Article

Urinary Copper Elevation in a Mouse Model of Wilson's Disease Is a Regulated Process to Specifically Decrease the Hepatic Copper Load

Department of Physiology, Johns Hopkins University, School of Medicine, Baltimore, Maryland, USA.
PLoS ONE (Impact Factor: 3.23). 06/2012; 7(6):e38327. DOI: 10.1371/journal.pone.0038327
Source: PubMed

ABSTRACT

Body copper homeostasis is regulated by the liver, which removes excess copper via bile. In Wilson's disease (WD), this function is disrupted due to inactivation of the copper transporter ATP7B resulting in hepatic copper overload. High urinary copper is a diagnostic feature of WD linked to liver malfunction; the mechanism behind urinary copper elevation is not fully understood. Using Positron Emission Tomography-Computed Tomography (PET-CT) imaging of live Atp7b(-/-) mice at different stages of disease, a longitudinal metal analysis, and characterization of copper-binding molecules, we show that urinary copper elevation is a specific regulatory process mediated by distinct molecules. PET-CT and atomic absorption spectroscopy directly demonstrate an age-dependent decrease in the capacity of Atp7b(-/-) livers to accumulate copper, concomitant with an increase in urinary copper. This reciprocal relationship is specific for copper, indicating that cell necrosis is not the primary cause for the initial phase of metal elevation in the urine. Instead, the urinary copper increase is associated with the down-regulation of the copper-transporter Ctr1 in the liver and appearance of a 2 kDa Small Copper Carrier, SCC, in the urine. SCC is also elevated in the urine of the liver-specific Ctr1(-/-) knockouts, which have normal ATP7B function, suggesting that SCC is a normal metabolite carrying copper in the serum. In agreement with this hypothesis, partially purified SCC-Cu competes with free copper for uptake by Ctr1. Thus, hepatic down-regulation of Ctr1 allows switching to an SCC-mediated removal of copper via kidney when liver function is impaired. These results demonstrate that the body regulates copper export through more than one mechanism; better understanding of urinary copper excretion may contribute to an improved diagnosis and monitoring of WD.

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    • "As body size and lifespan of rodents clearly hampers long-term sequential liver biopsies, longitudinal studies on liver samples following individual animals in time until chronic hepatitis has developed are not available. In contrast to the impossibility to acquire sequential mouse liver biopsies urinary copper excretion could be measured longitudinally as described in a recent study on ATP7b À/À mice [24]. "
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    • "As suggested in previous studies [18], [28], [29], copper is supposed to progressively accumulate in LEC hepatocytes during the first weeks of life until cytosolic storage capacities are overwhelmed. This could be accelerated by a massive burden of dietary copper as recently reported by Siaj et al. [18]. "
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    • "n , the regulation of intracellular Cu is complex and other yet to be characterized Cu transport path - ways may also be altered in PD . It has recently been shown , for example , that downregulation of Ctr1 in a murine model of Wilson disease is linked to the appearance of a redundant mechanism of Cu transport , the 2 - kDa small copper carrier ( Gray et al . , 2012 ) . A second Ctr protein , structurally related to Ctr1 , has also been identified in mammals , designated Copper transporter 2 ( Ctr2 ) . This protein has not been identified in human tissue but is thought to play a role in low - affinity Cu import ( Bertinato et al . , 2008 ) and in intracellular Cu mobilization ( Rees and Thiele , 20"
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