High Copper Selectively Alters Lipid Metabolism and Cell Cycle Machinery in the Mouse Model of Wilson Disease

Abstract

Copper is essential for human physiology, but in excess it causes the severe metabolic disorder Wilson disease. Elevated copper is thought to induce pathological changes in tissues by stimulating the production of reactive oxygen species that damage multiple cell targets. To better understand the molecular basis of this disease, we performed genome-wide mRNA profiling as well as protein and metabolite analysis for Atp7b ؊/؊ mice, an animal model of Wilson disease. We found that at the presymptomatic stages of the disease, copper-induced changes are inconsistent with widespread radical-mediated damage, which is likely due to the sequestration of cytosolic copper by metallothioneins that are markedly up-regulated in Atp7b ؊/؊ livers. Instead, copper selectively up-regulates molecular machinery associated with the cell cycle and chromatin structure and down-regulates lipid metabolism, particularly cholesterol biosynthesis. Specific changes in the transcriptome are accompanied by distinct metabolic changes. Biochemical and mass spectroscopy measurements revealed a 3.6-fold decrease of very low density lipoprotein cholesterol in serum and a 33% decrease of liver cholesterol, indicative of a marked decrease in cholesterol biosynthesis. Consistent with low cholesterol levels, the amount of activated sterol regulatory-binding protein 2 (SREBP-2) is increased in Atp7b ؊/؊ nuclei. However, the SREBP-2 target genes are dysregulated suggesting that elevated copper alters SREBP-2 function rather than its processing or re-localization. Thus, in Atp7b ؊/؊ mice elevated copper affects specific cellular targets at the transcription and/or translation levels and has distinct effects on liver metabolic function, prior to appearance of histopathological changes. The identification of the network of specific copper-responsive targets facilitates further mechanistic analysis of human disorders of copper misbalance.

Physiological and toxicological transcriptome changes in HepG2 cells exposed to copper

“…In addition, MT genes and genes associated with the cell cycle and chromosome structure were upregulated. Genes encoding proteins involved in cholesterol metabolism were significantly downregulated in the Atp7b Ϫ/Ϫ liver (32,33). Similar changes were observed in the levels of expression for these genes in copper-exposed HepG2 cells.…”

“…Atp7b Ϫ/Ϫ mice demonstrate intracellular copper accumulation, low serum oxidase activity, and increased copper excretion in the urine and liver pathology, similar to Wilson's disease patients (12,32). Transcriptome analysis of the Atp7b Ϫ/Ϫ mouse liver revealed copper-induced alterations of lipid metabolism and cholesterol homeostasis, which are also observed in Wilson's disease patients (33). In addition, MT genes and genes associated with the cell cycle and chromosome structure were upregulated.…”

“…The cellular and molecular mechanisms underlying copperregulated gene expression and toxicity have been investigated in yeast, mouse fibroblasts, and rodent strains with mutations in Atp7b (5,28,33,69). Atp7b Ϫ/Ϫ mice demonstrate intracellular copper accumulation, low serum oxidase activity, and increased copper excretion in the urine and liver pathology, similar to Wilson's disease patients (12,32).…”

Genetic Regulation of Serum Phytosterol Levels and Risk of Coronary Artery Disease

“…The use of human liver samples obtained from patients who underwent partial liver resection was approved by the Ethics Committee of the University of Leipzig (Leipzig, Germany) (registration number ). 14 …”

Wilson Disease at a Single Cell Level

“…Whether this sequestered copper is exchangeable and active is unclear. Furthermore, the severity and the onset of WD do not directly correlate with copper concentrations in the liver (6,8,9), suggesting that additional factors, such as spatial distribution of copper in the liver as well as environmental and genetic modifiers may play an important role in WD pathology. To begin addressing these unresolved issues, we have utilized the Atp7b Ϫ/Ϫ mice, an animal model of WD.…”