A systems approach implicates nuclear receptor targeting in the Atp7b−/− mouse model of Wilson's disease

Abstract

Wilson’s disease (WD) is an inherited disorder of copper metabolism characterized by liver disease and/or neurologic and psychiatric pathology. The disease is a result of mutation in ATP7B, which encodes the ATP7B copper transporting ATPase. Loss of copper transport function by ATP7B results in copper accumulation primarily in the liver, but also in other organs including the brain. Studies in the Atp7b−/− mouse model of WD revealed specific transcript and metabolic changes that precede development of liver pathology, most notably downregulation of transcripts in the cholesterol biosynthetic pathway. In order to gain insight into the molecular mechanisms of transcriptomic and metabolic changes, we used a systems approach analysing the pre-symptomatic hepatic nuclear proteome and liver metabolites. We found that ligand-activated nuclear receptors FXR/NR1H4 and GR/NR3C1 and nuclear receptor interacting partners are less abundant in Atp7b−/− hepatocyte nuclei, while DNA repair machinery and the nucleus-localized glutathione peroxidase, SelH, are more abundant. Analysis of metabolites revealed an increase in polyol sugar alcohols, indicating a change in osmotic potential that precedes hepatocyte swelling observed later in disease. This work is the first application of quantitative Multidimensional Protein Identification Technology (MuDPIT) to a model of WD to investigate protein-level mechanisms of WD pathology. The systems approach using “shotgun” proteomics and metabolomics in the context of previous transcriptomic data reveals molecular-level mechanisms of WD development and facilitates targeted analysis of hepatocellular copper toxicity.

Links between copper and cholesterol in Alzheimer's disease

“…Conversely, copper overload in the Atp7b −/− mouse model of Wilson disease is associated also with reduced brain and hepatic concentrations of cholesterol, lathosterol, desmosterol, 8-hydrocholesterol, and 7-dehydrocholesterol (Sauer et al, 2011). These changes are consistent with down-regulation of cholesterogenic gene expression and reduction in nuclear receptor transcription factors farnesoid X receptor (FXR) and glucocorticoid receptor (GR) in the liver of the same animal model (Huster et al, 2007; Wilmarth et al, 2012). However, the decrease in serum cholesterol observed in animal models of Wilson disease is not recapitulated in a study of human Wilson disease patients (Seessle et al, 2011).…”

The metabolomic window into hepatobiliary disease

“…Metabolomic studies have been reported that are of relevance to Wilson's disease [103, 104], primary biliary cirrhosis [105], primary sclerosing cholangitis [105], the hepatic stage of malaria [106–108], as well as various aspects of hepatic encephalopathy [109–112]. …”

The Role of Copper as a Modifier of Lipid Metabolism

“…Direct in situ imaging of copper using X-fluorescence revealed the nonuniform distribution of accumulating copper in Atp7b-/-hepatocytes with a predominant increase in the cytosol and nuclei (80). Mass-spectrometry in combination with generation of protein networks provided strong evidence that accumulating copper had a significant and specific functional impact on Atp7b-/-nuclei, where it remodeled the RNA-processing machinery (83) and altered abundance and activity of nuclear receptors (84). Specifically, using quantitative Multidimensional Protein Identification Technology (MuDPIT), Wilmarth and colleagues found that the ligand-activated nuclear receptors FXR/NR1H4 and GR/NR3C1 were less abundant in nuclear preparations from Atp7b-/-liver, whereas the DNA repair machinery and the nucleus-localized glutathione peroxidase SelH were more abundant, consistent with the earlier transcriptome studies (79).…”