and mirrors recently reported BA risk stratification linked to glutathione metabolism gene expression. Human BA can be causatively linked to genetic modulation of protein quality control. Combined treatment with NAC and cGMP signaling enhancers warrants further investigation as therapy for BA.What You Need to KnowBackground and ContextBiliary atresia (BA) is an obstructive fibrosing cholangiopathy that is the leading indication for liver transplantation in the pediatric population. There are no known treatments to prevent progressive liver injury after surgical restoration of bile flow.New FindingsThe authors identify factors that affect susceptibility of cholangiocytes to oxidative injury using a toxin-induced BA model. This information is used to validate genetic risk factors for human BA and identified PDE5i as a potential treatment for biliary atresia, either on its own or in combination with the anti-oxidant N-acetyl-cysteine.LimitationsThe work done in animal and cell culture models needs further study in human tissue-derived models and a larger cohort of BA patients.ImpactThe findings from this study provide a rationale for identifying new genetic risk factors that predispose to BA and for an interventional study to prevent progressive liver injury in this enigmatic disease.Short SummaryThis study uses zebrafish and human cell culture models to identify novel injury mechanisms, genetic risk factors and new therapies for the pediatric liver disease biliary atresia.